| 摘要 |
<p>Polyurethane elastomers made from diisocyanates, polyhydroxyl compounds (molecular weight 800-3500), glycols (molecular weight up to 300) and optionally triols (molecular weight up to 500) are produced in screw machines in the presence of lubricants. Self-cleaning, twin-screw machines with corotating screw shafts are used. In one screw zone therein, in which the kneading elements mix vigorously (kneading frequency up to 15 Hz), the critical reaction phase, in which the reaction mixture is highly tacky and has a viscosity of between 20 and 70 Pa.s, is passed through at a velocity gradient in the radial play between the comb and the housing wall of greater than 2000 s<-1>. The consequence of this is a homogeneous knot-free end product. The process enables the thermoplastic end product to be extruded directly with shaping.</p> |
