Process for preparation of high water-absorbent polymer beads

Claim 1

A process for preparing beads consisting of water-insoluble, crosslinked polymer, which beads have a particle size of from 100 to 1000 microns and have an absorbent capacity for physiological saline in the range of from 30 to 150 grams per one gram of the dried polymer, which consists of the steps of: dispersing droplets of (1) an aqueous solution consisting of water-soluble, ethylenically unsaturated monomer, from 0.01 to 5% by weight, based on the weight of said monomer, of water-soluble crosslinking agent, a water-soluble radical polymerization initiator, and the balance is water, said aqueous solution containing from 30 wt.% up to the saturation concentration of said monomer, into (2) a liquid dispersion medium having a temperature of higher than 40° C., said liquid dispersion medium consisting of an oil material selected from the group consisting of hydrocarbons having from 6 to 10 carbon atoms and halogenated aromatic hydrocarbons, and said oil material having dissolved therein from 0.05 to 10% by weight, based on the weight of said oil material, of a protective colloid selected from the group consisting of cellulose esters and cellulose ethers which are not soluble in said oil material at room temperature but are soluble in said oil material at a temperature of higher than 40° C., whereby to form a W/O suspension of said droplets in said liquid dispersion medium, the volumetric ratio of said dispersion medium/said aqueous solution being in the range of 1:1 to 5:1; suspension polymerizing said monomer, at a temperature higher than 40° C. in the presence of said crosslinking agent and said radical polymerization initiator, whereby to form said beads; and then recovering said beads from said liquid dispersion medium.