POLYESTER FILM AND MANUFACTURING METHOD THEREOF

摘要

PURPOSE: A method for preparing a polyester film is provided to control a contraction ratio of a mechanical direction and width direction without degrading properties and optical characteristic of a film. CONSTITUTION: A method for preparing a polyester film with excellent heat resistance and dimensional stability comprises the steps of: (a) preparing an undrawn sheet by extruding and cooling a polyester resin; (b) orienting the sheet in a machinery direction; (c) after machinery orientation and orienting the sheet in a width direction; (d) heat-treating the oriented sheet; (e) reliving the sheet in a width direction and a machinery direction by a rate more than 1%.