JP4655510B2 - Particle group for display device, image display device, and image forming apparatus - Google Patents

Description

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

  Conventionally, display technologies 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).

  The above display technique is excellent in that the image display medium is entirely composed of solid, and the display of white and black (color) can be switched 100% in principle. However, in the above technique, there are conductive colored toners that do not contact the charge transport layer provided on the inner surface of the electrode of the non-display substrate, and conductive colored toners that are isolated from other conductive colored toners. Since the colored toner does not move due to an electric field because charges are not injected, it is present between the electrode substrates at random, so that there is a problem that the density contrast becomes low.

As an image display medium having excellent density contrast using particles, a plurality of types of particles which are enclosed between a pair of substrates and the substrate so as to be movable between the substrates by an applied electric field and which have different colors and charging characteristics An image display medium including a group has also been proposed (see, for example, Patent Document 1).
According to this proposal, for example, the contrast is improved by setting one of the display colors to white, but this is not yet sufficient. The particle structure in this proposal may reduce image density and density contrast, particularly when rewriting is performed repeatedly over a long period of time.

When one color of the display color is white, sufficient contrast can be obtained by improving the whiteness of the white display. For this reason, titanium oxide is also used as a white pigment (see, for example, Patent Documents 2 and 3).
However, titanium oxide has a large specific gravity, and when used in a vertically arranged display medium, there is a problem that the image falls due to the influence of gravity during display and the image cannot be maintained. Reducing the amount of titanium oxide solved this problem, but this time the hiding power of the white particles was reduced, and sufficient contrast could not be obtained.
Japan Hardcopy '99 Proceedings p. 249-252 JP 2001-31225 A JP 2002-10771 A JP 2002-202531 A

  In view of the above, an object of the present invention is to solve the above problems. That is, a display device particle group that continues to maintain a clear image even after long-time display, exhibits a sufficient density contrast, and has a sufficient hiding power, and an image display device and image formation using the same An object is to provide an apparatus.

As a result of diligent research to solve the above problems, the present inventors include titanium oxide in at least one type of display device particles in the display device particle group, and further distribute this in the vicinity of the display particle surface. And found out that the above problems can be solved.
Further, it has been found that it is effective to apply a hydrophilic treatment to titanium oxide in order to disperse titanium oxide in the display device particles in the vicinity of the surface of the display particles. And it turned out that it is optimal to use a hydrophilic coupling agent for the hydrophilic treatment of the titanium oxide. Furthermore, it has been found that a hydrophilic silane coupling agent is preferably used as the hydrophilic coupling agent.
As described above, the present invention includes at least one type of display device particle having a property and color that can be positively charged, and at least one type of display device particle having a property and color that can be negatively charged. A particle group for a device,
At least one kind of the display device particles is present in a titanium oxide that has been subjected to a hydrophilic treatment,
It is a particle group for display devices, wherein the content of titanium oxide subjected to hydrophilic treatment is 15 to 30% by mass of the particles for display devices containing the titanium oxide.

  The hydrophilic treatment is preferably a treatment using a hydrophilic coupling agent. And it is preferable that the said hydrophilic coupling agent is a hydrophilic silane coupling agent.

Further, the present invention is an image display device in which a display device particle group is sealed between a pair of opposed substrates, wherein the display device particle group is the display device particle group of the present invention described above. It is an image display device characterized by being.
According to another aspect of the present invention, there is provided an image forming apparatus comprising an electric field generating means for generating an electric field corresponding to an image, and forming an image using the above-described image display device of the present invention.

  The hiding power of the white particles is expressed by the titanium oxide. However, the titanium oxide does not need to be present in the whole white particles, and only needs to be near the surface of the white particles in order to scatter light. In the present invention, titanium oxide can be unevenly distributed in the vicinity of the surface of the white particles by subjecting it to a hydrophilic treatment.

  According to the present invention, for a display device that can maintain a display image satisfactorily even when displayed for a long time without reducing the whiteness of the white image, and can form a stable image with high density contrast. Particles, an image display device, and an image forming apparatus can be provided.

  Hereinafter, the present invention will be described in detail by dividing it into “the particles of the display device particle group”, “the action mechanism of the display device particle group”, “image display device”, and “image forming apparatus”.

[The particles in the display device particle group]
The particles constituting the particle group for a display device of the present invention (hereinafter referred to as “particles in the present invention” is a general term for both particles that can be positively and negatively charged) are composed of at least a coloring material and a resin. Is done.

In addition, at least one kind of display device particles includes titanium oxide subjected to hydrophilic treatment, and the content of the titanium oxide subjected to the hydrophilic treatment includes titanium oxide subjected to the hydrophilic treatment. It is 15 to 30% by mass of the particles for display device.
By subjecting titanium oxide to a hydrophilic treatment, it can be unevenly distributed near the surface of the white particles. Therefore, the hiding power of the white particles can be efficiently expressed with a small amount, rather than using simple titanium oxide.
When the content of the titanium oxide subjected to the hydrophilic treatment is less than 15% by mass, sufficient hiding power cannot be obtained and the contrast is inferior. If it exceeds 30% by mass, it will fall under the influence of gravity during display when used in a vertically placed state, and a stable image cannot be maintained. The content of titanium oxide subjected to hydrophilic treatment is preferably 17 to 28% by mass.
In addition, normal titanium oxide (titanium oxide not subjected to hydrophilic treatment) may be present as long as a stable image can be maintained.

  Further, 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 white color materials include titanium oxides such as rutile titanium oxide and anatase titanium oxide.
As described above, these titanium oxides are used after being subjected to hydrophilic treatment (hydrophilic treatment). Examples of the method for hydrophilic treatment of titanium oxide include a method using a hydrophilic coupling agent such as a hydrophilic silane coupling agent and a hydrophilic titanium coupling agent, and a method of coating the surface with a hydrophilic resin. However, it is not limited to these.
Specifically, as the hydrophilic silane coupling agent, HO (CH ₂ ) ₄ Si (OCH ₃ ) ₃ , (HO (CH ₂ ) ₄ ) ₂ Si (OCH ₃ ) ₃ , HO (CH ₂ ) ₆ Si (OCH ₃ ) ₃ , (HO (CH ₂ ) ₆ ) ₂ Si (OCH ₃ ) ₃ HOCO (CH ₂ ) ₄ Si (OCH ₃ ) ₃ , (HOCO (CH ₂ ) ₄ ) ₂ Si (OCH ₃ ) ) ₃ , HOCO (CH ₂ ) ₆ Si (OCH ₃ ) ₃ , (HOCO (CH ₂ ) ₆ ) ₂ Si (OCH ₃ ) _{3 and the} like.
The addition amount of these surface treatment agents is preferably 0.2 to 40% by weight, more preferably 0.5 to 20% by weight, based on the total amount of titanium oxide to be subjected to hydrophilic treatment. Examples of the hydrophilic resin include cross-linkable polyvinyl alcohol.

Examples of the black color material include carbon black, titanium black, magnetic powder, oil black, organic and inorganic dye / pigment black materials.
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 further control the chargeability. As the charge control agent, known materials used for toner materials for electrophotography can be used. For example, cetylpyridyl chloride, BONTRON P-51, BONTRON P-53, BONTRON E-84, BONTRON E-81 (above, Surface treatment with quaternary ammonium salts, salicylic acid-based metal complexes, phenol-based condensates, tetraphenyl-based compounds, metal oxide fine particles, various coupling agents such as Orient Chemical Industries, Ltd., COPY CHARGESY VP2038: manufactured by Clariant Japan) The metal oxide fine particles made can be mentioned.

  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.

  The particles in the present invention (both particles that can be positively and negatively charged) are prepared through an emulsification step, and a water-insoluble calcium compound or the like is used as an emulsification aid. As the calcium compound hardly soluble in water, calcium carbonate, calcium phosphate and a mixture thereof are used, and calcium carbonate is preferably used. Further known anionic, nonionic, and cationic surfactants as emulsification aids and polymer dispersants such as polyvinyl alcohol, polyvinyl pyrrolidone, gelatin, methyl cellulose, polyacrylic acid, starch, and casein can be further added and used.

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 30% by mass or less.

  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 ionic substances, surfactants, polymer dispersants 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 action mechanism of the display device particle group of the present invention will be described. At least two or more kinds of particles sealed in a gap between a pair of substrates arranged opposite to each other are mixed and stirred in a stirring container at a predetermined ratio. 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 is positive (hereinafter, positively charged particles are referred to as first particles), and at least one of the other particles is negative (hereinafter negatively charged particles). Called the second particles), each charged and trying to adhere and agglomerate between the particles due to the Coulomb attractive force between the first and second particles, but the electric field applied at the end of this initialization step. The particles are separated according to the direction of 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 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 display device particle group is sealed between a pair of substrates arranged opposite to each other, and the display device particle group is used for the display device of the present invention described above. A group of particles.

  The substrate is a pair of opposed substrates, and the particles are enclosed in a gap between the pair of substrates. In the present invention, the “substrate” is a conductive plate-like body (conductive substrate). In order to have a function as an image display medium, at least one of the pair of substrates is a transparent conductive material. It is necessary to be a conductive substrate. 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 side 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 includes an electric field generating means for generating an electric field corresponding to an image, and forms an image using the above-described image display device of the present invention.
Hereinafter, an embodiment of an image forming apparatus of the present invention using an image display device of the present invention, which includes an electric field generating means for generating an electric field corresponding to an image, will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image display 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 a voltage generator 26 as shown in FIG. The image display medium 10 is the image display device of the present invention, and includes the display substrate 8, black particles 22, white particles 24, a non-display substrate 18, and spacers 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 voltage generation means 26 as electric field generation means, 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 particles 22 and white 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 voltage generating means 26, some of the negatively charged white particles 24 on the non-display substrate 18 side have an electric field. When the DC voltage of 500 V is first applied to the display substrate 8 due to the action, many white particles 24 move to the display substrate 8 and the display density is almost saturated. At this time, the black particles 22 charged to positive polarity move to the non-display substrate 18 side. Thereafter, even when the voltage applied by the voltage generating means 26 was set to 0 V, the white particles 24 attached to the display substrate 8 did not move, and the display density did not change.

As described above, the image display device of the present invention using the image display device of the present invention has been described with reference to the embodiment. However, the present invention is not limited to the aspect of the embodiment.
For example, as the color of the particles, white and blue are given as examples, but various color combinations can be adopted, and it is preferable that one of them is white as described above. Also, the size of each member is merely an example, and various sizes are selected according to the purpose of use.
In the image display medium of the present invention, the unit comprising the structure is a single cell, and a plurality of cells are arranged in a plane (or divided into planes in the gap between opposing substrates). And an image display device composed of 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 and comparative examples, the configuration of white particles and blue particles is changed using the image forming medium or the image display device having the configuration shown in FIGS. 1 and 2 described in the above section [Image forming apparatus]. Thus, the effect of the present invention was confirmed. 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>
White particles and black particles were produced as follows.
(1) Production of white mother particles:
a) Surface treatment of titanium oxide:
Titanium oxide (Tipaque CR63: manufactured by Ishihara Sangyo Kaisha, Ltd.): 100 parts by mass _{· HO (CH 2) 4 Si} (OCH 3) 3: 1 parts by weight Toluene: 400 parts by weight

The composition was stirred for 2 hours while irradiating ultrasonic waves at room temperature, decanted and the supernatant was removed, followed by heating and vacuum drying in a vacuum dryer set at 80 ° C. for 4 hours to form covalent bonds on the surface. Thus, surface-treated titanium oxide particles A1 having a hydrophilic group were obtained.
In addition, titanium oxide not subjected to surface treatment (Taipeku CR63: manufactured by Ishihara Sangyo Co., Ltd.) was designated as A5.

b) Preparation of dispersions B1-B5:
-Styrene monomer: 69 parts by mass-Surface-treated titanium oxide A1: 28 parts by mass-Charge control agent (COPY CHARGE PSYVP2038: manufactured by Clariant Japan KK): 2 parts 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 B1.

-Styrene monomer: 80 parts by mass-Surface-treated titanium oxide A1: A dispersion B2 was obtained in the same manner as the dispersion B1, except that 17 parts by mass was used.

-Styrene monomer: 62 mass parts-Surface treatment titanium oxide A1: Dispersion B3 was obtained like dispersion B1 except having used 35 mass parts.

-Styrene monomer: 84 mass parts-Surface treatment titanium oxide A1: Dispersion B4 was obtained like dispersion B1 except having used 13 mass parts.

  Dispersion B5 was obtained in the same manner as dispersion B1, except that untreated titanium oxide A5 was used instead of surface-treated titanium oxide A1.

c) Preparation of calcium carbonate dispersion C:
-Calcium carbonate: 30 parts by mass-Water: 70 parts by weight The mixture having the above composition was finely pulverized with a ball mill for 3 days in the same manner as in the preparation of Dispersion A to obtain Calcium Carbonate Dispersion C .

d) Preparation of emulsion D:
-Calcium carbonate dispersion C: 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 B1: 30 parts by mass" In addition, the mixture was emulsified for 3 minutes at 20 m / s using an emulsifier (Ultra Turrax) to obtain an emulsion D1.

  Emulsions D2, D3, D4, and D5 were obtained in the same manner as the emulsion D1, except that each of the "dispersions B2, B3, B4, and B5" was used instead of the "dispersion B1".

e) Particle preparation:
The obtained emulsion D1 was heated to 70 ° C. under a nitrogen stream and stirred for 20 hours to polymerize to obtain solid particles. to this,
-35% hydrochloric acid: 12 parts by mass-Ion exchange water: After adding 70 parts by mass, the mixture was stirred for 1 hour to dissolve calcium carbonate. Thereafter, suction filtration and washing with water were repeated 5 times, followed by suction filtration, followed by dry classification to obtain white particles E1.

  White particles E2, E3, E4 and E5 were obtained in the same manner as the white particles E1, except that the emulsions D2, D3, D4 and D5 were used instead of the emulsion D1.

2) Preparation of black mother particles:
-Styrene monomer: 90 parts by mass-Carbon black: 10 parts by mass-Polymerization initiator AIBN (azoisobutyronitrile): Similar to the white particles E1 except that the dispersion A was adjusted using 1 part by mass, Black particles F1 were obtained.
The composition of the obtained particles is shown in Table 1 below.

<Preparation of mixed particles (particle group for display device)>
The obtained white particles were used in combination with the black particles F1 and mixed to prepare mixed particles used in Examples 1 and 2 and Comparative Examples 1 to 3. At this time, the blending ratio (mass ratio) of the white particles and the black particles was set to be white particles: black particles = 2: 1. This was shaken by hand and charged to obtain mixed particles.

<Production of image display device and image forming apparatus>
Each obtained mixed particle was sealed in a gap between the substrates (display substrate 8 and non-display substrate 18) arranged to face each other, and an image forming apparatus as an image display device shown in FIG. 1 was produced. 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, white particles are positively charged, black particles are negatively charged, move in different directions according to the electric field between the display substrate 8 and the non-display substrate 18, and fix the electric field 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>
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 moved 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 density of the image density when the white particles are moved to the display screen side is the white image density, the image density when the white particles are moved to the display screen side and the image density when the black particles are moved The difference was taken as the contrast. The image density was evaluated using a Macbeth densitometer. When the white density was 0.4 or less, it was determined that there was sufficient whiteness, and when the density difference was 0.7 or more, it was determined that there was sufficient contrast.
The image was evaluated by leaving it for one week with the display screen placed vertically with the applied voltage turned off. The results are shown in Table 2 below.

  From the results of Table 2, Example 1 and Example 2 containing a predetermined amount of titanium oxide that has been subjected to hydrophilic treatment continue to maintain a clear image even after being displayed for a long time, and further exhibit a sufficient density of contrast. And it was confirmed that it has a sufficient hiding power.

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 ... black particles 24 ... white particles 26 ... voltage generating means (electrolytic generating means)

Claims (5)

A display device particle group comprising: 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. ,
At least one kind of the display device particles is present in a titanium oxide that has been subjected to a hydrophilic treatment,
The display device particle group, wherein the content of titanium oxide is 15 to 30% by mass of the display device particle containing titanium oxide.   The display device particle group according to claim 1, wherein the hydrophilic treatment is a treatment using a hydrophilic coupling agent.   The display device particle group according to claim 2, wherein the hydrophilic coupling agent is a hydrophilic silane coupling agent. An image display device in which a display device particle group is enclosed between a pair of substrates arranged opposite to each other,
The particle group for display devices is the particle group for display devices of any one of Claims 1-3, The image display device characterized by the above-mentioned.   An image forming apparatus comprising: an electric field generating unit that generates an electric field according to an image; and forming an image using the image display device according to claim 4.

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