PROCESS FOR PRODUCING BIAXIALLY ORIENTATED POLYESTER FILM

PURPOSE: A preparation method of a biaxially oriented polyester film is provided which improves uniformity in thickness and the uniformity of physical property in the thick direction. CONSTITUTION: A process for producing a biaxially oriented polyester film comprises the steps of melt-extruding a polyester resin and drawing an undrawn sheet in the longitudinal direction of a multistage fashion of two or more stages, wherein the drawing of the sheet in the longitudinal direction is carried out above 3.5 times as much as the total drawing ratio in a state of heating the sheet on a drawing roll by infrared heaters having a rated output power in the range of 5 to 15kW and a surface temperature of 500 to 1,000°C and drawn in the transverse direction. The method is suitable for manufacturing a polyester film used as a base film of electronic recording mediums such as floppy discs for videos, audios and computers.