POLYESTER FILM AND LAMINATE USING SAME

摘要

Provided is a polyester film, which is suitable for use in battery packages, particularly for use in deep drawn packages of lithium ion secondary batteries that comprise an electrolyte (in a solid state or in a liquid state), and which is also suitable for use in packages of pharmaceutical products that have various shapes. The polyester film is characterized in that the stresses at 5% elongation (F5 values) and the stresses at 10% elongation (F10 values) of the film in the machine direction and in the transverse direction at 25°C respectively satisfy the following formulae (I) and (II). 1.5 = F10MD/F5MD = 1 (I) 1.5 = F10TD/F5TD = 1 (II)