Patent GB-1018901-A (GB)
Title: Orientation of thermoplastic materials
IPC: B29C48/94
Filed: 1962-11-15
Abstract: 1,018,901. Making tubular films. MONSANTO CO. Nov. 15, 1962 [Nov. 15, 1961], No. 43228/62. Addition to 986,003. Heading B5B. A mandrel for use in effecting the biaxial orientation of extruded tubular films of thermoplastic polymeric material comprises a first smooth surfaced rigid tapering portion of circular or ellipsoidal cross-section and longitudinally increasing circumference, a second smooth surfaced rigid portion adjoining the wider end of the first portion and coincidental circumference therewith where the two adjoin, means adjoining the narrow end of the tapering portion for mounting the mandrel in axial alignment with an extrusion head, means enabling the withdrawal or escape of fluid in contact with the narrow end of the tapering portion and means for heating at least the greater part of the surface of the tapering portion. The means for enabling withdrawal or escape of fluid from the environment of the tapering portion may also be adapted to remove lubricating liquid which drains downwardly on the tapering portion. In Fig. 2 (not shown), the polymeric material is melt extruded through an annular die orifice 18 to form a tube and drawn over a hollow mandrel 14 consisting of a tapering portion 36 and a cylindrical portion 52. The walls of the die orifice 18 are constituted by a die head casing 20 and a die core 22 into which is screwed the threaded projecting portion 42 of the mandrel 14, the mandrel being thus attached to the extrusion head 16 in axial alignment with the die orifice. The tapering portion 36 of the mandrel is heated by circulating a heating fluid through the chamber 54 by means of inlet and outlet pipes 56 and 58, respectively. The cylindrical portion 52 of the mandrel may be cooled by the circulation of a cooling fluid through the annular chamber 60 by means of pipes 62 and 64. The die core 22 has an annular recess 24 from which a lubricating liquid 26 flows upwardly into the frusto-conical shaped portion of the extruded tube 12 between the die core 22 and the mandrel 14. The inner surface of the tube 12 is thereby coated with the lubricating liquid 26 prior to being drawn over the exterior of the mandrel 14. Fresh lubricating liquid 26 enters the recess 24 through a number of apertures 30 from a central passageway 32 of annular cross-section formed in die core 22 and extending through the die head casing 20 to a feed pipe 34. As the tube 12 is advanced over the portion 36 of the mandrel 14, excess lubricant is wiped off the inner surface of the tube and may either be allowed to drain back into the pool of lubricant above the recess 24 (which pool is maintained at a constant level) and/or, as shown in Fig. 2, the lubricant draining down the sharply tapering portion 38 of the mandrel may be allowed to flow into the discharge pipe 44 through a number of ducts 40 in the base of the mandrel 14. The biaxial orientation of the tube 12 and its expansion to form a tubular film is effected while the tube 12 is drawn over the heated conical portion 36 of the mandrel and the biaxial orientation of the tubular film is rendered permanent by its passage over the internally cooled cylindrical portion 52 of the mandrel, the tubular film, on leaving the mandrel 14, is slit by knives 72 and 72a into two sheet films of equal width which may each be passed through a bath to dissolve lubricant off the sheets and each advanced to the nip of a pair of take-off rolls. In Fig. 3 (not shown), a mandrel 100 is inverted so that an annular die orifice 102 is axially aligned above the mandrel and liquid lubricant is supplied to a conical frustrum shaped space 104 through a supply pipe 106. A stand-pipe 108, concentrically disposed within the supply pipe 106 serves as a vent to prevent accumulation of pressure within the space 104. The lubrication of the extruded tube, in accordance with the invention, as it is drawn over the mandrel, prevents marring of the inner surface of the tube.