Acid-modified polyesters and their use in stoving enamels

Claim 1

An acid-modified polyester consisting of reaction products of educts selected from the group consisting of the following reactants (a) from 20 to 60 mol % of at least one dicarboxylic acid selected from the group consisting of oxalic, malonic, glutaric, adipic, pimelic, azelaic, sebacic, succinic, fumaric, maleic acid itaconic acid, 1,2-cyclohexandedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, phthalic, terephthalic and isophthalic acid, 2,5-norbornanedicarboxylic acid, 1,4-naphthalene-dicarboxylic acid, biphenyldicarboxylic acid, 4,4'-sulfonyldibenzoic acid and 2,5-naphthalenedicarboxylic acid, and esters or anydrides thereof, (b) from 3 to 30 mol % of a dihydroxyalkanecarboxylic acid, (c) from 10 to 60 mol % of a diol selected from the group consisting of ethylene glycol, 1,2- and 1,3-propane diol, 2,2-dimethyl-1,3-propane diol, 1,3- and 1-4 butane diol, 1,5-pentane diol, 1,6-hexane diol, 2,2,4-trimethyl 1,6-hexane diol, 1,2-, 1,3- and 1,4-cyclohexane dimethanol, perhydrobisphenol A, p-xylylene diol, 2-ethyl and 2-butyl propane diol, (d) from 5 to 30 mol % of a polyalcohol having more than two OH groups selected from the group consisting of trimethylolpropane, trimethylolethane, glycerol, ditrimethylolpropane, pentaerythritol, dipentaeythritol, or a polycarboxylic acid having 3 to 6 carboxyl groups, and (e) from 0 to 20 mol % of a monocarboxylic acid selected from the group consisting of fatty acids of 10 to 18 carbon atoms, isovaleric acid and isooctanoic acid, the ratio of the sum of the hydroxyl equivalents to the sum of the carboxyl equivalents in the reactants being between 0.5 and 2.0, the quantities of free hydroxyl groups in the end product being between 30 and 350 mmol of hydroxyl groups per 100 g of solid resin, and the content of free, neutralized and/or neutralizable acid groups being between 5 and 340 mmol of acid groups per 100 g of solid resin wherein the polyester is prepared in a multi-step process, step 1 comprising the synthesis of a hydroxy-functional polyester, and step 2 comprising the reaction of the hydroxy-functional polyester with the dihydroxyalkane carboxylic acid (b) and further dicarboxylic acid (a).