JP4661096B2 - Particles for display device, image display medium and image forming apparatus - Google Patents

Description

  The present invention relates to an image display medium that can be rewritten repeatedly, particles for display devices used therefor, and an image forming apparatus.

Conventionally, display technologies such as Twisting Ball Display (two-colored 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 technique is excellent in image memory performance, there is a problem in that the display surface cannot be displayed in white like paper and the contrast is low.
As a display technique using toner that solves the above-described problems, conductive colored toner and white particles are sealed between opposing electrode substrates, and the charge transport layer provided on the inner surface of the electrode of the non-display substrate is used. Charge is injected into the conductive colored toner, and the charged conductive colored toner is moved to the display substrate side facing the non-display substrate by an electric field between the electrode substrates, and the conductive colored toner is moved to the display side. A technique has been proposed in which an image is displayed by the contrast between conductive colored toner and white particles attached to the inside of the substrate (see Non-Patent Document 1 below). This technique 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. 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 conductive colored toner does not move due to the electric field and is present in the substrate at random without being injected, there is a problem that the density contrast becomes low.

In order to improve such a problem, a pair of substrates and a plurality of types of particle groups that are sealed between the substrates so as to be movable between the substrates by an applied electric field and that have different colors and charging characteristics. An image display medium including this has been proposed (see Patent Document 1 below). With this image display medium, high whiteness and density contrast can be obtained.
However, this image display medium is excellent in white density, black density and density contrast in the initial stage, but when rewritten repeatedly, the image density is lowered and the density contrast is lowered or the uniformity of the image is lowered. There was sometimes unevenness.
JP 2001-31225 A Japan Hardcopy '99 Proceedings, p249-252

In order to solve this problem, the present inventors focused on the amount of nitrogen atoms contained in the particles for display devices, and by adding 0.03 mmol / g or more of nitrogen atoms in the particles, the chargeability was increased. It has been found that the image density does not decrease even after repeated image recording, and filed earlier (Japanese Patent Application No. 2002-370481).
This time, the present invention has found that the problems in the prior art as described above can be solved even if the nitrogen atom content in the particles is less than that of the prior invention.
That is, the object of the present invention is to provide a display device particle capable of preventing the occurrence of image unevenness by reducing the image density and reducing the image contrast even when rewritten, and further reducing the image uniformity. An object is to provide an image display medium and an image forming apparatus using the same.
Another object of the present invention is to provide an image display medium capable of setting a drive voltage low, and ensuring a stable display image for a long period of time even from an external impact and a long-time standing, and the same An object of the present invention is to provide an image forming apparatus using the above.

The above problems are solved by providing the following particles for a display device, an image display medium, and an image forming apparatus.
(1) In display device particles having properties that can be positively or negatively charged and colors, the element contains calcium element in an amount of 0.03 mg / 100 mg to 0.1 mg / 100 mg and a nitrogen atom with respect to the total amount of particles. Is contained in an amount of 0.004 mmol / g or more and less than 0.03 mmol / g.
(2) The display device particle according to (1), wherein the display device particle includes at least a coloring material, a resin, and a compound containing a nitrogen atom.

(3) An image display medium having a pair of substrates arranged opposite to each other and a display device particle group composed of at least two kinds of particles enclosed in a gap between the pair of substrates, the display device particles At least one kind of particles in the group has a property that can be positively charged and at least one other kind can be negatively charged, and the particles that can be positively and negatively charged have different colors and can be positively and negatively charged. At least one of the particles contains 0.03 mg / 100 mg or more and 0.1 mg / 100 mg or less of elemental calcium, and contains nitrogen atoms in an amount of 0.004 mmol / g or more and less than 0.03 mmol / g. Image display medium.
(4) The image display medium according to (3), wherein at least one of the positively and negatively charged particles is black or colored.
(5) The image display medium according to (4), wherein at least one of the positively and negatively chargeable particles is white.

(6) An electric field corresponding to image information is provided between a pair of substrates arranged opposite to each other, a particle group for display device composed of at least two kinds of particles enclosed in a gap between the pair of substrates, and the pair of substrates. An image forming apparatus provided with an electric field generating means for generating, wherein at least one type of particles in the display device particle group is positively charged and at least one other type can be negatively charged. The particles that can be charged have different colors, and at least one of the particles that can be positively and negatively charged contains 0.03 mg / 100 mg or more and 0.1 mg / 100 mg or less of elemental calcium, and nitrogen atoms are 0 An image forming apparatus comprising: .004 mmol / g or more and less than 0.03 mmol / g.

Since the particles for a display device of the present invention contain a specific amount of Ca element and nitrogen atom, when this is used for an image display medium, the image density is not lowered and the density contrast is not lowered even when rewritten repeatedly. Further, it is possible to prevent the occurrence of image unevenness due to a decrease in image uniformity.
In addition, the image forming apparatus of the present invention can set the drive voltage low, and can secure a stable display image over a long period of time even from an external impact and long-time standing.

  Hereinafter, the particles for a display device of the present invention, an image display medium using the same, and an image forming apparatus will be described in detail.

[Configuration of Particle for Display Device of the Present Invention]
The particles for display device of the present invention have properties and colors that can be positively or negatively charged, and contain 0.03 mg / 100 mg or more and 0.1 mg / 100 mg or less of calcium element with respect to the total amount of particles, and Nitrogen atoms are contained in an amount of 0.004 mmol / g or more and less than 0.03 mmol / g. Since the particles for display devices contain a specific amount of a specific element, the chargeability is improved, and even when rewriting is repeated, it is possible to prevent a decrease in image density and occurrence of image unevenness. Also, if the amount of calcium element is less than 0.03 mg / 100 mg, the effect of improving the charging property cannot be expected, so at least 0.03 mg / 100 mg or more, preferably 0.06 mg / 100 mg or more, more preferably 0.07 mg / 100 mg. The above is desirable. Further, if the amount of nitrogen atoms is less than 0.004 mmol / g, the effect of improving the chargeability cannot be expected, so at least 0.004 mmol / g or more, preferably 0.008 mmol / g or more, more preferably 0.01 mmol. / G or more is desirable.

  When the amount of calcium element contained in the display device particles exceeds 0.1 mg / 100 mg particles and the nitrogen atom content is 0.03 mmol / g or more, the display device particles agglomerate with each other. In this case, the image density is lowered and the density contrast is lowered, and further, the uniformity of the image is lowered and image unevenness is likely to occur.

  The particles for display devices of the present invention are not particularly limited as long as they have the characteristics as described above, but for practical purposes, it is preferable that the particles contain a coloring material and a resin, and if necessary, Other components such as a charge control agent and polymer fine particles may be contained. The color material may also serve as a charge control agent.

(Measurement of calcium element measurement)
The amount of calcium element is measured by fluorescent X-ray. The intensity of calcium contained in the toner resin was measured with fluorescent X-rays and converted from a separately measured calibration curve.

(Adjustment of the amount of calcium element)
The method for adding a specific amount of calcium to the particles for display device is not particularly limited as long as it is a method in which a predetermined amount of calcium is contained in the finally obtained particles. For example, a method of adding an inorganic calcium salt such as calcium carbonate in a controlled amount to the polymerization reaction liquid when producing particles for display device by suspension polymerization, the amount of hydrochloric acid when decomposing the inorganic calcium salt with hydrochloric acid after the polymerization reaction A method of adding by controlling, a method such as a combination of these methods can be used. Examples of the inorganic calcium salt include calcium chloride, calcium carbonate, calcium sulfate and the like.
Moreover, in order to make the particle | grains for display devices contain a calcium element, not only an inorganic calcium salt as mentioned above but arbitrary calcium containing compounds can be used.

(Adjustment of the amount of nitrogen atoms)
The nitrogen atom contained in the display device particle of the present invention functions as a starting point when the display device particle is charged. For example, the nitrogen atom-containing display device particles (black particles) shown in the Examples section are positively charged, and another type of display device particles (white particles) used in combination are negatively charged. Depending on the type of display device particles used, the nitrogen atom-containing display device particles are not necessarily positively charged.

Nitrogen atoms contained in particles for display devices may be supplied in a form contained in a color material or resin, or a compound containing a nitrogen atom separately from the color material or resin (hereinafter referred to as a color material or resin containing nitrogen). And other compounds may be collectively referred to as “nitrogen-containing compounds”). And it is preferable to perform nitrogen atom content in the particle | grains for display devices by adjusting the quantity of the said nitrogen-containing compound.
In addition, when the display device particles of the present invention are produced using a wet polymerization method such as suspension polymerization, the use of a resin and / or colorant containing nitrogen atoms is included in the display device particles. Adjustment of the content of nitrogen atoms, selection of the bonding form of nitrogen atoms, and the like are facilitated.

The binding form of nitrogen atoms in the nitrogen-containing compound contained in the particles for display device may be any binding form as long as it functions as a charging starting point. It is preferable to take an amine bond form.
The nitrogen-containing compound is preferably a monomer containing a reactive group that can undergo a polymerization reaction or a crosslinking reaction. The number of nitrogen atoms contained in the monomer is not particularly limited as long as it is 1 or more.
Specific examples of the nitrogen-containing compound having such a characteristic include a monomer containing one nitrogen atom as shown in the following general formula (1) and one group capable of polymerization reaction or crosslinking reaction. The nitrogen-containing compound used in the present invention is not limited to those represented by the following general formula (1).
Formula _{(1) Ra (CH 2)} n N (R 1) (R 2)

In the general formula (1), Ra represents a reactive group (polymerization reactive group and / or group capable of cross-linking reaction). For example, acryloyl group (CH ₂ ═CHCOO—), methacryloyl group (CH ₂ In addition to a group containing a double bond capable of undergoing a polymerization reaction such as ═C (CH ₃ ) COO—), a group containing a crosslinkable functional group is exemplified, and the group is not particularly limited. n shows the integer of 1-8.
R ₁ and R ₂ represent a substituent such as a hydrogen atom, an alkyl group, an aryl group (such as a phenyl group), an aralkyl group (such as a benzyl group or a phenethyl group), a carboxyl group, or a hydroxyl group, and R ₁ and R ₂ may be the same or different.

When R ₁ and R ₂ are alkyl groups, the carbon number thereof is preferably 1 to 8, more preferably 1 to 3, and particularly preferably a methyl group and an ethyl group.

  Specific examples of the nitrogen-containing compound represented by the general formula (1) as described above include, for example, diethylaminoethyl acrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate. And other monomers.

In addition, when producing the display device particles of the present invention using the monomer represented by the general formula (1), the content of nitrogen atoms contained in the display device particles is as described above. It is preferable to adjust the blending amount of the monomer represented by the general formula (1) so that the amount is 0.004 mmol / g or more and less than 0.03 mmol / g.

  In the display device particle of the present invention, “having color” means that the particle is not light-transmitting (transparent), and has black, white, gray and chromatic colors. Indicates.

(Coloring material)
Although it will not specifically limit if it is a well-known thing as a coloring material used for the particle | grains for display devices of this invention, Specifically, the following are mentioned. In the present invention, black, white, a mixed color (gray) thereof, and a chromatic color material are used as the color material for producing display device particles having color.
Examples of black colorants include organic and inorganic dye / pigment black materials such as carbon black, titanium black, magnetic powder, and oil black.
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 addition, as the chromatic color material, phthalocyanine-based, quinacridone-based, azo-based, condensed-based, insoluble lake pigment, and inorganic oxide-based dye / pigment can be used. 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. Blue 15: 1, C.I. I. Pigment Blue 15: 3 and the like are preferable examples.
These dyes and pigments may be subjected to a surface treatment for improving dispersibility, if necessary.

  In addition, chromatic color pigments include color filter pigments, blue pigments having a maximum absorption wavelength in the range of 400 nm to 500 nm, and green pigments having a maximum absorption wavelength in the range of 500 nm to 600 nm. And a red pigment having a maximum absorption wavelength in the range of 600 nm to 700 nm. More specifically, examples of blue pigments include C.I. I. Examples of green pigments such as C.I. Pigment Blue 15 (15: 3, 15: 4, 15: 6, etc.), 21, 22, 60, 64, etc. I. Examples of red pigments such as CI Pigment Green 7, 10, 36, and 47 include C.I. I. Pigment red 9, 97, 122, 123, 144, 149, 166, 168, 177, 180, 192, 215, 216, 224 and the like.

  These specific pigments are preferably used as master batch pigments. Here, the master batch was conceived for the purpose of improving the economics of blending color materials, improving the dispersion and uniformity of the color materials, and further improving the ease of injection, extrusion molding, weighing, etc. , A preliminary mixture for the final molded product (display device particles in the present invention), a pigment having a desired color mixed with a raw material resin at a high concentration (usually 5 to 50% by mass), kneaded, and pelletized (Or flake shape, plate shape).

  Examples of the raw resin used for the masterbatch pigment include styrene, methylstyrene, chlorostyrene, vinyl acetate, vinyl propionate, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, N-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, methacrylic acid Dodecyl, 2-ethylhexyl methacrylate, stearyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, glycidyl acrylate, glycidyl methacrylate, acrylic , Methacrylic acid, a radical polymerizable monomer homopolymers and copolymers such as 2-vinylpyridine, polyester resins, polyamide resins, epoxy resins, and the like.

The manufacturing method of a masterbatch pigment is shown below. First, the specific pigment and the raw material resin are pulverized and dispersed in an organic solvent to prepare a pigment dispersion. Here, a medium stirring mill such as a sand mill, a ball mill, or an attritor is used for the pulverization and dispersion treatment. Further, the pulverization / dispersion treatment may be performed by either a batch type or a continuous type. Thereafter, the organic medium is removed from the pigment dispersion and then pulverized to produce a master batch pigment in which the specific pigment is uniformly dispersed in the raw material resin.
When the particles for display devices of the present invention are produced using the masterbatch pigment thus obtained, the masterbatch pigment is added to the monomer and dispersed.

  Examples of the colorant that also serves as a 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 violet 23, C.I. I. Pigment black 1 and the like.

The addition amount of the color material is preferably in the range of 1 to 60% by mass, more preferably in the range of 5 to 50% by mass with respect to the whole particle, where the specific gravity of the color material is 1.
Moreover, when a color material is the said specific pigment, when the specific gravity of a color material is 1, it is preferable to set it as the range of 1-60 mass% with respect to the whole particle, and setting it as the range of 5-30 mass%. Is more preferable.

(resin)
Examples of the resins include polyolefin resins, polystyrene, acrylic resins, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl chloride, polyvinyl butyral, etc .; vinyl chloride-vinyl acetate copolymers; styrene-acrylic acid copolymers; organo Examples thereof include straight silicon resins composed of siloxane bonds and modified products thereof; fluorine resins such as polytetrafluoroethylene, polyvinyl fluoride, and polyvinylidene fluoride; polyesters, polyurethanes, polycarbonates; amino resins; and epoxy resins. These may be used alone or in combination with a plurality of resins. These resins may be cross-linked. Further, as the resin, a known binder resin known as a main component for toner used in conventional electrophotography can be used without any problem. In particular, it is preferable to use a resin containing a crosslinking component.
Moreover, it is preferable to include the nitrogen-containing monomer as described above in the resin.

(Polymer fine particles)
Conventionally known polymers can be used as the polymer fine particles, but those having a specific gravity lower than that of the color material to be used in combination are preferred, and when the polymer fine particles themselves have color, It is preferable to select and use them appropriately in consideration of the colors they have. Furthermore, as the resin used in combination, those described later can be used, but methacrylic or acrylic resins are preferably used.

  Specifically, as the polymer fine particles, for example, polystyrene resin, polymethyl methacrylate resin, urea polymarin resin, styrene / acrylic resin, polyethylene resin, polyvinylidene fluoride resin and the like can be used alone or in combination. However, it is not limited to these. These resins preferably have a crosslinked structure, and more preferably have a higher refractive index than the resin phase used in combination.

As the polymer fine particles, those having a shape such as a spherical shape, an irregular shape, and a flat shape can be used, but a spherical shape is more preferable.
Although the volume average particle diameter of the polymer fine particles can be used as long as it is smaller than the particles for display devices, it is preferably 10 μm or less, and more preferably 5 μm or less. The particle size distribution should be sharp, and more preferably monodisperse.

  Furthermore, from the viewpoint of producing particles for a display device having a smaller specific gravity, it is preferable that part or all of the polymer fine particles are made of hollow particles. The volume average particle diameter of the hollow particles can be used as long as it is smaller than the particles for display devices, but is preferably 10 μm or less, and more preferably 5 μm or less. In particular, in the case of hollow particles, from the viewpoint of light scattering, the volume average particle diameter is more preferably 0.1 to 1 μm, and particularly preferably 0.2 to 0.5 μm.

Here, “hollow particles” refer to those having voids inside the particles. The void is preferably 10 to 90%. Further, the “hollow particles” may be in the form of a hollow capsule, or the outer wall of the particles may be in a porous state.
Among hollow particles, those in a hollow capsule state have a difference in refractive index at the interface between the resin layer in the outer shell and the air layer inside the particle, and those in which the outer wall is in a porous state have an outer wall and a cavity. The whiteness can be increased by utilizing the light scattering caused by the difference in refractive index between the two and the hiding property can be enhanced.

  In addition, in the display device particles of the present invention, the amount of polymer fine particles added is preferably in the range of 1 to 40% by mass, and in the range of 1 to 20% by mass with respect to the entire display device particles. Is more preferable. When the addition amount of the polymer fine particles is less than 1% by mass, the effect of reducing the specific gravity due to the addition of the polymer fine particles may hardly appear. Moreover, when there are more addition amounts of polymer fine particles than 40 mass%, manufacturability, such as a dispersibility in producing the display device particle of a preferable form, may be inferior.

(Other additives)
If necessary, a charge control agent may be added to the display device particles of 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, quaternary ammonium salts such as cetylpyridyl chloride, P-51, P-53 (manufactured by Orient Chemical Industry), salicylic acid Examples thereof include metal oxide fine particles that have been surface-treated with a metal complex, a phenol condensate, a tetraphenyl compound, a calixarene compound, metal oxide fine particles, or various coupling agents.

  The charge control agent is desirably colorless, low coloring power, or a color similar to the color of the entire contained particles. By using a charge control agent that is colorless, has a low tinting strength, or a color similar to the color of the entire contained particle (that is, a color similar to the color of the coloring material contained in the particle), the hue of the selected particle can be adjusted. Impact can be reduced.

  Here, “colorless” means having no color, and “low coloring power” means having little influence on the color of the entire contained particles. In addition, “similar to the color of the entire contained particle” is a hue that is the same color as or similar to the color of the entire contained particle, although it has its own hue, and as a result, gives the color of the entire contained particle For example, in a particle containing a white pigment as a colorant, the white charge control agent is included in the category of “same color as the color of the entire particle”. In any case, the color of the charge control agent may be a desired color regardless of “colorless”, “low coloring power”, and “same color as the color of the entire particle”. If it becomes what becomes.

  The addition amount of the charge control agent is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass. As the size of the dispersion unit in the particles of the charge control agent, those having a volume average particle diameter of 5 μm or less are preferably used, and those having a volume average particle diameter of 1 μm or less are preferable. Moreover, you may exist in a compatible state in particle | grains.

  It is preferable that a resistance adjusting agent is further added to the display device particles of the present invention. By adding the resistance adjusting agent, it becomes possible to speed up the charge exchange between the particles, and it is possible to achieve early stabilization of the display image. Here, the resistance adjuster means a conductive fine powder, and in particular, a conductive fine powder that causes charge exchange and charge leakage appropriately is preferable. By coexisting the resistance adjusting agent, it is possible to avoid long-term friction between particles and increase in charge amount of particles due to friction between particles and the substrate surface, so-called charge-up.

As the resistance adjusting agent, an inorganic fine powder having a volume resistivity of 1 × 10 ⁶ Ωcm or less, preferably 1 × 10 ⁴ Ωcm or less is preferably exemplified. Specifically, for example, tin oxide, titanium oxide, zinc oxide, iron oxide, fine particles coated with various conductive oxides, for example, tin oxide-coated titanium oxide, and the like can be given. The resistance adjusting agent is preferably colorless, has a low coloring power, or has a color similar to the color of the entire contained particles. The meanings of these terms are the same as those described in the charge control agent. The addition amount of the resistance adjuster is preferably within a range of 0.1 to 10% by mass without any problem as long as it does not interfere with the color of the colored particles.

  As the particle diameter of the particles for display device of the present invention, it cannot be generally stated, but in order to obtain a good image, the volume average particle diameter is preferably about 1 to 100 μm, more preferably about 3 to 30 μm, These particle size distributions are preferably sharp, and more preferably monodisperse.

(Method for producing particles for display device)
Examples of the particles for display device of the present invention include a wet production method for producing spherical particles such as suspension polymerization, emulsion polymerization, and dispersion polymerization, and a pulverization classification method for producing conventional amorphous particles. Moreover, in order to make the shape of particle | grains uniform, heat processing can also be performed suitably.

  Moreover, it can adjust by classification operation as a method of arrange | equalizing a particle size distribution. Examples include, but are not limited to, various vibrating sieves, ultrasonic sieves, pneumatic sieves, wet sieves, rotor rotary classifiers using the principle of centrifugal force, and wind classifiers. These can be adjusted to a desired particle size distribution singly or in combination. In particular, when adjusting precisely, it is preferable to use a wet sieve.

  Further, as a method for controlling the particle shape (a method for controlling the shape factor), the following method and the like can be suitably exemplified. For example, as described in JP-A-10-10775, a polymer is dissolved in a solvent and a colorant is mixed, and the resulting mixed solution is dispersed in an aqueous medium in the presence of an inorganic dispersant, and the obtained dispersion is obtained. In the method of removing the solvent by freeze-drying the solution, or in the so-called suspension polymerization method, an organic solvent that is not compatible with the monomer (not compatible with the solvent or less) is added. A method of suitably selecting a drying method for removing the organic solvent in the step of carrying out suspension polymerization to produce, take out and dry the particles is preferable.

  A preferred example of the drying method in the suspension polymerization method is a freeze-drying method. In this freeze-drying method, the method is carried out in the range of −10 ° C. to −200 ° C. (preferably −30 ° C. to −180 ° C.). It is preferable. The freeze-drying method is performed at a pressure of about 40 Pa or less, but is preferably performed at 13 Pa or less. Here, as an organic solvent, ester solvents such as methyl acetate and propyl acetate, ether solvents such as diethyl ether, ketone solvents such as methyl ethyl ketone, methyl isopropyl ketone and methyl isobutyl ketone, hydrocarbon solvents such as toluene and cyclohexane Examples of the solvent include halogenated hydrocarbon solvents such as dichloromethane, chloroform, and trichloroethylene. These solvents are preferably capable of dissolving the polymer, and those having a solubility in water of about 0 to 30% by mass are preferable. In addition, cyclohexane is particularly preferable in view of safety, cost, and productivity in industrialization.

  Further, in addition to the above-described method, as described in JP 2000-292971 A, a method of mixing a plurality of fine particle dispersions to agglomerate and coalesce fine particles to increase to a desired particle size, In addition, mechanical impact force (for example, hybridizer (Nara Machinery Co., Ltd.), ong mill (Hosokawa Micron), θ composer (Tokuju Kosakusho), etc.) The shape of the particles can also be controlled by a method such as adding) or heating.

[Configuration of Image Display Medium of the Present Invention]
The image display medium of the present invention comprises a pair of substrates arranged opposite to each other, and a particle group composed of at least two types of particles enclosed in a gap between the pair of substrates, and at least of the two or more types of particles. An image display medium in which one type is positive and at least one other type can be negatively charged, and the particles that can be positively and negatively charged have mutually different colors, At least one kind of particles to be obtained is the display device particle of the present invention.

(Particle group consisting of two or more types of particles)
The particle group consisting of two or more types of particles in the present invention has a property that at least one of them (first particle) can be positively charged and at least one of the other types (second particle) can be negatively charged. The particles that can be positively and negatively charged have different colors.

  The image display medium of the present invention contains at least two kinds of particles for display devices as described above, and at least one kind of particles contains a specific amount of calcium element and nitrogen atom. Is reduced. Therefore, when the image display medium of the present invention is used for an image forming apparatus, a stable display image that can prevent a decrease in image contrast and occurrence of image unevenness can be maintained even when rewritten, and a driving voltage can be maintained. Can be set low, and a stable display image can be ensured over a long period of time even from external impact and long-time standing.

  In the image display medium of the present invention, the positively charged particles (first particles) and the negatively charged particles (second particles) may be either one type or two or more types, respectively. Even if there are two or more types without any problem, the effect of the present invention is exhibited by the same mechanism as described above, provided that one of them is composed of the particles for display device of the present invention.

  Hereinafter, in the image display medium of the present invention, the first particle and the second particle, that is, both particles that can be positively and negatively charged are collectively referred to as “display particles”. Both of these display particles are preferably composed of the display device particles of the present invention, but conventionally known display device particles that do not contain a nitrogen atom may be used in combination.

  The conventionally known particles that can be used in combination are composed of at least a color material and a resin, and the same color material and resin as those for the display device of the present invention can be used. In addition, other components such as a charge control agent and polymer fine particles may be included as necessary, and the color material may also serve as the charge control agent.

  In the image display medium of the present invention, one of the display particles is preferably white, in other words, it is preferable that one of the display particles includes a white color material. By making one particle white, the coloring power and density contrast of the other particle can be improved. At this time, titanium oxide is preferable as a white color material for making one particle white. By using titanium oxide as the color material, the hiding power can be increased in the range of the wavelength of visible light, and the density contrast can be further improved. As the white color material, rutile type titanium oxide is particularly preferable.

  The titanium oxide used in the present invention is preferably used in combination of two or more types having different particle diameters. Titanium oxide is generally poorly dispersible, and even when trying to improve dispersibility, those with a large diameter have a high specific gravity, so secondary and tertiary agglomeration occurs quickly, eventually resulting in poor dispersion stability. In some cases, the hiding power could not be fully demonstrated. On the other hand, those having a small particle size cannot cause sufficient light scattering, and have a low hiding power. Therefore, by using two or more types of titanium oxide having different average particle diameters in combination, it is possible to achieve both improvement in dispersion stability and concealment.

The primary particle diameter of titanium oxide that can be used is preferably at least one of 0.1 μm to 1.0 μm, which is an optically concealing particle diameter, and the other primary titanium oxide is primary. The particle diameter is preferably less than 0.1 μm.
Further, surface treatment may be performed on titanium oxide having a small particle diameter. As the surface treatment agent, various coupling agents and organic substances dissolved in a solvent can be used as long as the whiteness is not affected.

  Here, since the white display particles containing titanium oxide have a particularly large specific gravity as compared with the display particles having other colorants, it is particularly preferable to use display device particles including polymer fine particles as the display particles. . Moreover, since the whiteness also increases by making the polymer fine particles present in the particles for display devices into hollow particles, higher contrast can be expected.

The present invention is not limited to one of the display particles being white. For example, one of the display particles may be black or colored. However, the colored means a color other than black and white. In this case, for example, this is particularly effective when switching between black (or colored) characters and characters and symbols of other colors different from this color.
In addition, it is necessary to adjust the display particles so that one of them is positively charged and the other is negatively charged. However, when different types of particles collide or are rubbed to be charged, Depending on the positional relationship between the two charged columns, one is positively charged and the other is negatively charged. Therefore, for example, by appropriately selecting the above-described charge control agent, it is possible to appropriately adjust the position of the charge train.

  As the particle size of the display particles, when the display particles are composed of white particles and black particles, for example, the particle diameters and distributions of the white particles and the black particles are approximately equal to each other, so that the display particles are as large as a so-called two-component developer. Since the particle size particles are surrounded by the small particle size particles and an adhesion state that causes a decrease in the original color density of the large particles is avoided, a high white density and black density can be obtained. From such a viewpoint, the particle size distribution of the display particles is preferably about 15% or less in terms of variation coefficient, and particularly preferably monodisperse. The coefficient of variation is obtained by multiplying 100 times the value obtained by dividing the standard deviation of the volume average particle diameter in the particle size distribution of the display particles by the arithmetic average value of the volume average particle diameter.

  The contrast may also change depending on the mixing ratio of black and white particles. Therefore, a mixing ratio that allows the display particles to have the same surface area is desirable. If it deviates greatly from this, the color of particles with a large ratio may become strong. However, this is not the case when it is desired to provide contrast by displaying the same color with a dark color tone and a light color tone, or when it is desired to display with a color created by mixing two kinds of colored particles.

(substrate)
The substrates used in the image display medium of the present invention are used so as to form a pair so as to face each other, and the display 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), 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. It is necessary to be. In that case, the transparent conductive substrate becomes a display substrate.

  The conductive substrate may be conductive, or may be a conductive surface of an insulating support, and may be crystalline or amorphous. 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, gold, silver, copper, or the like 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 conductivity itself is used. Examples of the transparent support having conductivity per se include transparent conductive materials such as ITO (Indium Tin Oxide), 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, etc. 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 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 charge polarity of the display 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 consideration of the type of main component contained in the display particles to be used, and one having a small difference in frictional charge from the display particles is selected.

[Embodiment of Image Forming Apparatus of the Present Invention]
Hereinafter, an image forming apparatus of the present invention using the image display medium of the present invention will be described in detail with reference to the drawings. In addition, what has the same function attaches | subjects the same code | symbol through all the drawings, and the description may be abbreviate | omitted.

-First embodiment-
FIG. 1 is a schematic configuration diagram illustrating an example (first embodiment) of an image forming apparatus according to the present invention.
The image forming apparatus 12 according to the first embodiment includes a voltage applying unit 201 as shown in FIG. The image display medium 10 is provided with a spacer 204 between the display substrate 14 on the image display side and the non-display substrate 16 facing the display substrate 14 so as to seal the outer periphery of these two substrates. Black particles 18 and white particles 20 are enclosed as display particles in a gap partitioned by the substrate 14, the non-display substrate 16 and the spacer 204. A transparent electrode 205 is attached to the opposing surface of the display substrate 14 and the non-display substrate 16 as will be described later, but the transparent electrode 205 provided on the opposing surface of the non-display substrate 16 is grounded, and the display substrate The transparent electrodes 205 provided on the 14 opposing surfaces are connected to the voltage applying means 200.

Next, details of the image display medium 10 will be described.
The display substrate 14 constituting the image display medium 10 has, for example, a transparent electrode (for example, ITO transparent electrode) 205 and a protective layer 206 (for example, thickness) on the opposite surface of a 7059 glass substrate 201 having a size of 50 × 50 × 1.1 mm. 5 μm of “PC-Z” polycarbonate resin layer) is provided in this order. The non-display substrate 16 is formed on the glass substrate 202 having the same size as the 7059 glass substrate 201 and the transparent electrode 205 as described above. And a protective layer 206 are provided in this order.
As the spacer 204, a space formed by cutting out a central portion of a 40 × 40 × 0.3 mm silicon rubber plate into a 15 × 15 mm square can be used.

When the image display medium 10 is manufactured, this silicon rubber plate is placed on the opposite surface side of the non-display substrate 16. Next, as display particles, for example, titanium oxide-containing spherical white particles 20 with a volume average particle diameter of 20 μm and carbon-containing spherical black particles 18 with a volume average particle diameter of 20 μm are mixed at a mass ratio of 2: 1. About 15 mg of the mixed particles are shaken off through a screen into a square-cut portion of a silicon rubber plate placed on the opposite surface side of the non-display substrate 16. Thereafter, the opposite surface side of the display substrate 14 is brought into close contact with the silicon rubber plate, the two substrates are pressed and held with a double clip, and the silicon rubber plate and the two substrates are brought into close contact to form the image display medium 10.
The display device particles of the present invention are used for at least one of the black particles 18 and the white particles 20.

-Second Embodiment-
Hereinafter, a second embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 2 is a schematic configuration diagram showing another example (second embodiment) of the image forming apparatus of the present invention, and the image forming apparatus 12 for forming an image on the image display medium 10 using a simple matrix. It is shown.
In the plane direction of the image display medium 10 in which a plurality of display particle groups (not shown) having different charging properties are enclosed, electrodes 403An and 404Bn (n is a positive number) for controlling voltages in the vertical and horizontal directions are a simple matrix. Arranged to be a structure. The electrode 403An is connected to the power source 405A of the electric field generator 405 configured by the waveform generator 405B and the power source 405A, and the electrode 404Bn is the power source 402A of the electric field generator 402 configured by the waveform generator 402B and the power source 402A. It is connected to the. The electrode 404Bn, the power source 405A, and the electrode 403An are connected to the sequencer 406.

  When displaying an image, the electric field generator 402 or the electric field generator 405 generates a potential on each electrode 403An, 404Bn, and the sequencer 406 controls the potential drive timing of the electrode to drive the voltage of each electrode. And an electric field capable of driving display particles in units of one row is applied to the electrodes 403A1 to An on one side, and an electric field corresponding to image information is simultaneously applied to the electrodes 404B1 to Bn on the other side. Can do.

3 to 5 illustrate examples of schematic cross-sectional views of the image forming unit (image display medium 10) on an arbitrary surface of the image forming apparatus 12 illustrated in FIG.
The display particles 18 and 20 are in contact with the electrode surface or the substrate surface, and at least one surface of the substrate 14 or the substrate 16 is transparent so that the color of the display particles 18 and 20 can be transmitted from the outside. is there. As shown in FIG. 3, the electrodes 403A and 404B may be embedded and integrated on the surface side where the substrates 14 and 16 face each other, or embedded in the substrates 14 and 16 as shown in FIG. The display substrate 14 and the non-display substrate 16 may be separated from each other at a position slightly away from the surface opposite to the surface on which the display substrate 14 and the non-display substrate 16 face as shown in FIG. Good.

  By appropriately setting the electric field in the image forming apparatus 12, display by simple matrix driving becomes possible. The display particles 18 and 20 can be driven as long as they have a threshold value for movement with respect to the electric field, and the display particles 18 and 20 are not limited by the color, charge polarity, charge amount, and the like. Absent.

-Third embodiment-
Hereinafter, a third embodiment of the present invention will be described in detail with reference to the drawings. FIG. 6 is a schematic configuration diagram showing another example (third embodiment) of the image forming apparatus of the present invention, and specifically shows an image forming apparatus using print electrodes.
The image forming apparatus 12 shown in FIG. 6 includes a print electrode 11 and a counter electrode 26 that is disposed opposite to the print electrode and connected to the ground.
The image display medium 10 can be conveyed in the direction of arrow B between the print electrode 11 and the counter electrode 26. The image display medium 10 is composed of a pair of substrates (a display substrate 14 and a non-display substrate 16) and display particles 18 and 20 sealed between the substrates, and the non-display substrate 16 side faces when transporting in the arrow B direction. The display substrate side is conveyed so as to be close to or in contact with the electrode 26 and close to the print electrode 11.
The print electrode 11 includes a substrate 13 and an electrode 15 provided on the display substrate 14 side of the substrate 13, and the print electrode 11 is connected to a power source (not shown).

Next, the arrangement and shape of the electrode 15 provided on the display substrate 14 side of the print electrode 11 will be described. FIG. 7 is a schematic diagram showing an example of an electrode pattern provided on the print electrode. In FIG. 6, the surface of the print electrode 11 on which the electrode 15 is provided is moved from the non-display substrate 16 side toward the display substrate 14. It shows the case where it sees.
As shown in FIG. 7A, the electrode 15 is in a direction (that is, main scanning direction) substantially orthogonal to the conveyance direction of the image display medium 10 (the direction of arrow B in the figure) on one surface of the display substrate 14. Are arranged in a row at predetermined intervals according to the resolution of the image. The electrodes 15 may have a square shape as shown in FIG. 7B, or may be arranged in a matrix as shown in FIG. 7C.

Next, details of the printing electrode will be described. FIG. 8 shows a schematic configuration diagram of the print electrode.
As shown in FIG. 8, an AC power source 17 </ b> A and a DC power source 17 </ b> B are connected to each electrode 15 via a connection control unit 19. The connection control unit 19 has one end connected to the electrode 15 and the other end connected to the AC power source 17A, and once connected to the electrode 15 and the other end connected to the DC power source 17B. It is composed of a plurality of switches including the switch 21B.

  The switches 21A and 21B are ON / OFF controlled by the control unit 60, and electrically connect the AC power source 17A and the DC power source 17B to the electrode 15. Thereby, it is possible to apply an AC voltage, a DC voltage, or a voltage obtained by superimposing the AC voltage and the DC voltage.

Next, the operation in the third embodiment will be described.
First, when the image display medium 10 is transported in the direction of arrow B in the drawing by a transport means (not shown) and transported between the print electrode 11 and the counter electrode 26, the control unit 60 instructs the connection control unit 19. All the switches 21A are turned on. Thereby, an AC voltage is applied to all the electrodes 15 from the AC power source 17A.
Here, the image display medium 10 is a medium in which two or more types of display particle groups are enclosed in a space in a pair of substrates having no electrodes.

  When an AC voltage is applied to the electrode 15, the black particles 18 and the white particles 20 in the image display medium 10 reciprocate between the display substrate 14 and the non-display substrate 16. Thereby, the black particles 18 and the white particles 20 are frictionally charged due to the friction between the display particles and the friction between the display particles and the substrate. For example, the black particles 18 are positively charged and the white particles 20 are not charged or are negative. Is charged. In the following description, it is assumed that the white particles 20 are negatively charged.

Then, the control unit 60 instructs the connection control unit 19 to turn on only the switch 17B corresponding to the electrode 15 at the position corresponding to the image data, and applies a DC voltage to the electrode 15 at the position corresponding to the image data. For example, a DC voltage is applied to the non-image area, and no DC voltage is applied to the image area.
As a result, when a DC voltage is applied to the electrode 15, the positively charged black particles 18 in the portion where the print electrode 11 is opposed to the display substrate 14 as shown in FIG. Move to the display substrate 16 side. Further, the negatively charged white particles 20 on the non-display substrate 16 side move to the display substrate 14 side by the action of an electric field. Therefore, since only the white particles 20 appear on the display substrate 14 side, no image is displayed in a portion corresponding to the non-image portion.

On the other hand, when a DC voltage is not applied to the electrode 15, the positively charged black particles 18 in the portion where the print electrode 11 faces the display substrate 14 are maintained as they are on the display substrate 14 side due to the action of the electric field. The Further, the positively charged black particles 18 on the non-display substrate 16 side move to the display substrate 14 side by the action of an electric field. Accordingly, since only the black particles 18 appear on the display substrate 14 side, an image is displayed in a portion corresponding to the image portion.
Thereby, since only the black particles 18 appear on the display substrate 14 side, an image is displayed in a portion corresponding to the image portion.

  In this way, the black particles 18 and the white particles 20 move according to the image, and the image is displayed on the display substrate 14 side. Note that when the white particles 20 are not charged, only the black particles 18 move under the influence of the electric field. Since the black particles 18 at the portion where the image is not displayed move to the non-display substrate 16 and are hidden by the white particles 20 from the display substrate 14 side, the image can be displayed. Further, even after the electric field generated between the substrates of the image display medium 10 disappears, the displayed image is maintained by the adhesion force unique to the display particles. Further, since these display particles can move again if an electric field is generated between the substrates, the image forming apparatus 12 can repeatedly display images.

  Thus, since the display particles charged with air as a medium are moved by the electric field, safety is high. In addition, since air has a low viscous resistance, high-speed response can be satisfied.

-Fourth embodiment-
Hereinafter, a fourth embodiment of the present invention will be described in detail with reference to the drawings. FIG. 9 is a schematic configuration diagram showing another example (fourth embodiment) of the image forming apparatus of the present invention, and shows an image forming apparatus using an electrostatic latent image carrier.
The image forming apparatus 12 shown in FIG. 9 includes a drum-shaped electrostatic latent image carrier 24 that can rotate in the direction of an arrow A, and a drum-shaped counter electrode 26 that can be rotated in the direction of an arrow C and is disposed opposite thereto. Mainly configured, the image display medium 10 in which display particles are sealed between a pair of substrates can be inserted between the electrostatic latent image carrier 24 and the counter electrode 26 in the arrow B direction.

  A charging device 80 is disposed around the electrostatic latent image carrier 24 so as to be close to the electrostatic latent image carrier 24 on the substantially opposite side to the side where the counter electrode 26 is provided. A light beam scanning device 82 is arranged so that an electrostatic latent image can be formed on the surface of the electrostatic latent image carrier 24 on the arrow A direction side, and the electrostatic latent image forming unit 22 is configured by these three members. Has been.

  As the electrostatic latent image carrier 24, a photosensitive drum 24 can be used. The photoconductive drum 24 is formed by forming a photoconductive layer 24B on the outer peripheral side of a drum-shaped conductive base 24A such as aluminum or SUS, and various known materials can be used as the photoconductive layer 24B. . For example, an inorganic photoconductive material such as α-Si, α-Se, As2Se3, or an organic photoconductive material such as PVK / TNF can be used, and these are formed by plasma CVD, vapor deposition, dipping, or the like. Can do. Moreover, you may form a charge transport layer, an overcoat layer, etc. as needed. The conductive substrate 24A is grounded.

  The charging device 80 uniformly charges the surface of the electrostatic latent image carrier 24 to a desired potential. The charging device 80 may be any device as long as the surface of the photosensitive drum 24 can be charged to an arbitrary potential. In this embodiment, a high voltage is applied to the electrode wire and the electrostatic latent image carrier 24 is connected to the charging device 80. It is assumed that a corotron that generates corona discharge and uniformly charges the surface of the photosensitive drum 24 is used. In addition to this, various known chargers such as a conductive roll member, a brush, a film member, etc. are brought into contact with the photosensitive drum 24 and a voltage is applied to the photosensitive drum 24 to charge the surface of the photosensitive drum. can do.

  The light beam scanning device 82 irradiates a surface of a charged electrostatic latent image carrier 24 with a minute spot light based on an image signal, and forms an electrostatic latent image on the electrostatic latent image carrier 24. is there. The light beam scanning device 82 may be any device that irradiates the surface of the photosensitive drum 24 with a light beam in accordance with image information and forms an electrostatic latent image on the uniformly charged photosensitive drum 24. In this embodiment, a laser beam adjusted to a predetermined spot diameter by an imaging optical system including a polygon mirror 84, a folding mirror 86, a light source and a lens (not shown) provided in the light beam scanning device 82 is used as an image signal. Accordingly, a ROS (Raster Output Scanner) device that optically scans the surface of the photosensitive drum 24 by the polygon mirror 84 while being turned on and off accordingly. In addition, an LED head or the like in which LEDs are arranged according to a desired resolution may be used.

  The counter electrode 26 is made of a conductive roll member having elasticity, for example. As a result, the image display medium 10 can be more closely attached. Further, the counter electrode 26 is disposed at a position facing the electrostatic latent image carrier 24 with the image display medium 10 conveyed by a conveying means (not shown) in the direction of arrow B in the figure. The counter electrode 26 is connected to a DC voltage power supply 28. A bias voltage VB is applied to the counter electrode 26 by the DC voltage power supply 28. For example, as shown in FIG. 10, the bias voltage VB to be applied is set such that the potential of the positively charged portion on the electrostatic latent image carrier 24 is VH, and the potential of the uncharged portion is VL. The voltage is set to an intermediate potential between the two.

Next, the operation in the fourth embodiment will be described.
When the electrostatic latent image carrier 24 starts to rotate in the direction of arrow A in FIG. 9, an electrostatic latent image is formed on the electrostatic latent image carrier 24 by the electrostatic latent image forming unit 22. On the other hand, the image display medium 10 is conveyed in the direction of arrow B in the figure by a conveying means (not shown), and is conveyed between the electrostatic latent image carrier 24 and the counter electrode 26.

  Here, a bias voltage VB as shown in FIG. 10 is applied to the counter electrode 26, and the potential of the electrostatic latent image carrier 24 at a position facing the counter electrode 26 is VH. Therefore, when the portion of the electrostatic latent image carrier 24 facing the display substrate 14 is charged with a positive charge (non-image portion), it faces the electrostatic latent image carrier 24 of the display substrate 14. When the black particles 18 are attached to the portion, the positively charged black particles 18 move from the display substrate 14 side to the non-display substrate 16 side and adhere to the non-display substrate 16. Thereby, since only the white particles 20 appear on the display substrate 14 side, an image is not displayed in a portion corresponding to the non-image portion.

  On the other hand, when the portion facing the display substrate 14 of the electrostatic latent image carrier 24 is not charged with a positive charge (image portion), the black particles 18 are formed on the portion facing the counter electrode 26 of the non-display substrate 16. Is attached, the potential of the electrostatic latent image carrier 24 at the position facing the counter electrode 26 is VL, so that the charged black particles 18 are transferred from the non-display substrate 16 side to the display substrate. 14 moves to the display substrate 14. Thereby, since only the black particles 18 appear on the display substrate 14 side, an image is displayed in a portion corresponding to the image portion.

  In this way, the black particles 18 move according to the image, and the image is displayed on the display substrate 14 side. Even after the electric field generated between the substrates of the image display medium 10 disappears, the displayed image is maintained by the inherent adhesion force of the particles and the mirror image force between the particles and the substrate. Further, since the black particles 18 and the white particles 20 can move again when an electric field is generated between the substrates, the image forming apparatus 12 can repeatedly display images.

  As described above, since the bias voltage is applied to the counter electrode 26, the black particles 18 are moved regardless of whether the black particles 18 are attached to the display substrate 14 or the non-display substrate 16. Can do. For this reason, it is not necessary to adhere the black particles 18 to one substrate side in advance. In addition, an image with high contrast and sharpness can be formed. Furthermore, since particles charged with air as a medium are moved by an electric field, safety is high. In addition, since air has a low viscous resistance, high-speed response can be satisfied.

  The embodiments of the image forming apparatus of the present invention using the image display medium of the present invention have been described above with reference to the drawings. However, the image forming apparatus of the present invention is not limited to these embodiments. It can be set as desired. Moreover, although the combination of the colors of the display particles is black and white, the present invention is not limited to this combination, and display particles having a desired color can be appropriately selected as necessary.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, these examples do not limit the present invention. In the following examples and comparative examples, the image display medium and the image forming apparatus (shown in FIG. 1) according to the first embodiment described in the above-mentioned [Detailed Description of the Invention] section. Image display medium and image forming apparatus) were used. At this time, the size, material, and the like of each member were the same as those described in the above-mentioned [Best Mode for Carrying Out the Invention].

The amount of calcium element and the amount of nitrogen atoms contained in the display device particles of the present invention were measured as follows.
<Measurement of calcium element content>
The amount of calcium element was measured by fluorescent X-ray. The amount of calcium element in the display device particles was calculated by measuring the calcium intensity contained in the known amount of display device particles with fluorescent X-rays and converting from the separately measured calibration curve.

(Production of white particles)
-Preparation of dispersion A-
The following composition was mixed, and ball milling was performed for 20 hours with zirconia balls having a diameter of 10 mm to prepare dispersion A.
<Composition>
・ Cyclohexyl methacrylate: 64 parts by mass. Titanium oxide (white pigment): 30 parts by mass (primary particle size 0.3 μm, Type C CR 63: manufactured by Ishihara Sangyo)
Polymer fine particles (hollow particles): 5 parts by mass (primary particle size 0.3 μm, SX866 (A): manufactured by JSR)
Charge control agent: 1 part by mass (SBT-5-0016: manufactured by Orient Chemical Industries)

-Preparation of dispersion B-
The following composition was mixed and finely pulverized with a ball mill in the same manner as dispersion A to prepare dispersion B.
<Composition>
・ Calcium carbonate: 40 parts by mass ・ Water: 60 parts by mass

-Preparation of mixture C-
The following composition was mixed, degassed with an ultrasonic machine for 10 minutes, and then stirred with an emulsifier to prepare a mixed solution C.
<Composition>
-Dispersion B: 7.0 g
・ 20% saline: 50g

  35 g of dispersion A, 1 g of divinylbenzene, and 0.35 g of polymerization initiator V601 were weighed and mixed thoroughly, and deaerated with an ultrasonic machine for 10 minutes. This mixed solution was put into the mixed solution C and emulsified with an emulsifier. Next, this emulsified liquid was put into a bottle, and it was put into a silicone jar, and was sufficiently degassed under reduced pressure using an injection needle and sealed with nitrogen gas. Next, it was made to react at 70 degreeC for 10 hours, and particle | grains were obtained. The obtained fine particle powder was dispersed in ion-exchanged water, and calcium carbonate was decomposed with 50 g of 10% aqueous hydrochloric acid, followed by filtration. Then, it was washed with sufficient distilled water, and passed through a nylon sieve having openings of 10 μm and 15 μm to make the particle sizes uniform. This was dried to obtain white particles-1 (particles for display device) having an average particle size of 12.56 μm.

(Preparation of black particles 1)
Black particles-1 (indication of the present invention) were prepared in the same manner as the preparation of white particles-1 except that the following dispersion D in which diethylaminoethyl methacrylate was dissolved as a nitrogen-containing compound was used instead of the dispersion A. Device particles) were prepared. The average particle diameter of the obtained black particles-1 was 13.5 μm.
The amount of calcium element contained in the black particles 1 was 0.09 mg / 100 mg, and the amount of nitrogen atoms contained in the black particles 1 was 0.005 mmol / g.

-Preparation of dispersion D-
The following composition was mixed, and ball milling was performed with zirconia balls having a diameter of 10 mm for 20 hours to prepare dispersion D.
<Composition>
-Methyl methacrylate: 53.946 parts by mass-Diethylaminoethyl methacrylate: 0.054 parts by mass-Microlith black: 6 parts by mass

(Preparation of black particles 2)
Instead of Dispersion A, the following Dispersion E in which diethylaminoethyl methacrylate was dissolved as a nitrogen-containing compound was used, except that 80 g of hydrochloric acid was used. (Particles for display device of the present invention) were produced. The average particle diameter of the obtained black particles-2 was 13.34 μm.
The amount of elemental calcium contained in the black particles 2 was 0.05 mg / 100 mg, and the amount of nitrogen atoms contained in the black particles 2 was 0.023 mmol / g.

-Preparation of dispersion E-
The following composition was mixed, and ball milling was performed for 20 hours with 10 mmφ zirconia balls to prepare dispersion E.
<Composition>
-Methyl methacrylate: 52.92 parts by mass-Diethylaminoethyl methacrylate: 0.4 parts by mass-Microlith black: 6 parts by mass (manufactured by Ciba Specialty Chemicals)
Charge control agent: 1 part by weight (COPY CHARGE PSY VP2038: manufactured by Clariant Japan)

(Preparation of black particles 3)
Instead of the dispersion A, the following dispersion F was used, and the aqueous hydrochloric acid solution was the same as the preparation of the white particles-1 except that the calcium carbonate was decomposed with 10 g of hydrochloric acid water. (Particles for display device) were produced. The average particle diameter of the obtained black particles-3 was 12.87 μm.
The amount of calcium element contained in the black particles 3 was 0.16 mg / 100 mg, and the amount of nitrogen atoms contained in the black particles 3 was 0 mmol / g.

-Preparation of dispersion F-
The following composition was mixed, and ball milling with 10 mmφ zirconia balls was carried out for 20 hours to prepare dispersion F.
<Composition>
・ Methyl methacrylate: 90 mass parts ・ Microlith black: 10 mass parts (manufactured by Ciba Specialty Chemicals)

(Preparation of black particles 4)
Instead of Dispersion A, the following Dispersion G in which diethylaminoethyl methacrylate was dissolved as a nitrogen-containing compound was used, and calcium carbonate was decomposed with 20 g of hydrochloric acid. Black particles-4 (particles for display devices) were produced. The average particle diameter of the obtained black particles-4 was 13.25 μm.
The amount of calcium element contained in the black particles 4 was 0.12 mg / 100 mg, and the amount of nitrogen atoms contained in the black particles 4 was 0.89 mmol / g.

-Preparation of dispersion G-
The following composition was mixed, and ball milling with 10 mmφ zirconia balls was performed for 20 hours to prepare dispersion G.
<Composition>
-Methyl methacrylate: 51.3 parts by mass-Diethylaminoethyl methacrylate: 1.5 parts by mass-Microlith black: 6 parts by mass (manufactured by Ciba Specialty Chemicals)

<Examples 1-2 and Comparative Examples 1-2>
As shown in Table 1, a set (display particles 1 to 4) in which two sets of particles for display devices in which white particles and black particles 1 to 4 obtained as described above were combined was prepared.
These display particles 1 to 4 are enclosed in a gap between substrates (display substrate 14 and non-display substrate 16) arranged opposite to each other in the image display medium used in the image forming apparatus of the first embodiment shown in FIG. The image display media of Examples 1-2 and Comparative Examples 1-2 were obtained. At this time, the mixing ratio (number basis) of white particles and black particles was set to be white particles: black particles = 2: 1.

(Evaluation)
The obtained image display medium and image forming apparatus were evaluated as follows.
−Drive voltage−
When a DC voltage of 100 V is applied to the transparent electrode 205 of the display substrate 14 of the image display medium 10 in which a predetermined amount of two particles obtained by mixing white particles 20 and black particles 18 at a mass ratio of 2: 1 is enclosed, the non-display substrate 16 is applied. A part of the negatively charged white particles 20 on the side starts to move to the display substrate 14 side by the action of an electric field, and when a DC voltage (driving voltage) is applied, many white particles 20 are formed on the display substrate 14 side. The displayed density was almost saturated after moving.
At this time, the black particles 18 positively charged moved to the non-display substrate 16 side. Thereafter, even when the voltage was set to 0 V, the display particles on the display substrate 14 did not move, and the display density did not change. The DC voltage applied at this time is defined as a driving voltage, and this driving voltage is shown in Table 1.

Here, in the image evaluation method, in each of the images before and after the voltage polarity switching, five points in a 20 mm × 20 mm patch are measured with the density meter X-Rite 404, and the black reflection density of the five points is measured. The average value was calculated for each image. When the average reflection density was 1.2 or more, the image density was judged to be good (◯ in the table), and when the average reflection density was lower than 1.2, it was judged as not good (× in the table).
Further, the image unevenness was judged visually. In Table 1, o indicates that there is no problem with the image, and x indicates that large unevenness is observed and that it cannot be used practically.
Table 1 shows the results of evaluating the black reflection density and image unevenness after initial display and voltage polarity switching at 300 Hz for 1 minute and repeating this for a total of 5 times.

  From the results shown in Table 1, the content of nitrogen atoms contained in the black particles is 0.004 mmol / g or more and less than 0.03 mmol / g, and the calcium element contained in the black particles is 0.03 mg / 100 mg or more. By setting it to 0.1 mg / 100 mg or less, the black reflection density is sufficiently high, there is no image unevenness, and even after repeated display over a long period of time, the black reflection density is significantly reduced, and image unevenness It was found that there was no occurrence and a good image was obtained.

1 is a schematic configuration diagram illustrating an example (first embodiment) of an image forming apparatus of the present invention. It is a schematic block diagram which shows the other example (2nd Embodiment) of the image forming apparatus of this invention. It is a conceptual diagram which shows the cross section in the arbitrary places in the image display medium 10 used for the image forming apparatus 12 shown in FIG. It is a conceptual diagram which shows the cross section in the arbitrary places in the other image display medium 10 used for the image forming apparatus 12 shown in FIG. It is a conceptual diagram which shows the cross section in the arbitrary places in the other image display medium 10 used for the image forming apparatus 12 shown in FIG. It is a schematic block diagram which shows the other example (3rd Embodiment) of the image forming apparatus of this invention. It is a schematic diagram which shows the pattern of the electrode of a printing electrode. It is a schematic block diagram of a printing electrode. It is a schematic block diagram which shows the other example (4th Embodiment) of the image forming apparatus of this invention. It is a figure which shows the electric potential in an electrostatic latent image carrier and a counter electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image display medium 11 Print electrode 12 Image forming apparatus 13 Display substrate 14 side 14 of print electrode 11 Display substrate 15 Electrode 16 Non-display substrate 17A AC power supply 17B DC power supply 18 Display particle (black particle)
19 Connection control unit 20 Display particles (white particles)
22 Electrostatic latent image forming unit 24 Electrostatic latent image carrier (photosensitive drum)
24A conductive substrate 24B photoconductive layer 26 counter electrode 28 DC voltage power supply 60 controller 80 charging device 82 light beam scanning device 84 polygon mirror 86 folding mirror 204 spacer 205 transparent electrode 206 protective layer 402 electric field generator 402A power source 402B waveform generator 403 Electrode An
404 Electrode Bn
405 Electric field generator 405A Power source 405B Waveform generator 406 Sequencer

Claims (6)

  In the display device particles having a property that can be positively or negatively charged and a color, the calcium element is contained in an amount of 0.03 mg / 100 mg or more and 0.1 mg / 100 mg or less with respect to the total amount of the particles, and the nitrogen atom is 0.1%. A particle for a display device, comprising an amount of 004 mmol / g or more and less than 0.03 mmol / g.   The display device particle according to claim 1, wherein the display device particle includes at least a coloring material, a resin, and a compound containing a nitrogen atom.   An image display medium comprising a pair of substrates arranged opposite to each other and a display device particle group composed of at least two kinds of particles sealed in a gap between the pair of substrates, wherein the particles in the display device particle group At least one of the particles has the property of being positively charged and the other at least one of the particles can be negatively charged, and the particles that can be positively and negatively charged have different colors and at least positively and negatively charged particles. One type includes 0.03 mg / 100 mg or more and 0.1 mg / 100 mg or less of elemental calcium, and contains nitrogen atoms in an amount of 0.004 mmol / g or more and less than 0.03 mmol / g. .   The image display medium according to claim 3, wherein at least one of the positively and negatively charged particles is black or colored.   The image display medium according to claim 4, wherein at least one of the positively and negatively charged particles is white.   An electric field that generates an electric field corresponding to image information between a pair of substrates arranged opposite to each other, a display device particle group composed of at least two kinds of particles enclosed in a gap between the pair of substrates, and the pair of substrates. An image forming apparatus including a generation unit, wherein at least one type of particles in the display device particle group has a property of being positively charged and at least one other type of being negatively charged, and can be positively or negatively charged. At least one of the particles having mutually different colors and capable of being positively and negatively charged contains 0.03 mg / 100 mg or more and 0.1 mg / 100 mg or less of calcium element, and contains nitrogen atoms of 0.004 mmol / An image forming apparatus comprising an amount of g or more and less than 0.03 mmol / g.