Single lip rotary tubular extrusion die

Abstract

Disclosed is a single lip tubular extrusion die in which a plurality of separate melt streams passing through respective annular flow paths are fed to a common annular flow passage extending axially to and terminating at a die orifice. The annular flow passage is connected to the annular flow paths through respective groups of holes spaced annularly about the die axis. Each group of holes has its openings to the common annular flow passage spaced a different radial distance from the die axis to allow the separate melt streams to be layered in the common annular flow passage and co-extruded. One of the die lips is rotatable so that each melt stream produces a uniform layer of polymer in the extruded film while imparting a molecular orientation to the extruded film in the transverse direction (TD). An extruder-type seal may be provided adjacent a gap between a rotating and stationary part of the die to force melt attempting to penetrate the gap into the annular flow passage.