Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-03-06
2003-11-18
Kim, Robert H. (Department: 2882)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S165000, C349S166000, C359S296000
Reexamination Certificate
active
06650384
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-081597, filed 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 a liquid crystal display and a display method, particularly, to a liquid crystal display utilizing the combination of a liquid crystal display technology and an electrophoretic display technology and its display method.
2. Description of the Related Art
In the electrophoretic display technology, an image is displayed by utilizing the electrophoretic phenomenon of particles dispersed in a dispersion medium. The dispersion medium containing such particles, i.e., electrophoretic particles, is called an electric field sensitive pigment, i.e., an electrophoretic E-ink or an E-ink. The electrophoretic display technology is classified into two types described below.
In one type of electrophoretic display technology, used is a microcapsule prepared by dispersing charged titania particles
21
in a colored solvent
22
and encapsulating the resultant dispersion with a transparent film
23
, as shown in FIG.
1
A. In this technology, the displayed color can be switched between the white color of the titania particles and the color of the solvent by applying voltage across the microcapsule to cause the migration of the titania particles
21
within the transparent film
23
.
In the other type of electrophoretic display technology, used is a microcapsule prepared by dispersing charged particles
31
a
and
31
b
differing from each other in the polarity of the charge and in the color in a transparent solvent
32
, and encapsulating the resultant dispersion with a transparent film
33
. In the case of using the microcapsule thus prepared, it is possible to switch the displayed color between the color of the charged particle
31
a
and the color of the charged particle
31
b
depending on the state that the charged particles
31
a
are present on the side of the observer and the state that the charged particles
31
b
are present on the side of the observer.
Incidentally, these technologies are described in, for example, the publications given below:
[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 SID98, p1131; and
[3] Barrett Comiskey, J. D. Albert, Hidekazu Yoshizawa and Joseph Jacobson, Nature, 394, p253 (1998).
The electrophoretic display technology permits obtaining a high contrast. However, it is difficult to provide a full color image. To be more specific, in the display technology using the microcapsule shown in
FIG. 1A
, the displayed color is switched between two colors, i.e., the white color produced by the light-scattering by the titania particles
21
and the color of the colored solvent
22
, with the result that a color filter is required for producing a full color image. In the display technology using the microcapsule shown in
FIG. 1B
, the displayed color is also switched between two colors, i.e., the color of the electrophoretic fine particles
31
a
and the color of the electrophoretic fine particles
31
b
, with the result that it is also necessary to use a color filter for producing a full color image. In the case of using a color filter, however, the light utilization efficiency is lowered so as to lower the contrast.
In order to produce a full color image by the electrophoretic display technology, proposed is a method of coloring appropriately the electrophoretic particles. According to this coloring method, it is unnecessary to use a color filter. However, the reflectance is lowered in the case of displaying a white image. Also, the reflectance is increased in the case of displaying a black image. It follows that the image quality is lowered.
In order to realize a full color display while maintaining a high contrast, it is absolutely necessary to switch the displayed color among three colors of white, black and a color other than white and black in a single microcapsule. However, such a technology has not yet been developed to date.
In order to overcome the problem pointed out above, the present inventors have proposed an electrophoretic display technology that permits switching the displayed color among three colors in a single microcapsule. In the display technology proposed by the present inventors, used is a microcapsule prepared by dispersing fine particles such as titania particles in a P-type liquid crystal material containing a liquid crystal substance, a dichroic dye and an isotropic dye, and encapsulating the resultant dispersion with a transparent film. Where the dichroic dye contained in the microcapsule can exhibit a complementary color of the isotropic dye, it is possible to switch the displayed color among three colors of white, black and a color other than white and black in a single capsule. It follows that the electrophoretic display technology proposed by the present inventors makes it possible to achieve a full color display while maintaining a high contrast characterizing the display of electrophoresis mode.
It is expected to apply the electrophoretic display to an electronic paper. In such an application, it is required to decrease the power consumption of the display. Therefore, it is desirable for the electrophoretic display to be capable of holding the image displayed by the voltage application even after stopping the application of voltage. In other words, it is desirable for the electrophoretic display to exhibit a memory function.
The display noted above certainly exhibit the memory function in the case where an image is displayed by the electrophoresis mode. However, the memory function is not exhibited in the case where an image is displayed by the guest-host mode. To be more specific, it is certainly possible to hold white and black colors even after stopping the application of voltage. However, it is impossible to hold the color other than white and black. Such being the situation, a clear full color image, which is displayed under the state that voltage is applied, is switched into a monochromatic image immediately after stopping the application of voltage.
BRIEF SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a liquid crystal display, comprising a substrate and pixels arrayed on the substrate, each of the pixels comprising an electric field sensitive layer which comprises an N-type liquid crystal material containing a liquid crystal substance, a dichroic dye and an isotropic dye, and particles dispersed in the N-type liquid crystal material and configured to migrate in the N-type liquid crystal material by electrophoresis.
According to a second aspect of the present invention, there is provided a liquid crystal display, comprising a substrate and pixels arrayed on the substrate, each of the pixels comprising a first electric field sensitive layer which comprises an N-type liquid crystal material containing a first liquid crystal substance, a first dichroic dye and a first isotropic dye, and first particles dispersed in the N-type liquid crystal material and configured to migrate in the N-type liquid crystal material by electrophoresis, and a second electric field sensitive layer which is adjacent to the first electric field sensitive layer and comprises a P-type liquid crystal material containing a second liquid crystal substance, a second dichroic dye and a second isotropic dye, and second particles dispersed in the P-type liquid crystal material and configured to migrate in the P-type liquid crystal material by electrophoresis.
According to a third aspect of the present invention, there is provided a method of displaying an image, comprising changing a state of a first electric field sensitive layer among first to third states, the first electric field sensitive layer comprising an N-type liquid crystal materi
Iwanaga Hiroki
Oguchi Masayuki
Caley Michael H
Kim Robert H.
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