JPS5854090B2 - Method for forming transparent conductive film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a transparent conductive film on the surface of a substrate such as glass or ceramic.

BACKGROUND ART Electrode materials that are transparent to light are used in display elements such as crystal display elements, plasma display elements, and electroluminescent elements, and photosensitive elements such as photovoltaic cells and image pickup tubes.

Examples of these transparent conductive films include indium oxide with a trace amount of tin oxide added, or tin oxide with a trace amount of antimony oxide added.

The following method is known for forming a transparent conductive film.

(1) Indium or tin oxide or metal is deposited on the substrate surface in vacuum or in an oxygen atmosphere by vapor deposition or sputter deposition.

(11) A solution of an indium compound or a tin compound is sprayed onto a preheated substrate to cause thermal decomposition and oxidation reactions, thereby depositing a transparent conductive film on the surface of the substrate.

(*++) A liquid substance made of an indium compound, a tin compound, etc. is applied onto a substrate, and then heated to cause thermal decomposition and oxidation reactions to form a transparent conductive film on the substrate surface.

Methods ([) and (11) require complicated equipment and are poor in workability, and moreover, because they form fine conductive patterns,
There was a problem in that etching processing had to be performed later.

Method (11i) has the potential to solve the above-mentioned problems in methods (i) and (1:), but conventionally known coating liquids do not have enough high performance to withstand practical use. There was a problem that it was difficult to obtain a transparent conductive film.

That is, metal salts of monocarboxylic acids (Japanese Patent Publication No. 31-528
2゜Special Publication Showa 45-7181. JP-A-50-45995° JP-A-52-1497, Ger 0ffer 2,4
11.

If a solution containing 872) as the main component is used, poor wetting of the liquid to the substrate may occur, and even if this phenomenon is prevented, the conductive film after heating and baking is likely to crack or become cloudy, and low-resistance transparent It was difficult to obtain a conductive film.

An object of the present invention is to provide a method for forming a transparent conductive film with excellent workability and good conductive properties, eliminating the drawbacks of the conventional methods described above.

To achieve this objective, the method according to the invention comprises:
After applying a solution for forming a transparent conductive film (hereinafter referred to as composition liquid) containing an inorganic indium salt and a hydroxy acid, or an intramolecular or intermolecular ester of a hydroxy acid as the main components, the substrate is heated. , is characterized by forming a transparent conductive film on a substrate.

When the inorganic indium salt and the hydroxy acid or intramolecular and intermolecular ester of the hydroxy acid are mixed in the presence of water or an organic solvent, the inorganic indium salt and the hydroxy acid or the intramolecular and intermolecular ester of the hydroxy acid are mixed together. Reacts partially or quantitatively to form indium complex salts.

When such a composition liquid is used, a transparent conductive film with excellent wettability with the substrate, less volatilization of component substances during firing, and low resistance without cracking or clouding can be obtained.

The inorganic indium salt used in the present invention is preferably one that reacts well with hydroxy acids or intramolecular and intermolecular esters of hydroxy acids and produces a uniform solution, and chlorides, nitrates, perchlorates, etc. are useful. be.

These inorganic indium salts may be hydrated salts.

The hydroxy acid used in the present invention is not particularly limited as long as it contains one or more carboxyl group and one or more hydroxyl group in the same molecule, but it is a relatively low molecular weight compound with 12 or less carbon atoms, and has one or more carboxyl groups and one or more hydroxyl group in one molecule. Compounds containing up to five carboxyl groups and hydroxyl groups tend to be able to maintain a lower resistance value of the transparent conductive film.

For example, the following compounds are useful as hydroxy acids used in the present invention.

Glycolic acid, lactic acid, hydroacrylic acid, α-hydroxy-n-butyric acid, α-hydroxyiributyric acid, β-hydroxy-n-butyric acid, γ-hydroxybutyric acid, 3-hydroxyglutaric acid, 3-hydroxy-3-methylglutaric acid , leucinic acid, tartronic acid, glyceric acid, malic acid, oxaloacetic acid, citric acid, tartaric acid, gluconic acid, 3-hydroxy-3-phenylpropionic acid, hydroacrylic acid,
Salicylic acid, dihydroxybenzoic acid, 3-(hydroxyphenyl)propionic acid, hydroxytoluic acid, etc.

The intramolecular and intermolecular esters of hydroxy acids used in the present invention are not particularly limited as long as they have 12 carbon atoms.
Compounds composed of the following relatively low molecular weight units tend to be able to keep the resistance value of the transparent conductive film low.

Intramolecular and intermolecular esters of such hydroxy acids include glycolide, β-propiolactone, β-butyrolactone, γ-butyrolactone, γ-valerolactone, δ-valerolactone, α-acetyl-γ-butyrolactone, ε -Caprolactone, γ-hebutolactone, gluconic acid lactone, etc. are useful.

The blending ratio of the above-mentioned inorganic indium salt and the hydroxy acid or the intramolecular and intermolecular ester of the hydroxy acid is preferably 0.1 to 2.9 (molar ratio) to the inorganic indium salt, and in particular, A smaller ratio tends to provide a transparent conductive film with better characteristics.

Inorganic indium salts and hydroxy acids, or intramolecular and intermolecular esters of hydroxy acids, react partially or quantitatively, and when the solvent is removed, they tend to change from a viscous liquid to a glass-like substance. There is.

Therefore, when it is applied to a substrate, it is easy to form a good coating film, and moreover, it is possible to prevent abnormal volatilization of component substances and film cracking during heating and baking, and a high-performance transparent conductive film can be obtained.

The solvent added to the composition solution of the present invention is particularly limited as long as it plays a role such as adjusting the viscosity of the solution and assisting the mixing and reaction of the inorganic indium salt and the hydroxy acid or the intramolecular and intermolecular ester of the hydroxy acid. However, in addition to water, methanol, ethanol, propatool, ethylene glycol, propylene glycol, diethylene glycol, methyl celeryl, ethyl cellosolve, butyl celeryl, ethyl celeryl bu acetate, calpitol, etc., a mixture of these may be used. is possible.

Furthermore, organic and inorganic compounds containing tin and antimony elements are added to the composition liquid of the present invention, and ethyl cellulose and rosin are added to improve the wettability of the composition liquid to the substrate and to adjust the viscosity. You can also.

In applying the composition liquid of the present invention composed of the above-mentioned component substances to a substrate, ordinary coating techniques such as a dipping method, a spinner method, a spraying method, a screen printing method, and an offset printing method can be applied.

Further, when heating the substrate coated with the composition liquid of the present invention, a temperature of 400 to 900°C can be used.

By leaving the composition at this temperature for about 15 to 180 minutes, the constituent substances of the composition undergo thermal decomposition and oxidation reactions to form a transparent conductive film.

Next, the present invention will be explained by examples.

The inorganic indium salts shown in Tables 1 and 2) to (c) and the hydroxy acids shown in (g) to
A 1/1 mixed solution (parts by weight) of ethyl cellosolve and ethyl alcohol is prepared by combining the intramolecular or intermolecular esters of hydroxy acids shown in C) to C) in principle in equimolar amounts.
To this, tin salts shown in Table 1) or Tables 1 and 2 are added as a dopant, and Table 1,
Composition solutions 1 to 18 of Examples of the present invention shown in Table 2 were prepared.

In addition, as a comparative example, Composition Liquid 19 shown in Table 2 was prepared, the main component being indium monocarboxylate (E) shown in Tables 1 and 2.

After coating these compositions on a quartz glass substrate by offset printing, the solvent was dried in air at 100°C for 10 minutes, and then baked at 500°C for 1 hour to form a patterned transparent conductive film. did.

As shown in the lower part of Tables 1 and 2, those using composition solutions 1 to 17 of Examples in Tables 1 and 2 all have sheet resistances of 1.9'KJJ/crlt or less. The properties of the transparent conductive film were also good, with no cracks or cloudiness.

However, in the case of Comparative Example 19 in Table 2, clouding and cracking occurred in the conductive film, and the resistance value was 3 to 8/3.
It showed a high value of Cd.

In addition, as shown in the figure, a transparent conductive film with low sheet resistance has a mixing ratio of inorganic indium salt and hydroxy acid or intramolecular and intermolecular ester of hydroxy acid of 1:0.5 to 2.9 (mole ratio). was gotten.

As described above, when the method for forming a transparent conductive film according to the present invention is used, a transparent conductive film having excellent transparency and conductivity can be obtained.

Furthermore, since the composition liquid can be applied at room temperature, a simple application technique can be applied, and the manufacturing process can be greatly rationalized.

[Brief explanation of the drawing]

The figure shows the relationship between the mixing ratio of indium nitrate and malic acid and the sheet resistance value.

Claims (1)

[Scope of Claims] 1. A method for forming a transparent conductive film, which comprises applying a solution for forming a transparent conductive film containing an inorganic indium salt and a hydroxy acid as main components to a substrate, and then heating the substrate. 2. The method for forming a transparent conductive film according to claim 1, wherein the hydroxy acid is an intramolecular ester or an intermolecular ester of a hydroxy acid. 3. The method for forming a transparent conductive film according to claim 1, wherein the inorganic indium salt is one type of compound selected from chlorides, nitrates, and perchlorates. 4. The method for forming a transparent conductive film according to claim 2, wherein the mixing ratio of the inorganic indium salt and the hydroxy acid or the ester of the hydroxy acid is 1:0.1 to 2.9 in molar ratio. .