| 摘要 |
<p>Disclosed is an improved reactive extrusion process for the continuous preparation of a hard polyurethane having Tg values greater than 80°C. The polyisocyanate and polyol ingredients are reacted in a twin-screw extruder which is limited to a single zone of high shear mixing. The present process prevents the formation of small bubbles in the extruded polyurethanes as well as the formation of yellow coloration in what should be an essentially water white polymer, problems which are encountered in the preparation of these hard polyurethanes using the prior art processes wherein the high shear mixing is carried out in multiple zones.</p> |
