Method for producing isocyanate mixtures containing isocyanurate groups

A process for preparing an isocyanurate-containing isocyanate mixture, comprising:

• a) continuously providing an isocyanate mixture comprising isocyanate group trimerization catalyst by mixing a first isocyanate component, a second isocyanate component different from the first isocyanate component, and an isocyanate group trimerization catalyst;
• b) continuously guiding the mixture provided in step a) through a first dwell zone at a temperature in the range from 50° C. to 120° C. to obtain a uretdione- and isocyanurate-containing isocyanate mixture comprising the isocyanate group trimerization catalyst;
• c) continuously guiding the mixture obtained in step b) through a second dwell zone at a temperature in the range from 160° C. to 220° C. to obtain an isocyanurate-containing isocyanate mixture comprising inactive isocyanate group trimerization catalyst, wherein the guiding through the second dwell zone is optionally preceded by the addition of a stopper at a temperature in the temperature range from 50° C. to 120° C.;
• d) continuously guiding the mixture obtained in step c) through a third dwell zone at a temperature in the range from 10° C. to 100° C. to obtain the isocyanurate-containing isocyanate mixture.