Low surface energy polyisocyanates and their use in one- or two-component coating compositions

A polyisocyanate composition comprising

• A) a polyisocyanate adduct containing allophanate groups, siloxane groups and optionally isocyanurate groups that is prepared by reacting a compound a) which
• i) is substantially free of hydroxyl groups and isocyanate groups,
• ii) has an average of at least two urethane groups per molecule and
• iii) contains 20 to 50% by weight of siloxane groups, based on the weight of the polyisocyanate adduct,
• with an excess quantity, based on the equivalents of urethane groups, of a polyisocyanate b) to form a polyisocyanate adduct and optionally removing at least a portion of the unreacted excess polyisocyanate b), and
• B) a polyisocyanate adduct containing biuret, isocyanurate, allophanate, urethane, urea, carbodiimide and/or uretdione groups, wherein component A) and B) are present in amounts such that said polyisocyanate composition has a siloxane group content, based on solids, of 0.001 to 10% by weight.

A process for the preparation of a polyisocyanate adduct containing allophanate groups, siloxane groups and optionally isocyanurate groups which comprises reacting a compound a) which

• i) is substantially free of hydroxyl groups and isocyanate groups,
• ii) has an average of at least two urethane groups per molecule and
• iii) contains 0 to 50% by weight of siloxane groups, based on the weight of the polyisocyanate adduct,
• with an excess quantity, based on the equivalents of urethane groups, of a polyisocyanate b), which optionally contains siloxane groups, to form a polyisocyanate adduct and optionally removing at least a portion of the unreacted excess polyisocyanate b), provided that compound a) and polyisocyanate b) contain a total of at least 0.001% by weight, of siloxane groups, based on the weight of the polyisocyanate adduct.