JPH01225925A - Electro-chromic display element - Google Patents

Abstract

PURPOSE:To improve the reaction efficiency of coloring/decoloring of the title display element and to improve the display characteristic and to prolong the life of the element by allowing V to hold a metallic porous body a conductive paste containing a counter-electrode active substance by counter-electrode substance layer of the element. CONSTITUTION:A facing electrodes 8 is constituted of a facing electrode 9 and counter-electrode substance layer 10 formed on the electrode 9. The layer 10 is formed by thinly applying a conductive paste 10b containing a counter- electrode active substance to a metallic porous body 10a. Therefore, the electric resistance on the facing electrode 8 side is reduced, since the surface area on the facing electrode 8 side which contributes to the coloring and decoloring reactions becomes larger and, moreover, the metallic porous body 10a has excellent conductivity. Accordingly, the reaction efficiency to the coloring/decoloring is improved and high response speed is achieved even when the applied voltage is low. In addition, the coloring contrast becomes larger and the life of this display device can be prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrochromic display element used in various display devices, and particularly to the above-mentioned display element using tungsten oxide as an electrochromic substance.

[Prior art] As a typical display element of this type, a display device is made of a transparent conductive material such as indium-tin composite oxide (hereinafter referred to as ITO) on the inner surface of one of a pair of light-transmitting substrates. An electrochromic material layer is formed through an electrode to form a display electrode divided into segments constituting a required pattern, and a counter electrode material layer is provided through a counter electrode formed on the entire inner surface of the other substrate to form a counter electrode. There is one in which an electrolytic solution is sealed between the two electrodes of the two substrates arranged facing each other.

In such a display element, by applying a display voltage corresponding to a required segment using the above-mentioned counter electrode as a common electrode, a display is produced by a color change of a reacting substance through an electrolytic solution of an electrochromic substance and a counter electrode substance. Ru. In the case of blue display, tungsten oxide (WO3) is generally used as the electrochromic substance, and the color change in this case is, for example, when a lithium salt dissolved in a non-aqueous solvent is used as the electrolyte. It is based on the following reaction.

WO, +nLi"+ne-;: LinWO3 (transparent)
(Blue) By the way, conventionally, the counter electrode material layer of a display element using tungsten oxide as an electrochromic material as described above has a layer containing an oxide counter electrode active material such as iron tungstate, tungsten oxide, or manganese dioxide in the film. A conductive adhesive containing both powder and conductive material powder such as carbon powder, or carbon powder alone that serves as a counter electrode active material and a conductive material, is applied to the surface of the opposing electrode of the opposing substrate and cured by heating. It is formed by

[Problem to be solved by the invention]

However, as mentioned above, in the case of an electrocomic display element equipped with a counter electrode material layer formed by heat curing of a conductive adhesive, the surface of the counter electrode material layer is quite smooth and the surface area involved in the reaction is small. Therefore, the reaction efficiency is poor, and it is necessary to apply a high voltage between the two electrodes in order to achieve high-speed response and high-contrast color development, resulting in a problem that the device life is shortened.

In addition, as a countermeasure for this, there are means to increase the surface area by roughening the surface of the counter electrode M layer after forming it, or by pressing a mesh material onto the surface to form an uneven pattern after coating and before curing. In either case, the effects were small, and display characteristics such as response speed and color contrast could not be significantly improved.

Therefore, an object of the present invention is to provide an electrochromic display element with high reaction efficiency for coloring/decoloring, excellent display characteristics, and long life by solving the above-mentioned conventional problems.

[Means to solve the problem]

As a result of extensive studies to achieve the above object, the inventors found that when a counter material layer is made of a conductive paste containing a counter electrode active material held in a specific material,
The surface area involved in the reaction of this counter electrode material layer is extremely large, and the electrical resistance of the counter electrode is significantly reduced, compared to the conventional counter electrode material layer coated with a conductive adhesive and cured. With this method, the reaction efficiency was dramatically increased, and high-speed response and high-contrast color development were achieved with a low applied voltage, thereby extending the life of the device.This discovery led to the invention.

That is, the present invention includes a pair of substrates whose display side is translucent at least, a display electrode formed by forming an electrochromic material layer made of a tungsten oxide thin film on the inner surface of the display side substrate via a display electrode, and a pair of substrates whose display side is transparent. In an electrochromic display element having a counter electrode formed by forming a counter electrode material layer on the inner surface of a substrate via a counter electrode, and an electrolyte sealed between these two electrodes, the counter electrode material layer is a conductive material containing a counter electrode active material. The present invention relates to an electrochromic display element characterized in that it is made of a metal porous body holding a magnetic paste.

(Structure and operation of the invention) Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows an example of the electrochromic display element of the present invention, and FIG. 2 schematically shows an enlarged part of the counter electrode material layer.

In the figure, 1 is a display-side substrate made of a light-transmitting material such as glass, 2 is a counter-side substrate made of the same light-transmitting material or non-light-transmitting material, and 3 is both the above-mentioned substrates I.

This is a spacer made of glass, polyester resin, etc. that is placed between the two. Reference numeral 4 denotes a display electrode, which is made of a transparent conductive material such as ITO and has a thickness of 1.00 mm and is formed on the inner surface of the display side substrate 1 by a thin film forming method such as a vacuum deposition method, a sputtering method, or an ion blasting method.
A display electrode 5 of about 0 to 4,000 and a thickness of 3,000 to 10,000 formed thereon by the same means as above.
It is formed into a predetermined pattern divided into predetermined segments from an electrochromic material layer 6 made of a thin film of tungsten oxide. Reference numeral 7 denotes an insulating protective film made of S i 01 or the like, which covers the exposed surface of the display electrode 5 and the inner surface of the substrate 1 .

A counter electrode 8 is composed of a counter electrode 9 with a thickness of about 1,000 to 4,000 formed on the entire inner surface of the counter substrate 2 and a counter electrode material layer 10 formed thereon. .

The above-mentioned counter electrode 9 may be made of a transparent conductive material coated on the inner surface of the counter-side substrate 2 in the same way as the display electrode 5, or made of noble metals such as gold and platinum, or alloys of these and other metals. It is formed by pressing or gluing foil-like materials together.

The counter electrode material layer 10 includes a conductive paste l-10b containing a counter electrode active material in a metal porous body 10a, as shown in FIG.
is maintained in a thin film-like state.

Reference numeral 11 denotes a background material provided between the above-mentioned counter electrode 8 and display electrode 4, which hides the counter electrode 8 and uses its own color tone as the display background, and is made of pigments such as titanium dioxide and polyester. It is formed by placing a sheet-like molded mixture of a mixture with tetrafluoroethylene powder on the counter electrode 8, or by applying a gel body of pigment and electrolyte onto the counter electrode 8 using a screen printing method or the like. be done. 12 is a lead terminal on the display electrode side fixed to the side edge of the display side substrate l, 13 is a lead terminal on the counter electrode fixed in the same manner as above, and 14 is a lead terminal 13 on the counter electrode side and the counter electrode 9. This is an electrically sensitive layer made of silver paste etc. that electrically connects the

Reference numeral 15 denotes an electrolytic solution sealed between the display electrode 4 and the counter electrode 8, in which a lithium salt such as lithium perchlorate or lithium borofluoride is mixed with a non-aqueous solvent such as propylene carbonate or T-butyrolactone at a concentration of 0. A solution in which lithium salt is dissolved at a concentration of about 5 to 1.5 mol/l, or a solution in which about 0.3 to 2% by volume of pure water is added as a proton donor is used. In particular, lithium salt is dissolved in propylene carbonate. A solution to which a small amount of pure water is added is preferably used.

The electrochromic display element of the present invention having the above-described structure can be applied to the electrochromic material layer of the display electrode 4 by applying a required voltage between the display electrode 4 and the counter electrode 8 via the lead terminals 12 and 13. Due to the color change of the reactant between the tungsten oxide constituting the tungsten oxide 6 and the counter electrode active material of the counter electrode material layer 10 of the counter electrode 8 via the electrolyte 15, that is, the change from colorless and transparent to blue, the surface of the display side substrate 1 is colored. The desired pattern is displayed, and from this colored state both poles 4
, 8, the color is erased and the display returns to a non-colored state, and the display disappears.

Here, since the counter electrode material layer IO is formed by thinly coating the conductive paste 10b containing the counter electrode active material on the surface of the metal porous body 10a, the surface of the counter electrode that participates in the coloring/decoloring reaction is゛The area is very large and the metal porous body 10
Due to the good conductivity of a, the electrical resistance on the opposing electrode side is significantly reduced. As a result, the above-mentioned display element of the present invention has extremely high coloring/decoloring reaction efficiency, achieves a high response speed even when the applied voltage is low, and has a large color contrast, so that Shortening of life due to application of high voltage can be avoided.

As the metal porous body 10a, a sponge-like foamed metal with a porosity of 70% or more is preferable; if the porosity is too small, the surface area involved in the reaction will be small, making it impossible to achieve high reaction efficiency. It becomes difficult to obtain excellent display characteristics. The average diameter of the spherical foam spaces of the foamed metal is preferably about 200 to 700 μm; if it is too small, the space will be filled with the conductive paste (10b) and the surface area will become smaller; on the other hand, if it is too large, the The surface area becomes smaller.

Metals forming such a metal porous body 10a include:
Various materials can be used as long as they are not affected by the electrolytic solution 15 and do not adversely affect the coloring/decoloring reaction, but nickel is particularly preferred in terms of properties and ease of availability.

As the counter electrode active material to be mixed in conductive paste) 10b,
Powders of oxide-based active materials such as iron tungstate (WO-F et 03), tungsten oxide (WOx; x=2-3), manganese oxide (MnOz), carbon powder that also serves as a conductive material, etc. Any of the materials conventionally known as counter electrode active materials for this type of display element having an electrochromic material layer consisting of a thin tungsten oxide film can be used, but among these, iron tungstate and tungsten oxide powders are particularly suitable. recommended as such. Conductive paste is made by dispersing conductive material powder such as carbon powder in an adhesive component, and the adhesive component can be cured in various types such as heat curing type, solvent continuous failure curing type, radiation curing type, etc. Any type can be used.

The amount of the counter electrode active material to be blended is preferably about 50 to 300 parts by weight based on 100 parts by weight of the adhesive component of the conductive paste, and the amount of the conductive material to be blended is preferably about 5 to 30 parts by weight.

The means for holding the conductive paste 10b containing the counter electrode active material in the metal porous body 10a is not particularly limited, but usually the metal porous body 10b is placed in a diluted solution of the paste 10b.
After immersing 0a, take it out and dry it, and if necessary, heat and harden the adhered paste 10b,
A method is employed in which a thin hardened film of the paste 10b is formed on the porous surface of the porous body 10a.

The thickness of the metal porous body 10a is approximately 500 to 2.000 μm, and the amount of the conductive paste 10b applied is approximately 1 c4.
It is best to set it to about 5 to 20 centimeters per hit.

Note that such a counter electrode material layer IO is adhered to the surface of the counter electrode 9 of the counter substrate 2 through a conductive paste similar to that used therein.

〔Effect of the invention〕

In the electrocomic display element according to the present invention, since the counter electrode material 1 of the counter electrode is composed of a conductive paste containing a counter electrode active material held in a metal porous body,
The surface area involved in the coloring/decoloring reaction of the counter electrode material layer is extremely large, and the electrical resistance on the counter electrode side is extremely low due to the good conductivity of the metal porous material, which together make the efficiency of the coloring/decoloring reaction extremely high. Therefore, high response speed and large color contrast can be achieved with a low applied voltage, and shortening of life caused by conventional high voltage application can be avoided.

〔Example〕

Hereinafter, this invention will be specifically explained based on examples.

Example 1 A film with a thickness of 2.50 mm was deposited on one side of a display side substrate made of a transparent glass plate having a predetermined size and thickness by vacuum evaporation.
A display electrode consisting of an ITO film of 0.0 mm thick and an electrochromic material layer consisting of a tungsten oxide thin film of 5.000 mm thick are formed, and a layer of S i O of 5.000 mm thick is formed on the exposed surface of the substrate and the display electrode to a thickness of s, ooo mm S i O, A display electrode having a predetermined pattern was constructed by providing an insulating protective film consisting of the following.

On the other hand, conductive paste (product name: Carbon Ink RP-10 manufactured by Tokuriki Honten Co., Ltd.) and iron tungstate powder were mixed at a weight ratio of 1:1, and propylene carbonate was added to 1 part by weight of the conductive paste for viscosity adjustment. After mixing, a porous metal body made of a foamed nickel sponge with a thickness of 1.000 μm, a porosity of about 96%, and an average diameter of spherical foam spaces of about 300 μm was immersed in the mixed solution. , immediately pulled up and air-dried for 30 minutes, heated at 100°C for 10 minutes to harden the adhered paste, allowed to cool to room temperature, and then repeated the above process from dipping to cooling three times to form a metal porous A counter electrode material layer material was prepared in which 10 μm of conductive paste containing a counter electrode active material was deposited per body 1i.

Next, this material was applied to a counter substrate (surface electrical resistance: 10 Ω/- ) was adhered onto the electrode through a conductive paste (carbon ink RP-10; described above), and then heated at 200° C. for 4 hours to harden the paste, thereby forming a counter electrode.

Then, the side substrate was placed in such a way that the display electrode and the counter electrode faced each other, and between the two electrodes, a 200 μm thick sheet-like molded product (made by Sumitomo Electric Industries, Ltd.) of a mixture of titanium dioxide pigment and polytetrafluoroethylene powder was used. A background material made of Boaron (trade name) was loaded, and an annular spacer made of polyethylene terephthalate with a thickness of 1.5 tm was placed on the periphery to face each other, and the opposing surfaces of both bases 1 and the spacer were bonded with epoxy adhesive. The tube was sealed with adhesive, and 7 ml of an electrolytic solution prepared by adding 1% by weight of pure water to a propylene carbonate solution containing 1.0 mol/l of lithium perchlorate was sealed inside.

Finally, lead terminals were attached and a conductive layer was formed by applying silver paste, thereby producing an electrochromic display element having the configuration shown in FIG. 1.

Comparative Example 1 Conductive paste (same as Example 1) and iron tungstate powder (same as Example 1) were mixed at a weight ratio of 1:1, and propylene carbonate was added to 1 part by weight of the conductive paste for viscosity adjustment. Example 1
It was coated on the opposite electrode of the same opposite substrate by screen printing method so that the dry thickness was 250 μm.
After being air-dried for a minute, the material was heat-treated at 200° C. for 4 hours to harden it to form a counter electrode material layer, thereby configuring a counter electrode.

Next, an electrochromic display element was produced in the same manner as in Example 1 using this counter-side substrate and a display-side substrate on which a display electrode was formed in the same manner as in Example 1.

Example 2 Tungsten oxide (WO
, An electrochromic display element was produced in the same manner as in Example 1 except that this material was used.

Comparative Example 2 Tungsten oxide powder (
An electrochromic display element was produced in the same manner as in Comparative Example 1, except that the same amount of the same amount as in Example 2 was used.

For each of the display elements of the above examples and comparative examples, we measured the amount of electricity injected when a square wave AC voltage of ±1.5V, 2Hz was applied between the display panel and the counter electrode, and the results are shown in the table below. I got it.

As is clear from the above table, in the display element (Examples 1 and 2) of the present invention, which is equipped with a counter electrode material layer in which a conductive paste containing a counter electrode active material is held in a metal porous body, the counter electrode material layer is Compared to display elements with conventional configurations (Comparative Examples 1 and 2), which were formed by applying a chemical paste onto the counter electrode, the efficiency of the coloring/decoloring reaction is significantly higher at the same applied voltage, regardless of the type of counter electrode active material. It can be seen that a large amount of injected electricity can be obtained, and display characteristics such as response speed and color contrast are excellent.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of the structure of an electrochromic display element according to the present invention, and FIG. 2 is a cross-sectional view schematically showing an enlarged counter electrode material layer thereof. 1...Display side substrate, 2...Counter side substrate, 4...Display electrode, 5...Display electrode, 6...Electrochromic material layer, 8...Counter electrode, 9... Counter electrode, lO・
...Counter electrode material layer, 10a...Metal porous body, 10b...
・Conductive paste containing counter electrode active material, 15... Electrolyte patent applicant Hitachi Maxell Corporation IQd-

Claims (4)

[Claims] (1) a pair of substrates whose display side is translucent;
A display electrode formed by forming an electrochromic material layer made of a tungsten oxide thin film on the inner surface of a display side substrate via a display electrode, and a counter electrode formed by forming a counter electrode material layer on the inner surface of a counter side substrate via a counter electrode. and an electrolytic solution sealed between these two electrodes, wherein the counter electrode material layer is made of a conductive paste containing a counter electrode active material held in a porous metal body. Chromic display element. (2) The electrochromic display element according to claim 1, wherein the metal porous body is made of a foamed metal having a porosity of 70% or more. (3) The electrochromic display element according to claim (1) or (2), wherein the metal porous body is made of nickel. (4) The electrochromic display element according to any one of claims (1) to (3), wherein the counter electrode active material comprises iron tungstate and/or tungsten oxide.