Coextrusion head

摘要

A coextrusion head for the continuous production of laminated tubes to be used as parisons in blow molding. The tubes consist of a plurality of layers of synthetic resins. The synthetic resin layers include one or more supporting layers, usually a barrier layer, and adhesive layers as necessary. The layers are brought together by axial, annular feed passageways within the coextrusion head prior to the laminated tube being extruded through a nozzle in the head. Frequently one layer, generally the barrier layer, has different flow characteristics than those of the other layers, whereupon structural defects can arise in the formed tube. The apparatus described forestalls such structural defects by feeding the various layers into confluence in a manner that precludes, or sufficiently minimizes, the time layers having differing flow characteristics have contact with feed passageway walls while in confluence. As a result, shear stresses within or between the individual layers is avoided and the tube so produced is free of structural defects.