Aqueous polyurethane dispersions containing uretidione

摘要

The present invention relates to a composition being an aqueous dispersion of a polyurethane in water, said composition comprising water and the reaction product of (a) a water-dispersible isocyanate-terminated polyurethane prepolymer having an isocyanate content of between 1 and 15% by weight. The prepolymer comprises the following: an organic polyisocyanate adduct mixture having an average isocyanate functionality of between 2.0 and 4.0, and (b) an isocyanate reactive chain extender having a specified ratio of isocyanate reactive moiety to isocyanate index of the polyisocyanate adduct mixture. The polyisocyanate mixture must contain some dimer; however, other polyisocyanates, such as diisocyanates and polyisocyanate trimers, are advantageously added to the mixture. Also disclosed is a process for preparing this composition, and a method for coating a substrate with the composition.