Liquid crystal cells – elements and systems – Cell containing liquid crystal of specific composition
Patent
1998-06-29
2000-03-21
Kelly, C. H.
Liquid crystal cells, elements and systems
Cell containing liquid crystal of specific composition
349123, 25229901, C09K 1952
Patent
active
060408901
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an electric optical liquid crystal system. In more detail, it relates to a novel electric optical system having a good high-speed response, a wide visual range and a high contrast, characterized in that outsides of transparent upper and lower substrates in a bend cell are placed cross-nicolly between at least one birefringent film and at least two polarized plates, wherein the said substrates facing each other have such a relationship that a pre-tilt direction of liquid crystal molecules in one substrate interface and a pre-tilt direction of liquid crystal molecules in the other substrate interface of the substrates are planar symmetrical positions against center planes of both substrates, optionally with an active switch element formed on either transparent substrate in matrix form.
BACKGROUND ART
A liquid crystal panel (hereinafter referred to .pi. cell) having liquid crystals filled between one pair of facing substrates wherein crystals orient in such a quasi-parallel way that a pre-tilt direction of both substrate molecules are planar symmetrical against the center plane between substrates has certain characteristics, namely a short ON-OFF time (hereinafter referred to a response time) and an eminently low visual dependency (Philip J. Bos et al, SID 83 DIGEST P. 30-31, 1983).
Furthermore, a flat liquid crystal image display panel can be obtained by switching selectively an active switching element formed on either transparent substrate in .pi. cell in matrix form (Toku-Kai-Sho 61-116329).
Also, in .pi. cell, an OFF state (a bend orientation) is quasi-stable and may shift to a more stable quasi-homogeneous state (a splay orientation) within a relaxation time of several seconds to several dozen seconds. In order to carry out switching an ON state (a vertical orientation) and an OFF state stably, it is necessary to put a certain bias voltage before a bend orientation of an OFF state shifts to a splay orientation. Concretely, it may be a periodical ON voltage or an irregular pulse which does not obstruct displaying (Toku-Kai-Sho 61-128227).
Furthermore, those with a more improved visual dependency obtained by placing .pi. cells and a birefringent film between crossnicols are known as OCB cells (Y. Yamaguchi et al., SID 93 DIGEST P. 227, 1993).
In OCB cells, there are used cells with twist angles between upper and lower substrates of 0.degree. (the above-mentioned.pi. cells), biaxial phase different plates and nematic liquid crystal compositions without addition of any chiral agent, which are very different from cells of conventional TN (twist nematic) and STN (supertwist nematic) modes. A characteristic of the OCB cells on driving is to drive liquid crystal molecules in cells in a bend oriented state. That is, it is realized to obtain a very wide visual angle and a very high contrast compared to cells of conventional TN (twist nematic) and STN (supertwist nematic) modes by combining bend oriented liquid crystals with biaxial phase different plates. Furthermore, it is also realized to obtain a very fast response time such as 1/20 to 1/500 compared to cells of conventional TN (twist nematic) and STN (supertwist nematic) modes by driving liquid crystals in a bend oriented state.
However, any combination of OCB cell and an active switching element is not known from the above-mentioned prior arts.
Particularly in the case of using OCB cells combined with active switching elements, it is not known that characteristic combinations of materials, for example, liquid crystal materials, oriented membranes etc., influence display qualities of the cells.
For example, liquid crystals used in the above-mentioned prior arts are ZLI-1132 made by Merck Co. consisting of cyanophenylcyclohexane derivatives and E-44 made by BDH Co. consisting of cyanobiphenyl derivatives, etc. Furthermore, there is no description about an oriented membrane.
In the case that a flat liquid crystal image display panel is prepared by switching selectively an active switching element in .pi. cell
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Isoyama Toyoshiro
Murata Shizuo
Sawada Shin-ichi
Chisso Corporation
Kelly C. H.
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