| 摘要 |
Aqueous binder dispersion, coating composition containing this dispersion and use thereof, in particular for multicoat lacquer coatings. The dispersion contains: A) 45 to 95 wt.% of one or more polyurethanes, obtainable by free-radical initiated polymerisation of polyurethane macromonomers containing carboxyl, phosphonic and/or sulphonic acid groups and lateral vinyl groups, in the presence of one or more copolymerisable unsaturated monomers, in the form of an aqueous dispersion and B) 5 to 55 wt.% of one or more polyurethane resins containing ionic groups containing neither urea nor carbonate groups, which resins have a number average molar mass (Mn) of 10000 to 300000 and an acid value of 5 to 50 in the form of an aqueous dispersion, obtainable by preparing a polyurethane prepolymer containing OH groups and having an OH value of 5 to 75 and a number average molar mass (Mn) of 5000 to 50000 by the reaction in an organic medium of a) one or more isocyanate-reactive compounds with an acid value of 0 to 10 in the form of a1) 70 to 100 wt.% of polyols with a molecular weight of 500 to 6000, together with a2) 30 to 0 wt.% of one or more compounds differing from a1) with at least two isocyanate-reactive groups with a molecular weight of 60 to 400 with b) reaction products containing free isocyanate groups prepared from b1) compounds with two isocyanate-reactive groups and at least one anionic group or group capable of anion formation and b2) organic diisocyanates in a quantity ratio such that the molar ratio of the isocyanate-reactive groups of b1) to the isocyanate groups of b2) is 1:1.5 to 1:2.5, and with c) polyisocyanates with at least two free isocyanate groups per molecule in a quantity such that the molar ratio of the OH groups of component a) to the NCO groups of components b) and c) is 1.01:1 to 3:1, whereupon, the prepolymer obtained from a), b) and c) is subjected to chain extension in the organic medium or after conversion into the aqueous phase with d) polyfunctional isocyanates with a free NCO group functionality of at least 1.8, in proportions such that the finished polyurethane resins have the desired number average molar mass.
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