JP2742068B2 - Method for producing transparent conductive fine particles and method for producing transparent conductive thin film thereby - Google Patents

Description

The present invention relates to a method for producing transparent conductive ultrafine particles. In particular, it relates to a method for producing a thin film having excellent conductivity and transparency.

[Problems to be Solved by Conventional Techniques and Inventions] Generally, transparent electrodes are used for solar cells, liquid crystal display elements, electroluminescence (EL) display elements, and the like. These elements have a structure in which thin-film transparent electrodes and thin films having various functions are stacked on a glass substrate. It is necessary to manufacture this transparent electrode at low cost, but with current technology, vacuum deposition method, sputtering method,
There are a CDV method and a spray method, but the vacuum evaporation method, the sputtering method, and the CVD method all have low productivity, and the apparatus is expensive and costly. On the other hand, there are a spraying method and a coating method as methods with good productivity and low cost, and the spraying method has a high film forming speed.
When an aqueous solution of tin chloride is sprayed on the glass surface heated to 0 ° C., tin oxide and hydrogen chloride are generated on the glass surface, and the tin oxide becomes a thin film and adheres to the glass surface to form a transparent electrode film. . However, since the fog is generated by the radiation from the nozzle, there is a difference in the concentration of the film adhering to the glass plate.Also, droplets are generated due to the aggregation of the fog, and the fog tends to become spots. There is a problem that tin chloride powder adheres to the thin film due to dehydration, so it cannot be used for electronic devices that require film quality, uniformity of film thickness and reproducibility of characteristics, and is used for low-grade applications such as anti-fog glass Only limited.

On the other hand, the demand for a conductive thin film having transparency has been further increased due to advances in electronics technology, clean room technology, and the like.

Accordingly, the present invention provides a method for producing an ultrafine particle coating material for producing a thin film having significantly improved conductivity and transparency by a coating method, and a method for producing a transparent conductive thin film using the same. For the purpose.

[Means for Solving the Problems] The present invention provides an aqueous solution of an acidic salt of indium, or a mixed aqueous solution of an acidic salt of indium and an acidic salt of tin and an aqueous alkali solution for solving the above technical problem. Reacting, taking out a precipitate formed from oxides and / or hydroxides, and heating the precipitate to a temperature of 240 to 320 ° C. in a reducing atmosphere; And a method for producing the same. At this time, the acid salt of indium and the acid salt of tin are preferably chlorides, sulfates, and nitrates. Further, the alkali component is preferably ammonia, sodium hydroxide, potassium hydroxide, and sodium carbonate. Furthermore, the present invention utilizes the indium-based conductive ultrafine particles prepared as described above, mixed with a solvent and a paint, applied on a substrate, calcined, and removed the binder,
Next, the present invention provides a method for producing a transparent conductive thin film, which comprises performing a heat treatment at 200 ° C. to 400 ° C. in a reducing atmosphere.

According to the present invention, an aqueous solution of an acid salt of indium and tin is prepared so that the amount of tin oxide in terms of oxide is 1 to 10% by weight based on the total amount of indium oxide and tin oxide. Raw materials. In this case, the “acid salt” is a water-soluble and acidic compound such as chloride, sulfate, nitrate, etc., and reacts with an alkali to produce an insoluble indium compound and an insoluble tin compound. “Alkaline aqueous solution”
Are prepared using soluble alkali salts, for example, salts such as sulfites, nitrites, phosphates and oxyacids.

The alkali component of the alkaline aqueous solution to be reacted with the prepared acidic aqueous solution is preferably sodium hydroxide, potassium hydroxide or sodium carbonate. After the neutralization reaction, the alkali must be washed out of the precipitate of indium and tin by washing with water. Therefore, other alkali substances can be used as long as they can be easily washed away with water, and for example, sodium bicarbonate, calcium hydroxide, barium hydroxide, and the like can be used.

The precipitate deposited by such a neutralization reaction is washed with water to remove salt (chlorine, sulfate, nitrate, etc.) and alkali groups (sodium, potassium, calcium, etc.), dehydrated, and dried.

When performing this drying process, the part that has been partially agglomerated
By fir dissolving and drying treatment, ultrafine powder is obtained, but if the volume specific resistance value of this powder itself is measured,
It turns out that it is a completely electric insulating material. By heating this dried powder in a reducing gas atmosphere at a temperature of 240 to 320 ° C., preferably at a temperature of 260 to 280 ° C.,
Particle size is 100 ~ 300mm, volume resistivity value is 1-3x
A transparent and conductive ultrafine particle material of 10 ⁻³ Ωcm was obtained. In this case, hydrogen, ammonia gas, carbon monoxide, or the like can be used as the reducing gas. Further, among the above gases, a mixed gas of two or more reducing gases can be used. Further, it can be diluted with an inert gas such as nitrogen or argon before use.

However, if the reducing gas treatment is not carried out, the volume resistivity becomes very high, ie, 10 ⁴ Ωcm or more. This reducing gas atmosphere heat treatment according to the present invention appears to perform a very effective action at the same time, and this effect was first revealed by the present invention. That is, by the reduction treatment, the tin atom and the hydrogen atom having fixed electrification are bonded, and electrons as majority carriers are likely to drift, that is, the Fermi level may be very close to the conduction level. But the real reason is unknown. That is, since the transparent conductive ultrafine particle material according to the present invention has been neutralized, it can be safely used without any obstacle due to acid components. Further, by using such an ultrafine particle material, a thin film having excellent transparency and conductivity with a light transmittance of 80% or more can be obtained at a surface resistance value of about 50Ω / □.

That is, this transparent conductive ultrafine particle material can be mixed with a coating resin to form a transparent conductive coating.

As the resin that can be used in the transparent conductive coating according to the present invention, a resin that can be prepared and used by a normal coating technique is used, but there is no particular limitation, and polyvinyl acetate, urea formaldehyde resin, epoxy resin, polyester resin, and phenol are used. Resins, alkyd resins, polyurethane resins, vinyl resins and the like can be used. That is, a synthetic resin generally used in a transparent paint can be used as a main component for forming a coating film.

As a solvent for the above resin, a solvent such as water, alcohol, benzene, olefin, and boil oil can also be used. Examples of the solvent include methyl ethyl ketone (MEK), cyclohexanone, tetrahydrofuran (TH
F), ethyl acetate, acetone, and lower alcohols. In addition, solvents commonly used in coating materials such as toluene, xylene, cellosolves such as cellosolve acetate, petroleum spirit, solvent naphtha, and methylene chloride may be contained.

The transparent conductive paint prepared in this manner is used as a substrate,
For example, it can be applied to a glass plate by an ordinary method. Any material that can be used as a substrate can be used as long as it does not lose transparency and does not cause significant deformation or breakage by processing, such as a pair. For example, a glass plate, mica, quartz, transparent alumina, sodium chloride single crystal plate, gypsum single crystal plate, or the like can be used. Generally, a glass plate is used.

That is, the glass plate coated with the ultrafine transparent conductive paint prepared as described above is dried and heated to remove the resin component. The heating temperature for this varies depending on the resin and the solvent, but is 350 ° C. to 500 ° C., preferably 420 ° C.
470 ° C, and a temperature range in which the binder can be sufficiently evaporated and blown out is used. As described above, in the binder removal treatment, the surface resistance becomes about 10 ³ Ω / □.

Next, in a reducing atmosphere at 200 to 400 ° C., preferably 250
By heating to a temperature of from about 300 ° C. to about 300 ° C., a transparent conductive thin film having excellent performance with a total light transmittance of 80% or more and a surface resistance of about 50 Ω / □ is obtained.

On the other hand, conventional transparent conductive paints can be made only with a transmittance of 40-60% and a surface resistance of about 10 ³ Ω to 10 ⁴ Ω. It cannot be done. That is, due to the characteristics of the ultrafine particle material produced according to the present invention, the dispersibility and uniformity in the coating material are excellent, and therefore, a transparent conductive thin film having better transmittance and surface resistance value is formed by a gas phase. A technique that can be supplied at a lower cost than the method and the sputtering has become possible.

In the spraying method and the coating method using a paint containing the ultrafine particle material produced in the present invention, the transparent conductive fine powder is sprayed or applied.However, the transparency and conductivity of the film thus formed are It depends on the characteristics of the transparent conductive fine particles. On the other hand, in the prior art, an aqueous solution of chloride of indium and / or tin is sprayed or applied to a glass plate and heated to perform hydrolysis. That is, in the conventional manufacturing method, the surface resistance is
It is very high as 10 ³ to 10 ⁴ Ω / □ (for example, even in the case of graphite <20 Ω / □), and the transmittance of visible light is 40
It is as low as ~ 50% and is almost milky, and the chloride solution itself has the corrosive property of a strong acid. Further, hydrogen chloride generated during hydrolysis is also a problem.

Therefore, in the present invention, as a transparent conductive material in the spraying method and the coating method, indium-tin-based transparent, having a surface conductivity superior to graphite, and hydrogen chloride harmful to the environment We have established a method for producing ultrafine particle coating materials that do not emit toxic components such as urea.

That is, because of the ultra-fine particle paint, very good dispersibility, therefore, uniformity of the coating film can be very easily performed,
Thus, a transparent conductive coating material having excellent characteristics can be provided.

In the method for producing a transparent conductive thin film by the coating method according to the present invention, in a reducing atmosphere, the neutralization reaction product, 240 ° C.
Heating at 320320 ° C. indicates that it is an insulator in the measurement of volume resistivity because it remains a reaction product and is a gel-like non-crystal,
The transmittance is also about 50%. However, even if this reduction heat treatment is omitted and the heat treatment (500 ° C.) and reduction treatment (200 ° C. to 400 ° C.) after ultrafine particle formation and coating are performed, the transmittance is about 50% and the surface resistivity is 10%. ^{About 4}
It is not satisfactory and is not practical.

In addition, usually, after applying a transparent conductive material on a substrate, heating is performed in order to remove the binder, but at this time, the conductive fine particles dispersed in the binder are removed from the binder, so that they are mutually removed. However, the heating temperature should be set so as to be suitable for the particulate conductive material. On the other hand, according to the production method of the present invention, after the heat treatment for removing the binder, if reduction heat treatment is performed at a temperature of 200 to 400 ° C., the total light transmittance becomes 80% or more, and the surface resistance also decreases. , 50 Ω / □ or less, and excellent in both transparency and conductivity, which could not be obtained conventionally, were obtained. Further, since the transparent conductive coating material produced according to the present invention is ultra-fine particles, the dispersibility in a binder and a resin is excellent, and a highly uniform dispersion can be obtained. An excellent, economical and economical transparent conductive paint can be produced.

A film having excellent mechanical and chemical strength can be formed as the transparent conductive paint of the present invention.

The resin component that can be used in the transparent conductive paint of the present invention includes polyester resin, polyvinyl acetate, urea formaldehyde resin, epoxy resin, phenol resin, alkyd resin, polyurethane resin and the like.

In addition, water, alcohol, benzene, olefin, boil oil and the like can be used as the solvent.

As the binder used in the paint of the present invention, a known binder and a known technique can be used. It is not limited to a special method. For example,
As the binder, an inorganic binder such as ethyl silicate or water glass and an organic binder such as a polyester resin or an acrylic resin can be used.

The coating film produced by the coating material obtained by the present invention has a very high transparency and mass productivity as compared with the coating film produced by the coating method obtained by heating and doping a dry powder according to the prior art. It will be excellent.

The coating material obtained according to the present invention is effectively used, for example, as a transparent conductive film or electrode in products such as rapid start fluorescent lamp electrodes and touch panels.

Next, a method for producing a conductive coating material according to the present invention and a method for producing a transparent conductive thin film thereby will be described in detail with reference to examples, but the present invention is not limited thereto.

Example 1 A mixed aqueous solution of InCl ₃ and SnCl ₄ was poured into an excess aqueous ammonia solution so that SnO ₂ became 3% by weight in terms of oxide, and the resulting hydroxide of In and Sn was formed. The gel precipitate of was filtered, dehydrated, and washed with water. In the filtered cake,
When ammonium ions and chloride ions were no longer detected, washing and filtration were stopped to obtain a precipitate cake. The sediment cake is dehydrated, the dehydrated cake is dried at 100 ° C., and the loosely lumpy part of the cake is crushed,
Place the sheet in a furnace filled with H ₂ gas at 270 ° C, 30
After heating for an minute, an ultrafine particle having a particle size of 100 to 200 mm was obtained. A polyester resin binder is mixed at a ratio of 30% by weight into the ultrafine particles of In and Sn oxide blended powder, applied to the surface of a glass plate using a doctor blade, dried, and then dried.
Was heated at ° C., skip binder, in an oven at a H ₂ gas atmosphere at 300 ° C., placed in a funnel shape, and heated for 30 minutes to obtain a transparent conductive film on a glass plate surface. When the film itself is measured, the result is that the total light transmittance is 88%,
The surface resistance was 500Ω / □.

Example 2 An aqueous solution of InCl ₃ and SnCl ₄ blended to be 1% by weight of SnO ₂ was poured into an excess of an aqueous ammonia solution, and the formed gel precipitate was filtered, dehydrated, and washed with water. . Washing of the filter cake with water was performed until no ammonia and chlorine ions were detected. The obtained dehydrated cake is 100
C., and the loosely agglomerated part therein was crushed and then placed on a plate in an NH ₃ gas atmosphere,
When heated at 20 ° C. for 20 minutes, ultrafine powder having a particle size of 100 to 300 ° was obtained. To this powder, a polyester resin was mixed at a ratio of 35% by weight as a binder, applied to the surface of a glass plate with a doctor blade, dried, and then dried.
° C., then heated for 30 minutes, then heated to 250 ° C. in a NH ₃ gas atmosphere, to obtain a transparent conductive thin film. When the film itself was measured, the result was a total light transmittance of 87% and a surface resistance of 87%.
It was 55Ω / □.

Example 3 An aqueous solution of InCl ₃ was put into an excess aqueous ammonia solution, and the formed gel precipitate was filtered, dehydrated, and washed with water. Washing of the filter cake with water was performed until ammonia and chlorine ions were not detected. The resulting dehydrated cake is dried at 100 ° C., the cake is crushed and then H
₂ Place the plate in a gas atmosphere, heat it to 300 ° C, mix the obtained powder with polyvinyl acetate resin as a binder at a ratio of 40% by weight, and use a doctor blade to surface the glass plate. After applying on top and drying, 480 ℃
, And then heated at 300 ° C. for 30 minutes in an H ₂ gas atmosphere to obtain a transparent conductive thin film. When the film itself was measured, the result was a total light transmittance of 85% and a surface resistance of 45%.
Ω / □.

[Example 4] An aqueous solution of InCl ₃ and SnCl ₄ blended to be 3% by weight of SnO ₂ was poured into an excess aqueous ammonia solution, and the formed gel precipitate was filtered, dehydrated, and washed with water. . Washing of the filter cake with water was performed until ammonia and chlorine ions were not detected. The obtained dehydrated cake is heated at 100 ° C.
And crushed, then laid flat in a furnace under an atmosphere of H ₂ gas and heated at 270 ° C. for 30 minutes. The obtained powdery conductive filler was added at a ratio of 30% by weight in the polyester resin, and mixed with a ball in a pot mill. The mixture was sufficiently mixed in about 5 minutes.

On the other hand, silver powder (particle diameter: 0.1 μm), copper (particle diameter: 0.1 μm) and graphite were each added to the polyester resin at a ratio of 30% by weight as conductive fillers for comparison. Were mixed, and as a result, all were in a state of insufficient mixing.

[Effects of the Invention] In the method for producing a transparent conductive thin film according to the present invention, the following remarkable technical effects were obtained by the production method.

First, it is possible to form a transparent conductive thin film having better transparency and conductivity than conventionally known coating materials by a coating method.

Second, it is possible to provide a transparent conductive thin film capable of meeting recent strict requirements for transparency and conductivity.

Third, transparency that can reduce manufacturing costs,
An economical method for producing a conductive thin film can be provided.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 31/04 H

Claims (4)

(57) [Claims] An alkaline aqueous solution is reacted with an aqueous solution of an acidic salt of indium or an aqueous solution of a mixture of an acidic salt of indium and an acidic salt of tin, and a precipitate formed of oxides and / or hydroxides is taken out. The precipitate is reduced under a reducing atmosphere.
A method for producing indium-based conductive ultrafine particles, characterized by heating to a temperature of 240 to 320 ° C. 2. The method according to claim 1, wherein the indium acid salt and the tin acid salt are chlorides, sulfates and nitrates. 3. The method according to claim 1, wherein the alkali is ammonia, sodium hydroxide, potassium hydroxide or sodium carbonate. 4. The indium-based conductive ultrafine particles according to claim 1 are mixed with a solvent or a paint, coated on a substrate, calcined to remove a binder, and then reduced in a reducing atmosphere to 200 to 4 wt.
A method for producing a transparent conductive thin film, comprising performing heat treatment at 00 ° C.