Coating compositions and process for the production of multilayer coatings

An aqueous coating composition, comprising

• A) at least one water-dilutable hydroxy-functional binder and
• B) at least one polyisocyanate crosslinking agent with free isocyanate groups,
• wherein component A) comprises
• A1) 40-95 wt. % of at least one water-dilutable hydroxy-functional (meth)acrylic copolymer with a hydroxyl value of 60-250 mg of KOH/g and an acid value of 5-50 mg of KOH/g, which is obtained by free-radical copolymerization performed in a non-aqueous phase by
• I) polymerizing the following monomers in a first stage:
• a) 20-65 wt. % of a reaction product of a monoepoxy ester and an unsaturated acid-functional monomer,
• b) 5-20 wt. % of at least one hydroxy-functional unsaturated monomer which differs from component a),
• c) 0-15 wt. % of an unsaturated acid-functional monomer and
• d) 5-70 wt. % of at least one other polymerizable unsaturated monomer,
• wherein the weight percentages of components a) to d) add up to 100 wt. % and
• II) polymerizing the following monomers in at least one further stage:
• b) 1540 wt. % of at least one hydroxy-functional unsaturated monomer which differs from component a),
• c) 5-30 wt. % of an unsaturated acid-functional monomer and
• d) 30-80 wt. % of other polymerizable unsaturated monomers,
• wherein the weight percentages of components b) to d) add up to 100 wt. % and
• wherein the ratio of primary hydroxyl groups to secondary hydroxyl groups in the (meth)acrylate A1) copolymer is 1:0.1 to 1:1.2 and at least 80% of the secondary hydroxyl groups result from the monomers a), and
• A2) 5-60 wt. % of at least one water-dilutable polyester oligomer, wherein the total of the weight percentages of component A1) and A2) add up to 100 wt. % and wherein the free-radical polymerization for the production of component A1) is performed at least in part in the presence of component A2) and/or wherein component A2) is added during polymerization or after completion of polymerization.