JP4372653B2 - Method for producing rod-shaped conductive tin-containing indium oxide fine powder - Google Patents

Description

The present invention relates to a method for producing a rod-shaped conductive tin-containing indium oxide fine powder that is most suitable as a filler for a transparent conductive film-forming coating used for forming a transparent conductive film.

  Conductive tin-containing indium oxide, which is widely used as a transparent electrode or transparent conductive film for solar cells and flat panel displays, in particular, a tin-doped indium oxide (hereinafter abbreviated as ITO) film is usually formed by a sputtering method or an organic precursor. The film is formed by the sol-gel method used or the fine powder coating method.

  Among the film formation methods, the sputtering method is disadvantageous in terms of cost because it requires a large apparatus for large area processing, and the sol-gel method cannot be applied to a plastic film because high temperature heat treatment is necessary for thermal decomposition of organic matter. . For this reason, attention has been paid to a fine powder coating method in which a transparent conductive film can be produced only by low-temperature treatment with a simple apparatus.

  In the fine powder coating method, a transparent conductive paint using ITO fine powder as a filler is used. The ITO fine powder used in this method has a particle diameter that is considerably smaller than the particle diameter at which Mie resonance where the scattered light intensity is maximized in order to prevent a decrease in transparency due to light scattering, that is, 1 / wavelength of visible light. The particle size is considerably smaller than 2. In practice, in order to reduce the scattered light intensity to obtain practical transparency, it is necessary to use a particle having a particle diameter of 100 nm or less when the minimum wavelength of visible light is 380 nm.

  And in order to maintain electroconductivity by such particles contacting, what has the rod-shaped shape which adjacent particles are easy to contact is desired. In addition, the rod-shaped particles are not only easily contacted but also can be improved in conductivity by increasing the contact area by overlapping.

  However, as the rod-like particles of the ITO fine powder, Patent Document 1 discloses “ITO fine powder having a major axis of 5 μm or more and an aspect ratio of 5 or more”, and Patent Document 2 discloses “A major axis of 1 to 2 μm and a minor axis of 0. “ITO fine powder having an aspect ratio of 5 to 10 at 1 to 0.2 μm” is disclosed in Patent Document 3 as “ITO fine powder having a major axis of 0.2 to 0.95 μm and a minor axis of 0.02 to 0.10 μm”. Is only disclosed.

All of these particle diameters have a major axis of 200 nm or more, are not suitable as fillers for transparent conductive paints in terms of transparency and conductivity, and have ITO fine powder with a shorter major axis and a larger aspect ratio. Although it can be manufactured on an industrial scale at a low price, a manufacturing method has been strongly desired.
Japanese Patent Laid-Open No. 7-232920 Japanese Patent Laid-Open No. 10-17325 Japanese Patent Laid-Open No. 6-80422

An object of the present invention is to provide a method for producing a conductive tin-containing indium oxide fine powder that is optimal as a filler for a transparent conductive paint and has a shorter major axis and a larger aspect ratio.

  As a result of intensive studies in view of the above-described conventional circumstances, the inventor added a predetermined amount of hexamethylenetetramine to an aqueous solution containing tin (Sn) and indium (In), and calcined the deposited precipitate. It was found that a rod-shaped conductive tin-containing indium oxide fine powder having a small aspect ratio and a large aspect ratio can be obtained.

  That is, in the method for producing a rod-shaped conductive tin-containing indium oxide fine powder according to claim 1 of the present invention, a tin salt and an indium salt are dissolved in water, and the total amount of tin (Sn) and indium (In) is 0. Prepare an aqueous solution containing 0.001 mol / L to 0.05 mol / L, and add hexamethylenetetramine in an amount corresponding to 20 to 100 times the total molar amount of tin (Sn) and indium (In). The deposited precipitate is fired.

After the hexamethylenetetramine is added, the aqueous solution is preferably heated to 80 ° C. or higher prior to the baking.
The firing is preferably performed at a temperature of 300 ° C to 800 ° C.

  According to the present invention, a rod-shaped conductive tin-containing indium oxide fine powder having a major axis of 50 to 100 nm and an aspect ratio of 5 or more, which is suitable as a filler for a transparent conductive film-forming coating material excellent in transparency and conductivity, is provided. It can be manufactured efficiently and inexpensively on an industrial scale.

  The tin salt and indium salt used in the method for producing the rod-shaped conductive tin-containing indium oxide fine powder of the present invention may be water-soluble, such as tin chloride, tin nitrate, tin acetate, indium chloride, indium nitrate, indium acetate, etc. Is given as an example.

Such tin salts and indium salts are dissolved in water. In this case, the concentration of the aqueous solution should be 0.001 to 0.05 mol / L as the combined concentration of tin and indium.
The reason why the concentration is 0.001 to 0.05 mol / L is that the productivity is inferior when the concentration is less than 0.001 mol / L, and the aspect ratio of the rod-like particles that are generated when the concentration exceeds 0.05 mol / L. Is less than 5.

Next, an amount of hexamethylenetetramine corresponding to 20 to 100 times the number of moles of tin and indium in the system is added to an aqueous solution in which a tin salt and an indium salt are dissolved in water.
This hexamethylenetetramine acts as a precipitant for tin and indium. In the present invention, it is important to use hexamethylenetetramine as a precipitating agent. If ammonia water, alkali hydroxide, alkali carbonate, ammonium carbonate or the like conventionally used as a precipitant is used, the object of the present invention is achieved. Cannot be achieved.

  In the present invention, it is important that the amount of hexamethylenetetramine added is within the above range. The reason why the amount of hexamethylenetetramine added is 20 to 100 times the molar number of tin and indium in the system is that the aspect ratio of the produced rod-like particles is less than 5 if the amount is less than 20 times the molar amount. This is because no change is observed in the formed rod-like particles even when added in a molar amount exceeding 100 times.

When hexamethylenetetramine is added, hexamethylenetetramine is hydrolyzed into ammonia and formaldehyde to raise the pH in the aqueous solution, so that hydrates of tin and indium are precipitated.
Formaldehyde generated by hydrolysis of hexamethylenetetramine is considered to be adsorbed on the surface of the deposited precipitate and act as a crystal growth control agent.
When the aqueous solution is heated after adding hexamethylenetetramine, the reaction rate is increased and the precipitate can be obtained efficiently.
The heating temperature is preferably 80 ° C. or higher in order to obtain an effective reaction rate. The heating time is preferably about 12 to 24 hours.

The hydrates (precipitates) of tin and indium produced under the above conditions are baked after removing by-products as necessary and drying, so that the major axis is 50 to 100 nm and the aspect ratio is 5 or more. A fine powder composed of rod-like particles of conductive tin-containing indium oxide can be obtained.
If the calcination temperature is too low, the conversion from the hydrate to the oxide becomes insufficient, and if it is too high, the major axis or aspect ratio may fall below the above range, so 300 to 800 ° C, preferably 400 to 600 ° C. Is preferred.
The atmosphere for firing is not particularly limited as long as an oxidation reaction occurs at the firing temperature, and the firing is usually performed in the air.
In addition, it is preferable to further heat-treat in an inert gas atmosphere such as N ₂ or Ar or a reducing atmosphere such as H ₂ or NH ₃ after firing, as the conductivity is further improved.

If the long diameter is too small, the contact area between the particles becomes small, so that the conductivity tends to decrease. If the long diameter is too large, the transparency tends to decrease. On the other hand, if the aspect ratio is too small, the contact area between the particles becomes small, and the conductivity tends to decrease.
Since the fine powder obtained by the above production method has a major axis of 50 to 100 nm and an aspect ratio of 5 or more, both conductivity and transparency are good.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples.
"Example 1"
After adding pure water to a solution of 0.77 g of stannic chloride (SnCl ₄ .5H ₂ O) and 5.86 g of indium chloride (InCl ₃ .4H ₂ O) in pure water to make 1 L, 93 g of hexamethylene Tetramine was added to make a uniform aqueous solution (In + Sn: 0.02 mol / L, hexamethylenetetramine: 30-fold molar amount).
When this aqueous solution was heated and boiled, the pH of the solution was raised by the ammonia produced by the decomposition of hexamethylenetetramine, and indium and tin hydrates were precipitated. This precipitate was washed and dried, and then calcined at 400 ° C. for 3 hours in an air atmosphere to obtain a fine powder.
As a result of X-ray diffraction (XRD), this fine powder was found to be an ITO fine powder. Further, as shown in the transmission electron micrograph of FIG. 1, it had a large number of rod-shaped particles having a major axis of 60 nm and an aspect ratio of 6.
The major axis and the aspect ratio were measured as follows. 20 particles are randomly extracted from the transmission electron micrograph shown in FIG. 1, and the average value of the length of the longest part of the particle is taken as the major axis, and the part having the longest length in the direction perpendicular to the longest direction The average value of the length was taken as the minor axis, and the aspect ratio was calculated based on these.

"Example 2"
After adding pure water to a solution of 0.38 g of stannic chloride (SnCl ₄ .5H ₂ O) and 2.93 g of indium chloride (InCl ₃ .4H ₂ O) in pure water to make 1 L, 93 g of hexamethylene Tetramine was added to form a uniform aqueous solution (In + Sn: 0.01 mol / L, hexamethylenetetramine: 60-fold molar amount).
When this aqueous solution was heated and boiled, the pH of the solution was raised by the ammonia produced by the decomposition of hexamethylenetetramine, and indium and tin hydrates were precipitated. This precipitate was washed and dried, then calcined at 400 ° C. for 3 hours in an air atmosphere, and further calcined at 600 ° C. for 10 hours in nitrogen to obtain fine powder.
As a result of X-ray diffraction (XRD), this fine powder was found to be an ITO fine powder. Further, as shown in the transmission electron micrograph of FIG. 2, it had many rod-like particles having a major axis of 70 nm and an aspect ratio of 6.
The measuring method of the major axis and the aspect ratio is the same as in Example 1.

"Example 3"
After adding pure water to a solution of 0.77 g of stannic chloride (SnCl ₄ .5H ₂ O) and 5.86 g of indium chloride (InCl ₃ .4H ₂ O) in pure water to make 1 L, 310 g of hexamethylene Tetramine was added to obtain a uniform aqueous solution (In + Sn: 0.02 mol / L, hexamethylenetetramine: 100-fold molar amount).
When this aqueous solution was heated and boiled, the pH of the solution was raised by the ammonia produced by the decomposition of hexamethylenetetramine, and indium and tin hydrates were precipitated. This precipitate was washed and dried, and then calcined at 400 ° C. for 3 hours in an air atmosphere to obtain a fine powder.
As a result of X-ray diffraction (XRD), this fine powder was found to be an ITO fine powder. Further, as shown in the transmission electron micrograph of FIG. 3, it had a large number of rod-shaped particles having a major axis of 60 nm and an aspect ratio of 5.5.
The measuring method of the major axis and the aspect ratio is the same as in Example 1.

"Comparative Example 1"
Pure water was added to a solution of 3.8 g of stannic chloride (SnCl ₄ .5H ₂ O) and 29.3 g of indium chloride (InCl ₃ .4H ₂ O) in pure water to make 1 L, and then 466 g of hexamethylene. Tetramine was added to form a uniform aqueous solution (In + Sn: 0.1 mol / L, hexamethylenetetramine: 30-fold molar amount).
When this aqueous solution was heated and boiled, the pH of the solution was raised by the ammonia produced by the decomposition of hexamethylenetetramine, and indium and tin hydrates were precipitated. This precipitate was washed and dried and then calcined at 400 ° C. for 3 hours to obtain a fine powder.
As a result of X-ray diffraction (XRD), this fine powder was found to be an ITO fine powder. Further, this fine powder had a major axis of 60 nm as shown in the transmission electron micrograph of FIG. 4, but had only particles having an aspect ratio of less than 5.
The measuring method of the major axis and the aspect ratio is the same as in Example 1.

"Comparative Example 2"
After adding pure water to a solution of 0.77 g of stannic chloride (SnCl ₄ .5H ₂ O) and 5.86 g of indium chloride (InCl ₃ .4H ₂ O) in pure water to make 1 L, 31 g of hexamethylene Tetramine was added to obtain a uniform aqueous solution (In + Sn: 0.02 mol / L, hexamethylenetetramine: 10-fold molar amount).
When this aqueous solution was heated and boiled, the pH of the solution was raised by the ammonia produced by the decomposition of hexamethylenetetramine, and indium and tin hydrates were precipitated. This precipitate was washed and dried and then calcined at 400 ° C. for 3 hours to obtain a fine powder.
As a result of X-ray diffraction (XRD), this fine powder was found to be an ITO fine powder. Further, this fine powder had a major axis of 40 nm and an aspect ratio of less than 5 as shown in the transmission electron micrograph of FIG.
The measuring method of the major axis and the aspect ratio is the same as in Example 1.

`` Test example ''
30 g of the ITO fine powder obtained in Examples 1 to 3 was mixed with 10.5 g of tetramethoxysilane, 50 g of pure water and 175 g of propylene glycolpropylene glycol, and shaken for 60 minutes to prepare a coating material.
When a film having a thickness of 0.5 μm is formed on a glass plate using this paint, transparency (visible light transmittance is about 96% to 99%) and conductivity (surface resistivity is 12 kΩ / □ to 50 kΩ). A transparent conductive film excellent in (/ □) was able to be formed.

It is a photograph of the fine powder obtained in the Example. It is a photograph of the fine powder obtained in the Example. It is a photograph of the fine powder obtained in the Example. It is a photograph of the fine powder obtained in the comparative example. It is a photograph of the fine powder obtained in the comparative example.

Claims (3)

A tin salt and an indium salt are dissolved in water to prepare an aqueous solution containing a total amount of tin (Sn) and indium (In) of 0.001 mol / L to 0.05 mol / L. ) and indium (in) the total molar amount of 20 to 100 was added in an amount of hexamethylenetetramine equivalent to times, you and firing the deposited precipitate rod-shape conductive tin-containing indium oxide fine powder Manufacturing method.   2. The method for producing a rod-shaped conductive tin-containing indium oxide fine powder according to claim 1, wherein the aqueous solution is heated to 80 [deg.] C. or higher after the hexamethylenetetramine is added and prior to the firing. The method for producing a rod-shaped conductive tin-containing indium oxide fine powder according to claim 1 or 2 , wherein the firing is performed at a temperature of 300 ° C to 800 ° C.