FEINTEILIGE, STÄRKEHALTIGE POLYMERDISPERSIONEN

Finely divided, starch-containing polymer dispersions obtainable by emulsion copolymerization, with redox initiators, of ethylenically unsaturated monomers from the group consisting of (a) from 45 to 55% by weight of at least one optionally substituted styrene, methyl methacrylate, acrylonitrile and/or methacrylonitrile, (b) from 15 to 29% by weight of at least one C1-C12-alkyl acrylate and/or one C2-C12-alkyl methacrylate and (c) from 0 to 10% by weight of at least one other ethylenically unsaturated copolymerizable monomer in an aqueous medium in the presence of (d) from 15 to 35% by weight of a degraded cationized starch which has a molar mass Mw of from 1000 to 65 000, the sum (a)+(b)+(c)+(d) being 100% and being based on the total solids content, processes for the preparation of such polymer dispersions by emulsion polymerization of the monomers (a), (b) and (c) in an aqueous medium with redox initiators in the presence of (d) cationic starch, and use of the starch-containing polymer dispersions as size for paper, board and cardboard.