Stretching process of thermo-plastic film

1,044,772. Films. TOYO RAYON KABUSHIKI KAISHA.May 10, 1963 [May 10, 1962], No. 18727/63. Heading B5B. A process for stretching a thermoplastic film comprises moving the film longitudinally while subjecting it to preliminary general heating, preliminary local heating and, optionally, preliminary transverse stretching so as to cause softening and/or necking in a longitudinal region substantially parallel to the direction of movement of the film, and then subjecting the film to a main transverse stretching. The main transverse stretching may be effected with the aid of further local heating. In one embodiment, Fig. 2, a moving film is subjected to preliminary general heating in zone a, a1, b, l1 by hot air, and to preliminary local heeting by infra-red heater 1-2. In the main transverse stretching zone b, b1. c, C1, further local heating is carried out by infra-red heaters 3-2 and 4-2. In other arrangements, one or both edges of the film in zone a, a1, b, b1 are locally heated, and one or more heaters are arranged diagonally or in V-formation in zone b, b1, c, c1. The heaters in the two zones of the film are continuous. The preliminary general heating is suitably above 70‹ C., and the ratio of preliminary stretching, where applied, is not more than 1.7. In examples, films of polypropylene, and polycapramide are stretched to products of uniform thickness.