GB1292356A - Treatment of oriented heat stabilized thermoplastic film - Google Patents

Abstract

1292356 Heat-relaxation of films EASTMAN KODAK CO 30 Jan 1970 [3 Feb 1969] 4487/70 Heading B5B An oriented heat stabilized thermoplastic film is heat relaxed and cooled in a continuous manner by passing the hot film web through a heat relax zone in which the temperature of the film is maintained above its second order transition temperature and the film is maintained under only a slight tension, and the hot film is then passed through a cooling zone in which the temperature of the film is lowered to below its second order transition temperature, the cooling zone having a plurality of cooling means for gradually reducing the temperature of the hot film while the film is passing through the cooling zone, and independently reducing the cooling capacity of those cooling means being employed to cool at least one of the longitudinal web sections across the width of the film, if said at least one web section is detected to be relatively more limp than the remainder of the web sections. As shown in Fig. 1, an oriented heatstabilized thermoplastic film F is transported through a final heat relax zone 10 and then into a succeeding cooling zone 11, the two zones being separated by a partition 12. In the zone 10, the film F is guided and supported in an undulating path by a series of upper idler rolls 13 and lower idler rolls 13<SP>1</SP>. The last reach of the film F in the zone 10 passes over the idler rolls 25 vertically spaced along a support 26. Upon leaving the zone 10 the film F passes under the partition 12, over an idler roll 27 where it is redirected vertically upwards through the cooling zone 11 and over guide rolls 27 and upper guide rolls 15. As the film moves upwardly through the zone 11 it passes between two air plenums 20 which are provided along their length with openings 21 (Fig. 2) through which streams of cool air issue and impinge upon the full width of the film. The positions of the openings 21 in Fig. 2 have been divided by the dashed lines 1 to 8 into longitudinal areas 1 to 8 corresponding in spatial relationship across the full width of the film to the arbitrary sections indicated on the portion of the film shown in Fig. 3. The areas L and L 1 in Fig. 3 are areas in which the film displays a limpness or bagginess defect. These defects are removed by reducing the cooling capacities of those portions of the plenum 20 corresponding to areas 3, 4, 5, 7 and 8 of the film by completely closing the apertures of the plenums 20 indicated by the symbol X. Alternatively the cooling effect of these apertures may be reduced by means of electric heating units installed inside the apertures, with individual controls to regulate the amount of heat each unit can inject into the corresponding aperture. In another embodiment of the apparatus of the invention all or part of the cooling of the film in the zone 11 may be effected by means of rolls to individual sections of which cooling liquid is supplied, the temperature and/or flow rate of the cooling liquid supplied to these sections being individually controlled. The film may consist of a polyester such as poly-(ethylene terephthalate) or poly-(cyclohexane-1,4-dimethylene terephthalate).