JP4590566B2 - ITO powder and manufacturing method thereof, ITO conductive film paint, and transparent conductive film - Google Patents

Description

  The present invention relates to an ITO powder used for forming a transparent conductive film and a method for producing the same, an ITO conductive film paint containing the ITO powder, and a transparent conductive film formed using the ITO conductive film paint.

  In this specification, ITO is an In oxide containing Sn. The transparent conductive film containing ITO is used as a transparent conductive film for various display devices, solar cells, and the like because it exhibits high transparency and conductivity with respect to visible light. As a method for forming a transparent conductive film using ITO, a physical film forming method for forming the ITO film by sputtering or the like, and a coating film forming method for applying the ITO particle dispersion or an ITO-containing organic compound are known. ing.

The ITO coating film obtained by the coating film formation method has a slightly lower conductivity than the ITO film obtained by a physical film formation method such as a sputtering method, but it is necessary to use an expensive apparatus such as a vacuum apparatus for film formation. In addition, a film having a large area or a complicated shape can be formed. As a result, the ITO coating film obtained by the coating film forming method has an advantage that the cost is low.
Furthermore, among the coating film forming methods, the method using the ITO particle dispersion as the coating does not require thermal decomposition of the coating film as compared with the method using the ITO-containing organic compound as the coating, so that the temperature is relatively low. Films can be formed by the process, and good conductivity can be obtained. Therefore, the method for producing an ITO coating film by applying an ITO particle dispersion is widely used as a film forming method for an electromagnetic wave shielding film of a cathode ray tube, and further, application to a display device such as an LCD or an EL is being studied. Yes.

On the other hand, the composition of ITO particles also affects the conductivity of ITO. There are two types of mechanism of ITO conductivity. The first mechanism is that by replacing In ³⁺ in the ITO crystal with Sn ⁴⁺ , one free electron is generated per substituted Sn atom. The second mechanism creates oxygen vacancies in the ITO crystal, and two free electrons are created for each oxygen vacancy.

The Sn ⁴⁺ and oxygen deficiency increase the density of free electrons that are carriers, and increase the conductivity of the ITO particles. However, the ITO particles to which the oxygen vacancies are imparted have been desired to improve the storage stability of the conductive properties. This is because the ITO particles with oxygen vacancies recombine with oxygen in the atmosphere, the oxygen vacancies are reduced, and the conductivity of the ITO particles is lowered. In addition, since particles with a larger amount of oxygen deficiency react more rapidly with oxygen in the air, the change with time is accelerated, which is one factor that impairs storage stability.

  Next, a manufacturing method according to the prior art of the above ITO particles will be described. As a typical method for producing ITO particles, (1) a step of dissolving an aqueous Sn salt and an aqueous In salt at a predetermined ratio in water and adding a neutralizer to obtain an ITO precursor hydroxide (2) A step of firing the obtained ITO precursor hydroxide at a temperature of 250 ° C. or higher and 1000 ° C. or lower. This firing step is performed in a reducing atmosphere in order to impart oxygen deficiency to the ITO particles.

Here, in Patent Document 1, the specific surface area is 15 m ² / g or more and 30 m ² / g or less, and in the L * a * b * color system defined by CIE (International Lighting Commission), a * is − By using ITO particles having 12 or more, −7 or less, and b * of 15 or more and 25 or less, the reflectance of the visible light reflectance is 1% or less while the electrical resistance value of the film is 10 ³ Ω / □ or less. It is described that it is possible to obtain a transparent conductive film having a preventive property and having little decrease in conductivity due to a change with time.
JP 2005-225700 A

  However, according to the study by the present inventors, the method of obtaining the ITO coating film by applying the ITO particle dispersion liquid is a method having many advantages as described above, but the change in the resistance of the powder over time is large. There were problems with stability, such as the degree of change over time depending on the surrounding environment. That is, it is usually desirable that the ITO particles are not brought into contact with the atmosphere containing oxygen as much as possible, but in practice, it has been thought that it is impossible to avoid contact with the atmosphere at all during handling.

The object of the present invention has been made in consideration of the above-described circumstances, and includes ITO powder containing ITO particles with little change in conductivity over time even in the air, and a method for producing the same, and the ITO particles. An object is to provide an ITO conductive film paint and a transparent conductive film.
In the present invention, unless otherwise specified, the particle diameter of the ITO particles is the BET particle diameter. In addition, as for ITO particle | grains, the actual average primary particle size image by a TEM photograph and a BET particle size show a substantially close value.

The present inventors have intensively studied to solve the above-mentioned problems, and are green compacts of ITO powder molded at a predetermined pressure, after being stored for 1 hour at a temperature of 60 ° C. and a relative humidity of 90%. If the measured resistivity value is R ₁ and the resistivity value measured after storage for 64 hours under the same conditions is R ₆₄ , any ITO powder containing ITO particles with R ₆₄ / R ₁ ≦ 5.00 It was conceived that the ITO coating film obtained by applying the ITO particle dispersion became an ITO coating film with little change in conductivity over time even in the air.
Furthermore, the present inventors gently oxidize the fired ITO particles in an atmosphere having a low oxygen concentration (oxygen concentration of 3.0 vol% or less), thereby creating a thin stabilization layer near the surface of the ITO particles, Thereby, the structure which suppresses the oxidation in ITO particle | grains was conceived. The presence of the stabilizing layer can prevent oxygen deficiency present in the ITO particles from reacting with oxygen in the air when released to the atmosphere, improving the conductivity of the ITO particles, and suppressing the rate of change over time. The present invention has been completed.

That is, the first configuration for solving the above-described problem is:
An ITO powder compact molded at 98.1 MPa was stored for 1 hour under conditions of a temperature of 60 ° C. and a relative humidity of 90%, and the specific resistance value measured by the 4-probe method was R ₁ , and 64 under the same conditions. when the specific resistance value measured after a time storage was R _64,
R ₆₄ / R ₁ ≦ 5.00
It is ITO powder characterized by being.

The second configuration is
The ITO powder according to the first configuration, wherein the value of R ₁ is 1 × 10 ⁻⁴ Ω · cm or more and 1 × 10 ⁻¹ Ω · cm or less.

The third configuration is
The ITO powder according to the first or second structure, wherein the ITO powder contains SnO ₂ content of 20 % by mass or less and a BET particle size of 15 nm or more and 200 nm or less.

The fourth configuration is
When the transmitted color in the visible light region is evaluated by the L * a * b * color system defined by CIE (International Commission on Illumination), the value of b * is −15 or more and 15 or less. The ITO powder according to any one of the first to third configurations.

The fifth configuration is
An aqueous solution of a predetermined ratio is prepared from a water-soluble Sn salt and a water-soluble In salt, and neutralized to obtain an ITO precursor hydroxide. This ITO precursor hydroxide is 250 ° C. or higher in a reducing atmosphere. Firing ITO at 1000 ° C. or lower to obtain ITO particles, and then treating the ITO particles at a temperature of 200 ° C. or lower in an oxygen atmosphere with an oxygen concentration of 3.0 vol% or lower to produce an ITO powder. It is the manufacturing method of the ITO powder characterized.

The sixth configuration is
An ITO conductive film paint comprising the ITO powder according to any one of the first to fourth configurations.

The seventh configuration is
A transparent conductive film manufactured using the ITO conductive film paint according to the sixth configuration.

  The conductive film obtained by applying the ITO conductive film paint obtained by dispersing the ITO particles according to any one of the first to fourth structures in an appropriate solvent has a temporal change in conductivity even in the air. There are few things.

  According to the production of the ITO powder according to the fifth configuration, the ITO powder containing ITO particles having high conductivity and little change with time in the air even in the air is easily produced with high productivity. be able to.

  The ITO conductive film paint according to the sixth configuration can easily form an ITO conductive film having high conductivity and transparency and a low rate of change with time.

  The transparent conductive film according to the seventh configuration has high conductivity and transparency, and a low rate of change with time.

Hereinafter, the best mode for carrying out the present invention will be described.
The ITO powder according to this embodiment is a ratio obtained by measuring the green compact of the ITO powder molded at 98.1 MPa for 1 hour under conditions of a temperature of 60 ° C. and a relative humidity of 90% by a four-probe method. when the resistance value _{R 1,} the specific resistance value measured after storage for 64 hours under the same conditions and with _{R 64,} an _R 64 / R ₁ ≦ 5.00, an ITO powder. The ITO coating film obtained by applying the ITO particle dispersion was an ITO coating film with little change in conductivity over time even in the air.

Furthermore, when the value of R ₁ is an ITO powder having a value of 1 × 10 ⁻⁴ Ω · cm or more and 1 × 10 ⁻¹ Ω · cm or less, the ITO coating obtained by application of the ITO particle dispersion is used. The film was an ITO coating film with little change in conductivity over time and a low resistance.

  When an ITO precursor hydroxide (details will be described later), which is tin-containing indium hydroxide, is calcined, it is almost completely dehydrated at 250 ° C. to produce ITO having a BET particle size of about 15 nm. In principle, low-resistance and stable ITO cannot be expected when firing at lower temperatures. When the firing temperature is increased, ITO particles having a larger particle diameter can be obtained. However, since the ITO is also required to be transparent to visible light, the BET particle diameter of the ITO particles contained in the ITO coating film Is preferably 200 nm or less. This is because if the BET particle size in the ITO coating film is 200 nm or less, the transparency of the ITO coating film to visible light can be sufficiently maintained. From the above, the ITO powder according to this embodiment includes ITO particles having a BET particle size of 15 nm or more and 200 nm or less, more preferably a BET particle size of 15 nm or more and 100 nm or less.

The ITO powder according to the present embodiment preferably contains SnO ₂ at a ratio of 20% or less. SnO ₂ generates carriers and improves conductivity. Further, if SnO ₂ is 20 % by mass or less, there is no significant decrease in carrier mobility.

  The ITO powder according to the present embodiment has a b * value of −15 or more when the transmitted color in the visible light region is evaluated by the L * a * b * color system defined by the CIE (International Lighting Commission). 15 or less. This is because baking of ITO causes oxygen deficiency in the ITO crystal and gradually becomes blue. However, if firing is performed under too strong reducing conditions, InO or the like, which is a black nonconductor, is generated in the ITO, and the electrical conductivity and optical characteristics are deteriorated.

  Usually, ITO particles fired in a firing furnace have oxygen vacancies. However, oxygen vacancies in the ITO particles tend to decrease after reacting with oxygen in the atmosphere after being taken out from the furnace, and the conductivity tends to decrease.

  Here, the present inventors treat the ITO particles in a low oxygen concentration atmosphere before the fired ITO particles react with oxygen in the atmosphere to reduce oxygen deficiencies in the ITO particles. We have come up with a new configuration that allows a slow reaction with oxygen in an oxygen-concentrated atmosphere. And it discovered that an oxygen deficiency in the said ITO particle | grain can be made to react slowly with the oxygen in the said low oxygen concentration atmosphere, and the time-dependent fall of electroconductivity can be suppressed in oxygen presence, such as in air | atmosphere. This is because "(1) a thin stabilization layer is formed in the vicinity of the surface of the ITO particles by a slow reaction with oxygen in the low oxygen concentration atmosphere", "(2) the stabilization layer is the ITO. It is thought that this is because the particles react with oxygen in the atmosphere to reduce oxygen deficiency in the ITO particles.

Specifically, the stabilization treatment in which a stabilization layer is formed in the vicinity of the surface of the ITO particles described above specifically means that the ITO particles after completion of firing are exposed to an atmosphere having a low oxygen concentration of up to 3.0 vol% before being released to the atmosphere. It is to let you. And it is thought that the mild oxidation process can be performed on the ITO particles by the stabilization process.
The oxygen concentration in the stabilization treatment is preferably started from a low concentration of about 0.1 vol%, for example, and the concentration is increased stepwise or gradually so as not to cause a rapid exothermic reaction. Further, when firing in a strong reducing atmosphere in the preceding firing step, the amount of oxygen vacancies in the ITO particles increases, so that even in an atmosphere with a low oxygen concentration, stronger heat generation is accompanied. Since this heat generation has the effect of reducing the conductivity of the ITO particles after the stabilization treatment, the initial concentration of oxygen addition is adjusted to the low oxygen side so that the heat generation becomes as small as possible, and the subsequent increase in concentration is moderate. It is desirable to make it.

As described above, when a reducing gas such as NH ₃ gas, H ₂ gas, or CO gas is added to the furnace at a predetermined concentration in the ITO particle firing step, the amount of oxygen vacancies in the ITO particles can be adjusted. it can. By performing the addition of the reducing gas and the stabilization treatment in a low oxygen concentration atmosphere, it is possible to achieve both adjustment of conductivity and stability over time. Specifically, the specific resistance of the green compact molded at a pressure of 98.1 MPa by setting the firing temperature to 450 to 1000 ° C. and the NH ₃ gas concentration to 0.5 to 1.0 vol% is 1 × 10 ⁻¹ to 1 × 10 ⁻⁴ Ω · cm, and by performing the above-described stabilization treatment, the aging rate R ₆₄ / R ₁ can be reduced to a range of 5.00 or less.

[Production method of ITO particles of this embodiment]
First, as a first step, a prescribed amount of water-soluble Sn salt and water-soluble In salt are weighed and mixed, and then dissolved in pure water to obtain an aqueous solution. And the said aqueous solution is made to react with the alkali which is a neutralizing agent, and the slurry containing Sn hydroxide and In hydroxide is produced | generated.
Here, typical salts of water-soluble Sn and In are hydrochloride, sulfate, nitrate, etc., among which hydrochloride is preferable. In addition, ammonia, caustic soda, caustic potash, or carbonates thereof are used as the neutralizing agent, but from the viewpoint of improving the cleaning properties of the slurry of Sn hydroxide and In hydroxide after the neutralization reaction. Preferably, ammonia is used.

  The produced mixed slurry of Sn hydroxide and In hydroxide is collected by solid-liquid separation, and impurities are washed by pure water washing to obtain an ITO precursor hydroxide cake with improved purity. The obtained ITO precursor hydroxide cake is granulated and dried at a temperature of 100 ° C. or higher to obtain a dried powder of ITO precursor hydroxide.

In the ITO precursor hydroxide, Sn may be substituted with (1) In atom of In hydroxide, but (2) SnO ₂ or Sn hydroxide is coprecipitated with In hydroxide. (3) SnO ₂ or Sn hydroxide may be a mixture of In hydroxide and amorphous.

The particle size of the ITO precursor hydroxide is determined by the wet process for obtaining the hydroxide described above, but the particle size and shape are adjusted mainly by controlling the reaction temperature, reaction pH, and liquid concentration. be able to.
Preferably, one of the methods for obtaining fine particle monodispersed ITO precursor hydroxide is that a stock solution in which chlorides of In and Sn are dissolved in an NH ₃ aqueous solution of about twice the reaction equivalent amount is used. This is a method of adding in about a minute and performing a reverse neutralization reaction. At this time, when the reaction temperature is 20 to 70 ° C., the NH ₃ concentration is 1 to 10 % by mass , and the stock solution concentration is about 1 to 10 % by mass in terms of ITO, fine particle monodisperse precursor hydroxide of ITO is contained in the reaction solution. Precipitate.

Next, the step of firing the obtained ITO precursor hydroxide, which is the second step, will be described.
The purpose of the firing step is (1) to convert the ITO precursor hydroxide to ITO, which is an oxide, (2) to adjust the particle size of the obtained ITO particles, and (3) to the resulting ITO crystals. Giving oxygen deficiency. Therefore, the firing step is preferably performed in a weak reducing atmosphere in which an inert gas and a reducing gas are mixed in order to give oxygen deficiency to the ITO crystal.

As the weak reducing atmosphere, a mixed gas in which an inert gas such as nitrogen, helium, or argon is mixed with a reducing gas such as hydrogen, carbon monoxide, or ammonia gas is usually used. The mixing ratio of each gas in the mixed gas varies depending on the amount of oxygen deficiency to be imparted to the ITO crystal. However, if the reducing power of the mixed gas is too strong, the tin-containing indium hydroxide becomes InO, metal In, or the like. Moreover, it is desirable that the standard of the mixing ratio of hydrogen, carbon monoxide, or the like is such that the mixed gas does not exceed the explosion limit in the atmosphere. Preferably, an appropriate amount of oxygen can be imparted to the crystal by performing the reaction under N ₂ atmosphere containing NH ₃ in an amount of 0.2 to 5.0 vol% (more preferably 0.5 to 1.0 vol%).

  The firing temperature in the firing step is performed under conditions of 250 ° C. or more and 1000 ° C. If it is 250 degreeC or more, a perfect oxide can be obtained, and if it is 1000 degrees C or less, intense sintering between ITO particles can be avoided. Preferably it is 400 degreeC or more and 800 degrees C or less. The ITO particles produced by the firing step have a larger particle size as the sintering temperature increases as the firing temperature increases.

Here, a method for controlling the particle size of the ITO particles to a predetermined size will be further described.
Methods for controlling the ITO particle size to a predetermined particle size are roughly divided into the following two methods.
The first method is a method of synthesizing a fine ITO precursor hydroxide having a BET particle size of about 5 to 15 nm and controlling the firing temperature when firing the ITO precursor hydroxide to form ITO. The second method is to synthesize ITO precursor hydroxide tin-containing indium hydroxide having a predetermined particle size and good crystallinity, and firing while maintaining the particle size of the ITO precursor hydroxide. This is ITO.

In the first method, the firing temperature is usually 450 ° C. to 1000 ° C., but the higher the firing temperature, the finer ITO particles are sintered together, so that ITO particles having a large particle size are generated.
The BET particle size when calcined in an N ₂ atmosphere containing 0.5 vol% NH ₃ is about 15 nm at 450 ° C., about 25 nm at 600 ° C., and about 50 nm at 800 ° C., and the particle size increases with increasing temperature. To do.

The second method is a method of generating ITO precursor hydroxide particles having a predetermined particle diameter by controlling the temperature of the reaction liquid, the reaction time, and the reaction pH during the synthesis of ITO precursor hydroxide particles. is there. By firing the obtained ITO precursor hydroxide particles having a predetermined particle size at a relatively low temperature of 250 ° C. to 550 ° C., ITO particles can be obtained while maintaining the shape and particle size of the hydroxide. it can.
For example, when the reaction is carried out under conditions of a reaction temperature of 10 ° C., a reaction pH of 7, and a neutralization time of 1 hour, columnar particles having a major axis of 200 to 250 nm and a minor axis of about 20 nm can be obtained.
Alternatively, when the reaction is carried out under conditions of a reaction temperature of 10 ° C., a reaction pH of 9, and a neutralization time of 1 hour, plate-like particles having a particle diameter of about 50 to 100 nm can be obtained.

The third step is a step of stabilizing the obtained ITO particles.
When the ITO particles are subjected to stabilization treatment, the ITO particles obtained by the above-described method are baked and then kept in a furnace, and at a predetermined temperature of 200 ° C. or lower, the oxygen concentration (oxygen concentration 3. The stabilization treatment can be easily performed by circulating a gas having an atmosphere of 0 vol% or less.
For example, after firing the ITO, it is cooled in an N ₂ gas atmosphere, and at a predetermined temperature, it is first replaced with an N ₂ gas atmosphere containing 0.2 vol% oxygen for 20 minutes, and then an N ₂ gas containing 0.4 vol% oxygen. 5 minutes after replacement with an atmosphere, 5 minutes after replacement with an N ₂ gas atmosphere containing 0.8 vol% oxygen, and finally 10 minutes after replacement with an N ₂ gas atmosphere containing 2.0 vol% oxygen. Stabilization is performed by stepwise atmosphere replacement for a total of 40 minutes.
Alternatively, atmospheric substitution may be used in which the oxygen concentration in the furnace gradually increases from 0.2 vol% to 2.0 vol%.

  The ITO particles obtained by the stabilization treatment are taken out from the furnace and then dispersed by a hammer mill, a ball mill, a homogenizer or the like for monodispersion. At this time, it is preferable to disperse to the primary particle size as much as possible.

  Since the surface of the ITO particles that are not stabilized is active, oxygen is adsorbed in the atmosphere and the conductivity is lowered. However, the stabilized ITO particles have previously been reduced in surface activity, so that the conductivity is deteriorated over time. Deterioration can be suppressed.

[Method for producing paint (coating liquid) using ITO particles of this embodiment]
The ITO particles of the present embodiment are made into a paint as a liquid or paste-like dispersion by being dispersed in a liquid medium using a dispersant. A known method can be applied as the method for forming the paint. As the liquid medium, an organic solvent such as alcohol, ketone, ether or ester or water can be used, and as the dispersant, a surfactant, a coupling agent or the like may be used. The binder may be used as desired, but when used, an epoxy resin, an acrylic resin, a vinyl chloride resin, a polyurethane resin, a polyvinyl alcohol resin, or the like can be suitably used, but is not limited thereto. When dispersing the ITO particles of the present embodiment in a liquid medium, it is preferable to use a dispersing device such as a bead mill.

[Method for producing coating film using coating liquid containing ITO particles of this embodiment]
When applying or coating a liquid or paste-like dispersion containing the ITO particles of this embodiment, a known method such as screen printing, spin coating, dip coating, roll coating, brush coating, spray coating, or the like is used. Can do. For example, when the dispersion is applied onto a substrate, examples of the substrate material include organic polymers, plastics, and glass, and the substrate shape is generally a film. In particular, a polymer film is preferable for a substrate requiring flexibility such as a touch panel. As the polymer film, a film of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, aramid, polycarbonate, or the like can be used.

Example 1
30 ml of a mixed solution containing 1350 g of InCl ₃ and 431.4 g of SnCl ₂ .2H ₂ O (hereinafter referred to as a stock solution) was prepared by preparing In chloride and Sn chloride and having a molar ratio of Sn: In = 15: 85. Adjusted).
On the other hand, as a neutralizing agent for the stock solution, a 45 L NH ₃ aqueous solution containing twice the equivalent amount of In chloride and Sn chloride present in the stock solution was prepared. The stock solution and the NH ₃ aqueous solution were both adjusted to 50 ° C., and the stock solution was added to the NH ₃ aqueous solution over 3 minutes. At this time, stirring of the NH ₃ aqueous solution was continued. The slurry produced by the addition was filtered and then washed with pure water to obtain a wet cake of ITO precursor hydroxide.
This wet cake was granulated and then dried in the atmosphere at 250 ° C. for 12 hours to obtain a dry cake of ITO precursor hydroxide. This dry cake was baked in a baking furnace in the atmosphere at 400 ° C. for 30 minutes, and then the atmospheric atmosphere was replaced with an N ₂ gas atmosphere containing 0.5 vol% NH ₃ at 708 ° C. for 2 hours. Firing was performed.
After this firing, the furnace atmosphere is replaced with N ₂ gas and the furnace temperature is cooled to room temperature (about 25 ° C.), and then the N ₂ gas atmosphere is replaced with an N ₂ gas atmosphere containing 0.2 vol% oxygen. For 20 minutes, then replaced with an N ₂ gas atmosphere containing 0.4 vol% oxygen for 5 minutes, further replaced with an N ₂ gas atmosphere containing 0.8 vol% oxygen for 5 minutes, and finally Substituting with an N ₂ gas atmosphere containing 0 vol% oxygen for 10 minutes, a stabilization treatment was performed with a pattern of 40 minutes in total to obtain ITO particles. Table 1 shows the properties of the ITO particles.

Here, the chromaticity of the ITO particles was measured using reflected light using a colorimeter. In addition, Nippon Denshoku Industries Co., Ltd. Z-300A was used for the measurement type color difference meter. The specific surface area (BET) of the ITO particles was measured using MONOSORB manufactured by QUANTACHROME, and the BET particle size was converted from the value of the specific surface area according to the following formula.
BET particle size = 6 / BET value × 7.13 × 1000 (nm)

(Example 2)
Until the firing, the same operation as in Example 1 was performed, and then the furnace temperature was maintained at 100 ° C. In this state, the stabilization process was performed under the same atmosphere pattern as in Example 1 to obtain ITO particles. Table 1 shows the properties of the ITO particles.

(Example 3)
Until the firing, the same operation as in Example 1 was performed, and then the furnace temperature was maintained at 200 ° C. In this state, the stabilization process was performed under the same atmosphere pattern as in Example 1 to obtain ITO particles. Table 1 shows the properties of the ITO particles.

(Comparative Example 1)
The same operation as in Example 1 was performed until firing, and then the furnace temperature was cooled to 70 ° C. or lower, and the ITO particles were taken out into the atmosphere without performing the stabilization treatment. Table 1 shows the properties of the ITO particles.

(Measurement of resistance value of green compact)
Next, a green compact was manufactured from the ITO powder containing the ITO particles according to Examples 1 to 3, and the resistance value of the green compact was measured. Further, the same measurement was performed on the ITO powder containing ITO particles in Comparative Example 1. The measurement results are shown in Table 2.
Here, the resistance value measurement of the green compact of the ITO powder will be described. 4 g of the above-mentioned ITO powder was filled in a mold having an inner diameter of 25 mm, and a pressure of 98.1 MPa was applied to produce a cylindrical pellet having a diameter of 25 mm. The electric resistance value of the pellet was measured by a four-probe method. The measuring device used was LORESTAHP manufactured by Mitsubishi Chemical.

(Measurement of time-dependent change rate of resistance value of green compact)
Next, measurement of the rate of change with time of the resistance value in the green compact of ITO particles will be described. The green compact whose resistance value was measured was placed in a constant temperature and humidity chamber, and stored at 60 ° C. and 90% relative humidity for a total of 64 hours. For the green compact, the electric resistance value after a lapse of 1 hour after storage as R _1, an electric resistance value after storage X time in the thermo-hygrostat and _{Rx, R X / R 1 ×} 100 (%) From this, the rate of change with time of the electrical resistance value of the green compact was determined. In this example, the rate of change (R ₆₄ / R ₁ ) between R ₁ after 1 hour from storage and R ₆₄ after 64 hours was defined as the rate of change with time.

The measurement results are shown in Table 2 and FIG. FIG. 1 is a graph in which R _X / R ₁ × 100% is plotted on the vertical axis and elapsed time is plotted on the horizontal axis. In FIG. 1, Example 1 is plotted with ■, connected with a solid line, Example 2 is plotted with ▲, connected with a one-dot chain line, Example 3 is plotted with x, and connected with a two-dot chain line, Comparative Example 1 Is plotted with ● and connected with a broken line.

(Evaluation)
Examples 1 to 3 and Comparative Example 1 are evaluated.
As can be seen from Table 2 and FIG. 1, by performing the stabilization treatment, it is possible to suppress an increase in the green compact resistance over time.

  As mentioned above, although this invention was demonstrated based on the said embodiment, this invention is not limited to this.

It is a graph which shows the time-dependent change rate of the resistance value of the green compact containing the ITO particle which concerns on Examples 1-3 and the comparative example 1. FIG.

Claims (7)

An ITO powder compact molded at 98.1 MPa was stored for 1 hour under conditions of a temperature of 60 ° C. and a relative humidity of 90%, and the specific resistance value measured by the 4-probe method was R ₁ , and 64 under the same conditions. when the specific resistance value measured after a time storage was R _64,
R ₆₄ / R ₁ ≦ 5.00
ITO powder characterized by being. The ITO powder according to claim _{1, wherein} the value of R ₁ is 1 × 10 ⁻⁴ Ω · cm or more and 1 × 10 ⁻¹ Ω · cm or less. _3. The ITO powder according to claim 1, comprising ITO particles having a SnO ₂ content of 20 % by mass or less and a BET particle size of 15 nm or more and 200 nm or less.   When the transmitted color in the visible light region is evaluated by the L * a * b * color system defined by the CIE (International Commission on Illumination), the value of b * is -15 or more and 15 or less. Item 4. The ITO powder according to any one of Items 1 to 3.   An aqueous solution of a predetermined ratio is prepared from a water-soluble Sn salt and a water-soluble In salt, and neutralized to obtain an ITO precursor hydroxide. This ITO precursor hydroxide is 250 ° C. or higher in a reducing atmosphere. Firing ITO at 1000 ° C. or lower to obtain ITO particles, and then treating the ITO particles at a temperature of 200 ° C. or lower in an oxygen atmosphere with an oxygen concentration of 3.0 vol% or lower to produce an ITO powder. A method for producing ITO powder, which is characterized.   An ITO conductive film paint comprising the ITO powder according to claim 1.   A transparent conductive film produced using the ITO conductive film paint according to claim 6.

Images