CZ285999A3 - Mixed bed of a mixture of ion-exchange, gel-forming polymers and absorption elements comprising relatively high concentrations of such mixtures - Google Patents

Abstract

Absorbent beds are formed from a mixture comprising at least one one cation exchange polymer-forming hydrogel wherein; the composition exhibits improved absorption parameters. Absorbent members useful for storing body fluids what urine has at least one portion containing the mixed bed of urea mixtures of ion exchange hydrogel forming absorbent % of polymers at a concentration of 60 to 100 wt to the total weight of the absorbent member.

Description

Mixed bed of a mixture of ion-exchange hydrogel-forming polymers and absorbent members comprising relatively high concentrations of these mixtures

Technical field

The present invention relates to absorbent members for absorbing body fluids such as urine and menstrual discharge. In particular, the present invention relates to mixed beds of a mixture of ion-exchange hydrogel-forming polymers and absorbent members having at least one region comprising a relatively high concentration of such mixtures.

BACKGROUND OF THE INVENTION

The development of highly absorbent members usable as disposable diapers, incontinence pads and adult panty liners and sanitary napkin products, such as sanitary napkins, is of considerable commercial interest. The parameter that is highly demanded for these products is that they be thin. For example, thinner diapers are less bulky to wear, fit better under the garment and are less noticeable. Wrapped, they are denser, making it easier for the consumer to carry and store them. Packed density also brings manufacturers and distributors lower distribution costs, including less on-demand diaper storage space in the warehouse.

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The ability to provide thinner absorbent articles, such as diapers, depended on the ability to develop relatively thin absorbent cores or structures that can receive and contain large amounts of excreted body fluids, especially urine. The use of certain absorbent polymers, often referred to as hydrogels, superabsorbents or hydrocolloids, has become particularly important in this regard. See, for example, U.S. Patent 3,699,103, and U.S. Patent 3,770,731, which disclose the use of such absorbent polymers (hereinafter referred to as hydrogel-forming absorbent polymers) in absorbent articles. Indeed, the development of thinner diapers has been a direct consequence of thinner absorbent cores which utilize the advantageous ability of these hydrogel-forming absorbent polymers to absorb large amounts of secreted body fluids, typically used in combination with a fiber matrix. See, for example, U.S. Pat. No. 4,673,402 and U.S. Pat. No. 4,935,022, which disclose two-layer cores comprising a fiber matrix and hydrogel-forming absorbent polymers that can be used to manufacture thin, dense, bulky diapers.

These hydrogel-forming absorbent polymers are often prepared by first polymerizing unsaturated carboxylic acids or derivatives thereof, such as acrylic acid, alkali metal (e.g., sodium or potassium) or ammonium salts of acrylic acid, alkyl acrylates and the like. These polymers can be rendered insoluble in water but swellable by water by allowing their carboxyl group-containing polymer chains to crosslink easily with conventional difunctional or polyfunctional monomeric materials such as N, N'methylenebisacrylamide, trimethylolpropane triacrylate or triallylamine. These slightly crosslinked absorbent polymers still contain a plurality of anionic (charged) carboxyl groups attached to the polymer backbone. It is these charged carboxyl groups that allow the polymer to: · 0 0 0 · · 0 0 ·· • · 0 0 0 0 0 0 0 • 0 0 ·· 00 000000

0 0 0 0 0 0 0000 0000 000 00 00 00 absorbed body fluids as a result of osmotic forces and thus formed hydrogels.

These hydrogel-forming absorbent polymers are also often prepared by first polymerizing unsaturated amines or derivatives thereof, such as diallyldimethylammonium chloride, Ν, N'-dimethylaminoethyl methacrylate.HCl, N, N-dimethylaminoethyl acrylate.HCl, methacrylamidopropyltrimethylammonium hydroxide, and the like. These polymers are made water-insoluble but water-swellable by slightly crosslinking the polymer chains with conventional difunctional or polyfunctional monomer materials such as Ν, N'-methylenebisacrylamide, trimethylolpropane triacrylate, or triallylamine. These slightly crosslinked absorbent polymers still have multiple cationic (charged) amine groups attached to the polymer backbone. It is these charged amine groups that allow the polymer to absorb body fluids as a result of osmotic forces, thereby forming hydrogels.

The degree of cross-linking determines not only the insolubility of these hydrogel-forming absorbent polymers, but also an important factor imparting two additional parameters to these polymers, namely their absorption capacity and gel strength. The absorption capacity, or gel volume, is a measure of how much water or body fluid absorbs a given amount of this hydrogel-forming polymer. Gel strength refers to the tendency of a hydrogel formed from these polymers to deform or to flow under tension. Hydrogel-forming polymers useful as absorbents in absorbent structures and articles such as disposable diapers need to have an appropriately high gel volume as well as an appropriately high gel strength. The gel volume must be high enough to allow the hydrogel-forming polymer to absorb substantial amounts of aqueous body fluids that appear during use. · Absorbent article. · · · · · · · · · · · · · · · · · · · · · The gel strength must be such that the formed hydrogel does not deform and unacceptably fill the free capillary spaces in the absorbent structure of the article, thereby blocking the absorbent capacity of the structure or article as well as the distribution of fluid within the structure or article. See, for example, U.S. Patent 4,654,039 (reissued as a revised U.S. Patent RE 32,649) and U.S. Patent 4,834,735.

These hydrogel-forming polymers are generally slightly cross-linked polyelectrolytes, which swell in aqueous electrolyte solutions primarily as a result of osmotic driving force. The osmotic driving force for swelling of the hydrogel-forming polymer results primarily from polyelectrolyte counterions which are dissociated from the polyelectrolyte but are maintained within the swollen polymer due to electroneutral ratios. Hydrogel-forming polymers, which include weakly acidic or weakly basic polyelectrolytes (eg, carboxylic acid or mono / di / triamine functional groups) in their non-neutralized forms, are only slightly dissociated in urine solutions. These weakly acidic or weakly basic hydrogel-forming absorbent polymers must be at least partially neutralized with a base, respectively. acid to form substantial concentrations of dissociated counterions. Without neutralization eg for approx. 70% of these weakly acidic or weakly basic hydrogel-forming absorbent polymers do not swell to their maximum potential absorption capacity or gel volume. In contrast, the absorption capacity of hydrogel-forming polymers comprising strong acid or strong base functional groups (eg sulfonic acid or quaternary ammonium hydroxide) are much less sensitive to their degree of neutralization, but the use of these hydrogel-forming polymers based on strong acid or strong base in their neutralized forms have the potential to shift the pH of the urine solution to unacceptably low, respectively. high value.

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Even after neutralization, the osmotic driving force for swelling and hence the absorption capacity or gel volume of the polyelectrolyte hydrogel-forming polymers is greatly reduced by the high concentration of dissolved electrolyte normally present in the urine. The concentration of this dissolved electrolyte, expressed as% wt NaCl, may be up to 0.9% (physiological saline) or higher. It is known that decreasing the dissolved electrolyte concentration in the urine (eg by diluting with distilled water) can greatly increase the absorption capacity of the hydrogel-forming polyelectrolyte polymer, so that eg when Jayco synthetic urine is used to measure gel volume of partially neutralized sodium polyacrylate hydrogel-forming polymer a 10-fold dilution of Jayco's urine with distilled water to approximately triple the gel volume.

It is known that the concentration of dissolved electrolyte in aqueous solutions can be reduced by reacting the mixed bed solution of the ion exchange resin. (Ion exchange columns are often used commercially for deionization of water.) The electrolyte concentration decreases by the combined effect of (1) the exchange of dissolved cations (e.g. Na ⁺ ) in aqueous solution with H ⁺ ions from the cation exchange resin and (2) the exchange of dissolved anions (e.g. Cl) after OH ions of anion exchange resin. H ⁺ and OH from the resins combine in solution to give H 2 O. It is precisely the reaction of H ⁺ and OH 'giving H2O, which is the driving force of the transfer of dissolved anions and cations from solution to their corresponding resins, which leads to a decrease in the electrolyte concentration in the solution. Mixed-bed resins generally contain approximately the same equivalents of anion exchange and cation exchange functional groups. The anionic and cationic resin particles are appropriately intensively mixed or have high specific surfaces to reduce diffusion distance and increase ion exchange rates.

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Ion-exchange resins have been used to increase the absorbent capacity of absorbent articles comprising hydrogel-forming polymers. See, e.g., U.S. Patent No. 4,818,598. The need to incorporate large amounts of ion exchange resin or resins having little or no absorption capacity generally increases the bulkiness of the absorbent article to an unacceptable extent.

It is known that a mixture of (1) the anionic hydrogel-forming polymer in its acid form and (2) the cationic hydrogel-forming polymer in its basic form has the potential to act as a mixed bed ion exchange system in reducing the electrolyte solution concentration. Furthermore, if the anionic hydrogel-forming absorbent polymer in the mixed ion exchange system is a weak acid and starts in its non-neutralized form, the resulting exchange of H ⁺ for eg Na ⁺ results in the conversion of the hydrogel-forming anionic polymer from its non-neutralized to neutralized form. The osmotic driving force for swelling (and hence the absorption capacity of the hydrogel-forming polymer) of the weakly acidic anionic hydrogel-forming polymer increases as a result of the ion exchange in the mixed bed ion exchange system. Similarly, if the cationic hydrogel-forming polymer in the mixed-bed ion exchange system is a weak base and if it starts in its initial non-neutralized form, then the resulting OH exchange e.g. "for Cl" (or addition of HCl to the neutral amine group) results in transition of the cationic hydrogel forming polymer from its non-neutralized to neutralized form. Thus, the osmotic driving force for swelling of a weakly basic cationic hydrogel-forming polymer also increases as a result of ion exchange in the mixed bed ion exchange system. Whether or not the hydrogel-forming polymers in the mixed-bed ion exchange system are weak or strong acids or weak or strong bases, the aqueous electrolyte reactions are: · Mixed-bed solution of ion-exchange system · · · · se se roztoku se roztoku roztoku se roztoku roztoku roztoku roztoku roztoku roztoku roztoku roztoku roztoku roztoku roztoku roztoku roztoku roztoku roztoku roztoku roztoku roztoku it results in at least some reduction in the electrolyte concentration, resulting in at least some increase in the osmotic driving force for swelling. The combined effects of (1) a decrease in electrolyte concentration and (2) a conversion (if necessary) from a less swelling to a more swelling form result in a mixed bed of ion exchange hydrogel forming polymer system where both anionic and cationic hydrogel forming absorbent polymers starting from their non-neutralized forms, it has the potential to impart increased osmotic driving force for swelling relative to a mixture of comparable anionic and cationic hydrogel-forming polymers, each starting from its neutralized form. The use of a mixed bed of ion exchange hydrogel-forming polymers to increase the absorption capacity has been described in PCT applications WO 96/17681, WO 96/15162 and in US 5 274 018.

The degree to which a mixed bed of hydrogel forming polymer system can potentially reduce the electrolyte concentration depends on (1) the ion exchange capacity in the meq / g of the anionic and cationic hydrogel-forming polymers (2) pKa and pKb (and thus the extent of reaction) of anionic and cationic hydrogel-forming polymers (3) meq / l electrolyte in aqueous solution; and (4) 1 / g ratio of aqueous electrolyte solution to ion exchange hydrogel-forming polymers. For a given ion-exchange capacity of the mixed bed, pKa and pKb, and the electrolyte concentration, the reduction of the electrolyte concentration is maximized by minimizing the total volume of the solution in contact with the ion exchange hydrogel-forming polymers. In an absorbent structure (e.g., a mixture of hydrogel-forming polymers and fibers), only a portion of the total liquid is absorbed by the hydrogel-forming polymer. The remainder of the liquid is absorbed by other components (eg in the pores formed by the fibrous structure), although this liquid is not absorbed by the hydrogel-forming polymer.

The electrolyte in this liquid can diffuse into the hydrogel-forming polymer and thus increase the electrolyte concentration up to a level that would be higher than it would be if no external liquid was present. If the aim is to use a mixed bed of an ion exchange hydrogel forming polymer system to increase the absorption capacity, then the potential benefits of ion exchange are reduced as the percentage of the hydrogel forming polymer in the absorbent structure decreases. By contrast, reducing the amount of fibers (or other hydrogel-forming polymeric components capable of absorbing fluid) minimizes the amount of extra solution and hence the amount of extra salt that needs to be replaced to achieve a given decrease in electrolyte concentration. Thus, in principle, when a mixed bed of an ion exchange hydrogel forming polymer system is incorporated into an absorbent structure, this may utilize to a greater extent ion exchange when incorporated at a high concentration than at a low concentration.

Previous absorbent structures generally included relatively low amounts (ie, less than about 50 wt%) of these hydrogel-forming absorbent polymers. See, eg, US Patent 4,834,735 (preferably from about 9 to about 50% of the hydrogel-forming absorbent polymer in the fibrous matrix). There are several reasons for this. The hydrogel-forming absorbent polymers used in prior art absorbent structures generally did not have an absorption rate that would allow them to rapidly absorb body fluids, especially in situations where they are flowing. This necessitated the inclusion of fibers, generally wood pulp fibers, which served as temporary reservoirs for the temporary storage of the exuded fluids until absorbed by the hydrogel-forming absorbent polymer.

More importantly, many of the known hydrogel-forming absorbent polymers exhibited gel blocking. Gel blocking occurs when the hydrogel-forming absorbent polymer particles are moistened and the particles swell to inhibit liquid transfer to other regions of the absorbent structure. The wetting of these other regions of the absorbent member thus proceeds through a very slow diffusion process. Practically, this means that the absorbent structure absorbs fluids at a much slower rate than the rate at which the fluids are discharged, especially in situations where they flow through the stream. Leakage from the absorbent article may occur substantially before the hydrogel-forming absorbent polymer particles in the absorbent member are fully saturated, or before the liquid can diffuse or pass through the wicking effect behind the blocking particles into the remainder of the absorbent member. Gel blocking can be a particularly acute problem if the hydrogel-forming absorbent polymer particles do not have adequate gel strength and deform or expand under tension as the particles swell with the absorbed fluid. See U.S. Patent 4,834,735.

This gel blocking phenomenon generally required the use of a fiber matrix in which the hydrogel-forming absorbent polymer particles are dispersed. This fiber matrix keeps the hydrogel-forming absorbent polymer particles separated from each other. This fiber matrix also provides a capillary structure that allows the fluid to reach the hydrogel-forming absorbent polymer located in areas remote from the original fluid ejection point; see U.S. Pat. No. 4,834,735. However, dispersing the hydrogel-forming absorbent polymer in a fiber matrix at relatively low concentrations to minimize or eliminate gel blocking may reduce the overall fluid storage capacity of thinner absorbent structures. The use of lower concentrations of these hydrogel-forming absorbent polymers limits to some extent the real advantage of these materials, namely their 9

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In addition to increasing gel strength, other physicochemical parameters of these hydrogel-forming absorbent polymers have been adjusted to reduce gel blocking. One parameter is the particle size, and in particular the particle size distribution of the hydrogel-forming absorbent polymer used in the fiber matrix. For example, hydrogel-forming absorbent polymer particles having a particle size distribution such that the particles have a weight median particle size greater than or equal to 400 microns are mixed with hydrophilic fibrous materials to minimize gel blocking and to help maintain an open capillary structure within the absorbent structure to improved areal transport of fluids away from the original effluent area to the remainder of the absorbent structure. In addition, the particle size distribution of the hydrogel-forming absorbent polymer can be controlled to improve the absorption capacity and efficiency of the particles utilized in the absorbent structure. See U.S. Patent No. 5,047,023. However, adjusting the particle size distribution by itself does not, however, lead to absorbent structures that may have relatively high concentrations of these hydrogel-forming absorbent polymers. See U.S. Patent No. 5,047,023 (the optimum fiber to particle ratio based on cost / functionality ratio is from about 75:25 to about 90:10).

Another parameter of attention to these hydrogel-forming absorbent polymers is the level of extractables present in the polymer itself. See U.S. Patent 4,654,039 (revised edition like US RE No. 32,649). Many of these hydrogel-forming absorbent polymers contain considerable levels of extractable polymeric material. This extractable polymeric material can be leached from the resulting hydrogel by body fluids (e.g., urine) during the process. 99 999 99 99 99 99 99 99 99 99 999 99 99 99 t

at a time when body fluids remain in contact with the hydrogel-forming absorbent polymer. It is believed that such polymeric material extracted by a body fluid in this manner can alter both the chemical and physical parameters of the body fluid to such an extent that the fluid is absorbed more slowly and less well maintained in the hydrogel of the absorbent article.

Another parameter that has been addressed to minimize gel blocking is to improve the capillary capability of these hydrogel-forming absorbent polymers. In particular, it has been proposed that the particles of these hydrogel-forming absorbent polymers be formed into interparticle crosslinked aggregate macrostructures, in particular in the form of sheets or strips. See U.S. Patent No. 5,102,597, U.S. Patent No. 5,124,188, and U.S. Patent No. 5,149,344. Because the particulate nature of the absorbent polymer is retained, these macrostructures provide pores between adjacent particles that are interconnected such that the macrostructure is fluid permeable. (i.e., has capillary transport channels). Due to the interparticle crosslinks formed between the particles, the resulting macrostructures also have improved structural integrity, increased fluid acceptance, increased distribution rates, and minimal gel blocking parameters.

Yet another parameter known in the art for a period of time as a measure of gel blocking is the maximum Demand Wettability or Gravimetric Absorbency of these hydrogel-forming absorbent polymers. See, for example, U.S. Patent No. 5,562,644 and U.S. Patent No. 5,599,335, which discloses the desired wettability and gravimetric absorption performance as performance under pressure (PUP). In the PUP experiment, 100% concentration of absorbent gelling material (AGM) is placed, which is initially dry, and is initially dry, which is initially dry. to the piston / cylinder apparatus (where the bottom of the cylinder is solution-permeable but AGM-impermeable) where it is subjected to mechanical pressure under space constraints and allowed to absorb synthetic urine under conditions allowing maximum absorption at zero hydrostatic suction and high mechanical pressure, the PUP capacity is defined as the Jayco synthetic urine absorption in g / g in a 0.032 g / cm ² layer of absorbent hydrogel-forming polymer while the polymer is spatially constrained and is under a pressure of 5 kPa (about 0.7 psi) for one hour. A hydrogel-forming polymer is considered to have desirable PUP properties when it absorbs at least about 23 g / g within one hour. The high capacity of PUP is a critically important property of the hydrogel-forming polymer when used at high concentrations in the absorbent structure.

Ion exchangers at least partly of

Although maximizing the concentration of the mixed bed from the mixture of ion exchange hydrogel-forming polymers in the absorbent structure increases the osmotic driving force for swelling, this increase in osmotic driving force thus did not lead to the expected improvement in absorbency expressed as PUP capacity. It is believed that the poor performance at high concentration of the present mixed hydrogel-forming polymers results from the polymers that make up this mixed bed system and that their mixture is not optimized for use at high concentration and high limiting pressures. As a result, the current mixed bed of ion exchange hydrogel-forming polymers tend to block under gel pressure, further exhibit low absorption rates under PUP conditions, and have low PUP capacity after a reasonable period of time. As a result, the PUP absorption of the mixed bed mixture of the ion exchange hydrogel forming polymers is not significantly greater than the PUP absorption of a comparable mixture of cationic and anionic hydrogel forming polymers where the polymers are neutralized before

by measuring PUP or for either an anionic or cationic hydrogel-forming polymer itself, where the polymers are neutralized prior to measuring PUP. (They may also exhibit low Saline Flow Conductivity (SFC) conductivity, low Porosity of Hydrogel Layer (PHL) and slow ion exchange rate - see below). of ion exchange hydrogel-forming polymers at high concentrations is worth mentioning especially given the importance of using hydrogel-forming polymers at high concentrations in absorbent articles such as diapers.

For absorbent structures having relatively high concentrations of these hydrogel-forming absorbent polymers, other parameters of these absorbent polymers are also important. It has been found that the openness or porosity of the hydrogel layer that is formed when these absorbent polymers swell in the presence of body fluids is relevant to determining the ability of these absorbent polymers to absorb and transport fluids, especially when the absorbent polymer is present in the absorbent structure at high concentrations. Porosity refers to a portion of the volume that is not occupied by solid material. In a hydrogel layer formed entirely of a hydrogel-forming absorbent polymer, the porosity is the portion of the volume of the hydrogel-free layer. For an absorbent structure comprising a hydrogel as well as other components, the portion of the volume (also referred to as the void volume) that is not occupied by the hydrogel or other solid components (e.g. fibers) is porosity.

The openness or porosity of the hydrogel layer formed from the hydrogel-forming absorbent polymer can be defined as the porosity of the Hydrogel Layer (see, e.g., U.S. Patent No. 5,562,646).

A good example of a material having a very high degree of openness is an aerodynamically laid web of wood pulp fibers. For example, as a fraction of the degree of openness of an aerodynamically laid wood pulp fiber web having, for example, a density of 0.15 g / cm ³ , it is estimated to be 0.8 to 0.9 when wetted with body fluids at a 0.3 psi restraining pressure. 2 kPa.

It has been found that the PHL of the hydrogel-forming absorbent polymer does not need to approach this value for an aerodynamically laid wood pulp fiber web in order to obtain substantial performance advantages when these absorbent polymers are present at high concentrations. These advantages include (1) an increased void volume in the resulting hydrogel acquisition and distribution layer, and (2) an increased total amount of fluid absorbed by the absorbent polymer under conditions of maximum wettability or gravimetric absorbency (i.e., fluid storage). Increased porosity can also provide other performance benefits such as (3) increased permeability of the resulting hydrogel layer for fluid uptake and distribution, (4) improved wick effect on the resulting hydrogel layer so that the fluid will rise upward against gravitational pressures or the fluid will distribute away from the receiving layer, the resulting hydrogel layers improved.

and (5) adjusting the properties around the swelling rate so as to allow faster storage of the liquid. The hydrogel-forming polymer appears to have desirable PHL properties when its PHL is at least about 0.15.

Another important property at higher concentrations of these hydrogel-forming absorbent polymers is their permeability or high liquid conductivity. Permeability or high conductivity for fluids can be defined by their conductivity for saline flow, ie SFC (ie Salina Flow)

Conductivity). SFC measures the ability of a material to deliver saline fluids, such as the ability of a hydrogel layer formed from a swollen hydrogel-forming absorbent polymer to deliver body fluids. An aerodynamically laid web of wood pulp fibers (e.g. having a density of 0.15 g / cm ³ ) will generally exhibit an SFC of about 200 χ 10 ⁷ cm ³ s / g. Accordingly, it would be highly desirable to be able to use hydrogel-forming absorbent polymers closer to the aerodynamically laid wood pulp fiber web in terms of SFC conductivity. The hydrogel-forming polymer appears to have desirable permeability properties when its SFC is at least about 30x10 ^-7 cm ³ s / g.

Another factor to consider in order to take full advantage of the porosity and permeability properties of a hydrogel layer formed from these absorbent polymers is the wet cohesiveness of the area or areas in the absorbent member that includes these polymers. For hydrogel-forming absorbent polymers having relatively high porosity and SFC values, it is important that the area or areas in which the polymers are present have good wet cohesiveness. Good wet cohesiveness is understood to mean that the region or regions in the absorbent member having a high concentration of hydrogel-forming absorbent polymer have sufficient integrity in a dry, partially wet, or humid state such that physical continuity (and hence the ability to receive and transport liquid to and through the associated inserted voids or capillaries) of a hydrogel formed upon swelling in the presence of body fluids is not substantially disturbed or altered even when subjected to normal conditions of use. During normal use, absorbent cores in absorbent articles are typically subjected to tensile and torsional forces of varying intensity and direction. These tensile and torsional forces include crotch in the crotch region, the tension and torsion forces as the wearer of the absorbent article walks, sits, bends, and the like. If wet cohesiveness is inadequate, these tension and torsion forces can potentially cause a significant change or or impair the physical continuity of the hydrogel such that its ability to receive and further transport fluids to and from voids or capillaries is degraded, ie the hydrogel layer can be partially separated, completely separated, may have holes in it, have areas that are substantially thinned, or fragmented into many substantially smaller segments. Such a change can even minimize or completely negate any advantageous properties in terms of porosity and permeability or conductivity for the flow of hydrogel-forming absorbent materials.

Accordingly, it would be desirable to have the ability to provide a mixed bed of a mixture of ion-exchange hydrogel-forming polymers capable of absorbing an increased amount of urine-based electrolyte solution under PUP absorption conditions over a reasonable period of time compared to other comparable hydrogel-forming polymer blends. in their neutralized forms, the ability to provide bulking

It would also be desirable to have a bed of a mixture of ion exchange hydrogel-forming absorbent polymers capable of absorbing a large amount of urine-based electrolyte solution in a reasonable amount of time under PUP absorption conditions. It would also be desirable to have absorbent structures containing a high concentration of mixed bed of a mixture of ion exchange hydrogel forming polymers capable of absorbing an increased amount of urine-based electrolyte solution for a reasonable period of time under PUP absorption conditions compared to a comparable mixture of these hydrogel forming polymers. forms. It would also be desirable to have a mixed bed of a mixture of ion-exchange hydrogel-forming polymers having high SFC and PHL values.

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SUMMARY OF THE INVENTION

The present invention relates to absorbent materials and absorbent members useful for storing body fluids such as urine. In one aspect, the invention relates to a mixture of cation exchange hydrogel-forming polymers and anion exchange hydrogel-forming polymers, hereinafter referred to as a mixed bed of a mixture of ion exchange hydrogel-forming polymers, wherein the mixture exhibits enhanced absorbency for a urinary electrolyte solution under reasonable PUP conditions. absorption compared to a comparable blend consisting of anionic and cationic hydrogel-forming polymers, each of which is in its neutralized form. The invention also relates to absorbent articles having at least one region comprising the mixed bed of a mixture of ion exchange hydrogel-forming polymers at a concentration of from about 60% to 100% by weight. an ion-exchange hydrogel-forming polymer.

In another aspect, the invention relates to a mixed bed of a mixture of ion exchange hydrogel-forming polymers having a Performance Under Pressure (PUP) capacity after 225 minutes at a limiting pressure of 0.7 psi of at least about 25 g / g. . The invention further relates to absorbent articles having at least one region comprising such a mixed bed of mixtures of ion exchange hydrogel-forming polymers at a concentration of from about 60 to 100 wt%. an ion-exchange hydrogel-forming polymer.

Overview of the drawings

Figure 1 is a cross-sectional view of an absorbent article showing the absorbent core of the present invention.

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Figure 2 is a cross-sectional view of an absorbent article showing another absorbent core of the present invention.

Figure 3 is a cross-sectional view of an absorbent article showing another absorbent core according to the present invention.

Figure 4 is a cross-sectional view of an absorbent article showing another absorbent core of the present invention.

Figure 5 is a cross-sectional view of an absorbent article showing an alternative absorbent core to the core shown in Figure 4.

Figure 6 is a cross-sectional view of an absorbent article showing another alternative absorbent core to the core shown in Figures 4 and 5.

Figure 7 is a schematic view of an apparatus for measuring the conductivity value for Saline Flow Conductivity (abbreviated SFC) of hydrogel-forming absorbent polymers.

Giant. 8 is an enlarged cross-sectional view of the piston-cylinder assembly shown in FIG. 7.

Figure 9 is a plan view of the bottom of the piston head of the cylinder-piston assembly shown in Figure 8.

Figure 10 is a schematic view of an apparatus for measuring PUP capacity, i.e. Performance Under Pressure (PUP) for Performance Under Pressure (PUP) for absorbent hydrogel-forming polymers.

Figure 11 is an enlarged cross-sectional view of the cylinder piston assembly shown in Figure 10.

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Figure 12 is a cross-sectional view of a cylinder piston assembly used to measure the porosity of hydrogel-forming absorbent polymers.

Figure 13 is a plan view of the bottom of the piston head of the piston and cylinder assembly shown in Figure 12.

DETAILED DESCRIPTION OF THE INVENTION

A., Definition

As used hereinafter, the term body fluid means urine, menstrual and uterine discharge.

As used hereinafter, the term dimension Z means a dimension that extends perpendicular to the length and width of the member, core or article. The Z dimension typically corresponds to the thickness of the member, core or article.

As used herein, X-Y means a plane that is perpendicular to the thickness of the member, core, or article. The X-Y dimension typically corresponds to the length and width of the member, core or article.

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

As used herein, the term absorbent member means absorbent core components that typically provide one or more fluid handling properties, eg, fluid intake, fluid distribution, fluid transport, storage, and storage.

9 9 9 9 9 9 9 9 9 9 9 9 9 9 The absorbent member may comprise all or a portion of the absorbent core, i.e., the absorbent core may comprise one or more absorbent members.

As used herein, the terms mean a region or regions or zones or zones of an absorbent member.

As used herein, the term layer means an absorbent member whose primary dimension is X-Y, i.e. along the length and width. It is to be understood that the term layer is not necessarily limited to individual layers or sheets of material, so that the layer may include laminates or combinations of several sheets or strips of the desired types of materials. Accordingly, the term layer includes the terms layer and layered.

For the purposes of the present invention, it should also be understood that the term top refers to absorbent articles, such as layers that are closest to the wearer of the absorbent article and generally are facing the topsheet of the absorbent article. In contrast, the bottom refers to absorbent members further away from the wearer of the absorbent article and generally facing the backsheet.

As used herein, the term includes various components, members, steps and the like that can be used together according to the present invention. Therefore, the term comprising includes more restrictive terms consisting essentially of and consisting of, the following more restrictive terms having their standard meaning as understood in the art.

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

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Β. Materials and components of the absorbent member

A mixed bed of a mixture of ion-exchange hydrogel-forming absorbent polymers

Chemical composition (1) Cationic polymers

Absorbent hydrogel-forming polymers useful for the cationic polymer (s) include a variety of water-insoluble but water-swellable polymers capable of absorbing large quantities of fluids. Cationic types may have multiple cationic functional groups such as N-alkylamine, Ν, N'-dialkylamine, Ν, Ν'Ν trialkylamine, N, N'NN ^, '' tetraalkylammonium groups. Examples of polymers suitable for use herein include those polymers that are prepared from polymerizable, unsaturated, cation-containing monomers. Thus, these monomers include olefinically unsaturated amines and substituted amines containing at least one olefinic carbon-carbon double bond. More specifically, these monomers may be selected from olefinically unsaturated alkylamines, dialkylamines, trialkylamines, and tetraalkylammonium hydroxides such as vinylamine, allylamine, 4-aminobutene, 5-aminopentene and their Nalkyl, dialkyl and trialkylamine derivatives, acrylate and methacrylate esters and dialkylamines, tetraalkylammonium hydroxide groups such as N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylamide, Ν, N, N-trimethylaminoethyl (meth) acrylate, Ν, N, N-trimethylaminoethyl (meth) acrylamide and the like . and mixtures thereof. Cationic types may also include polyelectrolytes based on N, N-dialkyl, N, Ndiallylammonium salts such as dimethyldiallylammonium salts (see, e.g., PCT Publication No. WO 96/17681 and PCT Publication No. WO 96/17681).

• · · · ·

WO 96/15162, both of which are incorporated herein by reference.

Cationic types may also include mildly crosslinked anionic and nonionic basic polymers to which cationic functional groups are covalently attached. Examples of suitable basic polymers include polyacrylamide, (meth) acrylic acid, polyvinyl alcohol, ethylene-maleic anhydride copolymer, isobutylene-maleic anhydride copolymers, polyvinyl ether, polyvinylsulfonic acid, polyvinylpyrrolidone and polyvinyloubromolite, and hydrolyzed rimethylmorpholine. Cationic types may also include polyethyleneimine and derivatives thereof (e.g., alkyl derivatives). Cationic types may also include polysaccharide-based polyelectrolytes such as aminoethyl starch, aminoethyl cellulose, dimethylaminoethyl starch, dimethylaminoethyl cellulose, trimethylammonium ethylhydroxy starch, trimethylammonium methylhydroxide cellulose and the like, and polyamine acid-based polyelectrolytes such as polysinin. and other polyelectrolytes that are not prepared from polymerizable unsaturated monomers. See, for example, PCT Publication No. WO 96/15154, which is hereby incorporated by reference. Certain non-basic monomers, usually in small amounts, may also be included in the preparation of the hydrogel-forming absorbent polymers herein.

While the cationic hydrogel-forming absorbent polymer is preferably of one type (i.e. homogeneous), mixtures of cationic polymers can also be used in the present invention.

When used alone for absorbent applications, the cationic hydrogel-forming absorbent polymers have an initial state such that they are 50 to about 95% neutralized. When used as part of a mixed bed of a mixture of ion exchangers, the cationic hydrogel forming the absorbent polymer is from about 50% to about 100%, preferably from about 80% to about 100%. more preferably, from about 90% to about 100% in the non-neutralized basic form. When used as part of a mixed bed of a mixture of ion exchangers, the cationic absorption ion exchange hydrogel-forming polymer is at least partially converted to its neutralized form as a result of the ion exchange salt process. The resulting cationic polymer is reduced to at least at least preferably at least%, more preferably at least 75% and even more preferably 90% converted to its neutralized form as a result of ion exchange.

In order to maximize the mixed bed ion exchange capacity of a mixture of ion exchange hydrogel forming polymers, it is desirable that the cationic absorption hydrogel forming polymer have a high ion exchange capacity per gram. Therefore, it is preferred that the anion exchange capacity of the cationic hydrogel-forming polymer is at least about 4 meq / g, more preferably at least about 6 meq / g, even more preferably at least about 10 meq / g, and even more preferably at least about 15 meq / g, most preferably at least about 20 meq / g.

(2) Anionic polymers

The hydrogel-forming absorbent polymers useful as the anionic polymer (s) typically have multiple anionic functional groups, such as sulfonic acid, especially carboxyl groups. Examples of polymers suitable for use in the present invention include polymers that are prepared from polymerizable, unsaturated, acid-containing monomers. Thus, these monomers include olefinically unsaturated acids and anhydrides containing at least one olefinic carbon-carbon double bond. More specifically, these monomers may be selected from

0

0 0 · 00 · 00 000

0 • 0 00 olefinically unsaturated carboxylic acids and acid anhydrides, olefinically unsaturated sulfonic acids and mixtures thereof. Anionic types may also include polysaccharide-based polyelectrolytes such as carboxymethyl starch and carboxymethylcellulose and polyamino acid-based electrolytes such as polyaspartic acid, as well as other polyelectrolytes that are not prepared from polymerizable unsaturated monomers. For a description of hydrogel-forming polyamine acid polymers, see, for example, U.S. Patent No. 5,247,068, which is hereby incorporated by reference.

Certain non-acidic monomers, usually in small amounts, may also be included in the preparation of the anionic hydrogel-forming absorbent polymers of the present invention. Such non-acidic monomers may include, for example, water-soluble or water-dispersible esters of acid-containing monomers, as well as monomers which contain no carboxylic or sulfonic acid groups at all. Thus, the non-acidic monomers used may include monomers containing the following types of functional groups: carboxylic acid or sulfonic acid esters, hydroxyl groups, amide groups, amine groups, nitrile groups, quaternary ammonium salt groups, aryl groups (e.g., phenyl groups such as those which are derived from styrene monomer) and dienes such as butadiene and isoprene. These non-acidic monomers are well known materials and are described in more detail in, for example, U.S. Patent No. 4,076,663 and U.S. Patent No. 4,062,817, both of which are incorporated herein by reference.

Monomers based on olefinically unsaturated carboxylic acid and carboxylic anhydride include acrylic acids of the acrylic acid alone, methacrylic acid, etacrylic acid, α-chloroacrylic acid, α-cyanoacrylic acid, β-methylacrylic acid (crotonic acid), ·· · · · · α-phenylacrylic acid, β-acryloxypropionic acid, sorbic acid, α-chlorosorbic acid, angelic acid, cinnamic acid, p-chloroscinnamic acid, β-sterylacrylic acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid, aconitic acid maleic acid, fumaric acid, tricarboxyethylene anhydride, and maleic acid.

Olefinically unsaturated sulfonic acid monomers include aliphatic or aromatic vinyl sulfonic acids such as vinyl sulfonic acid, allylsulfonic acid, vinyl toluenesulfonic acid and styrene sulfonic acid, acrylic and methacrylic sulfonic acids such as sulfoethyl acrylate, sulfoethyl methacrylate, sulfopropyl acrylate, sulfopropyl acrylate, sulfopropyl acrylate 2-acrylamide-2-methylpropanesulfonic acid.

Particularly preferred anionic hydrogel-forming absorbent polymers for use herein contain carboxyl groups. These polymers include hydrolyzed starch and acrylonitrile graft copolymers, partially neutralized hydrolyzed starch and acrylonitrile graft copolymers, starch and acrylic acid graft copolymers, partially neutralized starch and acrylic acid graft copolymers, saponified acrylic acid acrylic acid acrylic acid copolymer or acrylic acid acrylate copolymer, crosslinked polymers of any of the foregoing copolymers, polyacrylic acid and slightly crosslinked polyacrylic acid polymers. These polymers can be used either alone or in the form of a mixture of two or more different polymers. Examples of these polymeric materials are disclosed in U.S. Pat. No. 3,661,875, U.S. Pat. No. 4,076,663, U.S. Pat.

U.S. Patent No. 4,093,776, U.S. Patent No. 4,666,983, and U.S. Patent No. 4,734,478.

· · Φ φ φ φ φ · · φ φ φ φ φ φ

The most preferred polymeric materials for use in the manufacture of anionic hydrogel-forming absorbent polymers are the slightly crosslinked polyacrylic acid polymers and their starch derivatives. Crosslinking makes the polymer substantially water insoluble and partially determines the absorbent capacity and extractable polymer content parameters of the hydrogel-forming absorbent polymers. The crosslinking processes of these polymers and typical crosslinking agents are described in more detail in US Patent No. 4,076,663.

While the anionic hydrogel-forming absorbent polymer is preferably of one type, i.e. homogeneous, mixtures of anionic polymers can also be used in the present invention. For example, mixtures of graft copolymers of starch with acrylic acid and slightly crosslinked polyacrylic acid polymers can be used according to the invention.

When used as such for absorbent applications, the hydrogel-forming anionic absorbent polymers are initially neutralized at about 50 to about 95%, preferably about 75%. A particularly preferred slightly crosslinked polyacrylic acid hydrogel-forming polymer is preferably about 25% in the form of non-neutralized acrylic acid and about 75% in the form of neutralized acrylate (i.e., sodium acrylate). When used as part of a mixed bed of an ion exchange mixture, the anionic hydrogel-forming absorbent polymer has an initial state of about 50% to about 100%, preferably about 80% to about 100%, even more preferably from about 90% to about 100%. non-neutralized acid form. Thus, the slightly crosslinked hydrogel-forming polyacrylic acid polymer is most preferably based on a state of from about 90% to about 100% in the non-neutralized form of acrylic acid. When used as part of a mixed bed of a mixture of ion exchangers, the anion exchange hydrogel-forming polymer is at least partially converted

9999 9999

9 · · · ·

9 9 · 9 9 * 9 9

99 99 99 to its neutralized form as a result of ion exchange. The resulting anionic polymer is preferably at least 50%, more preferably at least 75% and even more preferably at least 90% converted to its neutralized form as a result of ion exchange.

In order to maximize the mixed bed ion exchange capacity of the mixture of ion exchange hydrogel-forming polymers, it is desirable that the anionic cation exchange hydrogel-forming polymer have a high cation exchange capacity per gram. Therefore, it is more preferred that the cation exchange capacity of the anion exchange hydrogel-forming polymer be at least about 4 meg / g, more preferably at least about 8 meq / g, and even more preferably at least about 10 meq / g, most preferably at least about 13 meq / g.

(3)> Mixture and common material properties

In order to maximize the ion-exchange capacity of the mixed-bed from a mixture of ion-exchange hydrogel-forming polymers, it is desirable that the mixed-bed mixture includes approximately the same equivalents of anion-exchange and cation-exchange capacities, but it may be desirable to have some more equivalents of anionic or cation exchange hydrogel-forming polymer. compensate for differences in pK to compensate for differences in neutralization to change the pH (e.g., acidify) of the urine where the ion exchange has taken place, etc. the capacities of the components, i.e., the anionic and cation exchange hydrogel-forming polymers. Thus, for example, an ion exchange composition comprising about the same equivalents of a strongly acidic anionic hydrogel-forming polymer having a capacity for BBBB BBBB

Β Β Β Β Β Β Β Β Β ΒΒ ΒΒ ΒΒ Β Β Β Β Β Β Β Β Β Β Β Β Β

A cation exchange of about 4.8 meq / g and a strongly basic cationic hydrogel forming polymer having an anion exchange capacity of about 7.0 meq / g would comprise about 0.65 parts anionic hydrogel forming polymer and about 0.35 parts a cationic hydrogel-forming polymer with a mixed bed ion exchange capacity of about 3.1 meq / g. It is preferred that the mixed bed ion exchange capacity of the hydrogel-forming polymer mixture be at least about 2 meq / g, more preferably at least about 4 meq / g, even more preferably at least about 6 meq / g, and most preferably at least about 7 meq / g.

The cationic and anionic hydrogel-forming absorbent polymers useful in the present invention in neutralized form all have relatively high PUP, SFC and PHL values. The PUP capacity at a pressure of 4.8 kPa (0.7 psi) after 60 minutes is preferably at least about 23 g / g, more preferably at least 25 g / g, most preferably at least 30 g / g. The SFC is preferably at least about 30 10 ^-7 cm ³ s / g, more preferably at least about 50 χ 10 ^-7 cm ³ s / g, most preferably at least about 100 χ 10 ⁷ cm ³ s / g. The PHL is preferably at least about 0.15, more preferably at least about 0.20, most preferably at least about 0.25.

In a mixed bed hydrogel-forming polymer blend of one type, the hydrogel-forming polymer of one type may have a higher crosslink density than the hydrogel-forming polymer of the other type, for example, to advantageously affect the gel properties (e.g., PUP, SFC, PHL) of the mixture.

The cationic and anionic hydrogel-forming absorbent polymers useful in the present invention may have a size, shape, or morphology that varies widely. These polymers may be in the form of particles that do not have a large-to-small dimension (i.e. granules, largest dust particles, interparticle aggregates, interparticle crosslinked aggregates, etc.) and may be in the form of fibers,

ΦΦ φ · · · · • • φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ

Even sheets, foils, foams, flakes and the like. hydrogel-forming absorbent polymers may also include low level compositions of one or more additives, such as silica powder, surfactants, adhesive, binders, and the like. The components in the composition may be physically or or chemically combined to form such that the hydrogel-forming polymer component and the non-hydrogel-forming polymer additive are not readily physically separable.

The hydrogel-forming absorbent polymers may be substantially non-porous (i.e., have no internal porosity) or may have considerable internal porosity.

For the particles as described above, the particle size is defined as the dimension determined by sieve size analysis. Thus, for example, a particle that remains on a US standardized screen for testing having 710 micron apertures (i.e., screen # 25 according to the U.S. serial screen) is considered to have a size greater than 710 microns, a particle that passes through the screen with a 710 micron aperture and remain on a 500 micron sieve (i.e. No. 35 as indicated in the US) is considered to have a particle size between 500 and 710 microns and a particle that passes through a 500 micron sieve is considered a particle having a size of less than 500 microns. The weight median particle size of a given sample of hydrogel-forming absorbent polymer particles is defined as the particle size that divides the sample into two halves by weight, i.e., by weight, one-half of the sample has a particle size smaller than the median size The particle size is greater than the median particle size. To determine the mass median particle size when a 50% by weight value does not match the size of an orifice according to a standardized US test sieve, a standard particle size distribution method is generally used.

99 99

9

9

9,999,999

9 9 9

90 99

98 • 9 9 9

9 • 9 • 9

9999 9999 (where the cumulative weight percent of a sample of particles remaining or passed through a sieve opening against a sieve opening of a given probability paper is plotted. These methods for determining the particle size of a hydrogel-forming absorbent polymer are further described in U.S. Pat. No. 5,061,259, which is hereby incorporated by reference.

For the hydrogel-forming absorbent polymer particles useful in the present invention, the particles will generally range from about 1 to about 200 microns, more preferably from about 20 to about 1000 microns. The mass median particle size will generally be from about 20 to about 1500 microns, more preferably from about 50 microns to about 1000 microns, and even more preferably from about 100 to about 800 microns.

Within these size ranges, it may be preferable to select either larger or smaller particles depending on the need for faster or slower absorption kinetics. For example, for non-porous particles, the swelling rate will generally decrease as the particle size increases. It may also be advantageous to select either larger or smaller particles or narrower cuts of the size (fraction) of the larger or smaller block polymer particles to increase porosity (i.e. increase PHL), increase gel layer permeability (i.e., increase conductivity for saline flow ( SFC)), improved wick effect, etc. For particles of some hydrogel-forming absorbent polymers, it has been found that sections of narrower size ranges, generally containing larger particle sizes within the above specified size ranges, have higher SFC values without any significant degradation of other absorbent polymer properties such as is PHL, PUP, and extractable polymer level. Thus, for example, it may be useful to use a size slice having a weight median size in the range of about 500 to about 710 microns, with only minimal particle fractions having sizes of either greater than about 710 microns or less than about 500 microns.

• ·

Alternatively, a wider section size can be used, the particles generally having a size ranging from about 300 microns to about 800 microns.

Within these size ranges, it may be desirable to select particles having an internal porosity capable of contributing to faster swelling of the hydrogel-forming polymer by body fluids. The intrinsic porosity in the hydrogel-forming polymer particle can also contribute to the PHL value of the resulting hydrogel layer. Changes in this PHL component may have less impact on some PHL-dependent fluid handling properties (e.g., SFC) than changes in the PHL component resulting from voids between the swollen hydrogel-forming polymer particles in the hydrogel layer.

A mixed bed of a mixture of ion-exchange hydrogel-forming polymer in high-concentration absorbent cores cannot rely on the flow of solution, stirring, etc. to aid ion transport between particles and accelerate the rate of ion exchange. Therefore, it is desirable to have particles of such morphology that are capable of assisting rapid ion exchange kinetics. Desirable morphologies include large surface fibers and mixed bed aggregates with a large surface area of the particles (e.g., small and / or porous). Desirable morphologies also include (1) particles of, e.g., anionic hydrogel-forming polymer that contain smaller discontinuous domains of, e.g., a cationic hydrogel-forming polymer, (2) particles that contain the bicontinuous domains of both anionic and cationic hydrogel-forming polymers, and (3) ) particles of, eg, a hydrogel-forming anionic polymer, which is coated or coated with a surface layer of, eg, a hydrogel-forming cationic polymer. Other desirable properties of the mixed bed velocity of a mixture of ion exchange hydrogel-forming polymers may include the formation of a mixture of ion exchange hydrogel-forming polymers.

- 32 - ···· ......... ·· ·· l

include a very high free swelling rate and a very high absorption rate under conditions and pressures for measuring PUP.

Certain types of shape, aggregates, layered structures, microdomains, etc. may be beneficial to reduce pH extremes when combinations of strong and weak hydrogel-forming ion-exchange polymers are used. Thus, for example, a layered or microdomain structure where the strongly basic anion exchange hydrogel-forming absorbent polymer is completely enclosed in a weakly acidic, cation exchange hydrogel-forming polymer can provide rapid neutralization and thus reduce diffusion of free OH 'to the outside of the particle.

b. Physical Properties (1) Pressure Behavior (PUP)

An essential parameter of the mixed beds of the ion exchange hydrogel blend forming absorbent polymers useful in the present invention is their maximum possible absorption capacity under high limiting pressure. This maximum possible absorption capacity is defined by the mixed bed conditions of the hydrogel-forming ion exchanger mixtures as a capacity given by Performance Under Pressure (PUP). The PUP capacity measures the ability of a high bed mixed bed zone or layer from a blend of hydrogel-forming absorbent polymers to absorb body fluids at pressures in use. In one aspect, the present invention relates to the use of a mixed bed of a mixture of hydrogel-forming polymers which exhibits improved absorbency of the urine electrolyte solution as compared to a comparable mixture of cationic and anionic polymers when each is used in its neutralized form. The blended bed of the blend of hydrogel-forming polymers will preferably exhibit improved PUP capacity compared to a comparable blend of basic non-neutralized polymers when the PUP is measured at a limiting pressure of at least about 2 kPa (0.3 psi), preferably 4. , 0.7 psi, and even more preferably 1.4 psi. It is preferred that a relatively high PUP capacity be achieved over a period of time that is less than, preferably significantly less than the period of use (e.g., overnight) of the mixed bed products of the ion exchanger mixture. In this regard, the mixed bed of hydrogel-forming polymers will exhibit improved absorbency when the PUP capacity is measured over 225 minutes, preferably over 60 minutes, even more preferably over 5 minutes. The improved mixed bed of the ion-exchange hydrogel-forming polymer blend of the present invention will preferably be capable of absorbing at least about 20%, preferably at least about 50%, even more preferably at least about 100% more synthetic urine than a comparable blend of basic anionic and cationic polymers hydrogel when each is in its neutralized form. The improved mixed bed of the hydrogel-forming ion exchange polymer composition of the present invention will preferably be capable of absorbing at least about 20%, more preferably at least about 50%, even more preferably at least about 100% more synthetic urine than any of the basic anionic or cationic blend. hydrogel-forming polymers in their neutralized form.

In another aspect, the present invention relates to a mixed bed of a mixture of hydrogel-forming ion exchange polymers having a PUP capacity after 225 minutes (preferably 60 minutes) at a limiting pressure of 0.7 psi of at least 25 g / g, more preferably at least 40 g / g and even more preferably at least 50 g / g. Preferably, the absorbent capacity of the mixed bed PUP from the mixture of hydrogel-forming ion exchange polymers after 225 minutes (preferably 60 minutes) at a limiting pressure of 1.4 psi is at least 20 g / g, more preferably at least 30 g / g. more preferably at least 40 _ 34 - ............. * '”/

g / g. The absorbent capacity of the PUP after 225 minutes (preferably 60 minutes) at a pressure of 2 kPa (0.3 psi) is preferably at least 30 g / g, more preferably at least 45 g / g and even more preferably at least 60 g / g. When the hydrogel-forming absorbent polymers are incorporated into the absorbent member at high concentrations, the polymers must be able to absorb large amounts of body fluids for a reasonable period of time under pressures in use. Otherwise, the absorbent member will be less effective in absorbing fluid, i.e., distributing fluid from receiving components that provide a temporary ability to retain the fluid therein. When this occurs, it can be assumed that the absorbent core is left with insufficient temporary holding capacity to accommodate subsequent body fluid expulsions and may leak prematurely. Also, in order for the absorbent core to be capable of having a high storage capacity at the minimum weight and thickness of the absorbent core, a mixed bed of a mixture of hydrogel-forming ion exchange polymers needs a relatively high PUP capacity. Absorbent hydrogel-forming polymers with a relatively high PUP capacity are also needed to form economical absorbent cores.

The pressures that act on the hydrogel-forming absorbent polymers include both mechanical pressures (eg, exerted by the user's weight and movements, contact, etc.) and capillary pressures (eg, resulting from the receiving component or components in the absorbent core that temporarily retains fluid prior to absorbed by the hydrogel-forming absorbent polymer.) It is believed that a total pressure of about 5 kPa (0.7 psi) is the sum of these pressures on the mixed bed of hydrogel-forming absorbent polymers as it absorbs body fluids under conditions of use but under conditions of use. The absorbent hydrogel-forming polymer as it absorbs body fluids may also experience both higher and lower pressures (e.g., in the range of about 2 kPa (0.3 psi) to about 9.7 kPa). (1.4 psi) Therefore, it is desirable that a mixed bed of a mixture of hydrogels forming ion exchange The polymers of the present invention had a high PUP capacity in the pressure range from about 2 kPa (0.3 psi) to about 9.7 kPa (1.4 psi).

In a mixed bed of a mixture of hydrogel-forming ion exchange polymers, the rate of absorption of PUP may be affected by the rate of ion exchange kinetics. In a PUP experiment, this can sometimes lead to a lower rate of PUP uptake in a mixed bed of a hydrogel-forming ion-exchange polymer blend than a comparable blend of starting anionic and cationic hydrogel-forming polymers where the hydrogel-forming polymers are in their neutralized forms. By comparable composition is meant a composition wherein the weight ratios of anionic and cationic hydrogel polymers are approximately equal. As a result, it may be reasonable to allow a slightly longer period for the absorption of PUP than the 60 minutes used for PUP measurements, as described, for example, in U.S. Patent No. 5,562,646. The reasonable time period for a mixed bed of hydrogel-forming ion exchange polymer blend may be up to about 225 minutes. Therefore, it is desirable that the mixed bed of the hydrogel-forming ion exchange polymer composition of the present invention has a high PUP capacity for a measurement period of about 225 minutes, preferably for a measurement period of about 60 minutes, and most preferably for a measurement period of about 5 minutes.

The method for determining PUP for these hydrogel-forming absorbent polymers is described in the Test Method section herein.

(2) Porosity of the hydrogel zone or layer

Another important parameter of the mixed bed of a mixture of hydrogel-forming ion exchange absorbent polymers useful in the present invention is the openness or porosity of the hydrogel zone or layer formed when the polymers are swollen in body fluids under restrictive pressure. It is believed that when hydrogel-forming absorbent polymers are present at high concentrations in the absorbent member and then swell to form hydrogel under pressure, the hydrogel boundaries come into contact and internal voids in this high-concentration region will generally be bound by the hydrogel . When this occurs, it is believed that the openness or porous properties of this region generally reflect the porosity of the hydrogel zone or layer formed from the absorbent hydrogel-forming polymer itself. The term porosity as used herein means a portion of the volume (dimensionless) that is not occupied by the solid material. See JM Coulson et al., Chemical Engineering Vol. 2, 3 ^rd Edition, Pergamon Press, 1978, p. 126. In a hydrogel zone or layer formed entirely from a hydrogel-forming absorbent polymer, the porosity is that portion of the volume of the zone or layer that is not occupied by the hydrogel. In the region of the hydrogel-containing absorbent member as well as other components, the porosity is a portion of the volume of the region (also sometimes referred to as the void volume that includes the internal volume between the swollen hydrogel-forming polymer plus all volume in the swollen hydrogel-forming polymer) which is not occupied by the hydrogel or other solid components (eg fibers). The porosity of the absorption region is equal to the ratio of the void volume in the region to the total volume of the region.

Porosity is defined herein by the Porosity of Hydrogel Layer (abbreviated PHL) of the hydrogel-forming absorbent polymer. PHL measures the ability of the formed hydrogel zone or layer to remain open so that body fluids can be received and distributed under pressures in use. Furthermore, it is believed that increasing the porosity of these swollen highly concentrated areas to higher levels can provide excellent absorption and absorption properties.

the absorbent member and the absorbent core when handling the fluid, thereby reducing fluid leakage, particularly in cases of high fluid loading. Desirably, the void volume per gram occupied by voids in the hydrogel zone or layer is close to or even exceeds the void volume per gram having conventional offered and distributed materials such as cellulose wadding. (Higher PHL values also reflect the ability of the formed hydrogel to absorb body fluids under normal use conditions.)

The porosity of the hydrogel zone or layer is also important as it affects the desired wettability or gravimetric absorption capacity (i.e., the PUP capacity). In general, the additional void volume created by the higher porosity at the limiting pressure directly contributes to the higher value of the PUP capacity. It can also contribute to a higher PUP capacity due to its impact on the chemical composition of the fluid contained in the voids in the hydrogel layer. Thus, for example, increasing the void volume in the hydrogel layer may reduce the concentration of salts (eg, by dilution), including simple salts resulting from body fluids and / or hydrogel-forming absorbent polymer, as well as polymer salts (eg, extractable polymer), formed from a hydrogel-forming polymer. which tend to be secreted from the swollen hydrogel-forming absorbent polymer and concentrated in voids in the hydrogel zone or layer. Salts concentrated in these voids can reduce the swelling of the hydrogel-forming absorbent polymer and thus reduce the capacity of the PUP. Increased porosity may decrease the concentration of these precipitated salts and thereby increase the capacity of PUP.

The porosity of the hydrogel zone or layer is also important as it affects the permeability (i.e., the SFC values) of the hydrogel zone or layer. Higher porosity contributes significantly to higher permeability. In contrast, a hydrogel zone or layer with a relatively low porosity is less likely to have a high permeability.

Porosity of the hydrogel zone or layer can also be important as a consequence of the wick effect. The high specific surface area required for a hydrogel layer or zone capable of having a good wick effect (e.g., aspirating fluid as a wick up, thereby draining the fluid from the touching receiving layer, etc.) is desirably accompanied by high porosity so as to has reached or maintained an acceptable wicking rate by means of a wick effect.

The porosity of the hydrogel zone or layer may also be important as a result of its impact on the properties around the swelling rate. The high surface area size (e.g., inner surface area size) required of the unrestricted hydrogel-forming absorbent polymer to swell rapidly in body fluids is accompanied by high porosity (including intrinsic porosity for hydrogel-forming polymers having an inner surface area), in the hydrogel a zone or layer formed therefrom under restrictive pressure. Desirably, as a result of this high porosity, the swelling rate achieved under the limiting pressure of the hydrogel-forming polymers in the hydrogel layer reached the swelling rate achieved with the hydrogel-forming absorbent polymer when swelling without limitation with excess body fluid.

The increased osmotic driving force for swelling of the mixed bed of hydrogel-forming ion exchange polymer can also be used to increase the PHL value. Thus, for example, the degree of crosslinking, preferably the level of crosslinking of the surface of its forming anionic or or cationic hydrogel-forming polymers in a mixed bed of the hydrogel-forming ion-exchange polymer blend.

·· ·· »· · <

(· · (···) can be increased enough to ensure that the mixed bed PUP capacity of the mixture remains about the same as that of a comparable blend of anionic and cationic hydrogel-forming polymers in their neutralized forms where the cross-linking rate has not been increased. have a mixed bed of the hydrogel-forming ion-exchange polymer blend of approximately the same PUP value, but a higher PHL value than a comparable blend of anionic and cationic hydrogel-forming polymers in their neutralized forms where the cross-linking rate has not been increased.

The mixed bed PHL of the mixture of hydrogel-forming ion exchange absorbent polymers useful in the present invention is preferably increased by at least about 0.05, more preferably by at least about 0.1, as compared to a comparable blend of forming anionic and cationic polymers the hydrogel in its neutralized forms, wherein the crosslinking rates are such that the neutralized mixture has a PUP absorption capacity (4.8 kPa, i.e. 0.7 psi, elapsed 225 minutes) approximately equal to the PUP absorption capacity of the ion exchange composition.

The mixed beds of a mixture of hydrogel-forming ion exchange absorbent polymers useful in the present invention preferably have a PHL of at least about 0.15, more preferably about 0.18, even more preferably at least about 0.20, and most preferably at least about 0.25. The method for determining the PHL of these hydrogel-forming absorbent polymers is set forth in the Test Method section below.

(3) Conductivity for brine flow (SFC)

Another important parameter of the mixed beds of hydrogel-forming ion exchange absorbent polymer blends useful in the present invention is their permeability or flow conductivity when swollen by body fluids to form a hydrogel zone or layer. . This permeability or flow conductivity is defined herein in terms of the Saline Flow Conductivity (SFC) conductivity value of absorbent hydrogel-forming polymers. The SFC measures the ability of the formed hydrogel zone or layer to transport or distribute body fluids at pressures in use. It is believed that when hydrogel-forming absorbent polymers are present at high concentrations in the absorbent member and then swell to form the hydrogel at pressures in use, its permeability or flow conductivity are properties that generally reflect the permeability or conductivity of the hydrogel zone flow or layers formed from hydrogel-forming absorbent polymers themselves. Furthermore, it is believed that increasing the permeability of the swollen highly concentrated regions to a level that approaches or even exceeds conventional recovered or distributed materials, such as cellulose wadding, can provide excellent fluid handling properties for the absorbent member and absorbent core, thereby reducing the number of leaks, especially in the case of high fluid loads. (Higher SFCs also reflect the ability of the formed hydrogel to absorb body fluids under normal conditions of use.)

The increased osmotic driving force of the swelling of the mixed bed of hydrogel-forming ion-exchange polymer can also be used to increase the SFC value. Thus, for example, the level of cross-linking, in particular the level of surface cross-linking of the anionic and / or cationic hydrogel-forming polymers in the mixed bed of the ion exchange hydrogel-forming polymer composition can be increased enough to keep the PUP mixed bed capacity of the mixture roughly the same as the comparable composition. ·

0 0 0 0 0

0 0 0 0 · <· 0.000.000

0 · ·

00 ·· »0 · 0

The anionic and cationic hydrogel-forming polymers in their neutralized forms where the level of crosslinking has not been increased. For example, as a result of increased crosslinking, the mixed bed of the hydrogel-forming ion exchange composition may have approximately the same PUP, but a higher SFC than a comparable blend of anionic and cationic hydrogel-forming polymers in their neutralized forms where the level of crosslinking has not been increased.

The SFC for the mixed bed of hydrogel-forming ion exchange absorbent polymers useful in the present invention is preferably increased by at least about 50%, more preferably by at least about 100% relative to a comparable blend of anionic and cationic hydrogel-forming polymers in their neutralized forms, The crosslinking is such that the neutralized mixture has an absorption capacity of PUP (4.8 kPa, i.e. 0.7 psi, after 225 minutes) approximately equal to the capacity of the ion exchange mixture.

The SFC for the mixed bed of hydrogel-forming ion exchange absorbent polymers useful in the present invention is preferably at least about 30 x 10 ^-7 cm ³ s / g, more preferably at least about 100 x 10 ^-7 cm ³ s / g and most preferably at least about 300 χ 10 ' ⁷ cm ³ s / g. The method for determining the SFC of these hydrogel-forming absorbent polymers is set forth in the Test Method section below.

(4) Extractable polymer)

Another important parameter of the hydrogel-forming anionic and cation exchange ion exchange polymers useful in the present invention is the proportion of extractable polymeric material contained therein after neutralization. See U.S. Patent No. 4,654,039, revised edition as US RE 32,649. Many hydrogel-forming absorbent polymers contain significant proportions of t-phase.

44

I · Φ 4 · 4 4 4 4 4 4 4

44 of the extractable polymeric material. The extractable polymeric material may be leached from the resulting hydrogel by body fluids (e.g., urine) during the period in which the body fluids remain in contact with the hydrogel forming. It is believed, with the absorbent polymer, that such extracted polymeric material can change both chemical parameters (e.g.

osmolarity), as well as physical body fluids to the extent that parameters (e.g., viscosity) are absorbed more slowly and less well retained in the hydrogel. This polymer-contaminated fluid is also less readily transportable by the absorbent member. Such a situation may contribute to undesirable and premature leakage of body fluid from the absorbent article. It is therefore desirable to use hydrogel-forming absorbent polymers with lower proportions of extractable polymeric material.

transport

The importance of not adversely affecting the actual absorption or retention of body fluids by the swollen hydrogel-forming polymer or easy body fluids through the regions of the swollen absorbent member seems particularly true because (a) the amount of polymer in the absorbent member increases, (b) the amount or (c) the localized concentration of the polymer in the absorbent member is increased. Thus, for example, it is believed that at higher local concentrations of absorbent polymer by the absorbent member, there are smaller interstitial regions (i.e., outside the extractable polymeric material), thereby tending to increase its concentration in these interstitial regions. interstitial areas.

forming a hydrogel (volume of liquid in the hydrogel) to be diluted

The undesirable impact of these high extractable polymer fractions on the absorption or retention of fluid in absorbent 4 4 4 4 4 4 4 4 4 4 4444 4444 444444 . · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·> SFC values. Thus, for example, it is not uncommon for hydrogel-forming absorbent polymers having higher proportions of extractable polymeric material to have a PUP capacity value that decreases with time (i.e., is lower after 225 minutes than after 60 minutes). This decrease in fluid absorption or retention over time appears to be at least in part due to the presence of higher proportions of extractable polymer that alter the chemical properties of the interstitial fluid. Also, it is not uncommon for a hydrogel-forming absorbent polymer having higher proportions of extractable material to have an SFC value that is initially lower and then increases over time to a greater extent than that of a comparable hydrogel-forming absorbent polymer having a lower level of extractable polymer. It is believed that the lower initial SFC value for the more extractable polymeric material at least in part results from the higher initial viscosity for the interstitial fluid.

Accordingly, for the hydrogel-forming anionic and cation exchange absorbent polymers useful in the present invention, it is preferred that the proportion of extractable polymer after neutralization to about 75% is about 15% or less, more preferably about 10% or less, and most preferably about 7% or less of the total polymer. Methods for determining the amounts of extractable polymer after neutralization of these anionic and cation exchange hydrogel-forming absorbent polymers are further discussed in the Test Methods section herein.

• · ·> I I t t t t.

(5) Gel volume

Another parameter that may be important for the anionic and cation exchange hydrogel-forming absorbent polymers useful in the present invention is the gel volume after neutralization. As used herein, the gel volume of the hydrogel-forming absorbent polymer is defined as its free-swellable absorbent capacity on free swelling when swollen in excess Jayco synthetic urine and neutralized to 75%. This provides a measure of the maximum absorption capacity of the polymer under conditions of use where the pressures on the polymer are relatively low. Methods for determining gel volumes of these hydrogel-forming polymers are given in the Test Method section below.

It is preferred that the ion exchange hydrogel forming the anionic absorption and cationic polymers have a relatively high gel volume upon neutralization. This allows the polymer to absorb a greater amount of body fluids under conditions of use where the pressures on the polymer are low. It is preferred that the gel volume of the hydrogel-forming absorbent polymers of the present invention is at least about 20 g / g, preferably at least 25 g / g, and most preferably at least about 30 g / g. These gel volumes are generally in the range of from about 20 to about 100 g / g, in particular from about 25 to about 80 g / g, and most typically from about 30 to about 70 g / g.

(6) Gel Strength

Another parameter that may be important for the hydrogel-forming anionic and cation exchange absorption polymers useful in the present invention is the gel strength after neutralization. As used herein, gel strength refers to the tendency of a hydrogel formed from an absorbent polymer to deform or to flow under stress in use. The gel strength should be such that the hydrogel does not deform and does not unacceptably fill the voids between the hydrogel and the other components in the absorbent member. Generally, an increase in gel strength will result in an increase in the permeability and porosity of the hydrogel zone or layer formed from the absorbent hydrogel-forming polymer. The method for determining the gel strength after neutralization of the anionic and cation exchange hydrogel-forming ion exchange absorbent polymers of the present invention is set forth in the Test Method section below.

While maximizing gel strength is not critical as other properties, such as PHL, PUP capacity, and SFC, it is preferred that the anionic and cation exchange hydrogel-forming absorbent polymers of the present invention have a relatively high gel strength upon neutralization. This increases the ability of the formed hydrogel to withstand deformation under pressure in use. It is preferred that the gel strength after neutralization of the anionic and cation exchange hydrogel-forming polymers of the invention is at least about 10,000 dynes / cm ² , more preferably at least 20,000 dynes / cm ^2, and most preferably at least about 40,000 dynes / cm ² .

c. Production methods

The hydrogel-forming base absorbent polymer may be formed by any of the conventional methods. Typical and preferred processes for the production of these polymers are described in the corrected edition of U.S. Patent RE 32,649, U.S. Patent 4,666,983 and U.S. Patent 4,625,001, all of which are incorporated herein by reference.

Preferred methods for forming the hydrogel-forming base absorbent polymer are those which:

- 4 6 - ·· ♦ ····· ··· ··

include aqueous solution or other solution polymerization methods. As described in the aforementioned revised edition of US Patent RE 32,649, aqueous solution polymerization involves the use of an aqueous reaction mixture to effect polymerization. The aqueous reaction mixture is then subjected to polymerization conditions sufficient to form a substantially water insoluble, slightly crosslinked polymer mixture. The mass of polymer formed can be pulverized or chopped to form individual particles.

One element of the skeleton should be about 100

More specifically, the aqueous solution polymerization method for making a hydrogel-forming absorbent polymer comprises preparing an aqueous reaction mixture in which the polymerization of the reaction mixture is carried out is a monomer that forms the hydrogel-forming absorbent polymer formed. The reaction mixture will generally include parts by weight of monomer. Another component of the aqueous reaction mixture is a crosslinking agent. Crosslinking agents useful in forming the hydrogel-forming absorbent polymer of the present invention are described in more detail in the above-cited, corrected US Patent RE 32,649, US Patent 4,666,983, and US Patent 4,625,001. The crosslinking agent will generally be present in the aqueous reaction mixture. in an amount of from about 0.001 mole percent to about 5 mole percent, based on the total moles of monomer present in the aqueous mixture (about 0.01 to about 20 parts by weight based on 100 parts by weight of monomer). An optional additional component of the aqueous reaction mixture may be a free radical initiator including, for example, peroxygen compounds such as sodium, potassium and ammonium persulphates, capryl peroxide, benzoyl peroxide, hydrogen peroxide, peroxides, tertiary butyldiperphthalate, cumene hydrotercial butyl perbenzoate, sodium peracetate and sodium percarbonate. Other optional components of the aqueous reaction comonomer comprising esters of the mixture may be various unsaturated monomers containing acidic functionalities or containing no carboxylic or amine functional groups.

• ·

other comonomers of sulphonic sky

The aqueous reaction mixture is subjected to polymerization conditions which are capable of producing substantially water-insoluble but water-swellable, absorbent, slightly crosslinked hydrogel-forming polymers in the mixture. Polymerization conditions are also discussed in more detail in the three above-mentioned patents. These polymerization conditions generally include heating (thermal activation methods) to a polymerization temperature of from about 0 ° C to about 100 ° C, more preferably from about 5 ° C to about 40 ° C. The polymerization conditions under which the reaction mixture is maintained may also include, for example, subjecting the reaction mixture or part thereof to some conventional form of radiation that it activates by polymerization. Radioactive, electron, ultraviolet, or electromagnetic radiation are alternative conventional polymerization methods.

The functional groups formed in the non-neutralized hydrogel-forming absorbent polymer, the aqueous reaction mixtures, can be either partially or fully neutralized.

The neutralization may be carried out either before or after the polymerization by any conventional method that results in at least about 25 mole percent and more preferably at least about 50 mole percent neutralization of the total monomer used to form the polymer. The anionic hydrogel-forming polymers are neutralized by a salt-forming cation. Such salt-forming cations include, for example, alkali metals, ammonium, substituted ammonium, and amines as described in further detail in the above-referenced U.S. Patent RE 32,649, described above. Cationic hydrogel-forming absorbent polymers are typically neutralized with strong monovalent acids such as HCl. In some polymerization reactions, it may be advantageous because of the reaction mechanism to polymerize the monomer in either neutralized form

Φ φ · · · φ φ φ «φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ neutralized.

While it is preferred that particular versions of the hydrogel-forming absorbent polymer be produced using an aqueous solution polymerization process, it is also possible to carry out the polymerization process using multiphase polymerization production processes such as inverse emulsion polymerization or inverse suspension polymerization processes. In inverse emulsion polymerization or inverse suspension polymerization processes, the aqueous reaction mixture as described above is suspended in the form of tiny droplets in a matrix of a water-insoluble inert organic solvent such as cyclohexane. The resulting hydrogel-forming absorbent polymer particles are generally spherical in shape. Inverse suspension polymerization processes are described in more detail in U.S. Patent 4,340,706, U.S. Patent 4,506,052, and U.S. Patent 4,735,987, all of which are incorporated herein by reference.

Surface crosslinking of the initially formed polymers is the preferred process for obtaining absorbent hydrogel-forming polymers having relatively high PHL, PUP capacity and SFC values. Absorbent hydrogel-forming polymers that are surface-cross-linked generally have higher PHL, PUP, and SFC capacities than those for polymers having a comparable degree of functional cross-linking, but are free from surface cross-linking. Without being limited to any theory, it is believed that surface crosslinking increases the deformation resistance of absorbent hydrogel-forming polymeric surfaces, thereby reducing the degree of contact between adjacent polymer surfaces when the resulting hydrogel is deformed by external pressure. The degree of increase in PHL, PUP capacity, and SFC values by surface cross-linking depends on relative rates, and Φ ΦΦΦ Φ Φ 4

- 49 distributions of internal and surface crosslinking and the specifics of the chemistry and surface crosslinking process.

Functional crosslinks are those which are active and contribute to the increase in the modulus of absorbent hydrogel-forming polymers. The gel volume generally provides a reasonable measure of the overall degree of functional cross-linking in a hydrogel-forming absorbent polymer, and the cross-linking rate is believed to be the only significant variable. The gel volume is generally inversely dependent on the degree of crosslinking. Other means of determining the overall level of functional cross-linking include measuring the shear modulus and the modulus of elasticity of the resulting hydrogel formed by the swollen polymer.

The hydrogel-forming surface-cross-linked absorbent polymers have a higher degree of cross-linking near the surface than inside. The word surface as used herein describes the outwardly facing edge portions of particles, fibers, etc. For porous hydrogel-forming absorbent polymers (eg, porous particles, etc.), exposed inner edges may also be included. By high degree of crosslinking on the surface is meant that the degree of functional crosslinking of the hydrogel-forming absorbent polymer near the surface is generally higher than the degree of functional crosslinking of the polymer inside.

are swollen

The gradient of crosslinking from surface to interior can vary in both depth and profile. Thus, the depth of surface crosslinking may, for example, be shallow with a relatively sharp transition to a lower degree of crosslinking. Alternatively, for example, the depth of surface crosslinking may be a significant proportion of the dimensions of the absorbent hydrogel-forming polymer with a wider transition.

· “Ta ta ta ta ta ta ta ta ta ta ta ta ta ta ta ta ta ta ta« «« ««

Depending on the size, shape, porosity and functional considerations, the degree and gradient of surface crosslinking may vary in a given hydrogel-forming absorbent polymer. For particular hydrogel-forming absorbent polymers, surface crosslinking may vary with particle size, porosity, etc.

Depending on the changes in the surface to volume ratio in the hydrogel-forming absorbent polymer (i.e. between small and large particles), it is not uncommon for the overall level of cross-linking in the material to vary, e.g. greater for smaller particles.

Surface crosslinking is generally achieved after substantially forming the final edges of the hydrogel-forming absorbent polymer, e.g., by milling, extrusion, foaming, etc. However, it is also possible to influence surface crosslinking in parallel with the formation of the final edges. Furthermore, some other marginal changes may occur even after the crosslinking surface bonds have been introduced.

A number of processes for introducing crosslinking surface bonds are described in the prior art. These include those where: (1) a difunctional or polyfunctional reagent (ie, glycerol, 1,3-dioxolane-2-one, polyvalent metal ions, polyquaternary amines) capable of reacting with existing functional groups in the hydrogel-forming absorbent polymer is applied to the surface of the absorbent a hydrogel-forming polymer; (2) a di- or polyfunctional reagent that is capable of reacting with other added reagents and possibly existing functionalities in the hydrogel-forming absorbent polymer so as to increase the degree of crosslinking on the surface is applied to the surface (i.e. the addition of monomer plus crosslinking agent) (initiation of a second polymerization reaction); (3) no additional polyfunctional reagents are added, but other reagents are or are included among the existing components in the hydrogel-forming absorbent polymer either during or after the primary polymerization process so as to: • 9 9 9 9 9 9 9

9 9 9 • 99

51 produced a high degree of cross-linking on or near the surface (e.g., heating to induce the formation of anhydride and / or ester crosslinks between existing polymeric carboxylic acid and / or hydroxyl groups and suspension polymerization processes, wherein the crosslinking agent is present inherently to a higher degree in near the surface); and (4) other materials are added to the surface to induce a higher degree of crosslinking or otherwise reduce the surface deformability of the resulting hydrogel. A combination of these surface crosslinking processes, either concurrently or sequentially, may also be employed. In addition to the crosslinking reagents, other components can be added to the surface to assist in or control the distribution of crosslinking, e.g., dispersion and penetration of the surface by the crosslinking reagents.

For cationic hydrogel-forming polymers, surface crosslinking methods include those where (1) difunctional or polyfunctional reagents (eg, di / polyhaloalkanes, di / polyepoxides, di / polyacid chlorides, di / polytosylalkanes) capable of reacting with existing functional groups in the absorbent polymer the hydrogel-forming polymer is applied to the surface of the hydrogel-forming absorbent polymer; (2) A difunctional or polyfunctional reagent capable of reacting with other added reagents and possibly existing functional groups in the hydrogel-forming absorbent polymer to increase surface cross-linking is applied to the surface (eg, adding monomer and crosslinker and initializing) a second polymerization reaction); (3) no additional polyfunctional reagents are added, but other reactions are initiated or induced between the existing components in the hydrogel-forming absorbent polymer either during or after the primary polymerization process to produce a higher degree of cross-linking on or near the surface, e.g. slurry polymerization, wherein the crosslinker is present inherently to a greater extent near the surface), and (4) other materials are added to the surface to induce a higher degree of crosslinking. • · ·· ··

Crosslinking or otherwise reduced the deformability of the resulting hydrogel surface.

Suitable general methods for carrying out surface crosslinking of hydrogel-forming absorbent polymers of the present invention are described in U.S. Patent 4,541,871, PCT Publication WO 92/16565, PCT Publication WO 90/08789, PCT Publication WO 93/05080, US Patent 4 No. 824,901, U.S. Patent No. 4,789,861, U.S. Patent No. 4,587,308, U.S. Patent No. 4,734,478, U.S. Patent No. 5,164,459, German Patent Application No. 4,020,780 and European Patent Application No. 509,708, all of which are hereby incorporated by reference. link.

can convert neutralized ion exchange

The hydrogel-forming absorbent polymer in the non-neutralized ion exchange form can be converted to its partially neutralized form using standard neutralization procedures. For example, a stoichiometric amount of NaOH and HCl, respectively, in an aqueous solution sufficient to partially neutralize to, for example, 75% may be added to the non-neutralized anionic or cationic hydrogel-forming polymer in aqueous solution, followed by drying to remove added water. Similarly, the hydrogel-forming absorbent polymer is in its non-neutralized form using standard procedures.

For example, a slight stoichiometric excess of HCl or optionally NaOH in aqueous solution may be added to an aqueous suspension of the partially neutralized anionic or cationic hydrogel-forming polymer, followed by solvent exchange to remove excess reagents and water followed by drying to remove solvent residues. In the case of surface-cross-linked hydrogel-forming polymers, these conversion processes can generally be carried out either before or after surface cross-linking. For hydrogel-forming polymers, where surface cross-links are particularly sensitive to pH or exposure to an excess of aqueous solution and / or solvent, the flflfl flflflfl flflfl flflfl flflfl flflfl flflfl flflfl fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll flll it may be preferable to use some conversion procedures prior to crosslinking on the surface.

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

d. Specific examples

Example 1

Preparation of ion exchange and neutralized hydrogel-forming polymers:

A surface-crosslinked, partially neutralized, anionic polymer of sodium polyacrylic acid forming a hydrogel with a relatively high PUP capacity (4.8 kPa, i.e. 0.7 psi; 60 minutes) is obtained from Chemdal Corporation of Palantine, Illionois, USA ( ASAP 2300; batch No. 426152). The sample is sieved on a 50 mesh U.S. sieve to remove particles larger than about 300 microns in diameter (Sample 1-1). About 50 g of the sieved hydrogel-forming polymer is converted to an acid form by suspending the polymer in about 900 mL of distilled and deionized water containing 46.5 g of concentrated HCl (Baker; 36.5-38% HCl). After stirring the suspension for about 1.5 h, the hydrogel-forming polymer is allowed to settle and the supernatant is removed by decantation. After decantation, the solution is replaced with further distilled and deionized water, the suspension is stirred for an additional 30 minutes, the hydrogel-forming polymer is allowed to settle, and the supernatant is removed by decantation. This exchange process is repeated (about eight times) until the pH of the supernatant is in the range of 5-6. After decanting the supernatant, the hydrated hydrogel-forming polymer is sequentially exchanged three times for isopropanol (VWR; laboratory type), three times for acetone (VWR; laboratory type), and once for anhydrous ether (EM Science; laboratory type). The product is transferred to a sheet of Teflon and allowed to dry overnight. After gentle manual pulverization with a laboratory spatula, the product is freeze-dried for about 96 hours to remove any solvent residues. After passing through a 20 mesh U.S. sieve, about 30 g of the acid form of the anionic, ion-exchange polymer of the hydrogel-forming polyacrylic acid are obtained (sample 1-2).

The crosslinked partially neutralized hydrogel-forming N, N-dimethylaminoethyl methacrylate-HCl cationic polymer is prepared by the following procedure. The 1 liter resin-coated cauldron is equipped with a mechanical stirrer, a submersible thermometer, a deep-fried gas dispersion tube for nitrogen blowing, a condenser and a recirculating water bath for temperature control. In a separate beaker, add 45.0 g of dimethylaminoethyl methacrylate (DMAEM; Aldrich 98%) to about 40 ml of distilled and deionized water and cool in an ice bath. In another beaker, add 24 mL of concentrated HCl to about 40 mL of distilled and deionized water and cool in an ice bath. The HCl solution was slowly added to the DMAEM solution to convert the monomer to its HCl salt. The neutralized monomer solution is transferred to a resin kettle which is maintained at T = 22 ° C. In a 0.62 g vial, the crosslinking agent N, N-methylenebisacrylamide (Baker; electrophoresis type) was dissolved in a small amount of distilled and deionized water; the solution is then added to the resin pot. The resulting solution was then purged with nitrogen for about one hour. In separate vials, the initiators dissolved 0.010 g potassium persulfate (Aldrich; 99%) and 0.014 g metabisulfite (Aldrich; 97 +%) in small amounts of distilled and deionized water. The total amount of water is 90 ml. The gas dispersion tube is raised above the surface of the solution, the stirring speed is increased enough to produce a slight swirl, and potassium persulfate and sodium metabisulfite solutions are added dropwise over about five minutes. After about 35 minutes the vortex disappears and a slight increase in temperature is observed. The stirrer is lifted from the solution and the bath temperature is raised to about 50 ° C and allowed to equilibrate overnight. The resulting gel is removed from the resin kettle, chopped into small pieces and transferred to a 2 liter resin kettle equipped with a condenser, a Dean Stark trap, a submersible thermometer and a mechanical stirrer containing about one liter of cyclohexane (EM Science, Omnisolve). . During stirring, the temperature was raised due to reflux and water was removed by azeotropic distillation. Distillation is continued until no more water is removed and the temperature is raised to about 80 ° C. The product is filtered to remove cyclohexane, milled with a Wiley Milli mill and sieved through a 20 mesh US standard screen. The sieved product was allowed to dry overnight at room temperature under vacuum. About 54 g of a partially crosslinked product is obtained.

Ftft ft ftft ft ft ft ft ft ft ft ft ft ft ft ft ft of neutralized cationic polymer N, N-dimethylaminoethyl methacrylate.HCl forming a hydrogel (sample 1-3).

About 35 g of the partially neutralized product is suspended in about 1500 ml of distilled and deionized water, to which about 15.9 g of 50 percent sodium hydroxide (Baker; reagent analyzed) is added. After stirring the suspension for about 1.5 h, the hydrogel-forming polymer is allowed to settle and the supernatant is removed by decantation. After decantation, the solution is replaced with further distilled and deionized water, the suspension is stirred for an additional 30 minutes, the hydrogel-forming polymer is allowed to settle, and the supernatant is removed by decantation. This exchange process is repeated (about eight times) until the pH value for the supernatant is in the range of 6-7. After decanting the supernatant, the hydrated hydrogel-forming polymer is sequentially exchanged three times with isopropanol (VWR; reagent type), three times with acetone (VWR; reagent type) and twice with anhydrous ether (EM Science; reagent type). The product was transferred to a sheet of Teflon and allowed to dry overnight. After fine grinding with mortar and pestle, the product is freeze-dried for about 96 hours to remove any solvent residues. After passing through a 20 mesh U.S. sieve, about 22 g of the base form, a cationic N, N-dimethylaminoethyl methacrylate hydrogel-forming ion exchange polymer (sample 1-4) is obtained.

The moisture content of the above neutralized and ion exchange hydrogel-forming polymers is determined by weight loss after three hours at 105 ° C. PUP capacity is determined at a limiting pressure of 2 kPa (0.3 psi) and 4.8 kPa (0.7 psi) for 60 minutes and 225 minutes. Extractable substances for the acid form of the anionic hydrogel-forming polymer and the basic form of the cationic hydrogel-forming polymer are determined after in-situ neutralization with a stoichiometric amount of 1N NaOH (Baker analyzed) respectively. IN HCl (Baker analyzed). Volumes

99 9 99 • «· · · · ·

9 · 9 9 9 9

9 9 9

9999 9999 999 99

9

9

9 9 • 9

9

In 9 »9

The gel for the acid form of the anionic hydrogel-forming polymers and the basic form of the cationic hydrogel-forming polymers are determined both on the polymers as well as on the polymers after in-situ neutralization with a stoichiometric amount of IN NaOH (Baker analyzed) respectively. IN HCl (Baker analyzed). The gel volume values obtained for non-neutralized in-situ neutralizing hydrogel-forming polymers are also mass-corrected on a neutralized basis ”as compared to the gel volumes measured for comparable neutralized hydrogel-forming polymers. The results of these measurements (expressed on a dry weight basis) are summarized in Tables 1-1 and 1-2.

By comparing the gel volume value for Sample 1-1 and the weight adjusted gel volume value for Sample 1-2 after in-situ neutralization, it was concluded that the conversion of the anionic hydrogel-forming polymer from its neutralized form to the acidic form results in a small change in the underlying properties of the gel forming polymer. Thus, in addition to the degree of neutralization, samples 1-1 and 1-2 are comparable materials. Comparing the gel volume value for Sample 1-3 and the weight adjusted gel volume for Sample 1-4 after in-situ neutralization, it was also concluded that the conversion of the cationic hydrogel-forming polymer from its neutralized to its basic form leads to a small change in the underlying properties of the hydrogel-forming polymer. Thus, in addition to the degree of neutralization, samples 1-3 and 1-4 are comparable materials.

Table 1-1: Properties of samples

Sample

1-1 (anionic; neutralized form)

1-2 (anionic; acid form) 1-3 (cationic; neutralized form)

1-4 (cationic; basic form) (a) Neutralization gel volume, about 44 g / g.

(b) Neutralization gel volume. about 13 g / g.

·· · ··

- of Example 1 w · 9 9 9 • «« · · · • 9 9 · • · · · · • · · · humidity volume extract- (% wt) gel telný (g / g) polymer (% wt) 5, 5 42, 6 7.2 4.7 5.7 ^(al 1.1 1.3 15.4 <5 0, 5 6.0 ^b <5

• 4r 99 9 9 9

999 999

9

99 is 53.9 Corresponds to g / g after about weight%

adjusted is 16.3 g / g in about 100%

This corresponds to the weight-adjusted in-situ value of the in-situ value

Table 1-2: PUP Capacity Values for Example 1, Samples (b)

Sample

1-1 (anionic; neutralized form)

1-2 (anionic; acid form) 1-3 (cationic; neutralized form)

1-4 (cationic; basic

2 kPa 2 kPa 4.8 4.8 (0,3 (0,3 kPa kPa dogs) dogs) (0,7 (0,7 (60 (225 dogs) dogs) min) min) (60 (225 min) min) 38.2 (and) 31.9 (and) 8.2 (and) 6, 9 (and) 11.1 14.9 10.2 13, 7 5, 5 6.0 5.4 5, 8

(a) The value of the PUP capacity after 225 minutes for this sample is approximately equal to its value for a 60 minute sample.

(b) All values are corrected for humidity and are expressed in g / g.

Example 2

PUP Capacities for mixed-bed hydrogel-forming polymeric mixes:

The moisture-corrected cation exchange capacity of the hydrogel-forming polyacrylic acid-based polymer is estimated to be about 13.9 meq / g based on the molecular weight of its monomer. The moisture-corrected anion exchange capacity of the hydrogel-forming polydimethylaminoethyl methacrylate-based polymer is estimated to be about 6.4 meq / g based on the molecular weight of its monomer. Based on these values for cation exchange and anion exchange capacities, the mixed-bed ion exchange mixture containing polyacrylic acid polymers and polydimethylaminoethyl methacrylate having hydrogel-forming polymers with approximately the same cation exchange and anion exchange capacity equivalents has an anionic and anionic polymer weight ratio of about 0.3 to about 0.3: has a mixed bed ion exchange capacity of about 4.4 meq / g.

Ion-exchange, hydrogel-forming polymer blends having a total weight of about 0.9 g and a weight ratio of 0.31 parts of sample 1-2 to 0.69 parts of sample 1-4 are prepared by mixing aliquots of the two samples (sample 2-1). After mixing, the ion exchange hydrogel forming mixtures are transferred to a PUP measuring cylinder to measure the PUP capacity. Comparable mixtures in a weight ratio of 0.31: 0.69 samples 1-1 and 1-3, where the anionic and cationic hydrogel-forming polymers are also prepared by mixing. After mixing these neutralized forms, aliquots of both samples are also prepared. (sample 2-2). a comparable mixture of neutralized hydrogel-forming polymers is transferred to the PUP measuring cylinder to measure the PUP capacity. PUP capacity values are determined for limiting pressures of 2, 4.8, and 9.7 kPa (0.3, 0.7, and 1.4 psi) and measurement times of 60 minutes and 225 minutes. The measured moisture-corrected PUP capacitance values are shown in Table 2-1.

A comparison of the PUP capacity values at 225 minutes demonstrates that the hydrogel-forming ion-exchange polymer blend exhibits a greater than 50% increase in PUP capacity at limiting pressures of 4.8 kPa (0.7 psi) and 9.7 kPa (1.4 psi) compared to a comparable blend of anionic and cationic hydrogel-forming polymers, each in its neutralized form. The increase in PUP capacity at a limiting pressure of 2 kPa (0.3 psi) is more than 40%.

Table 2-1 PUP Capacity Values for Mixed Bed Ion Exchangers

Sample 2 kPa 2 kPa 4,8 kPa 4,8 kPa 9,7 kPa 9,7 kPa 0.3 psi 0.3 psi 0.7 psi 0.7 psi 1.4 psi 1.4 psi (60 min) (225 (60 min) (225 (60 min) (225 min) min) min) 2-1 25, 0 32.8 19, 0 29.7 15.1 22.4 2-2 22.8 23, 1 17.8 19.2 9.5 13, 9

2. Fibrous materials

The absorbent members of the present invention may comprise fibrous materials that form a fibrous web or fibrous matrix. Fibers useful in the present invention include natural fibers. The fibers used in the present invention include natural fibers. · - ol - ···················

I (both prepared and untreated) as well as synthetically produced fibers. Examples of suitable untreated or treated natural fibers include cotton, esparto grass, bagasse, psyllium, flax, silk, wool, wood pulp, chemically modified wood pulp, jute, rayon, ethylcellulose, and cellulose acetate. Suitable synthetic fibers may be made of polyvinyl chloride, polyvinylfluoride, polytetrafluoroethylene, polyvinylidene chloride, polyacrylates such as ORLON®, polyvinyl acetate, polyethylene vinyl acetate, insoluble or soluble polyvinyl alcohol, polyolefins such as polyethylene (for example, PULPEXam), and polypropylene, DACRON® or KODEL®, polyurethanes, polystyrenes and the like. The fibers used may include pure naturally occurring fibers, pure synthetic fibers or any compatible combination of naturally occurring and synthetic fibers.

The fibers used in the present invention may be hydrophilic, hydrophobic or a combination of both hydrophilic and hydrophobic fibers. The term hydrophilic as used herein describes fibers or fiber surfaces that can be wetted with aqueous liquids (e.g., aqueous body fluids) deposited on the fibers. Hydrophilicity and wettability are generally defined by the contact angle and surface tension of the liquids and solids involved. This is discussed in detail in the American Chemical Society publication entitled Angle of contact, wettability and adhesion, edited by Robert F. Gould (Copyright 1964). It is said that the fiber or fiber surface is wetted with fluid (i.e., is hydrophilic) when either the angle at contact between the fluid and the fiber or its surface is less than 90 ° or when the fluid tends to spontaneously propagate over the fiber surface, usually occur simultaneously. in contrast, a fiber or surface is considered hydrophobic if the angle is

contact greater than 90 ° and the fluid does not spread spontaneously over the fiber surface.

The particular choice of hydrophilic or hydrophobic fibers will depend upon the fluid handling properties and other parameters required of the resulting absorbent member. For example, for absorbent members to be used for total or partial replacement, it may be desirable that the hydrophobic, nonwoven topsheet of at least one of the absorbent members, typically the member adjacent the wearer of the absorbent article, include hydrophobic fibers. The use of hydrophobic fibers in at least one of the absorbent members may also be useful where the member comprising the hydrophobic fibers is in addition to the breathing but somewhat liquid pervious backsheet of an absorbent article such as toddler panties; the member comprising hydrophobic fibers provides a liquid impermeable barrier.

For many absorbent members of the present invention, the use of hydrophilic fibers is preferred. this is particularly true for absorbent members that are required to efficiently receive secreted bodily fluids and then rapidly transfer and distribute the received fluid to other distal regions of the absorbent member or absorbent core. The use of hydrophilic fibers is particularly desirable for absorbent members that include hydrogel-forming absorbent polymers.

Suitable hydrophilic fibers for use in the present invention include cellulose fibers, modified cellulose fibers, rayon, polyester fibers such as polyethylene terephthalate (i.e., DACRON®, hydrophilic nylon (HYDROFIL®) and the like. Suitable hydrophilic fibers may also be obtained by hydrophilizing hydrophobic fibers, such as thermoplastic fibers treated with a surfactant or silicate, derived from a surfactant or silicate, derived from For example, polyolefins such as polyethylene or polypropylene, polyacrylates, polyamides, polystyrenes, polyurethanes, etc. For reasons of availability and cost, cellulose fibers, particularly wood pulp fibers, are preferred for use in the present invention. .

Suitable wood pulp fibers can be obtained by well-known chemical processes such as kraft and sulphite processes, in particular it is preferred to use wood pulp fibers from southern softwoods because of their excellent absorption parameters. These wood pulp fibers can also be obtained from mechanical processes such as ground wood, refining mechanical, thermomechanical, chemical-mechanical and chemical-thermomechanical pulping processes. Recycled or secondary wood pulp fibers as well as bleached or unbleached wood pulp fibers may be used. Chemically reinforced cellulose fibers are a desirable source of hydrophilic fibers for use in the present invention, particularly for absorbent members, providing both fluid acquisition and distribution properties. As used herein, the term chemically reinforced cellulose fibers means those cellulose fibers that have been reinforced by chemical means so as to increase the stiffness of the fibers in both dry and wet conditions. These compositions may include the addition of a chemical hardener which, for example, covers or impregnates the fibers. Such compositions may also include reinforcing the fibers by altering the chemical structure, for example, by crosslinking the polymer chains.

Polymeric hardeners that can coat or impregnate cellulosic fibers include: cationic modified starches having nitrogen-containing groups (eg, amino groups) such as those available from National Starch and Chemical Corp., Bridgewater, NJ, USA; latices, resin for strength

wetting agents such as polyamide epichlorohydrin resin (e.g., Kymene®, 557H from Hercules, Inc., Wilmington, Delaware, USA), polyacrylamide resins described, for example, in US Patent No. 3,556,932; commercially available polyacrylamides marketed by American Cyanamid Co., Stamford, CT, USA under the trademark Paez®, 631 NC; urea-formaldehyde and melamine-formaldehyde resins and polyethyleneimine resins. A general dissertation on the wet-strength resins useful in the paper industry and generally applicable herein can be found in the TAPPI series of monographs under sequence number 29 and is entitled Wet Strength in Paper and Paperboard, published by Technical Asssociation of the Pulp Industry (New York, 1965).

These fibers can also be stiffened by a chemical reaction. For example, the crosslinking agents can be applied to the fibers by causing them to chemically crosslink the fibers within the fibers after application. These crosslinks can increase the stiffness of the fibers. While the use of crosslinks within the fibers for chemical fiber reinforcement is preferred, this is not meant to exclude other types of chemical fiber reinforcement reactions.

Fibers reinforced by cross-linking in an individualized form, i.e., individualized reinforced fibers, as well as processes for preparing them, are described, for example, in U.S. Patent No. 5,201,549.

No. 224,926, U.S. Patent No. 3,440,135, U.S. Patent No. 3,932,209, and U.S. Patent No. 4,035,147. More preferred stiffened fibers are described in U.S. Patent No. 4,822,453, U.S. Patent No. 4,922,453.

U.S. Patent No. 888,093, U.S. Patent No. 4,898,642, and U.S. Patent No. 5,898,642.

137,537, all of which are hereby incorporated by reference into the description.

In preferred reinforced fibers, the chemical treatment of crosslinking within the fibers with crosslinking agents while the fibers are in a relatively dehydrated state. , defibrated (i.e., individualized), twisted, curled state. Suitable chemical hardeners are generally monomeric crosslinking agents including, but not limited to, C ₂ -C ₈ dialdehyde, C ₂ -C ₈ monoaldehydes having acidic functionality, and in particular C ₂ -C ₉ polycarboxylic acids. These compounds are capable of reacting with at least two hydroxyl groups in a single cellulose chain or on cellulose chains located proximally in a single fiber. Specific examples of such cross-linking agents include, but are not limited to, glutaraldehyde, glyoxal, formaldehyde, glyoxylic acid, oxydisuccinic acid, and citric acid. The effect of crosslinking under these conditions is to form fibers that are reinforced and which tend to retain their twisted, curled arrangement during use in the thermally bonded absorbent structures of the present invention. Such fibers and processes for their manufacture are described in the aforementioned patents.

Preferred stiffened fibers that are twisted and curled can be quantified by indicating both the number of twists of the fiber and the curl factor of the fiber. As used herein, the number of twists means the number of twist nodes that are present over a certain fiber length. The number of twists is used as a means of measuring the extent to which the fiber is twisted about its longitudinal axis. The term twist node refers to a substantially axial twist of the fiber 180 ° around its longitudinal axis, wherein a portion of the fiber (eg, nod) appears dark compared to the rest of the fiber when viewed under a microscope under illumination. The twist node appears dark because the transmitted light at this point passes through another fiber wall due to the above twist. The distance between the nodes corresponds to an axial twist of 180 °. The number of twist nodes per fiber length (ie, the number of these nodes) directly indicates the degree of twist of the fiber, flflf flflf flflfl flfl flfl flflfl flfl which is the physical parameter of the fiber. Methods for determining twist nodes and total number of nodes are described in U.S. Patent No. 4,898,642.

Preferred stiffened fibers will have an average twist count for dry fibers of at least about 2.7, preferably at least about 4.5, or nodes per millimeter. Further, the average wet twist count of these fibers should preferably be at least about 1.8, preferably at least about 3.0, and should also preferably be at least about 0.5 twist nodes per millimeter less than the average twist count. for dry fiber. More preferably, the average number of twists of dry fiber is at least about 5.5 twist nodes per millimeter, and the average number of twists in wet fiber should be at least about 4.0 twist nodes per millimeter, and should also be at least 1.0 twist twists. nodes per millimeter less than its average number of twists for dry fiber. Most preferably, the dry fiber twist count is at least about 6.5 twist knots per millimeter, and the average wet twist number should be at least about 5.0 twist knots per millimeter, and should also be at least about 1.0 twist knots. per millimeter less than the average number of twists for dry fiber.

In addition to the twists, these preferred stiffened fibers are also crimped. Fiber curl can be described as a partial shortening of the fiber by loops, twists or bends in the fiber. For the purposes of the present invention, fiber curl is measured in a two-dimensional plane. The extent of fiber curl can be quantified by reference to the fiber curl factor. Fiber curl factor and two-dimensional curl measurement is determined by tracking the fiber in a two-dimensional plane. To determine the curl factor, both the length L _{R of the} fiber as measured by the longest dimension of the two-dimensional rectangle described around the fiber and the actual fiber length shall be measured.

0 · · 0 · · · 000 000 0 0 0 · 0 «··

0 0 0 0 0000

0 0 00 00 000000

0 0 0 0 0 0 _ _ 0000 0000 000 00 00 00

Lft. The fiber curl factor is then calculated from the following equation:

curl factor = (L _A / L _R ) -1.

An image analysis method that can be used to measure L _R and L _A is described in U.S. Patent No. 4,898,642. Preferably, the stiffened fibers will have a curl factor of at least about 0.30, and more preferably have a curl factor of at least about 0.50 .

These chemically stiffened cellulosic fibers have certain properties which make them particularly useful with certain absorbent articles of the present invention in relation to the non-stiffened cellulosic fibers. In addition to being hydrophilic, these stiffened fibers have a unique combination of stiffness and elasticity.

This allows the thermally bonded absorbent structures made with these fibers to have a high absorbency and to exhibit a high degree of flexibility and expansion response to wetting. In particular, the resilience of these stiffened fibers allows the absorbent member to better maintain its capillary structure in the presence of both liquid and compressive forces that normally occur during use and are thus more resistant to collapse.

3. Thermoplastic materials

In the case of the thermally bonded absorbent members of the present invention, the member may include, in addition to fibers, a thermoplastic material. At melting, at least a portion of the thermoplastic material migrates to the fiber intersections, usually due to capillary gradients between the fibers. These intermediate sections become places where the thermoplastic material is bound. Upon cooling, the thermoplastic materials solidify in these portions and form bonding sites that hold together a matrix or web of fibers in each of the respective layers.

• ··· ···· ·· · <

· Ta ta ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦

Due to their various bonding effects at the point of these fiber penetrations, they increase the overall modulus of compressibility and strength of the resulting thermally bonded member. In the case of chemically stiffened cellulosic fibers, the melting and migration of the thermoplastic material also has the effect of increasing the average pore size of the resulting web, while maintaining the density and basis weight of the web as originally formed. This may improve the fluid absorption properties of the thermally bonded member at initial discharge due to improved fluid permeability and subsequent effluents due to the combined ability of the reinforced fibers to retain their wetting stiffness and the ability of the thermoplastic material to remain bonded to the fiber penetration points when wet and wet compressed. . In the web, the thermally bonded strips of stiffened fibers retain their original total volume, but with the volume regions previously occupied by the thermoplastic material, they open and thereby increase the average capillary pore size between the fibers.

The thermoplastic materials useful in the present invention may be in any of a variety of forms including particles, fibers or combinations of particles and fibers. Thermoplastic fibers are a particularly preferred form because of their ability to form multiple sites between bonded fibers. Suitable thermoplastic materials can be made from any thermoplastic polymer that can be melted at temperatures that do not excessively damage the fibers that include the primary web or matrix of each layer. The melting point of the thermoplastic material will preferably be less than about 190 ° C and particularly preferably in the range of about 75 ° C to about 175 ° C. In any case, the melting point of the thermoplastic material should not be lower than the temperature at which the thermally bonded absorbent structures, when used in absorbent articles, are expected to be stored. Paragraph • 9

9

99 • 9 99 9 9 9 • 9 9 9 · 9 9 9

9 9

999 999 ·

the melting of the thermoplastic material is generally not less than about 50 ° C.

Thermoplastic materials, and especially thermoplastic fibers, can be made from a variety of thermoplastic polymers, including polyolefins such as polyethylene (e.g., PULPEX) and polypropylene, polyesters, copolyesters, polyvinyl acetate, polyethyl vinyl acetate, polyvinyl chloride, polyvinylidene chloride, polyacrylates, polyamides, copolyamides, polystyrenes, any of the foregoing polymers such as vinyl chloride / vinyl acetate and the like. One of the thermoplastic fibers for bonding is PLEXAFIL® polyethylene microfibers (manufactured by DuPont), which are also available as about 20% blend with 80% cellulose fibers, sold under the trade name KITTYHAWK® (manufactured by Weyerhaeuser Co.). Depending on the desired parameters for the resulting thermally bonded absorbent member, suitable thermoplastic materials include hydrophobic fibers that have been rendered hydrophilic, such as surfactant or silicate treated thermoplastic fibers, derived for example from polyolefins such as polyethylene or polypropylene, polyacrylates, polyamides, polystyrenes, polyurethanes, etc. The surface of the hydrophobic thermoplastic fibers may be maintained by hydrophilic treatment with a surfactant such as a nonionic or anionic surfactant, for example by spraying the surfactant onto the fibers, dipping the fibers into the surfactant or including the surfactant as part of the polymer melt in thermoplastic fiber production . Upon melting and re-solidification, the surfactant tends to remain on the surface of the thermoplastic fiber. Suitable surfactants include nonionic surfactants such as Brij® 76, manufactured by ICI Americas Inc. from Wilmington, Delaware and various surface

Active Agents sold under the trade name Pegosperse® by Glyco Chemical, Inc. from Greenwich, Connecticut. In addition to nonionic surfactants, anionic surfactants can also be used. These surfactants can be applied to the thermoplastic fibers at a rate of, for example, from about 0.2 to about 1 g / cm ^{2 of} thermoplastic fiber.

Suitable thermoplastic fibers can be made from a single polymer (mono-component fibers) or can be made from more than one polymer (e.g., bicomponent fibers). As used herein, bicomponent fibers are termoplastic fibers that include a core fiber forming a core made of one polymer surrounded by a thermoplastic sheath made of a different polymer. The polymer comprising the shell often melts at a different, generally lower, temperature than the polymer comprising the core. As a result, these bicomponent fibers provide thermal bonding by melting the sheath polymer while maintaining the desired strength properties of the core polymer.

Suitable bicomponent fibers for use in the present invention may include core and sheath fibers having the following polymer combinations: polyethylene / polypropylene, polyethylene vinyl acetate / polypropylene, polyethylene / polyester, polypropylene / polyester, copolyester / polyester, and the like. Particularly suitable bicomponent thermoplastic fibers for use in the present invention are those having a polypropylene or polyester core and a lower temperature melting sheath of copolyester, polyethylene vinyl acetate or polyethylene, e.g., bicomponent fibers of DANAKLON®, CELBOND®, or CHISSO®. The bicomponent fibers may be concentric or eccentric. As used herein, the terms concentric and eccentric means whether the sheath has a thickness that is the same or not the same as 9 9 9 9 9 9 · 9 · 9 99 9 · 9 · ·

9 9 9 9 • 9 999 99 99 99 cross-sectional area of bicomponent fiber. Eccentric bicomponent fibers may be desirable if they are to impart greater compressive strength at a lower fiber thickness. Suitable bicomponent fibers for use in the present invention may be either non-curled (i.e., not bent) or curled (i.e., bent). The bicomponent fibers may be crimped by typical textile means, such as a crushing method or a gear forming method, in order to achieve predominantly two-dimensional or flat curl.

In the case of thermoplastic fibers, their length may vary depending on the particular melting point and other properties desired for the fibers. Generally, the thermoplastic fibers have a length of from about 0.3 to about 7.5 cm, preferably from about 0.4 to about 3.0 cm, most preferably from about 0.6 to about 1.2 cm. The properties, including the melting point of these thermoplastic fibers, can also be adjusted by varying the fiber diameter (measured by the meter). The diameter of these thermoplastic fibers is generally defined either in denier (grams per 9,000 meters) or in decitex (grams per 10,000 m). Suitable bicomponent thermoplastic fibers may have a decitex ranging from about 1.0 to about 20, preferably from about 1.4 to about 10, and most preferably from about 1.7 to about 3.3.

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

• 9 99

9 9 9

9 9 9

999 999

4. Other components and materials

Additional ion exchange capacity may be added to the absorbent member or absorbent article constituting the absorbent member in the form of ion exchange fibers, ion exchange films, ion exchange resin particles, ion exchange coatings on fibers, ion exchange coatings on films, etc. for the purpose of (1) supplying total ion exchange capacity; (2) compensating for the imbalance in the anion exchange versus cation exchange capacity resulting from differences in amounts, pK values, etc. The above ion exchange components may also be substituted for one or more existing components in the absorbent member or absorbent article. Thus, for example, the conventional wood pulp fiber in the absorbent member may be replaced by an ion exchange fiber. See, for example, U.S. Patent 4,818,598, which is hereby incorporated by reference.

Other optional ingredients that may be present in the absorbent bands are described, for example, in the section entitled Other ingredients and materials in U.S. Patent No. 5,562,646, which is hereby incorporated by reference.

C. Absorbent members comprising hydrogel-forming absorbent polymers

1. Concentration, basis weight and fluid handling properties

At least one of the absorbent members of the present invention will include the previously described mixed beds of hydrogel-forming absorbent polymers with or without other optional components such as fibers, thermoplastic material, etc.. The absorbent members including the absorbent polymers may act as absorbent members within the absorbent core

9 9 9

9

9

9

9

fluid. The principle function of these fluid storage members is to absorb the excreted body fluid either directly or from other absorbent members (e.g., fluid acquisition and distribution members) and then retain the fluid therein even when subjected to pressures that normally occur as a result movements of the person wearing them. However, it should be understood that these polymer-containing absorbent members may also serve functions other than fluid storage.

An important aspect of the absorbent members of the present invention is that they comprise one or more regions having a high concentration of these hydrogel-forming absorbent polymers. In order to obtain relatively thin absorbent articles capable of absorbing and storing large quantities of body fluids, it is desirable to increase the level of these hydrogel-forming absorbent polymers and to reduce the level of other components, particularly fibrous components. However, in order to utilize these hydrogel-forming absorbent polymers at relatively high concentrations, it is important that the polymers have a relatively high absorbent capacity desired at a relatively high limiting pressure (i.e., a PUP capacity value) and preferably a relatively high porosity (e.g. high permeability under pressure (e.g., SFC), such that when the polymer is swollen in the presence of body fluids, it provides the proper ability to receive these excreted body fluids and then transport them through the gel continuous zone transporting the fluid or layer to other regions of the absorbent and / or storing such body fluids.

When measuring the concentration of hydrogel-forming absorbent polymers in a given region of the absorbent member, the weight percent of hydrogel-forming polymers relative to the combined hydrogel-forming polymers is used. 999 99 99 99 by weight of hydrogel-forming polymers and any other components (eg fibers, thermoplastic material, etc.) which are present in the polymer containing region. With this in mind, the concentration of hydrogel-forming absorbent polymers in the region of the absorbent member of the present invention can range from about 60 to 100%, preferably from about 70 to 100%, more preferably from about 80 to 100%, and most preferably from about 90 % to 100%.

Another important aspect is the basis weight of the hydrogel-forming absorbent polymers in the region of the absorbent member. The hydrogel layer porosity, gel permeability, and high absorbency required are the properties of these gel-forming absorbent polymers that have the greatest impact on the absorption behavior of the absorbent member and the absorbent core at certain minimum polymer basis weights. When measuring the basis weight of the hydrogel-forming absorbent polymer in a given region of the absorbent member, grams of polymer per square meter (g / m ² ) of area of the region are used. With this in mind, the basis weight of the hydrogel-forming absorbent polymers in the region of the absorbent member of the present invention is at least about 10 g / m ² , preferably at least about 20 g / m ² , more preferably at least about 50 g / m ² , and most preferably at least about 100 g / m ² . These basis weight values are generally in the range of from about 10 to about 1000 g / m ² , more usually from about 50 to about 800 g / m ^2, and most typically from about 100 to about 600 g / m ² .

When the hydrogel-forming absorbent polymers are incorporated into the absorbent storage member at a sufficiently high concentration and basis weight, swelling with body fluid under pressure brings the edges of the resulting hydrogel in the region into contact, i.e., the hydrogel in the region becomes continuous. In these expanded swollen highly concentrated regions, voids and capillaries are generally bound by a hydrogel to form a

4 44 44 »· 44 4 44 ·

4 4 4 4 4 4 4 4 4 4

4444 4444 444 4 · ·· ·· Gel area or layer for continuous fluid flow. In these regions, it is believed that porosity and fluid permeability are close to those of a comparable hydrogel layer formed under the pressure of the polymer itself. In addition, the use of the above-described gel-forming absorbent polymers having relatively high PHL values, and preferably relatively high SFCs, confirms higher porosity and preferably higher permeability, and thus good fluid acquisition and transport and storage properties of these continuous gel transport zones or layers.

2. The wet and wet integrity of the absorbent member and / or absorbent core

During the initial fluid intake, utilization of the absorbent core occurs in the immediate vicinity of the effluent. There are several ways to utilize the absorbent core beyond this starting point of fluid uptake. The fluid may move across the topsheet and enter the core over larger areas. This is not a desirable situation since the fluid is in contact with the skin and is susceptible to leakage from the absorbent article. Certain elements of the absorbent article, such as foot pads, may assist in this. Also, special fluid acquisition members have been used to transfer fluid under the topsheet before the fluid enters the storage areas of the absorbent core. Despite these measures to improve fluid handling, there remains a need to achieve as much transverse displacement (i.e., in the X and Y directions) in the core storage regions, particularly as the absorbent cores become thinner and thinner.

Potential improvement in lateral fluid movement offered by absorbent members comprising relatively high porosity and preferably high permeability of absorbent polymers forming

99 99 99

9 9 9 9 9

9 9 9 9 9

99,999,999

9

999 99 99 99 «« «9 • 9 · · · 9 9

9, the hydrogel described above requires some degree of physical continuity in the hydrogel-containing region, eg, a transport zone or continuous gel fluid layer, to adequately move fluid through contiguous internal voids and capillaries. The realization of the advantages of these highly porous and preferably highly permeable hydrogel-forming absorbent polymers is facilitated by absorbent members and absorbent cores designed to reduce or minimize the occurrence of fluid gel zone zones or layers that are formed when the polymer is swollen with body fluids. Absorbent members and / or cores that provide these parameters are referred to herein as cores having good wet integrity. By good wet integrity, it is meant that the region or regions in the absorbent member having a high concentration of absorbent hydrogel-forming polymer have sufficient integrity in the dry, partially wet, or wetted condition such that physical continuity and thereby the ability to receive and transport fluid through contiguous internal voids in places and capillaries of the continuous gel fluid transport zone or layer formed after the swelling of the hydrogel-forming absorbent polymer in the presence of body fluids has not been substantially disturbed or altered, even if subjected to conditions of normal use.

During normal use, absorbent cores in absorbent articles are generally subjected to tensile and torsional forces of varying intensity and direction. These tensile and torsional forces include crotch cramping, stretching and twisting forces as a person wears the absorbent article while walking, sitting, bending, and the like. If wet integrity is inadequate, then these tensile and torsional forces can potentially cause a substantial change and / or impair the physical continuity of the hydrogel to such an extent that its ability to transport fluids through continuous voids and capillaries deteriorates, i.e., a continuous gel zone or layer, it may partially detach, completely detach, interrupt, may have areas that become thinner or tear into many significantly smaller segments. Such a change can reduce or minimize the advantageous porosity and permeability or conductivity for the flux expected of the hydrogel-forming absorbent polymer described above.

Good wet integrity can be achieved according to the invention by various designs, arrangements, compositions, etc. in an absorbent member having a high concentration of absorbent hydrogel-forming polymer, other components in the core, eg, fluid acquisition members, other absorbent article, eg, topsheet. and or a backsheet, or other combination thereof. See U.S. Patent No. 5,562,646.

absorption components in

D. Absorbent cores

The absorbent members of the present invention, including high concentrations of hydrogel-forming mixed-bed absorbent polymers, can be used alone or in combination with other absorbent members in a variety of absorbent cores. These other absorbent members may include such members that are useful for the initial uptake of secreted body fluid before such fluids are distributed to the fluid storage member of the absorbent core. They include absorbent members that provide multiple fluid handling properties, eg, fluid intake and distribution, or fluid handling properties themselves, eg, fluid distribution. These other absorbent members may also include lower concentrations of hydrogel-forming absorbent polymers having the physical properties specified previously, e.g., a relatively high PUP capacity and preferably PHL and SFC values such as described in B (1) (b) above, or may include hydrogel-forming absorbent polymers having different physical properties, e.g., lower PHL, PUP capacity, or SFC values.

One suitable absorbent core of the present invention comprises (1) a topsheet having: (a) an absorbent layer substantially free of the hydrogel-forming absorbent polymer and (b) an absorbent polymer layer mainly consisting of a first hydrogel-forming absorbent polymer having an SFC of at least about 4 x 10 ⁷ cm ³ / g, preferably at least about 6 x 10 ⁷ cm ³ / g, even more preferably at least 9 x 10 ⁷ cm ³ / g and most preferably at least 15 x 10 ⁷ cm ³ / g which is present in an amount of at least about 20 g / m ^2; and (2) a backsheet comprising: (a) an upper layer having an void space for storing and redistributing body fluids; and (b) a backsheet containing a high concentration of mixed-bed ion exchange absorbent polymers forming hydrogels having at least a PUP capacity and preferably PHL and SFC values as described in B (1) (b) above and wherein at least about 70% of the total ion exchange absorber The hydrogel-forming mixed bed polymer is in the topsheet and the bottomsheet is in the lower half of the combined thickness of the topsheet and the backsheet.

One such absorbent core is shown in Figure 1. 1 is a cross-sectional view of an absorbent article designated 10 having a topsheet 12, a backsheet 16, and an absorbent core designated 20, positioned between the topsheet 172 and the backsheet 16. As shown in this figure, the core 20 includes a topsheet. 24 and bottom set, 28. The top assembly 24 includes an upper acquisition and distribution layer 32 and a layer 40 comprising a first absorbent hydrogel-forming polymer separated from the acquisition layer 32 by a tissue paper layer 36 having two Z-folds. The lower assembly 28 comprises an upper fibrous layer 44, a lower layer 48 comprising blended a bed of absorbent hydrogel-forming polymers and a tissue paper layer 52. The layers 32 and 40 may be separate layers as shown in FIG. 1 or may be combined into a single layer to serve as a storage and redistribution file. As is apparent from FIG. 1, it is not essential that the layers should be coextensive.

The acquisition layer 32 of the topsheet 24 is the top effective layer of the absorbent core and is generally substantially free of the hydrogel-forming absorbent polymer. If a hydrogel-forming absorbent polymer is included, the amount should be relatively low and preferably substantially free of superabsorbent material, at least in the upper half of the layer 32, and generally over most or all of the thickness. See U.S. Patent No. 5,217,445 and U.S. Patent No. 5,360,420, which are hereby incorporated by reference. The layer 32 may be of foam or any other suitable porous or capillary material, but is typically formed of a fibrous material. The fibrous material may be of any fibrous material that has suitable wet load resistance, i.e., is able to maintain a satisfactory void volume under these conditions. Particularly preferred fibrous materials for layer 32 are chemically reinforced fibers as described in B (2) above, usually in an amount of 50 to 100 wt% of layer 32.

The layer 40 of the topsheet 24 may be joined to the bottom of the layer 32, but is preferably a separate layer and may be separated from the layer 32 by tissue paper or other portion that acts as a barrier to the absorbent hydrogel-forming polymer. It is important that the layer 40 allow body fluids in the layer 32 to pass therethrough rapidly and be distributed beyond the layer 40. The amount of the first absorbent hydrogel-forming polymer in the layer 40 should be sufficient to form a hydrogel layer upon swelling by absorption body fluids. The first absorbent hydrogel-forming polymer is usually in particulate form and is usually present in an amount of at least about 20 g / m ² , but generally in an amount of at least about 50 g / m ² . Generally, however, the layer 40 should not be too thick, normally the amount of hydrogel-forming absorbent polymer is below about 320 g / m ² , but generally below about 200 g / m ² .

The bottom assembly 28 serves as a storage and redistribution component in the core 20 and comprises an upper, usually fibrous, layer of the second absorbent hydrogel-forming polymer. The topsheet 44 of the backsheet 28 is generally fibrous, but may be formed of foam or other capillary or porous material and may be formed from the same or different materials as the layer 32.

The topsheet 44 may be substantially or completely free of the hydrogel-forming absorbent polymer. However, it is often desirable for the topsheet 44 and the backsheet 48 to be formed to form a fibrous matrix, with more than half, and usually at least about 70%, of the hydrogel-forming absorbent polymer in these layers in their lower half, e.g. 100%, typically from about 75 to about 90% of the second absorbent hydrogel-forming polymer is in the lower 50% of the layers 44 and 48. For example, about 30% of the second absorbent hydrogel-forming polymer may be in the upper half of the layers 44 and 48.

The first hydrogel-forming absorbent polymer and sometimes also the mixed bed of hydrogel-forming absorbent polymers are formed as a layer comprising predominantly the absorbent polymer or polymers. The term predominantly " ¹ " means that at least about 50% or more, generally at least about 70% or about 80% of the layers 40 or 48 is a hydrogel-forming absorbent polymer. The hydrogel-forming absorbent polymer layers may be joined or otherwise supported by a backing layer. The distribution in the layers 40 or 48 may be uniform or vary, for example, to form a shaped structure that may be striped or profiled within the layer. See, for example, U.S. Patent No. 4,935,022.

The layers 40 or 48 may comprise a hydrogel-forming absorbent polymer integrated with or dispersed therein, such as cellulose-based tissue paper or other nonwoven material. The hydrogel-forming absorbent polymer may be integrated with the backing layer by bonding or by mechanical means such as extrusion or calendering. The layers 40 or 48 may alternatively comprise only the hydrogel-forming absorbent polymer.

Additional layers may be incorporated in the absorbent core 20, and as noted above, tissue layers may be incorporated. For example, a tissue paper layer may be used to wrap the first absorbent hydrogel-forming polymer or the second absorbent hydrogel-forming polymer.

Another suitable absorbent core of the present invention comprises a multilayer structure, preferably comprising: (1) a acquisition layer, (2) a storage layer, the absorption layers of which comprise a mixed bed of high concentration hydrogel-forming absorbent polymers having the physical properties listed above (including relatively high capacity) PUP, and preferably PHL and SFC values) located below the acquisition layer and optionally a liquid permeable, liquid-stable, central integration layer located between the acquisition layer and the storage layer. The acquisition layer and the storage layer comprise at least a portion of the moisture (i.e., liquid) insensitive fibers, such as crimped synthetic fibers, which enhance the wet integrity of the two layers and form stable bonds in the liquid to other φ ·

82 parts of the absorbent core or absorbent article. See U.S. Serial No. 08 / 153,739 and U.S. Serial No. 08 / 164,049, which are hereby incorporated by reference.

The inclusion of crimped synthetic fibers in the acquisition layer improves the integrity, speed of absorption, absorption capacity, and flexibility of the acquisition layer. Crimped synthetic fibers provide improved integrity both within the layer and between the layers. This is due to the interconnection between the crimped synthetic fibers in the acquisition layer and the storage layer and the availability of the crimped synthetic fibers on the surface of these layers to form fluid-stable bonds to the fluid-stable components in the absorbent core. Thus, the absorbent core has a plurality of layers including fluid-matrix bonding matrices that are joined by fluid-stable bonds to adjacent fluid-stable components. The absorbent core is also joined by fluid-stable bonds between the topsheet and the backsheet of the absorbent article to prevent the hydrogel-forming absorbent polymer from falling between the topsheet and the backsheet (in other words, falling within the skeleton of the absorbent article).

One such multilayer absorbent core is shown in Figure 2. 2 shows a cross-section of an absorbent article 110 having a topsheet 112, a backsheet 116, and an absorbent core 120 disposed between the topsheet 112 and the backsheet 116. As seen in FIG. 2, the core 120 preferably includes a acquisition and distribution layer (the acquisition layer). layer 130 and a storage layer in the core (hereinafter the storage layer) 132, preferably located below the acquisition layer 130 and a central liquid-stable layer (hereinafter the integration layer) 134 disposed between the acquisition layer 130 and the storage layer 132; they all exchange fluids with each other. The acquisition layer 130 may be of any suitable size and may not have the full length or width of the storage layer 132. For example, the acquisition layer 130 may be in the form of a tape or patch. In the embodiment shown in Fig. 2, the acquisition layer 130 is shown as a single patch (ie, a web or sheet) of nonwoven material. It is to be understood, however, that the acquisition layer 130 need not be a single layer.

In addition, in other embodiments, instead of being a separate layer that is positioned above the storage layer 132, the acquisition layer 130 may be an integral layer (or component) that includes the top layer of the laminated storage layer 132. In this regard, it should also be understood that multilayer the absorbent core 120 may be used as a whole core or may be used as one or more layers in a layered core construction. The multilayer absorbent core 120 may also be constructed without the acquisition layer 130.

The entire acquisition layer 130 is preferably hydrophilic, but may have hydrophobic components. The acquisition layer 130 may include a woven material, a nonwoven material, or any other suitable type of material. The acquisition layer 130 may comprise a woven material, a nonwoven material, or any other suitable type of material. Preferably, the acquisition layer 130 comprises a nonwoven material. When the acquisition layer 130 comprises a nonwoven material, it may be manufactured by a variety of processes including, but not limited to, wet laid, pneumatically laid, melt blown, spun bonded, carded (the latter including bonded thermally, pneumatically, powder, latex, solvent or interwoven). These latter processes (e.g. spinning bonded or carded) may be preferred if it is desirable to orient the fibers in the acquisition layer because it is easier to orient the fibers in a single direction in these processes.

In one preferred embodiment, the acquisition layer comprises at least some fibers that form fluid stable bonds. The term fluid stable bonds as used herein means bonds that are not affected by the presence of body fluids. Preferred fluid-stable bonds are crimped synthetic fibers, which are preferred especially since they provide a acquisition layer 130 with softness and flexibility. Curled synthetic fibers are also preferred because they are. they can interconnect and thus provide the receiving layer 130 with increased integrity. The acquisition layer 130 shown in FIG. 2 preferably comprises a blend of crimped synthetic fibers and either natural fibers or cross-linked cellulose fibers.

In one preferred embodiment, the acquisition layer 130 comprises a blended layer comprising a homogeneously pneumatically laid blend of about 20% crimped hydrophobic polyethylene terephthalate (PET) fibers and about 80% of either pneumatically laid felt or chemically reinforced cellulose fibers. PET fibers have a denier fiber weight of about 40, a crimped length of about 1.3 cm (0.5 inches) and a crimping frequency of about 2.36 crimps per cm (6 crimps per inch (2.54 cm) length) and a crimping angle of about 88 °.

While the preferred crimped fiber material in this embodiment is PET, an alternative embodiment may be of any water-absorbent material having a wet stiffness similar to PET. Other suitable materials for use as curled fibers include, but are not limited to, polypropylene, nylon, polyethylene, and biocomponent.

• · ··

9 9 9

9 9 9

999 999 • 9 • 9 9 9 fibers; in addition, the denier of fibers is preferably in the range of about 1.5 or 2 to about 30 dpf. The non-crimped fiber length preferably ranges from about 0.6 cm (0.25 inches) to about 5 cm (2 inches).

The curl frequency is preferably in the range of about 2 to about 6 curls per cm (5 to 15 per inch) of length. The curl angle is preferably in the range of about 60 ° to about 100 °. The amount of crimped fibers in the acquisition layer may range from about 5% to about 90% and so as to be practical for use in disposable absorbent articles in terms of cost, preferably in the range of about 10% to about 50% and most preferably from about 20% to about 40%.

The acquisition layer 130 may be substantially non-dense during the diaper manufacturing process. In alternative embodiments, the acquisition layer 130 may be compacted by compressing it to densities in the range of up to about 0.3 g / cm ³ (4.8 g / square inch) or more.

Additional variations may be desirable when the acquisition layer 130 is used in certain types of absorbent articles. In one embodiment preferred when the absorbent article comprises a sanitary napkin, the acquisition layer 130 preferably comprises a yarn non-woven nonwoven web consisting of permanently wettable fibers. Preferably, the acquisition layer 130 is a stitched 35 g / m ² (30 g / yard ² ) PET nonwoven web. The quilted nonwoven web is formed such that most of the fibers are oriented in a single direction, such as a longitudinal reference wick effect, a preferred receiving direction for

The fibers of the material for this layer 130 are made of PET resin and are covered by a patented, wettable, CELWET coating. These fibers are available from Hoechst Clanese Corporation of Charlotte, North Carolina. The optional inner liquid-stable layer 134 is preferably positioned between the acquisition layer 130 and the storage layer 132. The layer 134 serves two purposes: (1) as a support

4 4

4 444 4444 4 4 4 4 4

444 444

4

44 a substrate for an adjacent acquisition layer 130 and a storage layer 132, and (2) a structure to which stable fluid bonds can be formed can be formed with synthetic fibers in the acquisition layer 130 and the storage layer 132. The layer 134 preferably retains a high degree of integrity when wet, it should not interfere with fluid movement from the acquisition layer 130 of the storage layer 132 and is also preferably resilient such that the elasticity of the absorbent article is substantially unaffected by the presence of the fluid stable layer 134. In one preferred embodiment, the layer 134 is a quilted polyester nonwoven web.

A commercially available quilted polyester nonwoven web suitable for use as a liquid-stable layer 134 is a material known as REEMAY® 2055, sold by Reemay Incorporated of Old Hickory, TN. This material has a basis weight of about 18.6 g / m ² (0.55 oz / yd ² ) and consists of 4 denier fibers per filament with a three lobed cross-sectional shape. The REEMAY belt is similar to the material used in the BOUNCE® dryer sheets manufactured by The Procter & Gamble Company of Cincinnati, Ohio using US Patent Nos. 4,073,996, US 4,237,155 and US 5,094,761. The key factor in choosing a polyester web is its permeability. The REEMAY strip also includes interstice spaces of sufficient size to allow some of the fibers in the acquisition layer 130 to penetrate the storage layer 132 and some of the fibers in the storage layer 132 to penetrate the acquisition layer 130.

In alternative embodiments, the layer 134 may consist of other non-absorbent polyester-like materials. Examples of suitable materials for use as layer 134 include, but are not limited to, polypropylene, nylon, and polyethylene. In addition, in other embodiments, the layer 134 may be a high-grade material instead of a synthetic material.

00 · 0 · 000

0 0 0

00 00 · ♦ stretching (ie low

87 wet strength (low extensibility) located in a structure in which the bonds between the high wet strength material and the adjacent acquisition layer 130 and the storage layer 132 remain wet strength.

In alternative embodiments, a high wet strength adhesive can be used with any of the other types of wet stable layers 134, including, but not limited to, REEMAY®. In addition, in other alternative embodiments, the layer 134 may be of a nonwoven material produced by another suitable process. In yet other embodiments, the layer 134 may be of a non-woven type. For example, the layer 134 may include a scrim or mesh.

Further, the positioning of the liquid-stable layer 134 in the absorbent core may vary in different embodiments. The layer 134 is preferably positioned between the acquisition layer 130 and the storage layer 132. In other embodiments, however, the layer 134 may be positioned adjacent to other surfaces of portions of the multilayer absorbent core 120. Further, if the multilayer absorbent core 120 components such as the acquisition layer and the storage layer include more than one layer, then layer 134 may be positioned between layers comprising such components. In yet other alternative embodiments, the layer 134 comprises more than one layer. In this case, additional layers could be sandwiched between any of the components of the absorbent article.

In yet other alternative embodiments, a fluid-stable layer 134 can be excluded, in which case the synthetic fibers in the acquisition layer 130 and the storage layer 132 can be bonded directly to each other. In these later embodiments, the moisture-insensitive fibers in the acquisition layer 130 will be bonded to other moisture-insensitive fibers, the synthetic fibers in the storage layer 132.

The storage layer 132 is preferably located between the acquisition layer 130 and the backsheet of the absorbent article. The storage layer 132 provides a means for absorbing and storing bodily fluids and is generally at least slightly resiliently compressible (but preferably not compressible), conformable, and non-irritating to the skin of the wearer. This deposition layer 132 may be referred to as a stirred layer. The deposition layer 132 comprises a web or fiber web, preferably in the form of a homogeneous mixture of fibers. The blended storage layer 132 comprises at least two fiber groups (or types). These fibers include a first group (or type) of fibers and a second group (or type of fibers). The first group of fibers comprises low denier fibers, relatively short, hydrophilic fibers. The second group of fibers comprises from about 5%, preferably at least about 10 or 20% to about fibers in the storage layer or fibers having a higher denier, longer, non-moisture sensitive synthetic fibers. (The percentage of fibers in the storage layer 132 refers only to the relative weight of the fibers and does not include the weight of the hydrogel-forming absorbent polymer.) The ratio in the blend between the two groups of fibers may be varied to produce particular properties that require different types of absorbent articles. These components and properties of the storage layer 132 are discussed in more detail below.

The fibers in the first group of fibers may have different lengths and deniers, provided that these fiber properties are less than those of the fibers in the second group of fibers. The fibers in the first group of fibers preferably have a length of less than or equal to about 1.3 cm (1/2 inch), more preferably less than or equal to about 0.6 cm (about 1/4). The fibers in the first group of fibers preferably have a denier per fiber (or continuous filament) of less than or equal to about 15, more preferably less than or equal to about 10, and most preferably less than or equal to about 2.

· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · Φ · φ ·

The first group of fibers may include natural fibers such as cotton or cellulose. The cellulosic fibers may be in the form of pulverized wood pulp, known as airfelt. The first group of fibers may alternatively or additionally comprise synthetic fibers including, but not limited to, PET, polypropylene, polyethylene, rayon, chemical thermal or mechanically pulped pulp (or CTMP or TMP), ground wood or cross-linked cellulose fibers. The fibers in the first group of fibers are either naturally hydrophilic or can be treated to be hydrophilic by treatment with any of the methods described above

The function is improved by selecting a relatively stiff fiber from the first group, which retains a substantial part of its wetting resistance of the fibers of the first group. This means that the fibers should have a high compressibility modulus. Preferably, the selected fibers are both resistant to wet and dry compression and are both wet and dry resilient (i.e., they tend to both resist compression and roll back when compressed). Chemically reinforced fibers are particularly preferred in this regard.

The fibers in the second fiber group are generally longer than the fibers in the first fiber group. The fibers in the second group of fibers should also have a high modulus of compression and should maintain a relatively high modulus when wetted. The fibers in the second group of fibers should also be wet and dry elastic. Suitable fibers for inclusion in the second group include, but are not limited to, synthetic fibers included in any of the materials described above as being suitable for use as the acquisition layer fibers 130.

The lengths of fibers, denier, etc. may be the same but are not necessarily the same. For example, the synthetic fibers in the acquisition layer may be 94. 4 4 4 4 4 4

4 9 4 9 9 4 9 4 • · * · · 99 494444

4444 4444 444 94 ·· t> 4 be one denier, eg a denier may be about 15, to aid fluid uptake and for greatest flexibility and synthetic fibers in the storage layer may have a lower denier, such as about 2. Some preferred fiber lengths, eg, for synthetic fibers in the deposition layer are described below.

The fibers in the second group of fibers preferably have a curl length greater than or equal to about 0.6 cm (about 1/4 inch), more preferably greater than or equal to about 1.3 cm (1/2 inch). The fiber denier in the second fiber group is preferably larger than the fiber denier in the first fiber group. The fibers in the second fiber group preferably have a denier per fiber ranging from about 1 1/2 or 2 and about 50 or 60, and more preferably between about 6 and about 40. even more preferably, the denier of fibers in the second fiber group is between about 12 or 15 and about 30, and most preferably is between about 12 and about 25.

The fibers in the second group are insensitive to fluid. This means that the fibers in the second group of fibers are not substantially affected by the presence of moisture and therefore do not collapse when wetted. However, these fibers can transport fluids along their surfaces. The fibers in the second group may be hydrophilic, hydrophobic or partially hydrophilic and partially hydrophobic. The fibers in the second group of fibers preferably have at least some hydrophilic components (which may be cellulosic components. The fibers in the second group of fibers may be provided with a hydrophilic component in a number of suitable ways. These include but are not limited to coating or treating the fibers to be hydrophilic or at least their surfaces.

One suitable type of synthetic fiber for use in the second group of fibers is crimped polyester fibers. Suitable synthetic fibers are such as PET fibers previously available from Eastman Kodak Textile Fibers Division Kingsport, TN as the KODEL® series 200 and 400.

ΦΦ · · · ·

One suitable fiber type is KODEL® 410. A suitable polyester fiber is KODEL® 431. These KODEL® fibers have a denier of 15 per fiber and a length of about 1.3 cm (about 0.5 inches). and are preferably crimped at a curl frequency of between about 2 and 3.2, preferably about 2.4, more preferably 2.52 curls per linear cm (ie between 5 and 8, preferably about 6, even more preferably 6.3 curl per inch). Preferably, the fibers are crimped at an angle of curl in the range of 70 ° to about 91 °, more preferably about 88 °. The crimping ensures that the fibers have improved flexibility, among other desirable properties. The fibers may be coated with a hydrophilic or hydrophobic treatment by any suitable method of the prior art.

In alternative embodiments, it is possible to replace the natural fibers in the first group of fibers with very short, low denier synthetic fibers (with hydrophilic surfaces). The blended deposition layer in such embodiments would consist of a first group of short, low denier hydrophilic fibers (such as CELWET® treated polyester fibers) and a second group of long, crinkled high denier synthetic fibers. The blended deposition layer 132 also comprises absorbent hydrogel-forming polymers in amounts as set forth in C (1) above. The mixed storage layer 132 is also preferably compressed to a density of at least about 0.09 g / cm ³ (1.5 g / cubic inch). The blended layer 132 may be compressed to densities of at least about 0.25 g / cm ³ (4.0 cubic inches) to improve the wick effect for the fluid (i.e., the distribution of fluids to other parts of the storage layer) while maintaining good softness and flexibility. . The mixed storage layer 132 may be compressed to densities up to about 0.35 g / cm ³ to about 0.40 g / cm ³ (5.6 g / in ³ to about 6.4 g / in ³ ). However, these higher density cores can become relatively stiff. Therefore, if the storage layer 132 is compressed to a density of about 0.35 g / cm ³ to about 0.40 g / cm ³ , it is preferably mechanically bent or otherwise treated prior to being placed in place. • · · · ♦ * · ······ to make it more flexible. For simplicity, the above density values do not include the weight of all particles of absorbent hydrogel-forming polymer. Thus, the overall density of the storage layer will be greatly influenced by the amount of absorbent polymer in the hydrogel-forming storage layer, making it impractical to attempt to express everything including the overall range of densities for the storage layer.

The three components of the preferred multilayer absorbent core 120, the acquisition layer 130, the fluid stable layer 134, and the storage layer 132 are preferably joined together by adhesives applied between adjacent surfaces of the components. The bonds between the components of the multilayer absorbent core 120 are particularly illustrated in FIG. 2. The body facing side of the acquisition layer 130 is attached to the underside (or garment facing side) of the topsheet 112 by adhesive 166. The garment facing side of the acquisition layer 130 is bonded with the body-facing side of the fluid-stable layer 134 with adhesive 167. The garment-facing side of the fluid-stable layer 134 is in turn attached to the body-facing side of the storage layer 132 with adhesive 168. The multilayer absorbent core 120 is also bonded between the topsheet 112 and the backsheet 116 with adhesives shown as layers 166 and 169. These adhesives are applied between the multilayer absorbent core 120 and the respective inward facing surface (or garment side) of the topsheet 112 (as described above) and the backsheet side. 116.

Adhesives are shown schematically as layers in Fig. 2 for simplicity, but the adhesives need not be applied in the form of layers only. Adhesives may be applied by any of the methods described in connection with adhesives used to bond the acquisition layer to the topsheet (ie, spiral, etc.). In addition, other types of connection means can be used.

- 93 • ·

The multi-layer absorbent core components may be joined together by any of the attachment means described above with respect to the attachment of the acquisition layer to the topsheet. However, it is to be understood that the different distinct layers of the multilayer absorbent core may not all be attached by the same type of attachment means. The layers of the multilayer absorbent core may be bonded to each other by various attachment means or, if adhesives are used, different types of adhesive compositions or schemes may be used between layers. In the preferred embodiment shown in Fig. 2, the layers of the multilayer absorbent core are preferably held together by an open pattern adhesive mesh network comprising a series of adhesive fibers coiled into a spiral pattern.

The crimped synthetic fibers in the acquisition layer 130 and the storage layer 132 play an important role in the wet integrity of the components of the multilayer absorbent core 120. The crimped synthetic fibers in the acquisition layer 130 and the storage layer 132 should preferably be sufficiently long to form at least portions surfaces of these respective components. Synthetic fibers will generally be long enough to form at least a portion of the surface of a given layer if they have lengths ranging from lengths equal to the layer thickness in which they are up to lengths greater or equal to 50% greater in length than the thickness of the layer in which they are.

Synthetic fibers or portions thereof that form part of the surface of the acquisition layer and the storage layer can be bonded by adhesives to adjacent layers, since the synthetic fibers are moisture insensitive, will be able to bond to the topsheet 112 in a liquid (not shown). This ensures that the bonds do not fail when the absorbent article 110 is wetted with body effluents. Liquid-stable bonds are also formed. * Φ ♦ · · · φφφφφφ · * · · · · · · · · · «· ·

- 94 - ............ * · * ’· (

between the garment facing surface of the acquisition layer 130 and the fluid stable layer 134 (or there is no inner fluid stable layer then the body facing surface of the storage layer 132). The crimped synthetic fibers will also form fluid-stable bonds between the garment-facing surface of the fluid-stable layer 134 and the body-facing surface of the storage layer 132. The fluid-stable bonds will also be formed between the garment-facing surface of the layer 132 and the body-facing surface. backsheet 116.

The topsheet, the fluid-stable layer, and the backsheet are also fluid-stable in that they generally resist stretching when wet and are able to fold as support substrates for other layers such as the acquisition layer 130 and the storage layer 132. The acquisition layer 130 and the storage layer The layers 132 are subject to stretching and are stretched apart under the forces associated with carrying and loading the absorbent article 110 with body fluids. However, the acquisition layer 130 and the storage layer 132 are joined to these fluid-stable layers at designated locations with a fluid-stable bond. Thus, the acquisition layer and the storage layer are in fact anchored to the topsheet, the backsheet, and the middle in the liquid-stable layer in such a way that the bonds connect these nonwoven layers to the liquid-stable layers. Thus, the acquisition layer and the storage layer are able to utilize the stretching resistance of adjacent substrates to resist separation of the inner layers (i.e., failure in stretching or strain) by the forces accompanying the wearing of the absorbent article 110 such as bending, wearer and article loading. body fluids.

Consequently, the construction of the multilayer absorbent core described above provides an interconnected, compression-resistant, fluid-stable matrix of synthetic fibers and fluid.

999 999 ·

9 9 9 stable components that are connected to each other and remain connected during use. Thus, the multilayer absorbent core 120 is resistant to both compression and tensile forces (i.e., forces related to stress) so that its void volume is retained and may remain in this state prior to use when wetted and under load associated with the wear of the absorbent article. .

Another suitable absorbent core according to the present invention comprises a primary core integrity layer, preferably formed from a continuous network of melt blown material that surrounds the core to ensure integrity, especially when its improved U.S. Patent No.

No. 387,208, which is incorporated by reference, ensuring the integrity of the core, which in particular is connected to the body forming the skeleton of the absorbent article, is preferably directly connected to the topsheet. Preferably, the bond between the primary core integrity layer and the carcass component is relatively cohesive and thus tends to retain its strength in use, such as that in the sense that the absorbent core has a reduced tendency to separate from the carcass component The absorbent cores have a reduced tendency to slip and / or separate from one another, especially after wetting.

Preferably, the core core-coated absorbent core comprises a plurality of absorbent layers (one of the absorbent layers comprising a high concentration of a mixed bed absorbent hydrogel-forming polymer having at least a PUP capacity and preferably PHL and SFC values as described in B (1). (b) above) with at least one secondary core integrity layer positioned between the one or more absorbent layers. In a particularly preferred embodiment, the absorbent core is:

including a acquisition / distribution layer, a storage layer, and a material layer disposed between the acquisition / distribution layer and the storage layer. The secondary core integrity layer is preferably located between the acquisition and distribution layer and the material layer.

The primary and secondary core integrity layers are preferably formed from a thermoplastic material, more preferably hot melt adhesive, such that the core integrity layers can be easily formed during the on-line assembly of the absorbent article. More preferably, the core integrity layers are formed from a hot melt elastomer adhesive. Elastomeric hot melt adhesives tend to be elastic, so there is less tendency to break or break the bonding of the bonds that connect the individual parts in the product (as compared to non-elastomeric adhesives. As a result, the absorbent core tends to remain in place and retain its integrity. is when the core bonding layers are formed from an elastomeric hot melt adhesive The pressure sensitive adhesive further reduces the tendency of the absorbent core components in addition to the primary and secondary core integrity layers to separate from the other absorbent core components and, in particular, effectively reducing slippage or separation of the acquisition and distribution layers over the storage layer.

One such absorbent core is shown in Figure 3. 3 illustrates in cross-section an absorbent article designated 210 having a topsheet 212 a backsheet 216 and an absorbent core 220 positioned between the topsheet 212 and the backsheet 216. As shown in this figure, the core 220 is secured as including a storage layer 280 , which includes a highly concentrated mixed bed of absorbent bed 9 9 9 9 9 999999

9 · ·

- 97 - ........ * ·· ·· ^β · * · z

The hydrogel-forming polymers, the material layer 270, and the acquisition and distribution layer 250. As also shown in FIG. 3, the core 220 also has a primary core integrity layer 230 and a secondary core integrity layer 240. The core core integrity layer 230 is positioned between the bottom layer 216 and the storage layer 280. The core core integrity layer 240 is located between the acquisition and distribution layer 250 and the material layer 270. As also shown in FIG. the core integrity extends beyond and surrounds the side edges of the acquisition and distribution layer 250, the side edges of the material layer 270, the edges of the storage layer 280, and the garment facing surface of the absorbent core 220. Giant. 3 also shows structural layers 290, 292, 294 and 296 of adhesives.

As shown in FIG. 3, the secondary core integration layer 240 is attached to the material layer 270 by a structural adhesive layer 292. The secondary core cohesion layer 240 is located adjacent the acquisition and distribution layers 250. Depending on the bond strength of the secondary layer 240 providing core integrity to the acquisition / distribution layer 250, the core integrity layer 240 may be associated with the acquisition / distribution layer 250 based on the heat-melting properties or pressure-sensitive properties of the preferred core-layer secondary layer 240.

As further shown in Fig. 3, the material layer 270 is bonded to the deposition layer 280 by the structural adhesive layer 294. The primary core integrity layer 230 is positioned adjacent to the deposition layer 280. Depending on the bond strength of the core integrity layer 230 material For example, the core 230 may be bonded to the deposition layer 280 by properties associated with heat melting or sensitivity to the pressure of the preferred core layer material 230 providing core integrity.

As further shown in FIG. 3, the acquisition and distribution layer 250 is bonded to the top layer 212 by the structural adhesive layer 290. The primary layer 230, providing layer integrity, is bonded to the bottom layer 216 by the structural adhesive layer 296 and to the top layer 212 by material properties. core integrity layers 230 that are related to hot melt or pressure sensitivity.

As shown in Figure 3, the structural adhesive layer 290 extends beyond the side edges of the acquisition and distribution layers 250 and within the side edges of the material layer 270. The structural adhesive layer 290 may be wider than the material layer 270 to achieve a primary bond. However, for economic reasons, it will carry out separate application of the structural adhesive to effect this bond. The structural adhesive layer 292 is shown in FIG. 3 and has the same extent as the structural adhesive layer 290. The structural adhesive layer 294 extends within the side edges of the storage layer 280 and, for economic reasons, preferably extends transversely to a maximum width of about the narrowest width of the absorbent core storage layer 280 in the crotch region, as shown in FIG. adhesive 296 extends inside between the side edges of the primary layer 230, ensuring core integrity. Alternatively, the structural adhesive layer 296 may extend beyond the lateral edges of the core integrity layer 230 to provide core integrity to form a bond of the backsheet 116 to the topsheet 212. In the preferred embodiment, the structural adhesive layers 290, 292, 294 and 296 are applied along the entire length. (not shown) of at least one of the following layers:

99 acquisition and distribution layers 250, material layers 270, storage layers 280, bottom layers 216, or top layers 212.

A core integrity layer 230 that preferably surrounds at least one layer of absorbent core 220 and which is bonded, preferably directly bonded, to the carcass forming part (e.g., topsheet 212 or backsheet 216) of the absorbent article. The primary core integrity layer 230 tends to improve the integrity of the absorbent layers it surrounds. Thus, in a preferred embodiment, the core core integrity layer 230 surrounds each of the absorbent core layers 220. Thus, the following description focuses on the core core integrity layer 230 that surrounds each of the absorbent core layers 220. However, it is understood that improving integrity For example, the integrity of the acquisition / distribution layer 250, and hence the absorbent core 220, can be improved by surrounding only the acquisition and distribution core. In addition, the core integrity layer 230, which does not surround any of the absorbent core layers, can be used to improve the integrity of the absorbent core. core. For example, the surface dimensions of the core integrity layer 230 may be smaller than the dimensions of each absorbent core layer (the core integrity layer 230 would then be positioned and bonded as described herein for the secondary core integrity layer, which does not surround any layer of absorbent core). However, it is believed that the increased integrity of the absorbent core is achieved when the core core layer 230 provides the integrity of the core.

00 0 · 0 000

0 0 0 • ♦ ·

100 surrounds at least one layer of the absorbent core, so this embodiment is preferred.

By the term enclosed is meant that the primary core integrity layer 230 surrounds or envelops at least a portion of the absorbent core 220 (or layer thereof). In a preferred embodiment, the core core integrity layer 230 surrounds at least a portion of the side edges of the absorbent core 220 and at least one of the surfaces of the absorbent core. The primary core integrity layer 230 will generally surround the side edges of one or more layers in the Y-Z directions.

In addition, the core core integrity layer 230 serves to maintain the absorbent core 220 in a relatively stable position, since the absorbent core will be physically limited by the core core integrity layer 230. It is also contemplated that the core core integrity layer 230 helps to maintain adhesive bonds that typically connect the absorbent core and the chassis component of the absorbent article, e.g., where a structural adhesive is used to join the components. The primary core integrity layer 230 may be particularly useful in maintaining the integrity of the adhesive bonds, which typically bond the cellulosic fibers of the absorbent core 220 to a polymeric chassis, particularly a chassis made of or coated with a polymeric material (hereafter a synthetic polymer chassis).

Because the core bonding primary layer 230 forms a relatively strong bond and physically limits the absorbent core 220, the core bonding primary layer 230 tends to reduce the forces that occur with the relatively weak adhesive bonds between the cellulosic fiber structure and the polymeric chassis. so these second links tend to have a lower tendency.

- 101 «· ·· break. Further, if the adhesive bonds between the cellulosic fiber structure and the polymer chassis actually fail, the relatively strong bond between the primary layer ensuring core integrity tends to keep the absorbent core in a relatively stable position. Thus, the absorbent core has a reduced tendency to separate from the chassis forming member. This positive effect on adhesion can be particularly important when the absorbent article is wetted. When the cellulosic fibers and the hydrogel-forming absorbent polymer that are incorporated into the absorbent core expand upon wetting, the forces exerted by the expanding cellulosic fibers and the hydrogel-forming absorbent polymer tend to cause loss of adhesion between the fibers, the hydrogel-forming absorbent polymer and the chassis. adhesive failure occurs between the fibers and / or hydrogel-forming absorbent polymer and the structural adhesive rather than between the chassis and the structural adhesive).

By effectively reducing the absorbent core, the tendency of the core core layer 230 to reduce core integrity that other layers in the absorbent core 220 slip or separate from one another is also reduced. This tendency to slip or to separate further decreases where the core core integrity layer 230 includes a sticky pressure-sensitive material. It is believed that the physical constraints described above, the relatively strong bonding of the primary layer 230, providing core integrity, and / or stickiness reduce the tendency of the absorbent core or its components to collapse, crumble, or twist. As a result, the absorbent core can be used more efficiently so that the absorbent article has improved absorbent properties and reduced leakage.

The primary core integrity layer 230 includes a continuous liquid permeable network of thermoplastic material. The thermoplastic material is preferably fusible.

102 an adhesive, more preferably a hot melt pressure sensitive adhesive. The thermoplastic material is also preferably elastomeric.

It is understood that the thermoplastic material is in the form of strands which are interconnected to form holes. As produced by the melting process, the individual strands are preferably sinusoidal (wavy) and oriented substantially in the same direction with at least some transverse bonding to form an interwoven network of strands. The strands are meant to include fibers, yarns, long plastic fibers, and other forms having a relatively large longitudinal dimension relative to the cross-sectional dimension. A fluid permeable network is understood to mean that the network has a sufficient number of openings of sufficient size per unit area to allow relatively unhindered transport of fluid through the network, and hence, the network typically has a basis weight as described herein.

By continuous network is meant that substantially all of the strands are connected to at least one other strand. Ropes are usually cohesively bonded at all points where they intertwine. (In the art, cohesion is understood to mean the force that holds molecules of one and the same material together. Relatively cohesion is used herein in the sense that bonds result from an attractive force between two or more similar materials, eg two or more synthetic polymeric materials. )

Various thermoplastic materials as known in the art may be used to form the core integrity layer 230. Examples of thermoplastic materials include polymers of ethylenically unsaturated monomers such as polyethylene, polypropylene, polystyrenes, polyvinyl chloride, polyvinyl acetate, polymethylmethacrylate, polyethylacrylate, polyacrylonitrile and the like, copolymers of ethylenically unsaturated monomers such as copolymers of ethylene and propylene, styrene

Or polyvinyl acetate, styrene and maleic anhydride, methyl methacrylate, ethyl acrylate or acrylonitrile, methyl methacrylate and ethyl acrylate and the like; acrylonitrile-styrene-butadiene rubber and the like, saturated and unsaturated polyesters including alkyds and other polyesters, nylons and other polyamides, polyesteramides and polyurethanes, chlorinated polyethers, epoxy polymers and cellulose esters such as cellulose acetobutyrate and the like. Mixtures of thermoplastic materials, including but not limited to physical copolymer blends, may also be used. Particularly suitable thermoplastic materials are polyethylene, polypropylene, polyesters, ethylene vinyl acetate, and mixtures thereof.

Various hotmelt adhesives (adhesives) as known in the art may also be used. Hot melt adhesives are generally based on one or more types of thermoplastic materials such as those described above. Thus, the hot melt adhesives used in the present invention may be any thermoplastic material or a composition comprising a thermoplastic material. Various hot melt adhesives known in the art are useful for this purpose.

The thermoplastic material is preferably elastomeric. Elastomeric materials appear to be particularly suitable for maintaining the integrity of the absorbent core while the absorbent core is subjected to bending or torsion forces as encountered in use. It is believed that the elastomeric adhesives have better adhesion to the components of the absorbent article than the non-elastomeric adhesives, especially under the dynamic conditions occurring when the absorbent article is used. By elastomeric, elastic or elastic is meant that the material is capable of stretching to at least twice its initial length and shrinks back to approximately its original length upon release. Examples on

Elastomeric hot melt adhesives include thermoplastic elastomers such as ethylene, vinyl acetate, polyurethanes, mixtures of polyolefins with a hard component (generally a crystalline polyolefin such as polypropylene or polyethylene) and a soft component (such as ethylene-propylene rubber) copolyesters such as polyethylene terephthalate with ethylene azlate and thermoplastic elastomeric block copolymers having thermoplastic end blocks of a centric rubber block, referred to as block copolymers of the ABA type, blends of different homopolymers or copolymers, e.g., a blend of polyethylene or polystyrene with a block copolymer of ABA; a low molecular weight resin modifier, eg, a blend of styrene-isoprene-styrene block copolymers with polystyrene and an elastomeric hot melt adhesive described herein. Elastomeric hot melt adhesives of these types are described in more detail in U.S. Patent No. 4,731,066, which is hereby incorporated by reference.

Preferred hot melt adhesives for forming the core integrity layer are hot melt adhesives. Fusible pressure-sensitive adhesives as understood by those of ordinary skill in the art have some degree of surface tack at the temperature of use. These tacky materials typically have a viscosity at room temperature (about 20 ° C to about 25 ° C) which is low enough to permit good contact yet high enough so that the materials to resist separation under stress, typically on the order of 10 ⁴ - 10 ⁶ cP. Due to the surface tack, the pressure sensitive adhesives used herein tend to increase the coefficient of friction between the components of the absorbent article, which may be in addition to the pressure sensitive adhesive, such as absorbent core layers, moreover pressure sensitive adhesives provide flexibility in manufacture. with other components of the absorbent article, the medium may then be present

Tata through the pressure sensitivity of the adhesive after the adhesive has solidified. Various fusible pressure-sensitive adhesives known in the art are suitable for use herein.

Preferred hot melt pressure sensitive adhesives are also elastomeric. Elastomeric fusible pressure-sensitive adhesives are described in U.S. Pat. No. 4,731,066, incorporated herein by reference, and include those based on thermoplastic block copolymers, polyacrylates, and ethylene vinyl acetate. Suitable elastomeric, melt pressure-sensitive adhesives include A-B-A block copolymer adhesives, which are specified as H-2085 and H-2031 from Findley Adhesives Inc. from Wauwatosa, WI, USA.

The primary core integrity layer 230 can be formed using a pneumatic spinning process. Processes for the pneumatic deposition of fused fibers and devices are generally known in the art. Generally speaking, the thermoplastic material is heated and maintained at a temperature sufficient to allow pneumatic processing of the molten polymer, typically until the material is in a liquid or molten state (melting and liquefaction temperature). (Generally, the choice of any given temperature in the melt process is limited by the degradation temperature of the respective thermoplastic material being processed.) The molten and liquefied material is extruded under pressure (gun pressure) by spray gun nozzles. After extrusion, the molten liquid material is subjected to an air flow under pressure (air pressure), thereby spinning the material (forming strands). The molten material from the gun and the air are heated to the temperature required in the gun and the air pressure to facilitate formation of the fiber strand. During and after the strand formation, the thermoplastic material is cooled to form stabilized strands of thermoplastic.

0000 00 00 0000 00 000 00 0 00 0 00 00 00 000000

0 0 0 0 0 0 0000 0000 000 00 00 00

- 106 material. The apparatus is arranged to be laid on the desired substrate.

that the ropes are

The parameters of the spinning deposition process are preferably selected to give a web having a certain strand and denier orientation. These parameters include melting or liquefaction temperature, gun temperature, air pressure, and air temperature. In a particularly preferred embodiment, these parameters are varied to allow the formation of sinusoidal (wavy) strands that are oriented substantially in the same direction with certain transverse bonds to form an interwoven strand network. In addition, it is generally desirable to provide strands having a relatively large denier value since the degree of wetting of the thermoplastic material to the absorbent core of the absorbent core integrity has an increasing strand denier.

denier of at least about 60 microns, preferably from about 80 microns to about 200 microns, more preferably about 90 to about 200 microns, most preferably about 100 to about 200 microns.

the degree of improvement is increasing and hence the tendency

The strands preferably have

In general, as the viscosity of the thermoplastic material, which is pneumatically applied and spun, decreases, the formation of strands appears more easily, and the resulting strands tend to have a finer denier. Viscosity also affects the orientation of the strands, and the orientation tends to be more random as the viscosity decreases. The viscosity for a given material generally decreases with increasing melting or liquefaction temperature, and especially with increasing gun temperature. Therefore, the melting and liquefaction temperatures and gun temperatures are chosen to provide a viscosity that allows the formation of strands as needed.

The melting point is generally from about 121 ° C (250 ° F) to about 204 ° C (400 ° F), preferably about 149 ° C (300 ° F) to about 0 ° C (300 ° F). 107 107 - 107 107 107 107 - 107 107 107 107 107 107 107 107 107 107 107 107 107 107 107 107 107 107 107 107 107

190 ° C (375 ° F). The adhesives referred to as H-2031 and H-2085 are generally maintained at a temperature of about 135 ° C (275 ° F) to about 204 ° C (400 ° F), preferably about 149 ° C (300 ° F) to about 177 ° C (350 ° F), more preferably about 165 ° C (330 ° F).

The temperature in the gun is generally at the melting point, preferably above this second temperature to facilitate the formation of strands. The temperature in the gun is generally from about 149 ° C (300 ° F) to about 204 ° C (400 ° F), preferably about 163 ° C (325 ° F) to about 190 ° C (375 ° F), even more preferably about 182 ° C (360 ° F).

Air pressure affects both strand and denier orientation.

For a given material and group of process temperatures (especially gun temperature and air temperature) as air pressure increases, the strands tend to form with a more random orientation and a finer denier. The air pressure is preferably at least high enough to form strands of molten or liquefied thermoplastic material that contact and are therefore capable of bonding while the thermoplastic material is in a sufficiently molten / liquid state as described below. In a preferred embodiment, the air pressure is selected to allow the formation of sine-like strands in substantially the same direction with a particular transverse connection to form an interwoven strand network. Therefore, it is preferred that the air pressure is not so high as to cause random strands to be formed. The air pressure is generally from about 4 psi to about 15 psi, preferably about 6 to about 10 psi, even more preferably about 7 to about 9 psi, most preferably about 8 psi.

The air temperature will generally be chosen to maintain the extruded thermoplastic material in a molten or liquefied state. Therefore, the air temperature will usually be greater than or equal to the gun temperature to compensate for all the cooling effects, φ φ * ΦΦ ΦΦ

ΦΦ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ φ

- 108 ΦΦ φ φ φ «φ that might otherwise appear. The air temperature is preferably such as to provide bonding of the individual strands of thermoplastic material to the substrate (although the extruded material may not be in the same molten or liquefied state as when it was first extruded, preferably it is molten or liquefied to an extent sufficient to achieve strand bonding). the air temperature is preferably from about 204 ° C (400 ° F) to about 238 ° C (460 ° F), preferably from about 215 ° C (420 ° F) to about 227 ° C (440 ° F), more preferably about 221 ° C (430 ° F). After cooling to a temperature sufficient to re-solidify the thermoplastic material, the resulting network of interwoven strands stabilizes.

The thermoplastic material is deposited on the substrate (eg, an absorbent core component such that it does not substantially affect the absorption of the absorbent core. Therefore, the basis weight of the thermoplastic material network is generally from about 2 to about 8 g / m ² , preferably about 3 to about 7 g / m 2 ² , more preferably about 4 to about 6 g / m ² , most preferably about 5 g / m ² .

The particular melt application device used herein is generally selected according to the width of the absorbent core (or absorbent core plies) to be wrapped. Generally, a device is chosen which will provide in one step the width of the network of thermoplastic material sufficient to wrap the absorbent core. (Where a primary core integrity layer or a secondary core integrity layer is described herein that has wrapped at least a portion of the side edges of the core, it is selected that the molten adhesive spray gun provides a mesh width that is less than the width of the absorbent component core). For the absorbent articles of the present invention, a 2-module 3.0-wide gun is suitable.

AMBI-3.0-2 and 4 modules with width 6 called AMBI-6.0-4, • φφ * φ · · · · ·

Φ Φ Φ 4 * ΦΦΦ ΦΦΦ

ΦΦΦ · »φ φ φ φφ

- 109 # · φφ • φ · φ · · · · · · · available from J&M Laboratories in Dawsonville, GA.

The primary cohesive layer 230 is preferably formed by a spunbond process in the continuous process (on-line) during manufacture of the absorbent article. Alternatively, the primary cohesive layer 230 of the core 230 may be formed by the above-mentioned spinning process or conventional methods within that part of the process that occurs prior to later incorporation into the absorbent article. Thus, the primary cohesive layer 230 of the core 230 may be a preformed fluid-permeable nonwoven web comprising strands of thermoplastic material, but since the use of preformed nonwoven tends to increase the final cost of the absorbent article, this alternative is not preferred.

As described above, the core cohesive core layer 230 is preferably positioned to include an absorbent core 220. The core cohesive core layer 230 is also attached to at least one chassis component (i.e., topsheet 212 and bottomsheet 216) of the absorbent core. 210. In a particularly preferred embodiment, the core cohesive core layer 230 is directly attached to the chassis component, preferably to the topsheet 212. The primary cohesive core layer 230 may be attached to the chassis component by structural adhesive. Alternatively, the core cohesive core layer 230 may also be attached to the chassis component by properties of the core cohesive core layer 230 thermoplastic material that it has when it is a hot melt or by its pressure sensitivity when these types of materials are used.

- 110

In a particularly preferred embodiment, the cohesive primary layer 230 of the core 230 is directly attached to the chassis component by a structural adhesive. Suitable structural adhesives include any adhesive materials known in the art for attaching absorbent cores to chassis components, including those described herein in the section relating to bonding the backsheet 216 to the absorbent core 220. The structural adhesive may include any of the hot melt adhesives described in parts relating to thermoplastic materials for forming a primary layer to provide core cohesion 230.

The structural adhesive may be applied to a given substrate (i.e., the cohesive core layer 230 and core absorbent member or chassis component by conventional methods as described herein in the section for bonding the backsheet and absorbent core. The structural adhesive is preferably applied. As used herein, the term open adhesive construction is intended to be present on the substrate in a configuration that allows relatively free transfer of fluid into and through the absorbent core. U.S. Patent Nos. 4,573,986, 3,911,173, 4,785,996, and 4,842,666, which are hereby incorporated by reference, and thus the open configuration of the structural adhesive may include a fine arrangement of tiny spheres of the structural adhesive or a web of adhesive. The fine beads and fibers may have roughly the same diameters in the order of magnitude as the average diameter of the fibers that form the absorbent core 220. The structural adhesive may also be applied by a spinning process, including the process described for manufacturing the primary core cohesion layer 230.

9

In a particularly preferred embodiment, the absorbent core 220 comprises a secondary cohesive layer 240 provided between the different absorbent layers, preferably the absorbent core bands or webs. (It should be understood by those skilled in the art that such absorbent layers, like the absorbent core, may have a garment facing surface, a body facing surface, side edges and end edges.) thus, positioned between the primary core cohesion layer 230 and the part of the chassis to which the primary core integrity layer is attached. (Where the primary core cohesion layer but only surrounds a portion of the absorbent core layers 220, the secondary core strength layer 240 may be positioned between the absorbent core layers that are not surrounded by the primary core cohesion layer.) a network of thermoplastic material as defined in the core cohesive layer section 230. The secondary cohesive layer 240 is attached to the chassis component and may be directly attached thereto, e.g., where the secondary cohesive layer 240 surrounds the absorbent layers. a core positioned between the secondary layer to ensure the cohesion of the core 240 and the chassis.

The secondary cohesive layer 240 may or may not surround one or more absorbent layers of the absorbent core 220. As seen in FIG. 3, the transverse width of the secondary cohesive layer 240 is less than the transverse width of any of the different absorbent layers of the absorbent core. . the transverse width of the core integrity layer 240 is less than the transverse widths of any of the acquisition and distribution layers 250, the tissue paper layer 270, and the storage layer 280). Secondary layer · vrstva · * vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva vrstva · · · · ·················

The cohesive core 112, 112, does not surround the side edges of the acquisition / distribution layer 250, the tissue paper layer 270, and the storage layer 280.

Alternatively, the secondary cohesive layer 240 may surround the absorbent layers as described for the primary cohesive layer 230. The extent of the surrounding may be the same or different from the primary cohesive layer 230 or any other secondary layer. cohesion of the core. Thus, the cohesive secondary layer 240 may surround relatively other longitudinal portions of the side edges of the absorbent layer and / or other surface or relative surface portion of the absorbent layer.

The secondary core integrity layer 240 may be formed from a thermoplastic material and process as described for the primary core integrity layer. The secondary core integrity layer 240 may be formed from the same thermoplastic material as the primary core integrity layer 230, or other thermoplastic material. For ease of processing, the secondary core cohesion layer 240 is preferably formed from the same thermoplastic material as the primary core integrity layer 230. In addition, the secondary core integrity layer 240 may be formed using process parameters that are the same or different from those which are used to form a primary core layer 230 to provide core cohesion. Preferably, the same process parameters are used so that the secondary core cohesion layer 240 has a basis weight and the strands of the thermoplastic material from which it is formed have a denier and orientation that are substantially the same as the primary core cohesion layer.

- 113 -

The secondary cohesive layer 240 may be attached to one or more layers of the absorbent core or to the chassis components. The bonding may be accomplished using structural adhesive and / or by melt properties and / or pressure sensitivity of the core bonding core material 240 as described for the bonding of the core bonding primary layer 230 to the chassis component.

The absorbent article 210 shown in FIG. 3 can be formed as follows. A secondary core integrity layer 240 is formed on the garment facing surface of the acquisition and distribution layer 250. The core integrity layer 240 is bonded to the tissue paper layer 270 by a structural adhesive layer 292, which is preferably applied to the tissue paper surface 270 that is facing the body. The garment facing surface of the tissue paper web 270 is then bonded to the storage layer 280 by a structural adhesive layer 294 that is preferably applied to the garment facing paper web 270. The resulting laminate is then bonded to the topsheet 212 by a structural adhesive layer 290 that attaches the acquisition and distribution layer 250 to the topsheet 212. The primary bonding layer core 230 is formed on the garment facing surface 280 of a portion of the layer surface the garment-facing fine tissue paper 270 (corresponding to the difference transverse distances between the lateral edges of the storage layer 280 and the side edges of the tissue paper layer 270) and the garment-facing surface portion 112 of the upper layer 112 the side edges of the primary layer to provide core cohesion

- 114 230). The backsheet 216 is then bonded to the primary core bonding layer 230 by the structural adhesive layer 296 and to the topsheet 212 by the structural adhesive (not shown).

Another suitable absorbent core of the present invention may be in the form of a mixed bed layer of hydrogel-forming absorbent polymers positioned between two other fibrous layers, e.g., a laminated absorbent core. Suitable laminated absorbent cores of the present invention can be prepared using procedures similar to those described in U.S. Patents 4,260,443, 4,467,012, 4,715,918, 4,851,069, 4,950,264, 4,994,037, U.S. Pat. U.S. 5,009,650, U.S. 5,009,653, U.S. 5,128,082, U.S. 5,149,335 and U.S. 5,176,668 (all of which are hereby incorporated by reference) but using a mixed bed of mixed bed absorbent polymers having at least the PUP capacity and preferably the PHL and SFC values as described in paragraph B (1) (b) above.

Other suitable laminated absorbent cores according to the present invention including thermally bonded layers are disclosed in U.S. Patent No. 141,156, issued October 21, 1993, which is hereby incorporated by reference. These thermally bonded absorbent cores include:

(1) a primary thermally bonded fluid distribution layer;

(2) optionally but preferably, a secondary fluid distribution layer which communicates from a fluid standpoint and is capable of receiving aqueous body fluids from the primary distribution layer;

(3) a fluid storage layer that communicates in fluid terms with either the primary or secondary fluid distribution layer, which comprises a mixed bed of absorbent polymers forming a highly concentrated hydrogel having a PUP capacity and preferably the PHL and SFC values described in B (1) ( (b) above; and (4) optionally a dusting layer adjacent to the deposition layer.

layers. These absorbent cores are typically used in conjunction with a thermally bonded acquisition layer (called a secondary topsheet).

An embodiment of these thermally bonded absorbent cores is shown in Figure 4. 4 illustrates a cross-section of an absorbent article particularly useful as a sanitary napkin, designated 310, having a primary liquid permeable topsheet 312, a liquid impermeable backsheet 316, and an absorbent structure positioned between the topsheet 312 and the backsheet 316, including a liquid acquisition layer 314 which is commonly referred to as the secondary topsheet and absorbent core designated 320. As can be seen from this figure, the absorbent core 320 is shown in Figure 4 as a core comprising three components: a fluid distribution layer 324, a fluid storage layer 326 and the fibrous scrubbing layer 328. In forming this absorbent core, the scrubbing layer 328 provides an initial layer on which a mixed bed of absorbent hydrogel-forming absorbent polymers 326 is deposited. The distribution layer 324 is then placed over the deposited blended bed. e absorbent, hydrogel-forming material thereby forming a laminate structure of the type. While it is possible to bond the dusting layer 328 and the distribution layer 326 using adhesive, the two layers are generally joined together by hot sealing, since each of these layers comprises some thermoplastic material, typically thermoplastic bonding fibers.

An alternative embodiment of this heat-sealed absorbent core is shown in Fig. 5. Fig. 5 shows a cross-section of an absorbent article particularly useful as a sanitary napkin, designated 410, having an upper layer 412 and a lower layer 416 and an absorbent core designated 420, positioned. between the topsheet 412 and the backsheet 416. How is the fl layer 416?

- 116 - • · ·  · • fl · it is obvious FIG. 5, absorbent 420 core includes four components: primary layer on distribution fluid 424, secondary layer on distribution fluid 430, layer on

the fluid storage 426 and the fibrous dusting layer 428. Again, the dusting layer 428 provides a mixed bed deposition of absorbent hydrogel-forming absorbent polymers 426. The secondary and primary distribution layers 430 and 424 are then positioned above the stored absorbent polymers to form a laminate type structure. . This laminate is generally bonded together by hot sealing.

Giant. 4 and 5. As with the embodiment shown in FIG. 4, the absorbent article 510 comprises a topsheet 512, a backsheet 516, and an absorbent structure positioned between the topsheet 512 and the backsheet 516, including the secondary topsheet 514 and FIG. As shown in Figure 5, the absorbent core 520 of Figure 6 includes four components: a primary fluid distribution layer 524, a secondary fluid distribution layer 530, a fluid storage layer 526, and a fibrous dusting layer 528.

Other suitable absorbent cores of the present invention can be prepared from meltblown synthetic fibers and blends of various forms (eg, cellulose blends and meltblown synthetic fibers, etc.) as described in U.S. Patent No. 5,149,335 , which is hereby incorporated by reference. For example, a web comprising 75% hydrogel-forming absorbent polymer having a PUP capacity and preferably the PHL and SFC values described above in B (1) (b) and 25% fine fibers (less than 5 microns in diameter) from the melt by spinning the copolymer can be formed. of HYDROFIL® LCFX fibers. The meltblown web is then coated on one surface with a meltblown layer

- 117 -

The HYDROFIL® strip (see Examples 2 and 3 of U.S. Pat. No. 5,149,335). The absorbent core thus formed is then placed between two layers of bilobal polypropylene by spinning the bonded material (see Examples 2 and 3 of U.S. Pat. No. 5,149,335), wherein the spinning material is heat sealed around the edge of the absorbent structure.

Absorbent cores comprising a meltblown layer and absorbent hydrogel-forming polymer particles having a PUP capacity, and preferably the PHL and SFC values described in B (1) (b) above, also formed according to the process described in U.S. Pat.

No. 429,001, which is hereby incorporated by reference. In some absorbent articles, two or more separately formed layers of these hot melt fibers and absorbent polymer particles can be folded to form a thicker absorbent core, the melt stream by blowing the formed fibers and absorbent polymers can be deposited on another layer of material such as porous a nonwoven web to form part of an eventual absorbent core. Other fibers may be introduced into the absorbent core in addition to the meltblown fibers. For example, crimped fibers can be mixed with the meltblown fibers together with the absorbent polymer particles to increase volume to provide a more aerated or lighter absorbent core.

E. Absorbent products

Because of the unique absorbent properties of the absorbent cores of the present invention, these cores are particularly suitable for use in absorbent articles, especially disposable absorbent articles. As used herein, the term absorbent article means articles that absorb and contain body fluids, and more particularly means articles that are placed on or near the body of the wearer to absorb and

118 contained various fluids ejected from the body. In addition, disposable absorbent articles are those intended to be disposed of after a single use (i.e., the original absorbent article as a whole is not intended to be cleaned or otherwise remedied or reused as an absorbent article; when certain materials or the entire absorbent article can be recycled, reused or composted). A particularly preferred embodiment of the disposable absorbent article of the present invention is a diaper. As used herein, the term diaper means a piece of clothing generally worn by young children and incontinent persons, which is worn around the lower torso of the wearer. However, it should be understood that the present invention is also applicable to other absorbent articles such as incontinent pants, incontinent pads, sports pants, diaper inserts, sanitary napkins, sanitary napkins, facial tissues, paper towels and so on.

Such absorbent articles generally include a liquid impervious backsheet, a liquid pervious topsheet attached or otherwise bonded to the backsheet, and an absorbent core of the present invention positioned between the backsheet and the topsheet. The topsheet is positioned adjacent the body surface of the absorbent core. The topsheet is preferably bonded to the absorbent core and the backsheet by means of fasteners such as those well known in the art. The term associated as used herein includes an arrangement wherein the element is directly attached to the second element by attaching the element directly to the second element and the arrangement, wherein the element is indirectly attached to the second element by attaching the element to the element or elements that are therebetween to the next element. In particularly preferred products, the topsheet and the backsheet are directly bonded to one another by: Φ Φ ♦ ♦ φ φ

119 that is directly attached to the absorbent core by attachment means.

The backsheet is generally impervious to body fluids and is preferably made of a thin plastic film, although other flexible fluid impervious materials may also be used. The term flexible as used herein refers to materials that are compliant and easily conform to the general shape and contours of the human body. The backsheet prevents body fluids that are absorbed and contained in the absorbent core from wetting articles that come into contact with them, such as panties, pajamas, underwear, and the like. The backsheet may comprise a woven or nonwoven material, polymeric films such as thermoplastic films of polyethylene or polypropylene, or composite materials such as a nonwoven material covered with the film. Preferably, the backsheet is of polyethylene film having a thickness of from about 0.012 mm (0.5 mil) to about 0.051 mm (2.0 mil). Such polyethylene films are, for example, manufactured by Clopay Corporation of Cincinnati, Ohio, USA under the designation P18-0401 and by Ethyl Corporation, Visqueen Division of Terre Haute, Indiana, under the designation XP-39385. The backsheet is preferably embossed or matt to provide a more fabric-like appearance. The backsheet may further allow vapors to escape from the absorbent core (ie, to breathe) while still preventing body fluids from passing through the backsheet.

The top layer adapts, is soft to the touch and does not irritate the wearer's skin. Furthermore, the topsheet is liquid pervious and allows body fluids to readily penetrate through its thickness. A suitable topsheet can be manufactured from a wide range of materials such as woven and nonwoven materials, polymeric materials such as formed thermoplastic apertured films, plastic apertured films, and hydroformed thermoplastic materials.

- 120 9 · · »»

Foils, porous foams, reticulated foams, reticulated thermoplastic foils, and thermoplastic scratches. Suitable woven and nonwoven materials may consist of natural fibers (eg, wood or cotton fibers), synthetic fibers (eg, polymer fibers such as polyester, polypropylene or polyethylene fibers) or a combination of natural and synthetic fibers.

Preferred topsheets for use in the absorbent articles of the present invention are selected from high-air nonwoven topsheets and apertured films. The formed apertured films are particularly suitable for the topsheet because they are permeable to body fluids and yet do not absorb them and have a reduced tendency to allow the fluids to pass back and rewet the wearer's skin. The surface of the formed film that is in contact with the body remains dry, thereby reducing soiling of the body surface and making the wearer feel more comfortable. Suitable shaped films are described in U.S. Patent No. 3,929,135, U.S. Patent 4,324,246, U.S. Patent 4,342,314, U.S. Patent 4,463,045 and U.S. Patent 5,006,394. All of these patents are incorporated herein by reference. Particularly preferred topsheets of micro-hole formed film are described in U.S. Pat. No. 4,609,518 and U.S. Pat. A particularly preferred topsheet for use in the menstrual articles of the present invention is the molded film described in one or more of the above patents and marketed on sanitary napkins by The Procter & Gamble Company of Cincinnati, Ohio as DRI-WEAVE®.

The body-facing surface of the topsheet of the molded film may be hydrophilic to help body fluids pass through the topsheet faster than it would be if the surface was not hydrophilic to reduce

The likelihood that fluid will flow from the top surface instead of flowing into it and being absorbed by the absorbent structure. In a preferred embodiment, a surfactant is incorporated into the polymeric materials of the formed topsheet film as described in U.S. Patent Application Serial No. 07 / 794,745 entitled Absorbent Product Having a Nonwoven Perforated Film Covering, which is hereby incorporated by reference. . Alternatively, the body-facing surface of the topsheet may be rendered hydrophilic by treatment with a surfactant as described in the aforementioned U.S. Patent 4,950,254, incorporated herein by reference.

F. Testing methods

1. Conductivity for saline flow (SFC)

This test determines the conductivity for saline flow through a gel layer formed from a hydrogel-forming absorbent polymer, a mixture of hydrogel-forming polymers in neutralized form, or a mixed bed of a hydrogel-forming ion-exchange polymer blend (hereinafter referred to as a hydrogel-forming polymer) which swells in Jayco synthetic urine pressure. The aim of this test is to assess the ability of a hydrogel layer formed from absorbent hydrogel-forming polymers to absorb and distribute body fluids when the polymers are present at high concentrations in the absorbent member and are exposed to the mechanical pressures prevailing in their use. Darcy's law and steady-state flow methods are used to determine the conductivity for saline flow. (See, e.g., Absorbency, edited by P. K. Chatterjee, Elsevier, 1985, pages 42-43 and Chemical Engineering Vol. II, Third Edition, J.M. Coulson and J.F. Richardson, Pergamon Press, 1978, pp. 125-127.)

- 122 -

• 4 4 4 4

4 4 4 4

444 444 • 4 5

• 4

For hydrogel-forming polymers in neutralized form, the hydrogel layer used to measure SFC is formed by swelling the absorbent hydrogel-forming polymer in Jayco synthetic urine for 60 minutes. The hydrogel layer is formed and its flow conductivity is measured under a mechanical restraining pressure of 0.3 psi (about 2 kPa). Flow conductivity is measured using a 0.118 M NaCl solution. For hydrogel-forming absorbent polymers whose Jayco synthetic urine uptake has substantially equaled over time, it has been found that this NaCl concentration keeps the hydrogel layer thickness substantially constant during measurement. For some absorbent hydrogel-forming absorbent polymers, small variations in the thickness of the hydrogel layer may occur as a result of the polymer swelling, decreasing the swelling of the polymer, or changes in the porosity of the hydrogel layer. A constant hydrostatic pressure of 4920 dynes / cm ² (5 cm 0.118M NaCl) is used for measurement. For a mixed bed of a mixture of ion exchange polymers forming a hydrogel, the swelling time is typically extended to 225 minutes to give the sample more time to equalize and the NaCl concentration is generally adjusted (generally to a lower concentration) so that only minor changes in the hydrogel layer thickness occur.

The flow rate is determined by measuring the amount of solution flowing through the hydrogel layer as a function of time. The flow rate may vary during the measurement. The causes of the flow changes include changes in the thickness of the hydrogel layer and changes in the viscosity of the interstitial fluid as the fluid present initially in the interstitial voids (which may contain dissolved extractable polymer, for example) is replaced by a NaCl solution. If the flow rate depends on time, then the initial flow rate obtained by extrapolating the measured flow rates to zero time is generally used to calculate the conductivity for the flow. The conductivity for the saline solution is calculated from the initial flow rate, hydrogel layer dimensions and hydrostatic pressure. For systems where

- 123 • ··

99

9 9 9

9

9

9

9

As the flow rate is substantially constant, the permeability coefficient of the hydrogel layer can be calculated from the conductivity for the saline solution and the viscosity of the NaCl solution.

A suitable apparatus 610 for this test is shown in Figure 7. The apparatus comprises a constant hydrostatic pressure reservoir, generally designated 612, which sits on a laboratory jack, generally designated 614. The reservoir 612 has a cap 616 with a stopper bleed, designated 618, so that additional fluid may be added to the reservoir 612. An open end tube 620 is inserted through the lid 616 to allow air to enter the reservoir 612 to deliver fluid at a constant hydrostatic pressure. The lower end of the tube 620 is positioned to hold the fluid in the cylinder 634 at a height of 5.0 cm above the bottom of the hydrogel layer 668 (see Figure 8).

The reservoir 612 is provided with a generally L-shaped delivery tube 622 having an inlet 622a that is below the surface of the fluid in the reservoir, the fluid supply through the tube 622 being controlled by the shut-off valve 626. 628, there is a support screen (not shown) and a collection container 630, which sits on a laboratory scale 632.

Referring to Fig. 7, the assembly 628 consists essentially of a cylinder 634, a piston generally referred to as 636, and a cap 637 provided with piston holes 636 and a delivery tube 622. As can be seen from FIG.

7, output 622b tubing 622 is located below bottom end tubes 620 and therefore will be also under surface fluid (not as shown) cylinders 634. How it is evident from Fig. 8 composed

with a piston 636 of a generally cylindrical shaft 638 of LEXAN® having a concentric cylindrical bore 640 downwardly drilled in place of the longitudinal axis of the shaft. Both ends of the shaft 638 are machined to form the ends 642 and 646. At the end 642 a weight 648 rests having a cylindrical bore 648a in its center.

At the other end 646, a generally circular teflon piston head 650 having an annular recess 652 at its bottom is mounted. The piston head 650 is sized to slide within the cylinder 634. As shown in particular in Fig. 9, the piston head 650 is provided four concentric circles of the twenty-four cylindrical bores, generally designated 654, 656, 658 and 660. As shown in Fig. 9, concentric circles 654 to 660 fall within the area defined by recess 652. The apertures in each of these concentric circles they are drilled from top to bottom in the piston head 650. The holes in each circle are spaced about 15 ° apart and are deflected about 7.5 ° from holes in adjacent circles. The apertures in each circle have a progressively smaller diameter inwardly from circle 654 (0.204 inch diameter, i.e. 5.2 mm diameter) to circle 660 (0.111 inch diameter, i.e. 2.8 mm). The piston head 650 also has a cylindrical bore 662 drilled in its center extending to the end 646 of the shaft 638.

As shown in FIG. 8, a fritted circular glass disc 664 fits into the recess 652. A 400 mesh stainless steel mesh 666 is attached to the lower end of the cylinder 634, which is biaxially pulled prior to application. A sample of the mixed bed of absorbent hydrogel-forming polymer, designated 668, is supported by a sieve 666.

The cylinder 634 is drilled from a transparent LEXAN® bar or equivalent and has an inner diameter of 6.00 cm (area = 28.27 cm ² ), a wall thickness of about 0.5 cm, and a height of about 6.0 cm. The piston head 650 is made of a solid Teflon rod. It has a height

15.9 mm (0.625 inches) and a diameter that is slightly smaller than 9 9 ··· 4 • 9 ··

- 125 ··· the inside diameter of the cylinder 634, so it fits into the cylinder with minimal clearances on the walls but still so that it moves freely. The recess 652 is approximately 56 mm in diameter with a depth of 4 mm. Hole 662 in the center of piston head 650 has a 15.9 mm (0.625 inch) threaded hole (18 turns per inch = 7 turns per cm) for end 646 of shaft 638. Frit disc 664 is selected for high permeability (eg, Chemglass Cat No. CG201-40, 60 mm in diameter, coarse porosity in the X direction) and is milled so that it fits tightly into the recess 652 of the piston head 650 so that the bottom of the disc is flush with the bottom of the piston head. The shaft 638 is machined from a LEXAN® rod and has an outer diameter of 22.2 mm (0.875 inches) and an inner diameter of 6.3 mm (0.250 inches). The end 646 is approximately 0.5 inches long and threaded to fit into the bore 662 in the piston head 650. The end 642 is approximately one inch long and has a diameter of 15.8 mm (0.623 inches) to form an annular protrusion for support The fluid passing through orifice 640 in shaft 638 can reach directly to frit disc 664. Stainless steel annular weight 648 has an inner diameter of 15.9 mm (0.625 inches) so that it slides to end 642 of shaft 638 and rests on annular casting created in it. The combined weight of the fritted glass disc 664, the piston 636, and the weight 648 is 596 g, which corresponds to a pressure of 0.3 psi, i.e. 2.06 kPa per area

28.27 cm ² . The cap 637 is machined from LEXAN® or equivalent and is sized to cover the top of the cylinder 634. It has a 22.3 mm (i.e. 0.877 in) bore at its center for the piston shaft 638 and a second bore near its edges for the inlet pipe 622.

Roller 634 rests on a rigid 16 mesh stainless steel sieve (not shown) or equivalent, the sieve is sufficiently permeable to not impede the flow of fluid to the collecting container 630. The sieve is generally used to support the cylinder 634 when the brine is flowing file

- 126 9 9 9 9 9 · · 9 9 9 9 9 • •• 9 999 9 999 9

9 9 99 99 9

9 9 9 9 9

9999 99999 999 99 9 · 99 i

628 greater than about 0.02 g / s. For flow rates less than about 0.02 g / s, it is preferred that there be a continuous fluid path between the cylinder 634 and the collecting container. This can be accomplished by replacing the support sieve, collecting container 630, and analytical weights 632 with the analytical balances 716, the reservoir 712, the fritted funnel 718 and the associated coupling tubes and apparatus valves 710 (see FIG. 10) and placing the cylinder 634 on the frit disc in the frit funnel 718. .

Jayco Synthetic Urine used in this method is prepared by dissolving a mixture of 2.0 g KCl, 2.0 g Na ₂ SO ₄ , 0.85 g NH ₄ H ₂ PO ₄ ,

0.15 (NH ₄ ) ₂ HPO ₄ , 0.19 g CaCl ₂ and 0.23 g MgCl ₂ make up to 1.0 liter with distilled water.

A 0.118 M NaCl solution is prepared by dissolving 6.896 g of NaCl (Baker Analyzed Reagent or equivalent) to make up to a volume of 1.0 L with distilled water.

Typically, an analytical balance 632 to an accuracy of 0.01 g (e.g., a Mettler PM4000 or equivalent) is used to measure the amount of fluid flowing through the hydrogel layer 668 when the flow rate is about 0.02 g / sec or greater. For less permeable hydrogel layers having low flow rates, more accurate weights (eg, Mettler AE200 or equivalent) may be required. The scales are preferably connected to a computer to monitor the amount of fluid over time.

The thickness of the hydrogel layer 668 in the cylinder 634 is measured to an accuracy of about 0.1 mm. Any method having the desired accuracy can be used unless the weights are removed and the hydrogel layer is not additionally compressed or disrupted during measurement. For measuring the vertical distance between the bottom of the stainless steel weight 648 and the top of the lid 637 relative to this distance without the hydrogel layer 668 in the cylinder 634, use is acceptable

- 127 • 0 00 * ·· 00 0 0 • 0 0 0 00 0 0 »» · 0 · 00 0000 0000 0000 0000 0000 0000 0000 000000 • 0 0 0 0 0 0

0000 0000 000 00 00 00

calipers (eg Manostat 15-100-500 or equivalent). It is also acceptable to use a depth gauge (e.g.

Ono Sokki EG-225 or equivalent) to measure the position of piston 636 or stainless steel weight 648 relative to any solid surface as compared to its position without a hydrogel layer in cylinder 634.

The SFC measurement is performed at ambient temperature (ie 20 ° - 25 ° C) and is performed as follows:

The hydrogel-forming absorbent polymer is put in an aliquot of 0.9 g (corresponding to a basis weight of 0.032 g / cm ² ) into the cylinder 634 and distributed evenly on a sieve 666. For most hydrogel-forming absorbent polymers, the moisture content is generally less than 5% . In these, the amount of hydrogel-forming absorbent polymer to be added can be determined on a wet weight basis (as is). For hydrogel-forming absorbent polymers having a moisture content greater than about 5%, the added weight of the polymer should be corrected for moisture (i.e., the added polymer should be 0.9 g on a dry weight basis). Care should be taken to prevent the hydrogel-forming absorbent polymer from sticking to the cylinder walls. The piston 636 (minus the weight 648) with the disc 664) positioned in the recess 652 of the piston head 650 is inserted into the cylinder 634 and placed on top of the dry hydrogel-forming absorbent polymer 668. If necessary, the piston 636 can be gently rotated to distribute the gel forming absorbent polymer 668 more evenly across the screen. The cylinder 634 is then covered with the lid 637 and the weight 648 is then placed at the end 642 of the shaft 638.

The fritted disc (coarse or extra coarse) having a diameter greater than the diameter of the cylinder 634 is placed in a wide flat-bottomed shallow container which is filled up to the top of the fritted disc with jayco synthetic urine. Set of piston and cylinder

- 128 · «ftft · · · · · · ftft ft · · · ftftft ···· ft ftft ftft ftft • ftftft ftftft * • ftft ftftftft • · ftft ftftft ftftft • ftft ftft ftftft ftft ftft ftft

628 is then placed on top of the fritted glass disc. Fluid from the reservoir passes through the frit disc and is absorbed by the hydrogel-forming absorbent polymer 668. As the polymer absorbs liquid, a layer of hydrogel forms in the cylinder 634. After 60 minutes, the thickness of the hydrogel layer is determined. Care should be taken to ensure that the hydrogel layer does not lose fluid or absorb air during this process.

The piston / cylinder assembly 628 is then transferred to the apparatus 610. The support screen (not shown) and the gap between it and the piston / cylinder assembly 628 are pre-saturated with saline. If a frit funnel 718 of the PUP apparatus 710 is used to support the cylinder 634, the surface of the frit funnel should be at least increased relative to the fluid level in the collecting container with the valves between the frit funnel and the collecting container in the open position. (The height position of the fritted funnel should be sufficient to prevent the liquid from passing through the hydrogel layer in the funnel.)

SFC measurement is initiated by adding NaCl solution through hole 640 to shaft 638 to expel air from piston head 650 and then rotate shut-off valve 626 to open position so that supply tube 622 supplies fluid to cylinder 634 at a height of 5.0 cm above the bottom of the layer Although the measurement is considered to be initiated (t ₀ ) at the time the NaCl solution is first added, the time (t _s ) at which a stable hydrostatic pressure corresponding to 5.0 cm salt solution and a steady flow is achieved is noted. (The time t _s should generally be about one minute or less.) The amount of fluid passing through the hydrogel layer 668 as a function of time is determined gravimetrically for 10 minutes. After the time has elapsed, remove the plunger and cylinder assembly 628 and measure the thickness of the hydrogel layer 668. Generally, the change in thickness of the hydrogel layer is less than about 10 * ·

- 129 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 999 999 · * ·

The flow generally need not be constant. The time dependence of the flow through the system F _s (t) is determined in units of g / s by dividing the weight gain of the liquid passing through the system (in grams) by the increase in time (in seconds). Only data collected between time t _s and time 10 minutes are used to calculate the flow. The flow results over a period of time between ts and 10 minutes are used to calculate the value for F _s (t = 0), ie the initial flow through the hydrogel layer. F _s (t = 0) is calculated by extrapolating the least-squares results for F _s (t) at t = 0.

For a layer having a very high permeability (i.e., a flow greater than about 2 g / s), it may not be practical to collect the fluid for 10 minutes. For flow rates greater than about 2 g / s, the collection time may be reduced in proportion to the flow rate.

For some hydrogel-forming absorbent polymers having extremely low permeability, fluid absorption by the hydrogel competes with fluid transport through the hydrogel layer and either fluid does not flow through the hydrogel layer and into the reservoir, or it may be possible for the liquid to be absorbed cleanly from the PUP reservoir. For these extremely low permeability hydrogel layers, it is possible to extend the Jayco synthetic urine absorption time for a longer period (e.g., 16 hours).

Separately, the flow through the apparatus 610 and the piston assembly with the cylinder 628 (F _a ) are measured as described above except that the hydrogel layer is not present. If F _{a is} much greater than the flow F _s through the system when the hydrogel layer is present, then there is no need for correction for flow resistance in the SFC apparatus and in the cylinder piston assembly. At this limit state F _g = F _s , where F _g is the contribution of the hydrogel layer to the flow through the system, but

If this requirement is not satisfied, then it is used to calculate the value of F _g from the values of F _s and F _{and the} following corrections:

F _g = (F _and x F _s ) / (F _and -F _s )

The conductivity for the saline solution (K) of the hydrogel layer is calculated using the following equation:

K = {F _g (t = 0) χ! Ι ₀ } / {ρχΑχΔΡ}, where F _g (t = 0) is the flow in g / s determined from the results of flow regression analysis and eventual correction due to flow resistance in the set or apparatus , L _o is the initial thickness of the hydrogel layer in cm, p is the density of the NaCl solution in g / cm ³ . A is the area of the hydrogel layer in cm ² , ΔΡ is the hydrostatic pressure in dyn / cm ² and the conductivity for saline K is in cm ³ s / g.

The average of the three determinations should be reported.

For hydrogel layers where the cross-section is substantially constant, the permeability coefficient (k) can be calculated from the conductivity for the saline using the following equation:

κ = K η, where η is the viscosity of the NaCl solution in Pois and the permeability coefficient κ is in cm ² .

An example showing how the SFC of the present invention is calculated is given in U.S. Patent 5,552,646.

2. Pressure Behavior (PUP)

This test determines, in grams per gram, the absorption of synthetic urine in a hydrogel-forming absorbent polymer, in a mixture of hydrogel-forming polymers in neutralized form, or in a mixed bed of hydrogel-forming ion-exchange polymer mixture (hereinafter referred to as hydrogel-forming polymer).

- 131 -

The J-J is then enclosed in the space defined by the plunger and cylinder assembly at a limiting pressure, e.g. 0.3 psi ie. 2 kPa, 0.7 psi i.e. 4.8 kPa, 1.4 psi i.e. 9.7 kPa. The aim of the test is to assess the ability of a hydrogel-forming absorbent polymer layer to absorb body fluids over a practical period of time (e.g., 60 minutes and 225 minutes) when polymers are present at high basis weight and high concentrations in the absorbent member and exposed to pressures in use . The pressures prevailing in which the hydrogel-forming polymer is forced to absorb urine include mechanical pressures resulting from the weight and or movements of the wearer, mechanical pressures resulting from the elastic and fastening systems, and hydrostatic suction resulting from adjacent capillary (e.g., fibrous) layers or structures as liquid is drained from them.

The liquid test for measuring PUP capacity is a test using Jayco synthetic urine. This fluid is absorbed by the hydrogel-forming absorbent polymers under the desired absorption conditions at zero hydrostatic pressure.

A suitable apparatus 710 for this test is shown in Figure 10. At one end of the apparatus is a fluid reservoir 712 (such as a petri dish) having a lid 714. The reservoir 712 rests on analytical weights generally designated 716. The other end of the apparatus 710 is a frit funnel. designated generally as 718, a plunger and cylinder assembly generally designated 720 which fits within a funnel 718, and a cylindrical plastic frit lid designated generally as 722 which can be placed over the funnel 718 and is open at the bottom and closed at the top, Apparatus 710 has a system for conveying fluid in both directions, consisting of portions of glass capillary tubes designated 724 and 731a, flexible plastic tubes (eg, a 1/4 inch inner diameter Tygon tube, i.e. 6.35 mm),

3/8 inches (9.53 mm) labeled 731b, and the outside diameter of the closure sets 4 · · · <

»· · · · · · · · ·

132 taps 726 and 738 and teflon connectors 748, 750 and 752 to connect the glass tubes 724 and 731a and the sets of shut-off valves 726 and 738. The set of shut-off valve 726 consists of a 3-way valve 728, glass capillary tubes 730 and 734 the liquid system and the glass capillary tube portions 732 for replenishing the reservoir 712 and frying the frit disc forward in the frit funnel 718. The shut-off valve assembly 738 likewise consists of a 3-way valve 740, glass capillary tubes 742 and 746 in the main fluid line and portions with a glass capillary tube 744 that acts as a drain for the system.

Referring to Fig. 11, the assembly 720 consists of a cylinder 754, a bowl-shaped piston designated 756, and a weight 758 that fits into the piston 756. attached to the lower end of the cylinder 754 is a stainless steel woven sieve 759 No. 400 mesh which is biaxial stretching before connection. The hydrogel-forming absorbent polymers, generally referred to as 760, rest on a sieve 759. The cylinder 754 is drilled from a transparent rod of LEXAN (or equivalent) and has an inner diameter of 6.00 cm (28.27 cm ^{2 area} ) with a wall thickness of approximately 5 mm and a height of approximately 5 cm. The piston 756 is dish-shaped and is of Teflon and machined to fit into the cylinder 754 with a low tolerance. The cylindrical stainless steel weight 758 is machined to fit freely into the piston 756 and is provided with a lever (not shown) at the top for easy removal. For a limiting pressure of 0.7 psi, ie 4.8 kPa, the combined weight of the piston 756 and the weight is 758 1390 g, which corresponds to a pressure of 0.7 psi, ie 4.8 kPa for an area of 28.27 cm ² .

The components of apparatus 710 are sized so that the flow of synthetic urine through it at a hydrostatic pressure of 10 cm is at least 0.01 g / cm ² / s, normalized by the frit funnel area 718. Factors that have a particular impact on flow are frit permeability discs in fritted funnel • 9 · 9 9 · · 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 9 • · * · · · ·

133 718 and the inner diameters of the glass tubes 724, 730, 734, 742, 746 and 731a and the stopcocks 728 and 740.

The container 712 is mounted on an analytical balance 716 that is accurate to within 0.01 g with a drift of less than 0.1 g / h. Preferably, the scales are connected to a computer by software that then (1) monitors balance weight change at predetermined time intervals since the PUP test commences and (2) sets to start automatically at a weight change of 0.010.05 g depending on the sensitivity of the scales. The capillary tube 724 entering the container 712 should not touch either its bottom or the lid 714. The volume of fluid (not shown) in the container 712 should be sufficient to prevent air from entering the tube 724 during measurement. The fluid level in the cartridge should be approximately 2 mm below the top surface of the frit disc in the funnel 718 at the start of the measurement. This can be verified by placing a small drop of fluid on the frit disc and gravitationally monitoring its slow flow back into the cartridge 712. The cartridge should have a sufficiently large diameter (e.g., about 14 cm) such that withdrawal of about 40 mL results in a change in fluid height of less than 3 mm.

Prior to measurement, the sample was filled with jayco synthetic urine. The frit disc in the frit funnel 718 is flushed forward by being filled with fresh synthetic urine. To the extent possible, it is removed from the bottom surface of the fritted disc and the system that connects the funnel to the air bubble reservoir. The following procedures are performed by sequential control of three 3-way stopcocks:

1. Remove excess fluid on the top surface of the frit disc (i.e., pour from the frit funnel 718).

• · • ·

- 134 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·

2. Adjust the solution height / weight of container 712 to the correct level / value.

3. The fritted funnel 718 is positioned at the correct height relative to the cartridge 712.

4. The fritted funnel 718 is then covered with a funnel frit lid 722.

The cartridge 712 and the fritted funnel 718 are aligned with the valves 728 and 740 of the shut-off valve assemblies 726 and 738 in the open coupling position.

6. Valves 728 and 740 are then closed.

7. The valve 740 is then rotated so that the funnel is opened to the discharge tube 744.

8. In this position, the system is allowed to equilibrate for 5 minutes.

9. The valve 740 then returns to its closed position.

Steps 7 to 9 temporarily dry the surface of the frit funnel 718 by subjecting it to a small hydrostatic suction of about 5 cm. This suction is used if the open end of the tube 744 extends about 5 cm below the level of the frit disc in the frit funnel 718 and is filled with synthetic urine. Typically, about 0.2 g of fluid is withdrawn from the system during this procedure. This procedure prevents premature absorption of synthetic urine when the plunger and cylinder assembly 720 is placed in the frit funnel 718. The amount of fluid withdrawn from the frit funnel in this process (called frit funnel correction amount) is measured by performing a PUP test (see below) for 15 minutes without the plunger and cylinder assembly 720. Essentially all fluid withdrawn from the frit funnel by this procedure is quickly absorbed again by the funnel when the test begins. Therefore, this correction weight should be subtracted from the weight of fluid removed from the reservoir during the PUP test (see below).

0.9 g of hydrogel-forming absorbent polymer 760 (corresponding to a basis weight of 0.032 g / cm ² ) is added to the cylinder 754.

135 • 9

For most hydrogel-forming absorbent polymers, the moisture content is generally less than 5%. For these polymers, the added weight of the polymer can be determined on a wet weight basis (as is). For polymers having a moisture content greater than about 5%, the added weight of the polymer should be corrected for moisture (i.e., the added weight of the polymer should be 0.9 g on a dry weight basis). Care is taken to prevent the hydrogel-forming absorbent polymer 760 from sticking to the inner walls of the cylinder 754. The piston 756 is inserted into the cylinder 754 and placed on top of the hydrogel-forming absorbent polymer 760. The plunger may be gently rotated to aid in the distribution of the hydrogel-forming absorbent polymer. The plunger and cylinder assembly 720 is located on top of the fritted portion of funnel 718, the weight 758 is inserted into the piston 756, and the top of the funnel 718 is then covered with the funnel frit lid 722. After checking the data shown by the weights for stability, the test is initiated by opening the valves 728 and 740 to connect the funnel 718 and the reservoir 712. At automatic initiation, data acquisition immediately begins as the funnel 718 begins to absorb liquid.

Data is recorded as a function of time for 225 minutes.

The moisture content of the hydrogel-forming absorbent polymer is determined separately by measuring the loss in% wt for 3 h at 105 ° C. the measured moisture content is used to calculate the dry weight of the hydrogel-forming polymer used in the PUP test.

PUP capacity (g / g; t) = [W _r (t = 0) -W _r (t) -W f _C ] / {W _h fap _; where W _r (t = 0) is the weight in grams of the cartridge 712 before starting. W _r (t) is the weight in grams of container 712 after time t (eg 60 min or 225 min), W _fc is the correction mass of the frit funnel in grams (measured separately and W _h fa _P; of the hydrogel-forming polymer in grams.

Porosity of absorbent. - 136 *

3. Porosity of the hydrogel layer (PHL)

This test determines the porosity of a Hydrogel Layer (abbreviated PHL), formed from a hydrogel-forming polymer, a mixture of hydrogel-forming polymers in neutralized form, or a mixed bed of a mixture of hydrogel-forming ion-exchange polymers (hereinafter referred to as hydrogel-forming polymer) that swelled in synthetic urine. Jayco under restrictive pressure. The aim of this test is to assess the ability of a hydrogel layer formed from absorbent hydrogel-forming polymers to remain porous when the polymers are present at high concentrations in the absorbent member and exposed to mechanical pressures prevailing in use. PHL is a fraction of the layer volume that is not absorbed by the hydrogel. Excluded volume method is used to measure PHL under restrictive pressure.

PHL is measured using a modified version of the piston and cylinder apparatus used in the SFC method. The 0.118 M NaCl solution used in the SFC method is modified to measure PHL by dissolving the high molecular weight Blue Dextran polymer in sufficient quantity so that the resulting solution has an optical absorbency of about 0.8 absorption units at a polymer absorption maximum of about 617 nm. The molecular weight of Blue Dextran is sufficiently high that the polymer is excreted from the hydrogel. The hydrogel layer is formed and its porosity is measured under a mechanical restraining pressure of 0.3 psi, i.e. about 2 kPa.

The hydrogel layer used to measure PHL is formed by swelling approximately 0.9 g of hydrogel-forming absorbent polymer in a PHL apparatus with a Jayco synthetic urine cylinder for about 60 minutes. At the end of this period, the thickness of the hydrogel layer was determined. Fluid contained in gaps in the hydrogel ·

• · ·· · ·· ·

The layer was then replaced with a 0.118M NaCl solution containing Blue Dextran (SBDS) by flowing an excess of SBDS (optical absorbency equal to Ai) through the hydrogel layer at low hydrostatic pressure. The hydrogel-forming absorbent polymer whose Jayco synthetic urine uptake has substantially equaled over time has been found to maintain the thickness of the hydrogel layer substantially constant. It has further been found that the NaCl concentration in the SBDS keeps the hydrogel layer thickness substantially constant during this exchange step. Some hydrogel-forming absorbent polymers may exhibit minor changes as a result of polymer swelling or decreasing swelling rate. The flow of SBDS through the hydrogel layer continues until the exchange is complete. The SBDS feed is then stopped, any excess SBDS either above or below the hydrogel layer is allowed to drain or removed differently. The gaps in the hydrogel layer remain fully saturated with SBDS. The thickness of the hydrogel layer (tf) is then measured again (tf) and multiplied by the area of the cylinder (Ac) to obtain the volume of the hydrogel layer (Vhgi). The SBDS contained in the gaps in the hydrogel layer was then rinsed using an excess of (SS) NaCl solution at a concentration of 0.118M and quantitatively collected. SS flushing is continued until substantially all of the Blue Dextrin is extracted from the hydrogel layer. The volume of the collected solution containing the extracted Blue Dextrin (V _f ) is determined either volumetrically or gravimetrically and its optical absorbance (Af) is measured. The void volume (V _v ) in the hydrogel layer is determined from the measured values of V _f , Ai and A _f . The V _v value is divided by V _hg1 to determine the porosity of the hydrogel layer.

A suitable piston-cylinder apparatus for this test is shown in Fig. 12 and is similar to the piston-cylinder apparatus shown in Fig. 8. Referring to Fig. 12, the apparatus 828 basically consists of a cylinder 834, a piston generally labeled 836 and the cap 837 provided with holes for the piston 836 and the inlet and outlet

138 solution (not shown). As can be seen from Fig. 12, the piston 836 consists of a generally cylindrical shaft 838 of LEXAN® material having a concentric bore 840 drilled downwardly in the longitudinal axis of the shaft. Both ends of the shaft 838 are machined to form the ends 842 and 846. The weight designated 848 rests at the end 842 and has a cylindrical bore 848a in its center.

A generally circular piston head 850 is inserted at the other end 846. The piston head 850 is sized to slide within the cylinder 834. As specifically shown in Fig. 13, the piston head 850 is provided with an inner and an outer concentric ring of seven and eight, respectively. fourteen cylindrical apertures of 0.375 inches, i.

The holes in each of these concentric circles are drilled from the top side to the bottom side of the piston head 850. The piston head 850 also has a cylindrical bore 862 in its center to receive the shaft end 846 838.

Attached to the lower end of the cylinder 834 is a stainless steel mesh # 866 # 400 mesh, which is biaxially turned off prior to loading. Attached to the lower end of the piston head 850 is a stainless steel mesh 864 No. 400 mesh, which is biaxially turned off prior to attachment. A sample of the hydrogel-forming absorbent polymer designated 868 is deposited on a sieve 866.

The cylinder 834 is drilled from a rod of transparent LEXAN material or equivalent and has an inner diameter of 6.00 cm (area = 28.27 cm ² ), a wall thickness of approximately 0.5 cm and a height of approximately 6.0 cm. The piston head 850 is machined from a LEXAN rod. A height of approximately 0.625 and a diameter sized to fit into the cylinder with minimal wall clearance but to move freely. The bore 862 in the center of the piston head 850 has a threaded bore of 0.625 inch (18 turns / inch), i.e. 15.9 mm

(Ί threads per cm) for shaft end 846 of shaft 838. Shaft 838 is machined from a LEXAN® rod and has an outer diameter of 0.875 inches, i.e., an inch diameter. 22.2 mm and an inner diameter of 0.250 inches, ie 6.3 mm.

The end 846 is approximately 0.5 inches (12.7 mm) long and threaded to fit into the bore 862 in the piston head 850. The end 842 is approximately an inch and has a diameter of 0.623 inches, The liquid passing through the hole 840 in the shaft 838 can reach the screen 864 directly. The annular stainless steel weight has an internal diameter of 0.625 inches, i.e. 15.9 mm, so that it fits into the shaft end 842 and rests on an annular shoulder formed therein. The combined weight of the piston 836 and the weight 848 is approximately 596 g, which corresponds to a pressure of 0.3 psi, for an area of 28.27 cm ² . The lid 837 is machined from LEXAN® or equivalent and is sized to cover the top of the cylinder 834. 22.2 mm, for piston shaft 838 and second hole near its edge for solution inlet and outlet.

When the solutions pass through the piston-cylinder apparatus, the cylinder 834 generally rests on a rigid 16 mesh stainless steel carrier screen (not shown) or equivalent.

A spectrophotometer capable of measuring the optical absorption ability in the 617 nm band with an accuracy of at least 0.001 absorption units (eg a Bausch & Lornb Spectronic 21 or equivalent) is used to measure the optical absorbency. The optical absorption is measured to an accuracy of at least 0.001 absorption units relative to a 0.118M NaCl reference solution.

For measurement, a Blue Dextran polymer having an average molecular weight of about 2,000,000 (Sigma, Cat

- 140 -

Φ φ · • • • φ φ φ φ φ φ φ φ φ φ φ

D5376 or equivalent). A 0.118 M NaCl (SS) solution is prepared by dissolving 6.896 g of NaCl (Baker Analyzed Reagent or equivalent) to make up to 1.0 L with distilled water. An amount of Blue Dextran polymer is dissolved in the NaCl solution sufficient to achieve an optical absorbency of about 0.8 absorbent units (typically about 0.1 wt%). The optical absorption (Ai) of this saline solution of Blue Dextran (BBDS) is determined relative to the NaCl reference solution at a concentration of 0.118 M.

The thickness of the hydrogel layer 868 in the cylinder 834 is measured to an accuracy of at least about 0.1 mm. Any method that has the required accuracy can be used unless the weight is removed and the hydrogel layer is not compressed or disturbed during measurement. To measure the vertical distance between the bottom of the stainless steel weight 848 and the top of the lid 837 relative to the distance without the hydrogel layer 868 in the cylinder 834, it is acceptable to use a caliper (eg Manostat 15100-500 or equivalent). It is also acceptable to use a depth gauge (eg, Ono Sokki EG-225 or equivalent) to measure the position of the piston 836 or the stainless steel weight 848 relative to any of the solid surfaces for comparison with the position without the hydrogel layer in the cylinder 834.

Analytical balances of at least 0.001 g (eg Mettler AE200) are used to determine the weight of the hydrogel-forming polymer.

PHL measurement is performed at ambient temperature (ie 20 ° -25 ° C) and is performed as follows:

The hydrogel-forming absorbent polymer is put in an aliquot of 0.9 g (corresponding to a basis weight of 0.032 g / cm ² ) into

9 99 9 9 9

9999 9999 • ·

- 141 99 99 •

9 ♦ 9 * 99

9 99 99 · ··· • 9 9 9 9

99 99 99 of the roll 834 and is distributed evenly over the sieve 866. For most hydrogel-forming absorbent polymers, the moisture content is generally less than 5%. In these, the amount of hydrogel-forming absorbent polymer to be added can be determined on a wet weight basis (as is). For hydrogel-forming absorbent polymers having a moisture content greater than about 5%, the added weight of the polymer should be corrected for moisture (i.e., the added polymer should be 0.9 g on a dry weight basis). Care should be taken to prevent the hydrogel-forming absorbent polymer from sticking to the cylinder walls. The piston 836 (minus weight 848) is inserted into the cylinder 834 and placed on top of the dry hydrogel-forming absorbent polymer 868. If necessary, the piston 836 can be gently rotated to distribute the hydrogel-forming absorbent polymer more evenly over the screen 866. The cylinder 834 is then covered with the lid 837 and the weight 848 is then placed at the end 842 of the shaft 838.

The fritted disc (coarse or extra coarse) having a diameter greater than the diameter of the cylinder 834 is placed in a wide, shallow, flat bottom tray which is filled up to the top of the fritted disc with Jayco synthetic urine. The piston / cylinder assembly 828 is then placed on top of the fritted glass disc. The fluid from the reservoir passes through the frit disc and is absorbed by the hydrogel-forming absorbent polymer 868. As the polymer absorbs liquid, a layer of hydrogel forms in the cylinder 834. After 60 minutes, the thickness of the hydrogel layer is determined. Care should be taken to ensure that the hydrogel layer does not lose fluid or absorb air during this process.

The plunger and cylinder assembly 828 is then placed on a 16 mesh stainless steel rigid support mesh SBDS is then fed into the cylinder 834 through the fluid inlet (not shown) in the cylinder 837 and allowed to flow through the piston head 850 and the hydrogel layer 868, then leaves the cylinder through a sieve of cylinder 866. Suitable • flflfl ····

- 142 • flfl flflfl flfl fl flflfl flfl flflfl flfl flfl fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll fll flll 5 cm of water) is a constant hydrostatic height delivery apparatus shown in FIG. 7 (reference numerals 612-622). The solution entering through the sieve 866 is periodically sampled and measured for its optical absorbency. The flow of the SBDS is continued until essentially the replacement of the original solution contained in the voids in the hydrogel layer 8 68 with the SBDS is indicated, as indicated by the emerging solution having an obscure absorbency approximately equal to the SBDS absorbency (i.e. within about 0.001 absorption units). . Typically, the total amount of SBDS used in this step is approximately 10 * V _hg i. The addition of SBDS is then stopped and excess SBDS over the piston head 850 and the cylindrical bores 854 and 860 in the piston head 850 is drained with a hydrogel layer 868 and out of the cylinder 834 through a sieve roller 866. The thickness of the hydrogel layer (tf) is then measured again. Essentially any remaining solution remaining above the piston head 850 in the cylinder bores 854 and 860 in the piston head 850 or under the sieve of the cylinder 866 which does not flow spontaneously is then removed otherwise (eg using a disposable pipette) while minimizing any disruption to the hydrogel. layers. The volume (V _r ) of any remaining SBDS remaining in the gap between the piston head 850 and the cylinder 834 is estimated based on geometric considerations (ie the portion of the gap area (F _a ) between the piston head 850 and the inner wall of the cylinder 834 that is filled with the SBDS) multiplied by the calculated volume (V _g ) between the piston head and the cylinder wall). The gaps in the hydrogel layer 868 should remain fully saturated with SBDS. The plunger and cylinder assembly 828 are then moved, if necessary, to a different position on a rigid 16 mesh stainless steel support screen. SS cylinder 837 is then added to cylinder 834 for solution inlet and outlet (not shown) and allowed to flow through the piston head 850 and the hydrogel layer 868. The solution emerging from cylinder 834 through cylinder screen 866 in this step is quantitatively collected. Suitable • ·

- 143 -

ftft 100 99

9 9 9

989 99 9

9 9

The system for supplying SS to the cylinder and maintaining a constant but low hydrostatic pressure SS (e.g. up to about 5 cm of water column) is the apparatus for supplying a constant hydrostatic pressure, as shown in Figure 7 (reference numbers 612 to 626) . Optionally, the weights 848, the cylinder cover 837, and the piston 836 may be removed just prior to the SS replacement step (without removing the hydrogel-forming polymer or SBDS) to facilitate access to and removal of the Blue Dextran polymer contained in the gaps in the hydrogel layer. The solution emerging through the sieve of the roller 866 is periodically sampled and measured for its optical absorbency. Addition is continued until the rinse of the Blue Dextran polymer contained within the gaps in the hydrogel layer 868 is substantially complete as indicated by the emerging solution having an optical absorbency of approximately zero (e.g., less than about 0.001 absorbent units). The total volume of SS used in this step is generally about 10 * V _hg . In this step, the use of an excess of SS should be avoided as this may lead to excessive dissolution of the Blue Dextran polymer. The volume of the solution collected in this step (V _f ) is determined either gravimetrically or volumetrically. After mixing, the optical absorbency of this final solution (Af) is measured.

For a hydrogel layer having a very high permeability, a lower hydrostatic pressure is generally used in the SBDS and SS rinsing steps, or the solution may be added in some other way in portions (eg, by pipette) to control the flow rate and allow periodic sampling.

For some hydrogel-forming absorbent polymers (e.g., those having extremely low permeability), it may happen that the absorption of Jayco's solution by the hydrogel may not be in equilibrium after one hour and therefore additional fluid may be absorbed even during the solution exchange steps. For these polymers

Μ

- 144 9999 • 9

9999

99

9 9 9 ·

9 9 9 9 • 9,999,999

If desired, the hydrogel-forming hydrogens can be prolonged for a longer period of time (e.g. 16 hours) for absorbing the jayco solution. For hydrogel layers having a very low permeability, longer times for solvent exchange steps may also be required.

If the thickness of the hydrogel layer changes by more than about 10% as a result of the SBDS exchange step, then the NaCl concentration in this solution should be adjusted accordingly to reduce the extent of thickness change. This appears to be particularly necessary in the mixed bed of the hydrogel ion exchange composition, where the ion exchange has an impact on the interstitial concentration of the dissolved electrolyte.

The size-exclusive polymer used in this method should not be significantly adsorbed by the hydrogel. Thus, for example, for cationic polymers, mixtures of hydrogel-forming polymers in neutralized form that contain a cationic polymer and a mixed bed of a mixture of ion-exchange hydrogel-forming polymers, it may be necessary to use an alternative size-exclusive polymer (eg high molecular weight Dextran) or use an alternative method (eg. chromatography) to determine the relative concentrations of a solution of the size-exclusive polymer.

V _v and PHL are calculated using the following formulas: V _v = V _f * A _f / Ai-V _r PHL = V _v / V _hgl

The average of at least two determinations should be reported.

An example of how PHL is calculated in accordance with the present invention is given in U.S. Patent 5,552,646.

99

145 • 999

9

9999

9 9 9 *

9

9,999 9 ··

9 9

9 99

4. Gel volume

For most anionic hydrogel-forming absorbent polymers, gel volume can be determined by the method described in U.S. Reissue Patent 32,649 (which is hereby incorporated by reference) but using Jayco synthetic urine. The gel volume is calculated based on dry weight. The dry weight used to calculate the gel volume is determined after drying the hydrogel-forming absorbent polymers in an oven at 105 ° C for three hours.

An alternative method of measuring gel volume can be used for absorbent gel-forming polymers that absorb Blue Dextran on the surface of the formed hydrogel (eg, cationic hydrogel-forming polymers). For these hydrogel-forming polymers, the absorption capacity test is used, but the dry weight of the hydrogel-forming polymer is used in the calculation instead of the weight itself. See U.S. Patent 5,124,188, Columns 27-28 (which is hereby incorporated by reference) for a description of the absorption capacity test.

For the hydrogel-forming polymers in their non-neutralized forms, it is possible to modify the above in-situ neutralization methods to measure the gel volume of the hydrogel-forming polymer after neutralization. In these modified processes, a stoichiometric amount of either NaOH or HCl (e.g., 1.0 M Baker Analyzed Reagent) is added to Jayco synthetic urine sufficient to at least partially neutralize the hydrogel-forming polymer (e.g., from about 75% to 100%). Fine mixing is used to facilitate neutralization. For the Blue Dextran method, the added volume should be minimized as both the test and reference solutions need to be similarly adjusted and the measured optical absorbency needs to be appropriately corrected for changes in solution volume.

• 0

0

000

0 0 * 0 0 0 0 0 0 0 00 00 ·

0 · · 0 ·· ♦ · ··

5. Gel strength

The gel strength or shear modulus of the formed hydrogel is determined using the gel strength / shear modulus method described in the cited reissue US 32,649 with the following modifications: (1) the absorbent polymer forming the gel is swelled in Jayco synthetic urine (2) an oscillating rheometer having a parallel plate arrangement is used wherein the gap is set to 1.0 mm; (3) the shear modulus formula is modified for the above parallel plate arrangement; (4) the voltage amplitude is less than about 0.3% and (5) the gel forming polymers are milled (e.g., by passing a US No. 45 standard sieve (having 350 micron apertures)), if necessary, so that the hydrogel formed is filled at a high loading factor between the oscillating rheometer plates. For hydrogel-forming polymers in non-neutralized form, stoichiometric either NaOH or HCl (e.g., 1.0 M Baker Analyzed REagent) is added to Jayco synthetic urine sufficient to at least partially neutralize the hydrogel-forming polymer (e.g., from 75% to 100%).

6. Extractable polymer

The percentage of extractable polymer in carboxylic acid hydrogel-forming polymers is determined by the method of determining the extractable polymer content of hydrogel-forming carboxylic acid polymers, which is described in U.S. Patent 32,649, which is hereby incorporated by reference, but with reference to by using a 0.9% saline solution, filtering the supernatant through a Whatman glass microfiber filter of 0.7 microns GF / F (e.g., catalog number 1825-125) or an equivalent thereof and calculating the extractable polymer on a dry basis. In the reissue

147 of U.S. Pat. No. 32,640 also notes that Va should refer to the volume of the base and Vb should refer to the volume of the acid.

The percentage of extractable polymer for non-carboxylic acid-based hydrogel-forming absorbent polymers (eg weakly basic or strongly basic cationic hydrogel-forming absorbent polymers and saliva-acidic anionic hydrogel-forming absorbent polymers) is determined by a graphimetric method using distilled water, called the Extractable Content Determination. % of the polymer for the hydrogel-forming polymers containing sulfonic acid as described in said reissue US 32,649, but with the extractable polymer being calculated on a dry matter basis.

For non-neutralized hydrogel-forming polymers such as those used in mixed beds, mixtures of ion-exchange hydrogel-forming polymers are used to convert the non-neutralized hydrogel-forming polymer into its partially neutralized form of neutralization in-situ. In this procedure, a stoichiometric amount of either NaOH or HCl (e.g., 1.0 M Baker Analyzed Reagent) is added to the 0.9% saline solution, sufficient to at least partially neutralize the hydrogel-forming polymer (e.g., from about 75% to 100%).

Claims (15)

PATENT CLAIMS 1. A mixed bed of a mixture of ion exchange hydrogel-forming polymers comprising one or more cation exchange ion-forming hydrogel-forming polymers and one or more anionic ion exchange hydrogel-forming polymers, characterized in that the mixed bed of the mixture of ion-exchange hydrogel-forming polymers exhibits an increased capacity under pressure ( Performance Under Pressure (PUP) compared to a comparable blend of its cationic and anionic hydrogel-forming polymers, each at least 70% neutralized. Mixed bed of a mixture of ion exchange hydrogel-forming polymers according to claim 1, characterized in that it has a PUP capacity of at least 20% higher, preferably at least 50% higher, even more preferably at least 100% higher than the PUP capacity of a comparable mixture thereof. forming cationic and anionic hydrogel forming polymers, each of which is at least 70% neutralized. Mixed bed of a mixture of ion-exchange hydrogel-forming polymers according to claim 1 or 2, characterized in that the capacity of the PUP is measured after 225 minutes. Mixed bed of a mixture of ion-exchange hydrogel-forming polymers according to claim 1 or 2, characterized in that the capacity of the PUP is measured after 60 minutes. Mixed bed of a mixture of ion exchange hydrogel-forming polymers according to claim 1 or 2, characterized in that the PUP capacity is measured at a limiting pressure of 0.7 psi, i.e. 4.8 kPa. - 149 4 4 · 4 · * · · · · · · 4,444,444 4 4 4 4 A mixed bed of a mixture of ion exchange hydrogel-forming polymers according to claim 1 or 2, characterized in that the capacity of the PUP is measured at a limiting pressure of 1.4 psi, i.e. 9.7 kPa. 7. A mixed bed of a mixture of ion-exchange hydrogel-forming polymers comprising one or more cation-exchange ion-forming hydrogel-forming polymers and one or more anionic ion-exchange hydrogel-forming polymers, characterized in that the mixture has either (1) a PUP capacity after 225 minutes of at least 25 g / g, preferably at least 28 g / g, even more preferably at least 33 g / g at a limiting pressure of 0.7 psi, i.e. 4.8 kPa or (2) capacity PUP after 60 minutes of at least 25 g / g, preferably at least 28 g / g at a limiting pressure of 0.7 psi, i.e. 4.8 kPa. Mixed bed of a mixture of ion-exchange hydrogel-forming polymers comprising one or more cation-exchange ion-forming hydrogel-forming polymers and one or more anionic ion-exchange hydrogel-forming polymers, characterized in that the mixture has a PUP capacity after 225 minutes of at least 20 g / g, preferably at least 23 g / g, even more preferably at least 26 g / g at a limiting pressure of 1.4 psi, i.e. 9.7 kPa. A mixed bed of a mixture of ion exchange hydrogel-forming polymers according to any one of claims 1 to 8, characterized in that the cation exchange hydrogel-forming polymer (s) has an anion exchange capacity of at least 6 meq / g, preferably at least 10 meq / g, even more preferably. not less than 15 meq / g. ·················· - 150 • ············· 9 9 9 9 9 9 99 99 999 999 «· · · · 999 99 99 99 A mixed bed of a mixture of ion exchange hydrogel forming polymers according to any one of claims 1 to 9, wherein the cation exchange hydrogel forming polymer is selected from the group consisting of polydimethyldiallylammonium hydroxide, polydimethylaminoethyl acrylate, polydimethylaminoethyl methacrylate and derivatives and mixtures thereof. 11. A mixed bed of a mixture of ion-exchange hydrogel-forming polymers according to any one of claims 1 to 10, characterized in that the anionic ion-exchange hydrogel-forming polymer is selected from the group consisting of polyacrylic acid, polymaleic anhydride copolymers and derivatives and mixtures thereof. An absorbent member for storing aqueous body fluids, characterized in that it comprises at least one region comprising a mixed bed of a mixture of ion exchange hydrogel-forming polymers according to any one of claims 1 to 11. The absorbent member of claim 12, wherein the region comprises from 60% to 100%, preferably from 70% to 100%, even more preferably from 80% to 100% of the composition. An absorbent article comprising a liquid pervious topsheet, a backsheet, and an absorbent core positioned between the topsheet and the backsheet, wherein the absorbent core comprises an absorbent member according to claim 13 or 14. 15. The absorbent article of claim 14, wherein the absorbent article is a diaper.