Method of preparation of aqueous polyurethane-polyurea dispersion and aqueous base paint containing said dispersion

A method for producing a multicoat paint system, the method comprising:

• (1) applying a pigmented aqueous basecoat material to a substrate, thereby obtaining a coating material,
• (2) forming a polymer film from the coating material, thereby obtaining a basecoat film,
• (3) applying a clearcoat material to the basecoat film, thereby obtaining a clearcoat film on the basecoat film, and then (4) curing the basecoat film together with the clearcoat film,
• wherein the pigmented aqueous basecoat material comprises an aqueous polyurethane-polyurea dispersion comprising polyurethane-polyurea particles present in the dispersion, having an average particle size of 40 to 2000 nm and having a gel fraction of at least 50%, wherein the dispersion is obtained by
• dispersing, in an aqueous phase, a composition comprising, based in each case on the total amount of the composition, 15 to 65 wt % of at least one intermediate comprising isocyanate groups and blocked primary amino groups, and 35 to 85 wt % of at least one organic solvent which has a solubility in water of not more than 38 wt % at a temperature of 20° C., thereby obtaining a dispersion wherein the polymer dispersion comprises molecules that are intramolecularly crosslinked between an amino group and an isocyanate group, and
• at least partly removing the at least one organic solvent from the dispersion,
• wherein the at least one intermediate is prepared by a process comprising a reaction of
• at least one polyurethane prepolymer containing isocyanate groups and comprising anionic groups and/or groups which can be converted into anionic groups, with
• at least one polyamine comprising at least two blocked primary amino groups and at least one free secondary amino group,
• by addition reaction of isocyanate groups from the at least one polyurethane prepolymer with free secondary amino groups from the at least one polyamine.