JPS61275376A - Electrochromic display element - Google Patents

Abstract

PURPOSE:To obtain an electrochromic display element formed of a coloring membrane, which is excellent in coloring developing and discoloring characteristics and is in a colorless state when erased, by using a specific condensed tungstic acid contg. a peroxo or peroxide ion as a coloring material. CONSTITUTION:An electrochromic display element which uses a peroxo-contg. condensed tungstic acid of the chemical formula WO3.xCO2.yH2O2.XH2O (wherein 0<=x<=0.25; 0.05<=y<=1; 0.16<z<=3.5) or a condensed tungstic acid contg. a peroxo or a peroxide ion in which carbon constitutes a heteroatom. The condensed tungstic acid is easily soluble in a polar solvent such as water or alcohol unless it is heated at a temp. of 100 deg.C or above. When the soln. is applied onto a plate and dried at a temp. of 100 deg.C or above, a dehydration condensation reaction proceeds, which makes it difficult to dissolve in a polar solvent such as water, alcohol, propylene glycol, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electrochromic display element, and particularly to an electrochromic display element having a coloring material that is advantageous for cost reduction.

[Background of the invention]

Conventionally, electrochromic display elements (hereinafter referred to as EC) use a thin film of a transition metal oxide such as tungsten oxide as a coloring film, and an electrolytic solution such as a propylene carbonate solution of lithium perchlorate or a solid ion conductive material as an electrolyte.
D), or an ECD that combines a coloring film and a dielectric such as tantalum oxide, is known, but it has the drawback of being expensive. This is mainly due to the fact that the formation of thin films such as coloring films relies on vacuum techniques such as vapor deposition and sputtering.

In order to overcome the above-mentioned drawbacks, a method has recently been attempted in which a solution containing an organic compound of tungsten is applied onto a conductor and thermally decomposed (Japanese Patent Laid-Open No. 56-38379).

However, in this method, in order to obtain a thin film with good coloring and erasing characteristics, the decomposition temperature must be kept below 300C, and the problem is that the film decomposed at a temperature below 300C is colored brown. be. This coloration is thought to be due to the fact that the organic compound was thermally decomposed and a colored carbon compound remained in the film.

[Purpose of the invention]

An object of the present invention is to provide an electrochromic display element using a coloring film that is formed by an inexpensive coating method, has excellent coloring and erasing properties, and becomes colorless and transparent when erasing.

[Summary of the invention]

For this purpose, in the present invention, the chemical formula Wo3.xcOz
・YHzOx ・Condensed tungstic acid (nature
), vol. 312, p. A3994.537 (1984
)) was used as a coloring film. This condensed tungstic acid is easily dissolved in polar solvents such as water and alcohol unless heated to 100C or higher. Furthermore, when a solution is applied onto a substrate and dried at a temperature of 100C or higher, dehydration condensation progresses, making it difficult to dissolve in polar solvents such as water, alcohol, and propylene carbonate.

ECD has the property that dehydration condensation easily progresses by drying at a temperature of 1000°C or higher, making it difficult to dissolve in polar solvents.
This is an important property as a color-forming material. In particular, this property is essential for devices that use an electrolytic solution such as a propylene carbonate solution of lithium perchlorate. This property does not exist in phosphotungstic acid, which is a condensed tungstic acid with phosphorus as a petro atom, which has been widely known in the past. Phosphortungstic acid dissolves in water and propylene carbonate even when heated with aooc. The coloring film of the present invention is:

It can be obtained by drying preferably at a temperature between 100 and 300C.

As mentioned above, condensed tungstic acid containing peroxo or containing peroxo with carbon as a heteroatom can be formed into a uniform thin film by the extremely simple and inexpensive coating method. Further, it is also possible to easily form a pattern using a photoresist using a normal method. Therefore,
The device can be created using a method similar to ECD using tungsten oxide as a coloring film. An example of an element using an electrolytic solution as the electrolyte is shown in FIG.

In FIG. 1, l is a glass substrate on the display electrode side, 2 is a transparent conductive film, 3 is a coloring film, 4 is a protective film for the transparent conductor 2 formed of, for example, a vapor deposited film of silicon dioxide, and 5 is an electrolytic film. liquid,
6 is a counter electrode, 7 is a glass substrate on the counter electrode side, 8 is a spacer, and 9 is a background material inserted into the electrolytic solution.

For example, L I CZO4#Na
An organic solution of an alkali metal salt such as CZO4tLiBF4 in propylene carbonate or r-butyrolactone is used, and the background material 9 inserted therein includes a porous alumina substrate and a porous Teflon filled with titanium oxide powder as a white pigment. A sheet or the like is used. It is also possible to use a thin layered solid electrolyte such as Na-β-A12os instead of the electrolyte. The counter electrode 6 includes a conductor 6' such as a transparent conductor or metal provided on a glass substrate 7, and a conductor 6' provided on the conductor such as carbon and amorphous iron tungstate Few (WOJs or manganese oxide MnQ, etc.). It is formed using a fired product 6" which is mixed and fired with a transition metal oxide powder of The transparent conductor 61 is bonded to the spacer 8 using an adhesive such as epoxy so that it is in direct contact with the spacer 8 .

Using the method described above, elements containing peroxo or condensed tungstic acid containing peroxo with carbon as a heteroatom were created as a coloring material, and the one-shot decoloring characteristics, that is, response speed and coloring efficiency were investigated. It has been found that this device can provide properties comparable to those of conventional devices using vapor-deposited tungsten oxide films as coloring materials.

[Embodiments of the invention]

Hereinafter, the details of the present invention will be specifically shown in Examples.

Example 1 Condensed tungstic acid (named CWHPA) containing carbon as a heteroatom and containing peroxo was synthesized by the method shown below. After dissolving 16g of tungsten carbide in 200ml of 15% hydrogen peroxide solution.

Insoluble and undissolved components were removed by filtration to obtain a yellow aqueous solution. After removing excess hydrogen peroxide from this aqueous solution using a platinum mesh, it was dried at a temperature of room temperature to 50C to obtain a yellow amorphous solid (CWHPA). This substance was determined by compositional analysis, redox titration and thermogravimetric analysis, with the general formula WOa x
x, y, and z of COz-yH2o2-zH2° are each 0.08≦X≦0.25゜0.05≦y≦1.0.3≦
It was found that 2≦4. I think that the reason why there is a strange appearance in X + Y, z is due to the way hydrogen peroxide was added when obtaining the yellow aqueous solution, the way excess hydrogen peroxide was removed, and changes in atmospheric humidity. There is.

A solution in which 2 g of the obtained CWHPA was dissolved in 1-1 water was applied to the glass to which the conductive film was attached using a spin cord.

The rotation speed is i, ooo, aooo per minute.

The film thickness of CWHPA was 2°0.7 and 0.4μm at s and ooo rotational speeds, respectively. These in air at 150C
Heated for 920 minutes. By thermogravimetric analysis, the general formula x
, y remains unchanged, but 2 becomes approximately 2. The solubility of this heat-treated CWf (PA) in water was lower than before heating. A part of the heat-treated CWHPA was dissolved in an alkaline aqueous solution to form a current collecting part of a coloring electrode.

Using propylene carbonate containing lithium perchlorate as an electrolytic solution, the heat-treated CWHPA was reduced at a current of 0.03 mA/crn"#amount of electricity 10 m C7 cm". As a result, a blue color was observed regardless of the thickness of the thin film. On the other hand, it was also confirmed that oxidation causes decolorization.

Example 2 A carbon-free peroxo-containing condensed tungstic acid (named WIPA) was synthesized by dissolving tungsten metal powder in hydrogen peroxide. The details of the synthesis are the same as in Example 1.

The composition of the obtained yellow amorphous solid (WIPA) is represented by "*Y*z" in the general formula shown in Example 1, where X=0.0
．． It was found that 05≦y≦1, 0.3≦2≦4. As in Example 1, a thin film of WIPA was coated with a spin cord on glass to which a conductive film was attached, and 1501:
After heat treatment in ', color development and fading due to electrolytic reduction and oxidation was investigated, and it was found that the same properties as in Example 1 were exhibited.

Example 3 An experiment similar to Example 1 was conducted except that the heat treatment conditions were changed. Heat treatment at 100C for 10 seconds.

It was found by thermogravimetric analysis that when carried out at 300C for 20 minutes, 2 in the general formula of CWHPA becomes approximately 3.5 and 0.2, respectively. Color development and fading due to electrolytic reduction and oxidation was also observed in such samples. However, no color developed after heat treatment for 35,001 minutes. This is considered to be because CWHPA itself was decomposed.

Example 4 In the same manner as in Example 1, indium oxide (Inzos)
CWHPA was deposited at a thickness of 0.4 µm on a glass substrate coated with a transparent conductive film with a sheet resistance of 10 Ω/cm'' whose main component was
m was formed. Then, it is subjected to normal photoresist processing.
The cell shown in FIG. 1 was prepared by slamming V%'HPA. The cell electrolyte used was 1 M/l of lithium perchlorate dissolved in glopylene carbonate, the protective film of the transparent conductive film was silicon dioxide, and the background material was a porous Teflon sheet containing titanium dioxide, a white pigment. used. Also,
The counter electrode was created by adhering fibrous carbon onto a transparent conductive film with a sheet resistance of 10 Ω/cm.The voltage applied to the thus created cell during color development was 1.OV (negative on the color development film side).

The applied voltage during decolorization was 1.5 V (positive on the coloring film side, negative on the opposite electrode side), and a square wave of 1 cycle/second was continuously applied to develop and decolorize. We investigated the characteristics. As a result, with an application time of 0.5 seconds, the color density, expressed as a contrast ratio, was approximately 2. , reached O friend. Further, the amount of charge injected at this time was 5 mC/crn2. These values are comparable to those of elements using tungsten oxide vapor deposited films as coloring films, which have been widely studied in the past.

〔Effect of the invention〕

As detailed above, according to the present invention, a coloring material can be formed by a simple and inexpensive method.

It is possible to reduce the cost of ECD, and its industrial value is high.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the structure of an embodiment of an electrochromic display element. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Transparent conductive film, 3...Coloring film,
4... Protective film, 5... Protective film, 6... Counter electrode,
7... Board, 8 Tomi 1 Figure

Claims (1)

[Scope of Claims] 1. An electrochromic display element using condensed tungstic acid containing peroxo or peroxide ions, or containing carbon as a heteroatom and peroxo or peroxide ions as a coloring material. 2. Condensed tungstic acid has the general formula WO_3・xCO_2
・Represented by yH_2O_2・zH_2O, x, y, z
are respectively 0≦x≦0.25, 0.05≦y≦1, 0
．． The electrochromic display element according to claim 1, wherein the electrochromic display element is a condensed tungstic acid in the range of 16<z≦3.5. 3. The electrochromic display element according to claim 2, wherein the compound of the above general formula is synthesized by a reaction between tungsten or tungsten carbide and hydrogen peroxide.