Process for preparing stretched film and device for preparing the film

Abstract From the Canadian patent

A process and device for preparing a stretched film by passing a tubular thermoplastic film into pairs of nip rolls having different peripheral speed and by inflating an obtained bubble with internal pressure under heating, wherein the pairs of nip rolls comprise at least three pairs of nip rolls designated with R1 R2 and R3, respectively, pressurized air is admitted into the stretched bubble situated between the rolls R1 and R2 through a slit-like air injecting nozzle provided in a gap between the pair of rolls of R2, and the bubble formed by the supplied pressurized air is inflated and stretched under heating. In this stage if desired, the, amount of injected pressurized air is controlled …