Method of forming metallic coatings

Claim 1

In a method of forming a multilayer metallic coating on a substrate comprising the steps of applying a base coating composition comprising a first film-forming polymer having a plurality of cross-linkable functional groups, a cross-linker reactive with said first film-forming polymer, a volatile organic liquid diluent and a metallic pigment on said substrate, applying on the base coating wet-on-wet a clear top coating composition comprising a second film-forming acrylic polymer having a plurality of cross-linkable functional groups, a crosslinker reactive with said second film-forming polymer and a volatile organic liquid diluent, and curing both coatings simultaneously, the improvement wherein said first and second film-forming polymers have a number average molecular weight of from 1,000 to 4,000; and wherein said base coating composition and said top coating composition each contains an amount of internally crosslinked polymer microparticles which are insoluble in the mixture of said film-forming polymer, said cross-linker and said organic liquid diluent but stably dispersible in said mixture, and a catalytically effective amount of an organic acid catalyst which is a combination of an organic sulfonic acid having a pKa below 4.0 and an amount of organic secondary or tertiary amine sufficient to neutralize at least 60% of said sulfonic acid.