Patent ID: 8632863

Claim:
A polymer film comprising a cellulose acylate which is a protecting film for a polarizing plate and that has: a ratio R (VT/VM) of a sound velocity in a transverse direction VT to a sound velocity in a machine direction VM of from 1.05 to 1.50; a tensile modulus in a transverse direction of from 453 to 600 kgf/mm 2 (4.44 GPa to 5.88 GPa), a tensile modulus in the machine direction of from 230 to 480 kgf/mm 2 (2.25 GPa to 4.70 GPa); a ratio of a tensile modulus in a transverse direction to a tensile modulus in a machine direction of from 1.15 to 1.22; an in-plane retardation Re(λ) and a thickness-direction retardation Rth(λ) satisfying formula (I): 0 ≦Re (630)≦10, and | Rth (630)|≦25 (I) wherein Re(λ) represents an in-plane retardation at a wavelength of λ (nm); and Rth(λ) represents a thickness-direction retardation at a wavelength of λ (nm); and an in-plane retardation Re(λ) and a thickness-direction retardation Rth(λ) satisfying formula (II): | Re (400)− Re (700)|≦10, and | Rth (400)− Rth (700)|≦14; (II) wherein Re(λ) represents an in-plane retardation at a wavelength of λ (nm); and Rth(λ) represents a thickness-direction retardation at a wavelength of λ (nm), and wherein an acyl substituent in the cellulose acylate is substantially an acetyl group alone, and a total degree of substitution thereof is from 2.80 to 2.99.