BIAXIALLY ORIENTED POLYESTER FILM HAVING IMPROVED ISOTROPIC PROPERTY OF HEAT SHRINKAGE AND PREPARATION THEREOF

摘要

The present invention relates to a biaxially oriented polyester film with improved heat shrink isotropy, wherein both longitudinal heat shrinkage (S _MD ) and lateral heat shrinkage (S _TD ) when heated at 230 ° C. for 5 minutes without load. The heat treatment film according to the invention, characterized in that the range of 0.1 to 1%, and the heat shrink isotropic index (S _I = S _MD / S _TD ) is in the range of 0.5 to 2 by heat treatment in a heating furnace provided with a series of nip rolls It can be manufactured, and excellent in heat resistance, dimensional stability and smoothness, and can be usefully used for electrical and electronic materials or other industrial films.