JP4525077B2 - Particle group for display device, image display device, and image forming apparatus - Google Patents

Description

  The present invention relates to a particle group for a display device used for an image display medium or the like that can be rewritten repeatedly, an image display device using the particle group, and an image forming apparatus.

  Conventionally, display techniques such as Twisting Ball Display (two-color coating particle rotation display), electrophoresis, magnetophoresis, thermal rewritable medium, and liquid crystal having memory properties have been proposed as image display media that can be rewritten repeatedly. Although the display technology is excellent in image memory performance, there is a problem in that the display surface cannot be displayed in white like paper and density contrast is low.

  On the other hand, as a display technique using a toner that solves the above-mentioned problems, a charge transporting method in which conductive colored toner and white particles are sealed between opposing electrode substrates and provided on the inner surface of the electrode substrate on the non-display side Charge is injected into the conductive colored toner through the layer, and the charged conductive colored toner is applied between the two electrode substrates to the display-side electrode substrate located opposite to the non-display-side electrode substrate. There has been proposed a display technology that moves by an electric field, adheres to the inside of the electrode substrate on the display side, and displays an image by contrast between conductive colored toner and white particles (for example, see Non-Patent Document 1). This display technology is excellent in that the image display medium is entirely composed of solid, and white and black (color) display can be switched 100% in principle.

  The image display medium using particles is excellent in density contrast, and is enclosed between a pair of substrates and the substrates so as to be movable between the substrates by an applied electric field, and a plurality of types having different colors and charging characteristics. An image display medium including a particle group has also been proposed (see, for example, Patent Document 1). According to this proposal, high whiteness and density contrast can be obtained.

In these display methods, in order to increase the contrast of an image, a method of displaying an image in black or other colors with white as a background color is generally used. However, recently, there has been an increasing demand for color, and in order to make the entire display image stylish, there is a strong demand for chromatic colors even in the background portion of the image display. However, when conventional display particles such as red and blue for display are used as the background color, the actual situation is that the entire image has a very intense color tone and does not display a stylish image. In addition, there is a problem that eyes are tired if the display is continued for a long time.
JP 2001-31225 A Japan Hardcopy '99 Proceedings p. 249-252

  Therefore, an object of the present invention is to solve the above problems. That is, the present invention can be used for an image display medium or the like that has a color in the background color and can display an image that gives a stylish impression to the entire display image, and does not cause eye fatigue even when viewed for a long time. It is an object of the present invention to provide a display device particle group, an image display device using the display device particle group, and an image forming apparatus.

As a result of intensive studies to achieve the above object, the present inventors have found that the object can be achieved by the present invention described below. That is, the present invention
<1> Display device particle group including at least one type of display device particle having a property and color capable of being positively charged and at least one type of display device particle having a property and color capable of being negatively charged Because
Among the display device particles, at least one low concentrations have a pale color and lightness L ^* of 80 or more particles have a dark color of at least another one is the high concentration and lightness L ^* Are particles of 70 or less ,
A particle group for display devices, wherein the particles having a light color with a low concentration contain at least a black or chromatic color material and a white color material .

<2 > The particle group for display devices according to < 1 >, wherein the white color material is titanium oxide.
< 3 > The display device according to < 1 >, wherein a content of the black or chromatic color material is 0.05 to 20 parts by mass with respect to 100 parts by mass of the white color material. A group of particles.

The present invention also provides:
< 4 > An image display device in which a display device particle group is sealed between a pair of opposed substrates.
The display device particle group includes at least one kind of display device particle having a property and color capable of being positively charged, and at least one kind of display device particle having a property and color capable of being negatively charged. ,
Among the display device particles, at least one low concentrations have a pale color and lightness L ^* of 80 or more particles have a dark color of at least another one is the high concentration and lightness L ^* Are particles of 70 or less ,
In the image display device , at least a black or chromatic color material and a white color material are contained in the low-concentration light-colored particles .

Furthermore, the present invention provides
< 5 > An image forming apparatus including an image display device in which a display device particle group is sealed between a pair of opposed substrates.
The display device particle group includes at least one kind of display device particle having a property and color capable of being positively charged, and at least one kind of display device particle having a property and color capable of being negatively charged. ,
Among the display device particles, at least one low concentrations have a pale color and lightness L ^* of 80 or more particles have a dark color of at least another one is the high concentration and lightness L ^* Are particles of 70 or less ,
The particles having a light color with a low concentration contain at least a black or chromatic color material and a white color material,
An image forming apparatus comprising: an electric field generating unit configured to generate an electric field corresponding to an image between the pair of substrates.

Here, the display device particles with a pale color having a low concentration L ^* is 80 or more, more preferably 90 or more, more preferably 95 or more. The value of L ^* is 100 at the maximum and there is no upper limit.

  According to the present invention, it is possible to provide a display device particle group, an image display device, and an image forming apparatus that are stylish in appearance and have little eye fatigue even when viewed for a long time without impairing the contrast of the image. it can.

[The particles in the display device particle group]
The display device particle group of the present invention comprises at least one display device particle having a property and color capable of being positively charged, and at least one display device particle having a property and color capable of being negatively charged; including. At least one of them is a particle having a light color with a low concentration (hereinafter, sometimes referred to as “light color particle”), and at least another one is a particle having a dark color with a high concentration (hereinafter, “dark color”). Sometimes referred to as “color particles”).
By mixing the dark color particles and the light color particles, it is possible to display an image having a background color and giving a stylish impression to the entire display image.

Here, the brightness of the light-colored particles (L ^*) is 80 or more, more preferably 90 or more, more preferably 95 or more. By being 80 or more, sufficient density contrast with dark color particles can be obtained, and image display similar to the case where white particles are used can be performed.
In addition, the lightness of the light-colored particles can be adjusted by a method such as adding a desired amount of a white color material described later to a color material that is black or chromatic.

The lightness of the light-colored particles is measured by enclosing the light-colored particles appearing on the display screen in a state where at least the light-colored particles are sealed in an image display device and a sufficient voltage is applied so that the value of L ^* does not change depending on the applied voltage. (X-Rite (R) 938) may be used to measure at a viewing angle of 2 °.
In the range of the brightness, in light-colored particles, you and at least the color of black or chromatic material and the white colorant. From the viewpoint of distinguishing from white display and obtaining a stylish display color, the white color material is preferably titanium oxide.
In consideration of giving a stylish impression or a cute impression, the content of the black or chromatic color material in the light-colored particles is 0.05 to 20 parts by mass with respect to 100 parts by mass of the white color material. Preferably there is. The content of the black or chromatic color material is more preferably 0.1 to 10 parts by mass, and further preferably 0.2 to 5 parts by mass.

On the other hand, dark particles refer to particles having a higher content of black or chromatic color material than light-colored particles, and particles having an L ^* value of 70 or less.
Further, it is preferable that the light color particles and the dark color particles are charged with opposite polarities.

  The particles in the display device particle group of the present invention (hereinafter referred to as “particles in the present invention” are a general term for both particles that can be positively and negatively charged) are composed of at least a coloring material and a resin. However, a charge control agent may be included as necessary, and the color material may also serve as the charge control agent. Examples of the color material used in the present invention include the following.

Examples of the black color material include carbon black, titanium black, magnetic powder, oil black, organic and inorganic dye / pigment black materials.
Examples of white color materials include white pigments such as rutile titanium oxide, anatase titanium oxide, zinc white, lead white, zinc sulfide, aluminum oxide, silicon oxide, and zirconium oxide. In particular, rutile type titanium oxide is preferably used.

  In addition, examples of the chromatic color material include phthalocyanine, quinacridone, azo, condensation, insoluble lake pigments, and inorganic oxide pigments. Specifically, aniline blue, calcoil blue, chrome yellow, ultramarine blue, deyupon oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 180, C.I. I. Pigment yellow 185, C.I. I. Pigment blue 15: 1, C.I. I. Pigment Blue 15: 3 can be exemplified as a representative one.

  Examples of the structure of the coloring material that also serves as the charge control agent include those having an electron-withdrawing group or electron-donating group, and metal complexes. Specific examples thereof include C.I. I. Pigment violet 1, C.I. I. Pigment violet 3, C.I. I. Pigment black 1, C.I. I. And CI Pigment Violet 23.

  Examples of the resin constituting the particles in the present invention include polyvinyl resins such as polyolefin, polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, vinyl chloride, and polyvinyl butyral; vinyl chloride-vinyl acetate copolymer; styrene- Acrylic acid copolymer; straight silicone resin composed of organosiloxane bond and modified product thereof; fluorine resin such as polytetrafluoroethylene, polyvinyl fluoride, and polyvinylidene fluoride; polyester, polyurethane, polycarbonate; amino resin; epoxy resin, etc. Can be mentioned. These may be used alone or in combination with a plurality of resins. These resins may be cross-linked. Further, a known binder resin known as a main component for conventional electrophotographic toner can be used for the particles without any problem.

  If necessary, a charge control agent may be added to the particles in the present invention in order to control chargeability. As the charge control agent, known materials used for toner materials for electrophotography can be used. For example, cetylpyridyl chloride, BONTRONP-51, BONTRON P-53, BONTRON E-84, BONTRON E-81 (or more, Orient (Chemical Industry Co., Ltd.), COPY CHARGESY VP2038 (manufactured by Clariant Japan Co., Ltd.), etc. And metal oxide fine particles.

  In the two or more types of particles in the present invention, it is necessary to adjust so that at least one of them can be positively charged and at least one of the other particles can be negatively charged. When charging is performed by colliding or rubbing different types of particles, one is positively charged and the other is negatively charged due to the positional relationship between the two charged columns. In the present invention, for example, by appropriately selecting the charge control agent, the position of the charge train can be appropriately adjusted.

  The particles in the present invention (both particles that can be positively and negatively charged) can also be prepared through an emulsification step. When the emulsification step is performed, as an emulsification aid, known anions, nonions, cationic surfactants, It is preferable to use a polymer dispersant such as polyvinyl alcohol, polyvinyl pyrrolidone, gelatin, methyl cellulose, polyacrylic acid, starch, and casein, and fine-particle inorganic compounds such as silicon oxide, calcium carbonate, and aluminum oxide as necessary.

If necessary, a solvent may be used to dissolve the resin. As the solvent, a solvent that dissolves the resin and is not miscible with water is desirable.
Specifically, ester solvents such as methyl acetate, ethyl acetate, propyl acetate, and butyl acetate; ether solvents such as diethyl ether, dibutyl ether, and dihexyl ether; ketones such as methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, and cyclohexanone And hydrocarbon solvents such as toluene and xylene, and halogenated hydrocarbon solvents such as dichloromethane, chloroform, and trichloroethylene. These solvents are preferably those capable of dissolving the polymer and having a solubility in water of about 0 to 30% by mass.

  The shape of the particles in the present invention is preferably close to a true sphere. In the case of a particle close to a true sphere, the contact between the particles is almost a point contact, and the contact between the particle and the inner surface of the substrate is almost a point contact. Adhesive force based on Waals force is reduced. Therefore, even if the inner surface of the substrate is a dielectric, it is considered that the charged particles can move smoothly in the substrate by the electric field. Furthermore, if the particle is close to a true sphere, it also has the meaning of preventing deformation and sticking when the particle collides with the display surface.

As the method for producing particles in the present invention, a wet production method such as suspension polymerization, emulsion polymerization, or dissolution suspension method, which is known as a method for producing an electrophotographic toner, can also be used.
An apparatus used in the case of having an emulsification step is not particularly limited as long as it is generally commercially available as an emulsifier and a disperser. For example, Ultra Thalax (manufactured by IKA), Polytron ( Batch type emulsifiers such as Kinematica), TK auto homomixer (made by Special Machine Industries), National Cooking Mixer (made by Matsushita Electric Industrial Co., Ltd.), Ebara Milder (made by Ebara Corporation), TK pipeline homomixer , TK homomic line flow (manufactured by Koki Kogyo Kogyo Co., Ltd.), colloid mill (manufactured by Shinko Pantech Co., Ltd.), slasher, trigonal wet pulverizer (manufactured by Mitsui Miike Chemical Co., Ltd.), Cavitron (manufactured by Eurotech Co., Ltd.), fine flow mill Continuous type emulsifiers (made by Taiheiyo Kiko Co., Ltd.), Claremix (made by M Technique), Fillmix (special High-pressure emulsifiers such as batch, continuous-use emulsifier, microfluidizer (manufactured by Mizuho Kogyo), nano maker, nanomizer (manufactured by Nanomizer), APV gourin (manufactured by Gourin), membrane emulsification Membrane emulsifiers such as a machine (made by Chilling Industries Co., Ltd.), vibratory emulsifiers such as vibratory mixers (made by Chilling Industries Co., Ltd.), and ultrasonic emulsifiers such as an ultrasonic homogenizer (made by Branson). .

  Furthermore, when it has a drying step, a known dryer such as a vacuum dryer, a paddle dryer, a vibration fluid dryer, a tube dryer, a shelf dryer, an air dryer such as a flash dryer can be used. For drying in a short time, an air flow dryer such as a flash dryer is preferably used.

The said manufacturing method at the time of using a wet manufacturing method is demonstrated in detail below. The composition constituting the oil phase by dissolving and / or dispersing the components constituting the particles in the present invention, that is, a resin, a coloring material, and a charge control agent, a polymerization initiator, etc., which are added if necessary, in a monomer or a solvent. On the other hand, an aqueous material to be an aqueous phase is prepared.
The oil phase composition and the aqueous phase composition are emulsified using the emulsifier to obtain particles having a desired particle size. In addition, when using a monomer for the composition used as the said oil phase, after producing the said oil droplet, it is made to polymerize. If a solvent is used, it is removed. Further, washing is performed to remove the surfactant, polymer dispersant, inorganic salt, and the like. Further, it can be obtained by drying. Moreover, it can also classify as needed.

[Action mechanism of particles for display devices]
Next, the action mechanism of the display device particle group of the present invention will be described.
At least two or more kinds of particles (including at least light-colored particles and dark-colored particles) enclosed in a gap between a pair of substrates arranged opposite to each other are first mixed in a stirring container at a predetermined ratio and stirred. Is done. In this process of mechanical stirring and mixing, friction charging is performed between the particles and between the particles and the inner wall of the container, and each particle is considered to be charged. Thereafter, the mixed particles are sealed in a gap between the pair of substrates so as to have a predetermined volume filling rate. The encapsulated particles reciprocate between the substrates according to the electric field by switching the polarity of the DC voltage applied between the pair of substrates or by applying the AC voltage (initialization step). Even in the process of this initialization process, each particle is considered to collide and frictionally charge between particles and between the particle and the substrate surface layer. In addition, a desired triboelectric charge amount can be obtained by this initialization process.

  Due to the frictional charging, at least one of the particles (for example, light colored particles) is positive (hereinafter, positively charged particles are referred to as first particles), and at least one other (for example, dark colored particles). ) Are negative (hereinafter, the negatively charged particles are referred to as second particles), and the particles are each charged, and the particles adhere to each other due to the Coulomb attractive force between the first particles and the second particles. However, according to the direction of the electric field applied at the end of the initialization process, the particles are separated and attached to one substrate.

  Next, by applying an electric field according to the image signal, the first particles and the second particles are separated and moved in accordance with the electric field and are attached to different substrates. That is, the electrostatic force acting on each charged particle by an externally applied electric field is superior to the Coulomb force between each particle, the image force between the particle and the substrate surface, or the force due to the contact potential difference. For example, it is considered that each particle separates and moves to the opposite substrate.

The particles adhering to the substrate surface are considered to be adhered and fixed to the substrate surface by mirror image force or van der Waals force generated between the substrate surface. In this way, by using the light color particles, it is possible to display stylish images, and it is possible to reduce eye fatigue even if the display is continued for a long time.
In the above description, the expression based on the premise that there is one kind each of positively charged particles and negatively charged particles is used. Even if there are two or more types, there is no problem. Even in the case of two or more types, the effect of the present invention is exhibited by the same mechanism as described above.

[Image display device]
The image display device of the present invention is an image display device in which a particle group for display device is sealed between a pair of substrates arranged opposite to each other, and the display device of the present invention described above is used as the particle group for display device. Particles for use are used.
Since the image display device of the present invention is used in an image forming apparatus to be described later, the detailed configuration will be described in the section of the image forming apparatus. Here, the board | substrate used for an image display device is demonstrated.

  A substrate in the image display device is a pair of opposed substrates, and the particles are sealed in a gap between the pair of substrates. In the present invention, the substrate is a conductive plate-like body (conductive substrate), and in order to have a function as an image display medium, at least one of the pair of substrates is a transparent conductive substrate that is transparent. It is necessary to be. At this time, the transparent conductive substrate becomes a display substrate.

  As the conductive substrate used in the present invention, the substrate itself may be conductive, or the surface of the insulating support may be subjected to conductive treatment, and may be crystalline or amorphous. It doesn't matter. Examples of the conductive substrate in which the substrate itself is conductive include metals such as aluminum, stainless steel, nickel, chromium, and alloy crystals thereof, and semiconductors such as Si, GaAs, GaP, GaN, SiC, and ZnO.

  Examples of the insulating support include a polymer film, glass, quartz, and ceramic. Conductive treatment of the insulating support is performed by vapor deposition, sputtering, ion plating, or the like using the metal or gold, silver, copper, etc. mentioned in the specific example of the conductive substrate in which the substrate itself is conductive. A film can be formed.

  As the transparent conductive substrate, a conductive substrate in which a transparent electrode is formed on one surface of an insulating transparent support, or a transparent support having its own conductivity is used. Examples of the transparent support having its own conductivity include transparent conductive materials such as ITO, zinc oxide, tin oxide, lead oxide, indium oxide, and copper iodide.

Insulating transparent supports include transparent inorganic materials such as glass, quartz, sapphire, MgO, LiF, and CaF ₂ , and transparent organic resins such as fluorine resin, polyester, polycarbonate, polyethylene, polyethylene terephthalate, and epoxy. A film or plate-like body, optical fiber, selfoc optical plate or the like can also be used.

  As a transparent electrode provided on one side of the transparent support, a transparent conductive material such as ITO, zinc oxide, tin oxide, lead oxide, indium oxide, copper iodide is used, and by a method such as vapor deposition, ion plating, sputtering, etc. A formed one or a thin one made of metal such as Al, Ni, Au or the like so as to be translucent by vapor deposition or sputtering is used.

  In these substrates, since the surface on the opposite side affects the charging polarity of the particles, it is also a preferable aspect to provide a protective layer having an appropriate surface state. The protective layer can be selected mainly from the viewpoints of adhesion to the substrate, transparency, and the charge train, as well as low surface contamination. Specific examples of the material for the protective layer include polycarbonate resin, vinyl silicone resin, and fluorine group-containing resin. The resin is selected in such a manner that the constitution of the main monomer of the particles to be used and the difference in frictional charge from the particles are small.

[Image forming apparatus]
The image forming apparatus of the present invention is an image forming apparatus comprising an image display device in which a display device particle group is sealed between a pair of substrates arranged opposite to each other, the display device particle group for the display device As the particle group, the particle group for a display device of the present invention described above is used. In addition, an electric field generating means for generating an electric field corresponding to an image is provided between the pair of substrates.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of an image forming apparatus of the present invention using an image display medium of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment, and FIG. 2 is a cross-sectional view taken along line AA in FIG.

  The image forming apparatus according to the present embodiment includes an image display medium 10 and an electric field generator 26 as shown in FIG. The image display medium 10 is the above-described image display medium of the present invention, the display substrate 8, black or colored dark particles (dark color particles) 22, and low-density light particles (light color particles) 24. , The non-display substrate 18 and the spacer 20. The display substrate 8 is configured by sequentially laminating the transparent electrode 4 and the protective layer 6 on one side of the transparent support 2. Similarly, the non-display substrate 18 is sequentially laminating the electrode 14 and the protective layer 16 on one side of the support 12. Configured. The transparent electrode 4 of the display substrate 8 is connected to the electric field generating means 26, and the electrode 14 of the non-display substrate 18 is grounded.

  Next, details of the image display medium 10 will be described. For example, a 7059 glass substrate with a transparent electrode ITO of 50 mm × 50 mm × 1.1 mm is used for the transparent support 2 and the transparent electrode 4, and the support 12 and the electrode 14 constituting the outside of the image display medium 10. Note that the support 12 and the electrode 14 on the non-display substrate 18 side are not necessarily transparent. The inner surfaces (the surfaces of the transparent electrode 4 and the electrode 14) in contact with the particles of the glass substrate are coated with a polycarbonate resin (PC-Z) with a thickness of 5 μm, and protective layers 6 and 16 are formed.

  The spacer 20 is formed by providing a 15 mm × 15 mm square cutout 28 at the center of a 40 mm × 40 mm × 0.3 mm silicone rubber plate so that a space is formed during installation. The spacer 20 is configured by installing the silicone rubber plate provided with the cutout 28 on the surface of the non-display substrate 18 on which the electrode 14 and the protective layer 16 are formed.

  About 15 mg of mixed particles consisting of black or colored dark colored particles 22 and low density light colored particles 24 are screened through the screen into the space formed by the cutouts 28 of the spacers 20. Thereafter, the display substrate 8 is brought into close contact with the spacer 20 so that the surface on which the transparent electrode 4 and the protective layer 6 are formed faces the non-display substrate 18, and the substrate 8, 18 is pressed and held with a double clip. The spacer 20 and the substrates 8 and 18 are brought into close contact with each other to form the image display medium 10.

  When a DC voltage of 150 V is applied to the transparent electrode 4 of the display substrate 2 of the image display medium 10 by the electric field generating means 26, the particles having a low density and light color that are negatively charged on the non-display substrate 18 side Part of 24 begins to move to the display substrate 8 side by the action of an electric field, and when a DC voltage of 500 V is applied, many low-density light-colored particles 24 move to the display substrate 8 side and the display density is almost saturated. To do. At this time, the positively charged black or colored dark colored particles 22 move to the non-display substrate 18 side. Thereafter, even when the voltage applied by the electric field generating means 26 was set to 0 V, the low density light color particles 24 attached to the display substrate 8 did not move and the display density did not change.

  The image forming apparatus of the present invention has been described with reference to the embodiment, but the present invention is not limited to the embodiment. Also, the size of each member is merely an example, and various sizes are selected according to the purpose of use.

  Note that the image forming apparatus of the present invention described above has a unit of the configuration as one cell, and a plurality of cells are arranged in a plane (or divided into a plane between opposing substrates). Cell) to form an image forming apparatus including a plurality of image display media. By setting the number of cells to a desired number in the vertical and horizontal directions, a large-screen image forming apparatus having a desired resolution can be manufactured.

  Hereinafter, the present invention will be described more specifically with reference to examples. In the following Examples 1 to 4 and Comparative Examples 1 and 2, the image forming medium or the image forming apparatus having the configuration shown in FIG. 1 and FIG. The effect of the present invention was confirmed by changing the composition of light-colored particles and dark-colored particles having black or other colors. At this time, the size, material, and the like of each member were the same as those described in the above section [Image forming apparatus].

<Preparation of particles for display device constituting particles for display device>
In the following manner, light-colored particles at low concentration and dark-colored particles having black or other colors were produced, respectively.

1) Production of light colored particles:
a) Preparation of dispersion A:
Styrene monomer: 50 parts by mass Titanium oxide (Taipaque CR63: manufactured by Ishihara Sangyo Co., Ltd.): 30 parts by mass Yellow pigment (CI Pigment Yellow 74, Fast Yellow GC102: manufactured by Sanyo Dye): 0.15 parts by mass Charge control agent (COPY CHARGE PSY VP2038: manufactured by Clariant Japan): 1 part by mass / polymerization initiator AIBN (azoisobutyronitrile): 1 part by mass

  The mixture having the above composition was subjected to ball milling using 10 mmφ zirconia balls for 20 hours to obtain dispersion A1.

  A dispersion A2 was obtained in the same manner as the dispersion A1, except that a green pigment (CI Pigment Green 7, Hostaperm Green GNX-L: manufactured by Clariant) was used instead of the yellow pigment.

  Dispersion A3 was obtained in the same manner as dispersion A1, except that a blue pigment (CI Pigment Blue 15: 3, Fastogen Blue CT-BX130: manufactured by Dainippon Chemical) was used instead of the yellow pigment.

  Dispersion A4 was obtained in the same manner as dispersion A3, except that the amount of the blue pigment was 9 parts by mass.

  Dispersion A5 was obtained in the same manner as Dispersion A3, except that no titanium oxide was added. Furthermore, a dispersion A6 was obtained in the same manner as the dispersion A3 except that the amount of the blue pigment was 0.1 parts by mass.

b) Preparation of charcoal dispersion B:
-Calcium carbonate: 300 mass parts-Water: 700 mass parts About the mixture which consists of the said composition, it pulverized with the ball mill similarly to preparation of the dispersion liquid A, and the charcoal dispersion liquid B was obtained.

c) Preparation of emulsion C:
-Charcoal dispersion B: 18 parts by mass-20% saline: 50 parts by mass About the mixture having the above composition, after stirring and mixing with an emulsifier (Ultra Turrax), dispersion A1: 30 parts by mass was added, Using an emulsifier (Ultra Turrax), the mixture was emulsified at 20 m / s for 3 minutes to obtain an emulsion C1.

d) Production of particles:
The obtained emulsion C1 was heated to 70 ° C. under a nitrogen stream and stirred for 20 hours to polymerize to obtain solid particles. After adding 15 parts by mass of 35% hydrochloric acid and stirring to dissolve calcium carbonate, suction filtration and washing with water were repeated 5 times, followed by suction filtration, followed by drying at 70 ° C. for 3 hours using a vacuum dryer. Classification and pale particles D1 were obtained.

  In the same manner as the particle D1, except that the dispersion A2, the dispersion A3, the dispersion A4, the dispersion A5, and the dispersion A6 were used instead of the dispersion A1, the particles D2, D3, D4, D5, Particles D6 were obtained respectively.

2) Production of dark colored particles (dark colored particles) having black or other colors:
Styrene monomer: 90 parts by mass Blue pigment (CI Pigment Blue 15: 3, SANYO Cyanine Blue KRO: Sanyo Dye Co., Ltd.): 10 parts by mass Polymerization initiator AIBN (azoisobutyronitrile): 1 part by mass Blue particles E1 were obtained in the same manner as the particles D1, except that the dispersion A was prepared using the above-mentioned parts.

  Black particles E2 were obtained in the same manner as the blue particles E1, except that carbon black instead of blue pigment was used.

  The composition of the produced particles is shown in Table 1 below.

<Preparation of mixed particles>
The obtained particles were used in the combinations shown in Table 2 below and mixed to prepare mixed particles used in Examples 1 to 4 and Comparative Examples 1 to 3. At this time, the blending ratio (mass ratio) between the low-concentration light-colored particles and the black or chromatic dark-colored particles is “low-density light-colored particles: black or chromatic dark-colored particles = 2. : 1 ”. This was shaken by hand and charged to obtain mixed particles. In this example and comparative example, the low-density and light-colored particles were charged with positive polarity and the black or chromatic dark-colored particles were charged with negative polarity. The combinations of particles used are shown in Table 2 below.

<Production of image display device>
Each obtained mixed particle was enclosed in the space | gap between the board | substrates (display substrate 8 and non-display board | substrate 18) facing each other. By applying a voltage (500 V) between the transparent electrode 4 and the electrode 14 of the obtained image forming apparatus to cause a desired electric field to act on the particle group between the display substrate 8 and the non-display substrate 18, each particle 22 is obtained. , 24 move between the display substrate 8 and the non-display substrate 18. By switching the polarity of the applied voltage, each particle 22, 24 moves in a different direction between the display substrate 8 and the non-display substrate 18, and reciprocates between the display substrate 8 and the non-display substrate 18 by repeatedly switching the voltage polarity. To do. In this process, the particles 22 and 24 are further charged with different polarities due to the collision between the particles 22 and 24 and between the particles 22 and 24 and the display substrate 8 or the non-display substrate 18.

  In this example, low-density and light-colored particles, black or chromatic dark-colored particles are negatively charged, move in different directions according to the electric field between the display substrate 8 and the non-display substrate 18, When the electric field is fixed in one direction, the particles 22 and 24 adhere to the display substrate 8 or the non-display substrate 18, respectively, and an image is displayed.

<Evaluation test>
As described below, the lightness (L ^* ), the impression of the image display color, and the contrast were evaluated.
In the image forming apparatus using each mixed particle of the example or the comparative example, the voltage polarity switching described above is performed every second, and each particle 22, 24 is set to 1 in a different direction between the display substrate 8 and the non-display substrate 18. Moved every second. This switching was repeated 1,000 cycles to obtain the initial state. At this time, the difference between the image density when the low density and light color particles are moved to the display screen side and the image density when the black or chromatic color particles are moved is defined as contrast. The image density was evaluated using a Macbeth densitometer, and it was determined that there was sufficient contrast when the density difference was 0.7 or more. L ^* of the display color of the low density and light color image was measured using X-Rite. The impression of the image display color was evaluated by visual observation. The results are shown in Table 3 below.
In Table 3, “◎”, “◯”, “×”, and “XX” in the comprehensive evaluation indicate that, in this order, a strong impression is strong, there is no eye fatigue, and the contrast is good. .

From the results of Table 3 above, the image display devices of the examples using the light-colored particles all gave a stylish impression as compared with the comparative example, and the eye fatigue hardly occurred and the contrast was good. . In particular, Examples 1 to 3 having a lightness (L ^* ) of 90 or more strongly cause almost all people to have a cute impression such as “cute” or “beautiful”, and eye fatigue even if they continue to watch for a longer time. Did not occur.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus of the present invention using an image display medium of the present invention. It is AA sectional drawing of the image forming apparatus shown in FIG.

Explanation of symbols

2 Transparent Support 4 Transparent Electrode 6 Protective Layer 8 Display Substrate 10 Image Display Medium 12 Support 14 Electrode 16 Protective Layer 18 Non-Display Substrate 20 Spacer 22 Dark Colored Particles with Black or Color 24 Low Concentrated Light Colored Particles 26 Electric field generating means

Claims (5)

A display device particle group comprising at least one type of display device particle having a property and color capable of being positively charged and at least one type of display device particle having a property and color capable of being negatively charged. ,
Among the display device particles, at least one low concentrations have a pale color and lightness L ^* of 80 or more particles have a dark color of at least another one is the high concentration and lightness L ^* Are particles of 70 or less ,
A particle group for a display device, wherein the particles having a light color at a low concentration contain at least a black or chromatic color material and a white color material .   The display device particle group according to claim 1, wherein the white color material is titanium oxide.   2. The display device particle group according to claim 1, wherein the content of the black or chromatic color material is 0.05 to 20 parts by mass with respect to 100 parts by mass of the white color material. An image display device in which a display device particle group is sealed between a pair of substrates arranged opposite to each other,
The display device particle group includes at least one kind of display device particle having a property and color capable of being positively charged, and at least one kind of display device particle having a property and color capable of being negatively charged. ,
Among the display device particles, at least one low concentrations have a pale color and lightness L ^* of 80 or more particles have a dark color of at least another one is the high concentration and lightness L ^* Are particles of 70 or less ,
An image display device comprising at least a black or chromatic color material and a white color material contained in the low-concentration light-colored particles . An image forming apparatus comprising an image display device in which a display device particle group is sealed between a pair of opposed substrates.
The display device particle group includes at least one kind of display device particle having a property and color capable of being positively charged, and at least one kind of display device particle having a property and color capable of being negatively charged. ,
Among the display device particles, at least one low concentrations have a pale color and lightness L ^* of 80 or more particles have a dark color of at least another one is the high concentration and lightness L ^* Are particles of 70 or less ,
The particles having a light color with a low concentration contain at least a black or chromatic color material and a white color material,
An image forming apparatus comprising: an electric field generating unit that generates an electric field according to an image between the pair of substrates.

Images