| 摘要 |
The coextrusion heads hitherto known are only suitable for the processing of thermally stable plastic melts, for example PP and PE, because the latter can be formed on manifold cores with the known cardioidal (heart-shaped) distributions, to give tubes. Thermally sensitive plastics, for example PVDC and PET, but in particular rigid PVC cannot be processed in the known coextrusion heads, since the material would stagnate in the transition region of the open manifold channels and would decompose within a short time by the effect of heat. The coextrusion head according to the invention also allows the processing of, for example, rigid PVC by virtue of a combination of the mandrel-support principle, in which a rigid-PVC strand introduced at the top into the extrusion head is formed into a tube, with the cardioidal principle in which material strands of a different material which are introduced into the interior of the rigid-PVC tube are processed, for example, to form a barrier-layer tube and are formed into adhesion-promoter-layer tubes. <IMAGE>
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