JPS6244719A - Electrochromic display element - Google Patents

Abstract

PURPOSE:To obtain the titled element having an improved reactivity of an oxidation reduction substance and an improved responsitivity and a long display life by coating a counter electrode with a mixture of powders coated surroundings of an electric conductive powders with a white oxidation-reduction substance and a binder, and then by drying it, thereby providing the oxidation- reduction substance layer on the counter electrode. CONSTITUTION:The counter electrode 2 is formed on the counter electrode substrate 1 composed of a glass, and the oxidation reduction substance layer 3 is formed on the counter electrode 2. The oxidation reduction substance layer 3 comprises the powder coated the surroundings of the while electric conductive powders 5 with the white oxidation-reduction substance 4. The prescribed powders are dispersed and fixed in the binder 6. The white oxidation-reduction substance 4 is composed of a hexacyanostannous ferrate. The white electric conductive powder 5 is composed of W-10. Thus, the ECD having the improved reactivity of the oxidation-reduction substance layer and the good responsibility may be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an electrochromic display element (hereinafter referred to as
(abbreviated as ECD), and particularly relates to improvements in counter electrode materials.

"Prior Art and its Problems" In recent years, ECUs have been attracting attention as display devices because they have no viewing angle dependence, can display large areas, and have memory properties in their displays. As display materials for EC[l, inorganic materials such as tungsten oxide and Prussian blue, and organic materials such as dicarboxylated heptyl viologen are used. When viewed from the operating principle, the characteristics of ECD are that electrochromic substances (
This means that a coloring/decoloring reaction of the EC substance (hereinafter abbreviated as EC substance) is occurring. In this case, it must be noted that a reverse reaction of the display electrode is occurring at the opposite electrode. Therefore, what is required of the counter electrode is to stably perform a redox reaction with good reversibility, and to have little variation in the potential of the counter electrode itself due to one reaction, and to quickly converge to a constant potential. This includes things that are trending.

One way to satisfy these conditions is to form the same amount of the same EC material as the display electrode on the counter electrode. In this case, the reactions at the two electrodes are completely opposite and the amount of reaction is equal, so driving is easy. However, in such a symmetrical ECD, if the amount of reaction between the display electrode and the counter electrode differs due to external factors such as temperature changes and light irradiation, or internal factors such as peeling of the display electrode, the number of operations will decrease. The drawback is that as they are stacked, they accumulate colored or discolored particles and eventually stop working.

Another method is to mix a substance that exhibits a stable oxidation-reduction reaction, such as Prussian blue, and a substance with a very large specific surface area, such as carbon black, together with resin or other paint, and apply the mixture on the counter electrode. This is also being done. According to this method, although a good ECD can be obtained, there are problems in the cell structure, as with the symmetrical ECD described above. That is, in order to prevent the counter electrode from being seen from the display surface, it is necessary to provide a white background plate within the electrolyte between the display electrode and the counter electrode. As this white background plate, a ceramic plate with a thickness of 0.2 to 0.5 mm,
Alternatively, fluororesin molded plates are often used. However, these white background plates occupy a large portion of the ECD cell in terms of cost, and there is a problem in that the ECD cell thickness cannot be made thinner than the thickness of the white background plate.

To solve this problem, the applicant has already proposed an ECD in which a counter electrode is formed by coating and drying a mixture of a white redox substance, a white conductive powder, and a binder.

However, simply mixing a redox substance and a conductive powder has a limit to the efficiency of the electrochemical reaction, and the amount of white redox substance cannot be increased, so there is a limit to the stability of one reaction. The response to coloring and decoloring was also slow.

``Object of the Invention'' The purpose of the present invention is to solve the problems of the prior art described above, to provide the counter electrode with the dual functions of redox reaction and white color, and to further increase the reactivity of the redox substance to improve responsiveness. The purpose of the present invention is to provide an ECD with a fast display life and a long life.

"Structure of the Invention" The present inventor has studied various methods for improving the contact between the white redox substance and the conductive powder in order to improve the electrochemical reaction efficiency of the white redox substance, and as a result, the present inventor has developed the present invention. This is what led to the eggplant.

That is, the present invention provides an EdD in which an electrolyte is interposed between a display electrode and a counter electrode, and an EC material layer is formed at least on the inside of the display electrode, and a white redox material is coated on the counter electrode as a conductive powder. A redox substance layer is provided around the periphery of the oxidation-reduction substance layer formed by coating and drying a mixture containing a powder and a binder. However, here, white means white or a color close to white.

Therefore, due to the white redox substance coated around the conductive powder, the counter electrode becomes white or a color close to it, and the white background plate, which is essential in conventional reflective display type ECUs, can be omitted. can. In addition, since the white redox substance is coated around the conductive powder, electron transfer between the electrode and the white redox substance is smooth.
When used as an ECD, an element with quick response and long display life can be obtained.

The ECD of the present invention is not particularly limited, but may have the following configuration, for example. That is, a transparent display electrode made of indium oxide, tin oxide, etc. is formed on a transparent insulating substrate such as glass, and an EC material layer made of tungsten oxide, Prussian blue, etc. is roughly placed on top of this display electrode in a vacuum. It is formed by a 75 deposition method, an electrolytic deposition method, or the like. In this case, the display electrode and the EC material layer may be patterned. On the other hand, a counter electrode made of the same transparent electrode or metal thin film as above is formed on another insulating substrate. Furthermore, a mixture containing a binder and a powder in which a white redox substance is coated around conductive powder is applied onto the electrode and dried to form a redox substance layer. Then, the insulating substrate on which the display electrodes are formed and the insulating substrate on which the counter electrodes are formed are bonded together via a spacer, and the peripheral portions are adhesive-sealed with epoxy resin or the like. By injecting electrolyte into the cells thus formed, EGD
is configured. Potassium chloride is used as an electrolyte.

Various compounds such as rubidium chloride and cesium chloride can be used, and the pH may be adjusted as necessary. In the present invention,
Since there is no need to install a white background plate between the display electrode and the counter electrode, the thickness of the spacer can be arbitrarily set as required.

In the present invention, the white redox substance is not particularly limited, but polynuclear transfer metal cyanide represented by the following general formula 0 is preferred.

Regarding the polynuclear transition metal cyanide represented by the formula M2[Fe(Ill:N)6]・””・■(However, is Ni or Sn.)■The redox potential, oxidation color, and reduction color are It is shown in Table 1.

Table 1 In order to deposit the white redox substance consisting of the above polynuclear transition metal cyanide on the conductive powder, for example, the above general formula [
Preferably, a method can be employed in which M in formula 1] is preliminarily deposited around a conductive powder and then reacted with Fe(CN)6 ions to form a polynuclear transition metal cyanide. In this case, in order to adhere the wings in the above general formula 0 around the conductive powder, a method such as immersing the conductive powder in a solution containing this transition metal ion can be used, but a plating method is adopted. It is preferable. Among the plating methods, electroless plating is more preferred in order to uniformly plate the conductive powder.

Further, in the present invention, it is more preferable to use white conductive powder as the conductive powder. By using white conductive powder, the degree of whiteness can be further increased. As the white conductive powder, for example, rW-10J (trade name, manufactured by Mitsubishi Metals Corporation), which is made by coating the surface of titanium oxide fine particles with a transparent conductive film, can be used.

The thus obtained white redox substance coated around the conductive powder is mixed with a binder such as a 3% carpitol acetate solution of polymethyl methacrylate resin, applied onto the counter electrode, and dried. By doing so, it is possible to whiten the counter electrode and form a redox substance layer that imparts a redox function.

Embodiments of the Invention Example 1 FIG. 2 shows the structure of a counter electrode substrate employed in an ECD according to the present invention. That is, the counter electrode 2 is formed on a counter electrode substrate i made of glass or the like. A redox material layer 3 is formed on the counter electrode 2.

This redox substance layer 3 has a powder formed by coating a white redox substance 4 around a white conductive powder 5, and this powder is dispersed and fixed in a binder B.

In this example, tin hexacyanoferrate is used as the white redox substance 4, and rW-toJ (trade name, manufactured by Mitsubishi Metals Corporation) is used as the white conductive powder 5. White redox substance 4 is converted into white conductive powder 5
To describe the method of forming the white conductive powder 5 by coating it around the electroless plating pretreatment agent FAT-8,
After activation treatment with 0J (trade name 1 manufactured by World Metal Co., Ltd.), the plate was immersed in an electroless plating solution. This electroless plating solution was made by mixing 0.08M of stannous chloride, 0.34M of sodium citrate, 0.08M of ethylenediaminetetraacetic acid disodium salt, 0.20M of sodium nitrilotriacetate, and 0.04M of titanium trichloride. , P)I was adjusted to 9 with potassium hydroxide.

The immersion in the electroless plating solution was carried out at a solution temperature of 8° C. for 20 minutes. Thereafter, it was washed with water to obtain a white conductive powder 5 coated with a tin film. By dispersing this white conductive powder 5 in water and mixing it with a 0.02M aqueous solution of potassium ferrocyanide, the tin deposited around the white conductive powder 5 was made into tin hexadi7ferrate. This powder was washed with water and dried to obtain a powder nest in which a white redox substance 4 made of tin hexadipenferrate was adhered around the white conductive powder 5. This powder is mixed with a binder 6 consisting of a 3% calpitol solution of polymethyl methacrylate resin (abbreviated as PNMA, trade name "Acrivet", manufactured by Mitsubishi Rayon Co., Ltd.) to form a dispersion. Collect this dispersion with a dropper]
Then, it is dropped onto the counter electrode 2 of the counter electrode substrate l.

Then, it was dried at 100°C for 15 minutes, and the redox substance layer 3
was formed.

Using the counter electrode substrate 1 thus obtained, a cyclic portamogram was measured by a three-electrode method as shown in FIG. 3, and redox characteristics were investigated. In FIG. 3, 21 is a silver silver chloride reference electrode, 22 is a platinum mesh counter electrode, and 23 is a 0.0.
5M potassium sulfate aqueous solution.

24 is a beaker, 25 is a potentiostat, 2B is an X
-Y recorder, 27 is a waveform oscillator. The cyclic portammogram thus obtained showed redox peaks with good symmetry. ! ! The difference between the conversion peak potential and the reduction peak potential is shown in Table 2 (Example 1). Furthermore, after measuring the cyclic portamogram using the triangular wave of the waveform oscillator 27 in FIG.
A rectangular wave was applied to measure the reactivity of the redox material layer 3, that is, the time until the current value became constant. The results are also shown in Table 2. In addition, during the redox reaction,
The redox material layer 3 remained white.

FIG. 1 shows an ECD made using the counter electrode substrate 1 shown in FIG. 2. In FIG. That is, a transparent display electrode 8 is formed on a display electrode substrate 7 made of glass, and a transparent display electrode 8 made of a Zolcian blue thin film is further formed on this display electrode 8.
A C material layer 8 is formed. This EC material layer 9 is obtained by immersing the display electrode 8 of the display electrode substrate 7 in an equimolar mixed solution of ferric chloride and potassium ferricyanide, and polarizing the display electrode 8 negatively using a platinum electrode as a counter electrode. Then, the display electrode substrate 7 and the counter electrode substrate 1 are bonded together with the spacer 10 interposed therebetween, and the peripheral edges are sealed with epoxy resin.

Further, an electrolytic solution 11 consisting of a 0.5 molar potassium sulfate aqueous solution is injected into the cell. This EC[l
By applying +〇, 2V to the display electrode 8 with the counter electrode 2 as a reference, a blue color with a white background is displayed,
By applying -o, e v to the display electrode 2, a clear color change in which only the white background was visible was exhibited.

Example 2 In the above example, the white redox substance 4 was replaced with hexadiene 7
) It was carried out in the same manner as in Example 1 except that nickel ferrate was used. The white redox material 4 made of nickel hexacyanoferrate was deposited around the white conductive powder 5 in the following manner. The electroless plating solution is nickel 45g/i, sodium citrate 10g/i.
0 gel, ammonium chloride 50 g/u, and sodium hypophosphite 11 g/4, and the pH was adjusted to 9 with aqueous ammonia. After activating the white conductive powder 5 with an electroless plating pretreatment agent rAt-8o J (trade name, manufactured by World Metal Co., Ltd.), it was immersed in the electroless plating solution at 90°C for 20 minutes to remove nickel. Obtained white conductive powder 5 with
Next, by mixing this white conductive powder 5 with a 0.02M aqueous solution of potassium ferrocyanide in the same manner as in Example 1, the nickel deposited around the white conductive powder 5 was converted to nickel hexadipentaferrate. . This powder was washed with water and dried to obtain a powder in which a white redox substance 4 made of hexadiene, iron, and nickel was adhered around the white conductive powder 5.

Using this powder, a redox substance layer 3 was formed on the counter electrode 2 of the counter electrode substrate 1 in the same manner as in Example 1. Using this counter electrode substrate 1, a cyclic portamogram was measured by the three-electrode method shown in FIG. 3, and as a result, a redox peak with good symmetry as shown in FIG. 4 was obtained. Further, the difference between the oxidation peak potential and the reduction peak potential at this time is shown in Table 2 (Example 2). Furthermore, after measuring the cyclic portamogram using the triangular wave of the waveform oscillator 27 in FIG. The time was measured. The results are also shown in Table 2, and the color of the redox substance layer 3 was pale blue to white.

Comparative Example 1 As the redox substance layer 3, white conductive powder "To 10" (
(product name, manufactured by Mitsubishi Metals Corporation), tin hexacyanoferrate powder, and polymethyl methacrylate resin (abbreviated as PMN)
A, using a layer prepared by coating a solution mixed with a binder consisting of a 3% calpitol solution (trade name: "Acrypet", manufactured by Mitsubishi Rayon Co., Ltd.) and drying it, and otherwise forming a counter electrode in the same manner as in Example 1. A substrate 1 was formed. Furthermore, using this counter electrode substrate 1, the difference between the oxidation peak potential and the reduction peak potential and the redox substance layer 3 were measured in the same manner as in Example 1.2.
The reactivity, that is, the time it takes for the current value to become constant, was measured. These results are shown in Table 2 (Comparative Example 1).

Comparative Example 2 As the redox substance layer 3, white conductive powder “TolO” (
(product name, manufactured by Mitsubishi Metals Corporation), nickel hexadi-7-ferrate powder, and polymethyl methacrylate resin (abbreviated as P
A layer obtained by applying a mixture of MMA (trade name: "Acrypet", manufactured by Mitsubishi Rayon Co., Ltd.) with a binder consisting of a 3% carpitol solution and drying was used, and the rest was Example 1.
Similarly, the counter electrode substrate! was formed. Furthermore, using this counter electrode substrate 1, the difference between the oxidation peak potential and the reduction peak potential and the reactivity of the redox substance layer 3, that is, the time until the current value becomes constant, were measured in the same manner as in Example 1.2. It was measured. These results are shown in Table 2 (Comparative Example 2).

From Examples 1 and 2 and Comparative Examples 1 and 2, E according to the present invention
It can be seen that C[+ has good reactivity of the redox substance layer 3.

Table 2 "Effects of the Invention" As explained above, according to the present invention, there is a redox substance layer in which a powder coated with a white redox substance is fixed via a binder around a conductive powder. , it is possible to improve the reactivity of the redox substance layer and obtain an ECD with good responsiveness. Furthermore, the counter electrode can be made white, and the white background plate can be omitted.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the EGD according to the present invention, FIG. 2 is a partially enlarged view showing the opposing electrode portion of the ECD, and FIG.
The figure is a block diagram showing a circuit for investigating the electrochromism of the counter electrode portion, and FIG. 4 is a chart showing a cyclic portamogram obtained by the method of FIG. 3. In the figure, l is a counter electrode substrate, 2 is a counter electrode, 3 is a redox material layer, 4 is a white redox material, 5 is a white conductive powder,
6 is a binder, and 7 is a display electrode substrate. 8 is a display electrode, 9 is an EC material layer, and 11 is an electrolyte.

Claims (1)

[Claims] (1) An electrolyte is interposed between the display electrode and the counter electrode,
In an electrochromic display element in which an electrochromic material layer is formed inside at least the display electrode, a mixture containing a powder in which a white redox material is coated on the counter electrode around a conductive powder and a binder; An electrochromic display element characterized in that a redox substance layer is formed by coating and drying. (2) The electrochromic display element according to claim 1, wherein the white redox substance is a polynuclear transition metal cyanide represented by the following general formula [1]. M_2[Fe(CN)_6]...[1] (However, M represents Ni or Sn.) (3) In claim 2, M in the general formula [1] is previously set to the conductive After adhering to the surrounding powder,
An electrochromic display element in which the polynuclear transition metal cyanide is formed by reacting with Fe(CN)_6 ions. (4) In claim 3, the general formula [1
] An electrochromic display element in which M is deposited around the conductive powder by an electroless plating method.