Liquid crystal cells – elements and systems – Particular structure – Interconnection of plural cells in series
Reexamination Certificate
2002-02-07
2004-02-24
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Interconnection of plural cells in series
C349S113000, C349S149000, C349S150000
Reexamination Certificate
active
06697131
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a reflection liquid crystal display (LCD) using cholesteric liquid crystal, chiral nematic liquid crystal or liquid crystal in which these liquid crystals are blended, or holographic polymer dispersed liquid crystal.
It is strongly desired that a liquid crystal display having less power consumption is developed as a liquid crystal display (LCD) that is used for a portable telephone and a portable information terminal, whose technology has been remarkably progressed. Therefore, a display panel of a reflection liquid crystal display not requiring any back light has been actively developed. A reflection liquid crystal display of a TN system or STN system in which two polarization plates are used has been employed for watches and electronic calculators since previously. Also, a reflection liquid crystal display of a TFT system has been developed, in which the STN system and TN system that has reduced the number of polarization plates to one by disposing a reflection electrode which suppresses optical absorption by polarization plates.
Further, an STN birefringence ECB system LCD for color display, etc., has been developed, which does not employ a color filter having large optical absorption. Still further, as those in which no polarization plate and no color filter are used, a liquid crystal display has been developed, in which a guest host (GH), a holographic polymer dispersed liquid crystal (HPDLC), cholesteric liquid crystal and chiral nematic liquid crystal are used.
A reflection liquid crystal display, in which cholesteric liquid crystal, chiral nematic liquid crystal, or blended liquid crystal of these types of liquid crystal, or holographic polymer dispersed liquid crystal is used, utilizes Bragg's reflection depending on a cyclic structure of a refractive index of liquid crystal layers.
Wavelength &lgr; of the above-described Bragg's reflection is expressed by:
&lgr;=
n·p
where n is a mean refractive index of a liquid crystal layer, and p is a cycle of a refractive index.
Therefore, it is possible to produce a color LCD by stacking liquid crystal display panels having three reflection colors of RGB.
Also, in the present specification, a section of liquid crystal corresponding to respective pixels is defined to be a “liquid crystal cell”, a liquid crystal portion that expresses a picture brought about by aggregation of pixels displayed in the corresponding liquid crystal cells is defined to be a “liquid crystal display panel” (including a transparent substrate which is an obvious structure), and those including the corresponding liquid crystal panel, its drive circuit, and its control circuit are defined to be a “liquid crystal display (LCD)”.
SUMMARY OF THE INVENTION
However, in order for the color LCD to use the above-described three liquid crystal display panels, production costs are made remarkably expensive. Recently, there is a use for a black and white display in an electronic book, etc. However, as regards a liquid crystal display panel that utilizes Bragg's reflection, it is based on a reflection display principle, in which display panels, respectively, reflecting light of wavelengths being in a relationship of two or more complementary colors are stacked to display in terms of black and white. Therefore, it is very difficult to display black and white by a single panel. As a trial, a liquid crystal display using the following liquid crystal is taken into consideration.
(1) Reflection wavelength band width &Dgr;&lgr; is expressed by
&Dgr;&lgr;=&Dgr;
n·p
where &Dgr;n is a difference in the refractive index, and p is a cycle of the refractive index.
Black and white display can be achieved by making the reflection wavelength band width large by using two or more liquid crystals whose refractive index difference &Dgr;n is increased. However, the display image becomes only a white reflection color, which is not satisfactory as a black and white display image.
(2) As regards cholesteric liquid crystal, chiral nematic liquid crystal or a mixture of these types of liquid crystal, polymer networks are formed in the liquid crystal, and helical axes of liquid crystal particles are disordered, whereby black and white display is achieved by widening the reflection wavelength band width. That is, there is a PSCT (Polymer Stabilized Cholesteric Texture).
But, in a liquid crystal display employing the liquid crystal referred to in (1) or (2) described above, it is very difficult to obtain a complete black and white display image. Also, in the three-layered type full color LCD, it is very expensive to obtain a complete black and white display image.
An example was reported, which showed a liquid crystal display capable of displaying four colors consisting of white, black, yellow and blue by stacking a liquid crystal display panel that reflects yellow and a liquid crystal display panel that reflects blue, which are in a relationship of complementary colors. However, since it becomes necessary to provide two liquid crystal display panels and a voltage drive circuit for the respective liquid crystals, the display becomes expensive in comparison with the number of colors that can be displayed.
An object of the present invention is to provide an inexpensive lamination type reflection liquid crystal display, which is obtained by stacking two liquid crystal display panels, and a method for producing the same.
The above-described object of the present invention can be solved by the following inventions (1), (2) and (3).
(1) A reflection liquid crystal display including two liquid crystal layers having selected reflection wavelengths differing from each other, and two pairs of liquid crystal display panels provided with a pair of transparent electrodes between which the respective liquid crystal layers are placed, and being obtained by stacking the two pairs of liquid crystal display panels; wherein voltage supply between a pair of electrodes of one liquid crystal display panel and voltage supply between a pair of electrodes of the other liquid crystal display panel are composed of a common voltage drive circuit.
It is preferable that the selected reflection wavelengths of the two liquid crystal layers in the reflection liquid crystal display according to the present invention are made in the relationship of complementary colors, and the color tone of the reflection light is made into black and white colors. In addition thereto, it is possible to obtain reflection light of a desirable color tone other than black and white by adequately selecting the selected reflection wavelengths of two liquid crystal layers.
Also, the liquid crystal layers can employ any one of cholesteric liquid crystal, chiral nematic liquid crystal, mixture of them and holographic polymer dispersion liquid crystal.
Chiral nematic liquid crystal may be independently employed as the above-described liquid crystal layer, or a mixture containing chiral nematic liquid crystal may be used. Also, a composite material including chiral nematic liquid crystal and other materials may be used as a liquid crystal layer. It is preferable that, as the chiral nematic liquid crystal, a compound showing a cholesteric phase as a single body, for example, a liquid crystal compound such as cholesteryl nanoate having an asymmetric center, etc., or that showing a cholesteric phase by blending a chiral agent to nematic liquid crystal, is used.
Also, a biphenyl-based, phenylcyclohexane-based, cyclohexyl cychlohexane-based, or pyrimidine-based liquid crystal compound may be independently employed, or nematic liquid crystal composed of a mixture of these liquid crystal compounds may be employed.
As the above-described chiral agent, a compound showing a cholesteric phase as a single body or an optically-activated organic compound showing a cholesteric phase by being blended with nematic liquid crystal although not showing any cholesteric phase as a single body, etc., may be used. As the optically-activated chiral agent, there is a compound simil
Okafuji Masaharu
Takami Manabu
Chowdhury Tarifur R.
Intellectual Property Law Group LLP
Jackson Juneko
Lee Otto O.
Nanox Corporation
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