Production method for water-absorbing resin powder

摘要

A method for producing a water-absorbing resin comprises circulation of the water-absorbing resin in a predetermined amount in a pulverization step before a surface cross-linking step. At least a part of a classified polymer is supplied again to the same or a different pulverization step before the surface cross-linking step, wherein the circulation pulverization ratio in the pulverization step, represented by the following equation, is 1.10 to 1.50:
(Circulation pulverization ratio)=(total supply amount of the water-absorbing resin to the pulverization step)/(total discharge amount of the water-absorbing resin at the drying step)
wherein (total supply amount of the water-absorbing resin to the pulverization step)=(total discharge amount of the water-absorbing resin at the drying step)+(amount of the classified polymer supplied again to the same or a different pulverization step).

主权项

1. A method for producing water-absorbing resin powder, comprising sequentially:
a polymerization step for polymerizing an aqueous solution of acrylic acid (salt) to obtain a hydrogel-like cross-linked polymer; a drying step for drying the obtained hydrogel-like cross-linked polymer to obtain a dried polymer; a pulverization step for pulverizing the obtained dried polymer with a pulverizing means to obtain a pulverized polymer; a classification step for classifying the obtained pulverized polymer to obtain a classified polymer; and a surface cross-linking step for surface cross-linking the obtained classified polymer;characterized in that,at least a part of the classified polymer is supplied again to the same or a different pulverization step before the surface cross-linking step, the classified polymer thus obtained containing particles coarser than objective particles,wherein classifying is performed by sieving the pulverized polymer through two or more sieves, each sieve having a different mesh size; the pulverized polymer not passing through any of the sieves is subjected to the pulverization step again, the pulverized polymer passing through all of the sieves is recycled for drying, and a circulation pulverization ratio in the pulverization step, represented by the following equation is 1.10 to 1.50:
(Circulation pulverization ratio)=(total supply amount of the water-absorbing resin to the pulverization step)/(total discharge amount of the water-absorbing resin at the drying step)  [EXPRESSION 1]wherein (total supply amount of the water-absorbing resin to the pulverization step)=(total discharge amount of the water-absorbing resin at the drying step)+(amount of the classified polymer supplied again to the same or different pulverization step).