Patent ID: 7476425

Claim:
A wide-viewing angle compensation film, comprising: (i) an optical compensation film which comprises (a) 20-95% by weight an N-phenylmaleimide/isobutene copolymer (a) which has a weight-average molecular weight as calculated for standard-polystyrene of 5×10 3 −5×10 6 , and (b) 80-5% by weight an acrylonitrile/styrene copolymer in which a proportion of acrylonitrile residual units to styrene residue units is from 20:80 to 50:50 (by weight) and which has a weight-average molecular weight as calculated for standard polystyrene of 5×10 3 −5×10 6 , wherein said optical compensation film exhibits negative birefringence and has an in-plane retardation (Re 1 ) as represented by the following equation (1) of 60-220 nm and an orientation parameter (Nz) as represented by the following equation (2) in the range of 0±0.05 and has a glass transition temperature of 130° C. or higher; and (ii) a polarizing plate which comprises a polarizer and, stacked on both sides thereof, a transparent protective film comprising triacetvl cellulose and satisfying the requirements that an in-plane retardation (Re 2 ) as represented by the following equation (3) is 10 nm or less and an out-of-plane retardation (Rth) as represented by the following equation (4) of 40-100 nm so that the slow axis of the optical compensation film showing the negative birefringence is perpendicular or parallel to the absorption axis of the polarizing plate: Re 1=( nx 1− ny 1)× d 1 (1) Nz =( nx 1− nz 1)/( nx 1− ny 1) (2) wherein nx 1 , ny 1 , and nz 1 respectively represent the x-axis-direction refractive index, y-axis-direction refractive index, and z-axis-direction refractive index of the optical compensation film, provided that the x axis is an in-plane direction of the film parallel to the slow axis of the film, the y axis is an in-plane direction of the film perpendicular to the x axis and the z axis is an out-of-plane direction of the film perpendicular to the x axis; and d 1 represents the thickness of the optical compensation film: Re 2=( nx 2− ny 2)× d 2 (3) Rth =(( nx 2+ ny 2)/2− nz 2)× d 2 (4) wherein nx 2 , ny 2 and nz 2 respectively represent the x-axis-direction refractive index, y-axis-direction refractive index and z-axis-direction refractive index of the transparent protective film, provided that the x axis is an in-plane direction of the film parallel to the slow axis of the film, the y axis is an in-plane direction of the film perpendicular to the x axis and the z axis is an out-of-plane direction of the film perpendicular to the x axis; and d 2 represents the thickness of the transparent protective film; and wherein a relationship among the three-dimensional refractive indices of said optical compensation film satisfies nx 1 ≧nz 1 >ny 1 .