JP5131042B2 - Image display device - Google Patents

Description

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

  2. Description of the Related Art Conventionally, an image display device that displays an image by moving display particles in a gas phase is known. In an image display device, display particles are sealed in a powder form between two substrates, at least one of which is transparent, and an electric field is generated between the substrates to move and attach the display particles to one substrate. To display an image. When driving such an image display device, an electric field is generated by applying a voltage between the substrates, and the display particles move along the electric field direction. Therefore, an image can be displayed by appropriately selecting the electric field direction. And erasure can be executed repeatedly.

  However, once the display particles adhere to the substrate, the adhesion force is relatively large, so that the display particles remain attached to the substrate and cannot move, and the contrast between the image area and the non-image area is impaired. .

  Therefore, an attempt has been made to treat the substrate surface with hexamethyldisilazane (Patent Document 1). However, from the beginning, a sufficient adhesive force reduction effect could not be obtained, resulting in a contrast problem. In addition, the contrast problem is significant when the image display device is repeatedly displayed.

In addition, a technique for reducing the contact area of display particles to the substrate and reducing the adhesion force by dispersing particles having a small primary particle diameter on the substrate surface is disclosed (Patent Document 2). However, from the beginning, a sufficient adhesive force reduction effect could not be obtained, resulting in a contrast problem. In addition, the contrast problem is significant when the image display device is repeatedly displayed.
International Publication WO2004 / 077140 Pamphlet JP 2004-226768 A

  Therefore, the inventors of the present invention tried to attach inorganic fine particles surface-treated with a specific treatment agent to a substrate in advance, and repeated images with relatively good contrast from the initial stage up to a certain number of times. Although it can be displayed, the contrast decreased relatively early. For example, when display-erasure is repeated more than 10,000 times, the contrast decreases.

  An object of the present invention is to provide an image display device capable of repeatedly displaying an image excellent in contrast between an image portion and a non-image portion sufficiently over a long period of time.

The present invention
An image display device comprising at least one transparent substrate and display particles encapsulated in powder form between the substrates and generating an electric field between the substrates to move the display particles and display an image There,
The present invention relates to an image display device characterized in that mixed inorganic fine particles of positively chargeable inorganic fine particles and negatively chargeable inorganic fine particles are adhered to at least one substrate side surface in the gap between the substrates.

According to the present invention, the adhesion of the display particles to the surface to which the display particles are adhered is remarkably reduced, and such an adhesion reduction effect can be maintained even during durability. An image with excellent contrast can be displayed repeatedly for a sufficiently long time. Furthermore, the drive voltage can be set relatively low.
The characteristic that exhibits excellent initial contrast sufficiently for a long period of time is referred to as contrast durability.

[Image display device]
An image display device according to the present invention includes two substrates, at least one of which is transparent, and display particles encapsulated in a powder form between the substrates, and moves the display particles by generating an electric field between the substrates. An image display device for displaying an image,
Specific inorganic fine particles are adhered to at least one of the display particle contact surfaces in the gap between the substrates.
Hereinafter, the image display apparatus of the present invention will be described in detail. The image display device according to the present invention is also called a “powder display”.

  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 image display device in FIG. 1A, and an electric field is applied via an electrode provided outside the device to display particles. It can be moved. 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.
Two substrates 11 and 12 that are casings constituting the image display device are also arranged opposite to each other on the outermost part of the image display device 10 in FIG. The insulating layers 16 are provided on the surfaces of the substrates 11 and 12 facing each other. The substrates 11 and 12 are provided with an insulating layer 16, and display particles are present in a gap 18 formed by facing the surface having the insulating layer 16.

  In the image display device 10 shown in FIG. 1, two types of display particles, black display particles (hereinafter referred to as black particles) 21 and white display particles (hereinafter referred to as white particles) 22 are present in the gap 18 as display particles. . 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 the present invention, the specific inorganic fine particles 1 are attached to at least one substrate-side surface in the gap 18 to form an inorganic fine particle layer. The substrate side surface means a surface substantially parallel to the substrate among the display particle contact surfaces constituting the gap 18, and refers to the surfaces 20a and 20b in FIG. In FIG. 1A and FIG. 1B, the inorganic fine particles 1 are attached to both the substrate-side surfaces 20a and 20b in the gap 18, but are attached to at least one of the substrate-side surfaces. Preferably, it is attached to at least the substrate-side surface 20a upstream in the viewing direction.

  The substrate-side surface to which the inorganic fine particles 1 are attached varies depending on the structure of the image display device, and may be, for example, the surface of the insulating layer 16, the surface of the electrode 15, or the surface of the substrates 11 and / or 12. Specifically, for example, in the case of the image display device of FIGS. 1A and 1B, the inorganic fine particles adhere to the surface of the insulating layer 16. Further, for example, in the case where the image display apparatus of FIG. 1A does not have an insulating layer, the inorganic fine particles adhere to the surface of the electrode 15. Further, for example, in the case where the image display apparatus of FIG. 1B does not have an insulating layer, the inorganic fine particles adhere to the surface of the substrate 11 and / or 12.

  In the present invention, mixed inorganic fine particles of positively charged inorganic fine particles and negatively chargeable inorganic fine particles are attached as the inorganic fine particles 1. As a result, excellent contrast between the image area and the non-image area can be maintained not only in the initial stage but also for a significantly long time. Although details of the mechanism of such a phenomenon are not clear, it is considered that the chargeability of the display particles is stabilized by the adhesion of the positively chargeable inorganic fine particles and the negatively chargeable inorganic fine particles. Specifically, when display-erasure is repeated, the chargeability of the display particles changes due to frictional contact with the adhesion layer, and the charge amount fluctuates. For example, an adhesion layer composed only of negatively chargeable inorganic fine particles shifts the chargeability of the positively chargeable display particles in the positive direction by repeated frictional contact with the positively chargeable display particles. Adhesion increases. In addition, for example, the adhesion layer composed only of positively chargeable inorganic fine particles shifts the chargeability of the negatively chargeable display particles in the negative direction by repeated frictional contact with the negatively chargeable display particles. The adhesion force increases. As a result, it is considered that the contrast is lowered. In the present invention, since the mixed inorganic fine particles of the positively chargeable inorganic fine particles and the negatively chargeable inorganic fine particles are attached, the display particles are suppressed from variation in charge amount even by repeated frictional contact with the mixed inorganic fine particle layer. Chargeability can be maintained stably. As a result, it is considered that the initial adhesive force reduction effect is maintained even during durability, and the initial excellent contrast can be maintained for a sufficiently long period.

  The mixing ratio of the positively chargeable inorganic fine particles and the negatively chargeable inorganic fine particles is 10/90 to 90/10, preferably 15/85 to 85/15, by weight. If the proportion of one of the positively chargeable inorganic fine particles or the negatively chargeable inorganic fine particles is too large or too small, fluctuations in the charge amount of the display particles cannot be sufficiently suppressed, so that the contrast durability is lowered.

  The adhesion amount of the mixed inorganic fine particles is not particularly limited as long as the object of the present invention is achieved. Usually, the surface to which the fine particles adhere is 110 ° or more, particularly 110 to 170 ° as a contact angle with respect to water. The amount is preferably 130 to 160 °, more preferably 150 to 160 °. A large amount of adhesion correlates with the magnitude of the water contact angle. That is, the greater the amount of adhesion, the greater the water contact angle. On the other hand, the smaller the amount of adhesion, the smaller the water contact angle. If the contact angle is too small, the adhesion between the substrate and the display particles is large and the contrast is lowered.

  The positively chargeable inorganic fine particles and the negatively chargeable inorganic fine particles are inorganic fine particles that are charged to positive polarity and negative polarity by mutual frictional contact when they are mixed together.

  As the positively chargeable inorganic fine particles, inorganic fine particles that are positively charged by frictional contact with the reference carrier are used. In the present invention, the reference carrier is an iron powder carrier, and for example, Z150 / 250 (manufactured by Powdertech) can be used. The positively charged inorganic fine particles are meant to include inorganic fine particles that are positively charged and inorganic fine particles that can be positively charged.

  As the positively chargeable inorganic fine particles, for example, inorganic fine particles imparted with a positive charge by a surface treatment agent and inorganic fine particles that are inherently positively chargeable without using a surface treatment agent can be used. From the viewpoint of further improving contrast durability, the former surface-treated positively chargeable inorganic fine particles are preferably used.

  As the core material particles of the positively charged inorganic fine particles subjected to the surface treatment, known inorganic fine particles can be used. For example, metal oxides such as silicon oxide, titanium oxide, aluminum oxide, tin oxide, zirconium oxide, and tungsten oxide From the viewpoints of nitrides such as titanium nitride and surface treatment agent reactivity, preferred core material particles are silicon oxide.

  As the surface treatment agent that can impart positive chargeability, among those conventionally used as hydrophobizing agents for inorganic fine particles externally added to toner particles in the field of electrophotographic toner, those that can impart positive chargeability If it is, it will not restrict | limit in particular, For example, an aminosilane coupling agent, an amino modified silicone oil, etc. are mentioned. Specific examples of the aminosilane coupling agent include, for example, N-β (aminoethyl) -γ-aminopropyltrimethoxysilane, aminopropyltrimethoxysilane, aminopropyltriethoxysilane, dimethylaminopropyltrimethoxysilane, diethylaminopropyl. Trimethoxysilane, dipropylaminopropyltrimethoxysilane, dibutylaminopropyltrimethoxysilane, monobutylaminopropyltrimethoxysilane, dioctylaminopropyldimethoxysilane, dibutylaminopropyldimethoxysilane, dibutylaminopropylmonomethoxysilane, dimethylaminophenyltri Ethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N-methyl-azo-2,2,4-trimethyl Examples include silacyclopentane. Specific examples of the amino-modified silicone oil include terminal aminoalkyl-modified silicone oil.

  The surface treatment for imparting positive chargeability may be performed by adding a surface treatment agent to the inorganic fine particles, mixing them sufficiently, and then drying and crushing. The addition amount of the treatment agent may be a necessary amount in the surface coating treatment of the inorganic fine particles, and the treatment agent is usually added at a ratio of 1 to 50% by weight based on the inorganic fine particles to be treated. Two or more kinds of treatment agents may be used in combination, and in that case, the total amount thereof may be within the above range. Even with such surface treatment, the average primary particle size of the inorganic fine particles hardly changes.

The degree of the surface treatment is not particularly limited, but the surface-treated positively chargeable inorganic fine particles preferably have a degree of hydrophobicity of 40 to 95.
The degree of hydrophobicity is a value measured by the methanol wettability method, and is a measure of wettability to methanol. In the methanol wettability method, first, 0.2 g of inorganic fine particles to be measured is weighed and added to 50 ml of distilled water placed in a 200 ml beaker. Next, methanol is slowly dropped from a burette, the tip of which is immersed in a liquid, with slow stirring until the entire inorganic fine particles are wet. When the amount of methanol necessary to completely wet the inorganic fine particles is a (ml), the degree of hydrophobicity is calculated by the following formula (1).
Hydrophobic degree = {a / (a + 50)} × 100 (1)

  Examples of the inorganic fine particles that are inherently positively charged without using a surface treatment agent include polymethylsilsesquioxane.

  As the negatively chargeable inorganic fine particles, inorganic fine particles that are negatively charged by frictional contact with the reference carrier are used. The above-described iron powder carrier can be used as the reference carrier. The negatively chargeable inorganic fine particles are meant to include inorganic fine particles that are negatively charged and inorganic fine particles that can be negatively charged.

  As negatively chargeable inorganic fine particles, for example, inorganic fine particles imparted with negative chargeability by a surface treatment agent, and inorganic fine particles that are inherently negatively chargeable without using a surface treatment agent can be used. From the viewpoint of further improving contrast durability, the former surface-treated negatively chargeable inorganic fine particles are preferably used.

  As the core material particles of the negatively chargeable inorganic fine particles subjected to the surface treatment, known inorganic fine particles can be used, and examples thereof include the inorganic fine particles exemplified as the core material particles of the positively chargeable inorganic fine particles. A preferable core material particle from the viewpoint of the surface treatment agent reactivity is silicon oxide.

  Surface treatment agents that can impart negative chargeability are those that can impart negative chargeability among those conventionally used as hydrophobizing agents for inorganic fine particles externally added to toner particles in the field of electrophotographic toners. If it is, it will not restrict | limit in particular, For example, a disilazane coupling agent, a silane coupling agent, a silicone oil etc. are mentioned. Specific examples of the disilazane coupling agent include hexamethyldisilazane and the like. Specific examples of the silane coupling agent include n-octyltriethoxysilane, n-octyltrimethoxysilane, iso-butyltrimethoxysilane, and iso-butyltriethoxysilane. Specific examples of the silicone oil include methyl hydrogen silicone oil, dimethyl silicone oil, methylphenyl silicone oil and the like.

  As the surface treatment for imparting negative chargeability, a method similar to the surface treatment for imparting positive chargeability can be adopted except that a predetermined surface treatment agent is used.

  The degree of the surface treatment is not particularly limited, but the surface-treated negatively chargeable inorganic fine particles preferably have a degree of hydrophobicity of 40 to 95.

The charge polarity of the inorganic fine particles can be found based on the charge amount measured by the blow-off method. Specifically, the blow-off charge amount is obtained by putting 19 g of a reference iron powder carrier (Z150 / 250; manufactured by Powder Tech Co.) and 1 g of inorganic fine particles in a glass bottle and mixing them for 20 minutes with a shaker. Thereafter, 0.1 g of a sample is put into a measuring container having a 400 mesh stainless screen, and a blow-off charge measuring machine (TB-200: Toshiba Chemical Co., Ltd.) under the conditions of a nitrogen gas flow rate of 1.0 kgf / cm ² and an inflow time of 60 seconds. Measure the charge amount. As a result, if the measured value is a positive value, the inorganic fine particles have positive chargeability, and if the measured value is a negative value, the inorganic fine particles have negative chargeability.

  The particle size of the positively chargeable inorganic fine particles and the negatively chargeable inorganic fine particles is not particularly limited. For example, the average primary particle size is independently in the range of 1 to 500 nm, preferably in the range of 5 to 200 nm. .

  In this specification, the average primary particle size is the number average particle size of primary particles, and a value measured by LB-550 (manufactured by Horiba Ltd.) is used.

  The mixed inorganic fine particles of the positively charged inorganic fine particles and the negatively charged inorganic fine particles can be adhered by applying a dispersion liquid in which the mixed inorganic fine particles are dispersed to a desired surface and drying. The adhesion force of the mixed inorganic fine particles is based on the van der Waals force between the adhering surfaces and the inorganic fine particle layer can be formed with a sufficient adhesion force simply by applying the dispersion and drying. It is considered a thing.

  The solvent in which the mixed inorganic fine particles are dispersed is not particularly limited, and an organic solvent can be used. Specific examples of such an organic solvent include tetrahydrofuran, acetone, MEK, cyclohexanone, toluene and the like.

  The concentration of the mixed inorganic fine particles in the dispersion is not particularly limited. However, from the viewpoint of further improving initial contrast and contrast durability by forming an adhesion layer of mixed inorganic fine particles, 0.5 to 10% by weight, particularly 1 to 5%. % By weight is preferred. The concentration of the applied dispersion liquid correlates with the amount of adhesion. That is, the higher the mixed inorganic fine particle concentration, the greater the amount of adhesion. On the other hand, the lower the concentration, the smaller the amount of adhesion.

  The structure of the adhesion layer obtained by such treatment is not particularly limited as long as the above-described adhesion amount (water contact angle) of the mixed inorganic fine particles is achieved. For example, the structure of the primary particle layer as shown in FIG. It may be a structure of a multi-particulate particle layer having a thickness of two or more inorganic fine particles, a structure in which the surface to be adhered is partially exposed, or those A structure having a composite structure of A structure of a multi-particle layer having a thickness of two or more inorganic fine particles is preferable.

  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 200 μm. The volume occupancy of the display particles in the gap 18 is 5% to 70%, preferably 10% 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, charged display particles existing between the substrates 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 friction charging with a carrier to form charged display particles.
(2) Charged 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 charged display particles are attracted to the surface of the substrate along the direction of the electric field by the action of Coulomb force, so that the charged display particles move and image display can be performed.
(5) Further, the moving direction of the charged display particles is switched by changing the direction of the electric field 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 display particles are brought into contact with a carrier and charged by frictional charging, or display particles of two colors having different chargeability are mixed and stirred with a shaker. And a method of charging display particles by frictional charging between particles.

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 exist 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. The black particles 21 negatively charged by the voltage application move to the vicinity of the substrate 11 on the viewing side, and the white particles 22 are formed on the substrate. It has moved to the 12th 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, as in the image display device 10 having the electrodes 15, the black particles 21 that are negatively charged by voltage application move to the vicinity of the substrate 11 on the viewing side, and are positively charged. The white particles 22 have moved to the substrate 12 side.

  Next, the substrates 11 and 12, the electrode 15, the insulating layer 16, the partition walls 17, and the display particles (the black particles 21 and the white particles 22) constituting the image display device 10 illustrated 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 thicknesses of the substrates 11 and 12 are each preferably 2 μm to 5 mm, and more preferably 5 μm to 2 mm. 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 an expanded 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 has a configuration in which the inorganic fine particles 1 are adhered on the surface thereof, but the insulating layer 16 is not necessarily provided. In the present invention, an insulating layer is preferably provided from the viewpoint of further improving the initial contrast and contrast durability.
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 polyamide resin, silicone resin, epoxy resin, polyester resin, polycarbonate resin, and acrylic 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, and for example, a voltage at a level applied in image formation by electrophoresis is applied. Therefore, it is preferable because an image can be displayed.

  The partition wall 17 secures a gap 18 between the substrates, and can be formed not only at the edge portions 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 wall 17, the cells of the gap 18 partitioned by the partition wall 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 display particles include 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. Display particles including display particles to be used are used. Since the display particles are usually different not only in charge polarity but also in color, when an electric field is generated between the substrates in the image display device, the display particles move and adhere to the upstream substrate in the viewing direction, and the downstream in the viewing direction. The display image can be visually recognized based on the color difference between the display particles remaining on and adhering to the side substrate. For example, one of the positively charged display particles or the negatively charged display particles can be white and the other can be black. The black particles 21 and the white particles 22 at this time are shown in the above-described drawings.

  Each of the positively charged display particles and the negatively charged display particles is usually obtained by externally adding an external additive to the base particles. In the present specification, the term “display particles” simply includes positively charged display particles and negatively charged display particles.

  The content ratio of the positively charged display particles and the negatively charged display particles is not particularly limited as long as the object of the present invention is achieved, and is usually approximately the same amount.

  The base particles are colored resin particles containing at least a resin and a colorant, and may further contain additives such as a charge control agent and a fluorescent whitening agent as desired. The base particles usually contain colorants of different colors between the base particles contained in the positively charged display particles and the base particles contained in the negatively charged display particles. For example, white base particles and black base particles are used in combination.

  The resin constituting the base particle is not particularly limited, and a polymer called a vinyl resin shown below is a typical one. In addition to the vinyl resin, for example, a polyamide resin or a polyester resin, Examples thereof include condensation resins such as polycarbonate resins and epoxy resins. Specific examples of vinyl resins include, for example, polyolefin resins formed from ethylene monomers and propylene monomers, in addition to polystyrene resins, polyacrylic resins, and polymethacrylic resins. Examples of resins other than vinyl resins include polyether resins, polysulfone resins, polyurethane resins, fluorine resins, and silicone resins in addition to the above-described condensation resins.

The polymer constituting the resin that can be used for the base particles is produced 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 produced 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.
By selecting the resin, the charge polarity of the display particles can be controlled.

  The colorant is not particularly limited, and a pigment known in the field of electrophotographic toner is used. Among these, for example, the white pigment constituting the white base particles includes, for example, zinc oxide (zinc white), titanium oxide, antimony white, zinc sulfide, barium titanate, calcium titanate, strontium titanate, and the like. Of these, titanium oxide is preferable. For example, examples of the black pigment constituting the black base particles include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, and the like. Among these, carbon black is preferable. The content of the colorant is not particularly limited, and may be, for example, 1 to 200 parts by weight with respect to 100 parts by weight of the resin.

  The charge control agent is not particularly limited, and a charge control agent known in the field of electrophotographic toner is used. Among these, for example, base particles containing a negative charge control agent such as a salicylic acid metal complex, a metal-containing azo dye, a quaternary ammonium salt compound, a nitrile imidazole derivative, etc. tend to be negatively charged. In addition, for example, host particles containing a positive charge control agent such as a nigrosine dye, a triphenylmethane compound, or an imidazole derivative have a strong tendency to be positively charged. The content of the charge control agent is not particularly limited, and may be, for example, 0.1 to 10 parts by weight with respect to 100 parts by weight of the resin.

The method for producing the base particles is not particularly limited, and for example, a known method for producing particles containing a resin and a colorant, such as a method for producing a toner used for electrophotographic image formation, is applied. 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 producing 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;
(3) A polymerizable monomer is dropped into an aqueous medium containing a surfactant, and a polymerization reaction is performed in a micelle to produce polymer particles of 100 to 150 nm. A so-called emulsion polymerization aggregation method in which base particles are produced by adding and aggregating and fusing these particles.

  The volume average particle diameter D1 of the base 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 of all the base particles of the positively charged display particle base particles and the negatively charged display particle base particles may be D1, and the value may be within the above range.

The volume average particle diameter D1 of the base particles is a so-called 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 a sample is conditioned 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 dispersion. This dispersion is poured into a beaker containing ISOTON II (manufactured by Beckman Coulter, Inc.) in a sample stand with a pipette until the measured concentration reaches 10%, and the measurement is performed with a measuring machine count of 2500. The aperture size of the multisizer 3 is 50 μm.

As the external additive, inorganic fine particles and resin fine particles can be used.
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 an external additive in the field of electrophotographic toner can be used, and examples thereof include fine particles made of a resin exemplified as a resin constituting the base particle.

  The average primary particle size of the external additive is usually 5 to 250 nm, and from the viewpoint of imparting chargeability and improving fluidity, use one having an average primary particle size of 5 to 100 nm, or average primary particles. It is preferable to use a material having a diameter of 5 to 100 nm and a material having a diameter of 30 to 250 nm. 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 image display device can be manufactured by the following method, for example.
First, an electrode and an insulating layer are provided on a pair of glass substrates as desired, and the mixed inorganic fine particles are adhered thereon by the method described above. Subsequently, such a pair of glass substrates are stacked with the fine particle adhesion surface facing inward, the display particles are sealed, and the periphery of the glass substrate is bonded with a partition wall material (adhesive).

The image display device can also be manufactured by the following electrophotographic development method.
The electrodes 15 and, if desired, the insulating layer 16 are formed on the two substrates 11 to obtain a pair of substrates with electrodes. Further, the mixed inorganic fine particles are adhered thereon by the method described above to form an adhesion layer. 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. 5A to form an adhesion layer. The one electrode-attached substrate is placed at a predetermined interval from the stage 100. Next, as shown in FIG. 5A, a positive DC voltage and an AC voltage are applied to the electrode 15 to adhere the negatively charged display particles 21 on the adhesion layer 1.
The display particles 22 are positively charged by mixing the display particles 22 and the carrier 220, and the mixture (22, 220) is placed on the conductive stage 100 as shown in FIG. 5B to form an adhesion layer. The other substrate with electrodes 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 1. As shown in FIG. 5C, 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.

<Example 1>
[Manufacture of white display 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 with a turbo mill pulverizer (manufactured by Turbo Kogyo Co., Ltd.), and further finely classified with an airflow classifier utilizing the Coanda effect to produce white particles (base particles) having a volume average particle size of 10.0 μm. . 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 particles, and a vibratorizer (manufactured by Nara Machinery Co., Ltd.) is used. The number of revolutions 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 the same treatment was performed to produce white display particles.

[Production of black display 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 particles (base particles) having a volume average particle size of 10.0 μm. 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 particles, and a vibratorizer (manufactured by Nara Machinery Co., Ltd.) is used. The number of revolutions 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 the same treatment was performed to produce black display particles.

[Carrier A for charging white display particles]
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 black display particles]
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.

[Positively chargeable inorganic fine particles A]
30% by weight of aminopropyltrimethoxysilane was added to silica fine particles having an average primary particle diameter of 15 nm, mixed well, dried and crushed to obtain positively chargeable inorganic fine particles A. The degree of hydrophobicity was 78. When the charge amount of the inorganic fine particles with respect to the reference iron powder carrier was measured by the blow-off method described above, a positive value was shown.

[Negatively chargeable inorganic fine particles A]
30% by weight of hexamethyldisilazane was added to silica fine particles having an average primary particle diameter of 12 nm, mixed well, dried and crushed to obtain negatively charged inorganic fine particles A. The degree of hydrophobicity was 89. When the charge amount of the inorganic fine particles with respect to the reference iron powder carrier was measured by the blow-off method described above, a negative value was shown.

[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 of FIG. 1A except that the insulating layer 16 was not provided.
1 part by weight of positively charged inorganic fine particles A and 4 parts by weight of negatively charged inorganic fine particles A were dispersed in an tetrahydrofuran homogenizer (manufactured by BRANSON) at a concentration of 5% by weight in a tetrahydrofuran solvent.
The dispersion is applied at 2000 rpm with a spin coater on the electrodes of a pair of glass substrates (7 cm × 7 cm) provided with electrodes of indium tin oxide coating (ITO; thickness: 50 nm), and 30 minutes at 100 ° C. It was made to dry and the adhesion layer of mixed inorganic fine particles was formed.

  The display particles were charged by mixing 1 g of black 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. 5A, the obtained mixture (21, 210) is placed on a conductive stage 100, and one electrode-attached substrate on which an adhesion layer is formed is spaced from the stage 100 by about 2 mm. Installed. 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 negatively charged black display particles 21 on the adhesion layer.

  The display particles were charged by mixing 1 g of white display particles and 9 g of carrier A for 30 minutes with a shaker (manufactured by Yayoi, YS-LD Co., Ltd.). As shown in FIG. 5B, the obtained mixture (22, 220) is placed on a conductive stage 100, and the other electrode-attached substrate on which the adhesion layer is formed is spaced from the stage 100 by about 2 mm. Installed. 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 white display particles 22 on the adhesion layer.

  As shown in FIG. 5C, the substrate with electrodes to which black display particles are attached and the substrate with electrodes to which white display particles are attached are adjusted and overlapped with a partition so as to have an interval of 50 μm. Were bonded 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 black display particles and the white display particles is approximately 1/1 in terms of the number ratio.

<Example 2>
Instead of the negatively chargeable inorganic fine particles A, an image display device was obtained by the same method as in Example 1 except that the negatively chargeable inorganic fine particles B produced by the following production method were used.
[Negatively chargeable inorganic fine particles B]
30% by weight of methyl hydrogen silicone oil was added to silica fine particles having an average primary particle diameter of 12 nm, mixed well, dried and crushed to obtain negatively chargeable inorganic fine particles B. The degree of hydrophobicity was 84. When the charge amount of the inorganic fine particles with respect to the reference iron powder carrier was measured by the blow-off method described above, a negative value was shown.

<Example 3>
An image display device was obtained by the same method as in Example 1 except that instead of the positively chargeable inorganic fine particles A, the positively chargeable inorganic fine particles B produced by the following production method were used.
[Positively chargeable inorganic fine particles B]
30% by weight of N-β (aminoethyl) γ-aminopropyltrimethoxysilane is added to silica fine particles having an average primary particle diameter of 15 nm, and after mixing well, drying and crushing are performed, and positively charged inorganic fine particles B was obtained. The degree of hydrophobicity was 74. When the charge amount of the inorganic fine particles with respect to the reference iron powder carrier was measured by the blow-off method described above, a positive value was shown.

<Example 4>
An image display device was obtained in the same manner as in Example 1 except that 2.5 parts by weight of positively chargeable inorganic fine particles A and 2.5 parts by weight of negatively chargeable inorganic fine particles A were used.

<Example 5>
An image display device was obtained in the same manner as in Example 1 except that 4 parts by weight of positively chargeable inorganic fine particles A and 1 part by weight of negatively chargeable inorganic fine particles A were used.

<Comparative Example 1>
An image display device was obtained in the same manner as in Example 1 except that 5 parts by weight of the negatively chargeable inorganic fine particles B were used without using the positively chargeable inorganic fine particles A.

<Comparative example 2>
An image display apparatus was obtained in the same manner as in Example 1 except that 5 parts by weight of the positively chargeable inorganic fine particles B were used without using the negatively chargeable inorganic fine particles A.

<Comparative Example 3>
An image display device was obtained by the same method as in Example 1 except that a hexamethyldisilazane film was formed by the following method instead of the mixed inorganic fine particle adhesion layer.
Hexamethyldisilazane was applied onto a pair of glass substrate electrodes by a spin coater at 5000 rpm and dried at 50 ° C. for 30 minutes.

<Evaluation>
The display characteristics were evaluated by applying a DC voltage to the image display device according to the following procedure and measuring the reflection density of the display image obtained by the voltage application. 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 averaged by measuring five locations on the display surface at random using a reflection densitometer (Sakura DENSIMETER PDA-65; manufactured by Konica Minolta).

In the evaluation, the contrast was evaluated as a display characteristic at the initial stage and during durability.
(Initial contrast)
The contrast was evaluated based on the density difference between the black density and the white density.
The black density is the reflection density of the display surface obtained when a voltage of +200 V is applied to the electrode on the upstream side in the visual recognition direction of the image display device.
The white density is a reflection density of the display surface obtained when a voltage of −200 V is applied to the electrode on the upstream side in the visual recognition direction of the image display device.
Contrast of density difference of 1.40 or more was judged as the best (優), 1.20 or more as excellent (◯), 1.10 or more as pass (Δ), and less than 1.10 as fail (x).

(Contrast durability)
The contrast durability was evaluated based on the difference between the initial contrast and the contrast when the voltage application of +200 V and −200 V was alternately repeated 50,000 times (initial contrast−50,000 times contrast). When the difference was 0.10 or less, it was judged as the best (優), when 0.20 or less was judged as excellent (◯), when 0.30 or less was judged as acceptable (Δ), and when it exceeded 0.30, it was judged as unacceptable (x).

(Contact angle)
In the manufacturing process of the image display device, the contact angle of the adhesion layer of inorganic fine particles to water was measured with a contact angle meter (FACE contact angle meter CA-DT • A type; manufactured by Kyowa Interface Science Co., Ltd.). In Comparative Example 3, the contact angle of the hexamethyldisilazane film with respect to water was measured.

It is the schematic which shows the cross-sectional structure of an example of the image display apparatus of this invention. It is a schematic diagram which shows the example of the movement of the display particle by the voltage application between board | substrates. It is a schematic diagram which shows the example of the movement of the display particle by the voltage application between board | 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.

Explanation of symbols

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

Claims (7)

An image display device comprising at least one transparent substrate and display particles encapsulated in powder form between the substrates and generating an electric field between the substrates to move the display particles and display an image There,
An image display device, wherein mixed inorganic fine particles of positively chargeable inorganic fine particles and negatively chargeable inorganic fine particles are adhered to at least one substrate-side surface in the gap between the substrates.   The image display device according to claim 1, wherein a mixing ratio of the positively chargeable inorganic fine particles and the negatively chargeable inorganic fine particles is 10/90 to 90/10 in weight ratio.   The image display device according to claim 1, wherein a contact angle with respect to water of a surface on which the mixed inorganic fine particles are attached is 110 ° or more.   The positively charged inorganic fine particles are inorganic fine particles that are surface-treated with at least one kind of treatment agent selected from the group consisting of aminosilane coupling agents and amino-modified silicone oils. Image display device.   The negatively charged inorganic fine particles are inorganic fine particles that are surface-treated with at least one kind of treatment agent selected from the group consisting of a disilazane coupling agent, a silane coupling agent, and a silicone oil. An image display device according to claim 1.   The image display device according to claim 1, wherein the surface to which the mixed inorganic fine particles are attached is at least a surface on the substrate side upstream in the viewing direction.   The image display apparatus according to claim 1, wherein the average primary particle diameter of the positively chargeable inorganic fine particles is 1 to 500 nm, and the average primary particle diameter of the negatively chargeable inorganic fine particles is 1 to 500 nm.

Images