Patent ID: 7420018

Claim:
A production process for a water-absorbing agent, comprising the steps of: a) mixing water-absorbent resin particles, an ion blocking agent, and a surface-crosslinking agent to surface-crosslink said water-absorbent resin particles by said surface-crosslinking agent in the presence of said ion-blocking agent, wherein said ion blocking agent is an agent other than said surface-crosslinking agent, wherein said water-absorbent resin particles have a carboxyl group and are obtained by polymerizing and crosslinking an acrylic acid and/or a salt thereof as a main component, wherein said surface-crosslinking agent is reactive with said carboxyl group, and wherein said ion blocking agent is selected from a compound in groups (1) to (5) mentioned below: (1) aminocarboxylic acids and their salts which have at least three carboxyl groups selected from nitrilotriacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, cyclohexane-1,2-diaminetetraacetic acid, N-hydroxyethylethylenediaminetriacetic acid, ethylene glycol diethyl ether diaminetetraacetic acid, ethylenediaminetetrapropionic acid, and their alkaline metal salts, their alkaline earth metal salts, their ammonium salts, and their amine salts; (2) monoalkylcitramides, monoalkenylcitrarnides, and their salts; (3) monoalkyirnalonamides, monoalkenylmalonamides, and their salts; (4) monoalkyiphosphoric esters, monoalkenylphosphoric esters, and their salts; and (5) organic phosphoric acid compounds selected from ethylidenephophonic acid, 1-hydroxyethylidene-1,1-diphophonic acid, aminotrimethylenephophonic acid, ethylenediaminetetra (methylenephophonic acid), diethylenetriaminepenta (methylenephophonic acid), and their alkaline metal salts, their ammonium salts, and their amine salts; b) after said step of mixing, heating the water-absorbent resin particles to surface-crosslink the particles; and c) wherein, prior to said step of mixing, the water-absorbent resin particles having a carboxyl group contain a water-soluble content of 25% or below.