| 摘要 |
PROBLEM TO BE SOLVED: To prevent a sublimation of a dye from a laminated polyester film made of many layers and to improve executability by simultaneously satisfying specific conditions by the film. SOLUTION: After all layers are extruded by a co-extruding method for melt co-extruding from a mouth and then oriented, the extruded material is heat-set as needed to a film of three-layer structure as a laminated polyester film. The polyester film of the three-layer structure is made to simultaneously satisfy the formulae of CA/CB<=0.5, 0.02<=DA/DZ<=0.8, 1.0<=SMD<=2.5 and -1.0<=STD<=1.0, wherein CA is a dye concentration (%) in an outermost layer, CD is a dye concentration (%) in an intermediate layer, DA is a sum (μm) of a thickness of the outermost layer, DZ is a thickness (μm) of all the layers, SMD is a heat shrinkage factor (%) in a film longitudinal direction when heat treated at 140 deg.C for 5 min, and STD is a heat shrinkage factor (%) in a film lateral direction when heat treated at 140 deg.C for 5 min.
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