POLYACRYLIC ACID (SALT)-TYPE WATER ABSORBENT RESIN AND METHOD FOR PRODUCING OF SAME

• US 20120157625A1
• Filed: 08/27/2010
• Published: 06/21/2012
• Est. Priority Date: 08/27/2009
• Status: Active Grant

• Current Assignee: Nippon Shokubai Company Limited
• Original Assignee: Nippon Shokubai Company Limited
• Inventors: Kitano, Takahiro, Nogi, Kozo, Ishizaki, Kunihiko
• Granted Patent: US 8,907,021 B2
• Time in Patent Office: Days
• US Class Current: 525/53
• CPC Class Codes: A61L 15/24 Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds; Derivatives thereof A61L15/225 takes precedence
• CPC Class Codes: A61L 15/60 Liquid-swellable gel-forming materials, e.g. super-absorbents
• CPC Class Codes: C08F 120/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• CPC Class Codes: C08F 220/06 Acrylic acid; Methacrylic acid; Metal salts or ammonium salts thereof
• CPC Class Codes: C08F 222/102 of dialcohols, e.g. ethylene glycol di(meth)acrylate or 1,4-butanediol dimethacrylate
• CPC Class Codes: C08J 2300/14 Water soluble or water swellable polymers, e.g. aqueous gels
• CPC Class Codes: C08J 2333/02 Homopolymers or copolymers of acids; Metal or ammonium salts thereof
• CPC Class Codes: C08J 3/24 Crosslinking, e.g. vulcanising, of macromolecules mechanical aspects B29C35/00; crosslinking agents C08K
• CPC Class Codes: C08J 3/245 Differential crosslinking of one polymer with one crosslinking type, e.g. surface crosslinking
• CPC Class Codes: C08L 33/08 Homopolymers or copolymers of acrylic acid esters

Abstract

Disclosed is a method for producing a water absorbent resin, by which a surface-crosslinked water absorbent resin having excellent physical properties can be efficiently obtained at low cost, while assuring high productivity. When the production scale is increased to a continuous production at 1 t/hr or more, the physical properties are improved and stabilized (for example, standard deviation of the physical properties is reduced) by a surface-crosslinking treatment, and the absorption against pressure (AAP) and liquid permeability (SFC) are further improved. Specifically disclosed is a method for producing a water absorbent resin, which is characterized in that the stirring shaft of the continuous mixing apparatus for the surface-crosslinking agent is heated during the mixing step of the surface-crosslinking agent or that the continuous mixing apparatus for the surface-crosslinking agent is operated at a pressure that is reduced relative to the ambient pressure and a gas flow is passed through the mixing apparatus during the mixing of the surface-crosslinking agent so that the gas flow in the mixing apparatus is 40° C. or more (when defined with respect to the gas temperature at the exit).

Claims

1. A method for producing a polyacrylic acid (salt)-type water absorbent resin comprising steps of:

preparing an aqueous monomer solution of an acrylic acid (salt),

continuously polymerizing the aqueous monomer solution,

finely shredding a hydrous gel-like crosslinked polymer during or after polymerization,

drying the obtained particulate hydrous gel-like crosslinked polymer,

adding a surface-crosslinking agent to the dried water absorbent resin powder with a continuous mixing apparatus, and

carrying out reaction of the mixture, wherein

a stirring shaft of the continuous mixing apparatus for the surface-crosslinking agent is heated in the step of mixing the surface-crosslinking agent.

3. The production method according to claim 1 or 2, wherein the stirring shaft of the continuous mixing apparatus for the surface-crosslinking agent is so heated as to be at a higher temperature than the inner wall temperature of the continuous mixing apparatus.

4. The production method according to claim 1 or 2, wherein the pressure of the inside of the continuous mixing apparatus for surface-crosslinking agent is reduced.

5. The production method according to claim 1 or 2, wherein the pressure decrease degree in the inside of the continuous mixing apparatus in the reduced pressure state exceeds 0 kPa and is 10 kPa or lower, in comparison with the atmospheric pressure.

6. The production method according to claim 1 or 2, wherein 50 to 100% in the inner surface area of the continuous mixing apparatus is of a metal.

7. The production method according to claim 1 or 2, wherein the inner face of the inside of the continuous mixing apparatus for the surface-crosslinking agent is of a stainless steel with a surface roughness (Rz) of 800 nm or lower.

8. The production method according to claim 1 or 2, wherein the reaction step for the mixture is carried out at 150°

C. to 250°

C.

9. The production method according to claim 1 or 2, wherein the water absorbent resin powder is pneumatically transported by using compressed air with a dew point of −

5°

C. to −

100°

C.

10. The production method according to claim 1 or 2, wherein the mixing apparatus is a hoe type blender.

11. The production method according to claim 1 or 2, wherein the temperature of the mixture is 50 to 95°

C. until the mixture flows to the reaction step after the surface-crosslinking agent is mixed.

12. The production method according to claim 1 or 2, wherein the reaction step of the mixture has two or more lines for one line in the polymerization step.

13. The production method according to claim 1 or 2, wherein the average residence time of the water absorbent resin in the continuous mixing apparatus is within 1 minute.

14. The production method according to claim 1 or 2, wherein the temperature of the mixture is increased by 0.5°

C. or more by continuously mixing the crosslinking agent to the dried water absorbent resin powder.

15. The production method according to claim 1 or 2, wherein the water absorbent resin has 20 g/g or higher of water absorption against pressure (AAP) for an aqueous 0.9 wt. % sodium chloride solution at a pressure of 4.8 kPa, 1(×

10<sup>−

7</sup>·

cm³·

s·

g<sup>−

1</sup>) or higher of saline flow conductivity of 0.69 wt. % physiological saline solution (SFC), and 20 g/g or higher of water absorption under no pressure (CRC).

2. A method for producing a polyacrylic acid (salt)-type water absorbent resin comprising steps of:

preparing an aqueous monomer solution of an acrylic acid (salt),

continuously polymerizing the aqueous monomer solution,

finely shredding a hydrous gel-like crosslinked polymer during or after polymerization,

drying the obtained particulate hydrous gel-like crosslinked polymer,

adding a surface-crosslinking agent to the dried water absorbent resin powder with a continuous mixing apparatus, and

carrying out reaction of the mixture, wherein

the continuous mixing apparatus for the surface-crosslinking agent is operated in pressure decreased from the ambient pressure and gas current to adjust the outlet gas temperature of the gas current in the mixing apparatus to be at lowest 40°

C. is led to the mixing apparatus during mixing the surface-crosslinking agent.