Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-05-28
2001-05-29
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S241000, C359S237000
Reexamination Certificate
active
06239896
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an electrophoretic display device wherein colored electrophoretic particles or charged migrating particles are moved to effect a display, and a driving method therefor
In recent years, accompanying the progress of data processing apparatus, there has been an increasing demand for a display device requiring a small power consumption and a small thickness, and extensive study and development have been made on devices satisfying such a demand. Among these, a liquid crystal display device wherein an alignment of liquid crystal molecules is electrically controlled to change optical characteristics has been extensively developed and commercialized as a display device satisfying the demand described above.
However, such liquid crystal display devices are still accompanied with problems of visual load on human eyes, such as difficulty of recognizing characters on display depending on a viewing angle or due to reflection light, and flickering and low luminance of light sources. Accordingly, extensive study is still made for new-types of display devices causing less visual load on human eyes.
Reflection-type display devices are expected from the viewpoints of lower power consumption and less visual load on human eyes. As a type thereof, an electrophoretic display device has been proposed by Harold D. Lees, et al. (U.S. Pat. No. 3,612,758). Electrophoretic display devices are also disclosed in Japanese Laid-Open Patent Application (JP-A) 9-185087, JP-A 9-211499, and Japanese Patent Publication (JP-B) 6-52358.
A structure and an operation of an electrophoretic display device ares described with reference to
FIGS. 8A and 8B
. Referring to these figures, a display device
95
includes a dispersion layer comprising an insulating liquid
94
containing a colorant dissolved therein and charged electrophoretic or electrophoretically migrating particles
93
dispersed in the insulating liquid
94
, and a pair of oppositely disposed electrodes
91
and
92
sandwiching the dispersion layer. When a voltage is applied across the dispersion layer via the electrodes
91
and
92
, the colored electrophoretic particles
93
are attracted to an electrode of a polarity opposite to that of the charge of the particles
93
. A display is performed by a combination of the color of the electrophoretic particles
93
and the color of the insulating liquid
94
having a different color from the electrophoretic particles
93
due to the colorant dissolved therein.
More specifically, when the first electrode
91
is made a negative electrode and the second electrode
92
is made a positive electrode, positively charged colored electrophoretic particles
93
are moved or migrated and attached to the surface of the first electrode
91
disposed closer to a viewer, thereby displaying the color of the particles
93
(FIG.
8
B).
On the other hand, when the first electrode
91
is made a positive electrode and the second electrode
92
is made a negative electrode, the positively charged electrophoretic particles
93
are moved and attached to the surface of the second electrode farther from the viewer to display the color of colorant contained in the insulating layer
94
(FIG.
8
A).
Such a conventional electrophoretic display device as described with reference to
FIGS. 8A and 8B
, however, involves the following problems.
The colored electrophoretic particles
93
are attracted to an electrode by an electric field (or an electrostatic attractive force), so that when the voltage application to the electrodes is terminated, the electrophoretic particles are allowed to move, thus failing to exhibit a memory characteristic. Accordingly, In order to retain a display state, it is necessary to continually apply the voltage to the electrodes, thus requiring a substantial power consumption therefor.
Further, such a conventional electrophoretic display device fails to exhibit a clear threshold characteristic with respect to the movement of the electrophoretic particles
93
between the electrodes, which is required to effect a simple matrix drive display (as will be described with reference to
FIG. 7A
, etc. regarding an embodiment of the present invention).
It is essential that the insulating liquid
94
is colored or made opaque. Accordingly, it is difficult to compose the insulating liquid of a single component, so that some coloring particles have to be dispersed or some colorant has to be dissolved in the insulating liquid. Further, the reflectance of the display is liable to be lowered due to adsorption of the colorant dissolved in the insulating liquid onto the colored electrophoretic particles and intrusion of the colored insulating liquid between the electrode surface and the colored electrophoretic particles attached thereto, thus failing to provide a high contrast. Further, the presence of such colorant (particles) is liable to provide an unstable factor in electrophoresis, thus being liable to lower the performance, life and stability of the display device. Further, in the conventional display device, the number of displayable colors is limited to two, i.e., those of the colored electrophoretic particles and the insulating liquid, so that a multi-color display is difficult. Further, according to the conventional display device, a binary display is ordinarily performed, and so-called gradational display including a display of a halftone color is difficult.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems of the prior art, a principal object of the present invention is to provide an electrophoretic display device having a threshold characteristic and a memory characteristic.
According to the present invention, there is provided an electrophoretic display device, comprising: a first substrate and a second substrate disposed opposite to each other with a gap therebetween, a first electrode and a second electrode disposed at at least partially deviated positions on the first substrate, a transparent insulating liquid filling the gap between the first and second substrates, and colored electrophoretic particles carried in the insulating liquid so as to be movable between the first electrode and the second electrode, wherein
the first substrate has a magnetism, and the electrophoretic particles also have a magnetism.
According to the present invention, there is also provided a driving method, wherein the above-mentioned electrophoretic display device is driven by applying different level of voltages between the first electrode and the second electrode, so that the colored electrophoretic particles are moved between the first and second electrodes at a voltage exerting an electrostatic force larger than a magnetic Coulomb force acting between the electrophoretic particles and the first substrate, and the colored electrophoretic particles are retained on the first or second electrode at a voltage exerting an electrostatic force smaller than the magnetic Coulomb force acting between the electrophoretic particles and the first substrate.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
REFERENCES:
patent: Re. 28360 (1975-03-01), Evans et al.
patent: 3612758 (1971-10-01), Evans et al.
patent: 3670323 (1972-06-01), Sobel et al.
patent: 3909116 (1975-09-01), Kohashi
patent: 4126854 (1978-11-01), Sheridon
patent: 5966233 (1999-10-01), Fujiwara et al.
patent: 6-52358 (1994-07-01), None
patent: 9-185087 (1997-07-01), None
patent: 9-211499 (1997-08-01), None
Canon Kabushiki Kaisha
Dang Hung Xuan
Fitzpatrick ,Cella, Harper & Scinto
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