Liquid crystal cells – elements and systems – Particular structure – Interconnection of plural cells in series
Reexamination Certificate
1998-11-16
2002-05-21
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Interconnection of plural cells in series
C349S078000, C349S081000, C349S094000, C349S176000
Reexamination Certificate
active
06392725
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to a storage medium which displays images (including information such as characters, graphics and data) and stores a display status thereof. This invention also relates to a method and apparatus for writing images to the storage medium, a method of forming the storage medium and a storage medium formed using the method.
2. Description of Related Art
Bulk consumption of paper around offices results in destruction of forest resources and environmental pollution resulting from refuse disposal and incineration. However, with widespread use of personal computers and the advent of our advanced information-intensive society brought about by the Internet and the like, the trend is moving toward more and more consumption of paper as so-called short-life documents intended for temporary browsing of electronic information, so that the advent of display storage media to replace paper is desired.
Paper has the following advantageous information display characteristics not found in conventional displays: 1) paper is capable of a bright and high-contrast reflective full-color display, is easy to read, and displays large quantities of information; 2) paper is structurally lightweight, thin, and flexible and therefore, is viewable in a comfortable position and under desirable brightness; 3) paper has memory capability, can display and store information without power, and provides a flicker-free and easy-on-the-eyes display; and 4) paper is inexpensive and facilitates an easy understanding of simultaneous displays of a plurality of sheets of paper, thereby allowing information comparison and browsing. These characteristics of paper, in turn, drive users to print information displayed on a display unit on paper before reading it.
Therefore, there is a need for display storage media to replace paper that have the above-mentioned paper-specific characteristics with the addition of a rewritable capability which would contribute to resource saving and reduction in refuse.
A display method, generally called NCAP, disclosed in Japanese Patent Publication No. Hei 3-52843, which uses droplets of nematic liquid crystal having positive dielectric anisotropy dispersed in a polymer matrix as shown in
FIG. 23
, has been proposed. With this method, the following two states are produced and a black and white monochrome display is obtained by switching between the states and providing a light absorption layer on a non-display surface: (1) an initial state as shown in FIG.
23
(A) in which liquid crystal directors orient in random directions under the influence of the surface of the polymer matrix and incident light is scattered due to mismatch of refractive indexes between the polymer matrix and the liquid crystals; and (2) a state as shown in FIG.
23
(B) in which the liquid crystal directors orient in a field direction by applying a voltage and incident light transmits due to match of refractive indexes between the polymer matrix and the liquid crystals.
However, this method has a drawback in that, when a white display is performed by back scattering resulting from mismatch of refractive indexes between the polymer matrix and the liquid crystals, a reflectance of only 10 to 15% is obtained because the difference of refractive indexes between the polymer and the liquid crystal is not so large and a sufficient scattering is not obtained. Thus, a bright and high-contrast display cannot be obtained.
To overcome this drawback, dyes have been added to the liquid crystal to improve brightness and contrast. However, this method has a serious drawback in that there is no memory capability in transparent state of a black display and no information can be displayed and saved without power.
On the other hand, as a method of performing a display with memory capability, for example, there is known a method by which texture change is caused by heat and a field using a smectic liquid crystal as shown on Page 456 of the Liquid Crystal Device Handbook (published by Nikkan Kogyo Shimbun).
According to this method, the following two states are produced and a black and white monochrome display is obtained by switching between the states and providing a light absorption layer on a non-display surface: (1) a state in which incident light is scattered by a focal conic texture obtained by cooling electric-field-free a smectic liquid crystal heated to an isotropic state as shown in the upper portion of
FIG. 24
as shown in FIG.
24
(A); and (2) a state in which incident light is transmitted by a homeotropic texture obtained by cooling a smectic liquid crystal heated to an isotropic state as shown in the upper portion of
FIG. 24
while applying a field as shown in FIG.
24
(B).
However, this method has a drawback in that, although information can be displayed and saved without power, a white display is performed by the disorder of the layer structure of a smectic liquid crystal from which sufficient back scattering is not obtained, and the reflectance of the white display is low like the above-mentioned NCAP. Thus, a bright and high-contrast display cannot be obtained.
According to a method by which a display is performed while switching between transparent state and scattering state, such as conventional examples shown in
FIG. 23
or
24
, a color display can be performed using an “array system” which arranges pixels producing different colors on a display surface, such as a method of combination with color filters, for example.
However, the array system has a drawback in that, since it requires exact alignment of pixel portions each producing a different color, and addressing portions writing data corresponding to each color, it is difficult to write an image to a display element from the outside. It is necessary to provide electrodes subjected to patterning and the like within the display element. Thus, the display element becomes costly.
On the other hand, there are proposed several color display methods using a “stack system” which arranges elements producing different colors in an observation direction. For example, according to a method disclosed in Japanese Published Unexamined Patent Application No. Hei 3-209425, as shown in
FIG. 25
, three display layers
38
A,
38
B, and
38
C selectively reflecting blue, green, and red, respectively, are stacked between a pair of substrates
32
and
33
such that droplets of cholesteric liquid crystal
42
having negative dielectric anisotropy are dispersed in a polymer matrix
41
within each display layer. A separation substrate
34
intervenes between the display layers
38
A and
38
B and a separation substrate
35
intervenes between the display layers
38
B and
38
C. A light absorption layer
36
is provided on a non-display surface and drive electrodes
37
subjected to patterning of each of the display layers
38
A,
38
B, and
38
C are connected to a drive circuit
50
comprising a drive power supply and a switch
52
.
According to this method, the following two states are produced and a color display is obtained by switching between the states: an initial state in which liquid crystal directors orient in random directions under the influence of the surface of the polymer matrix
41
and incident light almost transmits; and a state in which the helical axes of cholesteric liquid crystals
42
are oriented in a field direction by applying a voltage and a specified color in incident light is selectively reflected.
Further, “Reflective Cholesteric Liquid-Crystal Displays,” Information Display, pages 18-21, December 1996, describes the use of cholesteric liquid crystals having positive dielectric anisotropy in a color display element of the stack system, as shown in
FIG. 25
, is described.
However, since these methods require that the stacked display layers
38
A,
38
B, and
38
C be switched separately, it is impossible to write an image to the display element from the outside. Accordingly, it becomes necessary to provide drive electrodes
37
subjected to patterning for each of the display layers
38
A,
Arisawa Hiroshi
Harada Haruo
Hiji Naoki
Kakinuma Takeo
Kobayashi Hideo
Chondhury Tarifur R.
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
Sikes William L.
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