Methods and compositions for coating substrates

Abstract

A method for applying a multilayer coating comprising a basecoat and a clearcoat is disclosed. The basecoat is a curable aqueous composition comprising (1) polymeric particles containing carboxylic acid functionality and prepared from ethylenically unsaturated compounds including a multi-ethylenically unsaturated monomer, and (2) a polycarbodiimide.

What is claimed is: 
     
         1 . A method of applying a multilayer coating to a substrate comprising:
 (a) applying, without application of an intermediate primer surfacer coating, a color-imparting, pigment-containing basecoat composition directly to a cured electrodeposited primer coating that is adhered to the substrate to form a curable color-imparting basecoat layer, and   (b) applying a curable unpigmented coating composition to the basecoat layer to form a clear or transparent coating layer over the basecoat layer, wherein the basecoat layer is formed by depositing a curable aqueous composition comprising:
 (i) a continuous phase comprising water, and 
 (ii) a dispersed phase comprising:
 (A) polymeric particles containing carboxylic acid functionality prepared from the polymerization of a mixture of ethylenically unsaturated monomer compounds, including ethylenically unsaturated monomers comprising a multi-ethylenically unsaturated monomer; and 
 (B) a polycarbodiimide. 
 
   
     
     
         2 . The method of  claim 1  wherein the basecoat layer is a composite coating in which an aqueous curable color-imparting coating composition containing one or more coloring pigments, not including a color effect pigment, is deposited directly on the cured electrodeposited layer to form a first curable basecoat layer and a curable color-imparting coating composition containing one or more coloring pigments, including a color effect pigment, is deposited directly on the first curable basecoat layer to form a second curable basecoat layer. 
     
     
         3 . The method of  claim 1  in which the first basecoat layer is dehydrated at a temperature within the range of ambient temperature to 90° C. to cure the first basecoat layer. 
     
     
         4 . The method of  claim 2  wherein the second basecoat layer is dehydrated at a temperature within the range of ambient temperature to 90° C. to cure the second basecoat layer. 
     
     
         5 . The method of  claim 2  wherein both the first and second basecoat layers are simultaneously dehydrated at a temperature range of ambient to 90° C. to cure the first and second basecoat layers. 
     
     
         6 . The method of  claim 1  in which the mixture of ethylenically unsaturated compounds includes an ethylenically unsaturated polyurethane. 
     
     
         7 . The method of  claim 6  in which the ethylenically unsaturated polyurethane is prepared from reacting an organic polyisocyanate with a polyol containing carboxylic acid functionality and a hydroxyalkyl (meth)acrylate such that the ethylenically unsaturated polyurethane is free of NCO groups. 
     
     
         8 . The method of  claim 1  in which a film of polymeric particles has a T g  less than 25° C. 
     
     
         9 . The method of  claim 1  in which the multi-ethylenically unsaturated monomer is present in amounts of 2 to 30 percent by weight based on total weight of the ethylenically unsaturated monomers. 
     
     
         10 . The method of  claim 6  in which the ethylenically unsaturated polyurethane has an acid value of 20 to 60 based on resin solids of the ethylenically unsaturated polyurethane. 
     
     
         11 . The method of  claim 1  in which the ethylenically unsaturated monomers comprise from 4 to 30 percent by weight of an alkyl ester of (meth)acrylic acid having at least 6 carbon atoms in the alkyl group; the percentage by weight being based on total weight of the ethylenically unsaturated monomers. 
     
     
         12 . The method of  claim 6  in which the ethylenically unsaturated polyurethane comprises from 30 to 60 percent by weight of the mixture of ethylenically unsaturated compounds and the ethylenically unsaturated monomers comprise from 40 to 70 percent by weight of the mixture of ethylenically unsaturated compounds; the percentages by weight being based on total weight of the mixture of ethylenically unsaturated compounds. 
     
     
         13 . The method of  claim 1  in which the equivalent ratio of polycarbodiimide to carboxylic acid is from 0.5 to 1.5:1. 
     
     
         14 . The method of  claim 1  in which the curable unpigmented coating composition comprises an active hydrogen-containing polymer and a polyisocyanate curing agent. 
     
     
         15 . The method of  claim 1  in which the basecoat is cured at ambient to 90° C. 
     
     
         16 . An aqueous thermosetting coating composition comprising:
 (a) a continuous phase comprising water, and   (b) a dispersed phase comprising:
 (i) pigments; 
 (ii) polymeric particles containing carboxylic acid functionality prepared from the polymerization of a mixture of ethylenically unsaturated compounds including ethylenically unsaturated monomers comprising from:
 (A) 2 to 30 percent by weight of a multi-ethylenically unsaturated monomer, 
 
  the percentage by weight being based on total weight of the ethylenically unsaturated monomers; and 
 (iii) a polycarbodiimide. 
   
     
     
         17 . The composition of  claim 16  in which the mixture of ethylenically unsaturated compounds includes an ethylenically unsaturated polyurethane having an acid value of 20 to 60 based on resin solids of the ethylenically unsaturated polyurethane. 
     
     
         18 . The composition of  claim 17  in which the ethylenically unsaturated polyurethane is prepared from reacting an organic polyisocyanate with a polyol containing carboxylic acid functionality and a hydroxyalkyl (meth)acrylate such that the ethylenically unsaturated polyurethane is free of isocyanate groups. 
     
     
         19 . The composition of  claim 16  in which the ethylenically unsaturated monomers comprise from 4 to 30 percent by weight of an alkyl ester of (meth)acrylic acid having at least 6 carbon atoms in the alkyl group; the percentages by weight being based on total weight of the ethylenically unsaturated monomers. 
     
     
         20 . The composition of  claim 18  in which the ethylenically unsaturated polyurethane comprises from 30 to 60 percent by weight of the mixture of ethylenically unsaturated compounds and the ethylenically unsaturated monomers comprise from 40 to 70 percent by weight of the mixture of ethylenically unsaturated compounds; the percentages by weight being based on total weight of the ethylenically unsaturated compounds. 
     
     
         21 . The composition of  claim 16  in which a film of the polymeric particles has a T g  less than 25° C. 
     
     
         22 . The composition of  claim 17  in which the equivalent ratio of carbodiimide to carboxylic acid is from 0.5 to 1.5:1.