Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/166—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect
  • G02F1/167—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect by electrophoresis
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/1675—Constructional details
  • G02F1/1679—Gaskets; Spacers; Sealing of cells; Filling or closing of cells
  • G02F1/1681—Gaskets; Spacers; Sealing of cells; Filling or closing of cells having two or more microcells partitioned by walls, e.g. of microcup type
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/165—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on translational movement of particles in a fluid under the influence of an applied field
  • G02F1/1675—Constructional details
  • G02F2001/1678—Constructional details characterised by the composition or particle type

Definitions

• the present invention generally relates to an electrophoretic fluid, an electrophoretic display medium, an electrophoretic display element, an electrophoretic display device, a display method, a production method of the electrophoretic display element, and a production method of the electrophoretic display device.
• CTR Cathode-ray tube
• liquid crystal displays are widely used to display text, images, videos, and so on.
• display devices can quickly display digital data and rewrite displayed images, they are not suitable to carry around.
• display devices are light-emitting devices, viewing displayed images for a long time strains the eyes. Further, those display devices cannot keep images displayed when turned off.
• hard copies reflect multiply-scattered light and therefore have better visibility and are easier on the eyes compared with light-emitting devices. Also, hard copies are lightweight and easy to handle, and therefore can be read in any posture. However, hard copies become waste after use. Although a part of used hard copies can be recycled, recycling is labor-intensive and costly. Thus, hard copies have a disadvantage in terms of resource savings.
• an electrophoretic display medium containing a dispersion liquid which includes electrophoretic particles dispersed in a dispersion medium having a color different from that of the electrophoretic particles, is placed between a pair of transparent electrodes.
• the surfaces of the electrophoretic particles in the dispersion medium are electrically charged.
• an electrophoretic display element displays a color using this mechanism.
• a structure for arranging the electrophoretic display elements is necessary.
• a honeycomb structure - A - sheet which is an aggregate of hollow structures, is suitable as an image display element structure used to arrange minute electrophoretic display elements.
• electrophoretic display elements each including electrophoretic particles and a dispersion medium are formed in the respective cells of the honeycomb structure.
• Patent document 1 discloses an electrophoretic display and a method of producing the electrophoretic display.
• the disclosed electrophoretic display is produced by filling cup-like recesses, which are formed by micro-embossing or image exposure, with a dispersion of charged pigment particles dispersed in a solvent or a solvent blend; and by curing an overcoat layer over the dispersion to seal the dispersion in the recesses.
• the overcoat layer is made of a sealing composition that has a specific gravity smaller than that of the dispersion and is at least partly immiscible with the dispersion.
• Patent documents 2 and 4 disclose a display using an electrophoretic liquid where three types of particles are dispersed for color display.
• Patent document 3 discloses a display using an electrophoretic liquid comprising electrophoretic particles and non- electrophoretic particles dispersed in a colored dispersion medium.
• Patent document 1 Japanese Patent No. 3680996
• Patent document 2 Japanese Patent Application Publication No. 2002-511607
• Patent document 3 Japanese Patent Application
• patent documents 2 and 4 disclose operations of displays, they do not disclose concrete examples of dispersed particles (their characteristics, materials, and production methods) . Therefore, with the technologies disclosed in patent documents 2 and 4, it is difficult to produce a color electrophoretic display device.
• Embodiments of the present invention provide an electrophoretic fluid, an electrophoretic display medium containing the electrophoretic fluid, an electrophoretic display element including the electrophoretic display medium, an electrophoretic display device including the electrophoretic display elements, and a display method of the electrophoretic display element that solve or reduce one or more problems caused by the limitations and disadvantages of the related art.
• An embodiment of the present invention provides an electrophoretic fluid that includes a solvent; and first, second, and third dispersible particles having different optical properties and dispersed in the solvent, the first dispersible particles being uncharged, the second dispersible particles being positively-charged electrophoretic particles, and the third dispersible particles being negatively-charged electrophoretic particles .
• the electrophoretic display element includes an electrophoretic display medium having a hollow structure that contains an electrophoretic fluid including a solvent, and first, second, and third dispersible particles having different optical properties and dispersed in the solvent, the first dispersible particles being uncharged, the second dispersible particles being positively-charged electrophoretic particles, and the third dispersible particles being negatively-charged electrophoretic particles; a transparent first electrode; and second and third electrodes facing the first electrode across the electrophoretic display medium.
• an electrophoretic display medium having a hollow structure that contains an electrophoretic fluid including a solvent, and first, second, and third dispersible particles having different optical properties and dispersed in the solvent, the first dispersible particles being uncharged, the second dispersible particles being positively-charged electrophoretic particles, and the third dispersible particles being negatively-charged electrophoretic particles; a transparent first electrode; and second and third electrodes facing the first electrode across the electrophoretic display medium.
• Still another embodiment of the present invention provides a display method of an electrophoretic display element that includes an electrophoretic display medium having a hollow structure containing an electrophoretic fluid including a solvent, and first, second, and third dispersible particles having different optical properties and dispersed in the solvent, the first dispersible particles being uncharged, the second dispersible particles being positively-charged electrophoretic particles, and the third dispersible particles being negatively-charged electrophoretic particles; a transparent first electrode; and second and third electrodes facing the first electrode across the electrophoretic display medium.
• an electrophoretic display medium having a hollow structure containing an electrophoretic fluid including a solvent, and first, second, and third dispersible particles having different optical properties and dispersed in the solvent, the first dispersible particles being uncharged, the second dispersible particles being positively-charged electrophoretic particles, and the third dispersible particles being negatively-charged electrophoretic particles; a transparent first electrode; and second and third electrodes facing the first electrode across the electrophoretic display medium.
• the display method includes the step of applying a voltage between the first and second electrodes and/or between the first and third electrodes in order that the second dispersible particles or the third dispersible particles accumulate at the transparent first electrode in the electrophoretic display medium and become observable through the transparent first electrode.
• FIG. 1 is a first drawing illustrating operations of an electrophoretic display element
• FIG. 2 is a second drawing illustrating operations of an electrophoretic display element
• FIG. 3 is a third drawing illustrating operations of an electrophoretic display element
• FIG. 4 is a drawing illustrating operations of a multicolor electrophoretic display device
• FIG. 5 is a drawing illustrating a first exemplary arrangement of electrophoretic display elements of different colors
• FIG. 6 is a drawing illustrating a second exemplary arrangement of electrophoretic display elements of different colors
• FIGs. 7A through 7D are drawings illustrating a method of assembling an electrophoretic display device
• FIGs. 8A through 8F are drawings illustrating another method of assembling an electrophoretic display device. BEST MODE FOR CARRYING OUT THE INVENTION
• An electrophoretic fluid according to an embodiment of the present invention is described below.
• An electrophoretic fluid of this embodiment comprises three types of dispersible particles dispersed in a solvent used as an electrophoretic medium.
• the three types of dispersible particles include first dispersible particles, second dispersible particles, and third dispersible particles having different optical properties and charge characteristics.
• the first dispersible particles are uncharged
• the second dispersible particles are positively-charged electrophoretic particles
• the third dispersible particles are negatively-charged electrophoretic particles.
• Optical properties include colors such as black and white and their brightnesses.
• Dispersible particles (may also be simply called “particles”) usable for an electrophoretic fluid of this embodiment include organic and inorganic pigment particles with or without color. Pigment particles preferably have low solubility in a solvent used as the electrophoretic medium and are able to exist in the solvent as a disperse phase.
• inorganic pigment particles include white lead, zinc white, lithopone, titanium dioxide, zinc sulfide, antimony oxide, calcium carbonate, kaolin, mica, barium sulphate, gross white, alumina white, talc, silica, calcium silicate, cadmium yellow, cadmium lithopone yellow, yellow iron oxide, titanium yellow, titanium barium yellow, cadmium orange, cadmium lithopone orange, molybdate orange, iron red, red lead, vermilion, cadmium red, cadmium lithopone red, umber, brown iron oxide, zinc iron chrome brown, chrome green, chromium oxide, viridian, cobalt green, cobalt chrome green, titanium cobalt green, iron blue, cobalt blue, ultramarine blue, cerulean blue, cobalt aluminum chrome blue, cobalt violet, mineral violet, carbon black, iron black, manganese ferrite black, cobalt ferrite black, copper chrome black, copper chrome manganese black, titanium black,
• organic pigment particles include fast yellow, disazo yellow, condensed azo yellow, anthrapyrimidine yellow, isoindoline yellow, copper azomethine yellow, quinophthalo yellow, benzimidazolone yellow, nickel dioxime yellow, monoazo yellow lake, dinitroaniline orange, pyrazolone orange, perinone orange, naphthol red, toluidine red, permanent carmine, brilliant fast scarlet, pyrazolone red, rhodamine 6G lake, permanent red, lithol red, bon lake red, lake red, brilliant carmine, Bordeaux 1OB, naphthol red, quinacridone magenta, condensed azo red, naphthol carmine, perylene scarlet, condensed azo scarlet, benzimidazolone carmine, anthraquinonyl red, perylene red, perylene maroon, quinacridone maroon, quinacridone scarlet, quinacridone red, diketopyrrolopyrrole red,
• polymer particles As organic pigment particles, polymer particles, especially, hollow polymer particles are preferable. Hollow polymer particles can be produced by known methods. For example, such methods are disclosed in “New Development of Particulate Polymer” (Toray Research Center, Inc.), “Microporous Polymer and Development in its Application” (Toray Research Center, Inc.), and “Latest Technology and Application of Polymer Microparticles” (CMC Publishing Co., Ltd.).
• Methods for producing hollow polymer particles include, but are not limited to, emulsion polymerization, seed emulsion polymerization, soap-free polymerization, dispersion polymerization, a combination of suspension polymerization and foaming, a combination of seed polymerization and foaming, a combination of seed polymerization and polymerization shrinkage, suspension polymerization of W/O/W emulsion, spray drying of liquid droplets, and seed coagulation where polymer emulsion is coagulated by adding solid electrolyte particles.
• polymer materials that are not soluble in a transparent dispersion medium may be used for hollow organic-polymer particles.
• Such polymer materials include styrene, styrene-acrylate, styrene-isoprene, divinyl benzene, methyl methacrylate, methacrylate, ethyl methacrylate, ethyl acrylate, n-butyl acrylate, acrylic acid, acrylonitrile, acrylate-methacrylate, ethylene, ethylene-acrylic acid, nylon, silicone, urethane, melamine, benzoguanamine, phenol, fluorine (tetrachloroethylene) , vinylidene chloride, vinylnaphthalene, vinylcarbazole, quaternary pyridinium salt, synthetic rubber, cellulose, cellulose acetate, chitosan, calcium alginate, and materials prepared by cross-linking the above polymer materials to improve the solvent resistance.
• Pigment particles may be composed of pigments only or may be surface-modified. Normal surface modification methods for pigment particles may be used for this purpose. For example, surface modification of pigment particles may be performed by coating the surface of a pigment with a chemical compound such as a polymer, by coupling using a coupling agent such as titanate or silane, or by graft polymerization. Also, pigment particles prepared by mechanochemical treatment may be used. For example, a composite particle of different pigment particles, a composite particle of a pigment particle and a polymer particle or a hollow polymer particle, and a composite particle of a pigment particle and a resin may be used.
• the diameter of the above particles may be determined in relation to a solvent used as the dispersion medium. In terms of dispersibility and electrophoretic mobility, the diameter of particles is preferably, but not limited to, between 0.01 and 100 ⁇ m.
• a solvent used as the dispersion medium As the material for the first dispersible particles having no or zero electric charge, polyvinylnaphthalene is preferable. Microparticles of polyvinylnaphthalene may be prepared by dispersion polymerization of vinylnaphthalene in a silicone oil, which is a nonpolar solvent, using a silicone macromonomer as a dispersing agent. Alternatively, particles prepared by coating titanium oxide with polyvinylnaphthalene or particles of polyvinyl carbazole may be used as the first dispersible particles. However, materials for the first dispersible particles of this embodiment are not limited to those described above.
• Preferable materials for the second dispersible particles having a positive electric charge include surface-modified carbon black, phthalocyanine pigment, quinacridone pigment, and monoazo pigment. These pigments are preferably surface-modified by graft polymerization of the 2-ethylhexyl group.
• materials for the second dispersible particles of this embodiment are not limited to those described above.
• Preferable materials for the third dispersible particles having a negative electric charge include surface-modified carbon black, titanium black, phthalocyanine pigment, quinacridone pigment, and monoazo pigment. These pigments are preferably surface-modified by heterocoagulation of a polymer having a carboxyl group. Or, these pigments may be surface-modified by graft polymerization of the lauryl group.
• materials of the third dispersible particles of this embodiment are not limited to those described above.
• solvents usable as the dispersion medium of the electrophoretic fluid of this embodiment include, but are not limited to, aromatic hydrocarbons such as benzene, toluene, xylene, phenylxylylethane, diisopropylnaphthalene, and naphthenic hydrocarbon; aliphatic hydrocarbons such as hexane, dodecylbenzene, cyclohexane, kerosene, and paraffinic hydrocarbon; halogenated hydrocarbons such as chloroform, trichloroethylene, tetrachloroethylene, trifluoroethylene, tetrafluoroethylene, dichloromethane, and ethyl bromide; phosphoric esters such as tricresyl phosphate, trioctyl phosphate, octyldiphenyl phosphate, and tricyclohexyl phosphate; phthalate esters such as dibutyl phthalate, di
• the above organic solvents may be used individually or in combination.
• paraffinic hydrocarbon is especially preferable as the dispersion medium of the electrophoretic fluid of this embodiment.
• the electrophoretic fluid of this embodiment may contain additives used, for example, to control the amount of surface charge or to improve the dispersibility of the dispersible particles.
• additives include, but are not limited to, surfactants and protective colloids.
• ionic surfactants including nonionic surfactants, anionic surfactants, cationic surfactants, and ampholytic surfactants, which are soluble or dispersible in a solvent of the electrophoretic fluid.
• the above surfactants may be used individually or in combination. Examples of surfactants are listed below, but other surfactants may also be used.
• Nonionic surfactants are nonionic surfactants:
• Polyoxyalkylene alkylphenol ethers such as polyoxyethylene nonylphenol ether, polyoxyethylene dinonylphenol ether, polyoxyethylene octylphenol ether, polyoxyethylene styrenated phenol, polyoxyethylene bisphenol A, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, and nonylphenol ethoxylate-
• Polyoxyalkylene ethers such as polyoxyethylene caster oil, polyoxyalkylene block polymer, polyoxyethylene cetyl ether, polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, and polyoxypropylene ether- Glycols such as monool type polyoxyalkylene glycol, diol type polyoxyalkylene glycol, triol type polyoxyalkylene glycol, monool block type polyalkylene glycol, diol block type polyalkylene glycol, and random type polyalkylene glycol
• R-NH-C3 H6 -NH2 (R represents oleyl, octyl, dodecyl, tetradecyl, hexadecyl, octadecyl, coconut oil, tallow, soybean oil, or the like)- Primary amines represented by the following formula:
• R-NH2 (R represents oleyl, octyl, dodecyl, tetradecyl, hexadecyl, octadecyl, coconut oil, tallow, soybean oil, or the like)- Secondary amines represented by the following formula:
• R1R2-NH R1R2-NH
• Rl and R2 each independently represents oleyl, octyl, dodecyl, tetradecyl, hexadecyl, octadecyl, coconut oil, tallow, soybean oil, or the like.
• R1R2R3N (Rl, R2, and R3 each independently represents oleyl, octyl, dodecyl, tetradecyl, hexadecyl, octadecyl, coconut oil, tallow, soybean oil, or the like.)- Synthesized higher alcohols and natural higher alcohols- Polymers and oligomers such as acrylic acid compounds, polycarboxylic acid compounds, hydroxyfatty acid oligomers, and derivatives of hydroxyfatty acid oligomers
• Anionic surfactants - Carboxylic acid salts such as polycarboxylic acid type polymer activator, polycarboxylic acid type nonionic activator, special fatty acid soap, and rosin soap- Alcohol sulfuric ester salts such as caster oil sulfuric ester salt, sodium salt of lauryl alcohol sulfuric ester, amine salt of lauryl alcohol sulfuric ester, sodium salt of natural alcohol sulfuric ester, and sodium salt of higher alcohol sulfuric ester Sulfuric ester salts such as amine salt of lauryl alcohol ether sulfuric ester, sodium salt of lauryl alcohol ether sulfuric ester, amine salt of synthesized higher alcohol ether sulfuric ester, sodium salt of synthesized higher alcohol ether sulfuric ester, amine salt of alkylpolyether sulfuric ester, sodium salt of alkylpolyether sulfuric ester, amine salt of natural alcohol ethylene oxide adduct sulfuric ester, sodium salt of natural alcohol ethylene oxide adduct sulfuric ester, amine salt
• Alkyltrimethyl amine quaternary ammonium salts represented by the following formula: R-N (CH3 )3X
• R represents stearyl, cetyl, lauryl, oleyl, dodecyl, coconut oil, soybean oil, tallow, or the like.
• Benzylamine quaternary ammonium salts such as lauryldimethylbenzyl ammonium salt (haloid salt, amine salt, or the like), stearyldimethylbenzyl ammonium salt (haloid salt, amine salt, or the like) , and dodecyldimethylbenzyl ammonium salt (haloid salt, amine salt, or the like)- Polyoxyalkylene quaternary ammonium salts represented by the following formula:
• R(CH3 )N(C2 H4 0)mH(C2 H4 O)n-X R represents stearyl, cetyl, lauryl, oleyl, dodecyl, coconut oil, soybean oil, tallow, or the like, and X represents halogen, amine, or the like.
• Amphoteric Surfactants - Betaine surfactants, imidazoline surfactants, ⁇ - alanine surfactants, and polyoctylpolyaminoethyl glycine hydrochloride
• any known protective colloid that is soluble or dispersible in the dispersion medium of the electrophoretic fluid may be used.
• An electrophoretic display medium of this embodiment contains an electrophoretic fluid as described above in a hollow structure at least one side of which is transparent. Normally, the electrophoretic display medium of this embodiment has a microstructure .
• An electrophoretic display element is produced by providing the electrophoretic display medium with electrodes for causing charged dispersible particles to migrate.
• the electrophoretic display medium is implemented by using a microcapsule as a hollow structure for containing the electrophoretic liquid.
• Microcapsules may be prepared, for example, by an in-situ method, interfacial polymerization, or coacervation.
• materials for the microcapsules include polyurethane, polyurea, polyurea-polyurethane, urea-formaldehyde resin, melamine-formaldehyde resin, polyamide, polyester, polysulfonamide, polycarbonate, polysulfinate, epoxy resin, acrylate, methacrylate, vinyl acetate, and gelatin.
• the diameter of the microcapsules is preferably between 30 and 200 ⁇ m.
• a honeycomb structure is used as hollow structures.
• a honeycomb structure is suitable to implement an electrophoretic display device comprising multiple electrophoretic display media or elements.
• Each cell of the honeycomb structure is used as an electrophoretic display medium.
• electrophoretic display media may be created by injecting an electrophoretic fluid into cells of a resinous honeycomb structure formed by photolithography on a substrate and sealing the cells with a resin that is insoluble in the electrophoretic fluid.
• an aggregate of electrophoretic display media can be formed by filling the cells of the honeycomb structure with the electrophoretic fluid.
• resins for the honeycomb structure include polyurethane, polyurea, polyurea-polyurethane, urea-formaldehyde resin, melamine- formaldehyde resin, polyamide, polyester, polysulfonamide, polycarbonate, polysulfinate, epoxy resin, acrylate, methacrylate, vinyl acetate, gelatin, and photoresists made from polymethylmethacrylate, novolac resin, or polystyrene.
• resins for sealing the cells include polyurethane, polyurea, polyurea-polyurethane, urea-formaldehyde resin, melamine-formaldehyde resin, polyamide, polyester, polysulfonamide, polycarbonate, polysulfinate, epoxy resin, acrylate, methacrylate, vinyl acetate, and gelatin.
• a film of resin is formed over the electrophoretic fluid by applying and drying the resin with a coater such as a slit coater.
• a surfactant may be added to the resin used for sealing the cells to make it easier to form a film over the electrophoretic fluid.
• the wall thickness of each cell is preferably between 0.5 and 20 ⁇ m, the depth of each cell is preferably between 30 and 200 ⁇ m, and the pitch between the cells is preferably between 30 and 200 ⁇ m.
• an electrophoretic display element is implemented by providing the electrophoretic display medium of the above embodiment with electrodes.
• an electrophoretic display element 1 of this embodiment includes three electrodes. As shown in FIG. 1, the electrophoretic display element 1 includes a transparent first electrode 3, a second electrode 4 facing the first electrode 3 across an electrophoretic display medium 2, and a third electrode 5 facing the first electrode 3 across the electrophoretic display medium 2.
• a side (first electrode side) of the electrophoretic display element 1 on which the first electrode 3 is placed is used as a display surface. Accordingly, the second and third electrodes 4 and 5 are disposed opposite to the display surface.
• the first electrode 3 is, for example, implemented by a transparent conductive thin film of ITO, SnO 2 , or ZnO/Al.
• a thin-film transistor that has a switching function and is able to apply an electric field is preferably used.
• An electrophoretic display device is implemented by arranging multiple electrophoretic display elements.
• the electrophoretic display elements of the electrophoretic display device are disposed such that their first electrode sides (or the first electrodes) face substantially the same direction.
• FIG. 4 shows an electrophoretic display device 10 of this embodiment.
• the number of electrophoretic display elements is not limited.
• a common first electrode 14 is provided for the three electrophoretic display elements, and second electrodes 15, 17, and 19 and third electrodes 16, 18, and 20 are provided for the respective electrophoretic display elements so that voltages can be applied independently.
• the first electrode sides of the electrophoretic display elements are arranged in the same plane so that dispersible particles in the electrophoretic display elements can be observed from the upper side of FIG. 4.
• the electrophoretic display device 10 may be supported by a substrate (not shown) made of, for example, glass or resin.
• Electrophoretic display elements of the electrophoretic display device 10 of this embodiment are preferably arranged using a honeycomb structure where cells are arranged next to each other.
• a honeycomb structure like a tetragonal lattice as shown in FIG. 5 or a honeycomb structure like a hexagonal close- packed structure as shown in FIG. 6 are preferable.
• cells of a honeycomb structure are assigned to electrophoretic display media of three different colors: yellow (Y), magenta (M) , and cyan (C) .
• the electrophoretic display media of the three colors are preferably arranged such that the display media of the same color do not adjoin each other.
• an electrophoretic display medium of an electrophoretic display element may contain one of three types of electrophoretic fluids: an electrophoretic fluid including dispersible particles of white, black, and yellow; an electrophoretic fluid including dispersible particles of white, black, and magenta; and an electrophoretic fluid including dispersible particles of white, black, and cyan.
• electrophoretic display elements containing the same type of electrophoretic fluid are preferably arranged apart from each other.
• the first dispersible particles are white
• the second dispersible particles are yellow, magenta, or cyan
• the third dispersible particles are black.
• White dispersible particles are preferably made of polymer particles, especially, hollow polymer particles
• black dispersible particles are preferably made of carbon particles.
• ⁇ DISPLAY METHOD OF ELECTROPHORETIC DISPLAY DEVICE> In the electrophoretic display element 1, when a voltage is applied between the first and second electrodes 3 and 4 and/or between the first and third electrodes 3 and 5, the second or third dispersible particles accumulate at the first electrode 3 in the electrophoretic display medium 2 and become observable through the transparent electrode (the first electrode 3) When a voltage is applied between the second and third electrodes 4 and 5 and not to the first electrode 3, the second and third dispersible particles accumulate at the second and third electrodes 4 and 5 in the electrophoretic display medium 2, and as a result, the first dispersible particles in the electrophoretic display medium 2 become observable through the transparent electrode (the first electrode 3) .
• FIGs. 1 through 3 An exemplary display method of the electrophoretic display element 1 is described in more detail with reference to FIGs. 1, 2, and 3.
• first particles 6 are uncharged
• second particles 7 are positively charged
• third particles 8 are negatively charged.
• a positive voltage is applied to the second electrode 4 and the third electrode 5 relative to the first electrode 3
• the positively- charged second particles 7 are attracted to the first electrode 3
• the negatively-charged third particles 8 are attracted to the second and third electrodes 4 and 5.
• the second particles 7 can be observed from an observation point above the first electrode 3 (see FIG.
• an embodiment of the present invention makes it possible to display three different colors with one electrophoretic display element.
• the electrophoretic display element can display white, black, and magenta.
• white, black, and yellow or white, black, and cyan can be displayed with one electrophoretic display element.
• electrophoretic display elements 11, 12, and 13 each contains white particles 21 and black particles 22, and also contains one of yellow particles 23, magenta particles 24, and cyan particles 25 as the third dispersible particles.
• the first electrode 14 is shared by the electrophoretic display elements 11, 12, and 13, and the second electrodes 15, 17, and 19 and the third electrodes 16, 18, and 20 are provided for the respective electrophoretic display elements 11, 12, and 13.
• the second electrodes 15, 17, and 19 and the third electrodes 16, 18, and 20 can be controlled independently.
• Each of the electrophoretic display elements 11, 12, and 13 can display white, black, or one of yellow, magenta, and cyan according to voltages applied to the electrodes as described above.
• an electrophoretic display device can display a color image using three types of electrophoretic display elements each of which can display white, black, and one of yellow, magenta, and cyan. Also, with the display method of this embodiment where all electrophoretic display elements can display black and white, it is possible to display a clear color image with no blur.
• the first electrode of the electrophoretic display element may be implemented by a transparent, conductive thin film of ITO, SnO 2 , or ZnO/Al.
• the conductive thin film is formed on a transparent glass substrate or a transparent film substrate of, for example, polyethylene terephthalate (PET) by sputtering, vacuum evaporation, chemical vapor deposition (CVD) , or an application method.
• PET polyethylene terephthalate
• CVD chemical vapor deposition
• the glass substrate or the film substrate on which the first electrode is formed is used as a display surface of the electrophoretic display element of this embodiment.
• a pair of thin-film transistors each of which has a switching function and is able to apply an electric field, are preferably used.
• the pairs of thin-film transistors are preferably arranged in a tetragonal lattice or a hexagonal close- packed array on a glass substrate or a film substrate of, for example, PET.
• the distance between the pairs of thin- film transistors is preferably between 30 and 200 ⁇ m.
• cells for containing the electrophoretic fluid of this embodiment are formed in positions corresponding to the pairs of second and third electrodes by, for example, photolithography.
• a photoresist resin is applied to the surface of the substrate on which the second and third electrodes are formed, and parts of the photoresist resin corresponding to the pairs of second and third electrodes are removed to form openings.
• the thickness of walls between cells (or openings) is preferably between 0.5 and 20 ⁇ m
• the depth of cells (or the thickness of the photoresist resin) is preferably between 30 and 200 ⁇ m
• the pitch between cells is preferably between 30 and 200 ⁇ m.
• the cells are filled with an electrophoretic fluid of this embodiment and are sealed with a resin that is not soluble in the electrophoretic fluid.
• resins for sealing the cells include polyurethane, polyurea, polyurea-polyurethane, urea-formaldehyde resin, melamine-formaldehyde resin, polyamide, polyester, polysulfonamide, polycarbonate, polysulfinate, epoxy resin, acrylate, methacrylate, vinyl acetate, and gelatin.
• a coater such as a slit coater and is dried to form a film.
• a surfactant may be added to the resin used for sealing the cells to make it easier to form a film over the electrophoretic fluid.
• the resin film sealing the cells is bonded to the glass substrate or the film substrate on which the first electrode is formed. As a result, multiple electrophoretic display elements are created.
• the cells may be filled with different types of electrophoretic fluids to implement a multicolor electrophoretic display device.
• an inkjet method may be used.
• FIG. 7A shows a substrate 31 on which pairs of second and third electrodes 32 and 33 are formed.
• FIG. 7B microcapsules 35 containing an electrophoretic fluid of this embodiment are placed in positions corresponding to the pairs of the second and third electrodes 32 and 33.
• the microcapsules 35 may be prepared as described above.
• the diameter of the microcapsules 35 is preferably between 30 and 200 ⁇ m.
• a sheet having openings in positions corresponding to the pairs of the second and third electrodes 32 and 33 is used to align the microcapsules and the electrodes.
• the openings of the sheet and the pairs of the second and third electrodes 32 and 33 are aligned, an adhesive is applied to the second and third electrodes 32 and 33, and the microcapsules 35 are placed in the openings.
• the microcapsules 35 are bonded to the corresponding pairs of the electrodes even after the sheet is removed.
• a first electrode 36 formed on a transparent substrate 37 is bonded to the microcapsules 35 placed on the pairs of the second and third electrodes 32 and 33.
• adjoining microcapsules of the multicolor electrophoretic display device contain different types of electrophoretic fluids.
• sheets having openings in different positions are used to place microcapsules containing different electrophoretic fluids in their corresponding positions.
• sheets 44, 46, and 48 having, respectively, first, second, and third opening patterns are prepared.
• the first, second, and third opening patterns correspond, respectively, to microcapsules 45, 47, and 49 containing first, second, and third electrophoretic fluids.
• the openings of the sheets 44, 46, and 48 correspond, respectively, to three types of electrophoretic display elements.
• FIG. 8A shows a substrate 41 on which pairs of second and third electrodes 42 and 43 are formed.
• FIG. 8B the microcapsules 45 of a first color are bonded to the corresponding pairs of the second and third electrodes 42 and 43 using the sheet 44 with the first opening pattern.
• FIG. 8C after the sheet 44 is removed, the microcapsules 47 of a second color are bonded to the corresponding pairs of the second and third electrodes 42 and 43 next to the microcapsules 45 using the sheet 46 with the second opening pattern.
• FIG. 8D after the sheet 46 is removed, the microcapsules 49 of a third color are bonded to the corresponding pairs of the second and third electrodes 42 and 43 next to the microcapsules 45 and 47 using the sheet 48 with the third opening pattern.
• FIGs. 8E and 8F are substantially the same as those described above with reference to FIGs. 7C and 7D.
• a multicolor electrophoretic display device of this embodiment is produced by arranging microcapsules containing different electrophoretic fluids next to each other.
• An electrophoretic fluid containing white, black, and yellow particles was prepared as described below.
• polyvinyl naphthalene was used for the white particles
• black toner was used for the black particles
• yellow toner was used for the yellow particles.
• Microparticles of polyvinyl naphthalene were prepared by dispersion polymerization of 2- vinylnaphthalene in Isopar G (isoparaffin hydrocarbon of Exxon Mobil Corporation) using a silicone macromonomer as a dispersing agent.
• Isopar G isoparaffin hydrocarbon of Exxon Mobil Corporation
• Polyvinyl naphthalene has good dispersion stability in Isopar G. The zeta potential indicating the amount of electric charge of the prepared microparticles was close to zero and the microparticles did not migrate in an electric field.
• Microcapsules containing the electrophoretic fluid of Example 1 are prepared.
• the microcapsules are prepared by coacervation of gelatin-gum arabic.
• the sizes of the microcapsules are adjusted to between 40 and 50 ⁇ m by separation.
• pairs of second and third electrodes are formed on a PET film.
• the pairs of the second and third electrodes are arranged in a hexagonal close-packed array with a pitch of 60 ⁇ m between them.
• An adhesive is applied to the second and third electrodes, and a sheet having openings arranged in a hexagonal close-packed array and corresponding to the pairs of the second and third electrodes is placed on the PET film such that the openings are aligned with the pairs of the second and third electrodes.
• microcapsules are applied to the sheet and are thereby put in the openings. After excess microcapsules are removed, the sheet is removed. As a result, the microcapsules remain on the corresponding pairs of electrodes. Then, an adhesive is applied to the microcapsules, and a PET film on which an ITO electrode is formed is bonded to the microcapsules. As a result, an electrophoretic display device capable of displaying three colors is produced.
• Electrophoretic display elements of the produced electrophoretic display device display yellow when a voltage of +100 V is applied to the second and third electrodes relative to the ITO electrode, display black when a voltage of -100 V is applied to the second and third electrodes, and display white when a voltage of +50 V is applied to the second electrodes and a voltage of -50 V is applied to the third electrodes.
• An electrophoretic fluid containing white, black, and magenta particles was prepared as described below.
• polyvinyl naphthalene was used for the white particles
• carbon black was used for the black particles
• quinacridon particles were used for the magenta particles.
• Microparticles of polyvinyl naphthalene were prepared by dispersion polymerization of 2-vinylnaphthalene in Isopar G (isoparaffin hydrocarbon of Exxon Mobil Corporation) using a silicone macromonomer as a dispersing agent.
• Isopar G isoparaffin hydrocarbon of Exxon Mobil Corporation
• the zeta potential indicating the amount of electric charge of the prepared microparticles was close to zero and the microparticles did not migrate in an electric field.
• the carbon black was surface-modified to charge it negatively.
• the surface of the carbon black was modified with an amino group by silane coupling.
• the surface of the carbon black was further modified by heterocoagulation of polymer microparticles formed by polymerization of a pigment dispersant with a carboxyl group, methyl methacrylate, and methacrylic acid.
• the surface-modified carbon black shows a negative charge characteristic because of the carboxyl group in the polymer microparticles .
• the zeta potential of the prepared black particles was negative and migration of the black particles in an electric field was observed.
• the quinacridon particles were surface-modified to charge them positively.
• PR-122 of Dainichiseika Color & Chemicals Mfg. Co., Ltd. was used as the quinacridon particles.
• the surfaces of the quinacridon particles were diazo-coupled with 2- vinylaniline and graft-polymerized with 2-ethylhexyl methacrylate.
• the graft chain was charge-controlled using a surfactant.
• the graft-polymerized quinacridon particles were dispersed in Isopar G, and Solsperse 17000 (Avecia) was added as a surfactant to the dispersion.
• the zeta potential of the quinacridon particles was positive and migration of the quinacridon particles in an electric field was observed.
• An electrophoretic fluid was prepared by mixing the above particles in ratios shown in table 2 below. [Table 2]
• An electrophoretic fluid containing white, black, and magenta particles was prepared as described below.
• polyvinyl naphthalene was used for the white particles
• titanium black was used for the black particles
• quinacridon particles were used for the magenta particles.
• the titanium black Black
• Titanium Oxide 13M of JEMCO Inc. was used.
• Microparticles of polyvinyl naphthalene were prepared by dispersion polymerization of 2-vinylnaphthalene in Isopar G (isoparaffin hydrocarbon of Exxon Mobil Corporation) using a silicone macromonomer as a dispersing agent.
• Polyvinyl naphthalene has good dispersion stability in Isopar G.
• the zeta potential indicating the amount of electric charge of the prepared microparticles was close to zero and the microparticles did not migrate in an electric field.
• the titanium black was surface-modified to charge it negatively.
• the surface of the titanium black was modified with an amino group by silane coupling and was graft-polymerized with a lauryl group.
• the graft chain was charge-controlled using a surfactant.
• the graft-polymerized titanium black was dispersed in Isopar G, and Solsperse 17000 (Avecia) was added as a surfactant to the dispersion. In the dispersion, the zeta potential of the titanium black was negative and migration of the titanium black in an electric field was observed.
• the quinacridon particles were surface-modified to charge them positively.
• PR-122 of Dainichiseika Color & Chemicals Mfg. Co., Ltd. was used as the quinacridon particles.
• the surfaces of the quinacridon particles were diazo-coupled with 2-vinylaniline and graft-polymerized with 2-ethylhexyl methacrylate.
• the graft chain was charge-controlled using a surfactant.
• the graft-polymerized quinacridon particles were dispersed in Isopar G, and Solsperse 17000 (Avecia) was added as a surfactant to the dispersion.
• the zeta potential of the quinacridon particles was positive and migration of the quinacridon particles in an electric field was observed.
• An electrophoretic fluid was prepared by mixing the above particles in ratios shown in table 3 below. [Table 3]
• An electrophoretic fluid containing white, black, and magenta particles was prepared as described below.
• polyvinyl naphthalene was used for the white particles
• carbon black was used for the black particles
• Disperse Red particles were used for the magenta particles.
• Microparticles of polyvinyl naphthalene were prepared by dispersion polymerization of 2-vinylnaphthalene in Isopar G (isoparaffin hydrocarbon of Exxon Mobil Corporation) using a silicone macromonomer as a dispersing agent.
• Isopar G isoparaffin hydrocarbon of Exxon Mobil Corporation
• the zeta potential indicating the amount of electric charge of the prepared microparticles was close to zero and the microparticles did not migrate in an electric field.
• the surfaces of the Disperse Red particles were graft-polymerized with abietic acid and carboxylic acid.
• the graft-polymerized Disperse Red particles showed good dispersion stability in Isopar G. After the graft polymerization, the Disperse Red particles show a negative charge characteristic because of the carboxyl group in the carboxylic acid. Actually, in Isopar G, the zeta potential of the Disperse Red particles was negative and migration of the Disperse Red particles in an electric field was observed.
• the surface of the carbon black was modified by heterocoagulation of an amino-group-containing polymer.
• an amino-group-containing polymer a copolymer of dimethylaminoethyl methacrylate and a silicone macromer was used.
• the surface-modified carbon black showed good dispersion stability in Isopar G.
• the surface-modified carbon black shows a positive charge characteristic because of the amino group in the amino-group-containing polymer.
• Isopar G the zeta potential of the surface-modified carbon black was positive and migration of the carbon black in an electric field was observed.
• An electrophoretic fluid was prepared by mixing the above particles in ratios shown in table 4 below. [Table 4]
• An electrophoretic fluid containing white, black, and yellow particles was prepared as described below.
• polyvinyl naphthalene was used for the white particles
• titanium black was used for the black particles
• monoazo particles were used for the yellow particles.
• As the titanium black Black Titanium Oxide 13M of JEMCO Inc. was used.
• Microparticles of polyvinyl naphthalene were prepared by dispersion polymerization of 2-vinylnaphthalene in Isopar G (isoparaffin hydrocarbon of Exxon Mobil Corporation) using a silicone macromonomer as a dispersing agent. Polyvinyl naphthalene has good dispersion stability in Isopar G.
• the zeta potential indicating the amount of electric charge of the prepared microparticles was close to zero and the microparticles did not migrate in an electric field.
• the titanium black was surface-modified to charge it negatively.
• the surface of the titanium black was modified with an amino group by silane coupling and was graft-polymerized with a lauryl group.
• the graft chain was charge-controlled using a surfactant.
• the graft-polymerized titanium black was dispersed in Isopar G, and Solsperse 17000 (Avecia) was added as a surfactant to the dispersion. In the dispersion, the zeta potential of the titanium black was negative and migration of the titanium black in an electric field was observed.
• the monoazo particles were surface-modified to charge them positively.
• PY-74 of Dainichiseika Color & Chemicals Mfg. Co., Ltd. was used as the monoazo particles.
• the surfaces of the monoazo particles were diazo- coupled with 2-vinylaniline and graft-polymerized with 2- ethylhexyl methacrylate.
• the graft chain was charge- controlled using a surfactant.
• the graft- polymerized monoazo particles were dispersed in Isopar G, and Solsperse 17000 (Avecia) was added as a surfactant to the dispersion. In the dispersion, the zeta potential of the monoazo particles was positive and migration of the monoazo particles in an electric field was observed.
• An electrophoretic fluid was prepared by mixing the above particles in ratios shown in table 5 below. [Table 5]
• An electrophoretic fluid containing white, black, and cyan particles was prepared as described below.
• polyvinyl naphthalene was used for the white particles
• titanium black was used for the black particles
• phthalocyanine particles were used for the cyan particles.
• As the titanium black Black Titanium Oxide 13M of JEMCO Inc. was used.
• Microparticles of polyvinyl naphthalene were prepared by dispersion polymerization of 2-vinylnaphthalene in Isopar G (isoparaffin hydrocarbon of Exxon Mobil Corporation) using a silicone macromono ⁇ ier as a dispersing agent.
• Polyvinyl naphthalene has good dispersion stability in Isopar G.
• the zeta potential indicating the amount of electric charge of the prepared microparticles was close to zero and the microparticles did not migrate in an electric field.
• the titanium black was surface-modified to charge it negatively.
• the surface of the titanium black was modified with an amino group by silane coupling and was graft-polymerized with a lauryl group.
• the graft chain was charge-controlled using a surfactant.
• the graft-polymerized titanium black was dispersed in Isopar G, and Solsperse 17000 (Avecia) was added as a surfactant to the dispersion. In the dispersion, the zeta potential of the titanium black was negative and migration of the titanium black in an electric field was observed.
• the phthalocyanine particles were surface- modified to charge them positively.
• As the phthalocyanine particles FG-7351 of Dainichiseika Color & Chemicals Mfg. Co., Ltd. was used.
• the surfaces of the phthalocyanine particles were diazo-coupled with 2-vinylaniline and graft-polymerized with 2-ethylhexyl methacrylate.
• the graft chain was charge-controlled using a surfactant.
• the graft-polymerized phthalocyanine particles were dispersed in Isopar G, and Solsperse 17000 (Avecia) was added as a surfactant to the dispersion.
• Microcapsules containing the electrophoretic fluid of Example 3, 4, or 5 are prepared.
• the microcapsules are prepared by coacervation of gelatin-gum arabic.
• the sizes of the microcapsules are adjusted to between 40 and 50 ⁇ m by separation.
• the second and third electrodes are formed on a PET film.
• the pairs of the second and third electrodes are arranged in a hexagonal close-packed array with a pitch of 60 ⁇ m between them.
• An adhesive is applied to the second and third electrodes, and a screen having meshes arranged in a hexagonal close-packed array and corresponding to the pairs of the second and third electrodes is placed on the PET film such that the meshes are aligned with the pairs of the second and third electrodes.
• microcapsules are applied to the screen and are thereby put in the meshes. After excess microcapsules are removed, the screen is removed. As a result, the microcapsules remain on the corresponding pairs of electrodes. Then, an adhesive is applied to the microcapsules, and a PET film on which an ITO electrode is formed is bonded to the microcapsules. As a result, an electrophoretic display device capable of displaying three colors is produced.
• electrophoretic display elements of the produced electrophoretic display device display magenta when a voltage of +15 V is applied to the second and third electrodes relative to the ITO electrode, display black when a voltage of -15 V is applied to the second and third electrodes, and display white when a voltage of +10 V is applied to the second electrodes and a voltage of - 10 V is applied to the third electrodes.
• electrophoretic display elements of the produced electrophoretic display device display magenta when a voltage of -15 V is applied to the second and third electrodes relative to the ITO electrode, display black when a voltage of +15 V is applied to the second and third electrodes, and display white when a voltage of +10 V is applied to the second electrodes and a voltage of -10 V is applied to the third electrodes.
• Pairs of the second and third electrodes are formed on a PET film.
• the pairs of the second and third electrodes are arranged in a hexagonal close-packed array with a pitch of 100 ⁇ m between them.
• a protective film is formed over the second and third electrodes.
• cells are formed in positions corresponding to the pairs of the second and third electrodes using a photoresist.
• a photoresist As the photoresist, SU-8 (Kayaku Microchem Co., Ltd) may be used.
• the thickness of walls between the cells is preferably between 10 and 15 ⁇ m, and the height of the walls is preferably between 40 and 50 ⁇ m.
• the electrophoretic fluids of Examples 4, 6, and 7 are injected into the corresponding cells.
• the electrophoretic fluids are injected into the cells using inkjet nozzles such that the resulting electrophoretic display elements are arranged as shown in FIG. 5.
• a sealing film is formed over the electrophoretic fluids to prevent the liquids from drying.
• a gelatin resin that is not soluble in the electrophoretic fluids may be used.
• a polyoxyethylene surfactant may be added to the gelatin resin to reduce the surface tension with the electrophoretic fluids.
• the gelatin resin is applied over the electrophoretic fluids using a slit coater and is then dried to form the sealing film.
• an adhesive is applied to the sealing film, and a PET film on which an ITO electrode is formed is bonded to the sealing film.
• Electrophoretic display elements of the produced electrophoretic display device display magenta, yellow, or cyan when a voltage of +15 V is applied to the second and third electrodes, display black when a voltage of -15 V is applied to the second and third electrodes, and display white when a voltage of +10 V is applied to the second electrodes and a voltage of -10 V is applied to the third electrodes.
• An embodiment of the present invention provides an electrophoretic display element capable of displaying three colors and having an excellent reflectance and contrast. Another embodiment of the present invention provides an electrophoretic fluid and an electrophoretic display medium containing the electrophoretic fluid that are used for the electrophoretic display element. Still another embodiment of the present invention provides an electrophoretic display device comprising the electrophoretic display elements, a display method using the electrophoretic display element, and methods of producing the electrophoretic display element and the electrophoretic display device.
• An aspect of the present invention provides a method of producing an electrophoretic display element.
• the method includes the steps of preparing an electrophoretic fluid by dispersing first, second, and third dispersible particles having different optical properties in a solvent, the first dispersible particles being uncharged, the second dispersible particles being positively charged electrophoretic particles, and the third dispersible particles being negatively charged electrophoretic particles; placing a pair of electrodes separated from each other on an insulating substrate; forming a sheet with a photoresist on a surface of the insulating substrate on which the pair of the electrodes are placed, the sheet having an opening that exposes the pair of the electrodes; filling the opening of the sheet with the electrophoretic fluid; forming a coating over the opening filled with the electrophoretic fluid; and placing a transparent electrode on the coating over the opening.
• Another aspect of the present invention provides a method of producing an electrophoretic display element.
• the method includes the steps of preparing an electrophoretic fluid by dispersing first, second, and third dispersible particles having different optical properties in a solvent, the first dispersible particles being uncharged, the second dispersible particles being positively charged electrophoretic particles, and the third dispersible particles being negatively charged electrophoretic particles; encapsulating the electrophoretic fluid in a microcapsule used as an electrophoretic display medium; placing a pair of electrodes separated from each other on an insulating substrate; covering a surface of the insulating substrate on which the pair of the electrodes are placed with a sheet having an opening that exposes the pair of the electrodes; placing the microcapsule on the insulating substrate through the opening of the sheet; and placing a transparent electrode on the microcapsule placed on the insulating substrate.
• Another aspect of the present invention provides a method of producing an electrophoretic display device.
• the method includes the steps of preparing an electrophoretic fluid by dispersing first, second, and third dispersible particles having different optical properties in a solvent, the first dispersible particles being uncharged, the second dispersible particles being positively charged electrophoretic particles, and the third dispersible particles being negatively charged electrophoretic particles; placing pairs of electrodes separated from each other on an insulating substrate; forming a sheet with a photoresist on a surface of the insulating substrate on which the pairs of the electrodes are placed, the sheet having openings that expose the corresponding pairs of the electrodes; filling the openings of the sheet with the electrophoretic fluid; forming a coating over the openings filled with the electrophoretic fluid; and placing a transparent electrode on the coating over the openings.
• Another aspect of the present invention provides a method of producing an electrophoretic display device.
• the method includes the steps of preparing an electrophoretic fluid by dispersing first, second, and third dispersible particles having different optical properties in a solvent, the first dispersible particles being uncharged, the second dispersible particles being positively charged electrophoretic particles, and the third dispersible particles being negatively charged electrophoretic particles; encapsulating the electrophoretic fluid in microcapsules used as electrophoretic display media; placing pairs of electrodes separated from each other on an insulating substrate; covering a surface of the insulating substrate on which the pairs of the electrodes are placed with a sheet having openings that expose the corresponding pairs of the electrodes; placing the microcapsules on the insulating substrate through the openings of the sheet; and placing a transparent electrode on the microcapsules placed on the insulating substrate.
• Still another aspect of the present invention provides a method of producing an electrophoretic display device.
• the method includes a first step of preparing an electrophoretic fluid by dispersing first, second, and third dispersible particles having different optical properties in a solvent and preparing first electrophoretic media by encapsulating the electrophoretic fluid in microcapsules, the first dispersible particles being uncharged, the second dispersible particles being positively charged electrophoretic particles, and the third dispersible particles being negatively charged electrophoretic particles; a second step of placing pairs of electrodes separated from each other on an insulating substrate; a third step of covering a surface of the insulating substrate on which the pairs of the electrodes are placed with a first sheet having openings that, respectively, expose a first set of the pairs of the electrodes; a fourth step of placing the first electrophoretic media on the insulating substrate through the openings of the first sheet; a fifth step of removing the first sheet from the insulating substrate; a sixth step of preparing second electrophoretic media as in the first

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