WO2013154057A1

WO2013154057A1 - Particles for display, dispersion liquid for electrophoretic display, display medium, and display device

Info

Publication number: WO2013154057A1
Application number: PCT/JP2013/060543
Authority: WO
Inventors: 尚森川; 氷治　直樹; 保夫山本; 中山　大輔; 浦野　千里; 関　三枝子; 真鍋　力; 良太水谷; 軍曹; 佐藤　忠伸; 律子森田
Original assignee: 富士ゼロックス株式会社; 富士フイルム株式会社
Priority date: 2012-04-10
Filing date: 2013-04-05
Publication date: 2013-10-17
Also published as: JP2013218184A

Abstract

Particles for display, wherein a coloring agent is eccentrically located in the particles for display in a region from the surface of the particles to a depth of 5% or more and 35% or less of the volume average particle diameter of the particles towards the center.

Description

Display particles, electrophoretic display dispersion, display medium, and display device

The present invention relates to display particles, a dispersion for electrophoretic display, a display medium, and a display device.

There has been proposed a display device in which charged colored particles are arranged between a pair of opposed electrodes and a voltage is applied between the electrodes to move a part of the particles in the dispersion to perform display.

For example, in Japanese Patent Application Laid-Open No. 2006-113390, in an electrophoretic particle in which a pigment is dispersed in a polymer fine particle, the polymer fine particle is grafted to a pigment, and the first polymer portion is bonded to the first polymer portion. A pigment having a copolymerized second polymer portion and a polymer grafted with the polymer to be the first polymer portion dispersed in a polymerizable monomer for forming the second polymer portion Electrophoretic particles obtained by polymerizing the polymerizable monomer are disclosed.

Japanese Patent Application Laid-Open No. 2008-145713 discloses a polymer graft fine particle for electrophoresis dispersed in an electrophoretic dispersion, wherein 16 to 100% by mass of the polymer is grafted to the pigment fine particle. Graft microparticles are disclosed.

Japanese Patent Application Laid-Open No. 2005-352054 discloses a method for producing electrophoretic particles, in which a polymer fine particle dispersion in which polymer fine particles having a functional group are dispersed in a liquid, and a colorant are dispersed in the liquid. A step of mixing the colorant dispersion and aggregating the polymer fine particles and the colorant to form aggregated particles, and heating and coalescing the aggregated particles to form composite particles composed of the polymer and the colorant. And a step of introducing a living radical polymerization initiating group into a functional group of the composite particle, and a step of forming a polymer chain from the introduced living radical polymerization initiating group by living radical polymerization. A method for producing electrophoretic particles is disclosed.

JP 2009-031794 discloses a shell-type electrophoretic particle having a shell having an internal cavity, an inner surface of the shell, a charged layer having an electrical polarity, Shell-type electrophoretic particles comprising an ionic liquid enclosed in a cavity of a shell are disclosed.

It is an object of the present invention to provide display particles having a small variation in optical density when arranged in a single layer.

In order to achieve the above object, the following invention is provided.
<1> Display particles in which the colorant is unevenly distributed in a region between the surface of the particle and a depth of 5% to 35% of the volume average particle diameter of the particle from the surface toward the center.
<2> The colorant is unevenly distributed in a region between the surface of the display particles and a depth of 12% or more and 23% or less of the volume average particle diameter of the display particles from the surface toward the center side. The display particle according to <1>.
<3> a core portion including a binder resin, a pigment that is the colorant, and a coating portion that includes the pigment dispersant and covers the core portion, and the binder resin and the dispersant. The display particle according to <1> or <2>, wherein one is basic and the other is acidic.
<4> A dispersion liquid for electrophoretic display, comprising a dispersion medium and the group of display particles according to any one of <1> to <3> dispersed in the dispersion medium.
<5> The dispersion liquid for electrophoretic display according to <4>, wherein a difference in refractive index between the dispersion medium and the display particles is less than 0.3.
<6> A pair of substrates at least one of which is translucent and disposed with a gap, and the dispersion liquid for electrophoretic display according to <4> or <5> enclosed between the pair of substrates, A display medium comprising:
<7> A pair of electrodes at least one of which is translucent and disposed with a gap; a region having the dispersion liquid for electrophoretic display according to <4> or <5> between the pair of electrodes; A display medium comprising:
<8> A display device comprising: the display medium according to <6> or <7>; and an electric field applying unit that applies a voltage between the pair of substrates of the display medium or the pair of electrodes.

According to the invention <1>, <2>, or <3>, there are provided display particles having a small variation in optical density when arranged in a single layer as compared with the case without the above-described configuration.
According to the invention of <4>, <5>, <6>, <7>, or <8>, compared with a case where display particles in which the colorant is not unevenly distributed on the surface side of the particles are applied. The dispersion liquid for electrophoretic display, the display medium, or the display device in which the variation in optical density when arranged in the above is small is provided.

It is a schematic sectional drawing which shows an example of the particle | grains for a display which concerns on this embodiment. It is a schematic sectional drawing which shows the other example of the particle | grains for a display which concerns on this embodiment. It is a schematic sectional drawing which shows the other example of the particle | grains for a display which concerns on this embodiment. It is a schematic sectional drawing which shows an example of the display apparatus using the particle | grains for a display which concerns on this embodiment. It is the TEM photograph which observed the cross section of the particle | grains for a display produced in the Example. It is a schematic sectional drawing which shows the particle | grains for a display in which the coloring agent has disperse | distributed to the whole particle | grain.

Hereinafter, the display particles according to the embodiment of the present invention, the dispersion liquid for electrophoretic display, the display medium, and the display device using the same will be described with reference to the drawings as appropriate.

<Display particles>
In the display particles according to the present embodiment (which may be simply referred to as “particles”), the colorant is 5% or more and 35% of the volume average particle diameter of the particles from the surface toward the center side. It is unevenly distributed in a region between the following depths (hereinafter may be referred to as “specific region”).
FIG. 1 schematically shows a cross section of an example of display particles according to the present embodiment. The display particles 11 shown in FIG. 1 are a core portion 13 (sometimes referred to as a “core portion”) and a covering portion 15 (sometimes referred to as a “shell portion”) covering the core portion 13. The core portion 13 does not contain a colorant and is transparent, and the colorant is included in the coating portion 15 so that it is unevenly distributed in a specific region of the particle 11. If the display particles according to the present embodiment are used, variation in optical density when arranged in a single layer is reduced. The reason is presumed as follows.

FIG. 6 schematically shows a cross section of the display particles in which the colorant is evenly dispersed throughout the particles. When the light L is incident on such display particles 61, the optical path length passing through the colored region in the particles varies greatly depending on the direction in which the light L is incident. For this reason, when the display particles 61 are observed from the outside, the difference in optical density tends to be large between a portion corresponding to the vicinity of the center of the particles 61 and a portion corresponding to the vicinity of the outer periphery in plan view. Therefore, when such display particles 61 are displayed side by side in a single layer, the optical density varies greatly between the center and the outer periphery of each particle 61, and the density unevenness also increases as a whole display. easy.

On the other hand, in the display particle 11 according to the present embodiment, since the colorant is unevenly distributed in a specific region of the particle 11, the light L incident on the display particle 11 and the particle 11 are incident as shown in FIG. 1. The difference in the optical path length in the region where the colorant is present in the particles 11 is small regardless of the direction in which the particles are taken. Therefore, when the display particles 11 are observed from the outside, the difference in optical density between the center and the outer periphery of the particles 11 in plan view is smaller than that of the display particles 61 shown in FIG. Therefore, when the display particles 11 according to the present embodiment are displayed in a single layer, the optical density variation is small near the center and the outer periphery of each particle 11, and the density unevenness is also observed in the entire display. It is suppressed.

According to the experiments by the present inventors, the colorant is at least 35% of the volume average particle diameter of the display particles 11 from the surface toward the center side of the display particles 11 according to the present embodiment. %, That is, a region that is unevenly distributed in the region from the surface of the particle 11 to a depth of 5% to 35% of the volume average particle diameter. It is more desirable to be unevenly distributed in a region from 7% to 30% of the diameter, and to be unevenly distributed from the surface of the particle 11 to a depth of 12% to 23% of the volume average particle diameter. Is more desirable. If the colorant is unevenly distributed in a region between the surface of the display particle 11 and a depth of 5% or more of the volume average particle diameter of the display particle 11 from the surface toward the center, a high optical density is obtained. If it is unevenly distributed in a region between the surface and a depth of 35% or less of the volume average particle diameter, variation in the optical density of the display particles 11 in a plan view can be effectively suppressed, and a pigment used as a colorant, etc. The amount of use is suppressed.
For example, as shown in FIG. 1, if the display particles 11 and the core portion 13 are each spherical, it is desirable that the transparent core portion 13 is 65% to 95% of the diameter of the display particles 11.

In addition, as a volume average particle diameter of the display particle 11 whole, 0.3 micrometer or more and 15 micrometers or less are mentioned, for example. The volume average particle diameter of each display particle 11 is a value measured by an SEM image. Specifically, after obtaining an image by SEM (scanning electron microscope S-4800, manufactured by Hitachi High-Technologies Corporation), the particle diameter (longest portion) r1 of each particle was measured. After measuring 100 particles 11 as r1 to r100, respectively, r1 to r100 are converted into sphere diameters to determine the volume, and the value when the accumulation from the first to the 100th becomes 50% is the volume average. The particle size.
On the other hand, for the region where the colorant is present relative to the volume average particle diameter of the particle, the region where the colorant is present is evaluated by TEM observation of the cross section of the particle, and the particle is deformed into an elliptical shape by cutting the particle in the preparation of the observation sample. Therefore, the average value of the diameter of the inscribed circle and the diameter of the circumscribed circle in the cross section of the particle after cutting is taken as the volume average particle size, and the ratio of the colorant existing region to the volume average particle size is obtained.

FIG. 2 schematically shows another example of display particles according to the present embodiment. In the display particles 21 shown in FIG. 2, a colorant is present from the surface to a deeper region than the display particles 11 shown in FIG. Even in the display particles 21, the colorant is not present in the vicinity of the center of the particles 21 or a minute amount is present, and the difference in optical path length in the colored region is smaller than that of the display particles 61 shown in FIG. 6. Therefore, even when the display particles 21 according to this embodiment are displayed in a single layer, the optical density variation is small between the center and the outer periphery of each particle 21 in plan view, and the density of the entire display is also high. Unevenness is suppressed.

The

display particles

11 and 21 shown in FIGS. 1 and 2 include

transparent core portions

13 and 23 that do not include a colorant, and covering

portions

15 and 25 that include the colorant and cover the

core portions

13 and 23. However, the display particles according to the present embodiment are not limited to these configurations, and the colorant may be unevenly distributed in a specific region on the surface side rather than the center side of the particles. For example, as shown in FIG. 3, the colorant may be unevenly distributed in a specific region on the surface side so that the concentration of the colorant gradually increases from the center of the display particle 31 toward the surface.

In addition, examples of the structure of the display particles according to the present embodiment include particles having the following structure.
(1) A non-hollow particle having a core portion made of a transparent material such as resin or glass, and a covering portion that includes a colorant and covers the core portion.
(2) Hollow particles comprising a transparent material such as resin or glass and a colorant.
(3) Non-hollow particles in which hollow particles composed of a transparent material such as resin and glass and a colorant are filled with a transparent liquid.
(4) Hollow particles in which transparent hollow particles made of a transparent material such as resin and glass are coated with a colorant.

Among the display particles having the structure of any of (1) to (4) above, display particles (hereinafter referred to as particles) in which display particles are dispersed in a liquid dispersion medium and electrophoresed in the dispersion medium by applying a voltage. The non-hollow particles having the structure (1) or (3) are preferable, and the non-hollow particles having the structure (1) are more preferable. In addition, as a liquid contained in the inside of the non-hollow particle | grains which have a structure of (3), it is desirable to use the same kind as a dispersion medium from the balance with the specific gravity of a dispersion medium.
On the other hand, if the hollow particles having the above structure (2) or (4) are dispersed in a dispersion medium, the inside of the particles is hollow, so that buoyancy affects the migration. Therefore, the hollow particles having the structure (2) or (4) are desirably used as display particles that move in a gas dispersion medium such as air by applying a voltage without using a liquid dispersion medium.

Next, the material constituting the display particles according to the present embodiment will be specifically described. Hereinafter, as an example of the display particles according to the present embodiment, the display particles 11 having the configuration shown in FIG. 1 and the case where the display particles 11 are dispersed in a dispersion medium and used as electrophoretic particles are mainly described. To do.
The display particle 11 shown in FIG. 1 includes a core portion 13 including a binder resin that is a transparent material, a pigment that is a colorant, and a dispersant for the pigment, and a covering portion 15 that covers the core portion 13. Have

-Transparent materials-
The core 13 of the display particle 11 according to this embodiment includes a transparent material. Examples of the transparent material contained in the core 13 include binder resins such as thermoplastic resins and thermosetting resins. Glass may be used as the transparent material contained in the core portion 13. In the present embodiment, “transparent” means that the visible light transmittance is 60% or more, and desirably 80% or more. Here, the transmittance means a maximum value in a wavelength range from 400 nm to 700 nm, which is measured by a spectrophotometer (U-4000, manufactured by Hitachi).

Examples of the thermoplastic resin used for the display particles 11 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 Carboxylic acid esters; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl butyl ether; homopolymers or copolymers of vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and vinyl isopropenyl ketone Combined are exemplified.

Examples of the thermosetting resin used for the display particles 11 include cross-linked copolymers mainly composed of divinylbenzene and cross-linked resins such as cross-linked polymethyl methacrylate; phenol resins, urea resins, melamine resins, polyester resins, A silicone resin etc. are mentioned. Typical binder resins include polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer. Examples of the polymer include polyethylene, polypropylene, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, and paraffin wax.

-Colorant-
As the colorant contained in the covering portion 15 of the display particle 11 according to the present embodiment, an organic or inorganic pigment, an oil-soluble dye, or the like is used. Magnetic powder such as magnetite, 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, quinacridone-based magenta color material, red color material, green Well-known colorants, such as a color material and a blue color material, are mentioned. Specifically, aniline blue, calcoil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment yellow 97, C.I. Blue 15: 1, C.I. I. Pigment Blue 15: 3, etc. are exemplified as typical examples.

The covering portion 15 of the display particle 11 according to the present embodiment may include a dispersing agent for dispersing a pigment as a coloring agent, a binder resin included in the core portion 13, and the like in addition to the coloring agent.
Further, the core 13 of the display particle 11 according to the present embodiment may contain some colorant. However, the concentration of the colorant in the core 13 needs to be lower than at least the concentration of the colorant in the covering 15. Specifically, it is preferably 1/5 or less, and more preferably 1/10 or less, of the concentration of the colorant in the covering portion 15.

-Other ingredients-
The display particles 11 according to the present embodiment may include a charge control agent as necessary. As the charge control agent, known ones used for electrophotographic toner materials can be used. Quaternary ammonium salts such as cetylpyridyl chloride, BONTRON (registered trademark) P-51, BONTRON P-53, BONTRON E-84, BONTRON E-81 (above, manufactured by Orient Chemical Industries), salicylic acid metal complexes, phenols Examples thereof include system condensates, tetraphenyl compounds, metal oxide particles, and metal oxide particles surface-treated with various coupling agents.

A magnetic material may be mixed in the core portion 13 and / or the covering portion 15 of the display particle 11 according to the present embodiment, if necessary. As the magnetic material, an inorganic magnetic material or an organic magnetic material that is color-coated as required is used. Further, a transparent magnetic material, in particular, a transparent organic magnetic material does not hinder the color development of the color pigment, and the specific gravity is smaller than that of the inorganic magnetic material, so that it is more desirable.
As the colored magnetic powder, for example, a small-diameter colored magnetic powder described in JP-A-2003-131420 may be used. Colored magnetic powder comprising 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 by coloring the magnetic powder opaque with a pigment or the like, but it is desirable 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 reflects light in a wavelength selective manner by optical interference in the thin film. is there.

An external additive may be attached to the surface of the display particles 11 as necessary. The color of the external additive is desirably transparent so as not to affect the color of the display particles 11.

As the external additive, inorganic particles such as metal oxides such as silicon oxide (silica), titanium oxide, and alumina are used. In order to adjust the charging property, fluidity, and environment dependency of the particles, they may be surface-treated with a coupling agent or silicone oil.

Coupling agents include positively chargeable ones such as aminosilane coupling agents, aminotitanium coupling agents, nitrile coupling agents, and silanes that do not contain nitrogen atoms (consisting of atoms other than nitrogen). There are negatively charged ones such as coupling agents, titanium-based coupling agents, epoxy silane coupling agents, and acrylic silane coupling agents. Silicone oil includes positively charged ones such as amino-modified silicone oil, dimethyl silicone oil, alkyl-modified silicone oil, α-methylsulfone-modified silicone oil, methylphenyl silicone oil, chlorophenyl silicone oil, fluorine-modified silicone. Examples include negatively chargeable oils. These are selected according to the desired resistance of the external additive.

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

The primary particles of the external additive are generally 1 nm or more and 100 nm or less, and preferably 5 nm or more and 50 nm or less, but are not limited thereto.

The blending ratio of the external additive and the display particle 11 is adjusted based on the balance between the particle size of the display particle 11 and the particle size of the external additive. If the added amount of the external additive is too large, at least a part of the external additive is liberated from the surface of the display particles 11 and adheres to the surface of the other display particles 11 so that desired charging characteristics cannot be obtained. . Generally, the amount of the external additive is more 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 display particles. .

In the present embodiment, a plurality of types of display particles 11 having different colors may be used in combination. When a plurality of types of display particles 11 having different colors are used in combination, the external additive may be added only to any one of the plurality of types of display particles 11, or a plurality of types or all types of display particles. 11 may be added.
When an external additive is added to the surface of all the display particles 11, the external additive is applied to the surface of the display particles 11 with an impact force, or the surface of the display particles 11 is heated to display the external additive. It is desirable to adhere to the surface of the particles 11 for use. As a result, the external additive is released from the display particles 11, the external additive having a different polarity is strongly aggregated, and formation of an aggregate of the external additive that is difficult to dissociate with an electric field is prevented. As a result, image quality deterioration is prevented.

The method for producing the display particles 11 according to this embodiment is not particularly limited as long as the colorant is unevenly distributed so that the concentration is higher in a specific region on the surface side than the center side of the particles 11. For example, a dispersing agent that contains a transparent binder resin and produces core particles to be a core portion (core portion) 13 by a submerged drying method, and disperses the pigment and the pigment on the surface of the core particles by a coacervation method. And a method of coating the shell resin to be the covering portion (shell portion) 15.
When the particles are produced by a submerged drying method, one of the binder resin constituting the particles and the dispersant contained in the pigment is basic, and the other is acidic. 13 and the covering portion 15, and the display particles 11 in which the colorant is unevenly distributed in the covering portion 15 are easily manufactured. If it is the display particle 11 produced by such a manufacturing method, it becomes the display particle 11 which has the core part 13 containing basic binder resin and the coating | coated part 15 containing an acidic dispersing agent, for example.
The particles may be formed using an acidic binder resin and a basic pigment dispersant.

<Electrophoretic display dispersion, display medium, and display device>
Next, the dispersion liquid for electrophoretic display, the display medium, and the display device using the display particles according to the present embodiment will be described.
The dispersion for electrophoretic display according to the present embodiment may be referred to as a group of display particles in which the dispersion medium and the colorant described above are unevenly distributed on the surface side (hereinafter referred to as “electrophoretic particles” or “electrophoretic particle group”). And).
In addition, the display medium according to the present embodiment includes at least one of a pair of substrates having translucency and disposed with a gap, and an electrophoretic display dispersion liquid sealed between the pair of substrates. .
Furthermore, the display device according to the present embodiment includes the display medium and an electric field applying unit that applies a voltage between the pair of substrates or the pair of electrodes of the display medium.

FIG. 4 schematically shows an example of the configuration of the display device according to the present embodiment. The display device 10 illustrated in FIG. 4 includes a display medium 12 and a voltage application unit 16 that applies a voltage to the display medium 12 to form an electric field between the display substrate 20 and the back substrate 22 of the display medium 12. . In FIG. 4, a part (one cell) of the display medium 12 is shown enlarged.

The display medium 12 includes a display side support substrate 38, a back side support substrate 44, a display side electrode 40, a back side electrode 48, and a gap member 24. The display substrate 20 includes a display-side support substrate 38 and a display-side electrode 40, and the back substrate 22 includes a back-side support substrate 44 and a back-side electrode 48.
A book including the dispersion medium 50 and the migrating particle group 11 in a cell (in a region between the pair of electrodes 40 and 48) that is a closed space surrounded by the pair of

substrates

20 and 22 and the gap member 24. The dispersion liquid for electrophoretic display of the embodiment is filled.

The display-side support substrate 38 is an image display surface and has translucency (as a specific example, the visible light transmittance is 70% or more).
The back side support substrate 44, which is a non-display surface, is disposed with a gap so as to face the display side support substrate 38. In addition, the back side support substrate 44 does not necessarily have translucency, but rather the visibility can be improved by blocking incident light from the back side.

Examples of materials included in the display side support substrate 38 and the back side support substrate 44 include glass, plastic, polyethylene terephthalate resin, polyethylene naphthalate resin, polycarbonate resin, acrylic resin, polyimide resin, polyester resin, epoxy resin, and polyether. A sulfone resin etc. are mentioned.

A display side electrode 40 and a back side electrode 48 are provided on the inside (opposite side) of the display side support substrate 38 and the back side support substrate 44, respectively.
Examples of materials included in the display side electrode 40 and the back side electrode 48 include oxides such as indium, tin, cadmium, and antimony; composite oxides such as ITO; metals such as gold, silver, copper, and nickel; polypyrrole, Examples thereof include organic materials such as polythiophene. These materials constitute the

electrodes

40 and 48 as, for example, a single layer film, a mixed film or a composite film.

The thickness of the display side electrode 40 and the back side electrode 48 is, for example, 100 mm or more and 2000 mm or less (10 nm or more and 200 nm or less).
The display side electrode 40 and the back side electrode 48 may be formed in a matrix shape or a stripe shape, for example.

The display side electrode 40 and the back side electrode 48 are electrically 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 has a function of applying a voltage according to the control of the control unit 18 to the display side electrode 40 and the back side electrode 48. By applying a voltage between the display side electrode 40 and the back side electrode 48 by the voltage application unit 16, an electric field is formed between the display side electrode 40 and the back side electrode 48.

The voltage application unit 16 of the display device 10 may be detachably connected to the display medium 12 (the display side electrode 40 and the back side electrode 48). In this case, for example, when it is necessary to rewrite or display the display medium 12, the display medium 12 is connected to the voltage application unit 16 to display image information. It is configured to improve portability.

Note that the display medium 12 of the present embodiment includes the display-side electrode 40 and the back-side electrode 48, both of which are connected to the voltage application unit 16. However, the present invention is not limited to this. One of the 40 and the back side electrode 48 may be grounded, and the other may be connected to the voltage applying unit 16.

In order to protect the display-side electrode 40 and the back-side electrode 48, a surface layer that covers the

electrodes

40, 48 may be provided with a fluororesin or the like.

The space between the display substrate 20 and the back substrate 22 (between the display side electrode 40 and the back side electrode 48) is partitioned into a plurality of closed spaces (cells) by the gap member 24. The gap member 24 has a function of maintaining a distance between the display substrate 20 and the back substrate 22 and a function of partitioning a plurality of gaps between the display substrate 20 and the back substrate 22.

Examples of the constituent material of the gap member 24 include thermoplastic resins, thermosetting resins, electron beam curable resins, photo curable resins, rubbers, metals, and the like.

The gap member 24 may be colored or colorless, but is preferably colorless and transparent so as not to adversely affect the display image displayed on the display medium 12. In this case, for example, polystyrene, polyester, acrylic, etc. Transparent resin or the like is used. Here, when the gap member 24 has transparency, it is only necessary to have a transmittance of 25% or more with respect to visible light.

-Dispersion medium-
Examples of the dispersion medium include an insulating liquid. Insulating property in this embodiment refers to a case where the volume resistance value is 10 ⁷ Ω · cm or more as a specific example.

Examples of the dispersion medium include silicone oil and hydrocarbon oil. Specifically, hexane, cyclohexane, toluene, xylene, decane, hexadecane, kerosene, paraffin, isoparaffin, silicone oil, modified silicone oil, dichloroethylene, and trichloroethylene. Perchlorethylene, high-purity petroleum, ethylene glycol, alcohols, ethers, esters, dimethylformamide, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, 2-pyrrolidone, N-methylformamide, acetonitrile, tetrahydrofuran, propylene carbonate , Ethylene carbonate, benzine, diisopropylnaphthalene, olive oil, isopropanol, trichlorotrifluoroethane, tetrachloro Ethane, and the like dibromotetrafluoroethane, mixtures thereof suitably.
Examples of the insulating liquid that can be used as the dispersion medium include water from which impurities are removed so as to obtain the following volume resistance value (so-called pure water).

Examples of the dispersion medium include polymers. Examples of the polymer include a polymer gel and a polymer. Specifically, examples of the polymer include gelatin, polyvinyl alcohol, poly (meth) acrylamide and the like.

The dispersion medium may be composed of an insulating liquid alone or a polymer alone, but may be a mixture of a resin insulating liquid and a polymer resin.
The volume resistance value of the dispersion medium 50 is, for example, 10 ⁷ Ω · cm or more, preferably 10 ⁷ Ω · cm or more and 10 ¹⁹ Ω · cm or less, more preferably 10 ¹⁰ Ω · cm or more and 10 ¹⁹ Ω or less. -It is cm or less. By setting the volume resistance value in this range, an electric field is applied to the migrating particle group, and generation of bubbles due to electrolysis of the dispersion medium due to electrode reaction is suppressed.

The difference in refractive index between the dispersion medium and the display particles 11 is preferably less than 0.3, and more preferably less than 0.1. By setting the difference in refractive index between the dispersion medium and the display particles 11 to be less than 0.3, the transmitted light that has passed through the particles is collected or the light is reflected on the particle surface, resulting in a variation in optical density. It is suppressed. The refractive index difference between the dispersion medium and the display particles 11 is calculated with reference to literature values.

-Electrophoretic particle group-
In the display device according to the present embodiment, as the migrating particle group 11, a group of display particles 11 in which the colorant is unevenly distributed on the surface side is used.
The electrophoretic particle group 11 is composed of a plurality of display particles (electrophoretic particles) 11 according to the present embodiment, each of which is positively or negatively charged, and is a solid particle group having electrophoretic properties in the dispersion medium 50. is there. That is, the direction of the electric field that has a large positive or negative charge in the dispersion medium 50 and is generated between the display-side electrode 40 and the back-side electrode 48 (that is, between the display substrate 20 and the back-side substrate 22). And moves in the dispersion medium 50 according to the strength. The change in the display color on the display medium 12 is caused by the movement of the migrating particles 11 constituting the migrating particle group 11 in the dispersion medium 50.

The migrating particle group 11 may be a particle group having a color corresponding to the image to be formed. The migrating particle group 11 may be, for example, one type (single color) or a plurality of types (multiple colors, for example, Y: yellow, C: cyan, M: magenta, R: red).

The resin constituting the migrating particle group 11 may be mixed with, for example, a charge control agent that controls chargeability, if necessary. Moreover, you may mix a magnetic material in the inside and the surface of the migrating particle group 11 as needed. Further, an external additive (for example, a polymer graft chain such as a silicone chain) may be attached to the surface of the migrating particle group 11 as necessary.

If a pigment having charging properties is used as the colorant unevenly distributed on the surface side of the migrating particles 11, variations in optical density when arranged in a single layer are suppressed, and charging properties are provided on the surface side of the particles 11. Due to the uneven distribution of the pigment to be contained, the charge of the migrating particles 11 as a whole is stabilized.

The content of the migrating particle group 11 (content (% by mass) with respect to the total mass of the display dispersion in the cell) is not particularly limited as long as the desired hue can be obtained. It is preferable that the layers are uniformly arranged in a single layer. For example, it is selected from the range of 0.5% by mass or more and 20% by mass or less depending on the particle diameter.

Examples of the volume average particle diameter of each particle 11 of the migrating particle group include 0.3 μm or more and 15 μm or less. Here, the volume average particle diameter of each migrating particle 11 is a value measured by an SEM photograph.
When two or more types of migrating particle groups 11 having different colors are included, the particle size of the migrating particles 11 in each particle group may be different or the same.

-Other-
In the display dispersion according to the present embodiment, for example, if necessary, an additive (stabilizer, antibacterial agent, antiseptic agent) for the purpose of acid, alkali, salt, dispersion stabilizer, antioxidant, ultraviolet absorption, etc. Etc.) may be added. Also, for example, charge control agents (anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, fluorosurfactants, silicone surfactants, metal soaps, alkyl phosphate esters Or succinimides) may be added. In any case, it is desirable to add so as to be in the range of the volume resistance value.

FIG. 4 shows a form including one color of migrating particles 11, but is not limited to this. For example, a non-migrating particle group that does not substantially move in the dispersion medium may be used in combination.

The non-electrophoretic particle group is a solid particle having a color different from that of the electrophoretic particle group 11 and not having electrophoretic properties in the dispersion medium 50. That is, the non-electrophoretic particle group has no charge in the dispersion medium 50 or has a small positive or negative charge, but the dispersion medium 50 is caused by the electric field generated between the display-side electrode 40 and the back-side electrode 48. Even if it does not move inside or moves, it is a particle group that can be regarded as not migrating (moving) because the average moving distance is much smaller than that of the migrating particle group 11.

Due to the electric field generated between the display substrate 20 and the back substrate 22 (display side electrode 40 and back side electrode 48), each particle of the migrating particle group 11 passes through the gap between the non-migrating particle group and from the back substrate 22 side. Display is performed by migrating (moving) from the display substrate 20 side or the display substrate 20 side to the back substrate 22 side.

The color of each non-electrophoretic particle constituting the non-electrophoretic particle group may be a color different from the color of each electrophoretic particle of the electrophoretic particle group 11. For example, white or black may be selected so as to be the background color, but other colors may be used. The non-electrophoretic particle group 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 (moves in accordance with an electric field, It may be a particle group whose movement distance is much smaller than that of the migrating particle group 11).

When the non-electrophoretic particle group is composed of white particles, examples of the constituent material include white pigments (titanium oxide, silicon oxide, zinc oxide, etc.) and resins (polystyrene resin, polyethylene resin, polypropylene resin, polycarbonate resin, Examples thereof include particles dispersed in methyl methacrylate resin (PMMA), acrylic resin, phenol resin, formaldehyde condensate, etc., resin particles such as polystyrene, polyethylene, and vinyl naphthalene.
Moreover, when applying particles other than white as the particles of the non-electrophoretic particle group, for example, the above-described resin particles containing a pigment or dye of a desired color may be used. If a pigment or dye is RGB or YMC color, for example, the general pigment or dye currently used for printing ink or a color toner is mentioned.

The volume average particle diameter of each particle of the non-electrophoretic particle group is, for example, 0.1 μm or more and 1.0 μm or less. The volume average particle diameter of each non-electrophoretic particle is a value measured by an SEM image. The volume average particle diameter of the non-electrophoretic particles is measured in the same manner as the volume average particle diameter of the display particles 11.

In the case of forming an image, the voltage application unit 16 applies a voltage according to the image formed on the display side electrode 40 and the back side electrode 48, and thereby at a position where the image is formed according to the electric field generated in the cell. The migrating particle group 11 is positioned on the corresponding display substrate 20 side to form an image. On the other hand, in a portion where the migrating particle group 11 is located on the back substrate 22 side (non-image forming portion), a white background is displayed by the non-migrating particle group.

In this embodiment, when the migrating particle group 11 and the non-migrating particle group are used in combination, the display particles according to the present embodiment in which the colorant is unevenly distributed in a specific region on the surface side of each particle are used as the migrating particle 11. It is more desirable to use.

The display medium 12 and the display device 10 according to the present embodiment include a bulletin board, a circulation board, an electronic blackboard, an advertisement, a signboard, a flashing sign, electronic paper, an electronic newspaper, an electronic book, or a copying machine that can store and rewrite images. Used for shared document sheets.

The configuration of the display particles, the display medium 12, and the display device 10 described in the present embodiment, the constituent materials of the dispersion medium 50, the migrating particle group 11, and the non-migrating particle group are examples, and depending on the application and the like. You only have to set it.

Further, in the display medium 12 and the display device 10 according to the above-described embodiment, the embodiment in which one type (one color) of particle group is mainly applied as the electrophoretic particle group 11 has been described. It is also possible to adopt a form to which the electrophoretic particle group is applied.

Examples of the present invention will be described below, but the present invention is not limited to the following examples.

<Example 1>
[Preparation of display particles]
1) Preparation of core (core particles) (in-liquid drying method)
Water dispersion Emacol (registered trademark) SF Blue H524F containing 7.2 g of X345 (trade name, manufactured by Seiko PMC) as a water-soluble resin (carboxylic acid) and 26% by mass of cyan pigment PB15: 3 (basic) 18.8 g (trade name, manufactured by Sanyo Color Co., Ltd.) and 24.1 g of distilled water were mixed while heating to 60 ° C., and the ink solid content concentration was 15% by mass and the pigment concentration after drying was 50% by mass. A dispersed phase was prepared as follows.

Next, 3.5 g of surfactant KF-6028 (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in silicone oil KF-96-2cs (trade name, manufactured by Shin-Etsu Chemical Co., Ltd.) to prepare 350 g of a continuous phase. 50 g of the above dispersed phase was added thereto, and emulsification was carried out for 10 minutes at a rotational speed of 10000 rpm and a temperature of 30 ° C. using an internal tooth tabletop disperser ROBOMICS (trade name, manufactured by Tokushu Kika Kogyo Co., Ltd.). As a result, an emulsified liquid having an emulsified droplet diameter of about 2 μm was obtained. This was dried using a rotary evaporator at a vacuum degree of 20 mbar and a water bath temperature of 40 ° C. for 18 hours.

Furthermore, using this silicone oil particle dispersion, the sedimentation step using a centrifuge and the redispersion step using an ultrasonic washer were repeated three times to remove excess surfactant KF-6028, and concentrated to a core. 6 g of particles were obtained. Centrifugation conditions are 15 minutes at 6000 rpm. As a result of SEM observation of the obtained particles and image analysis, the volume average particle size was 0.6 μm and the CV value was 30.

2) Formation of coating (shell) (coacervation method)
50 g of silaplane FM-0721 (trade name, manufactured by JNC) which is a silicone macromonomer, 32 g of hydroxyethyl methacrylate, 18 g of AMP-10G (trade name, manufactured by Shin-Nakamura Chemical Co., Ltd.) containing a phenoxy group, 2 g of Karenz MOI-BP (registered trademark, manufactured by Showa Denko KK), which is a monomer containing a blocked isocyanate group, was mixed and dissolved in 200 g of isopropyl alcohol. 0.2 g of AIBN (2,2′-azobis (isobutyronitrile)) as a polymerization initiator was dissolved in this, and polymerization was carried out at 70 ° C. for 6 hours under nitrogen.
The product was purified and dried using cyclohexane as a reprecipitation solvent to obtain a shell-forming resin. 2 g of this shell forming resin was dissolved in 20 g of t-butanol solvent to prepare a shell forming solution.

1 g of the above core particles was placed in a 200 mL eggplant flask, 15 g of silicone oil KF-96-2cs was added, and the mixture was stirred and dispersed at 25 ° C. while applying ultrasonic waves to obtain a core particle dispersion. To this, 7.5 g of t-butanol, 22 g of the above-mentioned shell forming solution, and 12.5 g of silicone oil KF-96-2cs were sequentially added. The input speed was all 2 mL / s.
The eggplant flask was connected to a rotary evaporator, and t-butanol was removed at a vacuum of 20 mbar and a water bath temperature of 50 ° C. for 1 hour.

This was further heated in an oil bath with stirring. First, after heating at 100 ° C. for 1 hour to remove residual moisture and residual t-butanol, heating is continued at 130 ° C. for 1.5 hours to remove the blocking group of the blocked isocyanate group, thereby forming a shell material. The crosslinking reaction was performed.
After cooling, the silicone oil particle dispersion was subjected to a sedimentation process using a centrifuge and a redispersion process using an ultrasonic cleaner three times to remove excess shell forming resin. The finally obtained cyan particles were 0.6 g.

[Evaluation of particles]
Using the obtained cyan particles, a dispersion for electrophoretic display and an evaluation cell were prepared, and the following evaluation was performed.

(Pigment concentration)
About the actual pigment concentration (substantial amount%) of the obtained cyan particles, when the thermogravimetric decrease was measured by EXSTAR6000 (TG / DTA6200) manufactured by Seiko Instruments Inc., there was a clear difference between the decomposition temperature of the resin component and the pigment component. From the two peak ratios, the pigment concentration was 33% by mass.

(Charge amount)
The obtained cyan particles were diluted to 1% by mass in silicone oil KF-96-2cs to give a dispersion for electrophoretic display, and the opposite electrode was surface-treated with Cytop CTL-809M (trade name, manufactured by Asahi Glass Co., Ltd.). The gap between the electrodes was sealed in an evaluation cell having a thickness of 50 μm. When the charge amount was examined by applying a triangular wave voltage of ± 30 V to this evaluation cell using a liquid crystal cell ion concentration measuring instrument (manufactured by Toyo Technica Co., Ltd.), a stable value of about 7 nC was obtained.

(Electrophoresis threshold)
The migration threshold is measured at the same time as the charge amount, and the reflection spectrum of the cell surface is measured using a fiber optic spectrometer manufactured by Ocean Optics. The saturation optical density at a wavelength of 650 nm is measured for C particles, and the saturation optics at a wavelength of 500 nm for R particles. The concentration was measured, and the suitability of the migration threshold was evaluated according to the following criteria. Note that that the migration threshold value is matched means that the optical density reaches 90% or more of the saturated optical density when 15 V is applied at a gap of 50 μm. An electric field strength of 0.25 V / μm or more is not suitable. When the threshold is too low, there is no memory property, so the display cannot be maintained after the electric field is removed, and 0.10 V / μm or less is out of conformity.
A: 0.20 V / μm or more B: 0.10 V / μm or more and less than 0.20 V / μm C: less than 0.10 V / μm

(Optical density uniformity within the particle)
Further, the uniformity of the optical density of one particle was evaluated by the following method.
Microscopic observation of the core emulsified liquid before drying is performed, a photograph of particles of 3 μm or larger is taken, and the diameter of the particle is measured from the center of a plurality of particles using image analysis software WinROOF (trade name, manufactured by Mitani Corporation). A comparison of the optical density of the part up to 80% was performed. Specifically, the maximum amount of change in the relative optical density represented by the following formula was examined at a wavelength of 650 nm for C particles and at a wavelength of 500 nm for R particles, and evaluated according to the following criteria. Here, the volume average particle size is determined by the method described above, that is, by obtaining an image of 100 particles by SEM (scanning electron microscope S-4800, manufactured by Hitachi High-Technologies Corporation) ) Was measured to determine the volume by spherical diameter conversion, and the value when the accumulation from the first to the 100th became 50% was taken as the volume average particle diameter. The determined volume average particle diameter is set to 100, and a site at a distance X from the center of the particle is represented as “X% site”.
Relative optical density at the X% site from the center = (Optical density at the X% site from the center) / (Maximum optical density from the center to the 80% site)
A: 0.78 or more and 1 or less B: 0.72 or more and less than 0.78 C: 0.70 or more and less than 0.72 D: less than 0.70

(Evaluation of the depth from the surface of the colorant existing area in the particle)
The colorant existing region depth was evaluated by TEM observation. Specifically, 10 particles having a particle diameter of 400 nm to 600 nm are selected from the observation field, and the depth from the particle surface of the region where the colorant is ubiquitous with respect to the particle radius is evaluated by cross-sectional observation of each particle. did. In addition, when cutting during the preparation of the observation sample, considering that the particles are deformed and become elliptical, the volume average particle diameter is obtained as an average value of the diameter of the inscribed circle and the diameter of the circumscribed circle, The ratio of the depth obtained above to the volume average particle diameter was obtained. In addition, there are locations where some of the colorant is thinly distributed inside the particle, but it can be clearly distinguished from the region where the colorant is ubiquitous from the image. Not applicable.

(Evaluation of refractive index difference from dispersion medium)
Based on literature values, the refractive index of air is 1.00, the refractive index of water is 1.30, the refractive index of X345 resin and phthalocyanine pigment is 1.53, and the refractive index of silicone oil is 1.50. The refractive index difference from the particles for use was calculated.

<Examples 2 to 9>
Cyan particles were produced in the same manner as in Example 1 except that the pigment concentration was changed, and evaluated in the same manner as in Example 1.

<Comparative Example 1>
When the pigment concentration at the time of preparing the core of C particles is 80% by mass or more, the actual pigment concentration (substantial amount%) of the obtained cyan particles is not 64% by mass or more. It was found that the center part was uniformly filled.

<Comparative example 2>
-Preparation of dispersion A-1A-
The following ingredients were mixed, and ball milling was performed for 20 hours with 10 mmφ zirconia balls to prepare dispersion A-1A.
-53 parts by weight of methyl methacrylate-0.3 parts by weight of 2- (diethylamino) ethyl methacrylate-R pigment (Red 3090: trade name, manufactured by Sanyo Dye) 1.5 parts by weight

-Preparation of dispersion A-1B (calcium carbonate dispersion A-1B)-
The following components were mixed and finely pulverized with a ball mill in the same manner as described above to prepare a calcium carbonate dispersion A-1B.
・ 40 parts by weight of calcium carbonate ・ 60 parts by weight of water

-Preparation of mixture A-1C-
The following components were mixed, degassed with an ultrasonic machine for 10 minutes, and then stirred with an emulsifier to prepare a mixed solution A-1C.
・ Calcium carbonate dispersion A-1B 60g
・ 20% saline 4g

-Preparation of colored particles-
Dispersion A-1A: 20 g, ethylene glycol dimethacrylate: 0.6 g, polymerization initiator V601 (Dimethyl 2,2′-azobis (2-methylpropionate): trade name, manufactured by Wako Pure Chemical Industries, Ltd.): 0.2 g Were measured, mixed well, and deaerated with an ultrasonic machine for 10 minutes. This was added to the mixed solution A-1C and emulsified for 10 minutes at a rotational speed of 10000 rpm and a temperature of 30 ° C. using an internal tooth tabletop dispersing machine ROBOMICS (trade name, manufactured by Tokushu Kika Kogyo Co., Ltd.). Next, this emulsified liquid was put into a flask, and a silicone bottle was put on it. Using an injection needle, vacuum deaeration was sufficiently performed and sealed with nitrogen gas. Next, it was reacted at 65 ° C. for 15 hours to prepare particles.
After cooling, the particles were filtered, and the obtained particle powder was dispersed in ion-exchanged water, and calcium carbonate was decomposed with hydrochloric acid water, followed by filtration.
Thereafter, it was washed with sufficient distilled water, and sieved through nylon sieves having openings of 5 μm and 1 μm to make the particle sizes uniform. The obtained particles had a volume average primary particle size of 3 μm and an actual pigment concentration of 9.6% by mass. When the charge amount was examined, a value of about 0.8 nC was obtained.
As a result of microscopic observation of the particles, the pigments were ubiquitous randomly in the particles, the omnipresent positions were different depending on the particles, and it was impossible to evaluate the optical density uniformity within the particles.
For this reason, sensory evaluation of the R display surface of the cell using these particles was performed. When the R color was displayed, the color uniformity was poor.

<Comparative Example 3>
-Preparation of aqueous phase-
To 50 g of water, 0.5 g of an aqueous polymerization initiator VA057 (trade name, manufactured by Wako Pure Chemical Industries, Ltd.) and 0.5 g of a reactive surfactant Latemul PD420 (trade name, manufactured by Kao Chemical Co., Ltd.) were added and stirred. The aqueous phase was adjusted.

-Preparation of oil phase-
1 g of surfactant KF-6028 is added to 100 g of silicone oil 10 CS, 5 g of methyl methacrylate and 0.5 g of diethylene glycol dimethacrylate are added as monomers, and solvent soluble blue colorant New Dymic N-DYM8626 (trade name, Dainichi Seika) 5 g) was added and stirred to adjust the oil phase.

-Preparation of colored particles-
The aqueous phase was added to the oil phase, and emulsification was performed for 10 minutes under the conditions of a rotational speed of 10,000 rpm and a temperature of 30 ° C. using an internal tooth tabletop dispersing machine ROBOMICS (trade name, manufactured by Tokushu Kika Kogyo Co., Ltd.). As a result, an emulsion having a volume average particle diameter of about 1 μm was obtained. With this transferred to a sample bottle and capped, the reaction was carried out for 18 hours at a water bath temperature of 65 ° C. As a result of microscopic observation, blue shell capsule particles having an aqueous phase inside were obtained. The thickness of the shell was 40 nm as a result of SEM observation.
Further, the sedimentation step using a centrifugal separator and the redispersion step using an ultrasonic washer are repeated three times for this dispersion of capsule particles to remove excess surfactant KF-6028 and unreacted monomers. 20 g of capsule particles were obtained. Centrifugation is performed at 3000 rpm for 10 minutes. Regarding the pigment concentration in the shell, the obtained capsule particles were heated and dried at 100 ° C. for 1 hour, and subjected to thermal analysis. The pigment concentration was determined in the same manner as other particles, and the pigment concentration was 20% by mass.
The capsule particles were taken out from the dispersion and evaluated in the same manner as the other particles.

<Comparative Example 4>
Cyan particles having a pigment concentration of 27% by mass were prepared in the same manner as in Example 1 except that the pigment concentration was changed. Next, it was heated and dried at 100 ° C. for 1 hour, and the silicone oil present around the particles was removed, and evaluation was performed in the same manner as other particles.

Table 1 shows the structures and evaluation results of the particles prepared in Examples and Comparative Examples.
Moreover, the cross section of the particle | grains manufactured in Example 5 was observed by TEM, and was shown in FIG.

The entire disclosure of Japanese Patent Application No. 2012-089766 is incorporated herein by reference.
All documents, patents, patent applications, and technical standards described herein are specifically and individually described as individual documents, patents, patent applications, and technical standards are incorporated by reference. To the same extent, it is incorporated herein by reference.

Claims

Display particles in which the colorant is unevenly distributed in a region between the surface of the particle and a depth of 5% to 35% of the volume average particle diameter of the particle from the surface toward the center.
The colorant is unevenly distributed in a region between a surface of the display particles and a depth of 12% or more and 23% or less of a volume average particle diameter of the display particles from the surface toward the center. 2. The display particle according to 1.
A core containing a binder resin;
Including a pigment that is the colorant and a dispersant for the pigment, and a covering portion that covers the core portion,
The display particles according to claim 1, wherein one of the binder resin and the dispersant is basic and the other is acidic.
A dispersion medium;
The group of display particles according to any one of claims 1 to 3, dispersed in the dispersion medium,
A dispersion for electrophoretic display.
The dispersion liquid for electrophoretic display according to claim 4, wherein a difference in refractive index between the dispersion medium and the display particles is less than 0.3.
A pair of substrates at least one of which is translucent and disposed with a gap;
The dispersion liquid for electrophoretic display according to claim 4 or 5 enclosed between the pair of substrates,
A display medium comprising:
A pair of electrodes, at least one of which is translucent and disposed with a gap;
A region having the dispersion liquid for electrophoretic display according to claim 4 or 5 between the pair of electrodes,
A display medium comprising:
A display medium according to claim 6 or 7, and
An electric field applying means for applying a voltage between a pair of substrates of the display medium or between the pair of electrodes;
A display device comprising: