Water-dilutable coating agent for preparing the base layer of a multilayer coating

A process for preparing a multi-layered, protective or decorative coating on a substrate surface comprising:

• (1) applying as a basecoating composition an aqueous dispersion which contains
• (a) a film-forming polyurethane resin having an acid number of from 5 to 70, which has been prepared from
• (A) linear polyetherdiol or polyesterdiol having a molecular weight of from 400 to 3,000,
• (B) diisocyanate, and
• (C) a compound which contains two groups which are reactive toward isocyanate groups, component C having one or more groups capable of anion formation which have preferably been neutralized before the reaction with a tertiary amine, components (A), (B) and (C) forming an intermediate which has terminal isocyanate groups and whose free isocyanate groups have subsequently been reacted with
• (D) a compound which contains groups reactive toward isocyanate groups, and
• (b) pigments;
• (2) forming from the composition applied in stage (1) a polymer film on the surface;
• (3) applying to the basecoat thus obtained a suitable transparent topcoat composition, and
• (4) baking the basecoat together with the topcoat,
• wherein the polyurethane dispersion forming the basecoating composition has been prepared by reacting the intermediate obtained from (A), (B) and (C) with a polyol which contains three or more hydroxyl groups.

A substrate coated with a multi-layered, protective or decorative coating which has been obtained by

• (1) applying as a basecoating composition an aqueous dispersion which contains
• (a) as a film-forming material one or more polyurethane resins having an acid number of from 5 to 70, which has been prepared from
• (A) linear polyetherdiol or polyesterdiol having a molecular weight of from 400 to 3,000;
• (B) diisocyanate, and
• (C) a compound which contains two groups which are reactive toward isocyanate groups, component C having one or more groups capable of anion formation which have preferably been neutralized before the reaction with a tertiary amine, components (A), (B) and (C) forming an intermediate which has terminal isocyanate groups and whose free isocyanate groups have subsequently been reacted with
• (D) further compounds which contain groups reactive toward isocyanate groups, and
• (b) pigments;
• (2) forming from the composition applied in (1) a polymer film on the surface;
• (3) applying to the basecoat thus obtained a suitable transparent topcoat composition, and
• (4) baking the basecoat together with the topcoat,
• wherein the polyurethane dispersion forming the basecoating composition has been prepared by reacting the intermediate obtained from (A), (B) and (C) with a polyol which contains three or more hydroxyl groups and transferring the reaction product thus obtained into an aqueous phase.