JP3191482B2 - Transparent conductive film and its forming material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent conductive film forming material capable of forming a transparent conductive film by coating or printing on an insulator, and a transparent conductive film formed therefrom. It is. More specifically, the present invention relates to a transparent conductor of ITO, which is not an organic solvent harmful to the environment but water or alcohol as a dispersion medium.
The present invention relates to a water-based or alcohol-based transparent conductive film forming material in which powder (tin-containing indium oxide powder) is dispersed in a medium.

When the material for forming a transparent conductive film of the present invention is applied or printed on glass, plastic, or the like and dried, a transparent film having high conductivity is formed. This transparent conductive film is effective for preventing static electricity and preventing dust from adhering to a glass or plastic film, and is used, for example, for preventing the electrification and dust of a TV cathode ray tube, preventing the electrification of a window glass of a measuring instrument, and preventing dust from adhering. be able to.

[0003]

2. Description of the Related Art ITO powder is a powder composed of indium oxide containing a small amount of tin oxide, and a base is added to an aqueous solution of a water-soluble salt of indium and tin (eg, indium chloride and tin chloride) to hydrate the salt. It is generally produced by a wet method of decomposing, coprecipitating indium and tin as hydroxide, and then calcining to convert to oxide.

[0004] Conductive powders such as ITO powders are IC
It is used in a large amount for applications such as package circuit formation, clean room interior materials, antistatic of glass and film, and surface heating elements, and it is said that demand will further increase in the future. As a result, the required performance has been increasing.
For coating-type compositions (film-forming materials) that apply TO powder by coating or printing, water-based or alcohol-based coatings are required due to the usage conditions where solvent regulations are becoming more stringent, in addition to electrical performance. A forming material has been sought.

[0005] However, although the conventional ITO powder has improved conductivity, it is inferior in dispersibility in water or alcohol, so that it is difficult to uniformly disperse it into primary particles. A film having high transparency could not be obtained from the film forming material. on the other hand,
In order to enhance the dispersibility of the ITO powder, surface modification with various dispersants has been performed, but none of them has been able to obtain high transparency. Therefore, when a conductive film containing ITO powder is formed by coating, at present, an organic solvent-based film forming material is still used.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to provide an IT
An object of the present invention is to provide a water-based or alcohol-based coating type ITO powder-containing transparent conductive film forming material which is capable of forming a transparent conductive film having excellent dispersibility of O powder and excellent transparency and conductivity.

[0007]

Means for Solving the Problems The present inventor paid attention to the surface condition of the ITO powder and examined the acid-base degree of the surface. As a result, the ITO powder obtained by a general wet method had a basicity It turned out to be high. Due to the high basicity, the dispersibility in an organic solvent having a relatively high polarity is excellent, but on the contrary, since the thixotropy increases, high transparency cannot be obtained by coating, and the It was thought that the electrons were trapped due to the high basicity and the conductivity was hindered.

Accordingly, the present inventors have conducted various studies on a method for reducing the basicity. As a result, it has been found that by performing surface modification such as immersion treatment in an organic solvent, the basicity of the surface of the ITO powder is reduced. In addition, the ITO powder having the reduced basicity has improved dispersibility in water or alcohol, and is easily dispersed therein. Therefore, the transparency and conductivity of the aqueous or alcohol-based film forming material are reduced. It was also found that an excellent ITO-containing film could be formed.

Further, it has been found that in such a water-based or alcohol-based film forming material, a metal alkoxide is also useful as a binder in addition to the organic resin.

[0010] Here, the present invention provides a method wherein the surface basic amount is 2 × 10
Abstract: A material for forming a transparent conductive film, characterized in that it contains ITO powder of ^-6 mol / m ² or less and a binder soluble or dispersible in water or alcohol in water and / or alcohol. .

As the above-mentioned binder, a lower alkoxide of Si, Al, Zr or Ti and / or a partial hydrolyzate thereof, an organic resin soluble or dispersible in water or alcohol, or a mixture thereof is used. Is preferred.

According to the present invention, there is provided a transparent conductive film formed from the above-mentioned transparent conductive film forming material .

[0013]

The material for forming a transparent conductive film according to the present invention is obtained by dispersing an ITO powder whose surface basicity is controlled to a certain level or less by surface modification together with a binder in water and / or alcohol, By applying or printing this, a coating film having high transparency and conductivity can be formed.

The ITO powder used in the present invention has a surface basic amount controlled to 2 × 10 ⁻⁶ mol / m ² or less.
If the surface basic amount exceeds 2 × 10 ⁻⁶ mol / m ² , the dispersibility of the ITO particles in water or alcohol is poor, and both the transparency and the conductivity of the resulting conductive film are reduced. It is presumed that the reason why the dispersibility in water or alcohol is improved when the surface basic amount is low is that aggregation of particles can be prevented by decreasing the polarity.

The surface basicity of the ITO powder is determined by thoroughly contacting a weighed amount of the ITO powder with a 0.01 N solution of perchloric acid in methyl isobutyl ketone to completely neutralize the base on the powder surface. Can be determined by reverse titration of the supernatant solution with a 0.01N methyl isobutyl ketone solution of tetrabutylammonium hydride. The value obtained by dividing the amount of base (mol / g) per weight of the ITO powder thus obtained by its specific surface area (BET value, m ² / g) is the surface basic amount (mol / m ² ). Hereinafter, the value of the surface basicity is indicated by the value obtained by this method.

The other properties of the ITO powder are not particularly limited, but preferably, the Sn / In composition ratio of the ITO powder is 0.01 to
Within the range of 0.15, the specific resistance (measured with a green compact at 50 kg / cm ² ) is 100 Ωcm or less, and the specific surface area is 25 m ² / g or more. S
When the n / In composition ratio is out of the above range, the specific resistance of the powder increases, and when the specific resistance exceeds 100 Ωcm, the surface resistance value of the conductive film increases, and when the specific surface area is smaller than 25 m ² / g, the specific resistance of the conductive film increases. Transparency tends to decrease.

As described above, In and In are formed by an ordinary wet method.
An ITO powder obtained by sintering a coprecipitated hydroxide of Sn as a starting material has a high surface basicity amount as it is, and 2 ×
The requirement of the present invention of 10 ⁻⁶ mol / m ² or less cannot be satisfied. Therefore, in order to use the ITO powder obtained by such a wet method in the present invention, an appropriate surface modification is performed to reduce the surface basicity to 2 × 10 ⁻⁶ mol / m ² or less. There is a need.

In this method for surface modification, the basic amount of the surface is 2
There is no particular limitation as long as it can be reduced to × 10 ⁻⁶ mol / m ² or less, but the above-described method of immersing the ITO powder in an organic solvent is simple in operation, and the effect of reducing the surface basicity is low. It is preferable because it is high.

The organic solvent used for the surface modification may be, for example, at least one organic solvent selected from alcohols, ketones, esters, amines and the like. Specifically, as alcohols, methanol, ethanol,
Examples thereof include propanol, hexanol, cyclohexanol, ethylene glycol, butoxyethanol, and 2- (2-butoxy) ethanol. Ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, 4-hydroxy-4-methyl-2-pentanone,
Examples include cyclohexanone, isophorone, diacetone alcohol and the like. Esters include ethyl acetate, butyl acetate, butyl carbitol acetate and the like. Examples of the amines include dimethylamine, tributylamine, ethanolamine, dimethylformamide, tetra-n-butylammonium hydroxide, trimethylamine, dimethyl-sec-butylamine, cyclohexylamine, and ethylenediamine.

A mixed solvent of the above organic solvent and at least one hydrocarbon solvent such as hexane, heptane, cyclohexane, benzene, toluene, xylene and the like can also be suitably used.

The immersion of the ITO powder in the organic solvent may be performed with stirring. The amount of the solvent used is suitably in the range of 0.3 to 0.7 by weight ratio of solvent / ITO powder. The immersion temperature is not particularly limited as long as the solvent is maintained in the liquid phase, and may be room temperature or lower or higher temperature. The immersion time may be selected to be sufficient to reduce the surface basicity to a desired value, and will vary depending on the temperature and solvent type, but will generally be from a few minutes to one hour.

After immersion in an organic solvent, the ITO powder is heat-treated under vacuum or in an inert gas stream to remove the solvent adhering to the powder surface. This heat treatment is performed at a temperature of 500 ° C. or less. When the temperature exceeds 500 ° C., the ITO powder tends to grow grains, and the transparency of the obtained conductive film is reduced. The heat treatment temperature may be selected according to the solvent type and the degree of vacuum so that the solvent is completely removed. The heat treatment time only needs to be a time sufficient for removing the solvent, and varies depending on the temperature and the type of the solvent.

Thus, the surface basic amount is 2 × 10 ^-6 mol / m
^When the ITO powder surface-modified to be ² or less is dispersed in water and / or alcohol together with a binder,
The transparent conductive film forming material of the present invention is obtained. As the binder, any substance that can be dissolved or dispersed in water or alcohol and can form a transparent film can be used, and preferably, a metal alkoxide, an organic resin, or a mixture thereof is used.

Examples of metal alkoxides usable as a binder in the present invention include lower alkoxides of metals selected from Si, Al, Zr and Ti. Examples of the lower alkoxide include methoxide, ethoxide, propoxide, butoxide, and isomers thereof (isopropoxide, sec-butoxide, t-butoxide), and one or more of these can be used. When the metal alkoxide is dissolved in water or alcohol and applied, the metal alkoxide is converted into an oxide by hydrolysis to form a film composed of the metal oxide. Therefore, it can be used as a binder for binding the ITO particles in the present invention.

Specific examples of suitable metal alkoxides include silicon tetraethoxide (ethyl silicate), aluminum triisopropoxide, zirconium tetrabutoxide, titanium tetraisopropoxide and the like.
A partial hydrolyzate of a metal alkoxide which is made into a polymer by adding a small amount of water and / or an acid to the metal alkoxide,
The metal alkoxide can be used instead of or mixed with the metal alkoxide. When a partial hydrolyzate is used, film formation after application is promoted.

Another binder usable in the transparent conductive film forming material of the present invention is an organic resin soluble or dispersible in water or alcohol and capable of forming a transparent film. Organic resins usable in the present invention include organic resins used in water-soluble paints or water-dispersible emulsion paints. Examples of this type of resin include water-soluble resins such as water-soluble alkyd resins, polyvinyl alcohol resins, and polybutyl alcohol resins, and emulsion-type water-dispersible resins such as acrylic resins, acryl-styrene resins, and vinyl acetate resins. . When alcohol is used as the dispersion medium for the ITO particles, a resin soluble or dispersible in alcohol can also be used as the binder.

When the binder is a metal alkoxide, IT
A completely inorganic conductive film in which O particles are dispersed in a metal oxide matrix can be obtained. This conductive film is particularly excellent in transparency and the film is hard, so that it is not easily scratched and has excellent heat resistance. On the other hand, when the binder is an organic resin, a conductive film having excellent flexibility can be obtained. Therefore, the type of the binder may be selected according to the type of the substrate on which the transparent conductive film is formed and the use of the transparent conductive film.

For example, when the substrate is a flexible plastic film, an organic resin is used as a binder to ensure flexibility in the conductive film so as not to impair the flexibility of the substrate. Is preferred. On the other hand, when the substrate is glass, and particularly when heat resistance is required as in a window glass of a measuring instrument, it is preferable to use a metal alkoxide as a binder.

Further, the above-mentioned metal alkoxide and the above-mentioned resin can be used in combination as a binder. This allows
When the binder is a metal alkoxide, flexibility can be imparted to the conductive film having excellent transparency.

In the present invention, water or alcohol is used as a dispersion medium for the ITO particles. As the alcohol, one or more of methanol, ethanol, propanol, isopropanol, butanol, hexanol, cyclohexanol and the like can be used. A mixed solvent of water and alcohol can also be used.

As described above, if the surface basicity of the ITO particles is reduced to 2 × 10 ⁻⁶ mol / m ² or less by surface modification,
ITO particles can be easily dispersed into primary particles in water or alcohol.

The mixing ratio of each component in the transparent conductive film forming material of the present invention is based on 100 parts by weight of the ITO powder and the binder.
(The amount of the metal alkoxide as an oxide and the amount of the resin as a solid) is preferably in the range of 5 to 35 parts by weight. The amount of water and / or alcohol in the dispersion medium may be any amount so as to obtain a viscosity suitable for coating or printing.
Usually, it is in the range of 100 to 900 parts by weight based on 100 parts by weight of the ITO particles.

When the binder is a metal alkoxide and the dispersion medium is an alcohol, if necessary, 1 part by weight or less of an acid or 100 parts by weight of an acid or 100 parts by weight of a metal alkoxide to promote hydrolysis of the alkoxide. 20 parts by weight or less of water may be added. When the binder is an organic resin, a small amount of a curing agent, a cross-linking agent, and the like can be added as necessary. The transparent conductive film forming material of the present invention may further contain a small amount of other optional components. Such optional additives include pH adjusters, defoamers, wetting agents and the like.

The material for forming a transparent conductive film of the present invention is excellent in dispersibility of ITO particles despite being water-based and / or alcohol-based. Therefore, it has sufficient storage properties.
However, when the dispersion medium is water, the hydrolysis proceeds with time, so that the storage property is inferior to that when the dispersion medium is alcohol.

The method of applying the transparent conductive film forming material of the present invention may be the same as the conventional one. That is, after applying to the substrate by means of coating or printing, the dispersion medium is removed under heating if necessary and dried, whereby a transparent conductive film is formed. The drying temperature may be selected according to the types of the dispersion medium and the binder.

The formed transparent conductive film varies depending on the type of the ITO particles and the binder, but is generally 75% or more.
Light transmittance in the visible light region of preferably 80% or more, and 10% or more.
Indicates a surface resistance value of ⁵ Ω / □ or less. It is difficult to obtain such a light transmittance and a surface resistance value with a transparent conductive film formed from a conventional water-based or alcohol-based ITO powder-containing film forming material, and particularly, a surface resistance of 10 ⁵ Ω / □ or less. No value was obtained. When the resistance can be reduced in this way, a thinner conductive film can perform functions such as antistatic and dust adhesion over a long period of time.
Examples are shown below, but they do not limit the present invention.

[0037]

【Example】

(Production Example 1) 900 ml of InCl ₃ aqueous solution (300 g of In metal) and 55
Aqueous SnCl ₄ solution (130 g) was mixed with water 6
An aqueous solution containing 1800 g of ammonium bicarbonate in a liter was reacted at a liquid temperature of 50 ° C. for 30 minutes to produce a coprecipitated hydroxide of In and Sn. The precipitate was washed with ion-exchanged water in an inclined manner, filtered, dried, calcined at 650 ° C. for 3 hours, and pulverized to obtain 250 g of ITO powder. The specific surface area of this powder is 30 m
^The powder specific resistance value (50 kg / cm ² compact) was 25 Ω · cm, and the surface basic amount was 3.5 × 10 ⁻⁶ mol / m ² . This powder is hereinafter referred to as unmodified ITO powder.

Next, 50 g of the ITO powder was added to ethanol 20
g for 1 minute and then 0.1 torr in 100 ℃ vacuum dryer
For 30 minutes, cooled to room temperature, and removed. The surface basicity of this powder was reduced to 1.0 × 10 ⁻⁶ mol / m ² . This powder is hereinafter referred to as modified ITO powder.

Example 1 Modified ITO powder obtained in Production Example 1
10 g was dispersed in 20 g of ethyl alcohol for 60 minutes using a paint shaker (25 g of glass beads). Next, 4 g of ethyl silicate as a binder, 0.4 g of 1N hydrochloric acid and 0.8 g of water were added to the dispersion of the ITO powder to promote the hydrolysis of the alkoxide, and the mixture was shaken for 30 minutes to remove the beads. A forming material was prepared.

Next, the film-forming material was applied to a PET (polyethylene terephthalate) film to a thickness of 2 μm using a bar coater and dried at 100 ° C., and the characteristics of the film were examined. As a result, the light transmittance was 85% and the surface resistance was 3.8 ×
It was 10 ⁴ Ω / □. The light transmittance is measured by Ubes spectrophotometer.
It was measured at a wavelength of 550 nm using a t-55 type (manufactured by JASCO Corporation), and the surface resistance was measured by Lorester AP (manufactured by Mitsubishi Yuka).

Example 2 Modified ITO powder obtained in Production Example 1
Disperse 10 g in 90 g of isopropyl alcohol for 60 minutes using a paint shaker (25 g of glass beads)
Next, 9 g of ethyl silicate and 3.5 g of titanium tetraisopropoxide were added, and the mixture was further shaken for 30 minutes to remove beads, thereby obtaining a film-forming material.

Next, this film-forming material was applied to a glass plate to a thickness of 2 μm using a bar coater and dried at 100 ° C., and the characteristics of the coating film were examined. As a result, the light transmittance was 82% and the surface resistance was 8.6 × 10 ⁴ Ω / □.

Example 3 Modified ITO powder obtained in Production Example 1
10 g was dispersed in 10 g of water for 120 minutes using a paint shaker (25 g of glass beads), then 7 g of a water-soluble alkyd resin (50% solids) and 0.3 g of cobalt naphthenate as a curing agent were added, and further 60 minutes. After shaking, the beads were removed to obtain a film-forming material.

Next, this film-forming material was applied to a PET film to a thickness of 2 μm using a bar coater and dried at 100 ° C., and the characteristics of the film were examined. As a result, the light transmittance is 80
%, And the surface resistance was 7.8 × 10 ⁴ Ω / □.

Example 4 Modified ITO powder obtained in Production Example 1
10 g was dispersed in 10 g of water for 120 minutes using a paint shaker (25 g of glass beads), and then 5 g of an emulsion type acrylic resin (solid content: 40%) was added.
After shaking for 60 minutes, the beads were removed to obtain a film-forming material.

Next, this film-forming material was applied to a PET film to a thickness of 2 μm using a bar coater and dried at 100 ° C., and the characteristics of the film were examined. As a result, the light transmittance is 78
%, And the surface resistance was 2.9 × 10 ⁴ Ω / □.

Example 5 Modified ITO powder obtained in Production Example 1
10 g was dispersed in 30 g of ethyl alcohol using a paint shaker (25 g of glass beads) for 60 minutes. Next, 10 g of ethyl silicate and 0.5 g of polybutyl alcohol resin dissolved in 10 g of ethyl alcohol were added, and the mixture was further shaken for 30 minutes to remove beads, thereby obtaining a film-forming material.

Next, this film-forming material was applied to a PET film to a thickness of 1 μm using a bar coater and dried at 100 ° C., and the characteristics of the film were examined. As a result, the light transmittance is 83
%, And the surface resistance was 7.8 × 10 ⁴ Ω / □.

Comparative Example 1 10 g of the unmodified ITO powder obtained in Production Example 1 was dispersed in 20 g of ethyl alcohol for 60 minutes using a paint shaker (25 g of glass beads) as in Example 1. Next, 4 g of ethyl silicate and 0.4 g of 1N hydrochloric acid and 0.8 g of water were added to promote hydrolysis of the alkoxide, and the mixture was further shaken for 30 minutes to remove beads, thereby obtaining a film forming material.

Next, this film-forming material was applied to a PET film to a thickness of 2 μm using a bar coater and dried at 100 ° C., and the characteristics of the film were examined. As a result, the light transmittance is 72
%, And the surface resistance was 2.4 × 10 ⁷ Ω / □.

Comparative Example 2 10 g of the unmodified ITO powder obtained in Production Example 1 was dispersed in 10 g of water for 120 minutes using a paint shaker (25 g of glass beads) in the same manner as in Example 4.
Next, 5 g of an emulsion type acrylic resin was added, and the mixture was further shaken for 60 minutes to remove beads and obtain a film-forming material.

Next, this film-forming material was applied to a PET film to a thickness of 2 μm using a bar coater, dried at 100 ° C., and the characteristics of the film were examined. As a result, the light transmittance is 65
%, And the surface resistance was 6.3 × 10 ⁷ Ω / □.

[0053]

According to the present invention, a transparent conductive film obtained from a film-forming material in which ITO particles whose surface basic amount is controlled to a certain level or less in water and / or alcohol is 100 times as large as the conventional one. As described above, it has high conductivity and excellent transparency. As a result, the film can be used as a high-performance antistatic film or dust adhesion preventing film, for example, for a cathode ray tube of a TV, a window glass of a measuring instrument and the like.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-237908 (JP, A) JP-A-64-54613 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 13/00 H01B 5/14

Claims (3)

(57) [Claims] Claims: 1. An aqueous and / or alcoholic solution containing an ITO powder having a surface basic amount of 2 × 10 ⁻⁶ mol / m ² or less and a binder soluble or dispersible in water or alcohol. Characteristic material for forming a transparent conductive film. 2. The binder is a lower alkoxide of Si, Al, Zr or Ti and / or a partial hydrolyzate thereof,
The transparent conductive film forming material according to claim 1, wherein the material is an organic resin soluble or dispersible in water or alcohol, or a mixture thereof. 3. A transparent conductive film formed from the transparent conductive film forming material according to claim 1.