Process for preparing rigid polyurethane foams.

Continuous process for the preparation of rigid polyurethane foams open compressed and deformed cells cold according to the procedure in double conveyor belt in which I) component A) and component B) are mixed in a mixing unit at from 20 at 35 ° C in a ratio such that the NCO index is 95 to 125, II) mixing of I) is inserted between the two protective layers of a dual-conveyor belt at temperatures of 40 to 100 ° C, III) after passing tape and after cooling optionally removed one or both protective layers and finally the cooled product is cut optionally, as component a) are used a) an organic polyisocyanate component a1) 70 to 90% by weight of monomeric diphenylmethane diisocyanate with a proportion of 18 to 32% by weight, based on the organic polyisocyanate component, of 2,4 '- diphenylmethane diisocyanate and a2) 10 to 30% by weight of polyphonic enilpolimetilenpoliisocianato and as component B) are used b) polyhydroxyl compounds b1) 20 to 35% by weight, based on component B), of polioloxialquilenos with a functionality of 2 to 3 and a hydroxyl number of 25 to 40, b2 ) 20 to 30% by weight, based on component B), of polioloxialquilenos with a functionality of 3 to 4 and a hydroxyl number of 400 to 650, b3) 5 to 15% by weight, based on component B), of polioloxialquilenos with a functionality of 2 and a hydroxyl number of 150-550, b4) 15 to 30% by weight, based on component B), of polyesterpolyols having a functionality of 2 and a hydroxyl number of 200 to 350, b5) 4 to 7% by weight, based on component B), glycerin c) 3.5 to 5.5% by weight, based on component B), of water as blowing agent, d) 0.5 to 4 % by weight, based on component B), of catalysts, e) 0.5 to 2% by weight, based on component B), of foam stabilizers, f) 1 to 3.5% by weight, based component B), cell openers, g) 0 to 7% by weight, based on component B), of auxiliaries and / or additives.