Polyisocyanate mixtures, processes for their production and their use as binders for coating compositions or as reactants for compounds reactive to isocyanate groups or carboxyl groups

A process for the production of a polyisocyanate mixture which has

• a) an average NCO functionality of 1.5 to 4.0,
• b) a content of (cyclo)aliphatically bound isocyanate groups (calculated as NCO, MW 42) of 2 to 40% by weight,
• c) a content of chemically incorporated carboxyl groups (calculated as COOH, MW 45) of 0.01 to 15% by weight and
• d) a content of (cyclo)aliphatically bound uretdione groups (calculated as C.sub.2 N.sub.2 O.sub.2, MW 84) of 1 to 23% by weight. which comprises reacting
• a polyisocyanate component comprising at least one diisocyanate having (cyclo)aliphatically bound isocyanate groups, (cyclo)aliphatically bound uretdione groups and a molecular weight of 168 to 1,000 with
• B) a hydroxycarboxylic acid component comprising at least one aliphatic hydroxycarboxylic acid having a molecular weight of 76 to 200
• while maintaining an equivalent ratio of isocyanate groups to hydroxyl groups of 1.05:1 to 80:1 during the reaction.

A process for the production of a polyisocyanate mixture which has

• a) an average NCO functionality of 1.5 to 4.0,
• b) a content of (cyclo)aliphatically bound isocyanate groups (calculated as NCO, MW 42) of 2 to 40% by weight,
• c) a content of chemically incorporated carboxyl groups (calculated as COOH, MW 45) of 0.01 to 15% by weight and
• d) a content of (cyclo)aliphatically bound uretdione groups (calculated as C.sub.2 N.sub.2 O.sub.2, MW 84) of 1 to 23% by weight which comprises
• i) reacting
• A) a polyisocyanate component which is essentially free from uretdione groups and comprises at least one diisocyanate having (cyclo)aliphatically bound isocyanate groups and a molecular weight of 168 to 1,000 with
• B) a hydroxycarboxylic acid component comprising at least one aliphatic hydroxycarboxylic acid having a molecular weight of 76 to 200, while maintaining an equivalent ratio of isocyanate groups to hydroxyl groups of 1.05:1 to 400:1 during the reaction,
• ii) subsequently dimerizing and optionally trimerizing 5 to 60% by weight of the isocyanate groups of the product obtained in i) in the presence of a dimerization catalyst and
• iii) optionally distilling off at least a portion of any unreacted, starting polyisocyanate.