JPS6230184A - Electrochromic display element - Google Patents

Abstract

PURPOSE:To provide the titled element capable of giving a multicolored display and having excellent reaction efficiency and color density, by interposing an electrolyte between a display electrode and a counter electrode, and applying a layer of an electrochromic substance containing a polynuclear transition metal cyanide to the inner face of the display electrode. CONSTITUTION:A display electrode substrate 10 is produced by attaching a display electrode 12 to a surface of a transparent insulation substrate 11 and coating the display electrode with a mixture of (A) powder obtained by coating the circumference of electrically conductive powder 14 (preferably electrically conductive white powder) with a polynuclear transition metal cyanide 15 of formula MKA[MB(CN)6]l.xH2O (MA is Fe, Co, Cu or Ag; MB is Fe, Ru, Os or Co; k, l and x are positive integer) (e.g. iron hexacyanoferrate, etc.) and (B) a binder 16, and drying the mixture to form an electrochromic substance layer 13. Separately, a counter electrode substrate 10 is produced by applying a counter electrode 22 on an insulation substrate 21. The objective element can be produced by injecting an electrolyte (e.g. potassium chloride solution) into the cell between the display electrode substrate 10 and the counter electrode substrate 20.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an electrochromic display element (hereinafter abbreviated as ECD) using an inorganic pigment exhibiting electrochromism as an electrochromic substance.

"Prior art and its problems" In recent years, ECDs have no viewing angle dependence and can display large areas.
It has been attracting attention as a display element for reasons such as its display having memory properties. A variety of organic and inorganic materials are used as display materials for ECDs, but recently, transition metal mixed-valence complexes such as iron hexacyanoferrate (Prussian blue), which is an inorganic material, have been used. , has attracted attention due to its vivid color and reversibility of the reaction. In the case of using iron hexadipenferrate, the film can be formed by an electrolytic film forming method.゛However, iron hexacyanoferrate can only display a blue color, and it is possible to change the display color by using other transition metal mixed valence complexes; In some cases, the electrolytic film forming method cannot be applied, and the electrolytic film forming process takes several hundred seconds and requires connection of electrodes for each cell, resulting in poor productivity.

The applicant focused on the fact that iron hexacyanoferrate is a type of inorganic pigment, and electrochemically produced the inorganic pigment by coating and drying a mixture of an inorganic pigment exhibiting electrochromism, a conductive powder, and a binder. They discovered that it is possible to form an EC material layer by fixing the material in such a way as to make it active, and have already applied for a patent.

However, in the EC material layer in which an inorganic pigment and a conductive powder are mixed as described above, there is a limit to the efficiency of the electrochemical reaction, and the amount of the inorganic pigment cannot be increased, so there is a limit to the color density. Also, the response to coloring and decoloring was slow.

"Objective of the Invention" The object of the present invention is to improve the clarity of the color of transition metal mixed valence complexes, typified by iron hexacyanoferrate, the stability of the reaction, and the ability to change the display color by changing the type of transition metal. While maintaining the diversity of display that can be achieved, the efficiency of the reaction can be increased and the color density can be increased.
The goal is to provide D.

"Structure of the Invention" The present inventor focused on the fact that a transition metal mixed valence cone, typified by iron hexacyanoferrate, is a compound of two types of transition metals, and developed a method for contacting an inorganic pigment with a conductive powder. The present invention was accomplished by studying various ways to improve the performance.

That is, the present invention provides an electrochromic display element in which an electrolyte is interposed between a display electrode and a counter electrode, and an electrochromic material layer is formed at least inside the display electrode, wherein the electrochromic material layer has the following: It is characterized in that it is formed by coating and drying a mixture containing a binder and a polynuclear transition metal cyanide represented by the general formula [1] coated around a conductive powder.

MC[MB(CN)61.1 ・! H20=...■
(However, M4 is Fe, Go, Cu, or Ag; P is Fe, Ru, Os, or Go; k
, 1. x represents a positive integer) In the present invention, an EC material layer is formed by applying and drying a mixture containing a powder in which polynuclear transition metal cyanide is coated around a conductive powder and a binder. Therefore, various polynuclear transition metal cyanides can be used as EC materials, and display colors can be diversified. In addition, EC substances (
Since the polynuclear transition metal cyanide (polynuclear transition metal cyanide) is deposited around the conductive powder, electron transfer between the electrode and the EC material is smooth, and an ECD with a fast response can be obtained.

Although the structure of the ECD of the present invention is not particularly limited, it can be, for example, the following structure. That is, a transparent display electrode made of indium oxide, tin oxide, etc. is formed on a transparent insulating substrate such as glass, and then an EC material layer is formed by coating and drying the above mixture on this display electrode. Ru. In this case, the display electrodes and the EC material layer are patterned. On the other hand, a counter electrode made of a transparent electrode or a metal thin film similar to the above is formed on another insulating substrate. Then, the insulating substrate on which the display electrode is formed and the insulating substrate on which the counter electrode is formed are bonded together via a spacer, and the peripheral portion is adhesively sealed with epoxy resin or the like. An electrolytic solution is injected into the cells thus formed to form an ECD. Note that an ion-permeable white background plate or the like may be provided between both substrates, and further,
If white conductive powder is used as the conductive powder, the white background plate can be omitted. Furthermore, the EC material layer may be formed on both the display electrode and the counter electrode.

To explain the EC material layer in more detail, in the present invention, a polynuclear transition metal cyanide represented by the general formula [1] is used as the EC material. The polynuclear transition metal cyanide is deposited around the conductive powder. As mentioned above, the conductive powder is preferably white, and specifically, rW-1 (N (trade name, manufactured by Mitsubishi Metals Corporation) etc. can be used. EC
In the case of a material layer, non-white powder such as carbon can also be used as the conductive powder.

As a method for depositing polynuclear transition metal cyanide around the conductive powder, for example, after depositing MA (transition metal) in the general formula (3) around the conductive powder in advance,
A method of reacting with (CN)6 ions (transition metal cyanide ions) can be adopted.

To form a thin film of transition metal around the conductive powder, there are methods such as immersing the conductive powder in a solution containing the transition metal ions, but a plating method is suitable. Furthermore, among the plating methods, electroless plating is more suitable for uniformly plating fine powder. Furthermore, in order to react this transition metal with transition metal cyanide ions, conductive powder with a thin transition metal film formed by a plating method or the like is dispersed in an aqueous solution and mixed with an aqueous solution containing transition metal cyanide ions. good.

The powder thus obtained is mixed with a binder, for example a 3% solution of polymethyl methacrylate resin in carpitol acetate. Then, by applying this liquid mixture in a predetermined pattern by means such as screen printing and drying, an EC material layer can be obtained.

Note that various electrolytes such as potassium chloride, rubidium chloride, cesium chloride, and potassium sulfate can be used as the electrolyte.

"Embodiments of the Invention" FIG. 2 shows the structure of a display electrode substrate 10 employed in an ECD according to the present invention. That is, a transparent electrode 12 is formed in a predetermined pattern on an insulating substrate such as glass.
is formed. Then, on this transparent electrode 12, an EC
A material layer 13 is formed. The EC material layer 13 includes a conductive powder 14 surrounded by a polynuclear transition metal cyanide 15, which is dispersed and fixed in a binder 18.

In this example, conductive white powder rW-10J (trade name, manufactured by Mitsubishi Metals Corporation) is used as conductive powder 14, polynuclear transition metal cyanide 15 is iron hexacyanoferrate, and binder 1B is is polymethyl methacrylate resin (abbreviation: PMMA, product name: ``Acrivet'')
A 3% carpitol acetate solution (manufactured by Mitsubishi Rayon Co., Ltd.) was used. That is, after activating the above conductive white powder with an electroless plating pretreatment agent rAT-804 (trade name, manufactured by World Metal Co., Ltd.), ferrous sulfate 30g1n, sodium potassium tartrate 50g/
l, sodium hypophosphite lOg/l was mixed into an electroless plating solution adjusted to pH 9 with potassium hydroxide,
It was immersed for 20 minutes at a liquid temperature of 75°C. Thereafter, it was washed with water to obtain a conductive white powder coated with an iron film. This powder is dispersed in water and mixed with a 0.02X aqueous solution of potassium ferrocyanide to form iron hexadi7onaferrate on the surface of the powder. This powder was washed with water and dried to obtain a blue powder. To this, polymethyl methacrylate resin was added as a binder.
% calpitol acetate solution was added and mixed in a mortar. The thus obtained dispersion liquid was collected with a dropper and dropped onto the transparent electrode 12 of the insulating substrate 11. And 1
The EC material layer 13 was formed by drying at 00° C. for 15 minutes.

Using the display electrode substrate 10 thus obtained, a cyclic portamogram was measured by a three-electrode method as shown in FIG. 3, and the electrochromism characteristics were investigated. In addition, in FIG. 3, 31 is a silver silver chloride reference electrode, 32 is a platinum mesh counter electrode, 33 is a 0.5 molar potassium sulfate aqueous solution, and 34
is a beaker, 35 is a potentiostat, and 36 is an X-Y
It's a recorder. The cyclic portamogram thus obtained is shown in FIG. 4. As shown, a clear redox peak was obtained, and at the same time, a clear color change from reddish-purple to white was obtained in the EC material layer 13. Further, the absorption spectrum of the EC material layer is shown in FIG. 5, and A and B in FIG. 5 correspond to points A and B in FIG. 4.

Further, after measuring a cyclic portamogram using a triangular wave, a rectangular wave was applied to investigate the response characteristics of the EC material layer 13. For comparison, the response characteristics of an EC material layer obtained by coating and drying a liquid mixture of iron hexacyanoferrate pigment powder, white conductive powder, and binder were similarly investigated. The results are shown in Table 1.

Table 1 (Voltage indicates the value of the reference electrode against silver and silver chloride).
A CD is shown. In this case, the counter electrode substrate 20 is
A counter electrode 22 is provided on the surface of an insulating substrate 21 made of glass or the like.
is formed, and an EC material layer 23 similar to the display electrode substrate 10 is further formed on this counter electrode 22.

Then, the one display electrode substrate lO and the counter electrode substrate 20 are bonded together via the spacer 17, and the peripheral portion is sealed with epoxy resin or the like. Furthermore, an electrolytic solution 18 consisting of a 0.5 molar potassium sulfate aqueous solution is injected into the cell, and the E
A CD is configured. This ECD exhibits a clear color change in which it becomes blue by applying +0.2 V to the display electrode 12 with the counter electrode 22 as a reference, and becomes white by applying 10.8 V to the display electrode 12. Ta.

Next, the electroless plating solution was mixed with 10 g/l of cupric sulfate, 50 g/l of potassium sodium tartrate, and 1 g/l of sodium hydroxide.
0g/41, formalin (37%) 10m/m instead of a solution, the conductive white powder was immersed in this solution for 20 minutes at room temperature, but otherwise the same method as above was used to coat the surface of the conductive white powder. A reddish-purple powder forming hexacyanoferrate steel was obtained. Similarly, cobalt is added to the conductive white powder.
After electroless plating with silver, a powder was obtained as a hexagonal iron complex. In addition, conductive white powder electrolessly plated with iron in the same manner as above was dispersed in water and mixed with a 0.02M aqueous solution of cobalt potassium cyanide to obtain a yellow powder with iron hexacyanocobaltate formed on the surface. Ta. Furthermore, the conductive white powder electrolessly plated with iron in the same manner as above was reacted with hexacyanide of ruthenium and osmium, respectively, to form iron hexacyanoruthenate and iron hexadi7noosmate on the surface. powder was obtained. The EC material layer 13 shown in FIG. 2 was formed using each of these powders in the same manner as described above. Using each display electrode substrate lO obtained in this way, a third
Electrochromism characteristics were investigated using the three-electrode method shown in the figure. The results are shown in Table 2. All the color changes in Table 2 showed good reversibility.

(Hereinafter, blank spaces) Table 2 It should be noted that ECDs can be created in the same manner for polynuclear transition metal cyanides other than the above-mentioned examples, and it is clear that a highly reversible display can be achieved thereby.

"Effects of the Invention" As explained above, according to the present invention, the EC material layer is formed by applying and drying a mixture of a powder coated with polynuclear transition metal cyanide and a binder around a conductive powder. So,
It becomes possible to use various polynuclear transition metal cyanides that could not be used as EC materials because they could not be electrolytically formed, thereby making it possible to diversify display colors. Further, electron transfer between the electrode and the EC material (polynuclear transition metal cyanide) is made smooth, and an ECD with a fast response can be obtained.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the ECD according to the present invention, FIG. 2 is a partially enlarged sectional view showing the display electrode substrate of the EGO, and FIG. 3 is a circuit for investigating the electrochromism characteristics of the display electrode substrate. FIG. 4 is a cyclic portamogram obtained by the method shown in FIG. 3, and FIG. 5 is a chart showing the absorption spectrum of the EC material layer in the display electrode substrate. In the figure, IO is a display electrode substrate, 11 is an insulating substrate, and 12
1 is a transparent electrode, 13 is an EC material layer, 14 is a conductive powder, 1
5 is a polynuclear transition metal cyanide, 1B is a binder, 17 is a spacer, 18 is an electrolytic solution, 20 is a counter electrode substrate, 21 is an insulating substrate, 22 is a counter electrode, and 23 is an EC material layer.

Claims (3)

[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, the electrochromic material layer includes a polynuclear transition metal cyanide represented by the following general formula [1] around a conductive powder. An electrochromic display element characterized in that it is formed by coating and drying a mixture containing deposited powder and a binder. M^A_k[M^B(CN)_6]_l・xH_2O...
...[1] (However, M^A represents any one of Fe, Co, Cu, or Ag, M^B represents any one of Fe, Ru, Os, or Co, and k, l, and x represent positive integers.) (2) In claim 1, the general formula [1
An electrochromic display element in which the polynuclear transition metal cyanide is formed by depositing M^A in advance around the conductive powder and then reacting it with M^B(CN)_6 ions. (3) In claim 2, the general formula [1
An electrochromic display element in which M^A according to ] is deposited around the conductive powder by an electroless plating method.