Permanently curved thermoplastic film - produced by passing through rollers system with specific temp. difference between its side

摘要

A permanent curvature is produced in thermoplastic film by passing it over a first guide roller, round a small dia. roller through >180 degrees, and over a second guide roller which is sepd. from the first by slightly more than double the film thickness. The small dia. roller lies between the other rollers and is sepd. from them by the thickness of the film. The film is heated whilst passing round the small roller with a difference of >10 degrees C between its side on the roller and its other hotter side, the former temp. being 15-70 degrees C and the latter 50 - 170 degrees C; the film is rapidly cooled to 30 degrees C on passing round the second guide roller.