JP4631191B2 - Electrophoretic display element - Google Patents

Description

【００６９】
得られた表面処理済み粉体を、下記構造を有する染料（チバ製、ＢＬ）を０．１ｇ、トリメチルベンゼン１００mlに溶解させたものに、４８時間浸漬し、浸漬前後の染料溶液の分光光度計による染料の透過率から吸着量を求めた。結果を表１に示す。
【００７０】
【化２】

【００７１】
【表１】

【００７２】
表１の結果から、ポリスチレン＋分散剤が最も効果的に吸着を抑制できることが解る。なお、ポリステアリルメタクリレートの吸着量が多いのは、構造中に存在するケトン基に染料が吸着したためであると推定される。
【００７３】
＜実施例１＞
溶剤（溶媒）としてトリメチルベンゼン（ＴＭＢ）：１０ｇとしてを用い、これに染料としてアントラキノン系染料〔Solvent Blue 136〕を０．５ｇ、分散剤（マリアリム）０．１ｇ、および増粘剤としてスメクタイト（コープケミカル（株）製、商品名：ＳＡＮ）０．５ｇを分散溶解させ、泳動媒質とした。
【００７４】
泳動粒子は、一次粒径が７０nmでγ−メタクリロイロキシプロピルトリメトキシシラン処理を施した酸化チタン１０ｇ、架橋剤としてトリメチロールプロパントリメタクリレートを２０ｇ、分散剤として日本油脂製AWS-0851 を１ｇ、重合開始剤として過酸化ベンゾイルを５ｇ、スチレンを８０ｇ混合し懸濁液を作製した。この懸濁液を、前記分散剤（日本油脂製AWS-0851 ）が１０ｇ溶解した水１ｋｇに激しく撹拌しながら滴下し、乳化懸濁液を作製した。撹拌した状態で温度を上昇させ、９０℃にて重合反応を促進させ、真球状の微粉体を得た。この微粉体の色調は白色、比重１．４９、平均粒径は５．１μm であった。
【００７５】
また、比較例として酸化チタンを造粒して平均粒径４．８６μm の粉体を得た。
【００７６】
これらの泳動媒質を図１および図２に示す装置のＩＴＯ透明電極間に配置し、両電極間に通電前、通電中における表示面の状態を観察し、これからコントラスト比を求めた。その結果、発明サンプルのコントラストは８．５であったのに対し、比較サンプルは５．４しかなかった。
【００７７】
【発明の効果】
以上のように本発明によれば、コントラスト比が高く、応答速度が速く、付着状態を長期間維持でき、安定した表示が可能な電気泳動表示素子を提供することができる。
【図面の簡単な説明】
【図１】本発明の電気泳動表示装置の基本構成を示す概略断面図である。
【図２】本発明の電気泳動表示装置の基本構成を示す概略断面図である。
【図３】泳動粒子核表面に高分子鎖が付着した状態を模式的示した断面図である。
【図４】図３の高分子鎖が架橋構造を有する状態を模式的示した断面図である。
【図５】スメクタイトの結晶構造を示した図である。
【図６】従来の電気泳動表示装置の基本構成を示す概略断面図である。
【図７】従来の電気泳動表示装置の基本構成を示す概略断面図である。
【符号の簡単な説明】
１ 泳動媒質
２ 泳動粒子
１１ａ，１１ｂ 基板
１２ａ，１２ｂ 電極[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophoretic display device that utilizes the movement of charged particles of an electrophoretic medium by application of a voltage.
[0002]
[Prior art]
Conventionally, an electrophoretic display element as shown in FIG. 6 is known. In this electrophoretic display device, at least one of a pair of light-transmitting glass substrates 11a and 11b, for example, is opposed to each other with a predetermined interval through sealing members 13a and 13b, and these glass substrates 11a and 11b and the sealing member A closed space is configured by 13a and 13b. The transparent electrodes 12a and 12b made of planar ITO or the like are fixed to the inner surfaces of the pair of glass substrates 11a and 11b facing each other.
[0003]
An electrophoretic display medium 1a is accommodated in the closed space. The electrophoretic display medium 1a is, for example, a medium 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. Yes.
[0004]
In such an electrophoretic display element, a positive voltage is applied to the upper electrode 12a by closing the switch 15 and connecting it to the power source 14 with respect to the pair of electrodes 12a and 12b, for example, as shown in FIG. When a negative voltage is applied to the lower electrode 12b, the negatively charged white pigment 2 is electrophoresed toward the anode by Coulomb force, and 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, a portion where the white pigment 2 adheres to form a layer appears white through 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 voltage is stopped, once the white pigment 2 adheres to the electrode, it is not necessary to apply a voltage except for maintaining the adhesion state.
[0005]
However, since the specific gravity difference is greatly different between the migrating particles 2 and the solvent used in the medium, methods such as adjusting the specific gravity of the two, adjusting the viscosity of the solvent, and miniaturizing the migrating particles are being studied. However, as is apparent from Rayleigh scattering, as the size of migrating particles becomes finer, the finer the migrating particles, the higher the transmittance and the more easily the color of the colored migrating medium is reflected. For this reason, the contrast ratio, the reflectance, the whiteness and the like are reduced.
[0006]
Further, the miniaturization of the migrating particles 2 has a problem that the surface area is increased, the dye in the migrating medium is adsorbed on the surface of the migrating particles 2, and the migrating particles themselves are colored.
[0007]
In order to improve such a defect, attempts have been made to increase the size of the migrating particles 2. However, the increase in size causes the gap between the migrating particles 2 to increase, resulting in the result that the color of the migrating medium is easily reflected as described above.
[0008]
[Problems to be solved by the invention]
An object of the present invention is to provide an electrophoretic display element that has a high contrast ratio, a high response speed, can maintain an adhesion state for a long period of time, and can display stably.
[0009]
[Means for Solving the Problems]
The above object is achieved by the following configuration.
(1) An electrophoretic display element having an electrophoretic medium between a pair of electrodes, in which electrophoretic particles are dispersed in the electrophoretic medium,
The electrophoretic particle is an electrophoretic display element in which a polymer chain is attached to the surface of the electrophoretic particle nucleus.
(2) The electrophoretic display element according to (1), wherein the nucleus of the electrophoretic particle is an inorganic pigment.
(3) The electrophoretic display element according to (1) or (2), wherein the polymer chain is attached to the surface of the migrating particle nucleus by a coupling agent.
(4) The electrophoretic display element according to (1) or (2), wherein the polymer chain has a functional group for charge control.
(5) The electrophoretic display element according to any one of (1) to (3), wherein the polymer chain has a crosslinked structure.
(6) The electrophoretic display element according to any one of (1) to (5), wherein the electrophoretic particle nucleus is porous.
(7) The electrophoretic display element according to any one of the above (1) to (6), wherein the electrophoretic medium has a color capable of obtaining at least contrast with electrophoretic particles and contains an additive.
(8) The electrophoretic display device according to any one of (1) to (7), wherein the electrophoretic medium contains a swellable lamellar viscosity mineral.
(9) The electrophoretic display element according to any one of (1) to (8), wherein the electrophoretic medium is enclosed in a structure in which each of a microcapsule or a cell is independent and disposed between the pair of electrodes. .
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The electrophoretic display element of the present invention is an electrophoretic display element having an electrophoretic medium 1 between a pair of electrodes 12a and 12b as shown in FIG. 1, for example, and electrophoretic particles 2 are dispersed in the electrophoretic medium 1. The electrophoretic particle 2 has a polymer chain attached to the core surface.
[0011]
Thus, by attaching the polymer chain to the surface of the migrating particle nucleus, the contrast ratio is high, the response speed is high, and the memory effect can be further improved. As a result, an electrophoretic display element capable of maintaining excellent display quality for a long period of time can be obtained.
[0012]
That is, for example, as shown in FIG. 3, by attaching the polymer chain 2b to the surface of the migrating particle nucleus 2a, the polymer layer 2b is interposed between the surface of the nucleus 2a and the migrating medium 1. For this reason, it is possible to prevent the migration medium 1 and the dye dispersed therein from adhering to or adsorbing to the nucleus 2a, and the contrast ratio is improved.
[0013]
In addition, the specific gravity of the electrophoretic particles can be adjusted, so that electrophoretic particles closer to the specific gravity of the electrophoretic medium can be obtained, and the memory performance is improved. Furthermore, the charge on the surface of the migrating particles can be adjusted, and the response speed can be improved.
[0014]
As shown in FIG. 3, the polymer chain 2b is preferably bonded to the nucleus 2a via a coupling group 2c. By interposing the coupling group, the binding between the polymer chain 2b and the nucleus 2a is facilitated, and the binding amount of the polymer chain 2b can be adjusted.
[0015]
The organic polymer material forming the polymer chain of the present invention is a material having good compatibility with the coupling group, easy charge control, easy control of the polymerization reaction, and low reactivity of the electrophoretic medium. It is not particularly limited. Specifically, styrene resin, styrene copolymer resin, polyester resin, polyol resin, polyvinyl chloride resin, phenol resin, natural modified phenol resin, natural resin modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate , Silicone resin, polyurethane resin, polyamide resin, furan resin, epoxy resin, xylene resin, polyvinyl butyral, terpene resin, coumarone indene resin, polyethylene resin, polypropylene resin, polycarbonate resin, nylon, petroleum resin, etc. Of these, styrene resins and acrylic resins are preferable.
[0016]
The ratio of the polymer chain to the nucleus is preferably 0.1 to 95% by mass, particularly 1 to 70% by mass. Further, the specific gravity of the migrating particles may be adjusted by adjusting the ratio of the polymer chains.
[0017]
As a coupling agent for introducing the polymer chain into the nucleus, a suitable coupling agent may be selected from known coupling agents depending on the material of the nucleus and the type of the polymer chain. Specifically, when an inorganic pigment, particularly titanium oxide, is used for the core, examples include Si-based coupling agents and Ti-based coupling agents. Specifically, amino groups, vinyl groups, and epoxy groups are added at the molecular chain ends. A group containing a functional group such as a group or halogen is preferred.
[0018]
The amount of the coupling agent added to the nucleus varies depending on the type and is not particularly limited, but is usually 0.1 to 5% by mass, particularly about 1 to 3% by mass.
[0019]
A functional group for controlling the surface charge may be introduced into the polymer chain. By introducing a functional group for controlling the surface charge, the response speed can be improved. Examples of such a functional group, a sulfonic acid, carboxyl groups, -NH _2, -OH, -Cl, may be mentioned polar group such as -NO _2, 4 ammonium salt. Also, known charge control materials may be used, such as organometallic complexes, metal salts, and chelate compounds, such as monoazo metal complexes, acetylacetone metal complexes, hydroxycarboxylic acid metal complexes, polycarboxylic acid metal complexes, and polyol metal complexes. can give. In addition, carboxylic acid derivatives such as metal salts of carboxylic acids, carboxylic acid anhydrides and esters, and condensates of aromatic compounds are also included. Also, phenol derivatives such as bisphenols and calixarene can be used.
[0020]
As a method for introducing a functional group into a polymer chain, a method in which a reactive group for binding to a charge control material is attached to the end of the polymer chain, or a monomer is previously modified with a charge control material and polymerized, etc. Good.
[0021]
The ratio of the functional group to the polymer chain is preferably about 0.1 to 50% by mass, particularly about 1 to 30% by mass, although it depends on the type of polymer chain and nucleus.
[0022]
It is desirable that the migrating particles used in the present invention are stably dispersed in the solvent of the migrating medium and have a single polarity from the viewpoint of the lifetime of the display device, contrast, resolution, and the like. If the particle diameter is within the above range, the light scattering efficiency does not decrease, and a sufficient response speed can be obtained when a voltage is applied.
[0023]
Examples of the core material of the migrating particles include inorganic materials such as 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. Pigments or organic pigments such as phthalocyanine blue, phthalocyanine green, Hansa yellow, watching red, and diary ride yellow can be used, but inorganic pigments are preferred. Among these, titanium oxide is preferable for obtaining a high contrast ratio, and rutile type is particularly preferable for titanium oxide. In particular, the present invention is effective when the migrating particle nucleus is porous.
[0024]
The migrating particle nucleus 2a has an average primary particle diameter of 0.01 to 0.7 μm, preferably 0.05 to 0.5 μm, more preferably 0.1 to 0.3 μm.
[0025]
By covering the periphery of the inorganic pigment with a resin, it is possible to prevent the dye in the migration medium from adsorbing to the inorganic pigment, and the contrast is improved. Further, the specific gravity of the electrophoresis medium can be approached by selecting a resin or the like.
[0026]
As a method for forming a polymer chain of the resin material on the surface of the pigment particle, for example, the pigment particle is dispersed in a resin solvent in which a resin monomer, a dispersant and a polymerization initiator are dispersed in advance, and the monomer is polymerized. That's fine.
[0027]
The specific gravity of the migrating particles is preferably closer to the migrating medium. Specifically, it is about 1.1 to 2.0.
[0028]
Furthermore, the polymer chain may have a crosslinked structure as shown in FIG. 4, for example. By having a cross-linked structure, the polymer chains 2b form a three-dimensional network structure around the migrating particle nucleus 2a to form a stronger resin layer, and the dye in the migrating medium is adsorbed to the inorganic pigment. This can be prevented and the contrast is improved.
[0029]
In order to obtain such a crosslinked structure, for example, a crosslinking agent may be added in the polymerization step. As such a crosslinking agent, although depending on the resin material, for example, in the case of styrene-based and acrylic-based, a polyfunctional monomer and the like can be mentioned.
[0030]
By introducing a crosslinked structure into the polymer chain, a complex structure in which a plurality of migrating particle nuclei are bonded by a resin can also be obtained. By using such a complex structure, larger-diameter electrophoretic particles can be obtained.
[0031]
In this case, the electrophoretic particles of the composite have an average primary particle size of 0.8 to 7 μm, preferably 0.8 to 5 μm. These particle sizes are values when the particles are converted into a spherical shape.
[0032]
In the present invention, as the solvent, the solubility in the migrating particles is small, the solubility in the dye and the swellable lamellar viscous mineral is large, and the dye, the electrophoretic particles, preferably the following swellable lamellar viscous mineral can be stably dissolved or dispersed, An insulating material that does not contain ions and does not generate ions when a voltage is applied is desirable.
[0033]
Examples of insulating liquids that can be used for a relatively large number of migrating particle materials include saturated hydrocarbons such as hexane, decane, hexadecane, and kerosene, aromatic hydrocarbons such as toluene and xylene, trichlorotrifluoroethane, and dibromo. Examples thereof include halogenated fluorine-based hydrocarbons such as tetrafluoroethane and tetrachloroethylene, and fluorine-based solvents. In addition, these liquids can also be mixed and used.
[0034]
In the present invention, the mixing ratio of the migrating particles in the migrating medium is not particularly limited as long as the electrophoretic properties of the migrating particles are not hindered and the reflection control of the migrating medium can be sufficiently performed. 1 mass% to 30 mass% is preferable.
[0035]
In the present invention, an additive such as a resin or a surfactant can be added to the above-described solvent as necessary in order to increase the charge of the migrating particles or to make the same polarity.
[0036]
The electrophoretic medium preferably has a color that provides a contrast with the electrophoretic particles. Such colors may have such colors themselves or other pigments may be dispersed in the migration medium. The color of the electrophoretic medium is preferably such that a contrast ratio with the color of the electrophoretic particles is 3 or more, particularly 5 or more.
[0037]
Examples of the dye dissolved in the electrophoresis medium include cyanine, phthalocyanine, naphthalocyanine, anthraquinone, azo, triphenylmethane, pyrylium or thiapyrylium salt, squarylium, croconium, and metal complex dyes. 1 type or 2 types or more may be appropriately selected depending on the purpose.
[0038]
The content of such a dye is not particularly limited, and may be appropriately adjusted depending on the type, desired color, brightness, and the like, but is preferably about 0.1 to 20% by mass.
[0039]
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. desirable. From such a viewpoint, the preferable thickness of the migration medium layer is 5 μm to 200 μm.
[0040]
The electrode material used in the present invention is preferably a highly conductive material such as aluminum, copper, silver, gold, or platinum. Moreover, as a transparent electrode material, thin films, such as a tin oxide, an indium oxide, and copper iodide, can be used preferably. Moreover, electrode formation can be performed by normal methods, such as vapor deposition, sputtering, and photolithography.
[0041]
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 have sufficient insulation and flatness and sufficient strength. As specific materials, glass, plastic, and ceramic are preferably used. Moreover, when making a board | substrate bear a contrast color with an electrophoretic particle, what mixed the suitable pigment | dye and the pigment with glass, plastics, and ceramics, or a colored ceramic can be used as a board | substrate.
[0042]
The method for disposing and enclosing the electrophoresis medium between the electrodes is not particularly limited, and various methods can be used, but it is particularly preferable to seal and dispose with a microcapsule or a cell. These microcapsules may be disposed between electrodes using an organic binder or the like.
[0043]
As a microencapsulation method, it can be produced by a method that has already been known in the art. For example, a phase separation method from an aqueous solution as shown in U.S. Pat. Nos. 2,800,547 and 2,800,498, Japanese Patent Publication Nos. 38-19574, 42-446, 42-771, etc. Interfacial polymerization method as shown, in-situ method by polymerization of monomers shown in JP-B-36-9168, JP-A-51-9079, etc., British Patent Nos. 952807 and 965074 Although there is a melt dispersion cooling method and the like shown in the specification, it is not limited thereto.
[0044]
As a material for forming the outer wall portion of the microcapsule, an inorganic material or an organic material may be used as long as the outer wall portion can be manufactured by the capsule manufacturing method. However, a material that transmits light sufficiently is preferable. Specific examples include gelatin, gum arabic, starch, sodium alginate, polyvinyl alcohol, polyethylene, polyamide, polyester, polyurethane, polyurea, polyurethane, polystyrene, nitrocellulose, ethylcellulose, methylcellulose, melamine-formaldehyde resin, urea-formaldehyde resin, and the like. And copolymers thereof.
[0045]
As a specific method for forming the microcapsules, first, the migrating particles 2 are uniformly dispersed in a solvent. Further, this dispersion and distilled water to which a surfactant is added are stirred and mixed to prepare an emulsion of the dispersion. The size of the dispersion emulsion is adjusted to a desired size depending on the stirring speed or the type and amount of the emulsifier and the surfactant. In addition, one or more emulsifiers, surfactants, electrolytes, lubricants, stabilizers, and the like can be appropriately added as necessary.
[0046]
In addition, two types of charged particles (for example, white charged particles and black charged particles) having different color tones and charged polarities may be encapsulated in a microcapsule together with a liquid solvent by the interfacial polymerization method.
[0047]
At this time, the electrophoretic particles preferably have a degree of dispersion of a particle size distribution represented by volume average particle diameter / number average particle diameter of about 2 or less.
[0048]
In the electrophoretic element of the present invention, the electrophoretic medium 1 may contain a swellable lamellar viscosity mineral. By including a swellable lamellar viscosity mineral in the electrophoresis medium 1, the thixotropic property is imparted to the electrophoresis medium 1. The thixotropic means a substance that maintains a jelly-like state at rest, while the fluidity is increased by applying force to the system and behaves like a liquid. For this reason, display particles can be held for a long period of time, and stable display can be performed.
[0049]
As the swellable layered viscosity mineral, smectite is preferable. Smectites, the unit structure as shown in FIG. 3, a kind of layered silicate, two tetrahedral sheets of Si-O 4 ₄ tetrahedron has spread to share oxygen vertices hexagonal mesh-like basically The 2: 1 structure in which the remaining apex oxygen faces each other and the cation is sandwiched to form an octahedron sheet of oxygen is used as a unit layer. And it swells in a solvent, a layered structure breaks down and shows colloidal properties. For this reason, the adsorbing ability of the guest substance is high, and further, for example, the anion of the display particles is easily adsorbed by the cation present, and the retention characteristics are remarkably improved.
[0050]
Smectite may be natural or industrially synthesized. In the present invention, either a natural product or a synthetic product may be used, but industrially synthesized products are preferable from the viewpoint of not containing characteristics or impurities in a solvent.
[0051]
Synthetic smectite is commercially available as an industrially synthesized product. Commercially available synthetic smectites include a hydrophilic type that swells in water and breaks down the layered structure into a colloidal shape and exhibits viscosity, and a lipophilic type that becomes colloidal in an organic solvent and exhibits viscosity. . As a hydrophilic type, there is a hydrophilic smectite marketed as SWN (manufactured by Corp Chemical Co., Ltd.). In the present invention, a lipophilic one is preferable.
[0052]
The lipophilic smectite is obtained by replacing Na ions or 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. Examples of such organic ions include, but are not limited to, tetramethylammonium and tetraethylammonium, for example, quaternary ammonium having an alkyl group having about 1 to 10 carbon atoms.
[0053]
By selecting the organic ion to be substituted, it can be well dispersed in various organic solvents, exhibiting colloidal properties and viscosity, and having excellent properties for intercalating guest materials such as ink and its solvent. is there. Such lipophilic smectites include those marketed as SAN, STN, SEN and SPN (all manufactured by Coop Chemical Co.). Of these, SAN and STN having affinity with many organic solvents are preferable.
[0054]
As described above, such a smectite has the property of swelling in a solvent and exhibiting a colloidal property and increasing the viscosity of the solution, as described above. When allowed to stand, this colloid forms a bulky network structure due to hydrogen bonding and exhibits elastic behavior. However, when an external force is applied to this, since this bond is weak, the network structure is easily broken and exhibits fluidity. For this reason, by including smectite, the electrophoretic medium 1 can be provided with thixotropic properties, the display particle retention ability is improved, and the display is stabilized.
[0055]
The smectite content is preferably 0.01 to 20% by mass of the migration medium, more preferably 0.1 to 15% by mass, and particularly preferably 1 to 10% by mass.
[0056]
The specific surface area of the smectite used is preferably 200~1000m ² / g, more preferably 500 to 1000 m ² / g, particularly preferably at, 710~800m ² / g.
[0057]
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, and particularly preferably 1 to 45 μm.
[0058]
The basic configuration of the electrophoresis apparatus of the present invention is shown in FIGS. In this electrophoretic display device, a pair of substrates 11a and 11b, at least one of which is translucent, face each other with a predetermined interval through sealing members 13a and 13b, and these substrates 11a and 11b and sealing members 13a and 13b are opposed to each other. The closed space is configured by. The transparent electrodes 12a and 12b made of planar ITO or the like are fixed to the inner surfaces of the pair of substrates 11a and 11b facing each other.
[0059]
The migration medium 1 is accommodated in the closed space. The electrophoretic medium 1 is a medium in which, for example, 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.
[0060]
In such an electrophoretic display element, for example, as shown in FIG. 2, the switch 15 is closed and connected to the power source 14 with respect to the pair of electrodes 12a and 12b, 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 is electrophoresed toward the anode by Coulomb force, and 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, a portion where the white pigment 2 adheres to form a layer appears white through the transparent electrode 12a and the glass substrate 11a.
[0061]
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, and the layer of the white pigment 2 is hidden behind the black electrophoretic medium 1. The display panel will appear black.
[0062]
And in this invention, even if it stops applying voltage, once the white pigment 2 adheres to an electrode, it can maintain an adhesion state for a long period of time, for example, about 2 or 3 months. This eliminates the need to apply the holding voltage again.
[0063]
The driving voltage of the electrophoretic display device of the present invention is not particularly limited, but is usually about 1 to 250 V DC, particularly about 5 to 150 V.
[0064]
The electrophoretic display device of the present invention is capable of 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.
[0065]
The electrophoretic display element of the present invention can be suitably used as a display device having a flat shape or a bent shape.
[0066]
The electrophoretic display device of the present invention is particularly effective in fields such as advertisements for shops, price display boards, information boards, road signs, road information boards, thin wall clocks, electronic notebooks, electronic books, electronic newspapers, and the like. is there.
[0067]
【Example】
Hereinafter, the present invention will be described more specifically based on experimental examples and examples.
<Experimental example>
Titanium oxide having a primary particle size of 250 nm was used and subjected to various surface treatments as shown in Table 1 below. At this time, polystyrene and polystearyl methacrylate were adhered so as to have the following structure.
[0068]
[Chemical 1]

[0069]
The obtained surface-treated powder was immersed in 0.1 g of a dye having the following structure (Ciba, BL) dissolved in 100 ml of trimethylbenzene for 48 hours, and a spectrophotometer of the dye solution before and after the immersion The amount of adsorption was determined from the transmittance of the dye. The results are shown in Table 1.
[0070]
[Chemical 2]

[0071]
[Table 1]

[0072]
From the results in Table 1, it can be seen that polystyrene + dispersant can most effectively suppress adsorption. In addition, it is presumed that the amount of adsorption of polystearyl methacrylate is large because the dye was adsorbed on the ketone group present in the structure.
[0073]
<Example 1>
Trimethylbenzene (TMB): 10 g was used as a solvent (solvent), 0.5 g of anthraquinone dye [Solvent Blue 136] was used as a dye, 0.1 g of a dispersant (Marialim), and smectite (corp) as a thickener. Chemical Co., Ltd., trade name: SAN (0.5 g) was dispersed and dissolved to prepare an electrophoresis medium.
[0074]
Electrophoretic particles were 10 g of titanium oxide having a primary particle size of 70 nm and treated with γ-methacryloyloxypropyltrimethoxysilane, 20 g of trimethylolpropane trimethacrylate as a cross-linking agent, and 1 g of AWS-0851 manufactured by NOF Corporation as a dispersing agent, As a polymerization initiator, 5 g of benzoyl peroxide and 80 g of styrene were mixed to prepare a suspension. This suspension was added dropwise to 1 kg of water in which 10 g of the dispersant (AWS-0851 manufactured by NOF Corporation) was dissolved with vigorous stirring to prepare an emulsified suspension. While stirring, the temperature was raised and the polymerization reaction was accelerated at 90 ° C. to obtain true spherical fine powder. The fine powder had a white color, a specific gravity of 1.49, and an average particle size of 5.1 μm.
[0075]
As a comparative example, titanium oxide was granulated to obtain a powder having an average particle size of 4.86 μm.
[0076]
These electrophoretic media were placed between the ITO transparent electrodes of the apparatus shown in FIGS. 1 and 2, and the state of the display surface before and during energization was observed between both electrodes, and the contrast ratio was determined therefrom. As a result, the contrast of the inventive sample was 8.5 while the comparative sample was only 5.4.
[0077]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an electrophoretic display element that has a high contrast ratio, a high response speed, can maintain an adhesion state for a long time, and can display stably.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a basic configuration of an electrophoretic display device of the present invention.
FIG. 2 is a schematic cross-sectional view showing a basic configuration of an electrophoretic display device of the present invention.
FIG. 3 is a cross-sectional view schematically showing a state in which polymer chains are attached to the surface of migrating particle nuclei.
4 is a cross-sectional view schematically showing a state in which the polymer chain of FIG. 3 has a crosslinked structure.
FIG. 5 is a view showing a crystal structure of smectite.
FIG. 6 is a schematic cross-sectional view showing a basic configuration of a conventional electrophoretic display device.
FIG. 7 is a schematic cross-sectional view showing a basic configuration of a conventional electrophoretic display device.
[Brief description of symbols]
DESCRIPTION OF SYMBOLS 1 Electrophoretic medium 2 Electrophoretic particle 11a, 11b Substrate 12a, 12b Electrode

Claims (6)

An electrophoretic display element having an electrophoretic medium between a pair of electrodes, in which electrophoretic particles are dispersed in the electrophoretic medium,
The electrophoretic particle has a polymer chain bonded to the electrophoretic particle nucleus surface via a coupling group ,
The polymer chains have a crosslinked structure,
The polymer organic material forming the polymer chain includes a styrene resin,
An electrophoretic display element in which the nucleus of the electrophoretic particle is an inorganic pigment . The polymer chains, the electrophoretic display device according to claim 1 having a functional group for charge control. The electrophoretic particle nuclei electrophoretic display device according to claim 1 or 2 which is porous. The electrophoretic display element according to any one of claims 1 to 3 , wherein the electrophoretic medium has a color capable of obtaining at least a contrast with electrophoretic particles and contains an additive. Any of the electrophoretic display device according to claim 1-4, containing a swellable layered clay mineral in the electrophoresis medium. The electrophoresis medium, microcapsules or each cell is sealed in a separate structure, either of the electrophoretic display device according to claim 1 to 5 disposed between the pair of electrodes.

Images