JP2010026451A - Display particle for image display and image display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide display particles which can lower a driving voltage sufficiently and can repeatedly display an image relatively high in a contrast between an image part and a non-image part, and to provide an image display with the display particles. <P>SOLUTION: Provided are the display particles used for the image display which has electrostatically charged display particles charged between two substrates at least one of which is transparent, and moves the display particles by generating an electric field between the substrates to display an image, the display particles containing positively electrostatically charged display particles and negatively electrostatically charged display particles of ≤20 mg/second in transfer index; and the image display having the display particles. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  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 the particles and storage stability of the colored solution, but it is necessary to move the charged display particles along the direction of the electric field formed by applying a voltage between the substrates. 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 the display particles, for example, Patent Document 1 proposes to use a powder fluid that exhibits high fluidity in an aerosol state in which a solid substance is stably suspended as a dispersoid in a gas, particularly a powder fluid that does not have an angle of repose. Yes. As a method for producing such a powder fluid, for example, a method of fixing inorganic fine particles on the surface of a substance constituting the powder fluid using a hybridizer (manufactured by Nara Machinery Co., Ltd.) or the like is disclosed.

However, even when such display particles are used, the driving voltage cannot be sufficiently reduced. There is also a problem that the contrast between the image portion and the non-image portion is relatively low. Such a problem of contrast was remarkable when image display and erasure were repeatedly performed.
International Publication Number WO2003-075087

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

  The present invention provides an image display device that displays an image by moving display particles by encapsulating charged display particles between two substrates, at least one of which is transparent, and generating an electric field between the substrates. In the display particles to be used, the display particles include positively charged display particles and negatively charged display particles, and the transportability index of each of the positively charged display particles and the negatively charged display particles is 20 mg / second or less, and The present invention relates to an image display device provided with the display particles.

  According to the present invention, since the transportability index of the display particles is sufficiently small, not only the adhesion between the display particles but also the adhesion between the display particle contact surface and the display particles between the substrates is effectively reduced. As a result, the driving voltage is reduced, and an image with sufficiently high contrast between the image portion and the non-image portion can be repeatedly displayed.

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

  The transportability index of each of the positively charged display particles and the negatively charged display particles included in the image display device is 20 mg / second or less, particularly in the range of 1 to 20 mg / second, and the drive voltage is further reduced and the contrast is further improved. From the viewpoint, it is preferably in the range of 1 to 10 mg / second, more preferably 1 to 5 mg / second. When both the positively charged display particles and the negatively charged display particles have a transportability index within the above range, it is possible to achieve a sufficient reduction in driving voltage and an improvement in contrast between the image portion and the non-image portion. If the transportability index is too large, not only the adhesion between the display particles during driving but also the adhesion between the display particle contact surface and the display particles between the substrates is too large, which increases the drive voltage and decreases the contrast. To do. Display particles having a transportability index of less than 1 mg / second are difficult to produce. Even if the transportability index of only one of the positively charged display particles or the negatively charged display particles is outside the above range, the drive voltage increases and the contrast decreases.

  The transportability index of the positively charged display particles and the transportability index of the negatively charged display particles need only be within the above ranges, and the difference between them is that the adhesion force between the substrate and the particles is positively charged display particles and negatively charged display particles. From the viewpoint that the particles do not change, it is preferably 5 mg / second or less, particularly 1 mg / second or less.

  The transportability index uses a value measured under a predetermined condition by a measuring device composed of a parts feeder (ME-14; manufactured by Shinko Electric Co., Ltd., stainless steel) and an electronic balance. The measurement environment is a place fixed at 20 ° C. and 50%. As shown in FIG. 1, the parts feeder 1 includes a drive unit 3 and a ball 4, and a slope 5 (made of stainless steel) is spirally provided on the inner peripheral surface of the ball. As shown in FIG. 2, a vibration exciter (electromagnet) 8 and a leaf spring 9 having an angle at the return position are arranged on the lower side of the slope 5, and are vibrated by an AC voltage applied to the drive unit 3. The vertical motion of the vibration exciter 8 is converted into a climbing force of the display particles P by the leaf spring 9. Therefore, the parts feeder 1 has a mechanism in which the display particles P in the ball 4 are transferred along the slope 5.

In the present invention, 1 g of display particles P are placed around the ball center 6, the drive unit 3 is started under AC voltage conditions of a frequency of 110 Hz and a voltage of 70 V, and the display particles P are climbed along the slope 5. Then, the display particles that have finished climbing the slope 5 fall on the tray 7. The weight (transfer amount) of the display particles on the tray 7 can be measured over time by the electronic balance 2, and a graph of transfer amount (w) -AC voltage application time (t) as shown in FIG. Create In such a graph, the weight of the display particles dropped on the tray 7 during the AC voltage application time of 2 to 4 minutes is obtained, converted to the weight of display particles falling per second, and this is used as the transportability index. . In this way, the transportability index is a physical property value that effectively indicates the ease of movement of the particles because the display particles are measured not only between the particles but also between the particles and the parts feeder. More accurately reflects the behavior of the particles inside.

  As shown in FIG. 2, the display particles of the present invention having a transportability index within the above range climb up the slope 5 in a scattered state. This means that the display particles have a relatively small adhesion between the particles, and at the same time have a relatively small adhesion with the stainless steel constituting the parts feeder. Therefore, considering the configuration of the actual machine (display), the display particles of the present invention have a relatively small adhesion force between the particles and the adhesion force between the particles and the display particle contact surface between the substrates. It is considered that the image can be sufficiently reduced and an image having a relatively high contrast between the image portion and the non-image portion can be repeatedly displayed.

  On the other hand, as shown in FIG. 10, the display particles having a relatively high transportability index climb the slope 5 in an aggregated state. This means that the display particles have a relatively large adhesion force between the individual particles, and at the same time, the display particles have a relatively large adhesion force with the stainless steel constituting the parts feeder. Therefore, considering the configuration of the actual machine (display), the display particles having a relatively large transportability index have a relatively large adhesion force between the particles and between the particle and the display particle contact surface between the substrates. It is considered that the drive voltage increases and the contrast between the image portion and the non-image portion is relatively low.

The transportability index between the positively charged display particles and the negatively charged display particles is obtained by separating and collecting the positively charged display particles and the negatively charged display particles from the image display device based on the following method, and using them for the measurement method described above. It can be measured.
First, a DC voltage of 500 V is applied between the upper and lower electrodes of the image display device to separate the positively charged display particles and the negatively charged display particles in the device, and then the device is disassembled. Next, positively charged display particles and negatively charged display particles are collected. By subjecting the collected positively charged display particles and negatively charged display particles to the measurement method described above, the transportability index of each display particle can be measured.

(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.
The content of the colorant is not particularly limited as long as the object of the present invention is achieved. For example, in the case of white base particles with respect to 100 parts by weight of the base particle constituent resin, 30 to 100 parts by weight, and in the case of black base particles. 5 to 10 parts by weight is preferred.

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

(Method for producing display particles)
The display particles of the present invention can be produced by using a predetermined second-order mixing method and using a predetermined external additive when an external additive is added to and mixed with the base particles.

Specifically, the following two-stage mixing method is adopted.
First, the 1st mixing process which mixes a base particle and hydrophobic silica with TK mixer (made by a special machine chemical industry company) is implemented. As a result, the hydrophobic silica can be fixed to the base particle surface with relatively high strength in the first mixing step, so that the titania added in the second mixing step can sufficiently exert the bearing effect on the display particle surface, and as a result The transportability index can be controlled within a predetermined range. The bearing effect is an effect of acting as a fluidizing material between display particles contact surfaces and display particles between display particles or between substrates, and reducing mutual adhesion between them.

  The hydrophobic silica added in the first mixing step is silica fine particles surface-treated with a hydrophobizing agent. As the hydrophobizing agent, a known hydrophobizing agent used for the surface treatment of inorganic fine particles externally added in the field of toner can be used, and examples thereof include an aminosilane coupling agent. Those obtained by subjecting inorganic fine particles other than silica to a hydrophobization treatment are difficult to achieve the average primary particle size described later.

  When untreated silica having no hydrophobicity is added instead of hydrophobic silica, the untreated silica absorbs moisture in the air, and the physical adhesion between the base particles and the substrate increases. Further, since titania added in the second mixing step cannot exhibit a sufficient bearing effect on the surface of the display particles, the transportability index becomes too large to obtain the display particles of the present invention.

  In this specification, the value measured by the contact angle measurement method is used for the degree of hydrophobicity. Specifically, 1% of hydrophobic silica fine particles are added and mixed in a tetrahydrofuran solvent, and then applied by spin coating to form a 1 μm thick layer. Water droplets are dropped on this film, and the substrate and water droplet angle are set. Measuring. Those having a high degree of hydrophobicity have a large contact angle because they repel water droplets, and in some cases, measurement is impossible. The contact angle of hydrophobic silica is usually 100 ° to 160 °, preferably 120 ° to 150 °.

  The average primary particle size of the hydrophobic silica is 60 to 200 nm, preferably 80 to 150 nm. If the average primary particle size is too small or too large, the titania added in the second mixing step cannot exhibit a sufficient bearing effect on the surface of the display particles, so that the transportability index becomes too large and the display of the present invention. Particles cannot be obtained.

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

  The amount of hydrophobic silica added is 2 to 8 parts by weight, preferably 3 to 7 parts by weight, based on 100 parts by weight of the base particles. If the amount added is too large, excess silica will be present on the surface of the display particles more than the titania added in the second mixing step and inhibit the bearing effect exerted by titania. The display particles of the invention cannot be obtained. If the amount added is too small, voids between the hydrophobic silicas increase on the display particle surfaces, and titania added in the second mixing step enters the voids of the hydrophobic silica. Since the sufficient bearing effect cannot be exhibited, the transportability index becomes too large, and the display particles of the present invention cannot be obtained.

  As long as the hydrophobic silica is within the above range, two or more types of hydrophobic silica having different particle sizes, types of hydrophobizing agents, hydrophobizing degrees, and the like may be used. In that case, those total addition amount should just be in the said range. In the first mixing step, inorganic fine particles or organic fine particles other than the hydrophobic silica are not added. This is because the fine particles inhibit the bearing effect of titania added in the second mixing step, and a predetermined transportability index is not achieved.

  In the first mixing step, the mixing speed is 20 to 60 m / second, preferably 30 to 50 m / second, and the mixing time is 20 to 40 minutes, preferably 20 to 30 minutes. If the mixing speed is too low or the mixing time is too short, the hydrophobic silica will not adhere to the base particles, the titania added in the second mixing step will not adhere, and the transportability index will become too large. Display particles cannot be obtained. If the mixing speed is too high or the mixing time is too long, the hydrophobic silica will be embedded in the base particles, and the area where the titania added in the second mixing step will be attached, and the amount of titania attached will decrease. The transportability index becomes too large, and the display particles of the present invention cannot be obtained.

  The TK mixer is a mixing device using shearing force. When such a TK mixer is not used, for example, when a hybridizer (manufactured by Nara Machinery Co., Ltd.) is used, the hydrophobic silica is embedded in the base particles because it is stronger than the TK mixer. Will be broken. Therefore, the transportability index becomes too large, and the display particles of the present invention cannot be obtained. Instead of the TK mixer, a mixing device using shearing force, such as a Henschel mixer, may be used in the same manner as the TK mixer. In that case, the mixing speed and mixing time may be within the above-mentioned ranges.

  Next, titania is added to the mixture obtained in the first mixing step, and a second mixing step is performed in which the mixture is mixed by a turbuler mixer (manufactured by Willy A Bachoffen). As a result, titania uniformly adheres to the surface of the base particles on which the hydrophobic silica is fixed in the first mixing step, and the bearing effect can be sufficiently exhibited.

  The titania added in the second mixing step may be surface-treated with a hydrophobizing agent or not. However, from the viewpoint of reducing adhesion to the substrate, titania is preferably titania fine particles that have been surface-treated with a hydrophobizing agent. As the titania hydrophobizing agent, the same hydrophobizing agent as that of hydrophobic silica can be used.

  In this specification, the value measured by the contact angle measuring method similar to hydrophobic silica is used for the degree of hydrophobicity. Specifically, 1% titania fine particles are added and mixed in a tetrahydrofuran solvent, and then applied by spin coating to form a 1 μm thick layer. Water droplets are dropped on this film, and the substrate and water droplet angle are measured. ing. Those having a high degree of hydrophobicity have a large contact angle because they repel water droplets, and in some cases, measurement is impossible. The contact angle of the titania fine particles is usually from 100 ° to a non-measurable region, and preferably from 120 ° to a non-measurable.

  If other inorganic fine particles are added instead of titania, the chargeability of the display particles is greatly changed, and therefore cannot be used in the image display element of the present invention.

The average primary particle size of titania is 5 to 40 nm, preferably 15 to 30 nm. If the average primary particle size is too small or too large, titania cannot exhibit a sufficient bearing effect on the surface of the display particles, so that the transportability index becomes too large and the display particles of the present invention cannot be obtained. From the viewpoint of more effectively reducing the transportability index, the ratio of the average primary particle size (r _t ) of titania and the average primary particle size (r _s ) of the hydrophobic silica added in the first mixing step (r _t / r _s ) is preferably 0.05 to 0.7, more preferably 0.1 to 0.4.

  The amount of titania added is 0.2 to 4 parts by weight, preferably 0.3 to 2 parts by weight, based on 100 parts by weight of the base particles. If the addition amount is too large, the titania particles are present as aggregates on the hydrophobic silica and do not exhibit the function as a fluidizing agent, so that the transportability index becomes too large to obtain the display particles of the present invention. If the amount added is too small, titania cannot sufficiently exhibit the bearing effect on the surface of the display particles, so that the transportability index becomes too large to obtain the display particles of the present invention.

  As long as the titania falls within the above range, two or more types of titania having different particle sizes, types of hydrophobizing agents, hydrophobizing degrees, and the like may be used. In that case, those total addition amount should just be in the said range. In the second mixing step, inorganic fine particles or organic fine particles other than the titania are not added. This is because the fine particles inhibit the titania bearing effect and a predetermined transportability index is not achieved.

  In the second mixing step, the mixing time is 2 to 20 minutes, preferably 5 to 10 minutes. If the mixing time is too short, titania will not adhere sufficiently and the bearing effect will not be sufficiently exhibited, so that the transportability index becomes too large and the display particles of the present invention cannot be obtained. Or, if the mixing time is too long, the titania particles are completely immobilized on the hydrophobic silica and do not exhibit the function as a fluidizing agent, so that the transportability index becomes too large to obtain the display particles of the present invention. .

  The turbuler mixer is a mixing device in which glass beads, base particles made in the first mixing step and titania are added to a pot, and mixing is performed using shearing force of the glass beads. When such a turbuler mixer is not used, for example, when a mixing device such as a Henschel mixer is used, the shearing force is too strong and the titania particles are buried in the hydrophobic silica surface and do not exhibit the function as a fluidizing agent. The transportability index becomes too large, and the display particles of the present invention cannot be obtained.

  In the display particle manufacturing method described above, the amount of hydrophobic silica added in the first mixing step, the average primary particle size, and the mixing speed and mixing time, the amount of titania added in the second mixing step, the average primary particle size, and the mixing By adjusting the time within the above range, the transportability index of the display particles can be controlled.

Specifically, for example, when the amount of hydrophobic silica added in the first mixing step is reduced within the above range, the transferability index increases in both cases.
Further, for example, when the average primary particle size of the hydrophobic silica is reduced within the above-described range in the first mixing step, the transportability index increases both when it is increased.
For example, if the contact angle that defines the degree of hydrophobicity of hydrophobic silica in the first mixing step is increased within the above range, the transportability index decreases. On the other hand, if the contact angle defining the degree of hydrophobicity is reduced within the above range, the transportability index increases.
In addition, for example, when the mixing speed or mixing time is increased or decreased within the above range and decreased or decreased in the first mixing step, the transportability index increases.

For example, when the addition amount of titania is increased within the above-described range in the second mixing step, the transferability index is increased when the addition amount is decreased.
Further, for example, when the average primary particle size of titania is reduced within the above range in the second mixing step, the transferability index is increased when it is increased.
For example, if the contact angle that defines the hydrophobicity of titania in the second mixing step is increased within the above range, the transportability index decreases. On the other hand, if the contact angle defining the degree of hydrophobicity is reduced within the above range, the transportability index increases.
Further, for example, when the mixing time is increased or decreased within the above-described range in the second mixing step, the transportability index increases.

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

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

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

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

  The image display device according to the present invention 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 the image display apparatus according to the present invention is shown in FIG. FIG. 4A shows a structure in which a layered electrode 15 is provided on the substrates 11 and 12 and an insulating layer 16 is provided on the surface of the electrode 15. The image display device shown in FIG. 4B has a structure in which no electrode is provided in the device, and an electric field is applied through an electrode provided outside the device so that the display particles can be moved. It is. The same reference numerals in FIGS. 4A and 4B denote the same members. FIG. 4 is meant to include FIGS. 4 (a) and 4 (b). As shown in the figure, the image display device 10 in FIG. 4 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. 4B 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. 6 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. 4 (a) and 4 (b).

  At the outermost part of the image display device 10 in FIG. 4A, 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. 4 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. 4, the gap 18 is surrounded by the substrates 11 and 12 and the two partition walls 17, and the display particles are present in a state of being enclosed in the gap 18 in the form of powder. is doing.

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

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

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

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

Examples of the movement of the display particles accompanying the voltage application between the substrates are shown in FIGS.
FIG. 5A shows a state before a voltage is applied between the substrates 11 and 12, and the positively charged white particles 22 exist in the vicinity of the substrate 11 on the viewing side before the voltage is applied. In this state, the image display device 10 displays a white image. FIG. 5B shows a state after a voltage is applied to the electrode 15, and the black particles 21 that are negatively charged by applying a positive voltage to the substrate 11 are located near the substrate 11 on the viewing side. The white particles 22 have moved to the substrate 12 side. In this state, the image display device 10 displays a black image.

  FIG. 6 shows a state in which the image display device 10 shown in FIG. 4B does not have an electrode is set in the voltage application device 30 and a voltage is not applied in this state (FIG. 6A). ) And the state after the voltage is applied (FIG. 6B). The image display device 10 of the type shown in FIG. 4B is similar to the image display device 10 having the electrode 15 in that the black particles 21 negatively charged by applying a positive voltage to the substrate 11 are in the vicinity of the substrate 11 on the viewing side. The positively charged white particles 22 have moved to the substrate 12 side.

  Next, the substrates 11 and 12, the electrode 15, the insulating layer 16, and the partition wall 17 constituting the image display device 10 illustrated in FIG. 4 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 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 sharpness 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 right and left drawings in the upper part of FIG.
By controlling the shape and arrangement of the partition walls 17, the cells in the gap 18 partitioned by the partition walls 17 can be arranged in various shapes. An example of the shape and arrangement of the cells when the gap 18 is viewed from the viewing direction of the substrate 11 is shown in the lower diagram of FIG. As shown in the lower diagram of FIG. 7, a plurality of cells can be arranged in a rectangular shape, a triangular shape, a line shape, a circular shape, a hexagonal shape, or the like in a honeycomb shape or a mesh shape.

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

The image display device according to the present invention can be manufactured by the following electrophotographic development system.
An electrode 15 and, if desired, an insulating layer 16 are formed on the two substrates 11 and 12 to obtain a pair of substrates with electrodes. By mixing the display particles 21 and the carrier 210, the display particles 21 are negatively charged, and the mixture (21, 210) is placed on a conductive stage 100 as shown in FIG. The substrate is placed at a predetermined interval from the stage 100. Next, as shown in FIG. 8A, a positive direct current voltage and an alternating current voltage are applied to the electrode 15 to adhere the 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. 8B, a negative DC voltage and an AC voltage are applied to the electrode 15 to adhere the positively charged display particles 22 on the adhesion layer of the negatively charged display particles 21. As shown in FIG. 8 (c), the substrate with one electrode to which the negatively charged display particles and the positively charged display particles are attached and the other substrate with the electrodes are adjusted with a partition so as to have a predetermined interval. Then, the image display device can be obtained by stacking and bonding the periphery of the substrate.

Further, it can be manufactured by another embodiment of the electrophotographic developing system described below.
An electrode 15 and, if desired, an insulating layer 16 are formed on the two substrates 11 and 12 to obtain a pair of substrates with electrodes. The display particles 21 and the carrier 210 are mixed to make the display particles 21 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. 9A, a positive DC voltage and an AC voltage are applied to the electrode 15, and the negatively charged display particles 21 are attached 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. 9B, 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. 9C, 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>
[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, 5.0 parts by weight of silica fine particles (average primary particle size 100 nm) subjected to aminosilane coupling treatment are added to 100 parts by weight of the white base particles, and a TK mixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) is used. The rotation speed was set to 55 m / sec, and a mixing process for 30 minutes was performed (first mixing). Subsequently, 0.5 parts by weight of titania fine particles having an average primary particle size of 20 nm subjected to silicone oil treatment were added, and white particles were obtained by performing a mixing treatment for 5 minutes using a turbuler mixer (manufactured by Willy A Bachoffen). Produced (second mix).

[Manufacture of negatively charged display particles (black particles)]
The resin and carbon black described below were put into a Henschel mixer (manufactured by Mitsui Miike Mining Co., Ltd.), the peripheral speed of the stirring blade was set to 25 m / sec, and the mixture was mixed for 5 minutes to obtain a mixture.
Styrene acrylic resin (weight average molecular weight 20,000) 100 parts by weight Carbon black (average primary particle size 25 nm) 10 parts by weight The above mixture is kneaded with a twin-screw extrusion kneader, then coarsely pulverized with a hammer mill, and then turbo milled. Coarse powder was pulverized by a machine (manufactured by Turbo Kogyo Co., Ltd.), and further finely classified by an airflow classifier utilizing the Coanda effect to produce black matrix particles having a volume average particle size of 8.0 μm and CV20. Next, to 100 parts by weight of the black base particles, 5.0 parts by weight of silica particles treated with disilazane (average primary particle size 100 nm) are added, and a TK mixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) is used. The rotation speed was set to 55 m / sec, and a mixing process for 30 minutes was performed (first mixing). Subsequently, 0.5 parts by weight of titania fine particles having an average primary particle size of 20 nm subjected to silicone oil treatment were added, and black particles were obtained by performing a mixing treatment for 5 minutes using a Turbuler mixer (manufactured by Willy A Bachoffen). Produced (second mix).

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

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

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

  The display particles were charged by mixing 1 g of the negatively charged display particles and 9 g of carrier B with a shaker (manufactured by YS-LD Co., Ltd., Yayoi) for 30 minutes. As shown in FIG. 9A, 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. The resulting mixture (22, 220) was placed on a conductive stage 100 as shown in FIG. 9B, and the other electrode-attached substrate 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. 9 (c), the electrode-attached substrate to which the negatively charged display particles are attached and the electrode-attached substrate to which the positively charged display particles are attached are adjusted with a partition wall so that the interval is 50 μm. Then, the periphery of the substrate was adhered with an epoxy adhesive to obtain an image display device. The volume occupation ratio between the two types of display particles between the glass substrates was 25%. The content ratio of the positively charged display particles and the negatively charged display particles is approximately 1/1 in terms of the number ratio of the positively charged display particles / negatively charged display particles.

<Examples 2 to 13 / Comparative Examples 1 to 24>
An image display device was produced in the same manner as in Example 1 except that the production conditions of the negatively charged display particles and the positively charged display particles were changed as shown in Table 1 or Table 2.

<Evaluation>
-Transportability index According to the method described above, positively charged display particles (white particles) and negatively charged display particles (black particles) were separated and collected from the image display device. The collected positively charged display particles (white particles) and negatively charged display particles (black particles) were each subjected to the above-described method for measuring the transportability index.

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

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

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

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

The schematic block diagram of the apparatus for measuring a transportability index | exponent is shown. An example of the expansion schematic diagram of the slope vicinity when the transportability index | exponent of the display particle | grains of this invention is measured with the measuring apparatus of FIG. 1 is shown. An example of the graph of the transfer amount (w) -AC voltage application time (t) created when a transportability index | exponent is measured using the measuring apparatus of FIG. 1 is shown. 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. An example of the expansion schematic diagram of the slope vicinity when the transportability index | exponent of the display particle | grains of a prior art is measured with the measuring apparatus of FIG. 1 is shown.

Explanation of symbols

  1: parts feeder, 2: electronic balance, 3: drive unit, 4: ball, 5: slope, 6: central part, 7: saucer, 8: shaker (electromagnet), 9: leaf spring, 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
Display particles, wherein the display particles include positively charged display particles and negatively charged display particles, and the transportability index of each of the positively charged display particles and the negatively charged display particles is 20 mg / second or less.   An image display device comprising the display particles according to claim 1.

Images