Process for the preparation of thermoplastic resin film

Abstract

A process for preparing a biaxially oriented thermoplastic resin film which comprises: extending a thermoplastic resin sheet in a longitudinal and a transverse directions to form a film thereof, and heat treating the film under a temperature gradient descending from both edges to the center of the film along the transverse direction within a zone defined by the following formula (1) by employing a heater which is located over the film with an angle .theta. of the following formula (3) from said both edges to the center of the film to produce a thermoplastic resin film having uniform physical end chemical properties in the transverse direction: 0.25.ltoreq.L.sub.1 /W.ltoreq.0.9 (1) tan.theta.=W/2L.sub.1 (3) wherein: L.sub.1 is the distance from the end point of the transverse extending to the end point of the heat treating; and W is the total width of the film.

Dependencies are inferred from the claim text.