MXPA99005655A - Treatment process for cellulosic fibers - Google Patents

Abstract

Disclosed is a process for treating cellulosic fibers using steam explosion that is effective to result in modified cellulosic fibers that exhibit desired properties such as wet curl values. The steam explosion process is quite efficient and has been found to produce cellulosic fibers that are essentially uniformly treated. Also disclosed is a handsheet prepared from the treated cellulosic fibers for use in disposable absorbent products.

Description

PROCESS OF TREATMENT FOR CELLULOSE FIBERS Background of the Invention Field of the Invention The present invention relates to a process for treating cellulose fibers. The cellulosic fibers prepared from such process can be used to prepare a hand sheet or other structure that can be used of a disposable absorbent product that is intended for the absorption of fluids, such as body fluids. Other possible uses of these fibers include various disposable paper products such as tissue and towels.

Description of Related Art Cellulosic fibers are well known in the art and are used in a wide variety of applications. However, natural or generally untreated cellulosic fibers have been found to generally not provide a level of performance that is desired and certain applications such as fluid absorption or handling, such as body fluids as such, are often desirable. increasing the capacity of liquid absorbent or the elasticity of the cellulosic fibers that are being used in such applications. For some applications, it has been recognized that the cellulosic fibers that are being used must first be structurally modified in order to improve the operation of such modified fibers in a particular application.

A known method for modifying cellulosic fibers is to crosslink chemically the cellulosic fibers. In general, a chemical crosslinking agent is added to either a solution containing cellulosic fibers or swollen cellulosic fibers. The chemical crosslinking agent is then allowed to form crosslinking either within a single cellulosic fiber or between the separate cellulosic fibers. Such processes evidently result in the use of a separate cross-linking agent thereby increasing the manufacturing costs of the chemically cross-linked cellulosic fibers. Additionally, use in certain cross-linking agents typically requires the specialization of handling procedures, further increasing manufacturing costs, and potentially limiting the applications to which chemically cross-linked cellulosic fibers can be used. Another disadvantage that relates to the use of chemical cross-linking agents is that they are often based on chemicals, such as aldehydes, which exhibit certain degrees of toxicity.

The variety of chemical treatments of cellulosic fibers are also known. An example of a known chemical treatment of cellulosic fibers is a mercerization process wherein the cellulosic fibers are treated with, typically, sodium hydroxide under conditions suitable to convert the cellulose from its native form to a less crystalline, more thermodynamically stable form. Because ercerized cellulose is less crystalline and more amorphous, mercerized cellulose is generally more accessible for additional treatment with additional reagents.

These and other known processes for chemically treating the cellulosic fibers typically disperse the cellulosic fibers and in a solvent, such as the aqueous solution. However, it has generally been recognized that in order to ensure adequate mixing of the cellulosic fibers and any chemicals that are being used to treat the cellulosic fibers, as well as for the ease of volume transport of the treatment mixture, such processes Known must have cellulosic fibers present in the solvent at a low consistency. Such processes therefore generally result in the use of more of the solvent in which the chemical treatment takes place, or the chemical treatment agent being used, then it would be ideally necessary, thereby increasing the manufacturing costs of the chemically treated cellulosic fibers. Additionally, the use of sodium hydroxide, or other caustic agents, typically requires specialized handling procedures as well as recycling processes to ensure that such materials are not discharged into the environment.

Another known method for modifying cellulosic fibers is to mechanically treat cellulosic fibers. An example of such mechanical treatment processes is where the cellulosic fibers are subjected to an upper cutting force which generally results in cellulosic or crimped or highly twisted fibers. However, such mechanical treatment processes generally require the use of specialized type and the use of large amounts of energy, thereby increasing the manufacturing costs of the mechanically treated cellulosic fibers. Furthermore, without any additional treatment, the fibers modified only by mechanical treatment generally do not retain their curling in wet conditions, because they swell and collapse. Therefore, the mechanical modification is generally not sufficient for the cellulosic fibers, which are used for the absorbent structures requiring more porosity or capacity.

It is therefore an object of the present invention to provide an object for the preparation of treated cellulosic fibers in which the amount of solvent and the chemical treatment agents accepted in the process are minimized or completely eliminated.

It is also an object of the present invention to provide a process for the preparation of treated cellulosic fibers in which the cellulosic fibers are essentially uniformly treated.

It is also an object of the present invention to provide a process for the preparation of treated cellulosic fibers which will significantly reduce manufacturing costs.

It is also an object of the present invention to prepare modified cellulosic fibers that exhibit improved liquid handling properties compared to untreated cellulosic fibers.

Synthesis of the Invention The present invention relates to an efficient and effective way to treat cellulosic fibers as well as treated cellulosic fibers prepared from such process.

One aspect of the present invention relates to a process for treating cellulosic fibers, wherein the cellulosic fibers are treated using a vapor explosion which is effective to result in modified cellulosic fibers exhibiting the desired properties.

One embodiment of such a process for treating cellulosic fibers comprises the steam-fired cellulose fibers in direct contact with saturated steam at a superatmospheric pressure and at a temperature in the range of about 130 ° C to about 250 ° C and then subjecting the cellulosic fibers to the explosive compression to give modified cellulosic fibers that exhibit a ripple value that is greater than about 0.2.

In another aspect, the present invention relates to the modified cellulosic fibers prepared by the process described herein.

One embodiment of such an aspect of the present invention are modified cellulosic fibers that exhibit a ripple index value that is greater than about 0.2 that are prepared by a process comprising steam-cooked cellulosic fibers in direct contact with saturated steam at a superatmospheric pressure and at a temperature within the range of about 130 ° C to about 250 ° C, and then subjecting the cellulosic fibers to explosive compression.

In another aspect, the present invention relates to an absorbent structure comprising modified cellulosic fibers prepared by the process described herein.

One embodiment of such an absorbent structure is a hand sheet comprising the modified cellulosic fibers prepared by the process described herein, wherein the hand sheet was prepared by a wet-laying process.

Brief Detailed Description of Preferred Incorporations It has been found that by using a steam explosion process to treat the cellulosic fibers and by using appropriate treatment conditions, the modified cellulosic fibers exhibiting desired properties can be prepared by an efficient and effective process.

A wide variety of cellulosic fibers can be employed in the process of the present invention. The cellulosic and illustrative fibers include, but are not limited to, wood and wood products, such as wood pulp fibers; non-woody paper fibers made of cotton, straw and grass, such as rice and cane esparto and reeds, such as bagasse, bamboos, stems with fibers, bast fibers such as jute, flax, soft rush, hemp, flax and ramie, and leaf fibers, such as abaca and henequen. It is also possible to use mixtures of one or more cellulosic fibers. Suitably, the cellulosic fibers used are from a wood source. Suitable wood sources include softwood sources, such as pines, firs and hardwood sources such as oaks, eucalyptus, poplar, beech and aspen.

As used herein, the term "fiber" or "fibrous" is meant a particulate material wherein the ratio of the diameter length of such particulate material is greater than about 10. Inverse form, a "non-fibrous" material or "without fiber" is meant to refer to a particulate material wherein the diameter length ratio of such particulate material is about 10 or less.

It is generally desired that the cellulosic fibers used herein be wettable. As used herein, the term "wettable" is intended to refer to a fiber or material that exhibits a contact angle of water in air at less than 90 ° C. Suitably, the cellulosic fibers useful in the present invention exhibit a contact angle of water in air of between about 10 ° to about 50 ° and more suitably between about 20 ° to about 30 ° Adequately, a wettable fiber refers to a fiber, which exhibits a water contact angle in air of less than 90 °, at a temperature between about 0 ° and about 100 ° C and suitably at ambient conditions, such as around 23 ° C.

Suitable cellulosic fibers are those, which are naturally wettable. However, naturally non-wettable fibers can also be used. It is possible to treat the fiber surfaces by an appropriate method to make them more or less humid. When treated surface fibers are employed, the surface treatment is desirably non-fugitive; that is, the surface treatment desirably does not wash away from the surface of the fiber with the first insult or discharge of the liquid or the first contact. For the purposes of this description, a surface treatment on a generally non-wettable fiber will be considered to be non-fugitive when a majority of the fibers demonstrate a water contact angle in air of less than 90 °, or three angle measurements. consecutive contact, with drying between each measurement. That is, the same fiber is subjected to three separate contact angle determinations and, if the three contact angle determinations indicate a water contact angle in air of less than 90 °, the surface treatment on the fiber will be considered which is not fugitive. If the surface treatment is fugitive, the surface treatment will tend to wash away from the fiber during the first contact angle measurement, thereby exposing the non-wettable surface of the underlying fiber, and will subsequently demonstrate contact angle measurements greater than 90. °. The beneficial wetting agents include polyalkylene glycols, such as polyethylene glycols. The agent is used in an amount which beneficially comprises less than about 5% by weight, suitably less than about 3% by weight, and more suitably less than about 2% by weight, of the total weight of the fiber, of the material or of the absorbent structure that is being treated.

In the present invention it is desired that the cellulosic fibers be used in a form in which the cellulosic fibers have been refined to a pulp. As such, the cellulosic fibers will be essentially in the form of individual cellulosic fibers even when such individual cellulosic fibers may be in an aggregate form such as a pulp sheet. The current process, then, are in contrast to the known vapor explosion processes which generally treat cellulosic fibers that are typically in the form of virgin wood chips or the like. Therefore, the current process is a process of modifying cellulose fiber after pulp reduction compared to vapor explosion processes with fibers that are generally used for the manufacture of high-performance pulp or recycling processes. waste.

The cellulosic fibers used in steam explosion processes are desirably poorly performing cellulosic fibers. As used herein, "low yield" cellulosic fibers are those cellulosic fibers produced by pulp reduction processes beneficially yielding about 85% or less, suitably about 80% or less, and more adequately around 55% or less. In contrast, "high performance" cellulosic fibers are those cellulosic fibers produced by pulping processes beneficially providing a yield of about 85% or greater. Such pulp-related processes generally leave the resulting cellulosic fibers with high levels of lignin.

In the process of the present invention it has been discovered that the use of vapor explosion alone may be sufficient to effectively modify the cellulosic fibers so that said modified cellulosic fibers exhibit desired properties, particularly the desired liquid absorbency properties. In general, it is desired that the cellulosic fibers be cooked in a saturated vapor environment that is essentially free of air. The process of air in the pressurized cooking environment can result in the oxidation of the cellulosic fibers, such that the cellulosic fibers are cooked in a saturated steam environment that beneficially comprises less than about 5% by weight, less than about 3% by weight, and more suitably less than about 1% by weight of air, based on the total weight of the gaseous environment present in the pressurized cooking environment.

The individual cellulosic fibers are cooked with steam at a higher temperature and at a higher pressure. In general, any combination of upper pressure, upper temperature and time, which is effective to achieve a desired degree of modification, without undesirable damage to the cellulosic fibers so that the cellulosic fibers exhibit the desired liquid absorbency properties as described herein, it is suitable for use in the present invention.

Generally, if the temperature used is too low, there will be no substantial and / or effective amount of cellulosic fiber modification to occur. Also, generally, if the temperature used is very high, substantial degradation of the cellulosic fibers can occur, which can negatively affect the properties exhibited by the treated cellulosic fibers. As such, as a general rule, the cellulosic fibers will be treated at a temperature within the range, beneficially from about 130 ° C to about 250 ° C, suitably from about 150 ° C to about 225 ° C, more suitably from about 160 ° C to about 225 ° C, and more suitably from about 160 ° C to about 200 ° C.

Generally, the cellulosic fibers will be subjected to high superatmospheric pressure over a period of time within the range of from about 0.1 minutes to about 30 minutes, beneficially from about 0.5 minutes to about 20 minutes, and suitably from about from 1 minute to around 10 minutes. In general, the higher the temperature used, the shorter is the period of time generally necessary to achieve a desired degree of modification of the cellulosic fibers. As such, it may be possible to achieve essentially equivalent amounts of modification for the different cellulosic fiber samples by using different combinations of high temperatures and times.

Generally, if the pressure used is very low, there will be no substantial and / or effective amount of cellulosic fiber modification to occur. Also generally, if the pressure used is very high, substantial degradation of the cellulosic fibers can occur, which will adversely affect the properties exhibited by the crosslinked cellulosic fibers. As such, as a general rule, the cellulosic fibers will be treated at a pressure that is superatmospheric (for example above normal atmospheric pressure), beneficially within the range of from about 40 to about 405 pounds per square inch, suitably from about from 40 to about 230 pounds per square inch and more adequately from about 90 to about 230 pounds per square inch.

As used herein, "consistency" is intended to refer to the concentration of cellulosic fibers present in an aqueous mixture. As such, the consistency will be presented as one percent by weight representing the amount of weight of the cellulosic fibers present in an aqueous mixture divided by the total weight amount of the cellulosic fibers and the water present in such mixture, multiplied by 100.

In general, cellulosic fibers can be used in the process of the present invention, in either a dry or wet state. However, it may be desirable to prepare an aqueous mixture comprising the cellulosic fibers wherein the aqueous mixture is stirred, whipped or mixed to effectively disperse the cellulosic fibers through the water. In an embodiment of the present invention, it is desired that the cellulosic fibers be steam cooked when the cellulosic fibers are in the form of a mixture of aqueous pulp which beneficially has a consistency between about 10 to about 100% by weight, suitably from about 20 to about 80% by weight, and more suitably from about 25 to about 75% by weight of cellulosic fibers, based on the total weight percent of the aqueous pulp mixture.

The cellulosic fibers are typically mixed with an aqueous solution beneficially comprising at least about 30% by weight, suitably about 50% by weight of water, more suitably about 75% by weight of water and more suitably 100% by weight. water weight. When another liquid is used with the water, such other suitable liquids include methanol, ethanol, isopropanol and acetone. However, the use or presence of such other nonaqueous liquids can prevent the formation of an essentially homogeneous mixture so that the cellulosic fibers do not effectively disperse in the aqueous solution and mix effectively and evenly with the water. Such a mixture should generally be prepared under conditions that are sufficient for the cellulosic fibers and the water to mix effectively together. Generally, such conditions will include using a temperature that is between about 10 ° C to about 100 ° C.

In general, cellulosic fibers are prepared by pulping or other preparation processes in which the cellulosic fibers are present in an aqueous solution. For use in the steam exclusion treatment of the present invention, therefore, it may be possible to use an aqueous solution directly from such preparation processes without having to separately recover the cellulosic fibers.

After steam cooking the cellulosic fibers, the pressure is released and the cellulosic fibers are exploited in a release vessel.

The equipment or method used to treat cellulosic fibers with steam explosion is not generally critical. Suitable equipment and methods for vapor explosion can be found, for example, in Canadian Patent No. 1,070,537 dated January 29, 1980; Canadian Patent No. 1,070,646 dated January 29, 1980; Canadian Patent No. 1,119,033 dated March 2, 1982; Canadian Patent No. 1,138,708 dated January 4, 1983; and U.S. Patent No. 5,262,003 issued November 16, 1993; all of which are incorporated herein in their entirety by reference.

The steam explosion process usually causes the fibers to change. Without attempting to be linked by this, it is believed that the steam explosion process causes the cellulosic fibers to suffer a ripple phenomenon, the cellulosic fibers exploded with steam, in addition to being modified, have been found to exhibit improved properties that make to such exploited cellulosic fibers suitable for use in the absorption of liquids or in liquid handling applications.

The cellulosic fibers suitable for use in the present invention will generally be without a substantial amount of crimping prior to the vapor explosion process.

After such vapor explosion process, the treated cellulosic fibers will generally exhibit a desired level of stable curl. As such, the process of the present invention generally does not require the use of any additional additives for the cellulosic fibers during the vapor explosion process or any post-treatment step after the vapor explosion of the fibers to achieve the desired curls .

In an embodiment of the present invention, the cellulosic fibers will be considered to be effectively treated by the vapor explosion process when the cellulosic fibers exhibit an effective wet rip value.

The curling of a fiber can be quantified by a ripple value, which measures the fractional shortening of a fiber due to kinking, twisting, and / or bending in the fiber. For the purposes of this invention, a fiber ripple value was measured in terms of a two-dimensional plane. To determine the ripple value of a fiber, the projected length of a fiber such as the longest dimension of a two-dimensional rectangle encompassing the fiber, I, and the current length of the fiber, L, with both measurements. An image analysis method can be used to measure L and I. A suitable image analysis method is described in U.S. Patent No. 4,898,642 incorporated herein in its entirety by reference. The ripple value of a fiber can be calculated from the following equation: Ripple Value = (L / I) - 1 Depending on the nature of the crimp of a cellulosic fiber, such a crimp may be stable when the cellulosic fiber is dry but may be unstable when the cellulosic fiber is wet. The cellulosic fibers prepared according to the process of the present invention have been found to exhibit an essentially stable fiber crimp when wet. This property of the cellulosic fibers can be quantified by a value of wet ripple, as measured according to the test method described there, which is an average of primary ripple weighed in length of a designated number of fibers, such as around 4,000, of a fiber sample. As such, the wet ripple value is the sum of individual wet ripple values for each fiber multiplied by the current length of the fiber, L, divided by the sum of the current fiber lengths. It is noted here that the wet ripple value as determined here, is calculated by only using the values needed for those fibers with the length of more than about 0.4 millimeters.

As used herein, cellulosic fibers will be considered to be effectively treated by vapor explosion treatment when the cellulosic fibers exhibit a wet rip value that is greater than about 0.2, beneficially from about 0.2 to about 0.4, more beneficially from about 0.2 to about 0.35, suitably from about 0.22 to about 0.33 and suitably from about 0.25 to about 0.33. In contrast, cellulosic fibers that have not been treated generally exhibit a wet ripple value that is less than about 0.2.

After the cellulosic fibers have been effectively steam operated, the treated cellulosic fibers are suitable for use in a wide variety of applications. However, depending on the intended use for the treated cellulosic fibers, such treated cellulosic fibers can be washed with water. If any additional processing procedures are planned due to the specific use for which the treated cellulosic fibers are intended, other steps of recovery and further processing are also well known.

The cellulosic fibers treated according to the process of the present invention are suitable for use in disposable absorbent products such as diapers, adult incontinence products, and bed pads; in catameneal devices such as sanitary napkins and plugs; other absorbent products such as cleansers, bibs, wound dressings, and surgical covers or layers; and tissue-based products such as facial or bath tissue, household towels, cleaners and related products. Therefore, in another aspect, the present invention relates to a disposable absorbent product comprising the cellulosic fibers treated according to the process of the present invention.

In an embodiment of the present invention, the treated fibers prepared according to the process of the present invention are formed into a hand sheet, which may represent a tissue-based product. Such a sheet of hands can be formed by either a wet process or by placing it in air. A wet-laid sheet can be prepared according to the method described in the test methods section given here.

It has been found that a wet-laid hand sheet prepared from the treated cellulosic fibers prepared according to the process of the present invention, can exhibit a density that is lower than that of a hand-laid wet laid sheet of cellulosic fibers. which have not been treated according to the process of the present invention.

It has also been discovered that a wet laid hand sheet prepared from the treated cellulosic fibers prepared according to the process of the present invention may exhibit a liquid transmission time which is faster than that of a wet laid handsheet prepared of cellulosic fibers that have not been treated according to the process of the present invention.

It has also been discovered that a wet-laid hand sheet prepared from the treated cellulosic fibers prepared according to the process of the present invention can exhibit a liquid transmission flow that is higher than that of a wet-laid hand sheet prepared from cellulosic fibers that have not been treated according to the process of the present invention.

It has also been discovered that a wet-laid hand sheet prepared for the cellulosic fibers prepared according to the process of the present invention can exhibit an increased volume and an absorbent capacity superior to that of the wet-laid hand sheet prepared from fibers. cellulosics that have not been treated according to the process of the present invention.

In an embodiment of the present invention, the treated cellulosic fibers prepared according to the process of the present invention are formed in a fibrous matrix for incorporation into an absorbent structure. A fibrous matrix can take the form of, for example, a block of shredded pulp of crushed wood, a layer of tissue, a sheet of hydroentangled pulp, or a sheet of mechanically smoothed pulp. An exemplary absorbent structure is generally described in the co-pending United States of America patent application, series No. 60 / 008,994 whose reference is hereby incorporated by reference in its entirety.

A fibrous matrix useful in the present invention can be formed by means of an air placement process or a wet laying process, or through essentially any other processes known to those skilled in the art to form a fibrous matrix.

In one embodiment of the present invention, there is provided a disposable absorbent product, which is a disposable absorbent product comprising a liquid pervious topsheet, a lower sheet secured to the liquid permeable topsheet, and an absorbent structure placed therebetween. liquid permeable upper sheet and lower sheet, wherein the absorbent structure comprises treated cellulosic fibers prepared using the process of the present invention.

Exemplary disposable absorbent products are generally described in U.S. Patent Nos. 4,710,187; 4,762,521; 4,770,656 and 798,603 whose references are incorporated herein by this mention.

Those skilled in the art will recognize suitable materials for use as the top sheet and the bottom sheet. Examples of materials suitable for use as the topsheet are liquid permeable materials, such as polypropylene or spunbonded polyethylene having a basis weight of from about 15 to about 25 grams per meter. Examples of materials suitable for use as the bottom sheet are liquid impervious materials, such as polyolefin films, as well as vapor permeable materials, such as microporous polyolefin films.

The absorbent products and structure according to all aspects of the present invention are generally subjected, during use, to multiple discharges of a body fluid. Therefore, absorbent products and structures are desirably capable of absorbing multiple insults of body fluids in amounts to which absorbent products and structures will exhibit during use. Insults or discharges are generally separated from each other for a period of time.

A desired liquid transport property of the absorbent structure of the present invention is that the absorbent structure exhibits a vertical liquid flow rate, at a height of about 15 centimeters, suitably at least about 0.002 grams. of liquid per minute per gram per square meter of absorbent structure (gsm) per inch of cross-sectional width of the absorbent structure (g / min * gsm * inch), more adequately of at least about 0.0025 g / min * gms * inch), more adequately of at least about 0.003 g / (min * gsm * inch), and up to about 0.1 g / (min * gsm * inch). As used herein, the vertical liquid flow rate value of an absorbent structure is intended to represent the amount of liquid transported through a boundary at a specified vertical distance outward from a centralized liquid discharge location per minute per minute. standardized amount of the absorbent structure. The vertical liquid flow rate at a height of about 15 centimeters of an absorbent structure can be measured according to the test method described herein.

Another desired liquid transport property of the absorbent structure in the present invention is that the absorbent structure exhibits a "vertical liquid flow rate, at a height of about 5 centimeters, suitably at least about 0.01. g / (min * gsm * inch), more suitably of at least about 0.015 g / (min * gsm * inch), more suitably of at least about 0.02 g / (min * gsn * inch) and up to about 0.5 g / (min * gsm * inch) The vertical liquid flow rate at a height of about 5 centimeters, of an absorbent structure, can be measured according to the test method described here.

Another desired liquid transport property of the absorbent structure of the present invention is that the absorbent structure exhibits a transmission time value to a liquid at an elevation of 15 centimeters suitably of less than 3.5 minutes, more adequately less than about 3 minutes, and more appropriately less than about 2.5 minutes. As used herein, the transmission time value of an absorbent structure is intended to represent the time necessary to transport a liquid to a specified vertical distance outward from the centralized liquid discharge site. The transmission time value of a liquid at an elevation of 15 centimeters for an absorbent structure can be measured according to the test method described herein.

The absorbent structure of the present invention should have a density such that the absorbent structure exhibits the desired liquid transport properties described herein. The density of an absorbent structure generally determines the porosity, permeability and capillary structure of the absorbent structure. If the density of the absorbent structure is very high, the capillary vessels of the absorbent structure will generally be very small so that the capillary vessels provide a relatively high capillary tension force, but, due to relatively small capillary vessels, the permeability of The absorbent structure will be relatively low. If the permeability of the absorbent structure is relatively low, the absorbent structure will generally only transport relatively small amounts of liquid so that the vertical liquid flow rate of the absorbent structure will be relatively low at, for example, each of about 5. centimeters and about 15 centimeters in height from a liquid source.

Conversely, if the density of the absorbent structure is very low, the permeability of the absorbent structure will be relatively high. However, the capillary vessels of the absorbent structure will generally be relatively large so that the capillary vessels provide a relatively low capillary tension force which results in the absorbent structure being generally unable to rapidly transport the liquid at relatively high elevations, such as about 15 centimeters high from a liquid front. Therefore, such an absorbent structure can exhibit a relatively high vertical liquid flow rate at a height of, for example, about 5 centimeters in height from a liquid source, but the liquid will move slower and slower, or it will stop altogether, the higher the front of the liquid transmitted. Thus, the vertical liquid flow rate of such an absorbent structure will be relatively low in, for example, about 15 centimeters in height from a liquid source.

Depending on the stability of the capillary structure of an absorbent structure, the density of the absorbent structure can change as the liquid enters the capillary structure of the absorbent structure. Generally, the structural stability of the absorbent structure will depend on such factors as stability, as measured, for example by shape, curl, stiffness or elasticity, of the fibers in the absorbent structure as well as the stability of the structure. absorbent structure as a whole. The structural changes of the absorbent structure are even more feasible if the absorbent structure is under tension or pressure as, for example, when the absorbent structure is used in a diaper that is being worn by a human. Therefore, it is desirable that the density of the absorbent structure does not change essentially when the absorbent structure absorbs liquid or otherwise becomes wet or under tension or pressure and / or the absorbent structure, essentially regains its density after the liquid or Tension or pressure is removed from the absorbent structure. The stability of the density of an absorbent structure can be quantified, for example, by the difference in density is exhibited by the absorbent structure when different loads are applied to the absorbent structure, such as each of the charges around 0.15 pounds per inch square and about 0.3 pounds per square inch. If the difference in the densities exhibited by the. Absorbent structure at different loads is relatively small, the absorbent structure can be considered as being structurally stable. Another method for characterizing the structure of an absorbent structure is by measuring the hollow volume of the absorbent structure.

Wet Curly Test Procedures The wet rip value for the fibers was determined by using an instrument which quickly, accurately and automatically determines the quality of the fibers, the instrument being available from Op Test Equipment, Inc., of Hawkesbury, Ontario, Canada, under the fiber quality analyzer designation, Op Test Product Code DA93.

A sample of dry cellulose fiber was obtained. The cellulose fiber sample was sold in a 600 milliliter plastic sample beaker for use in the fiber quality analyzer. The fiber sample in the beaker was diluted with tap water, until the fiber concentration in the beaker was about 10 to about 25 fibers per second for evaluation by the fiber quality analyzer.

An empty plastic sample beaker was filled with tap water and placed in the fiber quality analyzer test chamber. The < Verification System > of the fiber quality analyzer was then pressed. If the plastic sample beaker filled with water from the tap was properly placed in the test chamber, then the < OK > of the fiber quality analyzer. Then the fiber quality analyzer carries out the test. If a warning was not displayed on the screen after the self-test, the machine was ready to test the fiber sample.

The plastic sample beaker filled with tap water was removed from the test chamber and replaced with the weighted fiber sample beaker. The < Measure > of the fiber quality analyzer was then pressed after the button of < New Measurement > of the fiber analyzer. An identification of the fiber sample was then typed in the fiber quality analyzer. Then the button of < 0K > of the fiber quality analyzer. The button or key of < 0ptions > of the fiber quality analyzer, was then pressed. The fiber count was set to 4,000. The scaling parameters of a graphic to be printed can be set automatically or at desired values. The button or key < Previous > of the fiber analyzer was then pressed. The button < Start > of the fiber analyzer was then pressed. If the weighted beaker of fiber sample was properly placed in the test chamber, then the < 0K > of the fiber quality analyzer. Then, the fiber quality analyzer, the test exhibited the fibers that pass through the flow cell. The fiber quality analyzer also exhibited the frequency of fiber passing through the flow cell, which should be around 10 to about 25 fibers per second. If the fiber frequency is outside this range, the < High > The fiber quality analyzer should be pressed and the fiber sample should be diluted or have more fibers added to bring the fiber frequency within the desired range. If the fiber frequency is sufficient, the fiber quality analyzer tests the fiber sample until a count of 4,000 fibers has been reached at which time the fiber quality analyzer automatically stops. The button < Results > of the fiber analyzer was then pressed. The fiber quality analyzer calculates the wet ripple value of the fiber sample printed by the < Done > of the fiber quality analyzer.

Preparation of the Hand Hole placed in Wet A standard 17-inch by 17-inch hand sheet having a basis weight of about 200 grams per square meter was prepared using a desired fiber sample by using a 16-inch wet-set bronze wet-laid foil former. by 16 inches, available from Voith Corporation.

A British blender mixer, available from Testing Machines, Inc., was filled with about 2 liters of distilled water at room temperature (about 23 ° C) and about 37.3 grams of fiber sample. The counter on the British blaster was set to zero and the cover was placed on the British blaster. The British blaster was turned on until the counter ran around 600 .. Alternatively, the British blaster can run for about 5 minutes. A bucket was filled with about 8 liters of distilled water. The contents of the British blaster were then poured into the bucket. All the remaining fiber was also rinsed in the bucket.

The hand-sheet former, also having about 12 inches deep, was filled with water from the tap to about 5 inches below the top of the hand-sheet forming chamber. The contents of the bucket were then poured into the hand-sheet forming chamber. A dedicated agitator was then used to mix the suspension in the hand-sheet forming chamber. The agitator moved slowly up and down 6 times to cause small eddies, but to avoid causing large eddies, in the square pattern of the handleader. The agitator was then removed and the suspension was drained through the forming grid of the handleaver. The hand sheet former was then opened and the two layers of blotting paper were placed on top of the sheet of hands. A roller, having an equivalent of about 2.3 pounds of pressure per linear inch, moved back and forth once on each left side, the right side and the center of the formed hand sheet. The blotting paper, with the attached hand sheet, was then lifted from the forming grid. The blotting paper was then placed on a table so that the sheet of hands formed was facing upwards. A 18-inch by 18-inch four-mesh stainless steel grid was placed over the top of the blade. The blotting paper, the sheet of hands and the grid were then struck so that the grid was on the bottom and the blotting paper was on top. The blotting paper was then peeled from the sheet of hands, leaving the sheet of hands on the grid. The edges of the sheet of hands were fastened to the grid using the fasteners. The hand sheet was left overnight to air dry. The sheet of hands, attached to the grid was then placed in an oven and dried at about 105 ° C for about an hour. The hand sheet was then removed from the oven and removed from the grid. The hand sheet was then ready for evaluation regarding the properties of liquid distribution.

Dry volume and density of an absorbent structure From a hand sheet prepared according to the procedure described herein, a strip of sample hand sheet material was obtained, having a width of about 2 inches and a length of about 15 inches, by using an available textile saw , for example from Eastman, Machine Corporation, of Buffalo, New York. It was then cut at least about an inch out from the edge of the hand sheet as to avoid edge effects. The sample strip was then marked at around 10 millimeter intervals using a water soluble ink.

To measure the volume of the sample strip, an accurate volume meter was used to at least about 0.01 millimeter, such as an available volume meter from Mitutoyo Corporation. A plate with a diameter of about one inch was used to measure the volume, with the plate being parallel to the base of the volume meter. The volume of the sample strip was measured at intervals of about 50 millimeters along the length of the sample strip and then averaged. The average volume of the sample strip was then used to calculate the dry density of the sample strip, using the weight and dimensions of the sample strip. The wet density of the sample strip was then determined similarly after the sample strip was valued with respect to the liquid flow values.

Transmission Time and Vertical Fluid Flow of an Absorbent Structure From a hand sheet prepared according to the procedure described herein, a strip of a sample hand sheet material, having a width of about 2 inches to about 15 inches, was obtained by using an available textile saw, example from Eastman, Machine Corporation, of Buffalo, New York. The sample strip was cut at least about 1 inch out from the edge of the hand sheet, as to avoid edge effects.

The apparatus used to hold the sample material while the transmission time was measured and the vertical liquid flow values for the sample material consists of the male and female halves. The device has a length of about 21 inches and consists of Plexiglas pasted. Small screws are placed on the male rod about a one-inch gap. The female half has holes drilled to accommodate the screws. A 4-mesh nylon grid was stretched over the screws. The grid was about 1 inch shorter than the sample holder at both ends. The reinforcing plates fixed the bar, preventing the bar from curling under the tension of the nylon grid. The perpendicular, flat and short bars act as springs to stretch the nylon grid and keep the sample in place.

The sample strip was placed on the nylon grid with the lower end of the sample strip placed lower than the lower edge of the sample holder, so that when the sample strip was placed on top of the distribution manifold of the liquid at the beginning of the experiment, the lower part of the sample strip will touch just the surface of the liquid. A second 4-mesh nylon grid was stretched and placed on top of the sample strip. Two steel pins were driven through the sample strip at each of 5, 10, 15 and 30 centimeters from the bottom of the sample strip to prevent movement of the sample strip under the weight of absorbed liquid. The female half of the sample holder was fitted on the male half. The fasteners were used to keep the stand assembled together.

During the evaluation, the sample strip and the sample holder were contained in a tubular container Plexiglass having an inner diameter of about 7.25 inches and a height of about 24 inches. There is a slit (about 0.25 inches by about 3 inches) at the bottom of the tubular enclosure large enough to allow the tube of the vacuum bottle to pass to the liquid distribution manifold. The tubular enclosure was covered with a flat piece of Plexiglas. The distilled water was sprayed onto the walls of the tubular enclosure before the experiment to raise the relative humidity within the tubular enclosure so as to reduce the evaporation of water from the sample strip during the evaluation. The relative humidity should be maintained at around 90 to about 98 relative humidity during the evaluation. The liquid distribution manifold and tubular enclosure rests on top of the Plexiglas plate resting on two laboratory jacks used for adjustment, stability and maintenance level.

The aspirator bottle was filled with about 0.9% by weight of aqueous sodium chloride solution. The solution in the aspirator bottle was in equilibrium with the upper edge of the slit at the bottom of the tubular enclosure. On the scale, the tare was removed. The sample holder was placed on top of the liquid distribution manifold. A timing was started as soon as the lower edge of the sample strip touched the solution profile. The cover was placed on top of the tubular enclosure.

The vertical distance of the upstream liquid front demonstrates the weight of the liquid absorbed by the mixing strip at various times was recorded.

An outline of the time against the front height of the liquid was made to determine the transmission time around centimeters and to around 15 centimeters. The weight of the liquid absorbed by the sample strip from the beginning of the evaluation around 5 centimeters and to about 15 centimeters in height, was also determined from the data. The flow value of the vertical liquid of the sample strip by a particular height by dividing the grams of liquid absorbed by the sample strip each of: the basis weight, in grams per square meter, of the strip sample, the time, and minutes, necessary for the liquid to reach the particular height; the width, inches of the sample strip.

EXAMPLES Example 1 A sample of cellulosic fiber was prepared by dewatering, the centrifuge of the laboratory, of a kraft pulp of soft wood from the south never dried (available from Kimberly-Clark Corporation, under the designation CR 54 kraft pulp of soft wood of the South to form a mixture having a consistency of about 25% by weight of cellulosic fibers The additional samples having consistencies of about 50 to about 75% by weight of cellulosic fibers were prepared by heating the mixture to 25% by weight at a temperature of about 50 ° C. Samples of about 200 grams, based on the dry base of cellulosic fibers were added to a laboratory steam explosion reactor, available from Stake Tech, Limited of Canada. A capacity of two liters After closing the upper valve, the steam at a specific temperature was injected into the reactor. right in contact with the steam for a period of time. The cellulosic fibers were then decompressed explosively and discharged to a container by opening the lower valve. Steamed fibers were collected for evaluation.

The results of these evaluations are summarized in Table 1, which lists the consistency of the cellulose fiber pulps used; the temperatures used, the amount of time the cellulosic fiber sample was retained in the pressure vessel; and the ripple values for the samples.

The samples of cellulosic fibers were then formed into sheets of hands, according to the procedure described here and the hand sheets formed were valued with respect to the density and vertical liquid flow values.

Those skilled in the art will recognize that the present invention is capable of many modifications and variations without departing from the scope thereof. Therefore, the detailed description and examples set forth above, are intended to be illustrative only and are not intended to limit in any way the scope of the invention as set forth in the appended claims.

Table 1 * It is not an example of the present invention

Claims (27)

R E I V I N D I C A C I O N S

1. A process for the treatment of cellulosic fibers, the process involves steam cooking cellulosic fibers in direct contact with saturated steam at a superatmospheric pressure and at a temperature within the range of about 130 ° C to about 250 ° C, and then subjecting the individualized cellulosic fibers to an explosive decompression to give modified cellulosic fibers exhibiting a wet ripple value that is greater than about 0.2.

2. The process as claimed in clause 1, characterized in that the cellulosic fibers are from a wood source.

3. The process as claimed in clause 1, characterized in that the cellulosic fibers are low yielding cellulosic fibers.

4. The process as claimed in clause 1, characterized in that the cellulosic fibers are in the form of individual cellulosic fibers.

5. The process as claimed in clause 1, characterized in that the cellulosic fibers are treated at a temperature that is between about 150 ° C to about 225 ° C.

6. The process as claimed in clause 5, characterized in that the cellulosic fibers are treated at a temperature that is between about 160 ° C to about 225 ° C.

7. The process as claimed in clause 6, characterized in that the cellulosic fibers are treated at a temperature that is between about 160 ° C to about 200 ° C.

8. The process as claimed in clause 1, characterized in that the cellulosic fibers are treated for an amount of time that is between about 0.1 minutes to about 30 minutes.

9. The process as claimed in clause 1, characterized in that the cellulosic fibers are treated in the form of a pulp having a consistency of between about 20 to about 80% by weight of the cellulosic fibers, based on the weight total of the pulp.

10. The process as claimed in clause 1, characterized in that the cellulosic fibers are treated at a pressure of between about 40 to about 405 pounds per square inch.

11. The process as claimed in clause 1, characterized in that the saturated steam is essentially free of air.

12. The process as claimed in clause 1, characterized in that the cellulosic fibers exhibit a wet rip value which is between about 0.2 to about 0.4.

13. The process as such and claimed in clause 12, characterized in that the cellulosic fibers exhibit a wet ripple value that is between about 0.22 to about 0.33.

14. A modified cellulosic fiber that is prepared by a process comprising steam-cooked cellulosic fibers in direct contact with a saturated vapor at an atmospheric pressure and at a temperature in the range of about 130 ° C to about 250 ° C, and then the cellulosic fibers to explosive decompression to give modified cellulosic fibers that exhibit a ripple index value that is greater than about 0.2.

15. The modified cellulosic fiber as claimed in clause 14, characterized in that the cellulosic fibers are from a wood source.

16. The modified cellulosic fiber as claimed in clause 14, characterized in that the cellulosic fibers are low yielding cellulosic fibers.

17. The modified cellulosic fiber as claimed in clause 14, characterized in that the cellulosic fibers are in the form of individual cellulosic fibers.

18. The modified cellulosic fiber as claimed in clause 14, characterized in that the cellulosic fibers are treated at a temperature that is between about 150 ° C to about 225 ° C.

19. The modified cellulosic fiber as claimed in clause 18, characterized in that the cellulosic fibers are treated at a temperature that is between about 160 ° C to about 225 ° C.

20. The modified cellulosic fiber as claimed in clause 19, characterized in that the cellulosic fibers are treated at a temperature that is between about 160 ° C to about 200 ° C.

21. The modified cellulosic fiber as claimed in clause 14, characterized in that the cellulosic fibers are treated for an amount of time that is between about 0.1 minutes to about 30 minutes.

22. The modified cellulosic fiber as claimed in clause 14, characterized in that the cellulosic fibers are treated in the form of a pulp having a consistency of between about 20 to about 80% by weight of the cellulose fibers, based on the total weight of the pulp.

23. The modified cellulosic fiber as claimed in clause 14, characterized in that the cellulosic fibers are treated at a pressure of between about 40 to about 405 pounds per square inch.

24. The modified cellulosic fiber as claimed in clause 14, characterized in that the modified cellulosic fiber exhibits a wet ripple value that is between about 0.2 to about 0.4.

25. The modified cellulosic fiber as claimed in clause 26, characterized in that the cellulosic fiber exhibits a wet ripple that is between about 0.22 to about 0.33.

26. An absorbent structure comprising wettable cellulosic fibers, wherein the absorbent structure exhibits a vertical liquid flow rate value at a height of 15 centimeters of at least about 0.002 grams of liquid per minute per gram per square meter of the liquid. absorbent structure per inch of the cross-sectional width of the absorbent structure, wherein the cellulosic and wettable fibers are prepared according to the process as claimed in clause 1.

27. An absorbent structure comprising wettable cellulosic fibers, wherein the absorbent structure exhibits a vertical liquid flow rate value at a height of about 15 centimeters of at least about 0.002 grams of liquid per minute per gram per square meter of The absorbent structure per inch width in cross section of the absorbent structure.