JP2001265261A - Electrophoretic display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophoretic display device in which the deposition state can be maintained for a long period and stable display is possible. SOLUTION: The electrophoretic display device has a migration medium between a pair of electrodes 12a, 12b and migration particles 2 dispersed in the migration medium 1. The migration medium 1 contains a swellable sheet clay mineral.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophoretic display device utilizing the movement of charged particles in a migration medium by applying a voltage.

[0002]

2. Description of the Related Art Conventionally, an electrophoretic display device as shown in FIG. 6 has been known. In this electrophoretic display device, at least one of the pair is translucent, for example, a pair of glass substrates 11.
a and 11b are opposed to each other at a predetermined interval via the sealing members 13a and 13b.
1b and the sealing members 13a and 13b form a closed space. These pair of glass substrates 11
a and 11b are provided with flat ITO on the inner surfaces facing each other.
And the like transparent electrodes 12a and 12b are fixed.

[0003] In the closed space, an electrophoretic display medium 1a is accommodated. This electrophoretic display medium 1
“a” is, for example, a solution in which a dye such as black is dissolved in a dispersion medium, and includes white charged particles (electrophoretic particles, for example, white pigment) 2 dispersed in the medium 1a.

In such an electrophoretic display element, a switch 15 is closed and connected to a power source 14 as shown in FIG. 7, for example, to connect the pair of electrodes 12a and 12b to a positive electrode 12a. When a voltage is applied and a negative voltage is applied to the lower electrode 12b, the negatively charged white pigment 2 electrophoreses toward the anode by Coulomb force, and the white pigment 2 adheres to the upper anode electrode 12a. I do. When the electrophoretic display device in such a state is observed from an upper position, the portion where the white pigment 2 adheres to form a layer appears white via the transparent electrode 12a and the glass substrate 11a. On the other hand, if the polarity of the applied voltage is reversed, the white pigment 1 adheres to the facing electrode 12b to form a layer, and the layer of the white pigment 2 is hidden behind the black medium 1a. The panel will appear black. When the application of the voltage is stopped, once the white pigment 2 has adhered to the electrode, it is not necessary to apply the voltage except for maintaining the adhered state.

However, since the difference in specific gravity between the electrophoretic particles 2 and the solvent used for the medium is largely different, and the polarities of the surfaces thereof are also different, sedimentation and aggregation of the electrophoretic particles 2 occur, thereby deteriorating the display quality. Is inevitable.

The sedimentation and aggregation of the migrating particles have been improved by using a dispersant, a surface modifier and the like. But,
In some cases, these additives themselves may change due to aging or application of an electric field, and it is difficult to maintain a stable state.

In order to maintain the adhesion state,
If a voltage is applied periodically, power consumption increases, and a problem that an electric circuit becomes complicated occurs.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrophoretic display device which can maintain an adhered state for a long period of time and can perform stable display.

[0009]

The above object is achieved by the following constitution. (1) An electrophoretic display element having an electrophoretic medium between a pair of electrodes, in which electrophoretic particles are dispersed in the electrophoretic medium,
An electrophoretic display device comprising the swellable layered viscosity mineral in the electrophoretic medium. (2) The swellable layered viscosity mineral in the electrophoresis medium is 0.0
The electrophoretic display device according to the above (1), containing 1 to 20% by mass. (3) The electrophoretic display device according to (1) or (2), wherein the electrophoretic medium contains at least a swellable layered viscosity mineral, a dye, and an additive. (4) The electrophoretic display device according to any one of (1) to (3), wherein the swellable layered viscosity mineral is smectite. (5) The electrophoretic display element according to any one of (1) to (4), wherein the electrophoretic medium is a microcapsule or a cell in which each of the cells is sealed in an independent structure, and is disposed between the pair of electrodes. .

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrophoretic display device according to the present invention has a migration medium 1 between a pair of electrodes 12a and 12b, for example, as shown in FIG. 1, in which migration particles 2 are dispersed. An electrophoretic display element comprising a swellable layered viscosity mineral in the electrophoretic medium 1.

As described above, by including the swellable layered viscosity mineral in the electrophoretic medium 1, the electrophoretic medium 1 is given a thixotropic property. What is thixotropic?
It is a jelly-like one that maintains a jelly-like state at rest, while increasing the fluidity by applying a force to the system and behaving like a liquid. Therefore, the display particles can be held for a long period of time, and stable display can be performed.

The electrophoretic display device of the present invention can be suitably used as a flat display device or a display device having a bent flat surface.

The swellable layered clay mineral is preferably smectite. Smectite is a kind of layered silicate, as shown in FIG.
_{4 The} unit layer is a 2: 1 structure in which two tetrahedral sheets spread in a hexagonal mesh with the tetrahedron sharing the oxygen apex and the other apical oxygen faced to form an octahedral sheet of oxygen with cations interposed. This has an overlapping structure. Then, it swells in the solvent, the layered structure is broken, and it shows a colloidal property. Therefore, the ability to adsorb guest substances is high,
Further, the existing cations can easily adsorb, for example, the anions of the display particles, so that the retention characteristics are remarkably excellent.

[0014] Smectites include natural ones and industrially synthesized ones. In the present invention, either a natural product or a synthetic product may be used. However, industrially synthesized products are preferred in view of the characteristics in a solvent and the absence of impurities.

[0015] Synthetic smectite is commercially available as an industrially synthesized product. Commercially available synthetic smectites include a hydrophilic type that swells in water and collapses into a layered structure to become colloidal and viscous, and a lipophilic type that becomes colloidal and viscous in organic solvents. . As the hydrophilic type, there is a hydrophilic smectite commercially available as SWN (manufactured by Corp Chemical Co., Ltd.), but in the present invention, a lipophilic type is preferable.

The lipophilic smectite is obtained by replacing Na ions and the like in the layered structure of hydrophilic smectite with organic ions that can be solvated with a low-polarity solvent or a high-polarity solvent. Such organic ions are not particularly limited, and include, for example, quaternary ammonium having an alkyl group having about 1 to 10 carbon atoms, such as tetramethylammonium and tetraethylammonium.

By selecting an organic ion to be substituted, it can be dispersed well in various organic solvents, exhibit colloidal properties and viscosity, and have excellent properties of intercalating guest substances such as ink and its solvent. It has something. Such lipophilic smectites include SAN, STN,
Some are commercially available as SEN and SPN (both manufactured by Corp Chemical). Among these, SAN and STN, which have an affinity for many organic solvents, are preferable.

As described above, such a smectite swells in a solvent in both hydrophilicity and lipophilicity, exhibits colloidal properties, and has the property of increasing the viscosity of a solution. Upon standing, this colloid forms a bulky network structure by hydrogen bonding and exhibits elastic behavior. However, when an external force is applied thereto, the network structure is easily broken and the fluidity is exhibited because the bond is weak. For this reason, by including smectite, thixotropic properties can be imparted to the electrophoretic medium 1, the ability to retain display particles is improved, and display is stabilized.

The content of smectite is preferably 0.01 to 20% by mass of the electrophoretic medium, more preferably 0.1 to 20% by mass.
It is 15% by mass, particularly preferably 1 to 10% by mass.

The specific surface area of the smectite used is preferably from 200 to 1000 m ² / g, more preferably from 500 to 1
000 m ² / g, particularly preferably 710 to 800 m ² / g.

When observed with an optical microscope, the average major axis of smectite observed in an irregular shape is preferably 0.1 to 100 μm, more preferably 0.5 to 50 μm.
μm, particularly preferably 1 to 45 μm.

The electrophoretic particles used in the present invention are stably dispersed in the solvent of the electrophoretic medium, have a single polarity, and have a small particle size distribution. Desirable. Further, the particle size is preferably from 0.1 μm to 5 μm. Within this range, the light scattering efficiency does not decrease, and a sufficient response speed can be obtained when a voltage is applied.

Examples of the material of the migrating particles include titanium oxide, zinc oxide, zirconium oxide, iron oxide, aluminum oxide, cadmium selenide, carbon black, barium sulfate, lead chromate, zinc sulfide, cadmium sulfide, and calcium carbonate. Inorganic pigments or organic pigments such as phthalocyanine blue, phthalocyanine green, Hansa Yellow, Watching Red and Diary Ride Yellow can be used. Among them, titanium oxide is preferable in order to obtain a high contrast ratio, and rutile type is particularly preferable.

In the present invention, the solvent has a low solubility for electrophoretic particles, a high solubility for dyes and swellable layered viscosity minerals, and can stably dissolve or disperse dyes, swellable layered viscosity minerals and electrophoretic particles. And an insulating material which does not generate ions by applying a voltage is desirable.

Examples of the insulating liquid which can be used for a relatively large number of electrophoretic particle materials include saturated hydrocarbons such as hexane, decane, hexadecane and kerosene, aromatic hydrocarbons such as toluene and xylene, and trichlorotrifluoro. Examples thereof include halogenated fluorine-based hydrocarbons such as ethane, dibromotetrafluoroethane, and tetrachloroethylene, and fluorine-based solvents. Note that these liquids can be used as a mixture.

In the present invention, the mixing ratio of the electrophoretic particles in the electrophoretic medium is not particularly limited as long as the electrophoretic properties of the electrophoretic particles are not hindered and the reflection control of the electrophoretic medium can be sufficiently performed. It is preferably from 30% by mass to 30% by mass.

In the present invention, additives such as a resin and a surfactant can be added to the above-mentioned solvent as needed to increase the charge of the migrating particles or to make them the same polarity.

Examples of the dye dissolved in the electrophoretic medium include cyanine, phthalocyanine, naphthalocyanine, anthraquinone, azo, triphenylmethane, pyrylium or thiapyrylium salt, squalilium, croconium, and metal complex. One or two or more dyes may be appropriately selected depending on the purpose.

The content of such a dye is not particularly limited, and may be appropriately adjusted depending on the kind, desired color, lightness, and the like, but is preferably about 1 to 10% by mass.

In the present invention, the thickness of the electrophoretic medium layer is larger than the diameter of the electrophoretic particles, and is not particularly limited as long as the movement of the particles is not hindered. Desirably thin. From such a viewpoint, the preferable thickness of the electrophoresis medium layer is 5 μm to 2 μm.
00 μm.

As the electrode material used in the present invention, a material having good conductivity such as aluminum, copper, silver, gold and platinum is preferable. As the transparent electrode material, a thin film of tin oxide, indium oxide, copper iodide, or the like can be preferably used. Further, the electrodes can be formed by ordinary methods such as vapor deposition, sputtering, and photolithography.

In the present invention, the material and thickness of the substrate on which the electrodes are arranged are not particularly limited as long as they maintain sufficient insulation and flatness and have sufficient strength. As specific materials, glass, plastic and ceramic are preferably used. In the case where the substrate is made to have a contrasting color with the migrating particles, an appropriate dye or pigment mixed with glass, plastic, or ceramic, or a colored ceramic can be used as the substrate.

The method of arranging and enclosing the electrophoretic medium between the electrodes is not particularly limited, and various methods can be used, but it is particularly preferable to seal and arrange with a microcapsule or a cell. These microcapsules may be arranged between electrodes using an organic binder or the like.

[0034] As a method of microencapsulation, it can be prepared by a method known in the art. For example, US Patent No. 28004
No. 57, No. 2800458, etc., a phase separation method from an aqueous solution as described in JP-B-38-19574,
Interfacial polymerization methods as shown in JP-A-42-446 and JP-A-42-771, and in-situ polymerization by monomers described in JP-B-36-9168 and JP-A-51-9079. (In-situ) method, melting and dispersion cooling method disclosed in British Patent Nos. 952807 and 965074, and the like, but are not limited thereto.

The material for forming the outer wall of the microcapsule may be an inorganic substance or an organic substance, as long as the outer wall can be formed by the above-described capsule manufacturing method, but a material which sufficiently transmits light is preferable. Specific examples include gelatin, gum arabic, starch, sodium alginate, polyvinyl alcohol, polyethylene, polyamide, polyester, polyurethane, polyurea, polyurethane,
Polystyrene, nitrocellulose, ethylcellulose,
Methyl cellulose, melamine-formaldehyde resin,
Examples include urea-formaldehyde resins and the like, and copolymers thereof.

As a specific method for forming microcapsules, first, the migrating particles 2 are uniformly dispersed in a solvent. Further, this dispersion and distilled water to which a surfactant has been added are stirred and mixed to prepare an emulsion of the dispersion. The size of the dispersion emulsion is adjusted to a desired size by the stirring speed or the types and amounts of the emulsifier and the surfactant. If necessary, one or more kinds of emulsifiers, surfactants, electrolytes, lubricants, stabilizers and the like can be appropriately added.

Further, two kinds of charged particles having different color tone and charged polarity (for example, white charged particles and black charged particles) may be encapsulated in a microcapsule together with a liquid solvent by the above interfacial polymerization method.

At this time, the electrophoretic particles have a volume average particle diameter /
The degree of dispersion of the particle size distribution represented by the number average particle diameter is preferably about 2 or less.

The basic structure of the electrophoresis apparatus of the present invention is shown in FIG.
It is shown in FIG. In this electrophoretic display device, at least one of the pair of substrates 11a and 11b,
The substrates 11a and 11b and the sealing members 13a and 13b are opposed to each other with a predetermined space therebetween via a and 13b. Transparent electrodes 12a and 12b made of ITO or the like are fixed to inner surfaces of the pair of substrates 11a and 11b facing each other.

The electrophoresis medium 1 is accommodated in the closed space. The electrophoretic medium 1 is, for example, a solution in which a dye such as black is dissolved in a solvent, and includes white charged particles (electrophoretic particles, for example, white pigment) 2 dispersed in the electrophoretic medium 1.

In such an electrophoretic display element, the switch 15 is closed and the power supply 14 is connected to the pair of electrodes 12a and 12b, as shown in FIG. 2, and a positive voltage is applied to the upper electrode 12a. When a negative voltage is applied to the lower electrode 12b, the negatively charged white pigment 2 electrophoreses toward the anode by Coulomb force,
The white pigment 2 adheres to the upper anode electrode 12a. When the electrophoretic display device in such a state is observed from an upper position, the portion where the white pigment 2 adheres to form a layer appears white via the transparent electrode 12a and the glass substrate 11a.

On the other hand, if the polarity of the applied voltage is reversed, the white pigment 2 adheres to the facing electrode 12b to form a layer,
Since the layer of the white pigment 2 is hidden behind the black electrophoretic medium 1, the electrophoretic display panel will appear black.

In the present invention, even if the application of the voltage is stopped, once the white pigment 2 has adhered to the electrode, the adhered state can be maintained for a long time, for example, for about two to three months. Therefore, there is no need to apply the holding voltage again.

Although the driving voltage of the electrophoretic display device of the present invention is not particularly limited, it is usually 1 to 1 DC.
It is about 250 V, especially about 10 to 200 V.

The electrophoretic display device of the present invention can perform high-speed display, and can achieve a response speed of 0.5 seconds or less, particularly 0.1 to 0.5 seconds, depending on the applied voltage. .

The electrophoretic display device of the present invention can be used in fields such as advertisements of stores, price display boards, information boards, road signs, road information boards, thin wall clocks, electronic notebooks, electronic books, electronic newspapers, and the like. Especially effective.

[0047]

EXAMPLES Hereinafter, the present invention will be described more specifically based on experimental examples and examples. <Experimental Example 1> The development of thixotropic properties by the addition of a swellable layered viscosity mineral was evaluated.

Using trimethylbenzene as a solvent and Marialim (manufactured by Nippon Oil & Fats Co., Ltd.) as a dispersant, a sample in which only 0.5 part of a dispersant was added to a solvent and a sample in which 2.5 parts of smectite (SAN) were added , Dispersant 0.5
And a sample to which 2.5 parts of smectite (SAN) were added, and a viscosity tester (manufactured by Tokimec Co., Ltd .: Model B8)
M), the viscosity at each number of rotations was checked, and the thixotropy was judged from this. FIG. 4 shows the results.

As is apparent from FIG. 4, it is found that the sample to which smectite is added has thixotropy.

<Example 1> Trimethylbenzene (TMB): 10 g was used as a solvent (solvent), and a phthalocyanine dye [Solvent Blue] was used as a dye.
70]: 0.5 g, smectite (Corp Chemical Co., Ltd.)
2.5g, Dispersant (Mariarim)
0.5 g was dispersed and dissolved to obtain an electrophoresis medium. Further, titania (average particle size: 0.5 μm): 1 g as electrophoretic particles
Was dispersed. This electrophoretic medium was placed between the ITO transparent electrodes of the apparatus shown in FIGS. 1 and 2, and the state of the display surface between the two electrodes before, during, and after 10 minutes, 1 hour, 1 day, and 10 days after the current was applied. Observation was performed, and the contrast ratio was determined from this. FIG. 5 shows the results.

<Example 2> In Example 1, 5 g of smectite (manufactured by Corp Chemical Co., trade name: SAN) was used.
Was obtained in the same manner as in Example 1 except that was dispersed and dissolved. The contrast ratio of the obtained sample was determined and evaluated in the same manner as in Example 1. FIG. 5 shows the results.

<Example 3> In Example 1, an anthraquinone dye [Solvent Blue 136] was used as a dye.
]: A sample was obtained in the same manner as in Example 1 except that 0.5 g was used. The contrast ratio of the obtained sample was determined and evaluated in the same manner as in Example 1. Fig. 5 shows the results.
Shown in

Example 4 In Example 1, the prepared electrophoretic medium and distilled water containing 3% of an emulsifier were mixed and stirred by a stirrer to form an emulsion. During the stirring and mixing, the capsule wall material was added to obtain 100 μm microcapsules containing two kinds of charged particles and a liquid dispersion medium.

The microcapsules were dissolved and dispersed in distilled water at a weight ratio of 2: 1 with a water-soluble acrylic resin as a binder, and placed between transparent electrodes.

When the obtained display element was evaluated in the same manner as in Example 1, almost the same results were obtained. FIG. 5 shows the results.

<Comparative Example 1> 10 g of trimethylbenzene (TMB) was used as a solvent (solvent), and a phthalocyanine dye [Solvent Blue 70]: 0.5 was used as a dye.
g and a dispersant (Marialim) 0.5 g were dispersed and dissolved to prepare an electrophoretic medium. Further, 1 g of titania (average particle size: 0.5 μm) was dispersed as electrophoretic particles. This electrophoretic medium was placed between the ITO transparent electrodes of the apparatus shown in FIGS. 1 and 2, and the state of the display surface between the two electrodes before, during, and after 10 minutes, 1 hour, 1 day, and 10 days after the current was applied. Observation was performed, and the contrast ratio was determined from this. FIG. 5 shows the results.

Comparative Example 2 A sample was obtained in the same manner as in Comparative Example 1, except that 2 g of titania (average particle size: 0.5 μm) was dispersed as the migrating particles. The contrast ratio of the obtained sample was determined and evaluated in the same manner as in Comparative Example 1. FIG. 5 shows the results.

Comparative Example 3 A sample was obtained in the same manner as in Comparative Example 1, except that 1 g of titania (average particle size: 0.025 μm) was dispersed as electrophoretic particles. The contrast ratio of the obtained sample was determined and evaluated in the same manner as in Comparative Example 1. FIG. 5 shows the results.

As is clear from the above Examples and Comparative Examples, the sample of the present invention has high retention characteristics,
It can be seen that the contrast ratio of each of the samples of the comparative examples is extremely reduced after the current is applied.

[0060]

As described above, according to the present invention, it is possible to provide an electrophoretic display element capable of maintaining a sticking state for a long period of time and performing stable display.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a basic configuration of an electrophoretic display device of the present invention.

FIG. 2 is a schematic sectional view illustrating a basic configuration of an electrophoretic display device according to the present invention.

FIG. 3 is a view showing a crystal structure of smectite.

FIG. 4 is a graph showing the relationship between the viscosities of additives in Experimental Example 1.

FIG. 5 is a diagram showing the results of Examples 1 to 3 of the present invention.

FIG. 6 is a schematic sectional view showing a basic configuration of a conventional electrophoretic display device.

FIG. 7 is a schematic sectional view showing a basic configuration of a conventional electrophoretic display device.

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 Electrophoresis medium 2 Electrophoresis particles 11a, 11b Substrate 12a, 12b Electrode

Claims (5)

[Claims] 1. An electrophoretic display device having a migration medium between a pair of electrodes, wherein migration particles are dispersed in the migration medium, wherein the electrophoresis medium contains a swellable layered viscosity mineral. Display element. 2. The electrophoretic display device according to claim 1, wherein the electrophoretic medium contains 0.01 to 20% by mass of a swellable layered viscosity mineral. 3. The electrophoretic display device according to claim 1, wherein the electrophoretic medium contains at least a swellable layered viscosity mineral, a dye, and an additive. 4. The electrophoretic display device according to claim 1, wherein the swellable layered clay mineral is smectite. 5. The electrophoretic display device according to claim 1, wherein the electrophoretic medium is a microcapsule or a cell, each of which is sealed in an independent structure and arranged between the pair of electrodes.