Wednesday, March 5, 2008

The Invention of Acrylic Clear Coating

An improved process for forming multiple coats of finishes such as a basecoat/clear coat finish on a substrate using the following sequential steps of (a) applying to the substrate a color basecoat composition of a waterborne basecoat having a film forming binder of an acrylic polymer latex and contains pigment in a pigment to binder ratio of about 1:100 to 150:100 dispersed in an aqueous medium; (b) applying to the layer of the color basecoat composition before the basecoat composition is fully cured, a clear coat composition of an acrylic polymer having cross linkable groups and a cross linking agent in a volatile organic solvent and (c) subsequently simultaneously curing the basecoat composition and the clear coat composition; the improvement that is used with this process is a clear coating composition that contains about 40-80% by weight, based on the weight of the coating composition, of a binder and correspondingly, about 20-60% by weight of a volatile organic solvent; wherein the binder contains about 40-95% by weight, based on the weight of the binder, of an epoxy acrylic polymer of polymerized monomers of at least one alkyl methacrylate and glycidyl methacrylate or glycidyl acrylate and optionally, contains a hydroxy acrylic polymer of at least two alkyl methacrylates having about 2-12 carbon atoms in the alkyl group and a hydroxy alkyl methacrylate having 2-4 carbon atoms in the alkyl group and the epoxy acrylic polymer and hydroxy acrylic polymer each have a weight average molecular weight of about 3,000-10,000 and a glass transition temperature of about -20° to +50° C.; and 5-65% by weight, based on the weight of the binder, of an organic polyisocyanate crosslinking agent and
wherein a cured layer of the clear coat has a water permeability value of about 1400-3200.
Another aspect of this invention is an article coated by the above process and the clear coating composition.



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