Urethane coating compositions

Claim 1

In a polyurethane coating composition comprising an ungelled hydroxyl-containing urethane reaction product of an organic polyisocyanate and a polyhydric material having a hydroxyl value of at least 10, the improvement which comprises the presence therein of from about 2 percent to about 50 percent by weight, based on said coating composition, or insoluble crosslinked acrylic polymer microparticles formed by the free radical addition copolymerization of from about 0.5 percent to about 15 percent of alpha, beta-ethylenically unsaturated monocarboxylic acid, at least one other copolymerizable monoethylenically unsaturated monomer, and from about 0.5 percent to about 15 percent of crosslinking monomer selected from the group consisting of (1) epoxy group-containing compound and (2) a mixture of alkylenimine and organoalkoxysilane, wherein: a. said epoxy group-containing compound is monoepoxide compound which additionally contains ethylenic unsaturation, b. said organoalkoxysilane is selected from the group consisting of acrylatoalkoxysilane, methacrylatoalkoxysilane and vinylalkoxysilane, and c. said monomer percentages are based on the weight of monomers used in the copolymerization process, in the presence of hydrocarbon dispersing liquid which is a solvent for the polymerizable monomers but a non-solvent for the resultant polymer, and polymeric dispersion stabilizer containing at least two segments of which one segment is solvated by said dispersing liquid and a second segment is of different polarity than said first segment and is relatively insoluble in said dispersing liquid, wherein the reaction is carried out at elevated temperature such that the dispersion polymer first forms and then is crosslinked.