PURPOSE: To obtain a polyester film suppressed in light piping properties for a photosensitive material by a method wherein a refractive index of an outermost polyester film layer in a thick direction is determined to be larger than that of an adjacent inner polyester film layer in a thick direction.
CONSTITUTION: The use of a high-refractive polymer or a polymer copolymerized with a high-refractive component or the control of the orientation of a polymer at the time of film forming is preferably used as a method for increasing a refractive index of a polyester in a thick direction. As a high- refractive polymer to be laminated on a polyethylene terephthalate having a refractive index of approximately 1.58, a poly-1,4-cyclohexanedimethylene terephthalate having a refractive index of 1.60 is exemplified, and a polymer having a ring structure, a halogen atom or a bulky group in a molecular is preferably used.
KUROME TAIICHI
TSUNASHIMA KENJI
