UV light treatment of clear coat to improve acid etch resistance

Claim 1

In a process for forming multiple coats of finishes on a substrate used as the exterior of a motor vehicle other than a testing specimen comprising the sequential steps of (a) applying to the substrate a layer of a color basecoat composition comprising a film forming binder and pigment; (b) applying to the layer of color basecoat composition before the basecoat is fully cured a clear coat composition and subsequently (c) simultaneously curing the basecoat composition and clear coat composition to form a coating; the improvements used therewith comprise the use of a clear coating composition comprising about 40-80% by weight, based on the weight of the clear coating composition, of a binder of an acrylosilane polymer in a liquid carrier and exposing the clear coat of the substrate after curing to an artificial ultraviolet light source under ambient temperature and atmospheric conditions to a sufficient degree to increase the resistance of the coating to water spotting and acid etching when the substrate is exposed to natural outdoor weathering; wherein the acrylosilane polymer consists essentially of polymerized monomers of (1) a hydroxy containing monomer selected from the group consisting of a hydroxy alkyl methacrylate having 1-4 carbon atoms in the alkyl group or a hydroxy alkyl acrylate having 1-4 carbon atoms in the alkyl group; (2) a silane containing monomer having the following structural formula: ##STR7## wherein: R is selected from the group consisting of CH 3 , CH 3 CH 2 , CH 3 O, or CH 3 CH 2 O; R 1 and R 2 are individually selected from the group consisting of CH 3 , or CH 3 CH 2 ; and R 3 is selected from the group consisting of H, CH 3 , or CH 3 CH 2 and n is 0 or a positive integer of 1-10; and (3) monomers selected from the group consisting of an alkyl methacrylate having 1-12 carbon atoms in the alkyl group, an alkyl acrylate having 1-12 carbon atoms in the alkyl group, styrene or a mixture of these monomers.