Compositions and methods for coating food cans

Abstract

A composition for coating food cans is disclosed. The composition comprises a polyester, an acrylic copolymer and a crosslinker; the polyester and acrylic copolymer have been compatibilized in some way, such as through graft copolymerization. Methods for compatibilizing acrylics and polyesters are also disclosed as are methods for coating cans using compositions comprising acrylic and polyesters.

1 . A composition suitable for coating foods cans comprising:
 (a) a polyester;   (b) an acrylic copolymer;   (c) a crosslinker; and   (d) a solvent,   
     wherein the polyester and acrylic copolymer are blended together, but the acrylic copolymer does not have pendant glycidyl groups when the polyester is acid terminated and the acrylic copolymer does not have pendant hydroxy groups when the polyester is hydroxy terminated. 
   
   
       2 . The composition of  claim 1 , wherein the acrylic copolymer comprises acrylamide functionality. 
   
   
       3 . The composition of  claim 2 , wherein the acrylamide functionality derives from N—(N-butoxymethyl) acrylamide. 
   
   
       4 . The composition of  claim 1 , wherein the weight average molecular weight of the acrylic copolymer is within 1000 of the weight average molecular weight of the polyester. 
   
   
       5 . The composition of  claim 1 , wherein the solvent is a xylene, a propylene glycol monomethyl acetate, or a dibasic ester. 
   
   
       6 . The composition of  claim 1 , wherein the polyester is unsaturated. 
   
   
       7 . The composition of  claim 9 , wherein the polyester comprises maleic acid or anhydride and the acrylic copolymer comprises styrene. 
   
   
       8 . The composition of  claim 1 , wherein the polyester has a hydroxy value of 0 to 200. 
   
   
       9 . The composition of  claim 11 , wherein the polyester has a hydroxy value of 30 to 70. 
   
   
       10 . The composition of  claim 1 , wherein the polyester has an acid value of less than 10. 
   
   
       11 . The composition of  claim 1 , wherein the polyester has an acid value of less than 5. 
   
   
       12 . The composition of  claim 1 , wherein the weight ratio of a:b is 95:5 to 20:80. 
   
   
       13 . The composition of  claim 1 , wherein the weight ratio of a:b is 70:30. 
   
   
       14 . The composition of  claim 1 , wherein the crosslinker is or is derived from melamine. 
   
   
       15 . The composition of  claim 1 , wherein the crosslinker is or is derived from a resole or novalac that does not contain bisphenol A. 
   
   
       16 . A method for coating a food can comprising applying to the can the composition of  claim 1 . 
   
   
       17 . The composition of  claim 1 , wherein the polyester comprises maleic anhydride. 
   
   
       18 . The composition of  claim 1 , wherein the composition is substantially epoxy free.