UV curable powder coating compositions for improved through-cure

Abstract

UV curable powder coating compositions containing 5 to 60 wt % spherical or near spherical particles having a median diameter of greater than 10, and most preferably greater than 15 microns, which refract and scatter applied UV light in all directions through the coating layer during curing to enhance the through-cure properties of the resulting coating.

What is claimed is:  
     
         1 . An ultraviolet radiation curable powder coating composition wherein the improvement is the use in the composition of light-refractive spheroidal particles, wherein the spheroidal particles comprise 5 to 50 wt % of the coating composition and wherein said spheroidal particles have a median particle diameter of greater than 10 microns and have a maximum particle diameter of about 50 microns.  
     
     
         2 . The coating composition of  claim 1 , wherein the spheroidal particles have a median diameter of greater than 15 microns.  
     
     
         3 . The coating composition of  claim 1 , wherein the spheroidal particles are selected from the group consisting of glass microspheres, spheroidal minerals, and polymer microspheres.  
     
     
         4 . An ultraviolet radiation curable powder coating composition containing a particulate blend of 
 (a) at least one ethylenically unsaturated, photopolymerizable resin,    (b) a pigment or a dye, and    (c) a photoinitiator,    wherein the improvement is the use in the composition of light-refractive glass or polymer microbeads, which refract and scatter applied UV light in all directions through the coating layer during curing.    
     
     
         5 . The coating composition of  claim 4 , wherein the glass or polymer microbeads have a median diameter of greater than 10 microns.  
     
     
         6 . The coating composition of  claim 5 , wherein the glass or polymer microbeads have a maximum diameter less than the thickness of the cured coating layer.  
     
     
         7 . The coating composition of  claim 6 , wherein the glass or polymer microbeads comprise 5 to 50 wt % of the coating composition.  
     
     
         8 . The coating composition of  claim 7 , wherein the at least one photopolymerizable resin is selected from the group consisting of: unsaturated polyesters, unsaturated acrylics, acrylates, unsaturated polyester-urethanes, unsaturated acrylic-urethanes, epoxies, acrylated epoxies epoxy-polyesters, polyester-acrylics, and epoxy-acrylics.  
     
     
         9 . A process of improving the through-cure of a ultraviolet radiation curable powder coating, comprising the step of adding to a powder coating composition between 5 and 60 wt %, based on the weight of the composition, of spheroidal particles having a median particle diameter of greater than 10 microns and a maximum diameter of about 50 microns.  
     
     
         10 . The process of  claim 9 , wherein the spheroidal particles have a median diameter of greater than 10 microns.  
     
     
         11 . The process of  claim 9 , wherein the spheroidal particles have a median diameter of greater than 15 microns.  
     
     
         12 . The process of  claim 9 , wherein the spheroidal particles are selected from the group consisting of glass microspheres, spheroidal minerals, and polymer microspheres.