Uniform distribution of melt flow in the extrusion of blown films

摘要

An extrusion die having a plurality of die layers stacked one upon the other in a direction generally parallel to the central axis. Each of the layers has an annular flow distribution ring (40) having an outer generally cylindrical surface and an annular feed ring surrounding and engaging the outer surface of the distribution ring (42, 42d). At the engaged surfaces of the feed and distribution ring, the flow from the feed ring is divided into a number of substantially equal flow portions. Seals (43a, 43b) between adjacent engaged surfaces confine the flow between the circumferential surfaces of the feed and distribution ring. Half of the flow portions are directed to a recombination region (45, 46) on one side of the distribution ring (42d), and half are directed to a recombination region (45, 46) on the other side of the ring (42d). In recombining, weld lines are formed in high flow areas minimizing the deleterious effect of polymer degradation. Subsequently, the flows on the opposite sides of the distribution ring (42d) are recombined such that the weld lines from one half are first modified to exhibit lower flow and then are layered with non-weld line portions modified to exhibit higher flow from the other half. This further minimizes the negative effect of weld line areas. Flow from the two sides is regularly divided to yield even distribution of the combined flows. IMAGE