Low gloss free radical powder coatings

Abstract

The present invention is directed to a powder coating composition that produces a low gloss coating upon cure. The powder coating composition includes one or more crosslinkable base polymer, a crosslinkable acrylic polymer and one or more free radical initiators. By adding spheroidal particles to the powder coating composition further reduction in gloss can be obtained while improving smoothness. These compositions are well suited to produce coatings on metallic substrates, such as automotive bodies and non-metallic substrates, such as reconstituted wood substrates, used for desk or table tops.

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         9 . A process for producing a coating having low gloss, said process comprising the steps of: 
 applying over a substrate a layer of low gloss powder coating composition comprising a base polymer selected from the group consisting of a crosslinkable polyester, crosslinkable polyurethane, crosslinkable acrylated polyether and a combination thereof; about 5 percent to about 60 percent of crosslinkable acrylic polymer; and about 0.1 to 10 percent of one or more free radical initiators, all percentages in weight percent based on total weight of said crosslinkable base and acrylic polymer solids;    heating said layer into a film; and    curing said film into said coating having low gloss.    
     
     
         10 . The process of  claim 9  wherein said coating composition further comprises about 5 percent to 50 percent of spheroidal particles, all percentages being in weight percent based on the total weight of the coating composition and wherein said spheroidal particles have a median particle diameter ranging from about 10 microns to about 50 microns.  
     
     
         11 . The process of  claim 9  or  10  wherein said curing step comprises exposing said layer to actinic radiation.  
     
     
         12 . The process of  claim 9  or  10  wherein said curing step comprises exposing said layer to an elevated temperature ranging from 90° C. to 220° C.  
     
     
         13 . The process of  claim 9  or  10  wherein said curing step comprises simultaneously exposing said layer to actinic radiation and elevated temperature ranging from 90° C. to 220° C.  
     
     
         14 . The process of  claim 13  wherein said curing step further comprising continuing exposure for about 5 minutes to about 30 minutes of said layer to said elevated temperature after cessation of exposure to said actinic radiation.  
     
     
         15 . The process of  claim 9  or  10  wherein said curing step comprises exposing said layer to actinic radiation followed by exposure to an elevated temperature ranging from 90° C. to 220° C., or by exposure to an elevated temperature ranging from 90° C. to 220° C. followed by exposure to actinic radiation.  
     
     
         16 . The process of  claim 9  or  10  wherein said coating is smooth.  
     
     
         17 . The process of  claim 9  or  10  wherein said substrate is an automotive body or a reconstituted wood substrate.  
     
     
         18 . A process for producing a low gloss powder coating composition comprising the steps of: 
 mixing a base polymer selected from the group consisting of a crosslinkable polyester, crosslinkable polyurethane, crosslinkable acrylated polyether and a combination thereof with about 5 percent to about 60 percent of a crosslinkable acrylic polymer and about 0.1 to 10 percent of one or more free radical initiators to form a blend, all percentages in weight percent based on total weight of said crosslinkable base and acrylic polymer solids;    heating said blend into a molten blend;    melt extruding said molten blend into a molten extrudate;    solidifying said molten extrudate into a solid extrudate;    fracturing said solid extrudate into fragments; and    grinding said fragments.    
     
     
         19 . The process of  18  wherein said blend further comprises about 5 percent to 50 percent of spheroidal particles, all percentages being in weight percent based on the total weight of the coating composition and wherein said spheroidal particles have a median particle diameter ranging from about 10 microns to about 50 microns.  
     
     
         20 . The process of  claim 18  or  19  further comprising straining ground fragments through a 180-micrometer screen to remove coarse fragments.  
     
     
         21 . The process of  claim 18  or  19  further comprising adding water to said fragments to form aqueous slurry.