US 4,654,039 A · Hydrogel-forming polymer compositions for use in absorbent structures

Abstract

The present invention relates to improved hydrogel-forming polymer compositions which can be used as absorbents in absorbent structures and absorbent articles such as diapers, sanitary napkins and the like. Such hydrogel-forming polymer compositions are substantially water-insoluble, slightly cross-linked, partially neutralized polymers which are prepared from unsaturated polymerizable, acid group-containing monomers and cross-linking agents. These hydrogel-forming polymer materials, upon imbibing fluids, form hydrogels. Such polymer materials have relatively high gel volume and relatively high gel strength as measured by shear modulus of the hydrogel which forms therefrom. Such polymer materials also contain relatively low levels of extractable polymer material which can be extracted therefrom by contact with synthetic urine. Preferred hydrogel-forming polymers having these characteristics can be prepared by polymerizing the acid group-containing monomers in their free acid form at relatively low monomer concentrations, preferably using relatively low polymerization temperatures. Absorbent structures and absorbent articles containing these dried hydrogel-forming polymer materials are also disclosed.

Claims37

Dependent claims

A substantially water-insoluble, slightly cross-linked, partially neutralized, hydrogel-forming polymer composition consisting essentially of

(a) from about 50 mole percent to 99.999 mole percent of polymerized unsaturated, polymerizable, acid group-containing monomers;
and
(b) from about 0.001 mole percent to 5 mole percent of a cross-linking agent;
wherein said composition has a degree of neutralization of at least about 25% and is substantially free of graft polymerizable polymer moieties;
and further wherein said polymer composition, upon neutralization to a degree of neutralization of at least 50%, has or would have a gel volume of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer exhibits a shear modulus of at least about 2000 dynes/cm.sup.2, an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer.

2 more elements

A substantially water-insoluble, slightly cross-linked, partially neutralized, hydrogel-forming polymer composition consisting essentially of

(a) from about 75 mole percent to 99.99 mole percent of polymerized unsaturated, polymerizable, acid group-containing monomers;
and
(b) from about 0.01 mole percent to 3 mole percent of a cross-linking agent;
wherein said composition has a degree of neutralization of at least about 25% and is substantially free of graft polymerizable polymer moieties;
and further wherein said polymer composition, upon neutralization to a degree of neutralization of at least 50%, has or would have a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer exhibits a shear modulus, s, of at least about 2000 dynes/cm.sup.2, an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer, and further wherein the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation:
e.ltoreq.0.23v-3.0.

3 more elements

A substantially water-insoluble, slightly cross-linked, partially neutralized, hydrogel-forming polymer composition consisting essentially of

(a) from about 75 mole percent to 99.99 mole percent of polymerized unsaturated, polymerizable, acid group-containing monomers;
and
(b) from about 0.01 mole percent to 3 mole percent of a cross-linking agent;
wherein said composition has a degree of neutralization of at least about 25% and is substantially free of graft polymerizable polymer moieties;
and further wherein said polymer composition, upon neutralization to a degree of neutralization of at least 50%, has or would have a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer exhibits a shear modulus, s, of at least about 2000 dynes/cm.sup.2, an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer, and further wherein the relationship between gel volume, v, and equilibrium extractable polymer content, e, is defined by the equation:
e.ltoreq.0.23v-3.0;
and further wherein the relationship between gel volume, v, and gel strength as measured by shear modulus, s, is defined by the equation:
log s.gtoreq.-2.494 log v+8.090.

5 more elements

A process for preparing a substantially water-insoluble, slightly cross-linked, partially neutralized hydrogel or hydrogel-forming polymer material suitable for use in absorbent products, said process comprising

(a) preparing a reaction mixture consisting essentially of from about 5% to 35% by weight of unsaturated, polymerizable, acid group-containing monomers in the free acid form, from about 0.001 mole percent to 5 mole percent, based on moles of polymerizable monomers, of a cross-linking agent and from 0 mole percent to about 5 mole percent, based on the moles of polymerizable monomers, of a free radical initiator in an aqueous medium which is substantially free of graft polymerizable polymer moieties;
(b) subjecting said aqueous reaction mixture to polymerization conditions which are sufficient to produce therein a substantially water-insoluble, slightly cross-linked polymer material which, upon subsequent neutralization to a degree of neutralization of at least 50% and upon subsequent drying, has or would have, a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer material exhibits a shear modulus, s, of at least about 2000 dynes/cm.sup.2, an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer;
and a relationship between gel volume, v, and equilibrium extractable polymer content, e, defined by the equation:
e.ltoreq.0.23v-3.0;
and
(c) neutralizing at least a portion of the acid groups of the polymer material formed in the aqueous reaction mixture with salt-forming cations to form a partially neutralized polymer material having a degree of neutralization of at least about 25%.

3 more elements

A process for preparing a substantially water-insoluble, slightly cross-linked, partially neutralized hydrogel-forming polymer material suitable for use in absorbent products, said process comprising

(a) preparing a reaction mixture consisting essentially of from about 8% to 24% by weight of polymerizable acrylic acid monomers in the free acid form, from about 0.01 mole percent to 3 mole percent, based on total moles of polymerizable monomers, of a cross-linking agent selected from N,N'-methylenebisacrylamide, trimethylol propane triacrylate and triallyl amine, and from about 0.001 mole percent to 0.5 mole percent, based on the total moles of acrylic acid plus cross-linking agent monomers, of a free radical initiator in an aqueous medium which is substantially free of graft polymerizable polymer moieties;
(b) subjecting said aqueous reaction mixture to polymerization conditions, including a temperature of from about 5.degree. C. to 40.degree. C., which are sufficient to produce therein a substantially water-insoluble, slightly cross-linked polyacrylic acid-based polymer material having, upon subsequent neutralization and drying, a gel volume, v, of from about 25 to 80 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that said hydrogel formed from said polymer material exhibits a shear modulus, s, of from about 2500 to 92,000 dynes/cm.sup.2, an initial extractable polymer content, after one hour in synthetic urine, of no more than about 5% by weight of hydrogel-forming polymer, an equilibrium extractable polymer content, at equilibrium in synthetic urine, of no more than about 10% by weight of hydrogel-forming polymer, a relationship between gel volume, v, and equilibrium extractable polymer content, e, defined by the equation:
e.ltoreq.0.23v-3.0, and a relationship between gel volume, v, and shear modulus, s, defined by the equation:
log s.gtoreq.-2.494 log v+8.090;
and
(c) neutralizing at least a portion of the carboxyl groups of said polyacrylic acid-based polymer material formed in the aqueous reaction mixture with sodium cations to form a partially neutralized polymer material having a degree of neutralization of at least about 50%.

3 more elements

An absorbent structure suitable for use in disposable absorbent articles, said absorbent structure comprising:

(a) from about 50% to 98% by weight of said structure of hydrophilic fiber material;
and
(b) from about 2% to 50% by weight of said structure of discrete particles of substantially water-insoluble, slightly cross-linked, partially neutralized, substantially dry, hydrogel-forming polymer material;
wherein said polymer material has a degree of neutralization of at least about 25% and is substantially free of graft polymerizable polymer moieties;
and further wherein said polymer material, upon neutralization to a degree of neutralization of at least 50%, has or would have a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer material exhibits a shear modulus, s, of at least about 2000 dynes/cm.sup.2, an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, at equilibrium in synthetic urine, of no more than about 17% by weight of hydrogel-forming material.

2 more elements

A diaper article comprising:

(a) a liquid impervious backing sheet;
(b) a relatively hydrophobic, liquid pervious topsheet;
and
(c) an absorbent core positioned between said backing sheet and said topsheet, said absorbent core comprising an absorbent structure which consists essentially of
(i) from about 65% to 90% by weight of said structure of hydrophilic fiber material;
and
(ii) from about 10% to 35% by weight of said structure of discrete particles of substantially water-insoluble, slightly cross-linked, partially neutralized, substantially dry hydrogel-forming polymer material comprising polymerized acrylic acid monomers, cross-linked with a cross-linking agent selected from N,N'-methylenebisacrylamide, trimethylol propane triacrylate and triallyl amine;
wherein said polymer material has at least 50% of its acrylic acid groups neutralized with sodium cations and is substantially free of graft polymerized polymer moieties, and further wherein said hydrogel-forming polymer material has a gel volume, v, of at least about 20 grams of synthetic urine per gram of hydrogel-forming polymer, a gel strength such that the hydrogel formed from said polymer material exhibits a shear modulus, s, of at least about 2000 dynes/cm.sup.2, an initial extractable polymer content, after one hour in synthetic urine, of no more than about 7.5% by weight of hydrogel-forming polymer, and an equilibrium extractable polymer content, e, after 16 hours in synthetic urine, of no more than about 17% by weight of hydrogel-forming polymer.

5 more elements

Dependencies are inferred from the claim text.

Hydrogel-forming polymer compositions for use in absorbent structures

Life of this patent

Hydrogel-forming polymer compositions for use in absorbent structures

Life of this patent

Abstract

Claims37