| 摘要 |
PROBLEM TO BE SOLVED: To provide a biaxially oriented film achieving reduction in the film thickness while ensuring optical characteristics, heat resistance and mechanical characteristics as an optical film.SOLUTION: The biaxially oriented film comprises a thermoplastic resin containing an amorphous vinyl polymer having a cyclic structure in the main chain, and has a thickness of 35 μm or less. In the thermoplastic resin, a molecular weight Mebetween entanglement points represented by formula (A): Me=3cRT/E'is 10000 or more in a rubber-like flat region of a dynamic viscoelastic spectrum; and a temperature range, where an entanglement number N represented by formula (B): N=(MwE')/(3cRT) is 10 or more and 500 or less, is 25°C or higher. In the above formulae, c represents a density (at 25°C) of the resin; R is a gas constant; T represents a temperature of the resin; E' represents a storage modulus of the resin; Trepresents a temperature at the meddle point in the rubber-like flat region in the resin; E'represents a storage modulus of the resin at temperature T; and Mw represents a weight average molecular weight of the resin. |
