| 摘要 |
PROBLEM TO BE SOLVED: To improve slit property by constituting a biaxially orientated film of copolymerized polyethylene-2,6-naphthalate where spcified quantity of an isophthalic acid component is copolymerized and mixing the specified quantity of porous silica fine grains to a catalyst through the use of the specified quantity of metallic compound. SOLUTION: A biaxially orientated polyester film for capacitor contains 0.1 to 2 wt.% of porous silica fine grains whose average grain size is 0.5 to 5μm and contains 2,6-naphthalene dicarboxylic acid, ethylene glycol and 0.5 to 8 mol% of isophthalic acid component. In the biaxially orientated film of copolymerized polyethylene 2,6-naphthalate, the content of a diethylene glycol component is not more than 3 mol%. Mn compound used as reactive catalyst, Sb compound and P component used as stabilizer are contained by quantity satisfying formulas (1), (2) and (3). Alkali metal is set to be not more than 10 ppm, a planar orientation coefficient to be 0.230 to 0.270 and density to be not less than 1.350 g/cm3.
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