JP2679008B2 - Method for producing indium oxide-tin oxide powder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing indium oxide-tin oxide (hereinafter referred to as ITO) powder, and more specifically, a method for producing ITO powder having uniform and fine primary particles. It is about.

The present invention is a method for producing an ITO powder, which is extremely suitable as a raw material for an ITO target used when forming a transparent conductive film by a sputtering method, and as a raw material for an ITO coating used when forming a transparent conductive film by a coating method. Is provided.

[Conventional technology]

In recent years, there has been a rapid increase in demand for ITO thin films as transparent conductive films used for transparent electrodes and touch panels of solar cells and liquid crystal displays. These ITO thin films are formed on glass or PET film mainly by sputtering from an ITO target.

Conventionally, the ITO target is (1) ITO powder obtained by calcination and mixing of hydroxides of indium and tin, and (2) Calcination of mixed hydroxide of indium and tin prepared by a coprecipitation method or the like. (3) ITO powder obtained by thermally decomposing a mixed organic acid salt of indium and tin (JP-A-60-186416), etc. It is produced by firing after molding. However, the ITO powder obtained by either method has a primary particle size of about 0.1 μm, and the ITO target produced using these ITO powders has a sintering density of 6% of the theoretical density.
Only about 5% (up to 4.6 g / cm ³ ) was achieved and it was very fragile. As described above, the target having low strength is apt to be cracked during sputtering, which causes a serious obstacle in continuous operation of thin film production.

It is also possible to form an ITO thin film by applying these ITO powders. However, with conventional ITO powder, ITO
Since the particles were not fine, only a thin film having insufficient transparency was obtained.

[Problems to be solved by the invention]

The object of the present invention is to form an ITO sintered body having extremely high sintering density and high mechanical strength, and uniform and fine primary particles capable of forming a thin film having extremely excellent transparency by coating. The present invention provides a method for producing an ITO powder consisting of.

[Means for solving the problem]

As a result of intensive investigations on the production of ITO powder having a uniform and fine primary particle size, the present inventors have found that a mixed hydroxide of indium and tin is dispersed in an organic solvent, azeotropically dehydrated, and then dried. Extremely uniform and fine ITO by calcination
The inventors have found that a powder is produced and have completed the present invention.

From the powder, a sintered body having an extremely high sintered density can be obtained, and in addition, a coating film having excellent transparency can be formed from the powder coating material obtained by pulverizing the powder.

In the present invention, there is no particular limitation on the mixed hydroxide of indium and tin used as the starting material, but it is desirable that it has a uniform composition in order to obtain a powder that is a raw material for the ITO target and the ITO coating. Such a mixed hydroxide is prepared by adding a precipitant to a mixed solution of a water-soluble indium salt such as indium nitrate, indium sulfate or indium chloride and a water-soluble tin salt such as tin nitrate, tin sulfate or tin chloride, and mixing them. It can be obtained by coprecipitating a hydroxide and separating it. At this time,
As the precipitant to be added and mixed, any one may be used as long as it can give a hydroxide precipitate, but it is preferable to use a precipitant containing no metal element such as ammonia.

Further, in order to obtain ITO powder having a low specific resistance, the ratio of tin to indium in the mixed hydroxide is preferably 3 to 25 mol%, more preferably 5 to 15 mol%. . In the present invention, the mixed hydroxide of indium and tin obtained by the above method is dispersed in an organic solvent, and the mixed solution is distilled to dehydrate the hydroxide. A monohydrate is obtained. At this time, in the case of producing a sintered body such as when it is used as a target raw material, the distillation does not have to be performed until the water in the solution is completely dehydrated. But IT
When particularly fine powder is required, such as when used as a raw material powder for O paint, distillation is preferably performed until the water in the solution is dehydrated as completely as possible.

The organic solvent used for distillation may be any one that can be azeotropically dehydrated with water, and examples thereof include benzene, toluene, xylene, alcohols having 10 or less carbon atoms, and organic acid esters such as ethyl benzoate. These 1 type (s) or 2 or more types can be used. The distillation temperature at this time is usually in the range of 60 ° C. or higher to the boiling point of the solvent. In particular, when used as a raw material powder for paint, it is preferable to carry out distillation to the boiling point of the solvent.

The obtained oxide hydrate can be recovered by a method such as collecting or spray drying.

Next, the oxide hydrate obtained by azeotropic dehydration is dried, and this drying can be performed in the range of 50 ° C to 150 ° C. Further, at this time, it is efficient to carry out under reduced pressure.

If the temperature after calcination after drying is high, the resulting ITO powder may agglomerate, so it is preferably carried out at 350 to 800 ° C., more preferably calcination temperature is 400 to 6
00 ° C.

When the ITO powder obtained as described above is used as a raw material for an ITO target, it can be used as it is. However, in order to obtain a sintered body having a higher sintering density, this powder is used in a general method such as a ball mill. Can be crushed and used.

When it is used as a raw material for an ITO paint, it can be used by being dispersed in a solvent by wet pulverizing a paint shaker or the like.

〔Example〕

Hereinafter, the present invention will be described based on examples, but the present invention is not limited thereto.

FIG. 1 shows an example of a flow chart for carrying out the present invention, and this embodiment will be described based on this.

Example 1 Indium metal was dissolved in a 60% nitric acid aqueous solution to obtain 1.0 mol / mol.
Dissolve stannous sulfate in the one prepared so that
A mixed aqueous solution (1) of indium and tin was prepared. The ratio of tin to indium in the aqueous solution (1) was 10 mol%. To the mixed aqueous solution (1) under stirring, 14% ammonia water as a precipitating agent (2) was added dropwise until pH 6 was obtained to obtain a mixed hydroxide precipitate of indium and tin (3).

The hydrous hydroxide precipitate (200 g) was separated by decantation (4), dispersed in about 4 n-butanol in the form of a sol (5), and then heated and distilled under normal pressure (6). The temperature of the solution was 92 ° C during the azeotropic distillation of water and butanol, but with the progress of dehydration, the liquid temperature gradually increased, and when it reached 105 ° C, the distillation was stopped and the solution was allowed to cool.

Separately separate the amorphous oxide hydrate,
It was dried under reduced pressure at a temperature of 90-100 ° C. 500 ° C after drying
It was calcined (7) and crushed with a ball mill for 20 hours to obtain ITO powder (8).

When observing this powder with SEM, the primary particle size is 0.05μ.
m.

Further, this powder was pelletized at a CIP pressure of ² ton / cm ² and
Upon firing at 300 ° C., ITO pellets with a sintered density of 6.0 g / cm ³ could be obtained.

Example 2 ITO powder was obtained in the same manner as in Example 1 except that stannous chloride was used instead of stannous sulfate to prepare a mixed aqueous solution.

When observing this powder with SEM, the primary particle size is 0.05μ.
m.

Further, this powder was pelletized at a CIP pressure of ² ton / cm ² and
Upon firing at 300 ° C., ITO pellets with a sintered density of 5.5 g / cm ³ could be obtained.

Example 3 ITO powder was obtained in the same manner as in Example 1 except that stannous chloride was used instead of stannous sulfate to prepare a mixed aqueous solution.

When observing this powder with SEM, the primary particle size is 0.05μ.
m.

Further, this powder was pelletized at a CIP pressure of ² ton / cm ² and
Upon firing at 300 ° C., ITO pellets with a sintered density of 6.0 g / cm ³ could be obtained.

Example 4 ITO powder was obtained in the same manner as in Example 1 except that isoamyl alcohol was used as the organic solvent. S this powder
When observed by EM, the primary particle size was 0.05 μm.

Further, this powder was pelletized at a CIP pressure of ² ton / cm ² and
Upon firing at 300 ° C., ITO pellets with a sintered density of 5.7 g / cm ³ could be obtained.

Comparative Example 1 A mixed hydroxide of indium and tin (3) obtained by the same method as in Example 1 was dried without dispersion / azeotropic dehydration treatment in an organic solvent (5) and (6). After that, it was calcinated at 500 ℃ (7) and pulverized with a ball mill for 20 hours to make ITO
A powder was obtained.

When this powder was observed by SEM, the primary particle size was 0.1 to 0.
It was 2 μm.

Further, this powder was pelletized at a CIP pressure of ² ton / cm ² in the same manner as in Example 1 and fired at 1300 ° C. to obtain a density of 4.0 g.
ITO pellets of / cm ³ were obtained.

Example 5 ITO powder was obtained in the same manner as in Example 1 except that azeotropic dehydration was performed until the liquid temperature reached the boiling point of n-butanol.

This powder was wet milled for 30 hours with a paint shaker using methyl ethyl ketone as a solvent and zirconia beads as a media, and dispersed to obtain an ITO powder. Using this, an ITO thin film of 2 μm was formed on a PET film by a coating method, and the light transmittance at 700 nm was measured to show a value of 95%.

Comparative Example 2 A mixed hydroxide of indium and tin (3) obtained by the same method as in Example 1 was dried in an organic solvent without performing steps (5) and (6) of azeotropic dehydration. Then, an INO coating material was obtained in the same manner as in Example 4 except that calcination (7) was performed at 500 ° C.
2μm ITO on PET film by coating method using this
When a thin film was prepared and the light transmittance at 700 nm was measured, it was 60.
The value of% is shown.

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain an ITO powder in which primary particles are uniform and fine. Therefore, by using this ITO powder, a sintered body having a high sintering density can be obtained. Therefore, this makes it possible to obtain an ITO target that is less likely to crack during sputtering and can withstand continuous operation. Further, by using this ITO powder, an ITO coating material having excellent transparency can be obtained.

[Brief description of the drawings]

FIG. 1 shows an example of a flowchart for carrying out the present invention. 1 …… Indium and tin mixed aqueous solution 2 …… Precipitant 3 …… Indium and tin mixed hydroxide precipitation 4 …… Decantation 5 …… Dispersion in organic solvent 6 …… Azeotropic distillation 7 …… Calcination 8 …… ITO powder

Claims (1)

(57) [Claims] 1. A mixed hydroxide of indium and tin is dispersed in an organic solvent in a colloidal state, and then the mixed solution is azeotropically distilled to dehydrate a hydroxide, and then the obtained oxide hydrate is obtained. A method for producing an indium oxide-tin oxide powder, which comprises drying and calcining an object.