Patent ID: 7238743
Filing Date: 2007-07-03
Classification: C08F

Abstract:
1. A process for producing a water-absorbent resin by polymerizing a monomer solution including acrylic acid and/or its salt as major components, where the acrylic acid is obtained by catalytic gas-phase oxidation of propylene and/or propane, wherein the water-absorbent resin is a neutralized product salt having a neutralization ratio of not less than 50 mol % and has a crosslinked structure, wherein the acrylic acid is neutralized and polymerized by at least one of steps (1), (2) or (3), (1) acrylic acid containing protoanemonin of not more than 20 ppm is subjected to a strong-alkali treatment using an alkali-metal hydroxide to obtain an aqueous solution having a neutralization ratio of not less than 50 mol %, and then the polymerization of the solution is carried out, (2) acrylic acid containing protoanemonin of not more than 10 ppm is subjected to an alkali treatment to obtain an aqueous solution having a neutralization ratio of not less than 50 mol %, and then the polymerization of the solution is carried out, wherein the alkali treatment is carried out by using a weak base or carried out by gradually adding strong base to an excess of acrylic acid under the condition of a neutralization ratio of less than 100 mol %, (3) the polymerization of the solution of acrylic acid containing protoanemonin of not more than 5 ppm and having a neutralization ratio of 0 to 30 mol % is carried out, and then the obtained polymer is neutralized to obtain a neutralized product salt having a neutralization ratio of not less than 50 mol %.