Patent ID: 6605663
Filing Date: 2003-08-12
Classification: C04B,C08F,C09D,C09J

Abstract:
A process for preparing polyvinyl alcohol-stabilized addition polymers based on (meth)acrylate monomers in the form of their aqueous dispersions and water-redispersible dispersion powders by means of a polymerization selected from the group consisting of free-radically initiated emulsion polymerization and suspension polymerization of at least one monomer selected from the group consisting of the esters of acrylic acid, esters of methacrylic acid and further monomers copolymerizable therewith, in the presence of at least one protective colloid from the group of polyvinyl alcohols, which consists of the following steps and ingredients:a) conducting polymerization in the presence of from 0.001% to 0.01% by weight of initiator based on the total weight of the monomers, and b) including from 10% to 50% by weight of the monomers, based on the total weight of the monomers, in the initial charge and metering in the rest, and c) metering in the initiator comprising from 25% to 60% by weight of the total amount of initiator and, continuously until from 50% to 80% of the total polymerization time has elapsed, and d) in the remaining polymerization time, adding the remaining amount of initiator and at an accelerated metering rate which is at least twice as high as in step c); wherein the monomers and free-radical initiators are metered in such that the monomer conversion after 30 minutes of polymerization time is not more than 70%, after 60 minutes of polymerization time is not more than 75%, after 90 minutes of polymerization time is not more than 80%, after 120 minutes of polymerization time is not more than 85%, after 150 minutes of polymerization time is not more than 88%, after 180 minutes of polymerization time is not more than 90%, based in each case on the total amount of monomer introduced initially or metered in up to this point in time.