# US 2014/0193641 A1 · Polyacrylic Acid (Salt)-Based Water Absorbent Resin Powder and Method for Producing the Same

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- Number: US 2014/0193641 A1
- Document ID: US20140193641A1
- Status: Published application
- Kind: A1
- Application number: 14/129,792
- Filed: 2012-06-29
- Published: 2014-07-10
- Earliest claimed: 2011-06-29
- Assignees: Nippon Shokubai Co., Ltd.
- Inventors: Kazushi Torii; Reiko Nakatsuru; Yasuhisa Nakashima; Katsuyuki Wada; Kunihiko Ishizaki
- Web page: https://patentgrep.com/patent/US20140193641A1

## CPC

- A61L 15/26: Macromolecular compounds obtained otherwise than 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
- B29B 7/428: {Parts or accessories, e.g. casings, feeding or discharging means}
- B29B 9/06: in the form of filamentary material, e.g. combined with extrusion
- B29B 9/12: characterised by structure or composition
- B29C 48/0022: {combined with cutting}
- B29C 48/022: {characterised by the choice of material}
- B29C 48/05: Filamentary, e.g. strands
- C08F 20/06: Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
- C08F 220/06: Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
- C08J 3/245: {Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking}
- C08K 5/0091: {Complexes with metal-heteroatom-bonds}
- C08J 2333/02: Homopolymers or copolymers of acids; Metal or ammonium salts thereof
- C08K 5/175: {containing COOH-groups; Esters or salts thereof}
- C08L 33/02: Homopolymers or copolymers of acids; Metal or ammonium salts thereof
- Y10T 428/2982: Particulate matter [e.g., sphere, flake, etc.]
- 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)
- B29B: PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
- B29C: SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING (making preforms B29B11/00; making laminated products by combining previously unconnected layers which become one product whose layers will remain together B32B37/00 - B32B41/00)
- C08F: MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- 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)
- C08K: Use of inorganic or non-macromolecular organic substances as compounding ingredients (paints, inks, varnishes, dyes, polishes, adhesives C09)
- C08L: COMPOSITIONS OF MACROMOLECULAR COMPOUNDS (compositions based on polymerisable monomers C08F, C08G; artificial filaments or fibres D01F; textile treating compositions D06)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

Provided is a water absorbent resin having excellent liquid permeability, water absorbent speed, anti-impact stability, and weather resistance. Provided is a polyacrylic acid (salt)-based water absorbent resin powder in which the water absorption capacity without load (CRC) is 30 to 45 [g/g], the water absorption capacity under load (AAP 0.3) is 20 to 35 [g/g], the water absorption capacity under load (AAP 0.7) is 10 to 28 [g/g], and the weight average particle diameter (D50) is 300 to 500 μm, characterized by including p-methoxyphenol; having a degradable soluble component (0.05% L-A (saline) for 2 hours/60° C., one hour extraction rinse/room temperature) of 40% by weight or less; and having a internal gas bubbles ratio of 0.1 to 2.5%, as specified by the following equation. (Internal gas bubbles ratio)[%]={(True density)−(Apparent density)}/(True density)×100

## Claims

### Claim 1

A polyacrylic acid (salt)-based water absorbent resin powder in which the water absorption capacity without load (CRC) is 30 to 45 [g/g], the water absorption capacity under load (AAP 0.3) is 20 to 35 [g/g], the water absorption capacity under load (AAP 0.7) is 10 to 28 [g/g], and the weight average particle diameter (D50) is 300 to 500 μm, wherein the water absorbent resin powder comprises p-methoxyphenol, has a degradable soluble component (0.05% L-A (saline) for 2 hours/60° C., one hour extraction rinse/room temperature) of 40% by weight or less, and an internal gas bubbles ratio of 0.1 to 2.5%, as specified by the following equation.
(Internal gas bubbles ratio)[%]={(True density)−(Apparent density)}/(True density)×100

### Claim 2 (depends on 1)

The water absorbent resin powder according to claim 1, further comprising water-insoluble inorganic microparticles, a water soluble polyvalent metal salt (with the proviso that, iron salt is excluded), an inorganic or organic reducing agent, or a combination thereof.

### Claim 3

(canceled)

### Claim 4 (depends on 1)

The water absorbent resin powder according to claim 1, further comprising a metal chelating agent.

### Claim 5 (depends on 1)

The water absorbent resin powder according to claim 1, wherein content of an iron ion is 0.1 to 3 ppm.

### Claim 6 (depends on 1)

The water absorbent resin powder according to claim 1, wherein content of p-methoxyphenol is 5 to 50 ppm.

### Claim 7

(canceled)

### Claim 8 (depends on 1)

The water absorbent resin powder according to claim 1, wherein residual monomers are 500 ppm or less.

### Claim 9

(canceled)

### Claim 10 (depends on 19)

The water absorbent resin powder according to claim 19, wherein the degradable soluble component (0.05% L-A (saline) for 2 hours/60° C., one hour extraction rinse/room temperature) is 20% by weight or less.

### Claim 11 (depends on 1)

The water absorbent resin powder according to claim 1, wherein powder flowability after moisture absorption test is 70% by weight or more.

### Claim at position 12

12-13. (canceled)

### Claim 14 (depends on 3)

The water absorbent resin powder according to claim 3, wherein the metal chelating agent is comprised at 0.001 to 2% by weight relative to the water absorbent resin powder.

### Claim at position 14

15-17. (canceled)

### Claim 18 (depends on 1)

The water absorbent resin powder according to claim 1, wherein an increase amount of degradable soluble component (defined as degradable soluble component (%)−16 hour soluble component (%)) is 20% by weight or less.

### Claim 19 (depends on 3)

The water absorbent resin powder according to claim 3, wherein the chelating agent is a water soluble non-polymeric chelating agent selected from amino polyvalent carboxylic acid and amino polyvalent phosphoric acid.

### Claim 20

A method for producing a water absorbent resin powder which has internal gas bubbles ratio of 0.1 to 2.5% as specified by the following equation, the method comprising:
a polymerization step wherein performing foaming polymerization or boiling polymerization of an aqueous monomer solution containing p-methoxyphenol and also acrylic acid as a main component;
a gel-crushing step wherein kneading and grain refining a water-containing gel-like polymer having gas bubbles obtained from the polymerization;
a drying step wherein heating and drying it at 150 to 250° C. after gel-crushing,
a pulverizing and classification step wherein pulverizing and classifying a dried product to have a weight average particle diameter of 300 to 500 μm; and
surface crosslinking the pulverized and classified product with internal gas bubbles ratio 0.1 to 2.5% to have the water absorption capacity without load (CRC) of 30 to 45 [g/g], the water absorption capacity under load (AAP 0.3) of 20 to 35 [g/g], and the water absorption capacity under load (AAP 0.7) of 10 to 28 [g/g].
(Internal gas bubbles ratio)[%]={(True density)−(Apparent density)}/(True density)×100

### Claim 21

A method for producing a water absorbent resin powder which has internal gas bubbles ratio of 0.1 to 2.5% as specified by the following equation, the method comprising steps of:
performing foaming polymerization or boiling polymerization of an aqueous monomer solution containing p-methoxyphenol and also acrylic acid as a main component;
adding a chelating agent during the polymerization or after the polymerization step; and
surface crosslinking a water absorbent resin containing p-methoxyphenol and having internal gas bubbles ratio of 0.1 to 2.5% to have the water absorption capacity without load (CRC) of 30 to 45 [g/g], the water absorption capacity under load (AAP 0.3) of 20 to 35 [g/g] and the water absorption capacity under load (AAP 0.7) of 10 to 28 [g/g].
(Internal gas bubbles ratio)[%]={(True density)−(Apparent density)}/(True density)×100

### Claim 22

(canceled)

### Claim 23 (depends on 20)

The production method according to claim 20, wherein, for the gel-crushing step, the water-containing gel-like crosslinked polymer with resin solid content of 10 to 80% by weight is subjected to gel-crushing which satisfies at least one of the following (1) to (4):
(1) the gel-crushing is carried out with gel grinding energy (GGE) of 18 to 60 [J/g];
(2) the gel-crushing is carried out with gel grinding energy (2) (GGE (2)) of 9 to 40 [J/g];
(3) the weight average molecular weight of water soluble component of the water-containing gel-like crosslinked polymer is increased by 10,000 to 500,000 [Da]; and
(4) the gel-crushing is carried out until the water-containing gel-like crosslinked polymer has a weight average particle diameter (D50) of 350 to 2,000 μm, and logarithmic standard deviation (σζ) of particle size distribution of 0.2 to 1.0.

### Claim 24 (depends on 20)

The production method according to claim 20, wherein water-insoluble inorganic microparticles, a water soluble polyvalent metal salt (with the proviso that, iron salt is excluded), an inorganic or organic reducing agent, or a combination thereof are additionally mixed after the drying step.

### Claim 25

(canceled)

### Claim 26 (depends on 20)

The production method according to claim 20, wherein a metal chelating agent is additionally mixed after the polymerization step.

### Claim 27 (depends on 20)

The production method according to claim 20, wherein content of iron ion in monomer is 0.1 to 3 ppm.

### Claim 28 (depends on 20)

The production method according to claim 20, wherein content of p-methoxyphenol in monomer is 5 to 200 ppm (relative to monomer solid content).

### Claim 29

(canceled)

### Claim 30 (depends on 20)

The production method according to claim 20, further comprising a step of neutralizing whole or part of acrylic acid with a base having a Fe content of 0 to 7 ppm before the polymerization step,
wherein the polymerization step is a step of performing, under condition including maximum temperature of 130° C. or less and polymerization time of between 0.5 minutes to 3 hours, aqueous solution polymerization or reverse-phase suspension polymerization of an aqueous monomer solution with monomer concentration of 30 to 55% by weight, in which acrylic acid (salt) is contained at 90 to 100% by mol in the monomer, by using 0.001 to 1% by mol of a polymerization initiator (relative to the monomer),
the drying step is a step of drying the water-containing gel-like crosslinked polymer, which has been obtained in particle form by polymerization, to have a moisture content of 20% by weight or less with drying temperature of 100 to 250° C. and drying time of 10 to 120 minutes, and
the surface crosslinking step is a step of mixing 0.001 to 10 parts by weight of a surface crosslinking agent relative to 100 parts by weight of the water absorbent resin powder after completion of the pulverizing and classification step and performing a heating treatment for 1 minute to 2 hours at 70 to 300° C.

### Claim 31 (depends on 1)

An absorbent article comprising the water absorbent resin powder defined claim 1, wherein core concentration as defined by weight ratio of the water absorbent resin relative to total weight of the water absorbent resin and a hydrophilic fiber material is 30 to 100% by weight.

### Claim 32

(canceled)