JP6427381B2 - Method of producing ITO particles - Google Patents

Description

  The present invention relates to a method of producing ITO particles having a low volume resistivity when made into a green compact. In the present specification, ITO means indium tin oxide.

  A transparent electrode is used in a display device such as an LCD (Liquid Crystal Display), a PDP (Plasma Display Panel), an organic EL (ElectroLuminescence), and a touch panel. The transparent electrode is often made of a transparent conductive material made of ITO or the like. Such a transparent electrode is usually formed into a film shape by sputtering or the like (see, for example, Patent Document 1). However, the sputtering apparatus is expensive and the deposition efficiency is poor. Instead of this sputtering method, a method of applying a paint containing ITO particles to a substrate has been proposed. However, although this coating method is superior to the sputtering method in terms of productivity, manufacturing cost, utilization efficiency of raw materials, etc., when forming a film with a paint containing ITO particles, the conductive path is due to interparticle contact, As compared with the uniform film formed by the sputtering method, there is a problem that the resistance as the whole conductive film is high because the resistance of the particle interface is high, and the conductivity is inferior.

  In order to solve this problem, methods of manufacturing cube-shaped ITO particles are disclosed (for example, Patent Documents 2 and 3). According to these methods, the ITO particles are formed into a cubic shape, and when a paint containing such ITO particles is applied to a substrate to form a film, the ITO particles are densely arranged in a state of few voids, A transparent conductive film can be obtained in which the resistance of the particle interface is reduced.

JP, 2004-315951, A (paragraph [0002]) JP, 2009-007235, A (summary, claim 1, claim 5) JP, 2011-126746, A (claim 3, claim 5)

  In the method of producing ITO particles shown in Patent Documents 2 and 3, it is necessary to heat treat a precursor containing indium and tin in the presence of an organic solvent at a temperature of 200 ° C. or more. For this reason, the method of producing ITO particles shown in Patent Documents 2 and 3 requires a waste solution treatment of an organic solvent, and also has a problem of requiring a closed heating container such as an autoclave.

  An object of the present invention is to provide a method for producing cubic or rectangular ITO particles in uniform shape under low temperature and normal pressure using an aqueous solvent which is easy to handle waste liquid. Another object of the present invention is to provide a method for producing ITO particles having a low volume resistivity when made into a green compact.

According to a first aspect of the present invention, indium tin hydroxide particles are coprecipitated by keeping the temperature of a mixed aqueous solution in which indium salt, tin salt and urea are mixed at a temperature of 60 to 100 ° C. The liquid coprecipitated is separated into solid and liquid, and the separated indium tin hydroxide particles are dried and then heat-treated to decompose into indium tin oxide precursor particles, and the indium tin oxide precursor particles are exposed to the atmosphere Alternatively , it is a method for producing ITO particles to obtain indium tin oxide particles by heat treatment and reduction in an atmosphere of an inert gas , wherein the reduction includes indium tin oxide precursor particles obtained by the thermal decomposition. Heat treatment at a temperature of 200 to 600 ° C. for 0.5 to 5 hours in a mixed gas atmosphere in which an inert gas of nitrogen or argon and a reducing gas of hydrogen or carbon monoxide are mixed. The concentration of the reducing gas in the mixed gas is a concentration at which the mixed gas does not exceed the explosion limit in the atmosphere, and each particle of the indium tin oxide particles has an average ratio of the minor axis to the major axis The indium tin oxide particles have a volume resistivity of green compact when the pressure is changed in a range of 0.196 to 29.42 MPa. It is characterized by being 2.2 × 10 ^{−2 to} 1.5 Ωcm .

  A second aspect of the present invention is the invention based on the first aspect, wherein the mixed aqueous solution is prepared by adding and mixing a urea aqueous solution to a mixed aqueous solution of an indium salt and a tin salt, and It is the manufacturing method of the ITO particle | grains added so that the reaction equivalent of urea with respect to a salt and the said tin salt may become 2-500 times.

According to the present invention, since ITO particles are produced with an aqueous solvent under normal pressure at a low temperature of 100 ° C. or lower without using the organic solvents shown in Patent Documents 2 and 3, compared to when using an organic solvent The working environment does not decrease at the time of production of ITO particles, there is no need to pay attention to fire handling, waste liquid treatment can be performed easily, and a closed heating container such as an autoclave is not required. Further, according to the method of the present invention, the ITO particles produced from the indium tin hydroxide particles to be produced become cubes or rectangular parallelepipeds with uniform shape and size , and when the ITO particles are formed into a powder compact, The contact area can be increased to lower the volume resistivity.

It is the photography figure which imaged the ITO particle | grains obtained in the Example by SEM. It is the photography figure which imaged the ITO particle | grains obtained by the comparative example by SEM. It is a figure which shows the relationship between an applied pressure and the volume resistivity of an ITO green compact when it is made a green compact by applying a pressure to ITO particle obtained by each of an Example and a comparative example. It is a figure which shows the relationship between applied pressure and the relative density which divided the real density of green compact by theoretical density when it is made a green compact by applying pressure to ITO particle | grains obtained by the Example and the comparative example, respectively.

  Next, an embodiment of the present invention will be described.

The ITO particles of the present invention are produced by the following method. First, as a first step, a mixed aqueous solution of indium salt and tin salt is prepared. As a second step, urea aqueous solution is added to and mixed with this mixed aqueous solution, and the mixed aqueous solution obtained by mixing this urea aqueous solution is kept at a temperature of 60 to 100 ° C. to coprecipitate indium tin hydroxide particles by uniform precipitation. . As a third step, the liquid in which the indium tin hydroxide particles are coprecipitated is separated into solid and liquid. As a fourth step, the solid-liquid separated indium tin hydroxide particles are dried. As a fifth step, the dried indium tin hydroxide particles are heat treated to decompose into indium tin oxide precursor particles. Finally, in a sixth step, indium tin oxide (ITO) particles are obtained by reducing indium tin oxide precursor particles by heat treatment in the atmosphere or in an atmosphere of an inert gas.
In the present invention, a mixed aqueous solution of indium salt and tin salt is prepared, and the mixed aqueous solution is added and mixed with an aqueous urea solution to prepare a mixed aqueous solution, but the indium salt and tin salt are not limited. And urea may be mixed to prepare a mixed aqueous solution. That is, this method
In this method, a predetermined amount of indium salt, tin salt, urea powder or granules is directly charged into a predetermined amount of water and stirred and dissolved to prepare a mixed aqueous solution. The indium salt, tin salt, powder or granules of urea may be mixed and then dissolved, and the water to be dissolved may be preheated to a temperature for keeping warm.

The tin salt in the first step is at least selected from water-soluble anhydrous or hydrate salts of tin such as SnC ₂ O ₄ , SnCl ₂ , SnCl ₄ , Sn (NO ₃ ) ₂ , SnBr ₂ and SnSO _4. One type of tin compound is mentioned. Moreover, as indium tin, water-soluble indium anhydrous salts or indium salts such as In ₂ (C ₂ O ₄ ) ₃ , InCl ₃ , In (NO ₃ ) ₃ , In ₂ (CH ₃ COO) ₃ and In ₂ (SO ₄ ) ₃ At least one indium compound selected from hydrate salts can be mentioned. The mixed aqueous solution of tin salt and indium salt is obtained by weighing and mixing the above-mentioned tin salt and the above-mentioned indium salt in a predetermined ratio, and then separately dissolving tin salt and indium tin in pure water or ion exchanged water to obtain tin salt. An aqueous solution and an indium aqueous solution are prepared, and these aqueous solutions are mixed and prepared. Alternatively, it is possible to prepare a mixed aqueous solution of tin salt and indium salt by dissolving together with tin salt and indium tin weighed and mixed in pure water or ion exchange water at a predetermined ratio. In the first step, seed crystals of an ITO precursor prepared separately can be added.

  The aqueous urea solution in the second step is used as a basic precipitant. The addition amount of this urea aqueous solution is preferably set so that the reaction equivalent of urea to indium salt and tin salt is 2 to 500 times, and considering the time required to complete the reaction, 3 to 200 times More preferable. When the amount is less than 2 times, the coprecipitation amount of indium tin hydroxide particles is small, and when it is more than 500 times, the concentration of the solution is determined according to the solubility of urea. And the control of pH becomes difficult.

  A characteristic feature of the present invention is that the mixed aqueous solution mixed with an aqueous urea solution is kept warm at a temperature of 60 to 100 ° C., preferably 70 to 100 ° C., and a uniform precipitation method is adopted. Here, the homogeneous precipitation method refers to a method of obtaining a homogeneous precipitate from a homogeneous aqueous solution. By precisely controlling the temperature in the reaction system, it is possible to cause this coprecipitation to occur uniformly anywhere in the solution. Conventionally, as a method for obtaining the above coprecipitate, for example, a method in which a basic precipitant such as aqueous ammonia and a mixed aqueous solution of tin salt and indium salt are simultaneously dropped into a water bath (hereinafter referred to as a dropping method). However, when this method is adopted, coprecipitation occurs from the place where the solution is dropped, and therefore, it is not possible to coprecipitate indium tin hydroxide particles having a uniform shape.

However, according to the homogeneous precipitation method of the present invention, it is possible to coprecipitate indium tin hydroxide particles having a uniform shape by the mechanism described below. That is, by maintaining the mixed aqueous solution in which the aqueous urea solution is mixed at a temperature in the above range, the decomposition reaction of urea ((NH ₂ ) ₂ CO) proceeds and ammonia (NH ₃ ) is uniformly generated in the aqueous solution. The generated ammonia uniformly raises the pH of the aqueous solution and decreases the solubility of indium and tin, whereby the indium and tin in the aqueous solution are uniformly coprecipitated, and a suspension of tin-containing indium hydroxide (colloidal liquid) Is generated. This heat retention is performed, for example, in a water bath by heating the above-mentioned mixed aqueous solution contained in a container while stirring. The above temperature range is set because urea does not decompose sufficiently into ammonia if the temperature to be kept is less than 60 ° C, and the temperature does not exceed 100 ° C when an aqueous solvent is used under normal pressure which is one of the purposes. Ru.

  The incubation time of the mixed aqueous solution is 1 hour or more, preferably 5 to 24 hours. If the temperature is kept in the above temperature range for 1 hour or more, urea is decomposed to generate ammonia. The higher the temperature, the shorter the heat retention time, but in order to make the indium tin hydroxide particles uniform in shape, it is preferable to keep the temperature for a long time at a lower temperature within the above temperature range. By controlling the addition amount of urea aqueous solution, the incubation temperature and the incubation time, it is possible to control the size of the produced hydroxide particles and the ratio of the minor axis to the major axis of the particles.

  As a method for solid-liquid separation of a liquid in which indium tin hydroxide particles are coprecipitated in the third step, a centrifugal washing method of putting this liquid in a centrifugal separator and performing solid-liquid separation by centrifugal force is preferable because of high productivity . Alternatively, solid solution is precipitated by placing the solution in which indium tin hydroxide particles are coprecipitated in a container, and then the container is gently inclined to allow only the supernatant liquid to flow several times. May be In this case, decantation is performed by adding and stirring pure water in an amount equivalent to that of the supernatant liquid to be drained off. Impurities such as chloride salts are removed by the solid-liquid separation, and the resistivity of the finally obtained ITO particles can be lowered. Since most of the chloride salt is decomposed and volatilized during the heat treatment of the fifth step described later, removal by centrifugal washing may not be necessary, but the electric furnace used for the heat treatment is not damaged by the salt. As such, it is preferable to sufficiently remove the chloride salt.

  In the fourth step, the indium tin hydroxide particles obtained by solid-liquid separation are dried in the atmosphere, preferably in an inert gas atmosphere such as nitrogen or argon, for 2 to 24 hours in the range of 80 to 200 ° C. . This gives dry particles of indium tin hydroxide.

  In the fifth step, the dried indium tin hydroxide particles are heat-treated (fired) in the atmosphere at a range of 300 to 900 ° C. for 0.5 to 5 hours to be decomposed into indium tin oxide precursor particles. That is, the hydroxide is converted to an oxide. A complete oxide can be obtained at 300 ° C. or higher, and sintering between ITO particles can be avoided at a temperature of 900 ° C. or lower. The preferable heat treatment (baking) temperature is 350 to 800 ° C. If it is less than 0.5 hours, dehydration reaction may not be sufficient. The upper limit of 5 hours is determined from the viewpoint of terminating the dehydration reaction and suppressing sintering of particles.

  In the final sixth step, the indium tin oxide precursor particles obtained by thermal decomposition are reduced by heat treatment in the atmosphere or in an inert gas atmosphere. It is preferable to be under a weak reducing atmosphere in which an inert gas such as nitrogen or argon and a reducing gas such as mixed gas of hydrogen, carbon monoxide, ammonia gas, and alcohol mixed with each other are mixed. The reduction is preferably performed at 200 to 600 ° C. for 0.5 to 5 hours. By this reduction treatment, indium tin oxide (ITO) particles are obtained. By this reduction treatment, the interstitial oxygen of ITO is eliminated, the oxygen deficiency is given to the ITO, and the resistance of the ITO particles is lowered. The mixing ratio of each gas in the mixed gas is appropriately determined by the amount of oxygen deficiency to be imparted to the ITO crystal. However, when the reducing power of the mixed gas is too strong, insulating InO, metal In and metal Sn are precipitated from the ITO precursor, which is not preferable. In addition, the mixing ratio of hydrogen and carbon monoxide is such that the mixed gas does not exceed the explosion limit in the atmosphere.

Through the above steps, the ITO particles of the present invention can be obtained. The ITO particles have a cube or rectangular parallelepiped shape having an average of the ratio of the minor axis to the major axis of the particle (major axis / minor axis ratio) of 1.3 or less. As observed from the whole, in the present invention, since the uniform precipitation method is adopted, the shape and size of each particle are uniform. The resistivity of this ITO particle is measured in the state of a green compact obtained by filling the container with this ITO particle and pressing it. The volume resistivity of the green compact is measured by changing the pressure for forming the green compact in the range of 0.196 to 29.42 MPa ( ² to 300 kgf / cm ² ) and measuring the volume resistivity of the green compact: 2.2 × 10 ⁻² It will be ~ 1.5 Ω cm. Since the ITO particles of the present invention are cubes or rectangular parallelepipeds of uniform shape and size , when made into a green compact, the particles can be densely arranged with few voids, and the resistance at the particle interface is lowered. Lower volume resistivity is obtained as compared with a green compact comprising ITO particles obtained by the dropping method of When the average of the ratio of the minor axis to the major axis of the particles exceeds 1.3, when forming a green compact, the particles can not be densely arranged with few voids, and it is difficult to obtain a low volume resistivity. Become.

  Next, an example of the present invention will be described in detail along with a comparative example.

<Example>
First, InCl ₃ powder was dissolved in ion exchange water to obtain an InCl ₃ aqueous solution adjusted to 0.2M. Also to give a SnCl ₄ solution was adjusted SnCl ₄ powder 0.2M was dissolved in deionized water. 50 ml of an aqueous solution of SnCl ₄ was added to 450 ml of an aqueous solution of InCl _3, and the mixture was uniformly mixed by stirring at room temperature to obtain a mixed aqueous solution. Next, 1000 ml of an aqueous urea solution adjusted to 1.55 M was added to the mixed aqueous solution. The mixed aqueous solution which mixed the urea aqueous solution put into the container in the water bath was arrange | positioned, and it heat-retained at the temperature of 80 degreeC in the water bath for 8 hours, stirring this mixed aqueous solution. This caused a decomposition reaction of the aqueous urea solution, and the ammonia (NH ₃ ) generated in this reaction generated a suspension (colloidal liquid) of tin-containing indium hydroxide. In this example, the amount of urea added was 5 times the reaction equivalent of the metal salt. The final pH of the solution at the end of the reaction was adjusted to 5.5. The formed colloidal solution was subjected to centrifugal washing to perform solid-liquid separation, and the solid-liquid separated indium tin hydroxide particles were dried at 110 ° C. for 15 hours in the air. The dried indium tin hydroxide particles were heat-treated (fired) at 500 ° C. for 2 hours in the air to be decomposed into indium tin oxide precursor particles. After the heat treatment, the indium tin oxide precursor particles were reduced at a temperature of 300 ° C. for 2 hours in a weak reducing atmosphere containing 3 vol% of H ₂ and 97 vol of N ₂ to obtain ITO particles. The photograph which image | photographed this ITO particle by SEM (scanning electron microscope) is shown in FIG.

Comparative Example
In the same manner as in Example, a mixed aqueous solution of InCl ₃ aqueous solution and SnCl ₄ aqueous solution was obtained. The mixed aqueous solution and ammonia (NH ₃ ) water were simultaneously dropped into a water bath of ion exchange water at a liquid temperature of 30 ° C. During the addition, the water bath was adjusted to pH 7 at a liquid temperature of 30 ° C. The addition ended in 60 minutes. Indium tin hydroxide particles were coprecipitated in a water bath by simultaneous dropping of the mixed aqueous solution and aqueous ammonia. The solution in which the indium tin hydroxide particles were coprecipitated was subjected to centrifugal washing, drying, heat treatment and reduction treatment in the same manner as in Example to obtain ITO particles by a dropping method.

<Evaluation of ITO particles>
(1) Shape of ITO Particles The shape of the ITO particles of the comparative example was, as is apparent from FIG. 2, a mixture of various shapes such as spherical, elliptical and rod shapes. On the other hand, the shape of the ITO particles of the example was almost cubic as apparent from FIG. 1, and the ratio of the minor axis to the major axis was 1.2 on average. The ITO particles of the example had the same shape and size as viewed from the whole.

(2) Volume Resistivity of Green Powder Made of ITO Particles The ITO particles obtained in Examples and Comparative Examples were made into green powder. The volume resistivity of the powder compact was measured using a measuring apparatus (MCP-PD51 manufactured by Mitsubishi Chemical Analytic Co., Ltd.) by changing the pressure applied to make the powder compact and changing the pressure applied for each pressure applied. Specifically, a cylinder having an inner diameter φ of 25 mm is filled with 2.00 g of ITO particles, and the pressure is changed in the range of 0.196 to 29.42 MPa ( ^{2 to} 300 kgf / cm ² ) to obtain Examples and Comparative Examples. Each green compact consisting of the obtained ITO particles was prepared at 10 points as a sample. And the surface resistivity and sample thickness of each sample were simultaneously measured, respectively. The applied pressure was measured by a pressure sensor provided in the above-mentioned measuring apparatus, and the surface resistivity was measured by a direct current four-terminal method. The volume obtained from the sample thickness of the ITO particles and the inner diameter φ of the cylinder is divided by the packing mass of the sample to obtain the actual density, and this actual density is divided by the theoretical density to obtain a relative density. FIG. 3 shows the relationship between the applied pressure (horizontal axis) and the volume resistivity (vertical axis), and FIG. 4 shows the relationship between the applied pressure (horizontal axis) and the relative density (vertical axis).

As apparent from FIG. 3, the volume resistivity of the green compact made of ITO particles of the comparative example is 4.5 × 10 3 in the applied pressure range of 0.196 to 29.42 MPa ( ^{2 to} 300 kgf / cm ² ). against ^-2 of a which was ～3.0Omucm, the volume resistivity of the green compact made of ITO particles of example was 2.2 × ¹⁰ -2 ~1.5Ωcm. In particular, when a pressure of 0.98 MPa (10 kgf / cm ² ) was applied, the volume resistivity of the green compact comprising ITO particles of the comparative example exceeded 2.0 Ωcm. On the other hand, the volume resistivity of the green compact made of ITO particles of the example was 2.0 Ωcm or less. From the above, when the coating film is formed on the substrate with the coating material containing the ITO particles of the example, the resistivity of this coating film is the coating material formed with the coating material containing the ITO particles obtained by the dropping method of the comparative example. It is expected to be lower than the resistivity of the film, and it is expected that a highly conductive coating will be obtained. Furthermore, in the example using urea aqueous solution instead of the organic solvent, the working environment did not fall when producing ITO particles, and it was not necessary to pay attention to fire handling.

Claims (2)

A mixed aqueous solution in which indium salt, tin salt and urea are mixed is kept warm at a temperature of 60 to 100 ° C. to co-precipitate indium tin hydroxide particles, and solid-liquid separation of the liquid in which the indium tin hydroxide particles are co-precipitated and, wherein after the separated indium tin hydroxide particles was dried, heat-treated and thermally decomposed in an indium tin oxide precursor particles, indium tin by reducing the indium tin oxide precursor particles to heat treatment a manufacturing method of the ITO particles to obtain the oxide particles,
200 to 600 in the mixed gas atmosphere in which the indium tin oxide precursor particles obtained by the thermal decomposition are mixed with an inert gas of nitrogen or argon and a reducing gas of hydrogen or carbon monoxide in the reduction. The heat treatment is performed by heat treatment at a temperature of 0.5 ° C. for 0.5 to 5 hours, and the concentration of the reducing gas in the mixed gas is a concentration at which the mixed gas does not exceed the explosion limit in the atmosphere,
Each particle of the indium tin oxide particles is a cube or a rectangular solid of uniform shape and size of 1.3 or less in average of the ratio of the minor axis to the major axis,
The indium tin oxide particles have a volume resistivity of 2.2 × 10 ^{−2 to} 1.5 Ωcm when the pressure is changed in a range of 0.196 to 29.42 MPa. Of producing ITO particles. The mixed aqueous solution is prepared by adding and mixing an aqueous urea solution to a mixed aqueous solution of indium salt and tin salt, and adding the aqueous urea solution such that the reaction equivalent of urea to the indium salt and the tin salt is 2 to 500 times producing how the ITO particles according to claim 1,.