Absorbent foam materials for aqueous body fluids and absorbent articles containing such materials

What is claimed is:

1. An absorbent article especially suitable for absorbing and retaining aqueous body fluids, said article comprising;

A) a backing sheet; and

B) an absorbent polymeric foam material associated with said backing sheet such that the absorbent polymeric foam material is positioned between said backing sheet and the fluid discharge region of the wearer of the article; said absorbent polymeric foam material comprising, when dried, a hydrophilic, flexible structure of interconnected open cells, which structure has, when in contact with said aqueous body fluids:

i) a pore volume of from 12 to 100 mL/g;

ii) a specific surface area of from about 0.5 to 5.0 m.sup.2 /g as determined by capillary suction; and

iii) a resistance to compression deflection such that a confining pressure of 5.1 kPa produces after 15 minutes a strain of from about 5% to 95% compression of the structure when it is saturated at 37.degree. C. to its free absorbent capacity with synthetic urine having a surface tension of 65.+-.5 dynes/cm.

2. An absorbent article according to claim 1 wherein

A) the structure of the absorbent polymeric foam material component comprises a polymerizing water-in-oil emulsion, which emulsion prior to polymerization comprises

a) an oil phase comprising

i) from about 3% to 41% by weight of a substantially water-insoluble, monofunctional glassy monomer component;

ii) from about 27% to 73% by weight of a substantially water-insoluble, monofunctional rubbery comonomer component;

iii) from about 8% to 30% by weight of a substantially water-insoluble, polyfunctional cross-linking agent component, and

iv) from about 2% to 33% by weight of an emulsifier component which is soluble for forming a stable water-in-oil emulsion; and

b) a water phase comprising an aqueous solution containing from about 0.2% to 40% by weight of water-soluble electrolyte; the weight ratio of said water phase to said oil phase comprising said emulsion ranging from 12:1 to 100:1; and

B) the structure of the absorbent polymeric foam material component is hydrophilic to the extent that the structure exhibits an adhesion tension of from about 15 to 65 dynes/cm when absorbing synthetic urine having a surface tension of 65.+-.5 dynes/cm.

3. An absorbent article according to claim 2 wherein in the water-in-oil emulsion precursor of the absorbent polymeric foam material;

a) the substantially water-insoluble, monofunctional glassy monomer component of the oil phase comprises one or more styrene-based monomer types;

b) the substantially water-insoluble, monofunctional rubbery comonomer component of the oil phase comprises comonomer types selected from butylacrylate, 2-ethylhexylacrylate, butadiene, isoprene and combinations of these comonomer types;

c) the molar ratio of monofunctional glassy monomer component to the monofunctional rubbery comonomer component in the oil phase ranges from about 1:25 to 1.5:1;

d) the substantially water-insoluble cross-linking agent component of the oil phase comprises a difunctional monomer type selected from divinylbenzene, divinyltolulene, diallyphthalate, one or more diacrylic acid esters of a polyol or combinations of such difunctional monomer types;

e) the emulsifier component of the oil phase comprises an emulsifier selected from sorbitan fatty acid esters, polyglycerol fatty acid esters, polyoxyethylene fatty acids and esters and combinations of such emulsifiers;

f) the water-soluble electrolyte in the water phase comprises one or more water-soluble salts of an alkali metal or alkaline earth metal;

g) the water phase additionally comprises from about 0.02% to 0.4% by weight of a water-soluble, free radical polymerization initiator; and

h) the weight ratio of water phase to oil phase forming the emulsion ranges from about 20:1 to 70:1.

4. An absorbent article according to claim 1 wherein said backing sheet is relatively liquid-impervious, wherein the article also comprises a substantially liquid-pervious topsheet and wherein the absorbent polymeric foam material is present in an absorbent core structure which is positioned between said relatively liquid-impervious backing sheet and said substantially liquid-pervious topsheet.

5. An absorbent article according to claim 4 wherein the structure of the absorbent polymeric foam material is flexible to the extent that it exhibits a bending value of at least one cycle.

6. An absorbent article according to claim 4 wherein the absorbent core of the article comprises both the absorbent polymeric foam material and an additional component selected from cellulosic fibers, particles or fibers of polymeric gelling agents and combinations of such additional components.

7. An absorbent article according to claim 6 wherein the absorbent polymeric foam material in the absorbent core has a free absorbent capacity at 37.degree. C. of at least about 12 mL of synthetic urine having a surface tension of 65.+-.5 dynes/cm per gram of dry foam material and has an absorbent capacity for said synthetic urine under a confining pressure of 5.1 kPa maintained for 15 minutes at 37.degree. C. which is at least about 5% of its free absorbent capacity.

8. An absorbent article according to claim 7 wherein the absorbent core of the article is of multi-layered configuration, said core having an upper layer comprising cellulosic fibers selected from wood pulp fibers and stiffened, twisted, curled cellulosic fibers, with said upper layer containing from 0% to 10% by weight of said upper layer of polymeric gelling agent particles; and said absorbent core further having a lower layer comprising the absorbent polymeric foam material.

9. An absorbent article according to claim 8 in the form of a disposable diaper wherein

A) said topsheet is coextensive with one face of said absorbent core;

B) said backing sheet is coextensive with the face of the core opposite the face covered by said topsheet and has a width greater than that of the core, to thereby provide side marginal portions of the backing sheet which extend beyond the core; and

C) said absorbent core is hourglass-shaped.

10. An absorbent article especially suitable for absorbing and retaining aqueous body fluids, said article comprising:

A) a backing sheet; and

B) an absorbent polymeric foam material associated with said backing sheet such that the absorbent polymeric foam material is positioned in the fluid discharge region of the wearer of the article, said absorbent polymeric foam material comprising a collapsed polymeric foam material which, upon contact with aqueous body fluids, expands and absorbs said fluids, said polymeric foam material comprising, when dried, a hydrophilic, flexible, non-hydrolyzed structure of interconnected open cells, which structure has a capillary suction specific surface area of from about 0.5 to 5.0 m.sup.2 /g; and which structure further has incorporated therein from about 0.5% to 20% by weight of residual water-insoluble emulsifier and from about 0.1% to 7% by weight of a toxicologically acceptable hygroscopic, hydrated salt; said structure further having,

A) in its collapsed state,

i) a water content of from about 4% to 15% by weight of polymeric foam material; and

ii) a dry basis density of from about 0.08 to 0.3 g/cm.sup.3 ; and

B) in its expanded state,

i) a pore volume of from about 12 to 100 mL/g;

ii) a resistance to compression deflection such that a confining pressure of 5.1 kPa produces after 15 minutes of strain from about 5% to 95% compression of the structure when it is saturated at 37.degree. C. to its free absorbent capacity with synthetic urine having a surface tension of 65.+-.5 dynes/cm; and

iii) a dry basis density upon saturation to its free absorbent capacity in said synthetic urine which ranges from about 9% to 28% of its dry basis density in its collapsed state.

Description Submit all comments and votes

FIELD OF THE INVENTION

The present invention relates to flexible, microporous, open-celled polymeric foam materials having fluid absorption and retention characteristics which make such materials particularly suitable for use in body fluid, e.g., urine, absorbing articles such as diapers, adult incontinence garments, bed pads, panty liners, sweatbands, shoe liners and the like.

BACKGROUND OF THE INVENTION

The development of highly absorbent materials and structures for use in diapers, catamenial products, bandages, and the like, is the subject of substantial commercial interest. Originally, such products relied on various cloth or cotton fibers to provide absorbency. Further progress in the field of absorbent materials and structures came with the development of various air-laid cellulosic pulp batts which, in general, will absorb up to 5-6 times their own weight of aqueous body fluids such as urine. Most recently, the use of absorbent gelling materials, such as the polyacrylates, in combination with cellulosic fibers has substantially increased the absorbent capacity of absorbent articles such as diapers and has allowed the manufacture of the relatively thin diapers which are currently commercially marketed. However, even with these improvements, the search for still better absorbent materials and structures continues.

To the uninitiated, it might seem reasonable to suggest that ordinary sponge materials which, in their broadest aspects, might be considered to be open-celled foams, would be quite useful in absorbent structures and articles. For example, both natural sponges and artificial cellulosic sponges have been used to mop up water and other fluids since time immemorial. However, on closer consideration, it will be appreciated that such sponges are not particularly suitable in high performance body fluid absorbing articles of the type currently envisioned. For example, absorbent articles are, initially, used in the dry state. It is well known that many dry sponge materials are quite stiff (rigid) and harsh feeling to the skin and, therefore, would not be suitable for use in diapers and other incontinence products. Furthermore many common sponge materials can have non-uniform cell sizes and partially or completely closed cells which hinder fluid wicking through and fluid retention by the sponge. Finally, while common sponge materials can imbibe substantial quantities of aqueous fluids, they can also release the imbibed fluids with very little pressure. Accordingly, such sponge materials would be entirely unsuitable for use in situations where the absorbent structure is used under conditions wherein pressure is applied, for example, when a diapered child sits down.

Besides common "sponges," the literature and commercial practice are replete with descriptions of various types of polymeric foams which can imbibe a variety of fluids for a variety of purposes. It is also known to employ certain types of polymeric foam materials as elements of absorbent articles such as diapers and catamenial products. For example, Karami; U.S. Pat. No. 4,029,100, Issued Jun. 14, 1977 discloses a shape-retaining diaper which can employ a foam element in the crotch area of its absorbent pad assembly in order to provide high wet resiliency for the pad assembly.

Certain types of foam materials have also been disclosed as being useful in absorbent articles for the purpose of actually imbibing, wicking and/or retaining aqueous body fluids. For example, Lindquist; U.S. Pat. No. 3,563,243; Issued Feb. 16, 1971 discloses an absorbent pad for diapers and the like wherein the primary absorbent therein is a hydrophilic foam sheet formed from hydrophilic polymers. Such foam sheets are said to be formed by combining poly(oxyethylene) glycols with diisocyanates. Dabi; U.S. Pat. No. 4,554,297; Issued Nov. 19, 1985 discloses body fluid absorbing cellular polymers which can be used in diapers or catamenial products. Such cellular polymers comprise the reaction products of at least one epoxy resin and an amine-terminated poly(alkylene oxide). Garvey et al ; U.S. Pat. No. 4,740,528; Issued Apr. 26, 1988 discloses absorbent compositer structures such as diapers, feminine care products and the like, which contain a sponge absorbent composition made from a certain type of super-wicking, crosslinked polyurethane foam.

Notwithstanding the known uses of various polymeric foam types as elements in absorbent articles for body fluids, there is a continuing need to identify additional absorbent foam materials having an optimized combination of features and characteristics which render such foams especially useful in commercially marketed absorbent products such as diapers. It has now been determined that optimized absorbent foams for body fluids, and especially foams intended for use in diapers and adult incontinence products, should have the following characteristics:

a) Flexibility and preferably recovery from compression, for comfort and performance;

b) Acceptable fluid acquisition rate, in order for the foam to rapidly accept and imbibe gushes of urine or other fluids;

c) Relatively good wicking and fluid distribution characteristics in order for the foam to transport the imbibed urine or other fluid away from the zone wherein the fluid initially impinges onto the foam and into the unused balance of the foam structure, thereby allowing for subsequent gushes of fluid to be accommodated;

d) Relatively high total storage capacity with relatively high fluid capacity under load, i.e., under compressive pressure; and

e) Relatively low density in order for the foam to exhibit suitably high total storage capacity and to comprise a thin soft material.

f) Relatively greater affinity for absorbing body fluids than exhibited by other absorbent article components so that the foam material can drain (partition) fluids from these other components and keep such fluid stored within the foam structure.

It will be appreciated that absorbent foams having the foregoing characteristics would provide the features of fluid acquisition, transport, storage which are required for use in high performance absorbent articles. Optimized foams would, preferably, also be soft to the touch. Of course, absorbent foams intended for use in contact with or in proximity to the skin should cause no damage or irritation to the skin nor expose the user to toxic chemicals. Since they are intended for use in disposable articles such as diapers, such preferred optimized foams should also be relatively inexpensive and easy to manufacture and should be compatible with responsible solid waste disposal systems such as those based on landfills, incineration and/or composting.

It will also be appreciated by the manufacturer of absorbent articles that optimized absorbent foam materials of the type hereinbefore described would represent a substantial advance in the industry. Absorbent articles containing such foams would possess desirable wet integrity, would enable suitable fit through the entire period the article was being worn, would not degrade in shape during use, and would provide desirable skin dryness.

Absorbent articles containing such foam structures would also be easier to manufacture on a commercial scale. For example, diaper product cores could be simply stamped out of continuous foam sheets and could be designed to have considerably greater integrity and uniformity than air-laid absorbent cores. Such foams could furthermore be molded in any desired shape, or even formed into integral, unitary diapers or panty-like structures. Alternatively, such foam materials could be combined, e.g., blended, with other conventional absorbent structure components.

The present invention identifies the parameters which define optimized absorbent foam materials that are especially adapted for use in absorbent articles for body fluids such as urine. The invention herein also provides absorbent foams which overcome a number of the drawbacks of foam materials heretofore used in body fluid absorbing articles.

SUMMARY OF THE INVENTION

In its composition aspects, the present invention relates to a certain type of polymeric foam material which is especially suitable for absorbing and retaining aqueous body fluids, e.g. urine. Such a foam material comprises a hydrophilic, flexible structure formed from a plurality of interconnected open cells. This cellular foam structure has, in use as an absorbent material, a pore volume of from about 12 to 100 mL/g and a specific surface area of from about 0.5 to 5.0 m.sup.2 /g as determined by capillary suction. The foam structure also will exhibit a resistance to compression deflection such that a confining pressure of 5.1 kPa produces, after 15 minutes, a strain of from about 5% to 95% compression of the structure when it is saturated to its free absorbent capacity with 65.+-.5 dyne/cm synthetic urine at 37.degree. C.

Preferred absorbent foam materials having these characteristics can be prepared by polymerizing a specific type of water-in-oil emulsion having a relatively smaller amount of an oil phase and a relatively greater amount of a water phase. This type of polymerizable emulsion in general is known in the art as a high internal phase emulsion or "HIPE".

The oil phase forming the particular water-in-oil HIPE emulsions which can be used to prepare the preferred absorbent foams herein comprises from about 3% to 41% by weight of a substantially water-insoluble, monofunctional glassy monomer component, from about 27% to 73% by weight of a substantially water-insoluble, monofunctional rubbery comonomer component; from about 8% to 30% by weight of a substantially water-insoluble polyfunctional cross-linking agent component and from about 2% to 33% by weight of an emulsifier component which is soluble in the oil phase and which will enable realization of a stable emulsion for polymerization. The water or "internal" phase forming the water-in-oil HIPE emulsions which can be used to prepare such preferred foams comprises an aqueous solution containing from about 0.2% to 40% by weight of a water-soluble electrolyte. The weight ratio of the water phase to the oil phase in these water-in-oil HIPE emulsions ranges from about 12:1 to 100:1.

The water-in-oil emulsions which can be used to prepare the preferred absorbent foam material of this invention are polymerized under conditions that provide open-celled foam structures having the structural and resistance to compression deflection characteristics as hereinbefore set forth. Subsequent post-polymerization treatment of such foams will frequently be necessary to render the foam materials suitably hydrophilic and ready for absorbing aqueous body fluids.

In its article aspects, the present invention relates to absorbent articles for incontinence management such as diapers which utilize the polymeric foam absorbent materials herein as at least a portion of their fluid-absorbing "core" element. Thus, in the broadest sense, the absorbent articles of the present invention will generally comprise a relatively liquid-impervious backing sheet (or water impervious "skin" on the foam itself) and a polymeric foam absorbent material of the type hereinbefore described. The absorbent polymeric foam material is associated with the backing sheet in such a manner that the foam absorbent material is situated between the backing sheet and the fluid discharge region of the wearer of the absorbent article.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 of the drawings is a photomicrograph of the interstices of a typical absorbent HIPE foam of the present invention.

FIG. 2 of the drawings is a cutaway depiction of a disposable diaper which utilizes the absorbent foam material of the present invention as an hourglass-shaped fluid storage/distribution component in an absorbent diaper core of dual-layer configuration.

FIG. 3 of the drawings represents a cut-away view of a form-fitting article such as a disposable training pants product which employs an absorbent HIPE foam structure of this invention as an absorbent core.

FIG. 4 of the drawings represents a blown-apart view of the components of a diaper structure also of dual layer core configuration having an hourglass-shaped fluid acquisition layer overlying an absorbent foam fluid storage/distribution layer with a modified hourglass shape.

DETAILED DESCRIPTION OF THE INVENTION

As noted, the present invention is based on the use of a certain type of very specifically defined polymeric foam material as an absorbent for discharged aqueous body fluids such as urine. These polymeric foam absorbents can thus be employed as, or as part of, the absorbent cores of absorbent articles such as diapers, incontinence briefs or pads, training pants, and the like.

Polymeric foams can in general be characterized as the structures which result when a relatively monomer-free gas or relatively monomer-free liquid is dispersed as bubbles in a polymerizable monomer-containing liquid, followed by polymerization of the polymerizable monomers in the monomer-containing liquid which surrounds the bubbles. The resulting polymerized dispersion can be in the form of a porous solidified structure which is an aggregate of cells, the boundaries or walls of which cells comprise solid polymerized material. The cells themselves contain the relatively monomer-free gas or relative