Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Patent
1997-02-06
1999-09-14
Nguyen, Tiep H.
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
349 76, 349102, G02F 11347, G02F 11335
Patent
active
059530901
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a reflection type color liquid crystal display apparatus suitable for displaying an achromatic color by using a liquid crystal display element provided with a single polarizing plate and capable of displaying each color of red, blue and green.
BACKGROUND TECHNIQUE
There has been known a super-twisted element for a method of obtaining a high density dot matrix display by increasing a twist angle of liquid crystal molecules between a pair of electrodes to thereby cause a sharp change of voltage-transmittance characteristics (T. J. Scheffer and J. Nehring, Appl. Phycs. Lett. 45(10)1021-1023(1984).
In the conventional method, however, the product .DELTA.n.multidot.d of the refractive index .DELTA.n of liquid crystal in a liquid crystal display element used and the thickness d of a liquid crystal layer was substantially in a range of 0.8 .mu.m to 1.2 .mu.m (Japanese Unexamined Patent Publication No. 10720/1985 which is referred to as conventional technique 1). According to the conventional technique, an excellent contrast could be obtained only by a specified combination of colors such as yellowish green and dark blue, bluish purple and pale yellow and so on.
Thus, in the conventional technique using STN liquid crystal display element, a monochrome display could not be effected.
In order to improve the conventional technique, there was proposed a liquid crystal display apparatus capable of displaying a monochrome display and having a high contrast ratio wherein two liquid crystal cells of different helical structures are placed one on another; a voltage is applied to either cell and the other is merely used as an optically compensating plate (Report of Television Association 11 (27), p. 79 (1987) by Okumura et al.).
Also, there was proposed a method of providing a monochrome display by arranging a birefringent plate between the liquid crystal layer and a polarizing plate. Conventionally, a color liquid crystal display apparatus used for OA machines such as personal computers comprised the above-mentioned liquid crystal display element capable of effecting a monochrome display and color filters.
However, the color filters are expensive and have extremely low efficiency of utilization of light since a display is effected with three picture elements of red, blue and green. For instance, three picture elements of red, blue and green are used for displaying white, and even when the three picture elements are turned on, the brightness is 1/3 and accordingly, a bright display can not be obtained. Several techniques have been proposed for color display apparatuses providing a bright display without having color filters. For instance, an electrically controlled birefringence (ECB) effect type liquid crystal display apparatus is known. In this apparatus, when gradation voltages (e.g., voltages for 8 gradations) are applied to a pixel, the orientation of liquid crystal molecules is changed depending on gradation voltages applied whereby .DELTA.n.multidot.d of the liquid crystal cells is changed. And various colors caused by the effect of the birefringence in the liquid crystal cell are used.
In such ECB effect type liquid crystal display apparatus, however, since liquid crystal does not have a twisted structure, a state of liquid crystal to be changed depending on an applied voltage was small, and a display by multiplex driving could not be obtained.
Japanese Unexamined Patent Publication No. 118516/1990 (conventional technique 2) discloses that various colors can be displayed by changing a voltage applied to a liquid crystal cell including twisted liquid crystal molecules. In this conventional technique 2, however, there is a problem that colors which can be developed are yellow, red, purple, bluish purple, bluish green and green, and a display of achromatic color such as black or white is impossible, because it has been known that the visibility in usually used displays is considerably reduced if a display of black or white is not used.
In a display, the background po
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Mori Haruki
Ozeki Masao
Shidoji Eiji
Suzuki Toshihiko
Asahi Glass Company Ltd.
Nguyen Tiep H.
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