| 摘要 |
PROBLEM TO BE SOLVED: To provide a base film for photographic films by using the polyethylene 2, 6-naphthalenedicarboxylate which is lessened in the occurrence of the defect in the flatness of the film after the film is taken up to a roll form and is subjected to a heat treatment as an essential component. SOLUTION: The polyethylene 2, 6-naphthalenedicarboxylate is used as the essential component. The biaxially stretched film is heat-treated at the temp. of glass transition temperature (Tg) to (Tg-40) deg.C of the film in the state of taking up the film on a winding core. The winding core to be used for the heat treatment at this time is formed of a winding core which consists of a material having a coefft. of thermal expansion of <=0.7×10<-5> / deg.C, thermal conductivity of 0.2 to 0.6kcal/mhr deg.C and density of >=1.47 to <2.0g/cm<3> and has an outside diameter of 100 to 400mm.
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