| 摘要 |
1,064,712. Tubular films. T. J. SMITH & NEPHEW Ltd. Feb. 27, 1964 [Feb. 27, 1963], No. 7922/63. Heading B5B. Tubular films of thermoplastic material, especially polyethylene, polypropylene and polyvinyl chloride, are made by extrusion from an annular die 2, inflating air being supplied via inlet 10, the extruded material being confined by an exteriorly-cooled diverging inverted hollow conical or approximately conical member 4 of steel or other suitable material of desired apex angle with a low-friction non-stick coating or lining 5, to prevent the free expansion, due to the air pressure, of the extruded material until said material " freezes " (at dotted line 11) after which the material 6 leaves the larger end of the conical member and is free to be controllably expanded to the desired cylindrical diameter and thickness under the combined actions of the controlled internal pressure of the air in the bubble and the linear speed of the draw-off. Suitably the apex angle of the nonical member is 25-30 degrees, its larger end flared as shown, and the cooling means comprises a tubular coil 7 in connection with inlet and outlet pipes 8, 9 for a liquid coolant e.g. water. The expanded tubular film 21 is then flattened by guide rollers 12 and nip rollers 13, 14 and wound up. |
