Aqueous coating compositions based on PU-PAC hybrid dispersions

A process for preparing polyurethane-polyacrylate hybrid secondary dispersions, comprising

• (I) preparing a polyurethane (A) having an average molecular weight Mn of from 1,100 to 10,000, which contains no polymerizable double bonds, in non-aqueous solution, in the presence where appropriate of vinylically unsaturated monomers which carry no groups that are reactive towards isocyanate groups,
• (II) adding to the polyurethane solution (A), one or more vinylically unsaturated monomers (B) selected from at least one of the group containing
• (B1) acid-functional monomers,
• (B2) hydroxyl- and/or amino-functional monomers,
• (B3) other monomers different from (B1) and (B2), and subjecting the resultant mixture to free-radical polymerization in a homogeneous, non-aqueous phase to provide a hybrid polymer,
• (III) neutralizing at least some of the neutralizable groups, and
• (IV) dispersing the hybrid polymer into the aqueous phase, wherein the neutralization can take place before or after the vinyl polymerization or during the dispersing step.