Polyacrylic acid-type water absorbent resin and method for producing same

Patent metadata

Field	Value
Publication number	US-9315640-B2
Application number	US-201514723026-A
Country	US
Kind code	B2
Filing date	May 27, 2015
Priority date	Jun 30, 2010
Publication date	Apr 19, 2016
Grant date	Apr 19, 2016

Abstract

Provided is a method for producing a water absorbent resin, which promotes the formation of interconnected voids (continuous gas bubbles) in a foamed polymer (foam-like water absorbent resin) by a more convenient method, and produces with high efficiency a water absorbent resin which exhibits a high water absorption rate even when stepped into a sheet form or a powder form in hygiene articles and the like. Disclosed is a method for producing a polyacrylic acid-type water absorbent resin, comprising (A) a step of obtaining an aqueous solution of acrylic acid-type monomers containing gas bubbles dispersed therein; (B) a step of polymerizing the aqueous monomer solution and thereby obtaining a foamed polymer; and (C) a step of heating and drying the foamed polymer,
wherein gas bubbles are incorporated such that the volumetric expansion factor defined by the following formula (1); [Formula 1]

Volumetric expansion factor=(Volume of aqueous monomer solution after gas bubble dispersion)/(volume of aqueous monomer solution before gas bubble dispersion)  Formula (1);
exceeds 1.1 times, and the aqueous monomer solution having a monomer concentration defined by the following formula (2);
[Formula 2]

Monomer concentration [wt %]=(Weight of a monomer)/{(weight of a monomer)+(weight of solvent)}×100  Formula (2);

of 40% by weight or greater is boiling polymerized at a temperature of 100° C. or higher.

First claim

The invention claimed is:

1. A polyacrylic acid-type water absorbent resin having an open gas bubble ratio of 5% or greater and the content of p-methoxyphenol is 60 ppm or less.

2. The water absorbent resin according to claim 1 , wherein the independent gas bubble ratio is 5% or greater.

3. The water absorbent resin according to claim 1 , comprising at least any one of a metal chelating agent and a reducing agent.

4. The water absorbent resin according to claim 1 , wherein the water absorption rate (FSR) is 0.25 [g/g/s] or greater.

5. The water absorbent resin according to claim 1 , wherein the water absorbent resin is surface-crosslinked by using a covalently bondable crosslinking agent and/or an ionically bondable crosslinking agent.

6. The water absorbent resin according to claim 1 , which is in a sheet form.

7. The water absorbent resin according to claim 1 , wherein the water absorbent resin is in the form of a powder having a weight average particle diameter (D50) of greater than or equal to 300 μm and less than 600 μm.

8. A water absorbing article comprising the water absorbent resin according to claim 1 .

Assignees

• Nippon Catalytic Chem Ind

Inventors

• Takaai Toshihiro
• Wada Hidenori
• Fujino Sinichi

Classifications

• C08J2333/02

  Homopolymers or copolymers of acids; Metal or ammonium salts thereof · CPC title

• Y10T428/2982

  Particulate matter [e.g., sphere, flake, etc.] · CPC title

• C08J3/245

  Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking · CPC title

• C08J9/36

  After-treatment (C08J9/22 takes precedence) · CPC title

• C08F220/06

  Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof · CPC title