Liquid crystal cells – elements and systems – Particular structure – Particular illumination
Patent
1995-11-01
1998-11-17
Gross, Anita Pellman
Liquid crystal cells, elements and systems
Particular structure
Particular illumination
349 62, 349 57, 385146, G02F 11335, G02B 610
Patent
active
058384049
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a display device using a transparent-scattering type display element whose light scattering characteristics are changed in response to an external input.
BACKGROUND ART
Heretofore, a liquid crystal display element has been well known as a display element whose optical characteristics are changed in response to an external input. In particular, as a liquid crystal optical element in wide practical use, there is a twist nematic (TN) type liquid crystal optical element in which a pair of polarization films are attached to both sides of a liquid crystal display cell, which is used as a display element for a watch, a portable calculator, a word processor, a personal computer or the like.
However, the TN type liquid crystal optical element has such a drawback that when a high contrast ratio is to be obtained by increasing the polarizing property of the polarization films, light loss becomes large and a dark image is provided.
In recent years, use of a transparent-scattering type liquid crystal optical element has been noted. The transparent-scattering type liquid crystal optical element controls the switching between a transparent state and a scattering state by receiving an external input wherein an incident light is allowed to pass through without a substantial change of the direction of the incident light in the transparent state, while the incident light is scattered in the scattering state. Since the element does not need the polarization films, light loss is small and is suitable for providing a light image. Heretofore, a liquid crystal optical element of dynamic scattering mode (DSM) has been mainly used as the transparent-scattering type liquid crystal optical element. However, the element using a liquid crystal and cured material matrix composite has been recently proposed.
When the transparent-scattering type liquid crystal display element is used for a direct viewing type, a light absorption plane is often arranged at the back side of the transparent-scattering type display element. This is because an observer directly sees the light absorption plane in the transparent state, and accordingly, a dark image (black) is provided, while light is scattered in the scattering state, and accordingly, a light image (white) is provided.
In this case, however, the white image is very dark because when light is scattered in the transparent-scattering type display element, the quantity of light scattered forwardly with respect to the direction of light incidence is generally greater than the quantity of light scattered backwardly. The substantial portion of the forwardly scattered light is absorbed by the light absorption plane and is not returned to the observer. Accordingly, the quantity of light which the observer can observe when a white image is displayed is small.
In view of the above-mentioned problems, there have been proposed several methods wherein the observer takes as if the backwardly scattered light is increased by returning the forwardly scattered light caused by the transparent-scattering type display element to the same.
For instance, Japanese Unexamined Patent Publication No. 81797/1975, U.S. Pat. No. 476,662, Japanese Unexamined Patent Publication No. 333330/1993 or Japanese Unexamined Patent Publication No. 165330/1992 describes that a prism having a light absorption plane at a part of the surface is arranged at the back side of the transparent-scattering type display element.
FIG. 6 is a schematic cross-sectional view based on the description in U.S. Pat. No. 476,662. In the figure, an A face is a non-absorption face and a B face is an absorption face. Among the lights passed through the transparent-scattering type display element 31 from the side of an observer 33, light directing to the B face of the prism array 32 is absorbed by the B face. Further, among the lights directing to the A face of the prism array 32, light which satisfies the total reflection is absorbed by the B face after reflection. The other lights transmit through the A fa
REFERENCES:
patent: 3838909 (1974-10-01), Fitzgibbons
patent: 4726662 (1988-02-01), Cromack
patent: 5206746 (1993-04-01), Ooi et al.
patent: 5485354 (1996-01-01), Ciupke et al.
patent: 5600455 (1997-02-01), Ishikawa et al.
Hirai Yoshinori
Ooi Yoshiharu
Ozeki Masao
Asahi Glass Company Ltd.
Chowdhury Tarifur R.
Gross Anita Pellman
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