| abstract |
Coating compositions that are stable to thermal yellowing that include coating materials containing I) one or more dispersions of hydroxyl-free polyurethanes and/or polyurethane-ureas, II) one or more aqueous solutions or dispersions of ionically modified, hydroxyl-containing polyurethanes and/or polyurethane-ureas, other than the constituents of component I), and III) at least one crosslinker. The dispersions are obtained by A) preparing an NCO-containing polyurethane prepolymer by reacting polyisocyanates with polymeric polyols and/or polyamines having number-average molecular weights of 400 to 8000 g/mol, isocyanate-reactive, ionically or potentially ionically hydrophilicizing compounds and/or isocyanate-reactive nonionically hydrophilicizing compounds; B) either dissolving the prepolymer obtained from step A) in aliphatic ketones or, diluting the prepolymer solution if the preparation has already been carried out in the presence of A6) by further addition of aliphatic ketones, and C) reacting the remaining free NCO groups of the prepolymer with a chain extender component. |