| 摘要 |
The present invention relates to a process for the continuous production of thermoplastically processable polyurethanes having improved processing behaviour, wherein in a multistep reaction A) one or more linear hydroxyl-terminated polyols a) having a molecular weig ht of from 500 to 5000 are mixed continuously with a proportion of an organic diisocyanate b) in an NCO:OH ratio of from 2.0:1 to 5.0:1, in a mixing unit at high shear energy, B) the mixture prepared in step A) is reacted continuously to form an isocyanate-terminated prepolymer in a reactor at temperatures of > 120.degree.C, until a conversion of > 90%, referred to component a), is achieved, C) the prepolymer prepared in step B) is mixed with the remainder of component b), an NCO:OH ratio of from 2.05:1 to 6:1 being established overall in steps A) to C) and an NCO:OH ratio of 0.9 to 1.1 being established when all the components of steps A) to F) are included, D) the mixture prepared in step C) is cooled to a temperature of < 190.degree.C, E) the mixture obtained in step D) is mixed continuously and intensively for a maximum of 5 seconds with one or more diol and optionally triol and/or diamine chain extenders c) having a molecular weight of from 60 to 500 and F) the mixture obtained in step E) is reacted continuously in a different reactor from that used in step B), to form the thermoplastic polyurethane.
|
