JP2007248834A - Display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display element which has simple member constitution, can be driven with a low voltage, and has a high display contrast, the display element having sufficiently high white display reflectivity and small electrode staining due to repetitive driving. <P>SOLUTION: The display element has an electrolyte containing silver or a compound containing silver in a chemical structure and a porous white scattering layer between counter electrodes, and drives the counter electrodes so as to dissolve and deposit silver, the display element being characterized in that the porous white scattering layer is formed of particles of titanium oxide having surfaces processed with acetate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrochemical display element utilizing silver dissolution precipitation.

  In recent years, with the increase in the operating speed of personal computers, the spread of network infrastructure, the increase in capacity and price of data storage, information such as documents and images provided on printed paper on paper has become easier to use electronic information. Opportunities to obtain and browse electronic information are increasing more and more.

  As a means for browsing such electronic information, a conventional liquid crystal display or CRT, and in recent years, a light emitting type such as an organic EL display is mainly used. In particular, when the electronic information is document information, it is relatively long time. It is necessary to pay close attention to this browsing means, and these actions are not necessarily human-friendly means. Generally, as a disadvantage of the light-emitting display, eyes flicker due to flickering, inconvenient to carry, reading posture is limited It is known that it is necessary to adjust the line of sight to a still screen, and that power consumption increases when read for a long time.

  As a display means that compensates for these drawbacks, a reflection type display that uses external light and does not consume power for image retention (memory type) is known, but has sufficient performance for the following reasons. It's hard to say.

  That is, the method using a polarizing plate such as a reflective liquid crystal has a low reflectance of about 40% and is difficult to display white, and many of the production methods used for producing the constituent members are not easy. In addition, the polymer dispersed liquid crystal requires a high voltage and utilizes the difference in refractive index between organic substances, so that the resulting image has insufficient contrast. In addition, the polymer network type liquid crystal has problems such as a high voltage and a complicated TFT circuit required to improve the memory performance. In addition, a display element based on electrophoresis requires a high voltage of 10 V or more, and there is a concern about durability due to electrophoretic particle aggregation. In addition, the electrochromic display element can be driven at a low voltage of 3 V or less, but the color quality of black or color (yellow, magenta, cyan, blue, green, red, etc.) is not sufficient, and the memory property is low. In order to ensure, there is a concern that the display cell requires a complicated film configuration such as a vapor deposition film.

  As a display method that eliminates the drawbacks of each of the above-described methods, an electrodeposition (hereinafter abbreviated as ED) method that utilizes dissolution of metal or metal salt is known. The ED method can be driven at a low voltage of 3 V or less, has advantages such as a simple cell configuration, excellent black-white contrast and black quality, and various methods have been disclosed (for example, Patent Document 1). -3)).

The present inventors have found that the white reflectance can be improved by introducing a white scattering layer in the structure of the display element, but when the display element having such a structure is repeatedly driven, It has been found that there is a problem that the electrode on the viewing side is contaminated. This is because the silver particles deposited in an image-like manner on the viewing-side transparent electrode remain when the image is reset, that is, when the silver dissolution driving is performed, without completely dissolving the silver particles. It was found to occur. Further, the silver particles remaining without being dissolved become nuclei, and unnecessary silver image particles are formed in the next image display. The silver particles thus generated are difficult to dissolve even in the next erasing drive, and by repeating this, the transparent electrode becomes soiled, the contrast is lowered, and the image quality is deteriorated.
U.S. Pat. No. 4,240,716 Japanese Patent No. 3428603 JP 2003-241227 A

  The present invention has been made in view of the above problems, and its object is a display element that can be driven at a low voltage with a simple member configuration, has a high display contrast, has a sufficiently high white display reflectance, and is repeatedly driven. It is an object of the present invention to provide a display element that is less likely to cause electrode contamination.

  The above object of the present invention is achieved by the following configurations.

  1. A display element having an electrolyte containing silver or a compound containing silver in the chemical structure and a porous white scattering layer between the counter electrodes and driving the counter electrode so as to cause dissolution and precipitation of silver The display element is characterized in that the porous white scattering layer is composed of titanium oxide particles whose surface is treated with acetate.

  2. 2. The display element according to 1 above, wherein the acetate for surface treatment of the titanium oxide particles is magnesium acetate or zinc acetate.

  3. 3. The display element according to 1 or 2 above, wherein the titanium oxide particles are subjected to a surface treatment using sulfate, and then a porous white scattering layer is formed using the titanium oxide particles.

  4). In any one of 1 to 3 above, the particle size distribution of the titanium oxide particles contained in the porous white scattering layer has a maximum value in a range of at least 0.1 μm or more and less than 0.4 μm. The display element as described.

  5. 5. The display element according to any one of 1 to 4, wherein a particle size distribution of the titanium oxide particles has at least two maximum values.

  According to the present invention, it is possible to provide a display element that has a simple member configuration, can be driven at a low voltage, has a high display contrast, has a sufficiently high white display reflectance, and generates less electrode contamination.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  As a result of intensive studies in view of the above problems, the present inventor has an electrolyte containing silver or a compound containing silver in a chemical structure between a counter electrode and a porous white scattering layer, A display element for driving a counter electrode so as to cause dissolution and precipitation, wherein the porous white scattering layer is composed of titanium oxide whose surface is treated with acetate. The present inventors have found that a display element that can be driven at a low voltage with a simple member configuration, has a high display contrast, has a sufficiently high white display reflectance, and is less likely to cause electrode contamination. It depends on you.

  Details of the display element of the present invention will be described below.

[Basic cell structure]
FIG. 1 is a schematic cross-sectional view showing the basic configuration of the display element of the present invention.

  In FIG. 1, the display element of the present invention is provided with a porous white scattering layer 3 on a counter electrode (transparent electrode) 1 ′, holding an electrolyte 2 between the counter electrode 1 and the counter electrode 1 from a power source V. ′ By applying a voltage or current to 1, a dissolution reaction or a precipitation reaction of silver contained in the electrolyte 2 is caused, and a difference in optical characteristics of light transmission / absorption of a compound containing silver is utilized. This is a display element that changes the display state.

(Porous white scattering layer)
The porous white scattering layer in the present invention is a layer that exhibits a substantially white color, and is a layer that has a large number of pores into which the electrolyte solution can permeate in the layer structure.

  In the display element of the present invention, the porous white scattering layer according to the present invention constituting the display element is composed of titanium oxide particles whose surface is treated with acetate.

  In general, in display elements, it is difficult to obtain sufficient whiteness by simply dispersing a white pigment in the electrolyte. However, whiteness is improved by using a white pigment as a white scattering layer. can do.

  As the white pigment, titanium oxide, zinc oxide and the like are widely known. However, in the present invention, since the refractive index difference from the electrolyte is large and white can be obtained in a small amount, titanium oxide is used. Furthermore, the present inventors have found that the intended effects of the present invention can be sufficiently exhibited by applying titanium oxide.

  Surface treatment of titanium oxide particles is introduced in Chapter 2.5 of “Titanium oxide properties and applied technology” (Kyoto Seino, published by Gihodo Publishing, 1991). In many cases, it is known to treat with alumina, alumina and silica or titania. It is also known to treat with a polyol, alkanolamine, or silicon organic material.

  In the present invention, it has been found that by subjecting titanium oxide particles to surface treatment with acetate, the silver image precipitation / dissolution reaction can be improved without deteriorating the white scattering performance of titanium oxide. As a result, when the formed silver image is lost, the number of silver particles that cause poor dissolution is reduced, and as a result, white background stains are less likely to occur.

  A specific method for treating titanium oxide particles with acetate is to add acetate to the titanium oxide surface by heating the aqueous solution containing acetate to a temperature that is sufficient to add and boil titanium oxide. it can.

The acetate used for the surface treatment of the titanium oxide of the present invention is not particularly limited. For example, magnesium acetate [Mg (CH ₃ COO) ₂ ], zinc acetate [Zn (CH ₃ COO)], sodium acetate [Na (CH ₃ COO)] and the like, and preferably magnesium acetate or zinc acetate.

  Further, in the display element of the present invention, after the titanium oxide surface is treated with acetate according to the above method in a separate step, the surface-treated titanium oxide (hereinafter also referred to as surface-treated titanium oxide) is treated. It is preferable to form a porous white scattering layer between the counter electrodes from the viewpoint of further achieving the object effect of the present invention.

  Next, the particle size distribution of the surface-treated titanium oxide according to the present invention for forming the porous white scattering layer will be described.

  In the present invention, when the surface-treated titanium oxide constituting the porous white scattering layer has a particle size distribution as defined above, the object and effects of the present invention can be further exhibited.

  The measurement of the particle size distribution and the maximum value of the particle size of the surface-treated titanium oxide according to the present invention is, for example, 5.5. It can be determined according to the method described in Chapter 1 (p82 to 86).

  Specifically, two or more kinds of surface-treated titanium oxide mixtures to be measured are dispersed in a surface-treated titanium oxide-insoluble solvent, and then, for example, a laser scattering particle size distribution analyzer (for example, Measurement may be performed using SALD2200 (manufactured by Shimadzu Corporation), Zetasizer 1000 manufactured by Malvern, or the like, or the surface-treated titanium oxide mixture is directly observed with a transmission electron microscope or a scanning electron microscope. From the particle image, a method for obtaining the particle diameter can be used, and the volume particle diameter in terms of sphere is defined as the diameter of the surface-treated titanium oxide.

  For the particle size data measured in this way, the particle size value of the surface-treated titanium oxide is plotted on the horizontal axis, and the number of surface-treated titanium oxides at each particle size value is plotted on the vertical axis. Create a particle size distribution curve.

  FIG. 2 is a graph in which the particle size value of surface-treated titanium oxide is plotted on the horizontal axis and the number of surface-treated titanium oxides on each particle size value is plotted on the vertical axis based on the particle size distribution data obtained according to the above method. In FIG. 2a, the particle size distributions of the surface-treated titanium oxide A1 having a small particle size and a surface-treated titanium oxide B1 having a large particle size are completely separated. An example is shown, and FIG. 2 b) shows an example in which the particle size distribution of the surface-treated titanium oxide having a small particle size and a large particle size cannot be completely separated. In the present invention, in any case, the particle size of each maximum value is the average particle size of each particle group, and the particles constituting this particle size maximum value are the minimum values generated between both maximum values. Up to the part. That is, in b) of FIG. 2, it isolate | separates on the boundary of R3 which is the minimum particle diameter.

  In the porous white scattering layer according to the present invention, the particle size distribution of the surface-treated titanium oxide to be contained preferably has a maximum value in a range of at least 0.1 μm or more and less than 0.4 μm, and further contains More preferably, the particle size distribution of the surface-treated titanium oxide having at least two maximum values.

  Thus, in the titanium oxide having the maximum value of at least two particle size distributions, it is preferable that at least one maximum value is in the range of 0.1 μm or more and less than 0.4 μm, and further, the smaller particle It is more preferable that the radius maximum value (R2) in FIG. 2B is in the range of 0.1 μm or more and less than 0.4 μm.

  Further, in the porous white scattering layer according to the present invention, among the maximum values indicated by the particle size distribution of the surface-treated titanium oxide contained, the particle size R1 indicated by the maximum value having a large particle size and the maximum value having a small particle size are shown. The particle size R2 indicated by the value is preferably in a relationship of R1 / R2 = 1.5 to 4.5.

  Further, in the porous white scattering layer according to the present invention, it is preferable that the surface-treated titanium oxide constituting a large particle size maximum value is contained in an amount of 5% by mass or more and 50% by mass or less of the total surface-treated titanium oxide. .

  Further, particularly when the porous white scattering layer is provided on the transparent electrode, the average particle size of the surface-treated titanium oxide formed in the layer in contact with the transparent electrode, which forms a laminated structure of two or more layers due to the difference in particle size It is preferable that the diameter is larger than the average particle diameter of the surface-treated titanium oxide contained in the layer disposed above it.

  FIG. 3 is a schematic cross-sectional view showing an example of a display element in which a porous white scattering layer is configured using a surface-treated titanium oxide having a single particle diameter.

  FIG. 3 a is a schematic cross-sectional view of a display device having a porous white scattering layer composed of substantially uniform titanium oxide particles having a single maximum value of the particle size distribution.

  FIG. 3 b is a schematic diagram showing the state of the silver particles 5 deposited between the transparent electrode 1 ′ and the surface-treated titanium oxide 4.

  FIG. 4 is a schematic cross-sectional view showing an example of a display element having a porous white scattering layer composed of two types of surface-treated titanium oxides having different average particle diameters.

  4a is a cross-sectional view of the display element, and similarly to FIG. 3, the electrolyte 2 is provided between the counter electrodes 1 and 1 ', and the particle size is formed on the transparent electrode 1' as one of the counter electrodes. The porous white scattering layer 3 is composed of two different types of surface-treated titanium oxides, that is, surface-treated titanium oxide 4A having a large particle size and surface-treated titanium oxide 4B having a small particle size. In the surface-treated titanium oxide group having the configuration shown in a), a particle size distribution curve having two particle size maximum values is obtained.

  FIG. 4 b is a schematic diagram showing the state of the silver particles 5 deposited between the transparent electrode 1 ′ and the surface-treated titanium oxide 4.

  FIG. 5 is a schematic cross-sectional view showing another example of a display element having a porous white scattering layer composed of two types of surface-treated titanium oxides having different average particle diameters.

  In a) of FIG. 5, a group of surface-treated titanium oxides 4A having a large particle diameter is arranged on the side in contact with the transparent electrode 1 ′, which is one of the counter electrodes, and a surface-treated oxidation having a small particle diameter is placed on the upper part. The titanium 4B group is arranged.

  FIG. 5 b) is a schematic diagram showing the state of the silver particles 5 deposited between the transparent electrode 1 ′ and the surface-treated titanium oxide 4.

  As a method of forming the arrangement of the surface-treated titanium oxide as shown in FIG. 4, two or more kinds of surface-treated titanium oxides having different particle diameters are obtained by using an insoluble solvent for the surface-treated titanium oxide and, if necessary, an electrolyte. A water-soluble polymer that does not substantially dissolve in the solution can be uniformly dispersed in a solution containing a coating binder and then coated on a transparent electrode. At this time, desired white scattering can be formed by appropriately selecting the particle diameters and mixing ratios of two or more kinds of surface-treated titanium oxides to be used.

  Further, as a method of forming the arrangement of the surface-treated titanium oxide as shown in FIG. 5, two or more kinds of surface-treated titanium oxides having different particle diameters are used, and each surface-treated titanium oxide is used as an insoluble solvent and After preparing each coating solution containing surface-treated titanium oxide with different particle diameters by uniformly dispersing a water-soluble polymer that is not substantially dissolved in the electrolyte as necessary in a solution containing a coating binder, Forming the coating solution containing the surface-treated titanium oxide having the largest particle size on the transparent electrode with a predetermined film thickness and then applying the coating solution containing the surface-treated titanium oxide having a small particle size Can do.

  In the present invention, in order to form a porous white scattering layer using surface-treated titanium oxide, a water-soluble polymer that does not substantially dissolve in the electrolyte can be used as a coating binder.

Examples of water-soluble polymers that are substantially insoluble in the electrolyte solvent according to the present invention include proteins such as gelatin and gelatin derivatives or cellulose derivatives, natural compounds such as polysaccharides such as starch, gum arabic, dextran, pullulan and carrageenan, And synthetic polymer compounds such as polyvinyl alcohol, polyvinyl pyrrolidone, acrylamide polymers and derivatives thereof. Examples of gelatin derivatives include acetylated gelatin, phthalated gelatin, polyvinyl alcohol derivatives include terminal alkyl-modified polyvinyl alcohol, terminal mercapto group-modified polyvinyl alcohol, and cellulose derivatives include hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and the like. It is done. Furthermore, Research Disclosure and those described in pages (71) to (75) of JP-A No. 64-13546, US Pat. No. 4,960,681, JP-A No. 62-245260, etc. superabsorbent polymers described, namely -COOM or -SO ₃ M (M is a hydrogen atom or an alkali metal) homopolymer or a vinyl monomer together or with other vinyl monomers (e.g., sodium methacrylate in the vinyl monomer having a methacrylic acid Copolymers with ammonium, potassium acrylate, etc.) are also used. Two or more of these binders can be used in combination.

  In the present invention, gelatin and gelatin derivatives, or polyvinyl alcohol or derivatives thereof can be preferably used.

  In the present invention, “substantially insoluble in an electrolyte solvent” is defined as a state in which the dissolved amount per kg of electrolyte solvent is 0 g or more and 10 g or less at a temperature of −20 ° C. to 120 ° C. The amount of dissolution can be determined by a known method such as a component determination method using a chromatogram or a gas chromatogram.

  The water mixture of the water-soluble polymer and the white pigment according to the present invention preferably has a form in which the white pigment is dispersed in water according to a known dispersion method. The volume ratio of the water-soluble polymer / white pigment mixing ratio is preferably 1 to 0.01, and more preferably 0.3 to 0.05.

  The medium for applying the water mixture of the water-soluble polymer and the white pigment according to the present invention may be at any position as long as it is on the component between the counter electrodes of the display element, but at least one of the counter electrodes. It is preferable to apply on the surface. As a method for applying to a medium, for example, a coating method, a liquid spraying method, a spraying method via a gas phase, a method of flying droplets using vibration of a piezoelectric element, for example, a piezoelectric inkjet head, Examples thereof include a bubble jet (registered trademark) type ink jet head that causes droplets to fly using a thermal head that uses bumping, and a spray type that sprays liquid by air pressure or liquid pressure.

  The coating method can be appropriately selected from known coating methods. For example, an air doctor coater, blade coater, rod coater, knife coater, squeeze coater, impregnation coater, reverse roller coater, transfer roller coater, curtain coater, double coater Examples include roller coaters, slide hopper coaters, gravure coaters, kiss roll coaters, bead coaters, cast coaters, spray coaters, calendar coaters, and extrusion coaters.

  The water mixture of the water-soluble polymer and the white pigment applied on the medium according to the present invention may be dried by any method as long as water can be evaporated. For example, heating from a heat source, a heating method using infrared light, a heating method using electromagnetic induction, and the like can be given. Further, water evaporation may be performed under reduced pressure.

  Further, in the display element of the present invention, the water-soluble polymer can be reacted effectively with a curing agent during or after application of the water mixture described above.

  Examples of the hardener used in the present invention include, for example, U.S. Pat. No. 4,678,739, column 41, 4,791,042, JP-A-59-116655, and 62-245261. No. 61-18942, 61-249054, 61-245153, JP-A-4-218044, and the like. More specifically, aldehyde hardeners (formaldehyde, etc.), aziridine hardeners, epoxy hardeners, vinyl sulfone hardeners (N, N'-ethylene-bis (vinylsulfonylacetamide) Ethane, etc.), N-methylol hardeners (dimethylolurea, etc.), boric acid, metaboric acid or polymer hardeners (compounds described in JP-A-62-234157). When gelatin is used as the water-soluble polymer, it is preferable to use a vinyl sulfone type hardener or a chlorotriazine type hardener alone or in combination. Moreover, when using polyvinyl alcohol, it is preferable to use boron-containing compounds such as boric acid and metaboric acid.

  These hardeners are used in an amount of 0.001 to 1 g, preferably 0.005 to 0.5 g, per 1 g of water-soluble polymer. In addition, it is possible to perform heat treatment and humidity adjustment during the curing reaction in order to increase the film strength.

(Electrolytes)
To the electrolyte according to the present invention, compounds represented by general formulas (1) to (7) described in JP-A-2005-266652 can be added. Specifically, it is a compound as described in Paragraph Nos. [0036] to [0078] of JP-A-2005-266652. Particularly preferred are compounds of general formula (2) and general formula (6). Furthermore, in the case of the general formula (2), those having a triazole ring are more preferable. In the case of general formula (6), it is more preferable that the element directly bonded to the S atom is carbon.

  The electrolyte according to the present invention contains silver or a compound containing silver in the chemical structure. Silver or a compound containing silver in the chemical structure according to the present invention is a general term for compounds such as silver oxide, silver sulfide, metallic silver, silver colloidal particles, silver halide, silver complex compounds, and silver ions. Phase state species such as solid state, solubilized state in liquid, and gas state, and charged state species such as neutral, anionic, and cationic are not particularly limited.

  In the display device of the present invention, silver iodide, silver chloride, silver bromide, silver oxide, silver sulfide, silver citrate, silver acetate, silver behenate, silver p-toluenesulfonate, silver salt with mercapto, A known silver salt compound such as a silver complex with iminodiacetic acid can be used. Among these, it is preferable to use, as a silver salt, a compound that does not have a nitrogen atom having coordination properties with halogen, carboxylic acid, or silver, and for example, silver p-toluenesulfonate is preferable.

  The silver ion concentration contained in the electrolyte layer according to the present invention is preferably 0.2 mol / kg ≦ [Ag] ≦ 2.0 mol / kg. If the silver ion concentration is less than 0.2 mol / kg, it becomes a dilute silver solution, and the driving speed is delayed. If it is greater than 2 mol / kg, the solubility deteriorates, and precipitation tends to occur during low-temperature storage, which is disadvantageous. It is.

  Generally, in order to cause dissolution and precipitation of silver, it is necessary to solubilize silver in the electrolyte layer. For example, solubilize silver or a compound containing silver by coexisting with a compound containing a chemical structural species that interacts with silver, such as a coordinate bond with silver or a weak covalent bond with silver. It is common to use a means for converting to an object. As the chemical structural species, halogen atoms, mercapto groups, carboxyl groups, imino groups and the like are known, but in the present invention, the thioether group is also useful as a silver solvent and has little influence on the coexisting compound, It is characterized by high solubility in solvents.

  In the display element of the present invention, the molar concentration of halogen ions or halogen atoms contained in the electrolyte layer is [X] (mol / kg), and silver or silver contained in the electrolyte layer is a compound that contains silver in the chemical structure. When the total molar concentration of [Ag] is [Ag] (mol / kg), it is preferable that the condition defined by the following formula (1) is satisfied.

Formula (1)
0 ≦ [X] / [Ag] ≦ 0.01
The halogen atom as used in the field of this invention means an iodine atom, a chlorine atom, a bromine atom, and a fluorine atom. When [X] / [Ag] is larger than 0.01, X ⁻ → X ₂ is generated during the redox reaction of silver, and X ₂ easily cross-oxidizes with blackened silver to dissolve blackened silver. Therefore, the molar concentration of halogen atoms is preferably as low as possible relative to the molar concentration of silver. In the present invention, 0 ≦ [X] / [Ag] ≦ 0.001 is more preferable. In the case of adding halogen ions, the halogen species preferably have a total molar concentration of [I] <[Br] <[Cl] <[F] from the viewpoint of improving memory properties.

  Moreover, a solvent can be used in combination with the electrolyte according to the present invention as long as the target effect is not impaired. Specifically, tetramethylurea, sulfolane, dimethyl sulfoxide, 1,3-dimethyl-2-imidazolidinone, 2- (N-methyl) -2-pyrrolidinone, hexamethylphosphortriamide, N-methylpropionamide, N, N-dimethylacetamide, N-methylacetamide, N, N dimethylformamide, N-methylformamide, butyronitrile, propionitrile, acetonitrile, acetylacetone, 4-methyl-2-pentanone, 2-butanol, 1-butanol, 2 -Propanol, 1-propanol, ethanol, methanol, acetic anhydride, ethyl acetate, ethyl propionate, dimethoxyethane, diethoxyfuran, tetrahydrofuran, ethylene glycol, diethylene glycol, triethylene glycol monobuty Ether, water and the like. Among these solvents, it is preferable to include at least one solvent having a freezing point of −20 ° C. or lower and a boiling point of 120 ° C. or higher.

  Furthermore, as a solvent which can be used in the present invention, J.P. A. Riddick, W.M. B. Bunger, T.A. K. Sakano, “Organic Solvents”, 4th ed. , John Wiley & Sons (1986). Marcus, “Ion Solvation”, John Wiley & Sons (1985), C.I. Reichardt, “Solvents and Solvent Effects in Chemistry”, 2nd ed. VCH (1988), G .; J. et al. Janz, R.A. P. T. T. et al. Tomkins, “Nonqueous Electronics Handbook”, Vol. 1, Academic Press (1972).

  In the present invention, the electrolyte solvent may be a single type or a mixture of solvents, but a mixed solvent containing ethylene carbonate is preferred. The addition amount of ethylene carbonate is preferably 10% by mass or more and 90% by mass or less of the total electrolyte solvent mass. A particularly preferable electrolyte solvent is a mixed solvent having a mass ratio of propylene carbonate / ethylene carbonate of 7/3 to 3/7. When the propylene carbonate ratio is larger than 7/3, the ionic conductivity is inferior and the response speed is lowered. When the propylene carbonate ratio is smaller than 3/7, the electrolyte tends to be deposited at a low temperature.

In the display element of the present invention, when the electrolyte is a liquid, the following compounds can be included in the electrolyte. KCl, KI, KBr, etc. as potassium compounds, LiBF ₄ , LiClO ₄ , LiPF ₆ , LiCF ₃ SO ₃ etc. as lithium compounds, tetraethylammonium perchlorate, tetrabutylammonium perchlorate, tetraethylammonium borofluoride as tetraalkylammonium compounds And tetrabutylammonium borofluoride and tetrabutylammonium halide. Moreover, the molten salt electrolyte composition described in JP-A-2003-187881 paragraphs [0062] to [0081] can also be preferably used. Furthermore, a compound that becomes a redox pair such as I ⁻ / I ₃ ⁻ , Br ⁻ / Br ₃ ⁻ , and quinone / hydroquinone can be used.

  Further, when the supporting electrolyte is a solid, the following compounds exhibiting electron conductivity and ion conductivity can be contained in the electrolyte.

Vinyl fluoride polymer containing perfluorosulfonic acid, polythiophene, polyaniline, polypyrrole, triphenylamines, polyvinylcarbazoles, polymethylphenylsilanes, Cu ₂ S, Ag ₂ S, Cu ₂ Se, AgCrSe _2, etc. F-containing compounds such as chalcogenide, CaF ₂ , PbF ₂ , SrF ₂ , LaF ₃ , TlSn ₂ F ₅ , CeF ₃ , Li salts such as Li ₂ SO ₄ , Li ₄ SiO ₄ , Li ₃ PO ₄ , ZrO ₂ , CaO , Cd ₂ O ₃ , HfO ₂ , Y ₂ O ₃ , Nb ₂ O ₅ , WO ₃ , Bi ₂ O ₃ , AgBr, AgI, CuCl, CuBr, CuBr, CuI, LiI, LiBr, LiCl, LiAlCl ₄ , LiAlF _{4 , AgSBr, C 5 H 5 NHAg} 5 I 6, Rb 4 Cu 16 I 7 Cl 13, Rb 3 Cu 7 Cl 10, LiN, Li 5 NI 2 Compounds such as li ₆ NBr _3, and the like.

  Moreover, a gel electrolyte can also be used as the supporting electrolyte. When the electrolyte is non-aqueous, the oil gelling agents described in paragraphs [0057] to [0059] of JP-A No. 11-185836 can be used.

(Thickener added with electrolyte)
In the display element of the present invention, a thickener can be used in the electrolyte layer. For example, gelatin, gum arabic, poly (vinyl alcohol), hydroxyethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, poly ( Vinylpyrrolidone), poly (alkylene glycol), casein, starch, poly (acrylic acid), poly (methyl methacrylic acid), poly (vinyl chloride), poly (methacrylic acid), copoly (styrene-maleic anhydride), copoly ( Styrene-acrylonitrile), copoly (styrene-butadiene), poly (vinyl acetal) s (eg, poly (vinyl formal) and poly (vinyl butyral)), poly (esters), poly (urethanes), phenoxy resins, poly (PVC Redene), poly (epoxides), poly (carbonates), poly (vinyl acetate), cellulose esters, poly (amides), hydrophobic transparent binders such as polyvinyl butyral, cellulose acetate, cellulose acetate butyrate, polyester, Examples include polycarbonate, polyacrylic acid, polyurethane and the like.

  These thickeners may be used in combination of two or more. Moreover, the compound as described in pages 71-75 of Unexamined-Japanese-Patent No. 64-13546 can be mentioned. Among these, the compounds preferably used are polyvinyl alcohols, polyvinyl pyrrolidones, hydroxypropyl celluloses, and polyalkylene glycols from the viewpoint of compatibility with various additives and improvement in dispersion stability of white particles.

(Other additives for electrolyte layer)
Examples of the constituent layers of the display element of the present invention include auxiliary layers such as a protective layer, a filter layer, an antihalation layer, a crossover light cut layer, and a backing layer. Sensitizer, noble metal sensitizer, photosensitive dye, supersensitizer, coupler, high boiling point solvent, antifoggant, stabilizer, development inhibitor, bleach accelerator, fixing accelerator, color mixing inhibitor, formalin scavenger, Toning agents, hardeners, surfactants, thickeners, plasticizers, slip agents, UV absorbers, anti-irradiation dyes, filter light absorbing dyes, anti-bacterial agents, polymer latex, heavy metals, antistatic agents, matting agents Etc. can be contained as required.

  More specifically, these additives described above are described in detail in Research Disclosure (hereinafter abbreviated as RD), Volume 176 Item / 17643 (December 1978), Volume 184, Item / 18431 (August 1979), Volume 187. Item / 18716 (November 1979) and Volume 308 Item / 308119 (December 1989).

  The types of compounds and their descriptions shown in these three research disclosures are listed below.

Additive RD17643 RD18716 RD308119
Page Classification Page Classification Page Classification Chemical sensitizer 23 III 648 Upper right 96 III
Sensitizing dye 23 IV 648-649 996-8 IV
Desensitizing dye 23 IV 998 IV
Dye 25-26 VIII 649-650 1003 VIII
Development accelerator 29 XXI 648 Upper right Anti-fogging agent / stabilizer
24 IV 649 Upper right 1006-7 VI
Brightener 24 V 998 V
Hardener 26 X 651 Left 1004-5 X
Surfactant 26-7 XI 650 Right 1005-6 XI
Antistatic agent 27 XII 650 Right 1006-7 XIII
Plasticizer 27 XII 650 Right 1006 XII
Slipper 27 XII
Matting agent 28 XVI 650 Right 1008-9 XVI
Binder 26 XXII 1003-4 IX
Support 28 XVII 1009 XVII
(Layer structure)
The constituent layers of the display element of the present invention will be further described.

As a constituent layer according to the display element of the present invention, a constituent layer containing a hole transport material can be provided. Examples of hole transport materials include aromatic amines, triphenylene derivatives, oligothiophene compounds, polypyrroles, polyacetylene derivatives, polyphenylene vinylene derivatives, polythienylene vinylene derivatives, polythiophene derivatives, polyaniline derivatives, polytoluidine derivatives, CuI, CuSCN CuInSe ₂ , Cu (In, Ga) Se, CuGaSe ₂ , Cu ₂ O, CuS, CuGaS ₂ , CuInS ₂ , CuAlSe ₂ , GaP, NiO, CoO, FeO, Bi ₂ O ₃ , MoO ₂ , Cr ₂ O ₃ Etc.

(substrate)
Examples of the substrate that can be used in the present invention include polyolefins such as polyethylene and polypropylene, polycarbonates, cellulose acetate, polyethylene terephthalate, polyethylene dinaphthalene dicarboxylate, polyethylene naphthalates, polyvinyl chloride, polyimide, and polyvinyl acetal. Synthetic plastic films such as polystyrene can also be preferably used. Syndiotactic polystyrenes are also preferred. These can be obtained, for example, by the methods described in JP-A Nos. 62-117708, 1-46912 and 1-178505. Further, a metal substrate such as stainless steel, a paper support such as baryta paper and resin coated paper, and a support provided with a reflective layer on the plastic film, supported by JP-A-62-253195 (pages 29-31) The thing described as a body is mentioned. RDNo. 17643, page 28, ibid. No. 18716, page 647, right column to page 648, left column, and No. 307105, page 879 can also be preferably used. As these supports, those having resistance to curling due to heat treatment of Tg or less as in US Pat. No. 4,141,735 can be used. Further, the surface of these supports may be subjected to surface treatment for the purpose of improving the adhesion between the support and other constituent layers. In the present invention, glow discharge treatment, ultraviolet irradiation treatment, corona treatment, and flame treatment can be used as the surface treatment. Furthermore, the support body described in pages 44 to 149 of publicly known technology No. 5 (issued by Aztec Co., Ltd. on March 22, 1991) can also be used. Furthermore, RDNo. 308119, page 1009, Product Licensing Index, Volume 92, P108, “Supports”, and the like. In addition, a glass substrate or an epoxy resin kneaded with glass can be used.

(electrode)
In the display element of the present invention, it is preferable that at least one of the counter electrodes is a metal electrode. As the metal electrode, for example, known metal species such as platinum, gold, silver, copper, aluminum, zinc, nickel, titanium, bismuth, and alloys thereof can be used. The metal electrode is preferably a metal having a work function close to the redox potential of silver in the electrolyte. Above all, silver or a silver electrode having a silver content of 80% or more is advantageous for maintaining the reduced state of silver. Excellent in preventing dirt. As an electrode manufacturing method, an existing method such as an evaporation method, a printing method, an ink jet method, a spin coating method, or a CVD method can be used.

  In the display element of the present invention, it is preferable that at least one of the counter electrodes is a transparent electrode. The transparent electrode is not particularly limited as long as it is transparent and conducts electricity. For example, Indium Tin Oxide (ITO: Indium Tin Oxide), Indium Zinc Oxide (IZO: Indium Zinc Oxide), Tin Oxide (FTO), Indium Oxide, Zinc Oxide, Platinum, Gold, Silver, Rhodium, Copper, Chromium, Examples thereof include carbon, aluminum, silicon, amorphous silicon, and BSO (Bismuth Silicon Oxide). In order to form the electrode in this manner, for example, an ITO film may be vapor-deposited on the substrate by a sputtering method or the like, or an ITO film may be formed on the entire surface and then patterned by a photolithography method. The surface resistance value is preferably 100Ω / □ or less, and more preferably 10Ω / □ or less. The thickness of the transparent electrode is not particularly limited, but is generally 0.1 to 20 μm.

(Other components of the display element)
In the display element of the present invention, a sealant, a columnar structure, and spacer particles can be used as necessary.

  Sealing agent is for sealing so that it does not leak out. It is also called sealing agent. Epoxy resin, urethane resin, acrylic resin, vinyl acetate resin, ene-thiol resin, silicone resin, modified resin A curing type such as a polymer resin, such as a thermosetting type, a photocurable type, a moisture curable type, and an anaerobic curable type can be used.

  The columnar structure provides strong self-holding (strength) between the substrates, for example, a columnar body, a quadrangular columnar body, an elliptical columnar body, a trapezoidal array arranged in a predetermined pattern such as a lattice arrangement. A columnar structure such as a columnar body can be given. Alternatively, stripes arranged at predetermined intervals may be used. This columnar structure is not a random array, but can be properly maintained at intervals of the substrate, such as an evenly spaced array, an array in which the interval gradually changes, and an array in which a predetermined arrangement pattern is repeated at a constant period. The arrangement is preferably considered so as not to disturb the display. If the ratio of the area occupied by the columnar structure in the display area of the display element is 1 to 40%, a practically sufficient strength as a display element can be obtained.

  A spacer may be provided between the pair of substrates for uniformly maintaining a gap between the substrates. Examples of the spacer include a sphere made of resin or inorganic oxide. Further, a fixed spacer having a surface coated with a thermoplastic resin is also preferably used. In order to hold the gap between the substrates uniformly, only the columnar structure may be provided, but both the spacer and the columnar structure may be provided, or instead of the columnar structure, only the spacer is used as the space holding member. May be used. The diameter of the spacer is equal to or less than the height of the columnar structure, preferably equal to the height. When the columnar structure is not formed, the diameter of the spacer corresponds to the thickness of the cell gap.

(Screen printing)
In the present invention, a sealant, a columnar structure, an electrode pattern and the like can be formed by a screen printing method. In the screen printing method, a screen on which a predetermined pattern is formed is placed on an electrode surface of a substrate, and a printing material (a composition for forming a columnar structure, such as a photocurable resin) is placed on the screen. Then, the squeegee is moved at a predetermined pressure, angle, and speed. Thereby, the printing material is transferred onto the substrate through the pattern of the screen. Next, the transferred material is heat-cured and dried. When the columnar structure is formed by the screen printing method, the resin material is not limited to a photocurable resin, and for example, a thermosetting resin such as an epoxy resin or an acrylic resin or a thermoplastic resin can also be used. As thermoplastic resins, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polymethacrylate resin, polyacrylate resin, polystyrene resin, polyamide resin, polyethylene resin, polypropylene resin, fluororesin, polyurethane resin , Polyacrylonitrile resin, polyvinyl ether resin, polyvinyl ketone resin, polyether resin, polyvinyl pyrrolidone resin, saturated polyester resin, polycarbonate resin, chlorinated polyether resin and the like. The resin material is preferably used in the form of a paste by dissolving the resin in an appropriate solvent.

  After the columnar structure or the like is formed on the substrate as described above, a spacer is provided on at least one of the substrates as desired, and the pair of substrates are overlapped with the electrode formation surfaces facing each other to form an empty cell. . A pair of stacked substrates is heated while being pressed from both sides, whereby the display cells are obtained. In order to obtain a display element, an electrolyte composition may be injected between substrates by a vacuum injection method or the like. Alternatively, when the substrates are bonded together, the electrolyte composition may be dropped on one substrate, and the liquid crystal composition may be sealed simultaneously with the bonding of the substrates.

(Display element driving method)
In the display element of the present invention, it is preferable to perform a driving operation in which silver black is precipitated by applying a voltage equal to or higher than the precipitation overvoltage, and silver black is continuously precipitated by applying a voltage lower than the precipitation overvoltage. By performing this driving operation, the writing energy can be reduced, the driving circuit load can be reduced, and the writing speed as a screen can be improved. It is generally known that overvoltage exists in electrode reactions in the electrochemical field. For example, overvoltage is described in detail on page 121 of “Introduction to Chemistry of Electron Transfer—Introduction to Electrochemistry” (published by Asakura Shoten in 1996). Since the display element of the present invention can also be regarded as an electrode reaction between the electrode and silver in the electrolyte, it can be easily understood that overvoltage exists even in silver dissolution precipitation. Since the magnitude of the overvoltage is governed by the exchange current density, it is possible to continue silver black precipitation by applying a voltage equal to or lower than the precipitation overvoltage after the formation of silver black as in the present invention. However, it is estimated that electron injection can be easily performed with little extra electric energy.

  The driving operation of the display element of the present invention may be simple matrix driving or active matrix driving. The simple matrix driving in the present invention is a driving method in which a current is sequentially applied to a circuit in which a positive line including a plurality of positive electrodes and a negative electrode line including a plurality of negative electrodes are opposed to each other in a vertical direction. Say that. By using simple matrix driving, there is an advantage that the circuit configuration and driving IC can be simplified and manufactured at low cost. The active matrix drive is a system in which scanning lines, data lines, and current supply lines are formed in a grid pattern, and are driven by TFT circuits provided in each grid pattern. Since switching can be performed for each pixel, there are advantages such as gradation and a memory function. For example, a circuit described in FIG. 5 of JP-A-2004-29327 can be used.

(Product application)
The display element of the present invention can be used in an electronic book field, an ID card field, a public field, a traffic field, a broadcast field, a payment field, a distribution logistics field, and the like. Specifically, keys for doors, student ID cards, employee ID cards, various membership cards, convenience store cards, department store cards, vending machine cards, gas station cards, subway and railway cards, bus cards, Cash cards, credit cards, highway cards, driver's licenses, hospital examination cards, health insurance cards, Basic Resident Registers, passports, electronic books, etc.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<< Preparation of titanium oxide: Surface treatment of titanium oxide >>
[Preparation of titanium oxide 1]
Titanium oxide having an average particle size of 0.26 μm is immersed in a 30% by weight magnesium acetate aqueous solution, stirred for 1 hour while being heated at about 80 ° C., then filtered, washed with water, dried, and surface treated. A finished titanium oxide 1 was obtained.

[Preparation of titanium oxide 2]
Titanium oxide with an average particle size of 0.26 μm is immersed in a 20% by mass zinc acetate aqueous solution and stirred for 1 hour while heating at about 80 ° C., then filtered, washed with water, dried, and surface treated. Used titanium oxide 2 was obtained.

[Preparation of titanium oxide 3]
Titanium oxide having an average particle size of 0.26 μm is immersed in a 20% by mass aqueous sodium acetate solution, stirred for 1 hour while heating at about 80 ° C., then filtered, washed with water, dried and subjected to surface treatment. Used titanium oxide 3 was obtained.

[Preparation of titanium oxide 4]
In the preparation of the surface-treated titanium oxide 1, the surface-treated titanium oxide 4 was similarly prepared except that the titanium oxide having an average particle size of 0.26 μm was changed to titanium oxide having an average particle size of 0.40 μm. Was prepared.

[Preparation of Titanium Oxide 5: Two Titanium Oxide Mixtures with Different Particle Sizes]
In the preparation of the surface-treated titanium oxide 1, the surface-treated titanium oxide 5A was similarly prepared except that the titanium oxide having an average particle size of 0.26 μm was changed to titanium oxide having an average particle size of 0.45 μm. Was prepared. This surface-treated titanium oxide 5A and the above-prepared surface-treated titanium oxide 1 were mixed at a ratio of 1: 2 to obtain titanium oxide 5.

[Titanium oxide 6: Comparative example]
Untreated titanium oxide (Nanotech average particle size 31 nm, manufactured by C-I Kasei Co., Ltd.) was designated as titanium oxide 6.

[Titanium oxide 7: Comparative example]
Titanium oxide 7 was made of alumina-treated titanium oxide (R-630 average particle size 0.24 μm manufactured by Ishihara Sangyo Co., Ltd.).

<< Production of display element >>
[Production of Display Element 1]
(Preparation of electrolyte solution)
In 2.5 g of dimethyl sulfoxide, 90 mg of sodium iodide and 75 mg of silver iodide were added and completely dissolved, and then 150 mg of polyvinylpyrrolidone (average molecular weight 15000) was added and stirred for 1 hour while heating to 120 ° C. A liquid was obtained.

(Production of electrode 1)
A striped ITO film having a thickness of 1.5 mm and a pitch of 145 μm and an electrode width of 130 μm was formed on a 4 cm × 4 cm glass substrate according to a known method to obtain a transparent electrode (electrode 1).

(Preparation of electrode 2)
A striped silver-palladium electrode (electrode 2) having an electrode thickness of 0.5 μm, a pitch of 145 μm, and an electrode interval of 130 μm was obtained on a 4 cm × 4 cm glass substrate having a thickness of 1.5 mm.

(Preparation of porous white scattering layer 1)
Titanium oxide 1 prepared above was added in an amount equivalent to 20% by mass in an aqueous solution containing 2% by mass of gelatin, and mixed and dispersed by an ultrasonic disperser. This was applied to the electrode 1 with a wet film thickness of 100 μm by screen printing, dried at 15 ° C. for 30 minutes, and then completely dried at 45 ° C. for 30 minutes to obtain a porous white scattering layer 1.

(Formation of sealing wall)
The peripheral part of the electrode 1 provided with the porous white scattering layer was trimmed with an olefin-based sealant containing 10% glass spherical beads having an average particle diameter of 40 μm.

(Production of display element)
An electrolyte solution was applied on the electrode 1 provided with the porous white scattering layer and allowed to stand so that the electrolyte solution was sufficiently infiltrated into the white scattering layer. It was visually confirmed from the transparent electrode layer side that no bubbles were generated in the white scattering layer, and the electrolyte solution was filled up to the level of the sealant. In this state, the striped electrode 2 was put in contact with the electrolyte solution so that the electrode surface was perpendicular to the striped electrode of the electrode 1 and heated and pressed to obtain the display element 1.

[Production of display elements 2 to 7]
In the production of the porous white scattering layer 1 of the display element 1, display elements 2 to 7 were produced in the same manner except that titanium oxides 2 to 7 were used instead of the titanium oxide 1, respectively.

<< Measurement and evaluation of each characteristic value >>
(Measurement of average particle size of each titanium oxide)
Each titanium oxide described above was photographed using a transmission electron microscope (JEM-200FX, manufactured by JEOL Ltd.), and from the obtained titanium oxide particle image, using Image-Pro manufactured by Planetron Co., Ltd. as image processing software, 500 particle images were processed to determine each particle size, and statistical processing was performed to calculate the average particle size.

(Evaluation of electrode dirt resistance)
For each display element, the white background before driving was determined by measuring the L ^* ₁ value using a spectrocolorimeter CM-3700d manufactured by Konica Minolta Sensing. Thereafter, a driving experiment was performed using a known passive matrix circuit. First, a driving condition in which the reflectance at 550 nm is 10% in black display is obtained. Under this condition, white display (whitening) and black display (blackening) are driven 1000 times and then whitened again, before driving. Similarly, the L ^* ₂ value was measured, the L ^* difference (ΔL ^* value = L ^* _1- L ^* ₂ ) was determined, and this was used as a measure of electrode contamination. When the ΔL ^* value was 3 or more, it was determined that the level was such that dirt could be clearly recognized.

  The results obtained as described above are shown in Table 1.

  As is apparent from the results shown in Table 1, it can be seen that the display element of the present invention having a porous white scattering layer having a configuration defined in the present invention is superior in resistance to electrode contamination compared to the comparative example.

It is a schematic sectional drawing which shows the basic composition of the display element of this invention. It is a graph which shows an example of the particle size distribution profile of the titanium oxide particle group from which two types of average particle diameters differ. It is a schematic sectional drawing which shows an example of the display element which comprised the porous white scattering layer using the titanium oxide particle of single particle diameter. It is a schematic sectional drawing which shows an example of the display element which has a porous white scattering layer comprised from 2 types of titanium oxide from which an average particle diameter differs. It is a schematic sectional drawing which shows another example of the display element which has the porous white scattering layer comprised from 2 types of titanium oxides from which an average particle diameter differs.

Explanation of symbols

1 Counter electrode 1 'Counter electrode (transparent electrode)
2 Electrolyte layer 3 Porous white scattering layer

Claims (5)

A display element having an electrolyte containing silver or a compound containing silver in the chemical structure and a porous white scattering layer between the counter electrodes and driving the counter electrode so as to cause dissolution and precipitation of silver The display element is characterized in that the porous white scattering layer is composed of titanium oxide particles whose surface is treated with acetate. The display element according to claim 1, wherein the acetate for performing surface treatment of the titanium oxide particles is magnesium acetate or zinc acetate. The display element according to claim 1, wherein a porous white scattering layer is formed using the titanium oxide particles after the titanium oxide particles are subjected to a surface treatment using sulfate. The particle size distribution of the titanium oxide particles contained in the porous white scattering layer has a maximum value in a range of at least 0.1 µm or more and less than 0.4 µm. The display element as described in. 5. The display element according to claim 1, wherein a particle size distribution of the titanium oxide particles has at least two maximum values.

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