JP2009216879A - Display particle for image display device and image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide display particles for an image display device, the particles having a low driving voltage, little density unevenness in an image part and a non-image part and high contrast between the image part and the non-image part, and capable of repeatedly displaying images, and to provide an image display device having the display particles. <P>SOLUTION: The display particles are used in the image display device, as shown in the figure, displaying images by sealing charged display particles between two substrates 11, 12, at least one of which is transparent and generating an electric field between the substrates to move the display particles, wherein the display particles contain two kinds of particles, which are positive charging display particles 22 and negative charging display particles 21. In the charging distribution of the positive charging display particles, the content proportion of particles having charging amounts of +2 to +15 μC/g is not less than 70% on a number basis with respect to the whole positive charging display particles. In the charging distribution of the negative charging display particles, the content proportion of particles having charging amounts of -2 to -15 μC/g is not less than 70% on a number basis with respect to the whole negative charging display particles. The image display device includes the above display particles. <P>COPYRIGHT: (C)2009,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.

  2. Description of the Related Art Conventionally, image display devices using techniques such as an electrophoresis method, an electrochromic method, a thermal method, and a two-color particle rotation method have been proposed as a display device that can replace a liquid crystal display device (LCD). Since these technologies have the following merits, their development in next-generation image display devices such as display devices for mobile terminal devices and electronic paper has attracted attention. In other words, a wider viewing angle is obtained compared to a liquid crystal display device, so that an image with an image quality close to that of a normal printed matter can be obtained, power consumption is small, and image display continues even after the power is turned off, which is called memory performance. There is a merit of having the property of continuing.

  Among them, the electrophoretic image display technology is a method in which a dispersion liquid obtained by adding dispersed particles in a colored solution is disposed between opposing substrates, and a voltage of about several tens of volts is applied between the substrates. The particles move in the phase to display an image. As an electrophoretic image display technique, a technique of encapsulating a dispersion in a microcapsule and arranging it between opposing substrates (for example, see Non-Patent Document 1) has been proposed, and is expected to be the most practical technique. On the other hand, there was a problem that it was difficult to maintain the image display environment.

  Specifically, there is a problem of the specific gravity difference between the colored solution and the dispersed particles. When the specific gravity difference between the two is increased, the dispersed particles are likely to settle in the colored solution, and a stable image display cannot be performed. For example, when dispersed particles having a large specific gravity such as titanium oxide are used in a colored solution having a small specific gravity, the dispersed particles settle in the colored solution. In addition, the colored solution is often formed using a dye that is considered to have a problem in storage stability, and has a side that it is difficult to maintain a certain level of image display state.

  On the other hand, a technique for displaying an image without using a solution has also been proposed. For example, there is a method in which charged display particles are sealed 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. This method does not have the problem of sedimentation of particles or storage stability of the colored solution, but the particles are charged by applying a voltage between the substrates, and the display particles are charged along the direction of the electric field formed by the voltage application. Had to be moved. That is, there has been a demand for a technique for forming an environment between the substrates in which display particles can be smoothly charged and moved even under a low applied voltage. As a method for encapsulating the display particles between the substrates at that time, there are known a particle spraying method and a powder coating method in which the display particles are charged and then placed on pressurized air and supplied from the nozzle to the substrate ( For example, Patent Documents 1 and 2).

  However, in this method, the variation in charge amount for each display particle is large, the drive voltage is large, and when image display and erasure are repeated, the density variation is large in both the image portion and the non-image portion, or the image portion There is a new problem that the contrast between the non-image portion and the non-image portion is low.

  Thus, a panel is disclosed in which the absolute value of the charge amount of two types of display particles is 50 μC / g or less and the quantity ratio of the opposite polarity particles in each display particle is 10% or less (Patent Document 3). . As a result, the contrast can be improved while the drive voltage is reduced. However, the problem of density variation between the image area and the non-image area cannot be sufficiently solved.

On the other hand, in order to prevent scattering of display particles at the time of manufacturing an image display device, a method of encapsulating display particles between substrates using an electrophotographic developing method is known (for example, Patent Document 4). However, even image display devices manufactured by such a method still have problems of density variation and contrast.
JP 2005-258157 A Japanese Patent Laid-Open No. 2003-241231 JP 2006-18248 A JP 2006-308819 A

  The present invention relates to a display particle capable of reducing a driving voltage, relatively small density variation in an image portion and a non-image portion, and capable of repeatedly displaying an image having a relatively high contrast between the image portion and the non-image portion, and the display particle. An object of the present invention is to provide an image display device provided.

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 two kinds of positively charged display particles and negatively charged display particles, and the content ratio of the particles having a charge amount of +2 to +15 μC / g in the charge amount distribution of the positively charged display particles is an all positively charged display particle. And the content ratio of particles having a charge amount of −2 to −15 μC / g in the charge amount distribution of the negatively charged display particles is 70 number% or more with respect to the all negatively charged display particles. The present invention relates to a display particle and an image display device including the display particle.

  According to the present invention, since the charge amount distribution of the display particles is sharp, the driving voltage is reduced, the density variation between the image portion and the non-image portion is sufficiently small, and the contrast between the image portion and the non-image portion is sufficiently large. High images can be displayed repeatedly.

[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 particles and the negatively charged particles to white and the other to black.

The positively charged display particles included in the image display device have a content ratio of particles having a charge amount of +2 to +15 μC / g in the charge amount distribution with respect to all the positively charged display particles of 70% by number or more, particularly 70 to 70%. 95% by number, preferably 80 to 95% by number. The average charge amount of the positively charged display particles is usually +1 to +30 μC / g.
The negatively charged display particles have a charge amount distribution in which the content ratio of particles having a charge amount of −2 to −15 μC / g is 70% by number or more, particularly 70 to 95% by number, preferably 70% to 95% by number, preferably. 80-95% by number. The average charge amount of the negatively charged display particles is usually −1 to −30 μC / g.

  In this way, when the positively charged display particles and the negatively charged display particles have a relatively sharp charge amount distribution, each of the positively charged display particles and the negatively charged display particles moves quickly in a predetermined direction by the electric field, so that local density variation is reduced, and as a result The contrast between the part and the non-image part is improved. Particles having an absolute charge amount of less than 2 μC / g are difficult to move following the electric field. In addition, particles having an absolute value of the charge amount exceeding 15 μC / g have a strong electric adhesion force (Van der Waals force) to the substrate and a drive voltage becomes high. If the content ratio of particles having an absolute value of the charge amount of 2 to 15 μC / g is too small, the density variation in the image portion and the non-image portion becomes large, the contrast between the image portion and the non-image portion becomes low, or driving The voltage increases and the display characteristics deteriorate.

The charge amount distribution of the display particles defined in the present invention can be measured from an image display device based on the following method.
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, 2 to 4 mg each of positively charged display particles and negatively charged display particles are sampled, and the charge amount distribution of each display particle is measured by an E-Spart measuring machine (Model EST-II; manufactured by Hosokawa Micron). The average charge amount can also be measured simultaneously with the charge amount distribution.

(Construction material of display particles)
The positively charged display particles and the negatively charged display particles are made of base particles containing at least a resin and a colorant, and usually further contain 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. As the carrier used as the negatively charged display particles, a carrier having a core surface coated with cyclohexyl methacrylate is used.

The resin constituting the base particle is not particularly limited, and a polymer called a vinyl resin shown below is typical, and in addition to the vinyl resin, a polyamide resin, a polyester resin, or a polycarbonate resin is used. There are also condensation resins such as 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 resin that can be used for the base particles is prepared by combining a plurality of 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.

  The colorant contained in the base particles is particularly limited as long as colorants of different colors are used for positively charged display particles and for negatively charged display particles. Instead, known pigments are used. Among these, examples of the white pigment constituting the white base particles include titanium oxide, zinc oxide (zinc white), antimony white, and zinc sulfide. Among these, titanium oxide is preferable. Examples of the black pigment constituting the black base particles include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon and the like, and among these, carbon black is preferable.

(Preparation method of display particles)
The display particles can be prepared by adding an external additive to the base particles and mixing them.
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.

In general, inorganic fine particles and resin fine particles can be used as the external additive.
As the inorganic fine particles, known inorganic fine particles conventionally used as an external additive in the field of electrophotographic toner can be used. For example, silicon oxide, titanium oxide, aluminum oxide, tin oxide, zirconium oxide, tungsten oxide Metal oxides such as, nitrides such as titanium nitride, and titanium compounds. The inorganic fine particles preferably have hydrophobicity from the viewpoint of improving fluidity and environmental stability. Hydrophobicity can be imparted by subjecting inorganic fine particles to a surface treatment with a surface treatment agent such as an aminosilane coupling agent.
As the resin fine particles, known resin fine particles conventionally used as external additives in the field of electrophotographic toner can be used, and examples thereof include fine particles made of the resin exemplified as the resin constituting the base particles. .

  The average primary particle size of the external additive is usually 5 to 250 nm, but from the viewpoint of imparting chargeability and improving fluidity, the average primary particle size is 5 nm to 100 nm, or the average primary particle size is used. It is preferable to use a particle size of 5 to 100 nm and 30 nm to 250 nm in combination. This makes it possible to adjust the chargeability and improve the fluidity of the display particles and reduce the adhesion of the display particles to the substrate and the like, thereby reducing the drive voltage, reducing the density variation, and further improving the contrast.

  The content of the external additive is preferably from 0.1 to 50 parts by weight, particularly from 1 to 20 parts by weight, based on 100 parts by weight of the base particles, from the viewpoints of charge adjustment and fluidity improvement. Two or more types of external additives may be used in combination, and in that case, the total amount thereof may be within the above range.

  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 is configured to display the image by moving the display particles by enclosing the display particles described above between two substrates, at least one of which is transparent, and generating an electric field between the substrates. It is.

  A typical cross section of an image display device according to the present invention is shown in FIG. FIG. 1A shows a structure in which an electrode 15 having a layer structure is provided on 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. 1B 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 display particles can be moved. It is. The same reference numerals in FIGS. 1A and 1B denote the same members. FIG. 1 is meant to include FIGS. 1 (a) and 1 (b). As shown in the figure, the image display device 10 in FIG. 1 is configured to visually recognize an image from the substrate 11 side. However, in the present invention, the image display device 10 is not limited to an image viewed from the substrate 11 side. Further, the type shown in FIG. 1B 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 in the device itself. FIG. 3 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 device according to the present invention is not limited to that shown in FIGS.

  At the outermost part of the image display device 10 in FIG. 1A, 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 device 10 shown in FIG. 1 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. 1, 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 a powder form. 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, when a voltage is applied between the substrates on which the display particles exist, the charged display particles move between the substrates to display an image.

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.

An example of the movement of the display particles accompanying the voltage application between the substrates is shown in FIGS.
FIG. 2A shows a state before a voltage is applied between the substrates 11 and 12, and positively charged white particles 22 are present in the vicinity of the substrate 11 on the viewing side before the voltage is applied. In this state, the image display device 10 displays a white image. FIG. 2B 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 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. 3 shows a state in which the image display device 10 shown in FIG. 1B without an electrode is set in the voltage application device 30 and a voltage is not applied in this state (FIG. 3A). ) And a state after the voltage is applied (FIG. 3B). In the image display device 10 of the type shown in FIG. 1B, 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 that constitute the image display device 10 shown in FIG. 1 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 a 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 in the front and back directions or intermittently in the drawings on the right and left sides 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 diagram of FIG. 4, a plurality of cells can be arranged in a rectangular shape, a triangular shape, a line shape, a circular shape, a hexagonal shape, etc., 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 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. 5A, a positive direct current voltage and an alternating current voltage are applied to the electrode 15 to adhere 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. 5B, 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. 5 (c), 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. 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.
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. 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 insulating layer 16. As shown in FIG. 6C, 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 have a predetermined interval. Thus, the periphery of the substrate can be adhered to obtain an image display device.

  In the electrophotographic development system described above, when negatively charged display particles and positively charged display particles are attached, a DC voltage and an AC voltage applied between the electrode 15 and the stage 100, a voltage application time, and the electrode 15 By adjusting the gap distance with the stage 100, the charge distribution of the display particles can be controlled. For example, if the DC voltage or AC voltage is too small, the voltage application time is too short, or the gap distance is too large, the amount of particles attached tends to be insufficient, and the particles having a predetermined charge amount The content ratio decreases. Also, if the DC voltage or AC voltage is too large, the voltage application time is too long, or the gap distance is too small, particles with an absolute value of charge amount larger or smaller than the predetermined range are mixed and adhered. As a result, the content ratio of particles having a predetermined charge amount is reduced. Therefore, it is necessary to adjust the DC voltage, AC voltage, voltage application time, and the gap distance to the optimum conditions.

  Specifically, for example, when the AC voltage is 2 kV, the frequency is 2 kHz, and the gap distance between the electrode 15 and the stage 100 is about 2 mm, the absolute value of the DC voltage is 50 to 200 V, and the voltage application time is 2 to 2 mm. Set to 10 seconds.

  It is preferable that the carrier and the mixing conditions for charging the negatively charged display particles and the positively charged display particles are adjusted so that the charge amount distribution of these display particles becomes narrow. Generally, it is desirable to set the amount of particles covering about 50 to 80% of the surface area of the carrier particles and mix them. At this time, the condition for attaching the negatively charged display particles is adjusted so that the polarity is the same as that of the condition for attaching the positively charged display particles.

<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. The mixture was pulverized by a turbo mill pulverizer (manufactured by Turbo Kogyo Co., Ltd.), and further finely classified by 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, 0.6 parts by weight of silica fine particles (average primary particle size 50 nm) subjected to aminosilane coupling treatment are added to 100 parts by weight of the white base particles, and a vibratorizer (manufactured by Nara Machinery Co., Ltd.) is used. The number of rotations was set to 15,000 rpm, and a mixing process was performed for 10 minutes. Subsequently, 1.0 part by weight of silica fine particles having an average primary particle size of 15 nm subjected to amino coupling treatment was added, and white particles were produced by performing the same treatment.

[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, 0.6 parts by weight of silica fine particles (average primary particle size 50 nm) subjected to aminosilane coupling treatment are added to 100 parts by weight of the black base particles, and a vibratorizer (manufactured by Nara Machinery Co., Ltd.) is used. The number of rotations was set to 15,000 rpm, and a mixing process for 10 minutes was performed. Subsequently, 1.0 part by weight of silica fine particles having an average primary particle size of 15 nm subjected to amino coupling treatment was added, and black particles were produced by performing the same treatment.

[Carrier A for charging display particles for positive charging]
Conditions in which 2 parts of fluorinated acrylate 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 A.

[Carrier B for charging display particles for negative charge]
Under the condition that 2 parts of cyclohexyl methacrylate resin particles are added to 100 parts by weight of a 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, carrier B was produced by heating to 90 ° C. and stirring for 40 minutes.

[Manufacture of image display devices]
The image display apparatus 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. 6A, 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 +50 V, an AC bias of 2.0 kV, and a frequency of 2.0 kHz were applied for 10 seconds to adhere the negatively charged display particles 21 on the insulating layer 16.

  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. As shown in FIG. 6B, the obtained mixture (22, 220) was placed on a conductive stage 100, and the other substrate with electrodes was placed at an interval of about 2 mm from the stage 100. A DC bias of −50 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 for 10 seconds to adhere the positively charged display particles 22 on the insulating layer 16.

  As shown in FIG. 6 (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 50%. 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 2-4, Comparative Examples 1-6>
An image display device was produced in the same manner as in Example 1 except that the sealing conditions for the negatively charged display particles and the positively charged display particles were changed as shown in Table 1.

<Comparative Example 7>
The same method as in Example 1 except that the negatively charged display particles and the positively charged display particles are encapsulated according to the method described in Japanese Patent Application Laid-Open No. 2005-258157 using the spraying device shown in FIG. Thus, an image display device was manufactured. Specifically, when negatively charged display particles are encapsulated, the transport pipe is charged using a PFA tube, and when positively charged display particles are encapsulated, an SUS tube is charged.

<Comparative Example 8>
Encapsulation of the negatively charged display particles and the positively charged display particles was performed using the powder coating apparatus shown in FIG. 9 according to the method described in Japanese Patent Application Laid-Open No. 2003-241231. By this method, an image display device was manufactured. Specifically, when negatively charged display particles are encapsulated, a voltage of −40 kV is applied to the tip of the nozzle, and when positively charged display particles are encapsulated, a voltage of +40 kV is applied.

<Evaluation>
-Evaluation of charge amount distribution According to the method described above, positively charged display particles and negatively charged display particles are separated and collected from the image display device, and each display particle is measured by an E-Spart measuring machine (Model EST-II; manufactured by Hosokawa Micron). The charge amount distribution was measured. For example, graphs of charge amount distributions of the negatively charged display particles and the positively charged display particles separated from the image display device of Example 1 are shown in FIGS. 7A and 7B, respectively.

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 with respect to contrast and density variations 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 pass (◯) when the density difference was 1.00 or more, and reject (x) when less than 1.00.

(Density variation)
The difference between the maximum value and the minimum value was obtained for each of the five measured values of black density and white density measured in the contrast evaluation, and density variation was evaluated. Concentration variation was determined to be acceptable (◯) when the difference in density was 0.10 or less, and unacceptable (x) when exceeding 0.10.

(Minimum drive voltage V1)
The minimum drive voltage is the voltage V1 when the display density value becomes the following value when changed from 0V to + 250V at 10V intervals. V1 made 50V or less pass ((circle)) and less than 50V made disqualify (x).
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 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. (A) and (B) are both graphs of the charge amount distribution measured in the examples. 10 is a schematic diagram illustrating an example of a sealing method of Comparative Example 3. FIG. 10 is a schematic diagram illustrating an example of a sealing method of Comparative Example 4. FIG.

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 two kinds of positively charged display particles and negatively charged display particles, and the content ratio of the particles having a charge amount of +2 to +15 μC / g in the charge amount distribution of the positively charged display particles is an all positively charged display particle. And the content ratio of particles having a charge amount of −2 to −15 μC / g in the charge amount distribution of the negatively charged display particles is 70 number% or more with respect to the all negatively charged display particles. Display particles characterized by being.   An image display device comprising the display particles according to claim 1.

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