JP2010048948A - Image display medium and image display - Google Patents

Abstract

An image display medium and an image display device having an excellent display switching speed are provided by increasing the charging speed of the entire device and improving the initial response to the electric field of migrating particles.
A cell or capsule in which a fine particle dispersion composed of at least a nonpolar solvent and particles is divided into a plurality of compartments between two electrode substrates disposed at a desired interval and at least one of which is light transmissive. In an image display medium in which a display layer enclosed in a substrate is sandwiched and a display operation is performed by electrophoresis of the fine particles by applying a voltage between the two electrode substrates, the display layer and at least one electrode substrate And a resin thin film layer having a capacitance larger than that of the display layer.
[Selection] Figure 1

Description

  The present invention is based on the principle of electrophoresis, an image display medium that switches between a display state and a non-display state of an image by moving charged white or colored particles in the direction of an electric field, and an image including the image display medium The present invention relates to a display device.

  Conventionally, a CRT or a liquid crystal display is used as a terminal for displaying so-called images such as characters, still images, and moving images. They can display and rewrite digital data instantly, but it is difficult to always carry the device around, and it has many drawbacks such as eye fatigue when working for a long time and display when turning off the power. is there. On the other hand, when a character or a still image is distributed or stored as a document, it is recorded on a paper medium by a printer. This paper medium is widely used as a so-called hard copy. Hard copy is easier to read than display, less fatigue, and can be read freely. Furthermore, it has the characteristics that it is lightweight and can be carried freely. However, the hard copy is discarded and recycled after it is used. However, since the recycling requires a lot of labor and cost, there remains a problem in terms of resource saving.

  There is a great need for a rewritable and paper-like display medium that has the advantages of both the above-mentioned display and hard copy. So far, polymer-dispersed liquid crystals, bistable cholesteric liquid crystals, electrochromic devices, and electrophoretic devices A display medium using the above has been proposed, and has attracted attention as a display medium that can display brightly in a reflective display type and has a memory property. Among them, an electrophoretic element (electrophoretic display medium) is excellent in terms of display quality and power consumption during display operation, and is disclosed in, for example, Patent Documents 1 and 2.

  In the electrophoretic display medium, a dispersion liquid in which a plurality of electrophoretic particles having a color different from the color of the dispersion medium is dispersed in a colored dispersion medium is enclosed between a pair of transparent electrodes. In this case, the electrophoretic particles (also simply referred to as “electrophoretic particles”) are charged on the surface in the dispersion medium, and the particles can be moved by forming an electric field between the transparent electrodes. For example, when a charge opposite to the charge of the electrophoretic particles is applied to one of the transparent electrodes, the electrophoretic particles are attracted to the electrode and deposited near the electrode, and the color of the electrophoretic particles is observed. Conversely, when the same charge as that of the electrophoretic particles is applied, the electrophoretic particles move to the opposite side, and thus the color of the dispersion medium is observed. By changing the charge on the electrode surface in this way, various displays can be performed by applying the principle of changing the observed color.

At this time, the moving speed of the migrating particles is governed by the strength of the electric field applied to the migrating particles in addition to the charge amount of the particles. That is, generally, unless the dispersion medium causes dielectric breakdown, the migration speed of particles increases as the electric field strength increases. This electric field strength is caused by a potential difference when an external voltage is applied between the electrode substrates, but an electric field is not actually generated immediately after the initial voltage application, and the dispersion medium, which is an insulating liquid, is completely charged. It happens for the first time.
Therefore, if the time for completing the charging of the dispersion medium is slow, the time for starting the migration of the electrophoretic particles is delayed, and in particular, the time required for completing the charging is not short in the particle dispersion used for electrophoretic display so far. There was a problem that the display switching speed of was slow.

As a means for improving the display characteristics, there is a method by improving the material design on the side of the migrating particle, such as controlling the charge amount. However, as a more effective method, the display medium can be applied with a good electric field applied to the migrating particle. A method for improving the layer structure is mentioned. As an example, there is an electrophoretic display in which one electrode layer is provided with an adhesive layer containing a high dielectric polymer or oligomer and a radiation curable composition, and the dielectric constant of the adhesive layer is defined (see Patent Document 1). Also, as such an adhesive layer, an adhesive material having a volume resistivity in the range of 10 ⁹ to about 10 ¹¹ Ωcm, and having a volume resistivity of at least 5 × 10 ¹¹ Ωcm, and a volume of about 10 ⁷ Ωcm or more. An example including a mixture of fillers having resistivity is also given (see Patent Document 2).

  These are all characterized by the adhesive used when the display layer containing the display material and the electrode substrate are bonded together, but it is difficult to select a material that has both adhesive properties and the above-mentioned electrical properties. . Particularly in the case of bonding display media, it is not preferable to apply a solvent-based material as an adhesive, and since it is substantially limited to a thermosetting or chemically reactive material, the range of material selection is further increased. It is narrowed.

JP 2006-517038 A JP-T-2004-535599

  An object of the present invention is to provide an image display medium and an image display device that are excellent in display switching speed by increasing the charging speed of the entire device and improving the initial response to the electric field of the migrating particles in light of the above-described conventional problems. It is to be.

In order to solve the above problems, the image display medium and the image display device according to the present invention specifically have the technical features described in the following (1) to (7).
(1) In the invention described in claim 1, a plurality of fine particle dispersions composed of at least a nonpolar solvent and particles are provided between two electrode substrates which are arranged at a desired interval and at least one of which is light transmissive. In an image display medium in which a display layer enclosed in a partitioned cell or capsule is sandwiched and a display operation is performed by electrophoresis of the fine particles by applying a voltage between the two electrode substrates. An image display medium, wherein a resin thin film layer is disposed between a display layer and at least one of the electrode substrates, and a capacitance of the resin thin film layer is larger than a capacitance of the display layer .
(2) The invention according to claim ² is the image display medium according to claim 1, wherein the display layer has a capacitance of 1 to 1000 μF / m ² .
(3) In the invention described in claim 3, the difference between the capacitance of the resin thin film layer and the capacitance of the display layer is 100 μF / m ² or less. This is an image display medium.
(4) The image display medium according to claim 1, wherein the resin thin film layer comprises at least a cellulose derivative.
(5) The image display according to claim 1 or 4, wherein the resistance value in the film thickness direction of the resin thin film layer is 1 × 10 ¹¹ Ω or less per 1 cm ^2. It is a medium.
(6) According to the invention described in claim 6, the volume resistivity of the constituent material of the resin thin film layer is 1 × 10 ¹⁴ Ω · cm or less, and the image according to claim 1, 4 or 5 It is a display medium.
(7) The invention according to claim 7 is directed to the image display medium according to any one of claims 1 to 4, information input means for supplying image information to the image display medium, the image display medium, and the information input means. An image display device comprising power supply means for supplying power.

  According to the present invention, the resin thin film layer is disposed between the display layer and at least one of the electrode substrates, and the capacitance of the resin thin film layer is made larger than the capacitance of the display layer. The initial responsiveness of the particles to the electric field can be improved, thereby providing an image display medium and an image display device having an excellent display switching speed.

  The best mode for carrying out the present invention will be described with reference to the drawings as necessary. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of a preferred embodiment of the present invention, and does not limit the scope of the claims.

(First embodiment)
A first embodiment of the present invention will be described based on a schematic diagram of an image display medium shown in FIG.
In FIG. 1, reference numerals 1 and 2 denote electrodes made of a conductive layer, and at least one of them is light transmissive. As an electrode, a metal such as Al, Ag, Ni, Cu, or a transparent conductor such as ITO, SnO ₂ , ZnO: Al is formed into a thin film by sputtering, vacuum deposition, CVD, coating, etc. Or what mixed and apply | coated the electrically conductive agent with the solvent or the synthetic resin binder is used. Conductive agents include cationic polyelectrolytes such as polymethylbenzyltrimethyl chloride and polyallylpolymethylammonium chloride, anionic polyelectrolytes such as polystyrene sulfonate and polyacrylate, and electronically conductive zinc oxide and tin oxide. Indium oxide fine powder or the like is used.

  The conductive layer itself may be thick enough to have a self-supporting function, or the conductive layer may be provided on a substrate having a self-supporting function (not shown), which can be preferably used in either case. Note that at least one of the substrates having the self-supporting function is light transmissive. In addition, the conductive layers 1 and 2 may be layers showing anisotropic conductivity, or may be layers having a pattern or a multi-dot segment in which a conductive portion penetrates in the thickness direction. In any case, if a power supply electrode is brought into contact with a part of the conductive layers 1 and 2, an electric field can be generated between the conductive layers 1 and 2, so that white or colored particles can move reliably. For this reason, voltage display means between the conductive layers 1 and 2 may be prepared for display.

  In FIG. 1, 3 is a microcapsule containing an electrophoretic particle dispersion. The microcapsule is not an essential requirement of the present invention, and a particle dispersion described later may be enclosed in a cell provided with fine partition walls by photolithography or the like. In any case, it is preferable that the two electrode substrates are separated by a large number of fine cells because it is possible to prevent the deviation of particles due to gravity and the aggregation of particles. As a method for producing the microcapsules, a known method such as a coacervation method or a phase separation method can be used and is not particularly limited.

  In FIG. 1, 4 inside the microcapsule 3 is colored electrophoretic particles, and 5 is white electrophoretic particles, and the electrophoretic particles 4 and 5 have different charging polarities. In FIG. 1, 7 is a dispersion medium, and it is preferable that it is colorless and transparent because it does not adversely affect the contrast of the image based on the color difference between the white or colored electrophoretic particles 4 and 5.

  The dispersion medium 7 is preferably a nonpolar organic solvent having particularly high electrical insulation. Examples of such nonpolar organic solvents include paraffinic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, and dodecane, isoparaffinic hydrocarbons such as isohexane, isooctane, and isododecane, and alkylnaphthene hydrocarbons such as liquid paraffin. , Aromatic hydrocarbons such as benzene, toluene, xylene, alkylbenzene, solvent naphtha, silicone oils such as dimethyl silicone oil, phenylmethyl silicone oil, dialkyl silicone oil, alkylphenyl silicone oil, cyclic polydialkylsiloxane or cyclic polyalkylphenylsiloxane Etc. In order to control the dispersibility of the dispersed particles (electrophoretic particles 4, 5), a dispersant or the like may be further added to the dispersion medium 7 as necessary.

  A dispersant is a compound that is soluble in a solvent in a particle dispersion and adsorbs to the particles when present, and prevents aggregation between particles due to electrostatic repulsion or steric effects of dispersant molecules. is there. As the particle dispersant that can be used in the present embodiment, among the surfactants used as known particle dispersants, those having a reactive group, preferably a polymer-based dispersant. The group having reactivity may be the same as or different from the group having adsorptivity to particles. In addition, in the case where a plurality of groups having an adsorptivity to particles are included in the molecule, a portion that does not contribute to the adsorption to the particles may be modified with a group having another reactivity. For example, when the group having an adsorptive property to the particles is an amino group, a part of the group can be treated with a compound having a halogen group and a vinyl group, and the amino group and the halogen group can be reacted to modify the part into a vinyl group. . Examples of such a dispersant include commercially available modified polyurethane polymer dispersants and polyacrylate polymer dispersants. When the particle dispersant is added, the amount is suitably about 0.1 to 5 parts by weight with respect to 100 parts by weight of the dispersion medium.

As an example of the white electrophoretic particles 5 constituting the particle dispersion, solid particles of metal oxides such as silicon dioxide, aluminum oxide, and titanium oxide can be used.
As an example of the colored electrophoretic particles 4, for example, carbon black, aniline black, furnace black, lamp black, or the like can be used as the black colored particles. Examples of cyan colored particles include phthalocyanine blue, methylene blue, Victoria blue, methyl violet, aniline blue, and ultramarine blue. As magenta colored particles, for example, rhodamine 6G lake, dimethylquinacridone, watching red, rose bengal, rhodamine B, alizarin lake and the like can be used. As yellow colored particles, for example, chrome yellow, benzidine yellow, hansa yellow, naphthol yellow, molybdenum orange, quinoline yellow, tartrazine and the like can be used.

The surfaces of the colored or white particles 4 and 5 are preferably provided with a graft chain of a polymer component that is compatible with the dispersion medium for the purpose of improving the dispersion stability in the dispersion medium. In order to form the polymer component on the particle surface, a functional group contributing to the polymerization reaction may be added to the surface of the white or colored particle, and a known method can be used. In the case of particles having a metal oxide surface such as titanium oxide, it is preferable to treat with a coupling agent having a functional group that contributes to the polymerization reaction. For example, when a vinyl group is imparted to the surface, it may be reacted with a silane coupling agent having a vinyl group such as 3- (trimethoxysilyl) propyl methacrylate. In addition, when the particles are carbon black, it is known that a vinyl group can be imparted to the carbon black surface by reacting with, for example, vinyl aniline. Electrophoretic particles in which a polymer component is grafted are obtained by graft polymerization reaction of particles and functional groups that contribute to the polymerization reaction. Alternatively, as disclosed in Japanese Patent Application Laid-Open No. 2005-265938, a monomer is added in a state where colored or white particles are dispersed in a non-polar solvent. A polymer layer having a high part can also be formed.
The preferred particle size of the colored or white particles 4 and 5 in the present invention is 50 nm to 10 μm. Particularly preferred as the white electrophoretic particles is 200 nm to 1 μm (below, the light scattering ability is reduced to change from white to transparent, and above that, the electrophoretic speed or the dispersion stability in the dispersion medium is reduced). is there.

  The mass ratio of the electrophoretic particles in the electrophoretic particle dispersion is appropriately set so as to obtain a desired concentration of color, but about 1 to 50 mass% is appropriate. These components are added to a nonpolar solvent and mixed and dispersed to obtain a particle dispersion. In this case, a known dispersing means such as a homogenizer, a ball mill, a sand mill, or an attritor may be used as the dispersing means. Using this electrophoretic particle dispersion, microcapsules are prepared by a known method such as a coacervation method or a phase separation method.

  The particle size of the microcapsules is preferably 5 to 200 μm, more preferably 10 to 100 μm. When the particle size of the microcapsules is in the above range, clear image display characteristics can be obtained when applied to an image display medium. The thickness of the capsule wall made of the microcapsule substrate is preferably about 0.1 to 2 μm, more preferably about 0.2 to 1 μm. When the capsule wall thickness is in the above range, there is an advantage that both mechanical strength and clear image display characteristics can be achieved when applied to an image display medium.

In FIG. 1, 6 is a binder layer, and holds microcapsules in a thin layer shape. Although any known material capable of forming a coating film on the conductive layer can be used for the binder layer 6, it is preferably transparent and can be dispersed without agglomerating the microcapsules. Examples of such materials include water-soluble urethane resins and acrylic resins.
In FIG. 1, 8A is a resin thin film layer. The capacitance of the resin thin film layer is larger than the capacitance of the display layer 10. The resin used for the resin thin film layer may be any resin that is soluble in an arbitrary solvent, and it is preferable that a coating film can be formed on the electrode or the display layer. The thickness of the resin thin film layer 8A depends on the relative dielectric constant of the resin, but is suitably 0.1 to 5 μm, and preferably 1 to 2.5 μm.

  In order to manufacture the image display medium in the present embodiment (FIG. 1), the mixture obtained by mixing the particle dispersion-containing microcapsule 3 obtained above and the resin that becomes the binder layer 6 is applied to the electrode 1 for display. Layer 10 is formed. Next, a resin thin film layer 8A is formed by applying a resin solution. Finally, the adhesive layer 9 is formed on the resin thin film layer 8A or the counter electrode 2, and these are bonded together to produce the image display medium of the present invention. In addition, when forming said layer by application | coating, well-known coating-film formation methods, such as a blade, a wire bar, dipping, a spin coat, can be used as a method, and it does not specifically limit. Any known material can be used as the material for forming the adhesive layer 9, but it is preferably transparent and excellent in electrical insulation. A solvent-free curable material is particularly preferable. Examples of such a material include a photocurable epoxy resin, a urethane resin, and an acrylic resin.

  Another embodiment of the present invention is shown in FIG. In FIG. 2, 8B is a resin thin film layer. Unlike the embodiment shown in FIG. 1, the resin thin film layer 8 </ b> B is disposed not between the display layer 3 and the adhesive layer but between the display layer 10 and the electrode 1. Even in this case, the same effect as in the above embodiment is obtained. For the resin thin film layer 8B, the same material as the resin thin film layer 8A in the above embodiment can be used.

  In order to manufacture the image display medium in the present embodiment (FIG. 2), the resin thin film layer 8B is formed by applying a resin solution to the electrode 1. The thickness of the resin thin film layer 8B depends on the relative dielectric constant of the resin as with the resin thin film layer 8A, but is suitably 0.1 to 5 μm, preferably 1 to 2.5 μm. Subsequently, the display layer 10 is formed by applying a mixture obtained by mixing the particle dispersion-containing microcapsules 3 obtained above and the resin that becomes the binder layer 6. Finally, the adhesive layer 9 is formed on the display layer 10 or the counter electrode 2, and these are bonded together to produce the image display medium of the present invention. Even when the above layer is formed by coating, a known coating film forming method such as blade, wire bar, dipping, or spin coating can be used as the method, and the method is not particularly limited. Moreover, the material which forms the contact bonding layer 9 can also be the same as the above, such as a photocurable epoxy resin, urethane resin, and acrylic resin.

In the image display medium in the present embodiment (FIGS. 1 and 2), the capacitance (D ₈ ) of the resin thin film layer is larger than the capacitance (D ₁₀ ) of the display layer (D ₈ > D ₁₀ ) Requirement. Such a requirement can be obtained by controlling the thickness of the resin thin film layer with respect to the known capacitance of the display layer.

In the present invention, the capacitance (D ₁₀ ) of the display layer is suitably about 1 to 1000 μF / m ² . If the value of (D ₁₀ ) is less than 1 μF / m ² , it is difficult to supply charges necessary for particle migration, and display switching becomes difficult. If it is greater than 1000 μF / m ² , it is excessive for display switching. Power is required.
The difference (D ₈ -D ₁₀ ) between the capacitance (D ₈ ) of the resin thin film layer and the capacitance (D ₁₀ ) of the display layer is preferably 0 to 100 μF / m ² , The time until the migration of the electrophoretic particles is further shortened.

If the capacitance of the resin thin film layer (D ₈ ) ≦ the capacitance of the display layer (D ₁₀ ), the charging of the resin thin film layer is completed before the charging of the display layer is completed. As a result, there is a problem that complete display switching cannot be performed. On the other hand, when the electrostatic capacity of the resin thin film layer> the electrostatic capacity of the display layer, the dispersion medium 7 is charged from voltage application because the charging current flows through the display layer at the same time as charging the resin thin film layer instantaneously. The time until the migration is short and the migration time of the migrating particles is fast, and as a result, an image is formed immediately after the image display medium is turned on.

  The capacitance of the resin thin film layers 8A and 8B can be obtained by measuring the capacitance of a single resin film having the same thickness.

(Second Embodiment)
In the second embodiment of the present invention, the resin thin film layer is preferably made of a cellulose derivative. Cellulose derivatives are suitable as the resin thin film layer of the present invention because they have a relatively high relative dielectric constant among polymers and a low volume resistivity. Moreover, the film-forming property from the coating film obtained by apply | coating a solution is also good. Accordingly, when the resin thin film layer is quickly charged simultaneously with the application of the external voltage, the electrophoretic particles also immediately respond and migrate. Examples of such cellulose derivatives include methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, ethylhydroxyethylcellulose, hydroxypropylmethylcellulose, diethylaminoethylcellulose, triethylammoniumcellulose, 4-aminobenzylcellulose, cellulose acetate, cellulose triacetate, and cellulose acetate butyrate. , Cellulose propionate, sodium carboxymethylcellulose, sodium dicarboxycellulose, sodium cellulose glycolate, sodium cellulose sulfate, cyanoethyl cellulose, hydroxypropyl methylcellulose phthalate, cellulose hydrogen phthalate, cellulose hydroxyapatite, and the like.

(Third embodiment)
In the third embodiment of the present invention, the resin thin film layers 8A and 8B have a resistance in the film thickness direction of 1 × 10 ¹¹ Ω or less per 1 cm ² . If it is 1 × 10 ¹¹ Ω or more per 1 cm ^{2, a} large amount of voltage is distributed to the resin thin film layer, and no voltage is applied to the display layer. Therefore, display switching becomes difficult.

(Fourth embodiment)
In the fourth embodiment of the present invention, the volume resistivity of the constituent material of the resin thin film layers 8A and 8B is 1 × 10 ¹⁴ Ω · cm or less. By being 1 × 10 ¹⁴ Ω · cm or less, a thin film having a certain thickness can be formed without increasing the resistance in the thickness direction. When the volume resistivity exceeds 1 × 10 ¹⁴ Ω · cm, the film thickness of the resin thin film layer must be reduced in order to reduce the resistance in the film thickness direction, but such a thin film is uniformly formed in the plane. It is difficult to do.

(Fifth embodiment)
The image display device of the present invention will be described as a fifth embodiment with reference to FIG. As shown in FIG. 3, the image display device 11 of the present invention includes an image display medium 12, and includes an information input means 14, a drive circuit (not shown), an arithmetic circuit, an internal memory, a power supply means, and the like. The electrodes in the display medium form a dot matrix and display an image as a whole by displaying ON a specified dot. In FIG. 3, 13 is a housing. The power supply means may be provided with internal power such as a battery or a power receiving device such as an outlet receiving power from an external power source.

  The invention is explained in more detail by means of examples. However, the present invention is not limited to the following examples. In addition, in description of an Example and a comparative example, unless otherwise indicated, a part,%, etc. are a mass reference | standard.

[Example 1]
(Preparation of white electrophoretic particles)
A mixed solvent of 93 parts of ethanol and 7 parts of water was prepared in a reaction vessel equipped with a stirrer, and the pH was adjusted to 4.5 with glacial acetic acid. After dissolving 16 parts of 3- (trimethoxysilyl) propyl methacrylate, 100 parts of titanium oxide was added and stirring was continued for 10 minutes. Next, 180 parts of ethanol was added and stirred, and the solid content recovered by centrifugation was left to stand for one day and then vacuum dried at 70 ° C. for 4 hours to obtain surface-treated titanium oxide.
Subsequently, 130 parts of toluene was prepared in a reaction vessel equipped with a stirrer, a thermometer, and a reflux condenser, and 100 parts of lauryl methacrylate was dissolved. To this was added 75 parts of the above surface-treated titanium oxide and 50 parts of toluene in which 0.5 part of azobisisobutyronitrile was dissolved, and the mixture was heated and stirred at 70 ° C. for 6 hours in a nitrogen atmosphere. After completion of the reaction, the solid was repeatedly centrifuged and washed with toluene, and finally dried in vacuo at 70 ° C. for 4 hours to obtain the desired white electrophoretic particles.

(Preparation of black electrophoretic particles)
The black electrophoretic particles in this example were prepared based on the composite particle manufacturing method described in JP-A-2005-265938.
That is, 14 parts of methacryloxypropyl modified silicone (manufactured by Chisso Corporation, Silaplane FM-0711), 6 parts of dimethylaminoethyl methacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.), azobisdimethylvaleronitrile 0.1 which is a polymerization initiator The solution which melt | dissolved the part in 180 parts of silicone oil (the Shin-Etsu Chemical Co., Ltd. make, KF-96L 1cs) was accommodated, and it heated at 60 degreeC under nitrogen atmosphere for 6 hours. After completion of the reaction, the silicone oil was removed by evaporation to obtain a uniform and transparent resin.
In a reaction vessel equipped with a stirrer, a thermometer, and a reflux condenser, 1 part of the dispersant, 1.5 parts of carbon black, and 200 parts of silicone oil were combined and ultrasonically irradiated with a homogenizer for 1 hour while cooling with ice. Dispersed black. This is 6 parts of methyl methacrylate, 3 parts of methacryloxypropyl modified silicone (manufactured by Chisso Corporation, Silaplane FM-0725 molecular weight of about 10,000), 0.1 part of N, N-dimethylaminopropylacrylamide, and a polymerization initiator. 0.05 part of azobisdimethylvaleronitrile was added and reacted at 60 ° C. for 6 hours. After completion of the reaction, only the solid component was recovered and dried to prepare the desired black electrophoretic particles.

(Production and operation of image display medium)
A solution prepared by dissolving 10 parts of urea, 1 part of resorcinol and 10 parts of ethylene-maleic anhydride copolymer in 290 parts of water was adjusted to pH 3.5 with an aqueous sodium hydroxide solution. Separately, 15 parts of the white electrophoretic particles, 0.7 part of the black electrophoretic particles, and 20 parts of the oil-soluble surfactant (Solsperse 17000, Lubrizol Co., Ltd.) One part was added and ultrasonically dispersed to prepare a particle dispersion. This dispersion was added to the above aqueous solution, and further 25 parts of a formaldehyde solution was added and stirred at 50 ° C. for 3 hours. After completion of the reaction, the microcapsules were collected by suction filtration, washing with water and drying.
The obtained microcapsules were dispersed in a urethane resin and applied with a wire bar on a glass substrate with an ITO electrode to form a display layer. Next, a coating solution in which 5 parts of cellulose acetate (volume resistivity: 1 × 10 ¹² Ω · cm) is dissolved in 95 parts of ethyl lactate is dropped onto this, and a 1 μm-thick resin thin film layer (thickness direction: 1 cm) is applied by spin coating. Resistance per ² : 1 × 10 ⁸ Ω). Further, an image display medium was prepared by laminating and bonding with another ITO electrode using an adhesive for heat sealing.
In this image display medium, the capacitance of the resin thin film layer was 50 μF / m ² , and the capacitance of the display layer was 25 μF / m ² .
When -10V is applied to the upper ITO electrode with reference to the lower ITO electrode, the white electrophoretic particles quickly move to the lower electrode side, and the black electrophoretic particles quickly move to the upper electrode side. It looked black when seen. Next, when +10 V was applied to the upper ITO electrode, the white electrophoretic particles quickly moved to the upper electrode side, the black electrophoretic particles quickly moved to the lower electrode side, and looked white when viewed from the upper electrode side. FIG. 4 shows the change in light reflectance when changing from black to white.

[Example 2]
(Production and operation of image display medium)
A coating solution in which 5 parts of cellulose acetate (volume resistivity: 1 × 10 ¹² Ω · cm) is dissolved in 95 parts of ethyl lactate is dropped on a glass substrate with an ITO electrode, and a 1 μm-thick resin thin film layer (film thickness) is formed by spin coating. Resistance value per 1 cm ^{2 in the} direction: 1 × 10 ⁸ Ω) was formed. Next, the microcapsules in Example 1 were dispersed in a urethane resin and applied on the ethyl lactate layer with a wire bar. Further, it was laminated with another ITO electrode using a heat sealing adhesive.
In this image display medium, the capacitance of the resin thin film layer was 50 μF / m ² , and the capacitance of the display layer was 25 μF / m ² .
When -10V is applied to the upper ITO electrode with reference to the lower ITO electrode, the white electrophoretic particles quickly move to the lower electrode side, and the black electrophoretic particles quickly move to the upper electrode side. It looked black when seen. Next, when +10 V was applied to the upper ITO electrode, the white electrophoretic particles quickly moved to the upper electrode side, the black electrophoretic particles quickly moved to the lower electrode side, and looked white when viewed from the upper electrode side. FIG. 4 shows the change in light reflectance when changing from black to white.

Example 3
(Production and operation of image display medium)
Example 1 except that the ethyl lactate solution of cellulose acetate in Example 1 was replaced with one obtained by dissolving 5 parts of ethyl cellulose (volume resistivity: 1 × 10 ¹³ Ω · cm) in a mixed solvent of 80 parts of toluene and 20 parts of ethanol. An image display medium was produced in the same manner as in Example 1. At this time, the film thickness of the hydroxyethyl cellulose layer was 1 μm.
In this image display medium, the capacitance of the resin thin film layer was 30 μF / m ² , and the capacitance of the display layer was 25 μF / m ² .
When -10V is applied to the upper ITO electrode with reference to the lower ITO electrode, the white electrophoretic particles quickly move to the lower electrode side, and the black electrophoretic particles quickly move to the upper electrode side. It looked black when seen. Next, when +10 V was applied to the upper ITO electrode, the white electrophoretic particles quickly moved to the upper electrode side, the black electrophoretic particles quickly moved to the lower electrode side, and looked white when viewed from the upper electrode side. FIG. 4 shows the change in light reflectance when changing from black to white.

Example 4
(Production and operation of image display medium)
Example 2 except that the ethyl lactate solution of cellulose acetate in Example 2 was replaced with one obtained by dissolving 5 parts of ethyl cellulose (volume resistivity: 1 × 10 ¹³ Ω · cm) in a mixed solvent of 80 parts of toluene and 20 parts of ethanol. In the same manner as in Example 2, an image display medium was produced. At this time, the film thickness of the hydroxyethyl cellulose layer was 1 μm.
In this image display medium, the capacitance of the resin thin film layer was 30 μF / m ² , and the capacitance of the display layer was 25 μF / m ² .
When -10V is applied to the upper ITO electrode with reference to the lower ITO electrode, the white electrophoretic particles quickly move to the lower electrode side, and the black electrophoretic particles quickly move to the upper electrode side. It looked black when seen. Next, when +10 V was applied to the upper ITO electrode, the white electrophoretic particles quickly moved to the upper electrode side, the black electrophoretic particles quickly moved to the lower electrode side, and looked white when viewed from the upper electrode side. FIG. 4 shows the change in light reflectance when changing from black to white.

[Comparative Example 4]
(Production and operation of image display medium)
The microcapsules in Example 1 were dispersed in a urethane resin and applied on a glass substrate with an ITO electrode with a wire bar. Further, it was laminated with another ITO electrode using a heat sealing adhesive.
In this image display medium, the capacitance of the display layer was 25 μF / m ² .
When -10V is applied to the upper ITO electrode with reference to the lower ITO electrode, the white electrophoretic particles move to the lower electrode side, the black electrophoretic particles move to the upper electrode side, and black when viewed from the upper electrode side. Looked. Next, when +10 V is applied to the upper ITO electrode, the white electrophoretic particles move to the upper electrode side with a delay compared to the example, the black electrophoretic particles move to the lower electrode side, and white when viewed from the upper electrode side. Looked like. FIG. 4 shows the change in light reflectance when changing from black to white.

1 is a conceptual cross-sectional view of an image display medium of the present invention. It is a cross-sectional conceptual diagram of the other image display medium of this invention. It is a conceptual diagram of the image display apparatus of this invention. It is a figure showing the reflectance change at the time of switching from black display to white display in the Example and comparative example of the present invention.

Explanation of symbols

1: Electrode (conductive layer)
2: Electrode (conductive layer)
3: Microcapsule 4: Colored particle 5: White particle 6: Binder layer 7: Dispersion medium 8A, 8B: Resin thin film layer 9: Adhesive layer 10: Display layer 11: Image display device 12: Image display medium 13: Housing 14: Information input means

Claims (7)

  A fine particle dispersion composed of at least a nonpolar solvent and particles is enclosed in a plurality of compartmentalized cells or capsules between two electrode substrates arranged at a desired interval and at least one of which is light transmissive. In an image display medium in which a display layer is held and a display operation is performed by electrophoresis of the fine particles by applying a voltage between the two electrode substrates, the display layer is interposed between the display layer and at least one electrode substrate. An image display medium comprising a resin thin film layer having a capacitance larger than that of the display layer. The image display medium according to claim 1, wherein the display layer has a capacitance of 1 to 1000 μF / m ² . The image display medium according to claim 1, wherein a difference between the capacitance of the resin thin film layer and the capacitance of the display layer is 100 μF / m ² or less.   The image display medium according to claim 1, wherein the resin thin film layer comprises at least a cellulose derivative. 5. The image display medium according to claim 1, wherein a resistance value in a film thickness direction of the resin thin film layer is 1 × 10 ¹¹ Ω or less per 1 cm ² . 6. The image display medium according to claim 1, wherein the volume resistivity of the constituent material of the resin thin film layer is 1 × 10 ¹⁴ Ω · cm or less.   An image display medium according to any one of claims 1 to 6, information input means for supplying image information to the image display medium, and power supply means for supplying power to the image display medium and the information input means. An image display device comprising: