GB1126693A - An apparatus and method for longitudinally stretching continuous films of thermoplastic materials - Google Patents

Abstract

1,126,693. Stretching films longitudinally. FARBENFABRIKEN BAYER A.G. 30 Sept., 1966, No. 43882/66. Heading B5B. An apparatus for stretching film webs longitudinally in a continuous manner comprises an internally heated feed roll 1 (Figs. 1 and 2) positively driven at a peripheral speed equal to the linear speed at which a film web 3 is delivered on to the roll in the unstretched condition, an internally heated draw roll 2 positively driven at a peripheral speed several times that of the feed roll 1. A wedge (shown in cross-section at 8) whose length in a direction normal to the plane of the drawing is not less than the width of the film is arranged in the space between the rolls 1 and 2 on the side of the gap 4 between the rolls at which the film enters the gap to ensure that the layer of hot air 7 carried along on the surface of the roll 2 is directed towards the gap 4. Stretching takes place in this gap between the line 5 where the unstretched film travelling into the gap 4 leaves the feed roll 1 and the line 6 where the stretched film first contacts the roll 2. The lines 5 and 6 extend in a direction normal to the plane of the drawing. In an embodiment of the process of the invention using the above apparatus an unstretched film web consisting of the polycarbonate of 4,4- dihydroxydiphenyl-2,2-propane, the film in the unstretched state having a softening temperature of about 150‹ C., is delivered on to the feed roll 1 which is maintained at a surface temperature of about 130‹ C. The polycarbonate film travels through the gap 4 and passes over the draw roll 2 the surface temperature of which is maintained at about 210‹ C., i.e. well below the softening point of the stretched film which is about 240‹ C. The film in travelling through the stretching zone between the lines 5 and 6 is raised in temperature to the required stretching temperature of about 180‹ C. by the layer of hot air 7 carried into the gap 4.