JPH04324841A - Electrochromic element - Google Patents

Abstract

PURPOSE:To enhance the light transmissivity by using a hybrid solvent of 2.2- diphenylpropionitrile and polyether as a medium for ionic conductor, with which voids in a highpolymer porous thin film are to be filled. CONSTITUTION:As an electrolyte, an electrolytic thin film is used whose voids in a highpolymer porous thin film having a refraction factor of 1.48-1.56 are filled with ionic conductor including a hybrid solvent of 2.2-diphenylpropionitrile and polyether expressed by formula I. In this case, R<1> and R<3> are alkyl radical of hydrogen atom or carbon in the number 1-4, either may be the same or different, while R<2> is alkylene radical having carbon in the number 2-4, and (n) is integer 1 through 100. The highpolymer porous thin film is made of polyolefin having a mean molecular weight over 5X10<5>. The hybrid solvent contains the mentioned two components in a mix proportion by weight as 20:80 through 90:10.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a novel electrochromic device, and more specifically, a light control device and a light control device using a porous polymer thin film with low light scattering, whose pores are filled with an ionic conductor as an electrolyte. The present invention relates to an electrochromic device suitable as a display device or the like.

0002

[Prior Art] An electrochromic (hereinafter abbreviated as EC) element usually has a layer made of an EC material (hereinafter abbreviated as an EC layer) on a transparent electrode substrate, and an electrolyte is interposed between an EC electrode and a counter electrode. When a voltage is applied between the two electrodes, the color tone of the EC layer reversibly changes depending on the voltage. Such EC elements have characteristics such as being capable of large-area display, long driving life, fast response speed, high coloring efficiency, producing vivid colors, and high transmittance when decoloring. In recent years, it has been used in display elements and dimming devices that take advantage of color tone changes, in anti-glare materials that take advantage of their moderate response speed, and in memory sensors that take advantage of their memory properties. The electrolyte used in this EC device can be roughly divided into liquid electrolyte and solid electrolyte.The former liquid electrolyte has high ionic conductivity and has excellent responsiveness, but since it is a liquid, it is difficult to assemble the device. Moreover, it requires measures against liquid leakage, and even if measures are taken against liquid leakage, there is a risk that liquid leakage may occur due to damage or during use. On the other hand, although ordinary solid electrolytes do not have the above-mentioned problems, they have a drawback of poor response due to their low ionic conductivity. Therefore, the present inventors conducted intensive research to develop a solid electrolyte with high ionic conductivity, and first developed a polymer electrolyte thin film made by filling the pores of a porous polymer thin film with an ionic conductor. They discovered that it can be handled as a solid, has no risk of liquid leakage, and has excellent ionic conductivity. When such a polymer electrolyte thin film is used as an electrolyte in an EC device, it is sufficient to sandwich the thin film between two electrodes after forming the electrode, so that the electrolyte is not deteriorated during electrode formation, and the EC device can be used in the laminated glass process. It has the advantage of being able to produce On the other hand, as a method for interposing a solid electrolyte with high ionic conductivity between two electrodes, a method is known in which a thin film layer made of TaOx or the like is formed by vapor deposition, but in this method, an electrode forming step is subsequently performed. Therefore, there is a drawback that the thin film layer inevitably deteriorates during electrode formation. By the way, when producing a polymer electrolyte thin film by filling the pores of a porous polymer thin film with an ionic conductor, the solvent for the ionic conductor is usually propylene carbonate, dimethoxyethane, r-butyrolactone, acetonitrile, or polyester. Ethylene oxide, polypropylene oxide, etc. are used. However, all of these solvents have a refractive index (nD20) of 1.48 or less, which is lower than the refractive index of typical porous polymer thin films such as polyethylene and polypropylene. When a porous thin film filled with a porous body is used as an electrolyte in an EC device, light scattering occurs in the thin film, resulting in the problem that this EC device is difficult to use for optical applications such as display devices and EC windows. . Therefore, in this case, the selection of the organic solvent used for the ionic conductor is extremely important.

0003

[Problems to be Solved by the Invention] Under these circumstances, the present invention provides a light control element that uses a porous polymeric thin film with low light scattering and whose pores are filled with an ionic conductor as an electrolyte. The purpose of this invention is to provide an EC element suitable for use as an optical element such as a display element.

0004

[Means for Solving the Problems] As a result of intensive research to develop an EC device having the above-mentioned preferable properties, the present inventors have discovered that an ionic conductor to be filled into the pores of a porous polymer thin film. It was discovered that the object could be achieved by using a mixed solvent of 2,2-diphenylpropionitrile and polyether as a solvent, and the present invention was completed based on this knowledge. That is, the present invention
EC with an electrolyte interposed between the C electrode and the counter electrode
In the element, the electrolyte has a refractive index of 1.48 to 1.
In the pores of the porous polymer thin film of 56, (A) 2,2-diphenylpropionitrile and (B) the general formula

[0005]

[Case 2]

(R1 and R3 in the formula are each a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and they may be the same or different, and R2
is an alkylene group having 2 to 4 carbon atoms, and n is an integer of 1 to 100. It provides an element. The present invention will be explained in detail below.

In the EC device of the present invention, a polymer electrolyte thin film formed by filling the pores of a porous polymer thin film with an ionic conductor is used as the electrolyte. Since this electrolyte thin film can be handled as a solid as a whole, there is no need to worry about liquid leakage, and it has advantages such as excellent ionic conductivity and the ability to be made into a thin film. The porous polymer thin film usually has a thickness of 0.1 to 50 μm, preferably 1.0 to 25 μm, a porosity of 40 to 90%, preferably 60 to 90%, and a breaking strength of 200 kg/cm2 or more.
Preferably 500 kg/cm2 or more and average through hole diameter 0
．． 001 to 1.0 μm is used.

[0008] If the film thickness is less than 0.1 μm, the mechanical strength as a support film is poor and handling is poor, making it impractical, while if it exceeds 50 μm, the effective resistance becomes high, which is not preferable. When the porosity is less than 40%, the ionic conductivity as an electrolyte is insufficient, and when it exceeds 90%, the mechanical strength as a support membrane decreases, making it impractical. Furthermore, if the breaking strength is less than 200 kg/cm2, it is not practical as a support membrane. Furthermore, the average through-hole diameter may be any pore diameter that allows the ionic conductor to be immobilized in the pores.
It is not particularly limited, and is appropriately selected depending on the material of the polymer thin film and the shape of the pores, but is usually in the range of 0.001 to 1.0 μm.

The porous polymer thin film used in the present invention thus functions as a support for the ionic conductor and is made of a polymer material with excellent mechanical strength. Examples of such polymeric materials include polyolefin, polycarbonate, polyester, polymethacrylate, polyacetal, polyvinylidene chloride, polyvinylidene fluoride, and polytetrafluoroethylene. Vinylidene chloride and polytetrafluoroethylene are preferably used. Further, among these, from the viewpoint of forming a porous structure, ease of thinning, and mechanical strength, those having a weight average molecular weight of 5 x 105 or more, preferably 1 x 106 to 1 x
107 polyolefins are preferred.

Examples of the polyolefin include ethylene, propylene, butene-1, 4-methylpentene-1
Crystalline polyolefins consisting of homopolymers or copolymers of α-olefins such as polyethylene,
Polypropylene, ethylene-propylene copolymer, polybutene-1, poly-4-methylpentene-1, and the like are preferably used. Among these, those with a weight average molecular weight of 5
Polyethylene and polypropylene of ×105 or more are preferred.

The weight average molecular weight of this polyolefin affects the mechanical strength of the thin film obtained. For example, by using an ultra-high molecular weight polyolefin, an ultra-thin and high-strength thin film can be produced by ultra-stretching, so that the effective resistance A highly ionic conductive thin film with low ion conductivity can be obtained. Note that a polyolefin with a weight average molecular weight of less than 5 x 105 can be blended with the polyolefin, but in a system that does not contain a polyolefin with a weight average molecular weight of 5 x 105 or more, an ultra-thin, high-strength film can be obtained by ultra-stretching. I can't do it.

[0012] Next, an example of a preferred method for producing the porous polymeric thin film used in the present invention will be described. First, a polyolefin having a weight average molecular weight of 5 x 105 or more is added to a solvent such as liquid paraffin, and heated and dissolved. and concentration 1~1
After preparing a homogeneous solution of about 5% by weight, a sheet is formed from this solution and rapidly cooled to form a gel-like sheet. Next, this gel-like sheet is extracted with a volatile solvent such as methylene chloride to adjust the amount of solvent in the sheet to 10 to 90% by weight. Next, this gel-like sheet is heated at a temperature below the melting point of the polyolefin and stretched to an area ratio of 10 times or more, and then the solvent contained in this stretched film is extracted and removed with a volatile solvent such as methylene chloride. Then, by drying, a desired porous polymeric thin film is obtained.

In the present invention, it is necessary that the refractive index of the porous polymer thin film is in the range of 1.48 to 1.56. When this refractive index deviates from the above range, the difference between the refractive index and the ionic conductor used becomes large, and light scattering occurs in the porous polymer thin film whose pores are filled with the ionic conductor. The purpose of the present invention cannot be fully achieved. In the present invention, as a solvent for the ionic conductor, (A)
2,2-diphenylpropionitrile and (B) general formula

[
0014

[Chemical formula 3]

A mixed solvent with a polyether represented by the following formula (R1, R2, R3 and n have the same meanings as above) is used. R1 and R3 in the general formula [1]
are each a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and they may be the same or different. The alkyl group includes methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group,
Examples include isobutyl, sec-butyl and t-butyl. R2 is an alkylene group having 2 to 4 carbon atoms,
It may be linear or branched. Examples of the alkylene group include an ethylene group, a linear or branched propylene group, and a linear or branched butylene group. Also,
This polyether may have two or more types of alkylene groups in one molecule. Furthermore, n is an integer in the range of 1 to 100.

Examples of such polyethers include polyethylene glycol, polypropylene glycol,
Polybutylene glycol, polyoxyethylene polyoxypropylene glycol, polyoxyethylene monomethyl ether, polyoxyethylene dimethyl ether, polyoxyethylene monoethyl ether, polyoxyethylene diethyl ether, polyoxyethylene monopropyl (n- or iso) ether, poly oxyethylene dipropyl (n- or iso) ether, polyoxypropylene monomethyl ether, polyoxypropylene dimethyl ether, polyoxypropylene monoethyl ether,
Polyoxypropylene diethyl ether, polyoxypropylene monopropyl (n- or iso) ether, polyoxypropylene dipropyl (n- or iso) ether, polyoxyethylene polyoxypropylene monomethyl ether, polyoxyethylene polyoxypropylene dimethyl ether, poly oxyethylene polyoxypropylene monoethyl ether, polyoxyethylene polyoxypropylene diethyl ether, polyoxyethylene polyoxypropylene monopropyl (n- or iso) ether, polyoxyethylene polyoxypropylene dipropyl (n- or iso) ether, polyoxyethylene monobutyl (n-, iso, sec- or t-) ether,
Examples include polyoxyethylene dibutyl (n-, iso, sec- or t-) ether, polyoxybutylene monomethyl ether, polyoxybutylene dimethyl ether, but are not limited thereto. These polyethers may be used alone or in combination of two or more, but among these, polyoxyethylene dimethyl ether, polyoxypropylene dimethyl ether, etc. are particularly preferred. Further, these polyethers preferably have a molecular weight in the range of 200 to 3,000.

Regarding the ratio of the 2,2-diphenylpropionitrile as the component (A) and the polyether as the component (B), the refractive index of the resulting mixed solvent is the same as the refractive index of the porous polymer thin film. It is selected appropriately depending on the type of polyether so that the values are close to each other, but usually the (A) component and (B)
(
A) component and (B) component are mixed. In addition, 2,2-
The refractive index of diphenylpropionitrile is 1.572, and polyoxyethylene dimethyl ether (molecular weight 30
0) has a refractive index of 1.412.

[0018] Since this mixed solvent has a refractive index close to the refractive index of the porous polymer thin film used, light scattering in the polymer electrolyte thin film can be prevented by using this mixed solvent. Can be done. In the present invention, other organic solvents such as propylene carbonate, dimethoxyethane, γ-butyrolactone, acetonitrile, benzonitrile, benzaldehyde, methyl salicylate, One or more types of benzyl alcohol, 3-chlorobenzylnitrile, benzylnitrile, α-trinitrile, etc. may be added.

Ideally, the refractive index of the porous polymer thin film and the ionic conductor should match completely, but usually ±0.0.
A difference within the range of 1 is sufficient. The solute of the ionic conductor used in the present invention is not particularly limited as long as it is an electrolyte that is soluble in the mixed solvent, and for example, alkali metal salts, alkaline earth metal salts, protonic acids, etc. are used. Examples of the anions of these solutes include halogen ions, sulfate ions, phosphate ions, perchlorate ions, thiocyanate ions, trifluoromethanesulfonate ions, and borofluoride ions. Specific examples of the solute include lithium fluoride, lithium iodide, sodium iodide, lithium perchlorate, sodium thiocyanate, lithium trifluoromethanesulfonate, lithium borofluoride, lithium hexafluorophosphate, phosphoric acid,
Sulfuric acid, trifluorinated methanesulfonic acid, tetrafluorinated ethylene sulfonic acid, hexafluorinated butanesulfonic acid, etc. may be used, and one type of these may be used, or two or more types may be used in combination.

[0020] There are no particular restrictions on the method of filling the pores of the porous polymer thin film with the ionic conductor, and any method may be selected from among methods such as dipping, coating, and spraying. Can be done. The EC element of the present invention has a porous polymeric thin film formed by filling the pores thus obtained with an ionic conductor, interposed between an EC electrode and a counter electrode, and An EC electrode can be manufactured by providing an EC layer on a transparent electrode substrate. Further, as the transparent electrode substrate, one having a transparent conductive film such as indium tin oxide or tin oxide on a transparent substrate such as a glass plate or a transparent film is usually used.

Next, an example of the EC element of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of an example of the EC element of the present invention when used as a reflective display element,
A structure in which a counter electrode 2, a background plate 3, a polymer electrolyte thin film 4, an EC layer 5 and a transparent conductive film 6 constituting an EC electrode, a transparent conductive film 6, and a transparent substrate 7 are sequentially laminated on a substrate 1 is shown. Since this display element is in a reflective mode, the substrate 1 does not necessarily have to be a transparent body, and may be an opaque plate. The counter electrode 2 is made of a material that generates little hydrogen or oxygen, has good reversibility to electrochemical redox reactions, and has a large capacitance. Examples of such materials include carbon, a composite material of a transition metal compound and carbon, a composite material of a metal oxide and carbon, and the like. The thickness of this counter electrode 2 is usually selected in the range of 1000 Å to 10 μm.

The background plate 3 is usually made of a white background material, such as a sheet formed by kneading alumina powder with a binder, but the counter electrode 2 can also serve as the background plate 3. As the polymer electrolyte thin film 4, a porous polymer thin film is used in which the pores prepared as described above are filled with an ionic conductor. E used in the EC layer 5
C materials can be roughly divided into two types: cathodic materials that undergo reduction coloring and anodic materials that undergo oxidation coloring. Here, WO3, which is a typical reduction coloring material, is used. This WO3 becomes colored blue when, for example, cations with a small ionic radius such as H+ and Li+ are injected from the electrolyte and electrons from the power source. For example, when protonic acid and lithium salt are used as electrolytes, each

00
23]

[C4]

[0024]

[C5]

The reaction shown below is carried out. Although this reaction is reversible, when the power supply circuit is opened in the state of HxWO3 or LixWO3, the blue color (reduced state) is maintained for a long time. In addition to WO3, such reducing colorants include, for example, MoO3, MoS3, V2O5, MgWO4, Nb2
O5, TiO2, W4O6(C2O4)x, etc. can be used. This EC layer 5 has a thickness of about 500 to 1500 Å,
It is formed on the transparent conductive film 6. The transparent conductive film 6 is a current collecting electrode, and is usually made of indium tin oxide, tin oxide, etc., and its thickness is generally about 1000 to 5000 Å. This transparent conductive film 6 is formed on a transparent substrate 7, but since the substrate 7 is in a reflective mode, it must be transparent. A voltage is applied between the EC electrode composed of the EC layer 5 and the transparent conductive film and the counter electrode 2, and when reducing WO3, a negative voltage of about 1.3 to 1.9 V may be applied normally.

On the other hand, FIG. 2 is a sectional view of an example of the EC element of the present invention when used as a transmission type light control element, in which a transparent conductive film 12 and an EC layer constituting an EC electrode II are placed on a transparent substrate 11. 13 shows a structure in which a polymer electrolyte membrane 14, an EC layer 15 constituting an EC electrode I, a transparent conductive film 16, and a transparent substrate 17 are sequentially laminated. In this case, if a reduction colored EC material is used for the EC layer 15 and an oxidized colored EC material is used for the EC layer 13, an EC element with high coloring efficiency can be obtained. Furthermore, WO3 having different crystal states may be used for the EC layer 13, or IrOx, NiOx, CoOx, Prussian blue, polyaniline, or the like may be used.

The structure shown in FIG. 2 is different from the structure shown in FIG. 13 and transparent conductive film 12 (EC electrode I
I) is light transmittance. In the structure of FIG. 1, the background plate 3 is light-opaque, and the counter electrode 2 may be light-opaque or transparent. In the structure of FIG. 2, a voltage is applied between both electrodes to form the EC layer 15 and the E layer.
When the C layer 13 is colored, this EC element becomes a light control glass (E
C window). In addition, with this structure, EC
If the layer 15 (EC layer 13) is patterned, it can also be used as a transmissive display element.

In addition, when using the EC element of the present invention as an anti-glare mirror, the background plate 3 and the counter electrode 2 in FIG.
In this case, a reflective material such as aluminum may be used. In the EC element having the structure shown in FIGS. 1 and 2, the reflectance and transmittance of incident light in the display mode are about 20 to 80%, and the durability is about 104 to 107 times.

[0029]

EXAMPLES Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples in any way. Production Example 1 Production of Polymer Porous Thin Film Polyethylene having a weight average molecular weight (Mw) of 2×10 6 4.
Liquid paraffin containing 0% by weight (64cst/40°C)
0.125 parts by weight of 2,6-di-t-butyl-p-cresol and tetrakis (methylene-3
-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate) 0.25 parts by weight of methane was added as an antioxidant and mixed. This mixed solution was filled into an autoclave equipped with a stirrer, heated to 200° C., and stirred for 90 minutes to obtain a uniform solution. This solution was filled into a heated mold and rapidly cooled to 50° C. to obtain a gel-like sheet. After immersing this gel sheet in methylene chloride for 60 minutes,
Methylene chloride is evaporated to dryness while it is attached to a smooth board.
An original fabric sheet was obtained. 11 pieces of each of the obtained raw sheets
Simultaneous biaxial stretching is performed at a temperature of 5 to 130°C, and the resulting stretched film is washed with methylene chloride to extract and remove residual liquid paraffin, and then dried to obtain a porous thin film. (a) to (f) by changing the amount of liquid paraffin in the raw sheet, the stretching ratio of the raw sheet, and the heat treatment conditions after stretching.
) Six types of polyethylene porous thin films were produced, and the film thickness, porosity, average pore diameter, and refractive index of each thin film were determined. The results are shown in Table 1.

[0030]

[Table 1]

Example 1 Polyoxyethylene dimethyl ether (molecular weight 300)
An ionic conductor was prepared by dissolving lithium perchlorate in a mixed solvent of /2,2-diphenylpropionitrile (weight ratio 20/80) so that the concentration in the solution was 5 wt%. The refractive index of this ionic conductor was 1.538. Next, this ionic conductor was impregnated into the porous thin film (a) obtained in Production Example 1 to prepare a polymer electrolyte thin film, and its ionic conductivity, light transmittance, and haze value at room temperature were determined. Ta. The results are shown in Table 2.

Example 2 A polyethylene electrolyte thin film was prepared in the same manner as in Example 1 except that the electrolyte was impregnated with an ionic conductor having a lithium perchlorate concentration of 10 wt%.

Example 3 Solvent, polyoxyethylene dimethyl ether and 2,2-
A polyethylene electrolyte thin film impregnated with an ionic conductor was prepared in the same manner as in Example 1 except that the mixing ratio of diphenylpropionitrile was 40:60.

Example 4 A polyethylene electrolyte thin film impregnated with an ionic conductor was prepared in the same manner as in Example 1 except that the type of solvent was changed to polyoxypropylene dimethyl ether and 2,2-diphenylpropionitrile. Table 2 shows the ionic conductivity, light transmittance, haze value, and refractive index of the ionic conductor at room temperature of the electrolyte thin films prepared in Examples 2 to 4.

Comparative Examples 1 to 3 A polyethylene porous thin film (a) was impregnated with an ionic conductor in the same manner as in Example 1, except that the type and mixing ratio of the solvent were as shown in the Comparative Example column of Table 2. , an electrolyte thin film was prepared. The ionic conductivity, light transmittance, haze value, and refractive index of the ionic conductor of this electrolyte thin film at room temperature are also shown in Table 2.

[0036]

[Table 2]

[0037]

Effects of the Invention According to the present invention, the electrolyte layer of the EC element has sufficient transparency with little light scattering, so when applied as a light control element, it achieves excellent light transmission and displays. When applied as a device, the display becomes easier to see. Furthermore, the electrolyte layer can be made thicker, and as a result, even electrodes with poor smoothness can be sufficiently adhered to each other, so that it can be used as an EC electrode, which is advantageous in terms of cost.

[0038]

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an example of an EC element of the present invention when used as a reflective display element.

[0039]

FIG. 2 is a cross-sectional view of an example of the EC element of the present invention when used as a transmission type light control element.

[0040]

[Explanation of symbols]

1 Board 2 Counter electrode 3 Background board 4 Polymer electrolyte thin film 5 EC layer 6 Transparent conductive film 7 Transparent substrate 11 Transparent substrate 12 Transparent conductive film 13 EC layer 14 Polymer electrolyte thin film 15 EC layer 16 Transparent conductive film 17 Transparent substrate

Claims (3)

[Claims] 1. An electrochromic element comprising an electrolyte interposed between an electrochromic electrode and a counter electrode, wherein the electrolyte has a refractive index of 1.48 to 1.56.
(A) 2,2-diphenylpropionitrile and (B) the general formula [Formula 1] (where R1 and R3 are each a hydrogen atom or a carbon number of 1 to 4 alkyl groups, which may be the same or different, and R2 has 2 to 2 carbon atoms.
An electrochromic device characterized in that it uses an electrolyte thin film filled with an ionic conductor containing a mixed solvent with a polyether represented by an alkylene group of 4 and n is an integer of 1 to 100. Claim 2: The porous polymer thin film has a weight average molecular weight of 5×1.
Claim 1 consisting of a polyolefin of 05 or higher.
The electrochromic device described. 3. The electrochromic device according to claim 1, wherein the mixed solvent contains component (A) and component (B) in a weight ratio of 20:80 to 90:10.