Patent ID: 8623994

Claim:
A method for producing a water absorbent resin comprising: a polymerization step for polymerizing an unsaturated monomer; and a drying step for drying a particulate hydrogel crosslinked polymer having solid content concentration of 45% by weight or more, that is produced by micronization of the hydrogel cross linked polymer either during or after the polymerization, wherein a through-circulation belt dryer is used for drying in the drying step and drop and scatter ratio of the particulate hydrogel crosslinked polymer that is represented by following Formula 1 is set to 1% by weight or less: Drop and scatter ratio[% by weight]={1−(Amount of solid content in particulate hydrogel obtained from drying step/Amount of solid content in particulate hydrogel provided to through-circulation belt)}×100, wherein an aggregation zone for aggregating the particulate hydrogel on the through-circulation belt is included for the drying step, and wherein the method for aggregating the particulate hydrogel during the aggregation zone comprises at least one of the following (1), (2), (3), and (5): (1) ensuring aggregation time by suppressing drying speed at early phase of drying; (2) promoting aggregation by increasing hygroscopic moisture within a drying chamber at early phase of drying; (3) performing forced aggregation at early phase of drying by using a compression device; and (5) aggregating particulate hydrogel by cooling.