GB1040612A - Process and apparatus for treating biaxially stretched plastic film webs - Google Patents

Abstract

1,040,612. Films. KALLE A.G. June 18, 1963 [June 20, 1962], No. 24277/63. Heading B5B. Thermoplastic films which have been simultaneously stretched in the longitudinal and transverse directions in a stretching frame by means of clips which grip the edges of the film are further held by the clips which are caused to continue to travel along rails disposed parallel or substantially parallel with respect to one another, and immediately after stretching, the film is cooled below the stretching temperature, and then, without further longitudinal or transverse stretching, is heated to a temperature which is above the stretching temperature but below the melting temperature of the film, which is then cooled below the stretching temperature, after which the clips are caused to release the edges of the film web. At least one further heat-setting treatment, preferably at a temperature below that at which the first heat-setting was performed, may be carried out and the film then cooled again before finally causing the clips to release the edges of the web. During heat-setting the travelling speed of the film may be regulated by transport means which act on areas of the film not in contact with the clips while the film is at a temperature below the stretching temperature and the clips may each be independently pulled by the film along the rails. If desired, during heat-setting the length of the film may be reduced to a minor degree by reducing the transport speed of the film after the heat-setting below its speed before the heat-setting, and/or the width of the film may be reduced to a minor degree by guiding the clips on converging rails. Apparatus as shown comprises two rows of clips for holding the edges of the film (not shown), an endless travelling guide for each row of clips (indicated generally at 5, 5), the clips in each row being independent and therefore capable of relative movement varying their distances from one another, rails 4 for positioning the clips while they are holding the film and nip rollers, e.g. 1, 2<SP>1</SP>, 2<SP>11</SP>, located in cool zones bounding heating zones, thus forming, in a biaxial stretching zone 7, a stretching frame in which the rails diverge, and a heat-setting zone 8, 9 in which the rails are disposed substantially parallel to one another, heating means (e.g. hot air) being supplied to the heating zone 9 and cooling means, e.g. cold air to the cooling zone 8. Additional, correspondingly disposed, heating means 11, cooling means 10, 12, and nip rollers 3 may be provided for further heat-setting treatments. The process is especially suitable for films of materials having with increasing temperature an increasing tendency to form crystalline structures, e.g. polyethylene terphthalate, polyamides, polycarbonates and isotactic polyolefins, but may also be used for the heat-setting of stretched films of poly vinyl chloride and other plastic materials.