JP2011170199A - Display medium particles and information display panel using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide composite display medium particles having external additives capable of improving fluidity and charge performance and stuck thereto. <P>SOLUTION: The display medium particles are used for an information display panel configured to seal a display medium having optical reflectance and electrostatic property between two substrates at least one of which is transparent and moving the display medium by applying charges to display information. The display medium particles are provided as composite particles 31 having mother particles 32 and slave particles 33 fixed to the surface. Two or more kinds of external additives 34a and 34b different in hydrophilicity/hydrophobicity are added to the surface of the composite particles. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technology related to an information display panel that encloses a display medium configured as a particle group between two transparent substrates, and displays information such as an image by moving the display medium. The present invention relates to particles for a display medium constituting a display medium.

  A liquid crystal display (LCD) is widely used as an information display device. However, it is generally known that liquid crystal display devices have drawbacks such as large power consumption and narrow viewing angle. Accordingly, as an alternative to a liquid crystal display device, a plurality of cells partitioned by a partition are formed between two substrates (for example, glass substrates) at least one of which is transparent, and a display medium configured as a particle group in the cells is provided. In recent years, an information display panel that encloses and moves the display medium to display information such as an image has attracted attention.

  The information display panel as described above displays a desired image or the like by electrically moving a display medium between substrates according to information such as an image, for example. Here, the display medium particles (particle groups) repeatedly move in the space between the substrates in accordance with the information requested to be displayed. In addition, while an electric field for rewriting is not applied again after the movement, the state can be maintained and images and the like can be stably displayed, so that power consumption can be suppressed.

  Regarding the particles for display media used in the information display panel, a technique for imparting fine particles called external additives to the surface has been proposed for the purpose of improving the fluidity and charging characteristics of the particles. Yes. For example, Patent Document 1 discloses display medium particles to which such an external additive is attached.

  In addition, with respect to particles for display media, the matrix is formed on the surface of the base particles that are the main body of the particles for display media with the intention of stabilizing the electrical characteristics and improving the chargeability and durability when repeated display rewriting is performed. Proposals have also been made for so-called composite particles in which child particles smaller in size than particles are added. For example, Patent Document 2 discloses a composite type display medium particle and an information display panel using the same, and improves durability when the display medium is repeatedly moved for display rewriting.

JP 2006-64815 A JP 2006-72283 A

  By adding the above-mentioned external additive to the surface of the composite type display medium particle, it is expected that the fluidity and charging performance as the display particle can be improved. In general, when a particle is constituted as a display medium particle, an external additive is added to the particle surface in order to reduce the adhesion between the particle and the electrode and between the particles and increase the fluidity of the particle. As such an external additive, inorganic particles are often used. However, since the inorganic particles reduce the charge retention of the display medium particles, a sufficient charge amount cannot be obtained during driving. Therefore, a countermeasure is taken to improve the charge retention by hydrophobizing the surface of the inorganic particles as external additives. However, when the hydrophobicity of the particle surface is increased, the particles are strongly charged locally, and the adhesion between the particles or between the particles and the electrodes is increased, which may deteriorate the display performance. In order to diffuse the local charge and make the charge uniform, it is necessary to make the particle surface hydrophilic to some extent. Since hydrophobicity and hydrophilicity are contradictory properties, it is difficult to adjust them with one external additive. Furthermore, conventionally, a single external additive is generally used for the display medium particles, and in this case, the charge retention and charge diffusivity are unique due to the hydrophilicity / hydrophobicity of the employed external additive. Therefore, it is difficult to obtain display medium particles having the expected charging performance.

  Therefore, an object of the present invention is to propose composite type display medium particles to which an external additive capable of improving the charging performance as well as the fluidity is attached.

The above object is to display information by enclosing a display medium having optical reflectivity and chargeability between two substrates, at least one of which is transparent, and moving the display medium by applying a charge to the display medium. In particles for display media used in panels,
The display medium particles are configured as composite particles having mother particles and child particles fixed to the mother particles, and two or more external additives having different hydrophilicity / hydrophobicity on the surface of the composite particles. Can be achieved by particles for display media, which are characterized in that.

  The external additive may be formed by subjecting the surface of the inorganic fine particles to a surface treatment so as to have different hydrophilicity / hydrophobicity.

  Further, the degree of hydrophilicity / hydrophobicity is determined by a methanol wetting test, and the external additive is added at a mixing ratio of relatively hydrophilic inorganic fine particles to relatively hydrophobic inorganic fine particles of 80:20 to 20:80. Can be formed.

  Since the above-mentioned particles for display medium are excellent not only in fluidity but also in charging performance, an information display panel using the particles can be provided as a display device that has excellent display performance and can stably display for a long time.

  In the composite type display medium particles according to the present invention, two or more kinds of external additives having different hydrophilicity / hydrophobicity are used. Therefore, depending on the result of appropriate mixing (blending), the charge holding power and charge of the particles The diffusivity can be adjusted. Therefore, since the composite type display medium particles according to the present invention can have a degree of freedom in charging design, display particles to which external additives capable of improving not only fluidity but also charging performance are attached. it can.

(A), (b) is the figure shown in order to demonstrate the principle structure of the information display panel of the charged particle movement system used as an example using the particle | grains for display media produced with the manufacturing method of this invention. (A), (b) is the figure shown in order to demonstrate the other fundamental structure of the information display panel of the charged particle movement system used as an example using the particle | grains for display media produced with the manufacturing method of this invention. is there. It is the figure which showed typically the particle | grains for composite type display media which concern on this invention.

  Hereinafter, the configuration of particles suitable for display medium particles according to an embodiment of the present invention will be described in detail with reference to the drawings. Here, in order to facilitate understanding of the present invention, as an example, a moving type information display panel that employs charged particles as display medium particles and moves the display medium particles to display an image or the like. First, the schematic configuration will be described.

  The charged particle movement type information display panel includes a group of particles composed of composite mother particles having chargeability sealed in a space between two opposing substrates, and composite display medium particles having child particles on the surface thereof. An electric field is applied. The display medium particles are attracted by the electric field force or the Coulomb force along the applied electric field direction, and the display medium particles are moved by the change in the electric field direction, thereby displaying information such as an image. Therefore, it is necessary to design the information display panel so that the particles for the display medium move uniformly and can maintain the stability when the display information is rewritten or when the display information is continuously displayed. is there. Here, the force applied to the particles for the display medium constituting the display medium is the force due to the electric field, the force attracted by the Coulomb force between the particles, the electric mirror image force between the electrode and the substrate, the intermolecular force, the liquid crosslinking force, gravity, etc. Can be considered.

An example of the information display panel using the display medium particles of the present invention as a display medium will be described with reference to FIGS. 1 (a) and 1 (b) and FIGS. 2 (a) and 2 (b).
The examples shown in FIGS. 1A and 1B include at least two types having different optical reflectivity and charging characteristics that are configured as a particle group including particles for display medium having at least optical reflectivity and chargeability. The display medium (here, the white display medium 3W configured as a particle group including the negatively charged white particles 3Wa and the black display medium 3B configured as the particle group including the positively charged black particles 3Ba) is shown. Is generated by applying a voltage between an electrode pair formed by the electrode 5 (pixel electrode with TFT) provided on the substrate 1 and the electrode 6 (common electrode) provided on the substrate 2 in each cell formed in (1). The substrate is moved perpendicular to the substrates 1 and 2 according to the electric field. Then, the white display medium 3W is visually recognized by the observer as shown in FIG. 1A, or the black display medium 3B is visually recognized by the observer as shown in FIG. 1B. For example, black and white dot matrix display can be performed.
In addition, in FIG. 1 (a), (b), the partition in front is abbreviate | omitted. The electrodes 5 and 6 may be provided outside the substrates 1 and 2, inside the substrate, or embedded in the substrate. Although an example in which a pixel (dot) and a cell are associated with each other on a one-to-one basis is shown, the pixel and the cell may not be associated with each other.

Further, in the example shown in FIGS. 2A and 2B, at least two types having different optical reflectivity and charging characteristics are configured as a particle group including particles having at least optical reflectivity and chargeability. The display medium (here, the white display medium 3W configured as a particle group including the negatively charged white particles 3Wa and the black display medium 3B configured as a particle group including the positively charged black particles 3Ba) is shown by the partition walls 4. In each formed cell, a voltage is applied between a pair of pixel electrodes formed by an electrode 5 (line electrode) provided on the substrate 1 and an electrode 6 (line electrode) provided on the substrate 2 at an opposing orthogonal intersection. The substrate is moved perpendicular to the substrates 1 and 2 in accordance with the generated electric field. Then, the white display medium 3W is visually recognized by the observer as shown in FIG. 2A, or the black display medium 3B is visually recognized by the observer as shown in FIG. 2B. A black and white dot matrix display is possible.
In addition, in FIG. 2 (a), (b), the partition in front is abbreviate | omitted. The electrodes 5 and 6 may be provided outside the substrates 1 and 2, inside the substrate, or embedded in the substrate. Although an example in which a pixel (dot) and a cell are associated with each other on a one-to-one basis is shown, the pixel and the cell may not be associated with each other.

  In addition, as said board | substrates 1 and 2, substrates, such as a glass substrate, a resin sheet board | substrate, and a resin film board | substrate, can be used. The substrate 2 on the display surface side (observation side) is a transparent substrate. When an electrode for applying a voltage having a predetermined voltage and polarity (positive / negative) (common electrode or line electrode 5 described in FIG. 1 or the like) is disposed in the information display screen area of the substrate 2 Is a transparent electrode. On the surface of the substrate 1 constituting the information display panel shown in FIGS. 1 and 2, pixel electrodes or line electrodes with thin film transistors (TFTs) are formed so as to form matrix electrode pairs. When a voltage is applied to the counter electrode pair, the above-described structure in which a desired display is performed by moving by applying an electric field to the display medium (particle group) can be realized.

  As the substrate described above, at least one of the substrates is a transparent substrate on which the color of the display medium can be confirmed from the outside of the panel, and a material having high visible light transmittance and good heat resistance is preferable. The back substrate as the other substrate may be transparent or opaque. Examples of the substrate material include organic polymer substrates such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethylene (PE), polycarbonate (PC), polyimide (PI), polyethersulfine (PES), and acrylic. Alternatively, a glass sheet, a quartz sheet, a metal sheet, or the like is used, and a transparent one is used on the display surface side. The thickness of the substrate is preferably 2 to 2000 μm, more preferably 5 to 1000 μm. If it is too thin, it will be difficult to maintain the strength and the uniformity of the distance between the substrates, and if it is thicker than 2000 μm, it will be a thin information display panel. It becomes inconvenient.

If necessary, the electrode forming material provided on the substrate may be made of metals such as aluminum, silver, nickel, copper, and gold, indium tin oxide (ITO), indium zinc oxide (IZO), zinc aluminum oxide (AZO). And conductive metal oxides such as indium oxide, conductive tin oxide, antimony tin oxide (ATO), and conductive zinc oxide, and conductive polymers such as polyaniline, polypyrrole, and polythiophene. Can be used. As a method for forming the electrode, a method of patterning the above-exemplified materials into a thin film by sputtering, vacuum deposition, CVD (chemical vapor deposition), coating, or the like, or a method of laminating metal foil (for example, rolled copper foil) Method) and a method of forming a pattern by mixing a conductive agent with a solvent or a synthetic resin binder and applying it.
The electrodes provided on the information display screen region of the viewing side (display surface side) substrate need to be transparent, but the electrodes provided outside the information display screen region and on the back side substrate do not need to be transparent. In any case, the above-mentioned material that is conductive and capable of pattern formation can be suitably used. In addition, the electrode thickness should just be sufficient if electroconductivity is ensured and there is no trouble in light transmittance, and 0.01-10 micrometers, Preferably 0.05-5 micrometers is suitable. The material and thickness of the electrode provided on the back side substrate are the same as those of the electrode provided on the display surface side substrate described above, but need not be transparent.

The shape of the partition provided on the substrate is appropriately set according to the type of display medium involved in display, the shape and arrangement of the electrodes to be arranged, and is not generally limited. However, the width of the partition is 2 to 100 μm, preferably 3 ~ 50 μm. The height of the partition wall can be within the inter-substrate gap, the substrate gap securing portion being the same as the inter-substrate gap, and the other cell forming portions being the same or lower than the inter-substrate gap. In forming the partition wall, a both-rib method in which ribs are formed on each of the opposing substrates 1 and 2 and then bonded, and a single-rib method in which ribs are formed only on one substrate are conceivable. In the present invention, any method is preferably used. The height of the partition wall is adjusted to the distance between the substrates, but may be partially lower than the distance between the substrates.
The cells formed by the partition walls made of these ribs are exemplified by, for example, a square shape, a triangular shape, a line shape, a circular shape, and a hexagonal shape as viewed from the plane of the substrate. The shape is illustrated. It is better to make the portion corresponding to the cross section of the partition wall visible from the display surface side (the area of the cell frame) as small as possible, and the display state can be clearly displayed.
Examples of the method for forming the partition include a mold transfer method, a screen printing method, a sand blast method, a photolithography method, and an additive method. Any of these methods can be suitably used for an information display panel mounted on the information display device of the present invention, and among these, a photolithography method using a resist film and a mold transfer method are preferably used.

Furthermore, the display medium particle | grains used as the object of this invention are demonstrated in detail. The particles for display medium of the present invention can be applied to the information display panels shown in FIGS. 1A and 1B and FIGS. 2A and 2B, and constitute a display medium between two substrates. Is to be enclosed. In particular, the particles for display medium of the present invention are composite particles in which a plurality of child particles are fixed to the surface of a mother particle serving as a particle body, and the surface has two types having different hydrophilicity / hydrophobicity. It is formed in a novel form with the above external additives attached.
The hydrophilicity / hydrophobicity of the external additive can be measured by, for example, a methanol wetting test described later. Then, based on the result obtained in the methanol wetting test, external additives having different parent / hydrophobicity may be confirmed.
In the present invention, at least one of the particles having a strong hydrophilic tendency and the other having a strong hydrophobic tendency are employed as the external additive. Thus, external additives having different hydrophilicity / hydrophobicity may be appropriately mixed, and as a result, desired charging performance may be obtained for the display medium particles.

  As an external additive applicable to the present invention, for example, inorganic particles such as silica, titania, and alumina may be used, and the surface may be subjected to different surface treatments to form external additives having different hydrophilicity / hydrophobicity. As the surface treatment method here, a silane coupling agent, silicone oil or the like can be used. In addition, the hydrophilicity / hydrophobicity can be controlled by controlling the amount of the treatment agent to be used and the kind and amount of the functional group contained in the treatment agent. The particle size of the mother particles is, for example, 1 μm to 20 μm, the particle size of the child particles is, for example, 50 nm to 500 nm, and the particle size of the external additive is, for example, about 5 to 100 nm.

  FIG. 3 is a diagram schematically showing a state of the composite display medium particle 31 having an external additive added to the surface according to the present invention. As shown in FIG. 3 (a), a composite particle 31 in which a part of the surface of the mother particle 32 is dented and the child particle 33 is fixed in an embedded state may be used, or as shown in FIG. 3 (b). Alternatively, the composite particles 31 may be formed in such a manner that the child particles 33 are fixed on the surface of the mother particles 32. As shown in FIGS. 3 (a) and 3 (b), the surface of the composite particle 31 has two or more external additives 34a (two cases are illustrated in FIG. 3) having different hydrophilicity / hydrophobicity. An external additive 34b is provided.

Hereinafter, each structure of the particles for display media according to the present invention will be described in order.
First, the mother particles of the composite type display medium particles will be described. The base resin that is the main component of the mother particles is preferably a thermoplastic resin, and can contain a charge control agent, a colorant, an inorganic additive, and the like, if necessary. Examples of resins, charge control agents, colorants, and other additives will be given below.

  The base particles of the display medium particles include a pigment as a colorant in the base resin as a main component thereof, and may further include a charge control agent, an inorganic additive, and the like as necessary. Examples of resins, charge control agents, colorants, and other additives will be given below.

  Examples of base resin for base particles include urethane resin, urea resin, acrylic resin, polyester resin, acrylic urethane resin, acrylic urethane silicone resin, acrylic urethane fluororesin, acrylic fluororesin, silicone resin, acrylic silicone resin, epoxy resin , Polystyrene resin, styrene acrylic resin, polyolefin resin, butyral resin, vinylidene chloride resin, melamine resin, phenol resin, fluororesin, polycarbonate resin, polysulfone resin, polyether resin, polyamide resin, methacrylic resin, methylpentene resin, cycloolefin Resins etc. can be mentioned. Two or more of these may be mixed. Moreover, what grind | pulverized the resin superposed | polymerized previously may be used, and what was formed by suspension polymerization may be used. In the case of suspension polymerization, acrylic resin, acrylic fluororesin, polystyrene resin, and styrene acrylic resin are suitable because of their ease.

  The charge control agent is not particularly limited. Examples of the negative charge control agent include salicylic acid metal complexes, metal-containing azo dyes, metal-containing oil-soluble dyes (including metal ions and metal atoms), and quaternary ammonium salt systems. Examples thereof include compounds, calixarene compounds, boron-containing compounds (benzyl acid boron complexes), and nitroimidazole derivatives. Examples of the positive charge control agent include nigrosine dyes, triphenylmethane compounds, quaternary ammonium salt compounds, polyamine resins, imidazole derivatives, and the like. In addition, metal oxides such as ultrafine silica, ultrafine titanium oxide, ultrafine alumina, nitrogen-containing cyclic compounds such as pyridine and derivatives and salts thereof, various organic pigments, resins containing fluorine, chlorine, nitrogen, etc. are also charged. It can also be used as a control agent.

  As the colorant, various organic or inorganic pigments and dyes as exemplified below can be used. Examples of the black colorant include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon and the like. Examples of blue colorants include C.I. I. Pigment blue 15: 3, C.I. I. Pigment Blue 15, Bituminous Blue, Cobalt Blue, Alkaline Blue Lake, Victoria Blue Lake, Phthalocyanine Blue, Metal-free Phthalocyanine Blue, Phthalocyanine Blue Partial Chlorides, Fast Sky Blue, Indanthrene Blue BC and the like. Examples of red colorants include bengara, cadmium red, red lead, mercury sulfide, cadmium, permanent red 4R, resol red, pyrazolone red, watching red, calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, Alizarin Lake, Brilliant Carmine 3B, C.I. I. Pigment Red 2 etc.

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

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

Examples of inorganic additives include titanium oxide, zinc white, zinc sulfide, antimony oxide, calcium carbonate, lead white, talc, silica, calcium silicate, alumina white, cadmium yellow, cadmium red, cadmium orange, titanium yellow, Examples include bitumen, ultramarine blue, cobalt blue, cobalt green, cobalt violet, iron oxide, carbon black, manganese ferrite black, cobalt ferrite black, copper powder, and aluminum powder.
These pigments and inorganic additives can be used alone or in combination. Of these, carbon black is particularly preferable as the black pigment, and titanium oxide is preferable as the white pigment. The above colorant can be blended to produce mother particles that are display medium particle precursors of a desired color.

  And as the child particle 33 fixed to the surface of the mother particle 32 in FIG. 3, fine particles of an inorganic material such as silica, alumina, titanium oxide, etc. may be adopted, polystyrene resin, acrylic resin, melamine You may employ | adopt the microparticles | fine-particles by organic materials, such as resin and a phenol resin.

  In addition, it is preferable that the particle | grains for display media manufactured by this invention are the range whose average particle diameter d (0.5) is 1-20 micrometers, and is uniform. If the average particle diameter d (0.5) is larger than this range, the display is not clear. If the average particle diameter d (0.5) is smaller than this range, the cohesive force between the particles becomes too large, which hinders movement as a display medium.

Furthermore, in the present invention, regarding the particle size distribution of each display medium particle, it is desirable that the particle size distribution Span represented by the following formula is less than 5, preferably less than 3.
Span = (d (0.9) −d (0.1)) / d (0.5)
(However, d (0.5) is a numerical value expressing the particle diameter in μm that 50% of the particles are larger than this and 50% is smaller than this, and d (0.1) is a particle in which the ratio of the smaller particles is 10%. (Numerical value expressed in μm, and d (0.9) is a numerical value expressed in μm for a particle diameter of 90% or less.)
By keeping Span within a range of 5 or less, the size of each particle is uniform, and movement as a uniform display medium becomes possible.

  Furthermore, in an information display panel using two types of display media composed of two types of display media particles having different charging polarities, the average grain of the display media having the larger average particle diameter d (0.5) It is important that the ratio between the diameter and the average particle diameter of the display medium having the smaller average particle diameter d (0.5) is 10 or less. Even if the particle size distribution Span is reduced, the display medium particles with different charging polarities move in the opposite directions, so the particle sizes of each other are the same, and the display medium particles move easily in the opposite directions. It is preferable to be able to do this, and this is the range.

The particle size distribution and the particle size can be obtained from a laser diffraction / scattering method or the like. When laser light is irradiated onto particles to be measured, a light intensity distribution pattern of diffracted / scattered light is spatially generated, and since this light intensity pattern has a corresponding relationship with the particle diameter, the particle diameter and particle diameter distribution can be measured. .
Here, the particle size and particle size distribution in the present invention are obtained from a volume-based distribution. For example, using a Mastersizer 2000 (Sysmex Corp.) measuring instrument, particles can be introduced into a nitrogen stream and the particle size and particle size distribution can be measured with the attached analysis software.

Furthermore, in a dry information display panel in which a display medium composed of display medium particles is driven in a gas space, it is important to manage the gas in the gap surrounding the display medium between the substrates, which contributes to improved display stability. To do. Specifically, it is important that the relative humidity at 25 ° C. is 60% RH or less, preferably 50% RH or less with respect to the humidity of the gas in the void portion.
1A, 1B, 2A, and 2B, the gaps are defined as electrodes 5 and 6 (electrodes on the substrate). In the case of being provided on the inner side), a gas portion in contact with a so-called display medium excluding an occupied portion of the display medium 3, an occupied portion of the partition wall 4, and a seal portion of the information display panel is meant. The gas in the gap is not limited as long as it is in the humidity region described above, but dry air, dry nitrogen, dry argon, dry helium, dry carbon dioxide, dry methane, and the like are preferable. This gas needs to be sealed in an information display panel so that the humidity is maintained, for example, filling a display medium, assembling an information display panel, etc. in a predetermined humidity environment, It is important to apply a sealing material and a sealing method that prevent moisture from entering from the outside.

The distance between the substrate and the substrate in the information display panel in which the particles for a display medium according to the present invention are employed is only required to be able to move the display medium and maintain the contrast, but is usually 10 to 500 μm, preferably 10 to 200 μm In the information display panel of the charged particle movement type, the thickness is adjusted to 10 to 100 μm, preferably 10 to 50 μm.
The volume occupation ratio of the display medium in the gas space between the opposing substrates is preferably 5 to 70%, more preferably 5 to 60%. Note that if it exceeds 70%, the movement of the display medium is hindered, and if it is less than 5%, the contrast tends to be unclear.

  Hereinafter, the display medium particles, which are composite type particles produced by attaching two types of external additives having different hydrophilicity / hydrophobicity, manufactured as examples of the present invention will be described. The present invention will be described in the following examples. It is not limited at all.

  As shown below, the mother particles formed on the resin base are prepared by a kneading and pulverizing method, and are subjected to a treatment for fixing the child particles on the surface of the mother particles to form composite particles. As shown in FIG. 1, external additives were applied to produce display medium particles of Examples and Comparative Examples (see FIG. 3). After the display medium particles were filled in the panel, an image was displayed by applying voltage to evaluate the performance.

The hydrophilicity / hydrophobicity of the external additive was determined by a methanol wetting test as described below.
Specifically, the external additives shown in Table 1 below were used. In the methanol wetting test, 10 g of aqueous methanol solutions having different concentrations were prepared in vials, and 0.1 g of the external additive shown in Table 1 was added to each solution. The lid of the vial was closed and the bottle was shaken about 10 times by hand. The higher the methanol concentration, the easier the external additive is dispersed in the aqueous solution, but the higher the surface hydrophobicity of the external additive is, the higher the concentration in the methanol leak test. In the test, the methanol concentration was gradually increased, and the methanol concentration when the external additive was dispersed for the first time was used as the characteristic value of the surface hydrophobicity of the external additive. In this test, the concentration was increased by 5% from 0% methanol, and the dispersibility of the external additive was evaluated.

About production method of particles for display media 1) Production method of base particles 100 parts by weight of base resin (TOPAS 5013: manufactured by Polyplastics Co., Ltd.) and titanium dioxide (TiO2) as a pigment (TYPECR CR-90: Ishihara Sangyo) 100 parts by weight were melt-kneaded with a biaxial kneader to produce pellets, which were once made into coarsely pulverized products, which were further finely pulverized with a particle diameter of 9 μm as a peak.
The obtained pulverized particles were treated with Meteoleinbo MR-10 (manufactured by Nippon Pneumatic Co., Ltd.) at 550 ° C. to obtain spherical mother particles for white particles.
Base particles for black particles were prepared in the same manner as described above, using 5 parts by weight of carbon black (manufactured by Mitsubishi Chemical Corporation) instead of titanium dioxide as a pigment.
2) Preparation method of composite particles Polystyrene-based fine particles (particle size 280 nm) as a child particle were mixed with the white mother particles at a predetermined ratio, and treated with Nobilta (manufactured by Hosokawa Micron) to obtain white composite particles.
For the black mother particles, melamine-based fine particles (particle size 240 nm) were mixed as child particles at a predetermined ratio, and positively charged particles were obtained by the same treatment.

External additive treatment For 100 parts by weight of the white composite particles, the external additives shown in Table 1 were mixed in the mixing ratio shown in Table 2 below so that the total amount would be 1.5 parts by weight. To obtain particles for white display medium.
With respect to 100 parts by weight of the black composite particles, 1.5 parts by weight of fumed silica (H3050: manufactured by Wacker) as an external additive was treated in the same manner to obtain particles for a black display medium. These were designated as Examples 1 to 6. Moreover, the case where only the external additive A-external additive D was added was made into Comparative Examples 1-4, and the case where the difference of the mixing | blending of the external additive from which hydrophilicity degree differed further was made into Comparative Examples 5 and 6.

About panel filling One kind of particles for white display medium prepared according to the above-described method and a predetermined black display medium particle are combined and filled between panels on which transparent electrodes (ITO) are formed. Examples and comparison An example evaluation panel was prepared.

About panel evaluation By applying a voltage of 100 V while changing the direction of the voltage between the electrodes of each of the manufactured evaluation panels of the example and the comparative example, white display and black display were performed on the evaluation panel. In each of the white display and the black display, the OD value (optical density) was measured using an optical densitometer: RD19 (Sakata Inx Engineering). A contrast CR = 10 ^{(| BOD−WOD |)} was calculated based on OD: WOD for white display and OD: BOD for black display, and this was used as an index of panel performance.
The contrast when rewritten at intervals of 15 seconds is short intermittent CR, and the contrast when rewritten at intervals of 1 hour is long intermittent CR, ◎ (CR ≧ 7), ○ (7> CR ≧ 5), × Scoring was done in three stages (5> CR). The evaluation results for each external additive formulation are summarized in Table 2 below.

From Table 2, it can be confirmed that the display medium particles of the examples in which the external additives having different hydrophilicity / hydrophobicity are mixed have better charging performance.
Table 3 below summarizes the best modes based on the examples.

  It is preferable to determine the hydrophilicity / hydrophobicity by a methanol wetting test and to adopt a relatively hydrophilic external additive having a hydrophilicity / hydrophobicity of 10 to 35%. Moreover, it is preferable to employ a relatively hydrophobic external additive having a hydrophilicity / hydrophobicity of 40 to 70. From Table 2 above, it is preferable that the mixing ratio of the external additive made up of relatively hydrophilic inorganic fine particles and the external additive made up of relatively hydrophobic inorganic fine particles is 80:20 to 20:80. .

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed. In the above embodiment, the case of using two types of external additives is illustrated, but three or more types may be used as necessary.

  An information display panel that employs particles for a display medium according to the present invention includes a notebook computer, an electronic notebook, a portable information device called PDA (Personal Digital Assistants), a display unit of a mobile device such as a mobile phone and a handy terminal, Electronic paper such as books, electronic newspapers, electronic manuals (electronic instruction manuals), signboards, posters, bulletin boards such as blackboards and whiteboards, electronic desk calculators, home appliances, display parts for automobiles, point cards, IC cards, etc. Card display unit, electronic advertisement, information board, electronic POP (Point Of Presence, Point Of Purchase advertising), electronic price tag, electronic shelf label, electronic score, display unit of RF-ID equipment, POS terminal, car navigation device It is suitably used for display units of various electronic devices such as watches. In addition, it is also suitably used as a so-called rewritable paper in which the display is rewritten using the external electric field forming means or the external rewriting means only at the time of display rewriting.

1, 2 Substrate 3Wa, 3Ba Display medium particle 3W, 3B Display medium (particle group)
31 Composite type display medium particle 32 Base particle 33 Child particle 34a External additive 34b External additive

Claims (4)

Used in an information display panel in which a display medium having optical reflectivity and chargeability is sealed between two substrates, at least one of which is transparent, and the display medium is moved by applying a charge to display information. In the display medium particles,
The display medium particles are configured as composite particles having mother particles and child particles fixed to the mother particles, and two or more external additives having different hydrophilicity / hydrophobicity on the surface of the composite particles. The particle | grains for display media characterized by the above-mentioned.   2. The display medium particle according to claim 1, wherein the external additive is formed by subjecting the surface of the inorganic fine particles to a surface treatment so as to have different hydrophilicity / hydrophobicity.   The degree of hydrophilicity / hydrophobicity is determined by a methanol wetting test, and the external additive is formed with a mixing ratio of relatively hydrophilic inorganic particles and relatively hydrophobic inorganic particles being 80:20 to 20:80. The particles for display medium according to claim 2, wherein the particles are for display media.   An information display panel comprising the display medium particle according to claim 1.

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