Patent ID: 9328207
Filing Date: 2016-05-03
CPC Classification: C08F,C08J

Claim Text:
1. A process for producing water-absorbing polymer particles by polymerizing a monomer solution or suspension comprising a) at least one ethylenically unsaturated monomer which bears a carboxylic acid group and may be at least partly neutralized, b) at least one crosslinker, c) at least one initiator, d) optionally one or more ethylenically unsaturated monomer copolymerizable with the monomer mentioned under a), and e) optionally one or more water-soluble polymers, comprising drying, grinding, classifying, and surface postcrosslinking using a surface postcrosslinker to form covalent bonds with at least two carboxylate groups of the polymer particles and selected from the group consisting of glycerol, ethylene carbonate, a reaction product of a polyamide with epichlorohydrin, a mixture of propylene glycol and 1,4-butanediol, a 2-hydroxyethyloxazolidin-2-one, oxazolidin-2-one, and 1,3-propanediol, in which i) the surface postcrosslinked polymer particles are remoisturized, ii) optionally, the remoisturized polymer particles are pneumatically delivered, iii) the remoisturized polymer particles are classified using a tumbler screening machine having at least two screens to remove polymer particles having a particle size of less than 150 μm from the remainder of the polymer particles, and iv) recycling the excessively small polymer particles into the process for producing water-absorbing polymer particles before, during, or immediately after the polymerization of the monomer solution, wherein a time between the remoisturization i) and the classification iii) is at least 15 minutes.