Process for the preparation of powdered thermosetting compositions based on branched-chain carboxyl group-containing polyesters and epoxy compounds

A process for the preparation of a powdered thermosetting coating composition suitable for application as paint or varnish or electricity-conducting articles by electrostatic powder spray or fluidized bed coating processes, which comprises

• in a first stage, preparing a branched-chain hydroxyl group-containing polyester having a hydroxyl number between 50 and 100 by reacting (1) at least one aromatic dicarboxylic acid, (2) at least one aromatic tricarboxylic acid or pyromellitic acid and (3) an excess of at least one organic dihydric compound, the ratio of carboxyl equivalents of the tricarboxylic acid or pyromellitic acid to carboxyl equivalents of the dicarboxylic acid being from 5:95 to 35:65;
• in a second stage, esterifying said branched-chain hydroxyl group-containing polyester with an aromatic or hydro-aromatic dicarboxylic acid to produce a branched-chain carboxyl group-containing polyester having a molecular weight of from 1,000 to 3,000 and an acid number between 50 and 100, which acid number is substantially equal to the hydroxyl number of said hydroxyl group-containing polyester;
• in a third stage, homogeneously mixing said branched-chain carboxyl group-containing polyester with a solid epoxy compound containing at least two epoxy groups, the ratio of said epoxy compound to said carboxyl group-containing polyester being such that there are 0.7 to 1.3 equivalents of epoxy groups per equivalent of carboxyl groups in said carboxyl group-containing polyester;
• and
• converting the resulting homogeneous mixture into a powder.