MXPA97004832A - Absorbent structure having permeability to the best liquid - Google Patents

Abstract

An absorbent structure is described which contains a polymeric material formed of hydrogel, a wettable short fiber, and a wettable binder fiber. The absorbent structure exhibits improved permeability in the z-direction of a liquid compared to an otherwise essentially identical absorbent structure which does not comprise a wettable binder fiber. Also disclosed is a disposable absorbent product containing such structure absorb

Description

ABSORBENT STRUCTURE HAVING PERMEABILITY TO IMPROVED LIQUID Background of the Invention Field of the Invention The present invention relates to an absorbent structure suitable for use in disposable absorbent products. More particularly, the present invention relates to an absorbent structure, comprising a hydrogel-forming polymeric material, a wettable short fiber, a wettable binder fiber, exhibiting improved liquid handling capabilities.

Description of Related Art The purpose of disposable absorbent products is typically the management of body waste. In order to handle liquid waste from the body, the absorbent structure with an absorbent product must generally be capable of first taking the liquid into the absorbent product, and then distributing the liquid inside the absorbent product, and then retaining the liquid within the product. absorbent.

It is generally important that the absorbent structure take the liquid at around the rate of delivery of the liquid to the absorbent product or otherwise the liquid will drain off the surface of the absorbent structure and will not be present for the absorbent structure distribute and retain the liquid inside the absorbent product. That is, if the liquid intake rate of the absorbent structure is lower than the delivery rate of the liquid to the absorbent product, there is a possibility of the liquid being drained away from the absorbent product.

Furthermore, if the distribution of the liquid by the absorbent structure within the absorbent product is not adequate, the efficiency of the use of the absorbent structure will be lower. Typically, commercially available absorbent products are designed with a saturated retention capacity of excess absolute liquid. Therefore, the absorbent structure in the absorbent product is not frequently used completely. An increase in the efficiency of the liquid distribution by the absorbent material will potentially allow either a higher realized liquid saturation level for an absorbent product using the same amount of absorbent structure or the use of less absorbent structure to achieve the same level of liquid saturation performed on the absorbent product without any increase in liquid run-off. The use of the smaller absorbent structure to achieve the same level of liquid saturation performed in an absorbent product will typically result in less absorbent product being discarded into the environment.

Absorbent structures suitable for use in the absorbent products are generally known. Originally, it was a general practice to form the absorbent structures comprising a fibrous absorbent matrix completely of wood pulp fluff, such as a block of pulp of crushed wood pulp. Given the relatively small amount of liquid absorbed by the wood pulp fluff on one gram of wood pulp fluff, it is necessary to use relatively large quantities of wood pulp fluff, thus necessitating the use of structures thick and relatively large absorbents.

In order to improve the absorbent capacity of such absorbent structures, it is common to incorporate a hydrogel-forming polymeric material therein. Such hydrogel-forming polymeric materials are generally capable of absorbing at least about 10 times their weight in water. The interaction of hydrogel-forming polymeric materials within such absorbent structures allows the use of less wood pulp fluff, since the hydrogel-forming polymeric material has a superior liquid absorption capacity on a gram basis per gram that the erase of wood pulp. In addition, the hydrogel-forming polymeric materials are generally less sensitive to pressure than is the wood pulp fluff. Therefore, the use of hydrogel-forming polymeric materials generally allows the production and use of a thinner and smaller absorbent product.

A problem of the known absorbent structures comprising the hydrogel-forming polymer material and the fibers which are essentially wood pulp fluff fibers is that when they are wetted with too much liquid, the absorbent structure is prone to folding, thus inhibiting the flow of the liquid through the absorbent structure. In addition, such known absorbent structures generally have poor integrity when they are wetted, thereby rendering the absorbent structure liable to break and separate when wetted and rendering the absorbent structure difficult to handle separately without the use of coating materials such like the tissue wrapping sheet.

Synthesis of the Invention It is desirable to produce an absorbent structure capable of filling or exceeding the performance characteristics of known absorbent structures while containing a relatively high concentration of hydrogel-forming polymeric material. It is also desired to produce an absorbent structure which is capable of rapidly absorbing a discharged liquid under pressures typically encountered during use and to retain the absorbed liquid under pressures typically encountered during use. In addition, it is desired to produce an absorbent structure which, when moistened, essentially maintains its integrity and essentially maintains or improves its liquid handling capabilities.

These and other related objects are achieved by an absorbent structure comprising a hydrogel-forming polymeric material, a wettable short fiber, and a wettable binder fiber, wherein the absorbent structure exhibits improved Z-direction permeability values compared to an otherwise essentially identical absorbent structure which does not comprise a wettable binder fiber.

In one embodiment of the present invention, an absorbent structure comprises from about 20 to about 65% of a hydrogel-forming polymeric material, from about 25 to about 70% by weight of wettable short fiber and from more than about 7 to about 40% by weight wettable binder fiber, wherein all percents by weight are based on the total weight of the hydrogel-forming polymeric material, the wettable short fiber and the binder fiber or binder wettable in the absorbent structure. The absorbent structure exhibits a permeability in the Z-direction at a saturation of 60% which is not less than the permeability in the Z-direction of the absorbent structure at a saturation of 30%. The absorbent structure also exhibits a permeability in the Z-direction at a saturation of 60% which is greater than about 50 Darcy.

In another aspect, it is desirable to provide a thin disposable absorbent product, such as an infant diaper, which disposable absorbent product employs an absorbent structure which has a relatively small volume and a high concentration of hydrogel-forming polymeric material. In addition, it is desirable to provide a disposable absorbent product which has a relatively small hollow volume and a relatively high capacity.

In one embodiment, these objectives are achieved in a disposable absorbent product comprising a liquid pervious topsheet, a backsheet and an absorbent structure of the present invention positioned between the topsheet and the backsheet.

Brief Description of the Drawings Figure 1 is a perspective view of an embodiment of a disposable absorbent product according to the present invention.

Figure 2 is an illustration of the equipment used to determine the saturated liquid retention capacity of an absorbent structure.

Detailed Description of the Preferred Modality In one aspect, the present invention relates to a useful absorbent structure in a disposable absorbent product possessing desirable and improved liquid handling characteristics that can be achieved by the proper selection and use of a hydrogel-forming polymeric material, of a short fiber. wettable, and a wettable binder fiber used in the formation of such absorbent structures.

As used herein, the term "hydrogel-forming polymeric material" is meant to mean a high-absorbency material commonly referred to as a superabsorbent material. Such high-absorbency materials are generally capable of absorbing a quantity of a liquid, such as synthetic urine, an aqueous salt water solution of 0.9% by weight, or body fluids, such as menstrual fluids, urine, blood, so less about 10, suitably about 20, and up to about 100 times the weight of the hydrogel-forming polymeric material at the conditions under which the polymeric hydrogel-forming polymer material is being used. Such typical conditions include, for example, a temperature between about 0 ° C to about 100 ° C and suitable ambient conditions, such as 23 ° C and about 30 to about 60% relative humidity. With the absorption of the liquid, the hydrogel-forming polymeric material typically swells and forms a hydrogel.

The hydrogel-forming polymeric material can be formed of an organic hydrogel material which can include natural materials, such as agar, pectin, and guar gum, as well as synthetic materials, such as synthetic hydrogel polymers. Synthetic hydrogel polymers include, for example, carboxymethyl cellulose, alkali metal salts of polyacrylic acid, polyacrylamides, polyvinyl alcohol, ethylene maleic anhydride copolymers, polyvinyl ethers, hydroxypropyl cellulose, polyvinyl morpholinone, the polymers and copolymers of vinyl sulphonic acid, the polyacrylates, the polyacrylamides, and the polyvinyl pyridines. Other suitable hydrogel polymers include the hydrolyzed acrylonitrile grafted starch, the acrylic acid grafted starch, and the isobutylene maleic anhydride copolymers and mixtures thereof. The hydrogel polymers are preferably slightly degraded to render the material essentially insoluble in water but still swellable in water. The degradation can, for example, be done by irradiation or covalent, ionic, or Van der aals, or hydrogen bonding. Suitable hydrogel-forming polymeric materials are typically available from various commercial vendors such as The Dow Chemical Company, Hoechst Celanese, Allied Colloids Limited or Stockhausen, Inc.

The hydrogel-forming polymeric material, used in the absorbent structures or products of the present invention, must suitably be capable of absorbing a liquid under an applied load. For the purposes of this application, the ability of a polymeric hydrogel-forming material to absorb a liquid under an applied load, and thus carry out the work, is quantified as the Absorbency Value Under Load (AUL). The Absorbency Under Load value is expressed as the amount (in grams) of a sodium chloride solution of 0.9% by aqueous weight which can absorb the polymeric hydrogel-forming material in about 60 minutes per gram of polymeric material forming hydrogel under a load of about 0.3 pounds per square inch (approximately 2.0 kilopascals) while restricting swelling in the normal plane to the applied load. The hydrogel-forming polymer material employed in the absorbent structures of the present invention suitably exhibits an AUL value of at least about 15, more suitably at least about 20, and up to about 50 grams of the liquid per gram. of hydrogel-forming polymeric material. The method by which the value of Absorbency Under Load can be determined is established, for example, in detail, in US Pat. Nos. 5,149,335; 5,247,072 incorporated herein by reference.

Suitably, the polymeric hydrogel-forming material is in the form of particles which, in the non-inflated state, have maximum cross-sectional diameters in the range of from about 50 micrometers to about 1,000 micrometers, preferably in the range of from about 100 micrometers to about 800 micrometers, as determined by a sieve analysis according to test method D-1921 of the American Society for Testing and Materials (ASTM). It is understood that the particles of the hydrogel-forming polymeric material cne fall within the ranges described above may comprise solid particles, porous particles, or may be agglomerated particles comprising smaller particles agglomerated within particles falling within the size ranges described .

The hydrogel-forming polymeric material is typically present in an absorbent structure or product of the present invention in an amount effective to result in the absorbent structure or product being able to absorb a desired amount of liquid and in an absorbent structure exhibiting the desired absorbent properties. . As such, the hydrogel-forming polymeric material may be present in the absorbent structure in more than a minimal amount so that the absorbent structure exhibits the desired absorbent properties. However, the hydrogel-forming polymeric material must be present in the absorbent structure in less than an excessive amount so that the absorbent structure does not undergo gel blocking by the swollen hydrogel-forming polymer material which may undesirably affect the absorbent properties of the hydrogel-forming polymeric material. the absorbent structure.

The hydrogel-forming polymeric material is therefore desirably present in the absorbent structure of the present invention in an amount of from about 20 to about 65% by weight, suitably in an amount of from about 25 to about 60% by weight. weight, and more suitably from about 30 to about 55% by weight, based on the total weight of the hydrogel-forming polymeric material, of the wettable short fiber, and of the wettable binder fiber in the absorbent structure.

Because the hydrogel-forming polymeric materials present in the absorbent structures of the present invention can be present in high concentrations, the absorbent structures of the present invention can be relatively thin and light in weight, have a relatively small volume and still work in the desired way.

As used herein, the term "short fiber" is meant to refer to a natural fiber or to a section cut from, for example, a manufactured filament. Such staple fibers are intended to act in the absorbent structure of the present invention as a temporary reservoir for the liquid and also as a conduit for the distribution of the liquid.

Preferably the short fibers used in the absorbent structures herein should vary in length from about 0.1 to about 15 centimeters, and suitably from about 0.2 to about 7 centimeters. Short fibers of these size characteristics, when combined with the wettable binding fiber and the hydrogel-forming polymer material given herein, help to impart desirable bulk, improved liquid acquisition characteristics, liquid distribution and strength, and / or properties of flexibility and elasticity desirable to the absorbent structures of this invention.

As used herein, the term "wettable" is meant to refer to a fiber which exhibits a liquid, such as water, synthetic urine, or an aqueous salt water solution of 0.9% by weight, at an angle of contact with air of less than 90 °. As used herein, the contact angle can be determined, for example, as established by Robert J.

Good and Robert J. Stromberg, Ed., In the work "Science of Colloid and Surface - Experimental Methods" Volume 11, (Full Press, 1979). Suitably, a wettable fiber refers to a fiber which exhibits a synthetic urine at an air contact angle of less than 90 ° at a temperature between about 0 ° C and about 100 ° C and suitably at medium conditions environment, such as around 23 ° C.

Suitable wettable fibers can be formed of intrinsically wettable fibers or can be formed of intrinsically hydrophobic fibers by having a surface treatment thereon which makes the fiber hydrophilic. When the treated surface fibers are used, the surface treatment is desirably non-fugitive. That is, the surface treatment desirably does not wash away from the surface of the fiber with the first insult or contact with the liquid. For the purposes of this request, a surface treatment on a generally hydrophobic polymer shall be considered not to be fugitive since a majority of the fibers demonstrate a liquid contact angle in air of less than 90 ° for three consecutive contact angle measurements, with drying between each measurement. That is, the same fiber is subjected to three separate contact angle determinations, and, if all three contact angle determinations indicate a contact angle of the liquid in air of less than 90 °, the surface treatment of the fiber It will be considered that he is not a fugitive. If the surface treatment is fugitive, the surface treatment will tend to wash away from the fiber during the first contact angle measurement, thus exposing the hydrophobic surface of the underlying fiber and demonstrating subsequent contact angle measurements greater than 90 °. .

If a surface treatment is used, the surface treatment is suitably used in an amount of less than about 5% by weight, more suitably less than about 3% by weight, and more suitably less than about 2%. by weight, based on the amount of fibers that are being treated.

As used herein, the term "fibers" or "fibrous" is intended to refer to a particulate material in which the proportion of length or diameter of such particulate material is greater than about 10. Conversely, a "non-fibrous" material "or" without fiber "is meant to refer to a particulate material in which the proportion of length or diameter of such particulate material is about 10 or less.

A wide variety of short fiber materials can be used in the absorbent structures given here. The short fibers useful in the present invention can be formed of natural or synthetic materials and can include cellulosic fibers such as wood pulp fibers and modified cellulose fibers, textile fibers such as cotton or rayon, synthetic polymer fibers essentially non-absorbent For reasons of availability and cost, cellulosic fibers will often be preferred to use them as the short fiber component of the absorbent structures of this invention. Wood pulp fibers are more preferred. However, other cellulosic fiber materials, such as cotton fibers, can also be used as the short fiber.

The short fibers as used herein may be crimped so that the resulting absorbent structure has the elasticity and bulky resistance during use in the absorbent products. Curled short fibers are those which have a wavy, curved or nicked character along their length. Fiber curling of this kind is described more fully in U.S. Pat. No. 4,185,831, incorporated herein by reference.

Short fibers wettable must be present in the absorbent structure of the present invention in an amount effective to result in the desired improvement in absorbent properties described herein as compared to an identical absorbent structure essentially otherwise comprising no fiber wettable binder .

As such, the wettable short fibers must be present in the absorbent structure in less than an excessive amount so that the absorbent structure does not experience an undesirable loss of integrity or an undesirable structure fold when the absorbent structure is saturated with the liquid. In addition, the hydrogel-forming polymer material must be present in the absorbent structure in more than a minimal amount so that the absorbent structure exhibits the desired absorbent properties.

The wettable short fiber is therefore desirably present in an absorbent structure of the present invention in an amount of from about 25 to about 70% by weight, suitably from about 30 to about 65% by weight, and more suitably from about 35 to about 60% by weight of short fiber wettable, with all percentages by weight based on the total weight of the short fiber wettable, the polymeric hydrogel-forming material, and the fiber wettable binder in the absorbent structure.

As used herein, the term "otherwise essentially identical absorbent structure without any wettable binder fiber" and other similar terms is intended to refer to a control absorbent structure that is prepared using essentially identical materials and in an essentially identical process in comparison to an absorbent structure of the present invention, except that the control absorbent structure does not comprise or is not prepared with the wettable binder fiber described herein, but instead comprises an amount of a further wettable short fiber essentially identical to the amount of wettable binder fiber used in the absorbent structure of the present invention. As such, the otherwise essentially identical absorbent structure will not have any wettable binder fiber and the absorbent structure of the present invention will generally have substantially identical base weights. As a result of not understanding the wettable binder fiber, the essentially identical absorbent structure will generally not exhibit the desired absorbent properties described herein as compared to an absorbent structure of the present invention.

As used herein, the term "binder fiber" is meant to refer to a fiber that acts to form a composite fabric when the binder fiber is in its final form in the absorbent structure given herein. As such, the binder fibers interact with each other in some way to form a composite fabric. Such an interaction of the binder fibers can be in the form of a tangle or an adhesive interaction whereby the binder fibers are treated as, for example, by heating the binder fibers above their softening point temperature and allowing the fibers binders making contact with each other to form the adhesive bonds. Once treated in such a way, the binding fibers can not be reclaimed in their original form. This is in contrast to the short fibers and the hydrogel-forming polymer material which essentially retain their individual shape, even when such short fibers and the hydrogel-forming polymeric material can be adhered by the binder fibers in the absorbent structures of the present invention. .

The binder fiber can generally be formed of a thermoplastic composition capable of being extruded into fibers. Examples of such thermoplastic compositions include polyolefins such as polypropylene, polyethylene, polybutenes, polyisoprene, and their copolymers; polyesters such as polyethylene terephthalate; polyamides such as nylon; as well as copolymers and mixtures of these and other thermoplastic polymers.

A suitable binder fiber for the present invention comprises the meltblown fibers formed of a hydrophilic polypropylene material. Such meltblown fibers are typically very fine fibers prepared by extruding the liquefied or melted fiber copolymer through holes in a die into a high velocity gaseous stream. The fibers are attenuated by the gas stream and subsequently solidify. The resulting stream of solidified binder fibers can be collected, as for example on a grid placed in the gas stream, as a tangled coherent fibrous mass. Such a tangled fibrous mass is characterized by an extreme entanglement of the binding fibers. This entanglement provides coherence and resistance to the resulting fabric structure. Such entanglement also adapts the fabric structure to constrict or trap the short fiber and the hydrogel-forming polymeric material within the structure after the short fiber and the hydrogel-forming polymeric material have been incorporated into the fabric structure, since either during or after the formation of the tissue structure. The binder fibers are entangled sufficiently that it is generally impossible to remove a complete binder fiber from the mass of binder fibers or to trace a binder fiber from start to finish.

As used herein, the constriction or entrapment of the short fiber and the hydrogel-forming polymeric material within the fabric structure is intended to represent that the short fiber and the hydrogel-forming polymer material are essentially immobilized, so that the fiber The short and hydrogel-forming polymeric material are not free to essentially move or migrate in or out of the tissue structure. Such constriction or entrapment may, for example, be by adhesive means or by means of entangling the binder fibers of the fabric structure.

The binder fiber used here may be circular but may also have other geometries in cross section such as elliptical, rectangular, triangular or multi-lobal.

Suitably, in addition to, for example, the polypropylene component, a hydrophilic polypropylene material will generally comprise a hydrophilizing polymer component. Any polymer component capable of being polymerized with the polypropylene component, and capable of hydrophilizing the resulting copolymer material to make it wettable according to the definition of the present invention is suitable for use in the present invention.

The fiber-forming hydrophilic polypropylene copolymer material can be either a block or graft copolymer formed from its respective hydrophilizing polymeric and polypropylene components. The processes for preparing both block and grafted sopolymers, in general, are known in the art. Whether the copolymer useful for the fibers herein is a block or graft copolymer will depend on the particular nature of the hydrophilic polymer component which is used in the copolymer formation.

The wettable binder fibers must be present in the absorbent structure of the present invention in an amount effective to provide sufficient bulk or support to the absorbent structure, to effectively constrict or trap the wettable short fiber and the hydrogel-forming polymeric material, and to result in the desired improvement in the absorbent properties as compared to an otherwise essentially identical absorbent structure which does not comprise any wettable binder fiber.

As such, the wettable binder fiber must be present in the absorbent structure in more than a minimal amount so that the absorbent structure does not experience an undesirable loss of integrity or an undesirable structure fold when the absorbent structure is saturated with a liquid. However, the wettable binder fiber must be present in the absorbent structure in less than an excessive amount so that the wettable binder fiber does not undesirably restrict the hydrogel-forming polymer material from swelling or otherwise undesirably affects the absorbent properties of the structure. absorbent to saturate this with the liquid.

The wettable binder fiber is therefore desirably present in an absorbent structure of the present invention in a quantity of more than about 7 to about 40% by weight, suitably from about 8 to about 35% by weight, and more suitably from about 10 to about 30% by weight of wettable binder fiber, with all percent by weight based on the total weight of the wettable short fiber, the hydrogel-forming polymeric material, and the wettable binder fiber in the absorbent structure.

The absorbent structure of the present invention preferably comprises a fibrous matrix that includes the wettable binder fiber wherein the fibrous matrix constrains or traps the wettable short fiber and the hydrogel-forming polymeric material.

The fibrous matrix can be formed by the fibers placed by air, through a meltblown spinning, a carding process, a wetting process, or through essentially any other means, known to those skilled in the art. in art, to form a fibrous matrix.

Methods for incorporating the hydrogel-forming polymer material and the wettable short fiber into the fibrous matrix are known to those skilled in the art. Suitable methods include incorporating the hydrogel-forming polymer material and a wettable short fiber into the matrix during matrix formation, such as by air placement of the fibers of the fibrous matrix and the hydrogel-forming polymeric material. and / or the short fiber wettable at the same time or by wetting the fibers of the fibrous matrix and the hydrogel-forming polymer material and / or the short fiber at the same time. Alternatively, it is possible to apply the hydrogel-forming polymeric material and / or the wettable short fiber to the fibrous matrix after formation of the fibrous matrix. Other methods include sandwiching the hydrogel-forming polymeric material between two sheets of material, at least one of which is fibrous and permeable to liquid. The hydrogel-forming polymeric material may be generally placed uniformly between the two sheets of material or may be located in discrete bags formed by the two sheets. It is preferred that the wettable short fiber be distributed generally uniformly within the fibrous matrix. Nevertheless, the wettable short fiber may not be evenly distributed provided that the desired improvement in liquid permeability in the Z-direction of the absorbent structure is still achieved.

The fibrous matrix may be in the form of an integrally and uniquely formed layer of a composite comprising multiple layers. If the fibrous matrix comprises multiple layers, the layers are preferably in fluid communication with one another, so that a liquid present in a fibrous layer can flow or be transported to the other fibrous layer. For example, the fibrous layers may be separated by cellulosic tissue wrapping sheets known to those skilled in the art.

The hydrogel-forming polymeric material may be distributed in the individual layers in a generally uniform manner or may be present in the fibrous layers as a layer or other non-uniform distribution.

When the fibrous matrix comprises a single layer integrally formed, the concentration of hydrogel-forming polymeric material can increase along the thickness of the fibrous matrix in a non-stepped and gradual manner or in a more stepped form. Similarly, the density may decrease through the thickness in a non-stepped manner or in a staggered manner.

The absorbent structures of the present invention may generally be of any size or dimension as long as the absorbent structure exhibits the desired absorbent characteristics as described herein. Typically, the absorbent structures will have a volume of at least about 18 cubic centimeters such as with a width of about 6 centimeters, a length of about 6 centimeters, and a depth of about 0.5 centimeters. Suitably, the absorbent structure will have a volume of at least about 60 cubic centimeters, such as with a width of about 10 centimeters, a length of about 6 centimeters, and a depth of about 1 centimeter.

The absorbent structure of the present invention can also be used or combined with other absorbent structures, with the absorbent structure of the present invention being used as a separate layer or as a single zone or area within a larger composite absorbent structure. The absorbent structure of the present invention can be combined with other absorbent structures by methods well known to those skilled in the art, such as by using adhesives or simply by layering the different structures together and holding the composite structures together with, for example, a sheet of tissue.

The absorbent structures according to the present invention are suitable for absorbing many liquids, such as water, salt water, synthetic urine, and body fluids such as urine, menstrual, and blood, and are suitable for used in disposable absorbent products such as diapers, adult incontinent products, and bed pads; in catamenial devices, such as sanitary pads and plugs; and in other disposable absorbent products such as cleansers, bibs, wound dressings, and surgical drapes or layers. Therefore, in another aspect, the present invention relates to a disposable absorbent product comprising an absorbent structure as described herein.

The use of the absorbent structures described in the disposable absorbent products allows the formation of a disposable absorbent product which is capable of rapidly receiving a discharged liquid and yet whose disposable absorbent product is thin.

In one embodiment of the present invention, there is provided a disposable absorbent product, which is a disposable absorbent product comprising a liquid pervious topsheet, a backsheet attached to the topsheet, and an absorbent structure placed between the topsheet and the backup sheet.

While one embodiment of the invention will be described in terms of the use of the absorbent structure in an infant diaper, it is understood that the absorbent structure is equally suitable for use in other disposable absorbent products known to those skilled in the art.

Turning now to the drawing, Figure 1 illustrates a disposable diaper 11 according to an embodiment of the present invention. The disposable diaper 11 includes a backsheet 12, an upper sheet 14, and an absorbent structure 16, located between the backsheet 12 and the top sheet 14. The absorbent structure 16 is an absorbent structure according to the present invention.

Those skilled in the art will recognize suitable materials to be used as the top sheet and the backing sheet. Examples of materials suitable for use as the topsheet are liquid-permeable materials, such as polypropylene or polyethylene spun-bonded having a basis weight of from about 15 to about 25 grams per square meter. Examples of materials suitable for use as the backing sheet are liquid impervious materials, such as polyolefin films, as well as vapor permeable materials, such as microporous polyolefin films. Absorbent products and structures according to all aspects of the present invention are generally subjected, during use, to multiple insults of body liquids. Therefore, absorbent products and structures are desirably capable of absorbing multiple insults of body fluids in amounts to which absorbent products and structures will be exposed during use. The insults are usually separated from each other for a period of time.

The absorbent structures comprise fibers generally having pores or capillaries between the fibers that are used to acquire, distribute and store a liquid that is brought into contact with the absorbent structure.

However, many short fibers, such as wood pulp fibers, are not very stiff and do not have very good elasticity or integrity when moistened with a liquid. Absorbent structures comprising fibers consisting essentially of short fibers, such as wood pulp fibers, have been found, that upon sufficiently saturating with a liquid, they generally become highly flexible and fold into a structure of higher density and less gross. Such collapse of the absorbent structure generally results in a decrease in the average pore size between the short fibers as well as a decrease in the total pore volume of the absorbent structure. Such decreases generally result in the absorbent structure dripping into the liquid with which the absorbent has contacted, since the absorbent structure will generally have a reduced capacity for the liquid. The absorbent structure usually also has a reduced ability to imbibe the liquid so quickly! as said liquid is brought into contact with the absorbent structure. In addition, the absorbent structure generally has a reduced ability to transfer or distribute the liquid within the absorbent structure.

In addition, such an absorbent structure comprising fibers consisting essentially of short fibers, such as wood pulp fibers, generally loses its integrity when moistened with a liquid. Such loss of integrity in the absorbent structure generally results in an absorbent structure that breaks and is difficult to handle without the use of coating materials such as a tissue wrapping sheet.

The present invention addresses these problems by adding a quantity of binder fiber to the absorbent structure. The addition of the binder fiber to the absorbent structure has been found to impart integrity to the absorbent structure both when the absorbent structure is in a dry condition and when the absorbent is in a condition saturated at 100% liquid. This allows a much easier handling of the absorbent structure and helps prevent the absorbent structure from breaking during handling and during use, particularly when the absorbent structure is wet. The integrity of a material can be quantified by the tensile strength of the material, representing the cohesive strength of the material. As such, the tensile strength of a material represents the maximum load that can be placed on the material before the material breaks, or in other words, falls cohesively. A tensile strength that is very low will generally mean that the material will not have good integrity and will break easily, particularly when saturated with liquid.

As will be appreciated by one skilled in the art, a material such as an absorbent structure can trap a relatively minor amount of the liquid, such as water, within the material before use. For example, such liquid can be absorbed by the absorbent structure of moisture in the air. Such an absorbent structure is still intended to be considered in a dry condition for the purposes of this invention. Therefore, as used herein, the "dry condition" of a material is meant to represent that the material comprises an amount of liquid that is suitably less than about 5% by weight, more suitably less than about 3% by weight. % by weight, and more adequately less than about 1% by weight, based on the total weight of the material.

As used herein, the "100% liquid saturated condition" of a material is intended to represent that the material comprises an amount of liquid that is about 100% of the saturated retention capacity of the absolute liquid of the material.

It is desired that the absorbent structure of the present invention exhibit a tensile strength value in a dry condition that is at least about 50% higher, suitably at least about 100% higher, more adequately at least about 250% greater, and more suitably at least about 400% greater, than the tensile strength value exhibited by an otherwise essentially identical absorbent structure without a wetted binder fiber in a condition dry It is also desired that the absorbent structure of the present invention exhibit a tensile strength value in a dry condition that is at least about 400 grams force, suitably at least about 500 grams force, more adequately at least about 750 grams force, and more adequately at least about 1,000 grams force.

It is desired that the absorbent structure of the present invention exhibit a tensile strength value in a 100% liquid saturated condition that is at least about 50% higher, suitably at least about 100% higher, more suitably of at least about 250% greater, and more suitably at least about 400% greater than the tensile strength value exhibited by an otherwise essentially identical absorbent structure without any wettable binder fiber in a 100% saturated condition of the liquid.

It is also desired that the absorbent structure of the present invention exhibit a tensile strength value in a liquid saturated condition of 100% that is at least about 400 grams force, suitably at least about 500 grams. strength, more adequately of at least about 750 grams force, and more adequately of at least about 1,000 grams force.

The addition of the binder fiber to the absorbent structure has also been found to help avoid a collapse of the pore or capillary structure of the present absorbent structure when the absorbent structure is wet. This helps to essentially maintain the pore volume of the absorbent structure by saturating the absorbent structure with liquid. The need to maintain the pore volume of the absorbent structure becomes even more critical in relatively thin disposable absorbent structures such as diapers, wherein the absorbent structure has a relatively small pore volume to begin with and any increase in pore volume. resulting from the swelling of any hydrogel-forming polymer material with liquid should not be lost due to the collapse of the short fibers. The collapsing strength of the pore or capillary structure of the present structure can be quantified by the compressive strength of the absorbent structure. As used herein, the compressive strength of a material is intended to represent the inverse of the change in thickness, in millimeters, of the material when subjected to pressure. The value of compressive strength of the material can be measured according to the section of test methods given here.

In particular, it is desired that the absorbent structure of the present invention exhibit a value of compressive strength that is at least about 25% higher, suitably at least about 30% higher, more adequately at At least about 50% larger, and more suitably at least about 100% larger, than the compressive strength value exhibited by an otherwise essentially identical absorbent structure without a wettable binder fiber, wherein the value of compressive strength represents the inverse of the change in thickness of an absorbent structure when subjected to a pressure of about 0.5 pounds per square inch compared to the thickness of the absorbent structure when it is not subjected to pressure.

It is also desired that the absorbent structure of the present invention exhibit a value of compressive strength that is at least about 0.15 millimeters, suitably at least about 0.17 millimeters, more adequately than at least about 0.19 / millimeters, and more adequately at least about 0.25 / millimeters.

The resistance to collapse of the present structure of the present invention when wetted was also found to help improve the permeability of the absorbent structure in the Z-direction by saturating the absorbent structure with liquid. In general, the absorbent structures of the present invention have been found to exhibit improved Z-direction permeability with liquid saturation compared to an otherwise essentially identical absorbent structure not comprising a wettable binder fiber. As used herein, the "permeability in the z-direction" of a material is intended to represent the resistance of the material to the flow of liquid through the depth of the material. In general, the greater the permeability value in the z-direction of a material, the smaller the resistance of the material to the flow of liquid in the z-direction of, in other words, through the thickness of the material. Similarly, the lower the permeability value in the z-direction of a material, the greater the resistance of the material to the flow of liquid in the z-direction of the material.

In particular, the absorbent structures of the present invention have been found to exhibit a permeability value in the Z-direction at a saturation of 60% which is not less than, suitably at least about 20% greater than, more suitably at least about 25% greater than, and more adequately at least about 30% greater than, the permeability value in the Z-direction of the absorbent structure at 30% saturation. This is in contrast to an otherwise essentially identical absorbent structure without any wettable binder fiber which generally exhibits a permeability value in the Z-direction at a saturation of 60% which is much lower than the permeability value in the direction- Z at a saturation of 30%.

The absorbent structure of the present invention desirably has a permeability value in the Z-direction at a saturation of 60% which is at least about 50 Darcy, beneficially of at least about 75 Darcy, suitably so less than about 100 Darcy, more adequately of at least about 150 Darcy, and more adequately of at least about 200 Darcy. The Darcy is a unit representing the permeability of a porous material and is equivalent to about 9.87x10"9 square centimeters.

The absorbent structure of the present invention desirably has a permeability value in the Z-direction in a dry condition that is at least about 15 Darcy, suitably at least about 20 Darcy, more suitably at least of around 25 Darcy and more adequately of at least around 30 Darcy.

As used herein, the "absolute liquid saturated retention capacity" of an absorbent structure is intended to represent the maximum amount of liquid that the absorbent structure can hold: when a sufficient amount of time is given to reach a saturation of 100% and when an external pressure of about 0.5 psi is applied to the absorbent structure. Therefore, as used herein, "60% saturation" "30% saturation" and other related terms are meant to represent that a material has been saturated with a specific amount of a liquid based on the saturated retention capacity of absolute liquid of the material.

The absorbent structures of the present invention suitably have a specific saturated liquid retention capacity on one gram of liquid absorbed to one gram of base of absorbent structure of about 8 g / g around 40 g / g, beneficially about 10 g. g / ga about 35 g / g, and more beneficially about 15 g / g about 30 g / g.

The absorbent structures of the present invention suitably have a basis weight of about 100 grams per square meter (g / sm) to about 1,000 g / sm, beneficially from about 200 g / sm to about 800 g / sm, and more beneficially around 300 g / sm to around 700 g / sm.

The absorbent structures of the present invention suitably have a density of about 0.03 grams per cubic centimeter (g / cc) to about 0.5 g / cc, beneficially about 0.05 g / cc to about 0.45 g / cc and more beneficially from around 0.08 g / cc to around 0.4 g / cc.

TEST METHODS Saturated Liquid Retention Capacity The saturated liquid retention capacity was determined as follows. The material to be tested, having a moisture content of less than about 7% by weight, was weighed and immersed in an excess amount of an aqueous salt water solution of 0.9% by weight at room temperature ( around 23 ° C). The material that was to be tested was allowed to remain submerged for around 20 minutes. After submerging for 20 minutes, the material 31 was removed, and referring to Figure 5, it was placed on a fiberglass screen covered with TEFLON "* ™ 34 having 0.6 centimeter openings (commercially available from Taconic Plastics, Inc. , from Petersburg, New York) which in turn, is placed on a vacuum box 30 and covered with a flexible rubber dam material 32. A vacuum of about 3.5 kilopascals was pulled over the vacuum box by a period of about 5 minutes with the use of for example, a vacuum gauge 36 and a vacuum pump (38) .The material being tested is then removed from the grid and weighed in. The amount of liquid retained by the The material that is being tested was determined by subtracting the dry weight of the material from the wet weight of the material (after the application of the vacuum), and it was reported as the absolute liquid saturated retention capacity in grams of the liquid re If desired, the weight of the liquid retained can be converted to liquid volume by using the density of the liquid test and reported as the saturated retention capacity of the liquid in milliliters of liquid retained. For relative comparisons, this saturated liquid absolute retention capacity value can be divided by the weight of the material 31 to give the saturated retention capacity of the specific liquid in grams of the liquid retained per gram of material tested. If the material, such as a hydrogel or fiber-forming polymeric material, is pulled through the fiberglass grid while it is on the vacuum box, a grid should be used having smaller openings. Alternatively, a piece of tea bag or a similar material can be placed between the material and the grid and the final value adjusted to the liquid retained by the tea bag or similar material.

Resistance to Compression A rectangular sample about 4 inches wide, about 6 inches long, about 0.17 inches thick, and weighing about 700 grams per square meter was weighed and weighed. This was placed in an aqueous salt water solution loading of 0.9% by weight and allowed to stand for 20 minutes. At the end of this time the sample was essentially completely saturated. The thickness of the sample was measured using a volume meter available, for example, from Mitutoyo, Japan (Model number ID-1050ME). The sample is then placed on a vacuum box and covered with a rubber dam in a procedure similar to the liquid saturated retention capacity test method. A vacuum corresponding to a pressure of 0.5 pounds per square inch (psi) was applied for 5 minutes. The sample is then removed and the thickness of the sample was measured with the volume meter itself. The resistance to compression, defined as the force on the sample divided by the work done on the sample, is equal to the inverse of the change in thickness (in millimeters) of the sample at the given pressure. In this way a pressure of 0.5 psi: Compression Strength = l / (thickness at 0 psi-thickness at 0.5 psi) Resistance to stress The tensile strength of a material was evaluated by using a voltage tester such as an Instrom Model 4201 with Microcon II from Instron Corporation, of Canton, Massachusetts. The machine is calibrated by placing a weight of 100 grams in the center of the upper jaw, perpendicular to the jaw and hanging without obstruction. The voltage cell used is a self-identifiable electrically calibrating load cell of 5 kilograms. The weight is then displayed on the Microcon display window. The procedure was carried out in a room with a standard condition atmosphere such as around a temperature of about 23 ° C and a relative humidity of about 50%.

A rectangular sample of about 2 inches by about 6 inches was weighed and the pressure applied to the sample to achieve the desired density. The dry sample is then placed in the pneumatic action jaws with the one-inch by 3-inch rubber coated faces. The jaw length is around 4 inches and the cross head speed is around 250 m / minute. Cross-head velocity is the rate at which the upper jaw moves upward pulling the sample to failure. The tensile strength value is the maximum load to failure, recorded in grams, of force required to compress or tear the sample. The tensile strength is evaluated with respect to the material in both a dry condition and a liquid saturated condition of 100%. The tensile strength for the material in a 100% liquid saturated condition is done by placing a dry sample on the jaws of the tester and then moistening the sample with a desired amount of 0.9% saltwater solution, as determined by the saturated retention capacity of absolute liquid of the material. A time lapse of 10 minutes was allowed for the sample to equilibrate. Then the test was repeated as indicated for the sample in the dry state.

Stress resistance = highest load to failure (in force grams) Permeability in the Z-Direction A round sample about 3 inches in diameter was cut first using a die cutter. The density of the sample was calculated by determining its weight and thickness. The apparatus consists of an upper cylinder and a lower cylinder. The lower cylinder has a piston that is filled with mineral oil near the eyebrow (about 1 centimeter below the top edge). The bottom of the piston in the lower cylinder is connected to a pressure transducer, such as the Shaevitz Model No. P3061-50 apparatus. The piston is connected to the precision flipped screw connected to a speed controlled motor, such as the Velmex Unislide (Model No. 4036 IJ) that moves the piston up or down at a required speed (about 2 centimeters / minute). The pressure transducer is comitted to a computer that registers the presence of the transducer as pascals / volts. A typical experiment consists of placing the sample on a wire rack over the top of the lower cylinder. The upper hollow cylinder is then screwed onto the lower cylinder to retain the sample in place during the experiment. First the mineral oil in the piston of the lower cylinder moves up through the sample at a rate of about 2 centimeters / minute for about 2 minutes until all the air in the sample is displaced and the sample is saturated with mineral oil. Once saturated, the system is allowed to reach equilibrium through a measured pause time of around 20 seconds. The pressure recorded by the computer at this time is the baseline pressure. Then the mineral oil is moved upwards again through the sample to about 2 centimeters / minute and the maximum pressure is recorded by the computer. The difference between the baseline pressure and the maximum pressure is delta P, (in days per square centimeter). The sample is then taken. The viscosity of the mineral oil is known as being from about 6 centiposies to around 23 ° C. Then using the Darcy formula, the permeability "K" was calculated as follows: K = (viscosity) x (velocity) x (sample thickness / delta P) Where the viscosity is the viscosity of the liquid (in centipoises), the velocity is the velocity of the mineral oil (in centimeters per second), and the thickness is the thickness of the sample (in centimeters).

K is mentioned as being used here as the permeability value in the Z-direction. This would be the permeability value in the Z-direction for a sample of about 0% salt water saturation. The experiment is repeated for samples at around 30% and around 60% saturation by taking a similar but new sample each time and adding a 0.9% salt water solution to give a saturation of 30% or 60% of the sample. liquid. The amount of salt water required is calculated from the saturated retention capacity of the sample liquid.

Example Absorbent structures were prepared comprising a hydrogel-forming polymeric material, a wettable short fiber and a wettable binder fiber.

For the hydrogel-forming polymeric material, a partial sodium salt of a high-absorbency material of degraded polyprolopic acid, available from the Dow Chemical Company under the trade designation AFA 65-34 Sharpei, was used. For the wettable short fiber, the pulp of cellulose wood pulp was used. For the wettable binder fiber a polypropylene homopolymer comprising less than about 2% to about 2% by weight stabilizers, available from Himont USA, Inc., under the trade designation Valtec polypropylene homopolymer spheres, class PF-015 , combined with about 2% by weight of an internal wetting agent, available from PPG Industries, Inc., under the trade designation SF-19, was used. The wetting agent was combined with the polypropylene before being extruded into a fiber with an average diameter of about 5 microns.

The wettable binder fiber was formed by meltblowing into a composite fabric entangled with the hydrogel-forming polymer material fed into the meltblown stream and the short fiber fed into the composite fabric structure with a pick-up roll.

A sample 4 was a control sample that did not include any wettable binder fiber. Sample 4 was prepared by an air-forming process wherein the wettable short fibers and the hydrogel-forming polymeric material were mixed by a stream of air and then placed by air in a woven over the top of a box of liquid. empty. The composite fabric formed was then wrapped with a tissue paper of light basis weight to allow the handling and testing of the sample.

The absolute and relative weight basis amounts used of the different materials for the different samples are indicated in Table 1. Base weight amounts are given in grams per square meter (g / sm) of absorbent structure formed. The initial dry density of each sample material was about 0.17 grams per cubic centimeter.

Samples were evaluated for liquid saturated retention capacity, compressive strength, tensile strength, and permeability in the z-direction according to the procedures described herein. The results are described in Table 2.

Although the invention has been described in detail with respect to the specific embodiments thereof, it will be appreciated by those skilled in the art, upon achieving an understanding of the foregoing, that alterations, variations and equivalents of these modalities can easily be conceived. Therefore, the scope of the present invention should be established as that of the appended claims and any equivalents thereof.

TABLE 1 Fiber Agglutinante Hidrogel Fibra Curta Sample Weight Base Weight Base Weight Base Base Total No. (g / sm)% (g / sm)% (cr / sm)% (q / sm) 1 51 7 253 35 419 58 722 2 72 10 253 35 397 55 722 3 183 25 255 35 292 40 729 4 * 0 0 245 35 455 65 700 * It is not an example of the present invention.

TABLE 2 Resistance Permeability Resistance to Tension Retention Capacity-Z-Direction (Darcy) Compression Sample (Grams Strength) Saturated Saturation Saturation No. (1 / mm) Dry Saturated Absolute Boost (mi) 0% 30% 60% 1 0.19 436 488 130 57.3 153.6 69.6 2 0.28 1314 1292 124 45.7 166.3 221.7 3 0.17 4570 3938 127 32.7 190.6 256.8 4 * 0.13 220 144 90 29.1 122.1 77.1 * It is not an example of the present invention.

Claims (21)

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

1. An absorbent structure comprising: 5 a. from about 20 to about 65% by weight of a polymeric hydrogel-forming material; b. from about 25 to about 70% by weight of wettable short fibers; Y c. from about 7 to about 40% by weight of wettable binder fibers; where all percent by weight are based on 15 the total weight of the hydrogel-forming polymeric material, of the wettable short fiber, and of the wettable binder fiber in the absorbent structure, wherein the absorbent structure exhibits a permeability value in the Z-direction. 20 to about 60% saturation which is not less than the permeability value in the Z direction of the absorbent structure of about 30% saturation, and wherein the absorbent structure exhibits a permeability value in the Z direction 25 to about 60% saturation that is greater than about 50 Darcy.

2. The absorbent structure, as claimed in clause 1, characterized in that it comprises from about 25 to about 60% by weight of a polymeric hydrogel-forming material.

3. The absorbent structure, as claimed in clause 1, characterized in that the polymeric hydrogel-forming material is a polyacrylate material.

4. The absorbent structure, as claimed in clause 1, is characterized in that it comprises from about 30 to about 65% by weight of wettable short fiber.

5. The absorbent structure, as claimed in clause 1, characterized in that the wettable short fiber has a fiber length of from about 0.1 to about 15 centimeters.

6. The absorbent structure, as claimed in clause 1, characterized in that the wettable short fiber is selected from the group consisting of cellulosic fibers, textile fibers, and synthetic polymer fibers.

7. The absorbent structure, as claimed in clause 1, characterized in that the wettable fiber is fiber of wood pulp.

8. The absorbent structure, as claimed in clause 1, characterized in that it comprises from about 8 to about 35% by weight of wettable binder fiber.

9. The absorbent structure, as claimed in clause 8, characterized in that it comprises from about 10 to about 30% by weight of wettable binder fiber.

10. The absorbent structure, as claimed in clause 1, characterized in that the wettable binder fiber is a meltblown fiber comprising a polyolefin.

11. The absorbent structure, as claimed in clause 1, characterized in that the absorbent structure comprises a fibrous matrix comprising the wettable binder fiber, wherein the fibrous matrix constrains the wettable short fiber and the hydrogel-forming polymeric material.

12. The absorbent structure, as claimed in clause 1, characterized in that said absorbent structure exhibits a permeability value in the Z-direction at about a saturation of 60% which is at least about 20% greater than the permeability value in the Z direction of the absorbent structure at a saturation of about 30%.

13. The absorbent structure, as claimed in clause 12, characterized in that the absorbent structure exhibits a permeability value in the Z-direction at about a saturation of 60% which is at least about 25% greater than the permeability value in the Z direction of the absorbent structure at a saturation of about 30%.

14. The absorbent structure, as claimed in clause 1, characterized in that the absorbent structure exhibits a permeability value in the Z-direction at about a saturation of 60% which is greater than about 75 Darcy.

15. The absorbent structure, as claimed in clause 14, characterized in that the absorbent structure exhibits a permeability value in the Z-direction at about a saturation of 60% which is greater than about 100 Darcy.

16. The absorbent structure, as claimed in clause 1, characterized in that the absorbent structure exhibits a value of compressive strength that is at least about 25% greater than the value of compressive strength exhibited by a Absorbent structure otherwise essentially identical without any wettable binder fiber.

17. The absorbent structure, as claimed in clause 1, characterized park the absorbent structure exhibits a value of compressive strength that is at least about 0.15 / millimeters.

18. The absorbent structure, as claimed in clause 1, characterized in that the absorbent structure exhibits a tensile strength value in a dry condition that is at least about 50% greater than the resistance value to the tension exhibited by an otherwise essentially identical absorbent structure without any wettable binder fiber in a dry condition, and wherein the absorbent structure exhibits a tensile strength value in a 100% saturated liquid condition which is at least about 50% greater than the tensile strength value exhibited by an otherwise essentially identical absorbent structure without any wettable binder fiber in a 100% liquid saturated condition.

19. The absorbent structure, as claimed in clause 1, characterized in that the absorbent structure exhibits a tensile strength value in a dry condition that is at least about 400 grams force, and wherein the absorbent structure exhibits a tensile strength value in a 100% liquid saturated condition that is at least about 400 grams force.

20. An absorbent structure comprising: to. from about 25 to about 60% by weight of a polymeric hydrogel-forming material; b. from about 30 to about 65% by weight of a wettable wood pulp fiber; Y c. from about 8 to about 65% by weight of a wettable meltblown fiber comprising a polyolefin; wherein all percent by weight are based on the total weight of the hydrogel-forming polymeric material, the wettable wood pulp fiber, and the wettable melt blown fiber comprising a polyolefin in the absorbent structure, wherein the absorbent structure exhibits a permeability value in the Z-direction at about 60% saturation which is about 20% higher than the permeability value in the Z-direction of the absorbent structure of about 30% saturation, where the structure Absorber exhibits a permeability value in the Z-direction at about 60% saturation that is greater than about 75 10 Darcy, wherein the absorbent structure exhibits a tensile strength value in a dry condition that is at least about 50% greater than the tensile strength value exhibited by an absorbent structure of another 15 essentially identical without any wettable binder fiber in a dry condition, and wherein the absorbent structure exhibits a tensile strength value in a 100% saturated liquid condition which is at least 20 about 50% greater than the tensile strength value exhibited by an otherwise essentially identical absorbent structure without any wettable binder fiber in a 100% liquid saturated condition.

21. A disposable absorbent product comprising a liquid pervious topsheet, a backsheet, and an absorbent structure positioned between the topsheet and the backsheet, wherein the absorbent structure comprises: to. from about 20 to about 65% by weight of a polymeric hydrogel-forming material; b. from about 25 to about 70% by weight of wettable cut fibers; Y c. from more than about 7 to about 40% by weight of wettable binder fibers; wherein all per cent poi: weight are based on the total weight of the hydrogel-forming polymer material, of the wettable short fiber, and of the wettable binder fiber in the absorbent structure, wherein the absorbent structure exhibits a permeability value in the Z-direction at about 60% saturation which is not less than the permeability value in the Z-direction of the present absorbent structure of about 30% saturation, and wherein the absorbent structure exhibits a permeability value in the Z-direction at around 60% saturation that is greater than about 50 Darcy. SUMMARY An absorbent structure is disclosed which contains a hydrogel-forming polymeric material, a wettable short fiber, and a wettable binder fiber. The absorbent structure exhibits improved permeability in the z-direction of a liquid compared to an otherwise essentially identical absorbent structure which does not comprise a wettable binder fiber. A disposable absorbent product containing such an absorbent structure is also disclosed.