Process for the production of terephthalate polyester lacquers

Polyester lacquer resins containing more than 40 mol per cent terephthalic acid (including any other acids present) are prepared by the reaction of polyethylene terephthalate with polyols containing 3 or more hydroxy groups, possibly mixed with diols, wherein the ethylene glycol formed is either removed by azeotropic distillation or is chemically bound by the addition of the required amount of an aromatic and/or aliphatic polycarboxylic acid or an anhydride or C1- 4 alkyl ester thereof. Suitable polyols are glycerol, trimethylolethane and trimethylolpropane, which may be mixed with a diol, e.g. propylene glycol. Transesterification catalysts may be used, e.g. PbO, CaO, and Pb(OOC.CH3)2. Suitable entraining agents for the azeotropic distillation are tetrachloroethylene, ethylene glycol monoacetate, toluene, the cresols and the xylenes. The polyesters are dissolved in cresol, viscosity is adjusted with xylene, and a cross-linking agent, e.g. butyl titanate, is added to give a stoving lacquer for wires. A modified polyester for lacquers for thick wires is obtained by substituting for part or all of the added terephthalate ester normally preferred another acid, in particular adipic, sebacic or isphthalic acid or a benzene tricarboxylic acid or pyromellitic acid.