MXPA98008010A - Superapsorbient foams colapsa - Google Patents

Abstract

A porous material for absorption of aqueous body fluids comprising superabsorbent polymers, which can swell upon absorption of aqueous liquids, and which forms a porous structure having a surface to mass ratio of at least 0.2m2 / g, characterized wherein the pores of said porous structure are collapsed to less than a third of their expanded volume before being moistened with said aqueous body fluids, and in which the pores expand upon wetting with the aqueous liquids. Collapsed material may be in particles or in a similar way as laminated

Description

COLABSED SUPERABSORBIENT FOAMS FIELD OF THE INVENTION The present invention relates to disposable absorbent articles, such as diapers, diaper products, adult incontinence products, sanitary napkins, and more particularly to disposable absorbent articles that have the capacity to retain aqueous body excrements such as urine or menstrual fluids.

BACKGROUND OF THE INVENTION Disposable absorbent articles such as diapers, incontinence articles, sanitary napkins, training pants and the like are well known in the art. Typically the disposable absorbent articles comprise a liquid pervious topsheet facing the wearer's body, a backsheet impervious to the liquid that gives the wearer's clothes, and an absorbent core interposed between the liquid permeable topsheet and the backsheet. The absorbent core often must be capable of absorbing and handling relatively large fluid volumes such as urine and other exudates discharged from the user's body. The absorbent core needs to be able to acquire, distribute and store the discharges initially deposited on the absorbent article. Preferably, the design of the absorbent core is such that the core acquires the discharges substantially immediately after they have been deposited on the top sheet of the absorbent article, with the intention that the discharges do not accumulate on or leave the surface of the top sheet since this may result in the containment of inefficient fluid by the absorbent article, which may lead to the wetting of the outer garments and the discomfort of the wearer.

Numerous attempts have been made to direct the absorption of bodily fluids in absorbent members, with respect to the improved acquisition of fluids in the absorbent article, with respect to the improved distribution of these fluids throughout the article, but also with respect in providing final storage of the improved fluid. Several patent publications deal with improvements in fluid handling performance by adding specially treated cellulosic material. For example, U.S. Patent No. 4,898,642 to Moore et al. Discloses chemically hardened, twisted cellulosic fibers and absorbent structures made therefrom, and European Patent EP 0 640 330 to Bewick-Sonntag et al. , discloses the use of these fibers in a specific arrangement with specific superabsorbent materials. The European patent discloses an absorbent article with a fibrous topsheet with pores larger than the pores of the underlying transport layer, which in turn has larger pores than the underlying absorbent body. In addition, the transport layer must have a hydrophilic capacity that is less than that of the absorbent core, and can be generally characterized as being substantially hydrophobic. In particular, the use of superabsorbent materials (also called gelling absorbent materials or hydrogel materials) in these articles has gained wide use. The superabsorbent materials are polymeric materials capable of absorbing large amounts of fluid, such as urine, and retaining these absorbed fluids under conditions of use. Recent attempts have been made in the art to provide gelling absorbent materials that have the ability to swell compared to the pressure. The assumed advantage in that the absorbent gelling materials absorb fluid under real pressures exerted by the body during use. Yet another teaching in the art provides gelling absorbent materials that have a particular free swelling rate and absorbency under load. The alleged advantages of these gelling absorbent materials are lower volume and mass with approximately the same absorbent capacity, the ability to rapidly absorb a liquid discharged under pressures typically encountered during use, and the ability to retain the liquid absorbed under pressures typically encountered during use. Examples of these prior art attempts include U.S. Patents No. 5,147,343 issued September 15, 1992 to Kellenberger and 5,149,335 issued September 22, 1992 to Kellenberger et al. In order to increase the fluid handling properties of the absorbent structure, a number of attempts to increase the absorption rate of the superabsorbent material have been disclosed. U.S. Patent 5,154,713 (Lind et al.) Discloses superabsorbent materials in particles having pores introduced during the polymerization of the material, for example moderate foaming of the polymer, by, for example, the release of CO2 during the polymerization. After this, the polymer is treated in a conventional manner, that is, it can be ground, dried, ground finely, sieved (if necessary), and (optionally), surface crosslinked. This results in particulate superabsorbent materials that appear macroscopically identical to the untreated polymers, however, showing a microscopic view of the surface of the small pore particles in the form of "Swiss cheese". The effect is a moderate increase in the absorbency rate at a slightly compromised gel strength. U.S. Patent 5,149,334 (Berg et al.) Discloses absorbent members comprising crosslinked particulate aggregates that are made by agglomerating particles of a relatively small particle size and which remain aggregated even during wetting due to this cross-linking of the particles. nterparticle. This results in relatively high particle density structures with relatively few particles per aggregate structure. U.S. Patent 5,124,188 (Roe et al.), Applies the same principle to create reticulated macrostructures; -. Nterparticle such as in sheet form, that is, with relatively many particles per aggregate structure. For both approaches, the result is an increased absorption rate, but, unless using large amounts of plasticizers such as glycerol and / or water, also a relatively rigid structure. WO-95/22357 (Hayashi et al.), Discloses a process for creating an increased surface area of specific particle, by partially subjecting swollen superabsorbent particles to a drying-free process, whereby the particles "burst", and form irregular structures, with a high surface to mass ratio, but with a brittleness better or equal to conventional superabsorbent particles. All of these absorbent elements have in common that they result in relatively rigid structures. One approach to provide smooth structures with high absorbency is to use superabsorbent fibers. Generally, these fibers are described by Bourland (US-A-4,855,179), or are commercially available from Technical Absorbents, Ltd., United Kingdom, or Carmelot, United States. Noel et al. (EP-B-0 565 606) describe the use of these materials in absorbent structures. The superabsorbent fibers are comprised in low density webs, such as non-woven structures of densities in the scale of typically not more than 0.3 g / cm 3. Although these materials have a good smoothness and also exhibit relatively large surface to mass ratios, their low density has a disadvantage with respect to the logistical difficulties of production, and with respect to the high volume of the resulting absorbent article. In addition, U.S. Patent 5,338,766 (van Phan) discloses open cell foam materials with foam walls / poles which are superabsorbent polymers. With only moderate amounts of plasticizer (such as water at a level of less than about 30% and preferably less than 15% by weight), the result is a highly porous, low density, superabsorbent material with an increased absorption rate. Although this foam material is of low stiffness (or better softness), it carries essentially the same disadvantages as the low density weft structures made of superabsorbent fibers. An approach for reducing the dry volume of absorbent materials has been disclosed by Dyer (US-A-5,387,207). This is interested in an absorbent foam made by the internal high-phase emulsion polymerization process to form non-swellable polymers whereby the absorbent liquids are retained by the capillary absorption forces in the pores of the foam. These foams are then treated in such a way that pore volume collapses and the foams have from about 10% to about 20% of their initial volume. This small volume is kept until it comes into contact with the absorbed fluids (such as water), when it increases to the initial volume now providing absorbency in these pores. However, in these structures, a balance of the properties of absorbency and stiffness have to be found: soft and very flexible structures are more prone to the undesired effect of squeezing of liquid that is released upon the occurrence of pressure (which when localized occurrence). can reach relatively high values during use), relatively rigid structures are less prone to this effect, but less preferred by the lack of softness. Accordingly, it is an object of the invention to provide materials that offer a better balance of the properties of softness, absorbent capacity and absorbency rate. It is an object more to provide these materials in any particulate form, or in macrostructures such as sheet forms. It is a further object of the present invention to provide absorbent structures and articles comprising these improved materials.

BRIEF DESCRIPTION OF THE INVENTION The invention is concerned with a porous material for the absorption of aqueous body fluids comprising absorbent polymers, which can swell upon absorbing aqueous liquids and which forms a porous structure having a surface to mass ratio of at least 0.2m2. / g, characterized in that the pores of said porous structure are collapsed to less than one third of their expanded volume before being moistened with said aqueous body liquids; and in that the pores expand when moistening with the aqueous liquids. The collapsed material may be in particles or in a sheet-like manner.

BRIEF DESCRIPTION OF THE DRAWINGS Although the description concludes with the claims pointing out and claiming the present invention differently, it is believed that it will be better understood by the following drawings taken in combination with the accompanying description, wherein similar components are given with the same reference number and : Figure 1 shows a disposable absorbent article.

DETAILED DESCRIPTION OF THE INVENTION Absorbent Articles As used herein, the term "absorbent articles" refers to devices that absorb and contain exudates from the body, and, more specifically, refers to devices that are placed against or close to the user's body to absorb and absorb. contain the various exudates discharged from the body. The term "disposable" is used herein to describe absorbent articles that are not intended to be washed or otherwise restored or reused as an absorbent article (ie, they are intended to be discarded after a single use and, preferably, to be recycled, composted or otherwise disposed of in an environmentally compatible manner). An absorbent article generally comprises: an absorbent core (which may consist of sub-structure); - a fluid-permeable upper sheet; a back sheet impervious to the fluid; optionally additional features such as closure or elasticizing elements. A specific embodiment of an absorbent article of the present invention is the disposable absorbent article, diaper 20, shown in Figure 1. As used herein, the term "diaper" refers to an absorbent article generally worn by infants. and incontinent people, which is worn around the user's lower torso. However, it should be understood that the present invention is also applicable to other absorbent articles, such as incontinence briefs, incontinence undergarments, diaper liners and fasteners, feminine hygiene garments and the like.

Figure 1 is a plan view of the diaper 20 in its flattened, non-contracted state (ie, with the contraction induced by the elastic pulled outward) with portions of the structure that are cut away to more clearly show the construction of the diaper 20 and with the portion of the diaper 20 facing towards or contacting the user, the interior surface facing the viewer. As shown in Figure 1, the diaper preferably comprises a liquid-permeable upper sheet 24, a liquid-impermeable backsheet 26 bonded to the topsheet 24; an absorbent core 28 positioned between the topsheet 24 and the backsheet 26. The diaper 20 is shown in Figure 1 to have a first waist region 27 juxtaposed with the front of the wearer, while the diaper 20 is being worn, a second waist region 29 opposite the first waist region 27 and juxtaposed with the back of the wearer while the diaper 20 is in use, a crotch region 31 positioned between the first region 27 and the second waist region 29. and a periphery that is defined by the outer edges of the diaper 20, in which the longitudinal edges are designated 33 and the end edges are designated 35. The inner surface of the diaper 20 comprises that portion of the diaper 20 that is adjacent to the body of the diaper 20. user during use (i.e., the inner surface, is generally formed by at least a part of the first top sheet 24 and other components attached to the first upper ja 24). The outer surface comprises that portion of the diaper 20 that is positioned away from the wearer's body (i.e., the outer surface is generally formed by at least a portion of the back sheet 26 and other components attached to the back sheet 26) during use . Figure 1 shows a preferred embodiment of the diaper 20, wherein the topsheet 24 and backsheet 26 have length and width dimensions generally greater than those of the absorbent core 28. The topsheet 24 and the backsheet 26 extend beyond the edges of the absorbent core 28 to form thus the periphery 22 of the diaper 20. Although the upper sheet 24, the back sheet 26 of the absorbent core 28, can be assembled in a variety of well-known configurations, the preferred diaper configurations are generally described in US Patent 3,860,003 entitled "Shrinkable side portions for disposable diaper", which was issued to Kenneth B. Buell on January 14, 1975; and United States Patent Application 07 / 175,152, issued "Absorbing article with mechanical elastic waist feature", having a predisposed elastic flexion joint, "Kenneth B. Buell, et al., filed June 13, 1991. The backsheet 26 is positioned adjacent the garment surface of the absorbent core 28 and is preferably bonded thereto by attachment means (not shown), such as those well known in the art, For example, the backsheet 26 can be secured to the backing sheet 26. Absorbent core 28 by a uniform, continuous adhesive layer, a patterned adhesive layer or an array of separate lines, coils or spots of adhesive Adhesives that have been found to be satisfactory are manufactured by HB Fuller Company of St. Paul , Minnesota and which are marketed as HL-1258. The attachment means will preferably comprise an open-pattern network of filaments of adhesives as disclosed in US Pat. U.S. Patent 4,573,986, entitled "Garment for the containment of waste, disposable"; which was issued to Minetola et al. on March 4, 1986, more preferably several filament lines of adhesives twisted in a spiral pattern as illustrated as the apparatus and methods shown in United States Patent 3,911,173 issued to Sprague , Jr. On October 7, 1975; U.S. Patent 4,785,996 issued to Ziecker et al. on November 22, 1978; and U.S. Patent 4,842,666 issued to Werenicz on June 27, 1989. Alternatively, the joining means may comprise heat bonds, pressure joints, ultrasonic joints, mechanical dynamic joints, or any other suitable joining means or combinations of these joining means as are known in the art. The backsheet 26 is impervious to liquids (eg, urine), and is preferably manufactured from a thin plastic film, although other flexible liquid impervious materials may also be used. As used herein, the term "flexible" refers to materials that are docile and readily conform to the shape and general contour of the human body. The backsheet 26 prevents the exudates absorbed and contained within the absorbent core 28 from wetting the articles that come into contact with the diaper 20, such as sheets and undergarments. The backsheet 26 can thus comprise a woven or non-woven material, polymeric films such as polyethylene polypropylene thermoplastic films, or composite materials such as a film-coated nonwoven material. Preferably, the backsheet is a thermoplastic film having a thickness of from about 0.12 mm to about 0.051 mm. Particularly preferred materials for the backsheet include the RR8220 blown films and the RR5475 cast films as manufactured by Tredegar Industries, Inc. of Terre Haute, IN., E.U.A. The backsheet 26 is preferably embossed and / or dull finished to provide a more fabric-like appearance. In addition, the backsheet 26 can allow vapors to escape from the absorbent core 28 (ie, breathable), while still preventing the exudates from passing through the backsheet 26. The topsheet 24 is positioned adjacent the surface of the backing sheet. Absorbent core body 28 and is preferably bonded thereto and backsheet 26 by attachment means (not shown), such as those well known in the art. Suitable attachment means are described with respect to the attachment of the backsheet 26 to the absorbent core 28. As used herein, the term "attached" encompasses configurations with which the element is directly attached to the other element by fixing the element directly to the other element, and configurations with which the element is directly secured to the other element by fixing the element to a member or intermediate members, which in turn are fixed to the other element. Generally, the topsheet 24 is docile, gentle in feel, and non-irritating to the wearer's skin. In addition, the topsheet 24 is permeable to liquid, allowing liquids, eg, (urine), to easily penetrate through its thickness. A suitable top sheet can be manufactured from a wide range of materials, such as porous foams; cross-linked foams; plastic films with openings; or woven or non-woven webs of natural fibers (for example wood or cotton fibers), of synthetic fibers (for example, polyester or polypropylene fibers), or a combination of natural and synthetic fibers. There are a number of fabrication techniques that can be used to manufacture the topsheet 24. For example, the topsheet 24 can be a non-woven web of bonded, carded, wet-laid, melt-blown, hydroentangled, combinations of the fibers. previous or similar. The diaper 20 may further comprise elasticized leg cuffs (not shown), which provide improved containment of liquids and other exudates from the body. Each elasticized leg fold can comprise several different modalities to reduce leakage of body exudates in the leg regions (the leg fold can be and is sometimes also referred to as leg bands, side flaps, barrier folds or folds elastic). U.S. Patent 3,860,003 discloses a disposable diaper 20 that provides a collapsible pill opening having a side flap and one more elastic members to provide an elasticized leg fold (gusset fold). U.S. Patent 4,909,803 entitled "Disposable absorbent article having elasticized fins", issued to Aziz et al. On March 20, 1990, discloses a disposable diaper 20 having "vertical" elasticized flaps (barrier folds), to improve containment of the regions of the leg, commonly assigned U.S. Patent No. 4,695,278, entitled "Absorbent Article Having Double Folds", issued to Lawson on September 22, 1987, discloses a disposable diaper 20 having double folds which include a packing fold and a barrier fold The diaper 20 preferably further comprises an elastic waist feature (not shown), which provides improved fit and containment The elastic waist feature is that part or area of the diaper 20 that is designed to stretch and contract elastically to dynamically adjust to the user's waistline. at least extends longitudinally outward from at least one of the waist edges of absorbent core 28 and generally forms at least a portion of the end edge of diaper 20. Disposable diapers are generally constructed to have two elastic characteristics of waist, one placed in the first waist region 27 and one positioned in the second waist region 29, although the diapers can be constructed with a single elastic waist feature. In addition, although the elastic waist feature or any of its constituent elements may comprise a separate element secured to the diaper 20, the elastic waist feature is preferably constructed as an extension of other diaper elements 20, such as the back sheet 26 or the first top sheet 24, preferably both the back sheet 26 and the first top sheet 24. The elasticized waistband can be constructed in a number of different configurations, including those described in U.S. Patent 4,515,595 issued to Kievit and others on 7 May 1985 and the aforementioned United States patent application No. 07 / 715,152, each of these references being incorporated herein by reference.

The diaper 20 also comprises a fastening system (not shown), which forms a side closure, which maintains the first waist region 27 and thus the second waist region 29 in an overlapping configuration in such a manner that the tensions are maintained. lateral around the circumference of the diaper 20, to maintain the diaper 20 on the wearer. Exemplary fastener systems are disclosed in U.S. Patent 4,846,815 entitled "Disposable diaper having an improved fastener device", issued by Srcipps on July 11, 1989; U.S. Patent 4,894,060, "Disposable diaper with improved hook fastener portion", issued to Nestegrard on January 16, 1990; commonly assigned U.S. Patent 4,946,527, entitled "Pressure sensitive adhesive fastener and method for making the same, issued to Battrell on August 7, 1990; the commonly assigned United States patent 3,848,594, entitled "Disposable papal tape fastening system", issued Buell on November 19, 1974; the commonly assigned United States patent B1 4,662,875, entitled "Absorbing article", issued to Hirotsu et al. on May 5, 1987; and the previously referenced United States patent application No. 07 / 715,152; each of which is incorporated herein by reference. The diaper 20 is preferably applied to a wearer by placing one of the waist regions, preferably the second waist region 29, under the user's back and stretching the remainder of the diaper 20 between the wearer's legs, such that the other waist region, preferably the first waist region 27, is placed across the front of the user. The tape tabs of the fastener system are then released from a release portion. The diaper then wraps the elasticized side panel around the wearer, while still holding the tongue portion. The fastening system is secured to the outer surface of the diaper 20 to effect two lateral closures. Generally speaking, the absorbent core 28 must be non-irritating to the wearer's skin, and capable of absorbing and retaining liquids such as urine and other exudates from the body. As shown in Figure 1, the absorbent core 28 has a garment surface, a body surface, side edges and waist edges. The absorbent core 28 can be manufactured from a wide range of sizes and shapes (eg, rectangular, hourglass, capital T, symmetric, etc.) and could comprise in addition to the materials of the present invention an extensive variety of liquid absorbent materials commonly used in disposable diapers and other absorbent articles such as, but not limited to, crushed wood pulp which is generally referred to as air filters; melt blown polymers including coform; cross-linked or modified cellulose fibers, chemically hardened; Tissues including tissue wraps and tissue laminates. The configuration and construction of the absorbent core 28 may also be varied (eg, the absorbent core 28 may have gauge zones varying a hydrophilic gradient, a super-absorbent gradient, or lower average basis weight acquisition zones and lower average density; may comprise one or more layers or structures). However, the total absorbent capacity of the absorbent core 28 must be compatible with the design load and intended use of the diaper 20. In addition, the size and absorbent capacity of the absorbent core 28 can be varied to suit users ranging from infants to Adults. Exemplary absorbent structures to be used as the absorbent core 28 are described in U.S. Patent No. 4,610,678 entitled "High Density Absorbing Structures" issued to Weisman et al. On September 9, 1986; U.S. Patent No. 4,673,402 entitled "Absorbent articles with double-layered cores" issued to Weisman et al. on June 16, 1987; U.S. Patent No. 4,888,231 entitled "Absorbent Core Having A Dust Cap" issued to Angstadt on December 19, 1989; and U.S. Patent No. 4,834,735, entitled "High Density Absorbing Members Having Acquisition Areas of Lower Base Weight and Lower Density", issued in Alemany et al. on May 30, 1989; also European Patent No. 0,640,330 to Bewick-Sonntag et al .; U.S. Patent No. 5,180,622 (Berg et al.); United States Patent No. 5,102,597 (Roe et al.) Disclose structures that can be used to incorporate materials according to the present invention, which will now be explained in more detail. The present invention is concerned with collapsible superabsorbent materials with a high surface to mass ratio, which are in a collapsed state until (during use) they are contacted with bodily fluids such as urine or menstrual fluid. This provides additional benefits against the materials of the prior art. In particular, it allows to provide large quantities of absorbent capacity without compromising the volume of the article and on the good fluid handling properties, especially with the rapid uptake of the fluid and in the super-absorbent material as the final material for storage by the fluids. . In addition, in particular for sheet-like structures, the additional feature of flexibility ensures the urgency of negatives such that they could be introduced through too rigid materials. The materials according to the present invention can be made, starting from chemicals as for conventional super-absorbent materials. These hydrogel-forming absorbent polymers preferably have a multiplicity of amionic as well as functional groups, such as sulfonic acid, and more typically carboxy groups. Examples of polymers suitable for use herein include those prepared from polymerizable monomers containing unsaturated acid. Thus, these monomers include olefinically unsaturated acids and anhydrides containing at least one olefinic to carbon double bond. More specifically, these monomers can be selected through olefinically unsaturated carboxylic acids and acid anhydrides, olefinically unsaturated sulfonic acids and mixtures thereof. Some non-acidic monomers, usually in minor amounts, may also be included in preparing the hydrogel-forming absorbent polymers herein. These non-acidic monomers may include, for example, the water-soluble or water-dispersible esters of the acid-containing monomers, as well as monomers that do not contain carboxylic or sulfonic acid groups at all. Optional non-acidic monomers can thus include monomers containing the following types of functional groups: carboxylic acid or sulfonic acid esters, hydroxyl groups, amide groups, amino groups, nitrile groups and quaternary ammonium salt groups. These non-acidic monomers are well known materials and are described in greater detail, for example, in U.S. Patent No. 4,076,663 (masuda et al.), Issued February 28, 1978, and in the United States patent. Do not. 4,062,817 (Westerman), issued December 13, 1977, both of which are incorporated by reference. The olefinically unsaturated carboxylic acid and the carboxylic acid anhydride monomers include acrylic acids triplyified by acrylic acid by itself, methacrylic acid, is ethacrylic acid, chloroacrylic acid, α-cyanoacrylic acid, methylacrylic acid (crotonic acid), phenylacrylic acid, acryloxypropionic acid, sorbic acid, chlorosorbic acid, angelic acid, cinnamic acid, p-chlorocinnamic acid, sterilacrylic acid, itaconic acid, citroconic acid, mesaconic acid, glutaconic acid, aconitic acid, maleic acid, fumaric acid, tricarboxyethylene and maleic acid anhydrides . The olefinically unsaturated sulfonic acid monomers include aliphatic or aromatic vinyl sulphonic acids such as vinyl sulfonic acid, allyl sulfonic acid, vinyl toluene sulphonic acid and styrene sulfonic acid; acrylic acid and methacrylic acid sulphonic acid such as sulfoethyl acrylate, sulfopropyl acrylate, sulfopropyl methacrylate, 2-3-methacryloxypropyl sulfonic acid and 2-acrylamide-2-methylpropane sulfonic acid. Preferred hydrogel-forming absorbent polymers for use in the present invention contain carboxy groups. These polymers include hydrolyzed starch / acrylonitrile graft copolymers, partially neutralized starch-acrylonitrile graft copolymers, partially neutralized starch / acrylic acid graft copolymers, saponified vinyl acetate-acrylic ester copolymers, hydrolyzed acrylonitrile or acrylamide copolymers, polymers lightly crosslinked in the network of any of the above copolymers, partially neutralized polyacrylic acid and slightly crosslinked polymers in the partially neutralized polyacrylic acid network. These polymers can be used either alone or in the form of a mixture of two or more different polymers. Examples of these polymer materials are disclosed in U.S. Patent 3,661,875; United States Patent 4,076,663, patent of the United States 4,093,776, United States Patent 4,666,983, and United States Patent 4,734,478. As described above, the hydrogel-forming absorbent polymers are preferably lightly cross-linked in the network. Crosslinking in the network serves to render the polymer substantially insoluble to water, and, in part, determines the absorbent capacity and characteristics of the removable polymer content of the superabsorbent material. Processes for network crosslinking typical polymers and network crosslinking agents are described in greater detail in the aforementioned US Pat. No. 4,076,663 and German Patent DE-A-4020780 (Dahmen). The type of crosslinker and the crosslinking density can also be varied over the entire length of the material, in particular when different and / or additional crosslinking is applied to the surface of a particulate material, but also to different regions in a macrostructure in the form of sheet.

Tea Bag Centrifugal Capacity Test The tea bag centrifugal capacity test and tea bag centrifugal capacity values, which are a measure of the retention of liquids in gelling materials (superabsorbents) at hydrostatic pressure. The superabsorbent material is placed inside a "tea bag", immersed in a solution at 0.9% by weight of sodium chloride for 20 minutes, and then centrifuged for 3 minutes. The ratio of the retained weight of the liquid to the initial weight of the dry superabsorbent material and the absorbent capacity of the superabsorbent material. Two liters of 0.9% by weight of sodium chloride are emptied into a tray having diameters of 24 cm x 30 cm x 5 cm. The liquid filling height should be approximately 3 cm. The sachet of the tea bag has dimensions of 6.5 cm x 6.5 cm and is available from Teekanne in Dusseldorf, Germany. The bag is heat-sealable with a standard plastic bag sealing device (eg VACUPACK2 PLUS from Krups Germany). The tea bag is opened by carefully cutting it partially, and this is then weighed. A sample of 0.200g +/- 0.005g of superabsorbent material is placed inside the tea bag then closed with a heat sealer. This is called the sample tea bag. An empty tea bag is sealed and used as a model. The sample tea bag and model tea bag are then placed on the surface of the saline solution, and immersed for approximately 5 seconds using a spatula to allow complete wetting (the tea bags will float on the surface of the solution). saline, but are then moistened completely). The stopwatch is started immediately. After soaking for 20 minutes the sample tea bag and model tea bag are removed from the saline solution and placed in a centrifuge Bauknecht WS130, Bosch 772 NZK096 or equivalent (230 mm diameter), so that each bag sticks to the outer wall of the centrifuge container. The centrifuge lid is closed, the centrifuge is turned on and the speed is rapidly increased to 1, 400 rpm. Once the centrifuge has stabilized at 1, 400 rpm, the timer is turned on. After 3 minutes, the centrifuge is stopped. The sample tea bag, and the model tea bag are removed and weighed separately. The centrifugal capacity of the tea bag (TCC) for the sample of the hydrogel-forming superabsorbent material is calculated as follows: TCC = ((weight of sample tea bag after centrifugation), less (weight of model tea bag after centrifugation) minus (weight of hydrogel-forming dry superabsorbent material)) + (weight of dry superabsorbent material) It is essential for the present invention that the materials exhibit a large mass-surface ratio in Excess of at least 0.2g / m2. Suitable methods for determining surface to mass ratios are well described in the prior art, such as in U.S. Patent 5,328,935.

Surface area to mass unit of BET The specific surface area to mass unit (M2 / g) of materials with a high surface to mass ratio is determined using the Brunauer-Emmet-Teller gas absorption method (BET) . This method involves the accretion of a monolayer of a gas (nitrogen (N2)), over a known mass of a sample at liquid nitrogen temperature. The N2 acetoside is then deactivated by raising the temperature of the sample (thermal desorption) and detected by a thermal conductivity detector (TCD), whose output is connected to an integration recorder. The peak area of the desorbed N2 is thus known. The response desorption peaks are recorded for each sample, the average of which is the signal area (A). After the sample analysis, the instrument response (A ^,) is determined by injecting known quantities (Vc) of nitrogen gas (99.99% +) into the system and the response of the instrument is recorded through the integration recorder. A ^ is the average of the various instrument responses obtained by injecting the known N2 quantities. The values of A, A ^, and Vc are then used to determine the specific surface area of the sample using the multiple-point BET calculation. The specific equipment used for these analyzes is obtainable from Quantachrome Corporation (Syosset, N.Y) and consists of the gas outlet station Quantector, the flow controller, and the Quantasorb Jr. Sample Analysis Unit These instruments are used as described in the operation manuals for the Quantasorb Júnior® desorption system, 2/19985, incorporated herein by reference. Several specific helium-N2 mixtures obtained by mixing pure and pure helium through the flow controller are used as the atsorbate gas. Weigh 0.75 grams +/- 0.05 grams of the sample in the sample vitreous cell (approximately 2.5 ml) of the apparatus. The glass cell containing the sample is then placed inside the gas flow of the instrument. The samples are degassed with a flow of 30 gl / min of helium using the Quantector for a sufficient time to remove any other gases other than helium from the sample, typically a minimum of four hours. After degassing, the gas flow is changed to a specific mixture of N2-helium gas. The vitreous sample cell is submerged in liquid nitrogen and allowed to reach equilibrium. The supply curve is generated. The quiescent N2 generates a desorption curve and a peak value (used to calculate the signal area (A)). Measurement / desorption measurements are made on each sample using different samples of N2-helium gas. The specific surface area Sg is calculated as follows: Sg = S W; Where W is the weight of the sample and St equals Xm (6.02 x 1023) A ^, where A ^ is the cross-sectional area of the atsorbate. For N2, St becomes X ,,, (3.483 x 1? 3) m2; where Xm equals 1 / (S + I). S is the slope and I is the intercept of Y of the graph of 1 / Xípo / p) -1) versus P / Po. When calculating the values of x and y for the previous graph X = (A) Xc / (A) cal. A is the area of the signal; A ^, is the calibration area; and Xc = PaMaVc / 6.235 x 104 is the pressure T.Pa environmental; M is the molecular weight of the atsorbate that for N, becomes 28.0134; and it is the calibration volume and T is the room temperature in Kelv. P is the partial pressure of the atsorbate and P0 is the saturated vapor pressure, which is equal to f + F; where Pg is the vapor pressure (above the environmental) and Pa is the ambient pressure. The creation of materials having such high surface to mass ratios can begin from the formation of free weft structures of superabsorbent fibers with relatively thin thickness of about 20μm or less, as described in the European patent EP-B -0 565 606, or by finely grinding particulate materials and reconstituting them into macrostructures that remain essentially intact upon moistening, which is described in U.S. Patent No. 5,124,188. A preferred embodiment is to start from polymer superabsorbent foams as described in U.S. Patent 5,338,766, assigned to van Phan, which are made in accordance with the teachings of U.S. Patent 5,328,935, also assigned to van Phan: Approximately 250 grams of aqueous acrylic acid (50% by weight) are neutralized at 75% to sodium acrylate using 0.1N NaOH. To prevent the formation of polyacrylic acid, neutralization is carried out by gradually adding the NaOH to the acrylic acid solution with moderate mixing and cooling (with dry ice). A reaction mixture is prepared as follows: 200 grams of the highly prepared aqueous sodium acrylate solution; 0.050 grams of N2N1-methylbisacrylamide; 1.3 grams of v-50 (2,2'-azobis (2-amidinopropane) dihydrochloride, available from Wako Chemicals USA, Inc.) and 20 grams of PEG-600 (polyethylene glycol having a weight average molecular weight of about 600, available from Union Carbide Co., Danbury, Conn.), are added to a liter of vitreous reactor fitted with temperature and pressure controls and a high shear mixing apparatus (eg, an "Ultra Turray" mixer, available from Tekmar Company of Cincinnati, Ohio). The reactor is at room temperature (approximately 22 ° C) and ambient pressure (approximately 1 atmosphere). A mixture of 60 grams of Freon 1, 1, 2 (1, 1, 2-trichlorotrifluoroethane, available from Aldrich Chemical of Milwaukee, Wisc); 3.5 grams of SPAN® (sorbitan monolaurate, available from Aldrich Chemical) and 6.5 grams of TWEEN® 20 (ethoxylated sorbitan monolaurate, available from Aldrich Chemical) is then added to the reactor. This last mixture was prepared in advance by adding the components to a reactor similar to that described above and mixed well. The reaction mixture is mixed at 850 rpm for about 10 minutes to stably disperse the Freon 1, 1, 2. The mixing apparatus is then removed from the dispersion. A foam product is formed by increasing the reactor temperature to 60 ° C and maintaining the temperature at 60 ° C for about 1 hour; followed by increasing the temperature to 80 ° C and keeping it at 80 ° C for approximately 30 minutes, followed by which the temperature is increased to 120 ° C and maintained at 120 ° C for approximately 30 minutes. The reactor is then cooled to approximately ambient temperature (approximately 22 ° C). A mixture of 5 grams of glycerol and 25 grams of isopropyl alcohol is added to the foam inside the reactor to impregnate the foam with the mixture. The temperature of the reactor is then increased to and maintained at 180 ° C for about 1 hour. The reactor is cooled to room temperature (approximately 22 ° C), after which the foam is removed from the reactor and placed openly in a humidified room (80% relative humidity), for 6 hours. When having such materials, with high surface to mass ratio, one aspect of the present invention helps to provide these materials in a collapsed collapsed form., means in the context of the present invention, that the hollow volumes of the pore are reduced, but possibly to the limit that the porous structures are not easily apparent. However, although the pore walls which may be formed by the fibers or particles or posts, may be in direct contact with each other in the collapsed form (and therefore, the pore between the respective walls or dots essentially disappears or the the less it reduces its pore volume significantly), the surfaces remain permanently intact and do not conglutinate at the same time. Then, an expanded structure with comparable pore sizes can be achieved as the comparative non-compressed structure upon wetting, for example, by body fluids during use.

Without being bound by theory, it is believed, that in this aspect of the invention, residual amounts of the plasticizer in the materials (such as moisture or residual glycerol) provide contractive forces, such as through hydrogen bonds, which exceed the forces of restoration of the elastic deformation of the foam cells. Upon an increase in the amount of water molecules, the forces of contraction are weakened and the elastic forces are allowed to restore the open pore volumes. At this time, however, these materials not only begin to sink through the swelling mechanisms of the classic superabsorbent (or hydrogel), but also allow the liquid to penetrate into the material through and into the open pores, thus providing in an immediate manner the relatively large surface area for rapid transfer of fluid to the superabsorbent network of the polymer. The collapsed superabsorbent materials according to the present invention may be in various physical forms or forms, very important either in "free" or "three dimensional" form. The term "free" generally refers to structures of particles of varying shape and size, such as are obtained by cutting, crumbling, milling or agglomerating the particle structures of the precursor. Generally these structures can be described by characteristic dimensions such as an "average particle size", but the individual particles can vary very significantly from those neighboring, for example, in size, shape and so on. A preferred embodiment relates to the particle structures of relatively large dimensions. Although these particles have general advantages such as reduced tendency for blockage of distribution channels for fluids, or a reduced tendency of general dust, the present invention provides a reduction of the negative effects that generally occur from these materials, essentially low absorption. , (which is compensated by increasing the "internal surface" or "pockmarked" or "uncomfortable feeling" of the hard particles by users), which can be compensated for by the characteristics of increased softness to the materials in accordance with the present invention as discussed below. However, for too large (expanded) particle structures, there is a risk that the transport fluid from the surrounding material may not be adequate, such that the collapsed materials should not exceed approximately 300 μm in diameter. Another preferred form of the materials according to the present invention is the three-dimensional shape, such as sheets, strips and the like.These structures have a dimension (ie, length in the case of the strips), or two dimensions (ie say, length and width in the case of the sheets), significantly greater than the thickness or the caliber of the material, especially in the collapsed state.In addition, and in contrast to the particle structures with generally stochastic distribution of shape and size , the dimensions are essentially the same for at least a large part of the structures (ie, the dimensions and shapes vary only in narrowly defined limits in a narrow manner for essentially all the structures for a specific application.) These structures can be cut to from a "plate", of reacted foam material, or can react in molds that are filled with reagent foam, or can be applied in a form of a continuous foam layer on a carrier, which can be removed from the foam in sheet form when the reaction foam has remained in sufficient integrity or which can remain with the foam and be an element of the article final absorbent. Another preferred embodiment within the present invention, is to use absorbent fibers, which are composed of wefts, which can be formed by a wide variety of conventional weft manufacturing techniques, such as carding to create non-woven materials, or placed in air or the like. The webs may be joined by any conventional means, such as through resin bonding by the addition of suitable binders, or hydroentangling, such as by needle punching and interweaving the fibers into a web. A preferred embodiment of such wefts, include low percentages of about 10% polymer fibers, which melt at a lower temperature than the superabsorbent fibers. Subsequent to the heat induced fusion of these polymers, it is then to provide sufficient strength to these webs, without the unnecessary swelling of concealment of the fibers. Suitable frames can be received according to the teachings of Noel in the European patent No. EP-B-0 565 606, assigned to Noel and others, using 90% by weight of Fibersorb fibers type 7200 Fibers of Camelot Co., USA and a weight of 10% of fibers of ES-E-WA-3.3.dTex of DANKLON AS, Denmark and placing by air a structure of 140g / m2 with connection with air through posterior. If starting from these high porosity structures, this is an essential feature of this invention to collapse these at sufficiently high densities in impact primarily on the high surface area values, and also no other absorbent properties, such as absorbent capacity, absorbing speed and the like. This can be achieved by a number of different ways. In the case of starting from structures essentially in sheet forms, the collapsed structures according to the present invention can be made by placing these sheets in a conventional press, such as a hydraulic or mechanical press. In the case of essentially continuous structures, these can be collapsed by compressing the materials through a pair of compression rollers (or calendering). The subsequent winding compaction may further reduce the tendency of a certain degree of elastic return, optionally with the use of separation sheets between the two adjacent layers on the rolls. Also, the resulting structure can be transformed into a particle structure according to the invention such as conventional techniques such as milling, shredding and the like. These processes apply particularly when starting from foamed structures, but are uniformly applicable when starting from wefts, such as non-woven materials comprising superabsorbent fibers. Similar processes can be applied when starting from materials in the form of particles, when being expanded which are then compressed. However, there are two effects that have to be considered. First the collapse of the pores as described in the sheet-like structures, that is, the nterparticle compression. Second, the compression of the particles in the neroparticle voids by a deformation of the macroscopic shape of the particle. This second effect is not desired for superabsorbent materials that exhibit a relatively low strength or gel stiffness, such as (even under only moderate use pressures), such materials would not open the particulate voids, even if the pore particles were opened. Other ways of creating these collapsed structures also fall within the scope of the present invention, such as collapsing through evaporative removal of moisture, whereby care must be taken that the structure is not overdrawn, drained by suction at the empty and similar. For any of these process options, additional aids such as moisture, or plasticizer, may be added during the compression step as soon as the properties of the resulting structure are optimized with respect to elasticity and / or softness. Suitable plasticizers include water, high molecular weight hydrophilic organic solvents (eg, glycerol); 1,3-propanediol; or ethylene glycol) or polymer solutions (e.g., polyvinyl alcohol or polyethylene glycol), or mixtures thereof. The plasticizer can be applied in a number of different ways including spraying, coating, atomizing, immersing, or pouring the solution onto the structure. Alternatively, in the case of water, the plasticizer can be added by placing the structure in a highly humid environment (eg, greater than 70% relative humidity). The resulting structures will still be essentially dry, meaning that they have a moisture content of less than 50% by weight, preferably less than 20% by weight of the total structure. The general volume reduction (collapse ratio) can be measured by comparing the volume of the structure before and after compression, or by measuring the volume of the structure (essentially dry), before getting wet, and the volume of the structure re-dried, as is achieved by wetting the structure with a known amount of fluid to make the cell pores accessible, and then drying the structure without applying external pressure, for example, in an oven for 3 hours at 105 ° C. This can be applied to the three-dimensional structures (including the frames that comprise superabsorbent fibers), or to the particle structures. Although the ability to remain permanently compressed until wetting is the very essential property according to the present invention, the sheet-like structures according to the present invention can have particularly beneficial softness properties. Although softness is generally a subjective measurement, there are methods that describe the quantitative determination of this property: Determination of flexibility The flexibility of the sheet-like structures, for example, made of foams or fibrous webs, can be quantified by reference to a test procedure, which is a modification of the ASTM D 3574-86 test. uses a sample, which is 7 cm x 0.8 cm x 0.8 cm and which has been saturated at its equilibrium absorbing capacity (ie, soaked in synthetic urine or in 0.9% saline for approximately 15 minutes). The saturated strip is bent around a cylindrical mandrel of 0.8 cm in diameter at a uniform speed of one turn in 5 seconds until the ends of the strip meet. The sample is considered flexible if it tears or breaks during this test, that is, if it passes a bending cycle. It is important that the cutting process used to make the strip samples does not introduce defects in the edges of the strip. Strips of the required size should be cut, using a sharp reciprocating knife saw. The use of this or an equivalent type of sharpened type device serves to substantially eliminate imperfections at the edge of the sample and defects of densification at the edge, which can adversely impact the accuracy of certain measurements made in carrying out the test procedure. In addition, the caliber of the thickness measurements can be made when the sample of the absorbent structure is under a confining pressure of 350 Pa (0.05 psi). An additional requirement is good absorbency or "superabsorbency" of the material that is suitable for the present invention. On the one hand this is a quantitative term for the absorbent capacity of equilibrium and the materials used according to the present invention have no less than 15 grams of fluid absorbed per gram of material in the tea bag holding capacity test. On the other hand, it is a qualitative description of the absorption mechanisms, with which the predominant part of the absorbed fluid is, at least, under conditions of equilibrium, absorbed in the polymeric network of the structure (and not only maintained in the pores). .

Preparation of the absorbent structures Generally, the materials according to the present invention can be incorporated into absorbent structures to utilize conventional approaches well known to the person skilled in the art and explained above. Specifically in the case of particulate materials, mixing of the compressed superabsorbent granules with fibrous materials such as cellulosic fibers can be applied or laminates of such particles can be used with carriers such as tissue, or aggregates in the form of fluid-stable sheets. In the case of defined three-dimensional shapes, sheets, wefts in the form of sheets, strips, bars, or other essentially continuous structures, these can be introduced into the absorbent structures using, for example, roll-shaped materials and cutting to length as desired, for example, covering the total length of the absorbent structure. It can also be in specific reasons of the absorbent structure, only using for example the processes of cutting and sliding so-called. It is also possible to use pre-cut sheets to be introduced into the absorbent structures by generally known techniques.

Claims (20)

1. - A porous material for absorption of aqueous body fluids comprising a superabsorbent polymer, which is capable of swelling upon absorbing aqueous liquids, and which forms a porous structure having a surface to mass ratio of at least 0. 2m2 / g; characterized in that the pores of said porous structure are collapsed to less than one third of their expanded volume before being moistened with aqueous body fluids, and that the pores expand upon wetting with aqueous liquids.

2. A porous material according to claim 1, further characterized in that the expansion of the pores is not isotropic and in a dimension significantly greater in at least one of the other dimension.

3. A superabsorbent material according to claims 1, 2, further characterized in that it is flexibilized by means of a plasticizer material.

4. A superabsorbent material according to claim 3, further characterized in that the plasticizer comprises water and / or glycerol.

5. A superabsorbent material according to claim 1 to 4, further characterized in that it has in the collapsed state a density of between 0.05 g / cm3 and 1.6 g / cm3.

6. A superabsorbent material according to claims 1 to 5, further characterized in that it has in the collapsed state a moisture content of between 4% and 30% on a dry basis.

7. A superabsorbent material according to claims 1 to 6, further characterized in that the pores in the expanded state have a pore size less than 100μm, preferably from 5 to 100μm.

8. A superabsorbent material according to claims 1 to 7, further characterized in that the superabsorbent polymer is in the form of a foam comprising a plurality of mutually connected poles of superabsorbent polymer material to form open cells in the expanded state , and in that it is collapsed in such a way that the density is between 0.05g / cm3 and 1.6g / cm3.

9. A superabsorbent material according to claims 1 to 8, further characterized in that it forms a three-dimensional structure of at least 10 mm3 in volume, and this has an extension in one or two dimensions of at least

10 times the extension in the third dimension. 10. A superabsorbent structure according to claim 9, further characterized in that the expansion of the pores is non-isotropic and in a dimension significantly greater in at least the other dimension.

11. A superabsorbent material in accordance with the claims 1 to 7, further characterized in that it is made of a web comprising superabsorbent in fibrous form.

12. A superabsorbent material according to claims 1 to 11, further characterized in that it forms a flexible sheet.

13. A superabsorbent material in accordance with the claims 1 to 13, characterized in that it is in the form of particles consisting essentially of foamed superabsorbent.

14. A superabsorbent material according to claims 1 to 13, further characterized in that the collapsed particles have a size smaller than 300μm.

15. - A method for preparing a superabsorbent material, comprising the steps of: providing an unexpanded porous superabsorbent material containing a fluid in its pores; To collapse the pores of the material by removing the fluid from the pores of the material without collapsing.

16. A method for preparing a superabsorbent material according to claim 15, with which the collapse of the pores of the material is achieved by mechanical action on the material in at least one direction.

17. A method for preparing a superabsorbent material according to claim 15, with which the collapse of the pores of the material is achieved by evaporative removal of the fluids.

18. A method according to claim 17, further comprising the step of adding a plasticizer.

19. An absorbent structure comprising any of the materials according to claims 1 to 14.

20. A disposable absorbent article comprising an absorbent structure according to claim 19.