JP2008216902A - Particle dispersion and its manufacturing method, image display medium, and image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a particle dispersion manufacturing method capable of simply forming a particle dispersion, which uses a silicone oil as a dispersion medium and in which particles having a large charge amount are highly stably dispersed, without requiring a cleaning/drying process, and to provide the particle dispersion obtained by the manufacturing method. <P>SOLUTION: The particle dispersion manufacturing method comprises: an emulsification process for agitating and emulsifying a mixed solution containing a first solvent composed of ionic macromolecules, an emulsifier, a coloring agent, and the silicone oil and a second solvent which is non-soluble with the silicone oil, has a boiling point lower than that of the silicone oil and is capable of solving the ionic macromolecules; and a removable process for removing the second solvent from the emulsified mixed solution. The obtained particle dispersion is applied to an image display medium and an image forming apparatus. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  Conventionally, display technologies such as Twisting Ball Display (two-color particle rotation display), electrophoresis, magnetophoresis, thermal rewritable media, and liquid crystal with memory properties have been proposed as repetitively rewritable sheet-like image display media. Has been.

  As one of the above display technologies, conductive colored particles and white particles are sealed between opposing electrode substrates, and electric charges are injected into the conductive colored particles through the charge transport layer provided on the inner surface of the electrode of the non-display substrate. The conductive colored particles into which the charge has been injected move to the display substrate side facing the non-display substrate by an electric field between the electrode substrates, and the conductive colored toner adheres to the inside of the display-side substrate and is conductively colored. A display technique for displaying an image based on the contrast between particles and white particles has been proposed. This display technology is excellent in that the image display medium is entirely composed of solid, and white and black (color) display can be switched 100% in principle.

  By the way, in the display technique, particles moving between the substrates are sealed between the substrates in a state of being dispersed in a dispersion medium. As this dispersion medium, for example, an aromatic hydrocarbon solvent, an aliphatic hydrocarbon solvent, a halogenated hydrocarbon solvent, an oily polysiloxane such as silicone oil, or a highly insulating solvent such as high-purity petroleum is used. ing. Among these, a highly safe, chemically stable and long-term reliable silicone solvent is desirable, and straight dimethyl silicone is desirably applied from the viewpoint of high resistivity (for example, patents) References 1-2).

  For example, in Patent Document 1, in order to disperse in silicone, the particles are dispersed in silicone oil through a drying / solvent replacement step after the particles are produced. Further, in Patent Document 2, an aqueous hydrochloric acid solution is added to precipitate a reaction product (particles), the reaction solvent is removed, water washing and drying are performed, and then the particles are redispersed in silicone oil. Dispersed in silicone oil.

  On the other hand, Patent Document 3 proposes an example in which particles are produced in a silicone oil finally used as a dispersion medium without passing through a drying step, and the particles are dispersed in the dispersion medium. In Patent Document 3, in order to charge the particles efficiently, the particles are mainly composed of a pigment, a resin compound, and a charge control agent having a solubility in an aprotic solvent (silicone oil) of 5% by weight or less. is doing.

JP2003-015168A JP 2003-096191 A JP2004-279732

  However, as in Patent Documents 1 and 2, when particles are dispersed in silicone oil through a washing / drying process, there is a problem that the particles are aggregated and not redispersed. On the other hand, there is an example in which particles are produced in a solvent that is finally used as a dispersion medium without passing through a drying step as in Patent Document 3, but in the method for producing particles in this document, for example, a charging material that is a constituent material is used. Since the control agent is not physically immobilized on the particles and is soluble in the dispersion solvent, long-term charging characteristics are not stable, and particles with a large charge amount are produced. The current situation is difficult. In Patent Document 3, since a nigrosine dye or a monoazo dye which is colored itself is used as the charge control agent, its use as the charge control agent is practically limited to particles for displaying black. Therefore, it is difficult to use as particles for displaying colors other than black.

  Accordingly, an object of the present invention is to provide a method for producing a particle dispersion in which a particle dispersion in which particles having a large charge amount are dispersed is prepared without going through a washing / drying process, and a particle dispersion obtained thereby. Is to provide. Another object of the present invention is to provide an image display medium and an image display device using a method for producing a particle dispersion.

  The above problem is solved by the following means. That is,

The invention according to claim 1
A first solvent comprising an ionic polymer, an emulsifier, a colorant, silicone oil, and the silicone oil are incompatible with each other and have a lower boiling point than the silicone oil and dissolve the ionic polymer. An emulsification step of stirring and emulsifying the mixed solution containing
A removal step of removing the second solvent from the emulsified mixed solution;
It is a manufacturing method of the particle dispersion liquid characterized by having.

The invention according to claim 2
The method for producing a particle dispersion according to claim 1, wherein the emulsifier is a polymer having a dendritic structure.

The invention according to claim 3
The method for producing a particle dispersion according to claim 1, wherein the second solvent is water.

The invention according to claim 4
A first solvent comprising an ionic polymer, an emulsifier, a colorant, silicone oil, and the silicone oil are incompatible with each other and have a lower boiling point than the silicone oil and dissolve the ionic polymer. And an emulsification step of stirring and emulsifying the mixed solution comprising:
A removal step of removing the second solvent from the emulsified mixed solution;
It is a particle dispersion characterized by being produced through at least.

The invention according to claim 5
The particle dispersion according to claim 4, wherein the emulsifier is a polymer having a dendritic structure.

The invention according to claim 6
6. The particle dispersion according to claim 4, wherein the second solvent is water.

The invention according to claim 7 provides:
A pair of substrates at least one of which is translucent and disposed to face each other with a gap;
A particle dispersion liquid that includes a light-transmitting dispersion medium and a particle group that is dispersed in the dispersion medium and moves according to an electric field formed between the pair of substrates, and is sealed between the pair of substrates. A first solvent comprising an ionic polymer, an emulsifier, a colorant, a silicone oil, and a second solvent that is incompatible with the silicone oil and has a lower boiling point than the silicone oil and dissolves the ionic polymer. A particle dispersion produced through at least an emulsifying step of stirring and emulsifying the mixed solution, and a removing step of removing the second solvent from the emulsified mixed solution;
An image display medium comprising:

The invention according to claim 8 provides:
The image display medium according to claim 7, wherein the emulsifier is a polymer having a dendritic structure.

The invention according to claim 9 is:
The image display medium according to claim 7 or 8, wherein the second solvent is water.

The invention according to claim 10 is:
The particle dispersion has a plurality of types,
The particle groups contained in the plurality of types of particle dispersion liquids are different in absolute value of voltage required for moving according to an electric field and colored in different colors. 9. The image display medium according to any one of 9 above.

The invention according to claim 11 is:
The image display according to claim 10, wherein the particle groups included in the plurality of types of particle dispersions have a voltage range necessary for moving in accordance with an electric field, and the voltage ranges are different from each other. It is a medium.

The invention according to claim 12
The image display medium according to any one of claims 7 to 11,
Voltage applying means for applying a voltage between the pair of substrates of the image display medium;
It is an image display apparatus characterized by having.

  According to the first aspect of the present invention, there is an effect that a particle dispersion in which particles having a large charge amount are dispersed with good stability can be easily produced without going through a washing / drying step.

  The invention according to claim 2 produces an effect that a particle dispersion liquid in which particles are dispersed more stably is produced.

  The invention according to claim 3 produces an effect that a particle dispersion liquid in which particles having a larger charge amount are dispersed is produced.

  According to the invention which concerns on Claim 4, there exists an effect that particles with a big charge amount are disperse | distributed with sufficient stability.

  According to the invention which concerns on Claim 5, there exists an effect that particle | grains are disperse | distributed more stably.

  According to the invention concerning Claim 6, there exists an effect that particles with a larger charge amount can be obtained.

  According to the invention concerning Claim 7, there exists an effect that it is excellent in display property and reliability.

  According to the invention concerning Claim 8, there exists an effect that it is excellent in display property and reliability.

  According to the invention concerning Claim 9, there exists an effect that it is excellent in display property and reliability.

  According to the invention which concerns on Claim 10, there exists an effect that a clear color display is performed.

  According to the eleventh aspect of the invention, there is an effect that color mixing is suppressed and color display is performed.

  According to the invention which concerns on Claim 12, there exists an effect that it is excellent in display property and reliability.

  Hereinafter, embodiments of the present invention will be described.

(First embodiment)
The method for producing particles according to the first embodiment includes an ionic polymer, an emulsifier, a colorant, a first solvent composed of a silicone oil, and an ionic polymer that is incompatible with silicone oil and has a lower boiling point than silicone oil. It has the emulsification process which stirs and emulsifies the mixed solution containing the 2nd solvent which melt | dissolves, and the removal process which removes a 2nd solvent from the emulsified mixed solution, It is characterized by the above-mentioned.

  In the method for producing particles according to the present embodiment, through the above steps, a particle dispersion in which silicone oil is used as a dispersion medium and particles having a large charge amount are dispersed stably can be easily obtained without going through a washing / drying step. To be made. Hereinafter, it demonstrates according to a process.

-Emulsification process-
In the emulsification step, the ionic polymer, the emulsifier, the colorant, the first solvent composed of silicone oil, and the silicone oil are incompatible with each other, have a lower boiling point than the silicone oil, and dissolve the ionic polymer. Two solvents are mixed. Then, the obtained mixed solution is stirred and emulsified.

  In the emulsification step, the mixed solution is stirred to emulsify the first solvent (silicone oil) as a poor solvent in the continuous phase and the second solvent as a good solvent to form a dispersed phase. The emulsifier is dissolved or dispersed in the continuous phase, and the ionic polymer and the colorant are dissolved or dispersed in the dispersed phase.

  Stirring for emulsification is performed using, for example, a known stirring device (for example, a homogenizer, a mixer, an ultrasonic crusher, etc.). In order to suppress the temperature rise during emulsification, the temperature of the mixed solution during emulsification is desirably maintained at 0 ° C. or more and 25 ° C. or less. For example, the stirring speed of a homogenizer or mixer for emulsification, the output intensity of the ultrasonic crusher, and the emulsification time are set according to the desired particle diameter.

  Hereinafter, each material will be described. First, the ionic polymer will be described.

  An ionic polymer is a polymer having an ionic group and can be dissolved in a second solvent (good solvent). Specific examples of the ionic polymer include a copolymer of an ionic monomer and a nonionic monomer. The ionic polymer may be a salt of the copolymer.

  As the ionic monomer, either a cationic monomer or an anionic monomer is used. As the cationic monomer, a monomer having a hydroxyl group or a quaternized amine group in the compound is used. Examples of such monomers include N, N-dimethylacrylamide, N, N-dimethylaminoethyl acrylate, N, N-diethylacrylamide, ethyleneimine, acrylamine, vinylpyridine and the like.

  On the other hand, as the anionic monomer, a monomer having an anionic group such as a carboxyl group, a sulfonic acid group, or a phosphonic acid group in the compound is used. Examples of such monomers include acrylic acid, methacrylic acid, maleic acid, polyvinyl sulfonic acid, styrene sulfonic acid, acrylamidomethylpropane sulfonic acid and the like.

  Nonionic monomers include (meth) acrylonitrile, (meth) acrylic acid alkyl ester, (meth) acrylic acid dialkylaminoalkyl ester, (meth) acrylamide, ethylene, propylene, butadiene, isoprene, isobutylene, N -Dialkyl-substituted (meth) acrylamide, styrene, vinyl carbazole, styrene, styrene derivatives, ethylene glycol di (meth) acrylate, glyceryl (meth) acrylate, polyethylene glycol mono (meth) acrylate, vinyl chloride, vinylidene chloride, ethylene glycol di ( (Meth) acrylate, methylenebisacrylamide, isoprene, butadiene, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, butane Ruji (meth) acrylate, hexanediol di (main 30 data) acrylate, and vinyl pyrrolidone.

  Here, in the copolymer of the ionic monomer and the nonionic monomer, the copolymerization ratio of the ionic monomer and the nonionic monomer depends on the charge amount of the desired particle. It is changed appropriately.

  The weight average molecular weight of the ionic polymer is preferably 1,000 or more and 1,000,000 or less, and more preferably 10,000 or more and 200,000 or less.

Next, the emulsifier will be described. Preferable examples of the emulsifier include silicone-modified resins and modified silicone oils.
Examples of the silicone-modified resin include a silicone-modified acrylic resin, a silicone-modified polyurethane resin, and a silicone-modified epoxy resin. Among these, a silicone-modified acrylic resin is preferable as the silicone-modified resin from the viewpoint of improving the dispersion stability of the obtained particles.

  Examples of the silicone-modified acrylic resin include acrylic esters (for example, acrylic acid, alkyl acrylate, etc.), methacrylic esters (acrylamide, acrylonitrile, methacrylic acid, alkyl methacrylate, etc.), methacrylamide, and methacrylonitrile. Examples thereof include those obtained by modifying a silicone with respect to a homopolymer of a selected monomer or two or more types of copolymers.

  Specific examples of the silicone-modified acrylic resin include “KP545: manufactured by Shin-Etsu Silicone”, “FA-4001CM: manufactured by Toray Dow Silicone”, “Symac: manufactured by Toa Gosei Co., Ltd.”, and the like.

  On the other hand, examples of the modified silicone oil include carboxyl-modified silicone oil, fluorine-modified silicone oil, alcohol-modified silicone oil, epoxy-modified silicone oil, and amine-modified silicone oil. Among these, amine-modified silicone oil is preferable as the modified silicone oil from the viewpoint of improving the dispersion stability of the obtained particles.

  Specific examples of the modified silicone oil include “TSF4708: manufactured by GE Toshiba Silicone”, “TSF4709: manufactured by GE Toshiba Silicone”, and the like.

  Here, it is particularly preferable to apply a polymer having a dendritic structure as an emulsifier. By applying a polymer having a dendritic structure as an emulsifier, the dispersion stability of the obtained particles is particularly improved. The polymer having a dendritic structure is a polymer having a molecular structure in which side chains connected to the main chain are regularly branched (a molecular structure called a dendmary structure). Thus, as the polymer having a dendritic structure, a silicone-modified acrylic resin represented by “FA-4001CM: manufactured by Toray Dow Silicone” (for example, “FA-4001CM: manufactured by Toledo Silicone”) is suitable. Can be mentioned. In this silicone-modified acrylic resin, the side chain silicone linked to the acrylic main chain is composed of an oligomer in which a large number of trimethylsiloxane groups are regularly branched to form a sphere. Of course, the polymer having a dendritic structure is not limited thereto.

  The blending amount of the emulsifier is desirably 3% by weight or more and 40% by weight or less with respect to the first solvent, and desirably 5% by weight or more and 20% by weight or less.

  Next, the colorant will be described. As the colorant, those that can be dispersed in a second solvent (good solvent) are used, and various colorants such as organic pigments, inorganic pigments, and dyes are used. Examples of the colorant include magnetic powder such as magnetite and ferrite, carbon black, titanium oxide, magnesium oxide, zinc oxide, phthalocyanine copper-based cyan color material, azo-based yellow color material, azo-based magenta color material, and quinacridone-based magenta color. Known colorants such as materials, red color materials, green color materials, and blue color materials can be used. Specific examples of the colorant include aniline blue, calcoyl 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. Blue 15: 1, C.I. I. Pigment Blue 15: 3, etc. are exemplified as typical examples. In addition, as the colorant, porous sponge-like particles or hollow particles enclosing air can be used as the white colorant.

  The blending amount of the colorant is desirably 10% by weight or more and 99% by weight or less, and desirably 30% by weight or more and 99% by weight or less with respect to the resin (ionic polymer). In addition, it is good to mix | blend a coloring agent with a mixed solution in the state disperse | distributed to the 2nd solvent (good solvent).

Next, silicone oil as the first solvent will be described.
Silicone oil is used as a poor solvent that can form a continuous phase in a mixed solution. Specifically, silicone oils having hydrocarbon groups bonded to siloxane bonds (for example, dimethyl silicone oil, diethyl silicone oil, methyl ethyl silicone oil, methyl phenyl silicone oil, diphenyl silicone oil, etc.), modified silicone oil ( For example, fluorine-modified silicone oil, amine-modified silicone oil, carboxyl-modified silicone oil, epoxy-modified silicone oil, alcohol-modified silicone oil, and the like. Among these, dimethyl silicone is particularly desirable from the viewpoint of high safety, chemical stability, long-term reliability, and high resistivity.

  The viscosity of the silicone oil is desirably 0.1 mPa · s or more and 20 mPa · s or less, and more desirably 0.1 mPa · s or more and 2 mPa · s or less in an environment at a temperature of 20 ° C. By setting the viscosity within the above range, the moving speed of particles, that is, the display speed can be improved. In addition, Tokyo Keiki B-8L type | mold viscosity meter is used for the measurement of this viscosity.

Next, the second solvent will be described.
The second solvent is used as a good solvent that can form a dispersed phase in the mixed solution. In addition, a silicone oil that is incompatible with the silicone oil, has a boiling point lower than that of the silicone oil, and dissolves the ionic polymer is selected. Here, incompatible means a state in which a plurality of substance systems exist in independent phases without being mixed. Moreover, dissolution refers to a state where the residue of the dissolved material is not visually confirmed.

  Specific examples of the second solvent include water, lower alcohols having 5 or less (preferably not more than) carbon atoms (for example, methanol, ethanol, propanol, isopropyl alcohol, etc.), tetrahydrofuran, and acetone. Among these, water is particularly desirable from the viewpoint that particles having a larger charge amount can be obtained.

  The second solvent is selected from those having a boiling point lower than that of silicone oil because it can be removed from the mixed solution system by, for example, heating and decompressing, and the boiling point is preferably, for example, 50 ° C. or higher and 150 ° C. or lower. More desirably, the temperature is 50 ° C. or higher and 100 ° C. or lower.

  Next, other compounding materials will be described. You may mix | blend other compounding materials other than the said material in the mixed solution made to emulsify as needed.

  As another compounding material, for example, a charge control agent is used for the purpose of adjusting the charge amount of the obtained particles. 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 Industries), salicylic acid metal complexes, phenol condensates, tetraphenyl compounds, metal oxide fine particles, and metal oxide fine particles surface-treated with various coupling agents. In this embodiment, particles having a controlled charge amount can be obtained without using a charge control agent, but may be used for the purpose of adjusting charging characteristics, for example.

A magnetic material may be mixed in the inside or the surface of the particles as necessary. As the magnetic material, a color-coated inorganic magnetic material or organic magnetic material is used as necessary. Further, a transparent magnetic material, in particular, a transparent organic magnetic material does not hinder the color development of the color pigment, and the specific gravity is smaller than that of the inorganic magnetic material, and is more desirable.
As the colored magnetic powder, for example, a small-diameter colored magnetic powder described in JP-A-2003-131420 is used. A material provided with magnetic particles serving as nuclei and a colored layer laminated on the surface of the magnetic particles is used. The colored layer may be appropriately selected, for example, coloring the magnetic powder opaque with a pigment or the like, but it is preferable to use a light interference thin film, for example. This optical interference thin film is a thin film having a thickness equivalent to the wavelength of light made of an achromatic material such as SiO2 or TiO2, and reflects light in a wavelength selective manner by optical interference in the thin film.

  As other compounding materials, for example, an external additive may be used for the purpose of adhering the surface of the obtained particles. The color of the external additive is preferably transparent so as not to affect the color of the particles.

  As the external additive, inorganic fine particles such as metal oxides such as silicon oxide (silica), titanium oxide, and alumina are used. In order to adjust the chargeability, fluidity, environment dependency, etc. of the fine particles, these may 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. Similarly, silicone oil includes positively chargeable 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, fluorine-modified. Examples include negatively chargeable ones such as silicone oil. These are selected according to the desired resistance of the external additive.

Of these external additives, well-known hydrophobic silica and hydrophobic titanium oxide are preferable. In particular, TiO (OH) ₂ described in JP-A-10-3177 and a silane compound such as a silane coupling agent are used. The titanium compound obtained by the reaction with is suitable. As the silane compound, any of chlorosilane, alkoxysilane, silazane, and a special silylating agent can be used. This titanium compound is produced by reacting TiO (OH) ₂ produced in a wet process with a silane compound or silicone oil and drying it. Since it does not pass through the firing step of several hundred degrees, strong bonds between Ti are not formed, there is no aggregation, and the fine particles are almost in the state of primary particles. Furthermore, since the silane compound or silicone oil is directly reacted with TiO (OH) ₂ , the treatment amount of the silane compound or silicone oil is increased, and the charging characteristics are controlled and imparted by adjusting the treatment amount of the silane compound. The charging ability is also significantly improved over that of conventional titanium oxide.

  The primary particles of the external additive are generally 5 nm to 100 nm, preferably 10 nm to 50 nm, but are not limited thereto.

  The blending ratio of the external additive and the particles is appropriately adjusted based on the balance between the particle size of the particles and the particle size of the external additive. If the amount of the external additive added is too large, a part of the external additive is liberated from the particle surface and adheres to the surface of the other particle, so that desired charging characteristics cannot be obtained. Generally, the amount of the external additive is 0.01 part by weight or more and 3 parts by weight or less, more preferably 0.05 part by weight or more and 1 part by weight or less with respect to 100 parts by weight of the particles.

-Removal process-
Next, in removal fixation, the second solvent (good solvent) is removed from the mixed solution emulsified in the emulsification step. By removing the second solvent, the ionic polymer is precipitated and formed into particles while adhering other materials to the content or surface in the dispersed phase formed by the second solvent, and the target particles. Is obtained.

Here, examples of the method for removing the second solvent include a method of heating the mixed solution and a method of reducing the pressure of the mixed solution, and these methods may be combined.
When the mixed solution is heated to use the second solvent, the heating temperature is preferably 60 ° C. or higher and 200 ° C. or lower, and more preferably 60 ° C. or higher and 180 ° C. or lower.
On the other hand, when the mixed solution is depressurized to remove the second solvent, the depressurization pressure is preferably 0.01 mPa to 200 mPa, and more preferably 0.01 mPa to 20 mPa.

  As described above, a particle dispersion in which particles are dispersed using silicone oil as a dispersion medium can be obtained. In addition, an acid, an alkali, a salt, a dispersion stabilizer, a stabilizer for the purpose of preventing oxidation or ultraviolet absorption, an antibacterial agent, an antiseptic, and the like may be added to the obtained particle dispersion as necessary. Good.

  For the obtained particle dispersion, as a charge control agent, an anionic surfactant, a cationic surfactant, an amphoteric surfactant, a nonionic surfactant, a fluorosurfactant, a silicone surfactant, a metal Soap, alkyl phosphate esters, succinimides and the like may be added.

Charge control agents include ionic or nonionic surfactants, block or graft copolymers composed of a lipophilic part and a hydrophilic part, polymers such as cyclic, star-like or dendritic polymers (dendrimers) Examples thereof include compounds having a chain skeleton, metal complexes of salicylic acid, metal complexes of catechol, metal-containing bisazo dyes, tetraphenylborate derivatives, and the like.
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 agents are preferably 0.01% by weight or more and 20% by weight or less, particularly preferably 0.05% by weight or more and 10% by weight or less based on the solid content of the particles.

  In addition, the obtained particle dispersion may be diluted with a first solvent (a first solvent containing an emulsion as necessary) or an additive (for example, an emulsifier) as necessary. Good.

  The particle dispersion obtained by the method for producing a particle dispersion according to this embodiment is used for an electrophoretic image display medium, a liquid toner of a liquid development type electrophotographic system, and the like. In particular, since the obtained particle dispersion liquid is a highly safe, chemically stable and long-term reliable silicone oil, it can be used as it is without being replaced by another dispersion medium. And can be applied to various fields while maintaining good dispersion stability of the particles.

(Second Embodiment)
FIG. 1 is a schematic configuration diagram showing an image display apparatus according to a second embodiment of the present invention. The image display device 10 according to the second embodiment is obtained by the particle dispersion liquid manufacturing method according to the first embodiment as a particle dispersion liquid including the dispersion medium 50 and the particle group 34 of the image display medium 12. In this mode, a particle dispersion is applied. For this reason, the image display device (image display medium) according to the second embodiment has excellent display properties and reliability. In particular, in the method for producing a particle dispersion according to the first embodiment, a polymer having a dendritic structure is applied as an emulsifier, or water is applied as a second solvent. The image display device (image display medium) has excellent display properties and reliability.

  As shown in FIG. 1, the image display device 10 according to the second embodiment includes an image display medium 12, a voltage application unit 16, and a control unit 18. The control unit 18 is connected to the voltage application unit 16 so as to be able to exchange signals.

  The control unit 18 includes a CPU (Central Processing Unit) that controls the operation of the entire apparatus, a RAM (Random Access Memory) that temporarily stores various data, and a program indicated by a control program and a processing routine for controlling the entire apparatus. The microcomputer includes a ROM (Read Only Memory) in which various programs are stored in advance.

  The image display medium 12 corresponds to the image display medium of the present invention, the image display apparatus 10 corresponds to the image display apparatus of the present invention, and the voltage application unit 16 corresponds to the voltage application means of the image display apparatus of the present invention. To do.

  The voltage application unit 16 is electrically connected to the front electrode 40 and the back electrode 46. In this embodiment, the case where both the front electrode 40 and the back electrode 46 are electrically connected to the voltage application unit 16 will be described. However, one of the front electrode 40 and the back electrode 46 is grounded. The other may be connected to the voltage application unit 16.

  The voltage application unit 16 is a voltage application device for applying a voltage to the front electrode 40 and the back electrode 46, and applies a voltage according to the control of the control unit 18 between the front electrode 40 and the back electrode 46.

  Hereinafter, the image display medium 12 will be described in detail.

  As shown in FIG. 1, the image display medium 12 includes a display substrate 20 serving as an image display surface, a rear substrate 22 that faces the display substrate 20 with a gap, and holds these substrates at a predetermined interval. And the back substrate 22 are configured to include a gap member 24 that partitions the plurality of cells, and a particle group 34 enclosed in each cell.

  The cell indicates a region surrounded by the display substrate 20, the back substrate 22, and the gap member 24. A dispersion medium 50 is enclosed in this cell. Particle groups 34 (details will be described later) are dispersed in the dispersion medium 50 and move between the display substrate 20 and the back substrate 22 in accordance with the electric field strength formed in the cell.

  The gap member 24 is provided so as to correspond to each pixel when an image is displayed on the image display medium 12, and cells are formed so as to correspond to each pixel, so that the image display medium 12 is provided for each pixel. You may comprise so that a color display is attained.

  A plurality of types of particle groups 34 having different colors are dispersed in the dispersion medium 50 of the image display medium 12. The plurality of types of particle groups 34 are particles that are electrophoresed between the substrates, and the absolute value of the voltage required to move in accordance with the electric field is different for each color particle group.

  In the method for producing a particle dispersion according to the first embodiment, for example, each particle of the plurality of types of particle groups 34 having different absolute values of voltages necessary to move in accordance with the electric field is, for example, “ It can be obtained by preparing particle dispersions each containing particles having different charge amounts by changing the kind of “ionic polymer” and mixing them.

  Here, the content (% by mass) of the particle group 34 with respect to the total mass in the cell is not particularly limited as long as a desired hue can be obtained, and the content is adjusted by the thickness of the cell. This is effective as the image display medium 12. That is, in order to obtain a desired hue, the content may be small when the cell is thick, and the content may be increased when the cell is thin. Generally, it is 0.01 mass% or more and 50 mass% or less.

  Hereinafter, each component of the image display medium 12 will be described.

  The display substrate 20 has a configuration in which a surface electrode 40 and a surface layer 42 are sequentially laminated on a support substrate 38. The back substrate 22 has a structure in which a back electrode 46 and a surface layer 48 are sequentially laminated on a support substrate 44.

  Examples of the support substrate 38 and the support substrate 44 include glass and plastics such as polycarbonate resin, acrylic resin, polyimide resin, polyester resin, epoxy resin, and polyether sulfone resin.

  For the back electrode 46 and the surface electrode 40, oxides such as indium, tin, cadmium and antimon, composite oxides such as ITO, metals such as gold, silver, copper and nickel, organic conductive materials such as polypyrrole and polythiophene, etc. May be used. These can be used as a single layer film, a mixed film or a composite film, and are formed by vapor deposition, sputtering, coating, or the like. Moreover, the thickness is normally 100 angstroms or more and 2000 angstroms or less according to the vapor deposition method and the sputtering method. The back electrode 46 and the front electrode 40 are formed in a desired pattern, for example, a matrix shape or a stripe shape that enables passive matrix driving, by a conventionally known means such as etching of a conventional liquid crystal display element or a printed circuit board.

  Further, the surface electrode 40 may be embedded in the support substrate 38. Similarly, the back electrode 46 may be embedded in the support substrate 44. In this case, since the materials of the support substrate 38 and the support substrate 44 may affect the charging characteristics and fluidity of each particle of the particle group 34, the material is appropriately selected according to the composition of each particle of the particle group 34.

  The back electrode 46 and the front electrode 40 may be separated from the display substrate 20 and the back substrate 22 and disposed outside the image display medium 12. In this case, since the image display medium 12 is sandwiched between the back electrode 46 and the surface electrode 40, the inter-electrode distance between the back electrode 46 and the surface electrode 40 increases, and the electric field strength decreases. In order to obtain a desired electric field strength, it is necessary to devise measures such as reducing the thickness of the support substrate 38 and the support substrate 44 of the image display medium 12 and reducing the distance between the support substrate 38 and the support substrate 44.

  In the above description, the case where both the display substrate 20 and the back substrate 22 are provided with the electrodes (the front electrode 40 and the back electrode 46) has been described.

  In order to enable active matrix driving, the support substrate 38 and the support substrate 44 may include a TFT (thin film transistor) for each pixel. The TFTs are preferably formed not on the display substrate but on the back substrate 22 because wiring can be easily laminated and components can be easily mounted.

  In addition, when the image display medium 12 is a simple matrix drive, the configuration of an image display apparatus 10 to be described later including the image display medium 12 can be simplified. When the active matrix drive using TFTs is used, a simple matrix is used. The display speed is increased compared to driving.

  When the surface electrode 40 and the back electrode 46 are formed on the support substrate 38 and the support substrate 44, respectively, the electrodes between the electrodes that cause breakage of the surface electrode 40 and the back electrode 46 and adhesion of each particle of the particle group 34 are obtained. In order to prevent the occurrence of leakage, it is preferable to form a surface layer 42 and / or a surface layer 48 as a dielectric film on each of the surface electrode 40 and the back electrode 46 as necessary.

  Examples of the material for forming the surface layer 42 and / or the surface layer 48 include polycarbonate, polyester, polystyrene, polyimide, epoxy, polyisocyanate, polyamide, polyvinyl alcohol, polybutadiene, polymethyl methacrylate, copolymer nylon, and ultraviolet curable acrylic resin. Fluorine resin or the like may be used.

  In addition to the insulating material described above, an insulating material containing a charge transport material may be used. Inclusion of a charge transport material improves particle chargeability by injecting particles into the particle, and when the charge amount of the particle becomes extremely large, the charge of the particle is leaked and the charge amount of the particle is stabilized. An effect is obtained.

Examples of the charge transport material include a hydrazone compound, a stilbene compound, a pyrazoline compound, and an arylamine compound that are hole transport materials. Further, a fluorenone compound, a diphenoquinone derivative, a pyran compound, zinc oxide, or the like, which is an electron transport material, may be used. Further, a self-supporting resin having a charge transporting property may be used.
Specific examples thereof include polyvinyl carbazole and polycarbonate obtained by polymerization of a specific dihydroxyarylamine and bischloroformate described in US Pat. No. 4,806,443. Since the dielectric film may affect the charging characteristics and fluidity of the particles, it is appropriately selected according to the composition of the particles. Since the display substrate which is one of the substrates needs to transmit light, it is preferable to use a transparent one of the above materials.

  The gap member 24 for holding the gap between the display substrate 20 and the back substrate 22 is formed so as not to impair the transparency of the display substrate 20, and is made of a thermoplastic resin, a thermosetting resin, an electron beam curable resin, a photocuring agent. It is made of resin, rubber, metal or the like.

  The gap member 24 includes a cell type and a particle type. An example of the cellular type is a net. Since the net is easy to obtain, inexpensive, and has a relatively uniform thickness, it is useful when manufacturing an inexpensive image display medium 12. The net is not suitable for displaying a fine image, and is preferably used for a large image display apparatus that does not require high resolution. In addition, as other cellular spacers, a sheet in which holes are formed in a matrix by etching, laser processing, or the like can be cited. In this sheet, the thickness, the shape of the holes, the size of the holes, etc. are compared with the net. Easy to adjust. For this reason, the sheet is used for an image display medium for displaying a fine image, and is effective in further improving the contrast.

The gap member 24 may be integrated with any one of the display substrate 20 and the back substrate 22, and the support substrate 38 or the support substrate 44 is etched, laser processed, or using a prefabricated mold, The support substrate 38 or the support substrate 44 having the cell pattern of any size and the gap member 24 are produced by printing or the like.
In this case, the gap member 24 can be fabricated on either the display substrate 20 side, the back substrate 22 side, or both.

  The gap member 24 may be colored or colorless, but is preferably colorless and transparent so as not to adversely affect the display image displayed on the image display medium 12, and in this case, for example, polystyrene, polyester, acrylic, etc. A transparent resin or the like may be used.

  The particulate gap member 24 is preferably transparent, and glass particles are also used in addition to transparent resin particles such as polystyrene, polyester or acrylic.

  In the image display medium 12, insulating particles 36 are enclosed in each cell. The insulating particles 36 are different in color and insulative particles from the particle group 34 enclosed in the same cell, and have a gap through which each particle of the particle group 34 can pass. And the display substrate 20 are arranged along a direction substantially orthogonal to the facing direction. Further, between the insulating particles 36 and the back substrate 22 and between the display substrate 20 and the insulating particles 36, each particle of the particle group 34 included in the same cell is connected to the back substrate 22 and the display substrate 20. In the opposite direction, a plurality of intervals are provided so that a plurality of layers can be stacked.

  That is, each particle of the particle group 34 is moved through the gap between the insulating particles 36 from the back substrate 22 side to the display substrate 20 side or from the display substrate 20 side to the back substrate 22 side. As the color of the insulating particles 36, for example, white or black is preferably selected so as to be a background color.

  Insulating particles 36 include spherical particles of benzoguanamine / formaldehyde condensate, spherical particles of benzoguanamine / melamine / formaldehyde condensate, spherical particles of melamine / formaldehyde condensate (Nippon Shokubai Co., Ltd. poster), titanium oxide-containing crosslinking Spherical fine particles of polymethyl methacrylate (MBX-white manufactured by Sekisui Plastics Co., Ltd.), spherical fine particles of cross-linked polymethyl methacrylate (Kemisnow MX manufactured by Soken Chemical Co., Ltd.), fine particles of polytetrafluoroethylene (Lublon L manufactured by Daikin Industries, Ltd.) , Shamrock Technologies Inc. SST-2), fluorocarbon fine particles (CF-100 from Nippon Carbon, CFGL, CFGM from Daikin Industries), fine particles of silicone resin (Tospearl from Toshiba Silicone), fine particles of polyester containing titanium oxide (Nippon Paint Bilucia PL1000 Ho Wight T), titanium oxide-containing polyester / acrylic fine particles (Nippon Oil & Fats Konak No. 181000 white), silica spherical fine particles (Ube Nitto Kasei high pressure mica), and the like. Without limitation to the above, a white pigment such as titanium oxide may be mixed and dispersed in a resin, and then pulverized and classified to a desired particle size.

  Since these insulating particles 36 are provided between the display substrate 20 and the rear substrate 22 as described above, the insulating particles 36 are １ ／ the length of the cell in the opposing direction between the display substrate 20 and the rear substrate 22. It is preferable that the volume average primary particle diameter is 1 to 50, and the content is 1 volume% to 50 volume% with respect to the volume of the cell.

  The size of the cell in the image display medium 12 is closely related to the resolution of the image display medium 12, and the smaller the cell, the higher the resolution display medium can be made. Usually, the size is about 10 μm to 1 mm. is there.

  In order to fix the display substrate 20 and the back substrate 22, fixing means such as a combination of bolts and nuts, a clamp, a clip, and a substrate fixing frame can be used. Also, fixing means such as an adhesive, heat melting, and ultrasonic bonding can be used.

  The image display medium 12 includes a bulletin board that can store and rewrite images, a circulation version, an electronic blackboard, an advertisement, a signboard, a flashing sign, an electronic paper, an electronic newspaper, an electronic book, and a document sheet that can be shared with a copier / printer. Can be used for etc.

  In the image display medium 12, different colors are displayed by changing the applied voltage (V) applied between the display substrate 20 and the back substrate 22.

  In the image display medium 12, by moving according to the electric field formed between the display substrate 20 and the back substrate 22, each cell corresponding to each pixel of the image display medium 12 corresponds to each pixel of the image data. Colors can be displayed.

  Here, in the image display medium 12, as described above, as shown in FIG. 2, in the particle group 34, the particle group 34 moves for each color according to the electric field when electrophoresis is performed between the substrates. The absolute value of the voltage required for each is different. Each color particle group 34 has a voltage range necessary for moving each color particle group 34 for each color, and the voltage range is different. In other words, the absolute value of the voltage has the voltage range, and the voltage range is different for each color of the particle group 34.

  In this embodiment, as the particle group 34 enclosed in the same cell of the image display medium 12, as shown in FIG. 1, a magenta magenta particle group 34M, a cyan cyan particle group 34C, In the following description, the three-color particle group 34 of the yellow-colored yellow particle group 34Y is enclosed.

  The magenta magenta magenta particle group 34M, the cyan cyan particle group 34C, and the yellow color yellow particle group 34Y are magenta magenta as absolute values of voltages when the three color particle groups start moving. In the following description, it is assumed that the particle group 34M is | Vtm |, the cyan cyan particle group 34C is | Vtc |, and the yellow yellow particle group 34Y is | Vty |. Also, the absolute value of the maximum voltage for moving almost all of the three color particle groups of the magenta particle group 34M, the cyan cyan particle group 34C, and the yellow yellow particle group 34Y of each color particle group 34. Assuming that the magenta magenta particle group 34M is | Vdm |, the cyan cyan particle group 34C is | Vdc |, and the yellow yellow particle group 34Y is | Vdy |.

  The absolute values of Vtc, −Vtc, Vdc, −Vdc, Vtm, −Vtm, Vdm, −Vdm, Vty, −Vty, Vdy, and −Vdy described below are | Vtc | <| Vdc | <| Description will be made assuming that the relationship is Vtm | <| Vdm | <| Vty | <| Vdy |.

  Specifically, as shown in FIG. 2, for example, all the particle groups 34 are charged with the same polarity, and the absolute value of the voltage range necessary to move the cyan particle group 34C | Vtc ≦ Vc ≦ Vdc | (Vtc Absolute value of a value between Vtm and Vdm), absolute value of voltage range necessary to move the magenta particle group 34M | Vtm ≦ Vm ≦ Vdm | (absolute value of a value between Vtm and Vdm), and yellow particles The absolute value of the voltage range necessary to move the group 34M | Vty ≦ Vy ≦ Vdy | (the absolute value of the value between Vty and Vdy) is set to be large without overlapping in this order. Yes.

  Further, in order to independently drive the particle groups 34 of the respective colors, the absolute value | Vdc | of the maximum voltage for moving almost all the cyan particle groups 34M is the absolute value of the voltage range necessary for moving the magenta particle group 34M. Value | Vtm ≦ Vm ≦ Vdm | (the absolute value of the value between Vtm and Vdm) and the absolute value of the voltage range necessary to move the yellow particle group 34M | Vty ≦ Vy ≦ Vdy | (Vty to Vdy The absolute value of the value between) is set smaller. Further, the absolute value | Vdm | of the maximum voltage for moving almost all of the magenta particle group 34M is equal to the absolute value | Vty ≦ Vy ≦ Vdy | (Vty to Vdy) of the voltage range necessary for moving the yellow particle group 34M. Is set to be smaller than the absolute value).

  That is, in this embodiment, the voltage groups necessary for moving the color particle groups 34 are set so as not to overlap, so that the particle groups 34 for each color are independently driven.

The “voltage range necessary for moving the particle group 34” means the voltage necessary for the particle to start moving and the change in display density even if the voltage and voltage application time are further increased from the start of movement. It shows the voltage range until it disappears and the display density is saturated.
The “maximum voltage required to move almost all the particle groups 34” means that even if the voltage and the voltage application time are further increased from the start of the movement, the display density does not change and the display density is saturated. Indicates voltage.
Further, “almost all” means that there is a variation in the characteristics of the particle groups 34 of the respective colors, so that some of the characteristics of the particle groups 34 are different to the extent that they do not contribute to the display characteristics. That is, even if the voltage and the voltage application time are further increased from the start of the movement described above, the display density does not change and the display density is saturated.
“Display density” is the color density on the display surface side measured with the optical density (Optical Density = 0D) reflection densitometer X-rite's reflection densitometer. Apply a voltage and gradually change this voltage in the direction of increasing the measured concentration (increase or decrease the applied voltage) to saturate the concentration change per unit voltage, and in that state, adjust the voltage and voltage application time. Even when the density is increased, the density does not change, and the density is shown when the density is saturated.

  In the image display medium 12 according to the present embodiment, a voltage is applied from 0 V between the front substrate 20 and the rear substrate 22 to gradually increase the voltage value of the applied voltage, and the voltage is applied between the substrates. When the voltage exceeds + Vtc, the display density starts to change due to the movement of the cyan particle group 34C in the image display medium 12. Further, when the voltage value is increased and the voltage applied between the substrates becomes + Vdc, the change in display density due to the movement of the cyan particle group 34 in the image display medium 12 stops.

  When the voltage value is further increased and the voltage applied between the front substrate 20 and the rear substrate 22 exceeds + Vtm, a change in display density due to the movement of the magenta particle group 34M starts to appear in the image display medium 12. When the voltage value is further increased and the voltage applied between the front substrate 20 and the rear substrate 22 becomes + Vdm, the change in display density due to the movement of the magenta particle group 34M in the image display medium 12 stops.

  Further, when the voltage value is increased and the voltage applied between the substrates exceeds + Vty, a change in display density due to the movement of the yellow particle group 34Y starts to appear in the image display medium 12. When the voltage value is further increased and the voltage applied between the substrates becomes + Vdy, the change in display density due to the movement of the yellow particle group 34Y in the image display medium 12 stops.

  On the other hand, if the negative electrode voltage is applied from 0 V to the substrate between the front substrate 20 and the rear substrate 22 to gradually increase the absolute value of the voltage, and the absolute value of the voltage −Vtc applied between the substrates is exceeded. In the image display medium 12, the display density starts to change due to the movement of the yellow particle group 34C between the substrates. Further, when the absolute value of the voltage value is increased and the voltage applied between the front substrate 20 and the rear substrate 22 becomes −Vdc or more, the change in display density due to the movement of the cyan particle group 34 </ b> C in the image display medium 12. Stops.

  When the negative voltage is further applied by increasing the absolute value of the voltage value, and the voltage applied between the front substrate 20 and the rear substrate 22 exceeds the absolute value of −Vtm, magenta in the image display medium 12. A change in display density due to the movement of the particle group 34M begins to appear. When the absolute value of the voltage value is further increased so that the voltage applied between the front substrate 20 and the rear substrate 22 becomes −Vdm, the display density changes due to the movement of the magenta particle group 34M in the image display medium 12. Stop.

  When the absolute value of the voltage value is further increased to apply a negative voltage, and the voltage applied between the front substrate 20 and the rear substrate 22 exceeds the absolute value of -Vty, yellow is displayed on the image display medium 12. Changes in the display density begin to appear due to the movement of the particle group 34Y. When the absolute value of the voltage value is further increased so that the voltage applied between the substrates becomes −Vdy, the change in display density due to the movement of the yellow particle group 34C in the image display medium 12 stops.

  In other words, in the present embodiment, as shown in FIG. 2, the voltage applied between the substrates is within the range of −Vtc to Vtc (voltage range | Vtc | or less). 22 is applied between the substrate and the particle group 34 (the cyan particle group 34C, the magenta particle group 34M, and the yellow particle group 34Y) to the extent that the display density of the image display medium 12 changes. It can be said that no movement has occurred. When a voltage higher than the absolute value of the voltage + Vtc and the voltage −Vtc is applied between the substrates, a change occurs in the display density of the image display medium 12 for the cyan particle group 34C among the three color particle groups 34. The display density starts to change for a certain degree of particle movement, and when a voltage equal to or higher than the absolute value | Vdc | of the voltage −Vdc and the voltage Vdc is applied, the display density per unit voltage does not change.

  Further, when a voltage is applied between the front substrate 20 and the rear substrate 22 such that the voltage applied between the substrates is in the range of −Vtm to Vtm (voltage range | Vtm | or less), It can be said that there is no movement of the particles of the magenta particle group 34M and the yellow particle group 34Y to the extent that the display density of the image display medium 12 changes. When a voltage higher than the absolute value of the voltage + Vtm and the voltage −Vtm is applied between the substrates, the magenta particle group 34M and the magenta particle group 34M in the yellow particle group 34Y have the display density of the image display medium 12. The display density per unit voltage starts to change to such an extent that the particles move to the extent that the change occurs, and when a voltage equal to or higher than the absolute value | Vdm | of the voltage −Vdm and the voltage Vdm is applied, the change in the display density changes. No longer occurs.

  Further, when a voltage is applied between the front substrate 20 and the rear substrate 22 so that the voltage applied between the substrates is within the range of −Vty to Vty (voltage range | Vty | or less), the image It can be said that there is no movement of the particles of the yellow particle group 34Y to the extent that the display density of the display medium 12 changes. When a voltage greater than the absolute value of the voltage + Vty and the voltage -Vty is applied between the substrates, the yellow particle group 34Y starts to move particles to the extent that the display density of the image display medium 12 changes. When the display density starts to change and a voltage equal to or higher than the absolute value | Vdy | of the voltage −Vdy and the voltage Vdy is applied, the display density does not change.

  Next, with reference to FIG. 3, the mechanism of particle movement when an image is displayed on the image display medium 12 of the present invention will be described.

  For example, the image display medium 12 will be described assuming that the yellow particle group 34Y, the magenta particle group 34M, and the cyan particle group 34C described with reference to FIG.

  In the following, the voltage applied between the substrates that is larger than the absolute value of the voltage necessary for the particles constituting the yellow particle group 34Y to start moving and less than or equal to the maximum voltage of the yellow particle group 34Y is referred to as “large voltage”. The voltage applied between the substrates that is larger than the absolute value of the voltage necessary for the particles constituting the magenta particle group 34M to start moving and is equal to or less than the maximum voltage of the magenta particle group 34M is referred to as “medium voltage”. The voltage applied between the substrates that is larger than the absolute value of the voltage required for the particles constituting the cyan particle group 34C to start moving and below the maximum voltage of the cyan particle group 34C is referred to as a “small voltage”. To do.

  Further, when a higher voltage is applied between the substrates on the display substrate 20 side than the back substrate 22 side, the respective voltages are referred to as “+ large voltage”, “+ medium voltage”, and “+ small voltage”, respectively. . Further, when a higher voltage is applied to the back substrate 22 side than the display substrate 20 side, the respective voltages are referred to as “−large voltage”, “−medium voltage”, and “−small voltage”, respectively. I will explain.

  As shown in FIG. 3A, if all of the magenta particle group 34M, the cyan particle group 34C, and the yellow particle group 34Y as all the particle groups are positioned on the back substrate 22 side in the initial state, When “+ large voltage” is applied between the display substrate 20 and the back substrate 22 from the state, the magenta particle group 34M, the cyan particle group 34C, and the yellow particle group 34Y are displayed on the display substrate 20 side as all particle groups. Move to. In this state, even if the voltage application is canceled, each particle group does not move while adhering to the display substrate 20 side, and subtractive color mixing (magenta) by the magenta particle group 34M, the cyan particle group 34C, and the yellow particle group 34Y. In this case, the black color is displayed by the subtractive color mixture of cyan and yellow. (See FIG. 3B).

  Next, when “−medium voltage” is applied between the display substrate 20 and the back substrate 22 from the state of FIG. 3B, the magenta particle group 34 </ b> M among the particle groups 34 of all colors and cyan The particle group 34 </ b> C moves to the back substrate 22 side. Therefore, since only the yellow particle group 34Y is attached to the display substrate 20 side, yellow display is performed (see FIG. 3C).

  Further, when “+ small voltage” is applied between the display substrate 20 and the back substrate 22 from the state of FIG. 3C, the magenta particle group 34M and the cyan particle group 34C moved to the back substrate 22 side. The cyan particle group 34C moves to the display substrate 20 side. For this reason, the yellow particle group 34Y and the cyan particle group 34C are attached to the display substrate 20 side, and green is displayed by the subtractive color mixture of yellow and cyan (see FIG. 3D).

  3B, when a “−small voltage” is applied between the display substrate 20 and the back substrate 22, the cyan particle groups 34C of all the particle groups 34 move to the back substrate 22 side. To do. For this reason, since the yellow particle group 34Y and the magenta particle group 34M are attached to the display substrate 20 side, red display is performed by additive mixing of cyan and magenta (see FIG. 3I).

  On the other hand, when “+ medium voltage” is applied between the display substrate 20 and the back substrate 22 from the initial state shown in FIG. 3A, all the particle groups 34 (magenta particle group 34M, cyan particle group 34C) are applied. , And the yellow particle group 34Y), the magenta particle group 34M and the cyan particle group 34C move to the display substrate 20 side. For this reason, the magenta particle group 34M and the cyan particle group 34C adhere to the display substrate 20 side, so that blue is displayed by the subtractive color mixing of magenta and cyan (see FIG. 3E).

When a “−small voltage” is applied between the display substrate 20 and the back substrate 22 from the state of FIG. 3E, the magenta particle group 34M and the cyan particle group 34C adhering to the display substrate 20 side. Among them, the cyan particle group 34C moves to the back substrate 22 side.
Therefore, only the magenta particle group 34M is attached to the display substrate 20 side, so that a magenta color is displayed (see FIG. 3F).

When a “−large voltage” is applied between the display substrate 20 and the back substrate 22 from the state of FIG. 3F, the magenta particle group 34M adhering to the display substrate 20 side is moved to the back substrate 22 side. Moving.
For this reason, since nothing is adhered to the display substrate 20 side, white is displayed as the color of the insulating particles 36 (see FIG. 3G).

  When a “+ small voltage” is applied between the display substrate 20 and the back substrate 22 from the initial state shown in FIG. 3A, all the particle groups 34 (magenta particle group 34M, cyan particle group) are applied. 34C and the yellow particle group 34Y), the cyan particle group 34C moves to the display substrate 20 side. For this reason, the cyan particle group 34C adheres to the display substrate 20 side, so that a cyan color is displayed (see FIG. 3H).

Further, when a “−large voltage” is applied between the display substrate 20 and the back substrate 22 from the state shown in FIG. 3I, all the particle groups 34 appear on the back surface as shown in FIG. Moving to the substrate 22 side, white display is performed.
Similarly, when a “−large voltage” is applied between the display substrate 20 and the back substrate 22 from the state shown in FIG. 3D, all the particle groups 34 are formed as shown in FIG. Moving to the back substrate 22 side, white display is performed.

  Thus, in the present embodiment, by applying a voltage according to each particle group 34 between the substrates, the desired particles are selectively moved according to the electric field due to the voltage, so that a color other than the desired color can be obtained. The particles can be prevented from moving in the dispersion medium 50, color mixing with a color other than the desired color is suppressed, and color display is performed while image quality deterioration of the image display medium 12 is suppressed. In addition, if the absolute value of the voltage required for each particle group 34 to move according to the electric field is different from each other, even if the voltage ranges necessary for moving according to the electric field overlap with each other, clear color display is possible. However, when the voltage ranges are different from each other, color mixing is further suppressed and color display is realized.

  Further, by dispersing the three color particle groups 34 of cyan, magenta, and yellow in the dispersion medium 50, cyan, magenta, yellow, blue, red, green, and black can be displayed, and white insulation can be displayed. The white particles can be displayed by the active particles 36, and a desired color display can be performed.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Example A]
(Example A1)
Solution A (continuous phase) by dissolving 5 parts by weight of silicone-modified acrylic polymer (KP545 manufactured by Shin-Etsu Silicone) as an emulsifier in 95 parts by weight of dimethyl silicone oil (KF-96-2CS manufactured by Shin-Etsu Silicone) as a poor solvent Adjusted. Next, 7 parts by weight of cationized polyvinyl alcohol “K-210 manufactured by Nippon Synthetic Chemical Co., Ltd.” as an ionic polymer, and a cyan pigment dispersion as a colorant (Emacol manufactured by Sanyo Dye Co., Ltd .: equivalent to 20 parts by weight of pigment solids) Solution B (dispersed phase) was prepared by mixing 3 parts by weight and 63 parts by weight of water as a good solvent. Emulsification was carried out by mixing 80 parts by weight of Solution A and 20 parts by weight of Solution B to prepare an emulsion. The emulsification was performed for 10 minutes with an ultrasonic crusher (UH-600S manufactured by SMT).

  Next, the obtained emulsion is put into an eggplant flask and heated (65 ° C.) / Depressurized (10 mPa) with an evaporator while stirring to remove moisture (good solvent), and the cyan pigment-containing electrophoretic particles become silicone. A particle dispersion dispersed in oil was obtained.

  The produced cyan pigment-containing migrating particles were observed with an optical microscope, but no particles larger than 1 mm were observed, and no agglomerates could be confirmed, indicating that the electrophoretic particles were excellent in dispersion stability. It was. When observed with a scanning electron microscope (FE-SEM S-5500, manufactured by Hitachi), spherical particles were observed. Moreover, when measured by HORIBA LB-550 (dynamic light scattering type particle size distribution measuring device), the average particle size was 330 nm.

(Example A2)
5 parts by weight of a silicone-modified acrylic polymer (FA-4001CM manufactured by Toray Dow Corning Co., Ltd.) as an emulsifier is dissolved in 95 parts by weight of dimethyl silicone oil (KF-96-2CS manufactured by Shin-Etsu Silicone Co., Ltd.) as a poor solvent, and a solution A ( Continuous phase) was prepared. 7 parts by weight of an acrylic resin (UC-3000 manufactured by Toa Gosei Co., Ltd., acid value 74) as an ionic polymer, 3 parts by weight of a cyan pigment dispersion (Emacol manufactured by Sanyo Dye Co., Ltd .: equivalent to 20 parts by weight of pigment solids) as a colorant And 63 parts by weight of water as a good solvent were mixed to prepare a solution B (dispersed phase). Emulsification was carried out by mixing 80 parts by weight of Solution A and 20 parts by weight of Solution B to prepare an emulsion. The emulsification was performed for 10 minutes with an ultrasonic crusher (UH-600S manufactured by SMT).

  The obtained emulsion is put into an eggplant flask and heated (65 ° C.) / Reduced pressure (10 mPa) with an evaporator while stirring to remove moisture (good solvent), and cyan pigment-containing electrophoretic particles are dispersed in silicone oil. A particle dispersion was obtained.

  The produced cyan pigment-containing migrating particles were observed with an optical microscope, but no particles larger than 1 mm were observed, and no agglomerates could be confirmed, indicating that the electrophoretic particles were excellent in dispersion stability. It was. When observed with a scanning electron microscope (FE-SEM S-5500, manufactured by Hitachi), spherical particles were observed. When measured with HORIBA LB-550 (dynamic light scattering particle size distribution analyzer), the average particle size was 160 nm.

(Example A3)
The cyan pigment-containing electrophoretic particles were the same as in Example A2 except that the cationized polyvinyl alcohol used in Example 1 (K-210, 7 parts by weight manufactured by Nippon Synthetic Chemical Co., Ltd.) was used as the ionic polymer. A particle dispersion dispersed in silicone oil was obtained.

  The produced cyan pigment-containing migrating particles were observed with an optical microscope, but no particles of 1 mm or more were observed, and no agglomerates could be confirmed, indicating that the electrophoretic particles were excellent in dispersion stability. It was. When observed with a scanning electron microscope (FE-SEM S-5500, manufactured by Hitachi), spherical particles were observed. When measured with HORIBA LB-550 (dynamic light scattering particle size distribution analyzer), the average particle size was 148 nm.

(Example A4)
A particle dispersion in which cyan pigment-containing electrophoretic particles were dispersed in silicone oil was obtained in the same manner as in Example A2, except that methanol was used instead of water as a good solvent.

  The produced cyan pigment-containing migrating particles were observed with an optical microscope, but no particles of 1 mm or more were observed, and no agglomerates could be confirmed, indicating that the electrophoretic particles were excellent in dispersion stability. It was. When observed with a scanning electron microscope (FE-SEM S-5500, manufactured by Hitachi), spherical particles were observed. When measured with HORIBA LB-550 (dynamic light scattering particle size distribution analyzer), the average particle size was 170 nm.

(Comparative Example A1)
The following components were mixed to prepare a solution.
-Butyl methacrylate: 16.0 parts by weight-Lauryl methacrylate: 10.0 parts by weight-Styrene: 35.0 parts by weight-Methacrylic acid: 7.0 parts by weight-Glycidyl methacrylate: 12.0 parts by weight-X-22-174DX (Shin-Etsu Chemical Co., Ltd.): 20.0 parts by weight perbutyl O (Nippon Yushi Co., Ltd.) 8.0 parts

  100 parts of methyl ethyl ketone was weighed into a reaction vessel equipped with a nitrogen introduction tube, the temperature was fixed at 80 ° C. while sealing with nitrogen, and the solution was added dropwise over 2 hours. A polymer resin compound (carboxyl group-containing silicone graft acrylic resin compound) having a nonvolatile content of 50.7% and a number average molecular weight of 7,300 was synthesized.

  Measure the following <component (I)> in a 100 cc plastic bottle, disperse it with a paint shaker (manufactured by Toyo Seiki) for 2 hours, add the following <component (II)> to this, and mix To obtain a dispersed slurry.

<Ingredient (I)>
Carboxyl group-containing silicone graft acrylic resin compound: 12.0 parts (polymer resin compound having a number average molecular weight of 7300 synthesized above)
Carbon black (pigment): 6.0 parts by weight (manufactured by Degussa Huls; Printex 85)
Dispersant (manufactured by Zeneca; Solsperse 5000): 0.3 part by weightNigrosin compound (charge control agent): 0.3 part by weight (manufactured by Chuo Chemical Co., Ltd .; CHUO CCA-2)
・ Methyl ethyl ketone (MEK: good solvent): 12.0 parts by weight

<Ingredient (II)>
Methyl ethyl ketone (good solvent): 15.0 parts by weight Silicone oil (dispersion medium): 15.0 parts by weight (trade name: KF-96L-2)

  Next, the dispersion slurry was slowly dropped into silicone oil as a dispersion medium (KF-96L-2 manufactured by Shin-Etsu Silicone Co., Ltd.) to precipitate a resin compound on the pigment surface. After dropping, methyl ethyl ketone was removed by distillation under reduced pressure to obtain a particle dispersion in which a resin compound was deposited on the pigment surface in silicone oil.

(Comparative Example A2)
In a reaction vessel equipped with a stirrer, a thermometer and a reflux condenser, 50 parts by weight of dimethyl sulfoxide, 50 parts by weight of xylene, 2.2 parts by weight of potassium tert-butoxide, and 6.2 parts by weight of quinacridone are taken and heated to 60 ° C. Heated. Into this, 20 parts by weight of modified silicone (X-22-174DX, manufactured by Shin-Etsu Silicone) was dropped over 1 hour. After the dropwise addition, the reaction was further performed by stirring at this temperature for 6 hours. After completion of the reaction, 20 parts of a 1.0 mol / L aqueous hydrochloric acid solution was added to precipitate the reaction product, and the reaction solvent was removed. After further washing with water, it was dried to obtain an oily product.

  2 parts by weight of the magenta particles obtained above and 1 part by weight of ethyl laurate are added to 97 parts by weight of dimethyl silicone oil (KF-96-1CS, manufactured by Shin-Etsu Silicone Co., Ltd.), and dispersed for 30 minutes with a homogenizer. A particle dispersion liquid was prepared. When the obtained magenta particles were observed with an optical microscope, aggregates in which several magenta particles were agglomerated were found. The homogenizer was further treated for 30 minutes, but this agglomerate was not loosened.

(Evaluation)
-Measurement of zeta potential-
The zeta potential of the particles in the particle dispersions obtained in the above examples and comparative examples was measured. The results are shown below.
Example A1 Zeta potential: +82.2 mV
Example A2 Zeta potential: +94.6 mV
Example A3 Zeta potential: +75.4 mV
Example A4 Zeta potential: +72.1 mV
Comparative Example A1 Zeta potential: +70.5 mV
Comparative Example A2 Zeta potential: +60.1 mV

  From the above results, it can be seen that this example has a larger zeta potential and a larger charge amount than the comparative example. In Examples A1 to A4, it can be seen that electrophoretic particles having a larger zeta potential value than particles produced using the charge control agent as in Comparative Example A1 can be obtained without adding a charge control agent. Further, as shown in Example A2, it is understood that electrophoretic particles having different charging characteristics can be obtained without adding a charge control agent by changing the resin material. In addition, from comparison between Example A2 and Example A4, both of them have excellent zeta potential compared to Comparative Example, but compared to Example A4 using methanol as a good solvent, water is used as a good solvent. It can also be seen that the Example A2 used has improved zeta potential.

  In addition, in the obtained particle dispersion liquid, a zeta potential is generated at the interface between the dispersion medium and the particles constituting the zeta potential, that is, a zeta potential is generated. The value of increases. The zeta potential was measured using a laser zeta electrometer ELS-8000 manufactured by Otsuka Electronics.

-Dispersion stability-
The dispersion stability was evaluated for the particle dispersions obtained in the above Examples and Comparative Examples. Dispersion can be stabilized by using a centrifuge (top centrifuge LC-200 manufactured by Tommy Seiko Co., Ltd.), putting the particle dispersion in a 50 ml conical tube, centrifuging at 4000 rpm / 30 minutes, and then visually observing. did. The results are shown below.
Example A1 Little change was seen.
Example A2 Almost no change was observed.
Example A3 Almost no change was observed.
Example A4 Almost no change was observed.
Comparative Example A1 Particles settled, and 2/3 from the liquid level was transparent.
Comparative Example A2 Particles settled, and 2/3 from the liquid level was transparent.

Next, the evaluation was performed by changing the centrifugation conditions to 4000 rpm / 60 minutes. The results are shown below.
Example A1 Particles settled, and 2/3 from the liquid level was transparent.
Example A2 Almost no change was observed.
Example A3 Particles settled, and 2/3 from the liquid level was transparent.
Example A4 Almost no change was observed.
Comparative Example A1 Particles settled.
Comparative Example A2 Particles settled.

  From the above results, it can be seen that in this example, the dispersion stability is superior to the comparative example. In particular, Examples A2 and A4 using a polymer having a dendritic structure as an emulsifier were found to have further excellent dispersion stability compared to Examples A1 and A3.

[Example B]
As shown below, an image display device having the same configuration as that of the image display device according to the second embodiment was manufactured (see FIG. 1).

−Preparation of Particle Dispersion of Yellow Particle Group 34−
Except that a mixture of 90 parts by weight of a cationic polymer (PD-7 manufactured by Yokkaichi Gosei Co., Ltd.) and 10 parts by weight of polyacrylamide was used as the ionic polymer, yellow particles were added to silicone oil in the same manner as in Example A2. A particle dispersion in which the group 34 was dispersed was prepared. When the zeta potential of the obtained particles was measured, it was 73.1 mV.

-Preparation of particle dispersion of magenta particle group 34M-
A particle dispersion in which the magenta particle group 34M was dispersed in silicone oil was produced in the same manner as in Example A2, except that a cationic polymer (PD-7 manufactured by Yokkaichi Synthesis Co., Ltd.) was used as the ionic polymer. When the zeta potential of the obtained particles was measured, it was 83.5 mV.

-Production of cyan particle group 34C-
A particle dispersion in which cyan particle group 34C was dispersed in silicone oil was prepared in the same manner as in Example A2, except that cationized polyvinyl alcohol (K-210 manufactured by Nippon Seikagaku Co., Ltd.) was used as the ionic polymer. When the zeta potential of the obtained particles was measured, it was 96.2 mV.
-Production of insulating particles 36-
As the insulating particles 36, particles prepared as follows were used.
By carrying out ball milling for 20 hours using zirconia balls having a diameter of 10 mm with cyclohexyl methacrylate: 53 parts by weight, titanium oxide: (Taipaque CR63: manufactured by Ishihara Sangyo Co., Ltd.): 45 parts by weight, and cyclohexane: 5 parts by weight. Dispersion A is prepared.
The carbon dioxide dispersion B is prepared by pulverizing 40 parts by weight of calcium carbonate and 60 parts by weight of water with a ball mill. 2% serogen aqueous solution: 4.3 g, charcoal cal dispersion 8.5 g, and 20% saline: 50 g were mixed, degassed with an ultrasonic machine for 10 minutes, and stirred with an emulsifier to obtain a mixed solution C Create 35 g of dispersion A, 1 g of divinylbenzene, and polymerization initiator AIBN: 0.35 g are sufficiently mixed and degassed with an ultrasonic machine for 10 minutes. This is put in the mixed solution C and emulsified with an emulsifier.
Next, this emulsified liquid is put into a bottle, siliconized, and using an injection needle, vacuum deaeration is sufficiently performed, and nitrogen gas is sealed. Next, it reacts at 60 degreeC for 10 hours, and produces particle | grains. After cooling, the dispersion is freed from cyclohexane for 2 days at −35 ° C. and 0.1 Pa using a freeze dryer. The obtained particle powder is dispersed in ion-exchanged water, calcium carbonate is decomposed with hydrochloric acid water, and filtration is performed. Then, it is washed with sufficient distilled water to make the particle size uniform and dried. The color of the insulating particles 36 was white, and the volume average primary particle size was 20 μm. In addition, the measurement of the volume average primary particle diameter was performed using the above-mentioned method.

  -Fabrication of image display medium and image display device-

The image display medium 12 uses a transparent conductive ITO supporting substrate of 70 mm × 50 mm × 1.1 mm in this embodiment as the supporting substrate 38, and a width of 0.234 mm and an interval are formed on the supporting substrate 38 by etching. A plurality of 0.02 mm line-shaped surface electrodes 40 were prepared.
Similarly, a 70 mm × 50 mm × 1.1 mm ITO support substrate is used as the support substrate 44, and a plurality of line-shaped back electrodes 46 having a width of 0.234 mm and a spacing of 0.02 mm are formed on the support substrate 44 by etching. did.

  Then, on each of the surface electrode 40 and the back electrode 46, the surface layer 42 and the surface layer 48 were formed by applying a polycarbonate resin to a thickness of about 0.5 μm.

The average surface roughness of the surface layer 42 and the surface layer 48 was measured by an OLYMPUS, trade name: Laser Displacement Microscope OLS1100.
As described above, each of the front substrate 20 and the rear substrate 22 was produced.

  Next, a gap member 24 was provided on the back substrate 22 and formed so as to have a height of 100 μm. The gap member 24 was formed so as to be provided with cells (area surrounded by the gap member 24, the display substrate 20, and the back substrate 22) corresponding to each pixel when an image was displayed on the image display medium 12.

  The gap member 24 was formed in a desired pattern shape by a photolithography method using a photoresist film on the back substrate 22. As a cell pattern formed by the gap member 24, a square cell having a length and width of 0.254 mm was formed so as to substantially match the pixel. The gap member 24 is formed by applying a thermosetting epoxy resin to the back substrate 22 in a desired pattern shape by screen printing, heat-curing it, and repeating this process until the required height is reached. You can also. The gap member 24 can also be formed by adhering a thermoplastic film formed in a desired surface shape to the back substrate 22 by injection compression molding, embossing, hot pressing, or the like. Further, the gap member 24 can be integrally formed with the back substrate 22 by embossing or hot pressing. Of course, the gap member 24 may be formed on the display substrate 20 side as long as the transparency is not impaired, or may be integrally formed with the display substrate 20.

  Here, as the dispersion medium 50, silicone oil manufactured by Shin-Etsu Chemical Co., Ltd. was used.

  The particle dispersions of the yellow particle group 34Y, the magenta particle group 34M, and the cyan particle group 34C produced as described above were mixed so that the volume ratio of each particle group was a 1: 1 ratio. Further, after dispersing the insulating particles 36 at 10 parts by weight, the mixed particle dispersion is filled on the back substrate 22 on which the gap member 24 is formed. Each region).

  The insulating particles 36 are mixed at a ratio of 1/10 with respect to the dispersion medium 50 so that each particle of the particle group 34 is aligned along a direction orthogonal to the facing direction of the display substrate 20 and the back substrate 22. They were arranged in a cell so that the distances between the insulating particles 36 and the display substrate 20 and the back substrate 22 were substantially equidistant while being arranged with a gap that could pass.

  In the image display medium 12, the particle dispersion liquid containing the plural kinds of particle groups 34 and the insulating particles 36 as described above is put in each cell on the back substrate 22 provided with the gap member 24, and then the display is performed. It can be manufactured by disposing the substrate 20 and fixing the back substrate 22 and the display substrate 20 with a clamp or the like.

The total volume ratio of the particle group 34 to the void volume between the substrates (corresponding to the cell volume) was about 3%. The total volume ratio of the insulating particles 36 to the void volume between the substrates was about 10%.

  Next, the electrode on the front substrate of the obtained image display medium 12 was connected to Trek 610C manufactured by Trek as the voltage application unit 16, and the electrode on the rear substrate was grounded. Further, a personal computer (trade name CF-R1 manufactured by Panasonic Corporation) was connected to the voltage application unit 16 as a machine having the function of the control unit 18.

An image display device was manufactured as described above.
Here, the absolute value | Vty | of the voltage when the yellow particle group 34Y starts moving was 50V, and the absolute value | Vdy | of the maximum voltage for moving almost all the yellow particle group 34Y was 53V. .
Further, the absolute value | Vtm | of the voltage when the magenta particle group 34M starts moving was 34V, and the absolute value | Vdm | of the maximum voltage for moving almost all the magenta particle group 34Y was 38V.
Further, the absolute value | Vtc | of the voltage when the cyan particle group 34C starts moving was 20V, and the absolute value | Vdc | of the maximum voltage for moving almost all the cyan particle group 34C was 24V.
Then, as described with reference to FIG. 3, when the voltage applied between the substrates is controlled, the particle group 34 of each color is selectively moved according to the color to be displayed, and a desired color can be displayed. It was.

It is a schematic block diagram of the image display apparatus which concerns on 2nd Embodiment. It is a diagram which shows typically the relationship between the voltage to apply and the moving amount (display density | concentration) of particle | grains. It is explanatory drawing which shows typically the relationship between the voltage aspect applied between the board | substrates of an image display medium, and the movement aspect of particle | grains.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image display apparatus 12 Image display medium 16 Voltage application part 20 Display substrate 22 Back substrate 24 Gap member 34 Particle group 34C Cyan particle group 34Y Yellow particle group 34M Magenta particle group 36 Insulating particle 38 Support substrate 40 Surface electrode 42 Surface layer 44 Support substrate 46 Back electrode 48 Surface layer 50 Dispersion medium

Claims (12)

A first solvent comprising an ionic polymer, an emulsifier, a colorant, silicone oil, and the silicone oil are incompatible with each other and have a lower boiling point than the silicone oil and dissolve the ionic polymer. An emulsification step of stirring and emulsifying the mixed solution containing
A removal step of removing the second solvent from the emulsified mixed solution;
A method for producing a particle dispersion, comprising:   The method for producing a particle dispersion according to claim 1, wherein the emulsifier is a polymer having a dendritic structure.   The method for producing a particle dispersion according to claim 1, wherein the second solvent is water. A first solvent comprising an ionic polymer, an emulsifier, a colorant, silicone oil, and the silicone oil are incompatible with each other and have a lower boiling point than the silicone oil and dissolve the ionic polymer. And an emulsification step of stirring and emulsifying the mixed solution comprising:
A removal step of removing the second solvent from the emulsified mixed solution;
A particle dispersion characterized by being produced through at least.   The particle dispersion according to claim 4, wherein the emulsifier is a polymer having a dendritic structure.   The particle dispersion according to claim 4 or 5, wherein the second solvent is water. A pair of substrates at least one of which is translucent and disposed to face each other with a gap;
A particle dispersion liquid that includes a light-transmitting dispersion medium and a particle group that is dispersed in the dispersion medium and moves according to an electric field formed between the pair of substrates, and is sealed between the pair of substrates. A first solvent comprising an ionic polymer, an emulsifier, a colorant, a silicone oil, and a second solvent that is incompatible with the silicone oil and has a lower boiling point than the silicone oil and dissolves the ionic polymer. A particle dispersion produced through at least an emulsifying step of stirring and emulsifying the mixed solution, and a removing step of removing the second solvent from the emulsified mixed solution;
An image display medium comprising:   The image display medium according to claim 7, wherein the emulsifier is a polymer having a dendritic structure.   The image display medium according to claim 7, wherein the second solvent is water. The particle dispersion has a plurality of types,
The particle groups contained in the plurality of types of particle dispersion liquids are different in absolute value of voltage required for moving according to an electric field and colored in different colors. 10. The image display medium according to any one of items 9.   The image display according to claim 10, wherein the particle groups included in the plurality of types of particle dispersions have a voltage range necessary for moving in accordance with an electric field, and the voltage ranges are different from each other. Medium. The image display medium according to any one of claims 7 to 11,
Voltage applying means for applying a voltage between the pair of substrates of the image display medium;
An image display device comprising: