JP5380957B2 - Electrophoretic display device and electronic apparatus - Google Patents

Description

  The present invention relates to an electrophoretic display device and an electronic apparatus.

Generally, it is known that when an electric field is applied to a dispersion system in which fine particles are dispersed in a liquid, the fine particles move (migrate) in the liquid by Coulomb force. This phenomenon is called electrophoresis. In recent years, an electrophoretic display device that displays desired information (image) using this electrophoresis has attracted attention as a new display device.
This electrophoretic display device has characteristics such as a display memory property and a wide viewing angle property in a state where voltage application is stopped, and a high-contrast display with low power consumption.
In addition, since the electrophoretic display device is a non-light emitting (reflective) display device, the electrophoretic display device also has a feature that is easier on the eyes than a light emitting display device such as a cathode ray tube.

As such an electrophoretic display device, one in which a dispersion system in which electrophoretic particles (fine particles) including white particles and black particles are dispersed is disposed between a pair of substrates provided with electrodes (for example, Patent Document 1).
In this electrophoretic display device, a voltage is applied between a pair of electrodes for each pixel to cause an electric field to act on the electrophoretic particles. As a result, the electrophoretic particles migrate and the reflectance in the dispersion system changes. As a result, the reflected light can be controlled and desired information can be displayed.

Patent Document 1 discloses white particles having fine irregularities on the surface. According to Patent Document 1, white particles having such irregularities have an action of improving the white luminance rate by reducing the light transmitted through the particles and enhancing the effect of multiple reflection.
However, such white particles do not have sufficient suppression of light transmittance, and it is inevitable that the back of the white particles can be seen through. In particular, when irregularities are formed on the surface of the white particles by performing surface modification with a metal, the metal absorbs light and the light reflectance decreases. For this reason, the display contrast in the electrophoretic display device is lowered.

JP 2004-279545 A

  An object of the present invention is to provide an electrophoretic display device having high display contrast and reflectivity and excellent visibility, and a highly reliable electronic apparatus including the electrophoretic display device.

Such an object is achieved by the present invention described below.
An electrophoretic display device of the present invention includes a pair of electrodes arranged to face each other, and a display layer provided between the pair of electrodes,
The display layer contains an electrophoretic dispersion liquid in which at least one kind of electrophoretic particles that migrate in a predetermined direction by energization between the pair of electrodes and light reflecting particles are dispersed in a liquid phase dispersion medium,
The light reflecting particles have a light reflectance higher than that of the electrophoretic particles and have a scaly shape. A polymer is connected to the surface of the light reflecting particles, and the polymer has one end on the surface of the light reflecting particles. It has a main chain to be connected and a side chain connected to the main chain and including a liquid crystal portion.
Thereby, an electrophoretic display device having high display contrast and high reflectance and excellent visibility can be provided.

In the electrophoretic display device of the present invention, it is preferable that the main chain of the main chain is composed of an aliphatic hydrocarbon chain.
Thereby, the main skeleton becomes flexible, and each liquid crystal part can be relatively freely oriented while keeping each liquid crystal part around (near) the light reflecting particles. Therefore, display characteristics and operability of the electrophoretic display device, such as switching of display colors, are improved.
In the electrophoretic display device according to the aspect of the invention, it is preferable that the side chain is one in which the liquid crystal portion is connected to the main chain through a connecting body.
Thereby, the separation distance of each liquid crystal part and a main chain can be maintained moderately.

In the electrophoretic display device according to the aspect of the invention, it is preferable that the connected body has a main skeleton composed of an aliphatic hydrocarbon chain.
Thereby, a connection part becomes flexible and can arrange | position each liquid crystal part further smoothly, keeping each liquid crystal part in the circumference | surroundings (nearness) of a light reflection particle.
In the electrophoretic display device according to the aspect of the invention, it is preferable that the number of carbons existing between the main chain of the connector and the liquid crystal part is 5 to 18.
Thereby, it is possible to keep the liquid crystal part in the vicinity of the light reflecting particles while making the connecting part sufficiently flexible.

In the electrophoretic display device according to the aspect of the invention, it is preferable that the liquid crystal portion has an alignment characteristic that aligns along the direction of an electric field.
Thereby, when a voltage is applied between a pair of electrodes, it is suppressed that a liquid crystal molecule prevents migration of electrophoretic particles. For this reason, the display can be switched smoothly. In addition, since uneven distribution of the electrophoretic particles can be prevented, stable display can be performed. In addition, when no voltage is applied between the pair of electrodes, the reflected light from the light reflecting particles can be reliably directed to the display surface side. For this reason, the brightness and contrast of display can be further increased.

In the electrophoretic display device of the present invention, it is preferable that the density at which the polymer is bonded to the light reflecting particles is 0.5 to ⁵ nm ² / piece.
Thereby, the separation distance between the liquid crystal parts can be maintained at a necessary and sufficient distance and can be present around (near) the light reflecting particles.
In the electrophoretic display device according to the aspect of the invention, it is preferable that the liquid crystal portion has a functional group that is lyophilic with respect to the liquid phase dispersion medium.
Thereby, the liquid crystal molecules can be stably dispersed in the particle dispersion.

In the electrophoretic display device according to the aspect of the invention, it is preferable that the light reflecting particles are mainly composed of a metallic material having a metallic luster.
Thereby, the light reflecting particles have a high light reflectance.
In the electrophoretic display device according to the aspect of the invention, it is preferable that the metal material is aluminum or silver.
As a result, the light reflecting particles have a particularly high light reflectance. In addition, since these materials are less likely to cause unevenness in the color of light due to reflection, for example, when white light is incident, reflected light close to white is obtained. For this reason, it can suppress that the reflected light of light reflection particle influences the color of the reflected light of electrophoretic particle.

In the electrophoretic display device according to the aspect of the invention, it is preferable that the size of the light reflecting particle is larger than the particle size of the electrophoretic particle and larger than the wavelength on the longest wavelength side of visible light.
Thereby, since the light reflecting particles can totally reflect the incident external light, the light reflectance can be particularly increased.
In the electrophoretic display device of the present invention, it is preferable that the light reflecting particles are dispersed in the liquid phase dispersion medium in an uncharged state.
Thereby, the light reflecting particles are dispersed in the display layer without being influenced by the electric field. Therefore, the brightness and contrast of the display can be enhanced by the reflected light from the light reflecting particles without hindering the migration of the electrophoretic particles.

In the electrophoretic display device of the present invention, the particle dispersion is different from the first electrophoretic particles in that the first electrophoretic particles are different from the first electrophoretic particles in the electrophoretic direction as the electrophoretic particles. Second electrophoretic particles having low light reflectance,
The light reflecting particles are preferably charged to the same polarity as the second electrophoretic particles, and the charge amount is smaller than that of the second electrophoretic particles.
Accordingly, since the light reflecting particles migrate at a slower speed than the second electrophoretic particles, the light reflecting particles are always located on the side opposite to the first electrophoretic particles, and transmitted light that passes through the first electrophoretic particles. Can be reliably reflected.
In the electrophoretic display device of the present invention, it is preferable that the first electrophoretic particles have a white color and the second electrophoretic particles have a black color.
As a result, a large difference in reflectance occurs between the reflected light from the first electrophoretic particles and the reflected light from the second electrophoretic particles, thereby enabling display with high contrast.

In the electrophoretic display device of the present invention, the display layer is divided into a plurality of pixel spaces via partition walls,
It is preferable that an alignment film for aligning the liquid crystal portion is provided on at least one of the inner surface on the first electrode side and the inner surface on the second electrode side among the inner surfaces of the pixel spaces.
Thus, when there is no potential difference between the pair of electrodes, the liquid crystal portion of the polymer can be aligned along the groove forming direction of the alignment film.
An electronic apparatus according to the present invention includes the electrophoretic display device according to the present invention.
As a result, a highly reliable electronic device can be obtained.

Hereinafter, an electrophoretic display device and an electronic apparatus of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
1 is a longitudinal sectional view schematically showing a preferred embodiment of the electrophoretic display device of the present invention, FIG. 2 is a schematic enlarged view of light reflecting particles provided in the electrophoretic display device shown in FIG. 1, and FIG. FIG. 4 is a schematic diagram for explaining a change in the posture of the light reflecting particle shown in FIG. 2, FIGS. 4 to 6 are schematic diagrams for explaining the formation of the liquid crystal polymer shown in FIG. 2, and FIGS. FIG. 2 is a sectional view for explaining the operation of the electrophoretic display device shown in FIG. 1. In the following description, the upper side in FIGS. 1, 2, and 6 to 8 is referred to as “upper”, and the lower side is referred to as “lower”.

The electrophoretic display device 20 shown in FIG. 1 includes a first substrate 1 serving as a display surface, a second substrate 2 provided below the first substrate 1, and between the substrates 1 and 2. A sealing portion 7 is provided at the edge portion and hermetically seals the gap between the substrates 1 and 2.
Further, in the airtight space defined by the substrates 1 and 2 and the sealing portion 7, an electrophoretic dispersion liquid 10 including electrophoretic particles 5 (white particles 5a and black particles 5b) and light reflecting particles 8 is provided. Filled.

  Further, the airtight space is divided into a matrix shape by the partition walls 72, and each of the divided spaces is a pixel space 71 corresponding to each pixel constituting the display content. That is, each of the plurality of pixel spaces 71 is filled with the electrophoretic dispersion liquid 10. Then, the electrophoretic particles 5 are migrated according to the electric field applied to each pixel space 71, thereby controlling the light reflectance in each pixel space 71. As a result, in the plurality of pixel spaces 71, the reflected light is controlled by interlocking the control of the light reflectance, and the electrophoretic display device 20 can display information such as images and characters.

Here, in the present invention, the light reflecting particles 8 are included in the electrophoretic dispersion liquid 10. As shown in FIG. 2, the light reflecting particles 8 have a scale shape having a flat surface. Both surfaces of the light reflecting particles 8 are higher in light reflectance than the electrophoretic particles 5. Therefore, as will be described later, it is possible to display with high reflectivity, and to improve the visibility of the electrophoretic display device 20 in a particularly bright place. In particular, it is possible to increase the light reflectance in white (or light color) display, thereby increasing the display contrast.
In the present invention, the polymer (polymer) A is connected to the surface of the light reflecting particle B. This polymer A has a main chain A1 and a side chain A2 including a liquid crystal part A21. This polymer A will be described in detail later.

In the following, one pixel space 71 will be taken up, and the configuration of each part will be sequentially described. In addition, in the plurality of pixel spaces 71, the configuration of each part below is the same.
The first substrate 1 and the second substrate 2 that define the bottom surface and the ceiling surface of the pixel space 71 are each composed of a sheet-like (flat plate-like) member, and support each member arranged therebetween. And has the function of protecting.
Each of the substrates 1 and 2 may be either flexible or hard, but is preferably flexible. By using the substrates 1 and 2 having flexibility, it is possible to obtain the display device 20 having flexibility, that is, an electrophoretic display device 20 useful for constructing, for example, electronic paper.

  When each of the substrates 1 and 2 is flexible, the constituent materials thereof include, for example, polyolefins such as polyethylene, polypropylene, and ethylene-vinyl acetate copolymer, modified polyolefins, and polyamides (example: Nylon 6, nylon 46, nylon 66, nylon 610, nylon 612, nylon 11, nylon 12, nylon 6-12, nylon 6-66), thermoplastic polyimide, aromatic polyester and other liquid crystal polymers, polyphenylene oxide, polyphenylene sulfide, Polycarbonate, polymethyl methacrylate, polyether, polyether ether ketone, polyether imide, polyacetal, styrene, polyolefin, polyvinyl chloride, polyurethane, polyester, polyamide, Examples thereof include various types of thermoplastic elastomers such as rebutadiene, trans polyisoprene, fluoro rubber, and chlorinated polyethylene, or copolymers, blends, polymer alloys, etc. mainly composed of these. A seed or a mixture of two or more can be used.

  The average thickness of each of the substrates 1 and 2 is appropriately set depending on the constituent material, application, etc., and is not particularly limited. However, when it is flexible, it is preferably about 20 to 500 μm. More preferably, the thickness is about 40 to 200 μm. As a result, the electrophoretic display device 20 can be reduced in size (particularly thinner) while achieving harmony between the flexibility and strength of the electrophoretic display device 20.

The substrate 2 has a circuit (not shown) including a switching element such as a thin film transistor (TFT).
Among these substrates 1 and 2, a layered common electrode (first electrode) 3 is provided in the first substrate 1 so as to straddle a plurality of pixel spaces 71.

On the other hand, in the second substrate 2, layered pixel electrodes (second electrodes) 4 are provided corresponding to the respective pixel spaces 71.
Each pixel electrode 4 is connected to a switching element. Thereby, a voltage can be individually applied between the electrodes 3 and 4 in each pixel space 71.
Note that the common electrode 3 may also be divided into a plurality of parts similarly to the pixel electrode 4.
Further, the electrophoretic display device 20 may be of a so-called “simple matrix driving method” in which the common electrode 3 and the pixel electrode 4 are each formed as a striped electrode.

The constituent materials of the electrodes 3 and 4 are not particularly limited as long as they are substantially conductive. For example, copper, aluminum, nickel, cobalt, platinum, gold, silver, molybdenum, tantalum, or these Metal materials such as alloys containing carbon, carbon-based materials such as carbon black, carbon nanotubes, fullerenes, polyacetylene, polypyrrole, polythiophene, polyaniline, poly (p-phenylene), poly (p-phenylenevinylene), polyfluorene, polycarbazole, High ionic conductivity in which various ionic substances are dispersed in a matrix resin such as polysilane or derivatives thereof, or other matrix resins such as polyvinyl alcohol, polycarbonate, polyethylene oxide, polyvinyl butyral, polyvinyl carbazole, and vinyl acetate. Child material, indium tin oxide (ITO), fluorine-doped tin oxide (FTO), tin oxide (SnO _2), various conductive materials such as conductive oxide material such as indium oxide (IO) is 1 type or 2 types or more of these can be used in combination.

In addition, as a constituent material of each electrode 3, 4, for example, a conductive material such as gold, silver, nickel, carbon, etc. in a non-conductive material such as glass material, rubber material, polymer material, etc. Various composite materials in which (conductive particles) are mixed to add conductivity can also be used.
Specific examples of such a composite material include, for example, a conductive rubber in which a conductive material is mixed in a rubber material, a conductive rubber in which an electrically conductive material is mixed in an adhesive composition such as epoxy, urethane, and acrylic. In matrix resins such as conductive adhesive or conductive paste, polyolefin, polyvinyl chloride, polystyrene, ABS resin, nylon (polyamide), ethylene vinyl acetate copolymer, polyester, acrylic resin, epoxy resin, urethane resin Examples thereof include a conductive resin mixed with a conductive material.
The average thickness of the electrodes 3 and 4 is appropriately set depending on the constituent material and the like, and is not particularly limited. However, it is preferably about 0.05 to 10 μm, and preferably about 0.05 to 5 μm. More preferred.

Of the substrates 1, 2 and the electrodes 3, 4, the substrate and the electrode (in the present embodiment, the first substrate 1 and the common electrode 3) arranged on the display surface side each have light transmittance. That is, it is made substantially transparent (colorless transparent, colored transparent or translucent). Thereby, the state of the electrophoretic particles 5 in the electrophoretic dispersion liquid 10 described later, that is, the information (image) displayed on the electrophoretic display device 20 can be easily recognized visually.
Each of the electrodes 3 and 4 may have a multilayer structure in which a plurality of materials are sequentially stacked, for example, in addition to a single layer structure made of a single material as described above. That is, each of the electrodes 3 and 4 may have a single layer structure made of ITO, for example, or may have a two-layer structure of an ITO layer and a polyaniline layer.

Between each board | substrate 1 and 2, the frame-shaped sealing part 7 is provided along those edge parts. A space formed by filling the electrophoretic dispersion liquid 10 is hermetically sealed by the sealing portion 7. Thereby, it is possible to prevent moisture from entering the electrophoretic display device 20 and to prevent display performance of the electrophoretic display device 20 from deteriorating.
Further, as described above, the grid-shaped partition walls 72 are provided inside the frame-shaped sealing portion 7. By this partition wall 72, the space inside the frame-shaped sealing portion 7 is divided into a plurality of matrix-like pixel spaces 71, and each pixel space 71 is hermetically sealed.

Examples of the material constituting the sealing portion 7 and the partition wall 72 include thermoplastic resins such as acrylic resins, urethane resins, and olefin resins, epoxy resins, melamine resins, and phenol resins. Various resin materials such as a thermosetting resin can be used, and one or more of these can be used in combination.
Note that the separation distance between the substrates 1 and 2 can be controlled in accordance with the thickness (height) of the sealing portion 7 and the partition wall 72.

  The separation distance between the substrates 1 and 2 is not particularly limited, but is preferably about 10 to 500 μm, and more preferably about 40 to 100 μm. If such a separation distance is secured between the substrates 1 and 2, the electrophoretic dispersion liquid 10 when viewed from the display surface side while preventing the electrophoretic display device 20 from becoming too thick. Thus, it is possible to prevent the color of the second substrate 2 from being seen through. As a result, it is possible to prevent the display contrast in the electrophoretic display device 20 from being lowered.

  Further, the lattice spacing of the partition walls 72 in the form of a lattice (the distance between the adjacent partition walls 72) is equal to the size of the pixels in the electrophoretic display device 20 (the size in plan view of the pixel space 71). The size of the pixel is appropriately set according to the content of display and is not particularly limited, but is preferably about 50 to 1000 μm, and more preferably about 100 to 400 μm. Thereby, sufficient definition can be obtained when displaying information.

For aligning the liquid crystal portion A21 of the polymer (liquid crystal polymer) A on the ceiling surface (the lower surface of the first substrate 1) and the bottom surface (the upper surface of the second substrate) of the pixel space 71, respectively. An alignment film 91 and an alignment film 92 are provided. Each alignment film 91 and 92 has a plurality of grooves formed in parallel to each other on each surface, and each groove extends, for example, from the front side to the back side in FIG. (Formed). By forming such a groove, the liquid crystal part A21 can be aligned so that its molecular axis is parallel to the groove forming direction.
The constituent material of each of the alignment films 91 and 92 is not particularly limited, and examples thereof include organic materials such as polyimide, polyamide, and polyester, inorganic materials such as silicon oxide, and LB (Langmuir Broadgett) films. It is done.

  In addition, as a method for forming the alignment film 91, for example, an organic material as described above is formed on the first substrate 1, and then a rubbing process is performed on the film, or an inorganic material such as silicon oxide is used. Rubbing treatment such as a method of obliquely depositing a system material (oblique deposition method), a method of depositing an inorganic material by spray pyrolysis, a laser polymerization method, an LB method, a method of irradiating a polyimide film with polarized ultraviolet rays, etc. Examples include methods that do not accompany it. The same applies to the alignment film 92.

The electrophoretic dispersion liquid 10 is sealed in the pixel space 71 as described above.
This electrophoretic dispersion liquid 10 is obtained by dispersing (suspending) two types of electrophoretic particles 5 (first particles 5 a and second particles 5 b) and light reflecting particles 8 in a liquid phase dispersion medium 6. Is. The light reflecting particles 8 will be described in detail later.
The dispersion of the electrophoretic particles 5 and the light reflecting particles 8 in the liquid phase dispersion medium 6 is, for example, one or two of a paint shaker method, a ball mill method, a media mill method, an ultrasonic dispersion method, a stirring dispersion method, and the like. The above can be combined.

As the liquid phase dispersion medium 6, a medium having a relatively high insulating property is preferably used.
Examples of the liquid phase dispersion medium 6 include benzene hydrocarbons such as benzene, toluene, o-xylene, m-xylene, p-xylene, mixed xylene, ethylbenzene, hexylbenzene, dodecylbenzene, and phenylxylylethane. Aromatic hydrocarbons; paraffinic hydrocarbons such as n-hexane and n-decane, isoparaffinic hydrocarbons such as Isopar (Isopar, manufactured by Exxon Chemical), olefinic hydrocarbons such as 1-octene and 1-decene, Aliphatic hydrocarbons such as naphthenic hydrocarbons such as cyclohexane and decalin; petroleum and petroleum-derived hydrocarbon mixtures such as kerosene, petroleum ether, petroleum benzine, ligroin, industrial gasoline, coal tar naphtha, petroleum naphtha and solvent naphtha; Dichloromethane, chloroform, Carbon chloride, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, trichlorofluoroethane, tetrabromoethane, dibromotetrafluoroethane, tetrafluorodiiodoethane, 1,2 -Halogenated hydrocarbons such as dichloroethylene, trichloroethylene, tetrachloroethylene, trichlorofluoroethylene, chlorobutane, chlorocyclohexane, chlorobenzene, o-dichlorobenzene, bromobenzene, iodomethane, diiodomethane, iodoform; silicones such as dimethyl silicone oil and methylphenyl silicone oil Less selected from the group consisting of oils (organic silicone oils); fluorinated solvents such as hydrofluoroethers (organic fluorinated solvents) Even one is suitably used.
Among the organic solvents described above, long-chain alkylbenzenes such as hexylbenzene and dodecylbenzene, phenylxylylethane, and the like are particularly preferably used because of their high boiling point and flash point and little toxicity.

  In addition to the above-mentioned liquid phase dispersion medium 6, for example, cellosolves such as methyl cellosolve, ethyl cellosolve, phenyl cellosolve, esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl formate, acetone, methyl ethyl ketone, Ketones such as diethyl ketone, methyl isobutyl ketone, methyl isopropyl ketone and cyclohexanone, cycloaliphatic hydrocarbons such as cyclohexane and methylcyclohexane, aromatic heterocycles such as pyridine, pyrazine, furan, pyrrole, thiophene and methylpyrrolidone Rings, nitriles such as acetonitrile, propionitrile, acrylonitrile, amides such as N, N-dimethylformamide and N, N-dimethylacetamide, carboxylates, and the like can be used.

Further, in the liquid phase dispersion medium 6 (electrophoretic dispersion liquid 10), for example, a surfactant (anionic or cationic) such as an electrolyte or an alkenyl succinate, a metal soap, a resin material, if necessary. Various additives such as a charge control agent composed of particles such as rubber materials, oils, varnishes, and compounds, a dispersant such as a silane coupling agent, a lubricant, and a stabilizer may be added.
Further, when the liquid phase dispersion medium 6 is colored, various dyes such as anthraquinone dyes, azo dyes, and indigoid dyes may be dissolved in the liquid phase dispersion medium 6 as necessary.

The two kinds of electrophoretic particles 5, that is, the first particles 5a and the second particles 5b are charged with opposite polarities. Therefore, when an electric field acts on these particles 5a and 5b (when a voltage is applied between the pair of electrodes 3 and 4), the particles 5a and 5b are electrophoresed in the liquid phase dispersion medium 6 in opposite directions. .
Hereinafter, for convenience of explanation, the case where the first particles 5a are positively charged particles and the second particles 5b are negatively charged particles will be described as a representative. Note that this may be reversed.

The first particles 5a and the second particles 5b have different colors. The colors of the first particles 5a and the second particles 5b are not particularly limited as long as they are different from each other. For example, achromatic colors such as white, black, or an intermediate color (gray) thereof, red, blue, etc. And chromatic colors such as green.
In addition, the combination of the colors of the first particles 5a and the second particles 5b is not particularly limited. For example, the first particles 5a are white particles, and the second particles 5b are black particles. Examples include a combination of blue particles as the first particles 5a and red particles as the second particles 5b. Among these, the combination of white and black is particularly preferable as the color combination of the first particles 5a and the second particles 5b. Thereby, in the electrophoretic display device 20, monochrome display is possible and display contrast is improved.

Hereinafter, for convenience of explanation, the case where the first particles 5a are white particles and the second particles 5b are black particles will be described. Note that this may be reversed. Hereinafter, for convenience of explanation, the first particles 5a are also referred to as “white particles 5a”, and the second particles 5b are also referred to as “black particles 5b”.
As such electrophoretic particles 5 (white particles 5a and black particles 5b), any particles can be used as long as they have electric charges. Although there is no particular limitation, pigment particles, resin particles, or these particles can be used. At least one of the composite particles is preferably used. These particles have the advantage that they can be easily manufactured and the amount of charge can be controlled relatively easily.

Examples of pigments constituting the pigment particles include black pigments such as aniline black, carbon black, and titanium black, white pigments such as titanium oxide and antimony oxide, azo pigments such as monoazo, yellow such as isoindolinone and yellow lead. Pigments, red pigments such as quinacridone red and chrome vermilion, blue pigments such as phthalocyanine blue and indanthrene blue, green pigments such as phthalocyanine green, and the like. Of these, one or a combination of two or more may be used. it can.
Among these, as pigment particles, titanium oxide particles are suitably used as white particles 5a, and titanium black particles are suitably used as black particles 5b. These particles have high responsiveness to an electric field and a large difference in reflectance, so that display with high contrast is possible.

Examples of the resin material constituting the resin particles include acrylic resin, urethane resin, urea resin, epoxy resin, polystyrene, polyester, and the like, and one or more of these are combined. Can be used.
The composite particles include, for example, those in which the surface of the pigment particles is coated with a resin material or other pigment, those in which the surface of the resin particles is coated with a pigment, or a mixture in which the pigment and the resin material are mixed at an appropriate composition ratio. The particle | grains comprised by these, etc. are mentioned.
Examples of particles obtained by coating the surface of pigment particles with other pigments include those obtained by coating the surface of titanium oxide particles with silicon oxide or aluminum oxide.

Further, the shape of the electrophoretic particles 5 is not particularly limited, but is preferably spherical.
In consideration of dispersibility in the liquid phase dispersion medium 6, smaller particles are preferably used as the electrophoretic particles 5. Specifically, the average particle diameter is preferably about 10 to 500 nm. More preferably, it is about 50 to 300 nm. By setting the average particle diameter of the electrophoretic particles 5 within the above range, aggregation of the electrophoretic particles 5 and sedimentation in the liquid phase dispersion medium 6 can be reliably prevented and dispersed in the liquid phase dispersion medium 6. As a result, deterioration of display quality of the electrophoretic display device 20 can be suitably prevented.

In addition, when using two different types of particles as in the present embodiment, the average particle size of the two types of particles is made different. It is preferable to set. Thereby, the display contrast of the electrophoretic display device 20 can be further improved, and the holding characteristics can be improved.
Specifically, the average particle diameter of the black particles 5b is preferably about 50 to 200 nm, and the average particle diameter of the white particles 5a is preferably about 150 to 300 nm.

The specific gravity of the electrophoretic particles 5 is preferably set to be approximately equal to the specific gravity of the liquid phase dispersion medium 6. Thereby, even after the application of voltage between the electrodes 3 and 4 is stopped, the electrophoretic particles 5 can stay in a certain position in the liquid phase dispersion medium 6 for a long time.
That is, the electrophoretic display device 20 has a property (bistability) that can maintain a display state when a voltage is applied between the electrodes 3 and 4 even after the application of the voltage is stopped. .

  In the electrophoretic display device 20 having such a property (bistability), it is only necessary to apply a voltage between the electrodes 3 and 4 only at the time of switching the display, so that power consumption can be greatly reduced. In addition, since the electrophoretic particles 5 migrate stably, it is possible to apply voltages in various patterns, such as applying a voltage in small increments, and to control the electrophoretic particles 5 in a more complex manner. Become. For this reason, display quality can be improved.

Next, the light reflecting particles 8 will be described.
As described above, the light reflecting particles 8 have a scale shape (plate shape) having a flat surface. Both surfaces of such light reflecting particles 8 have higher light reflectivity than the electrophoretic particles 5.
If the light reflecting particles 8 are included in the electrophoretic dispersion liquid 10, external light incident on the electrophoretic display device 20 from the display surface side is efficiently reflected on the flat surface of the light reflecting particles 8. be able to. Thereby, the reflectance of a display can be raised and the brightness and contrast of the display in the electrophoretic display device 20 can be raised.

Such light reflecting particles 8 are dispersed in the liquid phase dispersion medium 6 in an uncharged state. Therefore, the light reflecting particles 8 are not affected by the electric field generated between the pair of electrodes 3 and 4, and are dispersed throughout the liquid dispersion medium 6 regardless of whether or not an electric field is generated in the pixel space 71. doing. As a result, the display contrast is improved as will be described later.
Examples of the constituent material of the light reflecting particles 8 include metal materials such as aluminum, silver, gold, nickel, chromium, tin, zinc, indium, and titanium, or one or more of these metal materials. Alloy (or mixture), silicon materials such as silicon, silicon oxide, silicon carbide, silicon nitride, various carbon materials such as graphite and diamond, various glass materials such as quartz glass, polyethylene, polypropylene, polyethylene terephthalate, polyethylene Examples thereof include various resin materials such as naphthalate, polytetrafluoroethylene, polyamide, polycarbonate, polyacetate, and polyimide, and various ceramic materials such as alumina and zirconia.

  Among these, the light reflecting particles 8 are preferably those containing a metallic material having metallic luster as the main material, and more preferably those containing aluminum or silver as the main material. Since these materials have an excellent metallic luster, the light reflecting particles 8 having a high light reflectance can be obtained. In addition, since these materials have little color deviation of reflected light, for example, when white light is incident, reflected light close to white is obtained. Thereby, it is possible to suppress the color of the reflected light of the light reflecting particles 8 from affecting the color of the reflected light of the electrophoretic particles 5.

Such light reflecting particles 8 have an average length (size) larger than the particle size of the electrophoretic particles 5 described above and larger than the wavelength (about 800 nm) on the longest wavelength side of visible light. Since the light reflecting particles 8 having such a size can totally reflect the incident external light, the light reflectance can be particularly increased.
Moreover, it is preferable that the average length of the light reflection particle 8 is about 1-40 micrometers, and it is more preferable that it is about 2-20 micrometers. If the light reflecting particles 8 have such a size, the light reflecting particles 8 can maintain a sufficient light reflectance and prevent the movement in the liquid phase dispersion medium 6 from being significantly deteriorated. it can. Further, it is possible to prevent the light reflecting particles 8 from rapidly settling or floating in the liquid phase dispersion medium 6.

  Further, the average thickness of the light reflecting particles 8 is preferably about 10 to 300 nm, and more preferably about 20 to 200 nm. By setting the average thickness of the light reflecting particles 8 within the above range, the light reflecting particles 8 are made too thin while preventing the weight of the light reflecting particles 8 from being remarkably increased. A significant increase can be prevented. That is, the light reflecting particle 8 having such a thickness has a sufficient light reflectance.

  In addition, when there is no potential difference between the pair of electrodes 3 and 4 (between the common electrode 3 and the pixel electrode 4), the light reflection is performed so that the light reflection particles 8 do not settle and float on the liquid phase dispersion medium 6. It is preferable that at least one of the size and thickness of the particles 8 is adjusted. In this way, the position of the light reflecting particles 8 can be maintained unless an external force is applied in the liquid phase dispersion medium 6. For this reason, the electrophoretic display device 20 can maintain a display state for a long time without consuming electric power.

Moreover, such light reflecting particles 8 can be produced by pulverizing a foil body such as a metal foil. The light reflecting particles 8 produced by such a method can easily make the thicknesses of the plurality of light reflecting particles 8 uniform. For this reason, in each light reflection particle 8, the dispersion with respect to the liquid phase dispersion medium 6 and the dispersion | variation in each reflection characteristic can be suppressed.
Examples of the pulverization method include a jet mill, a ball mill, a ring roll mill, a hammer mill, and the like, and these can be used in combination.

  As shown in FIG. 2, a plurality of polymers (polymers) A are connected to the surface of the light reflecting particles 8. Each polymer A has a main chain A1 and a plurality of side chains A2 connected to the main chain A1. Further, the side chain A2 includes a liquid crystal part A21 exhibiting liquid crystallinity, and a connecting part A22 that connects the liquid crystal part A21 and the main chain A1. That is, it can be said that the polymer A is a so-called “side-chain liquid crystal polymer”.

  The main chain A1 is linear. The main chain A1 is connected (coupled) to the surface of the light reflecting particle 8 at one end thereof. Such a main chain A1 is preferably relatively flexible. Thereby, the liquid crystal part A21 can be aligned while the liquid crystal parts A21 are kept around (near) the light reflecting particles 8. Therefore, the display characteristics and operability of the electrophoretic display device 20 such as switching between a white display state and a black display state as described later are improved.

The main chain A1 is preferably one that can be synthesized by living polymerization as described later so that the side chain A2 can be introduced at an arbitrary position. Such a main chain A1 is not particularly limited, but in consideration of easiness of synthesis by living polymerization, those having a main skeleton composed of an aliphatic hydrocarbon chain (particularly a saturated hydrocarbon chain) are preferable. Used for.
Further, when the main skeleton is composed of an aliphatic hydrocarbon chain (especially a saturated hydrocarbon chain), the main chain A1 has sufficient flexibility, and each liquid crystal part A21 is more smoothly located in the vicinity of the light reflecting particles 8. Can be oriented.

On the other hand, as described above, each side chain A2 has a liquid crystal part A21 exhibiting liquid crystallinity and a connecting part A22 that connects the liquid crystal part A21 and the main chain A1. Such a side chain A2 is formed by, for example, connecting a molecule that can be a liquid crystal alone (hereinafter, this molecule is also referred to as “liquid crystal molecule B”) to the main chain A1 via the connecting portion A22. Is.
By making each side chain A2 have such a configuration, one polymer A can include a plurality of liquid crystal portions A21. Therefore, a sufficient number of liquid crystal portions A21 can be present in the vicinity of the light reflecting particles 8, and the alignment of the light reflecting particles 8 as will be described later is performed more smoothly.
In the present embodiment, since the side chain A2 has the connecting part A22, the liquid crystal part A21 and the main chain A1 can be sufficiently separated. Therefore, each liquid crystal part A21 can be smoothly aligned.

  Such a connecting portion A22 is linear. In addition, the connecting portion A22 is connected to the main chain A1 at one end and is connected to the liquid crystal portion A21 at the other end. Such a main chain A1 is preferably relatively flexible. By making the connecting portion A22 flexible, the liquid crystal portion A21 can be displaced (orientated) relatively freely in the vicinity of the light reflecting particles 8. Therefore, as will be described later, display characteristics of the electrophoretic display device 20 such as display color switching are improved. In particular, when both the main chain A1 and the connecting portion A22 are flexible, the above effect becomes more remarkable.

As such a connection part A22, for example, one in which the main skeleton is composed of an aliphatic hydrocarbon chain (particularly a saturated hydrocarbon chain) is preferably used. Thereby, the flexibility of the connecting portion A22 becomes sufficient, and each liquid crystal portion A21 can be more smoothly aligned in the vicinity of the light reflecting particles 8.
More specifically, as the coupling portion A22, for _{example, - (CH 2) m -} , - (CH 2) m O -, - O (CH 2) m O- , and the like. Note that m represents an arbitrary integer of 1 or more.

  In addition, the connecting portion A22 has a number of carbon atoms linked in a straight chain among the atoms constituting the connecting portion A22, that is, the number of carbon atoms existing between the main chain A1 and the liquid crystal portion A21 is about 5 to 18. It is preferable that it is about 10-15. Thereby, each liquid crystal part A21 can be kept in the vicinity of the light-reflecting particles 8 while ensuring the flexibility of the connecting part A22.

  The liquid crystal part A21 connected to the main chain A1 through the connecting part A22 has a property of being aligned in the direction of the electric field. The liquid crystal part A21 (that is, the liquid crystal molecule B) may be any liquid crystal that can be aligned such as nematic liquid crystal, smectic liquid crystal, and the like, but when there is a potential difference between the pair of electrodes 3 and 4, its molecular axis (long axis) ) Preferably has an alignment characteristic that aligns along the normal direction of the electrode. That is, the liquid crystal part A21 preferably has a so-called positive dielectric anisotropy aligned along the direction of the electric field. Thereby, as will be described in detail later, the liquid crystal part A21 contributes to optimizing the migration direction of the electrophoretic particles 5.

  Examples of such liquid crystal part A21 (liquid crystal molecule B) include phenylcyclohexane derivative liquid crystal, biphenyl derivative liquid crystal, biphenylcyclohexane derivative liquid crystal, terphenyl derivative liquid crystal, phenyl ether derivative liquid crystal, phenyl ester derivative liquid crystal, bicyclohexane derivative liquid crystal, Examples include azomethine derivative liquid crystals, azoxy derivative liquid crystals, pyrimidine derivative liquid crystals, dioxane derivative liquid crystals, and cubane derivative liquid crystals.

Further, the liquid crystal part A21 preferably has a functional group exhibiting lyophilicity with respect to the liquid phase dispersion medium 6. The liquid crystal part A21 having such a functional group can be stably dispersed in the electrophoretic dispersion liquid 10.
Specifically, for example, when the liquid phase dispersion medium 6 is a fluorine-based dispersion medium, the liquid crystal portion A21 is added to the nematic liquid crystal molecules as described above with a monofluoro group, difluoro group, trifluoro group, trifluoro group. Those into which a fluorine-based substituent such as a methyl group, a trifluoromethoxy group, or a difluoromethoxy group is introduced are preferably used.

The number of liquid crystal portions A21 bonded to the main chain A1 is not particularly limited, but is preferably about 1 to 20, and more preferably about 5 to 10. When the liquid crystal part A21 (side chain A2) is bonded to the main chain A1 in such a number, a sufficient number of liquid crystal parts A21 to orient the light reflecting particles 8 are present around the light reflecting particles 8. Can do.
Density attached to the light reflecting particles 8 having the above polymer A is not particularly limited, but is preferably 0.5 to 5 nm ² / number of about, that is 1 to 3 nm ² / Pieces More preferred. Thereby, each liquid crystal part A21 can exist in the circumference | surroundings (near) of the light reflection particle | grains 8, maintaining sufficient space | interval of liquid crystal part A21.

The configuration of the polymer A has been described above.
Here, as shown in FIG. 3A, each liquid crystal portion A21 included in the polymer A has a ceiling surface of the pixel space 71 and a liquid crystal portion A21 in a state where no voltage is applied between the common electrode 3 and the pixel electrode 4. The pair of alignment films 91 and 92 formed on the bottom surface are aligned substantially parallel to the ceiling surface and the bottom surface of the pixel space 71. Therefore, correspondingly, the light reflecting particles 8 are also oriented so that their surfaces are substantially parallel to the ceiling surface and the bottom surface of the pixel space 71.

  On the other hand, as shown in FIG. 3C, each liquid crystal portion A <b> 21 is oriented in the direction of the electric field when a voltage is applied between the common electrode 3 and the pixel electrode 4. Therefore, corresponding to the orientation of each liquid crystal part A21, the light reflecting particles 8 are also oriented so that their surfaces are substantially perpendicular to the direction of the electric field. That is, the state shown in FIG. 3C is obtained through the state shown in FIG.

The light reflecting particles 8 as described above can be manufactured, for example, as follows.
First, the light reflecting particles 8 are prepared, and a reaction layer is formed on the surfaces (both sides). Here, the case where the polymer A shown in FIG. 4 is formed using living polymerization will be described as an example. 4-6 is a schematic diagram for demonstrating formation of the polymer A, respectively. In the following description, the upper side in FIGS. 4 to 6 is referred to as “upper” and the lower side is referred to as “lower”. Further, n in FIG. 4 is an integer of 1 or more, and is not particularly limited, but is preferably 10 to 200, and more preferably 20 to 100.

  <1> First, the following compound (A) having a chemical bond activated by a catalyst described later and a binding group X chemically bonded to the light reflecting particle 8 is prepared as a polymerization initiator 37.

Here, when the light reflecting particles 8 are made of a metal (noble metal) material such as gold, silver, or copper, or an alloy containing one or more of these metal materials, the bonding group X includes For example, a thiol group (SH group), a disulfide group (—SS— group), a monosulfide group (—S— group), a carboxyl group (—COOH group) and the like are selected.
When the light reflecting particles 8 are made of a metal material such as aluminum, nickel, chromium, tin, zinc, indium, titanium, or an alloy containing one or more of these metal materials, a silane cup A ring agent is suitably used, and for the bonding group X, for example, -Si (OCH ₃ ) ₃ group, -Si (OC ₂ H ₅ ) ₃ or the like which gives a silanol group (Si-OH group) by hydrolysis Is selected.

For example, when the binding group X is an SH group, the SH group is reacted with the surface of the light reflecting particle 8. As a result, the polymerization initiator 37 is bonded (linked) to the light reflecting particle 8 via the metal-thiol bond (—S—).
This can be performed, for example, by selectively bringing a liquid containing the polymerization initiator 37 represented by the compound (A) into contact with the surface of the light reflecting particles 8. Various liquid phase generation film methods are used as the method for selectively bringing the solution into contact with the surface of the light reflecting particles 8, and among these, the liquid ejection method is preferably used.
By such a process, as shown in FIG. 5, the polymerization initiator 37 is immobilized (solid phase) on the surface of the light reflecting particles 8. In FIG. 5, one surface of the light reflecting particle 8 is illustrated, but the same processing is performed on the other surface.

Next, a monomer in which the liquid crystal part A21 (liquid crystal molecule B) is connected is prepared.
Examples of the polymerization group possessed by this monomer include those containing a carbon-carbon double bond such as (meth) acryloyl group, vinyl group and styryl group, norbornyl group, epoxy group, oxetanyl group and the like. In view of relatively high polymerization activity and low cost, it is preferable to use a monomer containing a (meth) acryloyl group. Specific examples of this monomer include compounds represented by the following chemical formula (B).

［式中、ＬＣは、液晶部（液晶分子）を指す。また、Ｒ^１は、水素原子またはメチル基を、Ｒ^２は、アルキレン基をそれぞれ表す。］

[Wherein LC represents a liquid crystal part (liquid crystal molecule). R ¹ represents a hydrogen atom or a methyl group, and R ² represents an alkylene group. ]

Among these, for example, the compound represented by the chemical formula (B) including the liquid crystal part A21 can be synthesized as follows, for example.
First, after dissolving the liquid crystal molecule B in dichloromethane (DCM), Na ₂ Fe (CO) ₄ is added and mixed, and then oxygen gas is supplied to introduce a hydroxyl group into a part of the liquid crystal molecule B. To do. At this time, the reaction conditions for introducing a hydroxyl group into the liquid crystal molecule B are a reaction temperature of 0 ° C. and a reaction time of 30 minutes.

Next, the liquid crystal molecule B into which the hydroxyl group has been introduced is dissolved in ether such as diethyl ether or tetrahydrofuran (THF). Then, a basic catalyst such as pyridine, trimethylamine or dimethylamine is added to the solution thus obtained, and then a substituted or unsubstituted acryloyl chloride is added, whereby the terminal of the liquid crystal molecule B is substituted or unsubstituted. The acryloyl group is introduced.
As described above, the compound represented by the chemical formula (B) including the liquid crystal part A21 is obtained.

Next, as shown in FIG. 6, the liquid crystal part A21 (liquid crystal molecule B) is based on the polymerization initiator 37 (compound represented by the chemical formula (A)) immobilized on the surface of the light reflecting particle 8 as a base point. Polymer A is synthesized by polymerizing the linked monomers by living polymerization (in particular, atom transfer radical polymerization: ATRP).
This living polymerization can be performed by supplying a solution containing a catalyst to the surface of the light reflecting particles 8 and then adding the monomer to the solution.

  Any catalyst may be used as long as it can activate the growth terminal in the process of polymer growth. For example, transition metal halide, hydroxide, oxide, alkoxide, cyanide, cyanate , Thiocyanate, azide, and the like, but transition metal complexes having general ligands for transition metals such as bipyridyl, phosphine, and carbon monoxide may also be used. Of these, those containing a transition metal halide as the main component are preferred. A catalyst containing a transition metal halide as a main component is preferable because it is suitable for living polymerization. Moreover, it is preferable because it is relatively inexpensive and easily available, and is easy to handle.

Examples of the transition metal include Cu, Fe, Au, Ag, Hg, Pd, Pt, Co, Mn, Ru, Mo, Nb, and Zn.
Examples of the solvent used as a reaction field for the synthesis of the polymer A include water, alcohols such as methanol, ethanol and butanol, halogenated aromatic hydrocarbons such as o-dichlorobenzene, diethyl ether and tetrahydrofuran. And ethers.

By causing the monomer to act in the presence of the polymerization initiator 37 and the catalyst, first, the bond contained in the polymerization initiator 37 is activated by the catalyst and combined with the monomer, and the polymerization initiator 37 is activated by the catalyst. The atom contained in the formed bond moves to the monomer side, and the bond activated by the catalyst is regenerated as a growth terminal.
For example, by using the compound represented by the chemical formula (B) as a monomer and using CuBr as a catalyst, the monomer is combined with the polymerization initiator 37 as shown in FIG. 6, and at the tip (upper end). A growth end is formed.

Here, in the living polymerization, since the growth terminal always has polymerization activity in the growth process of the polymer (liquid crystal polymer) A, the monomer is consumed, and after the polymerization reaction is stopped, a new monomer is added. Goes further.
Therefore, the number of liquid crystal parts A21 in the polymer A can be controlled with high accuracy by changing the amount of monomer supplied to the reaction system. Thereby, the polymer A having a desired molecular structure can be formed on the surface of the light reflecting particle 8 by a simple process. Moreover, the dispersion | variation in the characteristic between the polymer A obtained can be suppressed.

The solution (reaction solution) is preferably subjected to deoxygenation treatment before starting the polymerization reaction. Examples of the deoxidation treatment include substitution after vacuum degassing with an inert gas such as argon gas and nitrogen gas, purge treatment, and the like.
Further, in the polymerization reaction, the monomer polymerization reaction can be performed more quickly and reliably by heating (heating) the temperature of the above solution to a predetermined temperature (temperature at which the monomer and catalyst are activated).
The heating temperature varies slightly depending on the heat-resistant temperature of the liquid crystal part A21, the type of catalyst, and the like, and is not particularly limited, but is preferably about 20 to 50 ° C. The heating time (reaction time) is preferably about 10 to 20 hours when the heating temperature is in the above range.
The polymer A linked to the surface of the light reflecting particle 8 is obtained by the above steps.

The configuration of the electrophoretic display device 20 has been described in detail above. Such an electrophoretic display device 20 operates as follows, for example.
-Operation of the electrophoretic display device 20-
Such an electrophoretic display device 20 operates as follows.
Hereinafter, an operation method of the electrophoretic display device 20 will be described.
7 and 8 are schematic views for explaining the operation method of the electrophoretic display device shown in FIG. In the following description, the upper side in FIGS. 7 and 8 is referred to as “upper” and the lower side is referred to as “lower”. In the following, for convenience of explanation, the case where the white particles 5a are positively charged and the black particles 5b are negatively charged will be described as a representative.

≪White display state≫
First, a state where white (the color of the white particles 5a) is visually recognized as a display color will be described.
As shown in FIG. 7A, when a voltage is applied between the common electrode 3 and the individual electrode 4 so that the common electrode 3 is at a negative potential and the individual electrode 4 is at a positive potential, ) Generates an electric field. By the action of this electric field, the liquid crystal part A21 of the polymer (liquid crystal polymer) A is aligned in the vertical direction. By the way, since the liquid crystal part A21 is located in the vicinity of the light reflecting particles 8, when the liquid crystal part A21 is aligned as described above, the light reflecting particles 8 are also aligned in the vertical direction. That is, when a voltage is applied between the common electrode 3 and the individual electrode 4, as shown in FIG. 7A, the light reflecting particle 8 has its normal direction (direction perpendicular to the surface) orthogonal to the electric field direction. Oriented to As described above, since the light reflecting particles 8 are in an uncharged state, they are dispersed throughout the liquid phase dispersion medium 6 even when the electric field is generated.

  When such a voltage is applied, the light reflecting particles 8 are oriented, and the white particles 5a and the black particles 5b migrate (electrophoresis) in the liquid phase dispersion medium 6, respectively. Specifically, since the white particles 5a are positively charged particles, the white particles 5a migrate toward the common electrode 3 side (upper side) so as to be electrically adsorbed to the common electrode 3 having a negative potential. Since one black particle 5b is a negatively charged particle, it migrates toward the individual electrode 4 side (lower side) so as to be electrically adsorbed to the individual electrode 4 having a positive potential ( (See the arrow in FIG. 7A).

  When such a voltage application state is maintained, as shown in FIG. 7B, the white particles 5 a reach the ceiling surface of the pixel space 71 (the surface of the alignment film 91), that is, gather near the common electrode 3. One black particle 5 b reaches the bottom surface of the pixel space 71. In other words, in this state, three layers of a layer in which the black particles 5b are concentrated on the lower side in the pixel space 71, a layer in which the white particles 5a are concentrated on the upper side, and a layer in which the light reflecting particles 8 are dispersed between these layers. It can be said that is formed.

When the electrophoretic particles 5 move (migrate), since the liquid crystal part A21 is oriented in the vertical direction, the viscosity of the liquid phase dispersion medium 6 in the direction orthogonal to the orientation direction of the liquid crystal part A21 increases. However, the viscosity in the direction parallel to the orientation direction (migration direction of the particles 5a and 5b) hardly changes. That is, in this state, the white particles 5a can move smoothly (smoothly) to the upper side and the black particles 5b to the lower side without any problem. On the other hand, since the electrophoretic particles 5 are difficult to move from side to side, the uneven distribution of the electrophoretic particles 5, particularly the white particles 5a, can be prevented. As a result, when the pixel space 71 is viewed from above in FIG. 7B, the entire pixel space 71 can be reliably covered with the white particles 5a, and the light reflectance in the white display state is reliably reduced. Can be prevented.
Further, since the light reflecting particles 8 are also aligned with the alignment of the liquid crystal molecules 9, it is possible to prevent the light reflecting particles 8 from interfering with the movement of the electrophoretic particles 5 that are moving.

When the application of voltage is canceled after the state shown in FIG. 7B is reached, each liquid crystal portion A21 is aligned such that its molecular axis is parallel to the grooves of the alignment films 91 and 92. With the orientation of each liquid crystal part A21, the light reflecting particle 8 also has an upper surface and a lower surface facing the common electrode 3 and the individual electrode 4, respectively, as shown in FIG. 7C. Align so that
As a result, when the electrophoretic display device 20 is viewed from above (display surface side), the color of the white particles 5a is visible as shown in FIG. 7C, and white is visually recognized as the display color.
7C, when the liquid crystal part A21 is oriented in the horizontal direction, the liquid phase dispersion medium 6 has a direction perpendicular to the orientation direction of the liquid crystal part A21 (the vertical direction in FIG. 7). Viscosity increases.

When the viscosity of the liquid phase dispersion medium 6 increases in this way, the electrophoretic particles 5 are difficult to move up and down, so that the retention of the position of the electrophoretic particles 5 is improved. That is, since the display memory property in the state where the voltage application between the pair of electrodes 3 and 4 is stopped is improved, for example, the display memory property in the white display state shown in FIG. 7C can be improved. In other words, the electrophoretic display device 20 can prevent a change in display color (white) with time while saving power.
Further, since the light reflecting particles 8 are floating with the surface thereof facing the common electrode 3, the movement of the electrophoretic particles 5 is inhibited (obstructed) by the light reflecting particles 8. This also improves the display memory performance.
The improvement of the display memory property as described above is the same in the black display state described later.

  Here, in the conventional electrophoretic display device, the white display shown in FIG. 7C has a problem that it looks slightly gray instead of white. The main cause of this is that the light reflectance of the white particles 5a is low and the light is transmitted. Therefore, when the electrophoretic display device 20 is viewed from above in FIG. 7C, the white particles 5a are behind the white particles 5a. It is conceivable that the color of the black particles 5b can be seen through.

  Therefore, in the present invention, the light reflecting particles 8 are mixed with the electrophoretic dispersion liquid 10 in addition to the electrophoretic particles 5. The light reflecting particles 8 in the electrophoretic dispersion liquid 10 are located between the white particles 5a and the black particles 5b in the white display state in which the white particles 5a are gathered in the vicinity of the common electrode 3, and the upper side thereof. The lower surface and the lower surface are opposed to the common electrode 3 and the individual electrode 4, respectively.

  Therefore, in this state, the surface of the light reflecting particle 8 more reliably covers the black particle 5b, and the reflected light from this surface is surely directed to the common electrode 3 (display surface) side. Therefore, the transmitted light transmitted through the white particles 5a is reliably reflected, and the user of the electrophoretic display device 20 can visually recognize not only the reflected light from the white particles 5a but also the reflected light from the light reflecting particles 8. As a result, the light reflectance in white display is increased. As a result, the display brightness and contrast of the electrophoretic display device 20 can be increased.

≪Black display state≫
Next, a state where black (the color of the black particles 5a) is visually recognized as the display color will be described.
For example, after the white display state described above, as shown in FIG. 8A, a voltage is applied between the common electrode 3 and the individual electrode 4 so that the common electrode 3 has a positive potential and the individual electrode 4 has a negative potential. Apply. Then, an electric field is generated in the vertical direction (vertical direction) in the figure, and by the action of this electric field, the light reflecting particles 8 are oriented so that their normal direction (direction perpendicular to the surface) is orthogonal to the electric field direction (this The principle is the same as that described in the white display state).

When such a voltage is applied, the orientation of the light reflecting particles 8 occurs, and the white particles 5a and the black particles 5b migrate (electrophoresis) in the liquid phase dispersion medium 6, respectively. Specifically, the white particles 5a migrate toward the individual electrode 4 side (lower side) so as to be electrically adsorbed to the individual electrode 4 having a negative potential, and one black particle 5b is It migrates toward the common electrode 3 side (upper side) so as to be electrically adsorbed to the common electrode 3 having a positive potential (see the arrow in FIG. 8A).
When such a voltage application state is maintained, as shown in FIG. 8B, the white particles 5 a gather near the individual electrode 4, and one black particle 5 b gathers near the common electrode 3.

When the application of the voltage is canceled after the state shown in FIG. 8B is reached, the light reflecting particle 8 has the upper surface and the lower surface thereof, as shown in FIG. And, it is oriented so as to face the individual electrode 4.
As a result, when the electrophoretic display device 20 is viewed from above (display surface side), the color of the black particles 5b is visible as shown in FIG. 8C, and black is visually recognized as the display color.
As described above, the black particles 5b hardly transmit light. Therefore, the black display has a sufficiently small light reflectance, and the light reflecting particles 8 do not possibly impair the display contrast.

  When the electrophoretic particles 5 move, the liquid crystal portion A21 is oriented in the vertical direction, so that the viscosity in the direction perpendicular to the orientation direction of the liquid crystal molecules 9 increases in the liquid phase dispersion medium 6. The viscosity in the direction parallel to the direction (the migration direction of the particles 5a and 5b) hardly changes. That is, in this state, the white particles 5a can be smoothly moved to the lower side and the black particles 5b can be smoothly moved to the upper side without any problem. Therefore, the white display state can be smoothly switched to the black display state. it can. Further, since the light reflecting particles 8 are also aligned with the alignment of the liquid crystal part A21, it is possible to prevent the light reflecting particles 8 from interfering with the movement of the electrophoretic particles 5 being moved.

As described above, the electrophoretic display device 20 can prevent a change in display color with time while reducing power consumption, and can display with high reflectivity and high contrast. In particular, in the electrophoretic display device 20, since the polymer (liquid crystal polymer) A is connected to the light reflecting particles, a large number of liquid crystal portions A 21 can be kept near the light reflecting particles 8. Therefore, the light reflecting particles 8 can be aligned more smoothly and reliably according to the alignment of each liquid crystal portion A21. That is, the attitude (orientation) of the light reflecting particles 8 can be controlled more precisely.
In such a configuration, by controlling the migration of the electrophoretic particles 5 for each pixel space 71, on the display surface side of the electrophoretic display device 20, based on the reflected light from the white particles 5 a and the black particles 5 b, Desired information (image) is displayed.

<Electronic equipment>
The electrophoretic display device 20 as described above can be incorporated into various electronic devices. Hereinafter, the electronic apparatus of the present invention including the electrophoretic display device 20 will be described.
<< Electronic Paper >>
First, an embodiment when the electronic apparatus of the present invention is applied to electronic paper will be described.
FIG. 9 is a perspective view showing an embodiment when the electronic apparatus of the present invention is applied to electronic paper.
An electronic paper 600 shown in FIG. 9 includes a main body 601 composed of a rewritable sheet having the same texture and flexibility as paper, and a display unit 602.
In such an electronic paper 600, the display unit 602 includes the electrophoretic display device 20 as described above.

<< Display >>
Next, an embodiment when the electronic apparatus of the present invention is applied to a display will be described.
FIG. 10 is a diagram showing an embodiment when the electronic apparatus of the present invention is applied to a display. Among these, (a) in FIG. 10 is a sectional view and (b) is a plan view.
A display (display device) 800 illustrated in FIG. 10 includes a main body 801 and an electronic paper 600 that is detachably attached to the main body 801. The electronic paper 600 has the same configuration as described above, that is, the configuration shown in FIG.

  The main body 801 has an insertion port 805 into which the electronic paper 600 can be inserted on its side (right side in FIG. 10A), and two pairs of conveying rollers 802a and 802b are provided inside. Yes. When the electronic paper 600 is inserted into the main body 801 through the insertion port 805, the electronic paper 600 is installed in the main body 801 in a state of being sandwiched between the pair of conveyance rollers 802a and 802b.

  A rectangular hole 803 is formed on the display surface side of the main body 801 (the front side in FIG. 10B), and a transparent glass plate 804 is fitted into the hole 803. . Thereby, the electronic paper 600 installed in the main body 801 can be viewed from the outside of the main body 801. That is, in the display 800, the display surface is configured by visually recognizing the electronic paper 600 installed in the main body 801 on the transparent glass plate 804.

Further, a terminal portion 806 is provided at the leading end portion (left side in FIG. 10) of the electronic paper 600 in the insertion direction, and the terminal is provided inside the main body portion 801 with the electronic paper 600 installed on the main body portion 801. A socket 807 to which the unit 806 is connected is provided. A controller 808 and an operation unit 809 are electrically connected to the socket 807.
In such a display 800, the electronic paper 600 is detachably installed on the main body 801, and can be carried and used while being detached from the main body 801.
In such a display 800, the electronic paper 600 is configured by the electrophoretic display device 20 as described above.

Note that the electronic apparatus of the present invention is not limited to the application to the above, and for example, a television, a viewfinder type, a monitor direct view type video tape recorder, a car navigation device, a pager, an electronic notebook, a calculator, an electronic Examples include newspapers, word processors, personal computers, workstations, videophones, POS terminals, and devices equipped with touch panels. The electrophoretic display device 20 of the present invention is applied to the display units of these various electronic devices. Is possible.
As described above, the electrophoretic display device and the electronic apparatus of the present invention have been described based on the illustrated embodiment, but the present invention is not limited to this, and the configuration of each unit is an arbitrary configuration having the same function Can be substituted. In addition, any other component may be added to the present invention.

It is a longitudinal section showing a suitable embodiment of an electrophoretic display device of the present invention typically. FIG. 2 is a schematic enlarged view of light reflecting particles provided in the electrophoretic display device shown in FIG. 1. It is a schematic diagram explaining the change of the attitude | position of the light reflection particle | grains shown in FIG. It is a schematic diagram for demonstrating formation of the liquid crystal polymer shown in FIG. It is a schematic diagram for demonstrating formation of the liquid crystal polymer shown in FIG. It is a schematic diagram for demonstrating formation of the liquid crystal polymer shown in FIG. It is sectional drawing explaining the action | operation of the electrophoretic display device shown in FIG. It is sectional drawing explaining the action | operation of the electrophoretic display device shown in FIG. It is a perspective view which shows embodiment at the time of applying the electronic device of this invention to electronic paper. It is a figure which shows embodiment at the time of applying the electronic device of this invention to a display.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... 1st substrate 2 ... 2nd substrate 3 ... Common electrode 4 ... Pixel electrode 5 ... Electrophoresis particle 5a ... White particle 5b ... Black particle 6 ... Liquid phase dispersion medium 7 ... Sealing part 71 ... Pixel space 72 ... Partition 8 ... Light reflecting particles 9 ... Liquid crystal molecules 91, 92 ... Alignment film 10 ... Electrophoretic dispersion liquid 20 ... Electrophoretic display device 37 ... Polymerization initiator 600 ... Electronic paper 601 ... Main unit 602 ... Display unit 800 ... Display 801 ... Main unit 802a, 802b ... Conveying roller pair 803 ... Hole 804 ... Transparent glass plate 805 ... Insertion slot 806 ... Terminal part 807 ... Socket 808 ... Controller 809 ... Operation part A ... Polymer A1 ... Main chain A2 ... Side chain A21 ... Liquid crystal part A22 ... Connection part

Claims (16)

A pair of electrodes opposed to each other, and a display layer provided between the pair of electrodes,
The display layer contains an electrophoretic dispersion liquid in which at least one kind of electrophoretic particles that migrate in a predetermined direction by energization between the pair of electrodes and light reflecting particles are dispersed in a liquid phase dispersion medium,
The light reflecting particles have a light reflectance higher than that of the electrophoretic particles and have a scaly shape. A polymer is connected to the surface of the light reflecting particles, and the polymer has one end on the surface of the light reflecting particles. An electrophoretic display device comprising a main chain to be connected and a side chain connected to the main chain and including a liquid crystal portion.   The electrophoretic display device according to claim 1, wherein the main chain includes an aliphatic hydrocarbon chain in the main skeleton.   The electrophoretic display device according to claim 1, wherein the side chain is one in which the liquid crystal part is connected to the main chain via a connecting body.   The electrophoretic display device according to claim 3, wherein a main skeleton of the connector is composed of an aliphatic hydrocarbon chain.   The electrophoretic display device according to claim 4, wherein the number of carbons present between the main chain of the connector and the liquid crystal part is 5 to 18.   The electrophoretic display device according to claim 1, wherein the liquid crystal unit has an alignment characteristic that aligns along a direction of an electric field. The electrophoretic display device according to claim 1, wherein the density of the polymer bonded to the light reflecting particles is 0.5 to ⁵ nm ² / piece. The electrophoretic display device according to claim 1, wherein the liquid crystal unit has a functional group that is lyophilic with respect to the liquid phase dispersion medium.   The electrophoretic display device according to claim 1, wherein the light reflecting particles are mainly composed of a metallic material having a metallic luster.   The electrophoretic display device according to claim 9, wherein the metal material is aluminum or silver.   The electrophoretic display device according to claim 1, wherein a size of the light reflecting particle is larger than a particle size of the electrophoretic particle and larger than a wavelength on a longest wavelength side of visible light.   The electrophoretic display device according to claim 1, wherein the light reflecting particles are dispersed in the liquid phase dispersion medium in an uncharged state. The particle dispersion is different from the first electrophoretic particles as the electrophoretic particles, and the second electrophoretic particles have a light reflectivity lower than that of the first electrophoretic particles. Electrophoretic particles,
13. The light reflecting particle according to claim 1, wherein the light reflecting particle is charged to the same polarity as the second electrophoretic particle, and the charge amount thereof is smaller than that of the second electrophoretic particle. Electrophoretic display device.   The electrophoretic display device according to claim 13, wherein the first electrophoretic particles are white and the second electrophoretic particles are black. The display layer is divided into a plurality of pixel spaces through partition walls,
The alignment film for aligning the liquid crystal portion is provided on at least one of the inner surface on the first electrode side and the inner surface on the second electrode side among the inner surfaces of the pixel spaces. The electrophoretic display device described.   An electronic apparatus comprising the electrophoretic display device according to claim 1.

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