Aqueous polyurethane having blocked NCO groups and process

Claim 1

A process for preparing an aqueous thermosetting polyurethane emulsion, which comprises: 1. reacting, the liquid phase and in a ketone solvent, at a temperature of from -20° to +70° C., (A) isocyanate-terminated urethane prepolymer prepared by reacting organic polyhydroxyl component having a molecular weight in the range of from 200 to 10,000 with an excess of organic polyisocyanate, said polyhydroxyl component comprising from 15 to 80 weight % of polyoxyethylene glycol, with (B) an excess of polyalkylene polyamine having at least two primary or secondary amino groups, the total mole number of primary and secondary amino groups in the polyalkylene polyamine being greater than the total mole number of isocyanate groups in the isocyanate-terminated urethane, prepolymer, the reaction being carried out until the presence of --NCO groups cannot be detected, whereby to form polyurethane-urea-polyamine, 2. reacting, in the liquid phase, the reaction product of step 1 with a blocked polyisocyanate having a single free isocyanate group in the molecule, at a temperature of -20° to +70° C., for about 0.5 to 2 hours, 3. adding water to the reaction product of step 2, and 4. treating the product of step 3 to remove the organic solvent therefrom and thereby obtaining an aqueous polyurethane emulsion as a final product.