GB986003A - Orientating tubular thermoplastic materials - Google Patents

Abstract

986,003. Tubular films. MONSANTO CO. Jan. 3, 1962 [Jan. 3, 1961], No. 220/62. Heading B5B. A mandrel for the biaxial orientation of tubular 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 said first portion and of substantially coincidental circumference therewith where the two adjoin, and disposed within the tapering portion, means for heating at least the greater part of the surface of that portion. Within the second rigid portion, means for cooling at least the greater part of the surface of that portion may be provided. The heating means may be a chamber located beneath the surface of the tapering portion fitted with tubular means within the mandrel for admitting and withdrawing fluid, and the cooling means may be an annular chamber located beneath the surface of the second portion fitted with tubular means within the mandrel for admitting and withdrawing fluid. The narrow end of the tapering portion may be fitted with means for mounting the mandrel in axial alignment with an extrusion head. Between the mounting means and the narrow end of the tapering portion may be fitted a tapering insulating portion and means for connecting same to a source of pressurized gas, and a preconditioning section and means for supplying fluid thereto. A film-slitting device may be located in spaced relationship with the end of the second rigid portion adjoining the tapering portion. As shown (Fig. 3) melt passes through extrusion head 14 and around die core 20 to form a tube 12, which is drawn over mandrel 22 by rolls 50, 52 (Fig. 2). Mandrel 22 is aligned with the die orifice 16 by the cylindrical aligning projection 24 which is tapped into a recess in die core 20. The mandrel comprises a smooth surfaced rigid longitudinally tapering portion 26 of circular cross-section, terminating at 24, and a rear portion 28 which is preferably, as shown, of constant diameter. Portion 26 is heated by introducing hot fluid at 34 which is withdrawn at 36. Portion 28 is cooled, fluid coolant being introduced at 38 and withdrawn at 40. Section 44 is an insulation zone, which can be supplied with pressurized air or other gas at 46, and m ay thus be heated or cooled as required. A filmslitting device 62, e.g. a knife, slits the film which is wound up in sheet form. Fig. 4 is an alternative apparatus. Melt passes around die core 20 to form a tube 12, drawn over mandrel 122 by rolls (not shown). Mandrel 122 is aligned with the die orifice 16 by the aligning projection 124 tapped into a recess in die core 20. The mandrel comprises a tapering portion 126 and a rear portion 128 of constant diameter. Portion 126 is heated, hot fluid being introduced at 134 and withdrawn at 136. Portion 128 is cooled, fluid coolant being introduced at 138 and withdrawn at 140. Section 144 is an insulation zone, which is operated as zone 46 in Fig. 3. Additional features of the apparatus of Fig. 4 are the preconditioning zone 142 separated from mandrel 122 by gasket 149 which may be supplied with heating or coolant fluid as required by pipe 145, the fluid being withdrawn by pipe 146, and a drainage system for water, monomer and volatile components collecting on the mandrel comprising projection 148 the exterior surface of which is circumferentially threaded, and drain 150. Biaxial orientation of the film is effected by the heating zone, and the orientation is rendered permanent by rapid cooling in the cooling zone. Particulars are given of treatment conditions for films of polystyrene, polyethylene, polypropylene, polyvinyl chloride and polyethylene terephthalate.