Branched hydroxyl-functional polyester resin and its use in aqueous cross-linkable binder compositions

Branched hydroxyl-functional polyester resin having an average hydroxyl functionality of >2, a hydroxyl number of 25 to 300 mg KOH/g, and a number average molecular weight within the range of from 500 to 3,000, which polyester resin comprises polyalkylene oxide groups and, optionally, sulphonate groups, wherein the polyester resin comprises the reaction product of1) a mixture of carboxylic acids comprising50 to 80 mole % of an m- and/or p-aromatic and/or cycloaliphatic dicarboxylic acid,20 to 50 mole % of an aliphatic dicarboxylic acid and/or aliphatic monocarboxylic acid with more than 6 carbon atoms, and, optionally, a tri- or higher-functional acid, and2) a mixture of alcohols comprisingan aliphatic diol with at least 4 carbon atoms and/or a cycloaliphatic diol with at least 4 carbon atoms, a C1-C4 alkoxy polyalkylene oxide glycol and/or C1-C4 alkoxy polyalkylene oxide 1,3-diol having a number average molecular weight of 500 to 3,000, and, optionally, a tri- or higher-functional polyalcohol, whereinthe polyester resin has a carboxylic acid number of