| 摘要 |
1,053,528. Tubular films. BADISCHE ANILIN- & SODA-FABRIK A.G. Oct. 11, 1963 [Oct. 12, 1962], No. 40145/63. Heading B5B. Highly transparent films of thermoplastics, e.g. polyolefins are made by extruding a tubular film at a temperature above the softening point of the thermoplastic, passing the film after inflation through an annular cooling zone in which the film is exposed to a gaseous cooling medium flowing at a uniform rate, and squeezing the film after cooling to a temperature below the range of crystallization of the thermoplastic, the thermoplastic being heated in an extruder to a temperature at least 30‹ C. above its softening point, and the tubular film being cooled in the region in which the thermoplastic changes from the plastic condition to the solidified condition, the flow velocity of the cooling medium, emanating from a porous surface, being 1 to 30 m/sec. in the whole region of the cooling zone, and the flow velocity of the cooling medium and the width of the cooling zone being such that the tubular film becomes cloudy in the first third of the cooling zone, adjacent the extruder, and then becomes clear again. The cooling medium may be air or nitrogen, dry or laden with water vapour. Apparatus for the process comprises an extruder, having an annular die, nip rollers for withdrawing the film, and a cooling ring provided in the region in which the film reaches its greatest diameter, the cooling ring surrounding the film and having means for supplying air thereto and having an annular wall facing its axis, and made of porous material. In one embodiment, a tubular film 2 of, e.g. isotactic polypropylene is extruded through die 1 inflated by air line 3 and squeezed between nip rolls 4. A hollow cooling ring 7 is provided with air supply lines 5 and water supply lines 6. Wall 8, facing the axis of the ring is porous and may be made of, e.g. ceramic, felt, multilayer fabric, sponge or particles of metal or plastic sintered together, particularly sintered bronze balls of 1 mm. diameter. In operation, air from 5 escapes from the porous surface and flows uniformly on to the surface of the film. The air may evaporate water contained in the porous material. The film issuing from the cooling zone is highly transparent and has low scattering power. |
