Processes for coating molded plastic substrates with aqueous coating compositions

Aqueous coating composition based on polyols with ammonium groups and polyisocyanates, which coating composition may contain pigments and/or extenders, customary lacquer additives and one or more organic solvents, and contains A) as binder at least one (meth)acrylic copolymer with a hydroxyl value of 20 to 150 mg KOH/g and with an amine value of 10 to 150 mg KOH/g, both values being related to solid resin, wherein 2 to 50 wt.% of the solid binder resin may be replaced with one or more other binders, wherein the (meth)acrylic copolymer is neutralised with an acid containing at least one isocyanate-reactive group; and B) as crosslinking agent at least one polyisocyanate, which may be blocked, wherein components A) and B) are present in quantities such that the ratio of the sum of isocyanate-reactive groups in the binder component A) to the blocked and unblocked isocyanates in component B) is 1:0.5 to 1:3. The coating composition is in particular suitable for use in the production of coatings on plastic substrates.