Optical: systems and elements – Holographic system or element – Using a hologram as an optical element
Patent
1993-04-14
1994-08-09
Sikes, William L.
Optical: systems and elements
Holographic system or element
Using a hologram as an optical element
359 63, G02F 11335
Patent
active
053371747
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an optical compensator capable of providing a liquid crystal display device with improved display coloration and contrast ratio.
BACKGROUND ART
As a liquid crystal display device utilizing a supertwisted nematic structure, an STN liquid crystal display of the construction: first polarizer/driver liquid crystal cell/hue compensating liquid crystal cell/second polarizer system has been developed [Nikkei Microdevices, August 1987, pp. 36-38 and Nikkei Microdevices, October 1987, pp. 84-88].
The light incident on and passing through the first polarizer becomes linear polarized light which, in turn, is converted to elliptically polarized light by birefringence as it passes through the driver liquid crystal cell. The elliptic polarization rate and orientational angle involved are dependent on the wavelength. However, the light emerging from the driver liquid crystal cell is twisted in the reverse direction as it passes through the hue-compensating liquid crystal cell, so that the elliptically polarized light is reconverted to linearly polarized light (that is to say the phase difference is cancelled), which is taken out through the second polarizer. In this way, the wavelength dependence of transmitted light is eliminated and a substantially white-and-black display is obtained. Therefore, if necessary, a full-color display can be implemented by adding color filters.
The above STN liquid crystal display incorporating a driver liquid crystal cell and a hue compensating liquid crystal cell is thick and heavy and, as an additional disadvantage, costly to manufacture. There also is the problem that the display is too dark in the reflecting mode.
Therefore, to overcome these disadvantages, a Formulated Super-Twisted Nematic system (hereinafter referred to as FTN mode) incorporating an optical compensator comprising a monoaxially oriented polymer film laminated with an optically isotropic film on either side thereof in lieu of said hue compensating liquid crystal cell is attracting attention. The basic architecture of this FTN liquid crystal display is: polarizer/liquid crystal cell/optical compensator/polarizer.
Japanese Patent Application Kokai No. 64-519, as filed earlier by one of the inventors of the present invention, discloses that, as the monoaxially oriented film mentioned above, polyvinyl alcohol, polyester, polyetheramide, polyethylene, etc. can be employed.
Japanese Patent Application Kokai No. 1-118805 describes an optical compensator obtainable by orienting a film of polyvinyl alcohol or a derivative thereof in one direction, treating the oriented film with an aqueous boric acid-containing solution and laminating an optically non-oriented poller film on one or either side of said oriented film. The derivative of polyvinyl alcohol mentioned above means a polyvinylacetal such as polyvinylbutyral, polyvinylformal, etc.
Japanese Patent Application Kokai No. 1-118819 and Japanese Patent Application Kokai No. 1-124821 disclose the use of an optically compensating film comprising an oriented synthetic resin film or an optical compensator comprising said optically compensating film and an optically isotropic amorphous film laminated at least on one side thereof as one of the transparent electrode-supporting substrates of a liquid crystal cell. Japanese Patent Application Kokai No. 1-127329 discloses a laminate having an optical compensating function which is obtainable by laminating an optical compensator similar to the above with a release sheet through an adhesive layer. It is disclosed in these patent literature that polycarbonate, phenoxy resin, polyparabanic acid resin, fumaric acid resin, polyamino acid resin, polystyrene, polysulfone, polyether polysulfone, polyarylene ester, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinyl chloride, polymethyl methacrylate, polyester, cellulosic polymer, etc. can be employed. Incidentally, it is to be noted that these patent applications as well as Japanese Patent Application Kokai No. 2-158701 referred to
REFERENCES:
patent: 5061042 (1991-10-01), Nakamura et al.
patent: 5142393 (1992-08-01), Okumura et al.
Hashimoto Kenji
Ichikawa Rinjiro
Okumura Osamu
Wada Hiroshi
Wada Shinji
Fujimori Kogyo Co. Ltd.
Mai Huy
Seiko Epson Corporation
Sikes William L.
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