JP2736492B2 - Method for producing indium oxide-tin oxide powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ITO film (Indium-T
Indium oxide-tin oxide powder (mixed powder of indium oxide powder and tin oxide powder, hereinafter referred to as ITO powder), which is suitable as a raw material for producing indium oxide-based display materials such as in oxide film) It relates to a manufacturing method.

[0002]

2. Description of the Related Art As the interesting properties of indium, which is contained in a very small amount in zinc ore and recovered as a by-product, have been gradually elucidated, many proposals for its use have been made. In recent years, attention has been focused on high conductivity and transparency of a thin film of indium oxide, particularly, “Indium oxide containing Sn (In ₂ O ₃ —SnO ₂ )” called “ITO”. A wide variety of applications have been opened, such as electroluminescent display devices, radiation detection elements, and transparent tablets for terminal equipment.

[0003] Meanwhile, indium oxide powder and tin oxide powder prepared as a raw material for manufacturing the above-mentioned devices and equipment are conventionally manufactured according to respective steps as shown in FIG.

That is, in the case of indium oxide powder, first, as a first step, metal indium is dissolved with nitric acid, which is neutralized with aqueous ammonia and precipitated as indium hydroxide. Then, the deposit (indium hydroxide) is filtered, washed, and dried. Next, as a second stage, the obtained indium hydroxide is roasted to obtain indium oxide powder.

[0005] In the case of tin oxide powder, as a first step, metal tin is dissolved with nitric acid and this is precipitated as metastannic acid. Then, the deposit (metastannous acid) is filtered, washed, and dried. As a second step, the obtained metastannic acid is roasted to obtain tin oxide powder.

[0006] The indium oxide powder and tin oxide powder thus produced are mixed together to form a sputtering target or the like, and then formed into a film forming material such as sputtering to form a thin film. Often used.

[0007] However, the following problems have been pointed out in the above-mentioned method relating to the production of indium oxide powder and tin oxide powder. a) The resulting oxide powder has large variations in various properties (average particle size, apparent density, etc.), which is a hindrance to "reducing the quality variation" or "improving the quality" of ITO-based display materials. ing. b) It is not always easy to control the production conditions (liquid temperature, reaction rate, etc.) at a constant level, and equipment costs increase to stabilize them. c) When a powder with different characteristics from the conventional one is required, it is not possible to respond flexibly to this requirement. d) The production equipment becomes relatively large-scale, so that constant control of the production conditions requires a considerable amount of labor, and it is not always easy to cope with increased production. e) Dissolved effluent (eg, ammonium nitrate) is generated each time and needs to be treated, which increases running costs.

In view of the above, an object of the present invention is to solve the above problems and provide an indium oxide powder and a tin oxide powder having excellent properties which can be sufficiently satisfied as a raw material of a display material. The objective is to establish a means that can be provided stably at a low cost with good manufacturability.

[0009]

The present inventors have conducted research from various viewpoints to achieve the above object, and have obtained the following findings.

In producing an oxide powder of indium or tin, an "electrolysis method" is adopted as a first step instead of the conventional "dissolution precipitation method", and in addition, indium and tin are separated from each other. Simultaneous electrolytic treatment of the anode makes it possible to produce a mixed deposit of "indium hydroxide" and "metastannic acid" in one step under stable conditions with relatively low equipment costs and running costs. By calcining this mixed sediment, an ITO powder (mixed powder of indium oxide powder and tin oxide powder) having various properties (average particle size, apparent density, etc.) in a very wide range can be stably obtained. It is also possible to finely control these characteristics by selecting the electrolysis conditions.

The present invention has been made based on the above findings and the like. "Indium and tin are simultaneously electrolyzed as separate anodes, and the resulting mixed deposit of indium hydroxide and metastannic acid is calcined. By doing so, it is possible to produce ITO powder with small variations in characteristics such as average particle diameter and apparent density, stably, at low cost, and easily control the characteristics. "

By the way, as described above, in the method for producing ITO powder according to the present invention, unlike the conventional method, first, indium hydroxide and metastannic acid are electrolyzed in an electrolytic solution using metal indium and metal tin as anodes. At the same time, and then calcining (roasting) the mixed sediment. However, the electrolytic solution used for anodic electrolysis of these metals is not particularly specified, and ammonium nitrate is used. Any of ammonium, ammonium sulfate, and other electrolytes may be used, but it can be said that an ammonium nitrate aqueous solution is preferable in terms of cost and maintenance of product purity.

As the "electrolysis method" for simultaneously depositing indium hydroxide and metastannic acid, any of a usual so-called flat-wave electrolysis method and a periodic reversal current electrolysis method (PR electrolysis method) is employed. May be. And, by selecting the electrolysis conditions when depositing indium hydroxide and metastannic acid, it is possible to control the average particle size, specific surface area, apparent density, etc. of the ITO powder obtained by calcining it. These adjustments lead to a remarkable improvement in product quality when used as a raw material such as an ITO display material.

FIG. 1 shows "an example of a process for producing an ITO powder" according to the present invention incorporating this electrolytic method. Here, in order to more stably produce the ITO powder in the process illustrated in FIG. 1, preferably, “electrolysis” for obtaining “a mixed deposit of indium hydroxide and metastannic acid” to be subjected to calcination.
Is carried out in an aqueous ammonium nitrate solution having an NH ₄ NO ₃ concentration of 0.2 to 5 mol / L (liter), a pH of 4 to 9.5, and a bath temperature of 0 to 50 ° C., and the current density at that time is 100 to 180
It is better to control the pressure within the range of 0 A / m ² .

That is, if the concentration of NH ₄ NO ₃ in the electrolytic bath (aqueous ammonium nitrate solution) is lower than 0.2 mol / L, the current efficiency may decrease or the power consumption may increase.
If it exceeds l / L, the increase in chemical consumption cannot be ignored.
If the pH of the bath is lower than 4, the sediment becomes finer and solid-liquid separation becomes difficult. On the other hand, handling of the bath higher than 9.5 is not preferable for safety or environmental disaster prevention.

Adjusting the bath temperature to less than 0 ° C. is disadvantageous in terms of cooling cost. On the other hand, if the temperature is to be maintained at a temperature exceeding 50 ° C., the heating cost cannot be ignored, and in particular, NH ₄ NO _In case ₃ , environmental measures must be taken to cope with the generation of ammonia vapor. Further, with respect to the current density, if the current density is lower than 100 A / m ² , the productivity is deteriorated. On the other hand, if the current density is higher than 1800 A / m ² , the cell voltage is significantly increased, which is economically disadvantageous.

According to the "production method of ITO powder" according to the present invention, the following advantages can be enjoyed, and it can be said that its industrial contribution is extremely large. 1) The obtained ITO powder has a wide range of "characteristics (average particle size, apparent density, etc.)", and these can be controlled by selecting the electrolysis conditions. 2) Since the production of mixed deposits of indium hydroxide and metastannic acid, which are intermediate raw materials to be calcined, is performed simultaneously by the electrolytic method, a continuous method can be adopted, and quality control is easier than the conventional method of the batch method. The quality itself is stable. 3) Various properties of the finally obtained ITO powder can be delicately controlled by selecting the electrolysis conditions, so that it is possible to achieve high quality and reduction in quality variation of the ITO display material used. 4) Compared with the conventional method of mixing individually obtained oxides (indium oxide, tin oxide) with each other to form ITO powder, calcining the mixed deposit obtained by the co-electrolysis method eliminates a substantial mixing step. I
In the method of the present invention in which a TO powder is used, the ITO powder obtained by mixing the oxides more uniformly is very homogeneous. 5) Since a so-called “closed system” can be made,
Waste of nitric acid and nitric acid aqueous solution of ammonium is a significant reduction in running costs can be achieved as compared with the conventional method that occurred each time the neutralization. 6) Since the manufacturing equipment is compact, the initial cost (construction cost) is low, and it is easy to respond to increased production.

The ITO powder according to the present invention is formed into the above-mentioned ITO sputtering target by molding it.
Particularly excellent results can be obtained when used for forming a TO film, but the steps shown in FIG. 2 are generally employed for producing an ITO target from ITO powder.

Next, the present invention will be described more specifically with reference to examples.

【Example】

Example 1 An aqueous solution of ammonium nitrate (NH ₄ ) at 10 ° C.
In NO ₃ concentration: 0.5 mol / L, pH: 8), PR was determined by using metal indium and metal tin having different surface areas as anodes and the cathode current density as 600 A / m ² , respectively.
Electrolysis was performed simultaneously by the pulse current of the formula. Then, the deposit at the bottom of the electrolytic cell was filtered, washed and dried to obtain a mixed deposit of indium hydroxide and metastannic acid. Next, this is 1
Roast at 100 ° C, average particle size 20μm, apparent density 1.7g / c
m ³ of ITO powder was obtained.

Next, an ITO sputtering target having a SnO ₂ content of 10 wt% was produced from the obtained ITO powder as a raw material by a cold press atmospheric sintering method, and the density of the sintered body was 6.70 g / g. It was cm ^3.

Further, when the characteristics of the transparent conductive film obtained by sputtering this ITO target, such as sheet resistance and transmittance, were examined, it was found that the film could be used sufficiently for LCD (liquid crystal). It has been confirmed that it shows possible results.

Example 2 An electrolytic bath having a bath temperature of 50 ° C.
Except for using an aqueous solution of ammonium nitrate having an NH ₄ NO ₃ concentration of 1.0 mol / L and a pH of 6, the pulse electrolysis of the PR method was performed under the same conditions as in Example 1, and the deposits at the bottom of the electrolytic cell were filtered and washed. Then, drying was performed to obtain a mixed deposit of indium hydroxide and metastannic acid. Next, when this was roasted at 1100 ° C., an ITO powder having a high apparent density and a uniform particle size was obtained.

Next, the obtained ITO powder was used and, as in Example 1, an SnO ₂ content of 10 wt%
When a TO sputtering target was manufactured, the density of the sintered body was 4.78 g / cm ³ .

The ITO target was sputtered, and various characteristics such as sheet resistance and transmittance of the obtained transparent conductive film were examined. Was confirmed.

[0025]

As described above, according to the present invention, for example, ITO powder which can be sufficiently satisfied as a raw material of a sputtering target for forming an ITO film can be produced at a low cost while responding to a wide range of required characteristics. And industrially useful effects are provided.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a “production process of ITO powder” according to the present invention.

FIG. 2 is an explanatory diagram of a process for producing an ITO sputtering target from ITO powder.

FIG. 3 is a schematic explanatory view showing a conventional process for producing indium oxide powder and tin oxide powder.

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Claims (2)

(57) [Claims] 1. A method for producing an indium oxide-tin oxide powder, comprising simultaneously electrolyzing indium and tin as separate anodes and calcining a mixed deposit of indium hydroxide and metastannic acid. . 2. The method for producing indium oxide-tin oxide powder according to claim 1, wherein indium and tin are electrolyzed using an aqueous solution of ammonium nitrate as an electrolytic solution.