Patent ID: 7811073
Filing Date: 2010-10-12
Classification: B29C,B29L

Abstract:
1. A multiple melt channel film die head suitable for the continuous production of single or multi-layer tubular film made of thermoplastic polymer, comprising: a melt feed unit for providing a melt of the polymer; a melt inlet opening; at least two melt channels in the form of annular slits arranged concentrically in relation to a central axis of the film die head so as to form an inside melt channel and an outside melt channel, wherein each melt channel has a first delimiting wall with a spiral distributor and a second delimiting wall formed by a cylindrical surface, whereby the first delimiting wall associated with the inside melt channel is located radially inside of the second delimiting wall associated with the inside melt channel and the first delimiting wall associated with the outside melt channel is located radially outside of the second delimiting wall associated with the outside melt channel, and where the first delimiting wall with a spiral distributor of the inside melt channel is essentially mirrored by the first delimiting wall with a spiral distributor of the outside melt channel; a single ring-shaped die within the die-head into which the at least two melt channels merge, wherein each spiral distributor has a spiral groove having a depth that decreases from the melt inlet opening toward the ring-shaped die and the at least two melt channels become wider from the melt inlet opening toward the ring-shaped die, in order to distribute the melt through the melt channels in both a tangential direction and an axial direction; and at least two primary distributors that divide the melt exiting the melt feed unit into a number of separate melt streams which then merge into the spiral distributors at corresponding melt inlet openings.