CZ20003303A3 - A high capillary suction absorbent member for absorbing body fluids - Google Patents

Abstract

A storage absorbent member with high capillary suction for absorbing body fluids such as urine comprises at least one osmotic absorbent, preferably an absorbent polymer forming a hydrogel, and a material with a large surface area and a high capillary suction capacity. Capillary suction capacity is measured as the ability to receive liquid at high capillary heights, which generally occur when the member is placed in an absorbent article. Capillary suction capacity is particularly measured as the absorbent capacity of the member by capillary sorption, which is measured in accordance with a method for measuring capillary sorption.

Description

Storage absorbent member with high capillary suction for absorbing body fluids

Technical field

The invention relates to storage absorbent members with high capillary suction for absorbing body fluids such as urine and menstrual discharge. This invention particularly relates to absorbent members having high capillary absorbency properties.

State of the art

The development of highly absorbent members for use in disposable diapers, incontinence pads, and panty liners and menstrual products such as sanitary napkins is of considerable commercial interest. Thinness is a highly desirable parameter for these products. For example, thinner diapers are easier to wear, fit better under clothing, and are less noticeable. They are also denser when still in the package, which means they are easier for consumers to carry and store. Their density in the package also results in lower distribution costs for the manufacturer and distributor, including requiring less shelf space per unit during storage.

The ability to provide thinner absorbent products, such as diapers, has been a benefit resulting from the ability to develop relatively thin absorbent cores or structures that are capable of receiving and storing large amounts of discharged body fluids, particularly urine. Of particular importance in this regard has been the use of certain absorbent polymers, often referred to as hydrogels, superabsorbents, or hydrocolloids. See, for example, U.S. Patent No. 3,699,103, which describes the use of such absorbent polymers (hereinafter referred to as hydrogel-forming absorbent polymers) in absorbent products. Indeed, the development of thinner diapers has been a direct result of thinner absorbent cores that take advantage of the ability of these hydrogel-forming absorbent polymers to absorb large amounts of discharged body fluids, particularly when used in combination with a fibrous matrix. See, for example, U.S. Patent Nos. 4,673,402 and 4,935,022, which describe two-layer core structures comprising a fibrous matrix and an absorbent core.

- 2 hydrogel-forming polymers, useful in creating thin, dense, not uncomfortably bulky diapers.

See also U.S. Patent No. 5,562,646 and U.S. Patent No. 5,599,335, both of which relate to absorbent cores comprising regions of high concentrations of hydrogel-forming polymer, where the polymer forms a gel-like continuous liquid-transporting zone upon swelling.

In addition to the use of hydrogel-forming absorbent polymers as primary components in absorbent article storage structures, the use of polymeric foam materials derived from high internal phase water-in-oil emulsions (HIPE materials) has also been reported. See U.S. Patents 5,260,345, 5,387,207, and 5,560,222. Foam materials, particularly those designed to act as fluid storage and redistribution components, have several advantages over storage structures incorporating hydrogel-forming absorbent polymers in a fibrous matrix, including good wicking and fluid distribution properties, high compressive storage capacity, flexibility, etc.

The main focus of previous work on both hydrogel-forming absorbent polymers and HIPE foam has been to maximize the storage capacity in a relatively thin material. Hydrogel-forming absorbent polymer materials absorb liquid and protect against leakage and keep absorbent products dry. When liquid is absorbed into absorbent polymers, it is tightly held within them by osmotic forces, which helps prevent rewetting of the top layer of the material previously absorbed by urine, but the hydrogel-forming polymer itself has little ability to absorb liquid unless the liquid is transported to its surface. This is especially true at high capillary heights, when the liquid is present only in small capillaries. For example, conventional softwood pulp shows almost no suction at a capillary suction height of 100 cm. It is not surprising, then, that a blend of pulp and hydrogel-forming polymer shows almost no uptake at 100 cm. It follows that instead of further development aimed at achieving high liquid storage capacity in thin materials, there is a continuing need to provide materials with high storage capacity that also exhibit high capillary suction capability. Storage materials that exhibit high capillary suction capability allow for the drainage of other absorbent core materials, such as acquisition and distribution materials, one or both of which are typically included in the absorbent cores of absorbent products.

- 3 products. By properly draining these other components of the absorbent core, these materials are then better able to cope with further liquid intake from the user. In addition to high capillary suction capabilities in general, the ability to provide these capabilities at relatively high capillary suction heights is a particularly desirable property. The movement of liquid from the discharge area, i.e. the crotch area of the product, to the front and back of the product can provide the user with greater comfort when the product is wetted with liquid. It is clear that the ability of the storage material to drain other components of the core, in particular the distribution material, which wicks to high capillary heights, is particularly relevant to their function as absorbent materials in absorbent products.

Therefore, it would be desirable to be able to provide a storage absorbent member having a high capillary suction capability, wherein the storage absorbent member would include an absorbent hydrogel-forming polymer or other material that would absorb liquids primarily by osmotic forces.

The essence of the invention

This invention relates to absorbent members useful in the storage, i.e., storage of body fluids such as urine. These storage absorbent members have a high capillary suction capacity. For the purposes of this invention, capillary suction capacity is measured by the ability of the members to receive liquid at high capillary pressures, which generally occur when the member is placed in an absorbent article. Capillary suction capacity is particularly measured as the absorbent capacity of the member by capillary sorption, which is measured by the method for measuring capillary sorption, which is described in the section entitled Test Methods, below.

Overview of images on the drawing

The invention will be explained in more detail with the help of the drawing, in which the individual figures show the following:

Fig. 1 is an exploded perspective view of a diaper having an absorbent core that includes a storage absorbent member with high capillary suction capability according to the present invention,

- 4 ··· ·· ·· Fig. 2a is an exploded perspective view of an example of a multilayer core for incorporation into the diaper shown in Fig. 1, Fig. 2b is an exploded perspective view of another example of a multilayer core for incorporation into the diaper shown in Fig. 1, Fig. 3 is a photomicrograph at five hundred times magnification of an example of a high surface area polymeric foam useful in storage absorbent members of the present invention, Fig. 4 is a photomicrograph of the high surface area polymeric foam shown in Fig. 3, but at one thousand times magnification, Fig. 5 is a photomicrograph of a storage absorbent member of the present invention comprising particles of a hydrogel-forming absorbent polymer and particles of a polymeric absorbent foam, Fig. 6 is a photomicrograph of a storage absorbent member of the present invention comprising particles of a hydrogel-forming absorbent polymer and fibers of cellulose acetate with a high surface area, Fig. 7 is a micrograph of a storage absorbent member according to the present invention, comprising particles of an absorbent polymer forming a hydrogel and glass microfibers with a large surface area, FIG. 8A is a schematic view of an apparatus for measuring the absorbent capacity by capillary sorption of an absorbent member, FIG. 8B is an enlarged cross-sectional view of the glass Brita shown generally in FIG. 8A. FIG. 8C is an enlarged cross-sectional view of the glass frit cylinder and piston assembly shown in FIG. 8B ; FIG. 8D is an enlarged cross-sectional view of the piston of the cylinder and piston assembly shown in FIG. 8C ; FIG. 9 is a schematic view of an apparatus for forming a representative storage absorbent member of the present invention, wherein the member comprises a mixture of polymeric foam particles and absorbent polymer particles forming a hydrogel; FIG. 10 is a schematic view of another apparatus for forming a representative storage absorbent member of the present invention; FIG. 11 is a perspective view of a storage absorbent member formed using the apparatus shown in FIG. 10 .

Examples of embodiments of the invention

I. Definition

As used herein, the term bodily fluid includes, in particular, urine, menstrual discharge, vaginal discharge, sweat, and feces.

As used herein, the term absorbent core means the component of an absorbent article that is primarily responsible for the liquid handling properties of the article, including the acquisition, transport, distribution, and storage of body fluids. The absorbent core as such generally does not include the topsheet or backsheet of the absorbent article.

As used herein, the term absorbent member refers to the portions of an absorbent core that typically provide one or more liquid handling properties, such as liquid acquisition, liquid distribution, liquid transport, liquid storage, etc. An absorbent member may comprise the entire absorbent core or only a portion of the absorbent core, i.e., the absorbent core may comprise one or more absorbent members. A storage absorbent member is a component or components of an absorbent core that function primarily to store absorbent liquids. As discussed above, a storage absorbent member may also function to distribute liquid as a result of a vertical wicking effect.

As used herein, the term "layer" means an absorbent member whose primary dimension is X-Y, i.e., along length and width. It is to be understood that the term layer is not necessarily limited to just one layer or sheet of material, so that a layer may include laminates or combinations of several sheets or webs of materials of the desired type. Accordingly, the term layer includes the terms layer and laminated.

As used herein, the term osmotic absorbent refers to a material or structure that absorbs a solution in response to a difference in chemical potential between the absorbed and unabsorbed solutions. This difference in chemical potential generally results from a higher solute concentration for the absorbed solution. To prevent equalization of solute concentration by diffusion of solute components, an osmotic absorbent typically has a diffusive • · · 4 4 • ·· « « 4

4 4 4

- 6 a barrier that selectively inhibits the diffusion of at least one component of the solute. Examples of suitable diffusion barriers are (1) a semipermeable reverse osmotic membrane, wherein the membrane provides a diffusion barrier for soluble salts, such as NaCl, and (2) a crosslinked polyelectrolyte network, such as used in hydrogels, wherein the polyelectrolyte network retains dissociated counterions within the gel as a result of electroneutrality considerations. Examples of osmotic packet or chamber absorbents are described in U.S. Patents 5,108,383 and 5,082,723. A particularly preferred osmotic absorbent for use in the storage absorbent member of the present invention are hydrogel-forming absorbent polymers, which are described in detail below.

As used herein, the term X-Y dimension refers to a plane perpendicular to the thickness of a member, core, or product. The X-Y dimension typically corresponds to the length and width of the member, core, or product.

As used herein, the terms region(s) or zone(s) refer to portions or sections of an absorbent member.

As used herein, the term Z dimension refers to the dimension perpendicular to the length and width of a member, core, or product. The Z dimension usually corresponds to the thickness of the member, core, or product.

For the purposes of this invention, it should also be understood that the term upper refers to absorbent members, such as the layers that are closest to the wearer of the absorbent article and are typically relatively close to the top layer of the absorbent article. In contrast, the term lower refers to absorbent members that are furthest from the wearer of the absorbent article and are typically closer to the bottom layer.

As used herein, the term "comprising" refers to various parts, members, steps, and the like that are used together in accordance with the present invention. Accordingly, the term "comprising" includes narrower terms consisting essentially of and consisting of, such narrower terms having their standard meaning as understood in the art.

All percentages, ratios and proportions used herein are by weight unless otherwise indicated.

- 7 • ·« 44 • · · · 4 · • 44 4 4 • 4 4 4 4 4 4 • · 4 4 4

II. Capillary suction properties of a storage absorbent member

The storage absorbent members of the present invention exhibit high capillary suction capability. For purposes of this invention, this high suction capability is measured as the ability of the Member to accept liquid at high capillary heights, which are generally encountered when the member is placed in an absorbent article. The capillary sorption absorbency test, hereinafter also referred to as the capillary sorption test, measures the amount of test liquid per gram of storage absorbent member that is received when the member is placed at various heights on a capillary sorption measuring apparatus. The capillary sorption absorbency test is described in more detail in the section entitled Test Methods below. Capillary sorption absorbent capacity data for certain materials are given in Table 1 below. In particular, capillary sorption absorption capacity data are provided for (1) a storage absorbent member composed of high surface area glass microfibers and hydrogel-forming absorbent polymer particles (made according to Example 1 below), (2) a storage absorbent member composed of high surface area polymer foam particles (made according to Example 2 below), (3) a storage absorbent member composed of high surface area polymer foam particles and hydrogel-forming absorbent polymer particles (made according to Example 5 below), and (4) a storage absorbent member composed of high surface area cellulose acetate fibers and hydrogel-forming absorbent polymer particles (made according to Example 6 below).

Capillary sorption absorption capacity data for prior art materials (referred to as Comparative A and Comparative B) are also shown in Table 1. Comparative Prior Art Sample A was a 5.4 cm diameter circular structure, perforated from a member (see discussion below), comprising a mixture of cellulose fine fibers (Flint River Pulp from Weyerhauser, Co., Washington, USA) at a weight fraction of about 42% and a hydrogel-forming absorbent polymer (available from Clariant GmbH, Frankfurt, Germany as IM 73000) at a weight fraction of about 58%. Comparative Prior Art Sample B is a polymeric foam material prepared according to U.S. Patent No. 5,650,222.

In one aspect, the high-capacity capillary suction storage absorbent member of the present invention has an absorbent capacity by capillary sorption at a height of 35 cm of at least about 12 g/g, preferably at least about 14 g/g, more preferably at least about 16 g/g, even more preferably at least

about 20 g/g, more preferably at least about 27 g/g. Typically, these storage absorbent members will have an absorbent capacity by capillary absorption at a height of 35 cm of from about 12 g/g to about 60 g/g, more typically from about 14 g/g to about 50 g/g, even more typically from about 20 g/g to about 40 g/g.

In another aspect, the high capillary suction capacity storage absorbent material has a capillary sorption absorbent capacity at a height of 70 cm of at least about 7 g/g, preferably at least about 9 g/g, more preferably at least about 11 g/g, and even more preferably at least about 14 g/g. These storage absorbent members will typically have a capillary sorption absorbent capacity at a height of 70 cm of from about 7 g/g to about 35 g/g, more typically from about 9 g/g to about 30 g/g, even more typically from about 11 g/g to about 25 g/g.

In yet another aspect, the high capillary suction storage absorbent material has a capillary sorption absorbent capacity at a height of 120 cm of at least about 4 g/g, preferably at least about 5 g/g, more preferably at least about 7 g/g, even more preferably at least about 11 g/g. These storage absorbent members will typically have a capillary sorption absorbent capacity at a height of 120 cm of from about 4 g/g to about 29 g/g, more typically from about 5 g/g to about 24 g/g, even more typically from about 7 g/g to about 19 g/g.

In yet another aspect, the high capillary suction storage absorbent material has a capillary sorption absorbent capacity at a height of 200 cm of at least about 3 g/g, preferably at least about 4 g/g, more preferably at least about 6 g/g, even more preferably at least about 8 g/g. These storage absorbent members will typically have a capillary sorption absorbent capacity at a height of 200 cm of from about 3 g/g to about 25 g/g, more typically from about 4 g/g to about 20 g/g, even more typically from about 6 g/g to about 15 g/g.

With respect to storage absorbent members comprising osmotic absorbents and high surface area materials, in addition to or as an alternative to defining the high wicking capabilities of the subject members in terms of absorbent capacity by capillary sorption, particularly preferred members, i.e., those where the high surface area material is a polymeric foam, can be characterized by the ability of the member to initially take up liquid at high heights at high rates. High wicking members that exhibit both high uptake at high wicking and high initial effective uptake rates should provide excellent dryness to the wearer because the extent of distribution from other

of absorbent core members, such as acquisition or distribution materials, and its rate will be favorably improved by a material with high capillary suction. For purposes of the present invention, this latter property is referred to herein as the initial uptake rate of the member at a capillary suction height of 200 cm, which is hereinafter referred to as the initial effective uptake rate at 200 cm, which is given in units of g/g/hour. The initial effective uptake rate of a storage absorbent member is calculated by dividing the capillary suction absorption capacity at 200 cm by the time spent at 200 cm. The capillary suction absorption capacity and time are readily determined using the capillary sorption method, which is discussed in detail in the test methods section below. Although not required, particularly preferred storage absorbent members will have an initial effective uptake rate at 200 cm of at least about 3 g/g/h, more preferably at least about 4 g/g/h, and most preferably at least about 8 g/g/h. The effective uptake rate at 200 cm will typically be from about 3 to about 15 g/g/h, more typically from about 4 to about 12 g/g/h, even more typically from about 8 g/g/h to about 12 g/g/h.

While the above minimum capillary sorption absorption capacities are important for absorbent members of the present invention, the members will also preferably, although not necessarily, have a capillary sorption absorption capacity of at least about 15 g/g at zero hydrostatic head, i.e. at 0 cm in the capillary sorption test. In another preferred aspect, the absorbent members will simultaneously exhibit the desired g/g uptake at at least two of the suction heights listed above. This means, for example, that preferred storage absorbent members will have 2 or more of the following properties:

(1) an absorption capacity by capillary sorption at a height of 35 cm of at least about 12 g/g, preferably at least about 14 g/g, even more preferably at least about 16 g/g, even more preferably at least about 20 g/g and even more preferably at least about 27 g/g, (2) an absorption capacity by capillary sorption at a height of 70 cm of at least about 7 g/g, preferably at least about 9 g/g, even more preferably at least about 11 g/g and even more preferably at least about 14 g/g, (3) an absorption capacity by capillary sorption at a height of 120 cm of at least about 4 g/g, preferably at least about 5 g/g, even more preferably at least about 7 g/g and even more preferably at least about 11 g/g,

-10(4) an absorption capacity by capillary sorption at a height of 200 cm of at least about 3 g/g, preferably at least about 4 g/g, even more preferably at least about 6 g/g, even more preferably at least about 8 g/g.

In another aspect, the storage absorbent members of the present invention can be characterized by exhibiting a relatively high absorption efficiency, which is hereinafter referred to as the capillary absorption efficiency at various heights in relation to the capacity of the material at zero hydrostatic head. The capillary absorption efficiency at a given suction head is determined by dividing the capillary suction absorption capacity of the material at a given height by the capillary suction absorption capacity of that material at zero hydrostatic head. In this regard, according to one aspect of the absorbent member, the absorbent member will have a capillary suction absorption capacity at zero height of at least about 15 g/g, preferably at least about 20 g/g, and even more preferably at least about 40 g/g, and most preferably at least about 60 g/g, and a capillary absorption efficiency at a height of 120 cm of at least about 40%. In another aspect, the absorbent member will have a capillary sorption absorption capacity at zero height of at least about 15 g/g, preferably at least about 20 g/g, more preferably at least about 40 g/g, and most preferably at least about 60 g/g, and a capillary absorption efficiency at a height of 70 cm of at least about 30%, preferably at least about 40%, even more preferably at least about 65%. In another aspect, the absorbent member will have a capillary sorption absorption capacity at zero height of at least about 15 g/g, preferably at least about 20 g/g, even more preferably at least about 40 g/g, and most preferably at least about 60 g/g, and a capillary absorption efficiency at a height of 35 cm of at least about 50%, preferably at least about 70%, even more preferably at least about 90%.

In another aspect, preferred storage absorbent members of the present invention will have a relatively high mean absorption height, which is defined as the height at which the member has a capillary sorption absorption capacity that is 50% of the capillary sorption absorption capacity at a height of 0 cm. In this regard, preferred storage absorbent members will have a capillary sorption absorption capacity at zero height of at least about 15 g/g, preferably at least about 20 g/g, more preferably at least about 40 g/g, and most preferably at least about 60 g/g, and a mean absorption height of at least about 35 cm, more preferably at least about 40 cm, even more preferably at least about 50 cm, and most preferably at least about 60 cm.

-lilii. Parts of high suction absorbent storage members

Representative materials useful in preparing the storage absorbent members of the present invention are described in detail below. In one particularly preferred embodiment, the storage absorbent member will be in the form of a hydrophilic polymer foam with a high surface area. In another particularly preferred embodiment, the storage absorbent member will be in the form of a hydrophilic polymer foam with a high surface area in combination with an osmotic absorbent material (e.g., a hydrogel-forming absorbent polymer). In another embodiment, the storage absorbent member will comprise a blend of high surface area fibers and an osmotic absorbent (e.g., a hydrogel-forming absorbent polymer).

A. Hydrophilic polymer foams with large surface area

As noted, polymeric foams with a large surface area, having a high capillary suction capacity, can be used as the primary component of a storage absorbent member or these foams can be used in combination with an osmotic absorbent material. While foams useful as a primary storage material (i.e., where no additional materials are used that contribute significantly to the absorbent capacity) will have many similar properties to foams used in combination with osmotic absorbents, there are certain foam properties that will vary depending on the particular embodiment. In this regard, in the discussion below of specific foam properties where no distinction is made between foams useful as a primary storage absorbent component and those used in combination with an osmotic absorbent, it should be assumed that the description of that foam property is applicable to both embodiments. Conversely, where different foam properties can be used depending on the particular embodiment, both embodiments are described.

To the extent that the high surface area polymeric foams useful herein are described in terms of their physical properties, it may be necessary to perform the analysis on the foam in sheet form. Therefore, to the extent that the foam is used in a particular form and is prepared from a previously formed sheet, physical property measurements will be made on the foam sheet (i.e., prior to particle formation). Where the foam is formed in situ into particles (or beads)

during the polymerization process, a similar foam (in terms of chemical composition, cell size, V:O ratio, etc.) can be formed into sheets for the purpose of performing these measurements.

(1) General parameters of polymer foam

High surface area polymeric foams useful in high-capacity absorbent members incorporating osmotic absorbents (e.g., hydrogel-forming absorbent polymers) of the present invention are known in the art. Particularly preferred foams for use in combination with osmotic absorbents are those obtained by polymerizing a high internal phase water-in-oil emulsion, such as the emulsions described in U.S. Patent Nos. 5,387,207 and 5,650,222. Other particularly preferred polymeric foams are described in more detail in copending U.S. Patent Applications Nos. 09/042,429 and 09/042,418. Particular, particularly preferred foams described in one or both of these copending applications are described in the examples set forth below.

The polymeric foams useful in the present invention are those foams which have relatively open cells. This means that many of the individual cells of the foam are unimpeded in communication with neighboring cells. The cells in such relatively open cell foam structures have openings or windows within the cells which are large enough to permit easy transfer of fluid from one cell to another in the foam structure.

These relatively open-cell foam structures will generally have a reticulated nature with individual cells defined by a plurality of interconnected three-dimensional branched webs. These strands of polymeric material forming these branched webs may be referred to as struts. For purposes of the present invention, the most preferred foam material will have at least about 80% of the cells in the foam structure that are at least 1 μm in size and that are in fluid communication with at least one adjacent cell.

In addition to being open-celled, these polymeric foams are sufficiently hydrophilic to allow the foam to absorb aqueous liquids. The interior surfaces of the foam structures are made hydrophilic by residual hydrophilizing surfactants.

left in the foam structure after polymerization or by selected post-polymerization foam treatment procedures as described below.

The extent to which these polymeric foams are hydrophilic can be quantified by the value of the adhesion tension exhibited when in contact with an absorbable test liquid. The adhesion tension exhibited by these foams can be determined experimentally using a procedure where the increase in weight due to the uptake of a test liquid, for example synthetic urine, is measured on a sample of known dimensions and specific surface area for capillary suction. Such a procedure is described in more detail in the section entitled Test Methods in U.S. Patent No. 5,387,207, infra. Foams which can be used as high surface area materials according to the present invention are generally those which exhibit an adhesion tension value of from about 15 to about 65 dynes/cm, more preferably from about 20 to about 65 dynes/cm, as determined by capillary absorption of synthetic urine having a surface tension of 65 ± 5 dynes/cm.

The polymer foams useful herein are preferably prepared in the form of collapsed (i.e., unexpanded) polymer foams which, upon contact with aqueous liquids, absorb such liquids and expand when the absorbed amount reduces the combined capillary pressure and ambient pressure below the foam expansion pressure described below. These collapsed polymer foams are typically obtained by forcing the aqueous phase from polymerized HIPE foam by compressive forces and/or heat drying and/or vacuum dewatering. After compression and/or heat drying/vacuum dewatering, these polymer foams are in a collapsed, unexpanded state.

The cell structure of an exemplary collapsed HEPE foam from which water has been squeezed out is shown in the photomicrographs in Figures 3 and 4 of U.S. Patent No. 5,650,222, cited above. As can be seen from these figures, the cell structure of the foam is distorted, especially when compared to the expanded HIPE foam structures shown in Figures 1 and 2 of U.S. Patent No. 5,650,222. It is also seen from Figures 3 and 4 that the voids or pores (dark areas) in the collapsed foam structure have been flattened or elongated. It is noted that the foams shown in U.S. Patent No. 5,650,222 are sheet-shaped. (As discussed below, foams in sheet form may be used in the present invention, but in a particularly preferred embodiment they are of a particular shape.) The cellular structure of another modified HIPE foam (in an expanded state) which may be used in the present invention is shown in Figures 3 and 4 of the present disclosure. The preparation of this particular foam and

Similar foams are described herein in Examples 2-4, and these very high surface area foams are described in more detail in copending U.S. Patent Application Serial No. 09/042,429 and copending U.S. Application Serial No. 09/042,418.

After compression and/or heat drying and vacuum drainage, the collapsed polymer foam can re-expand when wetted with an aqueous liquid. Surprisingly, these polymer foams remain in this collapsed or unexpanded state for a considerable period of time, for example, up to at least 1 year. The ability of these polymer foams to remain in this collapsed, unexpanded state is apparently due to capillary forces and in particular to the capillary pressure developed within the foam structure. As used herein, capillary pressure means the pressure difference across the liquid-air interface due to the curvature of the meniscus within the small space contained within the pores of the foam. [See Chatteijee, Absorbency, Textile Science and Technology, Vol. 7, 1985, p. 36],

After compression and/or heat drying and vacuum dewatering to a practical extent, these polymer foams have residual water which includes both hydration water associated with hygroscopic hydrated salts incorporated into the foams and free water absorbed into the foam. This residual water (together with hydrated salts) is likely to exert capillary pressures on the resulting collapsed foam structure. The collapsed polymer foams of the present invention, when stored at an ambient temperature of 22°C and 50% relative humidity, can have a residual water content of at least about 4%, typically from about 4% to about 40% by weight of the foam. Particularly preferred collapsed polymer foams have a residual water content of from about 5% to about 30% by weight of the foam.

A key parameter of these foams is their glass transition temperature, Tg, which represents the midpoint in the transition between the glassy and rubbery states of the polymer. Foams that have a higher _Tg than their application temperature may be very strong, but will also be very stiff and potentially prone to cracking. Such foams also typically take a long time to return to their expanded state when wetted with aqueous liquids that are cooler than the _Tg of the polymer after it has been stored in a collapsed state for extended periods. The desired combination of mechanical properties, particularly strength and flexibility, typically requires a relatively selective range of monomer types and levels to achieve these properties.

• ·

-15U foams used in this invention should have a T _g as low as possible, but the foam must have acceptable strength at the temperatures at which it is used. Accordingly, the monomers are selected as much as possible to achieve corresponding homopolymers having a lower T g. It has been found that the chain length of the alkyl group on the acrylate and methacrylate comonomers can be longer than would be predicted from the T _g of the homologous homopolymer series. In particular, it has been found that the homologous series of alkyl acrylate or methacrylate homopolymers have a minimum T _g at a chain length of 8 carbon atoms. In contrast, the minimum T _g of the copolymers of the present invention occurs at a chain length of about 12 carbon atoms. (Alkyl-substituted styrene monomers can be used instead of alkyl acrylates and methacrylates, but their availability is currently extremely limited.)

The shape of the glass transition region of a polymer as a function of temperature can also be important, i.e. whether it is narrow or wide. The shape of this glass transition region is particularly important where the temperature of use (usually ambient or body temperature) of the polymer is at or near the T _g . A wider transition region may, for example, indicate incomplete conversion at the temperature of use. If the transition is still incomplete at the temperature of use, the polymer will generally exhibit greater stiffness and be less flexible. In contrast, if the transition is already complete at the temperature of use, the polymer will exhibit a faster recovery from compression when wetted by aqueous liquids. It is therefore desirable to control the T _g and width of the polymer transition region to achieve the desired mechanical properties. In general, it is preferred that the T _g of the polymer is at least about 10 °C lower than the temperature of use. (The temperature T _g and the width of the transition region are derived from the tangent of the loss-temperature curve from Dynamic Mechanical Analysis (DMA) measurements as described in the test methods section of US Patent 5,650,222.) (2) Vertical gradient of sorption height

The large surface area polymer foams useful in the present invention can also be described by their vertical hang sorption height (VHSH). The vertical hang sorption height at X% is the height in cm up to which X% of the capacity at 0 cm (or FAC) is retained in the foam. A typical value of interest is VHSH at 90%, although in principle X can be any value. Experience with the subject • ·· ·· ·· * · · * ·

-16the invention, the most reproducible measure for VHSH is achieved at X = 90%. It will be apparent to one skilled in the art that this single point value does not fully represent the shape of the curve obtained when plotting capacity versus height. However, the single point serves as a convenient point for comparing foams useful herein. In this regard, foams will typically have a 90% VHSH of at least 20 cm, preferably at least about 70 cm, and more preferably at least about 80 cm. Preferred polymeric foams will typically have a 90% VHSH of from about 20 cm to about 90 cm, particularly from about 60 cm to about 90 cm, particularly from about 70 cm to about 90 cm, more typically from about 80 cm to about 90 cm. For foams used alone (i.e., no osmotic absorbent is used), the foam will have a 90% VHSH of at least about 60 cm, preferably at least about 70 cm, more preferably at least about 80 cm. Typically, when used alone, the polymeric foams will have a 90% VHSH of from about 60 to about 90 cm, more preferably from about 70 to about 90 cm, even more preferably from about 80 to about 90 cm.

The difference in the 90% VHSH values for the foams used in these two different embodiments is due primarily to the fact that when the foam is used in combination with an osmotic absorbent, the primary advantage provided by the foam is its large surface area, which contributes to the overall absorbent capacity of the member. This means that the foam acts primarily as a transport medium for delivering liquid to the osmotic absorbent and the absorbent capacity of the foam is of secondary importance. In contrast, when the foam is used alone, it must also have significant absorbent capacity to compensate for the lack of absorbent capacity provided by the osmotic absorbent. In this regard, 90% VHSH is a measure of absorbent capacity.

The method for measuring 90% VHSH is described in detail in the section entitled Test Methods, below. As indicated, where a high surface area polymeric foam is in particulate form when combined with an osmotic absorbent, the 90% VHSH is measured on the corresponding foam in sheet form (i.e., before particle formation). Where the foam is formed into particles (or beads) during the polymerization process, a similar foam may be formed into sheets to determine the 90% VHSH of the foam.

-17(3) Specific surface area for capillary suction

High surface area materials have generally been described in terms of their capillary sorption absorption capacity, but the high surface area polymeric foams useful herein can also be described in terms of their Capillary Suction Specific Surface Area (abbreviated as CSSSA). CSSSA is generally a measure of the surface area accessible to the test fluid of the polymer network forming a particular foam per unit weight of a block of foam material (polymer structural material plus solid residual material). Capillary suction specific surface area is determined by both the dimensions of the unit cells in the foam and the density of the polymer and is therefore a way to quantify the total amount of solid surface provided by the foam network to the extent that this surface participates in the absorption capacity. For the purpose of characterizing foams useful in the present invention, CSSSA is measured on the sheet of the foam in question as well as where the foam is in particulate form when incorporated into a storage absorbent member.

The CSSSA of a foam is particularly relevant to whether the foam will provide the desired capillary suction for use in preparing the storage absorbent members of the present invention. This is because the capillary pressure developed within the foam structure is proportional to the capillary suction of a specific surface area. In addition, the CSSSA is relevant to whether adequate capillary pressures will be developed within the foam structure to maintain it in a collapsed state until wetted by aqueous liquids. Assuming that other factors such as foam density and adhesive tension are constant, this means that as the CSSSA increases (or decreases), the capillary pressure within the foam structure will also increase (or decrease) proportionally.

For the purposes of this invention, CSSSA is determined by measuring the amount of capillary uptake of a low surface tension liquid (e.g., ethanol) that occurs in a foam sample of known mass and dimensions. A detailed description of this procedure for determining specific surface area is described in the section entitled Test Methods in U.S. Patent No. 5,387,207.

Collapsed polymeric foams of the present invention useful as absorbents are those having a CSSSA of at least 3 m ² /g. The CSSSA is typically in the range of from about 3 to about 30 m ² /g, with

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-18preferably from about 4 to about 17 m ² /g, most preferably from about 5 to about 15 m ² /g. Foams having such CSSSA values (with expanded densities of from about 0.010 to about 0.033 g/cm ³ ) will generally have a particularly desirable balance between absorbent capacity, liquid retention, and liquid wicking or distribution parameters for aqueous liquids such as urine. In addition, foams having such CSSSA values can develop sufficient capillary pressure to maintain the foam in a collapsed, unexpanded state until wetted by such aqueous liquids.

(4) Capillary pressures and forces in the foam structure

As discussed above with particularly preferred collapsible polymer foams in their collapsed state, the capillary pressures developed in the foam structure are at least equal to the forces developed by the elastic return to the original tent or modulus of the compressed polymer. In other words, the capillary pressure required to keep the collapsed foam relatively thin is determined by the opposing force exerted by the compressed polymer foam as it attempts to spring back. The tendency for polymeric foams to elastically return can be estimated from a stress-strain experiment, where the expanded foam is compressed to about 1/6 (17%) of its original expanded thickness and then held in that compressed state until the value at the relaxed stress is measured. Alternatively, and for purposes of this invention, the value at the relaxed stress is estimated from measurements on the polymeric foam in its collapsed state when in contact with aqueous liquids, e.g., water. This alternative value at the released tension is then reported as the foam expansion pressure. The expansion pressure of the collapsed polymeric foams of the present invention is about 50 kPa or less and typically from about 7 to about 40 kPa. A detailed description of the procedure for estimating the expansion pressure of foams is set forth in the section entitled Test Methods in U.S. Patent No. 5,387,207.

(5) Free absorption capacity

Another important property of the high surface area polymeric foams useful in the present invention is their free absorbent capacity. Free Absorbent Capacity (FAC) is the total amount of test fluid (synthetic urine) that a given foam sample absorbs into its cellular structure per unit weight of solid material in the sample. To make them particularly suitable for storage absorbent members of the present invention,

-19 the polymeric foams should have a free absorbent capacity of from about 30 to about 100 ml, preferably from about 30 to about 75 ml of synthetic urine per gram of dry foam material. A procedure for determining the free absorbent capacity of a foam is described in the section entitled Test Methods in U.S. Patent 5,650,222.

(6) Expansion coefficient

When exposed to aqueous liquids, particularly preferred collapsed polymeric foams absorb liquids and expand. Polymeric foams in their expanded state absorb more liquid than most other foams. The expansion coefficient of these foams is at least about four times (4x), i.e., the thickness of the foam in the expanded state is at least four times the thickness of the foam in the collapsed state. The collapsed foams preferably have an expansion coefficient in the range of about four times (4x) to about fifteen times (15x), more preferably from about five times (5x) to about ten times (10x).

For the purposes of this invention, the relationship between expanded thickness and collapsed thickness for compression-dewatered foams can be empirically calculated in advance from the following equation:

Expanded thickness collapsed thickness x ((0.0133 x V.O ratio) i 2)

Where: expanded thickness is the thickness of the foam in the expanded state, collapsed thickness is the thickness of the foam in the collapsed state and the V:O ratio is the water to oil ratio of the HIPE from which the foam is made.

A typical polymer foam is therefore made from a 60:1 water to oil emulsion and should have a predicted expansion coefficient of 8.0, i.e. an expanded thickness eight times the thickness of the collapsed foam. The procedure for measuring the expansion coefficient is described further in the section entitled Test Methods in U.S. Patent 5,650,222.

(7) Resistance to compression deflection

A relevant mechanical property of the large surface area polymer foams useful in the present invention is their strength in the expanded state as determined by Resistance to Compression Deflection (RTCD). RTCD

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-20 exhibited by the foams of the present invention is a function of the polymer modulus as well as the density and network structure of the foam. The polymer modulus is in turn determined by a) the composition of the polymer, b) the conditions under which the foam is polymerized (e.g., the degree of polymerization achieved, particularly with respect to crosslinking, and c) the extent to which the polymer is plasticized by residual material, such as emulsifiers, left in the foam structure after processing.

In order for polymeric foams to be useful as part of large surface area absorbent members, they should be suitably resistant to deformation or compression by the forces encountered in use. Foams that do not have sufficient RTCD strength may provide the required capillary suction capacity under unloaded conditions, but will not provide these capacities when subjected to compressive stresses caused by movement and activity of the wearer of absorbent articles containing the foam.

The RTCD exhibited by the polymeric foams useful in the present invention can be quantified by determining the amount of strain produced in a saturated foam sample maintained at a specified ambient pressure at a specified temperature and for a specified time. A method for performing this particular type of test is described in the section entitled Test Methods in U.S. Patent No. 5,650,222. The foams utilized herein will preferably exhibit such an RTCD that an ambient pressure of 5.1 kPa will produce a strain of typically about 90% or less by compressing the foam structure when saturated to free absorbent capacity with synthetic urine having a surface tension of 65 ± 5 dynes/cm. Advantageously, the strain produced under these conditions will be in the range of about 1 to about 90%, more preferably from about 1 to about 25%, even more preferably from about 2 to about 10%, even more preferably from about 2 to about 5%.

(8) Other properties of polymer foam

Cells, and particularly cells that are formed by polymerizing a monomer containing oil phase surrounding droplets of a water phase that is relatively free of monomer, will often be substantially spherical in shape. The size or diameter of these spherical cells is a commonly used parameter for characterizing foams in general. Since the cells in a given sample of polymeric foam will not necessarily be approximately the same size, the average cell size, i.e., the mean cell diameter, is often specified.

• ·

A number of techniques are used to determine the mean cell size of a foam. The most commonly used technique for determining the mean cell diameter in a foam is a simple measurement based on a scanning electron microscope micrograph of a foam sample.

The cell size measurements provided herein are based on the number average cell size of the foam in its expanded state, e.g., as shown in Fig. 1 of U.S. Patent No. 5,650,222. Foams useful in accordance with the present invention will preferably have a number average cell diameter of about 80 μm or less, typically from about 5 μm to about 50 μm.

Foam density (i.e., grams of foam per ^cubic centimeter of foam volume in air) is given here on a dry basis. The amount of absorbed water-soluble residual materials, such as residual salts and liquids left in the foam, for example after polymerization, washing, or hydrophilization, is not taken into account in calculating and expressing foam density. Foam density does not include, however, other water-insoluble residual materials such as emulsifiers present in the polymeric foam. Such residual materials may in fact contribute significantly to the mass of the foam material.

Any suitable gravimetric procedure that provides a determination of the mass of the rigid foam material per unit volume of the foam structure can be used to measure the density. One method that can be used to determine the density is, for example, the ASTM gravimetric procedure described in more detail in the Section entitled Test Methods ¹ ' of U.S. Patent No. 5,387,207. The polymeric foams useful in the present invention have, in the collapsed state, dry densities (without residual salts and/or water) in the range of from about 0.1 to about 0.2 g/cm ³ , preferably from about 0.11 g/cm ³ to about 0.19 g/cm ³ , and most preferably from about 0.12 g/cm ³ to about 0.17 g/cm ³ . The polymeric foams useful herein will have, in the expanded state, dry densities in the range of from about 0.01 g/cm ³ to about 0.033 g/cm ³ .

Vertical wicking, i.e., the wicking of liquid in a direction opposite to that of gravity, is a desirable attribute of the performance of the polymer foams used herein. For the purposes of this invention, the rate of vertical wicking is a reflection of the permeability of the material and therefore

the ability of the material to deliver liquid to a hydrogel-forming absorbent polymer or other osmotic absorbent.

The vertical wicking rate is determined by measuring the time required for a colored test liquid (e.g., synthetic urine) in a container to wick through a test strip of foam of a specified size to reach a distance of 5 cm. The vertical wicking procedure is described in more detail in the Test Methods Section of U.S. Patent No. 5,387,207, but is performed at 31°C instead of 37°C. To be particularly useful in absorbent members for absorbing urine, the foams used herein will preferably be capable of wicking synthetic urine (65 + 5 dynes/cm) to a height of 5 cm within 15 minutes. More preferably, the preferred foam absorbents of the present invention will provide wicking synthetic urine to a height of 5 cm within 10 minutes.

The vertical wicking absorption capacity test measures the amount of test liquid per gram of absorbent foam that is retained in each one inch (2.54 cm) of vertical section of a foam sample of the same standard size used in the vertical wicking test. Such determination is generally made after the sample has been allowed to wick the test liquid to an equilibrium state (e.g., for 18 hours). Like the vertical wicking test, the vertical wicking absorption capacity test is described in more detail in the section entitled Test Methods in U.S. Patent No. 5,387,207. High vertical wicking absorption capacities at high altitudes are theoretically equivalent to high capillary sorption absorption capacities at high altitudes. Since the sheet-like shape of the foams used herein is applicable to the previous test and the previous test is easier and less expensive to perform, data from the previous test is recommended as a means of characterizing this important parameter of the foams of the invention.

While high capillary suction foams may be in sheet form when combined with an osmotic absorbent (e.g., a hydrogel-forming absorbent polymer), in a particularly preferred embodiment, the polymeric foam will be in particulate form and will be mixed with particles of the hydrogel-forming polymer to form a mixture. That is, while the foam may initially be prepared in sheet form, these sheets may be processed into foam particles which are then combined with the hydrogel-forming polymer. As described above, foams useful herein and methods for their preparation are described in detail in U.S. Patents 5,387,207 , U.S. Patent Nos. 5,650,222 , and copending U.S. Patent Applications 09/042,429 and 09/042,418 . Foam Particles

can be prepared by first forming a sheet of foam as described in these references and then mechanically processing the foam into particles of the desired dimensions, for example by powdering, cutting, chopping, etc. The foam particles can alternatively be prepared directly from an emulsion in the form of polymer microbeads as described in US Patents 5,653,922 and 5,583,162. Specific embodiments for forming blends of polymer foam and hydrogel-forming polymer are discussed in more detail below.

It has also been found within the scope of the present invention that foams with a large surface area, when used as a transport medium for transporting a liquid to an osmotic absorbent, can optionally include a liquid to provide increased transfer of urine to the osmotic absorbent of the storage absorbent member. The pre-wetting liquid partially fills the polymeric foam and, without being bound by any particular theory, it is believed that this increases the rate of uptake of the foam. Ideally, the polymeric foam comprising the pre-wetting liquid or liquids should be storage stable with a water activity sufficiently low to prevent the growth of microorganisms and to prevent water loss by evaporation and to not migrate out of the foam over time. Water can be used as a pre-wetting liquid to provide absorbent performance, but by itself may not meet all requirements.

B. Storage absorbent members including osmotic absorbent and high surface area materials

As noted above, in one embodiment, the storage absorbent members of the present invention will include an osmotic absorbent, such as an absorbent polymer comprising a hydrogel, and a high surface area material that facilitates the transport of body fluids into the osmotic absorbent. In one such embodiment, the high surface area material will be in the form of a high surface area hydrophilic polymer foam, as discussed above. Other representative materials useful in preparing the storage absorbent members of the present invention are high surface area fibers, which are described in detail below. While other osmotic absorbents may be used in the storage members, hydrogel-forming absorbent polymers are preferred. As such, these materials are described in detail.

1. Absorbent hydrogel-forming polymers

a. Chemical composition

In one preferred embodiment, the storage absorbent members of the present invention comprise at least one hydrogel-forming absorbent polymer, also referred to as a hydrogel-forming polymer. The hydrogel-forming polymers useful in the present invention include a variety of water-insoluble but water-swellable polymers that are capable of absorbing large amounts of liquids. Such hydrogel-forming polymers are well known in the art, and any of these materials can be used in the high capillary suction absorbent members of the present invention.

Absorbent hydrogel-forming polymers are also commonly referred to as materials called hydrocolloids or superabsorbents and may include polysaccharides such as carboxymethyl starch, carboxymethyl cellulose and hydroxypropyl cellulose, nonionic types such as polyvinyl alcohol and polyvinyl ethers, cationic types such as polyvinylpyridine, polyvinylmorpholine and N,N-dimethylaminoethyl or N,N-dimethylaminopropyl acrylates and methacrylates and their respective quaternary salts. Absorbent hydrogel-forming polymers that can be used in the present invention generally have multiple anionic functional groups such as sulfonic acid groups and more typically carboxy groups. Examples of polymers suitable for use herein include those polymers that are prepared from polymerizable, unsaturated, acid-containing monomers. Such monomers thus include olefinically unsaturated acids and anhydrides that contain at least one olefinic double bond between two carbons. These monomers may more particularly be selected from olefinically unsaturated carboxylic acids and their anhydrides, olefinically unsaturated sulfonic acids and mixtures thereof. As indicated above, the nature of the absorbent polymer forming the hydrogel is not critical to the members of the present invention. However, the selection of an optimal polymeric material can enhance the performance parameters of the members of the present invention. The following description of the invention describes particularly advantageous properties of the absorbent polymers used herein. These properties should not be interpreted as limitations, but rather are indicative of the progress that has been made in the field of absorbent polymers over the past few years.

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In the preparation of the absorbent hydrogel-forming polymers disclosed herein, certain monomers that are not acids may also be included, usually in small amounts. Such non-acidic monomers may include, for example, water-soluble or water-dispersible esters of acid-containing monomers, as well as monomers that do not contain any carboxylic or sulfonic acid groups at all. Optional non-acidic monomers may thus include monomers containing the following types of functional groups: esters of carboxylic acids or sulfonic acids, hydroxyl groups, amide groups, amine groups, nitrile groups, quaternary ammonium salt groups, aryl groups (e.g., phenyl groups such as those derived from styrene monomer). These non-acidic monomers are well known materials and are described in more detail, for example, in U.S. Patents 4,076,663 and 4,062,817.

Monomers based on olefinically unsaturated carboxylic acids and carboxylic acid anhydrides include acrylic acids, of which this type includes acrylic acid itself, methacrylic acid, ethacrylic acid, α-chloroacrylic acid, α-cyanoacrylic acid, β-methacrylic acid (crotonic acid), α-phenylacrylic acid, β-acryloxypropionic acid, sorbic acid, α-chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid, β-sterylacrylic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene, and maleic anhydride.

Olefinically unsaturated sulfonic acid monomers include aliphatic or aromatic vinyl sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, vinyl toluene sulfonic acid and styrene sulfonic acid; acrylic and methacrylic sulfonic acids such as sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-hydroxy-3-methacryloxypropyl sulfonic acid and 2-acrylamide-2-methylpropane sulfonic acid.

Preferred absorbent hydrogel-forming polymers for use in the present invention contain carboxy groups. These polymers include hydrolyzed graft copolymers of starch and acrylonitrile, partially neutralized hydrolyzed graft copolymers of starch, and

-26acrylonitrile, graft copolymers of starch and acrylic acid, partially neutralized graft copolymers of starch and acrylic acid, saponified copolymers of vinyl acetate and acrylic ester, hydrolyzed copolymers of acrylonitrile or acrylamides, slightly cross-linked polymers of any of the above copolymers, partially neutralized polyacrylic acid and slightly cross-linked polymers of partially neutralized polyacrylic acid. These polymers can be used either alone or in the form of a mixture of two or more different polymers. Examples of these polymeric materials are described in US Patents 3,661,875, US Patent 4,076,663, US Patent 4,093,776, US Patent 4,666,983 and US Patent 4,734,478.

The most preferred polymeric materials for use in the manufacture of absorbent hydrogel-forming polymers are slightly cross-linked polymers of partially neutralized polyacrylic acids and starch derivatives thereof. The absorbent hydrogel-forming polymers most preferably comprise from about 50% to about 95%, preferably about 75%, neutralized, slightly cross-linked polyacrylic acid (i.e., poly(sodium acrylate/acrylic acid)). Cross-linking leaves the polymer essentially water-insoluble and in part determines the absorbent capacity and extractable polymer content parameters of the absorbent hydrogel-forming polymers. The processes for cross-linking these polymers and typical cross-linking agents are described in more detail in U.S. Patent 4,076,663.

While the absorbent polymer forming the hydrogel is preferably of a single type (i.e., homogeneous), mixtures of polymers may also be used in the present invention. For example, mixtures of grafted starch-acrylic acid copolymers and slightly crosslinked partially neutralized polyacrylic acid polymers may be used in the present invention.

The polymer component forming the hydrogel may also be in the form of a mixed bed ion exchange mixture comprising a cation exchange hydrogel forming absorbent polymer and an anion exchange hydrogel forming absorbent polymer. Such mixed bed ion exchange mixtures are described, for example, in patent applications U.S. No. 09/003565, U.S. No. 09/003905, U.S. No. 09/003918.

The absorbent hydrogel-forming polymers useful in the present invention may have a wide range of size, shape, and/or morphology. These polymers may be in the form of particles,

27which do not have a large ratio of the largest dimension to the smallest dimension (e.g., granules, powders, particle aggregates, crosslinked particle aggregates, and the like) and may be in the form of fibers, sheets, films, foams, flakes, and the like. Absorbent hydrogel-forming polymers may also include mixtures with low levels of one or more additives, such as powdered silicate, surfactants, adhesives, binders, and the like. The components in this mixture may be physically and/or chemically associated in such a form that the hydrogel-forming polymer component and the non-hydrogel-forming polymer additive are not readily physically separable.

The absorbent polymers forming the hydrogel may be substantially non-porous, i.e., without internal porosity, or have significant internal porosity.

For particles such as those described above, particle size is defined as the size determined by sieve analysis, so that, for example, a particle that is retained on a US standard test sieve having 710 micron openings (e.g., a No. 25 sieve as designated in the US) is considered to have a size greater than 710 microns; a particle that passes through a 710 micron sieve and remains on a 500 micron sieve (e.g., a No. 35 sieve as designated in the US) is considered to have a particle size between 500 and 710 microns, and a particle that passes through a 500 micron sieve is considered to have a size less than 500 microns. The weight median particle size of a given sample of hydrogel-forming absorbent polymer particles is defined as that particle size that divides the sample in half on a weight basis, i.e., one half of the sample by weight will have a particle size smaller than the weight median particle size and one half of the sample will have a particle size larger than the weight median particle size. The standard particle size plotting method, in which the cumulative weight percent of the sample of particles that remain or pass a given sieve size is plotted against the sieve opening size on a frequency plot, is typically used to determine the weight median particle size where 50% by weight does not correspond to the size of the test sieve opening according to the U.S. standard. These methods for determining the particle size of hydrogel-forming absorbent polymer particles are further described in U.S. Patent No. 5,061,259.

For the hydrogel-forming absorbent polymer particles useful in the present invention, the particles will generally range in size from about 1 pm to about 2000 pm, more preferably from about 20 pm to about 1000 pm. The weight median particle size will generally be from about 20 pm to about

-281500 pm, more preferably from about 50 pm to about 1000 pm, even more preferably from about 50 pm to about 1000 pm and even more preferably from about 100 pm to about 800 pm.

Where relatively high concentrations, e.g., 40% to 60% by weight or more, of the hydrogel-forming absorbent polymer are used in the absorbent members of the present invention, other properties of the absorbent polymer may be important. In such embodiments, the materials may have one or more of the properties described in U.S. Patent Nos. 5,562,646 and 5,599,335.

b. Production methods

The basic absorbent polymer forming the hydrogel can be formed by any conventional method. Typical and preferred processes for the production of these polymers are described in U.S. Patents Reissue 32,649, U.S. Patent Nos. 4,666,983 and 4,625,001.

Preferred methods for forming the basic absorbent polymer forming the hydrogel are those involving solution polymerization methods, where the solution is water or other solvent. As described in the aforementioned US Reissue 32,649, aqueous solution polymerization involves using an aqueous reaction mixture to carry out the polymerization. The aqueous reaction mixture is then subjected to polymerization conditions sufficient to produce a slightly crosslinked polymer mixture that is substantially insoluble in water. The mass of polymer formed can then be powdered or chopped into individual particles.

More specifically, the aqueous solution polymerization process for producing an absorbent hydrogel-forming polymer comprises preparing an aqueous reaction mixture in which the polymerization is to be carried out. One component of such reaction mixture is a monomer containing an acidic group which will form the backbone of the absorbent hydrogel-forming polymer to be produced. The reaction mixture will generally comprise about 100 parts by weight of monomer. Another component of the aqueous reaction mixture is a crosslinking agent. The network-forming crosslinking agents which can be used in the production of the absorbent hydrogel-forming polymer of the present invention are described in more detail in the aforementioned U.S. Reissue 32,649, U.S. 4,666,983 and U.S. 4,625,001. The network-forming crosslinking agent will generally be present in the aqueous reaction mixture in an amount of from about 0.001 * · · · ·

-29·· · ·· 9 9 9 99 9 9 9 mole percent to about 5 mole percent, based on 100 parts by weight of monomer). Another optional component of the aqueous reaction mixture will be a free radical initiator including, for example, peroxide compounds such as sodium, potassium and ammonium persulfates, caprylyl peroxide, benzoyl peroxide, hydrogen peroxide, cumendhydroperoxides, tertiary butyl diperphthalate, tertiary butyl perbenzoate, sodium peracetate, sodium percarbonate, etc. Other optional components of the aqueous reaction mixture include various non-acidic comonomers, including esters of essential, unsaturated, acid functional group-containing monomers or other comonomers containing no carboxylic or sulfonic acid functional groups at all.

The aqueous reaction mixture is subjected to polymerization conditions sufficient to form substantially insoluble but water-swellable, hydrogel-forming, absorbent, slightly crosslinked polymers in the mixture. Polymerization conditions are also discussed in more detail in the three patents cited above. These polymerization conditions generally include heating (thermal activation techniques) to a polymerization temperature of from about 0°C to about 100°C, more preferably from about 5°C to about 40°C. The polymerization conditions under which the aqueous reaction mixture is maintained may include, for example, subjecting the reaction mixture or portions thereof to any conventional form of polymerization activation irradiation. Radioactive, electronic, ultraviolet, or electromagnetic radiation are alternatives to conventional polymerization techniques.

The acidic functional groups of the hydrogel-forming absorbent polymer formed in the aqueous reaction mixture are also preferably neutralized. Neutralization can be carried out by any conventional method that results in at least 25 mole percent, and more preferably at least about 50 percent, of the total monomer used to form the polymer from monomers containing an acidic group being neutralized with a salt-forming cation. Such salt-forming cations include, for example, alkali metals, ammonium, substituted ammoniums, and amines as discussed in more detail in the aforementioned U.S. Patent Reissue 32,649.

While it is preferred that particular versions of the hydrogel-forming absorbent polymer be made using a polymerization process that utilizes an aqueous solution, it is also possible to carry out the polymerization process using multi-phase polymerization process techniques, such as inverse emulsion polymerization or inverse suspension polymerization procedures. In the case of inverse emulsion polymerization,

polymerization or inverse suspension polymerization processes, the aqueous reaction mixture, as described above, is suspended in the form of small droplets in a matrix of a water-immiscible inert organic solvent such as cyclohexane. The resulting hydrogel-forming absorbent polymer particles are generally spherical in shape. Inverse suspension polymerization processes are described in more detail in U.S. Patents 4,340,706, 4,506,052, and 4,735,987.

Surface crosslinking of initially formed polymers is a preferred process for obtaining hydrogel-forming absorbent polymers having relatively high Porosity Hydrogel Layer (PHL), Performance under Pressure (PUP), and Saline Flow Conductivity (SFC) values that may be advantageous in the context of the present invention. Suitable general methods for performing surface crosslinking of the absorbent hydrogel-forming polymers of the present invention are described in U.S. Patent No. 4,541,871, PCT Published Application WO 92/16565, PCT Published Application WO 90/08789, PCT Published Application WO 93/05080, U.S. Patents Nos. 4,824,901, 4,789,861, 4,587,308, 4,734,478, 5,164,459, German Published Application No. 4,020,780, and European Published Application No. 509,708. See also U.S. Patents Nos. 5,562,646 and 5,599,335.

The absorbent polymer hydrogel particles prepared according to the present invention are generally substantially dry. The term substantially dry is used herein to mean that the particles have a liquid content, typically water or other solute content, of less than about 50%, preferably less than about 20%, more preferably less than about 10% by weight of the particles. The liquid content of the absorbent polymer hydrogel particles is in the range of from about 0.01% to about 5% by weight of the particles. The individual particles can be dried by any conventional method, such as heating. When the particles are formed using an aqueous reaction mixture, water can alternatively be removed from the reaction mixture by azeotropic distillation. The aqueous reaction mixture containing the polymer can also be treated with a dewatering solvent such as methanol. Combinations of these drying methods can also be used. The dewatered polymer mass can then be chopped or powdered to form substantially dry absorbent polymer hydrogel particles.

2. Materials with a large surface area

With respect to the storage absorbent members of the present invention, such members include an osmotic absorbent (e.g., hydrogel-forming absorbent polymers) and the member also includes a high surface area material. It is this high surface area material that provides, either alone or in combination with the hydrogel-forming absorbent polymer, members with high capillary sorption absorbent capacity. As noted herein, high surface area materials are described in at least one respect based on their capillary sorption absorbent capacity, measured without the hydrogel-forming polymer or any other optional materials included in a particular storage absorbent member, such as adhesives, binding agents, etc. It is recognized that materials having a high surface area may have the ability to absorb at very high suction heights, such as 100 cm or higher. This allows the high surface area materials to provide one or both of the following functions: (1) a liquid capillary path for the osmotic absorbents and/or (2) additional absorbent capacity. Thus, while materials with a high surface area may be described by their surface area per mass or volume, the present application alternatively uses capillary sorption absorptive capacities to describe a material having a high surface area, since capillary sorption absorptive capacity is a performance parameter that will provide the absorbent members of the present invention with the desired wicking capabilities to provide improved absorbent products. It is believed that certain materials with a high surface area, such as glass microfibers, will not by themselves exhibit particularly high capillary sorption absorptive capacities at all heights, particularly very high heights, such as 100 cm and above. However, such materials may provide the desired liquid capillary pathway for an absorbent hydrogel-forming polymer or other osmotic absorbent to provide the desired capillary sorption absorptive capacities even at relatively high heights when combined with a hydrogel-forming polymer or other osmotic absorbent.

Any material having sufficient absorbent capacity by capillary sorption when used in combination with an absorbent hydrogel-forming polymer or other osmotic absorbent will be useful in the storage absorbent members of the present invention. In this regard, the term high surface area material refers to any material that exhibits, by itself,

by itself, i.e. measured without the osmotic absorbent or other optional material forming the storage absorbent member, one or more of the following capillary sorption absorption capacities: (1) a capillary sorption absorption capacity of at least about 2 g/g at a suction height of 100 cm, preferably at least about 3 g/g, even more preferably at least about 4 g/g and even more preferably at least about 6 g/g at a height of 100 cm; (2) a capillary sorption absorption capacity at a height of 35 cm of at least about 5 g/g, preferably at least about 8 g/g, more preferably at least about 12 g/g; (3) a capillary sorption absorption capacity at a height of 50 cm of at least about 4 g/g, preferably at least about 7 g/g, more preferably at least about 9 g/g; (4) an absorption capacity by capillary sorption at a height of 140 cm of at least about 1 g/g, preferably at least about 2 g/g, more preferably at least about 3 g/g, even more preferably at least about 5 g/g; or (5) an absorption capacity by capillary sorption at a height of 200 cm of at least about 1 g/g, preferably at least about 2 g/g, more preferably at least about 3 g/g, and even more preferably at least about 5 g/g.

In one embodiment, the high surface area material will be fibrous in nature. Hereinafter referred to as high surface area fibers. This results in a fibrous web or fibrous matrix when combined with an absorbent polymer that forms a hydrogel or other osmotic absorbent. Alternatively, in a particularly preferred embodiment, the high surface area material will be a hydrophilic, open-celled polymeric foam, hereinafter referred to as high surface area polymeric foams or more generally polymeric foams. These materials are described in detail above.

High surface area fibers useful in the present invention include those fibers that occur in nature (treated or untreated) as well as synthetically produced fibers. High surface area fibers have surface areas much greater than fibers typically used in absorbent products, such as wood pulp fibers. The high surface area fibers of the present invention will preferably be hydrophilic. As used herein, the term hydrophilic describes fibers or fiber surfaces that are wettable by aqueous liquids, such as aqueous body fluids, deposited on the fibers. Hydrophilicity and wettability are generally defined in terms of the contact angle and surface tension of the respective liquids and solids. This is discussed in detail in the American Chemical Society publication Contact Angle, Wettability and Adhesion, edited by Robert F. Gould (Copyright 1964). A fiber or

The surface of a fiber is considered to be wetted by a liquid, i.e., hydrophilic, when either the contact angle between the liquid and the fiber or its surface is less than 90° or when the liquid tends to spread spontaneously across the surface of the fiber, both conditions normally occurring simultaneously. In contrast, the fiber or surface is considered to be hydrophobic if the contact angle is greater than 90° and the liquid does not spread spontaneously across the surface of the fiber. The hydrophilic character of the fibers that can be used herein may be inherent in the fiber or the fibers may be naturally hydrophobic fibers that have been modified to become hydrophilic. Materials and methods for achieving hydrophilicity in naturally hydrophobic fibers are well known.

The high surface area fibers useful herein will have specific surface areas for capillary suction in the same range as the polymer foams described below. However, high surface area fibers are typically characterized by BET surface area.

High surface area fibers useful herein include glass microfibers such as glass wool, which is available from Evanite Fiber Corp. (Corvallis, OR, USA). Glass microfibers useful herein will typically have fiber diameters of no greater than about 0.8 pm, more preferably from about 0.1 pm to about 0.7 pm. These fibers will have surface areas of at least about 2 m ² /g, more preferably at least about 3 m ² /g. Typically, the surface area of glass microfibers will be from about 2 m ² /g to about 15 m ² /g. Representative glass microfibers for the present use are those available from Evanite Fiber Corp. as Type 104 glass fibers, which have a nominal fiber diameter of about 0.5 pm. These glass microfibers have a calculated surface area of about 3.1 m ² /g.

Other high surface area fibers useful herein are fibrillated cellulose acetate fibers. These fibers (referred to herein as fibrils) have a high surface area compared to cellulose-derived fibers commonly used in the absorbent products industry. Such fibrils have very small diameter regions such that their particle size range is typically from about 0.5 to about 5 pm. These fibrils typically have a surface area of about 20 m ² /g. Representative fibers useful herein as high surface area materials are available from Hoechst Celanese Corp. (Charlotte, NC, USA) as cellulose acetate fibers called Fibrets®. These fibers are discussed in detail, including their physical properties and methods of making them, in Cellulose Acetate Fibers: Fibrillated

• ·

-34Cellulose Acetate Fibrets: A Fibrillated Pulp With High Surface Area, Smith, J. Ίζ.,Ταρρΐ Journal, December 1988, p. 237, and in US Patent 5,486,410.

In addition to these fibers, it will be apparent to one skilled in the art that other fibers well known in the art can be modified to have a high surface area and be used in the present invention. Representative fibers that can be modified to achieve the high surface areas required by the present invention are described in U.S. Patent 5,599,335, supra (see particularly columns 21-24).

Regardless of the nature of the high surface area fibers used, the fibers and the osmotic absorbent will be discrete materials prior to combination. As used herein, the term discrete means that the high surface area fibers and the osmotic absorbent are both formed prior to being combined to form the storage absorbent member. In other words, the high surface area fibers are not formed subsequent to mixing with the osmotic absorbent, such as an absorbent polymer forming a hydrogel, nor is the osmotic absorbent formed subsequent to combination with the high surface area fibers. Combining the individual discrete components ensures that the high surface area fibers will have the desired morphology and, more importantly, that they will have the desired surface area.

C. Other components and materials, if any

The storage absorbent members of the present invention may include other optional components that may be present in the absorbent webs. For example, a reinforcing mesh may be placed in the storage absorbent member or between the respective absorbent members of the absorbent core. Such reinforcing meshes should be arranged so as not to form interfacial barriers to liquid transfer, particularly when placed between the respective absorbent members of the absorbent core. In addition, several binders may be used to ensure the integrity of the absorbent core in both dry and wet conditions, or of the absorbent storage member itself. In particular, hydrophilic adhesive fibers may be used to ensure the bonds between the high surface area materials and the osmotic absorbent material. This is particularly critical for particulate materials with high surface area. It is preferred that the amount of binder used be as small as possible so as not to impair the capillary sorption properties of the absorbent member, but it will be apparent to those skilled in the art that there are also

binders that can enhance the capillary sorption properties of the absorbent member, such as spunbond hydrophilic adhesives with a sufficiently large surface area. In this case, the hydrophilic adhesive with a large surface area can provide both a liquid handling function and an integrity function in one material. Also, the respective absorbent member or the entire absorbent core can be wrapped in a sheet that is permeable to liquid, such as a sheet of tissue paper, to prevent the movement of free particles of the absorbent polymer while not disrupting capillary continuity.

Other optional components that can be included are materials that control odors of fecal-containing materials, etc. Each absorbent member comprising a particulate osmotic absorbent or high surface area material, or the entire absorbent core, can also be wrapped in a sheet of liquid-permeable material, such as a sheet of tissue paper, to prevent movement of loose particles of absorbent polymer.

IV. Other materials and properties of the storage absorbent member

The high-capacity capillary suction absorbent storage members of the present invention function as liquid storage members within an absorbent core. The principal function of such liquid storage members is to absorb discharged body fluid either directly or from other absorbent members (e.g., liquid acquisition and distribution members) and then retain such fluid even when subjected to pressures normally encountered as a result of wearer movement. It is to be understood, however, that such absorbent members may serve functions other than liquid storage.

In those preferred embodiments where an osmotic absorbent is used, the amount of hydrogel-forming absorbent polymer or other osmotic absorbent contained in the storage absorbent member may vary significantly. The concentration of the osmotic absorbent may further vary within a given member. In other words, the member may have regions of relatively higher and relatively lower concentrations of the osmotic absorbent.

Without wishing to be bound by theory, it is believed that a minimal amount of a high surface area material mixed with a hydrogel-forming polymer or other osmotic

• ·· • 99 • 9 • • » 99 • • • » • • • 9 • • e · · · ·· ·· t ·· • • • · ·· •

The absorbent material must be sufficient to fill the interstices between the particles of the absorbent hydrogel-forming polymer or other absorbent to such a functional degree in the dry and wet state that capillary continuity and sufficient liquid flow into the absorbent hydrogel-forming polymer are ensured.

In those preferred embodiments where the osmotic absorbent is in the form of a hydrogel-forming absorbent polymer, the concentration in a given area of the absorbent member is measured as a weight percentage of the hydrogel-forming absorbent polymer relative to the combined weight of the hydrogel-forming absorbent polymer and all other components (e.g., fibers, polymer foams, etc.) present in the area containing the hydrogel-forming polymer. With this in mind, the concentration of hydrogel-forming absorbent polymers in a given area of the absorbent member of the present invention may be at least about 50%, more preferably at least about 60%, even more preferably about 70%, even more preferably about 80%, and most preferably about 90% of the total weight of the absorbent member. Similar ranges are contemplated where other osmotic absorbents are used.

Notwithstanding the fact that the storage areas of the absorbent member may include relatively high concentrations of the absorbent polymer forming the hydrogel or other absorbent polymer, where the high surface area material is fibrous in nature, the member will include on an aggregate basis (i.e., based on the total weight of the high surface area fibers used in the member divided by the total weight of the absorbent member times 100%) at least about 25% by weight of the high surface area fibers. It is believed that a lower limit of about 25% fibers is necessary to achieve the necessary desired capillary suction of the absorbent member. Storage absorbent members will preferably include at least about 30% by weight, more preferably at least about 35% by weight of the high surface area fibers. The absorbent member of the present invention will typically comprise, on an aggregate basis, from about 25% to about 90% by weight, more preferably from about 30% to about 85% by weight, even more preferably from about 35% to about 80% by weight of high surface area fibers.

In those embodiments where the high surface area material is a polymeric foam, the absorbent members will preferably include at least about 1% by weight (on an aggregate basis) of polymeric foam. It is believed that the ability to use very low levels of polymeric foam compared to • · > ♦

-37Φ ·· ·· · · • * · · · · • · 9 ··· ·· the amount of high surface area fibers discussed above is determined by various factors, including the very low density of these foams, the fact that the foams are open-celled, that the foams themselves contribute to the overall absorbent capacity, and the like. The storage absorbent member will preferably comprise at least about 10% by weight, more preferably at least about 15% by weight, even more preferably at least about 20% by weight of the polymeric foam. Such storage absorbent members will comprise from about 1% to about 98% by weight, more typically from about 10% to about 90% by weight, even more typically from about 15% to about 85% by weight, even more preferably from about 20% to about 80%, and even more preferably from about 20% to about 50% by weight of the polymeric foam material. As described above, these weight percent ranges are based on the total weight of the respective materials in the storage absorbent member. It is understood that regions of the storage absorbent member may contain greater and lesser amounts of materials.

The relative levels of osmotic absorbent, e.g., hydrogel-forming absorbent polymer, and high surface area material will be dictated by, for example, the absorbent capacity of the osmotic absorbent, the specific high surface area material used, the nature of the high surface area material, e.g., foam sheet or particle, particle size, etc. In this regard, while high levels of osmotic absorbent provide absorbent members for the manufacture of thin absorbent articles, to achieve the desired level of capillary suction discussed above, a material with a sufficiently large surface area must be available to provide such suction capacity. Without being bound by theory, it is believed that the three primary properties of the preferred collapsible polymeric foam materials described above enable these foams to perform particularly effectively in high suction storage absorbent members. These three properties are (1) relatively low density, (2) the ability to readily distribute liquid therein, and (3) the ability to remain collapsed but then expand upon absorption of sufficient liquid, with preferred hydrogel-forming absorbent polymers swelling upon imbibing liquid. This latter property maintains contact between the foam material and the hydrogel-forming particles as the member absorbs liquid.

Figures 3, 4, 5 and 6 show, in the form of microphotographs, examples of storage absorbent members according to the present invention. Figures 3 and 4 show high-absorption polymeric foams which can themselves (preferably in sheet form) act as a storage absorbent member. Figures 5, 6 and 7

-38 illustrate absorbent storage members comprising an osmotic absorbent (specifically, a hydrogel-forming absorbent polymer) and a high surface area material. FIG. 5 illustrates a mixture of particulate hydrophilic polymeric foam materials 102 and particulate hydrogel-forming absorbent polymer 106. Also illustrated are adhesive fibers 110 that provide structural integrity and maintain contact between the foam material particles 102 and the hydrogel-forming absorbent polymer 106. FIG. 6 illustrates a single hydrogel-forming polymer particle 116 surrounded by a plurality of fibers 114. FIG. 7 then illustrates a cross-section of a single hydrogel-forming particle 126 surrounded by a plurality of glass fibers 125.

With respect to storage absorbent members comprising a hydrogel-forming absorbent polymer, in addition to the high surface area material and the hydrogel-forming absorbent polymer, the storage absorbent members of the present invention may also comprise other optional materials. For example, to ensure the integrity of the mixture of desired materials, the storage absorbent members may comprise an adhesive or binding material. Such materials may be particularly desirable where the high surface area material is particulate in nature.

When integrity is achieved by means of a bonding material, suitable bonding materials are hot melt adhesives, such as those described in US Patent 5,560,878. Processes for combining hot melt adhesives with the desired hydrogel-forming polymer and high surface area material are also described in detail in US Patent 5,560,878.

Another example of a material that will provide the integrity of the blend in absorbent members comprising a blend of a hydrogel-forming polymer and high surface area fibers and/or particulate polymeric foams may include a thermoplastic material. Upon melting, at least a portion of the thermoplastic material migrates into the interstices of the respective components of the member, typically due to interparticle or intercapillary gradients. These interstices become bonding sites for the thermoplastic material. When cooled, the thermoplastic materials solidify in these interstices and form bonding sites that hold the matrix of materials together.

The individual thermoplastic materials useful herein may be in any of a number of forms, including particles, fibers, or combinations of particles and fibers. Thermoplastic fibers are a particularly preferred form because they are capable of forming numerous bonding sites. Suitable Thermoplastic Materials

They can be made of any thermoplastic polymer that can be melted at temperatures that do not significantly damage the materials of which the absorbent member is composed. The melting point of this thermoplastic material will preferably be less than about 190°C and preferably in the range of about 75°C to about 175°C. In any case, the melting point of this thermoplastic material should not be less than the temperature at which the thermally bonded absorbent structures are likely to be stored when used in absorbent articles. The melting point of the thermoplastic material is typically not less than about 50°C.

Thermoplastic materials, and in particular thermoplastic fibers, can be made from a variety of thermoplastic polymers, including polyolefins such as polyethylene (e.g., PULPEX® and polypropylene, polyesters, copolyesters, polyvinyl acetate, polyethylvinyl acetate, polyvinyl chloride, polyvinylidene chloride, polyacrylates, polyamides, copolyamides, polystyrenes, polyurethanes, and copolymers of the foregoing polymers such as vinyl chloride/vinyl acetate, and the like. One particularly preferred thermoplastic bonding fiber is PLEXAFIL®, which is polyethylene microfibers (manufactured by DuPont), which are also available as an approximately 20 percent blend with 80 percent cellulose fibers, sold under the trade name KITTYHAWK® (manufactured by Weyerhauser Co.). Depending on the desired parameters for the resulting heat-bonded absorbent member, thermoplastic materials include hydrophobic fibers that have been modified to be hydrophilic, such as surfactant-treated or silicate-treated fibers derived from, for example, polyolefins such as polyethylene or polypropylene, polyacrylates, polyamides, polystyrenes, polyurethanes, and the like. The surface of hydrophobic thermoplastic fibers can be made hydrophilic by treating them with a surfactant, such as a nonionic or anionic surfactant, e.g., by spraying the fibers with a surfactant, dipping the fibers in a surfactant, or including the surfactant as part of the polymer melt during the production of the thermoplastic fibers. After melting and resolidification, the surfactant tends to remain on the surface of the thermoplastic fibers. Suitable surfactants include nonionic surfactants such as Brij® 76, manufactured by ICU Americas, Inc. of Wilmington, Delaware, USA, and various surfactants sold under the trademark Pegosperse® by Glyco Chemical, Inc. of Greenwich, Connecticut, USA. In addition to nonionic surfactants, Anionic surfactants can also be used

surfactants. These surfactants can be applied to thermoplastic fibers at levels, for example, from about 0.2 g/cm ² to about 1 g/cm ² of thermoplastic fibers.

Suitable thermoplastic fibers can be made from a single polymer (monocomponent fibers) or can be made from more than one polymer, for example, bicomponent fibers. The term bicomponent fibers as used herein refers to thermoplastic fibers that consist of a core fiber made from one polymer and a thermoplastic sheath surrounding the core made from a different polymer. The sheath polymer often melts at a different, usually lower, temperature than the core polymer. As a result, these bicomponent fibers provide a thermal bond by melting the sheath polymer while maintaining the desired strength characteristics of the core polymer.

Suitable bicomponent cores for use in the present invention may include sheath and core fibers having the following polymer combinations: polyethylene/polypropylene, polyethylvinyl acetate/polypropylene, polyethylene/polyester, polypropylene/polyester, copolyester/polyester, and the like. Particularly suitable thermoplastic fibers for use in the present invention are those having a polypropylene or polyester core and a lower melting copolyester, polyethylvinyl acetate, or polyethylene sheath (e.g., DANAKON®, CELBOND®, or CHISSO® bicomponent fibers). These bicomponent fibers may be concentric or eccentric. The terms concentric and eccentric, as used herein, refer to whether the sheath has a thickness that is uniform or non-uniform over the cross-sectional area of the bicomponent fibers. Eccentric bicomponent fibers may be desirable in that they provide greater compressive strength at lower fiber thickness. Suitable bicomponent fibers can be crimped using typical textile means, such as a crimping process or a tooth crimping process, to achieve a predominantly two-dimensional or flat crimp.

In the case of thermoplastic fibers, their length can vary depending on the particular melting point and other properties desired for the fibers. These thermoplastic fibers typically have a length of from about 0.3 to about 7.5 cm, preferably from about 0.4 to about 3.0 cm, and most preferably from about 0.6 to about 1.2 cm. The properties, including the melting point, of these thermoplastic fibers can also be adjusted by varying the outer diameter (gauge) of the fibers. The diameter of these thermoplastic fibers is typically defined by parameters such as either denier

-41 (weight in grams per 9000 m length) or decitex (weight in grams per 10,000 m length). Suitable bicomponent thermoplastic fibers may have a decitex in the range of from about 1.0 to about 20, preferably from about 1.4 to about 10, and most preferably from about 1.7 to about 3.3.

The compressive modulus of these thermoplastic materials, and in particular thermoplastic fibers, may also be important. The compressive modulus of thermoplastic fibers is influenced not only by their length and diameter, but also by the composition and properties of the polymer or polymers from which they are made, the shape and arrangement of the fibers (e.g., whether they are concentric or eccentric, crimped or not), and similar factors. Differences in the compressive modulus of these thermoplastic fibers can be used to alter the properties and, in particular, the density parameters of the respective absorbent members during the preparation of the absorbent core.

Other materials known in the art may be included in absorbent storage members provided that they are included at levels low enough to achieve the desired capillary wicking properties. Optionally, other fibrous materials that are commonly combined with absorbent hydrogel-forming polymers may be included in the storage members of the present invention. For example, wood fibers may be included, as well as synthetic fibers, but since such materials will tend to reduce the capillary wicking ability of storage members comprising a high surface area material and a hydrogel-forming polymer, they will be included at relatively low levels so that the members still provide the desired absorbent capacity by capillary wicking. It may be preferred to avoid the use of such fibers because they increase bulk and reduce capillary sorption ability on a weight basis.

Numerous methods known in the art can be used to combine the hydrogel-forming polymer (or other osmotic absorbent) and the high surface area material. Of course, the physical form (e.g., fibrous, particulate, etc.) of the high surface area material and the hydrogel-forming absorbent polymer (or other osmotic absorbent) will dictate at least to some extent what methods can be used to form particular embodiments of storage absorbent members.

In one embodiment, the hydrogel-forming absorbent polymer particles may be attached to a fibrous material to prevent unwanted migration of the particles during manufacture, storage, or wear. Attachment of absorbent particles to a molten polymeric material is described in

-42EP 156 160, describing a molten polymeric material extruded to form a stream of meltblown polymeric microfibers and, while still tacky, absorbent particles are introduced into them so that they adhere to the fibers.

A method of entrapping particulate absorbent materials in a melt-spun web is described in U.S. Patent No. 4,923,454, which describes absorbent structures comprising microfibers and absorbent articles comprising wettable, hydrophilic, nylon, melt-spun microfibers and hydrogel-forming polymer particles, as well as in U.S. Patent No. 4,773,903, which describes melt-spun microfibers and hydrogel-forming polymer particles and crimped staple fibers and a hydrophilizing agent.

The embedding of high surface area materials and hydrogel-forming absorbent polymers by the process generally described in U.S. 4,764,325 is also possible. The high surface area material and hydrogel-forming polymer may also be encapsulated by the processes generally described in U.S. Patent Application Serial No. 08/585,278.

While the basis weight of the storage absorbent members of the present invention is not critical and will vary depending on the end use of the member (i.e., incorporation into, for example, a feminine hygiene product, a diaper for infants, an incontinent adult product, a bandage), the members will typically have a basis weight of from about 5 g/ ^m2 to about 3000 g/ ^m2 , or more preferably from about 40 g/ ^m2 to about 2500 g/ ^m2 , or even more preferably from about 100 g/ ^m2 to about 2000 g/ ^m2 , or even more preferably from about 150 g/ ^m2 to about 1500 g/ ^m2 , or even more preferably from about 250 g/m2 to about 1000 g/m2.

As noted, particularly preferred storage absorbent members are those where a high surface area polymeric foam with high capillary suction is used as the material. In one embodiment, the polymeric foam is in particulate form and is mixed with a particulate hydrogel-forming absorbent polymer to form a homogeneous mixture. Fig. 9 is a schematic of an apparatus 320 for forming such a homogeneous mixture. Fig. 9 shows that the absorbent member is prepared by introducing polymeric foam particles from a first inlet 301 into a first metering device 302, which device 302 is preferably a fluidized bed system operating on a loss-in-weight basis which will control the amount of particulate polymeric material metered into the line based on

-43weight loss from the device over a specified period of time, and introducing the particulate hydrogel-forming polymer from the second inlet 303 to a second measuring device 304. wherein the device 304 is preferably a weight loss weighing system commonly used in the commercial manufacture of diapers and feminine hygiene products, such as a weight loss weighing system manufactured by Acrison, Inc., Moonachi, NY, USA. This step sets the basis weight of the absorbent hydrogel-forming polymer in the product. The polymer foam particles and the hydrogel-forming polymer particles are introduced into a single mixing chamber 305. A homogeneous mixture of the two components is formed in the mixing chamber 305. This mixture is then conveyed by an air stream 306 using, for example, a Venturi ejector to increase the kinetic energy of the particles, through a fibrous adhesive stream emerging from a location 307. The foam pieces and hydrogel-forming polymer may also alternatively be agglomerated by any process capable of forming a relatively homogeneous mixture, bonding or binding the material together, yielding a free-flowing mixture that is introduced into the air stream 306. The fibrous adhesive stream may be introduced using a melt blowing adhesive system, such as that available from J&M Laboratories, Inc., Dawsonville, GA, USA. This stream of adhesive fibers entangles the polymeric foam particles and hydrogel-forming polymer to form a composite 308. Homogeneous mixing may be accomplished in the inlet chamber of, for example, a Venturi ejector from Fox, Dover, NJ, USA. If homogeneous mixing in chamber 305 is not feasible, two separate conveying streams may be required to combine the foam in the particles and the hydrogel-forming absorbent polymer particles with the fibrous adhesive supplied from location 307. The composite 308 is then optionally placed between a first web fed through a first device 309 and a second web fed through a second device 310 to form an absorbent storage member 311. The entire absorbent storage member 311 may then be compressed, for example using a nip between rotating rollers, to achieve the target density and overall thickness of the member. In one particular embodiment, one particular web is preferably a liquid distribution material as described above and the second web is a core covering material, such as a nonwoven fabric or a highly aerated material, which is positioned adjacent to the backsheet of the absorbent article.

A similar process to that described in the previous paragraph can be used to combine high surface area fibers with an osmotic absorbent, e.g., a particulate, hydrogel-forming absorbent polymer. That is, the fibers can be introduced using a device similar to the first material delivery device 301 shown in FIG.

-44 Fig. 10. Other well-known methods of combining fibers and hydrogel-forming polymers can be used. An example of a means for preparing such a composite is described in Example 1 below.

An alternative method of mixing and accelerating the particulate polymer foam and the hydrogel-forming polymer utilizes electrostatic forces. In this embodiment, both types of materials are charged to create an attractive force between them. This force is used to create a homogeneous mixture of the two materials and potentially provides a driving force to accelerate the mixture through the adhesive stream, thereby eliminating one of the process air streams.

In another preferred embodiment, the particulate, hydrogel-forming absorbent polymer is placed between two sheets of polymeric foam material. This laminate is then manipulated (e.g., by cutting along its width) in a machine or in a cross-machine direction to cause the sheets to separate into strips or pieces to ensure that the absorbent storage member comprises small portions of the laminate. It is noted that the laminate structure formed prior to cutting can also be used as an absorbent storage member and can provide advantages for commercial scale production, but it has been found within the scope of the present invention that further processing provides an absorbent storage member having particularly high absorbent capacity by capillary sorption at high suction heights. Fig. 10 describes an apparatus 420 for producing such a laminate, and Fig. 11 illustrates a sectioned laminate that can be used as an absorbent storage member in accordance with the present invention. In the apparatus 420 shown in FIG. 10, the first stretched sheet of polymeric foam material 402 is measured by any means well known in the art. Specifically, the flow of particulate hydrogel-forming absorbent polymer is measured from a measuring device 403, wherein the device 403 is optionally a weighing and loss measuring system commonly used in the commercial manufacture of diapers and feminine hygiene products, such as a measuring system available from Acrison, Inc. The hydrogel-forming polymer is metered into an accelerator 404 (e.g., a venturi ejector or fluidized bed system such as the Flexispray™ system available from Nordson, Inc., Atlanta, GA, USA), where it is transported in an air stream toward a fibrous (preferably hydrophilic) adhesive 406 (e.g., Cycloflex™ 34-5652 from National Starch, Bridgewater, NJ, USA) from a location 405. The fibrous adhesive entangles with and immobilizes the hydrogel-forming polymer particles, forming a mixture 407. A little further downstream, after the fibrous adhesive and hydrogel-forming polymer are combined, a second stretched sheet of polymer foam 408 is metered. The angular momentum of the mixture 407 of particles and

The adhesive carries the mixture to the gap point 409 where the sheets 402 and 408 are combined. This results in a laminated composite 410 comprising a layer of hydrogel-forming polymer and an adhesive sandwiched between the two sheets of polymeric foam material. The composite 410 is then combined with a nonwoven material 411 and the combination is fed to a folding plate 412 which folds (preferably into e) the nonwoven material 411 around the composite 410. (The nonwoven material ensures the integrity of the composite during subsequent forming operations and also ensures further integrity in the final structure.) The wrapped composite is then fed to a first forming device 413 and a second forming device 414. In the forming devices 413 and 414, the wrapped composite is selectively cut in multiple directions using shear planes. The shear planes separate the wrapped composite into columns of polymer foam and hydrogel-forming layers of polymer and adhesive fibers. The reshaping operation also reduces the basis weight of the composite, including the nonwoven material around the shear planes.

To fully understand the physical nature of a particularly preferred embodiment of the composite formed by the above operation, FIG. 11 shows in detail the composite 410 (without showing the nonwoven material wrapper) after it has been subjected to deformation in devices 413 and 414. In this embodiment, one of the deformation devices has cut the composite through its entire thickness into a plurality of cross-sectional strips, while another deformation device has cut the composite through its entire thickness in the machine direction. The result is a composite that consists of a plurality of discrete layered columns 451. One of these columns 451 is shown in an exploded view in FIG. 13, which more clearly shows that each column 451 includes particles 452 of a hydrogel-forming polymer, a fibrous adhesive 453, sandwiched between cubes 454 and 455 of a polymeric foam material. Gentle mixing (e.g., application of shear forces) of composite 410 during and/or after deformation in devices 413 and 414 can be used to increase the interface between the absorbent hydrogel-forming polymer and the polymeric foam material.

V. Absorbent products

The high-suction absorbent storage members of the present invention are particularly useful as a storage portion of absorbent structures (e.g., absorbent cores or core elements) for various absorbent articles. Absorbent articles herein are defined as a consumer product capable of absorbing significant amounts of urine, menstrual discharge, or other fluids (e.g., liquids).

-46such as watery feces (liquid diarrhea) excreted by an incontinent wearer or user of the article. Examples of such absorbent articles include disposable diapers, incontinence garments, menstrual products such as tampons and sanitary napkins, disposable exercise pants, bed pads, dressings, and the like. The storage absorbent members disclosed herein are particularly suitable for use in articles such as diapers, pads, or garments worn during incontinence, garment protectors, dressings, and the like.

In its simplest form, an absorbent article according to the invention need only comprise a storage absorbent member according to the invention, but will typically comprise a backsheet, typically relatively liquid-impermeable, and a high-suction storage member. In another simple form, the absorbent article need only comprise a backsheet, an acquisition material, and a high-suction storage material. The components will be assembled such that the acquisition material is positioned to receive liquid discharged by the wearer of the absorbent article. The high-suction member described herein is positioned to be in fluid communication with the acquisition member or with an optional liquid distribution member which is in fluid or capillary communication with the acquisition member. The liquid-impermeable backsheets may comprise any such material, for example polyethylene or polypropylene, having a thickness of about 0.038 mm, which will assist in retaining liquid in the absorbent article.

More typically, these absorbent articles will also include a liquid-permeable topsheet element that covers the side of the absorbent articles that contacts the wearer's skin. In this arrangement, the article includes an absorbent core comprising one or more storage absorbent members of the present invention sandwiched between the backsheet and the topsheet. Liquid-permeable topsheets may include any material such as polyester, polyolefin, rayon, and the like that is substantially porous and allows body fluids to pass readily through and into the underlying absorbent core. The topsheet material will preferably have no tendency to retain aqueous fluids in the interface between the topsheet and the wearer's skin.

In addition to the storage absorbent member of the present invention, the absorbent core of the absorbent articles of the present invention may also include other, e.g. conventional, elements or materials. In one embodiment comprising a combination of said absorbent member and other absorbent materials, the absorbent articles may utilize a multilayered arrangement.

-47absorbent core, wherein the core layer comprising one or more absorbent storage members of the present invention may be used in combination with one or more other separate core layers comprising other absorbent structures or materials. Such other absorbent structures or materials may, for example, include air-laid or wet-laid webs of wood pulp or other cellulosic fibers. Such other absorbent structures may also include foams, for example absorbent foams, or even sponges used as liquid acquisition and distribution members as described in U.S. Patent No. 5,563,179.

Another preferred embodiment includes further distribution of the various elements of the absorbent core. This preferred absorbent core includes an acquisition layer only around the crotch area of the wearer to handle the initial rapid burst of liquid. A distribution layer is positioned vertically to the front and back of the acquisition layer to wick liquid away from the solution area. A storage layer is positioned at a location that is adjacent to the front and back waist areas and is in contact only with the distribution material. The storage absorbent member or members must then be capable of absorbing liquid from the distribution layer and overcoming both the force due to gravity and the force due to the desorption pressures of the distribution material. The product thus described removes liquid from the crotch area in the time available between bursts, while the acquisition area is relatively dry and ready to receive more liquid, further maintaining the shape of the garment and keeping the crotch area relatively dry, resulting in healthier skin. See, for example, copending patent applications U.S. No. 08/825,072, U.S. No. 08/825,071, and U.S. Patent 5,827,253.

Fig. 1 illustrates a preferred embodiment of a diaper 60 in which the topsheet 61 and the backsheet 62 are of equal size and have length and width dimensions that are generally greater than the dimensions of the absorbent core 28. The topsheet 61 is joined to and laid over the backsheet 62 to form the edge of the diaper 60. The edge defines the outer perimeter or edges of the diaper 60.

The topsheet 61 is pliable, soft to the touch, and non-irritating to the wearer's skin. The topsheet 61 is liquid permeable, allowing liquids to readily penetrate through its thickness. Suitable topsheet 61 can be made from a wide variety of materials, such as porous foams, reticulated foams, apertured plastic films, natural fibers (e.g., wood or cotton fibers), synthetic fibers (e.g., polyester or polypropylene fibers), or a combination of natural and synthetic fibers. The topsheet 61 is typically made from

-4899 hydrophobic material that is initially treated to be hydrophilic to isolate the wearer's skin from liquids in the storage absorbent member 10. The hydrophilic treatment causes the topsheet to be initially wettable so that liquid discharges can penetrate through the topsheet. A particularly suitable topsheet 61 comprises polypropylene, which is sold by Hercules Inc. of Wilmington, Delaware, USA. As used herein, the term staple length fibers means fibers that are at least about 15.9 mm long.

There are a number of manufacturing techniques that can be used to make the topsheet 61. For example, the topsheet 61 can be woven, nonwoven, spunbonded nonwoven, carded, and the like. The preferred topsheet is carded and thermally bonded by means well known to those skilled in the textile art. The topsheet 61 preferably has a weight of from about 18 to about 25 g/m ² , a minimum dry tensile strength of at least 400 g/cm in the machine direction, and a wet tensile strength of at least 55 g/cm in the cross-machine direction.

It is preferred that the topsheet be the material closest to the wearer's skin, but this is not required. It is also contemplated that a suitable absorbent core arrangement could be used without a topsheet and still produce desirable results such as comfort and absorbency, as well as ease of manufacture and savings in material costs. For example, the body-side surface of the absorbent core itself could be made of liquid-permeable, soft, compliant, non-irritating materials that replace a separate topsheet. Such an absorbent core would only need to be used in combination with a backsheet to provide comfort and absorbency in the absorbent article.

The backsheet 62 is liquid-impermeable and is preferably made of a thin plastic film, although other liquid-impermeable materials may also be used. The backsheet 62 is preferably made of a polyethylene film having a thickness of from about 0.012 mm to about 0.051 cm, although other flexible liquid-impermeable materials may also be used. As used herein, the term flexible refers to materials that are pliable and will readily conform to the general shape and contours of the wearer's body.

A suitable polyethylene film is manufactured by Monsanto Chemical Corporation and is commercially available as film No. 8020. The backsheet 62 is preferably embossed or matted to provide a

-49 has achieved a more cloth-like appearance. The backsheet 62 may further be breathable and allow vapors to escape from the absorbent core 28 while still preventing exudates from passing through the backsheet 62. It is contemplated that a backsheet that is highly breathable but substantially liquid-impermeable may be desirable in some products.

The size of the backsheet 62 is dictated by the size of the absorbent core 28 and the exact design of the diaper. In a particularly preferred embodiment, the backsheet 62 has a modified hourglass shape extending below the absorbent core 28 and a minimum distance of at least about 1.3 cm to about 2.5 cm around the entire edge of the diaper.

The topsheet 61 and the backsheet 62 are joined together in any suitable manner. The term joined, as used herein, includes arrangements in which the topsheet is directly joined to the backsheet 62 by attaching the topsheet 61 directly to the backsheet 62 and arrangements in which the topsheet 61 is indirectly joined to the backsheet 62 by attaching the topsheet 61 to members therebetween, which in turn are attached to the backsheet 62. In a particularly preferred embodiment, the topsheet 61 and the backsheet 62 are joined directly to each other at the edge of the diaper by an attachment means (not shown), such as an adhesive or some other attachment means known in the art. For example, a uniform continuous layer of adhesive, a patterned layer of adhesive, or an array of spaced lines or locations of adhesive may be used to attach the topsheet 61 to the backsheet 62.

Fastening tape tabs 65 are typically used with the waistband 63 in the waist region of the diaper 60 to provide a fastening means for holding the diaper on the wearer. Fastening tape tabs 65 are typically used with the waistband 63 in the waist region of the diaper 60 to provide a fastening means for holding the diaper on the wearer. The fastening tape tabs 65 shown are just one possible example. The fastening tape tabs 65 may be as is well known in the art, such as the fastening tape described in U.S. Patent 3,848,594. These tape tabs or other means for fastening the diaper are typically used near the corners of the diaper 60.

Elastic members 69 are positioned adjacent the edge of the diaper 60, preferably along each longitudinal edge 64, such that the elastic members tend to pull and hold the diaper 60 against the wearer's legs. Additionally, elastic members 67 may be positioned adjacent one or both of the waist regions 63 in the region of the waist region.

-50 of the diaper waistband 60 to form a waistband as well as leg cuffs. A suitable waistband is described, for example, in U.S. Patent No. 4,515,595, which is incorporated by reference. Additionally, a method and apparatus suitable for making a disposable diaper having elastically contractible elastic elements is described in U.S. Patent No. 4,081,301.

The elastic members are attached to the diaper 60 in an elastically contractible condition such that in a normal unrestrained configuration, the elastic members effectively contract or gather the diaper 60. The elastic members can be secured in an elastically contractible condition in at least two ways. For example, the elastic members can be stretched and secured while the diaper 60 is in an uncontrolled condition. The diaper 60 can alternatively be shrunk, for example by pleating, and the elastic members can be secured and attached to the diaper 60 while the elastic members are in their unstretched or unstretched condition. The elastic members can extend along a portion of the length of the diaper 60. Alternatively, the elastic members can extend the entire length of the diaper 60 or any other length suitable to provide an elastically contractible line. The length of the elastic members is dictated by the design of the diaper.

During use, the diaper 60 is secured to the wearer by placing one belt region under the wearer's rear and guiding the remainder of the diaper 60 between the wearer's legs so that the other belt region is positioned across the wearer's front. The tape tabs 65 or other fasteners are then secured, preferably to the outer front region of the diaper 60. During use, disposable diapers or other absorbent articles incorporating the storage absorbent members of the present invention tend to store liquids more effectively and remain dry due to the high absorbency and high wicking capacity of the absorbent members.

When used as an absorbent core in a disposable diaper 60, a particularly preferred embodiment of the absorbent core 28 of the present invention is positioned such that the acquisition strip 52 is in fluid communication with the topsheet 61 and serves to rapidly receive and distribute body exudates from the wearer's body into the absorbent distribution strip 51. Adhesively attaching the acquisition strip 52 to the topsheet 61 can enhance fluid communication by providing an interface connection to prevent the separated topsheet from impeding fluid flow. The distribution material 51 moves fluid in the x and y directions within the core 28, and the fluid is subsequently desorbed by the storage absorbent member 10, which is the storage absorbent member of the present invention.

While components 52 and 51 are generally shown as straight and of the same size, other shapes and size relationships may be utilized. As will be appreciated, the generally straight components have a width 53 corresponding to a suitable width for the crotch region 66 of a disposable diaper. The length of the respective core components may also vary to provide a suitable size for wearers of different sizes.

As can be seen from Fig. 1, the storage absorbent member 10 may include two storage absorbent members 20 and 30 such that there is no element of the storage absorbent member 10 that is located in the diaper in the fluid discharge area. Because such a storage absorbent member 10 has little or no fluid storage material (the distribution material 51 may have a significant storage capacity and will contain the fluid at least until it is desorbed by a material with a higher storage capacity by suction) in the center of the core (corresponding to the crotch area of the core or the fluid discharge area of the core), products containing such cores may provide a better fit and provide greater comfort to the wearer both when the product is dry and after it has been filled with multiple doses of body fluid. See, for example, copending U.S. Patent Application Serial Nos. 08/825,072, 08/825,071, and U.S. Patent No. 5,827,253. Fig. 2a shows an exploded perspective view of an absorbent core 28 having two separate elements, each of which comprises a storage absorbent element according to the present invention. The front panel 20 generally corresponds to the front portion of the disposable diaper worn by the wearer. Similarly, the back panel 30 corresponds to the back portion of the disposable diaper worn by the wearer.

Alternatively, the storage absorbent member 10 may be a single layer or layers (i.e., where the dashed lines 70 in FIG. 1 indicate that the storage absorbent member 10 is also in the area where liquid discharge occurs) of the storage absorbent material of the present invention. Such an embodiment of the absorbent core 28 is shown in FIG. 2b.

In one embodiment, the acquisition strip 52 will be a liquid handling layer located in the area where the user of the product releases liquid, which is in the form of a high air, nonwoven material, but preferably is in the form of a liquid acquisition layer comprising a layer of modified cellulosic fibers, e.g., stiffened, crimped, cellulosic fibers, and preferably up to about 10% by weight of this liquid acquisition and distribution layer of a polymeric gelling material. In a particularly preferred embodiment, the acquisition layer 52 will

-52·· ·· · comprise a highly airy chemically bonded polyethylene terephthalate (PET) nonwoven layer (e.g., having a basis weight of about 42 g/m ² ) covering a layer of stiffened, crimped cellulose fibers (e.g., available from Weyerhauser Co., WA, USA as CMC®, also available from The Procter & Gamble Co., Paper Technology Division, Cincinnati, OH, USA), such that the nonwoven PET layer is positioned between the stiffened, crimped, cellulose fibers and the top layer 6T. The modified cellulose fibers used in the liquid acquisition layer 52 of such a preferred absorbent article are preferably wood pulp fibers that have been stiffened and crimped by chemical and/or thermal treatment. Such modified cellulose fibers are of the same type as those used in the absorbent articles described in U.S. Patent No. 4,935,022. A preferred embodiment is one in which the liquid distribution layer 51 is as described in copending U.S. Patent Application Serial No. 09/042,418 or U.S. Patent No. 5,800,416. (In a preferred embodiment utilizing the fibrous distribution materials described in U.S. Patent No. 5,800,416, the distribution material is passed through at least two rollers, each having ridges and grooves that are so close together that permanent deformation occurs in the web. Similar processes have been developed for the production of elongated laminate materials and are described in U.S. Patent No. 5,167,897, which relates to elongated materials. This process essentially constitutes a mechanical treatment of the web.) This optional distribution layer The liquid is typically positioned between and in fluid communication with a (top) layer that handles the liquid (e.g., a liquid acquisition material) and a (bottom) high-wicking absorbent storage layer. Absorbent products that can utilize the storage absorbent members of the present invention in a lower liquid storage layer underlying a top liquid acquisition and distribution layer comprising stiffened, crimped, cellulosic fibers are described in more detail in U.S. Patent No. 5,147,345.

As used herein, disposable absorbent articles are those articles that are intended to be discarded after a single use (e.g., the original absorbent article as a whole is not intended to be cleaned or otherwise reconditioned or reused as an absorbent article, although certain materials or the entire absorbent article may be recycled, reused, or composted). The term diaper, as used herein, refers to a garment generally worn by young children and incontinent individuals and worn around the lower torso by the wearer. It is to be understood, however, that the present invention is also applicable to other absorbent articles, such as incontinence pants,

-53·« »4 • * c ·

4 4 4 • · 9 4 · • · 4 4 • 44 ·« ·· >

4 4 4

4 4 • 4 4 4

4 4

44,444 incontinence pads, sports briefs, diaper liners, stool catchers, sanitary napkins, tampons, bandages, facial tissues, paper napkins and the like.

VI. Test methods

A. Capillary sorption

Purpose

The purpose of this test is to measure the absorption capacity or capillary sorption capacity as a function of height of the storage absorbent members of the present invention. (The test is also used to measure the absorption capacity by capillary sorption as a function of height of materials with a large surface area, i.e., without an osmotic absorbent, such as an absorbent polymer forming a hydrogel or other optional materials used in the absorbent member. However, the following section describes the capillary sorption method as it is used to measure the entire storage absorbent member.) Capillary sorption is a fundamental property of any absorbent that governs how liquid is absorbed into the absorbent structure. In a capillary sorption experiment, the capillary sorption capacity of the absorbent is measured as a function of the liquid pressure given by the height of the sample relative to the reservoir of the test liquid.

The method of determining capillary sorption is well known, see Burgeni, A. A. and Kapur, C., Capillary sorption equilibria in fibrous materials, Textile Research Journal, 37 (1967), 356366; Chatterjee, P.K., Absorbent capacity, Textile Science and Technology 7, Chapter II, pp. 29-84, Elsevier Science Publishers B.V., 1985; and U.S. Patent 4,610,678, which discusses a method for measuring capillary sorption of absorbent structures.

Principle

A porous glass frit is connected by an unbroken column of liquid to a liquid reservoir on a balance. The sample is maintained at a constant limiting weight during the experiment. As the porous structure absorbs liquid as required, the loss of weight in the liquid reservoir on the balance is recorded as the liquid uptake^ which is adjusted to accommodate the glass frit-like • «· ·· · ·· · * * 4 44 • · ♦ 4 4 7

-54*·· 44 44 444 • · ·

4 ·

function of height and evaporation. The uptake or capacity is measured at different capillary suctions (hyrostatic tensions or heights). The increase in absorption occurs due to the incremental reduction of the frit (i.e. reduction in capillary suction).

Time is also monitored during the experiment to allow calculation of the initial effective uptake rate (g/g/h) at 200 cm height.

Reagents

Test liquid: synthetic urine is prepared by completely dissolving the following materials in distilled water:

Compound F.W. Concentration (g/liter) KC1 74.6 2.0 Na ₂ SO ₄ 142 2.0 (NH4) _H2PO4 115 0.85 (NH4)2HPO ₄ 132 0.15 CaCl ₂ .2H ₂ O 147 0.25 MgCl2.6KtO 203 0.5

General description of the apparatus settings

The capillary sorption apparatus 220 shown in FIG. 8A used in this test is operated under TAPPI conditions (50% RH, 25°C). The test sample is placed on a glass frit 202, shown in FIG. 8A, which is connected by a continuous column of test liquid (synthetic urine) to a liquid reservoir 206 on a scale containing the test liquid. This reservoir 206 is placed on a scale 207 which is interfaced to a computer (not shown). The scale should be capable of weighing to the nearest 0.001 g. Such a scale is available from Mettler Toledo as the PR 1203 (Hightstown, NJ, USA). The glass frit 202 is mounted vertically on a drive rack 201, shown schematically in Fig. 8A, which allows the vertical movement of the test specimen such that the specimen is subjected to varying suction heights. The vertically movable drive rack 201 may be a rodless motion mechanism.

-55 which is connected to a computer for recording suction heights and corresponding times for measuring liquid uptake into the test sample. A preferred rodless motion mechanism is available from Industrial Devices (Novato, CA, USA) as a type 202X4X34N-1D4B-84-P-C-SE which can be driven by a ZETA 6104-83-135 motor drive available from CompuMotor (Rohnert, CA, USA). Where data is measured and transmitted from the vertically movable drive stand 201 and balance 207, capillary sorption absorption capacity data can be readily generated for each test sample. Also, a computer interface to the vertically moving drive stand 201 may allow controlled vertical movement of the glass frit 202. For example, the drive 201 may be directed to move the glass frit 202 vertically only after equilibrium (as defined below) has been achieved at each suction height.

The bottom of the glass frit 202 is connected to a Tygon® tube 203 that connects the frit 202 to a three-way drain stopcock 209. The drain stopcock 209 is connected to the liquid reservoir 205 by a glass tube 204 and a stopcock 210. (The stopcock 209 is opened for draining only during cleaning of the apparatus or when removing air bubbles.) A glass tube 211 connects the liquid reservoir 205 to the liquid reservoir 206 on the balance via a stopcock 210. The liquid reservoir 206 on the balance consists of a lightweight glass dish 206A with a diameter of 12 mm and a lid 206B. The cap 206B has an opening through which the glass tube 211 is in contact with the liquid in the reservoir 206. The glass tube 211 must not be in contact with the cap 206B, or an unstable balance reading will result and the measurement of the test sample will then be unusable.

The diameter of the glass frit must be sufficient to accommodate the piston and cylinder apparatus described below, designed to hold the test sample. The glass frit 202 has a jacket that allows constant temperature control from the heating bath. The frit is a 350 ml funnel with a frit disc having 4 to 5.5 µm pores and is available from Corning Glass Co. (Corning, NY, USA) as No. 36060-350F. The pores are fine enough to keep the frit surface wetted at capillary suction heights (the glass frit does not allow air to enter the continuous column of test liquid below the glass frit).

As shown, the frit 202 is connected by tubes to a liquid reservoir 205 or a liquid reservoir 206 on the scale, depending on the position of the three-way stopcock 210.

• 4

4 4

-56The glass frit 202 is provided with a jacket into which water from a constant temperature bath enters. This ensures that the temperature of the glass frit is maintained at a constant temperature of 31°C during the test procedure. As shown in FIG. 8A, the glass frit 202 is provided with an inlet port 202A and an outlet port 202B, which form a closed circuit with a circulating thermal bath 208. (The glass jacket is not shown in FIG. 8A, but the water introduced into the glass frit 202 with the jacket from the bath 208 is not in contact with the test liquid and the test liquid does not circulate through the constant temperature bath. The water in the constant temperature bath circulates through the jacket of the glass frit 202 wall. )

The reservoir 206 and the balance 207 are enclosed in a box 212 to minimize evaporation of the test liquid from the reservoir on the balance and to increase the stability of the balance during the experiment. This box 212 has a top and walls, the top having an opening through which a tube 211 is inserted.

The glass frit 202 is shown in more detail in FIG. 8B. FIG. 8B is a cross-sectional view of the glass frit, shown without the inlet port 202A and outlet port 202B. As shown, the glass frit is a 350 ml funnel with a frit disk having 4 to 5.5 μm pores. Referring to FIG. 8B, the glass frit 202 includes a cylindrical funnel 250 with a jacket, and a glass frit disk 260. The glass frit 202 further includes a cylinder and piston assembly 265 (which includes a cylinder 266 and a piston 268) that holds the test sample 270 and provides a small confining pressure on the test sample. To prevent excessive evaporation of the test fluid from the glass frit disc 260, a Teflon® ring 262 is placed on the glass frit disc 260. The Teflon® ring 262 is 0.0127 cm thick (available as sheet material from McMasterCarr as No. 8569K16 from which it is cut to size) and is used to cover the surface of the frit disc outside the cylinder 266 to minimize evaporation from the glass frit. The outer diameter of the ring and the inner diameter of the ring 262 are 7.6 and 6.3 cm, respectively. The inside diameter of the Teflon® ring 262 is about 2 mm smaller than the outside diameter of the cylinder 266. A Viton® o-ring (available from McMasterCarr as AS568A-150 and AS568A151) is placed on the Teflon® ring 262 to seal the space between the inside wall of the cylindrical funnel 250 with the jacket and the Teflon ring 262 to further help prevent evaporation. If the outside diameter of the o-ring exceeds the inside diameter of the cylindrical funnel 250 with the jacket, the diameter of the o-ring is reduced to fit the funnel as follows: The o-ring is. cut, the required portion of material, o• · Λ

The O-ring is cut out and the O-ring is glued back together so that the O-ring is in contact with the inner wall of the cylindrical funnel 250 with the shell along the entire circumference.

As noted, the cylinder and piston assembly 265, shown schematically in FIG. 8B, encloses the test sample and provides a small confining pressure to the test sample 270. As can be seen from FIG. 8C, the assembly 265 consists of a cylinder 266, a Teflon® cup-shaped piston 268, and, if necessary, one or more weights (not shown) that can be inserted into the piston 268. (The optional weight will be used if necessary to adjust the combined weight of the piston and weight to achieve a confining pressure of 0.2 psi depending on the dry diameter of the test sample. This is discussed below.) The cylinder 266 is a piece of Lexan® rod and has the following dimensions: outer diameter 7.0 cm, inner diameter 6.0 cm, and height 6.0 cm. The Teflon® piston 268 has the following dimensions: an outer diameter that is 0.02 cm smaller than the inner diameter of the cylinder 266. As shown in FIG. 8D, the end of the piston 268 that is not in contact with the test sample is drilled to create a diameter of 5.0 cm by a depth of 1.8 cm to create a chamber 290 into which any weights (determined by the specific dry diameter of the test sample) needed to obtain a confining pressure of 1.4 kPa will be placed. In other words, the total weight of the piston 268 and any weights (not shown in the figure) divided by the actual diameter of the test sample (when dry) should be such as to achieve a confining pressure of 1.4 kPa. The cylinder 266 and piston 268 (and any weights) are allowed to equilibrate at 31°C for at least 30 minutes before performing the capillary sorption absorption capacity measurement.

A perforated foil (14 cm x 14 cm) that is not treated with a surfactant (not shown) is used to cover the glass frit 202 during capillary sorption experiments to minimize air destabilization around the sample. The holes are large enough to prevent condensation on the underside of the foil during the experiment.

Preparation of the test sample

A test sample may be obtained by punching a 5.4 cm diameter sample of the structure from the storage absorbent member using a round punch. When the member is part of an absorbent article, other parts of the article must be removed before testing. In those situations where the member cannot be isolated from other parts of the article without. substantially changing its. structure (e.g., density,

• 9

-58relative arrangement of component materials, physical properties of materials used, etc.) or where the member is not part of an absorbent article, the test specimen is prepared by combining all the materials of which the member is composed so that the combination represents the member in question.

The sample weight per supha (used below to calculate the absorption capacity by capillary sorption) is the weight of the test sample prepared as described above under ambient conditions.

Experiment setup

1. A clean, dry glass frit 202 is placed in a funnel holder attached to a vertically sliding stand 201. The funnel holder of the vertically sliding stand is moved so that the glass frit is at a height of 0 cm.

2. The components of the apparatus are arranged as shown in Fig. 8 A and described above.

3. A 12 cm diameter liquid reservoir 206 is placed on a scale 207. A plastic lid 206B is placed over this liquid reservoir 206 and a plastic lid is also placed on the scale box 212, each lid having small holes for glass tubes 211 to pass through. The glass tubes must not touch the lid 206B of the liquid reservoir 206 on the scale 207 as this would cause an unstable reading on the scale and the measurement would not be usable.

4. The stopcock 210 is closed towards the tube 204 and opened into the glass tube 211. The liquid reservoir 205, previously filled with the test liquid, is opened to allow the test liquid to enter the tube 211 and fill the liquid reservoir 206 on the balance 207.

5. The glass frit 202 is placed at the correct level and secured in place. It is also ensured that the glass frit is dry.

6. Tygon® tubing 203 is connected to stopcock 209. (The tubing should be long enough to reach the glass frit 202 at its highest point of 200 cm without any kinks.) This Tygon® tubing 203 is filled with test fluid from fluid reservoir 205.

7. The tube 203 is connected to the glass frit 202 and then the stopcock 209 and the stopcock 210 leading from the liquid reservoir 205 to the glass frit 202 are opened. (The stopcock 210 should be closed to the glass tube 210.) The test liquid fills the glass frit 202 and removes any air in the glass frit 202 during the filling. The filling is continued until the liquid level exceeds the top of the glass frit disc 260. The funnel is • ·

-59 is emptied and any air bubbles in the tube and inside the funnel are removed. Air bubbles can be removed by inverting the glass frit 202, allowing the air bubbles to rise and escape through the drain at the stopcock 209. (Air bubbles typically collect at the bottom of the glass frit disk 260.) The frit is re-set at a level low enough to sit in the jacketed funnel 250 and on the surface of the glass frit disk 260.) The frit level is re-adjusted using a level small enough to sit inside the jacketed funnel 250 and on the surface of the glass frit disk 260.

8. The glass frit is zeroed with the liquid reservoir 206 on the balance 207. To do this, take a piece of Tygon® tubing of sufficient length and fill it with the test liquid. One end is placed in the liquid reservoir 206 on the balance and the other end is used to position the glass frit 202. The level of the test liquid indicated by the tube (which is equivalent to the level of the liquid reservoir on the balance) is 10 mm below the top of the glass frit disc 260. If this is not the case, either adjust the amount of liquid in the reservoir or re-set the zero position on the vertically sliding stand 201.

9. Connect the outlet and inlet ports from the temperature bath 208 with tubing to the inlet and outlet ports 202A and 202B of the glass frit. The temperature of the glass frit disk 260 is allowed to reach 31°C. This can be measured by partially filling the glass frit with the test liquid and measuring its temperature after it has reached equilibrium temperature. The bath will need to be set slightly higher than 31°C to account for heat loss as the water passes from the bath to the glass frit.

10. The glass frit is allowed to reach equilibrium for 30 minutes.

Capillary sorption parameters

The following describes a computer program that will determine how long the glass frit will remain at each level.

In the capillary sorption software program, the test sample is at a specific height above the liquid reservoir. As mentioned above, the liquid reservoir is on a scale, so that the computer can read the scale value at the end of a known time interval and calculate the flow rate (delta value/time interval) between the test sample and the reservoir. For the purposes of this method, the test sample is considered to have reached equilibrium when the flow rate is less than the specified •« » • · • · ·

-60 flow for a specified number of consecutive time intervals. It is recognized that for certain materials true equilibrium may not be reached when the specified equilibrium constant is reached. The time interval between readings is 5 seconds.

The number of readings in the delta table is specified in the capillary sorption menu as equilibrium samples. The maximum number of deltas is 500. The flow constant is specified in the capillary sorption menu as equilibrium constant.

The equilibrium constant is entered in units of g/s and ranges from 0.0001 to 100,000.

Below is a simplified example of the logic. The table shows the scale readings and the delta flow calculated for each time interval.

Equilibrium samples = 3 Equilibrium constant ~ 0.0015

in

Time interval

• φ

Time interval Value indicated by weight (g) Flow Delta (g/s) 0 0 1 0.090 0.0180 2 0.165 0.0150 3 0.225 0.0120 4 0.270 0.0090 5 0.295 0.0050 6 0.305 0.0020 7 0.312 0.0014 8 0.316 0.0008 9 0.318 0.0004

Delta table

Time 0 1 2 3 4 .5 6 7 8 9 Delta 1 9999 0.0180 0.0180 0.0180 0.0090 0.0090 0.0090 0.0014 0.0014 0.0014 Delta 2 9999 9999 0.0150 0.0150 0.0150 0.0050 0.0050 0.0050 0.0008 0.0008 Delta 3 9999 9999 9999 0.0120 0.0120 0.0120 0.0020 0.0020 0.0020 0.0004

The equilibrium intake for the above example is 0.318 g.

Below is the C code used to determine the equilibrium income.

/* takedata.C */ int take_data(int equilsamples. double equilibriumconstant) {

double delta;

static double deltas [500]; /*table to store up to 500 delta values*/ double value;

double prevvalue;

clockt nexttime;

int i;

-62for (i=0; i<equil_samples; i++) deltasfi] = 9999.;

deltatableindex = 0;

equilibriumreached ~ 0;

nexttime = clock ( );

prereading = 0.;

while (lequilibriumreached) { nexttime += 5000L while (clock () < nexttipie);

value = getbanancereading(); delta = fabs(prev_value - value) / 5.0;

prevvalue = value;

deltas [delta table index] = delta;

delta_table_index++;

if (deltatableindex = ^quilsamples) deltatableindex = 0;

/* initialize all values in delta table to 9999. gms/sec */ /* initialize where in the table to store the next delta */ /* initialize the flag indicating that equilibrium has not been reached */ /* initialize when to take the next reading */ /* initialize the value from the previous scale reading */ /* start the balance check loop */ /* calculate when to take the next reading */ /* wait until 5 seconds have passed since the previous reading */ /* read the value from the scale in grams */ /* calculate the absolute value of the flow in the last 5 seconds */ /* store the instantaneous value for the next loop */ /* store the instantaneous delta value in the delta value table */ /* increment pointer to the next position in the table */ /* when the delta number = the number of */ /* equilibrium samples specified, /* f* reset the pointer to the beginning of the table. This way */ /* the table always contains the last xx running samples. */

-63equilibriumreached = 1;

for (i=0; i < equilsamples; i++) if (deltas [i] >= equilibriqmconstant) equilibriumreached = 0;

} }

/* set the label to indicate equilibrium has been reached */ /* check all values in the delta table */ /*if any value is > or = the equilibrium constant */ /* set the equilibrium label to 0 (not at equilibrium) */ /*go to the beginning of the loop */

Capillary sorption parameters

Load description (confining pressure: 1.4 kPa Equilibrium samples (n): 50 Equilibrium constant: 0 _p 0005 g/s Set height value: 100 cm Final height value: 0 cm

Hydrostatic height parameters: 200, 180, 160, 140, 120, 100, 90, 80, 70, 60, 50, 45, 40 35, 30, 25, 20, 15,10, 5 and 0 cm.

The capillary sorption procedure is performed using all of the above heights to measure the capillary sorption absorption capacity in the specified order. Although it is desirable to determine the capillary sorption absorption capacity at a specific height (e.g., 35 cm), it is necessary to complete the entire series of hydrostatic height parameters in the specified order. Although all of these heights are used in conducting the capillary sorption test to establish capillary sorption isotherms for the test sample, the present invention describes the storage absorbent members in terms of absorption properties at specific heights of 200, 140, 100, 50, 35, and 0 cm.

Capillary sorption procedure

1) Follow the experiment setup procedure.

2) Check that the tempering bath 208 is turned on and that water is circulating through the glass frit 202 and that the temperature of the glass frit disk 260 is 31°C.

• · · · 4 · · · •» ·

-643) The glass frit 202 is placed at a suction height of 200 cm. The stopcocks 209 and 210 are opened to connect the glass frit 202 to the liquid reservoir 206 on the scale. (The stopcock 210 is closed towards the liquid reservoir 205.) The glass frit 202 is allowed to stabilize for 30 minutes.

4) The above capillary sorption parameters are entered into the computer.

5) Shut-off valves 209 and 210 are closed.

6) The glass frit 202 is moved to the set height of 100 cm.

7) A Teflon® ring 262 is placed on the surface of the glass frit disk 260. An O-ring 264 is placed on the Teflon® glass frit ring 262. A preheated cylinder 266 is placed concentrically on the Teflon® ring 262. A test sample 270 is placed concentrically in the cylinder 266 on the glass frit disk 260. A piston 268 is inserted into the cylinder 266. If necessary, additional constraining weights are placed in the chamber 290 of the piston 268.

8) The glass frit 202 is covered with perforated foil.

9) The value read on the scale at this moment determines the zero value or tare.

10) Glass frit 202 is moved to 200 cm.

11) The stopcocks 209 and 210 are opened (the stopcock 210 is closed to the liquid reservoir 2051) and the reading of the value indicated by the scale and time begins.

Glass frit correction (empty reception correction)

Since the glass frit disc 260 is a porous structure, the capillary sorption absorption uptake of the glass frit (202) (empty absorption correction) must be determined and subtracted to obtain the actual capillary sorption absorption uptake of the test sample. The glass frit correction is performed for each new glass frit used. The capillary sorption procedure is performed as described above, but without the test sample, to obtain the empty absorption (g). The elapsed time at each specified height is equal to the empty time (s).

Correction for evaporation loss

1) The glass frit 202 is moved to 2 cm above zero and allowed to equilibrate at this height for 30 minutes with the stopcocks 2Q9 and 210 (closed to the reservoir 205) open.

2) Close valves 209 and 210.

-653) A Teflon® ring 262 is placed on the surface of a glass frit disk 260. A ring 264 is placed on the Teflon® ring 262. A preheated cylinder 266 is placed concentrically on the Teflon® ring 262. A piston 268 is inserted into the cylinder 266. A perforated foil is placed on the glass frit 202.

4) Open stopcocks 209 and 210 (closed to tank 205) and record the value indicated by the scale and the time for 3.5 h. Calculate the sample haze (g/h) as follows:

[value indicated by scale at 1 h - value indicated by scale at 3.5 h]/2.5 h

Even after all the above precautions are taken, some evaporation loss will occur, typically around 0.10 g/h for both the test sample and the frit correction. The evaporation of the sample is best measured for each newly installed glass frit 202.

Cleaning the device

When installing a new glass frit 202. new Tygon® tubing is used. Glass tubing 204 and 211, liquid reservoir 205, and liquid reservoir 206 on the scale are cleaned with a 50% solution of Clorox Bleach® in distilled water, followed by a rinse with distilled water if microbial contamination is visible.

a. Cleaning after each experiment

At the end of each experiment (after the test sample has been removed), the glass frit is pre-flushed (i.e., the test liquid is fed under the glass frit) with 250 ml of test liquid from the liquid reservoir 205 to remove any remaining test sample from the pores of the glass frit disc. The taps 209 and 210 are opened to the liquid reservoir 205 and closed to the liquid reservoir 206 on the balance, the glass frit is removed from the holder, turned upside down, and rinsed first with the test liquid, then with acetone and the test liquid. During rinsing, the glass frit must be tilted upside down and the rinsing liquid is sprayed onto the contact surface of the glass frit disc with the test sample. After rinsing, the glass frit is rinsed forward a second time with 250 ml of synthetic urine. Finally, the glass frit is placed back into the holder and the surface of the frit is smoothed.

b. Monitoring the glass frit activity

The performance of the glass frit must be monitored after each cleaning process and for each newly installed glass frit, with the glass frit set at the 0 cm position. 50 ml of the test liquid is poured onto the surface of the leveled glass frit disc (without the Teflon® ring, o-ring and cylinder and piston parts). The time taken for the liquid level to drop to 5 mm above the surface of the glass frit disc is recorded. If this time exceeds 4.5 min, periodic cleaning is required.

c. Periodic cleaning

Glass frits are cleaned periodically (see frit monitoring above) to prevent clogging. The washing fluids are distilled water, acetone, 50% Clorox Bleach® in distilled water (to eliminate bacterial growth), and test fluid. Cleaning involves removing the glass frit from the holder and disconnecting all tubing. The glass frit is pre-rinsed (i.e., the rinsing fluid is introduced to the bottom of the glass frit) with the frit upside down, and the appropriate fluids are used in the following amounts and order:

250 ml distilled water

100 ml acetone

250 ml distilled water

100 ml of 50:50 Clorox®/distilled water solution

250 ml distilled water

250 ml of test liquid

The cleaning procedure is satisfactory when the glass frit performance is within the specified fluid flow criteria (see above) and when no residue is observable on the surface of the glass frit disc. If cleaning cannot be successfully performed, the frit must be replaced.

Calculations

The computer is set up to provide a report containing the capillary suction height in cm, the time and the uptake in grams at each given height. From these data the capillary suction absorption capacity can be calculated, which is corrected for both frit uptake and evaporation losses. Based on • ·· • ·

-67Absorption capacity by capillary suction at 0 cm, the absorption efficiency at specified heights can also be calculated. In addition, the initial effective uptake rate at 200 cm is calculated.

Correction for empty receipt

Correction for empty intake (g)

Empty time(s) * sample evaporation (g/h) = empty intake (g)-3600 (s/h)

Capillary suction absorption capacity (CSAC)

Sampling time(s) (s) * sample evaporation (g/h)

Sample intake (g)---Blank intake correction (g)

3600 rpm

CS AC(g/g) =Weight of dry sample (g)

Initial effective uptake rate at 200 cm (IEUR)

CSAC at 200 cm (g/g)

IEUR (g/g/h) = Sampling time at 200 cm (s)

Reporting

At least two measurements should be made for each test sample and the uptake should be averaged at each height to calculate the absorption capacity by capillary sorption for a given storage absorbent member or a given high surface area material.

B. Vertical gradient sorption height (VHSH)

The vertical slope sorption height test is carried out by taking a strip of foam of suitable length (usually at least 60 cm) and usually about 1 cm wide. The strip is hung in a chamber with a temperature controlled at 31°C using clips to hang the strip. The bottom of the strip is immersed in a test liquid, which is also at a temperature of 31°C. The test liquid is preferably synthetic urine as described in US Patent 5,599,335. After a certain period of time, the test liquid will soak into the strip and reach an equilibrium point where no further wicking occurs. The test liquid may be coloured to facilitate the determination of the equilibrium point. Care should be taken to prevent evaporation from the sample _, for example by surrounding it with a glass tube.

-68·· ♦ · • · with the glass not touching the sample and by appropriately capping the sample tube. The time required to reach equilibrium for the materials of the present invention can vary and range from about 24 to 96 h or more. When no observable change in the height of the rising liquid is achieved within 1 h, this state is considered to be at equilibrium.

The test strip is carefully removed from the test chamber to prevent liquid from being expelled. The strip is cut lengthwise into 2.5 sections and each section is weighed. The initial sections below about 50% of the total expanded height can be cut into sections that are 5.1 cm long. These weights are then divided by the mass of the foam after drying to calculate the capacity (g/g) at various foam heights. From these results, the graph shown in Figure 5 can be constructed by plotting the capacities against the heights at which the cuts were made. VHSH height with X% is the height in cm where X% of the capacity remains in the foam at 0 cm (or FAC). A typical value of interest is VHSH at 90%. X can be any value in principle. In the present invention, the most reproducible rate for VHSH is achieved at X - 90%. It will be apparent to one skilled in the art that this single point value does not fully represent the shape of the curve obtained by plotting capacitance versus height. However, the single point serves as a practical point for comparing the foams of the present invention.

-69VII. Examples

Example 1

Storage absorbent member comprising glass microfibers

This example describes a high capillary suction absorbent member comprising a hydrogel-forming absorbent polymer and high surface area glass microfibers as formed using a wet end forming process for increased density and structural organization after conventional air-laying processes. In order to form such a hydrogel-forming absorbent polymer containing member which approximates a homogeneous distribution of the absorbent polymer in the glass microfiber matrix, the following procedure is used.

A mixture of 4.0 g of ASAP 2300 (available from Chemdal LTD, a division of American Colloid Co., Arlington Heights, IL, USA; also available from The Procter & Gamble Co., Paper Technology Division, Cincinnati, OH, USA) and 4.0 g of glass microfibers (available as Q-FBBERS, Code 108, 110 Bulk from Manville Sales Corp., Denver, Co.) is combined in an explosion-proof three-gallon (11.36 liter) Warner commercial blender with approximately 500 ml of 3A alcohol (95% ethanol, 5% methanol) or isopropanol or similar liquids that do not degrade or absorb into the structure or blend of the respective polymers. By liquids that will not absorb into the structure or mixture of the respective hydrogels is meant that such liquids will absorb into the structure or mixture only to a negligible extent or to an extent less than about 5 grams of liquid per gram of the respective hydrogel-forming absorbent polymer (about 5 g/g by weight). The mixture is poured into a 152 mm x 152 mm papermaking box with an 80 mesh nylon forming screen (available from Appleton Mfg. Div., Productive Solutions, Inc., Neenah, WI, USA) at the bottom of the upper part of the forming box. The liquid level is adjusted to 203 mm above the screen by adding 3 A alcohol or a suitable solution. A paddle is used to thoroughly mix the solution above the screen in the box before draining the liquid. A valve is opened below the forming screen and the liquid is quickly drained to ensure uniform deposition on the forming screen. The sieve is removed from the forming box, placed on a vacuum source to remove any loose liquid, and allowed to dry overnight in a desiccator containing a desiccant (such as DRIERLTE,

Sigma Chem. Co., St. Louis, MO 63178) to ensure uniform moisture content. Once dry, the absorbent member is removed from the forming screen.

A cylindrical structure with a diameter of 5.4 cm is pierced into the arch with a capillary sorption absorption capacity measuring member. The capillary sorption absorption capacity data for the storage absorbent member are summarized in Table 1, below.

Example 2

Preparation of large surface area foam from HIPR

A) Preparation of HIPE

Anhydrous calcium chloride (36.32 kg) and potassium peroxydisulfate (189 g) are dissolved in 378 liters of water. This provides the water phase stream used in the continuous process for forming the JIPE emulsion.

To a monomer combination comprising distilled divinylbenzene (42.4% divinylbenzene and 57.6% ethylstyrene) (2640 g), 2-ethylhexyl acrylate (4400 g) and hexane diiodoacrylate (960 g) is added diglycerol monooleate emulsifier (480 g), ditallow dimethylammonium methyl sulfate (80 g) and Tinuvin 765 (20 g). Diglycerol monooleate emulsifier (Grindsted Products; Brabrand, Denmark) comprises approximately 81% diglycerol monooleate, 1% other diglycerol monoesters, 3% polyols and 15% other polyglycerol esters, provides a minimum oil/water interfacial tension value of approximately 2.7 dynes/cm and has a critical oil/water aggregate concentration of approximately 2.8 wt. %. After mixing, this combination of materials is allowed to settle overnight. No visible residue is formed and the entire mixture is drawn off and used as the oil phase in a continuous process for forming the HIPE emulsion.

Separate streams of the oil phase (25°C) and the water phase (53 to 55°C) are fed into a dynamic mixing apparatus. Thorough mixing of the combined streams in the dynamic mixing apparatus is achieved by means of a pin rotor. The pin rotor comprises a cylindrical shaft 36.5 cm long with a diameter of about 2.9 cm. The shaft holds six rows of pins, three rows having 33 pins and three rows having 34 pins, with each of the three pins at each level being positioned at an angle to each other.

-71120 °C, with each level below it offset by 60° relative to the adjacent level, with each level separated by 0.03 mm, each having a diameter of 0.5 cm extending outwardly from the center axis of the shaft for a length of 2.3 cm. The pin rotor is mounted in a cylindrical housing which forms a dynamic mixing apparatus and the pins are spaced 1.5 mm from the walls of the cylindrical housing.

A small portion of the material leaving the dynamic mixing apparatus is withdrawn and enters the recirculation zone as shown in the illustration in U.S. Patent No. 5,827,909. A Waukesha pump in the recirculation zone returns a small portion to the point of entry of the oil and water phases into the dynamic mixing zone.

The static mixer (TAH Industries Model 100-812) has 12 elements with an outer diameter of 2.5 cm. A hose is mounted downstream of the static mixer to facilitate delivery of the emulsion to the equipment used for crosslinking. Optionally, another static mixer is used to provide additional back pressure to keep the hose filled. Optionally, the static mixer can be a 2.5 cm diameter tube, the mixer is a twelve element (McMaster-Carr, Aurora, OH, USA, type 3529K53).

The combined mixing and recirculating apparatus is filled with oil phase and water phase in a ratio of 4 parts water to 1 part oil. The dynamic mixing apparatus is vented to allow air to escape and the apparatus to be completely filled. The flow rates during filling are 7.57 g/s oil phase and 30.3 cm ³ /s water phase.

Once the assembled apparatus is filled, mixing is started in the dynamic mixer, with its rotor having 1750 rpm and recirculation at a rate of about 30 cm ³ /s. The water phase flow rate is then increased steadily over a period of about 1 min to a rate of 151.3 cm ³ /s and the oil phase flow rate is reduced to 3.03 g/s over a period of about 3 min. The recirculation rate is then increased steadily to about 150 cm ³ /s. The back pressure created at this point by the dynamic zone and static mixers is about 137 kPa, which represents the total pressure drop of the system. The speed of the Waukesha pump (type 30) is then decreased steadily until a recirculation rate of about 75 cm ³ /s is reached.

9·

9 9 9

9 9

9 9 9

9 9

999 99 9

-72• ·· ·* • · · * · ·

9 9 99

9 9 9 9 9

9 Λ 9 9

999 99 99

Β) HIPE polymerization

The HIPE flowing from the static mixer at this location is collected in a round polyethylene container 102 cm in diameter and 31.8 cm high with removable sides, resembling a springform cake pan. A tubular polyethylene insert with a diameter of 31.8 cm at its bottom is firmly attached to the center of the base and is 31.8 cm high. The tubes containing the HIPE are maintained in a 65°C room for 18 h to achieve polymerization and foam formation.

C) Foam washing and dewatering

The crosslinked HIPE foam is removed from the crosslinking vessels. The foam at this point has a residual water phase (containing dissolved emulsifiers, electrolyte, initiator residues and initiator) of about 48 to 52 times the weight of the polymerized monomers. The foam is cut with a sharp rectilinear saw blade into sheets of 4.7 mm thickness. These sheets are then subjected to compression in a gap between two vacuum-equipped rollers, which gradually reduces the residual water phase content of the foam to about six times the weight of the polymer material. At this point, the sheets are re-saturated with a 1.5 percent CaCl solution at 60°C, then re-squeezed through the gaps of a series of three vacuum-equipped porous rollers to about four times the water phase content. The CaCl content of the foam is between 8 and 10 percent.

The foam remains compressed past the last gap to a thickness of about 0.053 cm. The foam is then air dried for 16 hours. Such drying reduces the moisture content to about 9 to 17% by weight of the polymer material. At this point, the foam sheets are very flexible and thin.

Capillary sorption absorption capacity data for the storage absorbent member are summarized in Table 1 below.

Example 3

Preparation of large surface area foam from HIPE

A) Preparation of HIPE

-73Aqueous and oil phases suitable for use in a continuous process for forming a HIPE emulsion are prepared according to Example 1. Separate streams of the oil phase (25 °C) and the aqueous phase (53 °C to 55 °C) are fed to a dynamic mixing device as described in detail in Example 1.

Once the apparatus is filled, mixing is started with a dynamic mixer, with its rotor at 1700 rpm, and recirculation is initiated at a rate of about 30 cm ³ /s. The water phase flow rate is then steadily increased to a rate of 151.3 cm ³ /s over a period of about 1 minute, and the oil phase flow rate is reduced to 3.36 g/s over a period of about 3 minutes. The back pressure created by the dynamic zone and static mixers at this point is about 136 kPa, which represents the total system pressure drop. The Waukesha pump speed is then steadily reduced to achieve a recirculation rate of about 75 crrťs.

B) HIPE polymerization

The HIPE flowing from the static mixer is collected at this point and crosslinked into a polymer foam as described in detail in Example 1.

C) Foam washing and dewatering

The crosslinked HIPE foam is removed from the crosslinking vessels. At this point, the foam has a residual water phase (containing dissolved emulsifiers, electrolyte, initiator residues and initiator) in an amount of 43 to 47 times the weight of the polymerized monomers. The foam is cut with a sharp blade of a reciprocating saw into sheets that are 4.7 mm thick. These sheets are then subjected to compression in a gap between a pair of vacuum-equipped rollers, which gradually reduce the residual water phase content in the foam to about six times the weight of the polymer material. At this point, the sheets are then re-saturated with a 1.5 percent CaCl2 solution, are compressed in a gap between a series of 3 vacuum-equipped porous rollers to a water phase content of about 4 times. The _CaCl2 content in the foam is between 8 and 10%.

After the last gap, the foam remains compressed to a thickness of about 0.071 cm. The foam is then air-dried for about 16 hours. The drying reduces the moisture content to about 9 to 17% by weight of the polymer material. At this point, the foam sheets are very flexible and thin.

• · 4

4

-74Example 4

Preparation of large surface area foam from HIPE

A) Preparation of HIPE

Aqueous and oil phases suitable for use in a continuous process for forming a HIPE emulsion are prepared according to Example 1. Separate streams of the oil phase (25 °C) and the aqueous phase (53 °C to 55 °C) are fed to a dynamic mixing device as described in detail in Example 1.

Once the apparatus is filled, mixing is started with a dynamic mixer, with its rotor at 1700 rpm, and recirculation is initiated at a rate of about 30 cm ³ /s. The water phase flow rate is then steadily increased to a rate of 151.3 cm ³ /s for about 1 minute, and the oil phase flow rate is reduced to 3.78 g/s over a period of about 3 minutes. The recirculation rate is then steadily increased to about 150 cm ³ /s. The back pressure created by the dynamic zone and static mixers at this point is about 129 kPa, which represents the total system pressure drop. The Waukesha pump speed is then steadily reduced to achieve a recirculation rate of about 75 cm 3 /s.

B) HIPE polymerization

The HEPE flowing from the static mixer is collected at this point and crosslinked into a polymer foam as described in detail in Example 1.

C) Foam washing and dewatering

The crosslinked HIPE foam is removed from the crosslinking vessels. At this point, the foam has a residual water phase (containing dissolved emulsifiers, electrolyte, initiator residues and initiator) in an amount of 38 to 42 times the weight of the polymerized monomers. The foam is cut with a sharp blade of a reciprocating saw into sheets that are 4.7 mm thick. These sheets are then subjected to compression in a gap between a pair of vacuum-equipped rollers which gradually reduce the residual water phase content of the foam to about six times the weight of the polymer material. At this point, the sheets are then re-saturated with a 1.5 percent CaCl 2 solution, compressed in

The gap between a series of 3 porous cylinders equipped with a vacuum to the content of the water phase is about 4 times. The CaCE content in the foam is between 8 and 10%.

After the last gap, the foam remains compressed to a thickness of about 0.071 cm. The foam is then air-dried for about 16 hours. The drying reduces the moisture content to about 9 to 17% by weight of the polymer material. At this point, the foam sheets are very flexible and thin.

Example 5

A storage absorbent member comprising a polymeric foam material with a large surface area

This example describes a high surface area absorbent member comprising a hydrogel-forming absorbent polymer and a high wicking polymeric foam material prepared according to Example 3. In order to construct a hydrogel-forming absorbent polymer approaching a relatively homogeneous distribution of the absorbent polymer and the polymeric foam, the following procedure is followed.

g of dry-dried foam (prepared according to Example 3 above) is placed in a blender (Osterizer, type 848-36L) equipped with a 1.25 liter container into which 1 liter of 2 percent potassium chloride solution is added. After ensuring that all of the foam material is immersed, the blender is mixed in the Liquify mode (which is a high setting) for 10 seconds and then additionally mixed in the Grate mode for 5 seconds. The resulting slurry is then transferred to a Buchner funnel (Coors USA, type 60283) lined with a paper towel. Approximately 500 ml of liquid is freely drained from the sample. The sample is then covered with a rubber membrane and a vacuum (approximately 500 mm Hg) is applied to drain the sample to a weight of 50 to 60 grams.

The sample is returned to the dry mixing vessel and dispersed by mixing in the Liquify mode while the vessel and base are inverted and inverted several times to disperse the sample into approximately individual particles. The dispersed sample is then air dried at room temperature and the foam particles are then combined with a hydrogel-forming absorbent polymer (ASAP 2300, available from Chemdal Corporation of Palantine, EL, USA; also available from The Procter & Gamble Co., Paper Technology Division, Cincinnati, OH, USA) to provide a storage absorbent member consisting of a homogeneous mixture of 50%

% by weight of hydrogel-forming polymer and 50% by weight of high surface area polymer foam.

Capillary sorption absorption capacity data for this storage absorbent member are summarized in Table 1 below.

Example 6

Storage absorbent member comprising fibers with a large surface area

This example describes a high capillary suction absorbent member comprising a hydrogel-forming absorbent polymer and high surface area fibers. The high surface area fibers, available from Hoechst Celanese Corp. (Charlotte, NC) as Fibrets® cellulose acetate fibers, are combined with a hydrogel-forming absorbent polymer (ASAP 2300, available from Chemdal Corporation of Palantine, IL, USA; also available from The Procter & Gamble Co., Paper Technology Division, Cincinnati, OH, USA) to provide a storage absorbent member consisting of a homogeneous blend of 50% by weight hydrogel-forming polymer and 50% by weight fibers.

The capillary sorption absorption capacity data for this storage absorbent member are summarized in Table 1 below.

Table 1

CSAC’0 cm (g/g) CSAC’ 35 cm (g/g) CSAC’ 70 cm (g/g) CSAC’ 120 cm (g/g) CSAC’200cm (g/g) Example 1 21.8 14.1 7.0 2.8 0.4 Example 3 36.3 31.1 8.5 5.3 4.2 Example 5 23.0 13.6 9.7 7.7 5.9 Example 6 17.2 10.6 7.3 5.2 3.1 Comparative A 21.9 5.0 1.1 0.8 0.5 Comparative B 43.9 9.9 6.3 1.9 0.5

*) CSAC = capillary sorption absorption capacity

Claims (10)

PATENT REQUIREMENTS 1. A high capillary suction storage absorbent member having at least one of the following: - an absorption capacity by capillary sorption at a height of 35 cm of at least 12 g / g, - an absorption capacity by capillary sorption at a height of 70 cm of at least 7 g / g, an absorption capacity by capillary sorption at a height of 120 cm of at least 4 g / g, or - an absorption capacity by capillary sorption at a height of 200 cm of at least 3 g / g. Storage absorbent member according to Claim 1, characterized in that it has an absorption capacity by capillary sorption at a height of 35 cm of at least 14 g / g, preferably of at least 20 g / g. Storage absorbent member according to claim 1 or 2, characterized in that it has an absorption capacity by capillary sorption at a height of 70 cm of at least 9 g / g, preferably at least 11 g / g · Storage absorbent member according to claims 1 to 3, characterized in that it has an absorption capacity by capillary sorption at a height of 120 cm of at least 5 g / g, preferably at least 7 g / g. 5. The absorbent article of claim 1, wherein the absorbent member has a capillary sorption absorption capacity of 200 cm at least 4 g / g, preferably at least 6 g / g. A storage absorbent member according to claims 1-5 wherein the member comprises a collapsible polymeric foam structure having interconnected open cells that, upon contact with aqueous liquids, can expand and absorb liquids, wherein the polymeric foam structure has an equilibrium 90 percent vertical sorption height gradient of at least 60 cm. A storage absorbent member according to claims 1-5 comprising osmotic absorbents and a high surface area discrete material, wherein the high surface area material is selected from the group consisting of high surface area fibers, high surface area hydrophilic polymeric foam. surface and with open cells and mixtures thereof. • «and« ·· ·· · -788. The storage absorbent member of claim 7, wherein the osmotic absorbent is a hydrogel-forming absorbent polymer. 9. A large capillary suction storage absorbent article comprising an osmotic absorbent and a large surface area discrete material, wherein the member having a capillary sorption absorption capacity of 0 cm at least 15 g / g and having a mean absorption height of at least 15 g / g an average absorption height of at least 35 cm, preferably at least 40 cm, more preferably at least 50 cm. 10. A large capillary suction storage absorbent article comprising an osmotic absorbent and a discrete material having a large surface area, having a capillary sorption absorption capacity of 0 cm at least 15 g / g and at least one of the following: - at least 25% capillary absorption efficiency at a height of 120 cm, - a capillary absorption efficiency at a height of 70 cm of at least 30%, a capillary absorption efficiency at a height of 35 cm of at least 50%. 11. An absorbent article comprising a storage absorbent member according to claims 1 to 10.