Polyurethane dispersions having improved film-forming properties

POLYURETHANE DISPERSIONS HAVING IMPROVED FILM-FORMING PROPERTIES The present invention relates to a process for preparing an aqueous coating composition by I) preparing a polyurethane dispersion that is free from NMP and other solvents by 1) preparing in a first step an NCO prepolymer solution which has a concentration of 66% to 98% by weight in a solvent having a boiling point of below I 000 C at atmospheric pressure and which is the reaction product of: a) one or more polyisocyanates with b) one or more polyols having average molecular weights Mn of 500 to 6000, c) one or more polyols having average molecular weights M, of 62 to 500, and d) one or more compounds which contain an ionic group or a potential ionic group, 2) in a second step dispersing NCO prepolymer 1.1) in water and at least partly neutralizing the potential ionic groups to form ionic groups before, during or after the dispersion, 3) in a third step chain extending NCO prepolymer 1.1) with e) one or more polyamines having average molecular weights Mn of below 500, and 4) in a fourth step removing the solvent completely by distillation, and ubsequently II) adding 1% to 7% by weight of an ethylene or propylene glycol ether and optionally other coating additives together or separately to polyurethane dispersion I). The present invention also relates to the aqueous coating composition obtained by the process of the invention.