JP5391518B2 - Electrophoretic particles and production method thereof, electrophoretic particle dispersion and image display device using the same - Google Patents

Description

  The present invention relates to electrophoretic particles, a method for producing the same, an electrophoretic particle dispersion, and an image display device using the same.

  CRTs and liquid crystal displays are widely used as display terminals for so-called images such as characters, still images, and moving images. They can display and rewrite digital data instantly, but it is not easy to always carry the device. In addition, since it is a self-luminous device, there are problems such as eye fatigue when working for a long time and display not being maintained when the power is turned off. On the other hand, when a character or a still image is distributed or stored as a document, it is recorded on a paper medium by a printer. This paper medium is widely used as a so-called hard copy. Since hard copy sees reflections due to multiple scattering, it has better visibility than a self-luminous device and is less tiring. Moreover, since it is lightweight and excellent in handling, it can be read in a free posture. However, the hard copy is discarded after it is used. Some of them are recycled, but the recycling requires a lot of labor and cost, and there are problems in terms of resource saving. In recent years, with the development of information equipment, information processing such as document creation has been performed on a computer, and the opportunity to read text on a display terminal has greatly increased.

  Under such circumstances, there is a growing need for a paper-like display medium that can be rewritten with the advantages of both display and hard copy and that is suitable for the act of reading. Recently, a display medium using a polymer dispersed liquid crystal, a bistable cholesteric liquid crystal, an electrochromic element, an electrophoretic element, etc. has been actively researched and developed as a reflective display medium that can display brightly and has a memory property. Has been done. In particular, a display medium using an electrophoretic element is excellent in terms of display quality and power consumption during display operation. For example, Patent Document 1 and Patent Document 2 disclose the principle of the invention.

  In an electrophoretic display medium, a dispersion liquid in which a plurality of electrophoretic particles having a color different from the color of the dispersion medium is dispersed in a colored dispersion medium between a pair of transparent electrodes. . In this case, the electrophoretic particles (also simply referred to as electrophoretic particles) are charged on the particle surface in the dispersion medium, and when a voltage for attracting the electrophoretic particles is applied to one transparent electrode side. Electrophoretic particles are attracted and accumulated on the transparent electrode side, and the color of the electrophoretic particles is observed. When a voltage repelling the charge of the electrophoretic particles is applied, the electrophoretic particles move to the opposite transparent electrode side. The color of the dispersion medium is observed. Display can be performed by using this change.

Electrophoretic particles used in image display media are required to have dispersion stability in a dispersion medium in addition to electrophoretic properties. As a method for satisfying such a requirement, Patent Document 3 and Patent Document 4 describe electrophoretic particles obtained by grafting a polymer having a dispersive part that enhances affinity with a dispersion medium on the particle surface. On the other hand, in Patent Document 5, surface treatment of electrophoretic particles is performed using a coupling agent that imparts chargeability to improve chargeability, and rapid electrophoretic properties are imparted to electrophoretic particles used in an image display device. Multiple names are listed.
JP-A-5-173194 Japanese Patent No. 2612472 Japanese Patent Laid-Open No. 3-249736 JP-A-5-173193 JP 2004-191418 A

  The electrophoretic particles used in the image display medium are first required to have dispersion stability that suppresses aggregation, sedimentation, and the like of the electrophoretic particles. Furthermore, electrophoretic properties that respond quickly to an electric field are required. Although the electrophoretic particles described in Patent Document 3 and Patent Document 4 can exhibit dispersion stability, there are not enough functional groups or the like to impart chargeability to the particle surface. The electrophoretic properties are not sufficient. Moreover, in the electrophoretic particles described in Patent Document 5, although the electrophoretic characteristics are improved, since the polymer that improves the dispersion stability is not introduced on the particle surface, the electrophoretic particles are resistant to diffusion and aggregation in the dispersion medium. There is a possibility that sufficient stability cannot be obtained, and there is a problem in image storage performance as a recording medium.

  In view of such problems, an object of the present invention is to provide an electrophoretic particle that has excellent dispersion stability in an electrophoretic dispersion, excellent electrophoretic properties, and does not cause diffusion or aggregation even after voltage application is stopped. Another object of the present invention is to provide an electrophoretic dispersion using the electrophoretic particles and an image display device having high display stability using the electrophoretic dispersion as a display medium.

The present inventors have found that the above object can be achieved by grafting a lipophilic polymer having a side chain of a polar polymer unit to a fine particle nucleus, and have completed the following invention.
The present invention provides an electrophoretic particles for an image display device of an electrophoretic system, the particulate core surface graft polymer having a side chain of a polar polymer unit having a polar group to a lipophilic polymer backbone, particle nucleation surface The electrophoretic particles are characterized by being grafted onto the surface.

  The present invention includes the electrophoretic particles, wherein the lipophilic polymer main chain is a hydrocarbon polymer, a halogenated hydrocarbon polymer, or polysiloxane.

  The present invention includes the electrophoretic particle, wherein the lipophilic polymer main chain has a number average molecular weight of 1,000 to 100,000.

  The present invention includes the electrophoretic particle, wherein a ratio of the graft polymer to the fine particle nucleus is 0.1 to 25% by mass.

The present invention relates to a method for producing an electrophoretic particle for an electrophoretic image display device, which has a functional group having reactivity to the surface of a fine particle core and a functional group serving as a polymerization initiation point of a monomer having a polar group. while polymerizing the monomer having the polar group in the oleophilic polymer, including manufacturing method of the electrophoretic particles, characterized in that grafting the lipophilic polymer to the particle core surface.

Preferably , the method includes producing the electrophoretic particles, wherein the monomer having a polar group is a vinyl monomer.
The present invention relates to a method for producing an electrophoretic particle for an electrophoretic image display device, wherein an oleophilic polymer having a polymer unit having a polar group formed in a side chain is grafted to the surface of a fine particle core, or the fine particle And a method of producing electrophoretic particles, wherein a polymer unit having a polar group is grafted to the lipophilic polymer grafted to the surface of the fine particle nucleus after the lipophilic polymer is grafted to the core surface.

  The present invention includes the method for producing electrophoretic particles, wherein after the coupling agent is reacted with the fine particle nuclei, the lipophilic polymer is grafted onto the fine particle nuclei.

  The present invention includes an electrophoretic dispersion characterized in that the electrophoretic particles are dispersed in a nonpolar dispersion medium.

  The present invention includes the electrophoretic dispersion, wherein the content of the electrophoretic particles is 0.1 to 25% by mass.

  The present invention includes the electrophoretic dispersion, which includes a dispersing agent that assists dispersion of the electrophoretic particles.

  The present invention includes an image display device in which the electrophoretic particle dispersion is disposed between a pair of opposed electrode plates, at least one of which is transparent.

  The present invention includes the electrophoretic particle dispersion liquid which is divided into minute regions and arranged.

  According to the present invention, an electrophoretic particle having excellent dispersion stability in an electrophoretic dispersion, excellent electrophoretic properties, and which does not cause diffusion or aggregation even after the application of voltage is stopped, a method for producing the same, and the electrophoresis It is possible to provide an electrophoretic dispersion using particles and an image display device having high display stability using the electrophoretic dispersion as a display medium.

(Electrophoretic particles)
The electrophoretic particles of the present invention are used in an electrophoretic image display device. The electrophoretic particles have a structure in which a graft polymer is grafted on the surface of a fine particle nucleus. The graft polymer has a side chain of a polar polymer unit having a polar group in a lipophilic polymer main chain. In the graft polymer in the electrophoretic particle of the present invention, the non-polar polymer main chain is usually bonded to the surface of the fine particle core via a polar group, but the polymer main chain having a strong affinity for the non-polar dispersion medium and , Have side-chain polymer units carrying charge.

  The lipophilic polymer main chain is made of a polymer having a high affinity with the electrophoretic medium when the electrophoretic particles are dispersed in the electrophoretic medium as a dispersion medium to form an electrophoretic particle dispersion. Usually, an electrophoretic medium is preferably a solvent that is not easily affected by an electric field and does not exert an electrical action on electrophoretic particles. Specifically, a saturated hydrocarbon, an alicyclic hydrocarbon, a halogenated carbon is preferable. Nonpolar solvents such as hydrogen and silicone are used. These nonpolar solvents are so-called lipophilic and have a strong affinity for lipophilic polymers and nonpolar or lipophilic polymer units. Therefore, the polymer main chain in the electrophoretic particles of the present invention preferably contains a polymer or a polymer unit having a chemical structure similar to that of the electrophoretic medium to be used in these electrophoretic particle dispersions. The polymer main chain in the electrophoretic particles of the present invention has a lipophilic polymer main chain such as a hydrocarbon-based polymer, a halogenated hydrocarbon polymer, or polydimethylsiloxane to increase the affinity with the electrophoretic medium. It is preferable.

  As monomers for polymerization that have a high affinity with hydrocarbon solvents and can provide stable hydrocarbon polymers, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) ) Acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, vinyl laurate, lauryl methacrylamide, stearyl methacrylamide, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, methyl ( (Meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate Rate, styrene, vinyl toluene, vinyl acetate, and the like. Polymers obtained by polymerizing one or more of these monomers can be suitably used as the structure of the polymer main chain in the electrophoretic particles of the present invention.

  Electrophoretic particles having a high affinity with the electrophoretic medium have good dispersibility in the electrophoretic particle dispersion and are less likely to cause phenomena such as aggregation and sedimentation. Further, in the state where the electric field is removed, the electrophoretic particles are less diffused and moved in the electrophoretic particle dispersion, and the effect of excellent long-term recording stability as an image recording apparatus is exhibited.

  The number average molecular weight of the lipophilic polymer main chain is preferably 1,000 to 100,000. In order to give dispersion stability to the electrophoretic particles, when the electrophoretic particles are dispersed in the electrophoretic dispersion medium, the lipophilic polymer main chain grafted on the particle surface is spread in the electrophoretic dispersion medium. Preferably there is. In such a state, the electrophoretic particles are stably dispersed in the electrophoretic dispersion medium. For that purpose, it is preferable that the lipophilic polymer main chain has a sufficiently large molecular weight to increase the affinity for the electrophoretic dispersion medium. For this reason, it is preferable that the number average molecular weight of the lipophilic polymer main chain is large from the viewpoint of stability in the electrophoretic particle dispersion. However, if the number average molecular weight of the oleophilic polymer main chain is too large, the affinity of the electrophoretic particles with the electrophoretic medium becomes too high, resulting in the movement speed and uniformity of movement of the electrophoretic particles when an electric field is applied. May cause problems. From such a viewpoint, the number average molecular weight of the lipophilic polymer main chain is desirably 1,000 to 100,000, preferably 2,000 to 50,000, particularly preferably 4,000 to 10,000. .

  The content ratio of the graft polymer in the electrophoretic particles of the present invention is preferably 0.1 to 25% by mass with respect to the fine particle nuclei. As for the ratio between the graft polymer and the fine particle nucleus, the dispersion stability of the electrophoretic particles cannot be sufficiently ensured if the graft polymer content is too small, like the number average molecular weight of the lipophilic polymer main chain described above. When the content of the graft polymer is too large, the affinity of the electrophoretic particles with the electrophoretic medium becomes too high, which may cause a problem in the moving speed and uniformity of movement of the electrophoretic particles when an electric field is applied. From such a viewpoint, the content of the graft polymer in the electrophoretic particles is 0.1 to 25% by mass, preferably 0.5 to 10% by mass, particularly preferably 1 to 8% by mass with respect to the fine particle nucleus. Is desirable. In addition, the one where the content rate of a graft polymer is smaller is preferable from an economical viewpoint.

  The fine particle nucleus in the electrophoretic particle of the present invention is a part that expresses the color of the electrophoretic particle. This fine particle nucleus consists of fine particles having various colors including white and black. The fine particle nuclei are preferably nearly spherical, and the size thereof may be appropriately selected from the electrophoresis speed and the ease of production and handling when the particles are electrophoretic particles. Usually, the size of fine particle nuclei is 0.05 to 10 μm, preferably 0.1 to 5 μm in terms of average particle size. The size of the fine particle nuclei is also determined in consideration of the content ratio of the graft polymer in the electrophoretic particles and the molecular weight of the graft polymer main chain.

  The fine particle nuclei used in the present invention may be particles of any material such as polymer particles, metal particles, metal oxide particles, inorganic particles, carbon particles, and pigment particles. Usually, the fine particle nucleus itself has a color or may be a fine particle nucleus colored by a pigment such as a pigment. Carbon particles, metal oxides, ceramics, etc. can be easily modified with a coupling agent, and the light absorption and scattering effects are large, improving the contrast when used in display devices. Effective above. Specific examples of the metal oxide used in the present invention include titanium oxide, zinc oxide, aluminum oxide and the like. In addition, those capable of being treated with a coupling agent are preferred, and any fine particle nucleus can be used. Examples of such fine particle nuclei include metal sulfides.

  As examples of white particles as fine particle nuclei, solid particles of metal oxides such as silicon dioxide, aluminum oxide, and titanium oxide can be used. As examples of black particles, carbon black, aniline black, furnace black, lamp black, and the like can be used. Examples of cyan colored particles include phthalocyanine blue, methylene blue, Victoria blue, methyl violet, aniline blue, and ultramarine blue. As magenta colored particles, for example, rhodamine 6G lake, dimethylquinacridone, watching red, rose bengal, rhodamine B, alizarin lake and the like can be used. As yellow colored particles, for example, chrome yellow, benzidine yellow, hansa yellow, naphthol yellow, molybdenum orange, quinoline yellow, tartrazine and the like can be used.

  In addition, it is also possible to use a dispersion or mixture of the above metal oxide or colored particles in at least a binder resin insoluble in a solvent serving as an electrophoretic dispersion medium. As the binder resin, any known thermoplastic resin and thermosetting resin that are insoluble in the dispersion medium can be used, but non-adhesive materials are particularly preferably used. Examples of such resins include polyester resins, styrene such as polystyrene, poly p-chlorostyrene, polyvinyltoluene, and homopolymers of substituted products thereof. The amount of the metal oxide or colorant that can be used is 0.1 to 300 parts by weight, preferably 1 to 100 parts by weight, based on 100 parts by weight of the binder resin. Good.

  The graft polymer grafted onto the surface of the electrophoretic particles has a side chain of a polar polymer unit having a polar group in addition to a lipophilic polymer main chain having an affinity for the dispersion medium. The polar group is a polar group including an acidic group and a basic group, and is a functional group that is charged in the electrophoretic particle dispersion and has an attractive action and a repulsive action on an electric field.

Examples of the acidic group include anionic groups such as —COOH group, —SO ₃ H group, —SO ₂ H group, —CH ₂ NO ₂ group, —CHRNO ₂ group, —ArOH group, and —ArSH group. (However, R is an alkyl group, Ar is an aryl group). Specific examples of the monomer before polymerization of the polar polymer unit include (meth) acrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, cinnamic acid, crotonic acid, vinylbenzoic acid, 2 -Methacryloxyethyl succinic acid, 2-methacryloxyethyl maleic acid, 2-methacryloxyethyl hexahydrophthalic acid, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, 2-sulfoethyl methacrylate, 2-acrylamido-2-methyl Examples thereof include propanesulfonic acid, 3-chloroamidophosphoxypropyl methacrylate, 2-methacryloxyethyl acid phosphate and the like.

  Examples of basic groups include amine compounds such as primary amines, secondary amines, tertiary amines, and quaternary ammonium salts, and those having at least one cationic group such as a pyridine residue. It is done.

  Specific examples of the monomer before polymerization of the polar polymer unit include N-methylaminoethyl (meth) acrylate, N-ethylaminoethyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dibutylaminoethyl acrylate, N, N-di-tert-butylaminoethyl acrylate, N-phenylaminoethyl methacrylate, N, N-diphenylaminoethyl methacrylate, amino Styrene, dimethylaminostyrene, N-methylaminoethylstyrene, dimethylaminoethoxystyrene, diphenylaminoethylstyrene, N-phenylaminoethylstyrene, 2-N-piperidylethyl (meth) acrylate, 2-vinylpyri Emissions, 4-vinyl pyridine, 2-vinyl-6-methylpyridine can be exemplified.

  Specific examples of monomers other than those described above before polymerization of a polar polymer unit having a polar group in a narrow sense include 2-hydroxyethyl (meth) acrylate, 2,3-dihydroxypropyl (meth) acrylate, 4- Hydroxybutyl (meth) acrylate, 2-hydroxy-3-propyl methacrylate, 2-chloroethyl (meth) acrylate, 2,3-dibromopropyl (meth) acrylate, (meth) acrylonitrile, isobutyl-2-cyanoacrylate, 2-cyanoethyl Acrylate, ethyl-2-cyanoacrylate, methacrylacetone, vinylpyrrolidone, N-acryloylmorpholine, tetrahydrofurfuryl methacrylate, trifluoroethyl methacrylate, p-nitrostyrene, acrylamide, methacrylate Amide, N, N-dimethyl methacrylamide, N, N-dibutyl methacrylamide and the like.

(Method for producing electrophoretic particles)
The method for producing an electrophoretic particle according to the present invention adds a monomer having a polar group to a lipophilic polymer having a functional group having reactivity to fine particle nuclei and a functional group serving as a polymerization initiation point of the monomer having a polar group. It is preferable to graft this lipophilic polymer onto the surface of the fine particle core while performing a polymerization reaction. The lipophilic polymer can be grafted onto the surface of the fine particle core after a polymer having a polar group in advance in the side chain is formed as a graft polymer. Alternatively, the lipophilic polymer before the graft polymer may be grafted on the surface of the fine particle core, and then the polymer unit having a polar group may be grafted on the lipophilic polymer main chain. However, the above-described method for producing electrophoretic particles, in which the lipophilic polymer main chain is grafted to the surface of the fine particle core and the polymer unit having a polar group to the lipophilic polymer main chain is simultaneously performed, is efficient and wasteful. There is no manufacturing method.

  In this case, the monomer for forming the polymer unit having a polar group is preferably a vinyl monomer. In the coupling treatment to the surface of the fine particle core, the functional group on the surface of the fine particle nucleus is often made into a vinyl group, so the lipophilic polymer as the main chain has a functional group having reactivity to the vinyl group. Yes. Therefore, by combining the functional group having reactivity with the vinyl group with the functional group having reactivity as a polymerization initiator with respect to the vinyl group, two or more of the above functional groups are added to the lipophilic polymer as one main chain. A group may be introduced. Then, the lipophilic polymer as the main chain is bonded to the surface of the fine particle core and at the same time reacts with the vinyl monomer to form a side chain of the vinyl polymer unit. Thus, the electrophoretic fine particles of the present invention can be easily produced. At this time, the functional group contained in the lipophilic polymer is preferably 3 or more, more preferably about 5 to 10. In this way, the active site of the lipophilic polymer increases, and the addition reaction of the lipophilic polymer to the surface of the fine particle core not only easily proceeds, but also side chains of a plurality of vinyl polymer units can be formed in the lipophilic polymer main chain. The electrophoretic characteristics of the electrophoretic fine particles can be improved.

  In the method for producing electrophoretic particles, it is preferable that the lipophilic polymer is grafted to the fine particle nuclei after the coupling agent is reacted with the fine particle nuclei. Grafting of polymer onto the surface of fine particle nuclei can be done without using a coupling agent, but grafting of fine particle nuclei can be efficiently carried out by introducing a highly reactive functional group onto the surface of fine particle nuclei. Done. The functional group introduced by the coupling agent can be determined in consideration of the suitability with the functional group having reactivity with the fine particle nucleus of the lipophilic polymer to be grafted in the subsequent step. Hydroxy group, epoxy group, styryl group, methacryloxy group, acryloxy group, amino group, mercapto group, sulfide group, isocyanate group, and the like. In order to introduce such a functional group to the surface of the electrophoretic particle, the electrophoretic particle can be treated with an end-reactive coupling agent having a functional group at its terminal.

  When a vinyl group is introduced as a functional group to the particle surface of the fine particle nucleus by the coupling agent, the terminal vinyl-modified silane coupling agent is reacted with the fine particle nucleus in an organic solvent, and the hydroxyl group present on the surface of the fine particle nucleus Etc. can be coupled with a coupling agent to introduce a vinyl group. The fine particle nuclei treated with the coupling agent in this manner are oleophilic having functional groups having high reactivity with vinyl groups, such as radical generating groups, after removing the silane coupling agent that has not reacted with the organic solvent. By reacting with the polymer, the fine particle core can be grafted with the lipophilic polymer.

  Examples of the terminal vinyl-modified silane coupling agent include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, and 3-methacryloxypropyltrimethoxysilane. , 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, and the like. In addition to the silane compound system, the coupling agent may be an aluminum compound system or a titanium compound system.

  The functional group having reactivity with the fine particle nucleus is determined by the correspondence with the functional group on the surface of the fine particle nucleus, and cannot be generally specified. However, it is preferable that a plurality of these functional groups are contained in the lipophilic polymer. The grafting reaction of the lipophilic polymer to the fine particle core is a solid-liquid reaction, and thus the reaction rate is slow. Therefore, it is preferable to promote the reaction by increasing the functional group. The reaction rate may be improved by increasing the functional group on the surface of the fine particle core with a coupling agent and increasing the number of the functional group contained in the lipophilic polymer.

  As the functional group having reactivity with the fine particle nucleus, when the functional group on the surface of the fine particle nucleus is a vinyl group, the reaction start point of the polymerization initiator in vinyl polymerization is preferable. For example, an azo group etc. are mentioned. As the polymer having this functional group, a polydimethylsiloxane unit-containing polymer azo polymerization initiator (for example, VSP-1001 manufactured by Wako Pure Chemical Industries, Ltd.) and an azo initiator having a plurality of azo groups having different decomposition temperatures are used. And a lipophilic polymer azo initiator such as a hydrocarbon chain-containing polymer azo initiator and a halogenated hydrocarbon-containing polymer azo initiator.

  If the functional group on the surface of the fine particle core is a hydroxy group, a lipophilic polymer having a hydroxy group such as carbinol-modified silicone, silanol-modified silicone, or polyhydroxystearic acid can be used. If it is an epoxy group, a lipophilic polymer having an amino group such as amino-modified silicone can be used. If it is an amino group, a lipophilic polymer having an epoxy group such as epoxy-modified silicone can be used. If it is a mercapto group, a lipophilic polymer having an allyl group or a vinyl group can be used. If it is an isocyanate group, a lipophilic polymer having a hydroxy group, an amino group or the like can be used. Thus, if the functional group on the surface of the fine particle core is a functional group other than a vinyl group, a lipophilic polyfunctional polymer having a functional group that reacts with the monomer having a functional group that reacts with them and a polar group (for example, various Both terminal-modified silicones and the like can be used.

(Electrophoretic particle dispersion)
The electrophoretic particle dispersion of the present invention is preferably 0.1 to 25% by mass, more preferably 0.3 to 10% by mass, and still more preferably 0 to the above-described electrophoretic particles of the present invention in a nonpolar dispersion medium. .5-5% by mass is dispersed. Furthermore, the electrophoretic particle dispersion of the present invention preferably contains a dispersant for dispersing the electrophoretic particles.

  The dispersion medium in the electrophoretic particle dispersion of the present invention is substantially a nonpolar dispersion medium. Nonpolar dispersion media include paraffinic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane and dodecane, isoparaffinic hydrocarbons such as isohexane, isooctane and isododecane, alkyl naphthenic hydrocarbons such as liquid paraffin, benzene , Aromatic hydrocarbons such as toluene, xylene, alkylbenzene, solvent naphtha, dimethyl silicone oil, phenylmethyl silicone oil, dialkyl silicone oil, alkylphenyl silicone oil, silicone oil such as cyclic polydialkylsiloxane or cyclic polyalkylphenylsiloxane, halogen And hydrocarbons.

Specific examples of these various silicone oils are as follows.
(1) Examples of dialkyl silicone oils: dimethyl silicone oil, diethyl silicone oil, dibutyl silicone oil, dihexyl silicone oil, dilauryl silicone oil, distearyl silicone oil.

  (2) Examples of cyclic polydialkylsiloxane and cyclic polyalkylphenylsiloxane: cyclic polydimethylsiloxane, cyclic polymethylphenylsiloxane, cyclic polydiethylsiloxane, cyclic polyethylphenylsiloxane, cyclic polydibutylsiloxane, cyclic polybutylphenylsiloxane, cyclic Polydihexylsiloxane, cyclic polyhexylphenylsiloxane, cyclic polydilaurylsiloxane, cyclic polymethylchlorophenylsiloxane, cyclic polydistearylsiloxane, cyclic polymethylbromophenylsiloxane.

  (3) Examples of alkylphenyl silicone oils: methylphenyl silicone oil, ethylphenyl silicone oil, propylphenyl silicone oil, butylphenyl silicone oil, hexylphenyl silicone oil, octylphenyl silicone oil, laurylphenyl silicone oil, stearylphenyl silicone oil.

  Examples of commercially available products of these silicone oils include KF-96L [viscosity grade: 0.65, 1.0, 1.5, 2.0 centistokes (cs)] manufactured by Shin-Etsu Chemical Co., Ltd., KF- 96 [viscosity grade: 10, 20, 30, 50, 500, 1000, 3000 (cs)], KF-56, KF-58, KF-54, etc., and TSF451 series manufactured by Toshiba Silicone Co., Ltd. , TSF456 series, TSF410, 411, 440, 4420, 484, 483, 431, 433 series, THF450 series, TSF404, 405, 406, 451-5A, 451-10A, 437 series, TSF440, 400, 401, 4300, 4445 4700, 4450, 4702, 4730 series, TSF434, 4600 series Over's, more like SH-200 manufactured by Toray Silicone Co..

  The dispersing agent for dispersing the electrophoretic particles has a function of preventing the electrophoretic particles from aggregating in the dispersion medium, maintaining a stable dispersion state of the particles, and storing an image formed by the electrophoretic particles for a long period of time. It is necessary to appropriately select such a dispersant having affinity for both the dispersion medium and the electrophoretic particles, and so-called cationic, anionic, nonionic, and amphoteric surfactants can be widely used. It is. These dispersants function as a dispersant by utilizing the fact that the hydrophilic group portion is adsorbed on the polar group portion on the particle surface and the electrophoretic particles repel each other due to the steric effect of the hydrophobic group portion.

  The content rate of a dispersing agent is 0.1-40 mass% with respect to an electrophoretic particle dispersion liquid, Preferably it is 1-20 mass%.

  In the present invention, when the electrophoretic particles are particles having a basic group such as an amino group, it is preferable to use a dispersant having an acidic group. At this time, it is possible to further improve the charging characteristics by ion generation by acid-base dissociation between the basic group on the particle surface and the acidic group of the dispersant adsorbed on the particle. Specific examples of such a dispersant include a long-chain carboxylic acid such as stearic acid and a surfactant such as dodecylbenzenesulfonic acid.

  The dispersant having an acidic group is preferably a polymer compound. The polymer compound having an acidic group can improve the dispersion stability of the dispersed particles due to the steric effect of the polymer chain. The polymer compound having an acidic group is obtained by copolymerizing a monomer having a high affinity with a nonpolar solvent, a monomer having an acidic group, and a monomer having a polar group as necessary. preferable.

  The polymerizable monomer will be described. First, examples of monomers having high affinity with nonpolar solvents include 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, and lauryl (meth) acrylate. , Stearyl (meth) acrylate, vinyl laurate, lauryl methacrylamide, stearyl methacrylamide, methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) Acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, styrene, vinyl toluene, vinyl acetate Over doors and the like.

  In addition, a silicone dispersant obtained by grafting polysiloxane to the side chain propyl group of propyl poly (meth) acrylate has a high affinity with silicone oil and can provide a stable dispersion.

Examples of the monomer having an acidic group include a vinyl group, a —COOH group, a —SO ₃ H group, a —SO ₂ H group, a —CH ₂ NO ₂ group, a —CHRNO ₂ group, a —ArOH group, and —ArSH. And those having at least one anionic group such as a group (wherein R is an alkyl group, and Ar is an aryl group). Specifically, (meth) acrylic acid, maleic acid, maleic anhydride, itaconic acid, itaconic anhydride, fumaric acid, cinnamic acid, crotonic acid, vinyl benzoic acid, 2-methacryloxyethyl succinic acid, 2-methacryloxy Ethyl maleic acid, 2-methacryloxyethyl hexahydrophthalic acid, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, 2-sulfoethyl methacrylate, 2-acrylamido-2-methylpropane sulfonic acid, 3-chloroamidophosphoxypropyl Methacrylate, 2-methacryloxyethyl acid phosphate and the like.

  Examples of monomers having a polar group include 2-hydroxyethyl (meth) acrylate, 2,3-dihydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxy-3-propyl methacrylate, 2-chloroethyl (meth) acrylate, 2,3-dibromopropyl (meth) acrylate, (meth) acrylonitrile, isobutyl-2-cyanoacrylate, 2-cyanoethyl acrylate, ethyl-2-cyanoacrylate, methacrylacetone, vinylpyrrolidone, N -Acryloylmorpholine, tetrahydrofurfuryl methacrylate, trifluoroethyl methacrylate, p-nitrostyrene, acrylamide, methacrylamide, N, N-dimethylmethacrylamide, N, N-dibutylmethacrylate Ruamido, and the like.

  In the polymer compound used as a dispersant in the present invention, the number average molecular weight may be 1,000 to 100,000, preferably 2,000 to 50,000.

  Usually, a colorant having a color different from the color of the electrophoretic particles is added to the electrophoretic particle dispersion and used in the image display device. For example, if the electrophoretic particles are white, the electrophoretic particle dispersion that is the background color is colored to be black or blue. The colorant used in the electrophoretic particle dispersion of the present invention includes a large amount of dye, and an oil-soluble dye that is soluble in a dispersion medium is preferable as the dye. For example, dyes classified as Solventdy in CoulorIndex are preferably used. Specific examples of oil-soluble dyes include azo dyes, anthraquinone dyes, phthalocyanine dyes, and triallylmethane dyes.

  Specific oil-soluble dyes include, for example, spirit black (SB, SSBB, AB), nigrosine base (SA, SAP, SAPL, EE, EEL, EX, EXBP, EB), oil yellow (105, 107, 129, 3G, GGS), Oil Orange (201, PS, PR), First Orange, Oil Red (5B, RR, OG), Oil Scarlet, Oil Pink 312, Oil Violet # 730, Macrolex Blue RR, Sumiplast Green G, Oil Brown (GR, 416), Sudan Black X60, Oil Green (502, BG), Oil Blue (613, 2N, BOS), Oil Black (HBB, 860, BS), Bali First Yellow (1101, 1105, 3108, 4120), Balifa Stranger (3209, 3210), Bali First Red (1306, 1355, 2303, 3304, 3306, 3320), Bali First Pink 2310N, Bali First Brown (2402, 3405), Bali First Blue (3405, 1501, 1603, 1605) 1607, 2606, 2610), Bali First Violet (1701, 1702), Vari First Black (1802, 1807, 3804, 3810, 3820, 3830). In addition, unless it is contrary to the objective of this invention, even if it is dye other than the dye described here, it can be used.

  In order to improve the solubility of the dye, a compatibilizing solvent can be added to the electrophoretic particle dispersion of the present invention. These compatibilizers are preferably substances that are soluble or miscible in the nonpolar solvent used as the dispersion medium. Examples of these compatibilizers include ethers, esters, alcohols, ketones, amides and the like. The mixing ratio of such other solvents is preferably about 0.1 to 10 parts by weight with respect to 100 parts by weight of the dispersion medium.

(Embodiment of image display device)
The image display device of the present invention has a structure in which the above-described electrophoretic particle dispersion is disposed between a pair of opposed electrode plates, at least one of which is transparent. The region in which the electrophoretic particle dispersion is disposed between the electrode plates is preferably divided into micro regions, and the electrophoretic particle dispersion is preferably sealed in each micro region. The micro area can be formed by dividing the space between the opposing electrode plates of the image display device into small areas into microcells or between the opposing electrode plates with microcapsules encapsulated in advance with an electrophoretic particle dispersion. The electrophoretic particle dispersion liquid can be divided and arranged in a minute region.

A first embodiment of an image display device will be described with reference to FIG. FIG. 1 is a schematic view showing a cross section of an image display device according to the present invention, wherein 1 and 2 are conductive layers, and at least one of them is light transmissive. As the conductive layer, a metal such as Al, Ag, Ni, Cu or a transparent conductor such as ITO, SnO ₂ , ZnO / Al is formed into a thin film by sputtering, vacuum deposition, CVD, coating, etc. on a glass substrate or the like. Or a conductive material mixed with a solvent or a synthetic resin binder and applied to a glass substrate or a transparent plastic substrate. Conductive agents include cationic polyelectrolytes such as polymethylbenzyltrimethyl chloride and polyallyl polymethylammonium chloride, anionic polyelectrolytes such as polystyrene sulfonate and polyacrylate, electronically conductive zinc oxide, and oxidation. Tin, indium oxide fine powder or the like is used.

  The conductive layer only needs to be provided on a substrate having a support function, but the conductive layer itself may be thick enough to have a self-holding function so that the substrate is not provided. Further, the conductive layers 1 and 2 may be layers showing anisotropic conductivity, or may be layers having patterned or multi-dot segments with conductive portions penetrating in the thickness direction. In any case, if a power supply electrode is brought into contact with a part of the conductive layers 1 and 2, an electric field can be generated between the conductive layers 1 and 2, so that the white or colored electrophoretic particles 3 move according to the electric field. Can be made. In order to perform the display, voltage applying means may be applied between the conductive layers 1 and 2, which is convenient.

  In FIG. 1, reference numeral 3 denotes white or colored electrophoretic particles. As an example of fine particle nuclei in which electrophoretic particles are colored, solid particles of metal oxides such as silicon dioxide, aluminum oxide, and titanium oxide can be used as long as they are white. Moreover, as black fine particle nucleus, carbon black, aniline black, furnace black, lamp black etc. can be used, for example. As fine particle nuclei of the cyan colorant, for example, phthalocyanine blue, methylene blue, Victoria blue, methyl violet, aniline blue, ultramarine blue and the like can be used. As the fine particle nucleus of the magenta colorant, for example, rhodamine 6G lake, dimethylquinacridone, watching red, rose bengal, rhodamine B, alizarin lake and the like can be used. As fine particle nuclei of the yellow colorant, for example, chrome yellow, benzidine yellow, hansa yellow, naphthol yellow, molybdenum orange, quinoline yellow, tartrazine and the like can be used.

  Alternatively, fine particles of the metal oxide or colorant may be dispersed or mixed in a binder resin insoluble in a solvent serving as a dispersion medium to form fine particle nuclei. As the binder resin, any known thermoplastic resin and thermosetting resin that are insoluble in the dispersion medium can be used, but non-adhesive materials are particularly preferably used. Examples of such resins include polyester resins, styrene such as polystyrene, poly p-chlorostyrene, polyvinyltoluene, and homopolymers of substituted products thereof. Content of the said metal oxide and a coloring agent is 0.1 mass part-300 mass parts of the said metal oxide and coloring agent with respect to 100 mass parts of binder resin, Preferably it is 1 mass part-100 mass parts.

  In FIG. 1, a voltage is applied between the conductive layers 1 and 2. For example, if the electrophoretic particles 3 are positively charged, the voltage is negative on the conductive layer 1 side and positive on the conductive layer 2 side. Indicates a state where is applied. The electrophoretic particles 3 are attracted to the conductive layer 1 side by an electric field, and the color of the electrophoretic particles 3 can be observed by observing the image display device 10 from the outside of the conductive layer 1 (downward in the drawing). Conversely, when the image display device 10 is observed from the outside of the conductive layer 2 (upward in the figure), the color of the dispersion medium 4 can be observed. In the image display device of the present invention, since the dispersion stability of the electrophoretic particles 3 in the dispersion medium 4 is good, the electrophoretic particles 3 do not move, aggregate or diffuse even when the application of voltage is stopped, The display state can be maintained for this period.

  On the other hand, when a positive voltage is applied to the conductive layer 1 side and a negative voltage is applied to the conductive layer 2 side, the electrophoretic particles 3 are attracted to the conductive layer 2 side by an electric field and move in the dispersion medium 4 to move to the conductive layer 2. Stick to the side. When the image display device 10 is observed from the outside of the conductive layer 2 (upward in the figure), the color of the electrophoretic particles 3 can be observed. Conversely, when the image display device 10 is observed from the outside of the conductive layer 1 (downward in the figure), the color of the dispersion medium 4 can be observed, and the display color is reversed on the conductive layer side. In the image display device of the present invention, since the electrophoretic particles 3 are grafted with an oleophilic polymer having a polymer unit having a polar group, the electrophoretic particles 3 have good responsiveness to an electric field and can be applied to the image display device. The electrophoretic particles 3 move rapidly in response to voltage application or switching. That is, the electrophoretic characteristics of the image display device are excellent.

  Since this image display device is a schematic diagram of the image display device for one pixel, the entire surface of the conductive layer 1 and the conductive layer 2 only represents the color of the electrophoretic particles 3 or the color of the dispersion medium 4. . If this image display device is used as one pixel, the electrophoretic particles 3 and the dispersion medium 4 are confined in a cell or microcapsule, and if only the necessary pixels are connected, an image display device that represents characters, figures, movies, etc. Can do.

  A second embodiment of the image display device of the present invention is shown in FIG. FIG. 2 is an example of an image display device that can display actual characters, graphics, moving images, and the like as described above. The image display device 10 includes an image display unit 11. The image display unit 11 is formed by arranging a large number of independent image display devices for one pixel shown in the first embodiment. The housing 12 includes a drive circuit, an arithmetic circuit, an internal memory, a power source, and the like (not shown). The electrodes in the image display unit 11 form a dot matrix, and display an image as a whole by displaying ON a designated dot. In FIG. 2, 13 is an information input means.

[Example]
EXAMPLES Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to the examples and the above-described embodiments, and the present invention can be changed and modified according to the purpose. . In the examples and comparative examples shown below, “part” or “%” means “part by mass” or “mass%” unless otherwise specified.

Example 1
1. Preparation of electrophoretic particles In a reaction vessel equipped with a cooling tube, 15 parts of sufficiently dried titanium dioxide fine particles, 250 parts of dehydrated toluene, and vinyl-modified coupling agent (3- (trimethoxysilyl) propyl methacrylate) 1 .5 parts was added and the reaction was carried out for 9 hours while sufficiently dispersing by heating to 120.degree. After completion of the reaction, a silanized titanium oxide having a methacryloxy group introduced on the particle surface was obtained through washing and drying processes. Next, in a reaction vessel equipped with a cooling pipe, 15 parts of the resulting silanized titanium oxide and 25 parts of toluene in advance with a polydimethylsiloxane unit-containing polymer azo polymerization initiator (trade name VSP-1001, Wako Pure Chemical Industries Ltd.) A solution prepared by dissolving 7.5 parts of a polymer main chain molecular weight 10,000) manufactured by company and 3 parts of 2-ethylhexyl methacrylate were added, and the reaction vessel was purged with nitrogen. The mixture was heated to 70 ° C. and reacted for 7 hours. After the completion of the reaction, an electrophoretic particle (1) in which a graft polymer in which a polymethacrylate unit was added to the main chain of a polydimethylsiloxane unit was grafted on the surface of titanium dioxide fine particles was obtained through a washing and drying process. The polymer content of the obtained electrophoretic particles (1) was about 7% by mass.

2. Preparation of electrophoretic particle dispersion liquid 100 parts of isoparaffin hydrocarbon (trade name Isopar H, manufactured by Exxon Chemical Co.) 5 parts of electrophoretic particles (1), dye (trade name: Macrolex Blue RR, manufactured by Bayer) 0.1 Part was added and subjected to ultrasonic dispersion for 1 hour to obtain an electrophoretic particle dispersion (1).

3. Production of Image Display Device A 50 μm thick polyester film having a square opening of 1 cm in length and width was sandwiched between two glass substrates with ITO electrodes to form a 50 μm thick space. An electrophoretic particle dispersion liquid (1) was sealed in the space to produce an image display device (1).

4). Evaluation of image display device As an image display simulation operation, a voltage of 50 V was applied between the two ITO electrodes of the image display device (1) to stop the electrophoretic characteristics of the electrophoretic particles (1) and the voltage application. Later electrophoretic particles (1) stability was observed. Further, as an operation corresponding to the display switching of the image display device, a voltage of −50 V is applied between the two ITO electrodes, the electrophoretic characteristics of the electrophoretic particles (1), and the electricity after the voltage application is stopped. Electrophoretic particles (1) Stability was observed. In any image display simulation operation, the electrophoretic characteristics such as the moving speed and uniformity of the electrophoretic particles, and the stability against dispersion and aggregation of the electrophoretic particles after the voltage application is stopped can be used as an image display device. Demonstrated performance.

(Example 2)
1. Preparation of electrophoretic particles In a reaction vessel equipped with a cooling tube, 15 parts of sufficiently dried titanium dioxide fine particles, 250 parts of dehydrated toluene, and vinyl-modified coupling agent (3- (trimethoxysilyl) propyl methacrylate) 1 .5 parts was added and the reaction was carried out for 9 hours while sufficiently dispersing by heating to 120.degree. After completion of the reaction, a silanized titanium oxide having a methacryloxy group introduced on the particle surface was obtained through washing and drying processes. Next, in a reaction vessel equipped with a cooling pipe, 15 parts of the resulting silanized titanium oxide and 25 parts of toluene in advance with a polydimethylsiloxane unit-containing polymer azo polymerization initiator (trade name VSP-1001, Wako Pure Chemical Industries Ltd.) A solution prepared by dissolving 7.5 parts of a polymer main chain molecular weight of 10,000) and 1.5 parts of methacrylic acid were added, and the reaction vessel was purged with nitrogen and stirred at 70 ° C. And reacted for 7 hours. After completion of the reaction, through washing and drying steps, electrophoretic particles (2) were obtained in which a graft polymer in which a polymethacrylic acid unit was added to the main chain of the polydimethylsiloxane unit was grafted on the surface of the titanium dioxide fine particles. The polymer content of the obtained electrophoretic particles (2) was about 6% by mass.

2. Preparation of electrophoretic particle dispersion liquid 100 parts of isoparaffin hydrocarbon (trade name Isopar H, manufactured by Exxon Chemical) 5 parts of electrophoretic particles (2), dye (trade name: Macrolex Blue RR, manufactured by Bayer) 0.1 Part was added and subjected to ultrasonic dispersion for 1 hour to obtain an electrophoretic particle dispersion (2).

3. Production of Image Display Device A 50 μm thick polyester film having a square opening of 1 cm in length and width was sandwiched between two glass substrates with ITO electrodes to form a 50 μm thick space. An electrophoretic particle dispersion liquid (2) was sealed in the space to produce an image display device (2).

4). Evaluation of image display device As an image display simulation operation, a voltage of 50 V was applied between the two ITO electrodes of the image display device (2), and the electrophoretic characteristics of the electrophoretic particles (2) and the voltage application were stopped. Later electrophoretic particle (2) stability was observed. Furthermore, as an operation corresponding to the display switching of the image display device, a voltage of −50 V is applied between the two ITO electrodes, the electrophoretic characteristics of the electrophoretic particles (2), and the electricity after the voltage application is stopped. Electrophoretic particle (2) stability was observed. As in Example 1, in any of the image display simulation operations, the electrophoretic characteristics such as the moving speed and uniformity of the electrophoretic particles, and the stability against dispersion and aggregation of the electrophoretic particles after the voltage application is stopped are also shown in the image. The performance which can be used as a display device was demonstrated.

(Comparative Example 1)
1. Preparation of electrophoretic particles In a 100 ml eggplant flask fitted with a cooling tube, 3 parts of titanium dioxide fine particles, 50 parts of dehydrated toluene, and an epoxy-modified coupling agent (3-glycidoxypropyltrimethoxysilane) 0. 3 parts were added, and the reaction was performed for 9 hours while sufficiently dispersing by heating to 120 ° C. After completion of the reaction, a silanized titanium oxide (3) having an epoxy group introduced on the surface of the titanium dioxide fine particles was obtained through washing and drying processes. Next, 3 parts of the silanized titanium oxide (3) and 30 parts of amino-modified silicone (trade name KF-864, manufactured by Shin-Etsu Silicone) were heated to 70 ° C. in a reaction vessel equipped with a cooling tube. The reaction was performed for 2 hours. After completion of the reaction, an electrophoretic particle (3) in which silicone was grafted onto the surface of the titanium dioxide fine particle was obtained through a washing and drying process.

  Using the electrophoretic particles (3), an electrophoretic dispersion and an image display device were prepared in the same manner as in Example 1 and evaluated as an image display device similar to that in Example 1. Although the dispersibility of the electrophoretic particles in the electrophoretic dispersion was good as in Example 1 and precipitation did not occur, the response to voltage application was worse than in Example 1 and there was a problem in electrophoretic characteristics. It was.

(Comparative Example 2)
To a 100 ml eggplant flask equipped with a condenser, add 3 parts of titanium dioxide fine particles, 50 parts of dehydrated and washed toluene, and 0.3 part of an amino-modified coupling agent (3-aminopropyltrimethoxysilane), The reaction was carried out for 9 hours while heating to 120 ° C. and sufficiently dispersing. After completion of the reaction, a silanized titanium oxide (4) having an epoxy group introduced on the surface of the titanium dioxide fine particles was obtained through washing and drying processes. Next, 3 parts of the silanized titanium oxide (4) and 30 parts of epoxy-modified silicone (trade name KF-101, manufactured by Shin-Etsu Silicone) were heated to 70 ° C. in a reaction vessel equipped with a cooling tube. The reaction was performed for 2 hours. After completion of the reaction, an electrophoretic particle (4) in which silicone was grafted onto the surface of the titanium dioxide fine particle was obtained through a washing and drying process.

  Using the electrophoretic particles (4), an electrophoretic dispersion and an image display device were prepared in the same manner as in Example 1 and evaluated as an image display device similar to that in Example 1. Although the dispersibility of the electrophoretic particles in the electrophoretic dispersion was good as in Example 1 and precipitation did not occur, the response to voltage application was worse than in Example 1 and there was a problem in electrophoretic characteristics. It was.

Schematic cross-sectional view of the image display device of the present invention Image display device of the present invention

Explanation of symbols

1: Conductive layer 2: Conductive layer 3: Electrophoretic particles 4: Dispersion medium 10: Image display device 11: Image display unit 12: Housing 13: Information input means

Claims (12)

A electrophoretic particles for an image display device of an electrophoretic system, characterized in that the particulate core surface graft polymer having a side chain of a polar polymer unit having a polar group to a lipophilic polymer backbone, are grafted Electrophoretic particles.   The electrophoretic particle according to claim 1, wherein the lipophilic polymer main chain is a hydrocarbon polymer, a halogenated hydrocarbon polymer, or polysiloxane.   3. The electrophoretic particle according to claim 1, wherein the lipophilic polymer main chain has a number average molecular weight of 1,000 to 100,000.   4. The electrophoretic particle according to claim 1, wherein a ratio of the graft polymer to the fine particle nucleus is 0.1 to 25% by mass. A method for producing electrophoretic particles for an electrophoretic image display device, comprising a functional group having reactivity to the surface of fine particle nuclei and a lipophilic polymer having a functional group serving as a polymerization initiation point of a monomer having a polar group A method for producing electrophoretic particles, wherein the lipophilic polymer is grafted onto the surface of the fine particle core while polymerizing the monomer having the polar group. A method for producing an electrophoretic particle for an electrophoretic image display device, wherein an oleophilic polymer having a polymer group having a polar group formed in a side chain is grafted to the surface of a fine particle core, A method for producing electrophoretic particles , comprising grafting an oily polymer and then grafting a polymer unit having a polar group to the lipophilic polymer grafted onto the surface of the fine particle core .   The method for producing electrophoretic particles according to claim 5 or 6, wherein after the coupling agent is reacted with the fine particle nuclei, the lipophilic polymer is grafted onto the fine particle nuclei.   An electrophoretic particle dispersion liquid, wherein the electrophoretic particles according to any one of claims 1 to 4 are dispersed in a nonpolar dispersion medium.   The electrophoretic particle dispersion according to claim 8, wherein the content of the electrophoretic particles is 0.1 to 25% by mass.   10. The electrophoretic particle dispersion according to claim 8, further comprising a dispersing agent that assists dispersion of the electrophoretic particles.   11. An image display device, wherein the electrophoretic particle dispersion liquid according to claim 8 is disposed between a pair of opposed electrode plates, at least one of which is transparent.   The image display device according to claim 11, wherein the electrophoretic particle dispersion is divided into minute regions.

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