JP2009145599A - Display medium and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display medium and display device, restraining lowering of contrast due to cohesion of particles. <P>SOLUTION: Two or more kinds of particle groups 34 different in size are dispersed in each cell in the display medium 12. Among the two or more kinds of particle groups 34, at least the smallest particle group is formed of electrophoretic particles, and at least one kind of particle group in the larger particle groups than the smallest particle group is a rugged particle group formed of rugged particles 60. The color of rugged particles 60 of the rugged particle group is different from the color of the particles of the particle groups other than the rugged particle group. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a display medium and a display device.

  Conventionally, a display medium using colored particles is known as an image display medium that can be rewritten repeatedly.

  These display media include, for example, a pair of substrates and a particle group sealed between the substrates so as to be movable between the substrates in accordance with an electric field formed between the pair of substrates.

  In this display medium, by moving the encapsulated particles by applying a voltage between a pair of substrates, an image of a color corresponding to the color of the particles moved to one of the substrates is displayed. Various techniques are known for suppressing a reduction in contrast ratio due to a mixture of particles of a plurality of colors and a display of a color different from the display target color (for example, see Patent Documents 1 to 3).

  In Patent Document 1, at least one of white particles and colored particles is electrophoresed in a gelled dispersion medium. Aggregation between two particles having different color tones is suppressed by electrophoresis of the particles in the dispersion medium in the gel state.

  In Patent Document 2, by setting the volume median diameter of the colored particles to 1/1 to 1/50 with respect to the volume median diameter of the white particles, sterically hindered dynamic interaction between the colored particles and the white particles. Is mitigated, thereby suppressing color mixing due to aggregation between particles having different color tones.

In Patent Document 3, the electrophoretic particles are aggregated and adhered to the electrode plate by providing a water- and oil-repellent surface layer having a critical surface tension of 20 dyne / cm or less on the surface of the electrophoretic white solid. Is preventing.
JP2003-149691A JP 2001-242492 A JP2001-033831A

  It is an object of the present invention to provide a display medium and a display device that can suppress a decrease in contrast due to aggregation of particles.

The above problem is solved by the following means. That is,
In the invention according to claim 1, at least one of the pair of substrates having translucency and disposed with a gap, a dispersion medium enclosed between the pair of substrates, and being dispersed in the dispersion medium, A plurality of types of particle groups having different sizes, and the dispersion medium according to an electric field in which at least the smallest first particle group of the plurality of types of particle groups is formed between the pair of substrates. The at least one kind of particle group that moves inside and larger than the first particle group is an uneven particle group having unevenness in at least a partial region of the surface of each particle of the particle group, The concavo-convex particle group is a display medium characterized in that it has at least a different color from a particle group other than the concavo-convex particle group among the plurality of types of particle groups.

  The invention according to claim 2 is the display medium according to claim 1, wherein the plurality of types of particle groups have different colors.

  The invention according to claim 3 is the display medium according to claim 1, wherein each type of particle group is composed of a plurality of types of color particle groups having different colors.

  The invention according to claim 4 is the display medium according to claim 1, wherein the uneven particle group is the largest particle group of the plurality of types of particle groups.

  The invention according to claim 5 is the display medium according to claim 1, wherein the lightness of the largest particle group among the plurality of types of particle groups is highest.

  The invention according to claim 6 is the display medium according to claim 4, wherein the uneven particle group is white.

  The invention according to claim 7 is the display medium according to claim 1, wherein in the uneven region, at least the opening of the recess is smaller than the volume average primary particle size of the particles of the first particle group.

  The invention according to claim 8 is characterized in that the uneven region is formed by attaching a plurality of third particles to at least a partial region of the surface of each particle of the uneven particle group. Display media.

  The invention according to claim 9 is the display medium according to claim 8, wherein the third particles are inorganic oxides.

  The invention according to claim 10 is the display medium according to claim 1, wherein the dispersion medium is a nonpolar solvent.

  The invention according to claim 11 is the display medium according to claim 9, wherein the dispersion medium is silicone oil.

In the invention according to claim 12, at least one of the pair of substrates having translucency and disposed with a gap, a dispersion medium enclosed between the pair of substrates, and being dispersed in the dispersion medium, A plurality of types of particle groups having different sizes, and the dispersion medium according to an electric field in which at least the smallest first particle group of the plurality of types of particle groups is formed between the pair of substrates. The at least one kind of particle group that moves inside and larger than the first particle group is an uneven particle group having unevenness in at least a partial region of the surface of each particle of the particle group, And the concavo-convex particle group is a display medium that is at least a color different from the particle group other than the concavo-convex particle group among the plurality of types of particle groups, and a voltage applying unit that applies a voltage between the pair of substrates;
A display device characterized by comprising:

  According to the first aspect of the present invention, at least one kind of particle group larger than the smallest particle group among the plurality of kinds of particle groups dispersed in the dispersion medium is at least a part of the surface. Since the concavo-convex particle group has concavo-convex regions, it is possible to suppress the aggregation of the concavo-convex particle group and other types of particle groups, and to suppress the decrease in contrast due to the aggregation.

  According to the invention which concerns on Claim 2, there exists an effect that a color display is attained with the suppression of the fall of contrast.

  According to the third aspect of the present invention, there is an effect that color display is possible with a simple configuration while suppressing a decrease in contrast.

  According to the invention which concerns on Claim 4, there exists an effect that suppression of the further fall of contrast can be aimed at.

  According to the invention which concerns on Claim 5, there exists an effect that suppression of the further fall of contrast can be aimed at.

  According to the invention which concerns on Claim 6, there exists an effect that suppression of the further fall of contrast can be aimed at.

  According to the invention which concerns on Claim 7, there exists an effect that aggregation with an uneven | corrugated particle group and another kind of particle group is further suppressed.

  According to the eighth aspect of the invention, the charging of the concavo-convex particle group is controlled, and there is an effect that adhesion of the first particle to the concavo-convex particle group and aggregation of the concavo-convex particle group are prevented. .

  According to the ninth aspect of the present invention, since the aggregation energy is smaller than that of the polymer particles, there is an effect that the aggregation between the uneven particle group and the other type of particle group is further suppressed.

  According to the invention which concerns on Claim 10, there exists an effect that aggregation of each particle | grains of multiple types of particle group is suppressed.

  According to the invention which concerns on Claim 11, there exists an effect that it is excellent in transparency and a display coloring is improved.

  According to the twelfth aspect of the invention, there is an effect that a decrease in contrast is suppressed.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol may be provided to the member which an action and a function bears the same function through all drawings, and the overlapping description may be abbreviate | omitted.

  As shown in FIG. 1, the display device 10 according to the present embodiment includes a display medium 12, a voltage application unit 16 that applies a voltage to the display medium 12, and a control unit 18.

  The display medium 12 includes a display substrate 20 that serves as an image display surface, a rear substrate 22 that faces the display substrate 20 with a gap, and holds the substrates at a predetermined interval, and between the display substrate 20 and the rear substrate 22. The gap member 24 is divided into a plurality of cells, and the particle group 34 is enclosed in each cell.

  The cell indicates a region surrounded by the display substrate 20, the back substrate 22, and the gap member 24. A dispersion medium 50 is enclosed in the cell, and the particle group 34 is dispersed in the dispersion medium 50.

  In the present embodiment, in order to simplify the description, the present embodiment will be described using a diagram focusing on one cell. Hereinafter, each configuration will be described in detail.

  First, the particle group 34 will be described.

  The particle group 34 includes a plurality of types of particle groups having different sizes, and each type of particle group includes a plurality of particles having the same size.

  The “size” in the present embodiment indicates a volume average primary particle size.

  The volume average primary particle size is measured by irradiating each type of particles with laser light and measuring the average particle size from the intensity distribution pattern of diffraction and scattered light emitted from the group. To do. In addition, the measurement was performed at 25 ° C. using a dynamic light scattering type particle size distribution measuring device (LB-550, Horiba, Ltd.).

  Among the plural types of particle groups having different sizes, at least the smallest particle group moves in the dispersion medium 50 according to the electric field formed between the display substrate 20 and the back substrate 22. (So-called electrophoresis). The display medium 12 may be configured such that at least the smallest particle group of the plurality of types of particle groups is electrophoresed, and the plurality of types of particle groups including the smallest particle group are electrophoresed. It may be.

  The change in display color on the display medium 12 is caused by movement of the electrophoretic particle group in the dispersion medium 50 among the plural types of particle groups constituting the particle group 34. That is, when the electrophoretic particle group moves to the display substrate 20 side or the back substrate 22 side, the color visually recognized from the display substrate 20 side is changed according to this movement, and the color displayed on the display medium 12 That is, the color when the display medium 12 is viewed from the display substrate 20 side changes.

  In addition, at least one kind of particle group larger than the smallest particle group among the plurality of kinds of particle groups having different sizes is at least one of the surfaces of the particles of the particle group. It is a concavo-convex particle group composed of concavo-convex particles having concavo-convex portions in the region, and each concavo-convex particle constituting the concavo-convex particle group has a color different from that of the particle group having no concavo-convex.

  In the present embodiment, “different colors” indicates that the color difference (CIE1976 (L * a * b *) color system, JIS Z8730) is 5 or more.

  Particles of at least one of the particle groups larger than the smallest among a plurality of types of particle groups of different sizes enclosed in the same cell are present in at least a part of the surface. Since it is uneven | corrugated particle | grains which have an unevenness | corrugation, aggregation of an uneven | corrugated particle and the particle | grains which do not have an unevenness | corrugation is suppressed by the unevenness | corrugation of the surface of this uneven | corrugated particle.

  In addition, since the irregular particles have irregularities in at least a part of the surface as described above and at least a color different from the particles of the particle group having no irregularities, the irregular particles and the irregular particles do not have irregularities. By suppressing aggregation between the particles, generation of color mixing due to aggregation between the particles of different colors is suppressed, and a decrease in contrast (light / dark difference) is suppressed.

  Note that, among the plurality of types of particle groups having different sizes enclosed in the same cell, at least one of the particle groups larger than the smallest particle group is the particle group composed of uneven particles as described above. The particle group composed of uneven particles is preferably the largest particle group for reasons of stability of adhesion control between particles.

  The opening of the concave portion in the region where the unevenness is provided on the surface of each uneven particle of the uneven particle group (hereinafter sometimes referred to as the uneven region) is the volume average primary particle of the smallest particle group. Smaller than the diameter.

  The opening of the recess is preferably not more than 1 times the volume average primary particle size of the smallest particle group among a plurality of types of particle groups of different sizes enclosed in the same cell. , 0.5 times or less is more preferable, and 0.3 times or less is particularly preferable.

  When the opening of the concave portion is larger than 1 times the volume average primary particle size of the particle group having the smallest size among the plurality of types of particle groups having different sizes, each particle of the smallest particle group through the opening of the concave portion May enter the recess, and as a result, the effect of suppressing aggregation between the uneven particles of the uneven particle group and the particle group having the smallest size and no unevenness may be reduced.

  In addition, as described above, the particle group including the uneven particles having unevenness is a particle group other than the smallest particle group among the plurality of types of particle groups having different sizes dispersed in the dispersion medium 50. Although it may be at least one kind in the particle group, a preferable form is a case where the largest particle group is composed of uneven particles having unevenness.

  If the largest particle group among the plural types of particle groups of different sizes enclosed in the same cell is composed of uneven particles having unevenness, the particle group not having the unevenness Since it is difficult to adhere to the concavo-convex particles, the effect of suppressing the aggregation between the concavo-convex particles and the particle group having a different color from the concavo-convex particles is high.

  In addition, as described above, the plurality of types of particle groups different in size enclosed in the same cell are the color of the uneven particle group made of uneven particles having unevenness and the particle group made of particles having no unevenness. The plurality of types of particle groups having different sizes are preferably different in color and size from one type to another.

  By configuring the particle group 34 from a plurality of types of particle groups having different sizes and colors, further multicolor display can be performed on the display medium 12.

  In addition, it is preferable that the brightness of the color of the largest particle group among these several types of particle groups is the highest, and it is more preferable that it is white.

  When the lightness of the color of the largest particle group is the highest, the reflected light of light is increased, the brightness of display is improved, the color reproduction range is expanded, and the color expression color is expanded.

  As described above, the particle group 34 is composed of a plurality of types of particle groups having different sizes. However, each type of particle group composed of particles of the same size is further divided into a plurality of different colors. You may comprise from a kind of color particle group.

  In this way, particles having the same size and different colors are further dispersed in the dispersion medium 50, so that the moving speed of the particles becomes uniform and stable, and display characteristics can be stably obtained. There is an effect.

  Hereinafter, the display medium 12 of the present embodiment will be described with specific examples.

  In the display medium 12 of the present embodiment, as shown in FIG. 1, the particle group 34 is a plurality of types of particle groups having different sizes, and is larger in size than the particle group 30 and the particles constituting the particle group 30. And a concavo-convex particle group 32 made of concavo-convex particles having a large surface and concavo-convex on the surface.

  The particle group 30 is composed of a plurality of particles having a volume average particle size smaller than that of the uneven particle group 32. Each particle constituting the particle group 30 is charged positively or negatively, and a predetermined voltage is applied between the surface electrode 40 and the back electrode 46 (that is, between the display substrate 20, the back substrate 22, and the substrate). When applied, an electric field of a predetermined electric field strength or more is formed between the display substrate 20 and the back substrate 22 to move in the dispersion medium 50.

  The change in display color on the display medium 12 is caused by the movement of each particle constituting the particle group 30 in the dispersion medium 50.

  Each particle of the particle group 30 includes glass beads, alumina, silica, insulating metal oxide particles such as titanium oxide, thermoplastic or thermosetting resin particles, and a colorant fixed on the surface of these resin particles. And particles containing a colorant in a thermoplastic or thermosetting resin, capsule-type pigment particles wrapped with a resin, and metal colloid particles having a plasmon coloring function.

  Examples of the thermoplastic resin used in the production of particles include styrenes such as styrene and chlorostyrene, monoolefins such as ethylene, propylene, butylene, and isoprene, vinyls such as vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl butyrate. Α-methylene aliphatic monocarboxylic acid such as ester, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate Homopolymers or copolymers of vinyl ethers such as acid esters, vinyl methyl ether, vinyl ethyl ether, vinyl butyl ether, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, vinyl isopropenyl ketone And the like.

  In addition, as thermosetting resins used for the production of particles, crosslinked resins mainly composed of divinylbenzene and crosslinked resins such as crosslinked polymethyl methacrylate, phenol resins, urea resins, melamine resins, polyester resins, silicones Examples thereof include resins. Particularly representative binder resins include polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer. Examples of the polymer include polyethylene, polypropylene, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, and paraffin wax.

  As the colorant, organic or inorganic pigments, oil-soluble dyes, etc. can be used, magnetic powders such as magnetite and ferrite, carbon black, titanium oxide, magnesium oxide, zinc oxide, phthalocyanine copper-based cyan colorant, Known colorants such as an azo yellow color material, an azo magenta color material, a quinacridone magenta color material, a red color material, a green color material, and a blue color material can be given. Specifically, aniline blue, calcoil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 238, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 128, C.I. Blue 15: 1, C.I. I. Pigment Blue 15: 3, etc. are exemplified as typical examples.

  The particle resin may be mixed with a charge control agent, if necessary. As the charge control agent, known materials used for toner materials for electrophotography can be used. For example, cetylpyridyl chloride, BONTRON P-51, BONTRON P-53, BONTRON E-84, BONTRON E-81 (above, Quaternary ammonium salts such as Orient Chemical Industry Co., Ltd., salicylic acid metal complexes, phenol condensates, tetraphenyl compounds, metal oxide particles, and metal oxide particles surface-treated with various coupling agents. .

  A magnetic material may be mixed in the inside or the surface of the particles as necessary. As the magnetic material, a color-coated inorganic magnetic material or organic magnetic material is used as necessary. Further, a transparent magnetic material, in particular, a transparent organic magnetic material does not hinder the color development of the color pigment, and the specific gravity is smaller than that of the inorganic magnetic material, so that it is more desirable.

As the colored magnetic powder, for example, a small-diameter colored magnetic powder described in JP-A-2003-131420 can be used. A material provided with magnetic particles serving as nuclei and a colored layer laminated on the surface of the magnetic particles is used. The colored layer may be selected by coloring the magnetic powder opaque with a pigment or the like, but it is desirable to use, for example, a light interference thin film. This optical interference thin film is a thin film having a thickness equivalent to the wavelength of light made of an achromatic material such as SiO ₂ or TiO ₂ , and reflects light in a wavelength selective manner by optical interference in the thin film. is there.

  As a method for producing the particle group 30, any conventionally known method may be used. For example, as described in JP-A-7-325434, a resin, a pigment, and a charge control agent are weighed to a predetermined mixing ratio, and after the resin is heated and melted, the pigment is added, mixed, dispersed, and cooled. Then, a method of preparing particles using a pulverizer such as a jet mill, a hammer mill, a turbo mill, etc., and then dispersing the obtained particles in a dispersion medium can be used. Also, by preparing particles containing a charge control agent in the particles by polymerization methods such as suspension polymerization, emulsion polymerization, dispersion polymerization, coacervation, melt dispersion, emulsion aggregation method, drying in liquid, etc. Thereafter, it may be dispersed in a dispersion medium to produce a particle dispersion medium. Furthermore, the resin, the colorant, the charge control agent and the dispersion medium can be plasticized, the dispersion medium does not boil, and the temperature is lower than the decomposition point of the resin, the charge control agent and / or the colorant. There is a method using an appropriate apparatus capable of dispersing and kneading the raw materials. Specifically, the pigment, the resin, and the charge control agent are heated and melted in a dispersion medium with a meteor mixer, a kneader, etc., and the molten mixture is cooled with stirring using the temperature dependence of the solvent solubility of the resin. The particles can be produced by solidification / precipitation.

  Furthermore, the above raw materials are put into a suitable container equipped with granular media for dispersion and kneading, for example, a heated vibration mill such as an attritor or a heated ball mill, and the container is placed in a desired temperature range, for example, 80 A method of dispersing and kneading at ˜160 ° C. can be used. As granular media, steels such as stainless steel and carbon steel, alumina, zirconia, silica and the like are desirably used. In order to produce particles by this method, the raw material that has been previously fluidized is further dispersed in a container by means of granular media, and then the dispersion medium is cooled to precipitate a resin containing a colorant from the dispersion medium. The granular media generates a shear and / or impact to reduce the particle size while maintaining a motion state during and after cooling.

  The content of the particle group 30 (content (mass%) with respect to the total mass in the cell) is not particularly limited as long as the desired hue is obtained, and the cell thickness (that is, the display substrate 20). It is effective for the display medium 12 to adjust the content by the distance between the substrate and the back substrate). That is, in order to obtain a desired hue, the content decreases as the cell becomes thicker, and the content can increase as the cell becomes thinner. Generally, it is 0.01 mass%-50 mass%.

  The concavo-convex particle group 32 is composed of a plurality of concavo-convex particles 60 which are larger than the particles constituting the particle group 30 and have a color different from the color of the particle group 30 and have irregularities on the surface. In the present embodiment, the case where the concavo-convex particle group 32 is white will be described, but the present invention is not limited to this color.

  In the present embodiment, the uneven particle group 32 is described as an uncharged particle group (that is, a particle group that does not undergo electrophoresis). In addition, each uneven particle 60 constituting the uneven particle group 32 is configured in such a size that each particle constituting the particle group 30 can move through the gaps between the plurality of uneven particles 60. For this reason, in this Embodiment, the uneven | corrugated particle group 32 also has a function as a space | gap member to move without inhibiting the movement between the display substrate 20 and the back substrate 22 between substrates.

  As shown in FIG. 2 (A), each uneven particle 60 constituting the uneven particle group 32 has a form in which the uneven region 65 is formed by attaching a plurality of third particles 64 to the surface of the mother particle 62. As shown in FIG. 2 (B), the uneven particle 60B having a form in which the uneven region 65 is formed by providing a plurality of recesses 68 on the surface of the mother particle 62, as shown in FIG. Also good.

  The ratio of the concavo-convex region 65 on the surface of the concavo-convex particle 60A and the concavo-convex particle 60B (generally referred to as the concavo-convex particle 60) may be a region that occupies at least 50% or more of the surface of the mother particle 62, Preferably, it is 70% or more, more preferably 80% or more.

  When the ratio of the concavo-convex region 65 on the surface of the concavo-convex particle 60 is less than 50% of the surface of the base particle 62, each of the concavo-convex particle 60 and the particle group 30 having a color different from the concavo-convex particle 60 without the concavo-convex particle In some cases, the effect of suppressing aggregation with particles is reduced, and it is difficult to suppress the decrease in contrast.

  On the other hand, if the ratio of the concavo-convex region 65 on the surface of the concavo-convex particle 60 is 50% or more of the surface of the base particle 62, aggregation between the concavo-convex particle 60 and each particle constituting the particle group 30 is suppressed, and the display medium 12 is suppressed.

  The opening of the recess 68 in the uneven region 65 is larger than the volume average primary particle size of the smallest particle group (the particle group 30 in the present embodiment) among a plurality of types of particle groups enclosed in the same cell. It is comprised, Preferably it is 1 time or more, More preferably, it is 2 times or more.

  In addition, the opening of the recessed part 68 has shown the maximum diameter of the opening of the several recessed part 68 in the uneven | corrugated area | region 65. FIG.

  When the opening of the recess 68 in the uneven region 65 is larger than the smallest particle group (particle group 30 in the present embodiment) of the plurality of types of particle groups enclosed in the same cell, the particle group 30 is configured. When the particles enter the recesses 68, the contrast in the display medium 12 may be reduced due to aggregation of the particles constituting the particle group 30 and the uneven particles 60.

  As the mother particles 62 constituting the concavo-convex particles 60, when the concavo-convex particles 60 are particles that do not undergo electrophoresis, for example, white pigments such as titanium oxide, silicon oxide, and zinc oxide are used as polystyrene, polyethylene, and polypropylene. Particles dispersed in polycarbonate, PMMA, acrylic resin, phenol resin, formaldehyde condensate, etc. are used. Moreover, when making the uneven | corrugated particle | grains 60 into particles other than white, the above-mentioned resin particle which included the pigment or dye of a desired color can be used, for example. If the pigment or dye is, for example, RGB or YMC color, a general pigment or dye used for printing ink or color toner can be used.

  In the present embodiment, the concavo-convex particles constituting the concavo-convex particle group 32 are described as being non-electrophoretic, but may be configured to perform electrophoresis. In this case, the mother particles 62 may be produced in the same manner as the particle group 30 using a white pigment or dye as the pigment or dye.

  As a method of providing the irregular region 65 in the mother particle 62, as described above, the irregular region 65 is provided by attaching a plurality of third particles 64 to the surface of the mother particle 62 to provide the irregular particle 60A (FIG. 2 ( When A) is configured, the following method may be used.

  The third particles 64 preferably have a volume average primary particle size that is 1/1000 times or more and 1/10 times or less that of the mother particles 62, and a volume average that is 1/5000 times or more and 1/100 times or less. A primary particle size is preferred. If the volume average primary particle size of the third particles 64 is less than 1/1000 times that of the mother particles 62, the contribution of unevenness may be small, and the problem that aggregation control is unstable may occur. If it exceeds, stable adhesion may not be achieved, and there may be a problem that the third particles 64 are easily detached.

  Specifically, the volume average primary particle size of the mother particles 62 is preferably in the range of 2 μm to 50 μm, and particularly preferably in the range of 5 μm to 20 μm. The volume average primary particle size of the third particles 64 is in the range of the above ratio with respect to the volume average primary particle size of the mother particles 62, and specifically, 0.01 μm or more and 2 μm. It is preferably within the following range, and particularly preferably within the range of 0.05 μm to 1 μm.

  The third particles 64 are preferably transparent or uncolored so as not to affect the color of the mother particles 62.

  As such third particles 64, inorganic particles such as metal oxides such as silicon oxide (silica), titanium oxide, and alumina are used. Among these, it is preferable to use an inorganic oxide for the reason of avoiding the deterioration of the solvent.

  In addition, in order to adjust the affinity with the dispersion medium 50, it is preferable that these third particles 64 have a surface-treated form with a coupling agent or a surfactant.

  Since the surface of the third particles 64 is subjected to charging treatment and anti-adhesion treatment by making the third particles 64 surface-treated with a coupling agent or a surfactant, the uneven particles 60 are dispersed in the dispersion medium 50. When dispersed therein, it has the effect of preventing adhesion and preventing separation from the mother particles.

  Coupling agents include positively chargeable ones such as aminosilane coupling agents, aminotitanium coupling agents, nitrile coupling agents, and silanes that do not contain nitrogen atoms (consisting of atoms other than nitrogen). There are negatively charged ones such as coupling agents, titanium-based coupling agents, epoxy silane coupling agents, and acrylic silane coupling agents. Silicone oil includes positively charged ones such as amino-modified silicone oil, dimethyl silicone oil, alkyl-modified silicone oil, α-methylsulfone-modified silicone oil, methylphenyl silicone oil, chlorophenyl silicone oil, fluorine-modified silicone. Examples include negatively chargeable oils. These are selected according to the desired resistance of the third particle 64.

Of the third particles 64, well-known hydrophobic silica and hydrophobic titanium oxide are desirable. In particular, TiO (OH) ₂ described in JP-A-10-3177 and a silane compound such as a silane coupling agent are used. A titanium compound obtained by the above reaction is preferred. As the silane compound, any of chlorosilane, alkoxysilane, silazane, and a special silylating agent can be used. This titanium compound is produced by reacting TiO (OH) ₂ produced in a wet process with a silane compound or silicone oil and drying. Since it does not pass through the firing step of several hundred degrees, a strong bond between Ti is not formed, there is no aggregation, and the particles are in the state of primary particles. Furthermore, since the silane compound or silicone oil reacts directly with TiO (OH) ₂ , the amount of silane compound or silicone oil treated can be increased, and the charging characteristics can be controlled by adjusting the amount of silane compound treated. The charging ability that can be imparted and can be imparted can be significantly improved over that of conventional titanium oxide.

  The compounding ratio of the third particles 64 and the mother particles 62 is such that the particle size of the mother particles 62 and the third particles are such that the coverage of the third particles 64 on the surface of the mother particles 62 is within the above range. It adjusts from the balance with the particle size of 64. When the added amount of the third particles 64 is too large, at least a part of the third particles 64 is liberated from the surface of the mother particles 62, causing problems such as unstable display driving and unstable contrast. There is. Specifically, the amount of the third particles 64 is more preferably 0.1 parts by weight to 220 parts by weight and also 0.5 parts by weight to 10 parts by weight with respect to 100 parts by weight of the base particles.

  As a method of externally adding (attaching) the third particles 64 onto the mother particles 62, the third particles 64 are driven into the surfaces of the mother particles 62 with an impact force, or the mother particles 62 are heated to form the third particles 64. It is desirable that the particles 64 be firmly fixed to the surface of the mother particles 62. As a result, the third particles 64 are released from the mother particles 62, and the third particles 64 are strongly aggregated to form an aggregate of the third particles 64 that is difficult to dissociate with an electric field. Thus, the deterioration of image quality is prevented.

  The following method may be used when the concave and convex particles 60B (see FIG. 2B) are formed by providing a plurality of concave portions 68 on the surface of the mother particles 62 themselves.

  Specifically, in the suspension polymerization method, a carbonate, for example, calcium carbonate fine particles are dispersed in a monomer, suspended and polymerized in an aqueous phase, and then the calcium carbonate is decomposed and eluted with an acid or the like. Alternatively, it can be prepared by a method in which a monomer and a solvent that is a poor solvent are contained in the monomer, suspended, polymerized, heated, and the poor solvent is removed.

The dispersion medium 50 is preferably an insulating liquid. Here, “insulating” indicates that the volume resistivity is 10 ¹¹ Ωcm or more. The same applies hereinafter.

  Specific examples of the insulating liquid include hexane, cyclohexane, toluene, xylene, decane, hexadecane, kerosene, paraffin, and isoparaffin (trade names: Isopar (G, H, L, M, etc.), manufactured by Exxon Chemical Co., Ltd.) , Silicone oil, dichloroethylene, trichloroethylene, perchlorethylene, high purity petroleum, ethylene glycol, alcohols, ethers, esters, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, 2-pyrrolidone, N- Methylformamide, acetonitrile, tetrahydrofuran, propylene carbonate, ethylene carbonate, benzine, diisopropylnaphthalene, olive oil, isopropanol, trichlorotrifluoroethane, tetrachloro Ethane, and the like dibromotetrafluoroethane, mixtures thereof can be preferably used.

  Among these, it is preferable to use non-polar solvents such as silicone oil and paraffin oil.

  The concavo-convex particle 60 in which the concavo-convex region 65 is formed by the third particle 64 using the non-polar solvent as the dispersion medium 50 and hydrophilizing the concavo-convex particle 60 with a coupling agent or a surfactant as described above. By using, the effect that aggregation between the uneven | corrugated particle | grains 60 and the particle | grains which comprise the particle group 30 is suppressed is acquired.

  If necessary, the insulating liquid may contain acid, alkali, salt, dispersion stabilizer, stabilizer for anti-oxidation or ultraviolet absorption, antibacterial agent, preservative, etc. It is desirable to add so that it may become the range of the specific volume resistance value shown above.

  For insulating liquids, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, fluorosurfactants, silicone surfactants, metal soaps as charge control agents Alkyl phosphate esters, succinimides, and modified silicone oils may also be added.

  More specific examples of the ionic and nonionic surfactants are as follows. Nonionic activators include polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene dodecyl phenyl ether, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, And fatty acid alkylolamide. Examples of the anionic surfactant include alkylbenzene sulfonate, alkylphenyl sulfonate, alkyl naphthalene sulfonate, higher fatty acid salt, sulfate of higher fatty acid ester, sulfonic acid of higher fatty acid ester, and the like. Examples of the cationic surfactant include primary to tertiary amine salts and quaternary ammonium salts. These charge control agents are preferably 0.01% by weight or more and 20% by weight or less, and particularly preferably in the range of 0.05 to 10% by weight, based on the solid content of the particles. If it is less than 0.01% by weight, the desired charge control effect may be insufficient, and if it exceeds 20% by weight, the conductivity of the dispersion medium 50 may increase excessively, making it difficult to use. Because it becomes.

  The particle group 34 sealed in the display medium 12 may be dispersed in a polymer resin as the dispersion medium 50. The polymer resin is preferably a polymer gel, a polymer, or the like.

  As this polymer resin, agarose, agaropectin, amylose, sodium alginate, propylene glycol ester of alginate, isolikenan, insulin, ethylcellulose, ethylhydroxyethylcellulose, curdlan, casein, carrageenan, carboxymethylcellulose, carboxymethyl starch, callose, agar, chitin , Chitosan, silk fibroin, gar gum, quince seed, crown gall polysaccharide, glycogen, glucomannan, keratan sulfate, keratin protein, collagen, cellulose acetate, gellan gum, schizophyllan, gelatin, elephant palm mannan, tunisin, dextran, dermatan sulfate, starch , Tragacanth gum, nigeran, hyaluronic acid, hydroxyethyl cellulose, hydroxy In addition to polymer gels derived from natural polymers such as propylcellulose, pustulan, funolan, decomposed xyloglucan, pectin, porphyran, methylcellulose, methyl starch, laminaran, lichenan, lentinan, locust bean gum, etc. Includes almost all polymer gels.

  In addition, polymers containing functional groups of alcohol, ketone, ether, ester, and amide in the repeating unit are exemplified. For example, polyvinyl alcohol, poly (meth) acrylamide and derivatives thereof, polyvinyl pyrrolidone, polyethylene oxide, and the like. Mention may be made of copolymers containing molecules.

  Among these, gelatin, polyvinyl alcohol, poly (meth) acrylamide and the like are desirably used from the viewpoints of production stability, electrophoretic characteristics and the like.

  These polymer resins are desirably used as the dispersion medium 50 together with the insulating liquid.

  Further, by mixing the following colorant in the dispersion medium 50, a color different from the color of the particle group 34 is displayed on the display medium 12.

  Examples of the colorant mixed in the dispersion medium 50 include carbon black, titanium oxide, magnesium oxide, zinc oxide, phthalocyanine copper-based cyan color material, azo-based yellow color material, azo-based magenta color material, quinacridone-based magenta color material, and red. Known colorants such as a color material, a green color material, and a blue color material can be listed. Specifically, aniline blue, calcoil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 238, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 128, C.I. Blue 15: 1, C.I. I. Pigment Blue 15: 3 is a typical example.

  Since the particle group 34 moves in the dispersion medium 50, the viscosity of the dispersion medium 50 is 0.1 mPa · s to 100 mPa · s in an environment at a temperature of 20 ° C. From the viewpoint of display speed, it is essential, preferably 0.1 mPa · s to 50 mPa · s, and more preferably 0.1 mPa · s to 20 mPa · s.

  By setting the viscosity of the dispersion medium 50 in the range of 0.1 mPa · sPa · s to 100 mPa · s, variation in the electrophoresis time of the electrophoretic particle group 30 dispersed in the dispersion medium 50 is suppressed.

  The viscosity of the dispersion medium 50 can be adjusted by adjusting the molecular weight, structure, composition, and the like of the dispersion medium. In addition, Tokyo Keiki B-8L type | mold viscosity meter was used for the measurement of this viscosity.

  The display substrate 20 has a configuration in which a surface electrode 40 is laminated on a support substrate 38. The back substrate 22 has a configuration in which a back electrode 46 is laminated on a support substrate 44.

  The display substrate 20 or both the display substrate 20 and the back substrate 22 are translucent. Here, the translucency in the present embodiment indicates that the transmittance of visible light is 60% or more.

  Examples of the support substrate 38 and the support substrate 44 include glass and plastics such as polyethylene terephthalate resin, polycarbonate resin, acrylic resin, polyimide resin, polyester resin, epoxy resin, and polyethersulfone resin.

  For the surface electrode 40 and the back electrode 46, oxides such as indium, tin, cadmium and antimon, composite oxides such as ITO, metals such as gold, silver, copper and nickel, organic materials such as polypyrrole and polythiophene are used. can do. These can be used as a single layer film, a mixed film, or a composite film, and can be formed by vapor deposition, sputtering, coating, or the like. Moreover, the thickness is 100-2000 mm normally according to a vapor deposition method and sputtering method. The back electrode 46 and the front electrode 40 may be formed in a desired pattern, for example, a matrix shape or a stripe shape that enables passive matrix driving by a conventionally known means such as etching of a conventional liquid crystal display medium or a printed board. it can.

  Further, the surface electrode 40 may be embedded in the support substrate 38. Further, the back electrode 46 may be embedded in the support substrate 44. In this case, the materials of the support substrate 38 and the support substrate 44 are selected according to the composition of each particle of the particle group 34 and the like.

  The back electrode 46 and the surface electrode 40 may be separated from the display substrate 20 and the back substrate 22 and disposed outside the display medium 12.

  In the above description, the case where both the display substrate 20 and the back substrate 22 are provided with electrodes (the front electrode 40 and the back electrode 46) has been described. Also good.

  In order to enable active matrix driving, the support substrate 38 and the support substrate 44 may include a TFT (thin film transistor) for each pixel. Since it is easy to laminate wiring and mount components, it is desirable to form the TFT on the back substrate 22 instead of the display substrate.

  The gap member 24 for maintaining a gap between the display substrate 20 and the back substrate 22 is formed so as not to impair the light-transmitting property of the display substrate 20, and is a thermoplastic resin, a thermosetting resin, or an electron beam curing. It can be formed of resin, photo-curing resin, rubber, metal or the like.

  The gap member 24 may be integrated with either the display substrate 20 or the back substrate 22. In this case, the support substrate 38 or the support substrate 44 can be manufactured by performing etching processing, laser processing processing, press processing processing, printing processing, or the like using a previously manufactured mold.

  In this case, the gap member 24 can be fabricated on either the display substrate 20 side, the back substrate 22 side, or both.

  The gap member 24 may be colored or colorless, but is preferably colorless and transparent so as not to adversely affect the display image displayed on the display medium 12, and in this case, for example, transparent such as polystyrene, polyester, or acrylic Resin or the like can be used.

  The particulate gap member 24 is also preferably transparent, and glass particles can be used in addition to transparent resin particles such as polystyrene, polyester or acrylic.

  In the present embodiment, “transparent” means having a transmittance of 60% or more with respect to visible light.

  The size of the cell in the display medium 12 is closely related to the resolution of the display medium 12, and the display medium 12 capable of displaying a high-resolution image as the cell is smaller can be manufactured. The length of the twelve display substrates 20 in the plate surface direction is about 10 μm to 1 mm.

  In order to fix the display substrate 20 and the back substrate 22 through the gap member 24, fixing means such as a combination of bolts and nuts, a clamp, a clip, and a frame for fixing the substrate can be used. Also, fixing means such as an adhesive, heat melting, and ultrasonic bonding can be used.

  The display medium 12 configured in this way is shared with bulletin boards, circular editions, electronic blackboards, advertisements, signboards, blinking signs, electronic paper, electronic newspapers, electronic books, and copiers / printers that can store and rewrite images. It can be used for document sheets that can be used.

  As described above, the display device 10 according to the embodiment of the present invention includes the display medium 12, the voltage application unit 16 that applies a voltage to the display medium 12, and the control unit 18. (See FIG. 1).

  The voltage application unit 16 is electrically connected to the front electrode 40 and the back electrode 46. In this embodiment, the case where both the front electrode 40 and the back electrode 46 are electrically connected to the voltage application unit 16 will be described. However, one of the front electrode 40 and the back electrode 46 is grounded. The other may be connected to the voltage application unit 16.

  The voltage application unit 16 is connected to the control unit 18 so as to be able to exchange signals.

  The control unit 18 stores in advance various programs such as a CPU (Central Processing Unit) that controls the operation of the entire apparatus, a RAM (Random Access Memory) that temporarily stores various data, and a control program that controls the entire apparatus. It is also possible to configure as a microcomputer including a ROM (Read Only Memory).

  The voltage application unit 16 is a voltage application device for applying a voltage to the front electrode 40 and the back electrode 46, and applies a voltage according to the control of the control unit 18 between the front electrode 40 and the back electrode 46.

  Next, the operation of the display device 10 will be described. This operation will be described according to the operation of the control unit 18.

  Here, the case where the particle group 30 enclosed in the display medium 12 is black and is negatively charged will be described. In the following description, it is assumed that the dispersion medium 50 is transparent and the uneven particle group 32 is white. That is, in this embodiment, the case where the display medium 12 displays black or white by the movement of the particle group 30 will be described.

  First, a signal indicating that the voltage is applied for a predetermined time so that the surface electrode 40 is a negative electrode and the back electrode 46 is a positive electrode is output to the voltage application unit 16. When a voltage equal to or higher than the voltage value at which concentration variation ends between the substrates is applied for a predetermined time, the particles constituting the particle group 30 charged on the negative electrode move to the back substrate 22 side, and the back substrate 22 (see FIG. 3A).

  At this time, the color of the display medium 12 visually recognized from the display substrate 20 side is visually recognized as white as the color of the uneven particle group 32.

  The predetermined time may be stored in advance in a memory such as a ROM (not shown) in the control unit 18. Then, information indicating the predetermined time may be read when the process is executed.

  Next, the polarity is reversed between the voltage applied between the substrates between the front electrode 40 and the back electrode 46, and the voltage is applied with the front electrode 40 as the positive electrode and the back electrode 46 as the negative electrode. As shown in B), each particle constituting the particle group 34 is electrophoresed in the dispersion medium 50 and moves to the display substrate 20 side through each of the uneven particle 60 of the uneven particle group 32. And as shown in FIG.3 (C), when each particle | grains which comprise the particle group 34 arrives at the display substrate 20 side, the color of the particle group 34 is visually recognized and black display is made | formed.

  Here, the concavo-convex particle group 32 is composed of the concavo-convex particles 60 having concavo-convex surfaces as described above. Therefore, even when each particle constituting the particle group 34 is in contact with each uneven particle 60 of the uneven particle group 32 when electrophoresis in the dispersion medium 50, as shown in FIG. Has an uneven region composed of recesses 68 whose opening diameter is smaller than the particle size of the particle group 34, the contact area is smaller than when the particle group 30 is in direct contact with the spherical mother particle 62, and the particle Aggregation between the particles constituting the group 30 and the uneven particles 60 is suppressed.

  Furthermore, as shown in FIGS. 2A and 4, the uneven particle 60 is attached to the surface of the mother particle 62 to form the uneven region 65, and the uneven particle 65 is formed on the surface of the mother particle 62. When the surface treatment layer 64A is provided by surface-treating the surface and a nonpolar solvent is used as the dispersion medium 50, the uneven particles 60 and the particle group 30 are constituted by the energy difference at the interface between the surface treatment layer 64A and the dispersion medium 50. Aggregation with each particle is further suppressed.

  As described above, according to the display medium 12 of the present embodiment, aggregation between the uneven particle group 32 including the uneven particles 60 and the particle group 30 having a color and a size different from the uneven particle 60 is suppressed. In addition, a decrease in contrast in the display medium 12 due to the color mixture of the color of the uneven particle group 32 and the color of the particle group 30 is suppressed.

  In the present embodiment, the case where the concavo-convex particle group 32 does not perform electrophoresis has been described. In this case, for example, the concavo-convex particles 60 constituting the concavo-convex particle group 32 and the particles constituting the particle group 30 are charged with opposite polarities, and one of them is on the display substrate 20 side and the other is on the back surface. By applying a voltage to be moved to the substrate 22 side between the display substrate 20 and the back substrate 22, the color of the uneven particle group 32 or the color of the particle group 30 may be displayed.

  Also in this case, since the uneven particles 60 constituting the uneven particle group 32 have unevenness on the surface, each particle constituting the particle group 30 and each uneven particle 60 constituting the uneven particle group 32 are dispersed by electrophoresis. Even when contact occurs when moving in the medium 50, aggregation between the surfaces of the uneven particles 60 is suppressed by the unevenness. Accordingly, a decrease in contrast is suppressed.

  In the example shown in FIG. 1, two types of particle groups (particle group 30 and concavo-convex particle group 32) are used as a plurality of types of particle groups 34 having different sizes dispersed in each cell in the display medium 12. ) Is encapsulated, but as described above, at least the smallest particle group of the plurality of types of particle groups 34 is composed of electrophoretic particles, and is larger than the smallest particle group. At least one kind of particle group is an uneven particle group composed of uneven particles 60, and the color of the uneven particle 60 of the uneven particle group is different from the color of the particles of the particle groups other than the uneven particle group. Any form may be used, and the form is not limited to that shown in FIG.

  For example, as shown in FIG. 5, as a plurality of types of particle groups 34 having different sizes enclosed in each cell in the display medium 13, particles having a particle size larger than the particles constituting the particle group 30 and the particle group 30. It may be composed of a particle group 33 and an uneven particle group 32.

  The particle group 30, the particle group 33, and the uneven particle group 32 may be configured such that only the smallest particle group 30 is electrophoresed, or the particle group 30, the particle group 33, The configuration may be such that either one or both of the uneven particle group 32 undergo electrophoresis.

  Of these particle group 30, particle group 33, and uneven particle group 32, only one of particle group 33 and uneven particle group 32 other than the smallest particle group 30 is composed of uneven particle 60. Or both may be comprised from the uneven | corrugated particle | grains 60. FIG.

  Further, among the particle group 30, the particle group 33, and the uneven particle group 32 constituting the particle group 34, the lightness of the largest uneven particle group 32 is the highest, and is preferably white, for example. Not limited to.

  The display medium 13 includes a display substrate 20, a back substrate 22, a gap member 24, and a dispersion medium 50. The display device 11 includes the display medium 13, the voltage application unit 16, and the display medium 13. And a control unit 18.

  The display medium 13 is the same as the structure of the display medium 12 except that there are three types of particle groups 34 dispersed in the cell. Omitted. The display device 11 has the same configuration as the display device 10 except that the display medium 13 is used in place of the display medium 12, and thus detailed description thereof is omitted.

  As a plurality of types of particle groups 34 of different sizes enclosed in each cell of the display medium 13, a particle group 30, a particle group 33 composed of particles larger than the particles constituting the particle group 30, and a particle group 33 are configured. The concavo-convex particle group 32 composed of the concavo-convex particles 60 having a particle size larger than that of the particles (the volume average primary particle size of the mother particles 62 is larger than the particles constituting the particle group 33) is used. It is assumed that the group 34 and the particle group 30 are composed of electrophoretic particles.

  In this case, similarly to the display medium 12, an electric field is formed between the display substrate 20 and the back substrate 22 of the display medium 13, thereby causing electrophoresis of the particle group 30 and the particle group 33 per unit time. The particle group 30 and the particle group 33 are selectively electrophoresed according to a difference in speed, a difference in absolute value of a voltage at which movement is started when moving between substrates according to an electric field, and the like. The corresponding color is displayed on the display medium 13.

  At this time, each concavo-convex particle 60 constituting the concavo-convex particle group 32 has the concavo-convex region 65 on the surface, and thus the particles of the particle group 30 to be electrophoresed and the particles of the particle group 33 adhere to the concavo-convex particle 60. And aggregation is suppressed. For this reason, the color mixture of the color of the uneven particle 60 and the color of the particle group 30 and the color of the particle group 33 that do not have the unevenness is suppressed, and a decrease in contrast in the display medium 13 is suppressed.

  Further, as shown in FIG. 6, the display medium includes a plurality of types of particle groups 34 having different sizes and a plurality of types of color particle groups having the same size and different colors. There may be.

  A display medium 15 shown in FIG. 6 includes a display substrate 20, a back substrate 22, a gap member 24, and a dispersion medium 50. The display device 17 includes the display medium 15, a voltage application unit 16, and a control unit 18.

  The display medium 15 has three types of particle groups 34 of different sizes dispersed in the cell, and one type of particle group of each type is a color group. Since the configuration is the same as the configuration of the display medium 12 except that the configuration includes a plurality of different types of color particle groups, the same number is assigned to the same configuration, and the description is omitted. The display device 17 has the same configuration as that of the display device 17 except that the display medium 15 is used instead of the display medium 12, and thus detailed description thereof is omitted.

  The display medium 15 includes a plurality of types of particle groups 34, for example, a particle group 30 including a yellow particle group 30 </ b> B and a magenta particle group 30 </ b> A, and a cyan color group including particle groups having a larger particle diameter than the particle group 30. It is composed of a particle group 33 and an uneven particle group 32.

  Then, the particle group 30B, the particle group 30A, and the particle group 33 are used as the electrophoretic particles so that the absolute value of the voltage value or the electrophoretic velocity per unit time that starts moving according to the electric field is different. Adjust in advance. As the adjustment of the absolute value of the voltage value at which this movement starts and the electrophoresis speed per unit time, the content of the magnetic agent, the charging method, etc. when adjusting each particle group may be adjusted.

  In the display medium 15, similarly to the display medium 12, an electric field is formed between the display substrate 20 and the back substrate 22 of the display medium 15, so that the particle group 30 </ b> A, the particle group 30 </ b> B, the particle group 33, The particle group 30A, the particle group 30B, and the particle group 33 are selected based on the difference in the electrophoresis speed per unit time, the difference in the absolute value of the voltage for starting movement when moving between the substrates according to the electric field, and the like. By electrophoretic electrophoresis, a color corresponding to the display target color is displayed on the display medium 15.

  At this time, each concavo-convex particle 60 constituting the concavo-convex particle group 32 has the concavo-convex region 65 on the surface. Therefore, the particles of the electrophoretic particle group 30A, the particle group 30B, and the particle group 33 are concavo-convex particles. It is suppressed that it adheres to 60 and aggregates mutually. For this reason, the color mixture of the color of the uneven particle 60 and the color of each of the particle group 30A, the particle group 30B, and the particle group 33 having no unevenness is suppressed, and the decrease in contrast in the display medium 15 is suppressed.

  Similarly in this case, only the uneven particle group 32 may be composed of the uneven particles 60 having unevenness, or particles larger than the particle group having the smallest particle size among a plurality of types of particle groups having different sizes. Similarly, the particle group 33, which is one of the groups, may be composed of uneven particles 60 having unevenness.

The present invention will be described below in more detail with reference to examples. However, the present invention is not limited to the following examples.
(Preparation of cyan particles)
A solution A was prepared by dissolving 5 parts by weight of a silicone-modified acrylic polymer (KP545 manufactured by Shin-Etsu Silicone) as an emulsifier in 95 parts by weight of dimethyl silicone oil (KF-96-2CS manufactured by Shin-Etsu Silicone) as a poor solvent. Next, 7 parts by weight of cationized polyvinyl alcohol “K-210 manufactured by Nippon Synthetic Chemical Co., Ltd.” as an ionic polymer, cyan pigment dispersion as a colorant (manufactured by Sanyo Dye Co., Ltd .: equivalent to 20 parts by weight of pigment solids) 3 A solution B (dispersed phase) was prepared by mixing 63 parts by weight of water and 63 parts by weight of water as a good solvent. Emulsification was carried out by mixing 80 parts by weight of Solution A and 20 parts by weight of Solution B to prepare an emulsion. The emulsification was performed for 10 minutes with an ultrasonic crusher (UH-600S manufactured by SMT).

  Next, the obtained emulsion is put into an eggplant flask and heated (65 ° C.) / Reduced pressure (10 mPa) with an evaporator while stirring to remove moisture (good solvent) and perform electrophoresis containing a cyan pigment. A particle dispersion in which particles were dispersed in silicone oil was obtained.

  This liquid was centrifuged and precipitated, and then re-dispersed in the silicone oil to obtain a cyan particle group dispersed in a silicone oil as a dispersion medium at a ratio of 8% by weight.

When the produced cyan particle group was measured with HORIBA LB-550 (dynamic light scattering particle size distribution measuring device), the volume average primary particle size was 330 nm.
(Adjustment of white particles with irregularities)
First, white mother particles were prepared.
-Preparation of dispersion AA-
The following components were mixed and ball milling was performed for 20 hours with 10 mmφ zirconia balls to prepare dispersion AA.
<Composition>
-53 parts by weight of cyclohexyl methacrylate-Titanium oxide 1 (white pigment) (primary particle size 0.3 µm, Type CR63: manufactured by Ishihara Sangyo Co., Ltd.) 45 parts by weight-5 parts by weight of cyclohexane-Preparation of charcoal dispersion AB-
The following components were mixed, and finely pulverized with a ball mill in the same manner as above to prepare a charcoal dispersion AB.
<Composition>
-Calcium carbonate 40 parts by weight-Water 60 parts by weight-Preparation of mixed liquid AC-
The following components were mixed, degassed with an ultrasonic machine for 10 minutes, and then stirred with an emulsifier to prepare a mixed liquid AC.
<Composition>
・ 4.3g of 2% serogen
-Charcoal dispersion AB 8.5g
・ 20% saline 50g
35 g of dispersion AA, 1 g of divinylbenzene, and polymerization initiator AIBN: 0.35 g were weighed and mixed well, and deaeration was performed for 10 minutes with an ultrasonic machine. This was added to the mixed solution AC and emulsified with an emulsifier. Next, this emulsified liquid was put into a bottle, put into a silicone bottle, used with an injection needle, sufficiently degassed under reduced pressure, and sealed with nitrogen gas. Next, it was reacted at 65 ° C. for 15 hours to prepare particles. After cooling, cyclohexane was removed from the dispersion with a freeze dryer at −35 ° C. and 0.1 Pa for 2 days. The obtained fine particle powder was dispersed in ion-exchanged water, calcium carbonate was decomposed with hydrochloric acid water, and filtered. Thereafter, it was washed with sufficient distilled water, and passed through a nylon sieve having openings of 15 μm and 10 μm to make the particle sizes uniform. This was dried to obtain a group of white particles having a volume average primary particle size of 12 μm. This was white mother particle.

  The volume average primary particle size was measured in the same manner as the cyan particle group.

  98 parts by weight of the adjusted white mother particles and 2 parts by weight of hydrophilic surface-treated titanium oxide (MT-100AQ, volume average primary particle size 15 nm, alginic acid treatment) were rotated at 13,000 rpm using a sample mill mixer. Were mixed for 60 seconds to prepare white irregular particles having irregularities.

  When the surface of the adjusted uneven particle was observed with an electron microscope, unevenness due to adhesion of hydrophobic surface-treated titanium oxide was observed on the surface of the mother particle.

The surface coverage of the mother particles with the titanium oxide is observed with several reflection electron microscopes SEM, the image is processed with an image analyzer, and the portion where the particles are not attached is observed. When the area was measured and the surface coverage was measured, it was 80%. Moreover, when the maximum value of the opening of the recessed part of the uneven | corrugated area | region formed with this titanium oxide was observed with SII (SII nanotechnology Co., Ltd. SPM (scanning probe microscope), and the undulation situation of the surface was measured, For this reason, the opening of the concave portion of the concave and convex region on the surface of the white particle having concave and convex portions was smaller than the average particle size of the adjusted cyan particles.
(Example 1)
A display medium having the same configuration as that of the display medium 12 described with reference to FIG. 1 was produced as follows.

  ITO was formed into a film with a thickness of 50 nm as an electrode on a support base made of glass having a thickness of 0.7 mm by sputtering. Thereafter, a layer was applied onto the substrate using a photosensitive polyimide varnish, and then a gap member having a height of 100 μm and a width of 20 μm was formed by performing exposure and wet etching. Further, after adjusting the white uneven particles adjusted as described above into a cell so as to be uniformly rubbed, a heat-bonding adhesive layer (not shown) was formed on the upper portion of the gap member, and then adjusted as described above. After filling a dispersion liquid in which 3% by weight of cyan particles are dispersed in silicone oil as a dispersion medium, the display substrates prepared in the same manner as the back substrate are bonded so that the electrode surfaces face each other. The display medium was produced by applying heat.

  Using the display medium thus produced, a voltage of 40 V was applied to both electrodes for 1 second so that the electrode of the display substrate was negative and the electrode of the back substrate was positive. As a result, it was observed that the positively charged cyan particles were moved to the display substrate side by the electric field generated by the voltage application, and the display medium displayed cyan.

  When the density of the display medium when this cyan color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 53.

  In the examples, the average value of the measurement results measured for any 10 points in the measurement target region using the optical densitometer was shown as the measurement result by the optical densitometer.

  Next, a voltage of 40 V was applied to both electrodes for 1 second so that the display substrate electrode was positive and the back substrate electrode was negative. As a result, it was observed that the positively charged cyan particles were moved to the back substrate by the electric field generated by the voltage application, and the display medium displayed white.

  When the density of the display medium when this white color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 90.

  Thereafter, the display between the cyan color display and the white color display is changed once and the display is repeated 300 times. Then, in the same manner as described above, both electrodes are set to 40 V so that the electrode on the display substrate is negative and the electrode on the rear substrate is positive. Was applied for 1 second. As a result, it was observed that the positively charged cyan particles were moved to the display substrate side by the electric field generated by the voltage application, and the display medium displayed cyan.

  The density of the display medium when the cyan color is displayed after the display switching of 300 times is measured with the optical density diameter X-Rite MODE L404 (manufactured by X-Rite) from the display substrate side. Was 58.

  Next, in the same manner as described above, a voltage of 40 V was applied to both electrodes for 1 second so that the electrode of the display substrate was positive and the electrode of the back substrate was negative. As a result, it was observed that the positively charged cyan particles were moved to the back substrate by the electric field generated by the voltage application, and the display medium displayed white.

  When the density of the display medium when this white color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 88.

Thus, there was no change in the density of both the displayed cyan and white before and after the display switching 300 times. For this reason, it can be said that a decrease in contrast is suppressed.
(Example 2)
The display medium 12 having the same configuration as that of the above embodiment was manufactured as follows (see FIG. 1).
In Example 1, white particles that do not undergo electrophoresis were adjusted as white particles having irregularities, but in this Example 2, white particles that were electrophoresed and had irregularities were adjusted as white particles having irregularities. A display medium was produced.
(Adjustment of white particles with irregularities)
First, white mother particles were prepared.
-Preparation of dispersion AA-
The following components were mixed and ball milling was performed for 20 hours with 10 mmφ zirconia balls to prepare dispersion AA.
<Composition>
-53 parts by weight of cyclohexyl methacrylate-Titanium oxide 1 (white pigment) (primary particle size 0.3 µm, Type CR63: manufactured by Ishihara Sangyo Co., Ltd.) 45 parts by weight-5 parts by weight of cyclohexane-Preparation of charcoal dispersion AB-
The following components were mixed, and finely pulverized with a ball mill in the same manner as above to prepare a charcoal dispersion AB.
<Composition>
-Calcium carbonate 40 parts by weight-Water 60 parts by weight-Preparation of mixed liquid AC-
The following components were mixed, degassed with an ultrasonic machine for 10 minutes, and then stirred with an emulsifier to prepare a mixed liquid AC.
<Composition>
・ 4.3g of 2% serogen
-Charcoal dispersion AB 8.5g
・ 20% saline 50g
35 g of dispersion AA, 1 g of divinylbenzene, and polymerization initiator AIBN: 0.35 g were weighed and mixed well, and deaeration was performed for 10 minutes with an ultrasonic machine. This was added to the mixed solution AC and emulsified with an emulsifier. Next, this emulsified liquid was put into a bottle, put into a silicone bottle, used with an injection needle, sufficiently degassed under reduced pressure, and sealed with nitrogen gas. Next, it was reacted at 65 ° C. for 15 hours to prepare particles. After cooling, cyclohexane was removed from the dispersion with a freeze dryer at −35 ° C. and 0.1 Pa for 2 days. The obtained fine particle powder was dispersed in ion-exchanged water, calcium carbonate was decomposed with hydrochloric acid water, and filtered. Thereafter, it was washed with sufficient distilled water, and passed through a nylon sieve having openings of 15 μm and 10 μm to make the particle sizes uniform. This was dried to obtain a group of white particles having a volume average primary particle size of 12 μm. This was white mother particle.

  The volume average primary particle size was measured in the same manner as the cyan particle group.

98 parts by weight of the prepared white mother particles and surface-treated titanium oxide (MT-100AQ, volume average primary particle size 15 nm, alginate treatment and amino-modified silicone treatment 10%)
2) parts by weight were mixed for 60 seconds at a rotational speed of 13000 rpm using a sample mill mixer to prepare white uneven particles having unevenness.

  When the surface of the adjusted uneven particle was observed with an electron microscope, unevenness due to adhesion of hydrophobic surface-treated titanium oxide was observed on the surface of the mother particle.

  When the surface coverage of the mother particles with the titanium oxide was measured in the same manner as described above, it was 60%. Further, the maximum value of the opening of the concave portion of the concave and convex region formed by the titanium oxide was measured in the same manner as described above, and was 400 nm. For this reason, the opening of the recessed part of the uneven | corrugated area | region in the surface of the white particle which has an unevenness | corrugation was smaller than the average particle diameter of the said adjusted cyan particle.

  A display medium was obtained in the same manner as in Example 1 except that the white particles having unevenness adjusted in Example 2 were used as the white particles having unevenness in place of the white particles having unevenness adjusted in Example 1. This was prepared and evaluated in the same manner as in Example 1.

  Using the display medium produced in Example 2, a voltage of 35 V was applied to both electrodes for 1 second so that the electrode of the display substrate was negative and the electrode of the back substrate was positive. As a result, it was observed that the positively charged cyan particles were moved to the display substrate side by the electric field generated by the voltage application, and the display medium displayed cyan.

  The density of the display medium when this cyan color was displayed was measured in the same manner as in Example 1 with the optical density diameter X-Rite MODE L404 (manufactured by X-Rite) from the display substrate side. Was 50.

  Next, a voltage of 35 V was applied to both electrodes for 1 second so that the display substrate electrode was positive and the back substrate electrode was negative. As a result, it is observed that the positively charged cyan particles move to the back substrate side due to the electric field by voltage application, and the negatively charged white particles having unevenness move to the display substrate side, and the display medium is A white color was displayed.

  When the density of the display medium when this white color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 90.

  Then, after switching the cyan display and white display once and repeating the display 300 times, in the same manner as described above, both electrodes are set to 35 V so that the electrode on the display substrate is negative and the electrode on the back substrate is positive. Was applied for 1 second. As a result, it was observed that the positively charged cyan particles were moved to the display substrate side by the electric field generated by the voltage application, and the display medium displayed cyan.

  The density of the display medium when the cyan color is displayed after the display switching of 300 times is measured with the optical density diameter X-Rite MODE L404 (manufactured by X-Rite) from the display substrate side. Was 52.

  Next, in the same manner as described above, a voltage of 35 V was applied to both electrodes for 1 second so that the electrode of the display substrate was positive and the electrode of the back substrate was negative. As a result, it is observed that the positively charged cyan particles move to the back substrate side due to the electric field by voltage application, and the negatively charged white particles having unevenness move to the display substrate side, and the display medium is A white color was displayed.

  When the density of the display medium when this white color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 88.

Thus, there was no change in the density of both the displayed cyan and white before and after the display switching 300 times. For this reason, it can be said that a decrease in contrast is suppressed.
Example 3
A display medium 13 having the same configuration as that of the above embodiment was manufactured as follows (see FIG. 5).
In Example 1 above, as a plurality of types of particle groups having different sizes, asperity white particles, a particle group 33 composed of particles smaller in size than the white particles, and particles constituting the particle group 33 A display medium was prepared by adjusting the particle group 30 composed of particles having a smaller size.

  In Example 3, the white particles having unevenness adjusted in Example 1 were used as the white particles having unevenness, and the cyan particles adjusted in Example 1 were used as the smallest particle group 30. Particle groups were used.

The particle group consisting of particles smaller than the volume average primary particle size of the white particles having irregularities adjusted in Example 1 and larger than the volume average primary particle size of the particles of the cyan particle group adjusted in Example 1 is as follows. Adjusted by the method.
(Preparation of magenta particles)
A solution A was prepared by dissolving 5 parts by weight of a silicone-modified acrylic polymer (KP545 manufactured by Shin-Etsu Silicone) as an emulsifier in 95 parts by weight of dimethyl silicone oil (KF-96-2CS manufactured by Shin-Etsu Silicone) as a poor solvent. Next, 7 parts by weight of an amine-based cationized resin “PD-7 manufactured by Yokkaichi Gosei Co., Ltd.” as an ionic polymer, a magenta pigment dispersion as a colorant (manufactured by Sanyo Dye Co., Ltd .: CI Pigment Red 238 (permanent carmine 3810) ) Equivalent to 20 parts by weight of pigment solid content) 3 parts by weight and 63 parts by weight of water as a good solvent were mixed to prepare a solution B (dispersed phase). Emulsification was carried out by mixing 80 parts by weight of Solution A and 20 parts by weight of Solution B to prepare an emulsion. The emulsification was performed for 10 minutes with an ultrasonic crusher (UH-600S manufactured by SMT).

  Next, the obtained emulsion is put into an eggplant flask and heated (65 ° C.) / Reduced pressure (10 mPa) with an evaporator while stirring to remove moisture (good solvent) and perform electrophoresis containing a cyan pigment. A particle dispersion in which particles were dispersed in silicone oil was obtained.

  This liquid was centrifuged and precipitated, and then re-dispersed in the silicone oil to obtain a magenta particle group dispersed in 3% by weight in the silicone oil as a dispersion medium.

  When the produced magenta color particle group was measured with HORIBA LB-550 (dynamic light scattering type particle size distribution measuring device), the volume average primary particle size was 500 nm.

  Using the display medium produced in Example 3, a voltage of 40 V was applied to both electrodes for 2 seconds so that the display substrate electrode was negative and the back substrate electrode was positive. As a result, it is observed that positively charged cyan particles move to the display substrate side by an electric field by applying a voltage, and positively charged magenta particles move to the display substrate by an electric field by applying a voltage. The display medium displayed a blue color.

  The density of the display medium when this blue color was displayed was measured in the same manner as in Example 1 using the optical density diameter X-Rite MODE L404 (manufactured by X-Rite) from the display substrate side. Was 45.

  Next, a voltage of 35 V was applied to both electrodes for 1 second so that the display substrate electrode was positive and the back substrate electrode was negative. As a result, the positively charged cyan particles are moved to the back substrate side by the electric field by voltage application, and the positively charged magenta particles are observed to move to the display substrate side, and the display medium is magenta. Displayed color.

  When the density of the display medium when this magenta color was displayed was measured with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite) from the display substrate side, the L * value was 40.

  Further, a voltage of 50 V was applied to both electrodes for 1 second so that the electrode of the display substrate was positive and the electrode of the back substrate was negative. As a result, the positively charged cyan particles move to the back substrate side by the electric field generated by voltage application, and the positively charged magenta particles are observed to move to the back substrate side, and the display medium is white. Is displayed.

  When the density of the display medium when this white color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 88.

  Further, a voltage of 35 V was applied to both electrodes for 1 second so that the electrode of the display substrate was positive and the electrode of the back substrate was negative. As a result, the positively charged cyan particles moved to the back substrate side by the electric field generated by the voltage application, and the positively charged magenta particles stayed on the back substrate side and the display medium displayed cyan.

  When the density of the display medium when this cyan color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 48.

  After that, the display was repeated 300 times with the above switching of blue color display → magenta color display → white color display → cyan color display as one time.

Thereafter, in the same manner as described above, a voltage of 40 V was applied to both electrodes for 1 second so that the electrode of the display substrate was negative and the electrode of the back substrate was positive. As a result, the positively charged cyan particles move to the display substrate side by the electric field generated by voltage application,
It was observed that the magenta-colored particles charged in the direction moved to the display substrate side by the electric field generated by the voltage application, and the display medium displayed a blue color.

  The density of the display medium when this blue color was displayed was measured in the same manner as in Example 1 with the optical density diameter X-Rite MODE L404 (manufactured by X-Rite) from the display substrate side. Was 44.

  Next, a voltage of 35 V was applied to both electrodes for 1 second so that the display substrate electrode was positive and the back substrate electrode was negative. As a result, the positively charged cyan particles move to the back substrate side by the electric field generated by the voltage application, and the positively charged magenta particles remain on the display substrate side, and the display medium displays the magenta color. did.

  When the density of the display medium when this magenta color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 39.

  Further, a voltage of 50 V was applied to both electrodes for 1 second so that the electrode of the display substrate was positive and the electrode of the back substrate was negative. As a result, the positively charged magenta particles are moved to the back substrate side by the electric field generated by the voltage application, and the positively charged magenta particles are observed to move to the back substrate side, and the display medium is white. Is displayed.

  The density of the display medium when this white color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), and the L * value was 87.

  Further, a voltage of 35 V was applied to both electrodes for 1 second so that the display substrate electrode was negative and the back substrate electrode was positive. As a result, the positively charged cyan particles moved to the display substrate side by the electric field generated by the voltage application, and the positively charged magenta particles were observed as they were, and the display medium displayed cyan.

  When the density of the display medium when this cyan color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 46.

Thus, there was no change in the density of the displayed cyan, magenta, blue, and white before and after switching the display 300 times. For this reason, it can be said that a decrease in contrast is suppressed.
(Example 4)
The display medium 12 having the same configuration as that of the above embodiment was manufactured as follows (see FIG. 1).
In Example 1, silicone oil was used as the dispersion medium. In Example 4, the display medium was adjusted and evaluated in the same manner as in Example 1 except that Isopar L; manufactured by Exxon Corporation was used. Went.

  Using the display medium produced in Example 4, a voltage of 30 V was applied to both electrodes for 1 second so that the electrode of the display substrate was negative and the electrode of the back substrate was positive. As a result, it was observed that the positively charged cyan particles were moved to the display substrate side by the electric field generated by the voltage application, and the display medium displayed cyan.

  When the density of the display medium when this cyan color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 45.

  Next, a voltage of 30 V was applied to both electrodes for 1 second so that the display substrate electrode was positive and the back substrate electrode was negative. As a result, it was observed that the positively charged cyan particles were moved to the back substrate by the electric field generated by the voltage application, and the display medium displayed white.

  When the density of the display medium when this white color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 88.

  Thereafter, the display between the cyan color display and the white color display is switched once and the display is repeated 300 times, and then, in the same manner as described above, both electrodes are 30 V so that the display substrate electrode is negative and the back substrate electrode is positive. Was applied for 1 second. As a result, it was observed that the positively charged cyan particles were moved to the display substrate side by the electric field generated by the voltage application, and the display medium displayed cyan.

  The density of the display medium when the cyan color is displayed after the display switching of 300 times is measured with the optical density diameter X-Rite MODE L404 (manufactured by X-Rite) from the display substrate side. Was 43.

  Next, in the same manner as described above, a voltage of 30 V was applied to both electrodes for 1 second so that the electrode on the display substrate was positive and the electrode on the back substrate was negative. As a result, it was observed that the positively charged cyan particles were moved to the back substrate by the electric field generated by the voltage application, and the display medium displayed white.

  When the density of the display medium when this white color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 86.

Thus, there was no change in the density of both the displayed cyan and white before and after the display switching 300 times. For this reason, it can be said that a decrease in contrast is suppressed.
(Comparative Example 1)
A display medium was prepared in the same manner as in Example 1 except that the white mother particles adjusted in Example 1 were used as white particles that did not undergo electrophoresis instead of the white particles having irregularities adjusted in Example 1 above. Evaluation was performed in the same manner as in Example 1.

  Using the display medium produced in Comparative Example 1, a voltage of 35 V was applied to both electrodes for 1 second so that the display substrate electrode was negative and the back substrate electrode was positive. As a result, it was observed that the positively charged cyan particles were moved to the display substrate side by the electric field generated by the voltage application, and the display medium displayed cyan.

  When the density of the display medium when this cyan color was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 65.

  Next, a voltage of 35 V was applied to both electrodes for 1 second so that the display substrate electrode was positive and the back substrate electrode was negative. As a result, it was observed that the positively charged cyan particles were moved to the rear substrate by the electric field generated by the voltage application, and the display medium displayed white.

  When the density of the display medium when white was displayed was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 70.

  After that, when the display switching is repeated a plurality of times with the switching between the cyan display and the white display being performed once, the display substrate electrode becomes positive and the back substrate electrode becomes negative after the display switching is performed 50 times. When a white display was performed by applying a voltage of 35 V to both electrodes for 1 second, a blue fog was visually recognized.

  When the density of the display medium when the white display is performed after performing the switching display 50 times is measured with the optical density diameter X-Rite MODE L404 (manufactured by X-Rite) from the display substrate side, the L * value is obtained. Was 68. For this reason, it can be said that a decrease in contrast has occurred compared to before 50 times of switching display.

  Further, after 100 display switching operations (total 150 times), a voltage of 35V is applied to both electrodes for 1 second so that the electrode of the display substrate is positive and the electrode of the back substrate is negative, and white display is performed. As a result, clear cyan display was confirmed.

  When the density of the display medium at this time was measured from the display substrate side with an optical density diameter X-Rite MODE L404 (manufactured by X-Rite), the L * value was 60. For this reason, it can be said that a further decrease in contrast occurred.

1 is a schematic configuration diagram of a display medium and a display device according to an embodiment. (A) (B) It is a schematic diagram which shows the uneven | corrugated particle enclosed in the display medium which concerns on embodiment. (A)-(C) It is explanatory drawing which shows typically the movement aspect of a particle group when a voltage is applied between the board | substrates of the display medium shown in FIG. 1, and an electric field is formed. It is a schematic diagram which shows the state which the uneven | corrugated particle | grains and the particle | grains which do not have an unevenness | corrugation contacted. It is a schematic block diagram which shows the form different from the form shown in FIG. 1 of the display medium and display apparatus which concern on embodiment. It is a schematic block diagram which shows the form different from the form shown in FIG.1 and FIG.5 of the display medium and display apparatus which concern on embodiment.

Explanation of symbols

10, 11, 17 Display device 12, 13, 15 Display medium 16 Voltage application unit 18 Control unit 20 Display substrate 22 Back substrate 30 Particle group 32 Concave particle group 33 Particle group 34 Particle group 50 Dispersion medium

Claims (12)

A pair of substrates at least one having translucency and disposed with a gap;
A dispersion medium sealed between the pair of substrates;
A plurality of types of particles dispersed in the dispersion medium and having different sizes from each other;
With
A particle group larger than the first particle group in which at least the smallest first particle group of the plurality of types of particle groups moves in the dispersion medium in accordance with an electric field formed between the pair of substrates. At least one kind of particle group is a concavo-convex particle group having undulations in at least a partial region of the surface of each particle of the particle group, and the concavo-convex particle group is one of the plurality of types of particle groups. A display medium having a color different from that of at least a particle group other than the uneven particle group.   The display medium according to claim 1, wherein the plurality of types of particle groups have different colors.   The display medium according to claim 1, wherein each type of particle group includes a plurality of types of color particle groups having different colors.   The display medium according to claim 1, wherein the uneven particle group is a largest particle group among the plurality of types of particle groups.   The display medium according to claim 1, wherein the brightness of the largest particle group among the plurality of types of particle groups is highest.   The display medium according to claim 4, wherein the uneven particle group is white.   2. The display medium according to claim 1, wherein at least the opening of the concave portion is smaller than the volume average primary particle size of the particles of the first particle group.   2. The display medium according to claim 1, wherein the uneven region is formed by attaching a plurality of third particles to at least a partial region of the surface of each particle of the uneven particle group.   The display medium according to claim 8, wherein the third particle is an inorganic oxide.   The display medium according to claim 1, wherein the dispersion medium is a nonpolar solvent.   The display medium according to claim 9, wherein the dispersion medium is silicone oil. A pair of substrates having at least one of translucency and disposed with a gap, a dispersion medium enclosed between the pair of substrates, and a plurality of kinds of different types dispersed in the dispersion medium and having different sizes from each other A particle group, and at least the smallest first particle group of the plurality of types of particle groups moves in the dispersion medium according to an electric field formed between the pair of substrates, and the first At least one kind of particle group larger than the particle group is an uneven particle group having unevenness in at least a partial region of the surface of each particle of the particle group, and the uneven particle group is A display medium having a color that is at least different from a particle group other than the uneven particle group among a plurality of types of particle groups;
Voltage applying means for applying a voltage between the pair of substrates;
A display device comprising:

Images