JP2010128075A - Display particle for image display device and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide display particles which can lower a driving voltage sufficiently and can repeatedly display an image having a relatively high contrast between an image part and a non-image part, and to provide an image display device equipped with the display particles. <P>SOLUTION: There a re provided the display particles used for the image display device which has electrostatically charged display particles, charged in between two substrates at least one of which is transparent, and moves the display particles, by generating an electric field between the substrates to display an image, the display particles containing display particles having a low resistance core-high resistance cell structure obtained by forming a shell layer 2 on a surface of a core particle 1. Here, the core particle has a volume resistance value of 1×10<SP>5</SP>to 1×10<SP>10</SP>Ω cm and the core particle and shell layer have a total volume resistance value of 1×10<SP>15</SP>to 1×10<SP>20</SP>Ω cm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a display particle and an image display device used in an image display device capable of repeatedly displaying and erasing an image by moving charged display particles by applying an electric field.

  Conventionally, there has been known a system in which charged display particles are enclosed in a gas phase, and a voltage is applied to move the display particles along the electric field direction so that an image can be displayed. In this method, since it is necessary to move the charged display particles along the direction of the electric field formed by applying a voltage between the substrates, a technique for smoothly moving the display particles even under a low applied voltage is required. It was done.

As the display particles, for example, Patent Document 1 proposes to use display particles that make the volume specific resistance of the resin constituting the display particles 1 × 10 ¹⁴ Ω · cm or more. However, since such display particles are polarized by an electric field, the driving voltage cannot be sufficiently reduced. Further, when image display and erasure are repeatedly performed, there is a problem that the contrast between the image portion and the non-image portion is significantly lowered. In particular, since white display particles are highly filled with titanium oxide, which is a high dielectric constant pigment, for whitening of the particles, the polarization in the particles increases, the chargeability decreases, and the drive voltage tends to increase. .
JP 2008-9422 A

  An object of the present invention is to provide a display particle capable of sufficiently reducing a driving voltage and repeatedly displaying an image having a relatively high contrast between an image portion and a non-image portion, and an image display device including the display particle. To do.

  Another object of the present invention is to provide white display particles having both excellent whiteness and a sufficiently low driving voltage.

The present invention provides an image display device that displays an image by moving display particles by encapsulating charged display particles between two substrates, at least one of which is transparent, and generating an electric field between the substrates. A display particle to be used, wherein a shell layer is formed on the surface of the core particle, and the volume resistance value of the core particle is 1 × 10 ⁵ to 1 × 10 ¹⁰ Ω · cm, and the core particle and the shell layer Display particles comprising display particles having a low-resistance core-high-resistance shell structure having an overall volume resistance value of 1 × 10 ¹⁵ to 1 × 10 ²⁰ Ω · cm, and an image including the display particles The present invention relates to a display device.

In the present invention, a shell layer is formed on the surface of the core particle, and the volume resistance value of the core particle is 1 × 10 ⁵ to 1 × 10 ¹⁰ Ω · cm, and the total volume of the core particle and the shell layer is The present invention relates to a white display particle having a low resistance core-high resistance shell structure having a resistance value of 1 × 10 ¹⁵ to 1 × 10 ²⁰ Ω · cm.

  Since the display particles of the present invention have a low resistance core-high resistance shell structure in which a relatively high resistance shell layer is formed on the surface of a relatively low resistance core particle, the display particles have a large dielectric constant and a large polarization. However, the storage time can be shortened by the low resistance core, and as a result, the influence of polarization can be reduced. Further, the charging property of the particles can be ensured by the high resistance shell. Such an effect of the present invention is even more effective particularly in white display particles. As a result, the driving voltage can be sufficiently reduced, and an image having a relatively high contrast between the image portion and the non-image portion can be repeatedly displayed.

[Display particles for image display devices]
The display particles for an image display device according to the present invention include display particles having a predetermined low resistance core-high resistance shell structure.

Having a low resistance core-high resistance shell structure means having a core-shell structure in which a shell layer having a relatively high volume resistance value is formed on the surface of core particles having a relatively low volume resistance value. In the present invention, the volume resistivity of the core particles is 1 × 10 ⁵ to 1 × 10 ¹⁰ Ω · cm, and the entire volume resistivity of the core particles and the shell layer is 1 × 10 ¹⁵ to 1 × 10 ²⁰ Ω · cm. cm. When the display particles include display particles having a low resistance core-high resistance shell structure, even in display particles having a large dielectric constant and a large polarization, the storage time can be shortened by the low resistance core. The influence of polarization can be reduced. Further, the charging property of the particles can be ensured by the high resistance shell. As a result, the drive voltage can be sufficiently reduced, and an image with relatively high contrast between the image portion and the non-image portion can be repeatedly displayed.

  The display particles for an image display device according to the present invention usually contain positively charged display particles and negatively charged display particles. When positively charged display particles and negatively charged display particles are brought into frictional contact with each other by mixing or when they are brought into frictional contact with a reference material such as iron powder (carrier) as a charge imparting material, the positively charged display particles have positive chargeability. And display particles exhibiting negative chargeability. Since these display particles usually have different colors as well as charging polarities, when an electric field is generated between the substrates in the image display device described in detail later, the display particles move and adhere to the upstream substrate in the viewing direction. And the display image can be visually recognized based on the color difference between the display particles remaining and attached on the substrate on the downstream side in the viewing direction. For example, the display image can be visually recognized clearly by setting one of the positively charged display particles and the negatively charged display particles to white and the other to black.

  In the present invention, at least one of such positively charged display particles and negatively charged display particles is a display particle having the above-described low resistance core-high resistance shell structure. For both positively and negatively charged display particles, if the volume resistivity of the core particles is too low or too high, or the overall volume resistance of the core particles and shell layers is too low or too high The driving voltage increases from the beginning, and good contrast and coloring are difficult to obtain. Even if a good contrast and coloring degree are obtained in the initial stage, the contrast and coloring degree deteriorate during durability.

When one of the positively charged display particles and the negatively charged display particles is a display particle having the above-described low resistance core-high resistance shell structure, the other display particle is usually not particularly limited. It may have a shell structure or may have a single layer structure without a shell layer. When the other display particle has a core-shell structure, the volume resistance value of the core particle may be 1 × 10 ⁴ to 1 × 10 ¹⁴ Ω · cm, and the total volume resistance value of the core particle and the shell layer is 1 It may be × 10 ¹⁴ to 1 × 10 ²¹ Ω · cm. From the viewpoint of further reducing the driving voltage at the initial stage and during durability, and further improving the contrast and coloring degree, the other display particles are also preferably display particles having the above-described low-resistance core-high-resistance shell structure. Since both the positively charged display particles and the negatively charged display particles are display particles having the above-described low-resistance core-high-resistance shell structure, the driving voltage is significantly reduced in the initial stage, and good initial contrast, driving voltage, and The coloring degree is effectively maintained even during durability.

When both the positively charged display particles and the negatively charged display particles are display particles having the above-described low resistance core-high resistance shell structure, from the viewpoint of improving contrast, between the positively charged display particles and the negatively charged display particles, When the ratio (positive / negative) of the volume resistance value of the core particles is x, the absolute value of Log ₁₀ x is preferably 7 or less, particularly 2 or less. Also, when the ratio of the overall volume resistivity of the core particles and the shell layer (positive / negative) and y, the absolute value of Log 10 _y is 5 or less, and particularly preferably 2 or less.

When at least one of positively charged display particles and negatively charged display particles, in particular, both are display particles having the above-described low low resistance core-high resistance shell structure, the display particles having the low resistance core-high resistance shell structure are Preferably, the core particles have a volume resistivity of 1 × 10 ⁷ to 1 × 10 ⁹ Ω · cm, and the core particles and the shell layer have a total volume resistivity of 1 × 10 ¹⁶ to 1 × 10 ¹⁹ Ω · cm. cm. In the present invention, from the viewpoint of further reducing the driving voltage at the initial stage and during the endurance and further improving the contrast and coloring degree, both the positively charged display particles and the negatively charged display particles are particularly such low resistance core-high resistance shell. It preferably has a structure. Since both the positively charged display particles and the negatively charged display particles have such a low-resistance core-high-resistance shell structure, the driving voltage is significantly reduced in the initial stage, and the contrast and the coloring degree are significantly improved. Good initial contrast, driving voltage and color are maintained effectively even during durability.

In this specification, the volume resistance value is a value measured by the following method.
A test piece having a diameter of 6 cm and a thickness of 0.5 cm is prepared by filling sample particles in a jig and compressing the sample particles at 500 kgf / cm ² for 1 minute. Next, a flat sample measurement electrode (SME-8311; manufactured by Toa Radio Industry Co., Ltd.) was connected to a super insulation / microammeter (DSM-8103; manufactured by Toa Radio Industry Co., Ltd.), and a test piece was sandwiched between the electrodes. The volume resistance value when a voltage of 100 V is applied is measured in an environment of temperature 20 ° C. and humidity 50%.

For example, the volume resistance value of the core particles can be measured by collecting the core particles produced in the production process of the display particles and using them as sample particles in the measurement method.
Further, for example, the total volume resistance value of the core particles and the shell layer can be measured by using the produced display particles as sample particles in the measurement method. When an external additive is externally added to the display particles, the display particles after the external additive is externally added may be used as the sample particles.

When one or both of the positively charged display particles and the negatively charged display particles are display particles having the low resistance core-high resistance shell structure described above, the display particles having the low resistance core-high resistance shell structure are shown in FIG. From the viewpoint of designing to a desired resistance value, where R1 (μm) is the volume average particle size of the core particle 1 and R2 (μm) is the total volume average particle size of the core particle 1 and the shell layer 2. ,Relational expression;
1.01 ≦ R2 / R1 ≦ 1.50, especially 1.01 ≦ R2 / R1 ≦ 1.10.
It is preferable to satisfy.

The volume average particle diameter R1 (μm) of the core particles is usually 0.5 to 20.0 μm, preferably 2.0 to 10.0 μm.
The total volume average particle diameter R2 (μm) of the core particle and the shell layer is the same as the volume average particle diameter of the display particles in the present specification, and is usually 0.6 to 25.0 μm, preferably 2 .1 to 15.0 μm.

In the present specification, the volume average particle diameter of the core particles and the display particles is a volume-based median diameter (d50 diameter), and an apparatus in which a computer system for data processing is connected to Multisizer 3 (manufactured by Beckman Coulter). Can be used for measurement and calculation.
As a measurement procedure, 0.02 g of sample particles were mixed with 20 ml of a surfactant solution (for dispersing particles, a surfactant solution obtained by diluting a neutral detergent containing a surfactant component 10 times with pure water). After that, ultrasonic dispersion is performed for 1 minute to prepare a particle dispersion. This particle dispersion is poured into a beaker containing ISOTON II (manufactured by Beckman Coulter, Inc.) in a sample stand with a pipette until the measurement concentration reaches 10%, and measurement is performed with a measuring machine count set to 2500 pieces. The aperture size of the multisizer 3 is 50 μm.

For example, the volume average particle diameter of the core particles can be measured by collecting the core particles produced in the production process of the display particles and using them as sample particles in the measurement method.
For example, the volume average particle diameter of the core particles and the shell layer as a whole can be measured by using the produced display particles as sample particles in the measurement method. When an external additive is externally added to the display particles, the display particles after the external additive is externally added may be used as the sample particles.

  In the present invention, one of the positively charged display particles and the negatively charged display particles is preferably white display particles having the low resistance core-high resistance shell structure. In white display particles, a white colorant that is a high dielectric constant pigment, for example, titanium oxide, is highly filled to improve whiteness, so that the polarization in the particles increases and the drive voltage tends to increase relatively. However, in the present invention, even such white display particles can reduce the driving voltage by adopting the low resistance core-high resistance shell structure.

(Manufacture of display particles)
The display particles having the low-resistance core-high-resistance shell structure are formed by forming a shell layer on the surface of the core particles containing at least a binder resin and a colorant, and optionally a resistance adjusting agent. It contains an agent. The charging polarity of the display particles is controlled mainly by selecting a carrier in a method for manufacturing an image display device described later, for example. For example, a carrier having a core surface coated with a fluorinated acrylate resin is usually used for a positively charged display particle. For those used as negatively charged display particles, a carrier having a cyclohexyl methacrylate resin coated on the core surface is used.

The binder resin that constitutes the core particle is not particularly limited, and a polymer called a vinyl resin shown below is typical, and in addition to the vinyl resin, polyamide resin, polyester resin, polycarbonate There are also condensation resins such as resins and epoxy resins. Specific examples of vinyl resins include polystyrene resins, polyacrylic resins, polymethacrylic resins, and polyolefin resins formed from ethylene monomers and propylene monomers. In addition to the above-described condensation resins, resins other than vinyl resins include polyether resins, polysulfone resins, polyurethane resins, fluorine resins, and silicone resins.
The polymer constituting the binder resin that can be used for the core particles is prepared by combining at least one kind of polymerizable monomer that forms these resins, or by combining a plurality of kinds of polymerizable monomers. You can also When a resin is prepared by combining a plurality of types of polymerizable monomers, for example, a method of forming a copolymer such as a block copolymer, a graft copolymer, or a random copolymer, or a mixture of a plurality of types of resins. There is also resin formation by a polymer blending method. As such a copolymer, for example, a styrene / acrylic resin is preferably used.

  The colorant contained in the core particle has a volume resistance value of the core particle and the entire volume resistance value of the core particle and the shell layer within a predetermined range, and is used for positively charged display particles. As long as a colorant having a different color from that used for the negatively charged display particles is used, the colorant is not particularly limited, and various organic or inorganic pigments and dyes can be used.

Examples of the white colorant include zinc white, titanium oxide, antimony white, zinc sulfide, and mixtures thereof, and titanium oxide is preferable.
Examples of the black colorant include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, and a mixture thereof, and carbon black is preferable.
Examples of blue colorants include C.I. I. Pigment blue 15: 3, C.I. I. Pigment Blue 15, Bituminous Blue, Cobalt Blue, Alkaline Blue Lake, Victoria Blue Lake, Phthalocyanine Blue, Metal-free Phthalocyanine Blue, Phthalocyanine Blue Partial Chloride, Fast Sky Blue, Indanthrene Blue BC, and mixtures thereof.
Examples of red colorants include bengara, cadmium red, red lead, mercury sulfide, cadmium, permanent red 4R, risor red, pyrazolone red, watching red, calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, Alizarin Lake, Brilliant Carmine 3B, C.I. I. Pigment Red 2, and mixtures thereof.

Yellow colorants include yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral first yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow G, Benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake, C.I. I. Pigment Yellow 12, and mixtures thereof.
Examples of green colorants include chrome green, chromium oxide, pigment green B, C.I. I. Pigment Green 7, Malachite Green Lake, Final Yellow Green G, and mixtures thereof.
Examples of the orange colorant include red chrome yellow, molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, indanthrene brilliant orange RK, benzidine orange G, indanthrene brilliant orange GK, C.I. I. Pigment Orange 31, and mixtures thereof.
Examples of purple colorants include manganese purple, first violet B, methyl violet lake, and mixtures thereof.

  Examples of extender pigments include barite powder, barium carbonate, clay, silica, white carbon, talc, alumina white, and mixtures thereof. Examples of various dyes such as basic, acidic, disperse, and direct dyes include nigrosine, methylene blue, rose bengal, quinoline yellow, ultramarine blue, and mixtures thereof.

  These pigments can be used alone or in combination. The colorant is appropriately selected and blended to produce display particles having a desired color. Hereinafter, the white display particles and the black display particles will be mainly described. However, the present invention should not be construed as being limited to these combinations.

  By adjusting the type and content of the colorant, the volume resistance value of the core particles and the entire volume resistance value of the core particles and the shell layer can be controlled. The smaller the colorant content, the larger the volume resistance value of the core particles and the entire volume resistance value of the core particles and the shell layer. However, since the degree of coloring decreases, the contrast tends to decrease. Increasing the colorant content decreases the volume resistivity of the core particles and the overall volume resistivity of the core particles and shell layers.

  The content of the colorant in the core particles is not particularly limited as long as the volume resistance value of the core particles and the entire volume resistance value of the core particles and the shell layer can be controlled within a predetermined range. From the viewpoint of the control of the volume resistivity of the core particles and the entire volume resistivity of the core particles and the shell layer, and the balance between reduction of driving voltage and improvement of contrast and coloring, In the case of a white colorant, the amount is usually 10 to 250 parts by weight, preferably 50 to 200 parts by weight. In the case of a black colorant, it is usually 1 to 100 parts by weight, preferably 2 to 60 parts by weight.

For details on the content of the colorant in the white particles in the white display particles, for example, when rutile titanium oxide is used together with a styrene / acrylic copolymer resin as a binder resin, On the other hand, it is usually 10 to 225 parts by weight, preferably 50 to 180 parts by weight.
For example, when anatase type titanium oxide is used together with a styrene / acrylic copolymer resin as a binder resin, the content in the core particles is usually 10 to 250 weights with respect to 100 parts by weight of the binder resin of the core particles. Part, preferably 50 to 200 parts by weight.

  Regarding the content in the core particles of the colorant in the black display particles, specifically, for example, when carbon black is used together with a styrene / acrylic copolymer resin as a binder resin, it is based on 100 parts by weight of the binder resin of the core particles. The amount is usually 1 to 90 parts by weight, preferably 2 to 60 parts by weight.

  The average primary particle size of the colorant is not particularly limited as long as the coloring power can be exerted, and usually 1 to 500 nm, particularly 100 to 350 nm is preferable in the case of the white colorant, and 1 to 500 nm in the case of the black colorant. 5-100 nm is particularly preferable.

In this specification, the average primary particle size is a value measured by the following method.
In a scanning electron microscope (commonly known as SEM), a photograph is taken at 10,000 times, and an average value of 100 particles of an actual image is used.

  When the resistance adjusting agent is contained in the core particle, the volume resistance value of the core particle and the entire volume resistance value of the core particle and the shell layer can be reduced and adjusted within a predetermined range. Specific examples of such resistance adjusting agents include, for example, conductivity such as phosphorus-tin oxide, antimony-tin oxide, indium-tin oxide, aluminum-doped zinc oxide, gallium-doped zinc oxide, tin oxide, and carbon black. Materials, mixtures thereof, etc. can be used. The resistance adjuster is not particularly limited when a black colorant is used. However, when a colorant of another color, particularly a white colorant is used, the resistance adjuster is preferably colorless and transparent, for example, indium-tin. Oxides and aluminum-doped zinc oxide are preferably used.

  By adjusting the content of the resistance adjusting agent, the volume resistance value of the core particles and the entire volume resistance value of the core particles and the shell layer can be controlled. For example, the larger the resistance adjuster content, the smaller the volume resistance value of the core particles and the total volume resistance value of the core particles and the shell layer. The smaller the resistance adjuster content, the larger the volume resistance value of the core particles and the entire volume resistance value of the core particles and the shell layer.

  The content of the resistance adjusting agent in the core particles is not particularly limited as long as the volume resistance value of the core particles and the entire volume resistance value of the core particles and the shell layer can be controlled within a predetermined range. From the viewpoint of the control of the volume resistivity of the core particles and the entire volume resistivity of the core particles and the shell layer, and the balance between reduction of driving voltage and improvement of contrast and coloring, In the case of white display particles, it is usually 1 to 200 parts by weight, preferably 5 to 150 parts by weight. In the case of black display particles, it is usually 100 parts by weight or less, preferably 60 parts by weight or less.

Specifically, the content of the resistance adjusting agent in the white display particles in the core particles is, for example, aluminum-doped titanium oxide, 100 parts by weight of styrene / acryl copolymer resin as binder resin, and 10 to 225 parts by weight of rutile titanium oxide. When using together, it is 1-180 weight part normally with respect to 100 weight part of binder resin of a core particle, Preferably it is 5-120 weight part.
For example, when aluminum-doped zinc oxide is used together with 100 parts by weight of a styrene / acrylic copolymer resin as a binder resin and 10 to 225 parts by weight of rutile titanium oxide, the content in the core particles is the binder resin of the core particles. Usually, it is 1-150 weight part with respect to 100 weight part, Preferably it is 5-100 weight part.

Regarding the content of the resistance adjusting agent in the black particles in the core particles, for example, when carbon black is used as the resistance adjusting agent, since carbon black also functions as a colorant, styrene / acrylic copolymer as a binder resin is used. The amount is usually 30 to 100 parts by weight, preferably 40 to 100 parts by weight with respect to 100 parts by weight of the combined resin.
For example, when aluminum-doped zinc oxide is used together with 100 parts by weight of a styrene / acrylic copolymer resin as a binder resin and 1 to 20 parts by weight of carbon black, the content in the core particles is 100 parts by weight of the binder resin of the core particles. Usually, it is 1-150 weight part with respect to part, Preferably it is 5-100 weight part.

  The average primary particle size of the resistance adjusting agent is not particularly limited as long as the predetermined volume resistance value can be controlled, and usually 1 to 500 nm, particularly 10 to 300 nm is preferable.

Other additives such as a charge control agent may be internally added to the core particles.
In the case of white display particles, for example, as a positively chargeable charge control agent, diglocin dyes, triphenylmethane compounds, quaternary ammonium salt compounds, polyamine resins, imidazole derivatives, and the like can be used.
In the case of black display particles, for example, salicylic acid metal complexes, metal-containing azo dyes, quaternary ammonium salt compounds, calixarene compounds, nitroimidazole derivatives, and the like can be used as negatively chargeable charge control agents.

The method for producing the core particles is not particularly limited, and for example, a known method for producing particles containing at least a resin and a colorant, such as a method for producing a toner used for electrophotographic image formation, is applied. It is possible to cope with it. Specific examples of the method for producing the core particles include the following methods.
(A1) A method of producing core particles by mixing and kneading at least a binder resin and a colorant and, if desired, a kneading agent, and then performing pulverization and classification steps;
(A2) At least a polymerizable monomer and a colorant for producing a binder resin in an aqueous medium, and optionally a resistance adjuster are mechanically stirred to form droplets, and then polymerized to form core particles. Is a so-called suspension polymerization method.
(A3) After dropping a polymerizable monomer for producing a binder resin into an aqueous medium containing a surfactant and carrying out a polymerization reaction in a micelle to produce 100 to 150 nm polymer particles. A so-called emulsion association method in which core particles are produced by adding colorant particles and aggregating agent and, if desired, resistance adjusting agent particles, and associating these particles.

  The shell layer is made of a resin that can be used as a binder resin for the core layer.

  The form of the shell layer may have the form of a particle layer in which an interface exists between resin particles (hereinafter referred to as shell particles), the form of a continuous phase of the resin, or You may have those composite forms.

The method for forming the shell layer is not particularly limited, and examples thereof include the following methods.
(B1) A method of forming a shell layer in the form of a particle layer by fixing the shell particles on the surface of the core particles by mixing the core particles and the shell particles and optionally additives with a mixing apparatus such as a hybridization system;
(B2) The core particles having the shell layer formed by the method of (B1) above are subjected to instantaneous heat treatment with a surfing system (manufactured by Nippon Pneumatic Industry Co., Ltd.), etc., so that the shell particles on the surface of the core particles are continuously Forming a shell layer in the form of a continuous phase into a phase;
(B3) Core-shell particle preparation method by so-called emulsion association method; specifically, first, a polymerizable monomer for producing a shell particle binder resin is dropped into an aqueous medium containing a surfactant, and micelles are obtained. Polymerization reaction is carried out in it to produce polymer particles (shell particles) of 100 to 150 nm. Next, the shell particles are dropped into the core particle dispersion and associated to obtain core-shell particles.

  By adjusting the thickness of the shell layer, the entire volume resistance value and volume average particle diameter of the core particles and the shell layer can be controlled. For example, the larger the thickness, the larger the volume resistance value and the volume average particle diameter of the core particles and the shell layer. The smaller the thickness, the smaller the volume resistance value and the volume average particle diameter of the core particles and the shell layer.

  The thickness of the shell layer can be produced by adjusting the amount of shell particles used and the shell layer forming conditions when forming the shell layer, and is usually 0.01 to 500 μm, preferably 0.01 to 1.00 μm.

  The amount of the shell particles used is not particularly limited as long as the entire volume resistance value of the core particles and the shell layer can be controlled within a predetermined range. From the viewpoint of controlling the overall volume resistance of the core particles and the shell layer, and balancing the reduction in driving voltage and the improvement in contrast and coloring, the amount of shell particles used is white relative to 100 parts by weight of the core particles. In the case of display particles, it is usually 1 to 300 parts by weight, preferably 5 to 150 parts by weight. In the case of black display particles, it is usually 1 to 300 parts by weight, preferably 5 to 150 parts by weight.

  The average particle size of the shell particles is preferably 1 to 350 nm, more preferably 50 to 250 nm.

  The shell layer may contain an additive such as the above-described resistance adjusting agent, if desired. By including the resistance adjusting agent in the shell layer, the entire volume resistance value of the core particles and the shell layer can be reduced.

The display particles of the present invention are usually used by adding and mixing external additives to the core particles having the shell layer formed as described above.
As the external additive, conventionally known external additives are used in the field of display particles of an image display device, and examples thereof include silica and titania.

  The external additive is preferably used after being surface-treated with a hydrophobizing agent from the viewpoint of reducing physical adhesion between the display particles and between the display particles and the electrode. As the hydrophobizing agent, known hydrophobizing agents used for surface treatment of inorganic fine particles externally added in the field of display particles can be used, and examples thereof include aminosilane coupling agents, disilazane compounds, and silicone oils. .

  The average primary particle size of the external additive is 10 to 200 nm, preferably 30 to 100 nm.

  The addition amount of the external additive is not particularly limited, and is preferably 0.1 to 20 parts by weight, particularly preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the core particles on which the shell layer is formed.

[Image display device]
An image display device according to the present invention is characterized by including the above-described display particles. Hereinafter, the image display apparatus of the present invention will be described in detail.

  The image display device according to the present invention encloses the display particles described above between two substrates, at least one of which is transparent, and generates an electric field between the substrates, thereby moving the display particles in the gas phase to generate an image. Is displayed.

  FIG. 2 shows a typical cross section of the image display apparatus according to the present invention. FIG. 2A shows a structure in which an electrode 15 having a layer structure is provided on the substrates 11 and 12 and an insulating layer 16 is provided on the surface of the electrode 15. The image display device shown in FIG. 2 (b) has a structure in which no electrode is provided in the device, and an electric field is applied through an electrode provided outside the device so that the display particles can be moved. It is. The same reference numerals in FIGS. 2A and 2B denote the same members. FIG. 2 is meant to include FIGS. 2 (a) and 2 (b). As shown in the figure, the image display device 10 in FIG. 2 is supposed to visually recognize an image from the substrate 11 side. However, in the present invention, the image display device 10 is not limited to the one that visually recognizes an image from the substrate 11 side. Further, the type shown in FIG. 2B has an advantage that the structure of the device can be simplified and the manufacturing process can be shortened because the electrode 15 is not provided on the device itself. FIG. 4 shows a state in which voltage application is performed by setting the image display device 10 of the type shown in FIG. The cross-sectional configuration of the image display apparatus according to the present invention is not limited to that shown in FIGS. 2 (a) and 2 (b).

  At the outermost part of the image display device 10 in FIG. 2 (a), two substrates 11 and 12 that are casings constituting the image display device are arranged to face each other. In the substrates 11 and 12, an electrode 15 for applying a voltage is provided on the surface on which both faces each other, and an insulating layer 16 is provided on the electrode 15. The substrates 11 and 12 are provided with an electrode 15 and an insulating layer 16, and display particles exist in a gap 18 formed by facing the surfaces having the electrode 15 and the insulating layer 16. The image display apparatus 10 shown in FIG. 2 has a gap between two types of display particles, which are negatively charged black display particles (hereinafter referred to as black particles) 21 and positively charged white display particles (hereinafter referred to as white particles) 22 as display particles. 18 is present. Further, in the image display device 10 of FIG. 2, the gap 18 is surrounded by the substrates 11 and 12 and the two partition walls 17, and the display particles are present in a state of being enclosed in the gap 18 in the form of powder. is doing.

  The thickness of the gap 18 is not particularly limited as long as the enclosed display particles can move and maintain the contrast of the image, and is usually 10 μm to 500 μm, preferably 10 μm to 100 μm. The volume occupation ratio of the display particles in the gap 18 is 5% to 70%, preferably 30% to 60%. By setting the volume occupancy of the display particles within the above range, the display particles can move smoothly in the gap 18 and an image with good contrast can be obtained.

Next, the behavior of display particles in the gap 18 of the image display device 10 will be described.
In the image display device according to the present invention, when a voltage is applied between two substrates to form an electric field, the charged display particles move along the electric field direction. In this way, by applying a voltage between the substrates on which display particles exist, the charged display particles move between the substrates to perform image display.

The image display in the image display apparatus according to the present invention is performed by the following procedure.
(1) The display particles used as the display medium are charged by a known method such as frictional charging with a carrier.
(2) Display particles are sealed between two opposing substrates, and a voltage is applied between the substrates in this state.
(3) An electric field is formed between the substrates by applying a voltage between the substrates.
(4) The display particles are attracted to the surface of the substrate along the direction of the electric field opposite to the polarity of the display particles by the action of the electric field force between the electrodes, so that image display can be performed.
(5) Further, the moving direction of the display particles is switched by changing the electric field direction between the substrates. The image display can be changed variously by switching the moving direction.

  The display particles can be charged by the above-described known methods, for example, a method in which the display particles are charged by contact with a carrier by frictional charging, or two color display particles having different charging polarities are mixed and stirred. In the present invention, it is preferable to use a carrier and enclose the charged display particles in a substrate.

Examples of the movement of the display particles accompanying voltage application between the substrates are shown in FIGS.
FIG. 3A shows a state before a voltage is applied between the substrates 11 and 12, and the positively charged white particles 22 exist in the vicinity of the viewing-side substrate 11 before the voltage is applied. In this state, the image display device 10 displays a white image. FIG. 3B shows a state after a voltage is applied to the electrode 15, and the black particles 21 that are negatively charged by applying a positive voltage to the substrate 11 are located near the substrate 11 on the viewing side. The white particles 22 have moved to the substrate 12 side. In this state, the image display device 10 displays a black image.

  FIG. 4 shows a state before the voltage is applied in this state in which the image display device 10 shown in FIG. 2B is set to the voltage application device 30 having no electrode (FIG. 4A). ) And the state after the voltage is applied (FIG. 4B). In the image display device 10 of the type shown in FIG. 2B, the black particles 21 negatively charged by applying a positive voltage to the substrate 11 as well as the image display device 10 having the electrode 15 are in the vicinity of the substrate 11 on the viewing side. The positively charged white particles 22 have moved to the substrate 12 side.

  Next, the substrates 11 and 12, the electrode 15, the insulating layer 16, and the partition wall 17 constituting the image display device 10 illustrated in FIG. 2 will be described.

  First, the substrates 11 and 12 constituting the image display device 10 will be described. In the image display device 10, the observer visually recognizes the image formed by the display particles from at least one side of the substrates 11 and 12, and therefore the substrate provided on the side viewed by the observer is required to be made of a transparent material. . Therefore, the substrate used on the side where the observer visually recognizes the image is preferably a light-transmitting material having a visible light transmittance of 80% or more, for example, and has a visible light transmittance of 80% or more. Sex is obtained. Of the substrates constituting the image display device 10, the material of the substrate provided on the opposite side of the image viewing side is not necessarily transparent.

The thickness of each of the substrates 11 and 12 is preferably 2 μm to 5 mm, and more preferably 5 μm to 2 m.
m is more preferable. When the thicknesses of the substrates 11 and 12 are in the above range, sufficient strength can be given to the image display device 10 and the distance between the substrates can be kept uniform. In addition, since the image display device can be provided in a compact and lightweight manner by setting the thickness of the substrate within the above range, the use of the image display device in a wide field is promoted. Further, by setting the thickness of the substrate on the side where the image is viewed to be in the above range, the display image can be accurately viewed without impeding the display quality.

  Examples of the material having a visible light transmittance of 80% or more include an inorganic material having no flexibility such as glass and quartz, an organic material typified by a resin material described later, a metal sheet, and the like. Among these, organic materials and metal sheets can impart a certain degree of flexibility to the image display device. Examples of the resin material having a visible light transmittance of 80% or more include polyester resins typified by polyethylene terephthalate and polyethylene naphthalate, polycarbonate resins, polyethersulfone resins, and polyimide resins. . In addition, a transparent resin obtained by radical polymerization of a vinyl polymerizable monomer such as an acrylic resin or a polyethylene resin, which is a polymer of acrylic acid ester or methacrylic acid ester represented by polymethyl methacrylate (PMMA). It is done.

  The electrode 15 is provided on the surfaces of the substrates 11 and 12, and forms an electric field between the substrates, that is, the gap 18 by applying a voltage. As with the above-described substrate, it is necessary to provide a transparent electrode 15 on the side where the observer visually recognizes the image.

  The thickness of the electrode provided on the side for visually recognizing the image is required to ensure conductivity and at a level that does not hinder the light transmittance. Specifically, the thickness is preferably 3 nm to 1 μm, and preferably 5 nm to 400 nm. More preferred. Note that the visible light transmittance of the electrode provided on the side where the image is viewed is preferably 80% or more, like the substrate. The thickness of the electrode provided on the side opposite to the side where the image is viewed is also preferably within the above range, but it is not necessary to be transparent.

  Examples of the constituent material of the electrode 15 include metal materials, conductive metal oxides, and conductive polymer materials. Specific examples of the metal material include aluminum, silver, nickel, copper, and gold. Specific examples of the conductive metal oxide include indium tin oxide (ITO), indium oxide, and antimony tin. An oxide (ATO), a tin oxide, a zinc oxide, etc. are mentioned. Furthermore, examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, and the like.

  As a method of forming the electrode 15 on the substrate 11 or 12, for example, when an electrode on a thin film is provided, a sputtering method, a vacuum evaporation method, a chemical vapor deposition method (CVD method), a coating method, or the like can be used. Can be mentioned. There is also a method of forming an electrode by mixing a conductive material with a solvent or a binder resin and applying the mixture to a substrate.

  The insulating layer 16 is provided on the surface of the electrode 15 and is in contact with the display particles 21 and 22 on the surface of the insulating layer 16. The insulating layer 16 has a role of relaxing the change in the charge amount by the voltage applied when the display particles 21 and 22 are moved. Further, by imparting a resin having a highly hydrophobic structure and unevenness, it is possible to reduce the physical adhesion with the display particles and to reduce the driving voltage. The material constituting the insulating layer 16 is an electrically insulating material that can be made into a thin film, and has transparency as desired. The insulating layer provided on the image viewing side preferably has a visible light transmittance of 80% or more, like the substrate. Specific examples include silicone resin, acrylic resin, and polycarbonate resin.

  The thickness of the insulating layer 16 is preferably 0.01 μm or more and 10.0 μm or less. That is, when the thickness of the insulating layer 16 is in the above range, the display particles 21 and 22 can move without applying a very large voltage between the electrodes 15. For example, a voltage at a level applied in image formation by electrophoresis is applied. It is preferable because the image can be displayed by applying.

  The partition wall 17 secures the space 18 between the upper and lower substrates, and can be formed not only at the edges of the substrates 11 and 12 but also inside as needed, as shown in the right and left diagrams in the upper part of FIG. . The width of the partition wall 17, particularly the thickness of the partition wall on the image display surface 18 a side, is preferably as thin as possible from the viewpoint of ensuring the clarity of the display image, as shown in the right side of FIG.

The partition walls 17 formed inside the substrates 11 and 12 may be formed continuously or intermittently in the front and back directions in the right and left drawings in the upper part of FIG.
By controlling the shape and arrangement of the partition walls 17, the cells in the gap 18 partitioned by the partition walls 17 can be arranged in various shapes. An example of the shape and arrangement of the cells when the gap 18 is viewed from the viewing direction of the substrate 11 is shown in the lower diagram of FIG. As shown in the lower drawing of FIG. 5, a plurality of cells can be arranged in a rectangular shape, a triangular shape, a line shape, a circular shape, a hexagonal shape or the like in a honeycomb shape or a mesh shape.

  The partition wall 17 can be formed, for example, by processing the substrate on the side opposite to the side on which the image is viewed using the following method. Examples of the method for forming the partition wall 17 include embossing with a resin material or the like, uneven formation by hot press injection molding, photolithography, screen printing, and the like.

The image display device according to the present invention can be manufactured by the following electrophotographic development system.
An electrode 15 and, if desired, an insulating layer 16 are formed on the two substrates 11 and 12 to obtain a pair of substrates with electrodes. By mixing the display particles 21 and the carrier 210, the display particles 21 are negatively charged, and the mixture (21, 210) is placed on a conductive stage 100 as shown in FIG. The substrate is placed at a predetermined interval from the stage 100. Next, as shown in FIG. 6A, a positive direct current voltage and an alternating current voltage are applied to the electrode 15 to attach negatively charged display particles 21 on the insulating layer 16. Next, the display particles 22 and the carrier 220 are mixed to positively charge the display particles 22, and the mixture (22, 220) is placed on the conductive stage 100 as shown in FIG. The electrode-attached substrate to which the display particles are attached is placed at a predetermined interval from the stage 100. Next, as shown in FIG. 6B, a negative DC voltage and an AC voltage are applied to the electrode 15 to attach the positively charged display particles 22 on the adhesion layer of the negatively charged display particles 21. As shown in FIG. 6C, the substrate with one electrode to which the negatively charged display particles and the positively charged display particles are attached and the other electrode-attached substrate are adjusted by a partition so as to have a predetermined interval. Then, the image display device can be obtained by stacking and bonding the periphery of the substrate.

Further, it can be manufactured by another embodiment of the electrophotographic developing system described below.
An electrode 15 and, if desired, an insulating layer 16 are formed on the two substrates 11 and 12 to obtain a pair of substrates with electrodes. The display particles 21 are negatively charged by mixing the display particles 21 and the carrier 210, and the mixture (21, 210) is placed on the conductive stage 100 as shown in FIG. The substrate is placed at a predetermined interval from the stage 100. Next, as shown in FIG. 7A, a positive DC voltage and an AC voltage are applied to the electrode 15, and the negatively charged display particles 21 are adhered on the insulating layer 16.
By mixing the display particles 22 and the carrier 220, the display particles 22 are positively charged, and the mixture (22, 220) is placed on the conductive stage 100 as shown in FIG. The substrate is placed at a predetermined interval from the stage 100. Next, as shown in FIG. 7B, a negative DC voltage and an AC voltage are applied to the electrode 15 to attach the positively charged display particles 22 on the insulating layer 16. As shown in FIG. 7 (c), the electrode-attached substrate to which the negatively charged display particles are attached and the electrode-attached substrate to which the positively charged display particles are attached are adjusted with a partition so as to be a predetermined interval. Thus, the periphery of the substrate can be adhered to obtain an image display device.

[Production of white particles W1, W2]
The following resin, colorant, and resistance adjuster were charged into a Henschel mixer (Mitsui Miike Mining Co., Ltd.), and the peripheral speed of the stirring blade was set to 25 m / second to perform a mixing treatment for 5 minutes to obtain a mixture.
Styrene acrylic resin (weight average molecular weight 20,000) 100 parts by weight Rutile type titanium oxide (average primary particle size 150 nm) 150 parts by weight Aluminum-doped titanium oxide (average primary particle size 30 nm) 100 parts by weight And then coarsely pulverized with a hammer mill, then coarsely pulverized with a turbo mill (manufactured by Turbo Kogyo Co., Ltd.), and further subjected to fine powder classification with an airflow classifier utilizing the Coanda effect. White particles W1 having a diameter of 10.00 μm were produced. The obtained particles were used as core particles. The volume resistance value of the core particles was measured by the method described above.

  White particles W1 (100 parts by weight) and 8.6 parts by weight of polystyrene fine particles having an average particle size of 100 nm were mixed for 3 minutes with an OM Tizer (manufactured by Nara Machinery Co., Ltd.) of a hybridization system, and further the hybridization system The white particles W2 having a volume average particle size of 10.50 μm were produced by treating the polystyrene fine particles on the surface of the white particles W1 and combining them with a hybridizer of 10000 rpm for 5 minutes. The volume resistance value of the obtained white particles was measured by the method described above.

[Production of white particles W3]
White particles W3 having a volume average particle size of 10.50 μm were obtained by the same method as the method for producing white particles W2, except that 50 parts by weight of aluminum-doped zinc oxide was used as a resistance adjuster during the production of white particles W1. .

[Production of white particles W4]
White particles W4 having a volume average particle size of 10.50 μm were obtained by the same method as the method for producing white particles W2, except that 150 parts by weight of aluminum-doped zinc oxide was used as a resistance adjuster during the production of white particles W1. .

[Production of white particles W5]
White particles W5 having a volume average particle diameter of 10.50 μm were obtained by the same method as the method for producing white particles W2, except that the resistance adjuster was not used during the production of white particles W1.

[Production of white particles W6]
White particles W6 having a volume average particle size of 10.10 μm were obtained by the same method as the production method of white particles W2, except that 3.0 parts by weight of polystyrene fine particles having an average particle size of 100 nm were used.

[Production of white particles W7]
The volume average particle diameter is 15.00 μm by the same method as the production method of the white particles W2, except that 8.6 parts by weight of polystyrene fine particles having an average particle diameter of 100 nm are changed to 250 parts by weight of polystyrene fine particles having an average particle diameter of 300 nm. White particles W7 were obtained.

[Production of white particles W8]
White particles W8 having a volume average particle size of 10.06 μm were obtained by the same method as the method for producing white particles W2, except that 2.0 parts by weight of polystyrene fine particles having an average particle size of 100 nm were used.

[Production of white particles W9]
A volume average particle diameter of 15.30 μm is obtained by the same method as the production method of the white particles W2, except that 8.6 parts by weight of polystyrene fine particles having an average particle diameter of 100 nm are changed to 280 parts by weight of polystyrene fine particles having an average particle diameter of 300 nm. White particles W9 were obtained.

[Production of white particles W10]
White particles W10 having a volume average particle size of 10.50 μm were obtained by the same method as the method for producing white particles W2, except that 200 parts by weight of aluminum-doped zinc oxide was used as a resistance adjuster during the production of white particles W1. .

[Production of white display particles W1 to W10 (positively charged display particles)]
Silica particles having an average primary particle size of 15 nm (hydrophobicity of 77%) obtained by treating 100 parts by weight of predetermined white particles W1 to W10 with positively charged inorganic fine particles and aminosilane coupling agent (aminopropyltrimethoxysilane). 1.2 parts by weight), is added to a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.), the peripheral speed of the stirring blade is set to 55 m / second, and mixed for 30 minutes. Manufactured.

[Production of black particles Bk1, Bk2]
The resin and carbon black described below were put into a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.), the peripheral speed of the stirring blade was set to 25 m / sec, and the mixture was mixed for 5 minutes to obtain a mixture.
Styrene acrylic resin (weight average molecular weight 20,000) 100 parts by weight Carbon black (average primary particle size 25 nm) 50 parts by weight The above mixture is kneaded with a twin-screw extrusion kneader, then coarsely pulverized with a hammer mill, and then turbo milled. Coarse powder was pulverized by a machine (manufactured by Turbo Kogyo Co., Ltd.), and further finely classified by an airflow classifier utilizing the Coanda effect, to produce black particles Bk1 having a volume average particle diameter of 10.00 μm. The obtained particles were used as core particles. The volume resistance value of the core particles was measured by the method described above.

  Black particles Bk1 (100 parts by weight) and 17 parts by weight of polystyrene fine particles having an average particle diameter of 160 nm were mixed for 3 minutes with an OM Tizer (manufactured by Nara Machinery Co., Ltd.) of the hybridization system, and further hybridized with the hybridization system. Black particles Bk2 having a volume average particle size of 10.30 μm were produced by treating with a tether for 10,000 minutes for 5 minutes to coalesce and combine polystyrene fine particles on the surface of black particles Bk1.

[Production of black particles Bk3]
Black particles Bk3 having a volume average particle size of 10.30 μm were obtained by the same method as the method for producing black particles Bk2, except that the amount of carbon black was changed to 10 parts by weight when producing black particles Bk1.

[Production of black particles Bk4]
A black particle Bk4 having a volume average particle size of 10.30 μm was obtained by the same method as the method for producing the black particle Bk2, except that 200 parts by weight of aluminum-doped zinc oxide was used as a resistance adjuster during the production of the black particle Bk1. .

[Production of black display particles Bk1 to Bk4 (negatively charged display particles)]
Silica particles having an average primary particle diameter of 15 nm (hydrophobic degree: 92%) obtained by treating 100 parts by weight of predetermined black particles Bk1 to Bk4 with silazane coupling agent (Mexamethyldisilazane) as negatively chargeable inorganic fine particles 1.2 parts by weight), is added to a Henschel mixer (made by Mitsui Miike Mining Co., Ltd.), the peripheral speed of the stirring blade is set to 55 m / second, and mixed for 30 minutes, and the black display particles Bk1 to Bk4 are mixed. Manufactured.

[Carrier A for charging white display particles]
Two parts by weight of fluorinated acrylate resin particles are added to 100 parts by weight of the ferrite core having an average particle diameter of 80 μm, and these raw materials are put into a horizontal rotary blade type mixer so that the peripheral speed of the horizontal rotary blade is 8 m / sec. After mixing and stirring at 22 ° C. for 10 minutes under the conditions, the carrier A was manufactured by heating to 90 ° C. and stirring for 40 minutes.

[Carrier B for charging black display particles]
Conditions in which 2 parts by weight of cyclohexyl methacrylate resin particles are added to 100 parts by weight of ferrite core having an average particle diameter of 80 μm, and these raw materials are put into a horizontal rotary blade type mixer so that the peripheral speed of the horizontal rotary blade is 8 m / sec. Was mixed and stirred at 22 ° C. for 10 minutes, and then heated to 90 ° C. and stirred for 40 minutes to produce Carrier B.

<Example 1>
[Manufacture of image display devices]
The image display device was manufactured according to the following method so as to have the same structure as that shown in FIG. Two glass substrates 11 having a length of 80 mm, a width of 50 mm, and a thickness of 0.7 mm are prepared, and each substrate surface is made of an indium tin oxide (ITO) film (resistance 30 Ω / □) having a thickness of 300 nm. The electrode 15 was formed by a vapor deposition method. On the electrode, a coating solution prepared by dissolving 12 g of polycarbonate resin in a mixed solvent of 80 ml of tetrahydrofuran and 20 ml of cyclohexanone is applied by spin coating to form an insulating layer 16 having a thickness of 3 μm. Got.

  The display particles were charged by mixing the black display particles Bk2 (1 g) and the carrier B (9 g) with a shaker (manufactured by YS-LD Co., Ltd., Yayoi) for 30 minutes. As shown in FIG. 7A, the obtained mixture (21, 210) was placed on a conductive stage 100, and one substrate with electrodes was placed at an interval of about 2 mm from the stage 100. Between the electrode 15 and the stage 100, a DC bias of +50 V, an AC bias of 2.0 kV, and a frequency of 2.0 kHz were applied for 10 seconds to deposit the black display particles 21 on the insulating layer 16.

  The display particles were charged by mixing the white display particles W2 (1 g) and the carrier A (9 g) with a shaker (manufactured by YS-LD Co., Ltd., Yayoi) for 30 minutes. The obtained mixture (22, 220) was placed on a conductive stage 100 as shown in FIG. 7B, and the other electrode-attached substrate was placed at an interval of about 2 mm from the stage 100. White display particles 22 were deposited on the insulating layer 16 by applying a DC bias of −50 V, an AC bias of 2.0 kV, and a frequency of 2.0 kHz between the electrode 15 and the stage 100.

  As shown in FIG. 7 (c), the substrate with electrodes to which black display particles are attached and the substrate with electrodes to which white display particles are attached are adjusted and overlapped with a partition so as to have an interval of 50 μm. Were bonded with an epoxy adhesive to obtain an image display device. The volume occupation ratio between the two types of display particles between the glass substrates was 50%. The content ratio of the white display particles and the black display particles is approximately 1/1 in the number ratio of the white display particles / black display particles.

<Examples 2 to 11 / Comparative Examples 1 to 3>
An image display device was produced in the same manner as in Example 1 except that the white display particles and black display particles shown in Table 1 were used.

＜評価＞
画像表示装置に対して以下の手順で直流電圧を印加し、電圧印加により得られる表示画像の反射濃度を測定することにより、表示特性を評価した。尚、電圧印加は、以下の手順で行い、印加電圧を０Ｖからプラス側に変化させた後、続いてマイナス側に変化させ、再び０Ｖに戻る経路（１サイクル）のヒステリシス曲線を描く様に電圧を印加した。すなわち、
（１）０Ｖから＋２５０Ｖまで５０Ｖ間隔で電圧を変化させながら印加を行う。
（２）＋２５０Ｖから−２５０Ｖまで５０Ｖ間隔で電圧を変化させながら印加を行う。
（３）−２５０Ｖより０Ｖまで５０Ｖ間隔で電圧を変化させながら印加を行う。
上記手順で各画像表示装置に直流電圧を印加したところ、白表示の状態でプラスの電圧を印加した時に、表示が白から黒に変化することが確認された。なお、画像表示装置の視認方向上流側の電極に印加する電圧を変化させ、他方の電極は電気的に接地させた。濃度は、反射濃度計「ＲＤ−９１８（マクベス社製）」を用いて測定した。

<Evaluation>
The display characteristics were evaluated by applying a DC voltage to the image display device according to the following procedure and measuring the reflection density of the display image obtained by the voltage application. The voltage is applied in the following procedure. After changing the applied voltage from 0V to the plus side, the voltage is changed to the minus side, and the voltage is drawn so as to draw a hysteresis curve of the path (1 cycle) returning to 0V again. Was applied. That is,
(1) Application is performed while changing the voltage from 0V to + 250V at intervals of 50V.
(2) Application is performed while changing the voltage from + 250V to -250V at intervals of 50V.
(3) Application is performed while changing the voltage from −250V to 0V at intervals of 50V.
When a DC voltage was applied to each image display device according to the above procedure, it was confirmed that the display changed from white to black when a positive voltage was applied in a white display state. The voltage applied to the electrode on the upstream side in the visual recognition direction of the image display device was changed, and the other electrode was electrically grounded. The density was measured using a reflection densitometer “RD-918 (manufactured by Macbeth)”.

  The evaluation was performed for the contrast, the minimum driving voltage, and the white density at the initial stage and during the durability. Evaluation at the time of endurance is evaluation after repeating the voltage application of + 200V and -200V alternately 10,000 times.

(Contrast and white density)
The contrast was evaluated based on the density difference between the black density and the white density.
The black density is the reflection density of the display surface obtained when a voltage of +200 V is applied to the electrode on the upstream side in the visual recognition direction of the image display device.
The white density is a reflection density of the display surface obtained when a voltage of −200 V is applied to the electrode on the upstream side in the visual recognition direction of the image display device.
Contrast of density difference of 1.30 or more was determined to be the best (◎), 1.20 or more to be excellent (◯), 1.10 or more to pass (Δ), and less than 1.10 to fail (x).

(Minimum drive voltage)
The minimum drive voltage is the voltage V1 when the display density value becomes the following value when changed from 0V to + 250V at 10V intervals.
Display density = CW + {(CB−CW) × 0.1}
The black density measured in the initial evaluation of contrast is “CB”, and the white density is “CW”.

It is a schematic diagram for demonstrating the structure of the display particle of this invention. It is the schematic which shows an example of the cross-sectional structure of an image display apparatus. It is a schematic diagram which shows the example of the movement of the display particle by the voltage application between base | substrates. It is a schematic diagram which shows the example of the movement of the display particle by the voltage application between base | substrates. It is a schematic diagram which shows the example of a shape of an image display surface. It is a schematic diagram which shows an example of the sealing method of a display particle. It is a schematic diagram which shows an example of the sealing method of a display particle.

Explanation of symbols

  1: Core particle, 2: Shell layer, 10: Image display device, 11:12: Substrate, 15: Electrode, 16: Insulating layer, 17: Partition, 18: Gap, 18a: Image display surface, 21: Black particle, 22: White particles.

Claims (7)

Display particles used in an image display device for displaying an image by moving display particles by encapsulating charged display particles between two substrates, at least one of which is transparent, and generating an electric field between the substrates And the core particle has a shell layer formed on the surface thereof, and the volume resistivity of the core particle is 1 × 10 ⁵ to 1 × 10 ¹⁰ Ω · cm, and the entire volume resistivity of the core particle and the shell layer is A display particle comprising a display particle having a low-resistance core-high-resistance shell structure having a value of 1 × 10 ¹⁵ to 1 × 10 ²⁰ Ω · cm. The display particles include positively charged display particles and negatively charged display particles;
The display particles according to claim 1, wherein at least one of the positively charged display particles and the negatively charged display particles is a display particle having the low resistance core-high resistance shell structure. The display particles include positively charged display particles and negatively charged display particles;
The display particles according to claim 1, wherein both positively charged display particles and negatively charged display particles are display particles having the low resistance core-high resistance shell structure. When the display particles having the low-resistance core-high-resistance shell structure have a volume average particle diameter of the core particles as R1 (μm) and a volume average particle diameter of the core particles and the shell layer as a whole is R2 (μm), formula;
1.01 ≦ R2 / R1 ≦ 1.50
The display particles according to claim 1, wherein The display particles include positively charged display particles and negatively charged display particles;
The display particles according to claim 1, wherein one of positively charged display particles and negatively charged display particles is white display particles having the low-resistance core-high-resistance shell structure.   The image display apparatus provided with the display particle in any one of Claims 1-5. A shell layer is formed on the surface of the core particle, and the volume resistance value of the core particle is 1 × 10 ⁵ to 1 × 10 ¹⁰ Ω · cm, and the entire volume resistance value of the core particle and the shell layer is 1 × white display particles having a high resistance shell structure - low resistance core is ^{10 15 ~1 × 10 20 Ω ·} cm.

Images