Powder coating compositions comprising a polyester and a fluoropolymer and coatings formed therefrom

Abstract

A powder coating composition can include: a polyester polymer having carboxylic acid functional groups; a first crosslinker reactive with the carboxylic acid functional groups of the polyester polymer; and a fluoropolymer unreactive with the polyester polymer and first crosslinker. A weight ratio of the polyester polymer to the fluoropolymer is from 80:20 to 60:40. When cured, the powder coating composition forms a single coating layer including the polyester polymer and the fluoropolymer.

The invention claimed is: 
     
         1 . A powder coating composition comprising:
 a polyester polymer comprising carboxylic acid functional groups and having an acid value of at least 15 mg KOH/g;   a first crosslinker reactive with the carboxylic acid functional groups of the polyester polymer; and   a fluoropolymer unreactive with the polyester polymer and first crosslinker,   wherein a weight ratio of the polyester polymer to the fluoropolymer is from 80:20 to 60:40, and   wherein when cured, the powder coating composition forms a single coating layer comprising the polyester polymer and the fluoropolymer.   
     
     
         2 . The powder coating composition of  claim 1 , wherein the polyester polymer comprises at least 20 weight % based on the total solids weight of the powder coating composition. 
     
     
         3 . The powder coating composition of  claim 1 , wherein the fluoropolymer comprises 40 weight % or less based on the total solids weight of the powder coating composition. 
     
     
         4 . The powder coating composition of  claim 1 , wherein the polyester polymer has an acid value within a range of from 20 to 70 mg KOH/g. 
     
     
         5 . The powder coating composition of  claim 1 , wherein the polyester polymer has a glass transition temperature within a range of from 10 to 100° C. 
     
     
         6 . The powder coating composition of  claim 1 , wherein the polyester polymer has a melt viscosity at 165° C. within a range of from 5 to 100 Pa s as measured by a Cone and Plate Viscometer according to ASTM D 4287. 
     
     
         7 . The powder coating composition of  claim 1 , wherein the fluoropolymer comprises a fluoropolyether polymer, a polyvinylidene fluoride polymer, or a combination thereof. 
     
     
         8 . The powder coating composition of  claim 7 , wherein the fluoropolymer comprises a fluoropolyether polymer. 
     
     
         9 . The powder coating composition of  claim 8 , wherein the fluoropolyether polymer is a fluoroethylene vinyl ether copolymer. 
     
     
         10 . The powder coating composition of  claim 7 , wherein the fluoropolymer comprises a polyvinylidene fluoride polymer. 
     
     
         11 . The powder coating composition of  claim 1 , wherein the fluoropolymer has a glass transition temperature within a range of from 10 to 100° C. 
     
     
         12 . The powder coating composition of  claim 1 , wherein the first crosslinker comprises a hydroxylalkyl amide compound, an epoxy-functional compound, or a combination thereof. 
     
     
         13 . The powder coating composition of  claim 13 , wherein the first crosslinker comprises both a hydroxylalkyl amide compound and an epoxy functional (meth)acrylic compound. 
     
     
         14 . The powder coating composition of  claim 14 , wherein an amount of the epoxy functional (meth)acrylic compound in the powder coating composition is greater than an amount of the hydroxylalkyl amide compound, the amounts based on the total solids weight of the powder coating composition. 
     
     
         15 . The powder coating composition of  claim 1 , wherein the powder coating composition further comprises a pigment. 
     
     
         16 . The powder coating composition of  claim 1 , wherein the powder coating composition is substantially free of epsilon-caprolactam and/or triglycidyl isocyanurate. 
     
     
         17 . The powder coating composition of  claim 1 , wherein the powder coating composition is substantially free of an organic ultraviolet absorber. 
     
     
         18 . The powder coating composition of  claim 1 , wherein the powder coating composition is substantially free of an isocyanate functional crosslinker. 
     
     
         19 . The powder coating composition of  claim 1 , wherein the powder coating composition further comprises 1 to 10 weight % of a second crosslinker reactive with the fluoropolymer, wherein the second crosslinker comprises an isocyanate functional crosslinker. 
     
     
         20 . The powder coating composition of  claim 1 , wherein the powder coating composition comprises a second crosslinker reactive with the fluoropolymer, wherein the second crosslinker comprises isocyanate groups and the fluoropolymer comprises hydroxyl groups such that a ratio of total isocyanate equivalents to total hydroxyl group equivalents is from 0.65:1 to 2:1. 
     
     
         21 . The powder coating composition of  claim 1 , wherein the first crosslinker comprises triglycidyl isocyanurate, and the powder coating composition further comprises a second crosslinker reactive with the fluoropolymer, wherein the second crosslinker comprises an isocyanate functional crosslinker. 
     
     
         22 . The powder coating composition of  claim 1 , wherein the polyester polymer has a hydroxyl value of less than 10 mg KOH/g. 
     
     
         23 . A substrate at least partially coated with a coating formed from the powder coating composition of  claim 1 . 
     
     
         24 . The substrate of  claim 23 , wherein the coating formed from the powder coating composition comprises a single coating layer formed directly over a surface of the substrate. 
     
     
         25 . The substrate of  claim 24 , wherein both the polyester polymer and the fluoropolymer are in direct contact with the substrate.