Process for producing composite elements

A process for producing a composite element comprising:

• at least one outer layer b;
• and
• at least one isocyanate-based rigid foam layer a),
• the process comprising applying the isocyanate-based rigid foam layer a) in the form of a flowable starting material a*) to the outer layer b), while the outer layer b) is moved continuously, such that the applying is carried out with a fixed applicator apparatus c),
• wherein:
• the flowable starting material a*) comprises:
• A) at least one polyisocyanate;
• B) at least one compound which reacts with isocyanate groups to form urethane;
• C) at least one blowing agent;
• D) catalysts comprising at least one compound D1) which catalyzes isocyanurate formation and at least one compound D2) which catalyzes polyurethane formation and which differs from the compound D1);
• and
• E) optionally auxiliaries and additives;
• the compound D2) comprises at least one amino group;
• an isocyanate index of the component A) is at least 180;
• and
• a ratio by weight of the compound D2) to the compound D1) is from 0.75 to 8.