Branched polyester for powder coatings

Abstract

The present invention relates to a carboxylic acid functional branched polyester, having an acid number of at least 77 mg KOH/g, said carboxylic acid functional branched polyester being the reaction product of a polybasic organic carboxylic acid or its anhydride, preferably trimellitic anhydride, and a branched hydroxyl functional polyester obtained from 70 to 100 mole % of terephthalic acid and/or isophthalic acid and, optionally, from 0 to 30 mole % of another polycarboxylic acid, referring to the polyacid constituents, from 10 to 50 mole % of ethylene glycol, from 50 to 87.5 mole % of at least one other aliphatic or cycloaliphatic diol and from 1.5 to 15 mole % of at least one polyol, referring to the polyol constituents, as well as to the use of this polyester to prepare powder coating compositions which present a low gloss, especially of below 35% (at 60°), when used in combination with standard powder coating polyesters and crosslinkers.

1 . A carboxylic acid functional branched polyester having an acid number of at least 77 mg KOH/g, said carboxylic acid functional branched polyester being the reaction product of:
 a) a polybasic organic carboxylic acid and/or its anhydride; and   b) a branched hydroxyl functional polyester obtained from:
 (i) a polyacid constituent comprising 70 to 100 mole % of terephthalic acid and/or isophthalic acid; and 
 (ii) a polyol constituent comprising 10 to 50 mole % of ethylene glycol, 50 to 88.5 mole % of at least one other aliphatic or cycloaliphatic diol, and 1.5 to 15 mole % of at least one polyol having at least 3 hydroxyl groups. 
   
   
   
       2 . The polyester according to  claim 1  wherein the anhydride of the polybasic organic carboxylic acid is trimellitic anhydride. 
   
   
       3 . The polyester according to  claim 1 , wherein said other aliphatic or cycloaliphatic diol is neopentyl glycol. 
   
   
       4 . The polyester according to  claim 1 , wherein the polyol is a triol. 
   
   
       5 . The polyester according to  claim 4 , wherein the triol is glycerol, trimethylolpropane or a mixture thereof. 
   
   
       6 . The polyester according to  claim 1 , having a polydispersity Mw/Mn of from 3 to 7. 
   
   
       7 . The polyester according to  claim 1 , wherein the branched hydroxyl functional polyester has a functionality of at least 2.2. 
   
   
       8 . A thermosetting powder coating composition comprising a binder wherein 100 parts by weight of said binder comprises:
 (A) from 30 to 70 parts by weight of at least one carboxylic acid functional branched polyester according to  claim 1 , and   (B) from 70 to 30 parts by weight of at least one carboxylic acid functional polyester having an acid number of lower than 50 mg KOH/g.   
   
   
       9 . (canceled) 
   
   
       10 . An entirely or partially coated substrate, wherein the coating material used is a powder coating composition according to  claim 8 . 
   
   
       11 . A polyester according to  claim 1 , wherein the polyacid constituent further comprises from 1 to 30 mole % of another polycarboxylic acid. 
   
   
       12 . A composition according to  claim 8  further comprising: (C) from 3 to 20 parts by weight of at least one crosslinking agent having functional groups reactable with the carboxylic acid groups of polyesters (A) and (B). 
   
   
       13 . A composition according to  claim 12 , wherein the crosslinking agent is a β-hydroxyalkylamide group containing compound.