Optical film, optical member and optical element

Details Optical film, optical member and optical element Optical film, optical member and optical element

2000-02-07

2002-03-26

Thomas, Alexander S. (Department: 1772)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

With viewing layer of specified composition

C428S001300

Reexamination Certificate

active

06361838

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an optical film which has excellent anisotropy in the scattering of linearly polarized light and excellent thermal stability and is suitable for use in improving the perceptibility, brightness, durability and other performances of liquid crystal displays and the like. The invention further relates to an optical member and optical element, using the optical film.
BACKGROUND OF THE INVENTION
Conventional optical films which comprise a matrix and dispersedly contained therein regions having anisotropy in refractive index and are anisotropic with respect to the scattering of linearly polarized light include a film comprising a combination of a thermoplastic resin and a low molecular weight liquid crystal, a film comprising a combination of a low molecular weight liquid crystal and a photocrosslinkable low molecular weight liquid crystal, a film comprising a combination of a polyester and either an acrylic resin or polystyrene, and a film comprising a combination of poly(vinyl alcohol) and a low molecular weight liquid crystal (see U.S. Pat. No. 2,123,901, WO 87/01822, EP 0506176, WO 97/32224, WO 97/41484, and JP-A-9-274108). (The term “JP-A” as used herein means an “unexamined published Japanese patent application”.)
The above optical films are intended to, for example, improve the perceptibility, brightness and other performances of liquid crystal displays or the like based on their polarizing/separating function and light-diffusing function both attributable to their property of anisotropically scattering linearly polarized light. However, the conventional optical films have problems that production thereof is troublesome and they are insufficient in stability required for practical use, such as heat resistance.
SUMMARY OF THE INVENTION
One object of the invention is to provide a practical optical film which has excellent anisotropy in the scattering of linearly polarized light, can be easily produced and has excellent thermal stability.
Another object of the invention is to provide an optical member using the optical film.
Further object of the invention is to provide an optical element using the optical film.
The optical film according to the present invention comprises an optically isotropic resin film and birefringent minute regions dispersedly contained therein, wherein the minute regions comprise a thermoplastic resin having a glass transition temperature of 50° C. or higher and showing a nematic liquid crystal phase in a range of temperatures lower than the glass transition temperature of the resin constituting the resin film, and the difference in refractive index between the resin film and the minute regions in a direction perpendicular to the axis direction in which a linearly polarized light has a maximum transmittance, &Dgr;n
1
, is 0.03 or larger and that in the maximum-transmittance axis direction, &Dgr;n
2
, is 50% or smaller of the &Dgr;n
1
.
The optical member according to the present invention comprises two or more layers of the optical film, which are superposed such that the &Dgr;n
1
directions for any of the layers are parallel to those for the adjacent layers.
The optical element according to the present invention comprises a multilayer structure which comprises at least one of a polarizing film and a retardation film and one or more layers of the optical film.


REFERENCES:
patent: 4688900 (1987-08-01), Doane et al.
patent: 5583673 (1996-12-01), Onishi et al.
patent: 5677024 (1997-10-01), Abe et al.

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