# US 9,751,995 B2 · Superabsorbent polymer and a preparation method thereof

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- Number: US 9,751,995 B2
- Document ID: US9751995B2
- Status: Granted
- Kind: B2
- Application number: 15/123,447
- Filed: 2015-08-04
- Published: 2017-03-16
- Granted: 2017-09-05
- Earliest claimed: 2014-08-04
- Assignees: LG Chem, Ltd.
- Applicants: LG Chem, Ltd.
- Inventors: Hyo Sook Joo; Ki Youl Yoon; Gi Cheul Kim; Ju Eun Kim; Hyeon Choi; Hee Jung Choi; Sung Soo Park; Sung Hyun Park; Myung Han Lee
- Web page: https://patentgrep.com/patent/US9751995B2

## CPC

- C08J 3/245: {Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking}
- A61L 15/24: Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives thereof {(A61L15/225 takes precedence)}
- A61L 15/60: Liquid-swellable gel-forming materials, e.g. super-absorbents
- B01J 20/267: {Cross-linked polymers}
- B01J 20/28004: {Sorbent size or size distribution, e.g. particle size}
- B01J 20/28059: {being less than 100 m2/g}
- B01J 20/28061: {being in the range 100-500 m2/g}
- B01J 20/28064: {being in the range 500-1000 m2/g}
- C08F 220/06: Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
- C08F 292/00: Macromolecular compounds obtained by polymerising monomers on to inorganic materials
- C08J 3/075: Macromolecular gels
- C08J 3/24: Crosslinking, e.g. vulcanising, of macromolecules (mechanical aspects B29C35/00; crosslinking agents C08K)
- C08K 3/00: Use of inorganic substances as compounding ingredients
- C08K 5/00: Use of organic ingredients
- C08F 222/02: Acids; Metal salts or ammonium salts thereof {, e.g. maleic acid or itaconic acid}
- C08J 2333/02: Homopolymers or copolymers of acids; Metal or ammonium salts thereof
- C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29)
- A61L: METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES (preservation of bodies or disinfecting characterised by the agents employed A01N; preserving, e.g. sterilising, food or foodstuffs A23; preparations for medical, dental or toiletry purposes A61K)
- B01J: CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- C08F: MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08K: Use of inorganic or non-macromolecular organic substances as compounding ingredients (paints, inks, varnishes, dyes, polishes, adhesives C09)

## Abstract

The present invention relates to a superabsorbent polymer that has more improved gel strength and is improved in both water retention capacity (centrifuge retention capacity, CRC) and absorption ability under pressure (AUP) because of an optimized cross-linked structure of a base resin powder inside a cross-linked surface layer, and a preparation method thereof. The superabsorbent polymer includes a base resin powder including a 1st cross-linked polymer of a water-soluble ethylenic unsaturated monomer having acid groups of which at least a part is neutralized, and a cross-linked surface layer that includes a 2nd cross-linked polymer further cross-linked from the 1st cross-linked polymer and is formed on the base resin powder, wherein an inorganic particle is chemically bonded to the 1st cross-linked polymer by the medium of a cross-linking bond, an oxygen-containing bond (—O—), or a nitrogen-containing bond (—NR—, where R is hydrogen or a C1-C3 alkyl or an amide bond).

## Claims

### Claim 1

A superabsorbent polymer, including: a base resin powder including a 1st cross-linked polymer of a water-soluble ethylenic unsaturated monomer having acid groups of which at least a part is neutralized; and a cross-linked surface layer that includes a 2nd cross-linked polymer further cross-linked from the 1st cross-linked polymer and formed on the base resin powder, wherein an inorganic particle is chemically bonded to the 1st cross-linked polymer by the medium of a cross-linking bond, an oxygen-containing bond (—O—), or a nitrogen-containing bond (—NR—, where R is hydrogen or a C1-C3 alkyl or amide bond).

### Claim 2 (depends on 1)

The superabsorbent polymer according to claim 1, wherein the water-soluble ethylenic unsaturated monomer includes one or more monomers selected from the group consisting of: an anionic monomer of acrylic acid, methacrylic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloyl ethane sulfonic acid, 2-methacryloyl ethane sulfonic acid, 2-(meth)acryloyl propane sulfonic acid, or 2-(meth)acrylamide-2-methyl propane sulfonic acid, and a salt thereof; a nonionic hydrophilic monomer of (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl(meth)acrylate, methoxy polyethyleneglycol(meth)acrylate, or polyethyleneglycol (meth)acrylate; and an amino-containing unsaturated monomer of (N,N)-dimethylaminoethyl (meth)acrylate, or (N,N)-dimethylaminopropyl (meth)acrylamide, and a quaternary compound thereof.

### Claim 3 (depends on 1)

The superabsorbent polymer according to claim 1, wherein the 1st cross-linked polymer includes a cross-linked polymer prepared by polymerizing the water-soluble ethylenic unsaturated monomer in the presence of an inner cross-linking agent including a multi-functional acrylate-based compound having a plurality of ethylene oxide groups.

### Claim 4 (depends on 1)

The superabsorbent polymer according to claim 1, wherein the 1st cross-linked polymer includes a cross-linked structure in which the polymer chains polymerized from the water-soluble ethylenic unsaturated monomer are cross-linked with the cross-linkable functional group of the inner cross-linking agent by the medium of a cross-linking bond, an oxygen-containing bond, or a nitrogen-containing bond of the inorganic particle.

### Claim 5 (depends on 3)

The superabsorbent polymer according to claim 3, wherein the inner cross-linking agent includes one or more compounds selected from the group consisting of polyethyleneglycol diacrylate (PEGDA), glycerin diacrylate, glycerin triacrylate, unmodified or ethoxylated trimethylol triacrylate (TMPTA), hexanediol diacrylate, and triethyleneglycol diacrylate.

### Claim 6 (depends on 1)

The superabsorbent polymer according to claim 1, wherein the inorganic particle is a silica nanoparticle or an alumina nanoparticle.

### Claim 7 (depends on 1)

The superabsorbent polymer according to claim 1, wherein the inorganic particle is surface-modified with a cross-linkable or hydrophilic functional group including at least one functional group selected from the group consisting of a (meth)acrylate-based functional group, an allyl group, a vinyl group, an epoxy group, a hydroxy group, an isocyanate group, and an amine group.

### Claim 8 (depends on 1)

The superabsorbent polymer according to claim 1, wherein the 2nd cross-linked polymer includes a polymer that is formed by further cross-linking the 1st cross-linked polymer with a surface cross-linking agent.

### Claim 9 (depends on 8)

The superabsorbent polymer according to claim 8, wherein the surface cross-linking agent includes one or more compounds selected from the group consisting of ethyleneglycol, 1,4-butanediol, 1,6-hexanediol, polypropyleneglycol, 1,2-hexanediol, 1,3-hexanediol, 2-methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropyleneglycol, glycerol, ethylene carbonate, and propylene carbonate.

### Claim 10 (depends on 1)

The superabsorbent polymer according to claim 1, wherein the centrifuge retention capacity (CRC) to a saline solution is 20 to 40 g/g, the absorption ability under pressure (0.7 psi) (AUP) to a saline solution is 15 to 35 g/g, and the gel strength is 4000 to 20000 Pa.

### Claim 11 (depends on 1)

The superabsorbent polymer according to claim 1, wherein 0.01 to 30 parts by weight of the inorganic particle is bonded to 100 parts by weight of the base resin powder.

### Claim 12 (depends on 1)

The superabsorbent polymer according to claim 1, having a particle diameter of 150 to 850 μm.

### Claim 13 (depends on 1)

A method of preparing the superabsorbent polymer of claim 1, including the steps of: preparing a hydrogel polymer by carrying out cross-linking polymerization of a water-soluble ethylenic unsaturated monomer having acid groups of which at least a part is neutralized, in the presence of an inner cross-linking agent and an inorganic particle of which the surface is modified with a cross-linkable or hydrophilic functional group including at least one functional group selected from the group consisting of a (meth)acrylate-based functional group, an allyl group, a vinyl group, an epoxy group, a hydroxy group, an isocyanate group, and an amine group; preparing a base resin powder by drying, pulverizing, and classifying the hydrogel polymer; and forming a cross-linked surface layer by further cross-linking the surface of the base resin powder in the presence of a surface cross-linking agent.

### Claim 14 (depends on 13)

The method of preparing the superabsorbent polymer of claim 13, wherein 2 to 200 functional groups per inorganic particle are introduced to the surface-modified inorganic particle.

### Claim 15 (depends on 13)

The method of preparing the superabsorbent polymer of claim 13, wherein the inorganic particle has a specific surface area of 5 to 600 m2/g and a diameter of 5 to 500 nm.

### Claim 16 (depends on 13)

The method of preparing the superabsorbent polymer of claim 13, wherein the surface-modified inorganic particle includes the inorganic particle of which the surface is bonded to the compound of Chemical Formula 1:
wherein, in Chemical Formula 1, R1 to R3 are independently a C1 to C10 alkyl group, a C1 to C10 alkoxy group, or a halogen, and at least one of them is not an alkyl group, R4 is a C2 to C20 aliphatic functional group including at least one functional group selected from the group consisting of a (meth)acrylate-based functional group, an allyl group, a vinyl group, an epoxy group, a hydroxy group, an isocyanate group, and an amine group at the end, or a C2 to C20 hetero-aliphatic functional group of which at least one carbon is substituted with oxygen or nitrogen, including at least one functional group selected from the group consisting of a (meth)acrylate-based functional group, an allyl group, a vinyl group, an epoxy group, a hydroxy group, an isocyanate group, and an amine group at the end.