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Abstract

Described are a method for the preparation of a multilayer coating and a coating material from an aqueous dispersion of a polymer with a particle diameter of the polymeric phase of 10 nm to 500 nm. The polymer has a number average molecular weight of 10,000 to 500,000 and an acid number of 12 to 40. The dispersion was obtained by polymerization without addition of emulsifier and in the presence of water insoluble initiators of a) 0.65 to 9 parts by weight of carboxyl group-free unsaturated monomers which, aside from the unsaturated bond, do not contain any other groups, which are reactive under the polymerization and curing conditions, together with 0 to 65% by weight, based on the total monomers of copolymerizable, hydroxyl group-containing monomers and/or 0 to 7% by weight, based on the total monomers, of ethylenically unsaturated monomers, in b) 1 part by weight, based on the resin portion, of an aqueous dispersion of a urea group-containing polyurethane, which was produced by chain extension of an NCO group-containing prepolymer based on polyester with an NCO group content of 1.0 to 10% with at least two urethane groups per molecule, with carboxyl groups corresponding to an acid number of 20 to 50 and a number average molecular weight of 600 to 6,000, with a polyamine with primary and/or secondary amino groups and/or with hydrazine in an aqueous medium without addition of emulsifier.

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