Process for producing biaxially oriented polyester film

摘要

A process produces polyester film which is effectively reduced in the disadvantageous lengthwise and widthwise heat shrinkages inherent in biaxially oriented film and which is excellent in flatness and mechanical characteristics. More specifically, process produces biaxially oriented polyester film by subjecting a biaxially oriented polyester film which has been drawn in the lengthwise and widthwise directions and heat-treated to widthwise relaxation and lengthwise relaxation by a method of shortening the clip intervals, wherein the biaxially oriented polyester film is held under stretching between the widthwise relaxation step and the lengthwise relaxation step.