COATED METAL SUBSTRATES AND METHODS OF PREPARING THEM

The present invention is directed to a method for forming a composite coating on a bare, untreated metal substrate comprising: (A) applying a first, waterborne coating composition directly to a surface of the bare substrate to form a first coating; and (B) applying a second, transparent coating composition to the first coating formed in step (A) to form a secondary coating thereon and yielding a composite coating; wherein the first coating composition comprises an aqueous dispersion of polymeric microparticles having a core-shell morphology and having reactive functional groups, wherein the core of the polymeric microparticles is prepared from a monomer mixture comprising substantially hydrophobic ethylenically unsaturated monomers and wherein the shell of the polymeric microparticles comprises a polyurethane polymer containing acid functional groups and/or a polyurethane-urea polymer containing acid functional groups. Coated metal substrates prepared by this method are also provided.