Patent ID: 8552134

Claim:
A method of producing a polyacrylic acid (salt)-based water-absorbent resin, comprising the steps of: (a) neutralizing an acid moiety derived from an acrylic acid monomer, (b) polymerizing an aqueous monomer solution containing the acrylic acid monomer in an amount of 90 mol % or more relative to the total monomers excluding a cross-linking agent in the presence of a cross-linking agent, and (c) drying the resultant polymer by heating; wherein the aqueous monomer solution comprises the acrylic acid monomer, the cross-linking agent and a mono(meth)acrylate compound; wherein the cross-linking agent comprises a multifunctional (meth)acrylate-based cross-linking agent (i) having polyethylene glycol structural units including a total of 6 to 200 ethylene oxide repeating units and (ii) in an amount of 1.0×10 −3 to 1.0 mol % relative to the amount of the acrylic acid monomer; wherein the mono(meth)acrylate compound has polyethylene glycol structural units; wherein the amount of the mono(meth)acrylate compound having polyethylene glycol structural units is 1.0×10 −5 to 0.5 mol % relative to the amount of the acrylic acid monomer; and wherein ratio of the mono(meth)acrylate compound having polyethylene glycol units is 0.5 to 11.8 mol % relative to the amount of the multifunctional (meth)acrylate-based cross-linking agent having polyethylene glycol structural units including a total of 6 to 200 ethylene oxide repeating units; and the surface tension of water absorbent resin obtained is from 55 mN/m to 85 mN/m.