To enhance permanent deformation resistance in use under a high temperature by using a biaxially oriented film whose main component is polyethylene-2,6-naphthalene dicarboxylate which has an endothermic peak in the specified temperature range as determined with a differential scanning calorimeter, and has an endothermic energy of the specified value or more.
A film whose main component is polyethylene-2,6-naphthalene dicarboxylate having a glass transition point higher than that of polyethylene terephthalate is used, and a special heat treatment is conducted. Specifically, a biaxially oriented film whose main component is polyethylene-2,6-naphthalene dicarboxylate which has an endothermic peak in the range of 110-160°C as determined with a differential scanning calorimeter(DSC) with an endothermic energy of 0.4 mJ/mg or more is used and heat-treated at 150°C for 30 minutes, and heat contraction ratio in the longitudinal and lateral directions is controlled to 1.2% or less.
WATANABE MASAYA
KAWAI SHINICHI
SUZUKI KENJI
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