HK1260519A1

HK1260519A1 - Multi-ply fibrous product comprising a laminating adhesive with a dermatologically acceptable acid

Info

Publication number: HK1260519A1
Application number: HK19120346.2A
Authority: HK
Inventors: D·哈格贝里; P·萨斯; E·普莱博尔; C·史密斯; Y·恩加塞尔; A·博恩; F·勒施
Original assignee: 易希提卫生与保健公司
Filing date: 2016-01-27
Publication date: 2019-12-20

Description

Multi-ply fibrous product comprising laminating adhesive having dermatologically acceptable acid

Technical Field

The present invention relates to a multi-ply fibrous product, in particular a nonwoven product, a tissue product or a mixture thereof, which is capable of contributing to the pH of healthy skin, in particular to a multi-ply fibrous product in which the individual plies are bonded to one another by means of an adhesive comprising a dermatologically acceptable acid and optionally a salt of said acid.

Background

Materials based on nonwovens and tissue paper are widely used in modern society. Toilet paper, paper towels such as hand towels or household (kitchen) towels, facial tissues, napkins and handkerchiefs are the main commercial products. These products generally contain cellulose fibers (papermaking pulp fibers) selected from hardwood types, softwood types and non-wood types, such as bamboo or mango (Miscanthus). These products may also contain a mixture of cellulosic and non-cellulosic fibers.

The most important physical characteristics of tissue products include their strength, softness, absorbency against primarily aqueous systems, and their lint and dirt resistance. These physical characteristics are typically tailored to meet common consumer demands.

Tissue products are typically in contact with human skin during use. For this reason, it has been considered in the art to treat certain tissue products, such as toilet tissue or handkerchiefs, with lotions containing various types of skin care components and often also pH adjusting substances. However, facial tissues, napkins or household (kitchen) towels are typically lotion free and there is currently a greater demand for lotion free grades for toilet tissue or handkerchiefs.

For lotion free products, the inventors noted a difference between the pH of conventional tissue products and that of healthy skin. Depending on the source of the papermaking fibers, if primarily virgin papermaking fibers are used, the pH of the raw tissue web without further treatment is very close to the neutral point (pH of about 6.5); if a greater proportion of recycled fibers is included, the pH of the raw tissue web without further treatment is slightly alkaline (pH about 8.5). Thus, the current pH of the tissue product is between 6.5 and 8.5, while the pH of healthy skin is between 4.5 and 6.0. This slightly acidic pH is caused by the acidic outer membrane of human skin. The acidic outer membrane of human skin is a very fine, slightly acidic membrane on the surface of the skin that acts as a barrier to bacteria, viruses, and other potential contaminants that may penetrate the skin. Therefore, it is important to minimize the influence of external factors on the skin pH.

The inventors of the present invention have noticed that it cannot be excluded that traditional lotion free tissue products have a negative effect on the pH of healthy skin, especially during prolonged or repeated contact with human skin. The same applies to nonwoven products comprising cellulose fibers.

It is therefore an object of the present invention to provide a multi-ply fibrous product, in particular a nonwoven product, a tissue product or a mixture thereof, which reduces the possibility of traditional multi-ply fibrous products to change the pH of healthy skin.

It is another object of the present invention to provide a multi-ply fibrous product, in particular a nonwoven product, a tissue product or a mixture thereof, with particularly effective means to prevent the negative effects of the pH of conventional multi-ply fibrous products on the pH of the skin.

Furthermore, according to another object of the present invention, it is preferred to provide such a multi-ply fibrous product without adversely affecting other properties associated with its use, such as delamination strength and/or softness and/or absorbency and/or other properties known in the art.

Other objects and objects of the present invention will be understood from the following description.

Disclosure of Invention

The present invention relates to:

1. a multi-ply fibrous product, preferably a multi-ply nonwoven product, a tissue paper product or a mixture thereof, comprising at least two tissue plies and/or nonwoven plies comprising cellulosic fibers, wherein at least two fibrous plies are bonded to each other by an aqueous binder composition comprising a binder component and a dermatologically acceptable acid, and optionally a salt of said acid; and

a process for making a multi-ply fibrous product, preferably a tissue product, comprising the steps of:

a) providing at least two fibrous webs of tissue and/or nonwoven,

b) optionally embossing at least one of said webs so as to provide at least one pattern of protrusions,

c) applying an aqueous binder composition to at least one side of at least one of the fibrous webs, the aqueous binder composition comprising a binder component and preferably a water-soluble dermatologically acceptable acid and optionally a corresponding salt of the acid, wherein, if at least one of the webs is embossed, the aqueous binder composition is preferably applied to at least a portion of the distal ends (dis) of the protrusions,

d) laminating the at least two webs such that the aqueous binder composition is located between the at least two laminated webs,

e) bonding the at least two webs together, an

f) An optional further step of converting the bonded web into a final multi-ply fibrous product,

wherein the characteristics of the multi-ply fibrous product and/or the aqueous binder composition are preferably as defined in the description and claims below.

The present invention encompasses the following embodiments ("items"):

2. a multi-ply fibrous product as described above, wherein the acid and optionally the salt of the acid are provided in an amount such that the ratio of acid to salt of acid is in accordance with ISO 6588-1:2012(E) is measured at a pH of the multi-ply fibrous product of from 3.5 to 7, preferably from 4 to 6.9, more preferably from 4.3 to 6.4, even more preferably from 4.5 to 6.2, for example from 4.8 to 6.0. (it should be noted that the description of broader and narrower ranges also discloses embodiments combining the lower and upper limits in different ways, therefore, item 2 also discloses pH ranges such as 3.5 to 6.9, 3.5 to 6.4, 3.5 to 6.2, 3.5 to 6.0, 4.0 to 7.0, 4.3 to 7.0, 4.5 to 7.0, 4.8 to 7.0, 4.0 to 6.4, etc.)

3. The multi-ply fibrous product of clauses 1 or 2, wherein the aqueous binder composition contains the acid and optionally a salt of the acid in a molar amount of from 0.1 to 10mol/l, preferably from 0.5 to 5mol/l, for example from 1 to 3 mol/l.

4. The multi-ply fibrous product of clauses 1, 2, or 3, wherein the aqueous binder composition is present in an amount of from 0.01 to 2 weight percent, preferably from 0.1 to 1.3 weight percent, relative to the weight of the multi-ply fibrous product, the aqueous binder composition being present in an amount based on the total weight of all ingredients of the binder composition, excluding water.

5. The multi-ply fibrous product of any of clauses 1, 2, 3 or 4, wherein the binder component is selected from the group consisting of: (a) natural polymers such as proteins and protein-based compounds, gums and gum-like materials, polysaccharide-based materials, gums derived from animal products, and (b) synthetic polymers such as PEI (polyethyleneimine), PAE (polyamidoamine-epichlorohydrin) and PVAm (polyvinylamine), polyvinyl alcohol (PVA), polyvinyl acetate (PVAC), vinyl acetate-ethylene copolymer (VAE), polyvinylpyrrolidone (PVP), polyurethane and styrene-butadiene copolymer, and water-soluble or water-dispersible cellulose-based compounds such as carboxymethylcellulose, sodium carboxymethylcellulose, methylcellulose and ethylcellulose; or any combination thereof.

6. The multi-ply fibrous product of any of clauses 1, 2, 3, 4, or 5, wherein the dermatologically acceptable acid is preferably water soluble and is selected from the group consisting of:

(i) the amount of inorganic acid, such as boric acid,

(ii) optionally hydroxylated organic acids having from 2 to 24 carbon atoms, preferably optionally hydroxylated organic acids having from 3 to 6 carbon atoms, more preferably citric acid, lactic acid, erythorbic acid and combinations thereof, and

(iii) polymeric organic acids, such as polyacrylic acid, and combinations thereof;

and wherein optionally present salts of said acids are salts corresponding to the selected acids.

7. The multi-ply fibrous product of any of clauses 1, 2, 3, 4, 5, or 6, wherein the aqueous adhesive composition comprises a dermatologically acceptable acid and salts thereof, and the acid and salts thereof are present in amounts that together provide a pH buffering capacity.

8. The multi-ply fibrous product of any of clauses 1, 2, 3, 4, 5, 6, or 7, wherein the plies comprise as papermaking fibers: (i) only non-regenerated cellulose fibers, (ii) only regenerated cellulose fibers, or (iii) a mixture of non-regenerated cellulose fibers and regenerated cellulose fibers in a weight ratio of 99/1 to 1/99, such as 90/10 to 10/90 or 80/20 to 20/80, wherein in any of (i), (ii), or (iii), the cellulose fibers can be selected from wood fibers, such as softwood fibers or hardwood fibers, and combinations thereof, and non-wood fibers, such as fibers from annual plants.

9. The multi-ply fibrous product of any of clauses 1, 2, 3, 4, 5, 6, 7, or 8, wherein the number of plies, particularly the number of tissue plies, is from 2 to 8, particularly from 2 to 6, such as from 2 to 5.

10. The multi-ply fibrous product according to any of items 1, 2, 3, 4, 5, 6, 7, 8 or 9 wherein the adhesive composition is applied to at least a portion of the surface of the ply, in particular a non-woven or tissue ply, in at least one regular or irregular pattern, wherein the regular or irregular pattern preferably covers at least the central region of the fibrous ply, in particular the non-woven or tissue ply.

11. The multi-ply fibrous product of any of items 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, which is preferably a tissue product, wherein the multi-ply fibrous product, preferably a tissue product, has two outer plies and optionally at least one further ply located between the two outer plies, wherein at least one of the outer plies is embossed, thereby forming protrusions, wherein the aqueous binder composition is applied to distal ends of at least a portion of the protrusions, the protrusions being arranged to bond the two outer plies and optionally at least one further ply located between the two outer plies together.

12. As in item 1,2.3, 4, 5, 6, 7, 8, 9, 10 or 11, which is preferably a tissue product, said multi-ply fibrous product comprising at least three plies: an embossed upper outer layer and an embossed lower outer layer, and a central layer, each outer layer comprising a relief pattern comprising at least a portion of discrete protrusions, at least a portion of the protrusions of each outer layer having distal end regions facing the central layer, and at least one of the upper outer layer and the lower outer layer having a pattern density of at least 10 protrusions/cm²Preferably at least 20 protrusions/cm²-said lower outer layer comprising a first pattern and a second pattern, the height of said first pattern being smaller than the height of said second pattern, wherein said central layer and said upper outer layer are connected in a nested manner and are connected to said lower outer layer (1) by means of an applied adhesive composition (12), wherein said central layer (2) and said upper outer layer (3) are connected to said lower outer layer (1) to the extent of at least a part of the tips of the second pattern connected to said lower outer layer, wherein the height of the protrusions of said second pattern is preferably between 50% and 200% greater than the height of the protrusions of said first pattern.

13. The multi-ply fibrous product of any of clauses 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12, wherein the percentage of the total surface of the multi-ply fibrous product bonded by the adhesive composition is from 1% to 20%, preferably from 2% to 10%, more preferably from 4% to 8%.

14. The multi-ply fibrous product of any of items 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 or 13, wherein the multi-ply fibrous product is selected from a wiping article (wipe), a hygiene product such as toilet paper, handkerchief paper, household towels, facial tissues, napkins/napkins, bedding (bed linen) or clothing, wherein the multi-ply fibrous product is preferably a hygiene paper product having from 2 to 8 plies, preferably from 2 to 6 plies.

Where the present specification refers to "preferred" embodiments/features, combinations of these "preferred" embodiments/features should also be considered disclosed, as long as such combinations of "preferred" embodiments/features are technically meaningful.

In the following, the use of the term "comprising" should be understood as disclosing the term "consisting of as well as the more restrictive embodiment, as long as this is technically meaningful.

Drawings

Fig. 1 is a schematic diagram showing an embossing/gluing station that can be used to make the three-ply tissue product of the present invention. In fig. 1, the following reference numerals denote:

(1) a layer (first outer layer) of A,

(2) a layer B (intermediate layer),

(3) a layer C (second outer layer),

(4) the gluing unit is used for gluing the adhesive tape on the adhesive tape,

(5) the gluing chamber is provided with a glue inlet and a glue outlet,

(6) anilox roll (engraving),

(7) an application roller (flat rubber roller),

(8a) (8b) a rubber roller,

(9a) (9b) an embossing roll,

(10) a binding roll (marrying roll),

(11) three-ply tissue paper product

As in all figures, these reference numerals apply to all figures. The direction of rotation of the different rollers and the direction of advance of the layers are indicated by arrows.

Fig. 2 is a schematic diagram showing the structure of a preferred embodiment of a three-ply tissue product. In fig. 2, the following reference numerals denote:

(12) an adhesive (adhesive composition),

(13') primary engraving (small embossing),

(14) secondary engraving (big embossing, decorative pattern).

Fig. 3a and 3b are schematic views of different embossing patterns of a tissue product. In fig. 3, the following reference numerals denote:

(15a, b) a small embossing pattern,

(16) a large embossing pattern.

Fig. 4 is a schematic view of a part of the surface of the emboss roller (9a) shown in fig. 1. The engraved protuberances of two different height levels result in correspondingly different embossing levels of the tissue paper product. In fig. 4, the following reference numerals denote:

(13) the first-stage engraving is carried out,

(14) and (5) secondary engraving.

Fig. 5 is a schematic view of a preferred example of a small embossing pattern of a tissue product. The number of the dots is 20/cm²。

Detailed Description

The present invention relates to a multi-ply fibrous product comprising at least two fibrous plies. It is preferably selected from:

(a) a multi-layer nonwoven product comprising at least two nonwoven layers, said nonwoven layers preferably comprising cellulosic fibers,

(b) a tissue product comprising at least two tissue plies, and

(c) a mixture of nonwoven products and tissue products comprising at least one tissue layer and at least one nonwoven layer, said nonwoven layer preferably comprising cellulosic fibers.

In the multi-ply fibrous product, at least two of the above-mentioned fibrous plies are bonded to each other by an aqueous binder composition comprising a binder component and a dermatologically acceptable acid, and optionally a salt of said acid.

The multi-ply fibrous product of the present invention is preferably a tissue paper product.

Tissue products, nonwoven products or mixtures thereof are bonded to one another by a specific binder composition from two or more layers.

The term "ply" as used herein refers to a distinguishable and usually separable cut-to-size (cut-to-size) tissue web obtained after processing ("converting") one or more base (coarse) tissue webs. Each individual layer may comprise one or more plies, for example one ply, two plies, three plies or four plies. In the case of nonwovens, the term "layer" as used herein refers to a distinguishable and generally separable size-cut nonwoven web.

With respect to a tissue web, the term "ply" refers to a layer (stratum) having a defined fiber composition within the web. The ply or plies are formed by depositing one or more slurry feed streams onto a wire using a pressurized single or multi-layer headbox (head box). Such techniques are well known to those skilled in the art. It enables the use of different kinds of fibres in each ply of the web.

By "tissue web" is understood a single-ply base tissue obtained from a tissue machine (tissue machine). The tissue web is made by a process comprising the steps of: an aqueous suspension of pulp fibers, the so-called "furnish", is formed, which is deposited onto a wire to form a wet web, dewatered, dried and creped.

The preferred basis weight (basis weight) of the tissue web and the resulting layer is 8g/m²To 50g/m²In particular 10g/m²To 30g/m²In particular 12g/m²To 25g/m². The same applies to the nonwoven web and the resulting layer.

Based on the inherent compatibility of the production process (wet forming), the "tissue" production is considered to be included in the papermaking art. Tissue paper production differs from paper production by its very low basis weight and much higher tensile energy absorption index. Paper and tissue paper also typically differ in terms of elastic modulus, which is a material parameter that characterizes the stress-strain characteristics of these planar products.

The high tensile energy absorption index of a tissue is caused by external or internal creping. The former is produced by pressing the paper web adhered to the drying cylinder by the action of a creping blade or, in the latter case, by the speed difference between the two wires ("fabrics"). This causes the still moist, plastically deformed paper web to break internally due to pressing and shearing, making it more stretchable under load than uncreped paper. High tensile energy absorption index can also be achieved by imparting a 3D structure to the tissue by the web itself. Most typical functional properties of tissue and tissue products derive from a high tensile energy absorption index (see DIN EN 12625-4 and DIN EN 12625-5).

Tissue Paper may be produced from papermaking fibers according to "conventional processes", such as in the production of "dry creped Tissue Paper" or "wet creped Tissue Paper" or in "process of structured Tissue Paper", for example, the through-air-Drying (TAD) production process, the production of uncreped through-air-Drying (ucad) Tissue Paper or alternative production processes, such as the Advanced Tissue Molding System (ATMOS) of the Voith corporation, or the energy Efficient Advanced Drying etad (energy Efficient Technology Advanced Drying etad) of the Georgia Pacific corporation, or the structured Tissue Technology sst (structured Tissue Technology sst) of the Metso Paper corporation. Hybrid processes, such as NTT (New textured Tissue), which is a variation of the conventional process, may also be used.

Conventional dry crepe making methods include the following steps:

-pressing and drying the wet paper fibres into sheets on large diameter heated cylinders (also known as Yankee dryers); and

-the dried paper fibre sheet is then separated and creped by means of a metal blade applied opposite the roll and crosswise to its direction of rotation.

The creping operation creates undulations in the sheet in a direction that intersects the direction of travel of the sheet. The creping operation increases the thickness of the sheet and imparts elasticity and tactile (soft-touch) properties to the sheet.

The TAD preparation method comprises the following steps:

-embossing a sheet of wet paper fibres on a fabric; and

-then drying the sheet at least partially by means of a flow of hot air through the sheet.

The dried sheet may then be creped.

Furthermore, in the preparation of the Tissue web to be used, a process as described in PCT/EP2015/059326 (application date: 2015, 4, 29, titled: Tissue paper comprising pulp fibers orienting from Miscanthus and method for manufacturing the same ", incorporated herein by reference) may be used. Reference is made in particular to the description of page 3 of this application and to the details of the TAD process disclosed therein (e.g. 3D shaped fabrics, permeable dryer cylinders, etc.). The parameters described in this paragraph are also valid for using the ATMOS technique.

Once the tissue has been prepared, a special preparation operation known as a converting operation is typically employed to form the tissue product (i.e., paper towels, toilet paper rolls, bath tissue, wipes, kitchen rolls, handkerchiefs, etc.).

The term "non-woven" is very common in the art and can equally be used for the purposes of the present invention according to ISO 9092: 2011 is further defined. Typical nonwoven production techniques include air-laid, spunlaid, dry-laid and wet-laid long fiber technologies.

According to a preferred embodiment, each nonwoven layer of the multi-ply fibrous product (i.e. multi-ply nonwoven product or nonwoven/tissue blend) used in the present invention comprises cellulosic fibers. In this case, the content of cellulose fibers is at least 20 wt. -%, more preferably at least 50 wt. -%, for example at least 80 wt. -%, based on the total weight of all fibers present in the respective layer. The remaining fibers are in these cases non-cellulosic fibers, such as synthetic fibers.

According to a preferred embodiment, the multi-ply fibrous product of the present invention comprises at least one, preferably at least two textured nonwoven plies. The preparation of textured nonwoven webs useful as one or more nonwoven layers in the present invention has been described in, for example, WO2014/009784 (incorporated herein by reference). Referring to fig. 12 of the international application, a preferred embodiment of the textured nonwoven is produced as follows:

a roll of fluff pulp 30 is used as the feedstock. It is fed into a crusher 31. The fluff pulp is defibered to form fluff or free papermaking fibers 32. Other raw materials may be used, such as a mixture of fluff pulp and synthetic, rayon or other natural fibers (e.g., cellulose fibers) or thermally bonded fibers. The papermaking fibers 32 are fed into a given number (e.g., two) of forming chambers 33. In the forming chamber 33, the papermaking fibers 32 are conveyed by the air flow. Papermaking fibers 32 are deposited onto a forming fabric 34, and forming fabric 34 travels endlessly under forming chamber 33. The formed web is compacted by a compactor 35 almost before leaving the forming fabric 34. The compacted web resulting from this step is then transferred from the forming fabric 34 to the transfer fabric 36. Adhesive is sprayed onto one side of the compacted web by a first adhesive sprayer 37. The adhesive is a latex composition, such as an ethylene and vinyl acetate copolymer composition. The compacted web is then dried in a first drying unit 38 (e.g., at a temperature of about 110 ℃ to 120 ℃). The compacted web is then calendered by calendering section 39. The calender section 39 includes calender rolls 40 and opposing mating rolls 41, which rotate in opposite directions. The reduction roll 40 is a reduction roll including a positive pattern (positive pattern) according to the present invention. The mating cylinder 41 may be a roller having a smooth surface (the mating cylinder may be made of steel or a rubber material). The calender rolls may be heated. A calendered web 42 results from this step. Adhesive (e.g., latex) is sprayed onto the other side of the calendered web 42 by a second adhesive sprayer 43. As an alternative to using the adhesive sprayed by the first and second adhesive sprayers 37, 43, thermally bondable fibers (e.g., thermally bondable fibers or thermally bondable fibers and latex) may be used and mixed with the papermaking fibers into the forming chamber 33. The calendered web 42 is then dried and cured in a second drying unit 44 (e.g., at a temperature of about 200 ℃). The resulting web 42 is further cured and cooked by a third drying unit 45 (e.g., at a temperature of about 200 ℃). The calendered web from the above steps forms a textured nonwoven fabric 46 comprising papermaking fibers. It may be wound onto a reel 50 as a roll of textured nonwoven fabric comprising papermaking fibers. The spool 50 of textured nonwoven fabric comprising papermaking fibers may then be fed into a conversion unit 60 for producing napkins, tissues, rolls of toilet paper, rolls of facial tissue, wiping paper products, rolls of kitchen tissue, skin care or cleaning wipes, handkerchiefs, and the like.

Papermaking fibers (hereinafter also referred to as "cellulosic fibers") can be produced from virgin and/or recycled pulp stock. The cellulose fibers used in the present invention generally contain long-chain cellulose moieties as the main structural building part, which are present in naturally occurring cellulose-containing cells, particularly cells of lignified plants. Preferably, the fibers are isolated from the lignified plant by a digestion step that removes or reduces the content of lignin and other extractables and an optional bleaching step. The cellulose fibers may also be derived from non-wood sources, such as annual plants.

Cellulose fibres which may be used may be of the regenerated type (eg Lyocell), but other types of pulp are preferably used. The pulp used may be primary fibrous material ("primary fibers") or secondary fibrous material (regenerated pulp). The pulp may be derived from lignin-free or low-lignin sources, such as cotton linters, esparto grass (alpha grass), bagasse (e.g. cereal straw, bamboo or hemp), dead-hair fibres (kemp fiber), miscanthus fibres or flax (also referred to as "non-wood fibres" in the description and claims). Preferably, the pulp is made of a lignocellulosic material, such as softwood (typically derived from coniferous trees) or hardwood (typically derived from deciduous trees).

"chemical pulp" or "mechanical pulp" may be used, wherein chemical pulp is preferably used.

According to DIN 6730, a "chemical pulp" is a fibrous material obtained from plant raw materials in which most of the non-cellulosic components are removed by chemical pulping without substantial mechanical post-treatment. "mechanical pulp" is the generic name for fibrous materials made entirely or almost entirely of wood by mechanical means, optionally at elevated temperature. Mechanical slurries can be subdivided into purely mechanical slurries (groundwood and refined mechanical slurries) and also into chemically pretreated mechanical slurries, such as chemical-mechanical slurries (CMP) or chemi-thermomechanical slurries (CTMP).

Typical properties of tissue paper include ready ability to absorb tensile stress energy, their drapability, good fabric-like flexibility, a property often referred to as bulk softness (bulk softness), high surface softness, high specific volume with appreciable thickness, as high a liquid absorbency as possible, and depending on the application, suitable wet and dry strength, and interesting visual appearance of the outer surface of the product. These properties allow the tissue to be used, for example, as a cleaning cloth (e.g., household towels), hygiene products (e.g., toilet paper, hand towels), handkerchiefs, cosmetic wiping products (facial tissues), or napkins/napkins.

An aqueous adhesive composition for bonding at least two fibrous layers together, such as tissue layers and/or nonwoven layers, comprises (i) an adhesive component and (ii) a dermatologically acceptable acid, and optionally a corresponding salt of said acid. In one embodiment, the remainder is water. An "aqueous adhesive composition" may also be referred to and described as a "water-based adhesive" comprising a dermatologically acceptable acid and optionally a corresponding salt of said acid.

The term "adhesive component" is understood to mean one or more chemical substances corresponding to the non-aqueous component of the water-based adhesive suitable for bonding/laminating the fibrous webs of tissue and/or nonwoven. The adhesive component preferably comprises an adhesive polymer as a major component (more than 50 wt%, for example more than 80 wt%, based on the total weight of the adhesive component) or as the sole component. In addition to the adhesive polymer, the adhesive component may also contain the usual auxiliary substances used in water-based adhesives, such as tackifiers, viscosity-regulating substances or dispersing aids.

The aqueous binder composition may also contain a colorant which may be used to visualize the pattern of application of the binder composition.

Preferably, the solids content of the binder component in the aqueous binder composition is from 2 to 50 wt%, preferably from 2.5 to 20 wt%, for example from 3 to 10 wt%.

The binder polymer may be a natural polymer or a synthetic polymer, preferably a synthetic polymer. It is soluble or dispersible in the final aqueous binder composition. Natural polymers can be made from sources such as: (i) proteins and protein-based compounds such as casein, soy protein, zein and gelatin, (ii) gums and gum-like materials such as gum arabic, tragacanth gum, ghatti gum (gum ghatti), ghatti gum, mucilage, and the like, (iii) polysaccharide-based materials such as starch and processed starch, dextrin, agar, pectin, and the like, (iv) gums derived from animal products such as hide, bone, and fish viscera. The synthetic polymer may be selected from PEI (polyethyleneimine), PAE (polyamidoamine-epichlorohydrin) and PVAm (polyvinylamine), polyvinyl alcohol (PVA), polyvinyl acetate (PVAC), vinyl acetate-ethylene copolymer (VAE), polyvinylpyrrolidone (PVP), sodium polyacrylate, polyethylacrylate, polymethacrylic acid, polyurethane and styrene-butadiene copolymer, and water-soluble or water-dispersible cellulose-based compounds such as carboxymethyl cellulose, sodium carboxymethyl cellulose, methyl cellulose and ethyl cellulose, or any combination thereof. Polyvinyl alcohol polymers or water-soluble or water-dispersible cellulose-based compounds are preferred. The natural or synthetic polymer may have any water soluble or water dispersible molecular weight sufficient to form the binder. In general, the binder polymer, i.e., natural polymer or synthetic polymer, preferably has a weight average molecular weight (as determined by GPC) of about 40,000 to about 120,000, more preferably 70,000 to 90,000.

The dermatologically acceptable acid (also referred to as a "skin compatible acid") is preferably water soluble. The solubility in water (at 25 ℃) is preferably at least 1g/L, particularly and increasingly preferably at least 10g/L, at least 50g/L, at least 100 g/L.

The acid is preferably selected from: (i) inorganic acids, such as boric acid, (ii) optionally hydroxylated organic acids having from 2 to 24 carbon atoms, and (iii) polymeric organic acids, such as polyacrylic acid. Optionally, each of these acids is combined with its salt, particularly its metal salt, to form a buffer.

The salt-forming metal is preferably selected from the group consisting of alkali metals and alkaline earth metals, including but not limited to sodium, potassium, calcium, and the like. Thus, in one embodiment, when the acid selected is lactic acid, suitable metal salts thereof include sodium lactate and potassium lactate.

The optionally hydroxylated organic acid according to item (ii) preferably has from 2 to 18, more preferably from 3 to 10, in particular from 3 to 6, carbon atoms. It may be saturated or unsaturated, the former being preferred. It may be a mono-or polycarboxylic acid (e.g. a dicarboxylic acid), preferably the former. It is preferably selected from citric acid, lactic acid, isoascorbic acid, glycolic acid, malic acid, tartaric acid, glycollic acid (cyclic dimer of glycolic acid, which hydrolyzes to form two glycolic acid molecules), acetic acid, dehydroacetic acid, oleic acid, palmitic acid, stearic acid, behenic acid, palm kernel oleic acid (palm kernel acid), tallow acid (tallow acid), salicylic acid, ascorbic acid, sorbic acid, benzoic acid, succinic acid or any combination thereof.

Preferred acids are saturated and hydroxylated, including citric acid, lactic acid, erythorbic acid, or any combination thereof. Among them, lactic acid is most preferably used together with its corresponding metal salt (e.g., sodium lactate or potassium lactate).

As previously mentioned, the acid and salt of the corresponding acid may be added together (e.g., lactic acid and sodium lactate) to provide a "buffering" effect, which helps to keep the desired pH stable. Thus, it is preferred to use an aqueous adhesive composition that includes both a dermatologically acceptable acid and its salts, and that the dermatologically acceptable acid and its salts be present in an amount that provides a pH buffering capacity.

In a preferred embodiment of the multilayer fibre product, the acid and optionally the salt of the acid are provided in such an amount that the acid is present in accordance with ISO 6588-1:2012(E) the pH of the multi-ply fibrous product, e.g. tissue product, nonwoven product or mixed product, is from 4.3 to 6.4, preferably from 4.5 to 6.2, e.g. from 4.8 to 6.

In a preferred embodiment, the aqueous binder composition contains the acid and optionally the salt of the acid in a molar amount of from 0.1 to 10mol/l, preferably from 0.5 to 5mol/1, for example from 1 to 3 mol/1.

The pH (measured at 25 ℃) of the aqueous binder composition is preferably from 1 to 6, more preferably from 1.5 to 4, especially from 2 to 3.

In a further preferred embodiment, the aqueous binder composition has been applied to a multi-ply fibrous product, in particular a nonwoven product or a tissue product or a mixture thereof, preferably a tissue product, and is present in an amount (based on the total weight of all ingredients of the binder composition except water) of from 0.01 to 2 wt. -%, preferably from 0.1 to 1.3 wt. -%, relative to the weight of the multi-ply fibrous product. These values can be determined by the amount of aqueous binder composition applied to the tissue product (total weight of all ingredients of the binder composition except water, in g/m)²) Divided by the basis weight of the dry tissue product (also in g/m)²) To calculate. 'drying'Tissue refers to conditioning as detailed in the experimental section below.

The aqueous adhesive composition preferably has a viscosity of from 1 to 500mPa.s, more preferably from 1 to 200mPa.s, measured using a Brookfield LV-DV-I viscometer from Brookfield Engineering Laboratories, Inc. using the spindle and rotational speeds given in the experimental section at 25 ℃. Even more preferably, the viscosity is adjusted to 25 to 150mpa.s, in particular 70 to 125 mpa.s.

Since the addition of dermatologically acceptable acids (e.g., lactic acid) to the adhesive composition will affect its viscosity and thus the handling and application properties of the adhesive composition, it is preferred to use amounts of acid that result in a viscosity within these ranges.

According to other embodiments of the present invention, the layers of the claimed multi-layered fibrous product comprise as papermaking fibers: (i) only non-regenerated cellulose fibers, (ii) only regenerated cellulose fibers, or (iii) a mixture of non-regenerated cellulose fibers and regenerated cellulose fibers in a weight ratio of 99/1 to 1/99, e.g., 90/10 to 10/90 or 80/20 to 20/80, wherein in any of (i), (ii), or (iii), the cellulose fibers may be selected from wood fibers, e.g., softwood fibers or hardwood fibers; and non-wood fibers, such as fibers from annual plants, and combinations thereof. Since fiber products made from regenerated cellulose fibers tend to have higher pH values, a greater amount of acid may be needed to prevent negative effects on the natural skin pH.

Depending on the type of the multi-layer fibre product, the number of fibre layers, such as tissue layers and/or non-woven layers, may be 2 to 8, in particular 2 to 6, for example 2 to 5. In very thick products with a higher number of layers, the adhesive composition is typically not added to one outer layer to bond all layers together, but to a second or third layer (if there are 2 or 3 inner layers between the two outer layers). The adhesive will then migrate from the layer to which it has been applied to the other layers, either spontaneously if the layers are brought into contact with each other or finally if pressure is applied to those areas carrying the adhesive composition, typically in a nip (rolnip). In this way, all layers may be bonded together.

The aqueous binder composition may be applied to the entire surface or a part thereof, the so-called "application zone". Within these application zones, the adhesive composition may be applied as a continuous coating or in the form of one or more regular or irregular patterns, preferably one or two regular patterns are used. The regular pattern may for example be produced by a combined adhesive/mechanical (e.g. by embossing) layer bonding technique as explained below. Preferably, the application zone or the sum of all application zones constitutes at least 50%, preferably at least 80%, of the surface area of the multi-ply fibrous product. More preferably, the application zone comprises the central area of the multi-ply fibrous product most likely to be in contact with the skin of the user.

The one or more patterns preferably include discrete and/or partially overlapping elements, such as dots, circles, lines, stripes, curves, polygons, etc., which may form design elements such as flowers, leaves, etc.

Preferably, the adhesive composition is applied in a pattern, preferably in a pattern that partially or completely coincides with the pattern of protrusions created by embossing the at least one ply. In one embodiment of the multi-ply fibrous product (e.g. toilet paper), at least one outer ply preferably comprises the embossed pattern on substantially at least 50%, preferably at least 80%, of its surface (preferably comprising the central region of the multi-ply fibrous product).

In a preferred embodiment, the multi-ply fibrous product exhibits substantially uniform coverage of the aqueous adhesive composition on its surface. "covering" means herein that the aqueous adhesive composition is distributed between at least two layers of the multilayer product by at least one regular or irregular pattern, preferably one or two regular patterns. The "cover" preferably comprises the central area of the multi-ply fibrous product.

The adhesive composition may be applied by techniques commonly used in the art, such as spraying, roll coating, printing, coating using a non-contact coating system developed by, for example, WEKO (Weitmann & Konrad GmbH & co.

No special drying step is required after application of the aqueous binder composition. Typically, fibrous layers such as tissue layers and/or nonwoven layers, preferably tissue layers, will adsorb the free water content of the aqueous binder composition. In addition, some water may also evaporate when the multi-ply fibrous product is left in air.

In the present invention, at least two fibrous layers, preferably all fibrous layers, such as tissue layers and/or non-woven layers, preferably tissue layers, are bonded together by using an aqueous adhesive composition comprising an acid or buffer system, or by combining adhesive layer bonding with mechanical layer bonding (e.g. by knurling or embossing). As explained in further detail below, during adhesive bonding, an adhesive film is deposited over the entire surface area of at least one layer or a portion of its surface, and the adhesive-treated surface is then placed in contact with the surface of at least one other layer. The two layers are bonded together by applying an adhesive composition to the inside of one of the preferably two layers. When more than two layers are to be bonded together, it is often sufficient to apply the adhesive composition to only one of the layers, for example to the inside of one of the two outer layers, because the adhesive composition will also migrate to the other layer and bond all the layers together, especially if the adhesive layer bonding is combined with mechanical layer bonding and the application of pressure to those areas carrying the adhesive composition. During mechanical bonding, the layers may be bonded by knurling, or by pressing, or by embossing. Embossing is a process that creates a raised or recessed design, typically by pressure between a plurality of engraved rollers or plates or by pressure between an engraved roller or plate and an elastic or deformable support surface. This can result in, for example, a dry creped tissue layer having specific embossments or indentations. The thickness of the dry-creped tissue layer or layers increases after embossing from its initial thickness.

In a further preferred embodiment, a multi-ply fibrous product, such as a tissue product, a nonwoven product or a mixture thereof, has two outer plies and optionally an additional ply located between the two outer plies, wherein at least one outer ply is embossed, thereby forming protrusions, and wherein an aqueous adhesive composition is applied to the distal ends (distend) of at least a part of the protrusions, the protrusions being arranged to bond the two outer plies and optionally the additional ply located between the two outer plies together. In this embodiment, the lower outer layer may also be "flat", i.e. without protrusions, e.g. produced by embossing, whereas the aqueous adhesive composition is applied only to the distal ends of the protrusions of the upper outer layer, in order to connect these outer layers (and, e.g. the optionally present central layer) together.

Preferred techniques for embossing fibrous plies, in particular nonwoven or tissue plies comprising cellulosic fibers, and for applying the aqueous binder composition are explained below.

For the production of multi-ply fibrous products, in particular tissue products, in particular bath tissue and household tissue, known production methods for embossing and adhesively bonding layers can be used, such as Goffra Incolla/point embossing, DESL (double embossing single lamination) and Pin-to-Pin (Pin-to-Pin)/Foot-to-Foot (Foot-to-Foot). The plies are typically embossed in the nip of an embossing roll and an anvil roll prior to their bonding.

In the first mentioned manufacturing method, Goffra Incolla, a first web is guided through a nip between an embossing roll and an anvil roll. In the nip, the web is imparted with an embossed pattern. The applicator roll then applies adhesive to portions of the first web where the protruding embossing elements within the embossing roll are present. The adhesive is transferred from the adhesive tank to the applicator roll by an adhesive transfer roll. The second web is transported to the first web and adhesively bonded to the first web in the nip between a so-called marrying roll and an embossing roll. Adhesive bonding occurs at those portions where adhesive is applied.

The second preparation method (DESL) is very similar to the Goffra Incolla method described above. It comprises a further pair of rolls comprising a second embossing roll and a second anvil roll. The additional pair of rolls is used to emboss the second web prior to adhesively bonding the second web to the first web using the bonding rolls. Typically, the further pair of rollers is positioned adjacent the first pair of rollers and the bonding roller. In one special case of the general DESL production method, the embossing elements of the first embossing roll and the embossing elements of the second embossing roll are arranged such that the embossing elements of the first embossing layer and the embossing elements of the second embossing layer cooperate with each other, similar to a gear system. This serves to achieve mutual stabilization of the two layers. However, for the DESL production method, such correlation between the embossing elements of the first, upper, layer and the embossing elements of the second, lower, layer is not required.

The third preparation method (pin-to-pin/foot-to-foot) is similar to the DESL method. The upper and lower layers are embossed separately by two pairs of rollers. The adhesive is applied to the embossing protrusions (protuberances) of the first layer. However, the layer bonding is not effected by means of a bonding roll as in the DESL method, but directly by means of the protruding embossing elements of the second embossing roll. For this reason, it is necessary to precisely adjust the width of the gap between the first embossing roller and the second embossing roller, which is mainly defined by the respective thicknesses of the two webs (upper and lower). Furthermore, the embossing rolls must be designed such that at least some of the protruding embossing elements of the two rolls face each other. This is why the term pin-to-pin or foot-to-foot embossing is used.

Further knurling may be used.

One suitable lamination technique of the present invention is described in WO 2011/035803, which produces a three-ply fibrous product comprising a first ply, a middle ply having projections nested into pillow-like cavities of the first ply, and a bottom ply preferably free of projections.

One preferred lamination technique of the present invention is shown in the drawings and explained in the examples and is associated with the teachings of US 2003/0129363 assigned to Georgia Pacific France. The embodiment also shown in fig. 1 to 4The embodiments relate to a multi-ply fibrous product, such as a tissue product, a nonwoven product or a mixture thereof, preferably a tissue product, comprising three plies, an embossed upper outer ply (3) and an embossed lower outer ply (1), and a central ply (2), each outer ply comprising a relief pattern comprising at least a portion of discrete protrusions, the distal end area of at least a portion of the protrusions of each outer ply (1,3) facing the central ply, and at least one of the upper outer ply (3) and the lower outer ply (1) having a pattern density of at least 10 protrusions/cm²Preferably at least 20 protrusions/cm²-the lower outer layer (1) comprises a first pattern (15a,15b) and a second pattern (16), the height (13) of the first pattern being smaller than the height (14) of the second pattern, wherein the central layer and the upper outer layer are connected in a nested (nested) manner and are connected with the lower outer layer (1) by means of an applied adhesive composition (12), wherein the central layer (2) and the upper outer layer (3) are connected with the lower outer layer (1) to the extent of at least a part of the tips of the second pattern connected to the lower outer layer, wherein the height of the protrusions of the second pattern is preferably 50% to 200% greater than the height of the protrusions of the first pattern.

In the present invention, the aqueous adhesive composition is preferably applied in such a way that the "tacky surface" (or "bonding surface") is from 1% to 20%, preferably from 2% to 10%, more preferably from 4% to 8%. By "tacky surface" is understood the proportion of the total surface of the outer layers of a multi-ply fibrous product comprising at least two fibrous layers, preferably a multi-ply nonwoven product, tissue product or a mixture thereof, which are bonded to each other by means of an aqueous binder composition, or, if applicable, the proportion of the total surface of the outer layers of said multi-ply fibrous product which are bonded to one or more inner layers by means of an aqueous binder composition. If there are two or more gluing units applying the mixed acid/glue in different non-overlapping patterns to one or more fibrous layers, e.g. tissue layers and/or non-woven layers, the respective gluing surfaces are added. Referring to, for example, fig. 2, the "tacky surface" can be determined (e.g., visually or with the aid of a microscope) by adding the individual adhesively bonded regions (12) corresponding to the large embossed regions (16) shown in fig. 3a and 3b and dividing the sum by the total surface area (plan view) of the tissue product. With reference to the design shown for example in fig. 3a and 3b, the "tacky surface" (in%) can also be calculated by dividing the total area of the large embossings (16) as a planar two-dimensional view by the total surface area of the fibrous product.

Various techniques exist in the art to adjust the amount of aqueous binder composition applied to a multi-ply fibrous product, and these techniques may also be used in the present invention. If, as described above, the aqueous adhesive composition is applied to the distal ends of at least a portion of the protrusions (resulting from embossing), the aqueous adhesive composition is preferably supplied to the embossing unit by a roller arrangement as shown in figure (1). Such an arrangement comprises a roll (6) with an engraved surface, such as an anilox roll, and an applicator roll (7), such as a rubber roll with a flat surface. In this case, the amount of the aqueous binder composition can be adjusted by: (i) changing the surface volume of the engraved cells of the roller (6) to 9cm³/m²To 30cm³/m²Value of (2) (preferred volume: 18 cm)³/m²To 21cm³/m²) (ii) a And/or (ii) the speed of the engraving roll (6) is adjusted to a value of 3% to 40% of the line speed (preferred speed: 7% to 15%, e.g. 10%).

Multi-ply fibrous products, such as tissue products, nonwoven products or mixtures thereof, preferably tissue products, preferably selected from wiping articles, hygiene products such as toilet tissue, handkerchiefs, household towels, facial tissues, napkins/napkins, bedding or clothing. More preferably, the multi-ply fibrous product is a toilet paper having 2 to 8 plies, preferably 2 to 6 plies.

The present invention also relates to a process for producing a multi-ply fibrous product, preferably a tissue product, a nonwoven product or a mixture thereof, comprising the steps of:

a) providing at least two fibrous webs, e.g. tissue webs and/or nonwoven webs, preferably at least two tissue webs

c) applying an aqueous binder composition to at least one side of at least one of the fibrous webs, the aqueous binder composition comprising a binder component and preferably a water-soluble dermatologically acceptable acid and optionally a corresponding salt of the acid, wherein the aqueous binder composition is preferably applied to the distal ends of at least a portion of the protrusions if at least one of the webs is embossed,

e) bonding the at least two webs together, an

f) An optional further step of converting the bonded web into a final multi-ply fibrous product.

With regard to steps a) to e), reference may be made to the preceding description of a multi-ply fibrous product, preferably a tissue product, a nonwoven product or a mixture thereof, and the preparation thereof.

In the present invention, a combination of multiple layers (at least two layers) can be used to impart specific properties to the final multi-ply fibrous product, such as thickness, bulkiness (bulk), softness and strength.

When processing a bonded fibrous web, such as a tissue web and/or a nonwoven web comprising cellulosic fibers, into a final product (optional converting step f), the following steps can be used alone or in combination: cut to size (longitudinal and/or transverse cut), folded, stamped, perforated, lotion applied, smoothed, stacked, rolled and packaged.

Examples

The following test methods were used to evaluate the produced tissue. Prior to testing, the test samples were conditioned at 50% relative humidity and 23 ℃ for at least 12 hours. When the present description or claims refer to the weight of a coarse tissue or tissue product, the weight is preferably determined after adjustment in the above-described manner.

4.1. Basis weight

According to EN ISO 12625-6: 2005, tissue and tissue products, part 6: basis weight was determined from the determination of grammage.

4.2. Paper thickness (Caliper)

According to a standard based on EN ISO 12625-3: 2014, modified method, measurement by precision micrometer (precision 0.001 mm). To this end, the distance created by the sample between the fixed reference plate and the parallel presser foot is measured. The diameter of the presser foot is 35.7 +/-0.1 mm (the nominal area is 10.0 cm)²). The applied pressure was 2.0 kPa. + -. 0.1 kPa. The presser foot moves at a rate of 2.0 + -0.2 mm/s.

A useful instrument is a type L & W SE050 thickness gauge (available from Lorentzen & Wettre, Europe).

The base tissue paper (web) to be measured was cut into pieces of 20 × 25cm and conditioned at 23 ℃ for at least 12 hours in an atmosphere of 50% RH (relative humidity). For measurement, a stack of 10 base tissues was prepared, placed under the press plate, and the press plate was lowered. The thickness value of the stack of tissues is then read 5 seconds after the pressure has stabilized. The thickness measurements were then repeated 9 times, and additional samples were processed and prepared in the same manner.

The average of 10 values was taken as the measured thickness of 10 base tissues (hereinafter referred to as "10-ply thickness").

The finished product to be measured (i.e. single-or multi-ply tissue product) is cut into pieces of 20X 25cm and conditioned at 23 ℃ for at least 12 hours in an atmosphere of 50% RH.

For measurement, a sheet is placed under the platen, and then the platen is lowered. Then, the thickness value of the sheet was read 5 seconds after the pressure was stabilized. The thickness measurements were then repeated 9 times and additional samples were processed in the same manner.

The average of the 10 values obtained was taken as the measured thickness of one sheet of the finished product (e.g. two-ply paper towel) ("one-sheet caliper").

4.3. Viscosity of the oil

The viscosity of the compositions was measured at 25 ℃ using a Brookfield LV-DV-I viscometer from Brookfield Engineering Laboratories, Inc. According to the desired viscosity range, the following rotors (sp) and rotational speeds (v) were used:

-for x < 0.1Pa s, sp 1/v 100rpm

-sp 2/v 100rpm for 0.1 pas < x < 1 pas

-sp 3/v 100rpm for 1 pas < x < 6 pas

-sp 4/v 100rpm for x > 6Pa s.

4.4 pH measurement (coarse tissue/tissue product)

As set forth in the appended claims, the pH of the tissue product is preferably measured using the following test method.

ISO 6588-1:2012(E) -Cold extraction Process

The process is based on extracting a representative sample of the corresponding tissue paper product (2g) with high purity water (100mL) at a temperature of 20 ℃ to 25 ℃ for 1 hour. The extract is prepared, filtered and processed according to this international standard. The pH of the extract was measured at a temperature of 20 ℃ to 25 ℃. The process achieves an average pH across the tissue product.

4.5 pH measurement on skin

Flat end face electrode method (Flat electrode method)

A skin surface pH study was conducted to investigate the effect of the low pH tissue products of the present invention on skin pH. Measurements were made on the palmar forearm before and after application of the test product. The pH of the skin surface was measured using a flat-faced electrode, calibrated in standard buffer solutions of pH 4.0 and pH 7.0. Prior to each measurement, the electrodes were immersed in 0.9 wt% NaCl in deionized water. 200 μ L of 0.9 wt% NaCl was added to the skin and wiped with the tissue of the present invention. A five-person panel was used to test the effect of the tissue paper products of the present invention on forearm skin surface pH.

Example 1

Preparation of aqueous adhesive compositions

By dissolving 85% lactic acid (264g, 15% water) and KOH (5g) in H₂O (736g), a potassium lactate buffer having a pH of about 11 of 2 was prepared. The molar content of lactic acid ("molar concentration of acid") calculated from these values was 2.366 mol/l. The molar concentration of acid refers to the total amount of acid added, regardless of whether a portion thereof is present as lactate due to the addition of KOH.

Then, the buffer solution was mixed with 429g of an aqueous binder based on polyvinyl alcohol (tak 1004, solids content of about 18.0%; available from h.b. fuller, europe, pH about 4.5) to give a ratio of 70 wt% potassium lactate buffer to 30 wt%tak 1004, respectively. After mixing, the solids content of the binder component was about 5.4 wt% based on the total aqueous binder composition. The pH of the resulting aqueous binder composition was about 2.3.

Preparation of tissue products

Prepared from a pulp mixture comprising 0.37 mm/sheet in thickness and 56.8g/m basis weight produced by a conventional dry-creping process²Of a non-embossed coarse tissue web.

The paper wrapper consists of three layers, using only non-recycled (virgin) papermaking fibers (100% virgin fibers). The composition of each layer is as follows:

the two outer layers were made of 9% softwood kraft fibers, 88% eucalyptus (eukalyptus) kraft fibers and 3% other hardwood kraft fibers;

one inner layer was made of 73% softwood kraft fibers, 20% hardwood kraft fibers, and 7% CTMP.

According to ISO 6588-1:2012(E) the pH of the coarse tissue web was measured to be 7.7.

Layer bonding step

Three prepared tissue webs were supplied to the embossing and gluing station shown in fig. 1.

The first web (1) and the third web (3) are each advanced to rubber rollers (8a and 8b) and embossed by engraved rollers (9a and 9 b). The second web (2), which later forms the middle layer in a three-layer product, first proceeds to a gluing unit (4) where the aforementioned aqueous adhesive composition is applied to one side of the web by means of (secondary) protrusions (14) of an engraved roll (9a), wherein the (secondary) protrusions (14) of the engraved roll (9a) press the web against an adhesive-applying roll (7). The adhesive (aqueous adhesive composition) is applied only on the secondary engravings (14) having a height approximately twice that of the primary engravings (13).

The gluing unit (4) comprises a glue chamber (5) containing an aqueous binder composition, an engraved anilox roll (6) transferring the aqueous binder composition (at room temperature) from the glue chamber to an applicator roll (7), a rubber roll with a flat surface transferring the binder composition to the second web (2). A doctor blade (not shown in fig. 1) meters the amount of adhesive on the anilox roll running at different speeds to reduce the amount of adhesive transferred to the applicator roll. The coating roll was run at linear speed. The surface of the anilox roll is provided with small holes, and a specific volume of adhesive can be conveyed per square meter.

According to a preferred embodiment, the throughput (volume) of the anilox roll is adjusted to 18cm³/m²To 21cm³/m²The speed of the anilox roll was adjusted to 10% of the line speed and the adhesive bonding area accounted for4% to 6% of the total surface of the tissue product, the adhesive bonding areas corresponding to the total area of all the bonding areas (12) as shown in fig. 2.

The three webs of tissue are superposed in the nip between the rolls (9a) and (9b), first superposing the webs (1) and (2) and then superposing the web (3), whereas no pressure is applied in the nip, and the webs are further advanced to the nip between the engraved roll (9a) and the marrying roll (10), in which nip all three webs are bonded together by pressing the adhesive covered areas (12) together.

The bonded web is then cut to size, perforated, and further converted into toilet paper rolls.

As can be seen from fig. 2 and 3, the resulting three-ply toilet paper exhibits three embossing patterns: small embossing patterns (15a,15b) (see primary engraving, 13) and large embossing patterns (16) (see secondary engraving, 14) also used as decorative patterns.

All of the embossing patterns of the prepared tissue product cover the entire surface of the tissue product.

The adhesive composition was applied in an amount of 0.39 wt.% based on the basis weight of the tissue product, based on all ingredients of the adhesive composition except water.

By ISO 6588-1:2012(E) the pH of the tissue product was 5.6.

Comparative example 1 and examples 2 to 12

With the exception of the differences shown in table 1 and explained below, 12 different three-ply tissue products (toilet tissue) were produced in the same manner as described in example 1.

In comparative example 1 and examples 2 to 5, and examples 8 to 12, the same papermaking fibers and layer compositions as in example 1 were used.

In examples 6 and 7, the paper wrapper consisted of three layers, containing 26% recycled fibers and 74% virgin fibers. The composition of each layer is as follows:

the two outer layers were made from 60% bleached eucalyptus kraft pulp and 40% bleached softwood kraft pulp

An inner layer made of 20% bleached eucalyptus kraft pulp and 80% deinked pulp fiber

In comparative example 1(CEx 1), no acid was added to the aqueous binder composition.

In examples 6 and 7, coarse tissue webs were prepared from a slurry mixture comprising 26% recycled fibers and 74% virgin fibers according to a conventional dry creping process.

The zelura adhesive used in example 12 is a methylcellulose-based binder available as a solid from Henkel. 33.3 parts by weight of the solids were dissolved in 966.7 parts by weight of water to yield an approximately 11 part aqueous binder.

From these results, it can be seen that all the examples lead to an effective change in pH. The prepared aqueous composition has good adhesion despite the presence of a greater amount of acid/buffer.

Example 13

The tissue product of example 7 was tested for its effect on forearm skin surface pH using the five panel and planar electrode method described above. The results are set forth in table 2 below.

TABLE 2

The above results show that the pH of healthy skin can be stabilized by the tissue paper of the present invention even if the coarse tissue paper used therein has a considerably high pH (pH 9.0 as in the case of example 7).

Claims

1. A multi-ply fibrous product comprising at least two fibrous plies, preferably selected from:

(b) a tissue product comprising at least two tissue plies, and

(c) a mixture of nonwoven products and tissue products comprising at least one tissue layer and at least one nonwoven layer, said nonwoven layer preferably comprising cellulosic fibers,

wherein the at least two layers are bonded to each other by an aqueous adhesive composition comprising an adhesive component, and a dermatologically acceptable acid and optionally a salt of said acid.

2. The multi-ply fibrous product of claim 1 wherein the acid and optionally the salt of the acid are provided in an amount such that the pH of the multi-ply fibrous product measured according to ISO 6588-1:2012(E) is from 3.5 to 7, preferably from 4.0 to 6.9, more preferably from 4.3 to 6.4, even more preferably from 4.5 to 6.2, for example from 4.8 to 6.0.

3. The multi-ply fibrous product according to claim 1 or 2, wherein the aqueous binder composition contains the acid and optionally a salt of the acid in a molar amount of from 0.1 to 10mol/l, preferably from 0.5 to 5mol/l, such as from 1 to 3 mol/l.

4. The multi-ply fibrous product of claim 1, 2 or 3 wherein the aqueous binder composition is present in an amount of from 0.01 to 2 weight percent, preferably from 0.1 to 1.3 weight percent, relative to the weight of the multi-ply fibrous product, the aqueous binder composition being present in an amount based on the total weight of all ingredients of the binder composition, excluding water.

5. The multi-ply fibrous product of any one of claims 1 to 4, wherein the adhesive component is selected from the group consisting of: (a) natural polymers such as proteins and protein-based compounds, gums and gum-like materials, polysaccharide-based materials, gums derived from animal products, and (b) synthetic polymers such as polyethyleneimine PEI, polyamidoamine-epichlorohydrin PAE and polyvinylamine PVAm, polyvinyl alcohol PVA, polyvinyl acetate PVAC, vinyl acetate-ethylene copolymer VAE, polyvinyl pyrrolidone PVP, polyurethane and styrene-butadiene copolymer, and water-soluble or water-dispersible cellulose-based compounds such as carboxymethylcellulose, sodium carboxymethylcellulose, methylcellulose and ethylcellulose; or any combination thereof.

6. The multi-ply fibrous product of any of claims 1 to 5, wherein the dermatologically acceptable acid is preferably water soluble and is selected from the group consisting of:

(i) the amount of inorganic acid, such as boric acid,

7. The multi-ply fibrous product of any one of claims 1 to 6, wherein the aqueous adhesive composition comprises a dermatologically acceptable acid and salts thereof, and the acid and salts thereof are present in amounts that together provide a pH buffering capacity.

8. The multi-ply fibrous product of any one of claims 1 to 7, wherein the plies comprise as papermaking fibers: (i) only non-regenerated cellulose fibers, (ii) only regenerated cellulose fibers, or (iii) a mixture of non-regenerated cellulose fibers and regenerated cellulose fibers in a weight ratio of 99/1 to 1/99, such as 90/10 to 10/90 or 80/20 to 20/80, wherein in any of (i), (ii), or (iii), the cellulose fibers can be selected from wood fibers, such as softwood fibers or hardwood fibers, and combinations thereof, and non-wood fibers, such as fibers from annual plants.

9. The multi-ply fibrous product according to any of claims 1 to 8, wherein the number of plies, in particular the number of tissue plies, is 2 to 8, in particular 2 to 6, such as 2 to 5.

10. The multi-ply fibrous product according to any of claims 1 to 9, wherein the adhesive composition is applied onto at least a part of the surface of the fibrous layer, in particular a non-woven or tissue ply, in at least one regular or irregular pattern, wherein the regular or irregular pattern preferably covers at least the central area of the fibrous layer, in particular a non-woven or tissue ply.

11. The multi-ply fibrous product according to any one of claims 1 to 10, which is preferably a tissue paper product, wherein the multi-ply fibrous product, preferably a tissue paper product, has two outer plies and optionally at least one further ply located between the two outer plies, wherein at least one of the outer plies is embossed, thereby forming protrusions, wherein the aqueous adhesive composition is applied to distal ends of at least a portion of the protrusions, the protrusions being arranged to bond the two outer plies and optionally at least one further ply located between the two outer plies together.

12. The multi-ply fibrous product of any one of claims 1 to 11, which is preferably a tissue product, comprising at least three plies: an embossed upper outer layer (3) and an embossed lower outer layer (1), and a central layer (2), each outer layer comprising a relief pattern comprising at least a portion of discrete protrusions, at least a portion of the distal end regions of the protrusions of each outer layer (1,3) facing the central layer, and at least one of the upper outer layer (3) and the lower outer layer (1) having a pattern density ofAt least 10 protrusions/cm²Preferably at least 20 protrusions/cm²-the lower outer layer (1) comprises a first pattern (15a,15b) and a second pattern (16), the height (13) of the first pattern being smaller than the height (14) of the second pattern, wherein the central layer (2) and the upper outer layer (3) are connected in a nested manner and are connected with the lower outer layer (1) by means of an applied adhesive composition (12), wherein the central layer (2) and the upper outer layer (3) are connected with the lower outer layer (1) to the extent of at least a part of the tips of the second pattern connected to the lower outer layer, wherein the height of the protrusions of the second pattern is preferably 50% to 200% greater than the height of the protrusions of the first pattern.

13. The multi-ply fibrous product of any one of claims 1 to 12, wherein the percentage of the total surface of the multi-ply fibrous product bonded by the adhesive composition is from 1% to 20%, preferably from 2% to 10%, more preferably from 4% to 8%.

14. The multi-ply fibrous product according to any of claims 1 to 13, wherein the multi-ply fibrous product is selected from a wiping product, a hygiene product such as toilet paper, handkerchiefs, household towels, facial tissues, napkins/napkins, bedding or clothing, wherein the multi-ply fibrous product is preferably a hygiene paper product having 2 to 8 plies, preferably 2 to 6 plies.

15. A process for making a multi-ply fibrous product, preferably a tissue product, comprising the steps of:

a) providing at least two fibrous webs of tissue and/or nonwoven,

e) bonding the at least two webs together, an

wherein the characteristics of the multi-ply fibrous product and/or the aqueous adhesive composition are preferably as defined in any one of claims 2 to 14.