Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-09-16
2003-11-25
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S062000, C349S110000, C349S114000
Reexamination Certificate
active
06654082
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display element applicable to a reflective type or a transflective type liquid crystal display, a method for producing the liquid crystal display element and a color display device.
2. Discussion of the Background
A liquid crystal display element has widely been used for a portable information device or the like because it is thin and light in weight. As such liquid crystal display element widely used, there are an active matrix liquid crystal display element using active elements such as thin-film transistors and a STN liquid crystal element as a simple matrix type liquid crystal display element which responds an effective value of voltage. Use of the active matrix liquid crystal element is currently in a main stream because it exhibits a high display performance. However, it is unsuitable for such a field of use that a variety of design or custom-made articles are required, because manufacturing steps are complicated and expensive and a plurality of masks are required for manufacturing a kind of display apparatus. Accordingly, the simple matrix type liquid crystal display device is often used in such field of use.
A liquid crystal display element assembled to an information system is often required to have a color display from the viewpoints that a display is easy to see and has a large amount of information to be displayed.
In order to realize a color display, a system in which a color filter is provided in a liquid crystal display cell is used. However, in the liquid crystal display element provided with a color filter, the transmittance of light is decreased due to the color filter, and when an additive color mixture method is used, it is necessary to divide a single pixel into three portions for three basic colors of red, green and blue (R, G, B) with the result that the numerical aperture decreases substantially.
For instance, the brightness of red in displaying red is expressed by (the transmittance of liquid crystal×the transmittance of a red color filter×numerical aperture/3). However, an obtainable value does not reach 3% of light entering into the liquid crystal cell. Therefore, a light source such as a backlight is provided at a position such as a rear face of the liquid crystal display element to form a transmission type liquid crystal display device. Further, for assurance of an attractive display in such construction, it is necessary to operate the light source all the time.
The characteristics required for the color display device used for a portable information device reside in the following two points: (a) a color display of multi-gray shades of almost the full colors can be provided regardless of a change of the lightness of the surroundings and (b) power consumption is low.
In the transmission type color liquid crystal display device used widely for a book type personal computer at the present time, the brightness of about 100 cd/cm
2
, which is an appropriate lightness in an ordinary office environment, is standard. However, the portable information device is nowadays used under various environments such as a large meeting room (which has a fixed illumination and a user's desire is not often satisfied), the outdoors, at night and so on.
On the other hand, since the visual performance of human is generally adaptable to an illuminance of outer light, there exists the optimum brightness of an object to be observed in response to the illuminance of an outer light.
For example, the illuminance of an outer light is about several ten luxes under a dark environment, and a human vision is adaptable to darkness. In this case, when the brightness of an object to be observed is too light, a stimulation to the optic nerve is strong and the observer feels fairly fatigue. Accordingly, the brightness of the backlight should be decreased to about several cd/m
2
-50 cd/m
2
. Further, under an environment of a high illuminance such as the outdoors in a fine weather, the illuminance of an outer light exceeds 20,000 luxes, and accordingly, a human vision is adaptable to lightness. In this case, when the brightness of an object to be observed is too dark, visibility to a display remarkably decreases. Therefore, the brightness of the backlight should be as high as about several hundred-1,000 cd/m
2
.
Accordingly, in order to allow the use of it in any environment, it is necessary to achieve the highest brightness of not less than several hundred cd/m
2
and to conduct a brightness control of 100:1 or more.
In conducting such brightness control, a large amount of consumption power and an accessory circuit are needed. In short, the transmission type color display device belonging to the conventional technique is not suitable for portable information devices from either the viewpoint of consumption power or the viewpoint of an increased number of elements for the accessory circuit.
On the other hand, since the portable information devices are generally of a type of battery-driven, there is a demand of lowering an amount of power to be consumed in order to prolong a driving time. Therefore, there is proposed, for the portable information devices, to use a reflective type color liquid crystal display device without using a backlight while an amount of power to be consumed can substantially be reduced.
In the reflective color liquid crystal display device, however, there is a problem that the brightness is very low because it does not have a backlight and both an incident light and a reflected light are passed through the color filter.
Namely, in the conventional reflective type color display device without having an auxiliary light source, although visibility to a display can sufficiently be assured under an environment of a high illuminance such as the outdoors in a fine weather, it is almost impossible to recognize a display under an environment of darkness. Accordingly, it is difficult to use the reflective type display device under such a change of environment.
Further, the transmission type liquid crystal display device generally uses a cold cathode ray tube as a backlight. Accordingly, the color filter is generally so designed as to utilize sufficiently light from the cold cathode ray tube. However, when light from a light source other than the cold cathode ray tube is passed through such color filter, an achromatic color can not be obtained at the time of mixing colors, and good color development cannot be obtained. For example, under a daylight condition, a color obtainable by the color filter at the time of mixing colors is yellowish green.
Further, JP-A-7-28010 and JP-A-8-179125 disclose a liquid crystal display element using a transflector.
However, the inventors of this application has revealed through their studies that even though the construction of the conventional transmission type display device is simply changed according to specifications for a transflective type, a sufficient performance of display can not be obtained.
It is an object of the present invention to provide a liquid crystal display element which can be used under various environments while a good color-developing performance is maintained, a method for producing the liquid crystal display element and a color display device.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a liquid crystal display element comprising a color filter having a plurality of colored portions each having a different spectral color and a reflector, wherein the color filter is so adapted that transmitted light from a standard C light source is substantially achromatic and the transmittance of visible light by the standard C light source is 30-65%.
Further, there is provided the above-mentioned liquid crystal display element wherein a colored portion having a spectral color of the color filter is formed to cover a pixel of a driving aperture, which corresponds to the colored portion having a spectral color of the color filter.
Further, there is provided a color display de
Hirai Yoshinori
Ozeki Masao
Sohda Yuji
Suzuki Toshihiko
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Optrex Corporation
Qi Mike
Ton Toan
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