JP2003005228A - Display device utilizing electrophoresis or rotation of particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique which reduces the driving voltage of a display device where a picture is displayed by electrophoresis or rotation of electrified particles. SOLUTION: A base material demarcates a plurality of cavities. Respective cavities of the base material are filled up with a dielectric liquid. The dielectric liquid includes a first liquid and a second liquid which are different by static charge characteristics. Particles having surface electric charge in the solid-liquid boundary are immersed in the dielectric liquid. The second liquid is electrified with the same polarity as electric charge which appears on the surfaces of particles when the particles are immersed in the first liquid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device which displays an image by utilizing electrophoresis or rotation of particles.

[0002]

2. Description of the Related Art A sheet-like display medium and a display device, which are called electronic paper, paper-like display, digital paper, etc., for displaying an image by changing an optical absorption rate or an optical reflection rate by an electric field have been proposed. . JP-A-1-86
Japanese Patent Laid-Open No. 116 discloses a display device having a microcapsule in which a solvent in which electrophoretic particles are dispersed is colored and which contains the solvent. Japanese Patent Application Laid-Open No. 8-234686 discloses a display device having a microcapsule containing a rotating body in which hemispheres having different colors and electrical characteristics are combined. In addition, a display device including a liquid crystal / polymer composite film containing a dichroic dye and a smectic liquid crystal is known.

These display devices have a memory property capable of holding image information without a power supply. Further, since the display layer can be formed on the PET film on which the electrodes are formed, it is expected as a sheet type display device which is thin, light and bendable.

The display medium described in US Pat. Nos. 4,126,854 and 4,143,103, that is, the surfaces of the charged particles, have different colors and different charging characteristics from each other. A display medium containing charged particles having two hemispherical regions shows superior contrast as compared with other systems.

Referring to FIG. 5, US Pat. No. 4,126,
The operation principle of the display medium described in the specification such as No. 854 will be described.

A plurality of voids 10 are provided inside the transparent substrate 100.
1 is formed. The void 101 is filled with charged particles 103 and filled with a translucent liquid 102. On the surface of the charged particle 103, two hemispherical regions having different colors and different charging characteristics, for example, a white region and a black region are defined. Surface charges generated at the solid-liquid interface are accumulated on the surface of the charged particles 103. Since the white area and the black area have different charging characteristics, the surface charge densities of the both are different.

Therefore, when an electric field is generated in the void 101, the charged particles 103 electrophores and rotate according to the direction of the electric field. For example, FIG. 5A shows a state in which the charged particles 103 are sunk below the void 101 with the white region facing downward. When an electric field is generated,
As shown in (B), the charged particles 103 float while rotating. Finally, as shown in FIG. 5 (C), the charged particles 103 cause the white region to face upward and the void 101.
Move to the upper part of the inside.

When the display device is viewed from above in the state of FIG. 5A, black is visually recognized. In addition, white is visually recognized in the state of FIG. In this way, the charged particles 10
It is possible to switch between white display and black display by rotating 3.

Japanese Unexamined Patent Publication No. 11-212501 discloses a method of driving a sheet type display device with a circuit having a simple matrix structure. According to this method, it is possible to shorten the image forming time and prevent the image quality from being deteriorated due to crosstalk. A method of using charged particles as a dipole electret is disclosed in Japanese Patent Application Laid-Open No. 11-327470. A dipole electret is formed by melting a wax or polymer medium wrapped in a shell and solidifying it under an electric field. As a material for charged particles,
A method using a ferroelectric material such as barium titanate or lead titanate is disclosed in JP-A-9-18687. In either method, polarization is induced in the charged particles by an electric field applied from the outside, and the polarization is maintained by the orientation of the resin and spontaneous polarization. By maintaining the polarization, the voltage (threshold voltage) at which the charged particles start to migrate in the dielectric liquid can be reduced.

Further, Japanese Patent Laid-Open No. 11-119704 discloses a display device using charged particles containing a quaternary ammonium compound in which a surfactant is added to a dielectric liquid. Accordingly, it is possible to prevent display unevenness due to aggregation of charged particles.

[0011]

In the conventional method for reducing the driving voltage, it is difficult to produce charged particles because there are many restrictions on the method and materials for producing charged particles.

In the method of forming the dipole electret, during the period when the wax or polymer medium is dissolved,
The pigment added therein precipitates, and areas of different colors are mixed. Therefore, the contrast is lowered. Further, in the method of using the ferroelectric material as the material of the charged particles, it is difficult to incorporate the pigment into the inside of the particles, so that the pigment must be deposited on the hemispherical region of the surface of the charged particles. Further, the ferroelectric material is inferior in processability to wax and resin.

In the method of adding the surfactant to the dielectric liquid, if the addition amount is small, the aggregation of the charged particles can be suppressed and the dispersion effect can be enhanced, but the charged amount of the charged particles should be increased. I can't.

An object of the present invention is to provide a technique capable of reducing the drive voltage of a display device for displaying an image by subjecting charged particles to electrophoresis or rotational movement.

[0015]

According to one aspect of the present invention, a base material that defines a plurality of cavities, and a first liquid and a first liquid that are filled inside each of the cavities of the base material and have different charging characteristics are provided. And a particle that is immersed in the dielectric liquid to generate a surface charge at a solid-liquid interface, and the second liquid contains the particles in the first liquid. Provided is a display device which is charged with the same polarity as the electric charge that appears on the surface of the particle when immersed in.

According to another aspect of the invention, a substrate defining a plurality of cavities, a dielectric liquid filled inside each of the cavities of the substrate and containing a silicone oil and a modified silicone oil, Provided is a display device having particles immersed in a dielectric liquid to generate a surface charge at a solid-liquid interface and an electrode for generating an electric field in the cavity.

By using the above-mentioned dielectric liquid, the driving voltage can be reduced. Further, it is possible to suppress sticking and aggregation of particles.

[0018]

1 is a sectional view of a display device according to a first embodiment of the present invention. A plurality of voids 11 are formed inside the sheet base material 10 having a thickness of 1 μm. As the sheet base material 10, a two-component silicone rubber (KE106 manufactured by Toray Dow Corning Co., Ltd.) was used. Charged particles 12 are loaded inside each void 11 and dielectric liquid 13
Is filled. The charged particles 12 are composed of a white hemisphere portion and a black hemisphere portion. The black hemisphere portion is formed of a polyester resin colored with carbon black, and the white hemisphere portion is formed of a polyester resin colored with titanium oxide. The particle size of the charged particles 12 is
It is about 300 μm. The surface of the hemispherical portion containing carbon black and the surface of the hemispherical portion containing titanium oxide have different charging characteristics.

Dielectric liquid 13 is dimethyl silicone oil (SH200, 10cs manufactured by Toray Dow Corning).
1% by weight of a fluorine-modified silicone oil (FS1265, 300 cs manufactured by Toray Dow Corning Co., Ltd.) was added to the mixture solution.

A transparent film 17A having a transparent electrode 15A made of indium tin oxide (ITO) is closely attached to one surface of the sheet base material 10. Similarly, the transparent film 17B on which the transparent electrode 15B made of ITO is formed is also adhered to the other surface. Transparent electrode 15
The planar shape of A and 15B is a square having a side length of 1 cm. The power supply 21 applies a drive voltage to the electrodes 15A and 15B.

Next, a method of manufacturing charged particles used in the display device according to the first embodiment will be described.

Polyester resin (softening point 100 ° C.) 27
0 parts by weight and titanium oxide (KA-30 manufactured by Titanium Industry Co., Ltd.)
30 parts by weight of S) are kneaded with a roll mill to obtain a white lump resin. Next, 294 parts by weight of polyester resin and carbon black (Regal 660 manufactured by Cabot Corporation) 6
By kneading with a part by weight with a roll mill, a black lump resin is obtained.

Each of these massive resins is heated to 120 ° C. and extruded from a nozzle having a diameter of 150 μm to obtain a fibrous resin. A white fibrous resin and a black fibrous resin are heated and adhered to each other to produce a fibrous resin whose cross section is divided into regions of two colors. This fibrous resin is
The particles are cut at a pitch of 0 μm to obtain particles divided into two colors. It is made spherical by dipping it in silicone oil (SRX310 manufactured by Toray Dow Corning Co., Ltd.) at a temperature of 100 ° C. In this way, charged particles composed of a white hemisphere and a black hemisphere are obtained. The charged polarity of the charged particles was negative.

Next, a method of manufacturing the display device shown in FIG. 1 using the charged particles will be described.

On a PET film having a thickness of 150 μm, I
By vapor-depositing the TO film, a laminated film composed of the transparent film 17A and the transparent electrode 15A and a laminated film composed of the transparent film 17B and the transparent electrode 15B are produced. A synthetic paper (manufactured by Oji Yuka Synthetic Paper Co., Ltd.) having a thickness of 80 μm is attached to the surface of one laminated film on the transparent film 17B side.

The prepared charged particles were dispersed in a two-component silicone rubber (KE106 manufactured by Toray Dow Corning Co., Ltd.) and a thickness of 500 μm was formed on a Teflon (registered trademark) sheet.
Apply evenly so that the thickness becomes m. The silicone rubber is cured in an environment of a temperature of 80 ° C. for 8 hours.

The cured silicone rubber is immersed for 12 hours in a mixture of dimethyl silicone oil and 1% by weight of fluorine-modified silicone oil. The silicone rubber swells, and voids 13 filled with a mixed liquid of silicone oil and fluorine-modified silicone oil are formed at the interface between the charged particles and the silicone rubber.

The swollen silicone rubber is sandwiched between laminated films having transparent electrodes formed thereon, and the laminated films are bonded together with a one-component silicone rubber. The process up to this point is shown in FIG.
The display device shown in FIG.

Transparent electrode 1 of the display device according to the first embodiment
When an AC voltage of 100 V was applied between 5A and 15B, it was possible to invert the white display state and the black display state every half cycle up to a frequency of 2 Hz. Even after being left at room temperature for 1 week, the charged particles did not stick to the silicone rubber and could be operated stably.

For comparison, a display device was prepared in which the fluorine-modified silicone oil was not added to the dielectric liquid filled in the voids. 20 between the transparent electrodes of this display device
A voltage of 00V was applied, but the migration of charged particles hardly occurred.

Further, instead of the fluorine-modified silicone oil, an amino-modified silicone oil showing positive polarity (BY16-853, 30 cs, manufactured by Toray Dow Corning Co., Ltd.) was added to prepare a display device. A voltage of 2000 V was applied between the transparent electrodes of this display device, but almost no movement of charged particles occurred.

From the evaluation results of this comparative example, it is considered preferable to use, as the modified silicone oil added to the silicone oil, one that is charged to the same polarity as the charged polarity of the charged particles. This is considered to be because, when the modified silicone oil is added, the chargeability of the charged particles is strengthened and the surface charge density thereof is increased, and migration and rotational movement of the charged particles occur even in a small electric field.

As the modified silicone oil exhibiting no negative polarity, chloroalkyl modified silicone oil, carboxyl modified silicone oil (BY, Toray Dow Corning Co., Ltd.
16-750, 125 cs), phenol-modified silicone oil (Toray Dow Corning BY16-752,
80 cs) and the like.

When the charge appearing on the surface of the charged particles has a positive polarity, it is possible to use amino-modified silicone oil as the modified oil added to the silicone oil.

An example of the method of determining the charging polarity will be described below. The charged particles are dispersed in silicone oil in a glass cell, and a DC electric field is applied to the cell. The charging polarity can be determined from the moving direction of the charged particles at this time. For example, if the charged particles approach the positive electrode side, it can be said that the charged particles are negatively charged.

By adding the modified silicone oil to the above silicone oil and measuring the change in the moving speed of the charged particles, the charging polarity of the added modified silicone oil can be determined. For example, it is considered that when the speed at which the charged particles approached the positive electrode side increased due to the addition of the modified silicone oil, an electrical repulsion occurred between the added oil and the charged particles. It is considered to be the same as the charging polarity. On the contrary, when the moving speed of the charged particles decreases, the charging polarity of the added oil is considered to be opposite to the charging polarity of the charged particles.

Although silicone oil was used as the dielectric liquid in the above-mentioned examples, in addition, aliphatic hydrocarbons, aromatic hydrocarbons, alicyclic hydrocarbons, halogenated hydrocarbons, various esters, various vegetable oils, Mineral oil can be used. In particular, silicone oil is suitable for use as a dielectric liquid because it is chemically stable, has no odor, and has various molecular weights and viscosities easily available.

As the additive to be added to the dielectric liquid, it is desirable that the additive has a high compatibility with the dielectric liquid, a viscosity equivalent to that of the dielectric liquid, and is chemically stable. In particular, a modified product having a dielectric liquid as a matrix and having a functional group having a strong polarity is desirable. As a modified product of silicone oil,
Examples include modified silicone oils such as fluorine-modified, chloroalkyl-modified, methylhydrogen-modified, alcohol-modified, carboxyl-modified, mercapto-modified, polyether-modified, amino-modified and epoxy-modified. The modified silicone oil is roughly classified into a side chain type, a both terminal type, a one terminal type, and a side chain both terminal type, depending on the position where the organic group is introduced, but any type of modified silicone oil may be used. The modified silicone oil is preferably added in such an amount that the insulation degree of the dielectric liquid is not extremely lowered.

In the first embodiment described above, polyester was used as the material for the charged particles.
Resins such as polystyrene, polyvinyl chloride, polypropylene, polyacetal, polycarbonate, acrylic and nylon may be used alone, or these resins may be mixed and used. Further, a copolymer of monomers forming these resins may be used. As a colorant, soluble azo pigments, monoazo pigments, disazo pigments, azo pigments, phthalocyanine pigments, quinacridone pigments, perillin pigments, perinone pigments,
A polycyclic pigment such as isoindoline, a black pigment such as carbon, and a white pigment such as titanium oxide, silica, alumina, and calcium carbonate can be used. The resin to which the pigment is added can be made into particles by a known method such as injection molding, blow molding, extrusion molding, calendar molding and the like.

In the first embodiment, the silicone rubber is swollen with the silicone oil to form the voids filled with the dielectric liquid at the interface between the charged particles and the sheet base material. It is also possible to manufacture a display device having a similar structure. For example, a method in which charged particles are coated with a toluene-soluble resin, dispersed in polyvinyl alcohol, cured and then immersed in toluene is described in "A.
Newly Developed Electrical Twisting Ball Display ''
(M. Saitoh et al .: Proc. Of SID, Vol.23 / 4, 1982)
Is disclosed in. Japanese Patent Application No. 7-343133 discloses a method of forming a microcapsule by covering a dielectric liquid and charged particles with a resin film by utilizing interfacial polymerization, and dispersing the microcapsule in a sheet base material. Has been done.

In the first embodiment, the pair of transparent electrodes are made of ITO. However, one electrode (electrode on the display surface side) may be made transparent and the other electrode may be made opaque. As the electrode material, a metal, a conductive polymer, a resin in which a conductive powder is dispersed, or the like can be used. Examples of metals include gold, silver, copper, iron and the like.

Examples of conductive polymers include polyacetylene-based polymers, polyphenylene-based polymers, heterocyclic polymers, ionic polymers and ladder-like polymers. Specific examples of the polyacetylene-based polymer include polyacetylene and poly (1,6-heptadiyne). Specific examples of the polyphenylene-based polymer include polyparaphenylene,
Examples thereof include polymetaphenylene, polyphenylene vinylene, polyphenylene oxide, polyphenylene sulfide, polypyrene, polyazulene and polyorfurene. Examples of the heterocyclic polymer include polypyrrole, polythiophene, polyselenophene, polytellurophene, polythienylene vinylene, and the like. Specific examples of the ionic polymer include polyanilene and the like. Examples of the ladder-like polymer include polyacene, polyphenanthrene, polyperinauterene, and the like.

Examples of the conductive powder dispersed in the resin include metals such as gold, silver, copper and iron, graphite and the like. It is also possible to use ITO powder having high transparency and conductivity. As a binder resin for dispersing ITO powder,
Polyesters, epoxies, silicones, polyvinyl acetals, polycarbonates, acrylics, urethanes, etc. can be used alone or in combination with these resins.

The thickness of the conductive resin film is 0.1 to 2 in order to make the display device thin and to reduce the change in color tone.
It is preferably 0 μm.

Further, it is preferable to provide a protective film made of resin on the electrode on the display surface side. This protective film can be formed, for example, by applying a solution of a known dielectric resin diluted with a solvent onto the electrode and drying it. As the dielectric resin used for the protective film, polyester, epoxy, silicone, polyvinyl acetal, polycarbonate,
Acrylic, urethane, etc. are mentioned. The thickness of the protective film is
In order to reduce the influence on the total thickness of the display device, 0.1
It is preferable that the thickness be ˜20 μm.

Next, a display device according to a second embodiment of the present invention will be described with reference to FIGS.

FIG. 2 shows a sectional view of a display device according to the second embodiment. One transparent electrode 15B shown in FIG. 1 is divided into a plurality of pixel electrodes. The diameter of the charged particles 12 is not larger than the size of one pixel. The DC power supply 25 applies a positive voltage to the transparent electrode 15A. The drive circuit 20
Based on a control signal from the control circuit 22, a signal voltage is selectively applied to a specific electrode of the plurality of pixel electrodes 15B.

3A and 3B are plan views of the pixel electrode 15B and the transparent electrode 15A, respectively. A plurality of pixel electrodes 15B are arranged in a matrix. Each pixel electrode 1
The wiring 18 is connected to 5B. The wiring 18 extends between the pixel columns and reaches an external connection terminal provided near the edge of the display device. A plurality of pixel electrodes 1 via wiring 18
Image display can be performed by selectively applying a signal voltage to 5B.

FIG. 3C shows another example of the structure of the transparent electrode. One transparent electrode 15C may be a plurality of linear electrodes extending in the column direction, and the other transparent electrode 15D may be a plurality of linear electrodes extending in the row direction. By applying a voltage between the specific electrodes 15C and 15D, an electric field can be generated at the intersection.

In the first and second embodiments, an electric field is generated in the space where the charged particles 12 are arranged by applying a voltage to the pair of electrodes 15A and 15B, but the electric field is separated from the display layer. It is also possible to write using a drive device for writing. For example, by using a writing device equipped with a small battery, a wireless communication unit, a one-dimensional electrode array, and a driver for driving the same, by scanning the display layer while applying a signal voltage to each electrode of the electrode array, writing is performed. It can be performed. Writing can also be performed by tracing the surface of the display layer using a pen-shaped writing device having a single electrode at the tip.

Next, a display device according to the third embodiment of the present invention will be described with reference to FIG. In the first and second embodiments described above, one charged particle is loaded in one void, but in the third embodiment, Japanese Patent Laid-Open No. 11-119.
As disclosed in Japanese Patent No. 704, a large number of charged particles are loaded in one microcapsule.

FIG. 4 shows a sectional view of a display device according to the third embodiment. A pair of transparent substrates 30 and 31 made of a glass plate or a plastic sheet are arranged to face each other with a predetermined gap. A large number of microcapsules 32 are arranged in this gap. Inside each of the microcapsules 32, a colored dielectric liquid 33 and a large number of charged particles 34 are contained. Such microcapsules can be produced by a method that has already become a known technique. For example, a method of phase separation from an aqueous solution as disclosed in the specifications of US Pat. Nos. 2,800,457 and 2,800,458, JP-B-38-19574, JP-B-42-446, and JP-B-42-771. It can be produced using an interfacial polymerization method as disclosed in the publication.

A striped transparent electrode 3 is formed on the inner surface of the transparent substrate 30.
5 is formed, and a striped transparent electrode 36 is also formed on the inner surface of the other transparent substrate 31. Transparent electrode 3
5 and 36 are orthogonal to each other and are driven by a simple matrix. Note that FIG. 4 shows a state in which only the transparent substrate 31 is rotated by 90 degrees for convenience of description. Ideally, the microcapsules 32 are spread in a single layer so that the microcapsules are in the closest packed state, and are fixed between the substrates by a fixing agent 38 such as an ultraviolet curable adhesive.

The colored dielectric liquid 33 is obtained by adding modified silicone oil to silicone oil. The added modified silicone oil is charged to the same polarity as the charged particles 34. Electrodes 35 and 3
By applying a voltage between 6 and 6, charged particles can be electrophoresed and unevenly distributed on the electrode 35 side or the electrode 36 side. When the microcapsules 32 in which the charged particles 34 are unevenly distributed on the electrode 36 side are viewed from the surface on the electrode 36 side,
The color of the charged particles 34 is visually recognized. On the contrary, when the charged particles 34 are unevenly distributed on the electrode 35 side, the color of the dielectric liquid 33 is visually recognized. By adding the modified silicone oil, it is possible to prevent the charged particles 34 from sticking or aggregating.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example, it will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0056]

As described above, according to the present invention,
The driving voltage of the display device that displays an image can be lowered by subjecting the charged particles to electrophoresis or rotational movement.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a display device according to a first exemplary embodiment of the present invention.

FIG. 2 is a sectional view of a display device according to a second embodiment of the present invention.

FIG. 3 is a plan view showing an electrode arrangement of a display device according to a second embodiment of the present invention.

FIG. 4 is a sectional view of a display device according to a third embodiment of the present invention.

FIG. 5 is a cross-sectional view of charged particles and voids for explaining the rotating operation of the charged particles.

[Explanation of symbols]

10 Sheet base material 11 void 12 charged particles 13 Dielectric liquid 15A, 15B transparent electrode 17A, 17B transparent film 21 power supply 22 Control device 25 DC power supply 30, 31 Transparent substrate 32 microcapsules 33 Dielectric liquid 34 charged particles 35, 36 transparent electrode

Claims (5)

[Claims] 1. A base material defining a plurality of cavities; a dielectric liquid filled in each of the cavities of the base material and containing a first liquid and a second liquid having different charging characteristics; Particles which are immersed in a dielectric liquid and generate a surface charge at a solid-liquid interface, and the second liquid is a charge that appears on the surface of the particles when the particles are immersed in the first liquid. A display device that is charged with the same polarity as that of. 2. The display device according to claim 1, further comprising an electrode for generating an electric field in the cavity. 3. A plurality of the particles are filled inside each of the cavities, and when an electric field is generated in the cavities, the particles electrophorese in the dielectric liquid, The display device according to claim 1 or 2, wherein the display is performed by being unevenly distributed. 4. The particles include at least two portions that differ from each other in both color and charging characteristics, and when an electric field is generated in the cavity, the particles rotate and change the orientation of the particles. The display device according to claim 1, wherein the display is performed by the display device. 5. A substrate defining a plurality of cavities, a dielectric liquid filled within each of the cavities of the substrate and containing a silicone oil and a modified silicone oil, and immersed in the dielectric liquid. A display device having particles that generate a surface charge at a solid-liquid interface, and an electrode for generating an electric field in the cavity.