Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2000-10-23
2004-02-17
Liang, Regina (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C359S296000
Reexamination Certificate
active
06693621
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophoretic display method capable of reversibly changing a display between the visually recognizable states by the action of an electric field or the like. The present invention also relates to an electrophoretic display liquid and display particles for use in the above-mentioned electrophoretic display method, an electrophoretic display medium for use with the above-mentioned electrophoretic display method, and further an electrophoretic display apparatus and reversible display material using the display medium.
2. Discussion of Background
The display apparatus using electrophoretic migration is constructed in such a configuration that two substrates, at least one substrate being made transparent, are disposed opposite via spacers to have a predetermined enclosed space therebetween. A display liquid is held in the enclosed space between the substrates to provide a display panel. The conventional display liquid comprises a dispersion medium and a pigment powder dispersed therein, the dispersion medium assuming a color different from that of the pigment powder. By the application of an electric field to the display panel, visual display can be observed through the transparent substrate serving as a display surface.
In the above-mentioned case, more specifically, the display liquid for use in the electrophoretic migration display method comprises a dispersion medium such as xylene or isoparaffin, a dispersed powder such as titanium dioxide, a dye for providing the dispersion medium with a different color from the color of the dispersed powder, a dispersant such as a surfactant, and an additive component such as a charge imparting agent.
By the application of an electric field to the above-mentioned display liquid, the dispersed powder in the liquid migrates to the transparent substrate side, so that a color of the dispersed particle can be recognized through the transparent substrate.
When the applied electric field is reversed, the dispersed powder migrates toward the other substrate, so that a color of the dispersion medium, which is colored with a dye, can be visually recognized through the transparent substrate.
The electrophoretic migration type display apparatus can provide a predetermined display by controlling the polarity of the applied electric field, as previously explained. Special attention has been paid to the electrophoretic migration type display apparatus because of the following advantages:
(1) The display apparatus is inexpensive since a display liquid for use in the apparatus is relatively easily available.
(2) The angle of field of the display apparatus is as wide as that of general printed matter.
(3) The consumption power can be reduced.
(4) The display apparatus has memory characteristics.
A display apparatus using electrophoretic migration is disclosed in Japanese Laid-Open Patent Application 1-86116, which is constructed in such a manner that a display liquid comprising a dispersed powder and a dispersion medium dyed with a color different from the color of the dispersed powder is enclosed in microcapsules, and the microcapsules are arranged between a pair of electrodes. This application is issued as Japanese Patent No. 2551783 in 1996. The electrophoretic display apparatus can be thus achieved by employing a simple structure.
In the display liquid for use in the conventional electrophoretic display apparatus, an inorganic pigment with a high refractive index, for example, titanium oxide powder, is dispersed in a dispersion medium in which a dye is dissolved for coloring the dispersion medium. However, when the color of the inorganic pigment powder is displayed, the color or the pigment powder is readily mixed with the color or the dispersion medium, thereby drastically lowering the contrast of display.
This problem is considered to result from adsorption of a dye for use in the display medium by the surfaces of the pigment particles, and permeation of the dye solution through the gap between the pigment particles. This problem is unavoidable for the electrophoretic display apparatus where a colored dispersion medium is employed for the display liquid.
The above-mentioned problem becomes noticeable when a white pigment is used as the dispersed powder. The degree of whiteness of a background portion in display, that is, a non-recorded portion, is considerably decreased, which may result in a fatal defect for the display medium.
To solve the above-mentioned problem, the following proposals are made: (a) to use a dye which is not readily adsorbed by the surfaces of pigment particles as a coloring agent for a dispersion medium (Philips Lab: Conference Record of 1980 Biennial Disp. Res. Conf.); (b) to decrease the concentration of a dye in a dispersion medium (Xerox PaloAlto: Proc. SID, Vol. 18, 3/4, 1977); and (c) to optimize the concentration of a dye, the concentration of a pigment, and the content of a surfactant (Matsushita: Proc. SID, Vol. 18, No. 3/4, 1977).
However, the above-mentioned proposals cannot produce sufficient effects in practice. To make matters worse, the density of a displayed image and the response speed are decreased.
As mentioned above, Japanese Patent No. 2551783 discloses a display method using display particles which are prepared by enclosing an electrophoretic display liquid in microcapsules. One of the advantages obtained by this electrophoretic display method is that the problem of uneven display as caused by non-uniform distribution of electrophoretic particles can be inhabited. However, even when the above-mentioned display method is adopted, the pigment powder tends to be colored by a dye solution, thereby lowering the display contrast because each microcapsule contains therein a dye solution and a dispersion of a pigment powder.
An electrophoretic display system using no dye solution is proposed in order to eliminate the above-mentioned shortcoming resulting from the dispersion medium colored with a dye.
For instance, Japanese Laid-Open Patent Application No. 62-269124 discloses an electrophoretic migration type display element constructed in such a manner that opposite electrodes, at least one of which is transparent, are superimposed via spacers to provide a cell therebetween, and a display liquid is enclosed in the cell. The display liquid comprises a colorless dispersion medium which has high electrical insulating properties and low viscosity, and at least two kinds of electrophoretic migration powders dispersed in the dispersion medium, those electrophoretic powders being different in color and polarity for electrophoretic migration.
However, there is a risk that the above-mentioned two kinds of electrophoretic migration powders with different colors tend to aggregate by electrical attraction because the two kinds of powders are charged to opposite polarities. Consequently, color mixing occurs, and it becomes difficult to achieve a display with high contrast.
According to Japanese Laid-Open Patent Application 63-50886, at least two kinds of electrophoretic migration powders are dispersed in a colorless dispersion medium which has high electrical insulating properties and low viscosity, thereby preparing a display liquid. The display liquid is held in the cell in the same manner as in the above, so that an electrophoretic migration type display element is provided. In this case, however, the two electrophoretic migration powders show the same polarity, but are different in color tone and electrophoretic velocity.
In this case, image display is attained on the ground of the difference in migration velocity of the electrophoretic migration powders with different colors. Those powders have inclinations to migrate in the same direction, so that it is impossible to simultaneously display two different colors on the identical display surface. This image display method is therefore considered to be impractical.
Further, WO98/03896 discloses an embodiment where the same dispersion system as in the aforementioned Japanese Laid-Open Pa
Harada Shigeyuki
Hayakawa Kunio
Morita Mitsunobu
Liang Regina
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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