Process for longitudinal stretching in the production of oriented polypropylene films

摘要

A process is claimed for the longitudinal orientation of thermoplastic film with at least one layer, in which the film is preheated in the low-speed part of the stretching apparatus to a temperature suitable for stretching and then transferred to a stretching zone (10). Special features are that (a) the low-speed part of the apparatus contains a driven roller (1) and the high-speed part contains a driven pair of rollers (2)/(3) with a gap (4) between (2) and (3), and (b) the film (9) is fed into gap (4) in such a way that it is gripped simultaneously or nearly so by the roller pair (2)/(3) at the contact points (5)/(6) and stretched between roller (1) and the couple (2)/(3). Also claimed is (i) an apparatus for this process, and (ii) a longitudinal stretching process in which part of the stretching force required for orientation is transmitted via both sides of the film.