JP2007187896A - Particle for display medium and information display panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide particles for a display medium showing preferable driving property as particles constituting a display medium such as a powder fluid and to provide an information display panel using the particles. <P>SOLUTION: The particles constitute a display medium to be used for an information display panel that contains the display medium having optical reflectance and charging property by sealing between two substrates at least one of which is transparent and that displays information such as an image by applying an electric field to the display medium and to move the display medium. The particles for a display medium shows such a property that the shape parameter SP of the particles is in a range of 1.0≤SP<1.4, wherein SP is determined by randomly selecting n particles, with n being 100 or more, from a sample image of the particles sufficiently and uniformly dispersed, obtaining a SPi of each particle, and obtaining SP defined by SP=(1/n)*ΣSPi (i=1 to n and n≥100). The above particles are used in an information display panel. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention encloses a display medium having optical reflectance and charging characteristics between two substrates, at least one of which is transparent, and applies an electric field to the display medium, thereby moving the display medium to obtain information such as an image. The present invention relates to particles that constitute a display medium used for an information display panel that displays and information display panels using the same.

Conventionally, a display medium having optical reflectance and charging characteristics is sealed between two substrates, at least one of which is transparent, and an electric field is applied to the display medium to move the display medium and display information such as an image. An information display panel is known (see, for example, Patent Document 1). As a method for producing the particles constituting the display medium used in this information display panel, for example, a break-down method in which a uniform compound material is prepared in a bulk, and then pulverized and classified to adjust to a desired particle diameter, from the molecular level It is possible to use a build-up method in which the compounding material is aggregated and grown to grow to a predetermined particle size.
WO / 2005/098525 brochure

  In general, particles produced by a breakdown method are subjected to a pulverization step, and thus become a group of particles having a non-uniform shape while maintaining a rugged non-uniform shape. On the other hand, since the particles produced by the build-up method are produced by chemical polymerization, they become a group of particles having a uniform shape while maintaining a substantially spherical shape. Furthermore, various methods for controlling the shape of each particle preparation method have been studied. For example, regarding electrophotographic toner, a technique for making a spherical shape by exposing a toner produced by a pulverization method to a high temperature atmosphere has been reported. Similarly, a technique has also been reported for a toner produced by a polymerization method, in which seed particles are agglomerated randomly one after another in the polymerization process to form a shape similar to that of an amorphous toner.

  The information display panel described above displays information such as images by moving charged particles instantaneously in the gas phase by electromagnetic force. By moving in the gas phase, superior characteristics such as high-speed response and memory characteristics can be obtained. However, as one problem, because of the gas phase system, the cohesion between particles and particles, particle-panel It can be mentioned that the adhesion force between the structural members is larger than that of a method of driving a liquid phase system such as an electrophoretic display.

  Solving this problem is indispensable for reducing the driving voltage of the information display panel to a practical level. In order to deal with this problem, attempts have been made to reduce the cohesion and adhesion by treating the surface of the particles for display media by various methods. However, there is currently no drivability improvement method that focuses on the particles themselves.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide particles for a display medium exhibiting good driveability as particles constituting a display medium such as a powder fluid and an information display panel using the same. It is.

  The particles for a display medium of the present invention move a display medium by enclosing a display medium having optical reflectance and charging characteristics between two substrates, at least one of which is transparent, and applying an electric field to the display medium. Particles constituting a display medium used for an information display panel for displaying information such as images, and the shape parameter SP obtained by the following method is in the range of 1.0 ≦ SP <1.4. (1) Take an image of a particle; (2) For a given particle image, obtain a line that forms the outer circumference from the image; (3) For the obtained outer circumference Of the circumscribed rectangles, find the one with the longest long side, and let Li be the length of the long side; (4) Find the area surrounded by the acquired outer circumference, and let this be Si; (5 ) SPi = (Li * Li * π) / (4 * i) define the shape parameter SPi of the particle i; (6) randomly select 100 or more n particles from the image of a sufficiently uniformly dispersed particle sample, and determine SPi for these. Above, SP = (1 / n) * ΣSPi (i = 1 to n, n ≧ 100) is obtained and defined as the particle shape parameter SP.

  Further, the information display panel of the present invention encloses a display medium by enclosing a display medium having optical reflectance and charging characteristics between two substrates, at least one of which is transparent, and applying an electric field to the display medium. In an information display panel that moves and displays information such as an image, at least one kind of the above-described display medium particles is used as a display medium.

  According to the present invention, when the shape parameter SP obtained by a predetermined method is in the range of 1.0 ≦ SP <1.4, good drivability is exhibited as particles constituting a display medium such as powdered fluid. Display medium particles and an information display panel using the same can be obtained.

  First, the basic configuration of the information display panel of the present invention will be described. In the information display panel which is an object of the present invention, an electric field is applied to a display medium sealed between two opposing substrates. Along with the applied electric field direction, the charged display medium is attracted by the electric field force or Coulomb force, etc., and the display medium changes the moving direction by the electric field direction change due to the potential switching, thereby displaying information such as an image. Made. Therefore, it is necessary to design the information display panel so that the display medium can move uniformly and maintain stability when rewriting the display repeatedly or when displaying the display information continuously. Here, as the force applied to the particles constituting the display medium, in addition to the force attracting each other by the Coulomb force between the particles, an electric mirror image force between the electrode and the substrate, an intermolecular force, a liquid cross-linking force, gravity and the like can be considered.

  An example of an information display panel that is an object of the present invention will be described with reference to FIGS. 1 (a) and (b) to FIGS. 3 (a) and 3 (b).

  In the example shown in FIGS. 1A and 1B, at least two kinds of display media 3 (here, white display medium particles 3Wa) having at least one kind of particles and having different optical reflectance and charging characteristics. A white display medium 3W composed of a group of particles and a black display medium 3B composed of a group of particles 3Ba for black display medium) are perpendicular to the substrates 1 and 2 according to the electric field applied from the outside of the substrates 1 and 2. The black display medium 3B is visually recognized by the observer and black display is performed, or the white display medium 3W is visually recognized by the observer and white display is performed. In the example shown in FIG. 1B, in addition to the example shown in FIG. 1A, a partition 4 is provided between the substrates 1 and 2, for example, in the form of a lattice to form a cell. In addition, in FIG. 1B, the partition in front is omitted.

  In the example shown in FIGS. 2A and 2B, at least two or more types of display media 3 (here, white display medium particles 3Wa) having different optical reflectance and charging characteristics composed of at least one type of particles. Between the electrode 5 provided on the substrate 1 and the electrode 6 provided on the substrate 2 is a voltage between the electrode 5 provided on the substrate 1 and the electrode 6 provided on the substrate 2. In accordance with the electric field generated by applying, the substrate is moved perpendicularly to the substrates 1 and 2 so that the black display medium 3B is visually recognized by the observer and black display is performed, or the white display medium 3W is provided to the observer. A white display is made by visual recognition. In the example shown in FIG. 2B, a cell is formed by providing partition walls 4 between the substrates 1 and 2, for example, in a lattice shape. Further, in FIG. 2 (b), the front partition is omitted.

  In the example shown in FIGS. 3A and 3B, the display medium 3 (here, from the particle group of the particles 3Wa for white display medium) having at least an optical reflectance and a charging property composed of at least one kind of particles. The white display medium 3W) is moved in a direction parallel to the substrates 1 and 2 in accordance with the electric field generated by applying a voltage between the electrode 5 and the electrode 6 provided on the substrate 1 to display white. The medium 3W is visually recognized by the observer and white display is performed, or the color of the electrode 6 or the substrate 1 is visually recognized by the observer and the color of the electrode 6 or the substrate 1 is displayed. In the example shown in FIG. 3B, for example, a lattice-shaped partition wall 4 is provided between the substrates 1 and 2 to form a cell. Moreover, in FIG.3 (b), the partition in front is abbreviate | omitted.

  The above description applies in the same manner to the case where the white display medium 3W including the particle group is replaced with the white medium including the powder fluid and the black display medium 3B including the particle group is replaced with the black display medium including the powder fluid. I can do it. The powder fluid will be described later.

  As a result of various studies on driveability of the display medium particles used in the information display panel having the above-described configuration, a combination in which two types of display media holding different polar charges are encapsulated in the information display panel However, it has been found that when the particles constituting at least one display medium are nearly spherical, suitable display characteristics can be exhibited at a lower voltage. This is because, in the case of irregular particles, the area in contact with other particles and panel structural members is larger than that of spherical particles, so interaction forces such as van der Waals forces that try to attract each other are more effective. It is presumed that this is because it works and as a result requires a larger driving force. In the case of spherical particles, since the contact surface on which the interaction force acts is as close to the point as possible, it is considered that the display medium can be driven with a smaller driving force. Even when one type of display medium is sealed in the information display panel, the display medium particles constituting the display medium are more nearly spherical, so that suitable display characteristics are revealed at a lower voltage. Similarly, when one of the particles is irregular and the other is a spherical particle, the situation is relatively easy to drive. This is because the spherical particles that are easier to drive move, the impact force when reaching the counter electrode surface is triggered, the irregular particles are shaken, and the interaction force is reduced to a level equivalent to spherical particles. It is presumed that the next move was possible. Furthermore, as a result of examining in detail how much the powder fluid deviates from the true spherical shape and affecting the drivability, when the following shape parameter SP is 1.0 ≦ SP <1.4, It has been found that such a suitable drive can be demonstrated.

<Calculation method of shape parameter>
The shape parameter SP here is assumed to be calculated as follows. This will be described using the example shown in FIG.
(1) An image of the particle 11 is taken.
(2) For an arbitrary particle image, a line 12 forming the outer periphery is obtained from the image.
(3) Among the rectangles 13 circumscribing the acquired outer peripheral line 12, a rectangle having the longest side is found, and the length of the long side is Li.
(4) The area surrounded by the acquired outer peripheral line 12 is obtained, and this is defined as Si.
(5) The shape parameter SPi of the particle i is defined as SPi = (Li * Li * π) / (4 * Si).
(6) From an image of a sufficiently uniform dispersed particle sample, 100 or more n particles are randomly selected and SPi is obtained for them, and then SP = (1 / n) * ΣSPi (i = 1 to n, n ≧ 100), and this is defined as the particle shape parameter SP.

  Specific methods for obtaining the shape parameter SP include taking a SEM photograph of the particle, measuring the length of the yarn along the outer periphery of the particle, and measuring the weight of the photo cut out along the outer periphery of the particle. However, there are methods that use the fact that the ratio of the total weight of the photo is the same as the known area ratio on the screen, and a method that converts the photo into an image file and analyzes it with software. Shall.

  Hereinafter, each member which comprises the information display panel of this invention is demonstrated.

  As for the substrate, at least one substrate is the transparent substrate 2 from which the color of the display medium can be confirmed from the outside of the information display panel, and a material having high visible light transmittance and good heat resistance is preferable. The substrate 1 may be transparent or opaque. Examples of substrate materials include polymer sheets such as polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polyethylene, polycarbonate, polyimide, and acrylic, flexible materials such as metal sheets, and glass and quartz. An inorganic sheet having no flexibility is mentioned. The thickness of the substrate is preferably from 2 to 5000 μm, more preferably from 5 to 2000 μm. If it is too thin, it will be difficult to maintain the strength and the spacing uniformity between the substrates, and if it is thicker than 5000 μm, it will be a thin information display panel. Is inconvenient.

  As an electrode forming material when an electrode is provided on an information display panel as required, metals such as aluminum, silver, nickel, copper, and gold, ITO, indium oxide, conductive tin oxide, conductive zinc oxide, etc. Conductive polymers such as conductive metal oxides, polyaniline, polypyrrole, and polythiophene are exemplified and appropriately selected and used. As a method for forming an electrode, a method of forming the above-described materials into a thin film by sputtering, vacuum deposition, CVD (chemical vapor deposition), coating, or the like, or mixing a conductive agent with a solvent or a synthetic resin binder. The method of apply | coating is used. The electrode provided on the display surface side substrate 2 which is on the viewing side and needs to be transparent needs to be transparent, but the electrode provided on the back side substrate 1 does not need to be transparent. In any case, the above-mentioned material that can be patterned and is electrically conductive can be suitably used. Note that the electrode thickness is not particularly limited as long as the conductivity can be secured and the light transmittance is not hindered, and is preferably 3 to 1000 nm, preferably 5 to 400 nm. The material and thickness of the electrode provided on the back side substrate 1 are the same as those of the electrode provided on the display surface side substrate described above, but need not be transparent. In this case, the external voltage input may be superimposed with direct current or alternating current.

The shape of the partition walls 4 provided on the substrate as required is appropriately set appropriately depending on the type of display medium involved in display, the shape and arrangement of electrodes to be arranged, and is not limited in general. The height of the partition is adjusted to 100 to 100 μm, preferably 3 to 50 μm, and the height of the partition wall to 10 to 100 μm, preferably 10 to 50 μm.
In forming the partition wall, a both-rib method in which ribs are formed on each of the opposing substrates 1 and 2 and then bonded, and a single-rib method in which ribs are formed only on one substrate are conceivable. In the present invention, any method is preferably used.
As shown in FIG. 5, the cells formed by the partition walls made up of these ribs are illustrated in a square shape, a triangular shape, a line shape, a circular shape, and a hexagonal shape as viewed from the substrate plane direction. And a mesh shape. It is better to make the portion corresponding to the cross section of the partition wall visible from the display surface side (the area of the cell frame) as small as possible, and the display becomes clearer.
Examples of the method for forming the partition include a mold transfer method, a screen printing method, a sand blast method, a photolithography method, and an additive method. Any of these methods can be suitably used for the information display panel of the present invention, and among these, a photolithography method using a resist film and a mold transfer method are suitably used.

  Next, the powder fluid used as a display medium composed of the display medium particles of the present invention will be described. As for the name of the powder fluid used in the information display panel of the present invention, the present applicant has obtained the right of “Electronic Powder Fluid (registered trademark): Registration No. 4636931”.

  The “powder fluid” in the present invention is a substance in an intermediate state of both fluid and particle characteristics that exhibits fluidity by itself without borrowing the force of gas or liquid. For example, liquid crystal is defined as an intermediate phase between a liquid and a solid, and has fluidity that is a characteristic of liquid and anisotropy (optical properties) that is a characteristic of solid (Heibonsha: Encyclopedia) . On the other hand, the definition of particle is an object with a finite mass even if it is negligible, and is said to be affected by gravity (Maruzen: Physics Encyclopedia). Here, even in the case of particles, there are special states of gas-solid fluidized bed and liquid-solid fluids. When gas is flowed from the bottom plate to the particles, upward force is applied to the particles according to the velocity of the gas. Is a gas-solid fluidized bed that is in a state where it can easily flow when it balances with gravity, and it is also called a liquid-solid fluidized state that is fluidized by a fluid (ordinary) Company: Encyclopedia). As described above, the gas-solid fluidized bed body and the liquid-solid fluid are in a state of using a gas or liquid flow. In the present invention, it has been found that a substance in a state of fluidity can be produced specifically without borrowing the force of such gas and liquid, and this is defined as powder fluid.

  That is, the pulverulent fluid in the present invention is in an intermediate state having both the characteristics of particles and liquid, as in the definition of liquid crystal (liquid and solid intermediate phase), and is the characteristic of the above-mentioned particles. It is a substance that is extremely unaffected and exhibits a unique state with high fluidity. Such a substance can be obtained in an aerosol state, that is, in a dispersion system in which a solid or liquid substance is stably suspended as a dispersoid in a gas, and the solid substance is regarded as a dispersoid in the information display panel of the present invention. To do.

The information display panel of the present invention encloses a powder fluid exhibiting high fluidity in an aerosol state in which solid particles are stably suspended as a dispersoid, for example, in a gas, between opposed substrates, at least one of which is transparent. In addition, such a powder fluid can be easily and stably moved by a Coulomb force or the like with a small electric field.
As described above, for example, the powder fluid used as a display medium in the present invention is a substance in an intermediate state between fluid and particles that exhibits fluidity by itself without borrowing the force of gas or liquid. It is. This powder fluid can be in an aerosol state in particular, and in the information display panel of the present invention, it is used as a display medium in a state where a solid substance floats relatively stably as a dispersoid in the gas.

Next, display medium particles (hereinafter also referred to as particles) constituting the display medium in the information display panel of the present invention will be described. The display medium particles are composed of the display medium particles as they are to form a display medium, or are combined with other particles to form a display medium, or adjusted and configured to become a powder fluid to form a display medium. Or used.
The particles can contain a charge control agent, a colorant, an inorganic additive, and the like, as necessary, in the resin as the main component, as necessary. Examples of resins, charge control agents, colorants, and other additives will be given below.

  Examples of the resin include urethane resin, urea resin, acrylic resin, polyester resin, acrylic urethane resin, acrylic urethane silicone resin, acrylic urethane fluororesin, acrylic fluororesin, silicone resin, acrylic silicone resin, epoxy resin, polystyrene resin, styrene Acrylic resin, polyolefin resin, butyral resin, vinylidene chloride resin, melamine resin, phenol resin, fluororesin, polycarbonate resin, polysulfone resin, polyether resin, polyamide resin and the like can be mentioned, and two or more kinds can be mixed. In particular, acrylic urethane resin, acrylic silicone resin, acrylic fluororesin, acrylic urethane silicone resin, acrylic urethane fluororesin, fluororesin, and silicone resin are suitable from the viewpoint of controlling the adhesive force with the substrate.

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

  As the colorant, various organic or inorganic pigments and dyes as exemplified below can be used.

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

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

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

Examples of inorganic additives include titanium oxide, zinc white, zinc sulfide, antimony oxide, calcium carbonate, lead white, talc, silica, calcium silicate, alumina white, cadmium yellow, cadmium red, cadmium orange, titanium yellow, Examples include bitumen, ultramarine blue, cobalt blue, cobalt green, cobalt violet, iron oxide, carbon black, manganese ferrite black, cobalt ferrite black, copper powder, and aluminum powder.
These pigments and inorganic additives can be used alone or in combination. Of these, carbon black is particularly preferable as the black pigment, and titanium oxide is preferable as the white pigment.

  The particles for display media of the present invention (hereinafter also referred to as particles) preferably have an average particle diameter d (0.5) in the range of 0.1 to 20 μm and are uniform and uniform. If the average particle diameter d (0.5) is larger than this range, the display is not clear. If the average particle diameter d (0.5) is smaller than this range, the cohesive force between the particles becomes too large, which hinders movement as a display medium.

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

  Furthermore, regarding the correlation between the particles, the ratio of the d (0.5) of the particles having the minimum diameter to the d (0.5) of the particles having the maximum diameter among the used particles is set to 50 or less, preferably 10 or less. It is essential. Even if the particle size distribution Span is reduced, particles with different charging characteristics move in opposite directions, so that the particle size is close to each other and each particle can be easily moved in the opposite direction by the equivalent amount. This is within this range.

The particle size distribution and the particle size can be obtained from a laser diffraction / scattering method or the like. When laser light is irradiated onto particles to be measured, a light intensity distribution pattern of diffracted / scattered light is spatially generated, and this light intensity pattern has a corresponding relationship with the particle diameter, so that the particle diameter and particle diameter distribution can be measured. .
Here, the particle size and particle size distribution in the present invention are obtained from a volume-based distribution. Specifically, using a Mastersizer2000 (Malvern Instruments Ltd.) measuring instrument, put particles into a nitrogen stream and use the attached analysis software (software based on volume-based distribution using Mie theory). The diameter and particle size distribution can be measured.

  The charge amount of the display medium particles naturally depends on the measurement conditions, but the charge amount of the display medium particles in the information display panel is almost the same as the initial charge amount, the contact with the partition walls, the contact with the substrate, and the elapsed time. It was found that depending on the charge decay, the saturation value of the charging behavior of the particles for the display medium is a dominant factor.

  As a result of intensive studies, the present inventors have been able to evaluate the range of proper charging characteristics of display medium particles by measuring the charge amount of the particles used in the display medium using the same carrier particles in the blow-off method. I found.

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

The distance between the substrates in the information display panel that is the subject of the present invention is not limited as long as the display medium can be moved and the contrast can be maintained, but is usually adjusted to 10 to 500 μm, preferably 10 to 200 μm.
The volume occupation ratio of the display medium in the space between the opposing substrates is preferably 5 to 70%, more preferably 5 to 60%. If it exceeds 70%, the movement of the display medium is hindered, and if it is less than 5%, the contrast tends to be unclear.

  A display medium comprising the display medium particles of the present invention was prepared as follows, an information display panel was prepared using the prepared display medium, and the shape parameter SP was evaluated.

1) Preparation of particles for display medium As particles for display medium, particles prepared as follows were prepared. These display medium particles are imaged with a scanning electron microscope S-2700 manufactured by Hitachi, Ltd., and the obtained images are analyzed using image analysis software Mac-View (manufactured by MOUNTECH Co., Ltd.). , SP was calculated.

  Cross-linked St / EGDMA copolymer resin particles prepared by suspension polymerization method containing 5 parts by weight of carbon black as a color pigment were adjusted so as to have an average particle size of 9.0 μm. With respect to 100 parts by weight of the particles, silica fine particles having an average primary particle diameter of 0.009 μm prepared by a pyrogenic method are subjected to surface treatment with hexamethyldisilazane, and further 2.2 parts by weight of fine particles subjected to surface treatment with trichloroaminosilane. Mixing and stirring were carried out at 3000 rpm for 30 minutes with a carbon mixer HFM-001C (manufactured by SMT Co., Ltd.) to obtain particles A for black display media. The SP of this was 1.19.

  A PMMA resin compound containing 5 parts by weight of carbon black as a coloring pigment was prepared, and this was classified using an airflow type pulverization classifier so as to have an average particle size of 9.0 μm. With respect to 100 parts by weight of the particles, 2.2 parts by weight of fine particles of silica fine particles having an average primary particle diameter of 0.009 μm prepared by a pyrogenic method and surface-treated with hexamethyldisilazane were added to a carbon mixer HFM-001C ((stock) ) Manufactured by SMT) and stirred at 3000 rpm for 30 minutes to obtain particles B for black display medium. Its SP was 1.67.

  During the polymerization after the suspension step, black display medium particles C were obtained by the same steps as the black display medium particles A except that the stirring in the tank was stopped. Its SP was 1.53.

  A cross-linked St / DvB copolymer resin prepared by a suspension polymerization method containing 100 parts by weight of titania for pigment surface-treated with a copolymer of methylhydrogenpolysiloxane and methylpolysiloxane as a coloring pigment has an average particle size of 9.0 μm. It was adjusted to become. With respect to 100 parts by weight of the particles, 2.2 parts by weight of fine particles of silica fine particles having an average primary particle diameter of 0.009 μm prepared by a pyrogenic method and surface-treated with hexamethyldisilazane were added to a carbon mixer HFM-001C ((stock) ) Manufactured by SMT) and stirred at 3000 rpm for 30 minutes to obtain particles D for white display medium. Its SP was 1.12.

  A cycloolefin resin compound containing 100 parts by weight of titania for pigment as a color pigment was prepared, and this was classified using an airflow type pulverization classifier so as to have an average particle size of 9.0 μm. With respect to 100 parts by weight of the particles, 2.2 parts by weight of fine particles of silica fine particles having an average primary particle diameter of 0.009 μm prepared by a pyrogenic method and surface-treated with hexamethyldisilazane were added to a carbon mixer HFM-001C ((stock) ) Manufactured by SMT) and stirred at 3000 rpm for 30 minutes to obtain particles E for white display medium. Its SP was 1.77.

  The produced display media are summarized in Table 1 below.

2) Production of display panel for evaluation test A display medium using black and white display medium particles was prepared as an evaluation sample. Both display media were triboelectrically charged by carrying N ₂ air current through the stainless steel tube. Further, a glass substrate (A) having an inner surface coated with ITO coated with a 100 μm spacer is prepared, and a bias voltage is superimposed between the stainless steel tube and the ITO surface of the glass substrate to stabilize the air flow. The sample to be evaluated was laminated by spraying the sample on the ITO surface in a dry air atmosphere at 5 ° C. and 5% rh. After the process was sequentially performed on both the black display medium and the white display medium, only the display medium attached to the spacer surface was removed.

  Further, a glass substrate (B) on which one side was coated with ITO was prepared, and bonded to the glass substrate on which the sample display medium was laminated so that the ITO surface faced inward. At this time, an ultraviolet (UV) curable one-part epoxy adhesive was used for adhesion. Finally, electrodes were pulled out from the ITO surfaces of both glasses to form a display test display panel. At this time, the display medium arranged in the test display panel has the same total volume of the black display medium and the white display medium, and the filling rate (volume occupation ratio) of the display medium in the test display panel. Was adjusted as appropriate so that it would be 25%. The substrate electrode and the power source were connected such that the glass substrate (A) was on the ground side and the glass substrate (B) was on the bias side.

  As a result of evaluating the series of display panels prepared this time, those in which the display medium was inverted were displayed in black when viewed from the glass substrate (A) side when a positive potential was superimposed. In addition, when a negative potential was superimposed, the display medium that was inverted was displayed in white when viewed from the glass substrate (B) side.

3) Evaluation of driveability and display characteristics of display medium Displayability of display medium is evaluated by producing a display panel using the display medium composed of the display medium particles to be evaluated as described above, and evaluating the display performance shown below. The driving performance evaluation index V90 obtained by the method was used for comparison.

  A voltage was superimposed on the produced display panel while inverting the polarity, and the reflection density when each voltage was applied was measured using a reflection image densitometer (RD918, manufactured by Macbeth). The hysteresis cycle was obtained by arranging the data found here on a graph of horizontal axis voltage and vertical axis reflection density. Here, among the applied voltages corresponding to the concentrations shown in the following formulas (4) and (5), when the voltages having large absolute values are V90a and V90b, the values shown in the following formula (6) are driven. The sex evaluation index was V90. Note that ODmax is the maximum reflection density shown in the hysteresis cycle. ODmin is the minimum reflection density shown in the hysteresis cycle. Further, as an evaluation index of image characteristics, a value represented by the following formula (7) was used as a density display characteristic evaluation index Ct, and the comparison was made. Further, the solid display spots (uniformity) were visually and sensory-evaluated.

0.9 * ODmax + 0.1 * ODmin Formula (4)
0.1 * ODmax + 0.9ODmin Formula (5)
V90 = 0.5 * (| V90a | + | V90b |) Formula (6)
Ct = ODmax−ODmin Formula (7)

  As Examples 1 to 3 and Comparative Examples 1 and 2, display media composed of black and white display media particles having the combinations shown in Table 2 below were prepared, and the above evaluation was performed at a maximum applied voltage of 300V. As a result, in Examples 1 to 3, a favorable inversion driving property with a low voltage and a high contrast was exhibited, and a suitable display performance free from display spots could be realized.

  The information display panel of the present invention can obtain a reflected image with a wide viewing angle by using the particles for display medium of the present invention, and has high visibility like a printed paper. Display units for mobile devices such as mobile phones and handy terminals, electronic papers such as electronic books and electronic newspapers, billboards such as signboards, posters, blackboards, display units for calculators, home appliances, automotive products, point cards, IC cards, etc. Card display unit, electronic advertisement, information board, electronic POP (Point Of Presence, Point Of Purchase advertising), electronic price tag, electronic shelf label, electronic score, display unit of RF-ID device, etc.

(A), (b) is a figure which shows an example of the information display panel of this invention, respectively. (A), (b) is a figure which shows the other example of the information display panel of this invention, respectively. (A), (b) is a figure which shows the further another example of the information display panel of this invention, respectively. It is a figure which shows an example of the shape at the time of measuring a shape parameter in the particle | grains for display media of this invention. It is a figure which shows an example of the shape of the partition in the information display panel of this invention.

Explanation of symbols

1, 2 Substrate 3 Display medium (particle group, powder fluid)
3W White display medium 3Wa White display medium particle 3B Black display medium 3Ba Black display medium particle 4 Partition 5, 6 Electrode 11 Particle 12 Peripheral line 13 Rectangular

Claims (2)

Information for displaying information such as an image by moving a display medium by enclosing a display medium having optical reflectance and charging characteristics between two substrates, at least one of which is transparent, and applying an electric field to the display medium Particles constituting a display medium for use in a display panel, wherein the shape parameter SP determined by the following method is in the range of 1.0 ≦ SP <1.4:
(1) Taking an image of particles;
(2) For an arbitrary particle image, a line forming the outer circumference is obtained from the image;
(3) Among rectangles circumscribing the acquired outer perimeter line, find the one having the longest long side, and let Li be the length of the long side;
(4) The area surrounded by the acquired outer circumference is obtained, and this is defined as Si;
(5) Define the shape parameter SPi of the particle i as SPi = (Li * Li * π) / (4 * Si);
(6) From an image of a sufficiently uniform dispersed particle sample, 100 or more n particles are randomly selected and SPi is obtained for them, and then SP = (1 / n) * ΣSPi (i = 1 to n, n ≧ 100), and this is defined as the particle shape parameter SP.   Information for displaying information such as an image by moving a display medium by enclosing a display medium having optical reflectance and charging characteristics between two substrates, at least one of which is transparent, and applying an electric field to the display medium In the display panel, at least one kind of particles for a display medium according to claim 1 is used as a display medium.

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