Polyisocyanate mixtures, a process for their preparation and their use as cross-linking agents in coating compositions

A process for the preparation of a polyisocyanate mixture having

• a) an average isocyanate functionality of at least 4.1,
• b) a (cyclo)aliphatically bound isocyanate group content of 12.0 to 20.5% by weight,
• c) a chemically incorporated carboxyl group content of 0.01 to 5.0% by weight and
• d) an ethylene oxide unit content arranged within terminal or lateral polyether chains of 0 to 10% by weight,
• which comprises reacting
• A) a polyisocyanate component having an (average) isocyanate functionality of at least 2.1 and containing one or more polyisocyanates having (cyclo)aliphatically bound isocyanate groups with
• B) a hydroxycarboxylic acid component containing one or more aliphatic hydroxycarboxylic acids having at least one sterically hindered carboxyl group and
• C) optionally a polyether alcohol component having at least 50% by weight, based on the total weight of the component, of ethylene oxide units within lateral and/or terminal polyether chains and containing one or more polyether alcohols having a molecular weight of 350 to 3,500, while maintaining an NCO/OH equivalent ratio of 2:1 to 75:1.