JP4586126B2 - ITO powder and manufacturing method thereof, ITO paint, and ITO 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 paint containing the ITO powder, and an ITO conductive film formed using the ITO paint.

  In this specification, ITO is an indium oxide containing tin. This film containing ITO is used as a transparent conductive film for various display devices, solar cells, and the like because it exhibits high transmissivity 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 the ITO-containing organic compound as an ITO paint It has been known.

  The ITO conductive film obtained by the coating film formation method is slightly lower in conductivity than the ITO film obtained by the physical film formation method such as the sputtering method, but an expensive apparatus such as a vacuum apparatus is used for film formation. In addition, film formation of a large area or a complicated shape is possible. As a result, the ITO conductive film obtained by the coating film forming method has an advantage of low cost. Furthermore, among the coating film forming methods, the method using the ITO particle dispersion as the ITO coating does not require thermal decomposition of the coating film as compared with the method using the ITO-containing organic compound as the ITO coating. The film can be formed by a low temperature process and good conductivity can be obtained. Therefore, an ITO conductive film manufacturing method using an ITO particle dispersion as an ITO paint is widely used as a method for forming an electromagnetic wave shielding film of a cathode ray tube, and further applied to display devices such as LCD and EL. It is being considered.

Here, the shape of the ITO particles used in the ITO particle dispersion will be described.
Conventionally, as the shape of the ITO particles used in the ITO particle dispersion, granular ITO powder has been generally used. However, in recent years, in order to further reduce the film resistance, to form a conductive path, the degree of contact between particles. In order to increase the thickness, it has been proposed to use ITO particles having a shape such as a needle shape or a plate shape.

Next, the composition of the ITO particles used in the ITO particle dispersion will be described.
The composition of the ITO particles also affects the conductivity of the ITO conductive film.
There are two types of mechanisms for expressing the conductivity of ITO. The first mechanism is to replace In ³⁺ in the ITO crystal with Sn ⁴⁺ . This substitution results in one free electron per Sn atom. The second mechanism is to create oxygen vacancies in the ITO crystal, and two free electrons are created for each oxygen vacancy.

The Sn ⁴⁺ and oxygen deficiency increases the free electron density is a carrier, and thus to increase the conductivity of the ITO conductive film. However, the ITO particles provided with the oxygen deficiency have a problem in storage stability as a powder. This causes the strain energy generated by lattice defects to decrease, that is, the ITO particles imparted with the oxygen vacancies and the oxygen in the atmosphere recombine to cause the oxygen vacancies to decrease. . And the reduction | decrease of the said oxygen deficiency leads to the time-dependent change of the electroconductivity of an ITO electrically conductive film.

Next, a method for producing ITO particles used in the ITO particle dispersion will be described.
As a typical manufacturing method of ITO particles used in paint,
(1) A step of mixing a tin salt and an indium salt at a predetermined ratio, adding water and then adding a neutralizer to obtain tin-containing indium hydroxide,
(2) A step of firing the obtained tin-containing indium hydroxide at a temperature of 250 ° C. or higher and 1000 ° C. or lower,
Some have
The firing step (2) is performed in a reducing atmosphere in order to impart oxygen deficiency to the ITO particles.

Here, in Patent Document 1, by using a mixture of acicular ITO particles and granular ITO particles, the visible light transmittance of 80% or more and 2 while the electrical resistance value of the film is 10 kΩ / □ or less. It is described that an ITO conductive film having a haze of not more than% can be obtained.
Patent Document 2 discloses that ITO powder has a specific surface area of 15 m ² / g or more and 30 m ² / g or less, and in the L ^* a ^* b ^* color system defined by CIE, a *: −12 or more, −7 Hereinafter, b *: using an anti-reflective material containing ITO particles of 15 or more and 25 or less, the film has an electric resistance value of 10 ³ Ω / □ or less, and an antireflection property that the visible light reflectance is 1% or less. It is described that it is possible to obtain a transparent conductive film that has a small decrease in conductivity due to changes over time.
Patent Document 3 describes that ITO particles that exhibit a low electrical resistance value are obtained by surface treatment of ITO particles using an organic solvent or reducing gas and adjusting the amount of oxygen vacancies and surface acidity. Has been.

JP2003-104725 JP 2005-225700 A Japanese Patent No. 3355733

  The method of applying an ITO particle dispersion as an ITO paint to obtain an ITO conductive film is a method having many advantages as described above. However, the ITO conductive film formed by this method is still low in conductivity and has a problem that it cannot be applied to an electromagnetic wave shielding film of a large cathode ray tube or a high-definition electrode of a display device. Accordingly, an object of the present invention is to provide an ITO powder capable of forming an ITO conductive film having high conductivity and little change in conductivity over time even in the air, a method for producing the same, and an ITO conductive film using the ITO powder. It is to provide a paint and a transparent conductive film.

  As a result of researches to solve the above-mentioned problems, the present inventors have obtained primary particles having a predetermined particle diameter in the primary particles of ITO constituting the ITO powder used for forming the transparent conductive film. The present invention has been completed by conceiving that the contact resistance between the primary particles can be reduced by making it exist at a predetermined mixing ratio.

That is, the first means for solving the above-described problem is:
ITO powder used for forming a transparent conductive film,
Among the primary particles of ITO contained in the ITO powder, the abundance ratio of those whose primary particle diameter is 1 nm or more and 20 nm or less is Awt%, and the abundance ratio of those whose primary particle diameter exceeds 20 nm and 100 nm or less. Is Bwt%, 3 ≦ A ≦ 50 and 50 ≦ B ≦ 97 (provided that A + B ≦ 100),
And the difference between the particle size value giving 95% particle size and the particle size value giving 5% particle size in the primary particle size is 30 nm or more,
In addition, the ITO powder is characterized in that the primary particles have a maximum particle size of 200 nm or less.

The second means is
The ITO powder according to the first means having at least two maximum values in the particle size distribution of the primary particles.

The third means is
The ITO powder according to the first or second means, which is a mixture of two or more kinds of ITO powders having different average particle diameters of primary particles.

The fourth means is
When mixing the two or more kinds of ITO powders, the ITO powder having the largest average particle diameter of the primary particles is the first kind component, and the ITO powder having the second largest average particle diameter of the primary particles. As a second type component, and sequentially adding numbers to each ITO powder,
The average particle diameter of primary particles of the ITO powder related to the first type component is R ₁ , the weight of the powder is W ₁ , and the average particle diameter of the primary particles of the ITO powder related to the nth type component and thereafter is R _n , when the total weight of the powder is W _n (n ≧ 2),
(Formula 2)
It is ITO powder as described in the 3rd means characterized by these.

The fifth means is
When mixing the two kinds of ITO powders, the ITO powder having a large average primary particle diameter is the first type component, and the ITO powder having the small primary particle average particle size is the second type component. age,
The average particle diameter of the primary particles of the ITO powder according to the first type component is R ₁ , the weight of the powder is W ₁ , and the average particle diameter of the primary particles of the ITO powder according to the second type component and thereafter is R ₂ , when the total weight of the powder is W ₂ ,
1.0 <R ₁ / R ₂ ≦ 10 and 0.05 ≦ W ₂ / (W ₁ + W ₂ ) ≦ 0.5
It is ITO powder as described in the 3rd means characterized by these.

The sixth means is
As the ITO powder according to the first type component, an ITO powder having an electric resistance value of 0.05 Ω · cm or less of a compressed body obtained by molding the ITO powder according to the first type component at 1 t / cm ² is used. ,
An ITO powder having an electric resistance value of 0.1 Ω · cm or less of a compressed body obtained by molding the ITO powder according to the second type component or later at 1 t / cm ² as the ITO powder according to the second type component or later. The ITO powder according to the fourth or fifth means, wherein the ITO powder is used.

The seventh means is
The measured initial resistance value of the ITO powder 1t / cm ² of were produced by performing pressurized compact (initial compact resistance), the green compact, the temperature 60 ° C., relative humidity When the electrical resistance value after being stored at 90% for 46 hours and changed with time (green compact resistance value after storage) was measured and the rate of change with time was calculated from Equation 1, the rate of change with time was 600% or less. The ITO powder according to any one of the first to sixth means, which is characterized in that it exists.
(Formula 1) Rate of change over time (%) = Green resistance after storage ÷ Initial green resistance × 100

The eighth means is
The ITO powder, it when evaluating the transmission color in the visible light region in CIE (International Commission on Illumination) defines ^{the L} * ^a * ^{b *} color system, ^{b *} value of -15 or more and 0 or less The ITO powder according to any one of the first to seventh means characterized by the above.

The ninth means is
An ITO paint comprising the ITO powder according to any one of the first to eighth means.

The tenth means is
An ITO conductive film comprising the ITO powder according to any one of the first to eighth means.

The eleventh means is
An ITO powder manufacturing method according to any one of the first to eighth means,
Having a step of mixing an ITO powder having an average primary particle diameter of 20 nm or more and 200 nm or less and an ITO powder having an average primary particle diameter of 1 nm or more and 20 nm or less in a predetermined ratio. It is the manufacturing method of the ITO powder characterized.

  The ITO powder according to any one of the first to eighth means exhibits high conductivity when formed into a green compact, and has little change with time in conductivity even in the air.

  According to the ITO paint according to the ninth means, an ITO film having high conductivity and transparency can be easily formed.

  The ITO film according to the tenth means has high conductivity and transparency.

  According to the method for producing ITO powder according to the eleventh means, the ITO powder according to any one of the first to eighth means can be produced easily and with high productivity.

  In the ITO powder according to the present invention, the existing ratio of primary particles having a particle diameter of 1 nm to 20 nm is 3 to 50%, and the existing ratio of primary particles having a particle diameter of 20 nm to 100 nm is 97 to 50%. It has a broader particle size range than the ITO powder related to the technology. Furthermore, in the ITO powder according to the present invention, the value obtained by subtracting the value of the 5% particle diameter from the value of the 95% particle diameter of the primary particles constituting the ITO powder is 30 nm or more. When the ITO powder has such a particle size distribution, the inventors have obtained that the conductivity of the compressed body obtained by compressing the ITO powder is obtained by compressing the ITO powder according to the prior art. It has been found that it exhibits a value greater than the conductivity of the resulting compact.

  Usually, the particle size distribution of ITO powder synthesized in a uniform state can be approximated by a lognormal distribution and has a maximum value of one peak. On the other hand, the ITO powder according to the present invention is composed of a mixture of a plurality of ITO powders synthesized in a plurality of states and having different lognormal distributions. That is, the particle size distribution of the ITO powder according to the present invention is obtained by superimposing the different lognormal distributions, and has a maximum point at least two points in the frequency distribution of particle diameters. That is, if a frequency distribution curve is created, the frequency distribution curve has a shape having at least two peaks. Further, considering the entire frequency distribution of particle diameters, it can be seen that the difference between the 95% particle diameter and the 5% particle diameter is 30 nm or more and has a broad particle size distribution with a broad base. As a result, in the ITO body according to the present invention, ITO powder particles having a plurality of lognormal distributions are mixed in the ITO powder, the porosity between the particles is reduced, and the electrical conductivity is improved. It is thought that it is.

  Based on this knowledge, the inventors of the present invention can use the ITO powder according to the present invention to improve the conductivity of the compressed body of the ITO powder. It was conceived that the conductivity of the ITO conductive film can be improved by manufacturing the film. However, since the ITO conductive film is required to have transparency to visible light in addition to conductivity, the maximum particle diameter of the particles in the ITO conductive film is required to be 200 nm or less. This is because if the maximum particle size of the particles in the ITO conductive film is 200 nm or less, the ITO conductive film can be kept transparent to visible light.

  As a method for obtaining an ITO powder having a particle size distribution having at least two maximum values according to the present invention, in the process of controlling the particle diameter at the production stage of the ITO powder, an intentionally uneven state is obtained. It is possible to create. Specifically, it is conceivable to carry out by widening the temperature distribution in the firing furnace in the firing stage of the ITO powder. Moreover, when adjusting the particle diameter of ITO powder by a wet reaction process, it can also consider performing control which makes the stirring speed in the said wet process extremely slow. However, the above temperature distribution control or stirring speed control in the firing furnace requires very precise control in all cases, and it is difficult to obtain ITO powder having a desired particle size distribution with good reproducibility. .

  Here, in order to produce ITO powder having a particle size distribution having a maximum value of at least two peaks according to the present invention easily and with high productivity at low cost, two or more kinds are used. It has been conceived that ITO powders having different particle size distributions may be mixed and manufactured. The mixing method is performed so that the two or more kinds of ITO powders are sufficiently mixed, and in the mixed ITO powder, secondary particles are pulverized to the primary particle size as much as possible. It is desirable.

  Of the above-mentioned ITO powders having two or more different particle size distributions, the first type of ITO powder is one having relatively large particles with an average primary particle size of 20 nm or more. As the powder after the second type component, at least one having an average primary particle size smaller than the average primary particle size of the first type component is used. Furthermore, it is preferable that the particle size ratio between the average primary particle size of the first type component and the average primary particle size after the second type component is large.

That is, the average particle size of the primary particles contained in the first type component is R ₁ , the average particle size of the primary particles contained in the second type component is R ₂ , and the average of the primary particles contained in the nth type component When the particle diameter is R _n , 20 nm ≦ R ₁ in the first type component powder, R ₂ <R ₁ in the second type component powder, and n type component powder, it is an _{R n} <R _n-1.

Next, the mixing ratio between the first type component and the second and subsequent components will be described.
First, the case where a 1st type component and a 2nd type component are included is demonstrated.
When the first type component and the second type component are included, the two components may be in a relationship satisfying the following formula.
1.0 <R ₁ / R ₂ ≦ 10 and 0.05 ≦ W ₂ / (W ₁ + W ₂ ) ≦ 0.5
W ₁ : Weight of the first component powder
W ₂ : Weight of the second kind component powder

In the general case of including the first type component to the nth type component, it is only necessary that the respective components satisfy the expression 2.
(Formula 2)
W ₁ : Weight of the first component powder
W _n : Weight of powder of the n-th component
n ≧ 2

Hereinafter, the case where a 1st type component and a 2nd type component are included is demonstrated as an example.
In Examples described later, R ₁ / R ₂ = 4.1, 0.05 ≦ W ₂ / (W ₁ + W ₂ ) ≦ 0.5, and R ₁ / R ₂ = 2.7, 0.05 ≦ W ₂ / (W ₁ + W ₂ ) ≦ 0.5 is described, but if the particle diameter ratio R ₁ / R ₂ is 1 or more, there is an effect in improving the geometric packing density. A larger diameter ratio is preferable because it approaches a close-packed structure. However, the smaller the particle size of the ITO particles, the more difficult it is to synthesize and the instability of oxygen deficiency increases. Accordingly, the lower limit of the particle diameter of the ITO particles is naturally limited, and the average particle diameter of the primary particles is at most about 7 nm, preferably about 15 nm or more. On the other hand, considering the transparency of the ITO particles to visible light, the average primary particle size is 70 nm or less, and the maximum particle size is 200 nm or less, preferably 100 nm or less. As a result, a 20nm ≦ _{R 1} ≦ _70nm, the preferred range of R 1 / _{R 2 is, 1.0 <R 1 / R 2} ≦ 10, more preferably is _{1.0 <R 1 / R 2 ≦} 5 .

When the value of W ₂ / (W ₁ + W ₂ ) is 0.05 or more, the mixing amount of W ₂ is ensured to be a predetermined amount or more, and the above-mentioned close-packing is completed, which has the effect of reducing resistance. Demonstrated. Further, since if _{W 2 / (W 1 + W} 2) value of 0.5 or less percentage of fine particles is equal to or less than a predetermined amount, aging rate decreases with time change of the resistance value can be avoided.

  As described above, the effect of mixing the first type component and the second type component has been described. However, the case where the third type component to the nth type component are mixed is considered. In this case, the role of the third and subsequent components is also to fill the voids of the ITO powder of the first type component. Therefore, it may be considered according to the case of the second type component from this viewpoint. As a result, the range of the primary particle diameter in the ITO powder after the second type component to be added is given by the weight average of the ITO powder from the second type component to the nth component. On the other hand, the weight ratio in the ITO powder after the second type component to be added is a ratio to the total from the second type component to the nth type component.

  It is considered that the above-described effect is manifested by mixing the particles having different particle diameters so that the structure of the packed bed of the green compact is closer to the closest packing. The packing density when two or more kinds of spherical particles having different particle diameters are mixed is calculated geometrically, but according to the calculation result, it is possible to blend 20 to 40 wt% of the first kind component particles. The optimum mixing ratio is in good agreement with the optimum mixing ratio in the present invention. Furthermore, according to the geometric calculation, it is possible to mix three or more kinds of particles to achieve a more closely packed structure. However, in consideration of the cost, it is realistic to mix two components.

  Of course, the conductivity of the green compact of each powder of the first type component and the second type component is also important. The higher the electrical conductivity of the green compact of each powder, the higher the electrical conductivity of the ITO powder mixed with them. From this viewpoint, it is preferable that the electric resistance value of the compact of the powder after the second type component does not exceed 0.1 Ω · cm.

Here, the ITO particles have a problem that an oxygen deficient state becomes unstable when it becomes small.
This is because ITO particles are made conductive by intentionally introducing oxygen vacancies into the crystal. However, when the primary particle diameter is about 30 nm or less, the specific surface area increases and surface oxygen defects occur. It becomes unstable. The oxygen deficiency is unstable especially near the particle surface, the oxygen deficiency is caused by moisture and oxygen in the atmosphere, and the conductivity decreases due to a decrease in the oxygen deficiency due to aging. Conceivable. For example, in the case of ITO particles having a particle diameter of 17 nm reduced and fired by a conventional method, the change over time increases the resistance value by 10 times or more compared to the initial resistance value after 46 hours under the conditions of 60 ° C. and RH 90%. To do.

The inventors of the present invention have a stable oxygen deficient state even if the ITO particles are fine by performing a process for a certain period of time in a low oxygen concentration atmosphere after the ITO powder firing step described below. As a result, it was possible to obtain fine ITO powder having a low resistance change rate.
Specifically, after reducing and firing in a mixed gas atmosphere of ammonia gas and nitrogen gas, cooling is performed to about room temperature, and stabilization treatment is performed in an oxygen atmosphere having a lower concentration than the atmosphere. It is considered that the resistance change rate of the ITO powder is reduced by the treatment because the surface of the ITO particles is covered with an extremely thin stabilization layer.

  On the other hand, in the ITO powder according to the present invention, the oxygen deficiency described above affects the color of the powder. That is, when the powder color is expressed in the L * a * b * color system, if the value of b * exceeds 0, the powder color is yellow, and the powder is in a state with few oxygen vacancies. It shows that. On the other hand, when the value of b * is smaller than 0, the powder color is bluish, indicating that the powder has many oxygen vacancies. According to the study by the present inventors, it was found that in the ITO powder according to the present invention, b * is preferably −15 or more and 0 or less, more preferably −15 or more and −5 or less.

[Production method of ITO powder according to the present invention]
The manufacturing method of the ITO powder according to the present invention will be described.
First, as a first step, a tin salt and an indium salt are weighed and mixed, the mixture is dissolved in pure water to obtain a mixed solution of a tin salt and an indium salt, and a mixed solution of the tin salt and the indium salt; Then, an alkali is reacted to form a slurry of tin hydroxide and indium hydroxide.
In addition, although the salt of tin and indium has hydrochloride, lead sulfate, nitrate, etc., hydrochloride is generally used. As the alkali, ammonia, caustic soda, caustic potash, and carbonates thereof are used. From the viewpoint of reducing impurities after slurry formation of tin hydroxide and indium hydroxide, it is preferable to use ammonia.

  The produced slurry of tin hydroxide and indium hydroxide is collected by solid-liquid separation, and impurities are washed with pure water to obtain a tin-containing indium hydroxide cake with improved purity. The obtained cake is dried at a temperature of room temperature or higher, preferably 80 ° C. or higher, whereby a dry powder of tin-containing indium hydroxide is obtained.

  In the tin-containing indium hydroxide, tin may be substituted for indium hydroxide in (1) indium hydroxide, but (2) tin oxide and / or tin hydroxide coexists with indium hydroxide. In some cases, it is precipitated, and (3) as tin oxide and / or tin hydroxide, it may be an amorphous mixture with indium hydroxide.

  The particle size of the tin-containing indium hydroxide is determined in the step of obtaining a hydroxide, but it is possible to obtain a hydroxide having a desired particle size mainly by controlling the reaction temperature, reaction pH, and reaction temperature. I can do it.

Next, the step of firing the obtained tin-containing indium hydroxide, which is the second step, will be described.
The purpose of the firing step is (1) changing tin-containing indium hydroxide to ITO, which is an oxide, (2) adjusting the particle diameter of the obtained ITO particles, and (3) obtaining the ITO crystals. Giving oxygen deficiency. Therefore, in order to give oxygen deficiency to the ITO crystal, the firing step is performed in a weak reducing atmosphere in which inert gas and reducing gas are mixed. Usually, as the weak reducing atmosphere, a mixed gas in which hydrogen, carbon monoxide, or ammonia gas is mixed with an inert gas such as nitrogen, helium, or argon is 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.

  The firing temperature in the firing step is performed under conditions of 300 ° C. or more and 1000 ° C. If it is 300 ° C or higher, a complete oxide can be obtained, and if it is 1000 ° C or lower, intense sintering between ITO particles can be avoided, so it is possible to disperse ITO powder when coating it. It becomes. Preferably it is 400 degreeC or more and 800 degrees C or less. The ITO particles produced by the firing step have a primary particle size that increases as the firing temperature increases, so that sintering of the particles progresses.

Here, a method for controlling the particle diameter of the ITO particles to a predetermined size will be described.
There are roughly two methods for controlling the particle diameter of ITO particles to a predetermined particle diameter.
In the first method, first, fine tin-containing indium hydroxide having a BET value of about 50 to 150 m ² / g is synthesized, and the firing temperature when firing the tin-containing indium hydroxide into ITO is controlled. Is the method. The second method is a method of first synthesizing a tin-containing indium hydroxide having a predetermined particle diameter and good crystallinity, and firing it into ITO while maintaining the particle diameter of the tin-containing indium hydroxide. It is.

  In the first method, the firing temperature is usually 450 ° C. to 1000 ° C., but the higher the firing temperature, the finer the tin-containing indium hydroxide particles sinter, so the ITO particles having a large primary particle diameter Generate. Therefore, the particle diameter of the primary ITO particles obtained by the first method is determined by the firing conditions. As described above, the average particle size of the primary particles of the first type component is 20 nm or more and coarse particles, and the firing temperature is about 550 to 1000 ° C., preferably 550 to 800 ° C. The firing time is preferably 30 min to 6 hr although predetermined particles are generated if the firing temperature is maintained for 10 min or more. The atmosphere during firing may be a weak reducing atmosphere, and a mixed gas of nitrogen and ammonia or nitrogen and hydrogen is preferable. Furthermore, the range of ammonia is preferably 0.1 to 10% by volume, and the range of hydrogen is preferably 0.01 to 5%.

The manufacturing conditions of the ITO powder after the second type component are within a range of 550 to 300 ° C., and a firing temperature at which a predetermined particle diameter can be obtained is obtained by experiments and firing is performed at the determined temperature. At this time, the atmosphere and time at the time of baking may be the same as in the case of producing the first component.
However, since the second and subsequent components are very fine particles, it is desirable to keep them in a low oxygen state for a certain period of time after being baked and before being exposed to the atmosphere. Specifically, after the firing is completed, the mixture is cooled to 100 ° C. or lower, and then placed in an atmosphere lower than the oxygen concentration in the atmosphere and held for 10 min to 2 hr. The retention treatment increases the stability of oxygen deficiency in the second and subsequent ITO powders.

  In the second method, tin-containing indium hydroxide particles having a predetermined particle diameter are generated by controlling the temperature of the reaction solution, the reaction time, and the reaction pH during the synthesis of tin-containing indium hydroxide particles. By firing the obtained tin-containing indium hydroxide particles having a predetermined particle size at a relatively low temperature of 300 ° C. to 550 ° C., ITO particles can be obtained while maintaining the shape and particle size of the hydroxide. .

  As a specific mixing method of the ITO powder such as the first type component and the second type component produced, for example, in the case of dry mixing, a ball mill or vibration mill, in the case of wet mixing, a ball mill, A sand grinder can be used.

  Furthermore, considering that the ITO powder according to the present invention is used as a coating liquid, the mixing operation is premixing using a V-type mixer or the like, and the ITO powder is converted into primary particles during the coating process. A method of dispersing to a particle size of is also preferred.

  As described above, the ITO powder according to the present invention is composed of ITO powder having a plurality of lognormal distributions synthesized in a plurality of states. As a result, the ITO powder has maximum points at at least two points in the frequency distribution of particle diameters. That is, if a frequency distribution curve is created, the frequency distribution curve has a shape having at least two peaks. Considering the entire frequency distribution of particle diameters, the difference between the 95% particle diameter and the 5% particle diameter is 30 nm or more, and a broad particle size distribution is obtained when the base is wide.

  Of the primary particles of ITO contained in the ITO powder, the abundance ratio of the primary particle diameter is 1 nm or more and 20 nm or less is Awt%, and the primary particle diameter is more than 20 nm and 100 nm or less. When the existing ratio is Bwt%, 3 ≦ A ≦ 50 and 50 ≦ B ≦ 97 (however, A + B ≦ 100), and a particle size value giving a 95% particle size in the primary particle size And the difference between the particle size value giving 5% particle size is 30 nm or more, and the maximum particle size of the primary particles is adjusted to the range of 200 nm or less, so that each ITO powder alone can reach. High electrical conductivity not obtained is obtained.

  Details will be described in Examples, but 25 wt% of the first type ITO powder having a resistance value of 0.041 Ωcm and the second type ITO powder having a resistance value of 0.096 Ωcm are mixed, When the difference in particle size between A = 15, B = 85, 5% particle size and 95% particle size was 80 nm, an ITO powder having a low resistance value of 0.022 Ωcm was obtained.

  In addition, when the particle size distribution of the primary particles is primary particles and the abundance ratio of the particles having a particle diameter of more than 20 nm and not more than 100 nm is Bwt%, 3 ≦ A ≦ 50 and 50 ≦ B ≦ 97 (however, , A + B ≦ 100), a method for improving conductivity is a highly versatile method. Therefore, the present invention is not limited to the ITO powder manufactured by the manufacturing method described above. That is, even when a lower resistance ITO powder manufactured by a different manufacturing method is used as the powder used in the first component and the second component, the resistance value of the first component ITO can be reduced. It is done.

  Further, it is said that the electric resistance value of the coating type film is two orders of magnitude higher in volume resistance value than a general sputtered film. However, when the ITO powder according to the present invention is used as the ITO powder to form a coating film, the difference is reduced to ½ or less. As a result, it is considered that the coating-type film according to the present invention can be applied to some uses where a sputtered film has been conventionally used.

[Example of production method of coating liquid using ITO powder according to the present invention]
The ITO powder according to the present invention is formed into a liquid or paste-like dispersion by dispersing it in a liquid medium using a dispersant. A publicly known method can be applied to 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. When used, an epoxy resin, an acrylic resin, a vinyl chloride resin, a polyurethane resin, a polyvinyl alcohol resin, or the like can be preferably used, but is not limited thereto. When dispersing the ITO powder according to the present invention in a liquid medium, it is preferable to disperse it using a dispersing device such as a bead mill.

[Example of manufacturing method of coating film using coating liquid containing ITO powder according to the present invention]
When applying or coating a liquid or paste-like dispersion containing the ITO powder according to the present invention, a known method such as screen printing, spin coating, dip code, roll coating, brush coating, spray coating or the like is used. I can do it. 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 that requires flexibility such as a touch panel, and the polymer film is a film of polyethylene terephthalate (PET), polyethylene tphthalate (PEN), polyimide, aramid, polycarbonate, or the like. Can be used.

[Measuring method]
(Method for measuring particle diameter of ITO particles)
A method for measuring the particle diameter of ITO particles will be described.
The particle diameter measurement of the ITO particles can be calculated by measuring the size of the ITO particles on a TEM photograph of the ITO particles. The calculation method will be described with reference to FIG. FIG. 1 is a 10,000 times TEM photograph of ITO particles according to the present invention. As is apparent from FIG. 1, the ITO particles are not completely spherical, but the length of the ITO particles (the length indicated by the white arrow in FIG. 1) is measured during the measurement. And the measured value was made into the diameter of the said ITO particle. In addition, it is so preferable that there are many ITO particles to measure, and it is preferable to measure at least 100 or more. In addition, in the said ITO particle | grains, the particle | grain boundary whose particle boundary is not clear was excluded from the object of a measurement.

  Based on the particle diameter measurement results of the ITO particles described above, volume particle diameter distributions of average particle diameter, 5% particle diameter, and 95% particle diameter can be obtained from the particle diameter and the number of particles. Specifically, first, the interval between the maximum primary particle diameter and the minimum primary particle diameter of the ITO particles contained in the sample powder is divided into 10 to 20 particle diameter sections. Next, the total particle amount of the volume ratio of the particle amount contained in each divided section with respect to all particles and the amount of particles having a particle diameter equal to or smaller than the particle diameter of the target section is the volume ratio with respect to the total particle amount. That is. At this time, the frequency distribution table shows the volume ratio of the amount of particles contained in each divided section with respect to all particles, and the total particle amount with the particle amount having a particle diameter equal to or smaller than the particle size of the target section is The cumulative distribution table shows the volume ratio with respect to the total particle amount.

  FIG. 2 is a graph in which a frequency distribution diagram and an integrated distribution diagram of an ITO sample according to Example 3 described later are superimposed. In FIG. 2, the left vertical axis indicates the frequency, the right vertical axis indicates the integration, and the horizontal axis indicates the primary particle size classification. In the horizontal axis, it is convenient to use a logarithmic scale when the particle diameter range is wide.

As shown in FIG. 2, two peaks appear in the frequency distribution diagram of the ITO powder obtained by mixing two kinds of ITO powder. On the other hand, in the cumulative distribution diagram, the total particle amount with the particle amount having a particle size equal to or smaller than the particle size of the target section reaches 5% in terms of the volume ratio with respect to the total particle amount. The particle diameter reaching% is referred to as the average particle diameter, and the particle diameter reaching 95% is referred to as the 95% particle diameter.
In addition, the average diameter of the primary particles measured from the TEM photograph described above and the average particle diameter determined from the BET value measured by the BET method almost coincided.

(Examples 1 to 10)
366 g of indium chloride aqueous solution (InCl ₃ ) having an indium concentration of 18.45 wt% and 22 g of tin chloride (SnCl ₂ ) are weighed and dissolved in pure water to prepare a mixed solution of 1.5 l of indium chloride and tin chloride. did. In the mixed solution, the concentration of tin is 15 mol% with respect to the total of indium and tin.
On the other hand, 275 g of an NH ₃ aqueous solution having a concentration of 25 wt% was diluted with 2100 g of pure water to adjust the liquid temperature to 50 ° C. In the NH ₃ aqueous solution, the amount of NH ₃ is twice the amount necessary to neutralize the mixed solution of indium chloride and tin chloride.
The NH ₃ aqueous solution was stirred, and the mixed solution of indium chloride and tin chloride was added thereto over 3 minutes to obtain a suspension of tin-containing indium hydroxide. The resulting suspension of tin-containing indium hydroxide was collected by filtration and washed with pure water to obtain a tin-containing indium hydroxide cake. The tin-containing indium hydroxide cake was dried at 100 ° C. The specific surface area of the obtained tin-containing indium hydroxide was 90 m ² / g. The tin-containing indium hydroxide was placed in a firing furnace and baked at 520 ° C. for 2 hours in a nitrogen atmosphere containing 0.5% ammonia. After the firing, the inside of the firing furnace is cooled to 30 ° C., and the atmosphere in the furnace is treated with a nitrogen atmosphere having an oxygen concentration of 0.1% for 10 minutes, and then the oxygen concentration in the atmosphere in the furnace is gradually increased for 1 hour. As a result, ITO sample 1 was produced at 20.9%. The properties of the obtained ITO sample 1 are shown in Table 1.

  Here, the chromaticity of the ITO powder was measured by measuring reflected light using a colorimeter. In addition, Nippon Denshoku Industries Co., Ltd. Z-300A was used for the measurement type color difference meter.

  Next, an ITO sample 2 was produced in the same manner as in the production of the ITO sample 1 except that the firing temperature of the firing furnace was set to 612 ° C. Properties of the obtained ITO sample 2 are shown in Table 1.

  Next, an ITO sample 3 was manufactured in the same manner as in the manufacture of the ITO sample 1 except that the baking temperature in the baking furnace was 640 ° C. The properties of the obtained ITO sample 3 are shown in Table 1.

  Furthermore, for the sake of comparison, it is the same as the production of the ITO sample 1, but after the firing was completed, the inside of the firing furnace was cooled to 30 ° C., and then the oxygen treatment was not performed, and the sample was taken out into the atmosphere as it was to produce the ITO sample 4. . Properties of the obtained ITO sample 4 are shown in Table 1.

  Here, 95 wt% of the ITO sample 3 and 5 wt% of the ITO sample 1 were mixed to produce an ITO powder according to Example 1.

  Here, 90 wt% of the ITO sample 3 and 10 wt% of the ITO sample 1 were mixed to produce an ITO powder according to Example 2.

  Next, 75 wt% of the ITO sample 3 and 25 wt% of the ITO sample 1 were mixed to produce an ITO powder according to Example 3.

  Here, 60 wt% of the ITO sample 3 and 40 wt% of the ITO sample 1 were mixed to produce an ITO powder according to Example 4.

  Next, 50 wt% of the ITO sample 3 and 50 wt% of the ITO sample 1 were mixed to produce an ITO powder according to Example 5.

  Next, 95 wt% of the ITO sample 2 and 5 wt% of the ITO sample 1 were mixed to produce an ITO powder according to Example 6.

  Next, 90 wt% of the ITO sample 2 and 10 wt% of the ITO sample 1 were mixed to produce an ITO powder according to Example 7.

  Next, 75 wt% of the ITO sample 2 and 25 wt% of the ITO sample 1 were mixed to produce an ITO powder according to Example 8.

  Next, 60 wt% of the ITO sample 2 and 40 wt% of the ITO sample 1 were mixed to produce an ITO powder according to Example 9.

  Next, 50 wt% of the ITO sample 2 and 50 wt% of the ITO sample 1 were mixed to produce an ITO powder according to Example 10.

  The properties of the ITO powders according to Examples 1 to 10 thus manufactured were measured. The measurement results are shown in Table 1.

  Next, with respect to the manufactured ITO powder according to Examples 1 to 10, the resistance value of the green compact and the rate of change over time of the resistance value of the green compact were measured, and for comparison, ITO samples 1 to 4 were used. The same measurement was performed for. The measurement results are shown in Table 1.

(Measurement of resistance value of green compact)
The resistance value measurement of the green compact of ITO powder will be described.
A pressure of 1 t / cm ² was applied to the ITO powder described above 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 apparatus used was LORESTA HP manufactured by Mitsubishi Chemical.

(Measurement of time-dependent change rate of resistance value of green compact)
The measurement of the rate of change over time of the resistance value in the green compact of the ITO powder will be described.
The green compact of ITO powder produced by the above-described measurement of the electrical conductivity of the green compact was placed in a high-temperature humidity chamber and stored at 60 ° C. and 90% relative humidity for 46 hours. Then, the electrical resistance value immediately after the green compact production is the electrical resistance value of the initial green compact, and the electrical resistance value after storage in the high temperature and humidity chamber is the electrical resistance value of the green compact after time change. The rate of change was calculated, and the rate of change over time in the electrical resistance value of the green compact was determined using Equation 1.
(Formula 1) Rate of change over time (%) = Green resistance after storage ÷ Initial green resistance × 100

(Summary of Examples 1 to 10)
As is clear from the results in Table 1, an ITO powder having a large particle size and an ITO powder having a small particle size are mixed, and among the primary particles of ITO contained in the ITO powder, the primary particle size. Is 1 wt% or more and 20 nm or less, Awt%, and the primary particle diameter is more than 20 nm and 100 nm or less is Bwt%, 3 ≦ A ≦ 50 and 50 ≦ B ≦ 97 (However, when A + B ≦ 100), the green compact resistance value is as low as 0.022 Ω · cm to 0.04 Ω · cm, and the time-dependent change rate of the green compact resistance value is as small as 330% to 520%. It has been found.

That is, compared with the case where each of the ITO samples 1 to 3 is used alone, the green compact resistance value is lower by mixing them at a predetermined ratio than the ITO samples 1 to 3 which are raw materials. An ITO powder having a small rate of change with time was obtained.
On the other hand, ITO sample 4 produced for comparison and measured for properties was greenish yellow, had a high powder resistance of 0.22 Ω · cm, and a rate of change with time of 1200%.
Furthermore, the ITO sample 4 is a sample corresponding to the case where the ITO sample 3 was not subjected to stabilization treatment. This ITO sample 4 has a high powder resistance value, and even when mixed with the ITO sample 3, a transparent conductive film having a low resistance value could not be obtained.

It is a TEM photograph of ITO particles concerning the present invention. It is the graph which piled up the frequency distribution figure and integrated distribution figure of the ITO sample which concerns on this invention.

Claims (11)

ITO powder used for forming a transparent conductive film,
Among the primary particles of ITO contained in the ITO powder, the abundance ratio of those whose primary particle diameter is 1 nm or more and 20 nm or less is Awt%, and the abundance ratio of those whose primary particle diameter exceeds 20 nm and 100 nm or less. Is Bwt%, 3 ≦ A ≦ 50 and 50 ≦ B ≦ 97 (provided that A + B ≦ 100),
And the difference between the particle size value giving 95% particle size and the particle size value giving 5% particle size in the primary particle size is 30 nm or more,
And the ITO powder characterized by the maximum particle diameter of the said primary particle being 200 nm or less.   2. The ITO powder according to claim 1, wherein in the particle size distribution of the primary particles, the ITO powder has at least two maximum values.   The ITO powder according to claim 1, wherein the ITO powder is a mixture of two or more kinds of ITO powders having different average particle diameters of primary particles. When mixing the two or more kinds of ITO powders, the ITO powder having the largest average particle diameter of the primary particles is the first kind component, and the ITO powder having the second largest average particle diameter of the primary particles. As a second type component, and sequentially adding numbers to each ITO powder,
The average particle diameter of primary particles of the ITO powder related to the first type component is R ₁ , the weight of the powder is W ₁ , and the average particle diameter of the primary particles of the ITO powder related to the nth type component and thereafter is R _n , when the total weight of the powder is W _n (n ≧ 2),
(Formula 2)
The ITO powder according to claim 3, wherein: When mixing the two kinds of ITO powders, the ITO powder having a large average primary particle diameter is the first type component, and the ITO powder having the small primary particle average particle size is the second type component. age,
The average particle diameter R ₁ of the primary particles of ITO powder according to the _{first-component,} the weight of the powder W _1, the average particle diameter of primary particles of ITO powder according to later the second-component R ₂ , when the total weight of the powder is W ₂ ,
1.0 <R ₁ / R ₂ ≦ 10 and 0.05 ≦ W ₂ / (W ₁ + W ₂ ) ≦ 0.5
The ITO powder according to claim 3, wherein: As the ITO powder according to the first type component, an ITO powder having an electric resistance value of 0.05 Ω · cm or less of a compressed body obtained by molding the ITO powder according to the first type component at 1 t / cm ² is used. ,
An ITO powder having an electric resistance value of 0.1 Ω · cm or less of a compressed body obtained by molding the ITO powder according to the second type component or later at 1 t / cm ² as the ITO powder according to the second type component or later. The ITO powder according to claim 4 or 5, wherein the ITO powder is used. The initial electrical resistance value (initial green compact resistance value) of the green compact produced by applying a pressure of 1 t / cm ^{2 to} the ITO powder was measured, and the green compact was measured at an air temperature of 60 ° C. and a relative humidity. When the electrical resistance value after being stored at 90% for 46 hours and changed with time (green compact resistance value after storage) was measured and the rate of change with time was calculated from Equation 1, the rate of change with time was 600% or less. The ITO powder according to claim 1, wherein the ITO powder is present.
(Formula 1) Rate of change over time (%) = Green resistance after storage ÷ Initial green resistance × 100 The ITO powder, it when evaluating the transmission color in the visible light region in CIE (International Commission on Illumination) defines ^{the L} * ^a * ^{b *} color system, ^{b *} value of -15 or more and 0 or less The ITO powder according to any one of claims 1 to 7, wherein:   An ITO paint comprising the ITO powder according to any one of claims 1 to 8.   An ITO conductive film comprising the ITO powder according to claim 1. A method for producing the ITO powder according to any one of claims 1 to 8,
Having a step of mixing an ITO powder having an average primary particle diameter of 20 nm or more and 200 nm or less and an ITO powder having an average primary particle diameter of 1 nm or more and 20 nm or less in a predetermined ratio. A method for producing ITO powder, which is characterized.