| 摘要 |
PROCESS FOR THE PREPARATION OF POLYISOCYANATES CONTAINING URETHANE GROUPS AND THE PRODUCTS OBTAINED The present invention is directed to a process for the preparation of polyisocyanates containing urethane groups in which the content in monomeric starting diisocyanate is at most 0.4% by weight by reacting in a urethane-forming reaction a) an excess quantity, based on component b), of a diisocyanate component containing at least one aromatic diisocyanate which is free from urethane groups with b) a polyol component containing at least one polyhydric alcohol in the molecular weight range of 62 to about 250 followed by distillative removal of the unreacted excess starting diisocyanate a), characterized in that before the distillative removal of the excess starting diisocyanate a) is carried out, c) an aliphatic polyisocyanate containing isocyanurate groups is incorporated in the urethane-containing reaction product of components a) and b) in a quantity of about 0.3 to 10% by weight, based on the undistilled reaction product of components a) and b), and the distillation residue is then optionally dissolved in an inert solvent and up to about 0.5 equivalents of an alcohol, per kg of solvent-free distillation residue on a solvent free basis is added to the resulting solution so that the amount of free starting diisocyanate a) is further reduced and urethane groups are formed. The present invention is also directed to the polyisocyanates containing urethane groups obtained by this process. |
