SK283196B6 - Absorbents containing stiffened fibres and superabsorbent materials - Google Patents

Abstract

Absorbent structures having a fluid acquisition/distribution layer (110) with an average dry density of less than about 0.30 g/cc, an average density upon wetting with 1.0 % NaCl aqueous solution of less than about 0.20 g/cc, and an average dry basis weight from about 0.001 to about 0.10 g/cm2; and a fluid storage layer (108) positioned beneath the acquisition/distribution layer (110) comprising at least about 15 % superabsorbent material. The fluid acquisition/distribution layer (110) comprises from about 50 % to 100 % chemically stiffened cellulosic fibres and from 0 % to about 50 % binding means.

Description

Technical field

The invention relates to absorbent units comprising a cellulosic fiber material and a superabsorbent material. These absorbent units can be used in a variety of absorbent articles, such as disposable diapers, incontinence pads and panties, and the like, which require the ability to retain and retain large amounts of excreted body fluids, particularly when repeatedly expelling relatively large amounts of these fluids over a relatively short time.

BACKGROUND OF THE INVENTION

Absorbent nonwoven webs of interwoven fibers, i. j. fibrous webs are well known in the art. Such webs can absorb fluids, such as excreted body fluids, into one another by an absorption mechanism in which the fluid is absorbed by the fibrous material itself and on the other hand by a wick mechanism in which the fluid is collected, distributed and accumulated in the capillary spaces between the fibers. One means to improve the absorbent properties of such fibrous webs is to introduce a superabsorbent into the web, such as a polymeric gelling material (similar materials are also referred to as hydrogel-forming substances, superabsorbent polymers, etc.) which soaks up the fluid. The superabsorbent material serves to contain fluids such as excreted body fluids. Absorbent structures of this type in which a hydrogel-forming material is introduced into the fibrous web are disclosed in U.S. Pat. No. 4,610,678 (Weisman, Goldmann, issued September 9, 1986).

The improvement in absorbent properties achieved by incorporating gel-forming absorbent units into absorbent articles has made it possible to produce articles such as diapers with a relatively thin absorbent core, which is manifested by the fact that the whole articles are relatively thin. Thinner diapers are easier to wear and fit better than clothing. They are also more compact in packaging and allow the consumer to carry and store easier. Packing compactness also results in reduced shipping costs from the manufacturer to the store.

One such absorbent core configuration that is suitable for use as an absorbent structure in relatively thin absorbent articles is described in U.S. Patent No. 4,765,780 (Angstadt, issued August 23, 1988). This patent discloses absorbent articles, such as diapers, that comprise an absorbent core with a two-layer configuration. The core comprises an upper primary layer and a lower layer. The primary layer is formed from a pneumatic web of hydrophilic fibrous material that contains a significant amount of admixed absorbent gelling material. The backsheet comprises a hydrophilic fibrous material and preferably contains no gel-forming absorbent.

A further configuration of the absorbent core is disclosed in US Patent No. 5,201,549. No. 4,673,402 (Weisman, Houghton and Gellert, issued June 16, 1987). This patent discloses absorbent articles comprising bilayer absorbent cores. In this two-layer configuration, the core comprises an upper primary layer which is a pneumatic web of hydrophilic fibrous material and which optionally contains a small amount of gelling polymer particles. Under the primary layer is a backing layer consisting of a pneumatic mixture (fleece) of hydrophilic fibers and a considerable amount of polymerizing gel-forming particles. The backing layer is typically disposed at the front of the absorbent article such that more than one half of the gelling agent in the article is in the front half of the article. Absorbent articles having a two-layer configuration according to US Patent 4,873,402 can be manufactured in the form of particularly thin, high-performance baby diapers with very low fluid permeability.

Regardless of the existence of the absorbent cores described above, there is still a need to develop absorbent cores with improved effective absorbent capacity. One theoretical way to achieve this is to increase the amount of gel-forming polymerization material in the absorbent core. Unfortunately, however, the high amount of polymeric gelling material (especially above about 15%) in fibrous webs typically used in absorbent cores tends to cause a phenomenon called gel blocking. Gel blocking occurs when the polymerization gelling material located in the area that first comes into contact with the fluid becomes bulky as it soaks in the liquid to form a hydrogel. If the concentration of the polymerization gelling material is too high, the hydrogel may prevent further fluid from entering other areas of the core with unused absorbent capacity. Blocking the gel can cause the absorbent article to leak fluid during use.

Polymerization gelling materials have been developed with a reduced tendency to gel block. Such materials are described in U.S. Pat. RE 32,649 (Brandt, Goldman and Inglin, patent issued April 19, 1988). However, the use of these improved polymerization gelling materials and other superabsorbent materials is limited by the functional properties of the cellulose fiber web in which the particles of the gelling material are distributed. In particular, upon initial wetting, the cellulose fibers become highly flexible and the web tends to collapse and densify, thereby reducing the average pore size. Since the pore size in the wetted areas is lower than the pore size in those nonwoven portions of the web, a capillary gradient is formed which counteracts the efficient transport of fluids to the dry portions of the absorbent article.

Another reason why many absorbent articles, such as diapers, leak fluid is their inability to absorb second and subsequent fluid outlets, although the first fluid outlet has been effectively absorbed. Fluid leakage during the second and subsequent effusions occurs mainly at night, when the user usually secretes several times while being treated. One reason for the inability of many absorbent articles to cope sufficiently with multiple fluid expulsions is, in addition to the above, the inability of the absorbent core to transport the exuded fluid away from the effluent region after the absorbent capacity of that region is exhausted. After fluid discharge, the fluid tends to remain in the area near the discharge. When subsequent fluid excretion occurs, a driving force is generated which transports the first entrained and newly conjugated fluid to the hips. However, the actual function of the absorbent article is limited by its ability to deliver fluid to the more distal regions of the core. For this reason, even in the absence of the polymeric gelling material, the total absorbent capacity of conventional absorbent diaper cores is generally not fully utilized before the failure occurs, i.e.. j. for passing fluid from the absorbent article.

Yet another reason for permeating fluid through conventional absorbent articles is the tendency of cellulosic fibers, which are typically used to capture and distribute fluid, after wetting, which impairs the permeability of structures.

SUMMARY OF THE INVENTION It is an object of the present invention to provide absorbent structures containing superabsorbent that will not be burdened by the problems arising from gel blocking and wet fiber collapse, and will utilize most of their absorption capacity.

It is a further object of the present invention to provide superabsorbent-containing absorbent structures which are capable of rapidly entrapping fluid in the region of its sprain and transporting it to a relatively large portion of the accumulative absorbent structure while being capable of effectively entrapping and distributing excreted body fluid upon second or further evacuation.

It is a further object of the present invention to provide absorbent structures that meet all of the above requirements while being relatively thin.

One of the proposed absorbent structures is described in U.S. Pat. No. 4,935,022 (Glen R. Lash and Leonard R. Thompson, patent issued June 19, 1990). This patent discloses disposable absorbent articles that comprise a multi-layer absorbent core positioned between the backsheet and the topsheet. The absorbent core comprises a topsheet of reinforced, twisted and curled cellulosic fibers and 3-15% by weight of a gel-forming absorbent in the form of large particles and a backsheet of reinforced twisted and curled cellulosic fibers and about 15 to 60% by weight of a gel-forming absorbent. The main purpose of the topsheet is to capture and distribute body fluid ejection. In this respect, the reinforced twisted and curled fibers have very good properties. The bottom layer, which is necessarily smaller than the top layer, serves mainly to store fluid.

Another absorbent structure is designed and described in U.S. Pat. No. 4,798,603 (S. C. Meyer et al., Issued January 17, 1989) entitled "Absorbent article comprising a hydrophobic transport layer". As is clear from the title, this patent describes an absorbent article having a hydrophobic transport layer made of known hydrophobic synthetic fibers. The transport layer is located between the topsheet and the absorbent body. The absorbent body must be more hydrophilic than the transport layer. The purpose of the transport layer is to act as an insulating layer between the topsheet and the absorbent body to reduce skin moisture. Regardless of whether or not the structures described meet the expectations, it is possible for the transport layer according to U.S. Pat. No. 4,798,603 foresees limited fluid acquisition and transport capability, which will at least partially cause the hydrophobicity of the layer. This will in particular be the case for the second and subsequent efflux of the fluid when all the surfactants that may be present in the layer have been washed out of the layer.

French document FR-A-1 472 852 discloses sanitary napkins having a base absorbent pad comprising a fluid control portion having a density substantially higher than that of a basic absorbent pad, wherein the dimensions of the fluid control portion are longitudinally and transversally shorter than the corresponding insert dimensions. However, the solution of the cited publication does not disclose a storage component of fluids using chemically stiffened cellulose fibers.

British Patent Specification 2,215,609 discloses articles such as diapers comprising a gelling agent particulate material and a stiffened, twisted, curled cellulosic fibrous material in a lower fluid storage layer and a higher fluid acquisition distribution layer that also includes stiffened, twisted, cellulosic fibrous portions gelling agent. The storage layer is smaller in area than the acquisition layer.

Regardless of the existence of the absorbent articles of the type described, there still remains a need to find further improved absorbent article configurations that provide improved fluid acquisition and distribution efficiency, particularly in the case of additional effluents.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide improved absorbent structures, elements for use in such structures, as well as absorbent articles comprising such structures based on a multi-layer absorbent core that effectively captures user's body fluids during initial and subsequent effusions. in further discharge, a relatively large portion of the surface of the absorbent structure accumulates and accumulates these fluids.

SUMMARY OF THE INVENTION

The invention relates to an absorbent structure which is particularly useful as the absorbent core of disposable absorbent articles, such as diapers and pants for incontinence sufferers. The structure includes a acquisition and distribution layer having an average dry density of less than about 0.3 g. cm ³ , the average density after saturation with 1% aqueous sodium salt solution, based on dry matter less than about 0.2 g. cm ³ and an average dry basis weight of from about 0.001 to about 0.10 g. cm ' ² . An accumulation layer is placed below the acquisition and distribution layer for storing the fluid. The acquisition and distribution layer comprises a web formed from 50 to 100 wt. % of chemically reinforced cellulose fibers and from 0 to about 50 wt. binder. The binding agent may be used to increase the physical integrity of the web, which facilitates its processing and / or improves its user properties, and / or increases the average effective pore size between the webs of the web. As used herein, a binding agent is understood to be an integral part of the reinforced fiber layer and may include, for example, non-reinforced cellulosic materials, synthetic fibers, chemical additives, and thermoplastic polymers. The binder is not limited to the materials mentioned. In combination with or instead of the binding means, the acquisition and distribution layer can also be provided with a wrapper of fabric or sparse nonwoven resulting from the joining of two perpendicular yarn assemblies, again aiming to increase the physical integrity of the layer.

The storage layer comprises at least about 15% superabsorbent by weight and 0 to about 85% superabsorbent carrier. The acquisition and distribution layer should contain no more than about 6.0% superabsorbent. Preferably, the acquisition / distribution layer will comprise substantially no superabsorbent. By " substantially no superabsorbent " it is understood that the superabsorbent content will be less than about 2.0%, preferably less than about 1.0%, and more preferably zero or nearly zero. The term " near zero content " refers to a very low superabsorbent content (less than about 0.5%) in the acquisition and distribution layer in contact with or in close proximity to the storage layer containing the superabsorbent.

The top surface of the acquisition and distribution layer is at least 15% of the top surface of the accumulation zone, but is smaller than the top surface of the accumulation layer. The acquisition / distribution layer is preferably positioned relative to the storage layer such that in the bent sheet configuration of the article no surface of the acquisition / distribution layer extends beyond the upper surface of the storage layer. Most preferably, the top surface of the acquisition / distribution layer is about 15 to about 95%, most preferably about 25 to about 90% of the top surface of the storage layer.

The absorbent structure of the invention may advantageously be used as an absorbent core in absorbent articles, such as disposable diapers and incontinence briefs. Such absorbent articles also include a liquid pervious topsheet and a liquid impervious backsheet, the topsheet and the backsheet being joined together and the absorbent core being therebetween. The absorbent core is disposed in such a product such that the acquisition and distribution layer lies between the topsheet and the storage layer, and the storage layer lies between the acquisition and distribution layer and the backsheet.

The superabsorbent used in the storage layer has an absorption capacity of at least about 10 g of synthetic urine (1.0% sodium salt solution in distilled water) per gram of superabsorbent. The absorption capacity measurement is described below. Suitable superabsorbents include polymeric gel-forming absorbents, which are typically used in the form of discrete particles and superabsorbent fibers such as acrylic grafted fibers and modified cellulose superabsorbent fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1 is a perspective view of a diaper having an absorbent core that is composed of multiple layers and configured in accordance with the invention. The absorbent core shown in FIG. 1 comprises a rectangular-shaped acquisition and distribution layer and an hourglass-like storage layer.

In FIG. 2 is a perspective view of a similar diaper structure as shown in FIG. 1, in this case, however, the storage layer has the shape of a modified watch glass.

In FIG. 3 is a frontal view of an absorbent core suitable for diaper applications, such as the diaper of FIG. 1 and 2, wherein the core comprises a modified watch glass-like accumulation layer and a similarly shaped acquisition and distribution layer.

DETAILED DESCRIPTION OF THE INVENTION

The absorbent structures of the present invention can be used in disposable products that are capable of absorbing significant amounts of body fluids such as urine or water in feces. These products can be manufactured in the form of diapers, incontinence pants, incontinence pads for adults and the like, all of which are disposable products.

The absorbent articles of interest generally comprise three basic structural components. One such component is a liquid-impermeable backsheet. On the lower sheet there is an absorbent core which itself contains two different layers and which in one of these layers contains a superabsorbent. The top side of the absorbent core is adjacent to the liquid-permeable top sheet. The lower and upper sheets are joined together. The topsheet is an element of the product that is adjacent to the user's skin.

By expressing that the topsheet and the bottomsheet are joined together, it is understood that the configuration in which the topsheet is directly attached to the bottomsheet, i. j. when the top sheet is directly affixed to the bottom sheet and configurations in which the top sheet is indirectly connected to the bottom sheet, i. j. when the top sheet is attached to the intermediate sheet, which is then joined to the bottom sheet. Preferably, the topsheet is directly attached to the bottomsheet on the periphery of the diaper by either a gluing or other suitable connection known in the art.

Especially suitable absorbent articles of the present invention are disposable diapers. Disposable diaper articles are described in detail in U.S. Pat. RE 26 151 (Duncan and Baker, issued Jan. 31, 1967); No. 3,592,194 (Duncan, issued July 13, 1971); U.S. Pat. No. 3,489,148 (Duncan and Gellert, issued Jan. 13, 1970); and U.S. Pat. No. 3,860,003 (Buelí, issued Jan. 14, 1975). A preferred disposable diaper according to the invention comprises an absorbent core, a top sheet disposed on one side of the absorbent core and a bottom sheet adjacent the opposite side of the absorbent core. Preferably, both the backsheet and the topsheet have a greater width than the core, thereby forming edges on the sides of the bottom and topsheets that extend beyond the core. Often, the top sheet is welded to the bottom sheet in these marginal regions. The diaper is preferably constructed in a configuration corresponding to the shape of the watch glass, but this is not necessary.

For example, the backsheet of such articles may be a thin film of plastic, such as polyethylene, polypropylene, or other substantially moisture-impermeable flexible material. Particularly preferred is embossed polyethylene with a thickness of about 0.038 mm.

The topsheet of the article may be made in part or wholly of synthetic fibers or films containing materials such as polyester, polyolefin, viscose fibers and the like, or natural fibers such as cotton. In nonwoven topsheets, the fibers are joined together by a thermal bonding process or by means of a polymerization binder such as polyacrylate. The topsheet is substantially porous and allows the fluid to rapidly penetrate into the underlying absorbent core.

Another suitable type of topsheet is a topsheet of a liquid impermeable polymeric material, such as polyethylene. Such topsheets may comprise conical capillaries of a certain diameter allowing the exuded fluid to pass through the topsheet into the underlying absorbent core of the article.

The topsheets used in the articles of the invention could be relatively hydrophobic compared to the absorbent core of the articles. The topsheet construction is generally described in U.S. Pat. No. 2,905,176 (Davidson, issued September 22, 1959); No. 3,063,452 (Del Guercio, issued Nov. 13, 1962); No. 3,113,570 (Holliday, issued Dec. 10, 1963); and U.S. Pat. No. 3,929,135 (Thompson, issued December 30, 1975). Preferred topsheets are made of polyester, regenerated cellulose fibers, a mixture of regenerated cellulose fibers and polyester, polyethylene or polypropylene. The topsheet may be treated with a surfactant to make it more wettable and thus less hydrophobic and, consequently, to increase fluid flow through the sheet at least at the initial wetting. However, the topsheet should still be more hydrophobic than that element of the absorbent article into which fluids enter after passing through the topsheet.

The absorbent core, which is preferably flexible, is positioned between the elongate backsheet and the topsheet to form an absorbent article. The core essentially comprises, on the one hand, an upper fluid acquisition / distribution layer and, on the other hand, a lower fluid storage layer. The term "layer" is used herein to denote two types of zones contained in the absorbent core, and this does not necessarily mean that the individual zones could not be formed by more than one layer of material. In fact, both the acquisition and distribution layer and the storage layer may be formed by a laminate or a combination of several sheets or webs of materials of the appropriate type as set forth below. The storage layer may be a single sheet of substantially 100% superabsorbent, as described below. As already mentioned, the term layer means not only one layer but also several layers. The term " topsheet " refers to a layer adjacent the topsheet of the absorbent article in the absorbent core. In contrast, the term backsheet means an absorbent core layer adjacent the backsheet of the absorbent article.

Optionally, between the acquisition / distribution layer and the storage layer is a liquid-permeable sheet (e.g., a fabric) or a sparse nonwoven material to increase the integrity of the acquisition / distribution layer during processing and / or use. Such a fabric or nonwoven material may wrap all or part of the acquisition / distribution layer or may be simply placed between the two layers without necessarily forming the acquisition / distribution layer envelope. Also, the superabsorbent-containing storage layer may optionally be placed in a wrapper of a liquid-permeable sheet material, such as tissue paper, to eliminate the user's concerns about the possible leakage of free superabsorbent.

Capture and distribution layer

One of the essential elements of the absorbent structures of the present invention is the top acquisition and distribution layer, which is a combination of a hydrophilic fibrous material described below. The acquisition and distribution layer has the task of quickly retaining and temporarily retaining the body fluid that has been discharged. Depending on the position of the user, a portion of the fluid to be discharged may pass through the acquisition and distribution layer and be absorbed by the storage layer, namely in the region close to the emptying point. However, since fluid is usually excreted in the form of discharges, the storage layer in this region may not be able to absorb the fluid as quickly as it is excreted. The top acquisition / distribution layer therefore also facilitates transport of fluid from the initial fluid contacting layer to the other parts of the acquisition / distribution layer. In the context of the present invention, a liquid is to be understood as a liquid state, for example urine.

As mentioned above, the acquisition and distribution layer is formed by a web comprising reinforced cellulose fibers. The acquisition and distribution layer comprises about 50 to 100% of these fibers and about 0 to about 50% of the binder. Suitable binding agents are described below.

The distribution function of the acquisition / distribution layer into the fluid is of particular importance in order to fully utilize the capacity of the storage layer. It is believed that the presence of larger amounts of superabsorbent in the acquisition / distribution layer, which swells upon contact with the fluid, adversely affects the partitioning ability of the acquisition / distribution layer.

The performance of the resulting absorbent articles is determined by a number of other factors relating to the acquisition / distribution layer of the absorbent structure of the present invention. Such factors are shape, basis weight, density, permeability, capillarity, wick ability, layer type, structural integrity and the nature of the fibrous material used. As already mentioned, the core acquisition and distribution layer is preferably elongated. The term "elongated" in the context of the present invention means that the acquisition and distribution layer, as well as the storage layer, do not have the same length as the width in a flat, bent configuration. In the bent state, the acquisition and distribution layer may have any desired shape, for example, rectangular, trapezoidal, oval, rectangular or watch glass. The shape of the core core acquisition / distribution layer may generally correspond to the shape of the storage layer, but this is not necessary. The top surface of the acquisition and distribution layer will preferably be about 25 to about 90% of the top surface of the storage layer, but at the same time it will preferably not extend beyond the edges of the storage layer. The acquisition and distribution layer will typically have a top surface area of less than about 80% of the top surface area of the storage layer.

Preferably, there is at least about 0.5 cm and preferably at least about 1.25 cm edge between the edge of the acquisition / distribution layer and the edge of the storage layer in the region opposite the fluid emptying point during use. In diapers, this hem will correspond, for example, to the middle portion 115 in FIG. 2 (which is in the crotch position in use), in particular the region at the narrowest portion of the storage layer 106 in the middle portion 115. In addition, especially in the case of male absorbent articles, such a rim is also formed in the region which is positioned in front. in the belt, as shown in FIG. 2 as part 112.

The acquisition and distribution layer will typically have an average dry density less than about 300 kg. m ^-3 (measured before use) and an average density after wetting - consisting of a saturation with synthetic urine (1.0% sodium salt solution in distilled water), based on dry matter, less than about 200, preferably less than about 150 kg. m ' ³ . Also, the preferred average dry density and the average density after soaking up to saturation are in the range of about 20 to about 200 kg. m ^-3 , preferably from about 20 to about 150 kg. rn ³ . The average dry basis weight of the acquisition / distribution layer of the absorbent core is generally in the range of about 0.01 to about 1.0 kg. m ^"2, preferably from about 0.1 to about 0.8 kg. m ² and more preferably from about 0.15 to about 0.4 kg. m ' ² . Unless otherwise stated, all density and basis weight data are calculated on a dry matter basis (ie, with an equilibrium moisture content not exceeding about 6%). The density and basis weight of the acquisition / distribution layer may be substantially uniform, although embodiments of non-uniform density and / or basis weight, density gradient and / or gradient basis weight are within the scope of the invention. Thus, the acquisition / distribution layer may comprise regions of relatively higher and relatively lower density and basis weight, but which do not exceed this range. The average values of dry density and density after soaking up to saturation with synthetic urine (1.0% sodium salt solution in distilled water) are calculated from the dry weight basis and layer thickness data. The layer thickness in the dry state and after soaking until saturation is measured under a limiting pressure of 1.43 kPa. The average density after soaking up to saturation is calculated from the dry basis weight and the layer thickness after saturation. The thickness of the post-saturation layer is measured by self-saturation of the layer (under conditions without limitation) with a 1.0% sodium salt solution in distilled water and after equilibration.

The acquisition / distribution layer of the absorbent structure of the invention typically comprises a web of hydrophilic chemically reinforced cellulose fibers. Typically such wood pulp fibers are wood pulp fibers which are reinforced with a chemical reinforcement interposed between the fibers.

The acquisition and distribution layer should contain no more than about 6.0% superabsorbent. Preferably, the acquisition and distribution layer is substantially free of superabsorbent. By " substantially no superabsorbent " it is understood that the superabsorbent content will be less than about 2.0%, preferably less than about 1.0% and more preferably less or nearly zero. is understood to be a very low superabsorbent content (less than about 0.5%) in the acquisition / distribution layer in contact with or in close proximity to the storage layer containing the superabsorbent.

If the superabsorbent is present in the entrapment and partition zone, especially if it is present in an amount greater than 2.0%, the gel-forming absorbent particles should have a relatively large diameter (e.g., the weight median particle diameter should be from about 400 to about 700 µm) ). A superabsorbent in the form of particles with a weight median particle diameter of less than 400 µm may also be used.

As already mentioned, chemically reinforced fibers are used in the products of the invention. The term 'chemically reinforced fibers' means any fibers which have been reinforced by a chemical process to increase their stiffness, both under dry and wet conditions. Such a chemical process involves the addition of chemical reinforcing agents, for example to coat or impregnate the fibers. The fibers can also be reinforced by altering their chemical structure itself, for example by crosslinking the chains.

Examples of polymerization reinforcing agents that can be used to coat or impregnate fibers include cationically modified starch containing nitrogen-containing groups (e.g., amino groups), such as a product available from the market by National Starch and Chemical Corporation Bridgewater New Jersey, USA latex, wet strength resins such as polyamide-epichlorohydrin resin (e.g., Kymene® 557H, Hercules Inc., Wilmington, Delaware, USA), polyacrylamide resin (described, for example, in U.S. Patent No. 3,556) 932, issued January 19, 1971, to Coscia et al., As well as commercially available polyacrylamide marketed by American Cyanamid Co., Stanford, Connecticut, USA under the tradename Perez ^R , 631 NC), urea-formaldehyde and melamine-formaldehyde resins and polyethyleneimine resins. resin. A general overview of the wet strength resins used in papermaking and which can generally also be used as the chemical reinforcing agents of the present invention can be found in TAPPI monograph no. 29, entitled "Wet Strength in Paper and Paperboard", Technical Association of the Pulp and Paper Industry (NewYork, 1985).

The fibers used in the structures of the invention may also be reinforced by a chemical reaction. For example, it is possible to treat the fibers with crosslinking agents which, upon application, cause a chemical reaction leading to cross-links within the fibers. These cross-links can increase the stiffness of the fibers. It is preferred from the chemical fiber reinforcement processes to form cross-links in the fibers, but this does not mean that other types of reactions leading to chemical fiber reinforcement are excluded.

Cross-reinforced fibers in an individualized (i.e., fluffy) form are disclosed, for example, in U.S. Patent No. 5,201,549. No. 3,224,926 (Bernardin, issued December 21, 1965); No. 3,440,135 (Chung, issued Apr. 22, 1969), U.S. Pat. No. 3,932,209 (Chatterjee, issued Jan. 13, 1976) and U.S. Pat. No. 4,035,147 (Sangenis et al., Issued Jul. 12, 1977). More preferred fibers are disclosed in U.S. Pat. No. 4,822,453 (Dean et al., Issued April 18, 1989), U.S. Pat. No. 4,888,093 (Dean et al., Issued December 19, 1989) and U.S. Pat. No. 4,898,642 (Moore et al., Issued Feb. 6, 1990). In addition to being hydrophilic, the stiffened fibers remain stiff even after wetting. For this reason, the nonwoven webs produced therefrom do not burn as they are made from conventional unreinforced fibers. This achieves an improved ability to collect and distribute fluids in the second and subsequent discharge.

For preferred reinforced fibers, chemical treatment involves crosslinking individual fibers with crosslinking agents in a state where the fibers are relatively anhydrous and fibrillated (i.e., individualized), twisted and curled. Non-limiting examples of suitable chemical reinforcing agents include monomerizing cross-linking agents, for example C 2 -C 8 dialdehydes and C 2 -C 8 monoaldehydes containing an acid functional group, which may be used to form the crosslinking solution. These compounds are capable of reacting with at least two hydroxy groups in a single cellulose chain or in adjacent cellulose chains of a single fiber.

Non-limiting examples of particular cross-linking agents that can be used in preparing reinforced cellulose fibers include glutaraldehyde, glyoxal, formaldehyde, and glyoxalic acid. Other suitable reinforcing agents include polycarboxylates such as citric acid. Polycarboxylic reinforcing agents and a method of making reinforced fibers using them are described in U.S. Pat. No. 596,606, issued October 17, 1990. The effect of crosslinking under these conditions is to produce reinforced fibers that tend to retain their twisted and curled configuration during use in the absorbent articles of the invention. Such fibers and methods of making the same are described in said patents.

Preferably, the reinforced fibers have a twist and are twisted and these properties can be expressed quantitatively by the value of the twist count and the twisting factor of the fiber. As used herein, the number of twists refers to the number of twist densities (nodes) per unit of fiber length. The number of twists is used as a means of measuring the degree of rotation of the fiber about its longitudinal axis. The term twist refers to a substantially 180 ° rotational rotation about the longitudinal axis of the fiber, in which a portion of the fiber 'node' appears darker with respect to the rest of the fiber when viewed under a light microscope. The fiber is darker in those places where the transmitted light had to cross the additional fiber wall due to the twist. The distance between the darker points (nodes) corresponds to an axis rotation of 180 °. Number of 'twist nodes' per unit of fiber length, t. j. the number of twists directly indicates the degree of twist of the fiber, which is the physical parameter of the fiber. Procedures for determining the number of twists and nodules are set forth in U.S. Pat. 4,898,642.

Preferred reinforced cellulose fibers will have an average dry twist of at least about 2.7, preferably at least about 4.5 knots per mm. In addition, the average number of twists in the wet state should preferably be at least about 1.8, preferably at least about 3.0 nodes per 1 mm. The number of wet twists should also preferably be at least about 0.5 nodes / mm lower than the average dry twist number. Even more preferably, the average dry fiber twist is at least about 5.5 nodes per mm and the average wet fiber twist is at least about 4.0 nodes / mm, wherein the wet twist value is at least 1.0 nodes / mm. mm less than the number of dry twists of the fiber. Most preferably, the average dry fiber twist is at least about 6.5 per 1 mm and the average wet fiber twist is at least about 5.0 nodes / mm, wherein the wet twist value is at least 1.0 node / mm less than the dry twist of the fiber.

In addition to being twisted, the preferred fibers used in the acquisition / distribution layer of the absorbent structure are also curled. The crimped fibers may be described as twisted fibers due to loops, twists, and / or bends in the fiber. For the purposes of the present invention, curl is measured in a plane. The extent of the sliver fiber can be quantified by the sliver factor. The fiber curl factor, measured as two-dimensional curl (i.e., in a plane), is determined by observing the fibers in a plane. First, the projected fiber length is measured as the longest dimension of the rectangle surrounding the fiber LR and the actual fiber length La. The boiling factor can then be calculated from the following equation the boiling factor = (L _A / L _R ) -1.

A method of image analysis that can be used to measure L _R and L _A is described in US Patent No. 5,201,549. The fibers used in the absorbent core layers of the invention will preferably have a tufting factor of at least about 0.30, and more preferably at least about 0.50.

The degree of reinforcement, which depends on the type and amount of reinforcing agent used (i.e. crosslinker), the degree of fiber drying, before curing with the crosslinking agent, the time and curing conditions affects the fiber's ability to absorb liquid and the tendency of the fiber to swell.

The stiffness of the fiber in relation to the fiber wall's swelling resistance of the fiber wall can be quantified by the water retention value (WRV) of the reinforced cellulose fiber used in the absorbent article of the invention. Water retention is a measure of the amount of water retained in the mass of fibers after removal of substantially all of the water present between the fibers. Another parameter that can be used to characterize the nature of the reinforced fibers produced by crosslinking the fibers in a substantially anhydrous state is the value of the Alcohol Tank (ARV). ARV is a measure of the extent to which a fluid, such as isopropyl alcohol, that does not cause substantial swelling of the fiber is received by the reinforced fibers. The ARV of the reinforced fibers is directly related to the extent of swelling of the fibers by the crosslinking agent solution in the reinforcing process. Relatively higher ARV values usually mean that the fibers were allowed to swell to a greater extent during crosslinking. Procedures for determining WRV and ARV are described in U.S. Pat. 4,898,642.

The WRV of the reinforced, twisted and curled fibers used according to the invention should preferably be in the range of about 28 to about 50%. In a more preferred embodiment of the invention, the WRV of the fibers should be in the range of about 30 to about 45%. Fibers with this WRV level usually provide the optimum balance of both the reduction in twist due to swelling and the stiffness of the fibers.

Preferred reinforced cellulose fibers for use herein have an ARV (isopropyl alcohol) of less than about 30%. The restriction of these fibers to fibers with an ARV (isopropyl alcohol) of less than about 30% is in fact a restriction to fibers which have been relatively dehydrated and non-swollen in the reinforcing process. For the purposes of the invention, it is even more preferred that the fibers have an ARV (isopropyl alcohol) value of less than 27%.

The reinforced cellulosic fibers of the invention, with a preferred number of twists, a tufting factor and WRV and ARV values, can be prepared by internal crosslinking of the fibers in relatively dehydrated form, during or after this operation, drying and fibrillation (i.e., fluff) as described. U.S. Pat. 4,898,642.

Hydrophilic chemically reinforced fibers other than those mentioned above are not excluded from the scope of the present invention. Such different fibers are described, for example, in the cited U.S. Pat. 3 224 926, 3 440 135, 4 035 147 and 3 932 209. However, the invention is not limited to these fibers.

A characteristic feature of the reinforced fibers, especially the twisted and curled reinforced fibers, is their ability to partially lose twist and curl after soaking. Thus, when such fibers are processed into webs of sufficient density, the webs may expand upon wetting, which means that their equilibrium density in the wet state, calculated as the dry matter of the fibers, is lower than the average dry density (ie before wetting) . The average dry density values of up to about 300 kg can thus be explained. cm ³ and lower average saturation density values at saturation. Non-woven webs that can expand after soaking are described in U.S. Pat. Those skilled in the art are able to adjust the relative amount of reinforcing agent used and the degree of twist and torsion imparted to the reinforced fibers to achieve the desired extent of expansion after soaking.

The reinforced cellulose fibers can be processed into webs by a variety of technologies, such as pneumatically and paper.

Pneumatic fleece

The reinforced cellulose fibers can be processed into a web by laying in an air stream, i. j. pneumatically. Thus, a web having the desired density and basis weight can be obtained. The reinforced fibers for use according to the invention can be processed into pneumatic webs by well known cellulose fiber laying techniques in the air stream. Typically, the air stream containing the fibers in the substantially dry state is directed to the wire screen and the resulting web is optionally compressed to the desired density. The fibers can also be laid on the screen without pressing the resulting web. The pneumatic web comprises at least about 50% of the reinforced cellulosic fibers described above and may contain up to 100% of these fibers including the cut-off value. Optionally, the web comprises a binding agent, such as those described herein, or other optional ingredients, such as fluid-modifying additives (e.g., hydrophilic surfactants) and the like.

Non-woven fabrics made of paper

The reinforced cellulose fibers can also be wet-processed instead of the pneumatic treatment, i.e., the webs. j. papermaking. Wet-webed webs comprise from about 50 to about 100% reinforced fibers and 0 to about 50% binding agent to enhance the physical integrity of the web, to facilitate wet and / or dry processing and to achieve increased integrity upon wetting the web in use. Typically, the wet webs comprise at least about 2% of a fibrous or cellulose binder having a high specific surface area (as described below). It is also possible to use chemical additives as binding agents, which are introduced into the scavenging and separating layer usually in an amount of from about 0.2 to about 2.0% by weight, based on the dry fleece weight.

Techniques for manufacturing sheet material such as dry webs and paper by wet-laying cellulosic fibers are well known in the art. In general, these technologies can also be used for wet laying of reinforced fibers to form webs that are useful in the absorbent structures of the invention. Suitable technologies include manual laying and fabrication using papermaking machines, such as described in US Patent No. 5,201,549. 3,301,746 (L. H. Sanford et al.). When working using paper machines, preferably the wet fiber laying process is somewhat modified as described below, since the reinforced fibers have a slightly different behavior, especially tend to flocculate in aqueous suspensions. In general, papermaking webs are produced by placing an aqueous fiber suspension on a perforated forming screen, dewatering the suspension to form a wet web, and drying the wet web. The aqueous wet-laid fiber suspensions preferably have a fiber consistency in the range of from about 0.05 to about 2%, preferably from about 0.05 to about 0.2%, based on the weight of the total suspension. Laying the suspension is usually carried out using a device known in the art as a headbox. The headbox comprises an opening, known as a spout, through which the aqueous fiber suspension is conveyed to a perforated forming screen. The perforated forming screen is often referred to in the art as the Fourdrinier screen. The Fourdrinier screen may be of a design and density that is typically used for dry fleece or other papermaking. Preferably, sieves with a density of about 70 to about 100 mesh are used (Tyler standard sieve set, with an aperture size of about 147 to about 200 μιτι). All mesh data given below refer to a standard Tyler set of sieves unless otherwise noted. Conventional type headboxes which are commonly used in the art for the production of dry webs and tissue paper may be used. Suitable headboxes obtainable on the market include fixed roof headboxes, double screen and headboxes with drum forming apparatus. After manufacture, the wet web is dewatered and dried. Dewatering may be performed by means of suction boxes or other vacuum devices. In dewatering, the fiber consistency is generally increased to a value of from about 8 to about 45%, preferably from about 8 to about 22%, based on the total weight of the wet web.

Dewatering to a consistency higher than about 22% may require wet pressing and is therefore less preferred. After dewatering, the web may optionally be transferred (but not necessary) from the forming screen to a desiccant on which the web is conveyed to a drying apparatus. The drying agent is preferably thicker than the forming screen to increase the drying efficiency. The aperture area of the drying fabric is preferably about 30 to about 50% of the total area, and the joint area is about 15 to about 25%, as is the case with 31 x 2555 (satin weave), which has been sandblasted to increase the hinge area to range. During the transfer from the forming screen to the fabric, a wet microcontraction is preferably performed. The wet microcontraction is achieved by allowing the forming screen to run at a rate that is about 5 to about 20% higher than the rate at which the drying agent moves. The drying may be carried out by means of a dryer in which the nonwoven is blown with warm air or by means of a vacuum device such as a drying cabinet. Warm air blowing is preferred. The webs of the present invention produced by the papermaking process are preferably completely dried using warm air blow dryers (usually to a fiber consistency in the range of about 90 to about 95%). Blow drying is believed to be an effective method for drying fiber reinforced webs, since these webs have a high void volume. Steam drying drums also known in the art (e.g., Yankee Drum driers) may also be used, but these devices are less preferred. Tumble dryers are considered to be less effective in drying reinforced fiber webs and can also compact the webs. The dried webs are preferably not creped.

The drying can also be carried out by removing the dewatered web from the forming screen and placing it on a drying screen, where it is dried (without limitation) by a batch process, for example by means of a hot air blow dryer or a convection oven heated by steam.

The reinforced fibers tend to flocculate and form in the aquatic environment. In order to avoid flocculation, the aqueous suspension must be pumped into the headbox at a linear velocity of at least 0.25 m. s' ¹ . It is also preferred that the linear flow rate of the slurry from the headbox outlet nozzle be about 2.0 to about 4.0 times the rate of the forming screen. Another way to reduce fiber flocculation in wet laying is described in U.S. Pat. No. 4,889,597 (issued Dec. 26, 1989). According to this patent, water nozzles are aimed at the wet laid fibers immediately after laying on the forming screen.

Binding agent

Compared to unreinforced cellulosic fibers, the cross-linked twisted and reinforced fibers described above form sheets of lower tensile strength, especially in the desiccated state. In order to facilitate the processing and to increase the integrity of the webs, especially those made by papermaking (although binding means can also be used in pneumatic webs), the binding means is incorporated into the webs as an integral component. The binding agent may either be added to the fibers prior to the web (whether pneumatic or papermaking) or may be added to the papermaking web after depositing the slurry on the forming screen and before drying, or it may be applied to a dry web (papermaking). In the latter two processes, a chemical additive is particularly suitable as a binding agent. Combinations of several different methods of introducing the binding agent may also be used.

Non-limiting examples of binding agents to be added to the stiffened cellulosic fibers prior to processing into a wet web of pulp suspension include various cellulosic and synthetic fibrous materials. These materials include unsaturated cellulose fibers (i.e., conventional cellulose pulp fibers), highly refined unreinforced cellulose fibers, which are refined to a dewatering rate

CSF (Canadian Standard Freeness) of less than about 200, preferably about 100 to about 200 CSF (highly refined fibers are referred to as krill), and high surface area cellulosic materials such as expanded cellulosic fibers (described below).

Various types of synthetic fiber material may be used in synthetic fiber-based binding agents. Throughout this specification, the use of synthetic fiber materials as a binding agent is understood to mean that these fiber materials are present in the resulting product in fiber form. (Preferably, the synthetic fibers used have at least a staple length, i.e., the average fiber length is preferably at least about 1.5 cm.) Any type of fibrous material that is suitable for use in the ultimate absorbent article can be used for use in the fleece trap and divider of the present invention. products. Specific examples of such fibrous materials include modified cellulose fibers, regenerated cellulose fibers, polyester fibers such as polyethylene terephthalate (Decron), hydrophilic polyamide (Hydrophil) and the like. Other fibers which may be used for this purpose include cellulose acetate, polyvinyl fluoride, polyvinylidene chloride, acrylates, polyvinyl acetate, polyamides (such as nylon), bicomponent fibers, tricomponent fibers, mixtures thereof and the like. Hydrophilic fibrous materials are preferred. Examples of suitable hydrophilic fibrous materials include hydrophilic hydrophobic fibers such as thermoplastic fibers derived, for example, from polyolefins such as polyethylene, polypropylene, polyacrylates, polyamides, polystyrenes, polyurethanes and the like in which hydrophilization has been carried out by surface, active or oxide treatment silica. Hydrophobic synthetic fibers may also be used, but are less preferred. Synthetic fibers which may be added to the fibers prior to web processing and which are present in the web in fibrous form include regenerated cellulose, polyethylene, polypropylene, and the like. Such fibers, when hydrophobic in nature, are preferably present in the web in an amount of less than about 30%, based on the weight of the entire web, so that the web remains substantially hydrophilic. It is possible to use unreinforced fibers, krill as well as synthetic fibers in pneumatic webs according to common practice.

In one preferred embodiment of the invention, when the acquisition and distribution layer is made by papermaking, the web comprises about 85 to about 95% reinforced cellulose fibers and about 5 to about 15% krill, preferably about 90 to about 95% reinforced fibers and about 5 to about 10% krill, most preferably about 92% reinforced fibers and about 8% krill. Suitable cellulosic fibers for use as krill include pulp fibers produced by chemical wood treatment, both softwood and hardwood, preferably softwood of southern tree species (e.g., Foley Fluff, The Procter & Gambia Cellulose Co., Memphis, Tennessee). , USA). All percentages given in relation to nonwoven fabrics refer, unless otherwise expressly, to the total dry weight of the nonwoven.

According to a further embodiment of the invention, the acquisition and distribution layer comprises reinforced fibers and up to 25% of a cellulose material having a high specific surface area, such as expanded cellulose fibers. Preferably, the acquisition / distribution layer comprising a web made of fiber reinforced paper will comprise about 85 to about 98% reinforced fibers, preferably about 90 to about 95% reinforced fibers and about 2 to about 15%, preferably about 5 to about 10% % cellulose with a high specific surface area. Cellulose material with a high specific surface area suitable for use in this application will typically have a specific surface area of at least about 10 m ² . g ^-1 , preferably at least about 20 m ² . g ¹ . A thorough review of the expanded cellulose fibers can be found, for example, in U.S. Pat. No. 4,761,203 (Vinson, issued Aug. 2, 1988).

Usually, however, multi-component structures made of cellulose polymers are suitable as cellulose fibers. Other substances such as lignin, hemicellulose and other ingredients known in the art may also be present. Cellulose polymers are laterally (laterally) aggregated to form thread-like structures called microfibrils. The microfibrils are said to have a diameter of about 10-20 nm and can be observed by electron microscopy. Microfibrils often exist in the form of small bundles, known as macrofibrils. Macrofibres can be defined as a larger number of microfibrils that are laterally aggregated to form a thread-like structure having a larger diameter than the microfibril but substantially smaller than the cellulose fiber. Cellulose fiber is generally made up of a relatively thin primary wall and a relatively thick secondary wall. The primary wall, a thin net-like envelope placed on the outer surface of the fiber, is mainly made of microfibrils. The main part of the fiber wall, i. j. secondary wall, consisting of a combination of microfibrils and macrofibrils (see Pulp and Taper Manufacture, vol. 1, Properties of Fibrous Raw Materials and Their Preparation for Pulping, ed. Dr. Michael Kocurek, Chapter VI "Ultrastructure and Chemistry", p. 35 - 44, joint publication of the Canadian Pulp and Pipe Industry (Montreal) and the Technical Association of the Pulp and Pipe Industry (Atlanta), 3rd edition, 1983. Expanded cellulose fibers are thus understood to mean microfibrils and macrofibrils that have been substantially separated or released of cellulose fiber ultrastructure.

Cellulose with a high specific surface area can also be made from cellulose fibers by passing a liquid suspension of cellulose fibers through a small diameter orifice at which the suspension is subjected to a pressure drop of at least 20.8 MPa at a high shear rate at which a high deceleration impact occurs. . The slurry is passed through the orifice until a substantially stable suspension is obtained (see U.S. Patent No. 4,483,743, Turbak et al., Issued Nov. 20, 1984).

A preferred process for preparing expanded cellulose fibers is described in the Vinson patent (see above). In this procedure, fibrous material with fibrillar ultrastructure (e.g., cellulose fibers) is treated with a fine medium to separate the microfibrils and macrofibrils from the ultrastructure of the fibrous material.

The particle length of the high surface area cellulosic material is preferably from about 20 to about 200 µm.

In the papermaking process, cellulose with a high specific surface area is available as wet pulp containing generally 15 to 17% solids. This pulp is diluted to a solids content below 4% and processed in a dutch or disc refiner to break up tangled clumps. Thereafter, the cellulose having a high specific surface area is well mixed with the reinforced fibers in suspension and the resulting suspension is processed into a web as described above. Mixers, deflakers or rafers (for example, single, conical or double, disk rafters or other devices known in the art) may be used to mix the reinforced fibers and cellulose with a high specific surface area. Preferably, small aperture sieves (e.g., 84 M (84 x 76, shed binding)) are used to improve the retention of cellulose with a high specific surface area rather than more open sieves, which are typically used for shaping.

Other binding means for enhancing the physical integrity of the acquisition / distribution layer and to facilitate the processing of webs, in particular paper webs for use in the acquisition / distribution layer, include chemical additives such as resin binder, latexes and starch known to be impart increased physical integrity to the fibrous webs. Suitable resin binders include binders known to impart wet strength to the paper, see, for example, the TAPPI monograph series no. 29 Wet Strength in Paper and Paperboard, Technical Association of the Paper and Paper Industry (New York, 1965). Particularly suitable resins include polyamide-epichlorohydrin and polyacrylamide resins. Other resins which can be used according to the invention include urea-formaldehyde and melamine-formaldehyde resins. Frequent functional groups of these polyfunctional resins include nitrogen-containing groups such as amino and methylol groups attached to nitrogen. Polyethyleneimine type resins can also be used for this purpose.

Starch, in particular cationically modified starches, can be used as chemical additives according to the invention. Such cationized starches, which are usually modified with nitrogen-containing groups such as amino and methyl-bonded nitrogen groups, are available from Natural Starch and Chemical Corporation of Bridgewater, New Jersey, USA. Non-limiting examples of other binders include polyacrylic acid and polyvinyl acetate.

The chemical additives, i.e., binders, are generally introduced into the webs in an amount of from about 0.25 to about 2%, based on the total weight of the web. However, if the chemical binders are hydrophilic, they may be present in larger amounts. When chemical binders are added to the reinforced fibers in an aqueous suspension, it is usually preferable for the non-reinforced cellulose fibers or cellulose with a high specific surface area to also be present in the suspension to increase the retention of the chemical binder. The chemical binders can be applied to the dried webs by printing, spraying or other methods known in the art.

Collection and distribution layer reinforced with thermoplastic material

According to another embodiment, the acquisition and distribution layer comprises a pneumatic or papermaking, preferably pneumatic, reinforced cellulose fiber web which is reinforced with about 10 to about 50, preferably about 25 to about 45, and preferably about 30 to about 45%, of the thermoplastic binder material. The binder material binds stiffened cellulose fibers at their crossing points. Such webs can be produced by a process in which the web is first made of reinforced cellulose fibers and thermoplastic fibers, which are preferably evenly distributed throughout the web. The web can be produced either pneumatically or by papermaking. After fabrication, the web is heated to a temperature at which the thermoplastic fibers melt. After melting, at least a portion of the thermoplastic material migrates to the intersection positions of the stiffened cellulosic fibers due to inter-fiber capillary gradients. These intersections become binding sites for the thermoplastic material. Thereafter, the web is cooled and, where the thermoplastic material has migrated, the reinforced cellulose fibers are joined. The melting and migration of the thermoplastic material into the intersection positions of the reinforced cellulose fibers results in an increase in the average pore size of the web, leaving the web density and basis weight at the original level. This can improve the distribution properties of the acquisition / distribution layer at initial fluid discharge, due to improved fluid permeability and other effluents due to the combination of the stiffened fiber retention capability and the ability of the thermoplastic binder to bond the fibers at their intersection and wetting points, and when pressed in a soaked state. The overall effect of this process is that the bonded web retains its total volume, but the volume initially occupied by the thermoplastic fibrous material becomes free, thereby increasing the average size of the inter-fiber capillary pores.

Heat-bonded absorbent webs reinforced with a thermoplastic binder based on conventional unreinforced cellulose fibers are described in U.S. Pat. No. 4,590,114 (D. C. Holtman, issued May 20, 1986) and in Peter G. Bither, " Thermally Bonded Cores Add Value to Absorbent Products ", Nonwovens World, November 1988, p. 49-55. The processing technologies described in these works are also suitable for the present invention.

The thermoplastic binder material must be uniformly distributed throughout the web. After forming the dry web, the web may be heated to a temperature at which the thermoplastic fibers melt, but without charring or other damage to the reinforced cellulose fibers. After cooling, at least a portion of the re-solidified thermoplastic material is present at the binding sites which ensure that the stiffened cellulosic fibers are joined together at the fiber crossing sites to form a stabilizing network of inter-fiber binding sites.

Suitable thermoplastic binders which are suitable for use in the acquisition / distribution layer are all thermoplastic polymers which can be melted at a temperature at which no significant damage to the cellulose fibers occurs. The melting point of the thermoplastic binder material should preferably be less than about 175 ° C and preferably should be in the range of about 75 to about 135 ° C. In any case, the melting point should not be lower than those that are considered when storing the finished products. For this reason, the melting point of the thermoplastic should generally not be less than about 50 ° C.

Suitable thermoplastic binder materials include, for example, polyethylene, polypropylene, polyester, polyvinyl chloride and polyvinylidene horide. Other synthetic fibrous materials that can be used in the heat-sealed web are mentioned above.

Preferably, the thermoplastic material does not contain or absorbs an aqueous liquid. The surface of the thermoplastic material may be hydrophilic or hydrophobic. (The terms hydrophilic and hydrophobic characterize the extent of surface wettability by water.) The surface of the thermoplastic can be hydrophilized by treating the hydrophobic thermoplastic binder material with a surfactant such as a nonionic or anionic surfactant. The material may be sprayed or soaked in the surfactant. After melting and re-solidifying, the surfactant tends to remain on the surface of the thermoplastic. Suitable surfactants include nonionic surfactants such as Brij 76, a product of ICI Americas, Inc. of Wilmington, Delaware, USA, and similar materials sold under the trade name Pegosperse by Glyco Chemical, Inc. , Greenwich, Connecticut, USA. Anionic surfactants can also be used. Surfactants are applied to the fibers in an amount of from about 0.2 to about 1 g per m ^{2 of} thermoplastic binder material. Hydrophilic materials are more desirable if the content of the thermoplastic material reaches a high value, in particular above about 40%, based on the dry fleece weight.

The thermoplastic fibers proposed for use herein should be of the order of about 0.1 to about 6 cm, preferably about 0.3 to about 3.0 cm.

A preferred type of thermoplastic fibrous material is the product marketed under the designation PULPEX® (Hercules, Inc., Wilmington, Delaware, USA). PULPEX is a polyolefin material that has a very high surface area to mass ratio and is produced by spraying molten polymer and gas through a nozzle into an evacuated space. PULPEX is available on both polyethylene and polypropylene basis.

The thermoplastic material used may be both hydrophilic and hydrophobic in nature.

As already mentioned, the web of reinforced cellulose fibers reinforced with a thermoplastic binder can be produced by a pneumatic or paper process. Pneumatic webs can be made by mixing cellulosic and thermoplastic fibers, and the mixture is pneumatically processed into the web by the techniques described. The stiffened cellulosic fibers and thermoplastic fibers can be mixed together in a pneumatic process by carding or mixing two air streams comprising both stiffened cellulosic fibers and thermoplastic fibrous material and processing the bonded system in a brush screen or other nonwoven equipment. These technologies are known. A suitable device is the pneumatic system supplied by Dan Webforming Intemational Ltd. (Risskov, Denmark). A suitable method of blending cellulosic and thermoplastic fibers for subsequent pneumatic web production and apparatus suitable for this purpose are also described in U.S. Pat. No. 4,590,114 (Holtman, D. C., issued May 20, 1986). In the papermaking process, the thermoplastic fibrous material may be admixed with the stiffened cellulosic fibers in an aqueous suspension prior to the web.

Preferably, the thermoplastic melts in the web by blowing hot air through the web, but other methods such as infrared radiation, etc. may also be used. In another alternative, the web is subjected to embossed hot embossing on either or both sides of the web. This technology is described in detail in the aforementioned U.S. Pat. 4,590 114.

As mentioned above, in addition to the binding means or in addition, outer reinforcing elements, such as sheets of tissue or tissue paper and other non-woven water-permeable materials, can also be used in the acquisition / distribution layer.

Accumulation layer

The second essential element of the absorbent core is a lower fluid storage layer comprising at least 15%, preferably at least 25% by weight of superabsorbent (more fully characterized below) and 0 to about 85%, preferably less than about 75% by weight of the superabsorbent carrier composition. The main function of the liquid storage layer is to absorb the excreted body fluid from the top acquisition and distribution layer and to retain the fluid even at pressures that occur by the user's movements. Thus, the storage layer is located below the acquisition and distribution layer and is in fluid communication with it. Ideally, the storage layer is capable of removing the topsheet of most of the entrapped fluid.

As already mentioned, the accumulation layer contains superabsorbent, generally but not necessarily, in the form of discrete particles of absorbent gelling material and superabsorbent fibrous material, such as acrylic grafted fibers and superabsorbent modified fibers. The superabsorbent may be in any form that can be introduced into a flexible web or sheet to form an accumulation layer. Superabsorbents are described in more detail below. Upon contact with water or body fluids, the superabsorbent absorbs these fluids. (Fluids in this specification are understood to mean substances of a liquid rather than a gaseous state.) The fluid excreted into the acquisition / distribution layer and transported to the storage layer can thus be captured and retained in a superabsorbent, thereby obtaining products with increased absorption capacity and / or improved fluid retention.

By superabsorbents according to the invention is meant absorbents which are capable of absorbing at least about 10 g, preferably at least about 15 g, and even more preferably at least about 20 g of synthetic urine (1% sodium salt in water) in 1 g of superabsorbent as determined below.

The superabsorbent used is usually in the form of discrete particles of absorbent gelling material. These particles are usually distributed in a web of fibrous material that serves as a carrier. The superabsorbent fibrous material may comprise synthetic or natural fibers. Suitable fibrous carriers include cellulose fibers in the form of feathers or tufts, as are typically used in absorbent cores. Modified cellulose fibers, such as the reinforced cellulose fibers described above, may also be used, but such fibers are generally not used in the storage layer. Synthetic fibers such as cellulose acetate fibers, polyvinyl fluoride, polyvinylidene chloride, acrylic polymers (such as Orion), polyvinyl acetate, insoluble polyvinyl alcohol, polyethylene, polypropylene, polyamides (such as nylon), polyesters, bicomponent fibers, tricomponent fibers can also be used. , mixtures thereof and the like. Preferably, the synthetic fibers have a titer of from about 3.3 dtex to about 27.5 dtex, preferably from about 5.5 to about 17.6 dtex. It is also preferred that the fiber surface is hydrophilic or hydrophilized.

The average dry density of the liquid storage layer, which contains non-superabsorbent fibers as the superabsorbent carrier, is typically in the range of about 30 to about 500 kg. m ³ , preferably in the range of about 100 to about 400 kg. m- ³ , more preferably from about 150 to about 300 kg. m ³ and most preferably from about 150 to about 250 kg. m ' ³ . The basis weight of the lower liquid storage layer may be from about 0.2 to about 1.2 kg. m ² , preferably from about 0.4 to about 0.8 kg. m ^-2 and most preferably from about 0.5 to about 0.7 kg. m ' ² .

As with the acquisition / distribution layer, the density and basis weight of the storage layer need not be uniform. The storage layer may comprise regions of relatively higher and relatively lower density and basis weight. As with the acquisition and distribution layer, the density values of the storage layer are calculated from the basis weight and layer thickness measured at a limiting pressure of 1.43 kPa. Density and basis weight include the weight of the superabsorbent. In addition, the storage layer may include a superabsorbent material gradient such that more superabsorbent is present in areas with high fluid absorption requirements (i.e., near the fluid secretion site) and less superabsorbent is present in areas with lower fluid absorption requirements.

As the superabsorbent material used in the storage layer of the absorbent core, a substantially water-insoluble, slightly crosslinked, partially neutralized, polymeric absorbent gelling material is most commonly used. It is a substance that forms a hydrogel upon contact with water. Such polymers can be made from polymerizable unsaturated monomers containing acid functional groups. Suitable acid monomers suitable for use in the preparation of the polymerization gelling materials used in the present invention include those disclosed in U.S. Pat. No. 4,654,039 (Brandt, Goloman, Inglin, issued March 31, 1987), which was later reissued under RE 32,649 on April 19, 1988. Preferred monomers are acrylic acid, methacrylic acid, and 2-acrylamido-2-methylpropenesulfonic acid. Particular preference is given to acrylic acid itself in the production of polymeric gelling agents.

The polymerization component, formed from an unsaturated monomer containing an acid functional group, can be grafted onto other types of polymers, such as starch or cellulose. Of these materials, the starch grafted with polyacrylate is most preferred.

Preferred polymeric absorbent gelling materials which can be made from conventional types of monomers include hydrolyzed polyacrylonitrile grafted starch, polyacrylate grafted starch, polyacrylates, maleic anhydride copolymers, and combinations thereof. Preference is given in particular to polyacrylate and starch grafted with polyacrylate.

Whatever the nature of the polymeric constituents used in the hydrogel-forming polymeric absorbent gelling material, the particulate nature of this material, and whether it is to be used in any layer of the absorbent core, is always a substance that is usually not only crosslinked. The crosslinking serves to make the hydrogel-forming polymeric gelling agents used in the invention substantially water insoluble. Thus, the degree of crosslinking in part determines the gel volume and the content of the extractable polymer from the hydrogel formed from the polymerization gelling agents. Suitable cross-linking agents are well known in the art, and examples thereof are set forth in more detail in U.S. Pat. No. 4,076,663 (Masuda et al., Issued Feb. 28, 1978). Preferred crosslinkers are di- or polyesters of unsaturated mono- or polycarboxylic acids with polyols, bisacrylamides and di- or trialkylamines. Other preferred crosslinking agents include N, N'-methylenebisacrylamide, trimethylolpropane triacrylate, and trialylamine. Typically, the crosslinker may comprise about 0.001 to 5 mole% of the resulting hydrogel-forming polymer. Preferably, the crosslinker constitutes about 0.01 to 3 mol% of the hydrogel-forming polymeric gel forming particles.

The slightly crosslinked polymeric gel-forming particles of the hydrogel-forming material that are present in the products of the invention are generally used in partially neutralized form. In this context, partially neutralized substances are considered to be those in which at least 25 mol% and preferably at least 50 mol% of the monomers used for the production of the polymers are monomers containing an acid group which is neutralized by a salt cation. Suitable salt-forming cations include alkali metals, ammonium, substituted ammonium cations, and amine residues. The percentage of monomers having a neutralized acid group relative to the monomer in total is referred to as the degree of neutralization.

The webs containing the gelling material particles and the non-superabsorbent fibrous carrier generally comprise about 10 to about 80%, more typically about 20 to about 75% of the polymeric gelling material, and about 20 to about 90%, preferably about 25 to about 80% of the carrier material. Such webs are usually manufactured pneumatically by measuring the air stream containing the gelling absorbent particles into the air stream carrying the fibrous support.

Also encompassed by the present invention are accumulation layers from which particles of absorbent gelling material are laminated between two or more webs of fibrous material, such as disclosed in U.S. Patent No. 5,201,549. No. 4,578,068 (Kramer et al., Issued Mar. 25, 1986).

As mentioned above, superabsorbent fibers can also be used in place of the gel-forming superabsorbent particles. Superabsorbent fibers have been described in the prior art. For example, superabsorbent fibers are disclosed in Textile Science and Technology, Vol. 7, Pronoy K. Chatterjee, ed. Elsevier Science Publishers B.V. (The Netherlands), 1985, in Chapters VII and VIII (p. 217 -

280). These fibers may be synthetic or modified natural fibers such as cellulose fibers. Superabsorbent fibers for use in the context of the present invention should have an absorption capacity of at least 10 g and preferably at least 15 g of synthetic urine per 1 g of superabsorbent dry matter.

One type of superabsorbent fibers include cellulose fiber modified with a polycarboxylate polymer, such as a slightly hydrolyzed methyl acrylic grafted kraft pulp of soft tree wood. Such superabsorbent fibers are described in U.S. patent application Ser. No. 07 / 378,154, filed

June 11, 1989 entitled "Absorbent Paper Containing Polymer Modified Fiber Pulp and Process for Making It by Wet Process" (Larry N. Mackey and S. Ebrahim Seyed-Rezal).

Other types of superabsorbent fibers include cross-linked carboxymethylcellulose fibers and polymer-grafted cellulose fibers. The polymer grafted cellulosic fibers include hydrolyzed polyacrylonitrile, polyacrylic acid esters and polyacrylic and polymethacrylic acid as grafted polymer. These superabsorbent fibers are disclosed in Chatterjee Vol. 7 of Textile Science and Technology, cited above in particular by A. H. Zahran et al., "Radiation Grafting of Acrylic and Methacrylic Acid to Cellulosic Fibers to Import High Water Sorbency", J. of App. Polymer Science, Vol. 25, 535-

542 (1980). As the title of this article suggests, the work involves radiation grafting of methacrylic acid and acrylic acid onto cellulose fibers. Further literature includes U.S. Pat. No. 4,036,588 (J. L. Williams et al., Issued July 19, 1977), which discloses polymerization with grafting a hydrophilic group-containing vinyl monomer to a cellulose-containing material, for example, regenerated cellulose yarn; No. 3,838,077 (H. W. Hoftiazer et al., Issued Sep. 24, 1974), disclosing cellulose fibers grafted with polyacrylonitrile.

The superabsorbent fiber may be fed into the webs of conventional or other non-superabsorbent fibers, such as the papermaking webs described above or pneumatic webs, and may also be processed into a nonwoven sheet material.

According to another alternative, the storage layer may comprise superabsorbent fibers which are processed to form nonwoven sheets. Such a sheet material may essentially consist only of superabsorbent fibers and the content of the carrier therein may be zero, although such sheet material may also contain a carrier and embodiments with the carrier also fall within the scope of the present invention. Nonwoven sheets made of superabsorbent fibers, such as methacrylate superabsorbent microfibers and superabsorbent fibers useful in the manufacture of such sheets are commercially available from Arco

SK 283196-6

Chemikal Co. (Newtown Square, Pennsylvania USA) under the trade name FIBERSORB ⁸ and from Japan Exlan Co., Ltd., (Osaka, Japan), which sells fibers containing a polyacrylonitrile core with a polyacrylic acid coating layer and polyammonium acrylate under the trade name LANSEAL®.

When the storage layer of the absorbent core is comprised of a pneumatic web containing the carrier, it can be produced by pneumatic laying of a substantially dry mixture of fibers and particles of absorbent gelling material, whereupon the resulting web is eventually densified. Such a procedure is described in more detail and more fully in U.S. Pat. No. 4,610,678 (Weisman and Goldman, issued September 9, 1986). The superabsorbent fibers together with the fibrous supports can be pneumatically processed into webs by conventional manufacturing methods. The superabsorbent fibers and the carrier fibers may be blended together, for example, by carding or in the Rand web manufacturing process.

In the storage layer of the absorbent core, the superabsorbent material can be evenly distributed. Alternatively, regions or zones having a higher superabsorbent concentration than other regions or zones of the layer may be present in the storage layer.

As already mentioned, the acquisition / distribution layer of the absorbent core preferably has a smaller surface area (in a bent configuration) than the storage layer. In fact, the surface area of the acquisition and distribution layer may be substantially smaller than the area of the accumulation layer, but it may also be equal to or greater than the surface area of the accumulation layer. Typically, the surface area of the acquisition and distribution layer is about 25 to about 100%, preferably about 30 to about 95%, even more preferably less than 90%, and most preferably less than 85% of the surface area of the storage layer.

The acquisition / distribution layer of the absorbent core according to the invention must be positioned specifically against the topsheet and the storage layer of the absorbent article. More specifically, the acquisition / distribution layer of the absorbent core must be positioned so as to effectively retain the secreted body fluid and transport it to other regions of the core. Thus, the acquisition and distribution layer must be located at the point where body fluid is excreted. These areas will include crotch and, in male subjects, areas where urination occurs on the front of the diaper. In a diaper, the portion of the absorbent article to be placed on the front of the wearer is considered to be the front of the absorbent article. In diapers intended for male subjects, the capture zone should expediently extend close to the waistband at the front of the user's body so as to be able to retain a relatively large amount of fluid secreted on the front of the male user and to compensate for changes in discharge direction. Corresponding areas of absorbent articles will vary depending on the type and composition of the absorbent article. The acquisition and distribution layer 110 of diaper 100 in FIG. 2 is an example of one embodiment. In this case, the acquisition and distribution layer 110 is suitably positioned so as to be able to retain the excreted stool and urine in both male and female individuals.

In a disposable diaper embodiment, the core acquisition / distribution layer is preferably positioned with respect to the stretched topsheet and / or storage layer so as to extend into an area corresponding to at least about 50%, preferably about 75% of the length of the storage layer. The length of the acquisition and distribution layers is thus determined. As far as its width is concerned, it must be sufficient to be able to trap body fluid discharges and not direct these discharges directly to the accumulation layer. In diapers such as that shown in FIG. 1 and 2, this width should be at least about 5 cm, preferably at least about 3 cm. It will be appreciated that for the purposes of the present invention, the individual portions of the absorbent article may be defined by reference to the top surfaces of the absorbent article in a bent state, which are located at a given point on the line defining the length of the absorbent article.

For the purpose of determining the position of the acquisition and distribution layer, the length of the absorbent article will normally be the longest length dimension of the backing sheet of the article. This normally longest dimension of the stretched backing sheet can be defined with respect to the application of the product to the user. When worn, the opposite ends of the backing sheet are joined together such that the joined ends form a circle around the wearer's belt. The normal length of the backing sheet is then the length of the line extending along the backing sheet from the point on the backing edge of the backing sheet, crotch to the point on the opposite edge of the backing sheet, centering the front of the user's belt. The size and shape of the top sheet generally correspond substantially to the size and shape of the backing sheet.

In the conventional case where the absorbent core storage layer generally defines the shape of the absorbent article, the longest dimension of the core storage layer will approximate the normal length of the topsheet of the stretched article. In some applications (such as adult incontinence products) where aspects such as volume reduction and minimum cost are important, the storage layer will not take on the general shape of the diaper or other incontinence structures. In this case, the storage layer will usually be positioned so as to cover only the genital area of the user and the limited space adjacent to the genital area. In this case, both the acquisition and distribution layer and the storage layer will be displaced towards the front of the article with respect to the top sheet, so that they will usually be in the front two-thirds of the article.

The storage layer of the absorbent core may have any desired shape allowing a comfortable fit, such as a round, square, trapezoidal or rectangular shape, for example, a watch glass, canine bone, half canine bone, oval or irregular shape. The storage layer need not be physically separated from the acquisition and distribution layers and may simply be a zone in which the superabsorbent material is concentrated in a continuous web of reinforced cellulosic fibrous material. Preferably, however, the storage layer of the absorbent core comprises a separate nonwoven which can be used as an insert placed below the acquisition and distribution layer.

Also, the acquisition and distribution layer may have any desired shape that allows for a comfortable fit and conforms to the stated size constraints. For example, it may have a round, square, trapezoidal or rectangular shape, for example, a watch glass, a dog bone, a half dog bone, an oval or irregular shape. The acquisition and distribution layer may have a shape similar to the storage zone or a different shape.

In FIG. 1 and 2, two embodiments of a diaper according to the present invention are shown. In both figures, a diaper 100 is shown with a topsheet 104 and a backsheet 102. Between the topsheet 104 and the backsheet 102 is disposed an absorbent core 106 comprising a storage layer 108 and a rectangular trap and a partition layer 110. In the storage layer 108 discrete absorbent particles are distributed. gel-forming material.

The absorbent core 106 of FIG. 2, the front portion 112 has a rear portion 114 and a middle portion 116. As mentioned above, the front portion 112 corresponds to the end of the diaper 100 that would cover the front of the wearer in use and the rear portion 114 of the diaper end when used to cover the back of the wearer. The absorbent core 106 of FIG. 2, in particular its accumulation layer 108, has the shape of a modified watch glass to better fit the diaper and reduce fluid penetration.

In FIG. 3 shows an absorbent core 106 that can be used in disposable diapers. The core 106 comprises an accumulation layer 108 of a similar type to that shown in FIG. 1 and 2. However, the acquisition and distribution layer 111 has a modified shape of a watch glass that is similar to the shape of the accumulation layer 108, although it has a smaller surface area.

The absorbent core 106 of FIG. 3 has a front section 112, a rear section 114 and a middle section 115. The front section 112 has a leading edge 117 and the rear section 114 has a trailing edge 119. The leading edge 117 is connected to the trailing edge 119 via side edges 122 and 123 of the accumulation layer corresponding to the middle section. 115. The acquisition and distribution layer 111 has a leading edge 116 in the front portion 112 and a trailing edge 116 in the rear portion 114. The leading edge 116 and the trailing edge 118 of the acquisition and distribution layer are joined together by the side edges 120 and 121.

In a preferred embodiment of the absorbent articles of the invention, i. j. in disposable diapers, the edges 116, 118, 120 and 121 of the acquisition and distribution layer 111 will be spaced inwardly from the edges 117, 119, 122 and 123 of the storage layer 108 by at least 5 mm, preferably at least 12.5 mm. This is particularly true of the middle part 115.

Method for measuring the absorption capacity of superabsorbent material

As mentioned above, the superabsorbents suitable for use in the invention have an absorption capacity of at least 10 g, preferably at least about 15 g, and even more preferably at least about 20 g of synthetic urine (1.0% sodium salt solution in distilled water) per g dry superabsorbent. . The following general procedure is used in the test. The superabsorbent is placed in a tea bag, immersed in an excess of synthetic urine for a selected time, and then centrifuged for a specified time. The absorption capacity is defined as the ratio of the final weight of the superabsorbent after centrifugation reduced by the initial weight of the superabsorbent to the initial weight of the superabsorbent. The procedure is carried out under standard laboratory conditions. The following is a detailed description of the procedure.

A 8 x 12 cm piece is cut from the tea bag material using a die die. The piece is folded across the length dimension and the material is thermally welded on the sides with a T-bar heat welding device to give a tea bag of 8x8 cm. The tea bag material used is a heat-weldable material such as 1234, supplied by CH Dexter, Division of the Dexter Corp., Windsor Locks, Connecticut, USA, or a material having similar properties. If the bag is to contain superabsorbent materials in the form of fine particles, it is necessary to use a material with a lower porosity. Weigh 0,200 g ± 0,005 g of superabsorbent onto the weighing paper, which is then transferred to the tea bag and the upper open end of the tea bag is welded. An empty tea bag is used for the blank test and is also welded at the top. Approximately 400 ml of synthetic urine is poured into a 1000 ml beaker. An empty comparative tea bag is immersed in synthetic urine. Tea bag containing superabsorbent material (the test sample is kept horizontal to distribute the material evenly inside the tea bag). The bag is placed on the surface of synthetic urine, allowed to moisten for a period not exceeding 1 minute, and then immersed and soaked for 60 minutes. Approximately two minutes after immersion of the first sample, a second set of tea bags, ie an empty bag and a bag filled with superabsorbent, is immersed in a synthetic urine bath, prepared exactly in the same manner as the first set and allowed to soak for 60 minutes in the same manner. pockets. After the prescribed soaking time of each of the tea bag sets, the pockets are quickly removed from the synthetic urine bath by means of tongs. The samples are then centrifuged. The Delux Dynac II Centrifuge, Fisher Model No. 1 is used. 05-100-26, available from Fisher Scientific (Pittsburgh, Pennsylvania, USA) or similar device. The centrifuge should be equipped with a direct indicating tachometer and electric brake. In addition, the centrifuge is equipped with a cylindrical basket insert whose outer wall is approximately 63.5 mm high, the outer diameter is 214.25 mm and the inner diameter is 201.55 mm. 9 rows of round holes with a diameter of 2.38 mm are regularly distributed around the outer wall of the basket. There are 106 holes in each row. The basket has a bottom with six 6.35 mm diameter drainage holes that are evenly spaced around its periphery so that the centers of the holes are about 12.7 mm from the inner surface of the outer wall. The basket is assembled in the centrifuge so that, together with the brake, it rotates in accordance with the entire centrifuge. The teabags with superabsorbent are placed in the centrifuge basket with the bent end in the direction of rotation of the centrifuge. Empty comparative tea bags are placed on each side next to the respective sample tea bag. The tea bag with superabsorbent from the second set must be placed opposite the tea bag with superabsorbent from the first set and likewise the empty bag from the first set must be placed against the empty bag of the second set to balance the centrifuge. The centrifuge is put into operation rapidly and allowed to roll to rotate at 1500 rpm ^first When the centrifuge speed is stabilized at 1500 min ⁴ , the timer is set to 3 minutes. After 3 minutes the centrifuge is switched off and the brake is applied. Remove the superabsorbent tea bag and empty bag from the first set and weigh separately. The same procedure is repeated for the pockets of the second set.

The absorption capacity (ac) of each of the samples is calculated as the ratio of the weight of the superabsorbent tea bag after centrifugation reduced by the weight of the empty tea bag after centrifugation and further reduced by the dry superabsorbent mass divided by the dry superabsorbent mass. The absorption capacity values reported in this description were obtained as the average of the two samples.

Example 1

A disposable diaper is produced comprising a hot-welded polypropylene topsheet, a liquid impervious polyethylene backsheet and a two-layer absorbent core positioned between the topsheet and the backsheet. The dual-layer absorbent core comprises an hourglass-like accumulation layer located below the rectangular acquisition and distribution layer, see FIG. First

The acquisition and distribution layer comprises reinforced, twisted, carbohydrate cellulose fibers and optionally a binding agent. The accumulation layer comprises a pneumatic web made of a mixture of conventional cellulose filaments (Foley Fluff, derived from the soft trees of the southern soft zone, Procter and Gambia Cellulose Co., Memphis, Tennessee, USA) and a polyacrylate-based sodium gel-forming superabsorbent polymerization gel. of the type described in US RE 32 349 (new edition dated April 19, 1988) having an absorption capacity of about 30 g / g. The acquisition and distribution layer comprises 92% of reinforced cellulose fibers and 8% of conventional non-reinforced cellulose fibers that have been web processed. In this case, the unreinforced fibers consist of a Foley Fluff product refined to a drainage rate of about 200 CSF. The reinforced, twisted, curled cellulosic fibers are made of softwood kraft pulp from the Southern Geographic Zone (Foley Fluff) trees and are cross-linked with glutaraldehyde in an amount of about 2.5 molar, based on the anhydroglucose base of the cellulose contained in the fiber. The fibers are crosslinked by the dry crosslinking process described in U.S. Pat. 4,822,453.

The reinforced fibers are similar to those whose properties are given in Table I.

Table I. Reinforced, twisted, curled cellulose fibers

Type Kraft softwood fibers of the southern geographical zone, cross-linked with glutaraldehyde in an amount of about 2.5 mole%. referring to the anhydroglucose basis of the cellulose contained in the fiber Number of dry twists 6,8 uzlín.mrn ' Number of wet twists 5.1 knot.mm ^-1 RET value for isopropyl alcohol 24% Water retention value 37% Skaderenia Factor 0.63

The acquisition and distribution layer consists of a homogeneous paper web as described in Example II. The acquisition and distribution layer has an average dry density of approximately 60 kg. m ' ³ . Its average density after saturation with synthetic urine, calculated on the dry matter, is approximately 70 kg. m ³ and the average basis weight is approximately 0.3 kg. m ' ² . The storage layer comprises 50% by weight of Foley Fluff cellulose filament and 50% of gel-forming superabsorbent particles. Its average dry density is approximately 240 kg. m ³ and its average dry basis weight is approximately 5 kg. m ²

The acquisition and distribution layer has dimensions of about 76 x 229 mm and is positioned relative to the accumulation layer in the manner shown in FIG. The accumulator layer has a crotch width (at the narrowest point) of about 89 mm, a width at the front of the waist of about 216 mm, and a width at the rear of the waist of about 165 mm.

In an alternative embodiment, the storage layer comprises about 15% superabsorbent gelling particles and about 85% Foley Fluff and has a basis weight gradient such that the front 60% of the storage layer has a basis weight of about 1.1 kg. m @ ² and a density of about 150 kg. m ³ and the rear 40% of the storage layer has a basis weight of about 0.4 kg. m ^-2 and a density of about 60 kg. m ' ³ .

In another embodiment, the storage layer comprises about 28% superabsorbent gelling particles and about 72% Foley Fluff cellulosic material and has a basis weight gradient and a density gradient as described in the preceding paragraph.

Example 2

This example illustrates a papermaking process for making a web that is suitable for use in the acquisition / distribution layer of the present invention. The web contains 92% of the reinforced fibers described in Example I and Table I and 8% of highly refined Foley Fluff (krill) cellulose fibers with a CSF value of 200.

The pulp suspension, consisting of reinforced and unreinforced fibers with a consistency of 0.1 to 0.2%, is pumped into a FORMAR paper machine at a linear speed of 25 m. s ¹ , at a flow rate of about 95 l. m ' ¹ . The suspension is divided by means of a rigid roof headbox into a 305 mm, 84 M, 5 shed 12 width sieve which moves at a continuous speed of 1.5 m. min '. The linear velocity of the pulp suspension at the outlet of the headbox is 50 to 100 m. s' ¹ . The flow rate and sieve movement are controlled to obtain a uniform wet sheet with a basis weight, based on dry matter, of about 0.3 kg. m ² and an average dry density of about 60 kg. m ' ³ . The consistency of the sheet is increased to about 16-22% by means of two vacuum cabinets located below the screen, the first working at about 10 kPa and the second at about 13.3 kPa, with a screen residence time under each of the vacuum boxes being about 1 second. . The sheet is then removed from the forming screen manually and dried by batch drying in a steam-heated convection oven for 4 hours at about 110 ° C.

Example 3

The absorbent core is produced in the same manner as in Example 1, except that the acquisition and distribution layer is made pneumatically and contains 100% reinforced fibers.

Example 4

Absorbent cores were produced in the same manner as in Example 3, except that the acquisition and distribution layers were made pneumatically and were thermally bonded by thermoplastic reinforcing means. The web comprises 55% reinforced fibers and 45% Pulpex® material (Hercules Inc., Wilmington, Delaware, USA), which are polyethylene microfibers with an average length of about 3 mm. The acquisition and distribution layer is produced by mixing the air streams bearing the reinforced fibers and Pulpex fibers together in an appropriate ratio and then producing a pneumatic web using a conventional pneumatic device. The web is thermally bonded by heating it with hot air which is guided through the web. During heating, the web is in a relaxed (i.e., uncompressed) state. After this operation, the web is allowed to cool.

Claims (12)

PATENT CLAIMS An absorbent structure (106) for collecting, dispensing and accumulating body fluids, comprising: i) a acquisition / distribution layer (110) having an average dry density of less than 0.3 g. cm ³ and an average dry basis weight of 0.001 to 0.10 g. cm ² , containing from 50% to 100% by weight on a dry basis basis weight; chemically reinforced cellulose fibers, and from 0% to 50% by weight on a dry weight basis of the binder, having a maximum of 6% by weight of superabsorbent material, and (ii) an accumulation layer (108) disposed below the acquisition and distribution layer and containing at least 15% with respect to the weight of the storage layer (108), the superabsorbent material and from 0% to 85% of the carrier means for the superabsorbent material, characterized in that the acquisition and distribution layer (110) - has an average density after saturation of 1% aqueous sodium chloride solution, calculated on a dry weight, of less than 0,20 g. cm ' ³ , - and its top surface area is from 15% to 95% of the top surface area of the storage layer (108). Absorbent structure (106) according to claim 1, characterized in that the acquisition and distribution layer (110) - has an upper surface area which is between 25% and 90% of the upper surface area of the storage layer, - has an average dry basis weight of from 0.01 to 0.08 g. cm ' ² , - has an average density after saturation of 1% aqueous sodium chloride solution, calculated on a dry weight, of less than 0,20 g. cm ³ , preferably between 0.02 g. cm ³ and 0.15 g. cm ' ³ , and the superabsorbent material has an absorption capacity of at least 15 g / g. The absorbent structure (106) of claim 1 or 2, wherein the acquisition / distribution layer (110) has from 2% to 50% binding agent and the binding agent comprises a non-chemically reinforced cellulosic material. The absorbent structure (106) of claims 1 to 3, wherein the binder comprises cellulosic fibers having a drainage rate of less than 200 CSF (Canadian Standard Freeness) and a acquisition and distribution layer (110) of from 5% to 15% high. refined fibers. Absorbent structure (106) according to claims 1 to 4, characterized in that the binding agent comprises cellulose with a specific surface area of at least 10 m ² / g and the acquisition and distribution layer (110) contains from 2% to 15% cellulose with a specific surface area of at least 10 m ² / g. Absorbent structure (106) according to claims 1 to 5, characterized in that the acquisition and distribution layer (110) is a pneumatic web. Absorbent structure (106) according to claims 1 to 6, characterized in that the acquisition / distribution layer (110) is formed by a thermally bonded web comprising reinforced fibers and from 10% to 50% thermoplastic material based on the total weight of the web. Absorbent structure (106) according to claims 1 to 5 or 7, characterized in that the acquisition and distribution layer (110) is formed by a paper web. The absorbent structure (106) of any one of claims 1 to 8, wherein the carrier means for superabsorbent material in the storage layer (108) comprises a cellulose fiber web and the storage layer (108) comprises from 15% to 75%. The superabsorbent material having an absorption capacity of at least 15 g / g and the storage layer is substantially free of chemically reinforced cellulose fibers. The absorbent structure of claim 9, wherein the storage layer (108) comprises from 50% to 75% superabsorbent material. The absorbent structure (106) of claim 9, wherein the superabsorbent material has an absorbent capacity of at least 20 g / g. Absorbent structure (106) according to claims 1 to 11, characterized in that the storage layer (108) comprises superabsorbent fibers.