| 摘要 |
1,248,171. Heat treatment of tubular film. IMPERIAL CHEMICAL INDUSTRIES Ltd. 18 Dec., 1969 [3 Jan., 1969], No. 479/69. Heading B5B. A process for the heat stabilization of tubular films of oriented thermoplastic materials comprises feeding such a tubular film filled with gas under pressure through a zone where it is heated to the required heat setting temperature gas being supplied under pressure to the outside of the tube to prevent any undesirable expansion of the tube. As shown, film is extruded from an annular extrusion die 2, to form a tubular film 1, and is cooled by passing over a mandrel 3, and/or through a cooling bath 4. The tube is drawn off by nip rolls 7, whose width is narrower than the collapsed tube, and which are rotating at a greater rate than the extrusion rate, thus forming an air tight seal on the mandrel 3, and preventing the inflation pressure from rupturing the tube at its point of extrusion. The tube is then heated to its orientation temperature by circular infra-red heaters 8, and stretched transversely by the high internal pressure introduced via the pipe 9, and longitudinally by a pair of nip rolls 10, rotating faster than nip rolls 7. The air pressure introduced inside the film can pass through these nip rolls 10 as the said nip rolls do not collapse the film across its entire width. The film passes into the heat treatment zone which consists of a sleeve 11, divided into two compartments. Heated gas under pressure is passed through pipe 13 and the perforations 12 into the upper compartment, surrounding the film and thus balancing the pressure and heating the film to the required temperature. Cold gas under pressure is introduced into the lower compartment through pipe 16 and perforations 18, to cool the film and balance the pressure to prevent expansion due to the high internal pressure. The film passes from the heat treating zone and is finally collapsed across its width by nip rolls 17. In examples polyethylene terephthalate film is heated to a temperature between 150-230‹ C. during heat setting; and film may be so made having an area shrinkage of less than 10% after heating at 140‹ C. for 1 minute. |
