| US 7,476,425 B2 | ||
| Wide-viewing angle compensation film and transmission type liquid-crystal display employing the same | ||
| Naoto Obara, Mie (Japan); and Shinsuke Toyomasu, Mie (Japan) | ||
| Assigned to Tosoh Corporation, Shunan-shi (Japan) | ||
| Filed on Mar. 21, 2006, as Appl. No. 11/277,102. | ||
| Claims priority of application No. 2005-088595 (JP), filed on Mar. 25, 2005. | ||
| Prior Publication US 2006/0216436 A1, Sep. 28, 2006 | ||
| Int. Cl. G02F 1/13363 (2006.01) | ||
| U.S. Cl. 428—1.31 [349/96; 349/118; 349/120] | 4 Claims |
| 1. 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 5×103−5×106, 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 5×103−5×106,
wherein said optical compensation film exhibits negative birefringence and has an in-plane retardation (Re1) 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 (Re2) 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:
Re1=(nx1−ny1)×d1 (1)
Nz=(nx1−nz1)/(nx1−ny1) (2)
wherein nx1, ny1, and nz1 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 d1 represents the thickness of the optical compensation film:
Re2=(nx2−ny2)×d2 (3)
Rth=((nx2+ny2)/2−nz2)×d2 (4)
wherein nx2, ny2 and nz2 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 d2 represents the thickness of the transparent protective film; and
wherein a relationship among the three-dimensional refractive indices of said optical compensation film satisfies nx1≧nz1>ny1.
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