JP2007241178A - Display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display element of simple member constitution which can be driven at a low voltage and has high display contrast, the display element having fully high white display reflection factor and less electrode staining caused by repeated 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 also drives the counter electrodes to dissolve and deposit silver. At least one of the counter electrodes is a transparent electrode, the porous white scattering layer is provided on the transparent electrode and contains at least particulates, and the particle size distribution of the particulates has at least two maximum values. <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 Wherein at least one of the counter electrodes is a transparent electrode, the porous white scattering layer is provided on the transparent electrode, the porous white scattering layer contains at least fine particles, and the particle size distribution of the fine particles Exhibits at least two local maximum values.

  2. The porous white scattering layer has a laminated structure of two or more layers due to the difference in the particle size of the contained fine particles, and the average particle size of the fine particles contained in the layer in contact with the transparent electrode is disposed above it. 2. The display element according to 1 above, wherein the display element has an average particle size larger than that of the fine particles contained in the layer.

  3. 1 or 2 above, wherein at least one of the maximum values indicated by the particle size distribution of the fine particles contained in the porous white scattering layer is in the range of 0.1 μm or more and less than 0.4 μm. 2. The display element according to 2.

  4). Among the particle size maximum values indicated by the particle size distribution of the fine particles contained in the porous white scattering layer, the smaller particle size maximum value is 0.1 μm or more and less than 0.4 μm. The display element as described in.

  5. Among the maximum values indicated by the particle size distribution of the fine particles contained in the porous white scattering layer, the particle size R1 indicated by the maximum value having a large particle size and the particle size R2 indicated by the maximum value having a small particle size are R1 / 5. The display element according to any one of 1 to 4, wherein R2 = 1.5 to 4.5.

  6). 6. The porous white scattering layer according to any one of 1 to 5 above, wherein particles constituting a large particle size maximum value are contained in an amount of 5% by mass or more and 50% by mass or less of all fine particles. Display element.

  7). 7. The display element according to any one of items 1 to 6, wherein at least one of the fine particles contained in the porous white scattering layer is titanium oxide.

  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 at least one of the counter electrode is a transparent electrode, the porous white scattering layer is provided on the transparent electrode, and the porous white The display element is characterized in that the scattering layer contains at least fine particles, and the particle size distribution of the fine particles exhibits at least two maximum values. The display element can be driven at a low voltage with a simple member configuration and has a display contrast. As soon as the present invention has been achieved, the present inventors have found that a display element that is a high display element, has a sufficiently high white display reflectance, and generates little electrode contamination.

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

  First, the average particle diameter and the maximum particle diameter in the present invention will be described.

  The measurement of the particle size distribution and the maximum value of the particle size of the fine particles according to the present invention is described in, for example, Chapter 5.5.1 (p82) It can be determined according to the method described in -86).

  Specifically, after a mixture of two or more kinds of fine particles to be measured is dispersed in a fine particle-insoluble solvent, for example, a laser scattering type particle size distribution analyzer (for example, SALD2200 (manufactured by Shimadzu Corporation), Malvern, etc.) It may be measured using a Zetasizer 1000 or the like manufactured by the company, or the fine particle mixture is directly observed with a transmission electron microscope or a scanning electron microscope. From the obtained particle image, the image processing software is made by Planetron. Using Image-Pro, it is possible to use a method of processing 300 particle images to determine the particle size and performing statistical processing, etc. At this time, the volume particle diameter in terms of sphere is defined as the diameter of the fine particle did.

  With respect to the particle size data measured as described above, the particle size value curve of fine particles is created by plotting the particle size value of fine particles on the horizontal axis and the number of fine particles at each particle size value on the vertical axis.

FIG. 1 is a graph in which the particle size value of fine particles is plotted on the horizontal axis and the number of fine particles at each particle size value is plotted on the vertical axis based on the particle size distribution data obtained according to the above method. FIG. 1 shows an example in which the particle size distributions of the small particle A ₁ and the large particle B ₁ having different particle diameters are completely separated. In FIG. An example is shown in which the particle size distribution of the fine particles having 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 FIG. 1 b), separation is performed with R3 being the minimum particle size as a boundary.

  The display element of the present invention has an electrolyte layer containing silver or a compound containing silver in the chemical structure between the counter electrodes, and performs field driving for driving the counter electrode so as to cause dissolution and precipitation of silver. This is a display element of the type.

  In the display element of the present invention, at least one of the counter electrodes is a transparent electrode, a porous white scattering layer is provided on the transparent electrode, the porous white scattering layer contains at least fine particles, and the particle size distribution of the fine particles Is based on a novel display element configuration that exhibits at least two maximum values. By providing a porous white scattering layer containing fine particles on the transparent electrode, stable white scattering can be obtained, and by making the white scattering layer porous, the electrolyte can be filled to the vicinity of the electrode.

[Basic cell structure]
FIG. 2 is a schematic cross-sectional view showing the basic configuration of the display element of the present invention.

  In FIG. 2, 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 the 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)
Porous as used in the present invention refers to a mixture of water-soluble polymer and white pigment mixed in water on an electrode and dried to form a porous white scattering material, and then silver or silver on the scattering material. After applying an electrolyte solution containing a compound containing the chemical structure in the chemical structure, it can be sandwiched between the counter electrodes, giving a potential difference between the counter electrodes and causing a silver dissolution and precipitation reaction, and ionic species can move between the electrodes This means a through state.

  The porous white scattering layer according to the present invention is composed of fine particles and has at least two particle size maximums of the fine particles.

  The present inventors have found that the whiteness can be improved by introducing a white scattering layer in the configuration of the display element, but when the display element having such a configuration is repeatedly driven, It has been found that there is a problem that the electrode on the browsing 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.

  In order to promote the dissolution reaction of the silver image as described above, it is an essential requirement that an electrolyte sufficient for the dissolution reaction exists in the vicinity of the transparent electrode. For this reason, the present inventor has intensively studied an optimum fine particle configuration to be applied to the porous white scattering layer in order to cause a sufficient dissolution reaction while maintaining a desired whiteness.

  Conventionally, the fine particles applied to the porous white scattering layer have been configured using fine particles having a single structure.

  FIG. 3 is a schematic cross-sectional view illustrating an example of a display element in which a porous white scattering layer is configured using fine particles having a single particle diameter.

  As shown in FIG. 3 a), when the porous white scattering layer 3 is composed of particles 4 having a relatively small particle size in the region where the electrolyte 2 is present, it is deposited between the transparent electrode 1 ′ and the particles 4. Since there is not enough electrolyte for the silver particles, residual silver particles are likely to occur.

  In order to improve the insolubility of silver particles when using fine particles having a small particle size as described above, the particle size of the fine particles 4 forming the porous white scattering layer 3 is increased as shown in FIG. In addition, there is a method of promoting dissolution of silver particles by forming a wide space between the transparent electrode surface 1 ′ and the fine particles 4 having a large particle diameter, and allowing a sufficient amount of electrolyte to exist. However, since the white scattering efficiency of the large particle size is low, it is necessary to increase the thickness of the porous white scattering layer to obtain the desired whiteness. As a result, the distance between the electrodes increases. As a result, sharpness decreases and image writing / erasing speed decreases.

  FIG. 3c) is a schematic diagram showing the state of the silver particles 5 deposited between the transparent electrode 1 'and the fine particles 4. For example, as shown in FIG. When the porous white scattering layer is formed using the fine particles 4, the space where the silver particles 5 deposited between the transparent electrode 1 ′ and the fine particles 4 are present is narrow, and there is no sufficient electrolyte.

  As a result of intensive studies to achieve both the erasing effect of the generated silver particles and the white scattering efficiency, the porous white scattering layer has fine particles whose particle size distribution shows at least two maximum values. The present inventors have found that the above-described problems can be solved by forming the film using the film.

  FIG. 4 is a schematic cross-sectional view showing an example of a display element having a porous white scattering layer composed of two kinds of fine particles 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' which is one of the counter electrodes. The porous white scattering layer 3 is composed of two different kinds of fine particles, that is, the fine particle 4A having a large particle size and the fine particle 4B having a small particle size. In the fine particle group having the structure shown in FIG. The particle size distribution curve has two particle size maximums.

  By forming a porous white scattering layer with such two kinds of fine particle structure, as shown in FIG. 4B, a porous structure composed of the transparent electrode 1 ', the fine particles 4A, and the small particle size 4B. Since a wide space with a sufficient electrolytic solution can be secured between the white scattering layer and the white scattering layer, a silver image composed of silver particles 5 deposited on the transparent electrode 1 ′ can be sufficiently dissolved. Further, by mixing and using two kinds of fine particles having different particle diameters, a sufficient white scattering efficiency can be obtained without excessively thickening the white porous layer.

  The porous white scattering layer has a laminated structure of two or more layers due to the difference in the particle size of the contained fine particles, and the average particle size of the fine particles contained in the layer in contact with the transparent electrode is disposed above it. The average particle diameter of the fine particles contained in the layer to be formed is preferably larger.

  FIG. 5 is a schematic cross-sectional view showing another example of a display element having a porous white scattering layer composed of two kinds of fine particles having different average particle diameters.

  In a) of FIG. 5, a configuration in which a group of fine particles 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 group of fine particles 4B having a small particle diameter are arranged thereon. By adopting such a configuration, as shown in FIG. 5 b, a wide space with a sufficient electrolytic solution can be secured on the surface of the transparent electrode 1 ′. The dissolution reaction of the silver image composed of the silver particles 5 deposited thereon can be sufficiently performed. Furthermore, by arranging the fine particle 4A group having a large particle diameter only in the vicinity of the transparent electrode 1 ', it is possible to obtain a more excellent white scattering efficiency without excessively thickening the white porous layer.

  In the present invention, as a method for forming the arrangement of fine particles as shown in FIG. 4, two or more types of fine particles having different particle sizes are dissolved in an insoluble solvent of the fine particles and, if necessary, water-soluble so as not to substantially dissolve in the electrolyte. The polymer can be obtained by uniformly dispersing it in a solution containing a coating binder and then coating it on a transparent electrode. At this time, desired white scattering can be formed by appropriately selecting the particle diameters of the two or more kinds of fine particles to be used and the mixing ratio thereof.

  Further, as a method for forming the arrangement of fine particles as shown in FIG. 5, two or more kinds of fine particles having different particle diameters are used, and each fine particle is dissolved in an insoluble solvent and, if necessary, an aqueous solution that does not substantially dissolve in the electrolyte. After uniformly dispersing the functional polymer in the solution containing the coating binder and preparing each coating solution containing fine particles having different particle diameters, the coating solution containing the largest particle size is first placed on the transparent electrode. It can be formed by applying with a predetermined film thickness and then applying a coating solution containing fine particles having a small particle diameter.

  As described above, in the display element of the present invention, the particle size distribution is formed using fine particles having at least two maximum values. The particle size distribution of the fine particles in this porous white scattering layer Is preferably a distribution having a maximum value of the particle size in a range of at least 0.1 μm or more and 0.4 μm or less, from the viewpoint of further achieving the object effect of the present invention, and further at least 0.15 μm or more and 0.0. A distribution having one maximum value of the particle diameter in the range of less than 35 μm is preferable. Furthermore, the component having the above average particle diameter is preferably a component having a smaller average particle diameter.

  In FIG. 1, a), b) or c) shows a typical particle size distribution profile. In the present invention, the average particle size of any of R1, R2, and R4 is 0.1 μm or more, 0. The range of less than 4 μm is preferable, and the particle size R2 of the fine particles A1 having a small particle size is particularly preferably in the range of 0.1 μm or more and less than 0.4 μm.

  Moreover, it is preferable that the relationship between the average particle diameter R1 of the component having a large particle diameter and the average particle diameter R2 of the component having a small particle diameter is Ra / R2 = 1.5 to 4.5.

  In the present invention, as shown in FIG. 1 c), a configuration in which three or more maximum values of the particle diameter exist is possible. In that case, it is preferable that the relationship between any two arbitrary particle size maximum values is as described above, and more preferably, the relationship between two maximum values having a large number is as described above.

In the present invention, the content of the fine particles B ₁ in the particle group having the maximum particle size maximum (a in FIG. 1) is preferably 5% by mass or more and 50% by mass or less of the total fine particles.

  Examples of the fine particles that can be used in the present invention include titanium oxide, aluminum oxide, zinc oxide, magnesium oxide, calcium carbonate, barium sulfate, zinc hydroxide, magnesium hydroxide, magnesium phosphate, magnesium hydrogen phosphate, and alkaline earths. Organic compounds such as metal salts, talc, kaolin, zeolite, acidic clay, glass, polyethylene, polystyrene, acrylic resin, ionomer, ethylene-vinyl acetate copolymer, benzoguanamine resin, urea-formalin resin, melamine-formalin resin, polyamide resin Etc. These particles are desired to have no solubility in the electrolyte. In the present invention, it is preferable to use titanium oxide among the above fine particles. Titanium oxide is particularly preferable because it has a large refractive index difference from the electrolyte and can obtain a white color in a small amount.

  In the present invention, in order to form a porous white scattering layer using fine particles, 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.

<< 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)
An 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 2 cm × 4 cm glass substrate according to a known method to obtain a transparent electrode (electrode 1).

(Preparation of electrode 2)
Using a known method, 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 2 cm × 4 cm glass substrate having a thickness of 1.5 mm.

(Preparation of porous white scattering layer 1)
In an aqueous solution containing 2% by weight of gelatin, 1% by weight of polymethylmethacrylate (hereinafter abbreviated as PMMA) particles having an average particle diameter of 1 μm and 19% by weight of titanium oxide particles having an average particle diameter of 0.28 μm. % Was added and mixed and dispersed with an ultrasonic disperser. This was applied onto the electrode 1 having the sealing wall formed thereon by a screen printing method, dried at 15 ° C. for 30 minutes, and then dried at 50 ° C. for 1 hour 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 electrode 2 was covered so that the electrode surface was in contact with the electrolyte solution and heated and pressed to obtain the display element 1.

[Production of Display Element 2]
In the production of the display element 1, a display element 2 was produced in the same manner except that the porous white scattering layer 2 produced by the following method was used instead of the porous white scattering layer 1.

(Preparation of porous white scattering layer 2)
In an aqueous solution containing 2% by mass of gelatin, 3% by mass of PMMA particles having an average particle size of 1 μm, 5% by mass of zinc oxide particles having an average particle size of 0.45 μm, and an average particle size of 0.1%. 28 μm of titanium oxide particles were mixed in an amount equivalent to 12% by mass, and mixed and dispersed with an ultrasonic disperser. This was applied onto the electrode 2 on which the sealing wall was formed using a wire bar, dried at 15 ° C. for 30 minutes, and then dried at 50 ° C. for 1 hour to obtain a porous white scattering layer 2.

[Production of Display Element 3]
In the production of the display element 1, a display element 3 was produced in the same manner except that the porous white scattering layer 3 produced by the following method was used instead of the porous white scattering layer 1.

(Preparation of porous white scattering layer 3)
Titanium oxide particles having an average particle diameter of 0.45 μm and titanium oxide particles having an average particle diameter of 0.24 μm were mixed at a mass ratio of 1: 1.5 and dispersed in ethanol. This was applied on the transparent electrode 2 before providing the sealing wall so as to have a thickness of 10 μm, and heated at 350 ° C. for 1 hour to obtain a porous white scattering layer 3.

[Production of Display Element 4]
In the production of the display element 1, a display element 4 was produced in the same manner except that the porous white scattering layer 4 produced by the following method was used instead of the porous white scattering layer 1.

(Preparation of porous white scattering layer 4)
To a 2% by mass aqueous solution of polyvinyl alcohol, zinc oxide particles having an average particle size of 0.45 μm were added in an amount corresponding to 20% by mass and dispersed with an ultrasonic disperser. This dispersion was applied onto the transparent electrode 2 provided with a sealing wall by a screen printing method and dried in an atmosphere of 45 ° C.

  Next, on this layer, titanium oxide having an average particle size of 0.24 μm is added to a 2% by weight aqueous solution of polyvinyl alcohol so that the titanium oxide is equivalent to 20% by weight, and dispersed by an ultrasonic disperser. The prepared liquid was applied and dried. The particle ratio of the porous white scattering layer 4 composed of these two layers was 1.8 for titanium oxide with respect to zinc oxide 1 in terms of weight.

[Preparation of display element 5]
In the production of the display element 1, a display element 5 was produced in the same manner except that the porous white scattering layer 5 produced by the following method was used instead of the porous white scattering layer 1.

(Preparation of porous white scattering layer 5)
An amount equivalent to 20% by mass of titanium oxide particles having an average particle diameter of 0.42 μm was added to a 2% by mass aqueous solution of polyvinyl alcohol, and the mixture was dispersed with an ultrasonic disperser. This dispersion was applied onto the transparent electrode 2 provided with a sealing wall by a screen printing method and dried in an atmosphere of 45 ° C.

  Next, on this layer, titanium oxide having an average particle size of 0.21 μm is added to a 2% by weight aqueous solution of polyvinyl alcohol so that the titanium oxide is equivalent to 20% by weight, and dispersed by an ultrasonic disperser. The prepared liquid was applied and dried. The particle ratio of the porous white scattering layer 5 composed of these two layers is 2.5% of titanium oxide having an average particle diameter of 0.21 μm with respect to titanium oxide 1 having an average particle diameter of 0.42 μm. Met.

[Production of Display Element 6]
In the production of the display element 1, a display element 6 was produced in the same manner except that the porous white scattering layer 6 produced by the following method was used instead of the porous white scattering layer 1.

(Preparation of porous white scattering layer 6)
In the production of the porous white scattering layer 5, the coating amount of the titanium oxide dispersion solution is adjusted, and the average particle size is 0.21 μm as the particle ratio with respect to titanium oxide 1 having an average particle size of 0.42 μm in terms of weight. A porous white scattering layer 6 was produced in the same manner except that the titanium oxide 1 was changed to the above.

[Production of display element 7]
In the production of the display element 1, a display element 7 was produced in the same manner except that the porous white scattering layer 7 produced by the following method was used instead of the porous white scattering layer 1.

(Preparation of porous white scattering layer 7)
To a 2% by weight aqueous solution of gelatin, titanium oxide particles having an average particle diameter of 0.036 μm are added in an amount corresponding to 12% by weight, and titanium oxide having an average particle diameter of 0.15 μm is added to an amount corresponding to 8% by weight. The porous white scattering layer 7 was produced by dispersing with a disperser, forming with a screen printing method, and drying.

[Production of Display Element 8: Comparative Example]
In the production of the display element 1, a display element 8 was produced in the same manner except that the porous white scattering layer 8 produced by the following method was used instead of the porous white scattering layer 1.

(Preparation of porous white scattering layer 8)
In a 2% by weight aqueous solution of polyvinyl alcohol, zinc oxide particles having an average particle size of 0.45 μm are added so as to be equivalent to 20% by weight, dispersed by an ultrasonic disperser, formed by screen printing, and dried. A porous white scattering layer 8 was produced.

[Production of Display Element 9: Comparative Example]
In the production of the display element 1, a display element 9 was produced in the same manner except that the porous white scattering layer 9 produced by the following method was used instead of the porous white scattering layer 1.

(Preparation of white scattering layer 9)
In a 2% by weight aqueous solution of polyvinyl alcohol, titanium oxide particles having an average particle size of 0.28 μm are added so as to be equivalent to 20% by weight, dispersed by an ultrasonic disperser, formed by screen printing, and dried. A porous white scattering layer 9 was produced.

[Production of Display Element 10: Comparative Example]
In the production of the display element 1, a display element 10 was produced in the same manner except that the porous white scattering layer 10 produced by the following method was used instead of the porous white scattering layer 1.

(Preparation of white scattering layer 10)
10% by mass each of titanium oxide particles having an average particle diameter of 0.30 μm and titanium oxide particles having an average particle diameter of 0.28 μm are added to a 2% by mass aqueous solution of gelatin and dispersed by an ultrasonic disperser. The white scattering layer 10 was produced by forming and drying by a printing method.

[Production of Display Element 11: Comparative Example]
In the production of the display element 1, a display element 11 was produced in the same manner except that the porous white scattering layer 11 produced by the following method was used instead of the porous white scattering layer 1.

(Preparation of white scattering layer 11)
10% by mass each of titanium oxide particles having an average particle diameter of 0.28 μm and titanium oxide particles having an average particle diameter of 0.036 μm are added to a 2% by mass aqueous solution of gelatin and dispersed by an ultrasonic disperser. The white scattering layer 11 was produced by forming and drying by a printing method.

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

(Evaluation of whiteness)
For each display element, the white background visible light average reflectance (%) is measured using a spectrocolorimeter CM-3700d manufactured by Konica Minolta Sensing Co., Ltd., and the white scattering layer film thickness (μm) is measured. The specific whiteness per unit film thickness was determined according to

Specific whiteness = average visible light reflectance on white background (%) / white scattering layer thickness (μm)
If this specific whiteness value was 3.0 or more, it was determined that the quality was acceptable for practical use as a display element.

(Evaluation of electrode dirt resistance)
For each display element, a driving experiment was performed using a known passive matrix circuit. First, a driving condition in which the reflectance at 550 nm was 10% in black display was obtained, and white display (whitening) and black display (blackening) were driven 1000 times under this condition. Thereafter, it was whitened again, and a 1 cm square on the transparent electrode surface side was observed with a 30-fold magnifier, and the resistance to electrode contamination was evaluated according to the following criteria.

5: No undissolved silver particles are observed on the transparent electrode surface. 4: 1 to 5 undissolved silver particles are observed on the transparent electrode surface, but no coarse silver particles are generated. 3: Transparent electrode 6-10 undissolved silver particles are observed on the surface, but no coarse silver particles are generated 2: 10 or more undissolved silver particles are observed on the transparent electrode surface, and 5 coarse silver particles are also present The following occurs 1: Ten or more undissolved silver particles are observed on the transparent electrode surface, and six or more coarse silver particles are generated. The results obtained as described above are shown in Table 1.

  As is clear from the results shown in Table 1, the display element of the present invention having a porous white scattering layer having the configuration defined in the present invention achieves both whiteness and electrode stain resistance compared to the comparative example. I understand that In addition, the display element 7 was a little slow in reaction rate compared with the display elements 1-6.

It is a graph which shows an example of the particle size distribution profile of the fine particle group from which two types of average particle diameters differ. It is a schematic sectional drawing which shows the basic composition of the display element of this invention. It is a schematic sectional drawing which shows an example of the display element which comprised the porous white scattering layer using the microparticles | fine-particles of a 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 microparticles | fine-particles 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 microparticles | fine-particles 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 4, 4A, 4B Fine particle 5 Silver particle V Power supply

Claims (7)

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 Wherein at least one of the counter electrodes is a transparent electrode, the porous white scattering layer is provided on the transparent electrode, the porous white scattering layer contains at least fine particles, and the particle size distribution of the fine particles Exhibits at least two local maximum values. The porous white scattering layer has a laminated structure of two or more layers due to the difference in the particle size of the contained fine particles, and the average particle size of the fine particles contained in the layer in contact with the transparent electrode is disposed above it. The display element according to claim 1, wherein the display element has an average particle size larger than that of the fine particles contained in the layer. 2. The maximum value indicated by the particle size distribution of the fine particles contained in the porous white scattering layer has at least one maximum value in a range of 0.1 μm or more and less than 0.4 μm. Or the display element of 2. The smaller one of the particle size maximum values indicated by the particle size distribution of the fine particles contained in the porous white scattering layer is 0.1 μm or more and less than 0.4 μm. 3. The display element according to 3. Among the maximum values indicated by the particle size distribution of the fine particles contained in the porous white scattering layer, the particle size R1 indicated by the maximum value having a large particle size and the particle size R2 indicated by the maximum value having a small particle size are R1 / The display element according to claim 1, wherein R2 = 1.5 to 4.5. The said porous white scattering layer contains 5 mass% or more and 50 mass% or less of all the microparticles | fine-particles which comprise a large particle size maximum value, The any one of Claims 1-5 characterized by the above-mentioned. Display element. The display element according to claim 1, wherein at least one of the fine particles contained in the porous white scattering layer is titanium oxide.

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