Patent ID: 8034885

Claim:
A process for the preparation of an aqueous polymer dispersion by free radical aqueous emulsion polymerization comprising polymerizing at least one ethylenically unsaturated compound (monomer) in the presence of at least one dispersant, wherein a) into a reaction vessel at a temperature which is less than or equal to the starting reaction temperature T S , a 1 ) at least one portion of demineralized water, a 2 ) at least one portion of at least one oil-soluble free radical initiator, a 3 ) at least one portion of at least one dispersant, a 4 ) optionally, a portion of the at least one monomer and a 5 ) optionally, a portion of at least one water-soluble free radical initiator are initially added to form a reaction mixture in the reaction vessel, thereafter b) the reaction mixture obtained is, optionally, heated to the starting reaction temperature T S , and thereafter c) the following are metered into the reaction mixture: c 1 ) optionally, the remaining amount of demineralized water, c 2 ) optionally, the remaining amount of the at least one oil-soluble free radical initiator, c 3 ) optionally, the remaining amount of the at least one dispersant, c 4 ) the total amount or, optionally, the remaining amount of the at least one monomer and c 5 ) the main amount of the at least one water-soluble free radical initiator, and d) the reaction mixture is heated to an end reaction temperature T E during the metering of the at least one monomer, and wherein the at least one water-soluble free radical initiator has a solubility of ≦1% by weight at 20° C. and atmospheric pressure in demineralized water, and the at least one oil-soluble free radical initiator has a solubility of <1% by weight under the process conditions and the total amount of water being such that the aqueous polymer dispersion obtained has a solids content of from 20 to 70% by weight, the at least one water-soluble free radical initiator initiates a free radical polymerization reaction of the at least one monomer at the starting reaction temperature T S , and at least one oil-soluble free radical initiator has a half-life of ≧10 hours at the starting reaction temperature T S and a half-life of ≦5 hours at the end reaction temperature T E .