JP5514570B2 - Method for producing tin-doped indium oxide powder and tin-doped indium oxide powder - Google Patents

Description

  The present invention relates to a method for producing tin-doped indium oxide (ITO) powder and tin-doped indium oxide powder.

  Conventionally, a transparent conductive film containing tin-doped indium oxide (hereinafter referred to as ITO: Indium Tin Oxide) exhibits high translucency for visible light and conductivity, so that various display devices and solar cells are used. It is used as a transparent electrode film. As a method for forming the transparent conductive film, a physical vapor deposition method such as a sputtering method, or a coating method in which a dispersion of ITO particles or an organic ITO compound is applied is known.

  The ITO film obtained by the coating method among the film forming methods described above uses an expensive device such as a vacuum device, although its conductivity is somewhat lower than that of an ITO film formed by a physical method such as sputtering. Therefore, it is possible to form a film with a large area or a complicated shape without any advantage of reducing the film formation cost.

  As a method for producing ITO powder, which is a raw material for coating materials used in the above coating method, for example, an indium-tin salt mixed aqueous solution is neutralized by adding an alkali such as ammonia or sodium hydroxide, and indium-tin coprecipitation water oxidation The product can be produced by washing with water, drying and calcining.

  Since the use of the transparent conductive film paint is for electronic materials, there is a problem that impurities, especially halogen element chlorine, is contained. When chlorine is present, corrosion and elution of the metal used in the electronic device is likely to occur, and deterioration with time is also likely to occur in the resin mixed with ITO powder.

Therefore, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2001-58822).
In the process of producing ITO powder, indium-tin coprecipitated hydroxide is produced, and then the hydroxide is washed with an aqueous ammonia solution having a pH of 9 to 12, and the chlorine content after the hydroxide is dried is 200. The manufacturing method which reduces the amount of chlorine which remains in the ITO powder finally obtained by making it mass ppm or less is disclosed.

JP 2001-58822 A

  However, in Patent Document 1, in the step of washing the indium-tin coprecipitated hydroxide with an aqueous ammonia solution before drying, the hydroxide is washed before drying. As a result, the chlorine content in the ITO powder is 50 to 50%. Although it can be reduced to 100 ppm by mass, ITO powder with further reduced residual chlorine content has been demanded, and there is room for further improvement in reducing the residual chlorine content in ITO powder.

  Then, this invention is made | formed in view of the above situation, and it aims at providing the manufacturing method of ITO powder in which the amount of residual chlorine was further reduced conventionally, and ITO powder.

  In order to achieve the above object, according to the present invention, the co-precipitated hydroxide of indium and tin produced by mixing an acidic solution and an alkaline solution of indium and tin using tin chloride as a tin raw material is washed and dried. In the method for producing tin-doped indium oxide powder by firing, the coprecipitated hydroxide after washing and drying is washed with ammonia water having a pH of 9 to 12, followed by washing and drying. A method for producing a tin-doped indium oxide powder is provided.

  In the method for producing the tin-doped indium oxide powder, the coprecipitated hydroxide is preferably washed with water. In the acidic solution of indium and tin, indium chloride or indium nitrate is preferably used as an indium raw material. The alkaline solution is preferably an aqueous ammonia solution. The heat treatment is preferably performed in an inert gas containing a reducing gas.

According to another aspect of the present invention, there is provided a tin-doped indium oxide powder produced by the method for producing a tin-doped indium oxide powder described above, wherein the residual chlorine content is 20 mass ppm or less. The

  In the tin-doped indium oxide powder, the coprecipitation hydroxide is preferably washed with water. In the acidic solution of indium and tin, indium chloride or indium nitrate is preferably used as an indium raw material. The alkaline solution is preferably an aqueous ammonia solution. The heat treatment is preferably performed in an inert gas containing a reducing gas.

  According to the present invention, an ITO powder manufacturing method and an ITO powder in which the amount of residual chlorine is further reduced than before are provided. Thereby, even if it is the manufacturing method of the ITO powder which uses the chloride as a starting material, since the ITO powder with which the residual chlorine amount was fully reduced can be manufactured, the ITO powder suitable for electronic materials Can be provided.

  As a result of earnest research, the present inventor has washed the indium-tin coprecipitated hydroxide produced by mixing an acidic solution of indium and tin using tin chloride as a tin raw material with an alkaline solution, and after drying It was found that the amount of chlorine remaining as an impurity in the ITO powder after the baking treatment is reduced by washing with an aqueous ammonia solution. Hereinafter, the manufacturing method of the ITO powder according to the present invention will be described in detail.

In the embodiment of the method for producing ITO powder according to the present invention, a soluble indium compound and a soluble tin compound are used as starting materials. As the soluble tin compound, tin chloride is used, but it is preferable to use stannous chloride (SnCl ₂ ) in order to increase oxygen deficiency and produce a lower resistance ITO powder. Further, there are chlorides, sulfates, nitrates and the like as soluble indium compounds, but in the case of preparing a mixed solution with tin chloride, indium chloride (InCl ₃ ) or indium nitrate (In (NO ₃ ) ₃ ) is preferable.

A ratio in which an aqueous solution of tin chloride and a soluble indium compound as described above is 0.1 to 30% by mass, preferably 2 to 15% by mass in terms of SnO _{2 in} terms of SnO ₂ after firing. Create by mixing with. The reason why the Sn content of the ITO powder is 0.1 to 30% by mass in terms of SnO ₂ is that good conductive powder cannot be obtained outside this range.

  The indium-tin co-precipitated hydroxide is obtained by mixing the indium-tin acidic solution thus obtained and the alkaline solution and stirring and reacting them. As the alkaline solution to be mixed, an aqueous solution or mixed solution of ammonia water, sodium hydroxide, potassium hydroxide, ammonium carbonate, ammonium bicarbonate or the like can be used, but if the metal component enters, conductivity is inhibited. Therefore, an aqueous solution of ammonia water, ammonium salt, ammonium carbonate or the like or a mixed solution thereof is preferable. Furthermore, it is more preferable to use an aqueous ammonia solution so that the influence of other ions can be reduced in order to exert more effect in removing chlorine in the washing step.

Next, the obtained indium-tin coprecipitated hydroxide is washed by decantation with pure water, etc., dehydrated, and then dried. Drying can be performed at a temperature of 110 ° C to 250 ° C. The indium-tin coprecipitated hydroxide after drying is washed with ammonia water having a pH of about 9 to 12, further washed with pure water, and then dried again. The reason why the dried coprecipitated hydroxide is washed with ammonia water is to further reduce chlorine, which is an impurity in the coprecipitated hydroxide. As a result, the surface of the coprecipitated hydroxide particles becomes active due to the loss of moisture compared to the coprecipitated hydroxide before drying, and the residual chlorine content of the coprecipitated hydroxide particles and ammonium ions are more likely to react with each other. It is estimated that the amount is further reduced. Further, the pH of the ammonia water is preferably about 9 to 12. However, when the pH of the ammonia water is less than 9, a sufficient cleaning effect (chlorine removal effect) cannot be obtained. This is because dissolution of the product occurs and the yield may be reduced. Thus, by washing with ammonia water, the chlorine content remaining in the coprecipitated hydroxide can be efficiently removed as ammonium chloride. The ammonium chloride can be replaced and removed by washing with pure water. In this way, by washing the coprecipitated hydroxide after drying with aqueous ammonia, the residual chlorine content in the ITO powder finally obtained by the firing treatment can be reduced to 20 ppm by mass or less.

Next, the coprecipitated hydroxide that has been washed with the aqueous ammonia and dried is calcined. Baking is performed by holding at a temperature of 500 to 800 ° C. for 0.5 hours or more in a baking atmosphere described later. In this firing process, a mixed gas of an inert gas and a reducing gas is used as the atmosphere in the furnace. The mixed gas can contain moisture. Nitrogen (N ₂ ), argon, carbon dioxide, or the like can be used as the inert gas, but it is preferable to use N ₂ which has characteristics and costs. At a temperature lower than 500 ° C., the above inert gas can be used as the atmospheric gas.

By making the inside of the furnace into a reducing atmosphere by containing a reducing gas in the inert gas, if only the inert gas is used, the obtained ITO powder may not be able to sufficiently generate oxygen deficiency, This is for causing sufficient oxygen vacancies in the ITO powder. As the reducing gas contained in the inert gas, hydrogen (H ₂ ), carbon monoxide (CO), ammonia (NH ₃ ), and the like can be used, but NH ₃ gas having a relatively low reducing power is used. preferable. As the amount of the reducing gas to be contained, it is preferable to add 0.005 to 5 volumes of reducing gas with respect to 100 volumes of inert gas, and more preferably 0.01 to 0.4 volumes. Reducing gas of 0.005 to 5 volumes is preferable because oxygen vacancies cannot be sufficiently generated if the volume is less than 0.005 volume, and reduction to indium oxide or indium metal tends to occur if the volume exceeds 5 volumes. It is because it becomes easy to sinter partially.

In addition, the inclusion of moisture in the inert gas reduces the influence of H ₂ O generated during the decomposition of the hydroxide, makes the atmosphere uniform, reduces variations in the physical properties of the oxide, and provides good transparency. This is to obtain the properties and dispersibility. That is, when the firing temperature is high, the sintering progresses during firing and the agglomeration becomes intense. When the obtained ITO powder is dispersed to form a paint, a dispersion failure occurs and the problem is that it is deposited in the paint. However, this problem can be suppressed by adding moisture to the firing atmosphere. The amount of water to be contained may be, for example, about the saturated water vapor pressure at room temperature, and it is preferable to add 0.05 to 10 volumes of water to 100 volumes of inert gas, and 0.5 to 5 volumes of water. It is more preferable to add. When moisture is present in the atmosphere together with NH ₃ gas in this way, adsorption of NH ₃ to the air flow rising portion in the furnace is hindered, and as a result, excessive sintered portions are reduced and the surface characteristics of the particles are controlled. Thus, it is possible to obtain an ITO powder having low resistance and good dispersibility.

The firing temperature is in the range of 500 to 800 ° C. The depreciation of the coprecipitated hydroxide occurs in the range of 300 to 400 ° C. If the firing temperature is lower than 500 ° C., the resistance of the powder obtained by insufficient firing. When the firing temperature is higher than 800 ° C., the sintering and aggregation progress, and the resulting powder has poor dispersibility, and the particles are not dispersed by sintering. This is because the diameter becomes large and the visible light transparency when formed into a coating film cannot be obtained.

  In the firing step, the flow rate of the aeration gas is preferably 1.0 ml / min · g (amount supplied per minute per 1 g of dry coprecipitated hydroxide) or more. When the flow rate of the aeration gas is 1.0 ml / min · g or more, the atmosphere can be made uniform, partial sintering can be suppressed, and powder with good dispersibility can be obtained. This is because if it is less than 0 ml / min · g, variations in atmosphere occur in the firing furnace, resulting in uneven characteristics.

  In the ITO powder produced by the process described above, the residual chlorine content can be reduced to 20 ppm by mass or less, and can be suitably used, for example, for electronic materials. In an electronic device manufactured by an electronic material using ITO powder containing a lot of chlorine, corrosion and elution of metal are likely to occur, and deterioration with time is also likely to occur in a resin mixed with ITO powder. The use of ITO powder with reduced residual chlorine as the electronic material is very effective in solving these problems.

  As mentioned above, although an example of embodiment of this invention was demonstrated, this invention is not limited to the form mentioned above. It is obvious for those skilled in the art that various modifications or modifications can be conceived within the scope of the idea described in the claims, and these naturally belong to the technical scope of the present invention. It is understood.

  In the above embodiment, an indium-tin coprecipitation hydroxide is obtained by mixing an indium-tin acidic solution and an alkaline solution, and stirring and reacting, and then the indium-tin coprecipitation hydroxide obtained. The case where the product is washed by decantation with pure water, dehydrated, and then dried has been described. However, washing of the indium-tin coprecipitated hydroxide is not necessarily performed by decantation with pure water. . For example, a known cleaning method such as mixing the indium-tin coprecipitated hydroxide with water to obtain a slurry, and solid-liquid separation of the slurry with a filter press or the like can be employed. The solvent used for washing is not limited to water, but water is preferable from an economical viewpoint.

  Hereinafter, based on an Example, the manufacturing method of the ITO powder by this invention is demonstrated in detail.

[Example 1]
67.5 g of indium metal is heated and dissolved in an aqueous hydrochloric acid solution to form an aqueous solution of indium chloride (InCl ₃ ). In this solution, 13.6 g of stannous chloride dihydrate (SnCl ₂ .2H ₂ O) (ITO after firing) The proportion of the tin content in the powder was 10% by mass in terms of SnO ₂ ) was mixed and dissolved, and pure water was added to prepare 1643 g of an indium-tin mixed aqueous solution. Further, an aqueous ammonia solution was prepared by adding 256 g of ammonia water (concentration: 25% by mass) to 2100 g of pure water. Next, while stirring the aqueous ammonia solution at 50 ° C., the indium-tin mixed aqueous solution adjusted to 45 ° C. was added and reacted for 150 seconds to produce indium-tin coprecipitated hydroxide. The obtained coprecipitated hydroxide was washed repeatedly by decantation with pure water, dehydrated by filtration, and dried at 250 ° C. Next, the dried coprecipitated hydroxide was put into 4 L of a 0.34 mol / L aqueous ammonia solution, stirred, filtered, washed with pure water, dehydrated, and dried at 110 ° C. Thus, a coprecipitated hydroxide which was washed with aqueous ammonia and dried was obtained.

The obtained coprecipitated hydroxide, which was washed with ammonia water and dried, was charged into a tubular furnace, and N ₂ gas was flown at a flow rate of 125 ml / min · g (amount supplied per minute per 1 g of dry coprecipitated hydroxide) in the furnace. The temperature was raised. When the furnace temperature reached 400 ° C., and 0.05 volume of NH ₃ gas to the _{N 2} gas 100 volumes of gas supplied into the furnace, a 1.5 volume relative to _{N 2} gas 100 volumes Water vapor was changed to a gas added to N ₂ gas. Thereafter, the temperature was further raised and maintained at 610 ° C. for 2 hours, and then the addition of NH ₃ gas and water vapor was stopped and the system was cooled. The fired ITO product thus obtained was crushed by a table mill to obtain ITO powder.

About the obtained ITO powder, the residual chlorine content was measured by the method described below (thermal hydrolysis-ion chromatography method).
An ITO powder as a sample was placed in the annular furnace, the inside of the annular furnace was replaced with oxygen gas, and the inside of the annular furnace was set to an oxygen gas atmosphere. Next, the inside of the annular furnace was heated to set the sample temperature to 1100 ° C. Thereafter, water vapor-containing oxygen gas generated by bubbling oxygen gas into pure water was allowed to flow through the annular furnace for 30 minutes. The steam-containing oxygen gas that passed through the annular furnace was bubbled through the sodium hydroxide solution for 30 minutes. The chlorine concentration in the bubbled sodium hydroxide solution was measured with an ion chromatograph (IC25, manufactured by DIONEX). From the chlorine concentration, the amount of sodium hydroxide solution used and the mass of the sample, the chlorine content (residual chlorine amount) in the sample was calculated.
Since the residual chlorine amount in the ITO powder was 17 ppm by this measurement, it was confirmed that the obtained ITO powder was able to sufficiently reduce chlorine as an impurity.

[Example 2]
An ITO powder was obtained by the same production method as in Example 1 except that the aqueous acid solution used for heating and dissolving indium metal was changed from hydrochloric acid to nitric acid. When the amount of residual chlorine was measured by thermal hydrolysis-ion chromatography on the obtained ITO powder, it was below the detection limit of 10 ppm by mass, and the obtained ITO powder was able to sufficiently reduce chlorine as an impurity. confirmed.

[Comparative Example 1]
An ITO powder was obtained in the same manner as in Example 1 except that the co-precipitated hydroxide in Example 1 was not washed with aqueous ammonia after drying at 250 ° C. When the amount of residual chlorine was measured by the thermal hydrolysis-ion chromatography method about the obtained ITO powder, it was 270 mass ppm. As a result, it was found that cleaning with ammonia water after drying the coprecipitated hydroxide in Example 1 was greatly effective in reducing the amount of residual chlorine.

[Comparative Example 2]
An ITO powder was obtained in the same manner as in Example 1 except that the coprecipitated hydroxide was not dried before washing the coprecipitated hydroxide with aqueous ammonia.

When the amount of residual chlorine was measured by the thermal hydrolysis-ion chromatography method about the obtained ITO powder, it was 90 mass ppm. As a result, when the ITO powder prepared by the ITO powder manufacturing method according to Patent Document 1 is compared with Example 1 of the present application and Comparative Example 1, the amount of residual chlorine can be reduced by washing the coprecipitated hydroxide with ammonia water before drying. Although it can be reduced, it has been found that the residual chlorine content of the ITO powder can be further reduced by the production method according to the present invention.

[Comparative Example 3]
After the coprecipitated hydroxide in Example 2 was dried at 250 ° C., it was not washed with aqueous ammonia, and thereafter firing was performed in the same manner as in Example 2 to obtain ITO powder. It was 24 mass ppm when the amount of residual chlorine was measured with the thermal hydrolysis-ion chromatography method about the obtained ITO powder. As a result, even when an indium nitrate aqueous solution is used as a starting material for indium in comparison with Example 2, the amount of residual chlorine can be effectively reduced by washing with aqueous ammonia after drying the coprecipitated hydroxide. all right.

[Comparative Example 4]
As a method effective in reducing the amount of residual chlorine, there is Japanese Patent Application Laid-Open No. 2007-331975, which is not ITO powder but indium oxide. When this method was applied to ITO powder, it was confirmed how much the amount of residual chlorine can be reduced.

In the same manner as in Comparative Example 2, the coprecipitated hydroxide was repeatedly washed by decantation with pure water, poured into 4 L of a 0.34 mol / L aqueous ammonia solution, stirred, filtered, washed with pure water, The coprecipitated hydroxide obtained by dehydration and drying at 250 ° C. was dispersed in a 0.1 mol / L ammonium nitrate aqueous solution, stirred, filtered, washed with water, and dried at 110 ° C.

The dried product of the coprecipitated hydroxide washed with the aqueous ammonium nitrate solution obtained was fired in the same manner as in Example 1 to obtain ITO powder. When the amount of residual chlorine was measured by the thermal hydrolysis-ion chromatography method about the obtained ITO powder, it was 45 mass ppm. As a result, it was found that when the method disclosed in Japanese Patent Application Laid-Open No. 2007-3311975 was applied to the ITO powder, the residual chlorine content could be reduced, but the residual chlorine concentration reducing effect was small as compared with the production method of the present invention. In addition, since there is a washing step with aqueous ammonia before drying the coprecipitated hydroxide, the number of steps is increased compared to the present invention. Was found to be excellent.

  The present invention can be applied to a method for producing tin-doped indium oxide (ITO) powder and tin-doped indium oxide powder.

Claims (6)

Method for producing tin-doped indium oxide powder by washing, drying and firing indium and tin coprecipitated hydroxides produced by mixing indium and tin acidic and alkaline solutions using tin chloride as a tin raw material The method for producing a tin-doped indium oxide powder characterized in that the co-precipitated hydroxide after washing and drying is washed with ammonia water having a pH of 9 to 12, followed by washing with water and drying. The method for producing a tin-doped indium oxide powder according to claim 1, wherein the coprecipitation hydroxide is washed with water. The method for producing a tin-doped indium oxide powder according to claim 1 or 2, wherein in the acidic solution of indium and tin, indium chloride or indium nitrate is used as an indium raw material. The method for producing a tin-doped indium oxide powder according to claim 1, wherein the alkaline solution is an aqueous ammonia solution. The method for producing a tin-doped indium oxide powder according to claim 1, wherein the heat treatment is performed in an inert gas containing a reducing gas. A tin-doped indium oxide powder produced by the method for producing a tin-doped indium oxide powder according to any one of claims 1 to 5, wherein the residual chlorine content is 20 mass ppm or less.