Patent ID: 7589148

Claim:
A method of preparing a polyurethane dispersion, comprising: i) reacting: a) a polyisocyanate component, b) 50 to 90 equivalent %, based on the NCO groups of component a), of a thermally eliminable blocking agent, c) 10 to 50 equivalent %, based on the NCO groups of component a), of a hydroxyl carboxylic acid as hydrophilicizing agent, and d) 0 to 15 equivalent %, based on the NCO groups of component a), of a chain extender component which is at least difunctional relative to isocyanate-reactive groups; ii) neutralizing the carboxylic acid groups with a neutralizing agent; and iii) dispersing the resulting polyurethane polymer in water; wherein step i) is carried out by first dissolving components c) and optionally d) in component b) to form a solution, then mixing the solution with component a) to form a mixture; wherein step ii) is performed before, during or after step iii); and wherein the resulting polyurethane dispersion is co-solvent free.