Clearcoat composition for use in waterborne basecoat-clearcoat composite coatings

Abstract

A process for forming a color-clear multilayer coating on a substrate is disclosed. The basecoat is a waterborne coating and the clear topcoat is isocyanate containing and comprises a polyene and a polythiol. The isocyanate can be present as a separate component or can be an isocyanate-functional polyene.

1 . A composition comprising:
 (a) an isocyanate-functional polyene;   (b) a polythiol.   
     
     
         2 . The composition of  claim 1  wherein (a) has the structural formula A-(X) m  where A is derived from a polyisocyanate; X is an olefinically unsaturated moiety and m is at least 2. 
     
     
         3 . The composition of  claim 2  in which A is derived from a (cyclo)aliphatic polyisocyanate. 
     
     
         4 . The composition of  claim 3  in which the polyisocyanate is selected from 1,6-hexamethylene diisocyanate, isophorone diisocyanate including isocyanurate and biuret derivatives thereof. 
     
     
         5 . The composition of  claim 2  in which X is selected from —C(O)CHR═CH 2  and —CH 2 —CHR═CH 2  where R is hydrogen or methyl. 
     
     
         6 . The composition of  claim 2  in which m is 2 to 4. 
     
     
         7 . The composition of  claim 2  is which A-(X) m  is an isocyanate-functional urethane (methacrylate). 
     
     
         8 . The composition of  claim 1 , which has an isocyanate equivalent weight of from 150 to 3000. 
     
     
         9 . The composition of  claim 1  in which (b) is a compound of the structure R—(SH) n  where R is an organic moiety and n is at least 2. 
     
     
         10 . The composition of  claim 9  in which R contains ester groups. 
     
     
         11 . The composition of  claim 9  in which (ii) is the reaction product of a thiol-functional organic acid and a polyol. 
     
     
         12 . The composition of  claim 9  in which n is from 2 to 6. 
     
     
         13 . The composition of  claim 1  in which (a) is present in the topcoat composition in amounts of 80 to 98 percent by weight and (b) is present in amounts of 2 to 20 percent by weight; the percentages by weight being based on weight of (a) and (b). 
     
     
         14 . The composition of  claim 1  in which (a) is present in the topcoat composition in amounts of 90 to 95 percent by weight and (b) is present in amounts of 5 to 10 percent by weight; the percentages by weight being based on weight of (a) and (b).