| abstract |
The present invention provides an optical film and a polarizing plate that are excellent in the expression of retardation in the front and in the film thickness direction and that have little fluctuation in the retardation value due to environmental changes such as humidity. A film is substantially composed of cellulose acylate in which a hydroxyl group of cellulose is substituted with an acetyl group and an acyl group having 3 or more carbon atoms, and the degree of substitution A of the acetyl group and the number of carbon atoms is 3 or more. The substitution degree B of the acyl group satisfies the formulas (I) and (II), the elastic modulus E (MD) in the casting direction, and the elastic modulus E (TD) in the casting width direction (vertical casting direction) An optical cellulose acylate film satisfying formulas (III) and (IV), a polarizing plate and a liquid crystal display device using the film. Formula (I): 2.0 ≦ A + B ≦ 3.0, Formula (II): 0 <B Formula (III): 1500 MPa ≦ E (MD) ≦ 3400 MPa Formula (IV): 1200 MPa ≦ E (TD) ≦ 3400 MPa [Selection figure] None |