Patent ID: 8308862

Claim:
An optical cellulose acylate film comprising a polymer component which is a cellulose acylate obtained by substituting hydroxyl groups of a cellulose by an acetyl group and an acyl group having 3 or more carbon atoms, wherein (i) a substitution degree A of the acetyl group and a substitution degree B of the acyl group having 3 or more carbon atoms satisfy the following formulae (I) and (II): 2.0 ≦A+B≦ 3.0 (I) 0<B (II) and (ii) an elastic modulus E(MD) in a casting direction and an elastic modulus E(TD) in a casting width direction satisfy the following formulae (III) and (IV): 1,500 MPa≦ E ( MD )≦3,400 Mpa (III) 1,200 MPa≦ E ( TD )≦3,400 Mpa (IV), wherein Re(λ) and Rth(λ) defined by the following formulae (IX) and (X) satisfy the following formulae (XI) and (XII): Re (λ)=( nx−ny )× d (IX) Rth (λ)={( nx+ny )/2 −nz}×d (X) 30 nm< Re (590) ≦200 nm (XI) 70 nm≦ Rth (590) ≦400 nm (XII) wherein Re(λ) is a front retardation value (unit: nm) at a wavelength of λ nm, Rth(λ) is a retardation value (unit: nm) in a film thickness direction at a wavelength of λ nm, nx is a refractive index in a slow axis direction in a film plane, ny is a refractive index in a fast axis direction in a film plane, nz is a refractive index in a film thickness direction, and d is a thickness of the film, and wherein Re (400) , Re (550) , Re (700) , Rth (400) , Rth (550) and Rth (700) of the film satisfy the following formulae (D1) and (E1): Re (400) <Re (550) <Re (700) (D1) Rth (400) >Rth (550) >Rth (700) (E1).