Powder composition

Abstract

There is described a powder coating composition suitable for food contact use comprising a mix of: (A) a first polyester that is amorphous and COOH functional being obtained from IPA and/or TPA and no more than 10 mole % neopentyl glycol (NPG); (B) a second optional COOH functional polyester obtained from analiphatic diacid and analiphatic diol, and (C) a curing agent that comprises functional groups reactable with the COOH of the polyester(s). The powders are suitable for coating the interior of metal cans especially those holding alcoholic beverages.

1 . A powder coating composition comprising as a binder a mixture of:
 (A) a first polyester that is amorphous and comprises at least one carboxy group; the first polyester being obtained from an acid comprising at least 50 mole % of isophthalic acid and/or terephthalic acid and from a polyol which comprises no more than 10 mole % neopentyl glycol (NPG), the first polyester having an acid number from 15 to 100 mg KOH/g;   (B) a second optional polyester that is amorphous and that comprises at least one carboxy group; the second polyester being obtained from an aliphatic diacid and an aliphatic diol, and   (C) a curing agent that comprises functional groups reactable with the carboxylic acid groups on the polyester(s) (A) and (where present) (B).   
     
     
         2 . A composition according to  claim 1 , in which the binder consists essentially of amorphous polyesters. 
     
     
         3 . A composition according to  claim 1 , in which the first polyester has an acid number from 20 to 80 mg KOH/g, more preferably from 30 to 70 mg KOH/g. 
     
     
         4 . A composition according to  claim 1 , comprising said second polyester (B). 
     
     
         5 . A composition according to  claim 1 , in which:
 the first polyester (A) is obtained and/or obtainable from:   (a) a dicarboxylic acid component comprising (by mole % of total acid)
 (i) from 50 to 100 mole % of a first acid selected from isophthalic acid, terephthalic acid and mixtures thereof and 
 (ii) from 50 to 0 mole % of a second acid selected from: 
 fumaric acid, maleic acid, phthalic anhydride, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, succinic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azealic acid, sebacic acid, 1,12-dodecanedioic acid, anhydrides thereof; and any mixtures thereof; and 
   (b) a polyol component comprising:
 (i) from 70 to 100 mole % of a first alcohol selected from: 
 propyleneglycol, 2-methyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 1-ethyl-2-methyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol, ethyleneglycol, and diethyleneglycol, used alone or in a mixture, 
 (ii) optionally from 0 to 30 mole % of a further diol preferably selected from 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, hydrogenated Bisphenol A; and/or mixtures thereof; from 
 (iii) optionally from 0 to 10 mole % of neopentyl glycol. 
   
     
     
         6 . A composition according to  claim 1 , in which the first acid is terephthalic acid, optionally in combination with isophthalic acid. 
     
     
         7 . A composition according to  claim 1 , in which the first acid is isophthalic acid. 
     
     
         8 . A composition according to  claim 1 , in which the first alcohol is propyleneglycol. 
     
     
         9 . A composition according to  claim 1 , in which the second polyester (B) is obtained and/or obtainable from:
 (a) a dicarboxylic acid component comprising (by mole % of total acid)
 (i) from 75 to 100 mole % of a first acid comprising at least one linear non-branched aliphatic diacid selected from: 
 succinic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azealic acid, sebacic acid, 1,12-dodecanedioic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid anhydrides thereof; and/or any mixtures thereof; and 
 (ii) optionally from 0 to 25 mole % of a second acid selected from fumaric acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, and/or any mixtures thereof; and 
   (b) a polyol component comprising:
 (i) from 75 to 100 mole % of a first alcohol selected from: 
 propyleneglycol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1-ethyl-2-methyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol, diethyleneglycol; 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated Bisphenol A; ethyleneglycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,14-tetradecanediol, 1,16-hexadecanediol, hydroxypivalate of neopentyl glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated Bisphenol A; and/or mixtures thereof; and 
 (ii) optionally from 0 to 25 mole % of neopentyl glycol. 
   
     
     
         10 . A composition according to  claim 1 , in which the curing agent is selected from an epoxy resin and/or a β-hydroxyalkylamide hardener. 
     
     
         11 . A composition according to  claim 1 , in which the first and/or second polyester is branched and is obtained from an acid mixture further comprising:
 (a)(iii) up to 15 mole % (relative to the total quantity of first acid (a)(i) and (where present) second acid (a)(ii)) of one or more polyacids that comprise at least three carboxy groups: preferably selected from: trimellitic acid, pyromellitic acid and their corresponding anhydrides.   
     
     
         12 . A composition according to  claim 1  wherein the thermosetting powder coating composition comprises a binder system comprising from 19 to 99 parts by weight of polyester (A), from 0 to 44.5 parts by weight of a polyester (B) having a Tg less than or equal to 50° C. and which comprises, with respect to the total amount of acids, from 75 to 100 mole % of an aliphatic diacid and, with respect to the total amount of alcohols, from 75 to 100 mole % of an aliphatic diol different from neopentyl glycol and from 1 to 65 parts by weight of a crosslinker having functional groups reactable with the polyesters' functional groups. 
     
     
         13 . A composition according to  claim 1 , in which the first and/or second polyester is branched and is obtained from a polyol mixture further comprising:
 (b) (iii) up to 15 mole % (relative to the total quantity of first alcohol (b)(i) and (where present) the NPG (b)(ii)) of one or more trifunctional or tetrafunctional polyols, preferably selected from: trimethylolpropane, ditrimethylolpropane, pentaërythrytol and mixtures thereof.   
     
     
         14 . A composition according to  claim 1  comprising:
 (A) from 19.0 to 99.0 parts by weight of the first polyester;   (B) from 44.5 to 0 parts by weight of the second polyester; and   (C) from 1 to 65 parts by weight of the curing agent   all parts being based on the total weight of polyester resins and curing agents.   
     
     
         15 . A composition according to  claim 1  comprising:
 (A) from 24.5 to 95.5 parts by weight of the first polyester;   (B) from 30.0 to 1.5 parts by weight of the second polyester; and   (C) from 3 to 50 parts by weight of the curing agent   all parts being based on the total weight of polyester resins and curing agents.   
     
     
         16 . A process for coating substrates comprising the steps of coating at least one surface of a substrate with a powder coating composition according to  claim 1 ; and
 heating the coated substrate to thermally cure the coating thereon to form an adherent layer of the coating composition on the substrate.   
     
     
         17 . A process according to  claim 16  wherein the substrate is selected from metal sheets for food and/or beverage products. 
     
     
         18 . A process according to  claim 16  wherein the substrate is selected from metal containers for food and/or for beverage products. 
     
     
         19 . A coated article obtained by a process according to  claim 16 . 
     
     
         20 . An article according to  claim 19 , which article is a metal can holding an alcoholic beverage. 
     
     
         21 . A process according to  claim 16 , wherein the interior and/or exterior of a food container coming into contact with alcohol is coated. 
     
     
         22 . A process according to  claim 16 , wherein at least the interior of a metal can for holding an alcoholic beverage is coated.