Patent GB-1285643-A (GB)
Title: Method and apparatus for the production of biaxially oriented polyamide film
IPC: B29C71/00
Filed: 1970-01-09
Abstract: 1285643 Polyamide films BADISCHE ANILIN- & SODA-FABRIK AG 9 Jan 1970 [10 Jan 1969] 1121/70 Heading B5B Biaxially oriented polyamide film is made by drawing non-oriented or only slightly oriented film successively in the machine direction on a roller-type drawing machine and the transverse direction, the substantially amorphous feed stock being heated to a temperature of from 70‹ to 150‹ C. before the initial draw in the machine direction, the preheating time being no longer than 30 seconds, and the film then being passed through a series of non-driven rollers, of diameter ranging from 40 mm. to 150 mm. and so spaced that the free path (L) of the film between successive rollers is less than 22 mm., only those rollers which assume a peripheral speed less than the take-off speed of the film (or said take-off speed less 10% of the maximum difference between feed-in and take-off speeds) being heated to a temperature from 120‹ to 160‹ C., the others being at a temperature below 80‹ C., the film being then passed through a series of driven rollers at a temperature below 80‹ C. and at a speed sufficient to stretch the film rapidly (in the free paths between the non-driven rollers) to from 2À5 to 4 times its original length, the resulting longitudinally stretched film being then drawn transversely to 3 to 6 times its original width at a drawing temperature of 165‹ to 205‹ C. and then cooled to below 80‹ C. whilst preventing the film shrinking transversely by more than 10%. The drawing time during drawing in the machine direction, that is the time in which a portion of the film is effectively drawn is preferably not more than 1À0 second. Drawing rollers maintained at the drawing temperature may number fewer than five and, in the extreme case, only one may be used. The transversely drawn film may be heat-set at a temperature between the final drawing temperature and the melting point of the polyamide before the film is cooled to below 80‹ C., whilst preventing the film shrinking transversely by more than 10%. In the apparatus of Fig. 2a, film 1 is conveyed by heated rollers 3 (driven at peripheral speed V 1 ), of pre-heating zone 2, to the non-driven heated rollers of the drawing zone 4, from which the film is conveyed by the cooled take-off rollers 5, driven at peripheral speed V 2 , thus drawing the film at a draw ratio of V 2  : V 1 . The film then passes either directly, or after an intermediate winding step on roller A, to a tenter where it is preheated, drawn transversely, heat-set, cooled, trimmed and wound in known manner. In the modified apparatus of Fig. 3, the driven rollers are shown chequered. Roller 24 is cooled and is horizontally displaced so that film 26 may be looped out of the train of drawing rollers at every other draw gap therein as desired, to be cooled and transported to the take-off rollers. Roller 25 may be a cooled pressure roller as shown, or may be an adjustable cooling roller with drive. In the example, a nylon 6 film is made having a tensile strength in the machine direction of over 2500 kg./cm.<SP>2</SP>, a shrinkage (15 mins. in hot air at 180‹ C.) of 1.5% in the machine direction and of 3À5% in the transverse direction, and a density of 1.145 g./cm.<SP>3</SP>.