Electrophoresis display

Details Electrophoresis display Electrophoresis display

2002-03-21

2004-09-28

Nguyen, Dung T. (Department: 2871)

Liquid crystal cells, elements and systems

Particular structure

Having significant detail of cell structure only

C349S089000, C349S165000

Reexamination Certificate

active

06798470

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. P2001-81595, filed on Mar. 21, 2001; the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophoresis display.
The invention is based on the guest-host effect which is realized by the switching of a dichroic coloring matter dissolved in a liquid crystal on applying voltage, and on the electrophoresis phenomenon of electrophoretic fine particles dispersed in a dispersion medium.
2. Discussion of the Background
The electric field inductive pigments of electrophorectic type used in the electrophoresis display at present are roughly classified in two types.
One of them is the type
1
shown in FIG.
7
A. This type of pigment comprises microcapsules which enclose a coloring solvent
12
. The coloring solvent
12
contains charged fine titania particles
11
dispersed therein. By using the electric field inductive pigment of this type, two colors, i.e., the white color of the fine titania particles
11
and the color of the solvent, can be displayed.
The other type of the electric field inductive pigment is the type
2
shown in FIG.
7
B. This type contains a transparent solvent
22
enclosed in the microcapsules. Two types of charged fine particles
21
a
and
21
b
differing in charge sign and in color are dispersed in the transparent solvent
22
. For instance, white colored positive charged fine particles
21
a
and black colored negative charged fine particles
21
b
are used. When negative voltage is applied to the upper side of the drawing, the white colored charged fine particles
21
a
concentrate to the upper side as shown in FIG.
7
B. On the other hand, when a positive voltage is applied to the upper side, the black colored charged fine particles
21
b
concentrate to the upper side. That is, the type of fine particles appearing on the surface can be selected by controlling the direction of the electric field applied to the microcapsule, and the dichroic display is thereby realized.
The following literatures describe the above.
[1] B. Comiskey, J. D. Albert and J. Jacobson, Digest of SID97, p75.
[2] P. Drzaic, B. Comiskey, J. D. Albert, L. Zhang, A. Loxley and R. Feeney, Digest of SID99, p1131.
[3] Barrett Comiskey, J. D. Albert, Hidekazu Yoshizawa and Joseph Jacobson, Nature, 394, p253 (1998).
Although a display using the electric field inductive pigment above is advantageous in that they yield high contrast, it suffers a problem that there is difficulty in providing color display.
More specifically, in case of an electric field inductive pigment of type
1
, the display is provided in two types, i.e., a white display using the scattering of fine titania particles
11
and a color display using the color of the dispersion medium
12
. Hence, a color filter is necessary to realize a color display. In case of an electric field inductive pigment of type
2
, the display is limited to two colors depending on the fine electrophoretic particles
21
a
and
21
b
. Hence, a color filter is indispensable in this case again.
FIG. 8
shows the method for realizing a color display by applying a color filter together with the electric field inductive pigment. In this case, the microcapsules, which contain a black colored solvent
12
having the white colored charged fine particles
11
dispersed therein, are densely arranged on the substrate. Red, green, and blue color filters are provided aligned to the position of each of the microcapsules. In case of realizing a red display, for instance, the green and the blue pixels are set in the light absorbing state (black display), while the red pixels alone are set in the light reflecting state. The intensity of the reflection light is reduced to about one third due to the absorption of the color filter
13
, and, the resulting intensity is further reduced to about one third because the green and blue pixels turn to the light absorption state. Hence, the resulting optical efficiency becomes as low as about {fraction (1/9)} (⅓×⅓={fraction (1/9)}).
Further, in case of realizing a white color display, the red, green, and blue pixels all turn to a light reflecting state, but due to the optical absorption of the color filter, the resulting display is reduced to about ⅓ of the incident light intensity despite the reflectance is at the maximum.
Accordingly, it is presumed that only a dark display is realized by the color filter type. Since an increase in optical transmittance of the color filter is in trade off with the improvement in color purity of the display color, the range of color reproduction decreases in an attempt to improve the transmittance of the color display by increasing the optical efficiency.
On the other hand, there is proposed a method of coloring the fine particles themselves in the three color primaries. More specifically, as shown in
FIG. 9
, this method comprises coloring the electrophoretic fine particles
31
, and pattern printing the color region.
In accordance with the method, a white display is realized by additive color mixture of red, green, blue colors, but it is a dark display with an optical efficiency of about ⅓.
Furthermore, as shown in
FIG. 10
, there is a method of realizing color display by using a colored solvent. This method comprises coloring the dispersion medium of the white colored electrophoretic fine particles
11
into red
41
, green
42
, and blue
43
colors. For instance, in case of red display, the red microcapsules are set to the light absorbing state, while the green and blue microcapsules are set to the light reflecting state. Although a bright color display can be obtained in this case, the display results in an unclear pale color display. A high reflectivity is obtained in white display, and, in the black display, an additive color mixture state of red, green, and blue is realized with high reflectivity and low contrast.
As shown in
FIG. 11
, there is a method of realizing a color display by using the fine particles
31
colored in three primaries and the color solvents
41
,
42
, and
43
. That is, this method comprises coloring both of the electrophoretic fine particles and the solvents. In this case, the colors of the solvents and the electrophoretic fine particles are set in the complementary relation with each other to obtain the black display and the colored display with a single capsule. Referring to
FIG. 11
, three types of microcapsules, i.e., the microcapsules containing red color fine particles with a cyan colored solvent
41
, the microcapsules containing green color fine particles with a magenta colored solvent
42
, and the microcapsules containing blue fine particles with a yellow colored solvent
43
, are densely arranged on the substrate. In a microcapsule containing red color fine particles with a cyan colored solvent
41
, as shown in
FIG. 11
, red color is displayed in case the red fine particles are present in the upper side. On the contrary, when the red fine particles are disposed on the lower side, the color of the fine particles is mixed with the color of the solvent to display a black color. In a microcapsule containing green color fine particles with a magenta colored solvent
42
, green color and black color are displayed in case the particles are disposed on the upper side and the lower side, respectively. Further, in a microcapsule containing blue color fine particles with a yellow colored solvent
43
, blue color and black color are displayed in case the particles are disposed on the upper side and the lower side, respectively.
For instance, in case of red color display, as shown in
FIG. 11
, the pixel on the left edge yields a red display, and the other two types of pixels yield a black display. The optical efficiency in this method is about {fraction (1/9)} to result in a dark color display.
In case of white display, red,

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