JP6201445B2 - Concealed particles for electrophoretic display devices, display particle dispersions for electrophoretic display devices, electrophoretic display media, and electrophoretic display devices - Google Patents

Description

  The present invention relates to concealed particles for electrophoretic display devices, particle dispersions for electrophoretic display devices, electrophoretic display media, and electrophoretic display devices.

  Conventionally, a display medium using electrophoretic particles is known as a display medium that can be repeatedly rewritten. This display medium includes, for example, a pair of substrates and particles sealed between the substrates so as to be movable between the substrates in accordance with an electric field formed between the pair of substrates. In addition, in order to display a background color (for example, white), particles having a low migration speed due to an electric field (for example, concealing particles such as white particles) may be sealed between the substrates in the display medium.

For example, Patent Document 1 states that “the content of particles having a particle size of 1 μm or more and the content of particles having a particle size of 100 nm or less are 0% by volume to 4% by volume and 0% by volume to 2% by volume, respectively. Some electrophoretic dispersions have been proposed.
Patent Document 2 states that "the average particle diameter of the electrophoretic particles is Do [nm], the maximum particle diameter is Dm [nm], and the average particle diameter of the electrophoretic particles after being stored at 50 ° C for 90 days. Is To [nm] and the maximum particle size is Tm [nm], the formula: 0 <To / Do ≦ 2 (100 ≦ Do ≦ 600) and the formula: 0 <Tm / Dm ≦ 3 Electrophoretic dispersion liquid "has been proposed.

JP 2009-186501 A JP 2009-186500 A

  The subject of this invention is providing the concealment particle | grains for electrophoretic display apparatuses which suppress the fall of the drive characteristic of an electrophoretic particle.

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

The invention according to claim 1
No colored particles are contained inside, the volume average particle diameter is 300 nm or more and 1000 nm or less, and the CV value (Coefficient of Variation) is 15% or less.
A concealing particle for an electrophoretic display device that does not migrate or does not migrate evenly when an electric field is applied to migrate the electrophoretic particles.

The invention according to claim 2
The concealing particles for electrophoretic display devices according to claim 1, wherein the existence frequency of particles having a particle size of 250 nm or less in the particle size distribution is 30% or less.

The invention according to claim 3
The concealing particles for an electrophoretic display device according to claim 1, comprising a copolymer containing at least 4-vinylbiphenyl as a polymerization component.

The invention according to claim 4
A group of particles comprising electrophoretic particles and concealing particles for an electrophoretic display device according to any one of claims 1 to 3,
A dispersion medium for dispersing the particle group;
A display particle dispersion for an electrophoretic display device.

The invention according to claim 5
A pair of substrates, at least one of which is translucent,
The display particle dispersion for an electrophoretic display device according to claim 4 enclosed between the pair of substrates,
An electrophoretic display medium comprising:

The invention according to claim 6
A pair of electrodes, at least one of which is translucent,
A region having a display particle dispersion for an electrophoretic display device according to claim 4, provided between the pair of electrodes,
An electrophoretic display medium comprising:

The invention according to claim 7 provides:
An electrophoretic display medium according to claim 5;
Voltage applying means for applying a voltage between the pair of substrates of the display medium;
An electrophoretic display device comprising:

The invention according to claim 8 provides:
An electrophoretic display medium according to claim 6;
Voltage applying means for applying a voltage between the pair of electrodes of the display medium;
An electrophoretic display device comprising:

  According to the first aspect of the present invention, there is provided a concealing particle for an electrophoretic display device that suppresses a decrease in driving characteristics of the electrophoretic particle as compared with a case where the CV value exceeds 15% or less.

According to the second aspect of the present invention, there is provided concealment particles for electrophoretic display devices in which the concealability of electrophoretic particles is improved as compared with the case where the presence frequency of particles having a particle size of 250 nm or less in the particle size distribution exceeds 30%. Provided.

  According to the invention concerning Claim 3, the concealment particle | grains for white electrophoretic display apparatuses are provided.

  According to the invention of claim 4, 5, 6, 7, or 8, the driving characteristics of the electrophoretic particles are reduced as compared with the case where the CV value of the concealing particles for the electrophoretic display device exceeds 15% or less. A particle dispersion, an electrophoretic display medium, or an electrophoretic display device for an electrophoretic display device to be suppressed is provided.

It is a schematic block diagram of the display apparatus which concerns on this embodiment. It is explanatory drawing which shows typically the movement aspect of a particle group when a voltage is applied between the board | substrates of the display medium of the display apparatus which concerns on this embodiment. 4 is a SEM photograph showing the concealed particles of Example 1. 4 is a SEM photograph showing the concealed particles of Comparative Example 1. It is a figure which shows the particle size distribution of the concealment particle | grains of Example 1 and Comparative Example 1.

Hereinafter, an embodiment which is an example of the present invention will be described in detail.
In the following description, the expression “(meth) acryl” is “acryl, methacryl”, the expression “(meth) acrylo” is “acrylo, methacrylo”, and the expression “(meth) acrylate” is “ This means both “acrylate and methacrylate”.

<Hiding particles for electrophoretic display devices>
The concealing particles for electrophoretic display according to this embodiment (hereinafter “concealing particles”) have a volume average particle size of 300 nm to 1000 nm and a CV value (Coefficient of Variation) of 15% or less.

Here, the concealing particles are particles for concealing particles other than the electrophoretic particles (electrophoretic particles migrated to the display substrate side) that are used in the electrophoretic particle device together with the electrophoretic particles and contribute to display. That is, the particles have a function of displaying the background color of the electrophoretic display device.
However, it has been found that when electrophoretic particles are repeatedly driven (migrated) in the presence of concealing particles, the driving characteristics thereof are degraded.

On the other hand, in the concealment particles according to the present embodiment, the volume average particle size is set to 300 nm to 1000 nm and the CV value (Coefficient of Variation) is set to 15% or less, so that the driving characteristics of the electrophoretic particles are reduced. Is suppressed. In other words, the concealment particles according to the present embodiment have been found that when the volume average particle diameter is in the above range, the monodispersibility is increased, thereby suppressing the decrease in driving characteristics of the electrophoretic particles.
Moreover, the concealment particle | grains which concern on this embodiment improve concealment property of concealment particle | grains by setting a volume average particle diameter to 300 nm or more and 1000 nm or less, and making CV value (Coefficient of Variation) 15% or less. That is, when the concealment particles are white, the whiteness is high.

  In addition, the concealment particles according to the present embodiment have a low charge amount and a response time to migrate according to electrolysis longer than the electrophoretic particles from the viewpoint of realizing the electrophoretic particle concealment function and the background color display function. The electrophoretic particles are applied as electrophoretic particles that do not migrate even when an electric field for electrophoretic particles is applied (driven) or does not migrate evenly.

  Hereinafter, the details of the concealment particles according to the present embodiment will be described.

(Characteristics of concealment particles)
The volume average particle size of the concealment particles according to the present embodiment is 300 nm or more and 1000 nm or less, but from the viewpoint of suppressing the decrease in driving characteristics of the electrophoretic particles and concealing properties of the concealment particles, it is preferably 300 nm or more and 800 nm or less. Desirably, it is 400 nm or more and 700 nm or less.

  The volume average particle diameter of the concealing particles is a value measured by a SEM (Scanning Electron Microscope image) image. Specifically, after obtaining an image by SEM (scanning electron microscope S-4800, manufactured by Hitachi High-Technologies Corporation), the diameter (longest portion) r1 of the concealment particle is measured for each concealment particle to be measured. This is measured for 100 particles, a particle size distribution is obtained, the volume is obtained by converting rl to r100 into a sphere, and the value when the accumulation from the first to the 100th is 50% is the volume average particle diameter. To do.

  The CV value of the concealment particles according to this embodiment is 15% or less, but is preferably 12% or less, more preferably 10%, from the viewpoint of suppressing the deterioration of the driving characteristics of the electrophoretic particles and concealing properties of the concealment particles. It is as follows.

In addition, the CV value of the concealment particle is a value measured by an SEM (Scanning Electron Microscope: scanning electron microscope image) image. Specifically, after obtaining an image by SEM (scanning electron microscope S-4800, manufactured by Hitachi High-Technologies Corporation), the diameter (longest portion) r1 of the concealment particle is measured for each concealment particle to be measured. This is measured per 100, the particle size distribution is obtained, the standard deviation and the volume average particle size are obtained, and the values are calculated by the following formula.
Formula: CV value [%] = (σ / D) × 100 (σ: standard deviation (nm), D: volume average particle diameter (nm))

The occurrence frequency of the particles following particle size 250nm in the particle size distribution of the concealment particles according to the present embodiment (hereinafter, "the frequency of presence of particle size 250nm particles") may be 30% or less, preferably 20% or less More desirably, it is 10% or less. By making the existence frequency of the particle size 250 nm 30% or less, the concealing property of the concealing particles is easily improved. That is, when the concealment particles are white, the whiteness is high. Further, the viscosity of the display dispersion liquid is easily reduced.

  In addition, the presence frequency of the particle | grains with a particle diameter of 250 nm of a concealment particle | grain is a value measured by a SEM (Scanning Electron Microscope: Scanning electron microscope image) image. Specifically, after obtaining an image by SEM (scanning electron microscope S-4800, manufactured by Hitachi High-Technologies Corporation), the diameter (longest portion) r1 of the concealment particle is measured for each concealment particle to be measured. This is measured for 100 pieces, the particle size distribution is obtained, and the existence frequency of particles having a particle size of 250 nm is obtained from the particle size distribution.

(Configuration of concealment particles)
Examples of the concealment particles according to the present embodiment include white particles containing a polymer containing at least a vinyl compound represented by the following general formula (1) (hereinafter referred to as “specific vinyl compound”) as a polymerization component. Since the vinyl compound represented by the following general formula (1) is a material exhibiting a high refractive index (for example, 1.56 or more and 1.70 or less), the concealing particles containing a polymer containing at least this as a polymerization component. Is preferable because it has high refractive index particles (that is, particles with high whiteness), improves concealment, and realizes white display with high whiteness as a background color.

  In addition to the specific vinyl compound, the concealing particle contains a polymer containing, as a polymerization component, another monomer such as a reactive compound having a silicone chain or an alkyl chain (hereinafter referred to as “specific reactive compound”). It may be a particle. However, the mass ratio of the specific vinyl compound is preferably 1% by mass to 99% by mass (preferably 10% by mass to 80% by mass) with respect to the entire polymer.

-Specific vinyl compounds-
The specific vinyl compound is a vinyl compound represented by the general formula (1).

  In general formula (1), Ar represents an unsubstituted aromatic ring, an aromatic ring substituted with an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, and n is 1 to 4 Represents the following integers:

In general formula (1), the unsubstituted aromatic ring represented by Ar may be monocyclic, polycyclic or condensed. For example, benzene (monocyclic aromatic hydrocarbons); polycyclic aromatic hydrocarbons in which multiple benzenes such as biphenyl and triphenyl are single-bonded; condensation of naphthalene, phenalene, phenanthrene, anthracene, triphenylene, pyrene, chrysene, tetracene, etc. Ring aromatic hydrocarbons; compounds in which two or more selected from benzene, the polycyclic aromatic hydrocarbons and the condensed ring aromatic hydrocarbons are single-bonded; a plurality of benzenes having an alkyl group having 1 to 6 carbon atoms (for example, Linear or branched alkyl group such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group, etc. ), A compound bonded with a single bond via benzene, the polycyclic aromatic hydrocarbon and the condensed ring aromatic hydrocarbon 2 or more alkyl groups having 1 to 6 carbon atoms (for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group) A straight-chain or branched alkyl group such as a hexyl group); a group in which n hydrogen atoms have been removed.
Among them, the unsubstituted aromatic ring is preferably a group in which n hydrogen atoms are removed from benzene, biphenyl, and naphthalene from the viewpoint of reducing the charge amount of the particles.

  In the substituted aromatic ring represented by Ar in the general formula (1), examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, Examples include isobutyl group, sec-butyl group, tert-butyl group, pentyl group, hexyl group and the like. On the other hand, examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a tolyl group, a mesityl group, a benzyl group, a xylyl group, and a naphthyl group.

  In general formula (1), n represents an integer of 1 or more and 4 or less, preferably 1 or 2.

Specific vinyl compounds include styrene: the following exemplary compound (1-1), divinylbenzene: the following exemplary compound (1-2), vinylbiphenyl: the following exemplary compound (1-3), divinylbiphenyl: the following exemplary Compounds (1-4) and (1-5), vinylnaphthalene: at least selected from the following exemplified compound (1-6), and divinylnaphthalene: at least selected from the following exemplified compounds (1-7) and (1-8) One type is desirable. The copolymer containing these specific vinyl compounds is easier to form particles than the copolymers containing other specific vinyl compounds, the viewpoint that the charge amount of the particles is low, and the viewpoint of showing a high refractive index. Is desirable.
In the divinylbenzene, vinylbiphenyl, divinylbiphenyl, vinylnaphthalene, and divinylnaphthalene, the position of one or two vinyl groups is not particularly limited.

  The specific vinyl compounds represented by the above exemplary compounds (1-1) to (1-8) have the same properties as polymerization components, and the properties of the copolymer containing any of these as polymerization components are , Both are comparable. Especially, the specific vinyl compound represented by exemplary compound (1-1), (1-2), (1-3) and (1-6) is easy to obtain.

  In particular, as the specific vinyl compound, vinyl biphenyl represented by the exemplified compound (1-3) (specifically, 4-vinylbiphenyl) is used from the viewpoint of realizing high concealability (whiteness) of the concealment particles as well as availability. ) Is preferred.

-Specific reactive compounds-
The specific reactive compound is a reactive compound having a silicone chain or an alkyl chain.

-Reactive compound having a silicone chain Examples of the reactive compound having a silicone chain (polymerizable monomer having a silicone chain) include well-known compounds such as linear silicone compounds and branched silicone compounds. In particular, when a branched silicone compound is applied, it is preferable in that sticking of concealing particles can be easily suppressed.
The reactive compound having a silicone chain may be a monomer or a macromonomer. This "macromonomer" is a generic term for oligomers having a polymerizable functional group (degree of polymerization of about 2 or more and about 300 or less) or polymers, and has the properties of both polymers and monomers. is there. Moreover, the reactive compound having a silicone chain may be used alone or in combination.

As a linear silicone compound, for example, a dimethyl silicone compound having a (meth) acrylate group at one end (a silicone compound represented by the following structural formula (1). For example, manufactured by JNC: Silaplane: FM- 0711, FM-0721, FM-0725, etc., manufactured by Shin-Etsu Chemical Co., Ltd .: X-22-174DX, X-22-2426, X-22-2475, etc.).
Examples of the branched silicone compound include silicone compounds represented by the following structural formulas (2) to (7).

In the structural formula (1), R ¹ represents a hydrogen atom or a methyl group. R ¹ ′ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. m represents a natural number (for example, 1 to 1000, preferably 3 to 100). x represents an integer of 1 to 3.

In the structural formulas (2), (3), (5), (6), and (7), R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁹ and R ¹⁰ are Each independently represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a fluoroalkyl group having 1 to 4 carbon atoms. R ⁸ represents a hydrogen atom or a methyl group. p, q, and r each independently represent an integer of 1 to 1000. x represents an integer of 1 to 3.

In the structural formula (4), R ¹ ′ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. m represents a natural number (for example, 1 to 1000, preferably 3 to 100).

In the silicone compounds represented by the structural formulas (2) and (5), R ¹ and R ⁵ are butyl groups, R ² , R ³ , R ⁴ , R ⁶ and R ⁷ are methyl groups, and R ⁸ is methyl In an embodiment, p and q are each independently an integer of 1 to 5, and x is an integer of 1 to 3.

In the silicone compounds represented by the structural formulas (3) and (6), R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁹ and R ¹⁰ are methyl groups, and R ⁸ Is preferably a hydrogen atom or a methyl group, p, q and r are each independently an integer of 1 to 3, and x is an integer of 1 to 3.

In the silicone compound represented by the structural formula (7), R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁹ and R ¹⁰ are methyl groups, and R ⁸ is a hydrogen atom or An embodiment in which p and q are each independently an integer of 1 to 5 and x is an integer of 1 to 3 in the methyl group is desirable.

  Examples of the silicone compound represented by the structural formula (2) include MCS-M11 and MFS-M15 manufactured by Gelest. Examples of the silicone compound represented by the structural formula (3) include RTT-1011 manufactured by Gelest, X22-2404 manufactured by Shin-Etsu Chemical Co., Ltd., and the like. Examples of the silicone compound represented by the structural formula (4) include MCR-V21 manufactured by Gelest. Examples of the silicone compound represented by the structural formula (5) include MCS-V12 manufactured by Gelest. Examples of the silicone compound represented by the structural formula (6) include VTT-106 manufactured by Gelest. Examples of the silicone compound represented by the structural formula (7) include RMS-044, RMS-033, and RMS-083 manufactured by Gelest. Typical structural formulas of these silicone compounds are shown below.

  In MCS-M11, m and n in the above structural formula are each independently an integer of 2 or more and 4 or less, and the molecular weight thereof is 800 or more and 1000 or less.

  RTT-1011 is a compound represented by the above structural formula.

  X22-2404 is a compound represented by the above structural formula.

  In MCR-V21, m is an integer of 72 or more and 85 or less in the above structural formula, and the molecular weight thereof is 5500 or more and 6500 or less.

  In MCS-V12, m and n are integers of 6 or more and 10 or less in the above structural formula, and the molecular weight thereof is 1200 or more and 1400 or less.

  VTT-106 is a compound represented by the above structural formula.

-Reactive compound having an alkyl chain Examples of the reactive compound having an alkyl chain (polymerizable monomer having an alkyl chain) include (meth) acrylic acid esters, specifically, (meth) acrylic. Examples include methyl acid, butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and the like. . Among them, a long-chain alkyl chain, specifically, for example, a (meth) acrylic acid ester having an alkyl chain having 4 to 30 carbon atoms is desirable.

-Other monomers other than the specific reactive compound-
Examples of other monomers (polymerizable monomers) other than the specific reactive compound include polymerizable monomers having no chargeable group. Examples of the polymerizable monomer having no charging group include nonionic polymerizable monomers (nonionic polymerizable monomers). For example, (meth) acrylonitrile, (meth) acrylic acid alkyl ester, (Meth) acrylamide, ethylene, propylene, butadiene, isoprene, isobutylene, N-dialkyl-substituted (meth) acrylamide, vinyl carbazole, vinyl chloride, vinylidene chloride, isoprene, butadiene, vinyl pyrrolidone and the like.

-Manufacturing method of concealment particles (white particles)-
The concealing particles (white particles) according to the present embodiment are, for example, an organic solvent, each raw material component (monomer) of the polymer that is a constituent element of the concealing particles (white particles), and, if necessary, A dispersion is prepared by adding and mixing with other additives such as a polymerization initiator.
Thereafter, for example, when the polymerization reaction is advanced by heating the dispersion, the polymer is precipitated together with the polymerization reaction to form a granular material.

  Specifically, for example, a polymerization portion of a specific vinyl compound as a polymerization component becomes a site incompatible with an organic solvent along with polymerization, and precipitates and grows particles. For this reason, in the case of a polymer containing other polymerization components as polymerization components, it is considered that particles grow while the polymerization sites of the vinylbiphenyl compound are oriented on the inside and the polymerization sites of the other polymerization components are oriented on the outside.

  Here, as the organic solvent to be used, for example, a solvent having a property of dissolving a polymerizable monomer such as a specific vinyl compound but not dissolving the polymer, specifically, for example, paraffin, hexane, etc. Or the like, or a mixed solvent of these solvents and an aromatic hydrocarbon solvent such as toluene.

In particular, in order to produce the concealing particles satisfying the above-mentioned particle diameter, CV value, and the existence frequency of the particle diameter of 250 nm, it is preferable to prepare the kind and amount of the organic solvent to be used. Specifically, as an organic solvent, a poor solvent for a polymerizable monomer such as a specific vinyl compound (for example, silicone oil; a hydrocarbon solvent such as Isopar (manufactured by ExxonMobil) or liquid paraffin) and a good solvent (for example, Use a mixed solvent of toluene, hexane, tetrahydrofuran, benzene, dimethyl sulfoxide, isopropanol, etc., and reduce the amount of the good solvent (for example, reduce the amount of good solvent to 1% to 25% by mass with respect to all solvents) By doing so, it becomes easy to obtain concealment particles satisfying the existence frequency of the particle size, CV value, and particle size of 250 nm.
In addition, you may obtain the concealment particle | grains which satisfy | fill the said particle size and CV value by performing a classification process after manufacturing concealment particle | grains.

-Others-
The concealing particles according to the present embodiment are not limited to the white particles described above, and may be other white particles or colored particles other than white particles.
Other white particles include, for example, white pigment (titanium oxide, silicon oxide, zinc oxide, etc.), resin (polystyrene resin, polyethylene resin, polypropylene resin, polycarbonate resin, polymethyl methacrylate resin (PMMA), acrylic resin, phenol Resin, formaldehyde condensate, etc.) or resin particles (polystyrene particles, polyvinyl naphthalene particles, bismelamine particles, etc.).
Examples of the colored particles other than white include the above-described resin particles encapsulating a target color pigment and dye. If the pigment or dye is, for example, RGB or YMC color, a general pigment or dye used for printing ink or color toner can be used.

<Particle dispersion for electrophoretic display>
A particle dispersion for an electrophoretic display device according to the present embodiment (hereinafter referred to as “display particle dispersion”) disperses the particle group including the electrophoretic particles and the concealment particles according to the present embodiment, and the particle group. And a dispersion medium. The display particle dispersion according to this embodiment may contain other known additives such as a charge control agent, if necessary.

-Electrophoretic particles-
Examples of the electrophoretic particles include well-known particles that migrate in a dispersion medium according to an electric field.
For example, examples of the electrophoretic particles include resin particles, particles in which a colorant is fixed on the surface of these resin particles, particles containing a colorant in the resin, and the like. Other examples of the electrophoretic particles include insulating metal oxide particles (for example, particles such as glass beads, alumina, and titanium oxide), metal colloid particles having a plasmon coloring function, and the like.

Examples of the thermoplastic resin used in the electrophoretic particles include styrenes such as styrene and chlorostyrene; monoolefins such as ethylene, propylene, butylene, and isoprene; vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate, and the like. Vinyl ester; α-methylene aliphatic mono, such as methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate Carboxylates; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl butyl ether; homopolymers of vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, vinyl isopropenyl ketone, or They include resins composed of these copolymers.
Examples of the thermosetting resin used for the electrophoretic particles include a crosslinked copolymer mainly composed of divinylbenzene and a crosslinked resin such as crosslinked polymethyl methacrylate, a phenol resin, a urea resin, a melamine resin, a polyester resin, and a silicone resin. Etc.

  Typical resins used for the electrophoretic particles include, for example, polystyrene resin, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, Examples thereof include styrene-maleic anhydride copolymer, polyethylene resin, polypropylene resin, polyester resin, polyurethane resin, epoxy resin, silicone resin, polyamide resin, modified rosin, and paraffin wax.

Examples of the colorant used for the electrophoretic particles include organic or inorganic pigments and oil-soluble dyes.
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 122C. I. Pigment red 57: 1, C.I. I. Pigment yellow 97, C.I. Blue 15: 1, C.I. I. Pigment Blue 15: 3 is a typical example.

  As content of a coloring agent, 10 mass% or more and 99 mass% or less are good with respect to resin which comprises electrophoretic particle, for example, It is 30 mass% or more and 80 mass% or less desirably.

  The electrophoretic particles may contain a charge control agent as necessary. Examples of the charge control agent include known ones used for toner materials for electrophotography. For example, cetylpyridyl chloride, BONTRON P-51, BONTRON P-53, BONTRONE-84, BONTRON E-81 (orientated above) Quaternary ammonium salts such as those manufactured by Chemical Industry Co., Ltd., salicylic acid metal complexes, phenol condensates, tetraphenyl compounds, metal oxide particles, and metal oxide particles surface-treated with various coupling agents.

The surface of the electrophoretic particles may be surface-treated with a silicone compound having a reactive group. That is, the electrophoretic particles may be particles having a core-shell structure in which the electrophoretic particles are core particles and a surface of the core particles has a silicone compound coating layer.
In the case of particles having a core / shell structure, the core particles may contain a resin having a reactive group that reacts with a reactive group of the silicone compound (for example, a hydroxyl group, a carboxyl group, a carbonyl group, an amino group, etc.). Good. Examples of the resin having such a reactive group include melamine resin, guanamine resin, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-maleic anhydride copolymer, polyvinyl alcohol resin, polyvinyl Preferred examples include butyral resin, gelatin, and agar.
Further, when the silicone compound has a chargeable group, the core particle may include a resin having no chargeable group.
If necessary, an external additive may be attached to the surface of the electrophoretic particles. The color of the external additive is desirably transparent so as not to affect the color of the electrophoretic particles.
Examples of the external additive include inorganic particles such as metal oxides such as silicon oxide (silica), titanium oxide, and alumina. The external additives may be surface-treated with a coupling agent or silicone oil in order to adjust the chargeability, fluidity, and environment dependency of the electrophoretic particles.
Coupling agents include aminosilane coupling agents, aminotitanium coupling agents, nitrile coupling agents and other positively chargeable ones, and silanes that do not contain nitrogen atoms (consisting of atoms other than nitrogen). Examples include negatively chargeable ones such as coupling agents, titanium-based coupling agents, epoxy silane coupling agents, and acrylic silane coupling agents.
Silicone oils include positively chargeable ones such as amino-modified silicone oils, dimethyl silicone oils, alkyl-modified silicone oils, α-methylsulfone-modified silicone oils, methylphenyl silicone oils, chlorophenyl silicone oils, fluorine-modified silicone oils, etc. Negatively chargeable ones.
These coupling agents and silicone oils are selected according to the desired resistance of the external additive.

  The primary particles of the external additive are, for example, preferably 1 nm to 100 nm, and preferably 5 nm to 50 nm, but are not limited thereto.

The external additive amount of the external additive is, for example, preferably 0.01 parts by mass or more and 3 parts by mass or less, and more preferably 0.05 parts by mass or more and 1 part by mass or less with respect to 100 parts by mass of the electrophoretic particles. is there.
The external addition amount of the external additive is preferably adjusted based on the balance between the particle size of the electrophoretic particles and the particle size of the external additive. When the amount of the external additive is within the above range, at least a part of the external additive is released from the surface of the electrophoretic particle and adheres to the surface of the other electrophoretic particle, thereby obtaining desired charging characteristics. This is advantageous in that it is easily prevented from being lost.

  The external additive may be added to any one of a plurality of types of electrophoretic particles, or may be externally added to a plurality of types or all types of electrophoretic particles. When an external additive is added to the surface of all electrophoretic particles, the external additive is applied to the surface of the electrophoretic particle with impact force, or the surface of the electrophoretic particle is heated to firmly attach the external additive to the surface of the electrophoretic particle. It is desirable to adhere to. This prevents the external additive from being released from the electrophoretic particles, and prevents the external additive having a different polarity from strongly agglomerating to form an aggregate of the external additive that is difficult to dissociate in an electric field, and thus This is advantageous in that image quality deterioration is easily prevented.

  The volume average particle diameter of the electrophoretic particles is, for example, preferably from 0.05 μm to 20 μm, and preferably from 0.1 μm to 10 μm. The size of the electrophoretic particles is not particularly limited, and a desirable range is determined according to the application.

Any conventionally known method may be used as a method for producing the electrophoretic particles. Specifically, the method shown below is mentioned, for example.
1) As described in JP-A-7-325434, the resin, the pigment and, if necessary, the charge control agent are weighed to the desired mixing ratio, the resin is heated and melted, and then the pigment is added and mixed A method of producing electrophoretic particles by dispersing, cooling, and then using a pulverizer such as a jet mill, a hammer mill, or a turbo mill.
2) A method for producing electrophoretic particles by a polymerization method such as suspension polymerization, emulsion polymerization, dispersion polymerization, or coacervation, melt dispersion, or emulsion aggregation.
3) When the resin has plasticity, the dispersion medium does not boil, and the resin, the colorant, and the dispersion are at a temperature lower than the decomposition point of at least one of the resin, the colorant, and if necessary, the charge control agent. A method of producing particles by dispersing and kneading the medium and, if necessary, the raw material of the charge control agent (specifically, the electrophoretic particles may be a resin, a colorant, and If necessary, a charge control agent is heated and melted in a dispersion medium, and using the temperature dependency of the solvent solubility of the resin, the molten mixture is cooled with stirring and solidified / precipitated to produce electrophoretic particles. Method).
4) The above raw materials are put into a suitable container equipped with granular media for dispersion and kneading, for example, a heated vibration mill such as an attritor or a heated ball mill, and the container is placed in a desired temperature range, for example, 80 ° C. A method of producing particles by dispersing and kneading at 160 ° C. or lower.

  As the granular media, for example, steel such as stainless steel and carbon steel, alumina, zirconia, silica and the like are desirably used. In order to produce electrophoretic particles by a method using granular media, a raw material that has been previously fluidized is further dispersed in a container using granular media, and then the dispersion medium is cooled to contain a colorant from the dispersion medium. It is good to precipitate. It is preferable that the granular media generate shear and / or impact while maintaining the motion state during and after cooling, and reduce the particle size of the resulting electrophoretic particles.

-Dispersion medium-
Various dispersion media used for display media are applied as the dispersion medium, but a low dielectric solvent (for example, a dielectric constant of 5.0 or less, preferably 3.0 or less) may be selected. The dispersion medium may use a solvent other than the low dielectric solvent, but preferably contains 50% by volume or more of the low dielectric solvent. Note that the dielectric constant of the low dielectric solvent is obtained by a dielectric constant meter (manufactured by Nippon Luft).

Examples of the low dielectric solvent include petroleum-derived high-boiling solvents such as paraffinic hydrocarbon solvents, silicone oils, and fluorine-based liquids, and may be selected according to the type of copolymer constituting the particles.
Specifically, for example, when a reactive compound having a silicone chain is applied as the specific reactive compound, silicone oil is preferably selected as the dispersion medium. When a reactive compound having an alkyl chain is applied as the specific reactive compound, it is preferable to select a paraffinic hydrocarbon solvent as the dispersion medium. Of course, it is not limited to this.

  Specific examples of the silicone oil include silicone oils in which a hydrocarbon group is bonded to a siloxane bond (for example, dimethyl silicone oil, diethyl silicone oil, methyl ethyl silicone oil, methyl phenyl silicone oil, diphenyl silicone oil, etc.). Of these, dimethyl silicone is particularly desirable.

  Examples of the paraffinic hydrocarbon solvent include normal paraffinic hydrocarbons and isoparaffinic hydrocarbons having 20 or more carbon atoms (boiling point of 80 ° C. or higher), but it is desirable to use isoparaffins for reasons such as safety and volatility. . Specifically, Shell Sol 71 (manufactured by Shell Petroleum), Isopar O, Isopar H, Isopar K, Isopar L, Isopar G, Isopar M (Isopar is a trade name of Exxon), IP Solvent (manufactured by Idemitsu Petrochemical), etc. Can be mentioned.

-Charge control agent-
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) Compounds having a chain skeleton, metal complexes of salicylic acid, metal complexes of catechol, metal-containing bisazo dyes, tetraphenylborate derivatives, copolymers of polymerizable silicone macromers (silaplane manufactured by JNC) and anionic monomers or cationic polymers, etc. Is mentioned.
More specific examples of the ionic and nonionic surfactants include the following. 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 desirably used in an amount of 0.01% by mass or more and 20% by mass or less, particularly 0.05% by mass or more and 10% by mass or less, based on the solid content of the particles.

-Well-known additives-
Known additives include acids, alkalis, salts, dispersants, dispersion stabilizers, stabilizers, antibacterial agents, preservatives, and the like.

-Others-
The concentration of the electrophoretic particles is not particularly limited as long as the target display color can be obtained. For example, the concentration is preferably 0.01% by mass or more and 50% by mass or less.
The concentration of the electrophoretic particles is preferably in the above range as the concentration in the display particle dispersion in a state of being enclosed between a pair of substrates of the display device. In addition, it is effective to adjust the concentration of the electrophoretic particles by the distance between a pair of substrates of the display device. In order to obtain the target hue, the particle concentration decreases as the distance between the pair of substrates of the display device increases, and the particle concentration increases as the distance decreases.

The concentration of the hiding particles is, for example, preferably 1% by volume or more and 50% by volume or less, and preferably 2% by volume or more and 30% by volume or less.
When the concentration of the concealing particles is within the above range, the increase in the viscosity of the dispersion medium due to the dispersion of the concealing particles is suppressed while the reflectance of the color display of the concealing particles is increased. This is advantageous in that it is easily suppressed.
Note that the concentration of the concealing particles is preferably in the above range as the concentration in the display particle dispersion in a state of being enclosed between a pair of substrates of the display device. It is also effective to adjust the concentration of the display white particles by the distance between the pair of substrates of the image display device. In order to obtain the target hue, the particle concentration decreases as the distance between the pair of substrates of the display device increases, and the particle concentration increases as the distance decreases.

  In the display dispersion according to this embodiment, the particle group and the dispersion may be included in a capsule. That is, the display dispersion according to the present embodiment may be arranged as capsule particles between the substrates (or electrodes) of the display device (display medium).

<Use of concealment particles and particle dispersion for display containing the same>
The concealing particles (and the display particle dispersion) according to the present embodiment are used in an electrophoretic display medium (including an electrophoretic light control medium (light control element)). In addition, as an electrophoretic display medium, a method of moving a particle group in a direction opposite to a known electrode (substrate) surface, and a method of moving in a direction along the electrode (substrate) surface (a so-called in-plane). Type element), or a hybrid element combining these.
In the display particle dispersion according to the present embodiment, color display can be realized by mixing and using a plurality of types of particles having different colors and charging polarities as electrophoretic particles that move in response to an electric field.

<Electrophoretic display medium, electrophoretic display device>
Hereinafter, an exemplary embodiment of a display medium and a display device of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a display device according to the present embodiment. FIG. 2 is an explanatory diagram schematically illustrating a movement mode of the particle group when a voltage is applied between the substrates of the display medium of the display device according to the present embodiment.
The display device 10 according to the present embodiment applies the display particle dispersion according to the present embodiment as a particle dispersion including the dispersion medium 50, the particle group 34, and the reflective particle group 36 of the display medium 12. It is a form to do. In other words, the electrophoretic particles as the particles of the particle group 34 and the concealing particles as the particles of the reflective particle group 36 are dispersed in the dispersion medium 50. However, in the present embodiment, the case where the particles of the reflective particle group 36 (that is, the concealment particles) are white will be described, but the present invention is not limited to this.

  As shown in FIG. 1, the display device 10 according to the present embodiment includes a display medium 12, a voltage application unit 16 (for example, a power source) that applies a voltage to the display medium 12, and a control unit 18. ing.

  The display medium 12 includes a display substrate 20 that serves as an image display surface, a rear substrate 22 that faces the display substrate 20 with a gap, and holds a space between these substrates at a specific interval, and between the substrates of the display substrate 20 and the rear substrate 22. The gap member 24 is configured to include a reflective particle group 36 having optical reflection characteristics different from that of the 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. The particle group 34 is composed of a plurality of particles. The particle group 34 is dispersed in the dispersion medium 50 and reflects between the display substrate 20 and the back substrate 22 according to the electric field strength formed in the cell. Move through the gap.

  In addition, the gap member 24 is provided so as to correspond to each pixel when the image is displayed on the display medium 12, and cells are formed so as to correspond to each pixel, so that the display medium 12 can display each pixel. It may be configured to do.

  Further, in the present embodiment, in order to simplify the description, the present embodiment will be described using a diagram focusing on one cell. Hereinafter, each configuration will be described in detail.

First, the pair of substrates 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 configuration in which a back electrode 46 and a surface layer 48 are laminated on a support substrate 44.

  The display substrate 20 or both the display substrate 20 and the back substrate 22 are translucent. Here, the translucency in the present embodiment indicates that the visible light transmittance is 60% or more.

  Examples of the material of the support substrate 38 and the support substrate 44 include glass, plastic, polyethylene terephthalate resin, polycarbonate resin, acrylic resin, polyimide resin, polyester resin, epoxy resin, and polyethersulfone resin.

  As materials for the front electrode 40 and the back electrode 46, oxides such as indium, tin, cadmium and antimony, composite oxides such as ITO, metals such as gold, silver, copper and nickel, organic materials such as polypyrrole and polythiophene, etc. Is mentioned. The surface electrode 40 and the back electrode 46 may be any of these single-layer films, mixed films, and composite films. The thicknesses of the front electrode 40 and the back electrode 46 are preferably, for example, 100 mm or more and 2000 mm or less. The back electrode 46 and the surface electrode 40 may be formed in a matrix shape or a stripe shape, for example.

  Further, the surface electrode 40 may be embedded in the support substrate 38. Further, the back electrode 46 may be embedded in the support substrate 44. In this case, the materials of the support substrate 38 and the support substrate 44 are selected according to the composition of each particle of the particle group 34 and the like.

  The back electrode 46 and the surface electrode 40 may be separated from the display substrate 20 and the back substrate 22 and disposed outside the display medium 12.

  In the above description, the case where both the display substrate 20 and the back substrate 22 are provided with electrodes (the front electrode 40 and the back electrode 46) has been described. However, only one of them is provided, and active matrix driving is performed. Also good.

  In order to perform active matrix driving, the support substrate 38 and the support substrate 44 may include a TFT (Thin Film Transistor) for each pixel. The TFT is preferably provided on the back substrate 22 instead of the display substrate.

Next, the surface layer will be described.
The surface layer 42 and the surface layer 48 are formed on the surface electrode 40 and the back electrode 46, respectively. Examples of the material constituting the surface layer 42 and the surface layer 48 include polycarbonate, polyester, polystyrene, polyimide, epoxy, polyisocyanate, polyamide, polyvinyl alcohol, polybutadiene, polymethyl methacrylate, copolymerized nylon, ultraviolet curable acrylic resin, fluorine resin, and the like. Is mentioned.

  The surface layer 42 and the surface layer 48 may be configured to include the above-described resin and a charge transport material, or may be configured to include a self-supporting resin having a charge transport property.

Next, the gap member will be described.
The gap member 24 for holding a gap between the display substrate 20 and the back substrate 22 is made of a thermoplastic resin, a thermosetting resin, an electron beam curable resin, a photocurable resin, rubber, metal, or the like.

The gap member 24 may be integrated with either the display substrate 20 or the back substrate 22. In this case, the support substrate 38 or the support substrate 44 is manufactured by performing etching processing, laser processing processing, press processing processing, printing processing, or the like using a previously manufactured mold.
In this case, the gap member 24 is 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. In this case, the gap member 24 is made of a transparent resin such as polystyrene, polyester, or acrylic.

The particulate gap member 24 is also preferably transparent, and glass particles are used in addition to transparent resin particles such as polystyrene, polyester, or acrylic.
Note that “transparent” means having a transmittance of 60% or more with respect to visible light.

Next, the reflective particle group will be described.
The reflective particle group 36 is composed of reflective particles having optical reflection characteristics different from that of the particle group 34, and functions as a reflective member that displays a color different from that of the particle group 34. And it also has a function as a gap member to move without hindering movement between the display substrate 20 and the back substrate 22. That is, each particle of the particle group 34 is moved 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 through the gap between the reflective particle groups 36.

Next, other configurations of the display medium will be described.
The size of the cell in the display medium 12 is closely related to the resolution of the display medium 12, and the smaller the cell, the higher the resolution of the display medium 12 that can be produced. The length of the display substrate 20 in the plate surface direction is about 10 μm or more and 1 mm or less.

  In order to fix the display substrate 20 and the back substrate 22 to each other through the gap member 24, fixing means such as a combination of bolts and nuts, a clamp, a clip, and a frame for fixing the substrate are used. Also, fixing means such as an adhesive, heat melting, and ultrasonic bonding may be used.

  As described above, the display device 10 according to the present embodiment includes the display medium 12, the voltage application unit 16 that applies a voltage to the display medium 12, and the control unit 18 (FIG. 1). reference).

  The voltage application unit 16 is electrically connected to the front electrode 40 and the back electrode 46. In the present 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 connected to the control unit 18 so as to exchange signals.

  The control unit 18 stores in advance various programs such as 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 control program that controls the entire apparatus. Further, it may be configured as a microcomputer including a ROM (Read Only Memory).

  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.

  Next, the operation of the display device 10 will be described. This operation will be described according to the operation of the control unit 18.

Here, a case where the particle group 34 enclosed in the display medium 12 is positively charged will be described. In the following description, it is assumed that the dispersion medium 50 is transparent and the reflective particle group 36 is white. That is, in the present embodiment, a case will be described in which the display medium 12 displays the color exhibited by the movement of the particle group 34 and displays white by the reflective particle group 36 as the background color.
In addition, the following operation | movement demonstrates the operation | movement from the state in which the particle group 34 adhered to the back substrate 22 side on description.

First, an operation signal indicating that the voltage is applied so that the front electrode 40 becomes a negative electrode and the back electrode 46 becomes a positive electrode for a specific time is output to the voltage application unit 16. When the voltage applied between the electrodes is increased from the state shown in FIG. 2A and a voltage equal to or higher than the threshold voltage at which the surface electrode 40 is a negative electrode and the concentration fluctuation ends is applied, the cohesive force of the particle group 34 is increased. In a reduced state, the particles constituting the particle group 34 charged to the positive electrode move to the display substrate 20 side and reach the display substrate 20 (see FIG. 2B).

  When the application between the electrodes is finished, the particle group 34 is constrained on the surface substrate 20 side, and the color exhibited by the particle group 34 is viewed from the display substrate 20 side with the white color as the color of the reflective particle group 36 being the background color. The color of the display medium 12 is visually recognized.

  Next, an operation signal indicating that a voltage is applied between the surface electrode 40 and the back electrode 46 so that the surface electrode 40 becomes a positive electrode and the back electrode 46 becomes a negative electrode for a specific time is applied to the voltage application unit 16. Output to. When the voltage applied between the electrodes is increased and a voltage equal to or higher than the threshold voltage at which the surface electrode 40 is the positive electrode and the concentration fluctuation ends is applied, the positive electrode is charged in a state where the cohesive force of the particle group 34 is reduced. The particles constituting the particle group 34 move to the back substrate 22 side and reach the back substrate 22 (see FIG. 2A).

  When the application between the electrodes is finished, the particle group 34 is constrained on the back substrate 22 side, while white as the color of the reflective particle group 36 is the color of the display medium 12 visually recognized from the display substrate 20 side. As visible. In addition, the particle group 34 is concealed by the reflective particle group 36 and is difficult to be visually recognized.

  Here, the voltage application time between the electrodes may be stored in advance in a memory such as a ROM (not shown) in the control unit 18 as information indicating the voltage application time in voltage application during operation. Then, information indicating the voltage application time may be read when the process is executed.

  Thus, in the display device 10 according to the present embodiment, the display is performed by the particle group 34 reaching the display substrate 20 or the back substrate 22 and adhering / aggregating.

  In the display medium 12 and the display device 10 according to the present embodiment, the surface electrode 40 is provided on the display substrate 20, the back electrode 46 is provided on the back substrate 22, and a voltage is applied between the electrodes (that is, between the substrates). Although the embodiment has been described in which the particle group 34 is moved between the substrates for display, the present invention is not limited thereto. For example, while the surface electrode 40 is provided on the display substrate 20, the gap member is provided with electrodes, and the voltage between the electrodes is The particle group 34 may be moved between the display substrate 20 and the gap member and displayed.

Further, in the display medium 12 and the display device 10 according to the above-described embodiment, the mode in which one type (one color) of particle group is applied as the particle group 34 has been described. Two or more types (two colors) of particle groups may be applied in different combinations of voltages (voltages at which the migrating particles start migrating).
Specifically, for example, as the particle group 34, a positively chargeable first particle group, a negatively chargeable second particle group, and a positively chargeable particle having a threshold voltage different from those of the first particle group, The form which applied the 3rd particle group with a big diameter is mentioned.

<Electronic apparatus provided with display medium (display device)>
The display medium (display device) according to the present embodiment is provided in an electronic device, an exhibition medium, a card medium, and the like.
Specifically, the display medium (display device) according to the present embodiment includes, for example, an electronic bulletin board capable of storing and rewriting images, an electronic circulation version, an electronic blackboard, an electronic advertisement, an electronic signboard, a blinking sign, electronic paper, Electronic newspapers, electronic books, electronic document sheets that can be used with copiers and printers, portable computers, tablet computers, mobile phones, smart cards, signature devices, watches, shelf labels, flash drives, etc.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
In the following, “part” and “%” are based on mass unless otherwise specified.

<Example 1>
4-vinylbiphenyl (manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.): 12 parts by mass Silaplane FM-0721 (manufactured by JNC, weight average molecular weight Mw = 5000: structural formula (1) [R ¹ = methyl group, R ^{1 '} = Butyl group, m = 68, x = 3]): 6 parts by mass / Isopar M (Isopar M: registered trademark, manufactured by ExxonMobil): 75 parts by mass / toluene (manufactured by Kanto Chemical Co.): 6 parts by mass / Lauroyl peroxide (manufactured by Aldrich): 1 part by mass The above materials were put into a flask and reacted at 75 ° C. for 24 hours. The resulting solution was centrifuged and the supernatant was removed, and 200 parts by mass of dimethyl silicone oil (KF-96L-2cs viscosity 2 cs manufactured by Shin-Etsu Chemical Co., Ltd.) was added. This centrifugal sedimentation treatment was performed three times, and the suspension was solvent-substituted with dimethyl silicone oil to a solid content concentration of 40% by mass or more to obtain a white concealed particle dispersion A1.

<Example 2>
4-Vinylbiphenyl: White concealed particle dispersion A2 was obtained in the same manner as in Example 1 except that 10 parts by mass and Silaplane FM-0721: 8 parts by mass were used.

<Example 3>
4-Vinylbiphenyl: White concealed particle dispersion A3 was obtained in the same manner as in Example 1 except that 14 parts by mass and Silaplane FM-0721: 4 parts by mass were used.

<Example 4>
A white concealed particle dispersion A4 was obtained in the same manner as in Example 1 except that Isopar M was 70 parts by mass and Toluene was 11 parts by mass.

<Example 5>
A white concealed particle dispersion A5 was obtained in the same manner as in Example 1 except that Isopar M was 61 parts by mass and Toluene was 20 parts by mass.

  A white concealed particle dispersion A6 was obtained in the same manner as in Example 1 except that Isopar M was 58 parts by mass and Toluene was 23 parts by mass.

<Comparative Example 1>
4-vinylbiphenyl (manufactured by Nippon Steel Chemical Co., Ltd.): 1 part by mass Silaplane FM-0721 (manufactured by JNC, weight average molecular weight Mw = 5000: structural formula (1) [R ¹ = methyl group, R ^{1 ′} = Butyl group, m = 68, x = 3]): 1 part by mass / Lauroyl peroxide (manufactured by Aldrich): 0.03 part by mass / Isopar M (Isopar M: registered trademark, manufactured by ExxonMobil): 10 mass Parts / hexane (manufactured by Kanto Chemical Co., Inc.): 2 parts by mass / toluene (manufactured by Kanto Chemical Co., Ltd.): 2 parts by mass The above materials were placed in a flask and reacted at 65 ° C. for 18 hours. The resulting solution was centrifuged and the supernatant was removed, and 200 parts by mass of dimethyl silicone oil (KF-96L-2cs viscosity 2 cs manufactured by Shin-Etsu Chemical Co., Ltd.) was added. This centrifugal sedimentation treatment was performed three times, and the suspension was solvent-substituted with dimethyl silicone oil to obtain a solid content concentration of 40% by mass or more to obtain a white concealed particle dispersion X1.

<Comparative example 2>
White concealed particle dispersion X2 was obtained in the same manner as in Example 1 except that 4-vinylbiphenyl: 0.5 parts by mass and Silaplane FM-0721: 1.5 parts by mass were used.

<Evaluation>
The following evaluation was performed about the concealment particle dispersion liquid obtained in each example.

(Characteristic evaluation)
The volume average particle diameter, CV value of the concealment particles in the concealment particle dispersion liquid obtained in each example, and the existence frequency of particles having a particle diameter of 250 nm in the particle size distribution were examined according to the method described above. The results are shown in Table 1.
In addition, the SEM photograph of the concealment particle | grains of Example 1 is shown in FIG. 3, the SEM photograph of the concealment particle | grains of the comparative example 1 is shown in FIG. 4, and the particle size distribution of the concealment particle | grains of Example 1 and the comparative example 1 is shown in FIG. .

(Function evaluation)
Using the concealment particle dispersion obtained in each example, the concentration of concealment particles is 25% by mass, the concentration of cyan particles as electrophoretic particles is 1% by mass, and the concentration of red particles is 2% by mass. A particle dispersion for evaluation was prepared by dispersing the particles in KF-96L-2cs viscosity 2 cs) manufactured by Shin-Etsu Chemical Co., Ltd. And this particle dispersion for evaluation is made into a 50 μm spacer (gap member between a pair of glass substrates (a thickness of the glass substrate 1.1 mm) on which an indium tin oxide (ITO) electrode is formed. A device sample encapsulated in a cell) was prepared. The following evaluation was performed using the obtained element sample.

  The cyan particles were added to 50 parts by mass of styrene-acrylic copolymer with copper phthalocyanine C.I. I. Positively charged cyan particles (volume average particle size 600 nm) containing 50 parts by mass of Pigment Blue 15: 3 were used. The red particles used were positively charged red particles (volume average particle size 600 nm) in which 30 parts by mass of Pigment Red 254 was blended with 70 parts by mass of a methyl methacrylate polymer prepared as a weight percent.

−Threshold voltage evaluation−
A voltage of a triangular wave of ± 30 V was applied between the electrodes of the element sample at 0.05 Hz, and cyan particles and red particles were repeatedly migrated 500 times to the display substrate side and the back substrate side. Then, the threshold voltage difference (ΔE _TV ) was examined from the driving profiles of the respective particles at the first time and the 500th time. Specifically, the measurement wavelength of cyan particles is 650 nm, the measurement wavelength of red particles is 500 nm, and a voltage of −15 V is applied to the display surface of the element sample to display cyan particles and red particles at 0.05 Hz. When a voltage of a triangular wave of 15 V is applied, each particle is migrated to the back substrate, and the reflectivity when each particle completes desorption from the display substrate is R, 0.1 × R Was the threshold voltage, and the threshold voltage difference (ΔE _TV ) between the first time and the 500th time was examined.

-Response time evaluation-
A voltage of a triangular wave of ± 30 V was applied between the electrodes of the element sample at 0.05 Hz, and cyan particles and red particles were repeatedly migrated 500 times to the display substrate side and the back substrate side. And the response time difference ((DELTA) _RT ) was investigated from the drive profile of each particle | grain of the 1st time and the 500th time. Specifically, the measurement wavelength of cyan particles is set to 650 nm, the measurement wavelength of red particles is set to 500 nm, and a voltage of −30 V is applied to the display surface of the element sample to display the cyan particles and the red particles. Is applied, and each particle is migrated to the back substrate, and when the reflectance when each particle completes desorption from the display substrate is R, the time at 0.9 × R is the response time. And the difference in response time (ΔE _RT ) between the first time and the 500th time was examined.

-Whiteness evaluation-
In each cell, only the concealment particle dispersion obtained in each example is placed between a pair of glass substrates on which indium tin oxide (ITO) electrodes are formed (a 50 μm spacer (gap member) is interposed between the pair of glass substrates). A device sample enclosed in () was produced.
Then, the solid content of the white particle dispersion having a whiteness of 50% in the produced element sample was examined.
The whiteness was determined by measuring the white reflection density using a color meter X-Rite 404 (manufactured by X-Rite) and converting it to white reflectance based on the following formula.
Formula: Whiteness (white reflectance) = 10− ^{(white reflection density)} * 100 (%)

From the above results, this example showed better results for both threshold voltage evaluation and response time evaluation than the comparative example. Thereby, it turns out that the fall of the drive characteristic of electrophoretic particle (cyan particle and red particle) is suppressed in a present Example compared with the comparative example.
In addition, this example also realizes high whiteness and is a concealing particle having a high concealing property.
Further, Examples 1 to 5 in which the existence frequency of particles having a particle size of 250 nm in the particle size distribution is 30% or less are compared with Example 6 in which the existence frequency of particles having a particle size of 250 nm in the particle size distribution is more than 30%. It can be seen that the concealability of the electrophoretic particles is improved.

DESCRIPTION OF SYMBOLS 10 Display apparatus 12 Display medium 16 Voltage application part 18 Control part 20 Display substrate 22 Back substrate 24 Gap member 34 Particle group 36 Reflective particle group 38 Support substrate 40 Surface electrode 42 Surface layer 44 Support substrate 46 Back electrode 48 Surface layer 50 Dispersion medium

Claims (8)

No colored particles are contained inside, the volume average particle diameter is 300 nm or more and 1000 nm or less, and the CV value (Coefficient of Variation) is 15% or less.
A concealing particle for an electrophoretic display device that does not migrate or does not migrate evenly when an electric field is applied to migrate the electrophoretic particles.   The concealing particles for electrophoretic display devices according to claim 1, wherein the existence frequency of particles having a particle size of 250 nm or less in the particle size distribution is 30% or less.   3. A concealing particle for an electrophoretic display device, comprising a copolymer containing at least 4-vinylbiphenyl as a polymerization component. A group of particles comprising electrophoretic particles and concealing particles for an electrophoretic display device according to any one of claims 1 to 3,
A dispersion medium for dispersing the particle group;
A display particle dispersion for an electrophoretic display device. A pair of substrates, at least one of which is translucent,
The display particle dispersion for an electrophoretic display device according to claim 4 enclosed between the pair of substrates,
An electrophoretic display medium comprising: A pair of electrodes, at least one of which is translucent,
A region having a display particle dispersion for an electrophoretic display device according to claim 4, provided between the pair of electrodes,
An electrophoretic display medium comprising: An electrophoretic display medium according to claim 5;
Voltage applying means for applying a voltage between the pair of substrates of the display medium;
An electrophoretic display device comprising: An electrophoretic display medium according to claim 6;
Voltage applying means for applying a voltage between the pair of electrodes of the display medium;
An electrophoretic display device comprising: