Abstract: The present invention relates to an aqueous copolymer dispersion consisting essentially of A) an aqueous dispersion of a copolymer having a solids content of from 20 to 65% by weight, said copolymer being composed of various monomers and the weight fractions of the various monomers being chosen within the stated limits such that a synthetic resin composed of these monomers alone would have a glass transition temperature in the range from −50 to 35° C., B) from 0 to 10% by weight, based on the copolymer A, of benzophenone, acetophenone, one or more acetophenone derivatives or benzophenone derivatives without an ethylenically unsaturated group, or a mixture thereof, C) from 0.3 to 10% by weight, based on the copolymer A, of emulsifiers, and D) from 0 to 5% by weight, based on the copolymer A, of protective colloids; to a process for its preparation and to its use.