Patent ID: 7713623

Claim:
A process for producing a water-absorbent resin particle having an amount of water absorption of 300 to 800 g/g and an average particle diameter of from 10 to 190 μm, said process comprising: (A) subjecting a water-soluble ethylenically unsaturated monomer to a first-step reverse phase suspension polymerization in a hydrocarbon-based solvent using a water-soluble radical polymerization initiator in the presence of a surfactant and/or a polymeric protective colloid, and optionally an internal crosslinking agent; (B) carrying out at least a second-step reverse phase suspension polymerization by adding an aqueous solution of a water-soluble ethylenically unsaturated monomer containing a water-soluble radical polymerization initiator and optionally an internal crosslinking agent to the reaction mixture after the termination of the first-step reverse phase suspension polymerization in a state that the surfactant and/or the polymeric protective colloid is dissolved in the hydrocarbon-based solvent, and subsequently subjecting the mixture to at least said second-step reverse phase suspension polymerization, wherein a temperature of the reaction mixture before addition and after addition of the aqueous solution of a water-soluble ethylenically unsaturated monomer is 30° to 60° C.; and (C) post-crosslinking the resulting water-absorbent resin, wherein the obtained water-absorbent resin particle has an amount of water absorption of 300 to 800 g/g and an average particle diameter of from 10 to 190 μm.