JP2011118225A - Electrophoretic display element and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress color mixing due to movement of particles between retention electrodes, compared with a system having no dielectric film on a retention electrode. <P>SOLUTION: An electrophoretic display element includes: a plurality of kinds of electrophoretic particles 12, which are sealed in between substrates, are charged into the same polarity and have different optical characteristics and migration speeds from one another; a surface electrode 28 having translucency; retention electrodes 32A, 32B disposed opposing to the surface electrode; and a dielectric film 34 provided on at least one retention electrode 32. An electric field applied across the substrates is controlled in such a manner that the electrophoretic particles 12 having optical characteristics of a color to be displayed and the electrophoretic particles 12 in a color other than the color to be displayed, successively move to the retention electrode 32A and the retention electrode 32B, respectively, and subsequently, the electrophoretic particles 12 having the optical characteristics of the color to be displayed move to the surface electrode 28 side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrophoretic display element and a display device.

  Various techniques for performing black and white display and color display using an electrophoretic display element in which electrophoretic particles are sealed between a pair of electrodes have been proposed (for example, Patent Documents 1 to 3).

  In the technique described in Patent Document 1, it is proposed that a plurality of types of particles charged with the same polarity are contained in a transparent dispersion fluid, and multicolor display is performed using a difference in mobility of each particle. .

  In the technique described in Patent Document 2, it is proposed to include at least three particles having different electrophoretic mobilities, and to dominantly control one of the particles by electric field control.

  In the technique described in Patent Document 3, a transparent ferroelectric layer and a ferroelectric layer are provided on a transparent electrode and an individual electrode so as to be stacked at positions facing each other, and colored particles and white are provided between the ferroelectric layers. An electrophoretic device is formed with an electrophoretic dispersion layer including a medium interposed therebetween, and by applying a voltage to the individual electrode and the transparent electrode, the colored particles are deposited in one ferroelectric layer, and at the same time, the ferroelectric layer The transparent ferroelectric layer is polarized, and the voltage applied between the electrodes is reversed, so that the polarization polarity of the ferroelectric layer and the transparent ferroelectric layer is reversed, and the colored particles move to the opposite side. Proposed.

JP 2006-058901 A JP 2009-086687 A JP-A-2005-241916

  An object of the present invention is to suppress color mixing due to the movement of particles between the reserved electrodes, as compared with the case where no dielectric film is provided on the reserved electrodes.

  The electrophoretic display element according to claim 1 is encapsulated between a surface electrode having translucency, a plurality of storage electrodes opposed to the surface electrode, and the surface electrode and the storage electrode. A plurality of types of particles that are each charged to the same polarity and have different optical characteristics and migration speed or threshold characteristics, and a dielectric film provided on at least one of the plurality of storage electrodes. It is characterized by.

  According to a second aspect of the present invention, in the first aspect of the present invention, the dielectric film is provided on each of the plurality of holding electrodes and has a different dielectric constant.

  The invention according to claim 3 is the invention according to claim 1 or 2, further comprising a solvent encapsulated between the surface electrode and the reserved electrode and in which the particles migrate, wherein the dielectric film comprises: The dielectric constant is different from that of the solvent.

  The display device according to claim 4 is the electrophoretic display element according to any one of claims 1 to 3, wherein the particles are to be displayed as particles having optical characteristics of a color to be displayed. The electrophoretic display element including particles having optical characteristics other than color, the particles having optical characteristics of the color to be displayed, and the particles having optical characteristics other than the color to be displayed are different from each other. The electric field applied between the surface electrode and the storage electrode is controlled so that the particles having the optical characteristics of the color to be displayed moved to the storage electrode move sequentially, and then move to the surface electrode side. And an electric field control means.

  According to the first aspect of the present invention, there is an effect that color mixing due to the movement of particles between the reserved electrodes can be suppressed as compared with the case where no dielectric film is provided on the reserved electrodes.

  According to the second aspect of the present invention, there is an effect that particles can be easily collected on each of the storage electrodes, compared to a case where a dielectric film is not provided on each of the plurality of storage electrodes.

  According to the third aspect of the present invention, the dielectric film can act as a potential barrier as compared with the case where the dielectric constant of the storage electrode and the dielectric constant of the solvent are not different from each other. There is.

  According to the invention described in claim 4, as compared with the case where the particles having the optical characteristics of the color to be displayed and the particles having the optical characteristics other than the color to be displayed are not sequentially moved to the different storage electrodes, There is an effect that color mixing due to movement of particles between the storage electrodes can be suppressed.

It is a figure which shows the outline of the display apparatus concerning embodiment of this invention. It is a figure for demonstrating the movement of an electrophoretic particle. It is a figure which shows the movement of the electrophoretic particle at the time of providing a dielectric film in a storage electrode. 10 is a diagram for explaining Experiment 3. FIG. FIG. 10 is a diagram for explaining Experiment 4;

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram schematically showing a display device according to an embodiment of the present invention.

  The display device 10 according to the embodiment of the present invention includes an electrophoretic display element 14 that displays an image by moving a plurality of types of electrophoretic particles 12 (12W, 12K), and an image displayed on the electrophoretic display element 14. And a drive control device 20 that controls the drive of the voltage application device 16 in response to an image display instruction from an external image signal output device 18 such as a personal computer. ing.

  The electrophoretic display element 14 includes a translucent display substrate 22 serving as an image display surface, and a rear substrate 24 disposed opposite to the display substrate 22 with a predetermined interval. .

  A transparent liquid dispersion 25 is sealed between the display substrate 22 and the back substrate 24, and a plurality of types of electrophoretic particles 12 colored in the dispersion liquid 25 are sealed. In the present embodiment, the plurality of types of electrophoretic particles are two types of electrophoretic particles 12, electrophoretic particles 12 </ b> W colored in white and electrophoretic particles 12 </ b> K colored in black. Each electrophoretic particle 12 moves according to the electric field strength formed between the substrates. The translucency means that the visible light transmittance is 70% or more, preferably 90% or more.

  Each electrophoretic particle 12 of the present embodiment is charged with the same polarity, and is positively charged in the present embodiment. In addition, the electrophoresis speeds are different from each other. In the present embodiment, the black electrophoretic particles 12K have a higher electrophoretic speed than the white electrophoretic particles 12W. The migration speed can be set by controlling the particle size, charge amount, and the like.

  The display substrate 22 is provided with a surface electrode 28 on a support substrate 26, and the back substrate 24 has a plurality of (two in this embodiment) reserved electrodes on the support substrate 30 facing the surface electrode 28. 32 is provided. In the present embodiment, one holding electrode 32A holds the electrophoretic particles 12 having optical characteristics of the color to be displayed, and the other holding electrode 32B has electrophoretic particles having optical characteristics other than the color to be displayed. Hold 12

  In addition, a dielectric film 34 is provided on at least one of the plurality of storage electrodes 32. In the present embodiment, an example in which the dielectric film 34 is provided on the side of the holding electrode 32A that holds the electrophoretic particles 12 having the optical characteristics of the color to be displayed will be described. However, the electric film having the optical characteristics other than the color to be displayed is described. A dielectric film 34 may be provided on the holding electrode 32B for holding the migrating particles 12, or a dielectric film 34 may be provided on each holding electrode 32. A dielectric film 34 having a different dielectric constant may be provided on each holding electrode 32.

  As the support substrates 26 and 30, glass or plastic can be applied. Examples of the plastic include polycarbonate resin, acrylic resin, polyimide resin, polyester resin, epoxy resin, and polyether sulfone resin.

  For the surface electrode 28 and the storage electrode 32, oxides such as indium, tin, cadmium and antimon, composite oxides such as ITO, metals such as gold, silver, copper and nickel, organic materials such as polypyrrole and polythiophene are used. can do. These can be formed by a single layer film, a composite film, or a composite film and a vapor deposition method, a sputtering method, a coating method, or the like.

  Although FIG. 1 shows an example in which the surface electrode 28 is embedded in the support substrate 26 and the storage electrode 32 is embedded in the support substrate 30, the surface electrode 28 and the storage electrode 32 may be provided on each support substrate. Good. As shown in FIG. 1, when the surface electrode 28 and the storage electrode 32 are embedded in each support substrate, the materials of the support substrates 28 and 30 may affect the electrical characteristics and fluidity of each electrophoretic particle 12. Therefore, it is necessary to select according to the composition of each electrophoretic particle 12.

  In addition, each of the front electrode 28 and the reserved electrode 32 may be separated from the display substrate 22 and the back substrate 24 and disposed outside the electrophoretic display element 14. In the present embodiment, a case will be described in which electrodes (surface electrode 28 and storage electrode 32) are provided on both the display substrate 22 and the back substrate 24, but only one of them may be provided.

The dispersion liquid 25 in which the electrophoretic particles 12 are dispersed is preferably a high resistance liquid. Here, “high resistance” indicates that the volume resistivity is 10 ⁷ Ω · cm or more, preferably 10 ¹⁰ Ω · cm or more, more preferably 10 ¹² Ω · cm or more.

  Specific examples of high-resistance liquids include hexane, cyclohexane, toluene, xylene, decane, hexadecane, kerosene, paraffin, isoparaffin, silicone oil, dichloroethylene, trichloroethylene, perchloroethylene, high-purity petroleum, benzine, diisopropylnaphthalene, and olive oil. , Trichlorotrifluoroethane, tetrachloroethane, dibromotetrafluoroethane, and the like, and mixtures thereof can be suitably used.

  In addition, to the high-resistance liquid, an acid, an alkali, a salt, a dispersion stabilizer, a stabilizer, an antibacterial agent, a preservative, and the like can be added for the purpose of preventing oxidation or absorbing ultraviolet rays. It is preferable to add so that it may become the range of the specific volume resistance value shown by.

  For high resistance liquids, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, fluorosurfactants, silicone surfactants, metal soaps as charge control agents , Alkyl phosphate esters, succinimides and the like can be added.

  More specific examples of the ionic and nonionic surfactants are as follows. Nonionic activators include polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, And fatty acid alkylolamide. Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkyl naphthalene sulfonate, higher fatty acid salt, sulfate of higher fatty acid ester, sulfonic acid of higher fatty acid ester, and the like. Examples of the cationic surfactant include primary to tertiary amine salts and quaternary ammonium salts. These charge control materials are preferably 0.01% by weight or more and 20% by weight or less, particularly preferably in the range of 0.05 to 10% by weight with respect to the solid content of the particles. If it is less than 0.01% by weight, the desired charge control effect is insufficient, and if it exceeds 20% by weight, an excessive increase in conductivity of the dispersion is caused.

  The electrophoretic particles 12 dispersed in the dispersion 25 include glass beads, metal oxide particles such as alumina and titanium oxide, thermoplastic or thermosetting resin particles, and a colorant on the surface of these resin particles. Examples thereof include fixed particles, particles containing a colorant in a thermoplastic or thermosetting resin, and metal colloid particles having a plasmon coloring function.

  Examples of the thermoplastic resin used in the production of particles include styrenes such as styrene and chlorostyrene, monoolefins such as ethylene, propylene, butylene, and isoprene, vinyls such as vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl butyrate. Α-methylene aliphatic monocarboxylic acid such as ester, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate Homopolymers or copolymers of vinyl ethers such as acid esters, vinyl methyl ether, vinyl ethyl ether, vinyl butyl ether, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, vinyl isopropenyl ketone It can be exemplified.

  In addition, as thermosetting resins used for the production of particles, crosslinked resins mainly composed of divinylbenzene and crosslinked resins such as crosslinked polymethyl methacrylate, phenol resins, urea resins, melamine resins, polyester resins, silicones Examples thereof include resins. Particularly representative binder resins include polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer. Examples thereof include a polymer, polyethylene, polypropylene, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, and paraffin wax.

  As the colorant, organic or inorganic pigments, oil-soluble dyes, etc. can be used, magnetic powders such as magnetite and ferrite, carbon black, titanium oxide, magnesium oxide, zinc oxide, phthalocyanine copper-based cyan colorant, Known colorants such as an azo yellow color material, an azo magenta color material, a quinacridone magenta color material, a red color material, a green color material, and a blue color material can be given. Specifically, aniline blue, calcoil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment yellow 97, C.I. I. Pigment blue 15: 1, C.I. I. Pigment Blue 15: 3, etc. can be exemplified as typical ones.

  The particle resin may be mixed with a charge control agent, if necessary. As the charge control agent, known materials used for toner materials for electrophotography can be used. For example, cetylpyridyl chloride, BONTRON P-51, BONTRON P-53, BONTRON E-84, BONTRON E-81 (above, Quaternary ammonium salts such as Orient Chemical Industry Co., Ltd., salicylic acid metal complexes, phenol condensates, tetraphenyl compounds, metal oxide particles, and metal oxide particles surface-treated with various coupling agents. .

  An external additive may be attached to the surface of the particles as necessary. The color of the external additive is preferably transparent so as not to affect the color of the particles. As the external additive, inorganic particles such as metal oxides such as silicon oxide (silica), titanium oxide, and alumina are used. In order to adjust the charging property, fluidity, and environment dependency of the particles, they can be surface-treated with a coupling agent or silicone oil. Coupling agents include positively chargeable ones such as aminosilane coupling agents, aminotitanium coupling agents, nitrile coupling agents, and silanes that do not contain nitrogen atoms (consisting of atoms other than nitrogen). There are negatively charged ones such as coupling agents, titanium-based coupling agents, epoxy silane coupling agents, and acrylic silane coupling agents. Silicone oil includes positively charged ones such as amino-modified silicone oil, dimethyl silicone oil, alkyl-modified silicone oil, α-methylsulfone-modified silicone oil, methylphenyl silicone oil, chlorophenyl silicone oil, and fluorine-modified silicone. Examples include negatively chargeable oils.

  As a method for producing each electrophoretic particle 12, any conventionally known method may be used. For example, as described in JP-A-7-325434, the resin, the pigment, and the charge control agent are weighed so as to have a predetermined mixing ratio, and after the resin is heated and melted, the pigment is added, mixed, dispersed, After cooling, a method of preparing particles using a pulverizer such as a jet mill, a hammer mill, a turbo mill, etc., and then dispersing the obtained particles in a dispersion medium can be used. Also, particles containing a charge control agent are prepared by polymerization methods such as suspension polymerization, emulsion polymerization, dispersion polymerization, coacervation, melt dispersion, emulsion aggregation, and then dispersed in a dispersion medium. A particle dispersion medium may be prepared. Furthermore, the resin can be plasticized, the dispersion medium does not boil, and the resin, the colorant, the charge control agent and the dispersion medium are at a temperature lower than the decomposition point of the resin, the charge control agent and / or the colorant. There are methods using suitable equipment that can disperse and knead the raw materials. Specifically, the pigment, the resin, and the charge control agent are heated and melted in a dispersion medium with a meteor mixer, a kneader, etc., and the molten mixture is cooled with stirring using the temperature dependence of the solvent solubility of the resin. The particles can be made by solidification / precipitation.

  On the other hand, the voltage applying device 16 is connected to each of the surface electrode 28 and the reserved electrode 32, and an electric field is formed between the substrates by applying a voltage to the surface electrode 28 and the reserved electrode 32 by the voltage applying device 16. The

  The voltage application device 16 is connected to a drive control device 20, and an image signal output device 18 is connected to the drive control device 20. The drive control device 20 includes a CPU, a ROM, a RAM, a hard disk, and the like, and the CPU displays an image on the display device 10 according to a program stored in the ROM, the hard disk, or the like. The image signal output device 18 may apply a hard disk or the like to store and output a display image for displaying an image on the electrophoretic display element 14. That is, the drive control device 20 controls the voltage application device 16 according to the display image stored in the image signal output device 18 to apply a voltage between the substrates, so that each electrophoretic particle 12 corresponds to the voltage. Move and display the image. The display image stored in the image signal output device 18 may be taken into the image signal output device 18 via various recording media such as a CD-ROM and a DVD and a network.

  Each electrophoretic particle 12 maintains its state when a voltage is applied, even after the application of the voltage between the substrates is stopped, by an adhesive force such as van der Waals force or mirror image force.

  Next, color display of the display device 10 according to the embodiment of the present invention configured as described above will be described.

  In the present embodiment, as described above, the two reserved electrodes 32A and 32B are provided for the surface electrode 28, and each electrophoretic particle 12 is charged to the same polarity, and the moving speed is different.

  Therefore, the voltage applied to the storage electrode 32A is controlled so that the electrophoretic particles 12 are sequentially moved to the storage electrode 32A or the storage electrode 32B in order of increasing migration speed according to the color to be displayed. At this time, the electrophoretic particles 12 having the optical characteristics of the color to be displayed on one holding electrode 32A move, and the electrophoretic particles 12 having the optical characteristics other than the color to be displayed on the other holding electrode 32B move. In addition, by controlling the voltage applied to each holding electrode 32, the electrophoretic particles 12 having optical characteristics other than the color to be displayed on one holding electrode 32A move, and the color to be displayed on the other holding electrode 32B. Electrophoretic particles 12 having the following optical characteristics move.

  Specifically, first, the surface electrode 28 is grounded, and a positive voltage is applied to each holding electrode 32, whereby each electrophoretic particle 12 is moved to the display substrate 22 side to be in an initial state. That is, since each electrophoretic particle 12 is positively charged, by applying a positive voltage to the storage electrode 32, the electrophoretic particle 12 moves to the surface electrode 28 side.

  Subsequently, the voltage applied to the storage electrodes 32A and 32B is controlled in order from the electrophoretic particle 12 having the fastest migration speed according to the color to be displayed. For example, when the electrophoretic particle 12 to be moved is the electrophoretic particle 12 having the optical characteristics of the color to be displayed, a negative voltage is applied to the reservation electrode 32A, the reservation electrode 32B is grounded, and the movement is performed. When the target electrophoretic particles 12 are electrophoretic particles 12 having optical characteristics other than the color to be displayed, the reserved electrode 32A is grounded and a negative voltage is applied to the reserved electrode 32B.

  As a result, the electrophoretic particles 12 having optical characteristics other than the color to be displayed on one holding electrode 32A are held, and the electrophoretic particles 12 having the optical characteristics of the color to be displayed on the other holding electrode 32B are held. . That is, by sequentially moving from the electrophoretic particles 12 having a high migration speed, each electrophoretic particle 12 is moved to the reserved electrode 32A or the reserved electrode 32B according to the color to be displayed.

  When all the electrophoretic particles 12 have moved to the holding electrode 32A or the holding electrode 32B, a positive voltage is applied to the holding electrode 32A holding the electrophoretic particles 12 having the optical characteristics of the color to be displayed. By grounding the storage electrode 32A, the electrophoretic particles 12 having the optical characteristics of the color to be displayed move from the storage electrode 32 to the display substrate 22 side, and a desired color is displayed.

  Here, as an example, a case where black is displayed in the present embodiment will be described as an example. FIG. 2 is a diagram for explaining a display method when displaying black in the display device 10 according to the embodiment of the present invention.

  In the display device 10 according to the present embodiment, first, the surface electrode 28 is grounded, and a + V voltage is applied to each holding electrode 32 to be in a reset state. As a result, each electrophoretic particle 12 moves to the display substrate 22 side to be in the state shown in FIG.

  Subsequently, since the black electrophoretic particles 12 </ b> K having the fastest electrophoretic speed are colors that contribute to the color to be displayed, the black electrophoretic particles 12 </ b> A are applied to the holding electrode 32 </ b> A that holds the electrophoretic particles 12 having the optical characteristics of the color to be displayed. The holding electrode 32B that holds the electrophoretic particles 12 having optical characteristics other than the color to be displayed is grounded by applying a voltage of V. As a result, the black electrophoretic particles 12K move to the holding electrode 32A, and the state shown in FIG.

  In addition, the electrophoretic particles 12W of white (the electrophoretic particles 12 which are the two types of electrophoretic particles 12 in the present embodiment, but the next high electrophoretic particles 12 in the case of three or more types) are Since the color does not contribute to the color to be displayed, when the black electrophoretic particles 12K move to the storage electrode 32A, the storage electrode 32B stores the electrophoretic particles 12 having optical characteristics other than the color to be displayed. The holding electrode 32A for holding the electrophoretic particles 12 having the optical characteristics of the color to be displayed is grounded. As a result, the white electrophoretic particles 12W move to the storage electrode 32B, and the state shown in FIG.

  Then, a voltage of + V is applied to the holding electrode 32A that holds the electrophoretic particles 12 having the optical characteristics of the color to be displayed, and the holding electrode 32B that holds the electrophoretic particles 12 having the optical characteristics other than the color to be displayed is applied. By grounding, the black electrophoretic particles 12K that contribute to the color to be displayed move to the display substrate 22 side. As a result, black is displayed.

  By the way, in the present embodiment, the dielectric film 34 is provided on the holding electrode 32A that holds the electrophoretic particles 12 having the optical characteristics of the color to be displayed. However, when a voltage is applied to the holding electrode 32A, the dielectric film is provided. Polarization occurs in 34, and the lines of electric force are bent, so that the electrophoretic particles 12 are easily collected on the holding electrode 32A. Accordingly, when the electrophoretic particles 12 having the optical characteristics of the color to be displayed are moved to the reserved electrode 32A, the electrophoretic particles 12 having the optical characteristics of the color to be displayed and the electric characteristics having an optical characteristic other than the color to be displayed. The separation performance from the migrating particles 12 is improved, and as a result, color mixing is suppressed.

  Furthermore, when the dielectric constant of the dielectric film 34 and the dielectric constant of the dispersion liquid 25 are set to different dielectric constants, the electrophoretic particles 12 move as indicated by arrows in FIG. 3, and the dielectric film 34 functions as a potential barrier. Thus, it is possible to prevent the electrophoretic particles 12 from flowing backward to the adjacent reserved electrode 32, and as a result, color mixing is prevented. That is, when a voltage of −V is applied to the holding electrode 32A as shown in FIG. 3B from the reset state of FIG. 3A, the dielectric film 34 functions as a potential barrier, and FIG. Electrophoretic particles 12K move as indicated by arrows. Similarly, when a voltage of −V is applied to the holding electrode 32B from the state of FIG. 3B, the dielectric film 34 functions as a potential barrier, as shown by the arrow in FIG. When the electrophoretic particles 12W move and a voltage of + V is applied to the holding electrode 32A from the state of FIG. 3C, the dielectric film 34 functions as a potential barrier, and the arrow shown in FIG. Thus, the electrophoretic particles 12K move.

  In the above embodiment, the case where two types of electrophoretic particles 12 are used has been described. However, three or more types of electrophoretic particles 12 may be used. In the above embodiment, the charged electrophoretic particles 12 are moved to display the color, but the uncharged white electrophoretic particles 12 are mixed and suspended in the dispersion liquid 25. You may make it improve whiteness.

  Subsequently, a result of an experiment for verifying the effect of the dielectric film 34 using a specific electrophoretic display element 14 will be described.

  The electrophoretic display element 14 used in the experiment was one in which uncharged white particles, charged magenta electrophoretic particles 12M, and charged cyan electrophoretic particles 12C were enclosed.

  First, a method for adjusting white particles used in the experiment will be described.

  In a 100 ml three-necked flask equipped with a reflux condenser, 5 g of 2-vinylnaphthalene (manufactured by Nippon Steel Chemical Co., Ltd.), 5 g of silicone macroma FM-0721 (manufactured by Chisso Corp.), lauroyl peroxide as an initiator 0.26 g and silicone oil (KF-96L-1CS: manufactured by Shin-Etsu Chemical Co., Ltd.) 20 ml, and bubbling with nitrogen gas for 15 minutes, followed by polymerization at 65 ° C. for 24 hours in a nitrogen atmosphere. went. The produced white particles had a volume average particle diameter of 650 nm (measured with FPAR-1000, manufactured by Otsuka Electronics Co., Ltd.) and were not charged in silicone oil.

  The white particles are used as a white reflective layer, and when the electrophoretic particles 12 move to the back substrate 24 side, they are hidden by the white particles and thus display white.

  Next, a method for adjusting the magenta electrophoretic particles 12M will be described.

  Silaplane FM-0711: 95 parts by mass, methyl methacrylate: 3 parts by mass, glycidyl methacrylate 2 parts by mass are mixed with 50 parts by mass of silicone oil, and 0.5 parts by mass of azobisvaleronitrile is added as a polymerization initiator. Then, polymerization was carried out to produce a reactive silicone polymer (reactive dispersant) having an epoxy group. The weight average molecular weight was 600,000. And the 3 mass% silicone oil solution of the reactive silicone type polymer was prepared. In addition, as silicone oil, dimethyl silicone oil (KF-96L-2CS manufactured by Shin-Etsu Silicone) was used.

  Next, a 9/1 copolymer (weight average molecular weight 60,000) in mass ratio of N-vinylpyrrolidone and N, N-diethylaminoethyl acrylate is synthesized by ordinary radical solution polymerization as a polymer having a charged group. Used.

  Next, 3 parts by mass of a 10% aqueous solution of the above copolymer was mixed with 1 part by mass of a Ciba water-dispersed pigment solution (Unisperse / magenta color: pigment concentration of 16% by mass), and this mixed solution was mixed with the reactive silicone system. A suspension obtained by mixing 10 parts by weight of a 3% by weight silicone polymer solution and stirring the mixture for 10 minutes with an ultrasonic crusher, and dispersing and emulsifying an aqueous solution containing a polymer having a charged group and a pigment in silicone oil. Was prepared.

  Next, the suspension is decompressed (2 KPa), heated (70 ° C.) to remove moisture, and a silicone oil dispersion in which colored particles containing a polymer having a charged group and a pigment are dispersed in silicone oil is obtained. Obtained. Further, this dispersion was heated at 100 ° C. for 3 hours to react with and bind to the reactive silicone polymer. Next, butyl bromide corresponding to 50% of the molar amount of N, N-diethylaminoethyl acrylate in the solid content of the particles is added to the dispersion and heated at 80 ° C. for 3 hours to perform quaternization of amino groups. Thereafter, the particles were washed and classified using a centrifuge. The produced magenta colored particles had a volume average particle size of 900 nm (manufactured by Otsuka Electronics Co., Ltd., measured with FPAR-1000) and were positively charged in silicone oil.

  Next, a method for adjusting cyan electrophoretic particles 12C will be described. The migration speed of the cyan electrophoretic particles 12C is slower than the migration speed of the magenta electrophoretic particles 12M.

  Silaplane FM-0711: 95 parts by mass, methyl methacrylate: 3 parts by mass, glycidyl methacrylate 2 parts by mass are mixed with 50 parts by mass of silicone oil, and 0.5 parts by mass of azobisvaleronitrile is added as a polymerization initiator. Then, polymerization was carried out to produce a reactive silicone polymer (reactive dispersant) having an epoxy group. The weight average molecular weight was 600,000. And the 3 mass% silicone oil solution of the reactive silicone type polymer was prepared. In addition, as silicone oil, dimethyl silicone oil (KF-96L-2CS manufactured by Shin-Etsu Silicone) was used.

  Next, a 9/1 copolymer (weight average molecular weight 60,000) in mass ratio of N-vinylpyrrolidone and N, N-diethylaminoethyl acrylate is synthesized by ordinary radical solution polymerization as a polymer having a charged group. Used.

  Next, 3 parts by mass of a 10% aqueous solution of the above copolymer was mixed with 1 part by mass of a Ciba water-dispersed pigment solution (Unisperse cyan color: pigment concentration 26 mass%), and this mixed solution was mixed with the reactive silicone system. A suspension obtained by mixing 10 parts by weight of a 3% by weight silicone polymer solution and stirring the mixture for 10 minutes with an ultrasonic crusher, and dispersing and emulsifying an aqueous solution containing a polymer having a charged group and a pigment in silicone oil. Was prepared.

  Next, the suspension is decompressed (2 KPa), heated (70 ° C.) to remove moisture, and a silicone oil dispersion in which colored particles containing a polymer having a charged group and a pigment are dispersed in silicone oil is obtained. Obtained. Further, this dispersion was heated at 100 ° C. for 3 hours to react with and bind to the reactive silicone polymer. Next, butyl bromide corresponding to 50% of the molar amount of N, N-diethylaminoethyl acrylate in the solid content of the particles is added to the dispersion and heated at 80 ° C. for 3 hours to perform quaternization of amino groups. Thereafter, the particles were washed and classified using a centrifuge. The produced cyan particles had a volume average particle diameter of 300 nm (Otsuka Electronics Co., Ltd., measured with FPAR-1000) and were positively charged in silicone oil.

  Subsequently, production of the substrate will be described.

  The display substrate 22 was produced by forming a film of ITO on a glass having a thickness of 1.1 mm with a thickness of 50 nm by a sputtering method.

  Next, the ITO electrode of the produced substrate was patterned with a width of 80 μm and a space of 20 μm, and a back substrate 24 having a reserved electrode 32 group was produced.

  Next, 30 parts by volume of titanium oxide fine particles (Ishihara Sangyo Co., Ltd., Taipei CR-63) and 70 parts by volume of photosensitive epoxy resin SU-8 are mixed and coated on the back substrate 24 at a thickness of 30 μm. A dielectric film 34 was produced by patterning with a width of 100 μm and a space of 100 μm so as to overlap the 24 electrodes. At this time, the dielectric constant of the produced dielectric film 34 was 8.

  A display cell was manufactured by sandwiching a Teflon (registered trademark) sheet spacer having a thickness of 100 μm between the display substrate 22 and the back substrate 24.

  Further, for the back substrate 24, the back substrates A to E were manufactured in the same manner by changing the mixing ratio of the titanium oxide fine particles and the photosensitive epoxy resin in the manufacture of the display substrate 22 described above. Table 1 shown below shows the mixing ratio and dielectric constant of the titanium oxide fine particles and the photosensitive epoxy resin of each substrate.

The display cell was manufactured by sandwiching a spacer of a 100 μm Teflon (registered trademark) sheet between the display substrate and the back substrate. Table 2 shows the correspondence between the display cells and the back substrate.

Here, Experiments 1 to 5 were performed using the display cells A to E.

  First, in Experiment 1, the color of the magenta electrophoretic particles 12M was measured. The produced display cell E was filled with white particles at 30 parts by weight, magenta electrophoretic particles 12M at 1 part by weight, and silicone oil at 69 parts by weight. Next, 0V is applied to the display substrate electrode (surface electrode 28) and + 30V is applied to all of the back substrate electrode (reserved electrode 32) for 1 s to move the electrophoretic particles 12M to the display substrate 22 side in magenta color. The color was measured.

  In Experiment 2, color measurement of cyan electrophoretic particles 12C was performed. The produced display cell E was filled so that the white particles were 30 parts by weight, the cyan electrophoretic particles 12C were 1 part by weight, and the silicone oil was 69 parts by weight. Next, 0 V was applied to the surface electrode 28 and +30 V was applied to all the reserved electrodes 32 for 1 s to move the cyan electrophoretic particles 12C to the display substrate 22 side, and color measurement was performed using X-Rite.

  In the following description, the display cell E does not have the dielectric film 34, but an electrode at the same position as the display cells A to D is shown (a dielectric film exists for every other electrode).

  In Experiment 3, magenta color display measurement was performed in a mixed state of magenta electrophoretic particles 12M and cyan electrophoretic particles 12C. In each of the produced display cells A to E, white particles are 30 parts by weight, magenta electrophoretic particles 12M are 1 part by weight, cyan electrophoretic particles 12C are 1 part by weight, and silicone oil is 68 parts by weight. Filled. Next, as shown in FIG. 4A, 0V is applied to the surface electrode 28 and + 30V is applied to all of the storage electrodes 32 for 1 second to display the magenta electrophoretic particles 12M and the cyan electrophoretic particles 12C on the display substrate. Next, as shown in FIG. 4B, 0V is applied to the storage electrode 32B on which the surface electrode 28 and the dielectric film 34 are not provided, and −15V is applied to the storage electrode 32A on which the dielectric film 34 is provided. Was applied for 600 ms, and magenta electrophoretic particles 12M having a high migration speed were adhered to the holding electrode 32A on which the dielectric film 34 was provided. Subsequently, as shown in FIG. 4C, 0V is applied to the holding electrode 32A provided with the surface electrode 28 and the dielectric film 34, and -30V is applied to the holding electrode 32B provided with no dielectric film 34 for 1 s. Cyan electrophoretic particles 12C having a low migration speed were adhered to the storage electrode 32B on which the film 34 was not provided. Subsequently, as shown in FIG. 4D, 0V is applied to the storage electrode 32B on which the surface electrode 28 and the dielectric film 34 are not provided, and + 30V is applied to the storage electrode 32A on which the dielectric film 34 is provided for 1 s. The cyan electrophoretic particles 12C attached to the storage electrode 32B provided with the film 34 were moved to the display substrate 22 side, and colorimetry was performed using X-Rite. Further, the optical change at this time was measured with a spectroscope (OceanOptics, USB2000 +).

  In Experiment 4, cyan display measurement was performed in a mixed state of magenta electrophoretic particles 12M and cyan electrophoretic particles 12C. In each of the produced display cells A to E, white particles are 30 parts by weight, magenta electrophoretic particles 12M are 1 part by weight, cyan electrophoretic particles 12C are 1 part by weight, and silicone oil is 68 parts by weight. Filled. Next, as shown in FIG. 5A, 0V is applied to the surface electrode 28 and + 30V is applied to all of the reserved electrodes 32 for 1 second to display the magenta electrophoretic particles 12M and the cyan electrophoretic particles 12C on the display substrate. Next, as shown in FIG. 5B, 0V is applied to the storage electrode 32A provided with the surface electrode 28 and the dielectric film 34, and -15V is applied to the storage electrode 32B provided with no dielectric film 34. Was applied for 700 ms, and magenta electrophoretic particles 12M having a high migration speed were adhered to the reserved electrode 32B on which the dielectric film 34 was not provided. Subsequently, as shown in FIG. 5C, 0 V is applied to the storage electrode 32B on which the surface electrode 28 and the dielectric film 34 are not provided, and −30 V is applied to the storage electrode 32A on which the dielectric film 34 is provided for 1 s. Cyan electrophoretic particles 12C having a low migration speed were adhered to the storage electrode 32A provided with the dielectric film 34. Subsequently, as shown in FIG. 5D, 0V is applied to the storage electrode 32B in which the dielectric film 34 is not provided among the surface electrode 28 and the storage electrode 32, and + 30V is applied to the storage electrode 32A in which the dielectric film 34 is provided. For 1 s, cyan electrophoretic particles 12C attached to the storage electrode 32A provided with the dielectric film 34 were moved to the display substrate 22 side, and colorimetry was performed using X-Rite. Further, the optical change at this time was measured with a spectroscope (OceanOptics, USB2000 +).

  The results of the above experiments 1 to 4 are shown in the following table.

ΔE indicates a color difference based on the display of Experiment 1 and Experiment 2 (no color mixing).

  Moreover, 2.4 of “No dielectric film relative dielectric constant (2.4)” indicates the dielectric constant of the solvent. The relative permittivity of the solvent (silicone oil) is 2.42.

  As shown in Table 3, the higher the relative permittivity of the dielectric film 34, the smaller the color difference, improving the particle separation performance and reducing the color mixture.

  It can also be seen that the higher the relative dielectric constant of the dielectric film 34 is, the shorter the response time is, and the responsiveness is improved. In other words, the presence of the dielectric film 34 increases the electric field strength between the electrodes (between the upper portion of the dielectric film and the display substrate), and the larger the dielectric constant of the dielectric film, the larger the electric field strength, thereby shortening the response time.

  That is, by providing the dielectric film 34 on the storage electrode 32, the movement of the electrophoretic particles between the storage electrodes 32 is suppressed, color mixing is suppressed, and the responsiveness is improved.

  In the above-described embodiment, the case where the migration speeds of the plurality of types of electrophoretic particles 12 are different from each other has been described as an example. However, the present invention is not limited to this, and the threshold characteristics of the electric field for moving are different. A plurality of types of electrophoretic particles 12 may be applied. That is, by controlling the voltage applied between the substrates so that the electrophoretic particles 12 are sequentially moved to the storage electrode 32A or the storage electrode 32B in accordance with the threshold characteristic, the display of a desired color can be performed as in the above embodiment. Done.

DESCRIPTION OF SYMBOLS 10 Image display apparatus 12 Image display medium 14 Voltage application apparatus 18 Drive control apparatus 20 Display substrate 22 Back surface substrate 28 Colored particle 30, 32 Large diameter colored particle 36 Surface electrode 40 Back electrode

Claims (4)

A surface electrode having translucency;
A plurality of holding electrodes disposed opposite to the surface electrode;
A plurality of types of particles encapsulated between the surface electrode and the storage electrode, each charged with the same polarity, and having different optical characteristics and migration speed or threshold characteristics,
A dielectric film provided on at least one of the plurality of storage electrodes;
An electrophoretic display device comprising:   The electrophoretic display element according to claim 1, wherein the dielectric film is provided on each of the plurality of holding electrodes and has a different dielectric constant. Further comprising a solvent encapsulated between the surface electrode and the storage electrode and in which the particles migrate;
The electrophoretic display element according to claim 1, wherein the dielectric film has a dielectric constant different from that of the solvent. The electrophoretic display element according to any one of claims 1 to 3, wherein the particles include particles having optical characteristics of colors to be displayed and particles having optical characteristics other than colors to be displayed. Including an electrophoretic display element,
The particles having the optical characteristics of the color to be displayed and the particles having optical characteristics other than the color to be displayed are sequentially moved to different reserved electrodes, and then the particles moved to the reserved electrode are to be displayed. An electric field control means for controlling an electric field applied between the surface electrode and the storage electrode so that particles having color optical properties move to the surface electrode side;
A display device comprising: