Aqueous polyurethane having blocked NCO groups and process

摘要

An aqueous polyurethane emulsion is prepared by reacting a polyhydroxyl component containing 15 to 80% by weight of a polyoxyethylene glycol having a molecular weight of 200 to 10,000 with an excess of an organic polyisocyanate to obtain an isocyanate-terminated urethane prepolymer, reacting that prepolymer with an excess of a polyalkylene polyamine thereby to form a polyurethane-urea-polyamine, reacting the free amino groups in the polyurethane-urea-polyamine with a blocked polyisocyanate having a single free isocyanate group, and mixing the resulting product with water, or reacting said resulting product with a cyclic dicarboxylic acid anhydride followed by mixing with water.