| 摘要 |
PROBLEM TO BE SOLVED: To provide a base material with a low phase difference and small dependability on an angle of visibility by specifying a beam transimissivity, a thickness, a phase difference, the dispersion of an optical axis and a phase difference when measured at an inclination to a direction perpendicular to the optical axis. SOLUTION: This optical film has a beam transmissitivity of 80% or more, a thickness of 10-1000 μm, a phase difference (R0 ) of 20 nm or less, the dispersion of an optical axis in a film plane being within ±30 deg. and the ratio (R45 /R0 ) of a phase difference (R45 ) to a phase difference (R0 ) being 1-3 when measured at 45 deg. to a direction perpendicular to the optical axis. A material used in manufacture is preferably amorphous polymeric material, with high heat resistance which is important to increase durability in film producing processes thereafter. The heat resistance of the polymeric material usually requires a glass transition temperature of 120 deg.C or more, preferably 140 deg.C or more or specially 180 deg.C or more. Desirably, polyrarylate or polycarbonate has aromatic groups in main rings. |
