JP2002201027A - Ito microparticle for daylight screening, method for producing the same, and coating liquid and daylight screening film using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain indium tin oxide (ITO) microparticles for forming a daylight screening film having high transmittance of visible light, low transmittance of daylight and low haze, to obtain a coating liquid capable of forming a film by a simple coating method without using physical film forming method of high cost, and to obtain a daylight screening film using this. SOLUTION: This ITO microparticles are characterized by having <=100 nm average particle size, and a powder color according to L*a*b* colorimetric system (JIS Z8729) of 20 to 52 L*, -4.4 to -0.1 a* and -10 to -3 b*. This coating liquid for forming a daylight screening film is a dispersion of the ITO microparticles in a solvent where a resin binder or an inorganic binder is added. This method for producing ITO microparticles comprises treating ITO microparticles having <=100 nm average particle size at 200 to 300 deg.C for >=10 minutes under inert atmosphere containing an alcohol or, after reducing residual impurities comprising chloride ion, nitrate ion and sulfate ion to 0.6% or less, under inert gas or inert gas containing an alcohol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention requires glass, plastics, and other solar radiation shielding functions such as windows of vehicles, buildings, offices, and general houses, telephone boxes, show windows, lighting lamps, and transparent cases. The present invention relates to indium tin oxide fine particles for solar shading used for a transparent base material to be applied, a coating solution using the fine particles, and a solar shading film.

[0002]

2. Description of the Related Art Conventionally, as a method of removing or reducing a heat component from an external light source such as sunlight or a light bulb, it has been practiced to form a film made of a material that reflects infrared rays on a glass surface to obtain a heat ray reflective glass. Had been The material is FeOx,
Metal oxides such as CoOx, CrOx, TiOx, and A
Metal materials having a large amount of free electrons, such as g, Au, Cu, Ni, and Al, have been selected. However, these materials have the property of simultaneously reflecting or absorbing visible light in addition to infrared rays which greatly contribute to the thermal effect, and thus have a problem in that the visible light transmittance is reduced.

[0003] Transparent substrates used for building materials, vehicles, telephone boxes, and the like require a high transmittance in the visible light region. Therefore, when using the above materials, the film thickness must be extremely thin. Therefore, spray baking and CV
It has been common practice to form a thin film having a thickness of 10 nm using a physical film forming method such as a method D or a sputtering method or a vacuum evaporation method. However, these film forming methods require large-scale equipment and vacuum equipment, have problems in productivity and increase in area, and have disadvantages such as high film manufacturing cost. In addition, the solar shading characteristics (wavelength range 30
Attempting to increase the characteristic of blocking light of 0 to 2100 nm) also tends to increase the reflectance in the visible light region at the same time, giving a glare-like appearance like a mirror and impairing the aesthetic appearance. In addition, many of these materials have high conductivity of the film, and if the conductivity of the film is high, a mobile phone or a T
V, radio and other radio waves are reflected and become unreceivable,
There are drawbacks such as causing radio interference in the surrounding area.

In order to remedy the above-mentioned drawbacks of the prior art, as physical properties of the film, the reflectance of light in the visible light region is low, the reflectance in the infrared region is high, and the conductivity of the film is approximately 10%. ^It was necessary to form a film that could be controlled to ⁶ Ω / □ or more. Antimony tin oxide and indium tin oxide (hereinafter abbreviated as ITO) are known as materials having a high visible light transmittance and an excellent solar shading function. Although these materials have a relatively low visible light reflectance and do not give a glare-like appearance, the reflection and absorption effects of these films in the near infrared region close to visible light are sufficient because the plasma frequency is in the near infrared region. Was not.

[0005] To solve this problem, Japanese Patent Application Laid-Open Publication No. HEI 9-205, discloses a method of using a specific color of ITO powder heat-treated in an inert gas or a weak reducing gas so that light in the near infrared region close to visible light can be reflected and absorbed. JP-A-7-69632, JP-A-Hei-8
No. 41441. According to this method,
Although a low solar radiation transmittance is obtained while maintaining a high visible light transmittance, a material that forms a film having a haze value of less than 1% has not been realized. The haze value is the ratio of the diffuse transmitted light to the total transmitted light, and when this value is high, it appears cloudy to human eyes. Therefore, a film having a haze value of less than 1% has been desired for window materials that require transparency, particularly for vehicles that require more transparency.

[0006]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art, and has a high visible light transmittance, a low solar transmittance, and a low haze value. It is another object of the present invention to provide a coating liquid capable of forming a film by a simple coating method without using an expensive physical film forming method, and a solar shading film using the same.

[0007]

In addition, the present inventors have prepared ITO fine particles having a specific powder color.
Fabrication of highly dispersed membranes allows transmission in the visible light range
Strong in the near-infrared region near the visible light region
Has plasma absorption to minimize transmittance and
Completed the present invention by finding the phenomenon that
did. That is, the solar radiation shielding ITO fine particles of the present invention are:
L recommended by the International Commission on Illumination (CIE)^*a^*b^*
The powder color in the color system (JIS Z8729) is L ^*
Is 20-52, a^*Is -4.4 to -0.1, b^*Is -1
0-3, or L ^*Is 52-80, a^*But -10
−0.1, b^*Is 0 to 20 and the average particle size is 100 n
m or less. The solar shading of the present invention
The coating liquid for film formation is obtained by dispersing the ITO fine particles in a solvent.
And a resin binder or inorganic binder.
It is a dispersion of inders. Furthermore, the solar shading of the present invention
The shielding film contains the ITO fine particles, and
Silicon, zirconium, titanium, etc.
Or multilayer with aluminum oxide film
It may be a solar shading film. According to the above invention, the visible light
Wavelength range of 300 to 2100 nm when transmittance is 80% or more
Is less than 70% and the haze value is 1.0
% Can be realized. In addition, the I of the present invention
The TO fine particles are fine ITO particles having an average particle diameter of 100 nm or less.
Of inert gas containing alcohol or reducing gas.
In a mixed gas atmosphere of
ON, nitrate ion, sulfate ion
0.6% or less, then inert gas or alcohol
Containing inert gas or reducing gas and inert gas
10 minutes at 200 ° C to 300 ° C under mixed gas atmosphere
By performing the above processing, L^*a^*b^*In color system
Powder color^*Is 20-52, a^*Is -4.4 to-
0.1, b^*Is -10 to -3, or L^*Is 52-8
0, a^*Is -10 to -0.1, b^*Is 0 to 20
You.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below. In the ITO fine particles for solar shading of the present invention, the tin content in terms of element is preferably 1 to 15% by weight. If less than 1% by weight, the effect of adding tin is not seen,
On the other hand, if it exceeds 15% by weight, the solid solution of tin becomes insufficient. Further, the average particle size is set to 100 nm or less. If the thickness exceeds 100 nm, the film becomes a light scattering source and fogging of the film, that is, haze occurs, or visible light transmittance is decreased, which is not preferable. In addition, although the particle size is represented by the average particle size here, a fine powder having a small particle size distribution and a small ratio of coarse powder particularly exceeding 100 nm is preferable, and the economically available minimum particle size is The fine particles are about 2 nm, but the lower limit is not limited to this.

The ITO fine particles of the present invention have a powder color L ^* of 2
0 to 52, a ^* is -4.4 to -0.1, b ^* is -10
-3, or L ^* is 52 to 80, a ^* is -10 to-
0.1 and b ^* are set to 0 to 20, and the reasons will be described below. To explain the general interaction between light and electrons in a substance, it is known that a substance has a unique plasma frequency, and light with a wavelength longer than this frequency is reflected and light with a shorter wavelength is transmitted. ing. The plasma frequency ω _p is represented by the following equation 1.

[0010]

[Formula 1] ω _p ² = nq ² / εm (1) where n is the conduction electron density, q is the charge of the electron, ε is the dielectric constant, and m is the effective mass of the electron.

In general, when the density of conduction electrons increases, the plasma frequency increases, so that light at shorter wavelengths is reflected. Conduction electron density is 10 ²² / cm ^{3 for} metal
Since the base is 10 ²¹ / cm ³ for ITO, the reflectance is already high from the visible light region for metals, but the visible light is transmitted and the reflectance is high from the near infrared region for ITO,
It can be used as a solar shading film.

As described in Japanese Patent Application Laid-Open No. 8-41441, an ITO fine particle is converted into an alcohol-containing inert gas,
Alternatively, when treated with a mixed gas of a reducing gas and an inert gas, the powder color changes from yellow to yellow green to light blue to dark blue to dark blue to black, and at the same time, the powder resistance decreases. This is because, when the ITO is treated with the above-described gas, vacancies are generated, and the vacancies act as donors for indium oxide, which is an n-type semiconductor like tin, so that free electrons are generated by the increase of vacancies. Is thought to have increased, and it is expected that there is a deep relationship between the powder color and the conduction electron density, that is, the plasma frequency.

[0013] Then, the relationship between the powder color by the treatment of the ITO fine particles and the solar transmittance when these were formed into a film was investigated in detail, and the optimum conditions for solar shading were determined. The average particle size was 100 nm or less. powder color by ^{the L} * ^a * ^{b *} color system of the ITO fine particles, ^{L *} is 20-52, ^{a *} -4.
4 to -0.1, b ^* is -10 to -3, or L ^* is 5
When 2-80, a ^* was -10 to -0.1, and b ^* was 0 to 20, it was found that the solar radiation transmittance was reduced while maintaining a high visible light transmittance, and the haze value was reduced. .

The processing method for obtaining such a powder color is as follows.
Alcohol is supplied using an inert gas such as nitrogen, argon, helium or the like alone or a mixed gas thereof as a carrier gas, or a mixed gas of a reducing gas and an inert gas is supplied, or chlorine ions or nitrate ions in ITO fine particles are supplied. ,
The amount of residual impurities such as sulfate ions was reduced by 0.6
% Or less, an inert gas alone or a mixed gas thereof, an inert gas containing alcohol, or a mixed gas of a reducing gas and an inert gas is supplied. The alcohol used is not particularly limited, but methanol, ethanol, propanol and the like are preferable from the viewpoint of volatility and cost. The alcohol concentration and the supply amount in the inert gas may be appropriately selected so as to obtain the powder color.

[0015] The processing temperature is in the range of 200 to 300 ° C. When the temperature exceeds 300 ° C., the aggregation and sintering of the ITO fine particles become remarkable. The reduction time may be appropriately selected according to the temperature. However, if the reduction time is too short, a desired powder color cannot be obtained. In addition, before the reduction treatment, if necessary, a baking treatment may be performed in the air beforehand, but the treatment temperature at that time is preferably less than 800 ° C. from the viewpoint of the haze value, and the time is not particularly limited. Absent.

Since impurities such as chloride ions, nitrate ions, and sulfate ions remaining in the ITO fine particles act as a reduction inhibitory factor, especially when reducing with an inert gas alone, it is desirable that the residual amount is large so that the desired powder can be obtained. It takes a long time to color,
Productivity becomes very poor. Therefore, particularly when reducing with an inert gas alone, the amount of residual impurities is reduced by 0.6% by washing.
Or less, preferably 0.3% or less.

The coating liquid of the present invention is obtained by dispersing ITO fine particles in a solvent, but the solvent is not particularly limited, and the coating conditions, coating environment, and when an inorganic binder or a resin binder is contained, It is appropriately selected according to the binder. For example, water, ethanol, propanol, butanol, isopropyl alcohol, isobutyl alcohol, alcohols such as diacetone alcohol, ethers such as methyl ether, ethyl ether, propyl ether, esters, acetone, methyl ethyl ketone, diethyl ketone, cyclohexanone, isobutyl Various organic solvents such as ketones such as ketones can be used, and the pH may be adjusted by adding an acid or an alkali as needed. Furthermore, in order to further improve the dispersion stability of the fine particles in the coating liquid, it is of course possible to add various surfactants and coupling agents.

The type of the inorganic binder or the resin binder is not particularly limited. Examples of the inorganic binder include metal alkoxides of silicon, zirconium, titanium or aluminum, partially hydrolyzed polycondensates thereof, and organosilazanes. As the resin binder, a thermoplastic resin such as an acrylic resin, a thermosetting resin such as an epoxy resin, or the like can be used.

The method of dispersing the ITO fine particles is not particularly limited as long as it is a method of uniformly dispersing the particles in the coating solution, and examples thereof include a bead mill, a ball mill, a sand mill, a paint shaker, and an ultrasonic homogenizer. When the film is formed using this coating liquid, the conductivity of the film is performed along a conductive path passing through the contact portion of the ITO fine particles. Therefore, for example, by adjusting the amount of a surfactant or a coupling agent, The conductive path can be partially cut, and it is easy to lower the conductivity of the film to a surface resistance value of 10 ⁶ Ω / □ or more. The conductivity can also be controlled by adjusting the content of the inorganic binder or the resin binder.

The solar shading film of the present invention comprises the above-described IT
O particles are deposited at a high density to form a film. A resin binder or an inorganic binder contained in the coating solution improves the adhesion of the ITO particles to the substrate after coating and curing, and furthermore, the hardness of the film. Has the effect of improving. Further, a film made of silicon, zirconium, titanium, or a metal alkoxide of aluminum or a partially hydrolyzed polycondensate thereof is further applied as a second layer on the thus obtained film, and silicon, zirconium, By forming an oxide film of titanium or aluminum, IT
O-particles as the main component of the film binding strength and film hardness,
The weather resistance can be further improved.

Further, the film obtained when the coating solution does not contain a resin binder or an inorganic binder has a film structure in which only the above-mentioned ITO fine particles are deposited on a substrate. Although it shows a solar shading effect as it is, silicon,
It is preferable to apply a coating solution containing an inorganic binder or a resin binder such as a metal alkoxide of zirconium, titanium, or aluminum or a partially hydrolyzed polycondensate thereof to form a coating film to form a multilayer film. By doing so, the coating liquid component is formed so as to fill the gap where the ITO fine particles of the first layer are deposited, so that the haze of the film is reduced, the visible light transmittance is improved, and the fine particle base material is formed. Improves binding to

As a method for binding to a film of ITO fine particles alone or a film containing ITO fine particles as a main component, using a film made of a metal alkoxide of silicon, zirconium, titanium, or aluminum or a partially hydrolyzed polycondensate thereof, the following method is used. The coating method is effective from the viewpoint of the easiness of the film process and the cost. The coating liquid contains one or more of metal alkoxides of silicon, zirconium, titanium, and aluminum and partially hydrolyzed polycondensation products thereof in water or alcohol, and the content thereof is the amount of oxide obtained after heating. It is preferably 40% by weight or less in the total solution in terms of conversion. It is also possible to adjust the pH by adding an acid or an alkali as needed. Such a liquid is further applied as a second layer on a film containing ITO fine particles as a main component, and heated, so that silicon,
An oxide film of zirconium, titanium, aluminum, or the like can be easily formed. Further, an organosilazane solution may be used as a binder component used in the coating solution of the present invention or as a coating solution for overcoating.

The coating solution of the present invention and the coating method for forming a film used in the present invention are not particularly limited. For example, any method, such as a spin coating method, a bar coating method, a spray coating method, a dip coating method, a screen printing method, a roll coating method, and a flow coating method, may be used as long as the processing liquid can be applied flat and thinly and uniformly.

When the coating liquid containing a metal alkoxide of silicon, zirconium, titanium, or aluminum as an inorganic binder and a hydrolyzed polymer thereof is applied at a substrate heating temperature of less than 100 ° C., the alkoxide contained in the coating film or In many cases, the polymerization reaction of the hydrolyzed polymer remains uncompleted, and water or an organic solvent remains in the film, causing a reduction in visible light transmittance of the film after heating.
The heating is preferably performed at 0 ° C. or higher, more preferably at a temperature higher than the boiling point of the solvent in the coating solution.

When a resin binder is used, it may be cured according to each curing method. For example, an ultraviolet curable resin may be appropriately irradiated with ultraviolet light, and a room temperature curable resin may be left as it is after application. Therefore, it can be applied to an existing window glass or the like on site.

In the film of the present invention, since the ITO fine particles are dispersed, compared with a film having a mirror-like surface in which crystals are densely filled, such as an oxide thin film produced by a physical film formation method, Reflection in the visible light region is small, and it is possible to avoid giving a glare-like appearance. On the other hand, since the plasma frequency is in the visible to near-infrared region as described above, the accompanying plasma reflection increases in the near-infrared region. When it is desired to further suppress the reflection in the visible light region, a luminous reflectance can be easily formed by forming a low refractive index film such as SiO ₂ or MgF ₂ on the ITO fine particle dispersion film of the present invention. A multilayer film of 1% or less can be obtained.

In order to provide the ultraviolet ray shielding function of the indium tin oxide particles for solar radiation shielding of the present invention, the coating liquid, and the solar radiation shielding film, fine particles of inorganic titanium oxide, zinc oxide, cerium oxide, and the like; One or more of benzophenone and benzotriazole may be added.

The coating liquid of the present invention does not form a target solar radiation shielding film by utilizing decomposition or chemical reaction of coating components due to heat at the time of baking, so that a transparent film having a uniform thickness and a stable characteristic can be obtained. Can be formed.

As described above, according to the present invention, the above properties I
It is possible to produce a film exhibiting a solar shading effect by reducing the TO fine particles. However, since the indium tin oxide fine particles are inorganic materials, they have extremely high weather resistance as compared with organic materials. Even if it is used for the corresponding part, the color and various functions hardly deteriorate.

[0030]

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples. In addition, the visible light transmittance and the sunlight transmittance of the obtained film and the color of the powder (standard light source C, 10 ° visual field) were measured using a spectrophotometer U-4000 manufactured by Hitachi, Ltd. In addition, the haze value is H value manufactured by Murakami Color Research Laboratory Co., Ltd.
It measured using R-200. In the film evaluation, the film was formed using three types of bar coaters having different wire diameters, and the visible light transmittance was 86.
%, The solar transmittance and the haze value were determined from a three-point plot of the film.

Example 1 ITO fine particles having a tin content of 10% by weight, a residual impurity amount of 0.7%, and an average particle diameter of 0.03 μm (manufactured by Sumitomo Metal Mining Co., Ltd.)
25 g was placed in a 500 ml separable flask, heated while supplying methanol-containing nitrogen gas with stirring, and subjected to a reduction treatment at a temperature of 300 ° C. for 5 hours, so that L ^* was 40.16 and a ^* was -2. 821, b ^* is-
7.279 powder-colored ITO fine particles were obtained. Subsequently, 20% by weight of the fine particles, 63.3% by weight of methyl isobutyl ketone, and 16.7% by weight of a dispersant were dispersed in a paint shaker containing 0.3 mm zirconia beads equivalent to a filling rate of 63% for 12 hours. Next, a coating liquid composed of 67.5% by weight of the dispersion, 27.5% by weight of an acrylic resin solution dissolved in methyl isobutyl ketone as a binder, and 5% by weight of a curing agent was coated with bars of numbers 40, 24, and 6, respectively. After coating on a soda lime glass substrate of 100 mm × 100 mm × 3 mm, it is baked at 180 ° C. for 1 hour to form a film a
I got The solar transmittance and haze value of the film a were 6
7.2% and 0.5%.

Examples 2 and 3 The membrane b was prepared in the same manner as in Example 1 except that the alcohol supplied during the reduction treatment was changed from methanol to ethanol.
A film c (Example 3) was obtained in the same manner as in Example 1 except that (Example 2) was changed to propanol. As shown in Table 1, the powder colors L ^* a ^* b ^* of Example 2 were each 39.6.
8, -2.787 and -7.190, and the powder colors L ^* a ^* b ^* of Example 3 were 39.01 and -2.65, respectively.
3, -6.951. Example 2 and Example 3
Had a solar transmittance of 66.4% and 66.5%, respectively, and both had a haze value of 0.5%.

Example 4 A film d (Example 4) was obtained in the same manner as in Example 1 except that the dispersion time in the paint shaker was changed to 24 hours. Table 1
As shown in the figure, the powder color L ^* a of the ITO fine particles of Example 4
^* B ^* is 40.16, -2.821, and -7.2, respectively.
The solar transmittance and the haze value were 6 respectively.
6.4% and 0.4%.

Example 5 A film e (Example 5) was obtained in the same manner as in Example 1 except that the reduction was performed at 250 ° C. for 4 hours. As shown in Table 1, the powder color L ^* a ^* b of the ITO fine particles of Example 5
^* Indicates 43.50, -3.920, -5.473, respectively.
And the solar transmittance and the haze value were respectively 69.0.
% And 0.9%.

Comparative Example 1 A film f (Comparative Example 1) was obtained in the same manner as in Example 1 except that no reduction treatment was performed. As shown in Table 1, Comparative Example 1
The powder color of the ITO fine particles was such that L ^* was 85.14, the solar radiation transmittance exceeded 70%, and the haze value also exceeded 1%.

Comparative Example 2 Reduction temperature in methanol-containing nitrogen gas was 150 ° C.
G in the same manner as in Example 1 except that the
(Comparative Example 2) was obtained. As shown in Table 1, I of Comparative Example 2
The powder color of the TO fine particles had an L ^* of 80, as in Comparative Example 1, and the solar transmittance exceeded 70% and the haze value also exceeded 1%.

Example 6 A film h (Example 6) was obtained in the same manner as in Example 1 except that the reduction was performed at 300 ° C. for 3 hours. As shown in Table 1, the powder color L ^* a ^* b of the ITO fine particles of Example 6
^* Indicates 46.37, -3.753, and -9.124, respectively.
And the solar transmittance and the haze value were respectively 69.0.
% And 0.5%.

Example 7 to Example 8 After washing with 2.8% NH ₄ OH, water was washed six times with 600 ml of ion-exchanged water. The tin content was 10% by weight.
ITO with a residual impurity amount of 0.1% and an average particle size of 0.03 μm
Example 1 Example 1 was conducted except that fine particles (manufactured by Sumitomo Metal Mining Co., Ltd.) were reduced at 300 ° C. for 15 minutes under a flow of nitrogen gas containing methanol.
In the same manner as in Example 1, except that the film i (Example 7) was reduced for 40 minutes, a film j (Example 8) was obtained. Table 1
As shown in Table 7, the powder colors L ^* a ^* b ^* of the ITO fine particles were 39.42, -1.955, and -5.
470, Example 8 was 35.60, -0.893,-
4.586, the solar radiation transmittance and the haze value were 66.9% and 0.5% in Example 7, and 6 in Example 8 respectively.
8.5% and 0.3%.

Comparative Example 3 Example 1 except that a reduction treatment was performed for 5 hours with nitrogen gas alone.
A film k (Comparative Example 3) was obtained in the same manner as described above. As shown in Table 1, the powder colors L ^* a ^* b ^* of the ITO fine particles of Comparative Example 3 were 76.30, -3.636, and 21.680, respectively, and the solar transmittance and haze value were 71.30, respectively. 0%,
1.0%.

Example 9 After washing with 2.8% NH ₄ OH, and washing with water six times with 600 ml of ion-exchanged water, the tin content was 10% by weight.
ITO with a residual impurity amount of 0.1% and an average particle size of 0.03 μm
Fine particles (Sumitomo Metal Mining Co., Ltd.)
A membrane 1 was prepared in the same manner as in Example 1 except that a time reduction treatment was performed.
(Example 9) was obtained. As shown in Table 1, I of Example 9
The powder colors L ^* a ^* b ^* of the TO fine particles are 47.3, respectively.
2, -2.297 and -6.391, and the solar radiation transmittance and haze value were 69.1% and 0.5%, respectively.

Example 10 A silica sol solution obtained by hydrolyzing tetraethyl silicate in the presence of a small amount of hydrochloric acid was applied to a film a obtained in the same manner as in Example 1 with a spin coater (180 rpm), and the solution was heated at room temperature. After drying for 5 minutes, the film was cured at 150 ° C. for 20 minutes to obtain a film m (Example 10). As shown in Table 1, the solar transmittance and the haze value were 68.0% and 0.4, respectively.
%Met.

Comparative Example 4 Tin content: 5.5% by weight, residual impurity content: 0.15%, 0.1%
A film n (Comparative Example 4) was obtained in the same manner as in Example 1 except that indium tin oxide fine particles having an average particle diameter of 0.013 μm in which coarse particles of 2 μm were mixed were used. As shown in Table 1, the powder colors L ^* a ^* b ^* of the ITO fine particles of Comparative Example 4 were 57.22, -4.691, and -9.959, respectively, and the solar radiation transmittance exceeded 70%. And the haze value also exceeded 1%.

Example 11 25 g of ITO fine particles having a tin content of 10% by weight, a residual impurity amount of 0.3% and an average particle size of 0.01 μm were put into a 500 ml separable flask, and 9% of which was stirred with nitrogen as a carrier. By heating while supplying H2 gas and performing a reduction treatment at a temperature of 300 ° C. for 4.5 hours, L ^* becomes 6
6.18, a ^* was -6.352, b ^* was 3.960, and powdery ITO fine particles were obtained. Except for using the fine particles,
A film o was obtained in the same manner as in Example 4. As shown in Table 1,
The solar transmittance and haze value of the film o were 64.5, respectively.
% And 0.3%.

Example 12 A film p was obtained in the same manner as in Example 11, except that the reduction treatment was performed at a temperature of 240 ° C. for 6 hours. As shown in Table 1, the solar radiation transmittance and the haze value of the film p were 67.5% and 0.4%, respectively.

[0045]

[Table 1]

[0046]

As described above, the present invention relates to a specific ITO.
By using fine particles, a film can be formed by a simple coating method without using an expensive physical film forming method, and a film having a high visible light transmittance and a low solar transmittance and a haze value can be provided. Is extremely useful.

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Claims (9)

[Claims] 1. The powder color in the L ^* a ^* b ^* color system is
Indium tin for solar shading, wherein L ^* is 20 to 52, a ^* is -4.4 to -0.1, b ^* is -10 to -3, and the average particle size is 100 nm or less. Oxide fine particles. 2. The powder color in the L ^* a ^* b ^* color system is
L ^* is 52 to 80, a ^* is -10 to -0.1, b ^* is 0
To 20 and an average particle diameter of 100 nm or less. 3. A coating liquid for forming a solar shading film, wherein the indium tin oxide fine particles for solar shading according to claim 1 or 2 are dispersed in a solvent. 4. The coating solution for forming a solar shading film according to claim 3, wherein the binder further comprises an inorganic binder or a resin binder. 5. A solar shading film comprising the indium tin oxide fine particles for solar shading according to claim 1 or 2. 6. The solar shading film according to claim 5, wherein an oxide film of silicon, zirconium, titanium, or aluminum is formed on the solar shading film according to claim 5. 7. The solar cell according to claim 5, wherein the solar radiation transmittance is less than 70% and the haze value is less than 1.0% in a wavelength range of 300 to 2100 nm when the visible light transmittance is 80% or more. The solar radiation shielding film as described. 8. An alcohol-containing inert gas containing indium tin oxide fine particles having an average particle diameter of 100 nm or less,
The method for producing indium tin oxide fine particles for solar radiation shielding according to claim 1 or 2, wherein the treatment is performed at a temperature of 200 to 300 ° C for 10 minutes or more in a mixed gas atmosphere of a reducing gas and an inert gas. . 9. An indium tin oxide fine particle having an average particle diameter of 100 nm or less contains an inert gas or alcohol after the amount of residual impurities comprising chlorine ions, nitrate ions and sulfate ions is reduced to 0.6% or less. In an inert gas or mixed gas atmosphere of a reducing gas and an inert gas, 200
The method for producing indium tin oxide fine particles for solar shading according to claim 1 or 2, wherein the reduction is carried out at a temperature of 300 ° C for 10 minutes or more.