JPS589927B2 - electrochromic display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a display device (hereinafter referred to as ECD (Ele
ctrochromic display)
Regarding.

The outline of ECD is that a thin film layer of an EC material, such as a transition metal oxide, is formed on one transparent electrode and the other electrode is electrochemically connected via an electrolyte that provides ion conduction.
When a base potential below a certain potential is applied to the transition metal thin film layer, a current flows as if the oxide thin film had been reduced, and the oxide layer changes from the first absorption state to the second absorption state. However, when a negative potential is applied, the second absorption state returns to the first absorption state.

Here, in the first absorption state, there is no absorption in the visible region (transparent), and in the second absorption state, an amorphous tungsten oxide vapor deposited film ( When using a WO3 film), the coloring states are explained as follows.

When the positive charge transfer carrier of the electrolytic solution is proton (H+) (;'4Muro1 metal (M+) (usually an alkali metal is used), a general ECD cell structure is shown in FIG.

Here, 1 is a counter electrode, and if the cell is a transmission type, an indium oxide transparent conductive film (obtained by vacuum evaporation method)
Or Nesa film (obtained by SnO2, vapor deposition method, spray method, etc.), or in the case of reflective type, graphite or platinum,
A thin film of noble metal such as palladium is used.

2 is a substrate made of glass, plastic, metal, ceramic, etc., and 3 is a spacer and sealing resin.

4 is the transparent electrode mentioned above, and 6 is a thin film of transition metal oxide, both of which constitute a display electrode.

7 is an electrolyte, 5 is a transparent substrate made of glass or plastic, etc., and 8 is a reference electrode made of the same material as 1.

The present invention relates to the above-mentioned electrolyte of an ECD using tungsten oxide as the transition metal oxide.

Conventionally, as an electrolyte, ■glycerin/sulfuric acid mixture (for example, U.S. Pat. No. 3,708,220, @sulfuric acid/
Water/ethylene glycol mixture (e.g. B.W.
Faughnan et al, RCA Rev-+碍(4), 177, (1975)), O propylene carbonate, lithium perchlorate system (e.g. SID75Dig
est, 50, C1975), but each of these has the drawbacks described below.0 ■ A glass substrate on which a sulfuric acid-glycerol-based In203 transparent electrode is formed is 5 x 10''.
heated to 150°C in a vacuum, and placed W03 on top of it.
/secC to a film thickness of 5,000 people, using a 36N sulfuric acid solution in glycerol as the electrolyte,
A transmission type ECD cell having the structure described above was constructed, and the characteristics of the electrolyte were investigated.

The display electrode of this ECD cell is grounded, and the reference electrode (material: In 2 03 film) is connected to ±l. Constant potential driving was performed so that the voltage was OV, and the response characteristics were investigated.

As a result, the response characteristics (writing: transmittance changed from 100% to 30%)
The time required for erasing (the time required for transmittance to go from 30 to 90%) is 30 seconds for writing and 40 seconds for erasing at 25°C, respectively, and the response characteristics are poor (speed is slow), making it difficult to use as a display device such as a watch. is inappropriate.

However, this response characteristic improves depending on the applied voltage, but the hydrogen overvoltage of protons is usually about 1.5 V in an aqueous solution system, and no detailed data have been published regarding it in a glycerin solution. It is thought that there is almost no difference from that in an aqueous solution.

(I measured a value of 1.5V in a simple experiment.)
.

For this reason, if a voltage higher than the above-mentioned voltage is applied, hydrogen gas is generated at the counter electrode and the ECD cell is destroyed.

(b) Sulfuric acid, water, enalene glycol system Construct an EC cell as described in (■) using an aqueous solution of ethylene glycol (20%) mixed with sulfuric acid at a concentration of 2N as the electrolyte, and Similarly, the reference electrode is
l. The response characteristics were measured by driving at OV.

The results were 0.8 seconds for writing and 0.4 seconds for erasing, respectively, which is superior in response characteristics compared to ■, but the EC of this system
The cell has the disadvantage that the WO3 film or the In203 electrode dissolves and is destroyed in a standing test for one to several days.

(c) Lithium perchlorate, propylene carbonate An EC cell was constructed as described in (2) using a 1.0 M/e lithium perchlorate propylene carbonate solution as the electrolyte.

In this system, the redox potential of lithium ions (Li+) is about 3.0V, so compared to the two systems mentioned above,
It has the advantage of being able to apply a stronger voltage, and the response characteristics when driven at constant potential so that the reference electrode voltage is 1.5V as mentioned above are 0.6 seconds for writing and 0.6 seconds for erasing at 25°C. It is relatively fast in seconds, but like @, 5000 in a few days
The WO3 film, which has a human thickness, will dissolve and the EC cell will be destroyed.

However, if the electrolytic solution is saturated with sodium tungstate in advance, the lifespan will be extended by several days, but the lifespan is still only a few days.

The present invention overcomes these drawbacks and makes it possible to provide an ECD cell with a fast response speed and long life.

In the present invention, first, a solvent that does not dissolve tungsten oxide and a supporting electrolyte such as lithium perchlorate are dissolved and ionized, and the electrolyte has a conductivity (approximately
To provide a paste-like electrolytic solution mixed with barium sulfate fine powder to give a white background to a solvent that does not exhibit absorption characteristics in the visible region.

Table 1 shows lithium perchlorate as the solvent used in the present invention.
If it is 0 or not completely dissolved, the specific resistance is when it is dissolved to a saturation concentration, and when an ECD cell similar to the one described above is constructed and the reference electrode is driven at a constant potential with a voltage of ±1.5V. Indicates response characteristics.

Items marked with an x in the lifespan column of Table 1 can be said to be inappropriate as electrolytes for ECD cells because they can be considered to have the property of dissolving the WO3 membrane.

Also, the Δ mark may be inappropriate depending on the experimental conditions.

On the other hand, electrolyte systems other than those mentioned above are currently being subjected to storage tests, but they still function as ECD cells after about 6 months.

Next, we conducted a memory test.

This test is similar to the previous response characteristic.
Heated to 150°C in a vacuum of orr and WO at 10 people/second
A sample prepared by growing No. 3 was colored to a transmittance of 30 cm, and then left for 12 hours, and those with a transmittance of 40% or less were considered to have good memory.

Tests were conducted on each of the solvents listed in Table 1, including ethylene glycol monomethyl ether, 2-ethoxyethyl acetate (used in this test instead of bunal carbitol acetate in Table 1), ethylene glycol, dimethyl Sulfoxide was good.

From these results, the following solvents are good.

(a) Chemical formula CnH2 rL4-I C O Cn
'H2n'+1 (n-1,2,n'=1~4) Ketones, (Q Chemical formula Cn H2n 4-1 0
Alcohols consisting of H (n = 2 to 4), (c) Enalene glycol monomenal ether, ethylene glycol dimethyl ether, ethylene glycol monoenal ether, ethylene glycol dienal ether, (d) Chemical formula C Ha C 0 0 Cn H2n+
1 (n = 2 to 4), (e) dimethyl sulfoxide, (f) butyl carbitol acetate, (th) dioxane, among the above, those with a larger number of carbon atoms are It was unsuitable as an electrolytic solution because its resistance was too thick.

Furthermore, methyl alcohol, N-methylformamide, dimethylformamide, propylene carbonate, and γ-bunarolactone are unsuitable because they dissolve the WO3 film.

The conditions that must be met for the electrolyte used in the ECD display device must take into consideration the response characteristics of the EC phenomenon, the chemical and electrochemical stability of the EC material, and not impairing the display quality.

Furthermore, it is necessary to consider the operating temperature or storage temperature of the display device.

Therefore, the response characteristics of the ECD cell using the solvent mentioned earlier, E
By taking into account the chemical stability of the C material, it is possible to extend the storage and operating temperature range of the EC cell.

Example 1 Dimenal sulfoxide 70 parts, ethylene glycol 3
0 parts, l. When lithium perchlorate is added to the OM/Al' concentration to form an electrolyte for an ECD cell, the lower operating temperature is 10°C to 16°C when using dimethyl sulfoxide alone.
℃, but by adding ethylene glycol, it was improved to below -20℃, while the response characteristics were written: 0
．． The effect was great with almost no change after 7 seconds and 0.5 seconds of erasure.

The transmission type ECD cell has been described above.

However, ECD cells are usually used with certain background.

In other words, it is more practical to use it as a reflective type.

Therefore, the reflection type ECD cell will be described below.

FIG. 2 shows an ECD cell used in the present invention.

In the figure, 9 and 18 are glass substrates.

A display electrode is formed by three materials: an SiOx film 10, an In 2 O s film 11, and a WO3 film 15 obtained by vacuum evaporation.

12 is a sealing resin (R240 1HC-1 1 manufactured by Somar Kogyo Co., Ltd.) which also serves as a spacer, and its thickness is 1 mm.

Reference numeral 13 indicates an In203 film, and reference numeral 14 indicates a WO3 film, both of which are deposited by vacuum evaporation, and both form a counter electrode.

1e is an electrolytic solution, and 17 is an In203 membrane reference electrode.

The present invention relates to this electrolyte.

Detailed examples are shown below.

The method of providing a white background to the ECD cell is characterized by impregnating barium sulfate fine powder into the electrolyte.

The method for producing the white background electrolyte is as follows.

1. 100 parts of methyl ethyl ketone (G.R., Kishida Chemical Co., Ltd.) solution of lithium perchlorate (E.P., manufactured by Kishida Chemical Co., Ltd.) at a concentration of o M/e, and 100 parts of fine barium sulfate powder (manufactured by Takeda Pharmaceutical Co., Ltd.) were placed in a mortar. Mix well in
A white pasty substance is obtained.

The above-mentioned paste-like white electrolyte was injected into the above-mentioned ECD cell using a syringe and sealed with a quick-drying epoxy sealant (Quick Bond, manufactured by Gisuke Konishi Co., Ltd.) to obtain a reflective ECD cell.

The cell is 5 9 for standard white (magnesium oxide)
The reflectance in the wavelength region of 0 nm was measured with a double beam spectrophotometer UV-200 manufactured by Shimadzu Corporation, and the result was 65.

On the other hand, a transmission type ECD cell using an electrolyte of lithium perhydrochloride and methyl ethyl ketone was used with a qualitative filter paper (N manufactured by Toyo Roshi Co., Ltd.).
O. When the reflectance of a reflective ECD cell using 2) was measured in the same manner, it was 58%, and the reflective layer made of white paste was less effective.

Furthermore, barium sulfate is non-toxic and does not change color, making it ideal for practical use.

Here, we will describe the W03 film layer that we provided on the counter electrode.

The effectiveness of this WO3 film layer of the counter electrode is to facilitate the transfer of electric charge by the In203 counter electrode when driving the ECD cell, and to protect the electrode by lowering the voltage that needs to be applied to the electrode. It is something.

Constant potential drive (In203
Table 2 shows the measurement results of the potential of the counter electrode and the results of the aging test.

As can be seen in Table 2, when the WO3 film is used as the counter electrode, the applied voltage is 1.3V during writing compared to the In20g electrode.
, 1.5V decreases during erasing, reducing power consumption.

Moreover, the aging test results also improved dramatically.

By using the invention of the electrolytic solution, the reflective layer made of barium sulfate, and the counter electrode provided on the W03 film In203 electrode, it has become possible to manufacture a highly reliable OECD cell with low power consumption.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of one embodiment of the present invention, and FIG. 2 is a cross-sectional view of another embodiment. 1... Counter electrode, 2, 5, 9, 18...
・Substrate, 3, 12... Spacer/sealing resin, 4, 11... Transparent conductive film of display electrode, 6, 1
4,15...Transition metal oxide film, 7,16...
...Electrolyte, 8,17...Reference electrode.

Claims (1)

[Claims] 1. In an electrochromic display device having a transition metal oxide that causes a coloring and decoloring reaction when an electric field is applied, and an electrolyte that controls the coloring and decoloring reaction of the transition metal oxide, the electrolyte is mixed with lithium perchlorate. Electrolyte and Cn H2 n+
I C O Cn'H2 n'-H 1 (n""1
, 2, n'-1 to 4), ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, or ethylene glycol diethyl ether.