Method for production of hydrophilic resin

• US 6,388,000 B1
• Filed: 04/24/1995
• Issued: 05/14/2002
• Est. Priority Date: 06/10/1992
• Status: Active Grant

• Current Assignee: Nippon Shokubai Company Limited
• Original Assignee: Nippon Shokubai Company Limited
• Inventors: Ishizaki, Kunihiko, Irie, Yoshio, Kajikawa, Katsuhiro, Hatsuda, Takumi
• Primary Examiner(s): WILSON, DONALD R
• Application Number:
  US08/427,734
• Time in Patent Office: 2,577 Days
• Field of Search: 525/119, 524/556, 528/502.R, 528/502.F, 528/503
• US Class Current: 524/556
• CPC Class Codes: A61L 15/60 Liquid-swellable gel-forming materials, e.g. super-absorbents
• CPC Class Codes: C08F 20/04 Acids, Metal salts or ammonium salts thereof
• CPC Class Codes: C08L 33/02 Homopolymers or copolymers of acids; Metal or ammonium salts thereof

Abstract

In the production of an acrylate polymer by the steps of preparing a water-soluble unsaturated monomer having a ratio of neutralization in the range of 30 to 100 mol % and containing 50 to 100 mol % of an acrylate and then polymerizing the monomer, a method for the production of a hydrophilic resin which comprises using a water-soluble unsaturated monomer having a β-hydroxy propionic acid (salt) content of not more than 1,000 ppm. The hydrophilic resin obtained by this method exhibits excellent physical properties and has only a small residual monomer content. Further, a residual monomer content neither occurs nor increases in any using conditions.

Claims

1. A method for the production of an absorbent resin having a cross-linked structure which comprises preparing a mixture solution of a water-soluble unsaturated monomer or monomer mixture containing 50 mol % or greater of acrylic acid which has been partially neutralized or completely neutralized in an amount of 30 to 100 mol % to form alkali metal and/or ammonium salts, 1 to 1,000 ppm of β

-hydroxy propionic acid or a salt thereof and a first cross-linking agent, polymerizing the mixture solutions drying the gel polymer thus obtained by heating at a temperature of not less than 130°

C., and optionally pulverizing and/or granulating to obtain powdered absorbent resin.

2. A method according to claim 1, wherein said water-soluble unsaturated monomer contains 50 to 0 mol % of at least one unsaturated monomer selected from the group consisting of hydrophilic unsaturated monomers and hydrophobic unsaturated monomers, said hydrophilic unsaturated monomers being selected from methacrylic acid, methacrylic acid salt, 2-(meth)acryloyl ethane sulfonic acid, 2-(meth)acryloyl ethane sulfonate acid salt, 2-(meth)-acrylamide-2-methyl propane sulfonic acid, 2-(meth)acrylamide-2-methylpropane sulfonic acid salt, methoxy polyethylene glycol (meth)acrylate, N,N-dimethylaminoethyl(meth)acrylate, or acrylamide, said hydrophobic unsaturated monomers being selected from styrene, vinyl chloride, butadiene, isobutene, ethylene, propylene, stearyl (meth)acrylate, or lauryl (meth)acrylate.

3. A method according to claim 2, wherein said mixture solution contains not more than 300 ppm of β

-hydroxy propionic acid (salt).

4. A method according to claim 1, said method resulting in a final polymer product obtained by drying has a residual monomer content below 300 ppm.

5. A method according to claim 1, wherein said partially neutralized or completely neutralized acrylic acid is an acrylic acid alkali metal salt and an acrylic acid ammonium salt.

6. A method according to claim 5, wherein said acrylic acid ammonium salt accounts for 10 to 40 mol % of the neutralized acrylic acid.

7. A method according to claim 5, wherein the temperature of said heat drying is carried out in the range of 150°

to 250°

C.

8. A method according to claim 1, wherein said β

-hydroxy propionic acid salt is sodium β

-hydroxy propionate.

11. A method according to claim 1, wherein said powdered absorbent resin has not more than 40 ppm of a potential residual monomer calculated by the following formula:

12. A method according to claim 1, wherein said mixture solution of the water-soluble unsaturated monomer or monomer mixture is subjected to polymerization within 24 hours after the preparation.

13. A method according to claim 1, wherein the acrylic acid is purified by distillation and is used for neutralization or preparation of the water-soluble unsaturated monomer or monomer mixture within 24 hours after the distillation.

14. A method according to claim 1, wherein said first cross-linking agent is a polymerizable cross-linking agent having at least two polymerizable unsaturated groups and the first cross-linking agent is used in the range of 0.005-5 mol % to said water-soluble unsaturated monomer based on the monomer.

9. A method for the production of a hydrophilic resin which comprises polymerizing a water-soluble unsaturated monomer or monomer mixture containing 50 mol % or greater of acrylic acid which has been neutralized in an amount of 30 to 100 mol % to form at least a sodium or potassium salt, 1 to 1000 ppm of β

-hydroxy propionic acid or a salt thereof and optionally a first cross-linking agent, and said water-soluble unsaturated monomer is polymerized within 24 hours after preparation, and drying the gel polymer by heating at a temperature of at least 130°

C.

10. A method according to claim 9, wherein said water-soluble unsaturated monomer or monomer mixture is prepared and then polymerized within 6 hours after preparation.