Solid powder coating composition

Abstract

Powder coating compositions that have a low melt viscosity contain: (1) 20 to 80 parts of a multifunctional epoxy resin component; (2) 80 to 20 parts of an essentially linear acid-terminated polyester resin component.

What is claimed is: 
     
       1. A solid powder coating composition comprising: (1) 20 to 80 phr of an epoxy resin component that contains on average more than two epoxy groups per molecule;   (2) 80 to 20 phr of an essentially linear acid-terminated polyester resin component.   
     
     
       2. The solid powder coating composition of claim 1 wherein the multifunctional epoxy resin component contains on average at least about 2.05 epoxy groups per molecule. 
     
     
       3. The solid powder coating composition of claim 1 wherein the multifunctional epoxy resin component has an epoxy equivalent weight of between about 450 and about 900. 
     
     
       4. The solid powder coating composition of claim 1 wherein the epoxy resin component contains an epoxy resin that has a first epoxy resin that contains on average more than 2 epoxy groups per molecule and a second epoxy resin that contains about 2 epoxy groups per molecule. 
     
     
       5. The solid powder coating composition of claim 1 wherein the polyester resin component contains on average about 1.8 to 2.2 acid groups per molecule. 
     
     
       6. The solid powder coating composition of claim 5 wherein the polyester resin component contains on average no more than about 2.1 acid groups per molecule. 
     
     
       7. The solid of Claim 5 wherein the polyester resin contains on average no more than about component contains on average no more than about 2 acid groups per molecule. 
     
     
       8. The solid powder coating composition of claim 1 wherein the polyester resin has an acid number between about 20 and about 110. 
     
     
       9. The solid powder coating composition of claim 1 wherein the polyester resin has a viscosity of no more than about 100 poise at 175° C. 
     
     
       10. The solid powder coating composition of claim 1 wherein the polyester resin has a viscosity of no more than about 75 poise at 175° C. 
     
     
       11. The solid powder coating composition of claim 1 wherein the polyester resin has a viscosity of no more than about 50 poise at 175° C. 
     
     
       12. The solid powder coating composition of claim 1 wherein the composition contains about 50 to 70 phr polyester and about 50 to 30 phr epoxy resin. 
     
     
       13. A cured powder coating composition of claim 1. 
     
     
       14. A coated article comprising a substrate and a coating on the substrate that contains a cured composition of claim 1. 
     
     
       15. A process to use the solid powder coating composition of claim 1, comprising the step of contacting a substrate with the powder coating composition at a temperature high enough to cause the composition to melt and cure. 
     
     
       16. A solid powder coating composition comprising: (1) about 30 to about 50 phr of a multifunctional epoxy resin component that contains on average about 2.05 to about 6 epoxy groups per molecule; and   (2) about 70 to about 50 phr of an essentially linear acid-terminated polyester component that contains on average about 1.8 to about 2 carboxylic acid groups per molecule and has an number average molecular weight of about 1000 to about 10,000.