JP2005266666A - Electrolyte and display element using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte used for a display element which can be driven with a low voltage and the low-voltage driven display element using the same. <P>SOLUTION: Disclosed is the electrolyte containing 1. decoloring/coloring compound (1) which decolors and colors through electrochemical oxidation-reduction reaction and 2. a compound (2) which has an oxidation overvoltage and a reduction overvoltage smaller in absolute value than an oxidation overvoltage and a reduction overvoltage of the decoloring/coloring compound (1), and the display element such that the electrolyte is held between two substrates with electrodes set opposite each other with the electrodes in, one of the electrodes and one of the substrates being a transparent electrode and a transparent substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to an electrolytic solution, in particular, an electrolytic solution used for a display element and a display element using the same.

In recent years, based on the concept of electronic paper, various methods have been studied for display elements using reflected light that have high visibility and are easy on the eyes. As one of the techniques of a reflective display element, an electrochemical display element that utilizes a reversible change in hue that occurs in a solid or liquid by applying a voltage is known. With this device, it is possible to perform excellent display with clear hue and no viewing angle dependency during colored display. A polymer material layer that is fixed on a polymer matrix with an electrolytic solution that is discolored by electrochemical redox present on a transparent electrode, and a polymer that contains a pigment such as titanium oxide in contact with the polymer material layer An electrochromic display element having a solid electrolyte layer is known (for example, see Patent Document 1). Patent Document 1 also describes an electrodeposition type display element in which a polymer solid electrolyte layer containing metal ions as a decolorizing material is sandwiched between electrodes. In addition, a white semiconductor or insulator powder such as titanium oxide or magnesium oxide is dispersed in an electrolytic solution in which a silver salt (discoloring material) and a supporting electrolyte are dissolved in a solvent, and this liquid is sandwiched between transparent electrodes. An electrodeposition type display device is known (for example, Patent Document 2).

However, both methods of Patent Documents 1 and 2 have a problem that the driving potential is high and the power consumption is high because the driving potential depends on the deposition overvoltage of the decolorizing material.
JP 2002-258327 A U.S. Pat.No. 4,240,716

It is an object of the present invention to provide an electrolytic solution that can be driven at a low voltage in an electrochemical redox reaction type display element and a low voltage driven electrochemical redox reaction type display element using the same.

As a result of intensive studies, the present inventor has found that the electrolyte solution is a decolorized compound (1) that is decolored in association with an electrochemical redox reaction, and an oxidation overvoltage and reduction with an absolute value lower than the oxidation overvoltage and reduction overvoltage of this compound. By containing the compound (2) having each overvoltage, the compound (2) is preferentially oxidized and reduced by the electrical redox over the decolorized compound (1), and the decolorized compound (1) and the compound (2) ) Forms a redox pair, and the oxidized or reduced compound (2) exchanges electrons with the decolorized compound (1), thereby enabling an efficient reversible electrochemical redox reaction at a low voltage. The inventors have found that the design is possible and have completed the present invention.

That is, in the present invention, the electrolytic solution is 1. A decolorizing compound (1) that decolorizes with an electrochemical redox reaction;
2. Compound (2) having an oxidation overvoltage and a reduction overvoltage each having an absolute value smaller than the oxidation overvoltage and reduction overvoltage of the decolorizing compound (1)
And an electrolytic solution characterized by comprising:

The present invention also relates to a display element in which an electrolyte is held between two substrates, each having a transparent electrode and a transparent substrate, each having an electrode and facing each other with the electrodes facing inside. The liquid is 1. A decolorizing compound (1) that decolorizes with an electrochemical redox reaction;
2. Compound (2) having an oxidation overvoltage and a reduction overvoltage each having an absolute value smaller than the oxidation overvoltage and reduction overvoltage of the decolorizing compound (1)
The display element which hold | maintains the electrolyte solution containing these is provided.

In the present invention, the electrolytic solution contains a compound that is oxidized / reduced by an oxidation potential and a reduction potential having a small absolute value, and a material that is decolored by the transfer of electrons from this compound. The chemical oxidation-reduction reaction type display element can be driven at a low voltage.

The electrolytic solution of the present invention is 1. A decolorizing compound (1) that decolorizes with an electrochemical redox reaction;
2. Compound (2) having an oxidation overvoltage and a reduction overvoltage each having an absolute value smaller than the oxidation overvoltage and reduction overvoltage of the decolorizing compound (1)
Containing.

The oxidation overvoltage and reduction overvoltage referred to here are referred to as the oxidation overvoltage and reduction overvoltage, which are the differences between the equilibrium oxidation-reduction potential of the compound and the respective potentials at which the oxidation and reduction reactions actually start.

(Discoloring compound (1))
The decolorizing compound (1) (hereinafter sometimes referred to as the decoloring compound (1)) that is decolored with the electrochemical redox reaction used in the present invention is colored by reduction and decolorized by oxidation. A compound or a compound that is colored by oxidation and decolored by reduction.
(Compound colored by reduction)
Among these, an organic compound and a metal compound can be used as the decoloring compound (1) colored by reduction.
Examples of the organic compound used as the decolorizing compound (1) include organic quinones such as benzoquinone, naphthaquinone, anthraquinone, diphenoquinone, diphenylquinone, dibenzoanthraquinone, violanthrone, isoviolanthrone, and pyranthrone. These organic quinones are reduced by applying a driving voltage to the electrodes to produce a colored state peculiar to each compound.
Examples of the metal compound used as the decolorizing compound (1) include halides such as silver, bismuth, copper, iron, chromium and nickel, sulfides, nitrates, perhalogenates and the like. By dissolving these compounds in the electrolytic solution, each metal is ionized, so that the electrolytic solution can be used as a decoloring material. For example, when an electrolytic solution in which a silver compound is dissolved is used, when a driving voltage is applied to the electrode, a reduction reaction of Ag ⁺ + e ⁻ → Ag occurs on the cathode side, and the Ag deposit causes the black color on the electrode. To change. Among the above metals, bismuth and silver are particularly preferably used because they are almost transparent in a state dissolved in an electrolytic solution, and the precipitate has a deep color and a good decoloring reversible reaction.

(Compound colored by oxidation)
Examples of the decolorizing compound (1) colored by oxidation used in the present invention are black based on a fluorane skeleton such as ODB (2-amino-6-diethylamino-3-methylfluorane) manufactured by Yamamoto Kasei Co., Ltd. Leuco dye, crystal violet blue dye such as CLV (3,3-bis (4-dimethyl-aminophenyl) -6-dimethylaminophthalide) manufactured by Yamamoto Kasei Co., Ltd., Red-3 (manufactured by Yamamoto Kasei Co., Ltd.) Red leuco dyes such as 9-diethylaminobenzo [α] fluorane) and RED-40 (3,3-bis (1-n-butyl-2-methyl-indol-3-yl) phthalide)).

(Decolorizing compound (2))
As the compound (2) (hereinafter sometimes referred to as the compound (2)) having an oxidation overvoltage and a reduction overvoltage whose absolute values are smaller than the oxidation overvoltage and reduction overvoltage of the decolorizing compound (1), an organic compound is used. Can be used.
As the compound (2) used for the decoloring material colored by the reduction of the decolorizing compound (1), a structure in which a hydroxyl group or an amino group is added to a benzene ring or naphthalene ring as in the case of a phenol compound is desirable. Examples of such phenolic compounds include phenol, hydroquinone, pyrocatechin, p-aminophenol, metol, methylhydroquinone, chlorohydroquinone, bromohydroquinone, edinol, pyrogallol, amidole, iconogen, glycine, p, p-biphenol, etc. An organic compound can be illustrated. These phenolic compounds can be selected so as to generate protons and electrons by oxidation at a potential having an absolute value smaller than the decoloring potential of the decolorizing compound (1), and assist the reduction of the decolorizing compound. Of the phenolic compounds, phenolic compounds exhibiting a reversible redox reaction such as hydroquinone and p, p-biphenol are particularly preferred.

Examples of the compound (2) used for the decoloring material colored by oxidation of the decoloring compound (1) include organic quinones such as 1,4-benzoquinone, 1,4-naphthoquinone and p-toluquinone. it can. These compounds generate protons and electrons by oxidation at a potential having an absolute value smaller than the decoloring potential of the decolorizing compound (1), and assist in the oxidation of the decolorizing compound (1). Of the quinone organic compounds, quinone organic compounds exhibiting a reversible redox reaction like benzoquinone are particularly preferable.

The difference in absolute value between the oxidation overvoltage and the reduction overvoltage between the decolorizing compound (1) and the compound (2) is preferably 0.1 V or more.

  The concentration of the compound (2) of the present invention is preferably in the range of 0.01 to 1.00 mol / L with respect to the electrolytic solution. When the addition amount is 0.01 mol / L or less, the amount of electrons and protons generated is small even when the material is electrochemically oxidized, and it becomes difficult to drive at a low potential. On the other hand, when the addition amount is 1.00 mol / L or more, coloring of the electrolytic solution at the time of decoloring due to light absorption of the benzene ring becomes remarkable, resulting in low contrast.

(solvent)
The electrolytic solution of the present invention contains compound (1) and compound (2) in a solvent. The solvent used in the present invention may be either aqueous or non-aqueous. In addition to water, propylene carbonate, dimethyl carbonate, 2-ethoxyethanol, 2-methoxymethanol, isopropyl alcohol, methanol, ethanol, N-methylpyrrolidone, dimethyl Examples include polar solvents such as acetamide, dimethylformamide, acetonitrile, butyronitrile, glutaronitrile, dimethoxyethane, γ-butyrolactone, ethylene glycol, diethylene glycol, propylene glycol, and glycerin. In the case of an aqueous system, in order to satisfy the operation under a low temperature condition by preventing solidification at 0 ° C. or lower, among the above solvents, a solvent compatible with water can be used by being dissolved.

(Supporting electrolyte)
A supporting electrolyte may be added to the electrolytic solution. Examples of supporting electrolytes that can be added include perchloric acid, lithium chloride, lithium bromide, lithium iodide, lithium perchlorate, lithium nitrate, lithium sulfate, and lithium borofluoride. Lithium salt of sodium chloride, sodium bromide, sodium iodide, potassium chloride, potassium bromide, potassium iodide and other alkali metal halides, tetrabutylammonium bromide, tetrabutylammonium chloride, tetraethylammonium perchlorate, perchlorine Examples thereof include ammonium salts such as acid tetra-n-butylammonium acid, tetraethylammonium borofluoride, and tetrabutylammonium borofluoride.

(Resin for immobilization)
In the electrolytic solution of the present invention, a resin may be dissolved for fixing to the display element. Examples of the dissolving resin include a polymer material having repeating units of alkylene oxide, alkyleneimine, and alkylene sulfide, a copolymer containing a plurality of these different units, or a polymethyl methacrylate derivative, polyvinylidene fluoride, polyacrylonitrile, polyvinyl Alcohol, a polycarbonate derivative, sodium carboxymethylcellulose, etc. can be mentioned.

(substrate)
The substrate constituting the display element of the present invention comprises a base material and an electrode.
(electrode)
The electrode used in the present invention must be transparent if it is located on the viewing side. These include ATO (antimony tin oxide), TO (tin oxide), ZO (zinc oxide), IZO (indium zinc oxide), FTO in addition to ITO (indium tin oxide), which is currently most widely used. (Fluorine tin oxide) etc. can be illustrated. The higher transparency of the transparent electrode is desirable, and the transmittance is desirably 75% or more, and more preferably 80% or more. Further, the resistance value of the electrode is desirably smaller, preferably 100 ohms or less, more preferably 50 ohms or less.
On the other hand, the electrode facing the transparent electrode does not necessarily need to be transparent. Therefore, in addition to the above metal oxide, an electrochemically stable metal such as platinum, gold, cobalt, palladium, or a carbon material should be used. You can also.

(Base material)
The substrate used in the present invention is not particularly limited as long as the material used on the viewing surface side has a smooth surface, high light transmittance, and the above transparent electrode can be installed. Specific examples include plastic sheets such as polyethylene terephthalate, polyester, and polycarbonate, and glass plates. In the case of the base material used on the opposite side of the viewing surface, it is not always necessary that the light transmittance is high.
(Encapsulant)
Since the sealing material 5 is disposed between the electrodes, it needs to be an insulating material. The material of the sealing material is not particularly limited, but the sealing material has a role of holding the electrolyte solution between the substrates and a role of a spacer for giving a thickness between the substrates. Therefore, the thickness is determined by the white hiding property when displaying black. However, since the power consumption increases when the spacer is thick, it is preferable that the spacer is thinner. For example, the thickness is preferably 500 μm or less, and more preferably 100 μm or less.
As the sealing material, the display recording element of the present invention can be obtained by bonding the spacer to the electrode with an adhesive or the like, or adding the spacer to the adhesive or the pressure-sensitive adhesive to adhere the substrate.

A structure of a display element using an electrolytic solution is shown in FIG.

When the upper side of FIG. 1 is viewed, 1 is an electrolytic solution containing the decolorizing compound (1) and the compound (2), 2 is a transparent substrate such as glass or plastic, 3 is a transparent electrode such as ITO, 4 Is a counter electrode, 5 is a sealing material, and 6 is a counter substrate.

Next, the present invention will be described in detail by way of examples. Unless otherwise specified, both “parts” and “mixing ratio” are based on mass.
<Preparation of electrolyte>

(Example 1)
1.6 parts of bismuth oxyperchlorate manufactured by Mitsuwa Chemical Co., Ltd. as the decolorizing compound (1), 0.8 parts of hydroquinone manufactured by Kanto Chemical Co., Ltd. as per compound (2), perchlorine manufactured by Wako Pure Chemical Industries, Ltd. An electrolytic solution 1 was prepared by dissolving 1.6 parts of an acid (60% aqueous solution) in 96.0 parts of pure water.

(Example 2)
1.0 part of ODB (2-amino-6-diethylamino-3-methylfluorane) manufactured by Yamamoto Kasei Co., Ltd. as the decolorizing compound (1) and 1,4-benzoquinone manufactured by Tokyo Chemical Industry Co., Ltd. as the compound (2) An electrolytic solution 2 was prepared by dissolving 1.0 part and 1.0 part of tetra-n-butylammonium perchlorate manufactured by Tokyo Chemical Industry Co., Ltd. in a mixed solvent of 97.0 parts of propylene carbonate.

(Comparative Example 1)
As the decolorizing compound (1), 1.6 parts of bismuth oxyperchlorate manufactured by Mitsuwa Chemicals Co., Ltd. and 1.6 parts of perchloric acid (60% aqueous solution) manufactured by Wako Pure Chemical Industries, Ltd. are 96.8 pure water. Electrolyte solution 3 was prepared by dissolving in part.

(Comparative Example 2)
1.0 part of ODB (2-amino-6-diethylamino-3-methylfluorane) manufactured by Yamamoto Kasei Co., Ltd. as a decolorizing compound (1), tetra-n-butylammonium perchlorate 1 manufactured by Tokyo Chemical Industry Co., Ltd. Electrolyte solution 4 was prepared by dissolving 0.0 part in a mixed solvent of 98.0 parts of propylene carbonate.

<Production of display element and display device>

(Example 3)
A glass substrate (thickness 1 mm) on which a transparent conductive film (ITO film) having a surface resistance of 10Ω / □ is formed on one side, the electrolyte solution 1 is sandwiched between a pair, and the periphery is sealed, whereby the display element 1 shown in FIG. Produced. The display device 1 was produced by connecting the ITO electrode of this display element to a function generator.

Example 4
A display element 2 and a display device 2 were produced in the same manner as in Example 1 except that the electrolytic solution 2 was used as the electrolytic solution.

(Comparative Example 3)
A display element 3 and a display device 3 were produced in the same manner as in Example 1 except that the electrolytic solution 3 was used as the electrolytic solution.

(Comparative Example 4)
A display element 4 and a display device 4 were produced in the same manner as in Example 1 except that the electrolytic solution 4 was used as the electrolytic solution.

(Measuring method)
<Measurement of oxidation overvoltage and reduction overvoltage>
For the measurement of oxidation overvoltage and reduction overvoltage, an electrolysis cell in which the distance between the two ITO electrodes was adjusted to 50 μm, 0.1 M of the decolorizing compound (1) or compound (2) and a supporting electrolyte (perchloric acid or manufactured by Enclose an electrolytic solution consisting of tetra-n-butylammonium perchlorate (0.1M) and a solvent (water or propylene carbonate) and perform cyclic voltammetry measurement. The potential at which the current value becomes 10 μA or more is the oxidation overvoltage and reduction overvoltage. did. For the reference electrode and the counter electrode at that time, the same ITO electrode was used, and measurement was performed using the ITO electrode on the counter electrode side as the reference electrode.
<Measurement of reflectance, drive potential, and contrast>
The manufactured display element is connected to a function generator, the current direction is switched at a frequency of 200 mHz, and a rectangular wave potential of 1.0 to 2.5 V is sequentially applied in steps of 0.1 V to obtain a display color. The lowest reflectance with a response of 200 mHz was taken as the reflectance of the display color, and the contrast between the display portion and the non-display portion at that time was taken as the maximum contrast. In addition, the point where the reflectance of the display color was 15% was defined as the driving potential. The display color reflectivity was measured for each display color using Display Measuring System DMS501 (manufactured by AUTRONIC). The measurement is performed with white light, 45 ° irradiation−0 ° light reception, and the value when the reflectance of the standard white plate is 100%.

<Measurement results>
The measurement results of oxidation overvoltage and reduction overvoltage are shown in Table 1 below.

反射率、駆動電位、及びコントラストの測定結果を以下の表２に示す。
（下の表に記載の表示色の反射率及びコントラストの値を得たときの駆動電圧条件が明確になるように記載して下さい。）

The measurement results of reflectance, drive potential, and contrast are shown in Table 2 below.
(Please describe the driving voltage conditions when the reflectance and contrast values for the display colors shown in the table below are obtained.)

  From Table 1, it can be seen that the oxidation overvoltage and reduction overvoltage of the compound (2) have smaller absolute values than the oxidation overvoltage and reduction overvoltage of the decolorized compound (1). Moreover, it is high by using the electrolyte solution containing the decoloring compound (1) and compound (2) of this invention from the comparison of Example 3 and Comparative Example 3 in Table 2, and the comparison of Example 4 and Comparative Example 4. It can be seen that the display of contrast can be obtained at a low voltage.

Sectional drawing which shows an example of a structure of the display element which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolyte solution of this invention containing decoloring compound (1) and compound (2) 2 Transparent base material 3 Transparent electrode 4 Counter electrode 5 Sealing material 6 Counter base material

Claims (5)

Electrolyte is 1. A decolorizing compound (1) that decolorizes with an electrochemical redox reaction;
2. Compound (2) having an oxidation overvoltage and a reduction overvoltage each having an absolute value smaller than the oxidation overvoltage and reduction overvoltage of the decolorizing compound (1)
An electrolyte solution characterized by containing. 2. The electrolytic solution according to claim 1, wherein the difference between the absolute values of the oxidation overvoltage and the reduction overvoltage between the decolorizing compound (1) and the compound (2) is 0.1 V or more. The electrolytic solution according to claim 1 or 2, wherein the decolorizing compound (1) is a compound colored by reduction, and the compound (2) is a phenolic compound. The electrolytic solution according to claim 1 or 2, wherein the decolorizing compound (1) is a compound colored by oxidation, and the compound (2) is a quinone compound. In a display element in which at least one is a transparent electrode and a transparent substrate, and the electrolyte solution is held between two substrates having electrodes facing each other with the electrodes facing inside, the electrolyte solution is claimed in claim 1. 4. A display element that holds the electrolytic solution according to any one of 4 above.

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