Powder compositions for heat sensitive substrates

Abstract

The invention is directed to a powder coating composition comprising a first component (A) and a second component (B) that is dry-blended or melt blended with the first component (A). The first component (A) comprises at least one polyepoxy resin and at least one catalyst. The second component (B) comprises at least one carboxylic acid functional acrylic resin. The polyepoxy resins include non-crystalline polyepoxy resins, crystalline polyepoxy resins, and mixtures thereof. The powder coating compositions can be applied to heat sensitive substrates and cured at lower temperature or for shorter time to provide finishes having controllable gloss and/or high hardness.

We claim:  
     
         1 . A powder coating composition comprising: 
 A). about 50% to about 99% by weight of a first component comprising 
 a-1) at least one polyepoxy resin; and  
 a-2) at least one catalyst, and  
   B). about 1% to about 50% by weight of a second component dry-blended with said first component (A), comprising at least one carboxylic acid functional acrylic resin.    
     
     
         2 . The powder coating composition of  claim 1 , wherein said polyepoxy resin is selected from the group consisting of non-crystalline polyepoxy resins, crystalline polyepoxy resins, and mixtures thereof.  
     
     
         3 . The powder coating composition of  claim 2 , wherein said polyepoxy resin is a mixture of at least one non-crystalline polyepoxy resin and at least one crystalline polyepoxy resin.  
     
     
         4 . The powder coating composition of  claim 2 , wherein said non-crystalline polyepoxy resin is selected from the group consisting of glycidyl ethers of aromatic polyols, epoxy-functional acrylic resins, and mixtures thereof.  
     
     
         5 . The powder coating composition of  claim 2 , wherein said crystalline polyepoxy resin is selected from the group consisting of triglycidyl isocyanurate (TGIC), diglycidyl ester of terephthalic acid, triglycidyl ester of trimellitic acid, tetramethylbisphenol diglycidyl ether, bisphenol S diglycidyl ether, 2,5-di-t-butylbenzene-1,4-diglycidyl ether, 2,5-di-t-butylhydroquinone diglycidyl ether, diglycidyl isophthalate, epoxypropoxydimethylbenzyl acrylamide, and mixtures thereof.  
     
     
         6 . The powder coating composition of  claim 1 , wherein said catalyst is selected from the group consisting of imidazoles, imidazole/epoxy adducts, and mixtures thereof.  
     
     
         7 . The powder coating composition of  claim 1 , wherein said second component further comprises at least one catalyst.  
     
     
         8 . The powder coating composition of  claim 1 , wherein either of said first component or second component further comprises at least one ingredient selected from the group consisting of acid functional polyesters, fillers, slip additives, pigments, dyes, UV stabilizers, antioxidants, fluidizing agents, flow control agents, degassing agents, flexibilizing agents, texturing agents, and mixtures thereof.  
     
     
         9 . The powder coating composition of  claim 1 , wherein said composition provides a coating having 60° gloss of from about 2 to about 95.  
     
     
         10 . The powder coating composition of  claim 9 , wherein said composition provides a coating with 60° gloss of from about 5 to about 60.  
     
     
         11 . The powder coating composition of  claim 1 , wherein said composition provides a coating having pencil hardness of greater than about F.  
     
     
         12 . The powder coating composition of  claim 11 , wherein said composition provides a coating having pencil hardness of greater than about 3H.  
     
     
         13 . A powder coating composition comprising: 
 a). about 1% to about 50% by weight of at least one carboxylic acid functional acrylic resin;    b). about 50% to about 99% by weight of polyepoxy resins, of which from about 2% to about 15% by weight, based on the total epoxy resins, being at least one crystalline polyepoxy resin; and    c). a catalyst in an effective amount to cure said composition.    
     
     
         14 . The powder coating composition of  claim 13 , wherein said catalyst is selected from the group consisting of imidazoles, imidazole/epoxy adducts, tertiary amines, imidazolines, imidazoline salts of mono- or di-carboxylic acids, tetraalkylammonium salts, phosphonium salts, and mixtures thereof.  
     
     
         15 . The powder coating composition of  claim 13 , wherein said composition provides a coating having 60° gloss of from about 2 to about 95.  
     
     
         16 . The powder coating composition of  claim 13 , wherein said composition provides a coating with 60° gloss of from about 5 to about 60.  
     
     
         17 . The powder coating composition of  claim 13 , wherein said composition provides a coating having pencil hardness of higher than about 3H.  
     
     
         18 . The powder coating composition of  claim 13 , wherein said crystalline polyepoxy resin is selected from the group consisting of triglycidyl isocyanurate (TGIC), diglycidyl ester of terephthalic acid, triglycidyl ester of trimellitic acid, tetramethylbisphenol diglycidyl ether, bisphenol S diglycidyl ether, 2,5-di-t-butylbenzene-1,4-diglycidyl ether, 2,5-di-t-butylhydroquinone diglycidyl ether, diglycidyl isophthalate, epoxypropoxydimethylbenzyl acrylamide, and mixtures thereof.  
     
     
         19 . An article comprising a heat sensitive substrate, and coated and cured on at least one surface of said substrate with a powder coating composition of  claim 1 .  
     
     
         20 . An article comprising a heat sensitive substrate, and coated and cured on at least one surface of said substrate with a powder coating composition of claim  13 .