POLYESTER FILM AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To obtain a polyester film low in heat shrinkage factor and capable of being widely put to practical use as a polyester film suitable for a magnetic recording medium, a printing ribbon, a condenser or packing. SOLUTION: A polyester film is produced by stretching an unstretched film based on polyethylene terephthalate in at least one of the longitudinal and lateral directions thereof and subsequently irradiating this film with UV rays in at least one direction of the thickness direction thereof to reduce the heat shrinkage factor of the film. Energy density at a time of the irradiation with UV rays is pref. 0.1-10 J/cm2.