Curable compositions

Abstract

This invention relates to a curable composition comprising a solvent solution of a mixture comprising: (i) at least one hydroxy-functional acrylic polymer; and (ii) at least one low molecular weight polyol reactive diluent; (iii) at least one polyisocyanate; (iv) a metal catalyst, such as a tin compound, for accelerating the isocyanate/hydroxyl reaction; and (v) propionic acid.

The invention claimed is:  
     
         1 . A curable composition comprising a solvent solution of a mixture comprising: 
 (i) at least one hydroxy-functional acrylic polymer; and    (ii) at least one low molecular weight polyol reactive diluent;    (iii) at least one polyisocyanate;    (iv) a metal catalyst for accelerating the isocyanate/hydroxyl reaction; and    (v) propionic acid.    
     
     
         2 . The composition of  claim 1  wherein the composition has a viscosity less than about 25 seconds when measured by a #2 Zahn cup when formulated at a VOC level of 3.5 pounds/gallon.  
     
     
         3 . The composition of  claim 1  wherein the polyol diluent has a number average molecular weight less than about 1,000.  
     
     
         4 . The composition of  claim 1  wherein the polyol diluent has a number average molecular weight less than about 500.  
     
     
         5 . The composition of  claim 1  wherein the hydroxy-functional acrylic polymer has a number average molecular weight less than about 3,000.  
     
     
         6 . The composition of  claim 1  wherein the hydroxy-functional acrylic polymer has a number average molecular weight less than about 2,400.  
     
     
         7 . The composition of  claim 1  wherein the polyisocyanate is present at a level to provide about 0.3 to about 2.0 equivalents of isocyanate for each equivalent of active hydrogen from the acrylic resin and the polyol diluent.  
     
     
         8 . The composition of  claim 1  wherein the polyisocyanate is present at a level to provide about 0.7 to about 1.3 equivalents of isocyanate for each equivalent of active hydrogen from the acrylic resin and the polyol diluent.  
     
     
         9 . The composition of  claim 1  wherein the metal catalyst is a tin compound.  
     
     
         10 . The composition of  claim 1  wherein the propionic acid is present at a level of at least 0.1% of the total vehicle weight solids.  
     
     
         11 . A curable composition comprising (on a weight solids basis of the vehicle solids): 
 (i) 20-70% parts of a hydroxy functional acrylic polymer having a number average molecular weight less than about 3,000, and preferably less than 2,400;    (ii) 2-30% of a low molecular weight polyol reactive diluent;    (iii) 10-55% of a polyisocyanate;    (iv) at least 0.01% of a tin catalyst compound; and    (v) 0.1 to about 3.0% propionic acid.    
     
     
         12 . The composition of  claim 11  wherein the composition has a viscosity less than about 25 seconds when measured by a #2 Zahn cup when formulated at a VOC level of 3.5 pounds/gallon.  
     
     
         13 . The composition of  claim 11  wherein the polyol diluent has a number average molecular weight less than about 1,000.  
     
     
         14 . The composition of  claim 11  wherein the polyol diluent has a number average molecular weight less than about 500.  
     
     
         15 . The composition of  claim 11  wherein the hydroxy-functional acrylic polymer has a number average molecular weight less than about 3,000.  
     
     
         16 . The composition of  claim 11  wherein the hydroxy-functional acrylic polymer has a number average molecular weight less than about 2,400.  
     
     
         17 . The composition of  claim 11  wherein the polyisocyanate is present at a level to provide about 0.3 to about 2.0 equivalents of isocyanate for each equivalent of active hydrogen from the acrylic resin and the polyol diluent.  
     
     
         18 . The composition of  claim 11  wherein the polyisocyanate is present at a level to provide about 0.7 to about 1.3 equivalents of isocyanate for each equivalent of active hydrogen from the acrylic resin and the polyol diluent.  
     
     
         19 . In a substrate coated with a multi-layer decorative and/or protective coating which comprises: 
 (a) a basecoat comprising a pigmented film-forming polymer; and    (b) a transparent clearcoat comprising a film-forming polymer applied to the surface of the basecoat composition;    the improvement which comprises utilizing as the clearcoat and/or the basecoat a curable composition comprising:    (i) at least one hydroxy-functional acrylic polymer, and    (ii) at least one low molecular weight polyol reactive diluent;    (iii) at least one polyisocyanate;    (iv) a metal catalyst for accelerating the isocyanate/hydroxyl reaction; and    (v) propionic acid.