Low reflectance powder coating compositions

Abstract

A powder coating composition comprising: (a) a first acrylic powder resin having a hydroxyl value of at least about 180; (b) a second acrylic powder resin having a hydroxyl value between about 45 and about 80; (c) a crosslinker reactive with the hydroxyl functional acrylic resins; and (d) an acicular filler.

We claim: 
     
         1 . A powder coating composition comprising:
 (a) a first hydroxyl functional acrylic powder resin having a hydroxyl value of at least about 180;   (b) a second hydroxyl functional acrylic powder resin having a hydroxyl value between about 45 and about 80;   (c) a crosslinker reactive with the first and second hydroxyl functional acrylic resins; and   (d) an acicular filler;   
       and wherein the weight ratio of the first acrylic powder resin to the second acrylic powder resin is greater than 0.5. 
     
     
         2 . The powder coating composition of  claim 1  wherein the coating composition when applied to a substrate and cured will have a 60° gloss less than 1 and an 85° gloss 3.5 or less. 
     
     
         3 . The powder coating composition of  claim 1  wherein the first acrylic powder resin has a hydroxyl value between 180 and 250. 
     
     
         4 . The powder coating composition of  claim 1  wherein the second acrylic powder resin has a hydroxyl value between 45 and 60. 
     
     
         5 . The powder coating composition of  claim 1  wherein the second acrylic powder resin has a hydroxyl value of about 60. 
     
     
         6 . The powder coating composition of  claim 1  wherein the acicular filler is wollastonite. 
     
     
         7 . The powder coating composition of  claim 1  wherein the wollastonite is present at a level of at least 10% by weight solids of the coating composition. 
     
     
         8 . The powder coating composition of  claim 1  wherein the wollastonite is present at a level of at least 15% by weight solids of the coating composition. 
     
     
         9 . The powder coating composition of  claim 1  wherein the wollastonite is present at a level of at least 25% by weight solids of the coating composition. 
     
     
         10 . The powder coating composition of  claim 1  wherein the first acrylic powder resin and the second acrylic powder resin each have a Tg of at least 35° C. 
     
     
         11 . The powder coating composition of  claim 1  wherein the first acrylic powder resin has a Tg of at least 45° C. 
     
     
         12 . The powder coating composition of  claim 1  wherein the first acrylic polymer is present at a level to provide between about 33.3 weight percent and 85.1 weight percent of the total combined weight of the first acrylic polymer and the second acrylic polymer. 
     
     
         13 . The powder coating composition of  claim 1  wherein the first acrylic polymer is present at a level to provide between about 33.3 weight percent and 66.6 weight percent of the total combined weight of the first acrylic polymer and the second acrylic polymer. 
     
     
         14 . The powder coating composition of  claim 1  wherein the crosslinker is an isocyanate compound. 
     
     
         15 . The powder coating composition of  claim 14  wherein the isocyanate compound is present at a level to provide about 1.0 to about 1.5 equivalents of isocyanate functionality for each equivalent of active hydrogen of the first and second hydroxyl functional acrylic resins. 
     
     
         16 . A process of coating a substrate which process comprises:
 (i) applying a powder coating composition to a substrate; and   (ii) heating the coated substrate at a temperature and for a length of time sufficient to cause the composition to form an insoluble polymer network;   
       and wherein the powder coating composition comprises:
 (a) a first hydroxyl functional acrylic powder resin having a hydroxyl value of at least about 180; 
 (b) a second hydroxyl functional acrylic powder resin having a hydroxyl value between about 45 and about 80; 
 (c) a crosslinker reactive with the hydroxyl functional acrylic resins; and 
 (d) wollastonite; 
 
       and wherein the weight ratio of the first acrylic powder resin to the second acrylic powder resin is greater than 0.5.