JPH07242842A - Composition for forming transparent electrically-conductive film and transparent electrically-conductive film - Google Patents

Abstract

PURPOSE:To obtain the subject composition useful as an antistatic film, having excellent transparency, electrical conductivity, etc., by adding a metallic coupling agent containing a specific group to a dispersion having dispersed a tin-doped indium oxide powder (ITO powder) as electrically-conductive powder. CONSTITUTION:This composition comprises (A) ITO powder having <=0.2mum, preferably <=0.1mum average primary particle diameter [preferably the one having 0.01-0.15 atomic ratio of Sn/(Sn+In) and <=100OMEGA.cm powder specific resistance] as electrically-conductive powder under 50kg/cm<2>, (B) a metal alkoxide and/or its partial hydrolyzate (preferably silicon alkoxide, especially ethyl silicate) as a binder and (C) a metallic coupling agent containing a phosphate group, phosphite group or their ester groups as a binder in a solvent. The composition is applied to a transparent base and the coating film is dried at <200 deg.C to give a transparent electrically-conductive film having <=1X10<5>OMEGA/square surface resistance value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composition capable of forming a transparent conductive film having excellent transparency and conductivity, and a method for forming a transparent conductive film using this composition. More specifically, the present invention relates to tin-doped indium oxide (hereinafter referred to as ITO).
The present invention relates to a composition for forming a transparent conductive film and a method for forming a transparent conductive film, wherein the powder of 1. is used as a conductive powder.

The transparent conductive film formed from the composition of the present invention is suitable as an antistatic film for various semiconductor device packaging materials, clean room interior materials, cathode ray tubes, electronic equipment and the like. Moreover, since this transparent conductive film has a lower resistance than conventional products, it can be used as a transparent electrode, a circuit, or the like.

[0003]

2. Description of the Related Art As a conductive material for forming a transparent conductive film,
Metal oxides such as tin oxide, zinc oxide and indium oxide have been conventionally used. Among them, ITO composed of a mixed oxide obtained by doping indium oxide with a small amount of tin oxide is
It is known that both conductivity and transparency are good.

The method of forming a transparent conductive film using ITO is
In a vapor phase method in which ITO is deposited on the substrate by a method such as vacuum deposition, sputtering, or ion plating, and in a solution containing a submicron fine ITO powder as a binder (eg, metal alkoxide or carbon-based organic resin) It is roughly classified into a coating method in which a dispersion liquid obtained by dispersing into a coating material is used to apply it to a substrate by a method such as coating or printing.

Conventionally, the vapor phase method has been widely used, but the area of the transparent conductive film to be obtained is limited and it is difficult to increase the area, and the equipment cost is high and the productivity is poor. Also,
The adhesion efficiency during film formation is low, and the effective utilization rate of ITO is 40-50.
Very low at%. In addition, when the circuit is drawn by the etching method after the film formation, most of the ITO adhering to the substrate is removed, so that there is a disadvantage that the amount of material is further wasted.

On the other hand, in the coating method, since the circuit can be directly drawn by a method such as screen printing, the construction is simple and the material is not wasted. Therefore, the conductive film can be obtained at a low cost and the productivity is high. However, since the film formed by the coating method is a film having a structure in which ITO powder is bonded with a binder, it is generally inferior in conductivity to a film composed of ITO alone obtained by the vapor phase method. .

As the binder in the coating method, a metal alkoxide is used more than an organic resin because it gives a transparent conductive film having good heat resistance and hardness. However, when the metal alkoxide is used as a paint, the dispersibility of the ITO powder is lowered, and the powder is apt to agglomerate during drying and baking after coating, resulting in low transparency and conductivity of the obtained film. There was a flaw.

[0008]

Therefore, the transparency of a transparent conductive film formed by coating method using ITO powder is improved, and at the same time, the conductivity and other characteristics are close to those obtained by the vapor phase method. Is required to improve.

It is generally known to add a surfactant or a coupling agent to the dispersion liquid or to surface-treat the powder with these before the preparation of the dispersion liquid in order to improve the dispersibility of the powder. . However, if the powder is conductive powder,
By improving the dispersibility in this way, on the other hand, the powder is completely covered with the binder, so that the powders are not in contact with each other in the obtained film, and the conductivity of the film is lowered. Therefore, it has been difficult to achieve both conductivity and transparency of the film.

As an example of applying a coupling agent to ITO powder, Japanese Patent Laid-Open No. 1-261469 discloses conductive fine particles surface-treated with a silane coupling agent (eg, ITO powder).
A transparent conductive film having excellent surface hardness, which is mainly composed of a resin and a vehicle (eg, alkoxysilane), has been proposed. It is described that by pre-treating the ITO powder with a silane coupling agent, the dispersibility of the powder in the vehicle (binder) is improved and the hardness is increased. However, as is clear from the comparison between the examples and the corresponding comparative examples in the above publication, even if the ITO powder is surface-treated with the silane coupling agent, the hardness is high, but the transparency is almost the same as in the case of no treatment. There is no change, and the conductivity shows a slight decrease.

An object of the present invention is to provide a method for forming a transparent conductive film having improved transparency and conductivity by using ITO powder by a coating method, and a composition for forming a transparent conductive film used in this forming method. And to provide.

[0012]

According to the present invention, the above object is to provide a metal-based coupling agent having a phosphoric acid group, a phosphorous acid group or an ester group thereof in a dispersion liquid in which ITO powder is dispersed. It is achieved by adding.

Here, the gist of the present invention is that ITO powder is used as the conductive powder, metal alkoxide and / or its partial hydrolyzate is used as the binder, and phosphoric acid group, phosphorous acid group or the like as the bonding aid. Containing a metal-based coupling agent having an ester group in a solvent,
It is a composition for forming a transparent conductive film.

The composition for forming a transparent conductive film is applied onto a transparent substrate, and the coating film is dried at a temperature of less than 200 ° C. to obtain a transparent conductive film having a surface resistance value of 1 × 10 ⁵ Ω / □ or less. Can be formed. Further, the above-mentioned composition for forming a transparent conductive film is applied on a transparent substrate, the coating film is dried at a temperature of less than 200 ° C., and then baked at a temperature of 200 to 900 ° C. A transparent conductive film having a density of × 10 ⁴ Ω / □ or less can be formed.

[0015]

The structure of the present invention will be described in detail below together with its operation.

The ITO powder used in the present invention is Sn / (Sn + I
It is preferable that the atomic ratio of n) is in the range of 0.01 to 0.15 and the powder specific resistance of the powder compact of 50 kg / cm ² is 100 Ω · cm or less. If this atomic ratio is less than 0.01 or more than 0.15, the powder resistivity becomes high and it is difficult to obtain high conductivity. In addition, even if the powder specific resistance of 50 kg / cm ² green compact exceeds 100 Ω · cm, the surface resistance of the transparent conductive film becomes high and it becomes difficult to obtain high conductivity. .

The average primary particle diameter of the ITO powder is 0.2 μm or less, preferably 0.1 μm or less. This particle size is 0.2
When it exceeds μm, the influence of scattering by visible light becomes large, and the transparency of the obtained transparent conductive film decreases.

The above-mentioned ITO powder is prepared, for example, by reacting an aqueous solution in which chlorides of In and Sn are dissolved with an alkaline aqueous solution to obtain an In--Sn coprecipitated hydroxide, which is 350 to 1000 ° C., preferably 400 to 1000 ° C. It can be produced by firing in the range of up to 800 ° C to convert it into an oxide. However, the method for producing the ITO powder is not limited to this.

The metal alkoxide used as the binder in the present invention is a lower alkoxide of a metal selected from Si, Ti, Zr and Al, and one kind or two or more kinds can be used. The lower alkoxide means an alkoxide formed from an alcohol having 1 to 4 carbon atoms, specifically, methoxide, ethoxide, n-propoxide, i-propoxide, n-butoxide, i-butoxide, sec-
Butoxide and tert-butoxide.

Specific examples of the metal alkoxide include silicon tetraethoxide (commonly known as ethyl silicate), aluminum triisopropoxide, zirconium tetrabutoxide, titanium tetraisopropoxide and the like. A particularly suitable metal alkoxide for use in the present invention is a silicon alkoxide, with the use of ethyl silicate being particularly preferred.

When the metal alkoxide is coated on the substrate, it is hydrolyzed by the water in the composition or in the air to release alcohol. When this alcohol is removed by drying, a coating film composed of a metal-oxygen cross-linking bond can be formed on the substrate, so that the metal alkoxide functions as a binder. Moreover, the hardness and heat resistance of the formed film are higher than those of the organic resin, and it is possible to completely convert it into a metal oxide film by firing.

The partially hydrolyzed product obtained by adding water or acid to the metal alkoxide for hydrolysis can also be used in place of part or all of the metal alkoxide. This promotes film formation by hydrolysis after coating. Therefore, when the composition of the present invention does not contain water or acid having a hydrolysis promoting action, it is preferable to use a partial hydrolyzate of a metal alkoxide as a binder.

In the present invention, a metal-based coupling agent having a phosphoric acid group, a phosphorous acid group, or an ester group thereof is used as a bonding aid for enhancing the dispersion of the ITO powder and at the same time assisting the bonding between the ITO powder and the binder. To use. The phosphoric acid group is meant to include a condensed phosphoric acid group such as pyrophosphoric acid. The metal-based coupling agent suitable for use in the present invention is an aluminum-based or titanate-based coupling agent containing these groups, and one type or two or more types can be used. A specific example is shown below.

Aluminum-based coupling agent

[0025]

[Chemical 1]

Titanium coupling agent

[0027]

[Chemical 2]

This metal-based coupling agent also undergoes hydrolysis after coating and participates in film formation together with the metal alkoxide of the binder. Therefore, the obtained film has one kind of copolymer structure in which the hydrolyzates of both the metal alkoxide and the metal-based coupling agent are bonded to each other.

By adding a metal-based coupling agent having a (phosphite) group or its ester group as a binding aid in addition to the metal alkoxide of the binder to the dispersion medium of the ITO powder, the ITO powder is obtained. Moderately dispersed, I
A chain network structure is formed between the TO powders. Therefore, the dispersion state of the powder is stable, agglomeration of the ITO powder is avoided even during drying and baking after coating, the ITO powder is uniformly distributed in the film, and a film having excellent transparency without cracking or peeling is formed. It is formed. Moreover, if a (phosphite) group or its ester group is present in the binding aid, the addition of the binding aid or a conventional silane coupling agent (eg, amino group, vinyl group, glycidoxy group, etc.) It has been found that the conductivity of the obtained film is remarkably increased as compared with the case where the silane coupling agent having the functional group (1) is added.

It is preferable to use water or alcohol as a solvent (dispersion medium for ITO powder) in which the ITO powder, the binder and the binding aid are mixed. As alcohol, methanol, ethanol, n-propanol, iso-propanol, butanol, hexanol,
One kind or two or more kinds such as cyclohexanol can be used. A mixed solvent of alcohol and water can also be used. A preferred solvent is a mixed solvent of alcohol and a small amount (20 vol% or less with respect to alcohol) of water.

The composition of the transparent conductive film-forming composition of the present invention is 1 to 200 parts by weight, preferably 2 to 100 parts by weight, as a metal alkoxide as an oxide, based on 100 parts by weight of ITO powder. The agent is 0.01 to 100 as an oxide
Parts by weight, preferably 0.1 to 10 parts by weight, the solvent is 100 to 1000
It is preferable that the content is within the range of parts by weight. With a composition outside this range, it becomes difficult to obtain a transparent conductive film having both high transparency and conductivity.

In addition to the above essential components, the composition for forming a transparent conductive film of the present invention further comprises 10 parts by weight or less per 100 parts by weight of a metal alkoxide in order to accelerate the hydrolysis of the metal alkoxide of the binder. The acid may be added. Particularly, when the metal oxide is not a partial hydrolyzate, it is preferable to add an acid. Acids include hydrochloric acid, nitric acid,
Any of inorganic acids such as phosphoric acid and carboxylic acids such as acetic acid, formic acid and oxalic acid, and organic acids such as sulfonic acids can be used.

The conductive film-forming composition of the present invention may further contain other optional additives, if necessary.
Examples of such additives include thickeners (eg hydroxypropyl cellulose), coating aids (various surfactants) and the like. Each of these additives is added in an amount within a range that does not significantly impair the transparency, conductivity, hardness and other properties of the obtained transparent conductive film.

The composition for forming a transparent conductive film of the present invention comprises an ITO powder, a binder, a bonding aid and other additives, according to a conventional method.
It can be prepared by mixing a solvent and uniformly dispersing ITO powder in the liquid. For dispersing the powder, a conventional device such as a paint shaker, a ball mill, a sentry mill, a sand grind mill and a homogenizer can be used.

For example, using any of the above devices, I
The composition of the present invention can be prepared by first dispersing TO powder in alcohol as a dispersion medium (solvent), sufficiently wetting the surface with alcohol, and then adding the remaining components and continuing mixing.

The composition for forming the transparent conductive film may be applied by any of conventional coating means such as a roll coater, a spin coater, dipping and spraying. When forming a pattern such as a circuit or an electrode, the composition of the present invention can be applied to the substrate by a printing technique such as screen printing. The substrate material is not limited, but is usually a transparent material such as glass or plastics.

After coating or printing, preferably by heating and drying, the metal alkoxide of the binder and the metal-based coupling agent of the binding aid are hydrolyzed, and the ITO powder is converted into the binder and the binding aid. A transparent conductive film bonded with a hydrolyzate is obtained. The drying temperature may be appropriately determined depending on the type of solvent used and the heat resistance of the substrate, but, for example, a temperature from room temperature to 200 ° C. is suitable.

The transparent conductive film of the present invention obtained after drying is
The surface resistance is 1 × 10 ⁵ Ω / □ or less. Further, when the film having a thickness of 0.5 μm is formed on a glass substrate having a light transmittance of 90%, the light transmittance of the obtained film is 87% or more.
On the other hand, when the binding aid is not added or the binding aid is a silane coupling agent, the surface resistance value of the film is 1
× 10 ⁶ Ω / □ or more. That is, according to the present invention, the conductivity can be remarkably enhanced without lowering the light transmittance of the transparent conductive film.

When the substrate is made of a material having high heat resistance such as glass, the transparent conductive film obtained after drying may be further fired in the air or an inert gas. This baking removes the organic components remaining in the film, densifying the film,
The conductivity of the film is further improved and the surface resistance value is 1 × 10 ⁴ Ω
/ It can be less than or equal to □. The firing conditions may be selected so that this purpose is achieved, and for example, 200 to 90
20 minutes to 10 hours at 0 ° C is suitable. Firing temperature is 350
It is more preferable that the temperature is not lower than 0 ° C.

[0040]

EXAMPLES Examples will be shown below, but these do not limit the present invention.

Preparation of ITO Powder 900 mL of InCl ₃ aqueous solution containing 300 g of In metal and 55 wt% Sn
After mixing with 130 g of Cl ₄ aqueous solution, it was reacted with an ammonium bicarbonate aqueous solution (1800 g / 6 L) at a liquid temperature of 50 ° C. to coprecipitate In and Sn hydroxides [Sn / (Sn + In) The atomic ratio is 1/10].
The precipitate is decanted with ion-exchanged water, filtered and dried,
After firing at 650 ° C. for 3 hours, ITO powder was obtained. The specific surface area of this powder was 30 m ² / g (corresponding to an average primary particle diameter of 0.03 μm) as measured by the BET method, and the specific resistance value of the powder of 50 kg / cm ² was 25 Ω · cm.

In the following examples and comparative examples, transparent conductive films were formed using the above ITO powder. Also,
The light transmittance of the film is UBEST55 spectrophotometer manufactured by JASCO Corporation, and the surface resistance value is ROLLESTA AP MCP-T manufactured by Mitsubishi Yuka Co., Ltd.
I checked each with 400.

Example 1 10 g of ITO powder was dispersed in 20 g of ethyl alcohol for 60 minutes by shaking using a paint shaker (25 g of glass beads). 1.8 g of ethyl silicate and bis (dioctyl pyrophosphate) oxyacetate were added to the obtained dispersion.

Totitanate (

Compound of formula 2) 0.2 g, 12N hydrochloric acid 0.02 g, water 2
After adding g and shaking for 30 minutes, the beads were removed to prepare a composition for forming a transparent conductive film.

This transparent conductive film-forming composition was dried on a glass plate having a light transmittance of 90% with a bar coater to give a dry film thickness of 0.1.
A transparent conductive film was formed by applying the solution to a thickness of 5 μm and drying at 100 ° C. for 2 hours. The transparent conductive film thus obtained was visually observed and found to be free from cracks and peeling. The film characteristics were a light transmittance of 89% and a surface resistance value of 4.2 × 10 ⁴ Ω / □.

Example 2 The transparent conductive film obtained in Example 2 was
Further, it was baked in the air at 400 ° C. for 30 minutes. Neither cracking nor peeling was observed in the film after baking. The film characteristics after baking did not change at a light transmittance of 89%, and the surface resistance value was 1.8 ×
It decreased to 10 ³ Ω / □. That is, the conductivity was further improved by firing.

(Example 3) 2.5 g of titanium isopropoxide was used as a binder, and isopropoxydio was used as a binding aid.

Cutyl Phosphate Aluminum Ethyl Acetoacetate (

A composition for forming a transparent conductive film and a transparent conductive film were formed in the same manner as in Example 1 except that the compound of [Chemical Formula 1] was changed to 0.001 g. The film characteristics are that the light transmittance is 87% and the surface resistance value is
It was 5.7 × 10 ⁴ Ω / □.

Example 4 A mixture of 1.2 g of ethyl silicate and 0.6 g of zirconium n-butoxide was used as a binder, and tetraisopropyl (dioctyl phosphite) ti was used as a binder.

Tanate (

A composition for forming a transparent conductive film and a transparent conductive film were formed in the same manner as in Example 1 except that 10 g of the compound of Chemical formula 2 was used. Regarding the film characteristics, the light transmittance was 87% and the surface resistance value was 6.2 × 10 ⁴ Ω / □.

Comparative Example 1 A transparent conductive film-forming composition and a transparent conductive film were formed in the same manner as in Example 1 except that bis (dioctylpyrophosphate) oxyacetate titanate as a binding aid was not added. The film characteristics were a light transmittance of 86% and a surface resistance value of 2.6 × 10 ⁷ Ω / □.

Comparative Example 2 The transparent conductive film obtained in Comparative Example 1 was further baked at 400 ° C. for 30 minutes, and the characteristics of the transparent conductive film were examined. As a result, the light transmittance is 87% and the surface resistance value is
It was 8.3 × 10 ⁵ Ω / □.

Comparative Example 3 A transparent conductive film-forming composition and a transparent conductive film were formed in the same manner as in Example 3 except that the binding aid isopropoxydioctyl phosphate aluminum ethyl acetoacetate was not added. The film characteristics were a light transmittance of 86% and a surface resistance value of 3.3 × 10 ⁷ Ω / □.

(Comparative Example 4) Tetraisopropyl as a binding aid
(Dioctyl phosphite) A transparent conductive film-forming composition and a transparent conductive film were formed in the same manner as in Example 4 except that titanate was not added. The film has a light transmittance of 84.
%, And the surface resistance value was 1.1 × 10 ⁸ Ω / □.

Comparative Example 5 A composition for forming a transparent conductive film and a transparent conductive film were formed in the same manner as in Example 1 except that 0.2 g of isopropyltriisostearoyl titanate was used as the binding aid. As for the film characteristics, the light transmittance was 89% and the surface resistance value was 8.7 × 10 ⁶ Ω / □.

Comparative Example 6 Ethyl silicate as a binder
A transparent conductive film was formed in the same manner as in Example 1 except that a mixture of 1.2 g and zirconium n-butoxide (0.6 g) was used as a binding aid, and 10 g of N-β (aminoethyl) γ-aminopropyltriethoxysilane was used. And a transparent conductive film were formed. As for the film characteristics, the light transmittance was 87% and the surface resistance value was 1.2 × 10 ⁶ Ω / □.

[0057]

As described above, the transparent conductive film formed from the composition for forming a transparent conductive film of the present invention by the coating method has a high light transmittance and a dry surface resistance value. 1 × 10 ⁵ Ω / □ or less, and when fired after drying, it is 1 × 10 ⁴ Ω / □ or less, significantly improved conductivity.
(Low resistance) That is, both conductivity and transparency can be compatible. Therefore, the transparent conductive film formed according to the present invention is useful as a high-performance antistatic material having both high conductivity and excellent transparency, and a transparent conductive film whose resistance is further reduced by firing is particularly suitable for circuits and electrodes. It can also be used for purposes.

Claims (3)

[Claims] 1. A tin-doped indium oxide powder having an average primary particle diameter of 0.2 μm or less as a conductive powder, a metal alkoxide and / or a partial hydrolyzate thereof as a binder, and a phosphate group, a phosphite group or a binding aid. A composition for forming a transparent conductive film, which comprises a metal-based coupling agent having such an ester group in a solvent. 2. The composition for forming a transparent conductive film according to claim 1 is applied onto a transparent substrate, and the coating film is dried at a temperature of less than 200 ° C. and has a surface resistance value of 1 × 10 ⁵ Ω / □ The following method for forming a transparent conductive film. 3. The composition for forming a transparent conductive film according to claim 1 is applied on a transparent substrate, the coating film is dried at a temperature of less than 200 ° C., and then baked at a temperature of 200 to 900 ° C. And a method for forming a transparent conductive film having a surface resistance value of 1 × 10 ⁴ Ω / □ or less.