Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-11-09
2003-06-17
Dudek, James (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S074000
Reexamination Certificate
active
06580482
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-color display device used as a display panel of an electric apparatus.
2. Description of the Related Art
A transmission type liquid display device has widely been used as a flat panel display device, in which a liquid crystal element is formed to serve as an optical shutter for transmitting or intercepting an illumination light from a backlight arranged at the back side thereof to perform displaying. However, a transmission type liquid crystal device has a problem of using a great amount of consumptive electric power, being hard to see the display under a strong external light such as outdoors light.
In order to solve this problem, a reflective type liquid crystal device has been drawing attention which performs displaying utilizing reflection of an external light not utilizing the backlight. A cholesteric liquid crystal device has been known as one of a type thereof.
The cholesteric liquid crystal contains a rod like molecule and has a multi-layer formation. The molecular major axis is oriented in one direction in one layer, but its orientation direction is slightly twisted between the adjacent layers, to thereby form a helical structure as a whole. The period of the helix can be made to an optical wavelength order by depending upon a suitable selection of a material. In this case, the cholesteric liquid crystal selectively reflects a visible light. This phenomenon is known as selective reflection of the cholesteric liquid crystal.
The display device utilizing the selective reflection of the cholesteric liquid crystal has been known as a kind of the reflective-type display device. As shown in
FIG. 15
, this cholesteric liquid crystal display device has two transparent substrates
11
and
12
each provided with a transparent electrode
21
and
22
, between which a cholesteric liquid crystal
30
is injected to form a liquid crystal cell. Further, a black light-absorbing layer
41
is mounted at the backside of the substrate
12
that is opposite to the observation side (the side from which the external light is incident).
There are three kinds of the orientation state of the cholesteric liquid crystal
30
in the cell, i.e., a planar orientation shown in
FIG. 16A
, a focal conic orientation in
FIG. 16B and a
homeotropic orientation in FIG.
16
C. The planar orientation has a state in which the helical axis is oriented in approximately perpendicular to the substrate, whereby a light of a color in the wave band of a selective reflection is observed. The focal conic orientation has a state in which the helical axis is approximately parallel to the substrate, whereby the liquid crystal itself is achromatic but the light-absorbing layer
41
is observed, so that black appearance is obtained. The homeotropic orientation has a state in which the molecule of the liquid crystal is oriented in perpendicular to the substrate by disarranging the helical structure. Therefore, the liquid crystal itself is achromatic, so that the light-absorbing layer
41
is observed for obtaining black appearance.
A change-over of the above-mentioned orientation states can be electrically performed. Specifically, when a voltage is applied to the portion between the electrodes
21
and
22
in the planar orientation state, the state is changed into the focal conic orientation. The state is further changed into the homeotropic orientation upon increasing the voltage. Conversely, when the voltage is slowly reduced from the homeotropic orientation state, the focal conic orientation is attained, while the planar orientation is not obtained even if the voltage becomes zero. When the voltage is rapidly decreased from the homeotropic orientation state, the state becomes not the focal conic orientation but the planar orientation.
Accordingly, the cholesteric liquid crystal can be used as a display device by performing an electrical change-over between the planar orientation and the focal conic orientation or between the planar orientation and the homeotropic orientation. Further, in the cholesteric liquid crystal, both of the focal conic orientation state and the planar orientation state stably exist when the voltage is not applied, whereby display of memory utilizing its characteristics is possible.
Additionally, the orientation state can thermally be changed over. For example, the focal conic orientation is obtained when the cholesteric liquid crystal is once heated to a temperature of an isotropic phase and then cooled down until the liquid crystal phase is obtained. The use of this phenomenon is made possible to perform the change-over between the focal conic orientation and the planar orientation by both utilizing heat and electricity. It has been known that the orientation state can be changed over in response to the external stimulus such as a magnetic force, light, stress or the like, not being limited to an electricity and heat.
The orientation state of the cholesteric liquid crystal is greatly influenced with the interface which is in contact with the cholesteric liquid crystal. Therefore, a method has been known for improving the optical characteristics, electric characteristics, stability or the like of each orientation state by forming an orientation film between the cholesteric liquid crystal layer and the electrode or by dispersing a macromolecular material in the cholesteric liquid crystal.
As for such a multi-color display device using the cholesteric liquid crystal, the one for performing multi-color displaying disclosed in Japanese Unexamined Patent Publication No. Hei 8-304848, for example, is provided in which three cholesteric liquid crystal layers each selecting and reflecting blue, green and red respectively are laminated with one another and multi-color displaying is performed by an additive process of each layer.
FIG. 17
shows this conventional cholesteric liquid crystal multi-color display device. A blue cell
51
is formed such that a display layer
31
containing a cholesteric liquid crystal which reflects blue colored light is mounted between two transparent substrates
11
and
12
each provided with a transparent electrode
21
and
22
, while a green cell
53
is formed such that a display layer
33
containing a cholesteric liquid crystal which reflects green colored light is mounted between two transparent substrates
13
and
14
each provided with a transparent electrode
23
and
24
. Further, a red cell
55
is formed such that a display layer
35
containing a cholesteric liquid crystal which reflects red colored light is mounted between two transparent substrates
15
and
16
each provided with a transparent electrode
25
and
26
. A black light-absorbing layer
41
is formed at the back side of the cell which is most remote from the observation side, for example, the red cell
55
.
The blue, green and red mean herein a color light belonging to a wave band of 400 to 500 nm, 500 to 600 nm and 600 to 700 nm respectively. Concretely, the blue, green or red display can be obtained by bringing one of the blue display layer
31
, green display layer
33
and red display layer
35
into the selective reflection state and bringing the other two layers into the achromatic state. Moreover, the cyan, magenta or yellow display can be obtained by bringing two of the blue display layer
31
, green display layer
33
and red display layer
35
into the selective reflection state and bringing the other one layer in the achromatic state. Further, the white display can be obtained by bringing all of the blue display layer
31
, green display layer
33
and red display layer
35
in the selective reflection state, while the black display can be obtained by bringing all of the blue display layer
31
, green display layer
33
and red display layer
35
into the achromatic state.
In this case, the cholesteric liquid crystal having the same helix sense has been used for the cholesteric liquid crystal of each display layer
31
,
33
and
35
. The reason is as follows. The general method for ma
Hiji Naoki
Hikichi Takehito
Suzuki Tei-ichi
Yamamoto Shigeru
Dudek James
Fuji 'Xerox Co., Ltd.
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