JP2010061061A - Display particles for image display device and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide display particles capable of sufficiently reducing a drive voltage and capable of repeatedly displaying an image having relatively high contrast between an image part and a non-image part, and to provide an image display device including the display particles. <P>SOLUTION: Regarding the display particles for use in the image display device, the charged display particles are enclosed in between two substrates, at least one of which is transparent, and an electric field is generated between the substrates, then, the display particles are moved to display the image. The display particles include positive-charged display particles and negative-charged display particles. A dielectric constant of positive-charged display particle and a dielectric constant of negative-charged display particle are independently in the range of 2.0 to 4.0. Further, there is provided the image display device including the display particles. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

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

As the display particles, for example, Patent Document 1 proposes to use display particles that make the volume specific resistance of the resin constituting the display particles 1 × 10 ¹⁴ Ω · cm or more. However, since such display particles have a relatively high dielectric constant and polarization is caused by an electric field, the driving voltage cannot be sufficiently reduced. Further, when image display and erasure are repeatedly performed, there is a problem that the contrast between the image portion and the non-image portion is significantly lowered.
JP 2008-9422 A

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

The present invention provides an image display device that displays an image by moving display particles by encapsulating charged display particles between two substrates, at least one of which is transparent, and generating an electric field between the substrates. In the display particles used,
The display particles include positively charged display particles and negatively charged display particles, and the dielectric constants of the positively charged display particles and the negatively charged display particles are independently in the range of 2.0 to 4.0. The present invention relates to particles and an image display device including the display particles.

  According to the present invention, it is possible to effectively reduce the drive voltage and to repeatedly display an image having sufficiently high contrast between the image portion and the non-image portion.

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

  The positively charged display particles and the negatively charged display particles each independently have a dielectric constant in the range of 2.0 to 4.0. The dielectric constants of the positively charged display particles and the negatively charged display particles are preferably independently 2.2 to 3.5 from the viewpoint of further improving the initial contrast and further reducing the driving voltage. From the viewpoint of further improving the contrast and further reducing the driving voltage, it is preferably independently 2.2 to 3.0. The positively charged display particles and the negatively charged display particles each have the above-described dielectric constant, so that when the electric field is formed between the substrates, the individual display particles are effectively moved based on the electric field without causing polarization. Become. Therefore, the driving voltage can be effectively reduced, and an image with sufficiently high contrast between the image portion and the non-image portion can be repeatedly displayed. If the dielectric constant is too small, the display particles are not effectively driven by the electric field, so that it is difficult to move the display particles based on the electric field. For this reason, the drive voltage increases and the contrast decreases. If the dielectric constant is too large, polarization in the display particles is promoted when an electric field is formed between the substrates, and the driving action by the electric field is canceled, so that the movement of the display particles based on the electric field becomes difficult. For this reason, the drive voltage increases and the contrast decreases. Even if the dielectric constant of only one of the positively charged display particles or the negatively charged display particles is outside the above range, the drive voltage increases and the contrast decreases.

  The dielectric constant of the positively charged display particles and the dielectric constant of the negatively charged display particles may be independently within the above ranges, and the difference between them is to allow both display particles to be driven in the same electric field. Preferably it is 0.5 or less, and 0.3 or less is more preferable.

  In this specification, the dielectric constant is a value measured using an impedance measuring device. As a specific measuring apparatus, for example, “4284A Precision LCR Meter (manufactured by Hewlett-Packard Company)” or the like can be used. Hereinafter, a method for obtaining the dielectric constant of display particles using a “4284A Precision LCR meter (manufactured by Hewlett-Packard Company)” will be described with reference to FIG.

  First, in an environment of 25 ° C. and 50%, 0.6 g of predetermined display particles are weighed, a load of 34300 kPa is applied, and a disk-shaped measurement sample 1 having a diameter of 25 mm and a thickness of 1 mm or less is molded. Next, the prepared measurement sample 1 is mounted and fixed to a dielectric constant measurement jig (electrode) 2 “SE-71 type fixing electrode Ando Electric” having a diameter of 25 mm. Then, applying a load of 3.43N (350g), measuring the dielectric constant three times with LCR meter 3 “TYPE AG4311 LCR METER Ando Electric” under the condition of AC applied voltage 5V and frequency 100kHz, the average The value is the dielectric constant.

The dielectric constant of the positively charged display particles and the negatively charged display particles is measured by separating and collecting the positively charged display particles and the negatively charged display particles from the image display device according to the following method, and using the obtained measurement method. it can.
First, a DC voltage of 500 V is applied between the upper and lower electrodes of the image display device to separate the positively charged display particles and the negatively charged display particles in the device, and then the device is disassembled. Next, positively charged display particles and negatively charged display particles are collected. By subjecting the collected positively charged display particles and negatively charged display particles to the measurement method described above, the dielectric constant of each display particle can be measured. As for the DC voltage, +500 V is applied to one electrode and 0 V is applied to the other electrode.

(Manufacture of display particles)
The positively charged display particles and the negatively charged display particles are composed of base particles containing at least a binder resin and a colorant, and usually further include an external additive. The charging polarity of the display particles is controlled mainly by selecting a carrier in a method for manufacturing an image display device described later, for example. For example, a carrier having a core surface coated with a fluorinated acrylate resin is usually used for a positively charged display particle. For those used as negatively charged display particles, a carrier having a core surface coated with cyclohexyl methacrylate is used.

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

  The colorant contained in the base particles has different colors depending on whether the display particles have a predetermined dielectric constant and are used for positively charged display particles and those used for negatively charged display particles. As long as a colorant is used, it is not particularly limited, and a known pigment is used. Hereinafter, the white base particles and the black base particles will be described, but the present invention should not be construed as being limited to these combinations.

For example, specific examples of the white pigment constituting the white base particles include anatase type titanium oxide, rutile type titanium oxide, zinc oxide (zinc white), antimony white, and zinc sulfide. From the viewpoint of controlling the dielectric constant, anatase-type titanium oxide, rutile-type titanium oxide, and zinc oxide are preferable, and anatase-type titanium oxide and rutile-type titanium oxide are particularly preferable. Two or more white pigments can be contained in combination.
For example, specific examples of the black pigment constituting the black base particles include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, and the like. Carbon black is preferable from the viewpoint of controlling the dielectric constant. Two or more black pigments can be contained in combination.

  The dielectric constant of the display particles can be controlled by adjusting the type and content of the colorant. For example, when used in the same content, for example, zinc oxide has a smaller dielectric constant of display particles than titanium oxide. Further, for example, the smaller the colorant content, the smaller the dielectric constant of the display particles, but the degree of coloration decreases, so the contrast tends to decrease. Increasing the colorant content increases the dielectric constant.

  The content of the colorant is usually 20 to 200 parts by weight in the case of white base particles with respect to 100 parts by weight of the binder resin, from the viewpoint of controlling the dielectric constant and the balance between reduction in driving voltage and improvement in contrast. In the case of black matrix particles, it is usually 5 to 20 parts by weight.

Regarding the content of the colorant in the white base particles, specifically, for example, when anatase type titanium oxide is used together with a styrene-acrylic copolymer resin as a binder resin, it is usually 20 to 100 parts by weight of the binder resin. 180 parts by weight, preferably 25 to 160 parts by weight, more preferably 30 to 150 parts by weight.
For example, when rutile type titanium oxide is used together with a styrene / acrylic copolymer resin as a binder resin, it is usually 20 to 180) parts by weight, preferably 25 to 160 parts by weight with respect to 100 parts by weight of the binder resin. Parts, more preferably 30 to 150 parts by weight.
For example, when using zinc oxide together with a styrene / acrylic copolymer resin as a binder resin), it is usually 40 to 200 parts by weight, preferably 50 to 180 parts by weight, with respect to 100 parts by weight of the binder resin. More preferably, it is 60-160 weight part.
When the content of the colorant is too small, the dielectric constant becomes too small, and the coloring degree is lowered. Therefore, the drive voltage increases and the contrast decreases. When the content of the colorant is too large, the dielectric constant becomes too large, so that the driving voltage increases and the contrast decreases.

  Specifically, for example, when carbon black is used together with a styrene / acrylic copolymer resin as a binder resin, the content of the colorant in the black base particles is preferably 8 to 20 weights with respect to 100 parts by weight of the binder resin. Part, more preferably 5 to 15 parts by weight.

  The average primary particle size of the colorant is not particularly limited as long as the coloring power can be exerted, and is usually 50 to 500 nm, particularly 100 to 300 nm in the case of a white pigment, and 10 to 50 nm, particularly 15 in the case of a black pigment. ˜35 nm is preferred.

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

Other additives such as a charge control agent may be internally added to the base particles.
In the case of white base particles, as a positively chargeable charge control agent, digrosine dye, triphenylmethane compound, quaternary ammonium salt compound, polyamine resin, imidazole derivative, etc. Examples of the control agent include salicylic acid metal complexes, metal-containing azo dyes, quaternary ammonium salt compounds, calixarene compounds, nitroimidazole derivatives, and the like.

The display particles of the present invention can be produced by adding an external additive to the base particles and mixing them.
As the external additive, conventionally known external additives are used in the field of display particles of an image display device, and examples thereof include silica and titania.

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

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

  The addition amount of the external additive is not particularly limited, and is usually 0.1 to 20 parts by weight, particularly preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the base particles.

The method for producing the base particles is not particularly limited. For example, a known method for producing particles containing a resin and a colorant is applied, such as a method for producing toner used for electrophotographic image formation. It is possible to cope with it. Specific examples of the method for producing the base particles include the following methods.
(1) A method of preparing base particles through kneading and classification steps after kneading a resin and a colorant;
(2) a so-called suspension polymerization method in which a polymerizable monomer and a colorant are mechanically stirred in an aqueous medium to form droplets and then polymerized to produce base particles; and (3) interface A polymerizable monomer is dropped into an aqueous medium containing an activator, a polymerization reaction is performed in micelles to produce polymer particles of 100 to 150 nm, and then colorant particles and an aggregating agent are added. So-called emulsification association method in which base particles are produced by associating particles.

  The volume average particle diameter D1 of the display particles is 0.1 to 50 μm, and preferably 1 to 20 μm from the viewpoint of ease of movement by an electric field and reduction of concentration variation.

The volume average particle diameter D1 of the particles is a volume-based median diameter (d50 diameter), and is measured and calculated using a device in which a computer system for data processing is connected to Multisizer 3 (manufactured by Beckman Coulter). Can do.
As a measurement procedure, 0.02 g of particles are mixed with 20 ml of a surfactant solution (for dispersing particles, a surfactant solution obtained by diluting a neutral detergent containing a surfactant component 10 times with pure water). After that, ultrasonic dispersion is performed for 1 minute to prepare a particle dispersion. This particle dispersion is poured into a beaker containing ISOTON II (manufactured by Beckman Coulter, Inc.) in a sample stand with a pipette until the measurement concentration reaches 10%, and measurement is performed with a measuring machine count set to 2500 pieces. The aperture size of the multisizer 3 is 50 μm.

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

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

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

  At the outermost part of the image display device 10 in FIG. 2 (a), two substrates 11 and 12 that are casings constituting the image display device are arranged to face each other. In the substrates 11 and 12, an electrode 15 for applying a voltage is provided on the surface on which both faces each other, and an insulating layer 16 is provided on the electrode 15. The substrates 11 and 12 are provided with an electrode 15 and an insulating layer 16, and display particles exist in a gap 18 formed by facing the surfaces having the electrode 15 and the insulating layer 16. The image display apparatus 10 shown in FIG. 2 has a gap between two types of display particles, which are negatively charged black display particles (hereinafter referred to as black particles) 21 and positively charged white display particles (hereinafter referred to as white particles) 22 as display particles. 18 is present. Strictly speaking, the external additives described above are added to the surfaces of the black particles 21 and the white particles 22, but they are not shown. Further, in the image display device 10 of FIG. 2, the gap 18 is surrounded by the substrates 11 and 12 and the two partition walls 17, and the display particles are present in a state of being enclosed in the gap 18 in the form of powder. is doing.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

<Example 1>
[Production of positively charged display particles (white particles)]
The resin and titanium oxide described below were put into a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.), the peripheral speed of the stirring blade was set to 25 m / second, and the mixture was mixed for 5 minutes to obtain a mixture.
Styrene acrylic resin (weight average molecular weight 20,000) 100 parts by weight Anatase type titanium oxide (average primary particle size 150 nm) 30 parts by weight The above mixture was kneaded with a twin-screw extrusion kneader and then coarsely pulverized with a hammer mill. Coarse powder pulverization was performed with a turbo mill pulverizer (manufactured by Turbo Kogyo Co., Ltd.), and fine powder classification was performed with an airflow classifier utilizing the Coanda effect to produce white base particles having a volume average particle size of 8.2 μm and CV20. . Next, 5.0 parts by weight of silica fine particles (average primary particle size 100 nm) subjected to aminosilane coupling treatment are added to 100 parts by weight of the white base particles, and a TK mixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) is used. The rotation speed was set to 50 m / sec, and a mixing process for 30 minutes was performed (first mixing). Subsequently, 0.5 parts by weight of titania fine particles having an average primary particle size of 15 nm subjected to silicone oil treatment were added, and white particles were obtained by performing a mixing treatment for 5 minutes using a turbuler mixer (manufactured by Willy A Bachoffen). Produced (second mix).

[Manufacture of negatively charged display particles (black particles)]
The resin and carbon black described below were put into a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.), the peripheral speed of the stirring blade was set to 25 m / sec, and the mixture was mixed for 5 minutes to obtain a mixture.
Styrene acrylic resin (weight average molecular weight 20,000) 100 parts by weight Carbon black (average primary particle size 25 nm) 10 parts by weight The above mixture is kneaded with a twin-screw extrusion kneader, then coarsely pulverized with a hammer mill, and then turbo milled. Coarse powder was pulverized by a machine (manufactured by Turbo Kogyo Co., Ltd.), and further finely classified by an airflow classifier utilizing the Coanda effect to produce black matrix particles having a volume average particle size of 8.0 μm and CV20. Next, to 100 parts by weight of the black base particles, 5.0 parts by weight of silica particles treated with disilazane (average primary particle size 100 nm) are added, and a TK mixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) is used. The rotation speed was set to 50 m / sec, and a mixing process for 30 minutes was performed (first mixing). Subsequently, 0.5 parts by weight of titania fine particles having an average primary particle size of 15 nm subjected to silicone oil treatment were added, and black particles were obtained by mixing for 5 minutes using a Turbuler mixer (manufactured by Willy A Bachoffen). Produced (second mix).

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

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

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

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

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

  As shown in FIG. 7 (c), the electrode-attached substrate to which the negatively charged display particles are attached and the electrode-attached substrate to which the positively charged display particles are attached are adjusted with a partition wall so that the interval is 50 μm. Then, the periphery of the substrate was adhered with an epoxy adhesive to obtain an image display device. The volume occupation ratio between the two types of display particles between the glass substrates was 25%. The content ratio of the positively charged display particles and the negatively charged display particles is approximately 1/1 in terms of the number ratio of the positively charged display particles / negatively charged display particles.

<Examples 2 to 6 / Comparative Examples 1 to 4>
An image display device was produced in the same manner as in Example 1 except that the production conditions of the negatively charged display particles and the positively charged display particles were changed as shown in Table 1.

<Evaluation>
Dielectric constant According to the method described above, positively charged display particles (white particles) and negatively charged display particles (black particles) were separated and collected from the image display device. The collected positively charged display particles (white particles) and negatively charged display particles (black particles) were each subjected to the dielectric constant measurement method described above.

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

  The evaluation was performed on contrast as display characteristics at the initial stage and after voltage application of 10,000 cycles. For the repetitive voltage application, a rectangular wave having an AC voltage of 250 V and a frequency of 2 Hz was applied.

(contrast)
The density (black density) when +250 V was applied and the density (white density) when -250 V was applied were measured. The concentration was measured at any five locations, and the average value thereof was used. Contrast was evaluated based on the difference between black density and white density. Contrast was determined as acceptable (Δ) when the density difference was 1.00 or more, and rejected (x) when less than 1.00. In particular, the density difference is preferably 1.05 or more (◯), more preferably 1.10 or more (◎).

(Minimum drive voltage V1)
The minimum drive voltage is the voltage V1 when the display density value becomes the following value when it is changed from 0V to + 250V at 1V intervals. As for V1, 50V or less was set to pass ((triangle | delta)), and when it exceeded 50V, it was set as the rejection (x). In particular, V1 is preferably 40 V or less (◯), more preferably 30 V or less (◎).
Display density = C _W + {(C _B −C _W ) × 0.1}
The black density measured in the initial evaluation of contrast is “C _B ”, and the white density is “C _W ”.

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

Explanation of symbols

  10: image display device, 11:12: substrate, 15: electrode, 16: insulating layer, 17: partition, 18: gap, 18a: image display surface, 21: black particles, 22: white particles.

Claims (2)

Display particles used in an image display device for displaying an image by moving display particles by encapsulating charged display particles between two substrates, at least one of which is transparent, and generating an electric field between the substrates In
The display particles include positively charged display particles and negatively charged display particles, and the dielectric constants of the positively charged display particles and the negatively charged display particles are independently in the range of 2.0 to 4.0. particle.   An image display device comprising the display particles according to claim 1.

Images