JP5936188B2 - Image display particles, image display particle dispersion, display medium, and display device - Google Patents

Description

  The present invention relates to an image display particle, an image display particle dispersion, a display medium, and a display device.

  An image display medium has been actively studied as a display having image maintainability (so-called memory property). In this display system, particles for image display (particles for image display) charged in a liquid are used, and electrophoretic particles are placed in a cell by applying an electric field (two electrode substrates are stacked and an image display material is put together with a dispersion medium between them. Display is performed by alternately moving to the viewing surface and back surface of the encapsulated configuration.

For example, Patent Document 1 discloses that “crosslinking of a resin is performed by suspension polymerization using a divinyl compound” together with “image display particles in which pigments are dispersed in polymer particles”.
Patent Document 2 discloses “emulsion polymerization of a crosslinkable monomer composed of a crosslinkable monomer and polyvalent acrylic acid” together with “hollow polymer particles and an aqueous dispersion thereof”.
Patent Document 3 discloses that “polymer particles having avoidable protrusions on the surface” and “crosslinking of the resin is performed by suspension polymerization using a divinyl compound”.
Patent Document 3 discloses that “a dispersion in which a colorant is encapsulated in a dispersion polymer”, “crosslinking a dispersion polymer (dispersant)”, and “the functional group of the dispersion polymer and the crosslinking agent is a carboxyl group. , A hydroxyl group, an amino group, a blocked isocyanate group, and an epoxy group.
Patent Document 4 discloses “polymer graft fine particles in which pigment fine particles and a polymer are cross-linked”.

JP 2005-345568 A JP 2005-154568 A JP 2002-179716 A JP 2006-31724 A JP 2008-145713 A

  An object of the present invention is to provide particles for image display having a high voltage (hereinafter, this voltage is referred to as “threshold voltage”) for starting movement by an electric field.

The above problem is solved by the following means. That is,
<1> A resin crosslinked product of a composition comprising a water-soluble resin, at least one crosslinking agent selected from an epoxy compound, a carbodiimide compound, an isocyanate compound, an aziridine compound, and a hydrazide compound, and a colorant. Core particles,
A coating layer covering the surface of the core particles, a parent dispersion medium part that dissolves in the dispersion medium in which the image display particles are dispersed, and a sparse insoluble in the dispersion medium in which the image display particles are dispersed. A coating layer formed of a composition containing a resin having a dispersion medium part;
Particles for image display having

<2> A resin crosslinked product of a composition comprising a water-soluble resin, at least one crosslinking agent selected from an epoxy compound, a carbodiimide compound, an isocyanate compound, an aziridine compound, and a hydrazide compound, and a colorant. Core particles,
A coating layer covering the surface of the core particle, and formed by a composition comprising a resin comprising at least a polymer component having a silicone chain or a polymer component having an alkyl chain and a polymer component having a chargeable group A coated layer,
Particles for image display having

  <3> The image display particle according to <1> or <2>, wherein the content of the crosslinking agent is 0.5% by mass or more and 20% by mass or less with respect to the entire core particle.

<4> a dispersion medium;
Image display particles dispersed in the dispersion medium, the image display particles according to any one of <1> to <3>,
A particle dispersion for image display comprising:

<5> a pair of substrates at least one of which has translucency;
The particle dispersion for image display according to <4>, encapsulated between the pair of substrates,
A display medium comprising:

<6> a pair of electrodes at least one of which has translucency;
A region provided with the particle dispersion for image display according to <4>, provided between the pair of electrodes;
A display medium comprising:

<7> The display medium according to <5> or <6>,
Voltage application means for applying a voltage between the pair of substrates or the pair of electrodes of the display medium;
A display device comprising:

According to the inventions according to <1> and <2>, in the image display particles having a coating layer on the core material particles, the core material particles are not composed of a resin crosslinked body with the specific crosslinking agent. In comparison, the image display particles having a higher threshold voltage can be provided.
According to the invention according to <3>, it is possible to provide image display particles having a higher threshold voltage than the content of the crosslinking agent outside the above range.

  According to the invention according to <4>, image display particles in which the core material particles are not composed of a resin cross-linked body by the specific cross-linking agent are applied to the image display particles having a coating layer on the core material particles. Compared to the case, an image display particle dispersion liquid having a higher threshold voltage can be provided.

  According to the inventions according to <5>, <6>, and <7>, in the image display particle having a coating layer on the core material particle, the core material particle is constituted by a resin cross-linked body by the specific cross-linking agent. As compared with the case where non-image display particles are applied, it is possible to provide a display medium and a display device that can realize display in which display defects due to a low threshold voltage of the image display particles are suppressed.

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.

  Embodiments that are examples of the present invention will be described below.

[Image display particles]
The image display particles according to the present embodiment include core material particles (hereinafter referred to as “core particles”) and a coating layer that covers the surfaces of the core particles.

  The core particle is comprised with the resin crosslinked body of the composition containing water-soluble resin, a crosslinking agent, and a coloring agent. The crosslinking agent is at least one crosslinking agent selected from an epoxy compound, a carbodiimide compound, an isocyanate compound, an aziridine compound, and a hydrazide compound.

On the other hand, the coating layer comprises a resin having a parent dispersion medium part that dissolves in the dispersion medium in which the image display particles are dispersed and a sparse dispersion medium part that is insoluble in the dispersion medium in which the image display particles are dispersed. It is formed by the composition containing. Specifically, for example, the coating layer is formed of a composition including a resin composed of a copolymer of at least a polymerization component having a silicone chain or a polymerization component having an alkyl chain and a polymerization component having a chargeable group. It is good. Moreover, the coating layer may be configured to include a non-crosslinked resin, or may be configured to include a crosslinked resin. In the coating layer, the resin made of the copolymer may contain other polymerization components as necessary.
In addition, the hydrophobic part after superposition | polymerization originating in hydrophobic polymerization components, such as a polymerization component with a silicone chain or a polymerization component with an alkyl chain, corresponds to a parent dispersion medium part among each polymerization component.

In the image display particles according to the present embodiment, the threshold voltage is increased by the above configuration. The details are unknown, but this is because when the core particle is composed of a resin cross-linked body with the above specific crosslinking agent, the density of the core particle is improved and the van der Waals force between molecules inside the core particle is also improved. Thus, as a result of the influence of the polar group of the crosslinking agent and the like, it is considered that the threshold voltage of the image display particles is increased.
In particular, in the presence of a low dielectric solvent (for example, a dielectric constant of 5.0 or less) as a dispersion medium for dispersing the image display particles, although the cause is not clear, the threshold voltage of the image display particles is difficult to increase. Even in such a case, the image display particles according to the present embodiment are effective because the threshold voltage is increased by the above configuration.

And in the display medium and display device which employ | adopted the image display particle which concerns on this embodiment, the display in which the display defect (for example, display density fall, mixed color display) resulting from the low threshold voltage of the image display particle was suppressed was suppressed. Is realized.
In addition, when two or more kinds of image display particles having the same polarity are used in combination, migration of each image display particle is easily realized, for example, multicolor display in one pixel is easily realized. .

  Details of the image display particles according to the present embodiment will be described below.

(Core particles)
The core particle is composed of a resin cross-linked product of a composition containing a water-soluble resin (hereinafter referred to as “core particle resin”), a cross-linking agent, and a colorant.
Specifically, the core particle has, for example, a structure including a resin and a cross-linked resin and a colorant (that is, a structure in which a colorant is dispersed in a resin cross-linked body of a resin and a cross-linking agent). ).

-Core particle resin-
The resin of the core particle is a water-soluble resin and has a reactive functional group (for example, a hydroxyl group, a carboxyl group, a carbonyl group, an amino group, etc.) for forming a resin crosslinked body with a crosslinking agent.
Water-soluble means that the target substance dissolves 1% by mass or more in water at 25 ° C.

The core particle resin may be a chargeable resin (a resin having a chargeable group (for example, a polarizable functional group: polar group)) or a non-chargeable resin (a resin having no chargeable group). However, from the viewpoint of improving the charge amount, a chargeable resin is preferable.
The core particle resin may be a mixture or copolymer of a non-chargeable resin and a chargeable resin.

Examples of the chargeable resin include a homopolymer of a polymerization component having a chargeable group, and a copolymer of a polymerization component having a chargeable group and a polymerization component having no chargeable group.
On the other hand, examples of the non-chargeable resin include a homopolymer of a polymerization component having no chargeable group.
Each of these polymerization components may be used alone or in combination of two or more.

Here, examples of the chargeable group (for example, a polar group; a polarizable functional group) include a base and an acid group.
Examples of the base (hereinafter referred to as cationic group) as the charging group include an amino group and a quaternary ammonium group (including salts of these groups). These cationic groups tend to impart positively charged polarity to the particles, for example.
Examples of the acid group (hereinafter referred to as anionic group) as the charging group include a phenol group, a carboxyl group, a carboxylate group, a sulfonate group, a sulfonate group, a phosphate group, a phosphate group, and a tetraphenylboron group. (Including salts of these groups). These anionic groups tend to impart negatively charged polarity to the particles, for example.
Other examples of the chargeable group include a fluorine group, a phenyl group, and a hydroxyl group.

Hereinafter, each polymerization component will be described.
In the following description, the description such as “(meth) acrylate” is an expression including both “acrylate” and “methacrylate”.

Examples of the polymerization component having a cationic group (hereinafter, cationic polymerization component) include the following. Specifically, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, N, N-dibutylaminoethyl (meth) acrylate, N, N-hydroxyethylaminoethyl (meta) ) Acrylate, N-ethylaminoethyl (meth) acrylate, N-octyl-N-ethylaminoethyl (meth) acrylate, N, N-dihexylaminoethyl (meth) acrylate and other aliphatic amino groups (meth) Acrylates; aromatic substituted ethylene monomers having a nitrogen-containing group such as dimethylaminostyrene, diethylaminostyrene, dimethylaminomethylstyrene, dioctylaminostyrene; vinyl-N-ethyl-N-phenylaminoethyl ether; Vinyl-N-butyl-N-phenylami Nitrogen-containing vinyl ether monomers such as ethyl ether, triethanolamine divinyl ether, vinyl diphenylaminoethyl ether, N-vinylhydroxyethylbenzamide, m-aminophenyl vinyl ether; pyrroles such as vinylamine and N-vinylpyrrole; Pyrrolines such as N-vinyl-2-pyrroline and N-vinyl-3-pyrroline; Pyrrolidines such as N-vinyl pyrrolidine, vinyl pyrrolidine amino ether and N-vinyl-2-pyrrolidone; N-vinyl-2- Imidazoles such as methylimidazole; imidazolines such as N-vinylimidazoline; indoles such as N-vinylindole; indolines such as N-vinylindoline; N-vinylcarbazole, 3,6-dibromo-N -Vinyl carbazole, etc. Carbazoles; pyridines such as 2-vinylpyridine, 4-vinylpyridine and 2-methyl-5-vinylpyridine; piperidines such as (meth) acrylic piperidine, N-vinylpiperidone and N-vinylpiperazine; Quinolines such as vinylquinoline and 4-vinylquinoline; pyrazoles such as N-vinylpyrazole and N-vinylpyrazoline; oxazoles such as 2-vinyloxazole; 4-vinyloxazine and morpholinoethyl (meth) acrylate Oxazines; and the like.
The cationic polymerization component may be quaternized ammonium chloride before or after polymerization to form a salt structure. Quaternary ammonium chloride is realized, for example, by reacting a cationic group with alkyl halides or tosylate esters.

Examples of the polymerization component having an anionic group (hereinafter, anionic polymerization component) include a polymerization component having a carboxylic acid group, a polymerization component having a sulfonic acid group, and a polymerization component having a phosphoric acid group.
Examples of the polymerization component having a carboxylic acid group include (meth) acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, their anhydrides, monoalkyl esters, carboxyethyl vinyl ether, carboxypropyl vinyl ether. And vinyl ethers having a carboxyl group, and salts thereof.
Examples of the polymerization component having a sulfonic acid group include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) click acid ester, bis- (3-sulfopropyl) -itaconic. And acid esters and salts thereof. In addition, examples of the polymerization component having a sulfonic acid group include sulfuric acid monoesters of 2-hydroxyethyl (meth) acrylic acid and salts thereof.
Examples of the polymerization component having a phosphoric acid group include vinyl phosphonic acid, vinyl phosphate, acid phosphoxyethyl (meth) acrylate, acid phosphoxypropyl (meth) acrylate, bis (methacryloxyethyl) phosphate, diphenyl-2-methacrylate. Examples include leuoxyethyl phosphate, diphenyl-2-acryloyloxyethyl phosphate, dibutyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxyethyl phosphate, dioctyl-2- (meth) acryloyloxyethyl phosphate It is done.
Note that the anionic polymerization component may be ammonium chlorided before or after polymerization to form a salt structure. Ammonium chloride is realized, for example, by reacting an anionic group with a tertiary amine or quaternary ammonium hydroxide.

  Examples of the polymerization component having a fluorine group include a (meth) acrylate monomer having a fluorine group, specifically, trifluoroethyl (meth) acrylate, pentafluoropropyl (meth) acrylate, and perfluoroethyl (meth). Acrylate, perfluorobutylethyl (meth) acrylate, perfluorooctylethyl (meth) acrylate, perfluorodecylethyl (meth) acrylate, trifluoromethyltrifluoroethyl (meth) acrylate, hexafluorobutyl (meth) acrylate, etc. It is done.

  Examples of the polymerization component having a phenyl group include styrene, phenoxyethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, and phenoxyethylene glycol (meth) acrylate. Is mentioned.

  Examples of the polymerization component having a hydroxyl group include hydroxyalkyl (meth) acrylate (eg, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, etc.), allyl alcohol, polyethylene glycol mono (meth) acrylate, and the like. Other examples include those obtained by copolymerizing a monomer having a glycidyl group and then ring-opening, and those obtained by polymerizing a monomer having t-butoxy and the like and then hydrolyzing the monomer.

  Examples of the polymerization component having no chargeable group include nonionic polymerization components (nonionic polymerization components). For example, (meth) acrylonitrile, (meth) acrylic acid alkyl ester, (meth) acrylamide, ethylene, propylene, Examples include butadiene, isoprene, isobutylene, N-dialkyl-substituted (meth) acrylamide, vinyl carbazole, vinyl chloride, vinylidene chloride, isoprene, butadiene, vinyl pyrrolidone, and the like.

  The weight average molecular weight of the resin of the core particle is desirably 1,000 or more and 1,000,000 or less, and more desirably 10,000 or more and 200,000 or less.

-Crosslinking agent-
The crosslinking agent is at least one crosslinking agent selected from an epoxy compound, a carbodiimide compound, an isocyanate compound, an aziridine compound, and a hydrazide compound.

The content of these crosslinking agents is preferably 0.5% by mass or more and 20% by mass or less, more preferably 0.5% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more with respect to the entire core particle. It is from 5% by mass to 5% by mass.
When the content of the crosslinking agent is within the above range, a high threshold voltage of the image display particles can be easily realized.

-Epoxy compound The epoxy compound is a compound having a plurality of (for example, 2 or more and 5 or less) epoxy groups, and is preferably water-soluble. Specific examples include polyfunctional aliphatic polyglycidyl ether compounds.

  Examples of the epoxy compound include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, diglycerol polyglycidyl ether, glycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, (poly ) Ethylene glycol diglycidyl ether and the like.

-Carbodiimide compound A carbodiimide compound is a compound having a "-N = C = N-" group, and is preferably water-soluble. Specific examples include carbodiimide compounds represented by the following general formula (B).
General formula (B)
R ¹ —N═C═N—R ²

In general formula (B), R ¹ and R ² each independently represents a substituted or unsubstituted alkyl group or a substituted or unsubstituted phenyl group.

  Examples of the carbodiimide compound include dicyclohexylcarbodiimide, diisopropylcarbodiimide, 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride, Nt-butyl-N-ethylcarbodiimide, di-t-butylcarbodiimide, di- Examples include p-tolylcarbodiimide.

-Isocyanate compound Water-dispersed isocyanate is mentioned as an isocyanate compound. The water-dispersed isocyanate functions as a crosslinking agent for water-based resins since other isocyanates are protected by the hydrophilicized isocyanate and are stably dispersed in water, and crosslinking proceeds when water evaporates.
Examples of the water-dispersed isocyanate compound include hexamethylene diisocyanate and isophorone diisocyanate.

-Aziridine compound As an aziridine compound, a polyfunctional aziridine compound is mentioned, for example, Specifically, 2,2bishydroxymethylbutanol-tri [3- (1-azilinidyl propionic acid)], 4,4 Bis (ethyleneiminocarbonylamino) diphenylmethane is mentioned.

-Hydrazide compound As a hydrazide compound, a polyfunctional hydrazide compound is mentioned, Specifically, adipic acid dihydrazide, sebacic acid dihydrazide, isophthalic acid dihydrazide, polyacrylic acid hydrazide etc. are mentioned.

-Colorant-
Examples of the colorant include organic or inorganic pigments, oil-soluble dyes, etc., for example, magnetic powders such as magnetite and ferrite, carbon black, titanium oxide, magnesium oxide, zinc oxide, phthalocyanine copper-based cyan colorants, azo Known colorants such as a yellow color material, an azo magenta color material, a quinacridone magenta color material, a red color material, a green color material, and a blue color material can be used. Specifically, 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. I. Pigment blue 15: 1, C.I. I. Pigment Blue 15: 3, etc. are exemplified as typical examples.

  The blending amount of the colorant is preferably 10% by mass or more and 99% by mass or less, and more preferably 30% by mass or more and 99% by mass or less with respect to the resin of the core particles.

-Other ingredients-
The core particles may contain other compounding materials.
Examples of other compounding materials include charge control materials and magnetic materials.
As the charge control material, known materials used for electrophotographic toner materials can be used. For example, cetylpyridyl chloride, BONTRON P-51, BONTRON P-53, BONTRON E-84, BONTRON E-81 (above, Quaternary ammonium salts such as Orient Chemical Industry Co., Ltd., salicylic acid metal complexes, phenol condensates, tetraphenyl compounds, metal oxide particles, and metal oxide particles surface-treated with various coupling agents.

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 is more preferable because it hardly inhibits the coloring of the colored pigment and has a smaller specific gravity than the inorganic magnetic material.
Examples of the colored magnetic material (color-coated material) include small-diameter colored magnetic powder described in JP-A-2003-131420. 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 selected such that the magnetic powder is opaquely colored with a pigment or the like, but it is preferable to use, for example, a light interference thin film. 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 SiO ₂ or TiO ₂ and selectively reflects the wavelength of light by optical interference in the thin film. It is.

(Coating layer)
The coating layer includes a resin having a parent dispersion medium part that dissolves in the dispersion medium in which the image display particles are dispersed, and a sparse dispersion medium part that is insoluble in the dispersion medium in which the image display particles are dispersed ( (Hereinafter referred to as “resin of coating layer”).
Here, the parent dispersion medium part of the resin of the coating layer means that the polymerization component constituting the parent dispersion medium part is soluble in the dispersion medium. And being soluble in the dispersion medium means that the target substance is dissolved by 1 mass% or more in the dispersion medium at 25 ° C.
On the other hand, the sparse dispersion medium part of the resin of the coating layer means that the polymerization component constituting the sparse dispersion medium part is insoluble in the dispersion medium. And insoluble in the dispersion medium means that the target substance is dissolved at 0.01% by mass or less in the dispersion medium at 25 ° C.

The resin of the coating layer is soluble in the dispersion medium when the resin alone (that is, before coating with the core particles) is used from the viewpoint of the production method of the image display particles, and is dispersed after coating with the core particles. The coating layer is preferably configured so as to be insoluble in the medium.
Examples of a method for realizing this include a method of crosslinking the resin of the coating layer, a method of bonding the resin to the surface of the core particle, and a method of causing the resin to be adsorbed on the surface of the core particle.

-Resin of coating layer-
Specific examples of the resin for the coating layer include, for example, a polymerization component having a polymerization component having a silicone chain or a polymerization component having an alkyl chain, a polymerization component having a chargeable group, and, if necessary, another polymerization component. Resins composed of coalesced are listed.

Here, the coating layer may include a non-crosslinked resin or may include a crosslinked resin.
That is, the coating layer may be composed of, for example, a composition containing a resin, or may be composed of a resin crosslinked body of a composition containing a resin.
In particular, when the coating layer is composed of a crosslinked resin, a high threshold voltage of the image display particles is easily realized.
As a method of crosslinking the resin of the coating layer, a polymerization component having a reactive group (crosslinkable group) is polymerized as a polymerization component of the resin, a method of crosslinking the resin, a crosslinking agent is added separately from the resin, A method of crosslinking the resin is mentioned.

-Polymerization component having a silicone chain As a polymerization component having a silicone chain (a monomer having a silicone chain), for example, a macromonomer having a silicone chain, specifically, for example, (meth) acrylate at one end Dimethyl silicone monomer having a group (silicone compound represented by the following structural formula 1: manufactured by Chisso Corporation: Silaplane: FM-0711, FM-0721, FM-0725, etc., Shin-Etsu Silicone Co., Ltd .: X-22 174DX, X-22-2426, X-22-2475, etc.).

In 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. n represents a natural number (for example, 1 to 1000, preferably 3 to 100). x represents an integer of 1 to 3.

-Polymerization component which has an alkyl chain As a polymerization component which has an alkyl chain, long-chain alkyl (meth) acrylate is mentioned, for example. As the long-chain alkyl (meth) acrylate, for example, those having an alkyl chain having 4 or more carbon atoms are preferable, such as butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and dodecyl (meth). Examples include acrylate and stearyl (meth) acrylate.
The long chain alkyl means, for example, an alkyl chain having 4 to 30 carbon atoms.

-Polymerization component having a charging group The polymerization component having a charging group is the same as the polymerization component having a charging group described as the polymerization component of the core particle resin.

Other polymerization components Examples of other polymerization components include a polymerization component having no charging group and a polymerization component having a reactive group.
The polymerization component having no chargeable group is the same as the polymerization component having no chargeable group described as the polymerization component of the core particle resin.

As a polymerization component having a reactive group, for example, glycidyl (meth) acrylate having an epoxy group, an isocyanate monomer having an isocyanate group (for example, Showa Denko: Karenz AOI (2-isocyanatoethyl acrylate), Karenz MOI ( 2-isocyanatoethyl methacrylate)), an isocyanate monomer having a blocked isocyanate group (for example, Showa Denko: Karenz MOI-BM (2- (0- [1′-methylpropylideneamino] carboxyamino) methacrylic acid ethyl) ), Karenz MOI-BP (2-[(3,5-dimethylpyrazolyl) carbonylamino] ethyl methacrylate)) and the like.
When a polymerization component having a reactive group is used as the polymerization component of the resin of such a coating layer, the resin itself of the coating layer is crosslinked, and the coating layer is composed of a crosslinked resin. In addition, the coating layer is coated on the core particle in a state where the reactive group of the resin of the coating layer is bonded to the functional group on the surface of the core particle.

  Here, the polymerization component having a reactive group is added to the system as a crosslinking agent separately from the resin of the coating layer, in addition to being used as a polymerization component of the resin of the coating layer, so as to crosslink the resin of the coating layer. It may be.

In the resin of the coating layer, the polymerization component having a silicone chain is preferably 1 mol% or more and 30 mol% or less, more preferably 1 mol% or more and 20 mol% in terms of the molar ratio to the total polymerization components (total polymerization components). It is as follows.
In the resin of the coating layer, the polymerization component having a chargeable group is preferably 1 mol% or more and 50 mol% or less, more preferably 10 mol% or more and 30 mol% in terms of the molar ratio to the total polymerization components (total polymerization components). % Or less.
In the resin of the coating layer, the polymerization component having a reactive group is preferably 1 mol% or more and 40 mol% or less, more preferably 1 mol% or more and 30 mol, in terms of the molar ratio to the total polymerization components (total polymerization components). % Or less.

  As a weight average molecular weight of resin of a coating layer, 500 or more and 1 million or less are desirable, More desirably, they are 1000 or more and 1 million or less.

-Other ingredients-
The coating layer may contain other compounding materials.
Examples of other compounding materials include a charge control agent and a magnetic material.

-Suitable configuration of coating layer-
The coating layer described above is 1) a resin having a silicone chain as a resin for the coating layer,
A configuration including 2) a resin having a chargeable group, 3) a resin having a crosslinkable group, and 4) a resin having a functional group that crosslinks with the crosslinkable group is particularly preferable.

(Characteristics of image display particles)
The average particle diameter (volume average particle diameter) of the image display particles according to the present embodiment is, for example, 0.1 μm or more and 10 μm or less, but is selected according to the application and is not limited thereto.
The average particle size is measured using a Photo FPAR-1000 (dynamic light scattering particle size distribution measuring device) manufactured by Otsuka Electronics Co., Ltd., and analyzed by the MARQUAARD method.

(Method for producing image display particles)
An example of the method for producing image display particles according to the present embodiment includes the following production method, but is not limited thereto.
First, a core particle resin, a crosslinking agent, a colorant, and other compounding materials are mixed in a first solvent to prepare a mixed solution in which the core particle resin and the crosslinking agent are dissolved.
Here, the first solvent is a good solvent capable of forming a dispersed phase in a second solvent described later (a poor solvent capable of forming a continuous phase), has a lower boiling point than the second solvent, and is a core particle resin. And a solvent that dissolves the cross-linking agent.
For example, water is applied as the first solvent.

Next, the obtained mixed liquid is mixed with the second solvent, stirred, and the mixed liquid is emulsified using the second solvent as a continuous phase to prepare an emulsified liquid.
Then, the first solvent in the emulsified liquid is removed (dried) by heating or the like to precipitate the core particle resin and the cross-linking agent, and together with these, the core particles (first particles) Core particles dispersed in two solvents).
Here, the second solvent is a poor solvent that can form a continuous phase with respect to the first solvent that becomes the dispersed phase, has a boiling point higher than that of the first solvent, and is insoluble in the resin and the crosslinking agent of the core particles. Select from.
Examples of the second solvent include a dispersion medium for dispersing the obtained image display particles.

Next, the resin of the coating layer and other compounding materials are mixed in a third solvent to prepare a mixed solution in which the resin of the coating layer is dissolved.
Here, the third solvent is also a good solvent that can form a dispersed phase in the second solvent (a poor solvent that can form a continuous phase), has a lower boiling point than the second solvent, and dissolves the resin of the coating layer. Select from the solvents to be used. The third solvent is preferably selected from solvents in which the core particle resin and the crosslinking agent are insoluble.
Examples of the third solvent include isopropyl alcohol (IPA), methanol, ethanol, butanol, tetrahydrofuran, ethyl acetate, and butyl acetate.

Next, the obtained mixed solution is dropped into the second solvent in which the core particles are dispersed while applying ultrasonic waves.
Then, the third solvent in the emulsion is removed (dried) by heating, depressurizing, etc., and the resin of the coating layer is deposited on the surface of the core particles, and the coating layer containing other compounding materials is also added to the surface of the core particles. To form.
Thereafter, for the purpose of making the core particles (and the coating layer) a resin crosslinked body, a heat treatment for crosslinking the resin is performed.

In this manner, image display particles having a coating layer formed on the surface of the core particles are obtained, and an image display particle dispersion containing the particle is obtained.
Here, the obtained image display particle dispersion may be diluted with, for example, a dispersion medium (solvent) as necessary. In order to obtain an image display particle dispersion containing two or more kinds of image display particles, these dispersions may be prepared and then mixed.

[Particle dispersion for image display]
The particle dispersion for image display according to the present embodiment includes a dispersion medium and image display particles dispersed in the dispersion medium, and the image display particle according to the present embodiment.

The dispersion medium is not particularly limited, but a low dielectric solvent (for example, a dielectric constant of 5.0 or less, desirably 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. In addition, the dielectric constant of a low dielectric constant is calculated | required with a dielectric constant meter (made 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.
The low dielectric solvent may be selected according to the type of polymerization component of the resin of the coating layer of the image display particles, for example. Specifically, for example, when a component having a silicone chain is applied as the polymerization component of the resin of the coating layer, silicone oil is preferably selected as the dispersion medium. Moreover, when applying the component which has an alkyl chain as a polymerization component of resin of a coating layer, it is good to select a paraffinic hydrocarbon solvent as a dispersion medium.
However, the present invention is not limited to this. For example, even when a component having a silicone chain is applied as the polymerization component of the resin of the coating layer, a paraffinic hydrocarbon solvent may be selected as the dispersion medium.

  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.

  In the particle dispersion for image display according to the present embodiment, an acid, an alkali, a salt, a dispersant, a dispersion stabilizer, a stabilizer for the purpose of preventing oxidation or ultraviolet absorption, an antibacterial agent, an antiseptic agent, as necessary. Etc. may be added. Further, a charge control agent may be added to the image display particle dispersion according to this embodiment.

  The concentration of the image display particles in the image display particle dispersion according to the present embodiment is variously selected depending on display characteristics, response characteristics, or use thereof, but is selected in a range of 0.1% by mass to 30% by mass. It is desirable. When mixing particles of different colors, it is desirable that the total amount of particles be in this range.

The particle dispersion for image display according to this embodiment is used for an image display type display medium, an image display type light control medium (light control element), a liquid toner of a liquid development type electrophotographic system, and the like. In addition, as a display medium of an image display system and a light control medium (light control element) of an image display system, a method of moving a particle group in a direction opposite to a well-known electrode (substrate) surface, an electrode (substrate) is different. There is a method of moving in a direction along a plane (so-called in-plane type element), or a hybrid element combining these.
Note that, in the image 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 the image display particles.

[Display medium, display device]
Hereinafter, examples of the display medium and the display device according to the embodiment will be described.

  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 is a form in which the image display particle dispersion according to the present embodiment is applied as a particle dispersion including the dispersion medium 50 of the display medium 12 and the particle group 34. That is, the image display particles according to the present embodiment are dispersed in the dispersion medium 50 as the particle group 34.

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

  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 and plastics such as 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. Examples thereof include resins.

  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, for example, a thermoplastic resin, a thermosetting resin, an electron beam curable resin, a photocurable resin, rubber, metal, or the like. The

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 that case, the gap member 24 is made of, for example, 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. As the color of the reflective particle group 36, for example, white or black is preferably selected so as to be the background color, but other colors may be used. The reflective particle group 36 may be an uncharged particle group (that is, a particle group that does not move in response to an electric field) or a charged particle group (a particle group that moves in response to an electric field). May be. In the present embodiment, the case where the reflective particle group 36 is an uncharged particle group and is white is described, but the present invention is not limited to this.

  The particles of the reflective particle group 36 include, for example, a white pigment (for example, titanium oxide, silicon oxide, zinc oxide), a resin (for example, polystyrene resin, polyethylene resin, polypropylene resin, polycarbonate resin, polymethyl methacrylate resin (PMMA), acrylic resin). Resin, phenol resin, formaldehyde condensate, etc.). Moreover, when applying particles other than white as the particles of the reflective particle group 36, for example, the above-described resin particles containing a pigment or dye of a desired color may be used. 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.

  In order to enclose the reflective particle group 36 between the substrates, for example, an inkjet method or the like is performed. Further, when the reflective particle group 36 is fixed, for example, after the reflective particle group 36 is sealed, the particle group surface layer of the reflective particle group 36 is melted by heating (and pressurizing if necessary). It is performed while maintaining the gap.

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 addition, 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 cell thickness (that is, the display substrate 20 and It is effective for the display medium 12 to adjust the content by the distance between the substrate and the back substrate). That is, in order to obtain a desired hue, the content can be decreased as the cell becomes thicker, and the content can be increased as the cell becomes thinner. Generally, it is 0.01 mass% or more and 50 mass% 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.

  The display medium 12 configured as described above includes, for example, a bulletin board, a circulation version, an electronic blackboard, an advertisement, a signboard, a flashing sign, an electronic paper, an electronic newspaper, an electronic book, and a copier / printer in which images are stored and rewritten. Used for document sheets etc.

  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 and displayed between the display substrate 20 and the gap member.

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. It may be a form in which two or more types (two colors) of particle groups are applied in different combinations of voltages.
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.

  Hereinafter, the present invention will be described more specifically with reference to examples. Hereinafter, the present invention will be described more specifically with reference to examples. However, these examples do not limit the present invention. In the text, “part” and “%” mean “part by mass” and “% by mass” unless otherwise specified.

[Example 1]
40 parts by mass of styrene acrylic resin X345 (manufactured by Seiko PMC) as the core particle resin, and carbodiimide compound (1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride (manufactured by Wako Pure Chemical Industries, Ltd.)) as the crosslinking agent An aqueous dispersion was prepared by adding 5 parts by mass and 50 parts by mass of a cyan pigment (“H525F (manufactured by Sanyo Dye))” as a colorant to water so that the total amount was 15% by mass.
Next, a silicone oil “KF-96-2CS (manufactured by Shin-Etsu Chemical Co., Ltd.) added with 1% by mass of a silicone oil solution (surfactant“ KF-6028 (manufactured by Shin-Etsu Chemical Co., Ltd.) ”) using the obtained aqueous dispersion as a dispersed phase. ) ") As a continuous phase, these were mixed at a mass ratio (continuous phase: dispersed phase) of 10: 1 and emulsified with a homogenizer to prepare an emulsion.
Next, the obtained emulsion was dried with an evaporator at 60 ° C. for 6 hours to remove water in the emulsion to obtain core particles. The obtained core particles had an average particle size of 0.6 μm and C.I. V. The value (index indicating monodispersity: Coefficient of Variation: CV [%] = (σ / D) × 100 (σ: standard deviation, D: average particle diameter)) was 25%.
Next, the dispersion of core particles dispersed in the liquid was washed with silicone oil using a centrifugal separator to prepare a 10 mass% core particle dispersion.

Next, as a polymerization component having a silicone chain, “Silaplane FM-0721 (manufactured by Chisso Corporation), weight average molecular weight Mw = 5000, structural formula 1 [R ₁ = methyl group, R ₁ ′ = butyl group, n = 68, x = 3] ”, a polymerization component“ AMP-10G (manufactured by Shin-Nakamura Chemical Co., Ltd.) having a phenoxy group as a polymerization component having a chargeable group, and an isocyanate monomer as a polymerization component having a reactive group (crosslinkable group) ” (Polyisocyanate monomer having a blocked isocyanate group “Karenz MOI-BP (manufactured by Showa Denko KK): 2-[(3,5-dimethylpyrazolyl) carbonylamino] ethyl methacrylate” and a polymerization component that undergoes a crosslinking reaction with isocyanate) As a copolymer with HEMA (2-hydroxyethyl methacrylate) [molar ratio 3/26/2/69: in the order of description] The prepared. This was designated as resin A of the coating layer.
Next, 2 g of the resin A of this coating layer was added to t-butanol to prepare a 10% by mass solution of t-butanol.

Next, 10 g of t-butanol, 20 g of a 10% by mass solution of t-butanol, and 18 g of silicone oil were added to 10 g of the core particle dispersion at a drop acceleration of 2 ml / s, stirred, and then at 50 ° C. for 1 hour with an evaporator. After drying, t-butanol in the core particle dispersion was removed, and the resin of the coating layer was allowed to precipitate the core particles, whereby a granular material having a coating layer formed on the surface of the core particles was obtained.
Next, this particle dispersion was heated at 130 ° C. for 1 hour to crosslink the resin constituting the core particles and the coating layer.

Through the above steps, a dispersion of image display particles having a coating layer formed on the surface of the core particles was obtained.
The image display particles dispersed in the liquid were washed with silicone oil using a centrifugal separator to obtain an image display particle dispersion liquid dispersed in silicone oil.

[Examples 2 to 15]
According to Table 1, the dispersion liquid was obtained together with the image display particles in the same manner as in Example 1 except that the composition of the core particles was changed.

[Comparative Example 1]
In the production of the core particles, a dispersion liquid was obtained together with the image display particles in the same manner as in Example 1 except that no crosslinking agent was added.

[Comparative Example 2]
According to Table 2, the composition of the core particles was changed, and the dispersion liquid was obtained together with the image display particles in the same manner as in Example 1 except that the heating at 130 ° C. was not performed and the crosslinking was not performed.

[Comparative Examples 3 to 4]
According to Table 2, a dispersion liquid was obtained together with image display particles in the same manner as in Example 1 except that the composition of the core particles was changed.

[Example 16]
The dispersion liquid was obtained together with the particles for image display in the same manner as in Example 1 except that the resin B described later was used as the resin for the coating layer, and particles were prepared.

(Preparation of resin B)
“Stearyl methacrylate” as a polymerization component having an alkyl chain, a polymerization component “AMP-10G (manufactured by Shin-Nakamura Chemical Co., Ltd.) having a phenoxy group as a polymerization component having a chargeable group, and a reactive group (crosslinkable group). As a polymerization component having an isocyanate monomer (isocyanate monomer having a blocked isocyanate group “Karenz MOI-BP (manufactured by Showa Denko KK): 2-[(3,5-dimethylpyrazolyl) carbonylamino] ethyl methacrylate”; As a polymerization component that undergoes a crosslinking reaction with isocyanate, a copolymer with HEMA (2-hydroxyethyl methacrylate) [molar ratio 5/26/2/67: described order] was prepared. This was designated as resin B of the coating layer.

[Examples 17 to 24]
According to Table 1, the dispersion liquid was obtained together with the image display particles in the same manner as in Example 16 except that the composition of the core particles was changed.

[Example 25]
According to Table 1, the dispersion liquid was obtained together with the image display particles in the same manner as in Example 1 except that the composition of the core particles was changed.

[Comparative Examples 5 to 7]
According to Table 2, a dispersion liquid was obtained together with image display particles in the same manner as in Example 16 except that the composition of the core particles was changed.

[Evaluation]
(Preparation of display particle dispersion (CW mixture))
The image display particles (cyan particles) and white particles obtained in each example are weighed and mixed so that the solid content of the image display particles (cyan particles) is 0.1 g and the white particles are 2.0 g. Then, silicone oil KF-96L-2cs (manufactured by Shin-Etsu Chemical Co., Ltd.) was added so that the liquid amount became 10 g, and ultrasonic dispersion was performed to prepare a particle dispersion for image display.
In addition, what produced as follows was used for the white particle.

(Production of white particles)
In a 500 ml three-necked flask equipped with a reflux condenser, 45 g of 2-vinylnaphthalene (manufactured by Nippon Steel Chemical Co., Ltd.), 45 g of Silaplane FM-0721 (manufactured by Chisso Corporation), silicone oil KF-96L-1CS (Shin-Etsu Chemical Co., Ltd.) 240 g) was added. After raising the temperature to 65 ° C., bubbling with nitrogen gas was performed for 15 minutes, and 2.3 g of lauroyl peroxide (manufactured by Aldrich) was added as an initiator. Polymerization was performed at 65 ° C. for 24 hours in a nitrogen atmosphere. The resulting suspension was centrifuged at 8,000 rpm for 10 minutes, the supernatant was removed, and then the washing step for redispersion with silicone oil KF-96-2CS (manufactured by Shin-Etsu Chemical Co., Ltd.) was repeated three times. . Finally, the particle solid content concentration was adjusted to 40% by mass with silicone oil to obtain a dispersion of white particles. The volume average particle diameter was 450 nm.

(Production of evaluation cell)
As an electrode, a solution of fluororesin CYTOP (manufactured by Asahi Glass Co., Ltd.) is spin-coated on a glass substrate on which indium tin oxide (ITO) having a thickness of 50 nm is formed by sputtering, and dried at 130 ° C. for 1 hour. A surface layer having a thickness of 80 nm was formed. Two ITO substrates with a surface layer thus prepared were prepared, and used as a display substrate and a back substrate. Using a 50 μm Teflon (registered trademark) sheet as a spacer, the display layers were superimposed on the back substrate with the surface layers facing each other, and fixed with clips.
The particle dispersion was injected into the evaluation empty cell thus prepared to obtain an evaluation cell.

(Evaluation of threshold voltage)
The threshold voltage (initial threshold voltage) of the image display particles was measured using a densitometer (X-Rite 939 manufactured by X-Rite). The threshold voltage at which the reflectance on the viewing surface of the produced evaluation cell was 90% (denoted as “E90”) was measured as follows.
Using the produced evaluation cell, a potential difference of 15 V was applied between the electrodes for 5 seconds so that the surface electrode was negative. The dispersed positively charged cyan particles moved to the negative electrode, that is, the surface electrode side, and cyan color was observed when observed from the display substrate side. At this time, the reflectance at 600 nm, which is the absorption wavelength of the cyan pigment, was measured.
The results are shown in Tables 1 and 2.

When comparing Examples 1 to 12, Comparative Example 1 and Examples 16 to 22 and Comparative Example 5, the threshold voltage of the particles in which the core particles are crosslinked is higher than the threshold voltage of the particles in which the core particles are not crosslinked. I understand that. Furthermore, when Examples 13 to 14 and Comparative Example 3, Example 23 and Comparative Example 6, Example 15 and Comparative Example 4, and Example 24 and Comparative Example 7 were compared, all crosslinked the core particles. It can be seen that the threshold voltage of the obtained particles is higher than the threshold voltage of the particles not cross-linking the core particles. Further, as shown in Comparative Example 2, when the crosslinking by heating was not performed, the density was low and the threshold value did not increase. On the other hand, as shown in Example 25, when the amount of the crosslinking agent is 30 parts by mass, the threshold value becomes high, and when the potential difference of 15 V is applied for 5 seconds, the threshold value cannot be observed, and the potential difference of 18 V is increased to 10 seconds. The threshold could be observed when applied.
As described above, good results have been obtained in the examples.

Details of abbreviations and the like in Table 1 and Table 2 are as follows.
-Core particle resin-
・ X345: Styrene acrylic copolymer (manufactured by Seiko PMC)
・ X310: Acrylic resin ((made by Seiko PMC))
GAFQUAT-755N: Vinylpyrrolidone-dimethylaminomethacrylate copolymer (APS Japan)

-Crosslinking agent-
Carbodiimide: 1-ethyl-3- (3-dimethylaminopropyl) carbodiimide hydrochloride (manufactured by Wako Pure Chemical Industries, Ltd.)
Epoxy (EX-614B): water-soluble epoxy compound (sorbitol polyglycidyl ether “Denacol EX-614B (manufactured by Nagase ChemteX Corporation)”)
Epoxy (EX-321): polyfunctional epoxy compound (trimethylolpropane polyglycidyl ether “Denacol EX-321 (manufactured by Nagase ChemteX Corporation)”)
Aziridine: Tris [3- (1-azilinidyl) propionic acid] trimethylolpropane (Wako Pure Chemical Industries, Ltd.)
・ Isocyanate: No-back (manufactured by DIC)
・ Hydrazide 1: Adipic acid hydrazide (manufactured by Tokyo Chemical Industry)
・ Hydrazide 2: Isophthalic acid hydrazide (manufactured by Tokyo Chemical Industry)

-Colorant-
-H525F: Cyan pigment ("H525F (manufactured by Sanyo Dye)")

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 (7)

A core material comprising a resin cross-linked product of a composition comprising a water-soluble resin, at least one cross-linking agent selected from an epoxy compound, a carbodiimide compound, an isocyanate compound, an aziridine compound, and a hydrazide compound, and a colorant. Particles,
A coating layer covering the surface of the core particles, a parent dispersion medium part that dissolves in the dispersion medium in which the image display particles are dispersed, and a sparse insoluble in the dispersion medium in which the image display particles are dispersed. A coating layer formed of a composition containing a resin having a dispersion medium part;
Particles for image display having A core material comprising a resin cross-linked product of a composition comprising a water-soluble resin, at least one cross-linking agent selected from an epoxy compound, a carbodiimide compound, an isocyanate compound, an aziridine compound, and a hydrazide compound, and a colorant. Particles,
A coating layer covering the surface of the core particle, and formed by a composition comprising a resin comprising at least a polymer component having a silicone chain or a polymer component having an alkyl chain and a polymer component having a chargeable group A coated layer,
Particles for image display having   3. The image display particle according to claim 1, wherein a content of the cross-linking agent is 0.5% by mass or more and 20% by mass or less with respect to the entire core particle. A dispersion medium;
The image display particles dispersed in the dispersion medium, the image display particles according to any one of claims 1 to 3,
A particle dispersion for image display comprising: A pair of substrates, at least one of which is translucent,
The particle dispersion for image display according to claim 4 enclosed between the pair of substrates,
A display medium comprising: A pair of electrodes, at least one of which is translucent,
The region having the image display particle dispersion according to claim 4 provided between the pair of electrodes;
A display medium comprising: A display medium according to claim 5 or 6,
Voltage application means for applying a voltage between the pair of substrates or the pair of electrodes of the display medium;
A display device comprising: