Diphenylmethane diisocyanate based polyisocyanates containing allophanate groups and having blocked isocyanate groups

A process for the production of a polyisocyanate having, based on solids,

• A) a content of unblocked and blocked isocyanate groups (calculated as NCO) of 9% to 13%,
• B) a content of allophanate groups (calculated as C.sub.2 HN.sub.2 O.sub.3, molecular weight 101 ) of 3% to 9% and
• C) a calculated average functionality of 2.0 to 2.5, which comprises reacting diphenylmethane diisocyanate with a monoalcohol, optionally blended with a minor amount of a diol, to form urethane groups, converting the urethane groups to allophanate groups in the presence of a catalyst and subsequently blocking at least 95% of the isocyanate groups with diethyl malonate.

A polyisocyanate i) which is prepared from diphenylmethane diisocyanate and a monoalcohol which contains 2 to 22 carbons and which may only be substituted with ether or ester groups, ii) wherein at least 95% of the isocyanate groups are blocked with diethyl malonate and iii) wherein the polyisocyanate has, based on solids,

• A) a content of unblocked and blocked isocyanate groups (calculated as NCO) of 9% to 13%,
• B) a content of allophanate groups (calculated as C.sub.2 HN.sub.2 O.sub.3, molecular weight 101 ) of 3% to 9% and
• C) a calculated average functionality of 2.0 to 2.5.