| 摘要 |
PURPOSE:To provide the titled film with low molecular weight substances little precipitating on the surface thereof by satisfying a specific relationship between the density of the film thermally treated for film formation and the index of refraction vertical to the film plane. CONSTITUTION:In a biaxially oriented film of polyethylene terephthalate, the density rho(g/cm<2>) of the film thermally treated for film formation and the index of refraction (n) measured by sodium D line vertical to the film plane satisfies the formula. The index of refraction (n) shall be 1.491 or less, preferably 1.485 or less and the density rho is 1.390g/cm<2> or more, preferably 1.397-1.412g/cm<2>. This provide a property of causing none of low molecular weight substance to move and precipitate on the surface of the film in substance though existing therein. |
