The present invention relates to a polymer dispersion obtainable by at least one two-stage emulsion polymerization, by 1) preparing a polymer A by a radical polymerization from a 1st composition comprising A) at least one monomer, B) at least one anionic copolymerizable emulsifier, 2) admixing the polymer A prepared at 1) with a base, 3) in the presence of the polymer A treated at 2), preparing a polymer B by radical polymerization from a 2nd composition comprising A) at least one monomer, B) at least one anionic copolymerizable emulsifier. The present invention also relates to a process for preparing the polymer dispersion of the invention, to coating materials in the form of an aqueous composition comprising the polymer dispersion of the invention, and to the use of the polymer dispersion of the invention for coating compositions or paints and varnishes.