Process for the manufacture of flat thermoplastic films having improved dimensional stability

摘要

1. Process for the production of biaxially stretched flat sheets of a thermoplastic polymer, which have an improved dimensional stability, by extruding the thermoplastic polymer from a slot die, cooling it to form a pre-film, heating the pre-film to the respective stretching temperature and stretching it, stepwise or simultaneously, in the orthogonal directions, then heat-setting the stretched pre-film, cooling it and winding it up, if required, wherein the film is, exclusively during cooling after heat-setting, convergently guided or allowed to converge freely in the transverse direction and, preferably also in the longitudinal direction, the speed of the film is reduced in comparison to the film speed in the heat-setting zone.