JPH1149990A - Coating liquid for forming clear conductive film and method for forming clear conductive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coating liquid for forming a clear conductive film having a low resistance and a high transmittance by incorporating at least one glycol selected from among ethylene glycol, propylene glycol, and butanediol, an indium salt, a tin salt, and a monohydric alcohol at least having a specified number of carbon atoms into the same. SOLUTION: Pref., the indium salt is indium nitrate; the tin salt is at least either tin acetate or tin oxalate; and the alcohol is at least one alcohol selected from among methanol, ethanol, and isopropanol. Pref., this coating liquid for forming a clear electrode is applied to a substrate and thermally treated at 350 deg.C or higher to form a clear conductive film. Pref., the wt. ratio of the indium salt to the tin salt is (95/5)-(85/15); that of the glycol to the sum of the indium salt and the tin salt is (10/100)-(300/100); and the content of the alcohol in the coating liquid is 10-80 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a coating solution for forming a transparent conductive film and a method for forming a transparent conductive film.

[0002]

2. Description of the Related Art Antimony-doped tin oxide (ATO) and tin-doped indium oxide (ITO), which are typical examples of transparent conductive materials, have been widely applied to display elements and on-surface heating elements as thin films. , Many of these are CV
It is manufactured by a dry film forming method such as a D method or a sputtering method. However, these methods require equipment costs and also have a problem in productivity. As a simpler method, there have been proposed many methods of applying a solution of an indium salt or the like and thermally decomposing the solution to obtain a film.

[0003] However, in those proposed so far, for example, even if easily available indium nitrate or indium chloride is dissolved in a solvent and applied as it is, the coating is liable to be cloudy and has poor mechanical strength. I can't get it. The metal alkoxide known as the sol-gel method is very expensive as a raw material, and it is difficult to liquefy a coating liquid because of a small amount of a good solvent. However, there is a problem that the stability of the resin tends to be low.

[0004] In order to solve these problems, it has been proposed to coordinate an indium salt with an organic ligand to enhance the thermal stability and to reduce the white turbidity and the decrease in mechanical strength when forming a film. It is a technique to prevent. As organic ligands, β-diketones (Ceramics, 21 236 (1986)), amino alcohols (JP-A-1-287278), polyhydric alcohol condensates (JP-A-7-320541) and the like have been proposed.

[0005] However, β-diketones such as acetylacetone and amino alcohols are too disadvantageous for improving the denseness of the film because organic substances tend to remain in the film because the stability of the complex formed by coordination is too high. The polyhydric alcohol condensate is not as stable as the acetylacetone complex, so it was advantageous for forming a denser film. There was a problem that it easily remained.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a coating liquid for forming a transparent conductive film capable of forming a transparent conductive film having low resistance and high transmittance. It is intended to provide. The present invention also provides
It is an object of the present invention to provide a method for forming a transparent conductive film having low resistance and high visible light transmittance.

[0007]

The present invention comprises at least one glycol selected from ethylene glycol, propylene glycol and butanediol, an indium salt, a tin salt, and a monohydric alcohol having 8 or less carbon atoms. It is intended to provide a coating liquid for forming a transparent conductive film,
A transparent conductive film forming coating solution containing at least one glycol selected from ethylene glycol, propylene glycol and butanediol, an indium salt, a tin salt, and a monohydric alcohol having 8 or less carbon atoms is coated on a substrate. And a method for forming a transparent conductive film by performing a heat treatment at a temperature of 350 ° C. or higher.

In the present invention, the indium salt includes
Inorganic salts such as indium nitrate, indium sulfate, and indium chloride which can be easily obtained can be used, and among them, indium nitrate which is excellent in reactivity with glycol described later and solubility in alcohol is preferable. As tin salts, acetate,
An organic acid salt having a short carbon chain such as oxalate, tin chloride, tin sulfate, or the like can be used, but from the viewpoint of solubility and reactivity, at least one tin salt selected from tin acetate and tin oxalate is preferable. In the coating solution of the present invention, the ratio of indium salt to tin salt may be In / Sn = 95/5 to 85/15 in terms of weight ratio of indium to tin in order to obtain a low-resistance transparent conductive film. preferable.

Glycol in the coating solution of the present invention is an important part that forms the basis of the present invention. As the glycol, it is important to use at least one of ethylene glycol, propylene glycols (two isomers), and butanediols (four isomers) having a relatively short carbon chain. There are two types of isomers of propylene glycols, 1,2-propylene glycol and 1,3-propylene glycol, but 1,2-propylene glycol is preferred from the viewpoint of the stability of the complex. There are four isomers of butanediols: 1,2-, 1,3-, 1,4-, 2,3-, but from the viewpoint of complex formation, 1,2- and 2,2- The 1,3-isomer is most preferred, and the 1,3-isomer is somewhat inferior but fully operable.

[0010] The glycol in the coating solution of the present invention functions to form a complex by coordinating with the indium salt and the tin salt, thereby increasing the thermal stability of the metal salt. A transparent continuous film is formed by this action, but when glycols having a larger number of carbon atoms are used, the higher volatility tends to remain in the film at high temperatures due to its low volatility, which causes a reduction in the denseness of the film after firing. This is because For this reason, among these, ethylene glycol is particularly used as the most preferred glycol.

The mixing ratio of glycol in the coating solution of the present invention is (glycol) / (indium salt + tin salt) = 10 with respect to indium salt and tin salt.
A ratio of / 100 to 300/100 is preferred. If the amount of glycol is less than this, the function as a complex cannot be expected, and if it is more than this, unnecessary high-boiling components will increase, which may be a factor that hinders the denseness of the film as described above. It is.

[0012] In the coating solution of the present invention, 1 having not more than 8 carbon atoms.
The dihydric alcohol has an extremely high viscosity with glycol alone, and is therefore an important component having not only a function as a solvent for diluting to a viscosity suitable for coating but also a function as a reducing agent. Indium oxide based transparent conductive material is n
Since it is a type semiconductor and generates conduction electrons by generation of oxygen vacancies, a material having higher conductivity can be obtained by shifting the equilibrium to the reduction side. By the addition of the alcohol, a reducing action during the heat treatment works, and a film having a lower specific resistance is obtained.

The alcohol used is not particularly limited as long as it has an extremely high boiling point and does not easily remain at a high temperature in the film, but methanol, ethanol, isopropanol and the like are preferred examples in consideration of the action as a diluent. However, in order to further improve the wettability with glass, monohydric alcohols having 8 or less carbon atoms, such as ethylene glycol ethers and propylene glycol ethers, can be used together with methanol, ethanol, isopropanol and the like.

The proportion of the alcohol in the coating solution of the present invention is appropriate depending on the coating method described later, and cannot be specified unconditionally. However, it is preferable that the alcohol accounts for 10 to 80% by weight of the pre-coating solution. . If it is more than this, the film thickness that can be applied at one time becomes too small, and if it is less than this, the effect of alcohol may not be obtained.

The coating liquid of the present invention may contain a surfactant or the like for improving the wettability to the substrate, if necessary. That is, most of the surfactants are medium to high molecular weight organic substances having low volatility, and when added in large amounts, the denseness of the coating film may be reduced and the electrical properties may be deteriorated.

After the coating solution of the present invention is applied to a substrate and dried, a heat treatment is performed at a temperature of 350 ° C. or higher to form a transparent conductive film. The thickness of the transparent conductive film is 10
The thickness is preferably from 500 to 500 nm, particularly preferably from 50 to 200 nm.

The substrate is not particularly limited as long as it has a heat resistance of 350 ° C. or higher, but generally, glass, ceramics or the like is used. In addition, as a coating method, a known method can be used, and a dip coating method,
Spin coating, screen printing, roll coating,
And the like. Of these, spin coating and dip coating are preferred. The firing is not particularly limited as long as it is 350 ° C. or higher and is lower than the temperature at which the substrate deteriorates. The firing atmosphere is generally air. However, when it is necessary to reduce the resistance value by reducing the atmosphere as described above, the firing may be performed in an atmosphere of a reducing gas containing an inert gas or hydrogen.

[0018]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples.

(Example 1) 10 g of indium nitrate trihydrate,
0.58 g of stannous oxalate (In / Sn = 91/9 (weight ratio)) and 100 cc of 17 g of ethylene glycol
The mixture was added to an eggplant-shaped flask and heated at 75 ° C. for 3 hours to obtain a pale yellow transparent viscous solution. 17 g of methanol and 17 g of isopropanol were added to this solution, and the mixture was stirred well to obtain a coating solution. This coating solution was formed into a film on a non-alkali glass substrate by spin coating, dried at 60 ° C. for 10 minutes, and baked in an electric furnace at 550 ° C. for 1 hour in the air.
Table 1 shows the results. In Table 1, regarding transparency,
In the haze computer manufactured by Suga Test Instruments, those having a total transmittance (scattered transmittance + non-scattered transmittance) of 85% or more and a haze value of 0.5% or less were evaluated as ○. The sheet resistance was measured by a DC four-point probe method. Regarding the denseness, in the measurement of the refractive index by ellipsometry, a value of 1.90 or more was evaluated as O, and a value of less than 1.90 was evaluated as X.

(Example 2) The amount of tin oxalate added in Example 1 was changed,
Coating and baking were performed in the same manner as in Example 1 except that In / Sn = 85/15 (weight ratio) to obtain glass with a film. Table 1 shows the results.

Example 3 The amount of tin oxalate added in Example 1 was changed.
Coating and baking were performed in the same manner as in Example 1 except that In / Sn = 94/6 (weight ratio) to obtain glass with a film. Table 1 shows the results
Shown in

Example 4 Indium nitrate trihydrate 1 of Example 1
Example 1 except that 0 g was changed to 7.8 g of indium chloride.
Was applied and baked in the same manner as described above to obtain a glass with a coating (In /
Sn = 91/9 (weight ratio)). Table 1 shows the results.

EXAMPLE 5 17 g of methanol and 17 g of isopropanol of Example 1 were replaced with 17 g of methanol and 17 g of methanol.
Coating and baking were performed in the same manner as in Example 1 except that the amount of propylene glycol monomethyl ether was changed to 17 g to obtain glass with a film. Table 1 shows the results.

Example 6 17 g of methanol and 17 g of isopropanol in Example 1 were replaced with 17 g of ethanol and 17 g of ethanol.
Coating and baking were performed in the same manner as in Example 1 except that the amount of isopropanol was changed to 17 g, to obtain a glass with a film. Table 1 shows the results
Shown in

(Example 7) Coating and firing were performed in the same manner as in Example 1 except that tin oxalate of Example 1 was changed to tin acetate to obtain a glass with a coating (In / Sn = 91/9 (weight ratio)). Table 1 shows the results.

Example 8 The coating obtained in Example 1 was heat-treated again at 400 ° C. for 30 minutes in nitrogen. Table 1 shows the results.

Example 9 17 g of ethylene glycol of Example 1
Was changed to 17 g of 1,2-propylene glycol to obtain glass with a coating in the same manner as in Example 1. Table 1 shows the results
Shown in

Example 10 Ethylene glycol 17 of Example 1
Glass with a coating was obtained in the same manner as in Example 1 except that g was changed to 17 g of 2,3-butanediol. Table 1 shows the results.

Example 11 (Comparative Example) A coated glass was obtained in the same manner as in Example 1 except that 17 g of ethylene glycol in Example 1 was replaced with 17 g of diethylene glycol. Table 1 shows the results
Shown in

Example 12 (Comparative Example) A coated glass was obtained in the same manner as in Example 1 except that "17 g of methanol and 17 g of isopropanol" in Example 1 was changed to 34 g of 1-decanol. Table 1 shows the results.

Example 13 (Comparative Example) A coated glass was obtained without adding the ethylene glycol of Example 1. Table 1 shows the results.

[0032]

[Table 1]

[0033]

According to the present invention, a transparent conductive film having excellent conductivity and transparency can be obtained at a low cost by a simple method.

Claims (5)

[Claims] 1. A coating liquid for forming a transparent conductive film, comprising at least one glycol selected from ethylene glycol, propylene glycol and butanediol, an indium salt, a tin salt, and a monohydric alcohol having 8 or less carbon atoms. 2. The coating liquid for forming a transparent conductive film according to claim 1, wherein the monohydric alcohol having 8 or less carbon atoms is at least one selected from methanol, ethanol, and isopropanol. 3. The coating solution for forming a transparent conductive film according to claim 1, wherein the indium salt is indium nitrate. 4. The coating solution for forming a transparent conductive film according to claim 1, wherein the tin salt is at least one selected from tin acetate and tin oxalate. 5. A coating solution for forming a transparent conductive film, comprising at least one glycol selected from ethylene glycol, propylene glycol and butanediol, an indium salt, a tin salt and a monohydric alcohol having 8 or less carbon atoms. A method for forming a transparent conductive film, which is applied on a substrate and heat-treated at a temperature of 350 ° C. or higher to form a transparent conductive film.