Process for the production of self-cross-linking lacquers

The process for preparing a lacquer utilizing an aqueous dispersion, the lacquer being pigmented or non-pigmented, being self-cross linking upon heat treatment and containing a binder consisting essentially of the copolymer obtained from the copolymerization of the following monomers:

• a. 30 to 70 parts by weight, based on the total weight of the binder, of at least one monomer whose homopolymer has a theoretical glass temperature of less than 10.degree. C.,
• b. 30 to 70 parts by weight, based on the total weight of the binder, of at least one monomer whose homopolymer has a theoretical glass temperature of more than 30.degree. C.,
• c. 0.5 to 5 parts by weight, based on the total weight of the binder, of at least one polymerizable acid or anhydride thereof or a compound thereof which is an amide, halide, nitrile or semiester thereof, said polymerizable acid being an olefinic acid having 3 to 7 or more carbon atoms, an unsaturated dibasic acid having 4 to 8 or more carbon atoms,
• d. 2 to 35 parts by weight, based on the total weight of the binder, of at least one reactive monomer, said reactive monomer being a monomer having at least one hydroxyl group and which is the reaction product of a dihydric alcohol having 1 to 8 carbon atoms or of a trihydric alcohol having 1 to 8 carbon atoms and an olefinic acid having 3 to 8 carbon atoms, a monomer having at least one hydroxyl group and which is the ester of an unsaturated dibasic acid having 4 to 8 carbon atoms in the acid group, a chlorohydroxy ester of an unsaturated acid, a monomer having a functional amide group or groups, a monomer having a methylolized amide group, n-butoxymethyleneacrylic amide, a monomer with a functional allyl grouping or groups or a monomer having a functional aziridinyl grouping or groups,
• e. 0.5 to 35 parts by weight, based on the total weight of the binder, of at least one alkali metal or ammonium salt of a polymerizable sulfonic acid compound, which comprises conducting the polymerization in an aqueous dispersion in a reaction vessel at a preselected temperature between 15.degree. and 30.degree. C. and at a starting pH of 3 to 4 in the presence of a redox system consisting of 0.005 to 0.5 percent by weight, based on the total weight of the monomers, of at least one alkali metal and/or ammonium persulfate, 0.001 to 0.5 percent by weight ascorbic acid, based upon the total weight of the monomers, and 10 to 30 p.p.m., of at least one iron (II)-salt, no more than 30 percent of the monomers and the majority of the persulfate being inserted into the reaction vessel before the polymerization step itself starts, after the polymerization step itself starts, dosing in the remaining amount of monomers concurrently and parallel with the iron (II)-salt and the ascorbic acid in such a manner that the preselected polymerization temperature remains almost constant.