| 摘要 |
PURPOSE:To obtain a video tape which is thin and has excellent runnability, etc. by providing a magnetic layer on a polyester film which contains a specific repeated unit at specific mol% or above and of which the refractive index in the thickness direction, the difference in the refractive index in the longitudinal and transverse directions, thickness and density are within a specific range. CONSTITUTION:The polyester which contains >=50mol% the repeated unit expressed by the formula, particularly the unit having Cl in the ortho place with respect to O adjacent to an aromatic ring and the balance having terephthalic acid, naphthalene-2,6-dicarboxylic acid, bis alpha,beta-(phenoxy) ethane 4,4-dicarboxylic acid, etc., or a compolymer component of diol such as propylene glycol is biaxially oriented to manufacture a substrate film for a video tape of which the refractive index in the thickness direction ranges 1.50-1.57, the difference in the refractive index in the longitudinal and transverse directions -0.18-+0.18, the density 1.45-1.50g/cm<3> and the thickness 2-12mu. A thin magnetic metallic film is formed on the substrate. The video tape having excellent runnability for 1.0- 12.0m/sec relative speed of a head is thus obtd.
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