JP2963296B2 - Method for producing conductive fine powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing tin-containing indium oxide (ITO) fine powder having excellent conductivity and transparency, and more particularly to a method for producing ultrafine ITO powder.

More specifically, a tin-containing material having excellent conductivity and transparency used for forming a transparent conductive film such as an antistatic film and a transparent electrode such as a liquid crystal display by a coating method. The present invention relates to a method for producing ultrafine indium oxide powder.

[0003]

2. Description of the Related Art An ITO film widely used as a transparent electrode such as a solar cell or a liquid crystal display or a transparent conductive film such as an electroluminescent display or a touch panel is generally formed by a sputtering method, a vacuum deposition method, a coating method or the like. Among them, the coating method is capable of processing into a large area or a complicated shape which is difficult by the sputtering method or the vacuum evaporation method, and is advantageous in cost. An organic sol-gel method is generally used as such a coating method, but with the development of fine particle manufacturing technology in recent years, a method of applying this using fine powder has attracted attention. ing. As a method for producing a tin-containing indium oxide fine powder that can be used in such a coating method, for example, JP-A-63-115
No. 19 contains an aqueous solution of an indium compound or a tin compound in 8
A method of hydrolyzing under a pH condition of ~ 12, filtering and washing the sol containing the formed colloid particles, and then subjecting the sol to a heat treatment;
JP-A-1-290527 discloses a method of dispersing an indium / tin mixed hydroxide in an organic solvent, azeotropically dehydrating and calcining the mixture, and JP-A-3-54114 discloses a method in which the amount of water in the reaction system is determined by using an organic solvent. There has been proposed a method in which an alkali aqueous solution is added to a solution of an indium salt and a tin salt to produce a mixture of an indium hydroxide and a tin hydroxide, and a heat treatment is performed. However, according to the method described in JP-A-63-11519, it is not easy to remove by-product salts when colloid particles are separated from the sol by filtration.
The method described in Japanese Patent Application Laid-Open No. 7-54114 and Japanese Patent Application Laid-Open No. 3-54114 involve problems such as disadvantages in safety and cost because a large amount of organic solvent is required.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a method for producing a tin-containing indium oxide fine powder having excellent conductivity and transparency.

[0005]

According to the present invention, a tin salt and indium oxide hydrate obtained by adding an aqueous alkali solution to a tin salt and indium salt solution while maintaining the temperature at 30 ° C. or less is subjected to heat treatment. And a method for producing an ultrafine powder of conductive tin-containing indium oxide.

The tin salt and the indium salt used in the present invention may be any water-soluble salts, and examples thereof include tin chloride, tin sulfate, tin nitrate, indium chloride, indium sulfate, indium nitrate and the like. Either a tin salt or a stannic salt may be used. After dissolving such tin salt and indium salt in water, and if necessary, adding a water-soluble organic solvent such as alcohol and acetone and / or a mineral acid such as hydrochloric acid and nitric acid, the temperature is reduced to 30 ° C. or lower, preferably. While maintaining the temperature at 0 to 20 ° C., an aqueous alkali solution is added. When the temperature exceeds 30 ° C., the particle size is generally coarse, depending on other conditions, and a needle-shaped or aggregated form is formed. 0 ° C
Even if it is less than the above, the effect is not particularly improved, and the cost of the cooling refrigerant or the like increases. In this case, the ratio of tin to indium was 1:99 to 20:80 in terms of SnO ₂ : In ₂ O ₃ weight ratio,
The ratio is preferably 4:96 to 15:85, and if the amount of tin is too large or too small, the desired conductivity cannot be obtained.

At this time, the concentration at the end of the reaction (SnO ₂
+ In ₂ O ₃ ) concentration in the range of 2 to 50 g / l is appropriate, and 2 g /
If it is less than 1 liter, the yield is small and uneconomical, and if it exceeds 50 g / l, the particle size becomes coarse.

As the alkaline aqueous solution, ammonia water,
Aqueous solutions such as alkali hydroxide, alkali carbonate, and ammonium carbonate can be exemplified, but alkali metal salts containing a component that inhibits conductivity are not suitable, and aqueous ammonia and aqueous ammonium salts are preferred. Then, a hydrate of tin oxide and indium oxide is formed by adding such an alkaline aqueous solution so that the pH finally becomes 5.0 to 9.0. If the pH is less than 5.0, the reaction is incomplete.
On the other hand, if it exceeds 9.0, deflocculation of a part of the product occurs, and in any case, sintering is caused in the subsequent heat treatment step, and coarse particles are generated.

The addition time of the aqueous alkali solution is not particularly limited, but is preferably about 30 minutes to 12 hours.
If the time is less than 30 minutes, the product will be in a gel state, which will be difficult to filter and wash, and will cause sintering in the subsequent heat treatment step. If the addition time is longer than 12 hours, the productivity decreases and the particle size becomes coarse.

Under the above conditions, the primary particle size is 0.01
A hydrate of tin oxide and indium oxide of about 5 to 0.05 μm is formed. In the present invention, the desired tin-containing substance is obtained by removing the salt produced as a by-product if necessary, drying the hydrate, and further heat-treating the hydrate at 300 to 1200 ° C, preferably 500 to 1000 ° C. Indium oxide fine powder can be obtained. In this case, if necessary, the conductivity is further improved by performing the treatment in an inert gas atmosphere such as N ₂ or Ar or a reducing atmosphere such as H ₂ or NH ₃ . The obtained ITO fine powder has the same shape and shape as the hydrate of the raw material tin oxide and indium oxide.

[0011]

The present invention will be described below with reference to examples of the present invention.
The present invention is not limited to this.

EXAMPLE 1 5.9 g of stannic chloride (SnCl ₄ .5H ₂ O) and 75.9 g of indium chloride (InCl ₃ ) were dissolved in 4000 ml of water, and 2% aqueous ammonia was added thereto over 58 minutes to adjust the pH. Was finally set to 7.85 to coprecipitate a hydrate of tin oxide and indium oxide. During this time, the liquid temperature was kept at 5 ° C. Next, the coprecipitate was washed, dried, and calcined at 900 ° C. for 2 hours to obtain a fine powder of tin-containing indium oxide (ITO).
As shown in the electron micrograph of FIG. 1, the fine powder had a primary particle diameter of about 0.02 μm and a fine and uniform particle size.

Example 2 3.9 g of stannous chloride (SnCl ₂ .2H ₂ O) and 121.6 g of indium nitrate [In (NO ₃ ) ₃ .3H ₂ O] were dissolved in 4000 ml of water, and 2% aqueous ammonia was added thereto. Was added over 73 minutes to finally adjust the pH to 7.80, thereby co-precipitating a hydrate of tin oxide and indium oxide. During this time, the liquid temperature was maintained at 20 ° C. Next, the coprecipitate was washed, dried, and further 900
C. for 2 hours to obtain a tin-containing indium oxide fine powder. As shown in the electron micrograph of FIG. 2, the fine powder had a primary particle size of about 0.035 μm and a fine and uniform particle size.

Example 3 5.9 g of stannic chloride (SnCl ₄ .5H ₂ O) and 75.9 g of indium chloride (InCl ₃ ) were dissolved in 4000 ml of water, and 4.5%
NH ₄ HCO ₃ aqueous solution is added over 360 minutes to finally adjust pH.
By setting to 5.8, a hydrate of tin oxide and indium oxide was coprecipitated. During this time, the liquid temperature was kept at 25 ° C. Next, the coprecipitate is washed, dried, and further dried at 700 ° C for 2 hours.
Calcination was performed for a period of time to obtain a tin-containing indium oxide fine powder. As shown in the electron micrograph of FIG. 3, the fine powder had a primary particle size of about 0.045 μm and a fine and uniform particle size.

Comparative Example 1 Tin-containing indium oxide fine powder was obtained in the same manner as in Example 1 except that the liquid temperature was maintained at 35 ° C. The fine powder has a short axis diameter of 0.05 to 0.07 μm and a long axis diameter as shown in the electron micrograph of FIG.
It had a needle shape of 0.30 to 0.35 μm.

Comparative Example 2 A hydrate of tin oxide and indium oxide was coprecipitated in the same manner as in Example 1 except that the pH was finally adjusted to 4.5. Since the coprecipitate is in a gel state, it takes a long time to wash with water, and 900 ° C.
As shown in FIG. 5, almost all of the tin-containing indium oxide powder obtained by firing for 2 hours was sintered to form coarse particles.

Comparative Example 3 A hydrate of tin oxide and indium oxide was coprecipitated in the same manner as in Example 1 except that the pH was finally adjusted to 9.5. As in Comparative Example 2, the coprecipitate is in a gel state, and thus requires a long time for water washing, and most of the tin-containing indium oxide powder obtained by firing at 900 ° C. for 2 hours is coarse and coarse. Had become particles.

Comparative Example 4 A hydrate of tin oxide and indium oxide was coprecipitated in the same manner as in Example 1 except that the addition time was changed to 20 minutes. As in Comparative Example 2, the coprecipitate is in a gel state, and thus requires a long time for water washing, and most of the tin-containing indium oxide powder obtained by firing at 900 ° C. for 2 hours is coarse and coarse. Had become particles.

Test Example 1 10.5 g of each of the tin-containing indium oxide fine powders of Examples 1 to 3 and Comparative Examples 1 to 4 was mixed with 5.0 g of an alkyd resin (Betcosol manufactured by Dainippon Ink and Chemicals, solid content 70% by weight) and xylol. The mixture was mixed with 7 ml and 50 g of glass beads and shaken in a paint shaker for 60 minutes to prepare a paint. This was applied to a glass plate so that the dry film thickness became 5 μm, dried, and then the surface resistivity was measured with a Loresta FP (manufactured by Mitsubishi Yuka) at 700 nm.
The light transmittance of light was measured with a spectrophotometer U-2000 (manufactured by Hitachi, Ltd.). Table 1 shows the results.

[0020]

[Table 1]

[0021]

As described above, according to the present invention, while the conventional method is a colloidal particle at the stage of forming as a hydrate, it already has a form as a primary particle of about 0.015 to 0.05 μm. Therefore, it becomes an oxide without sintering even in the heat treatment step, and can be commercialized without taking any special grinding means.

[Brief description of the drawings]

FIG. 1 is an electron micrograph (40) showing the particle structure of a tin-containing indium oxide fine powder obtained according to Example 1 of the present invention.
000 times).

FIG. 2 is an electron micrograph (40) showing the particle structure of the tin-containing indium oxide fine powder obtained according to Example 2 of the present invention.
000 times).

FIG. 3 is an electron micrograph (40) showing the particle structure of the tin-containing indium oxide fine powder obtained according to Example 3 of the present invention.
000 times).

FIG. 4 is an electron micrograph (40) showing the particle structure of the tin-containing indium oxide fine powder obtained according to Comparative Example 1 of the present invention.
000 times).

FIG. 5 is an electron micrograph (40) showing the particle structure of the tin-containing indium oxide fine powder obtained according to Comparative Example 2 of the present invention.
000 times).

Continuation of the front page (56) References JP-A-3-54114 (JP, A) JP-A-1-290527 (JP, A) JP-A-2-6332 (JP, A) JP-A-2-120374 (JP) JP, A 62-7627 (JP, A) JP, 63-11519 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 1/00-23/08

Claims (1)

(57) [Claims] 1. The temperature of the tin salt and indium salt solution is adjusted to 30.
A method for producing an ultrafine powder of conductive tin-containing indium oxide, comprising subjecting a hydrate of tin oxide and indium oxide obtained by adding an aqueous alkali solution to heat treatment at a temperature of not more than ° C.