Processes for coating molded plastic substrates with aqueous coating compositions

A method of coating plastic components including the steps of:

• (i) forming a molded plastic substrate;
• (ii) applying an aqueous coating composition to said substrate;
• (iii) such aqueous coating composition being 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, characterized in that it 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 neutralized 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.