Patent ID: 7786211

Claim:
A process for producing a water-absorbing resin by polymerization of a reaction mixture comprising at least one hydrophilic monomer and, optionally, at least one crosslinker in a reactor, which comprises admixing the reaction mixture with at least one first portion of a particulate additive before a reaction mixture has reached a residence time of 40% of the overall residence time in the reactor and with at least one second portion of a particulate additive when the reaction mixture has reached a residence time of 45% or more of the overall residence time in the reactor, the additive being selected from the group consisting of water-absorbing resin powders, fillers, and mixtures thereof, a total solids content of monomer and additive being in the range from 30% to 60% by weight, an amount of additive being in the range from 5% to 50% by weight, based on the monomers, and a weight ratio of the first portion to the second portion of the additive being in the range from 10:1 to 1:5, wherein an aqueous solution of monomer is fed to an input end of a continuous operated reactor having at least two axially parallel rotating shafts, in which the reaction mixture is transported from the input end of the reactor to its output end as the polymerization progresses, and the first and second portions of the additive are admixed at two locations of the reactor which are spaced apart in the direction of transport of the monomer solution.