JP7417918B2 - Composite tungsten oxide particles - Google Patents

Description

The present invention relates to composite tungsten oxide particles.

Various technologies have been proposed as near-infrared shielding technologies that have good visible light transmittance and reduce solar transmittance while maintaining transparency. Among these, near-infrared shielding technology using inorganic conductive particles has advantages such as excellent near-infrared shielding properties, low cost, and radio wave transparency compared to other technologies.

For example, in Patent Document 1, the general formula M _x W _y O _z (where M is H, He, alkali metal, alkaline earth metal, rare earth element, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh , Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te , Ti, Nb, V, Mo, Ta, Re, Be, Hf, Os, Bi, I, W is tungsten, O is oxygen, 0.001≦x/y≦ An infrared shielding material fine particle dispersion in which composite tungsten oxide fine particles expressed as 1, 2.2≦z/y≦3.0 are dispersed as infrared shielding material fine particles in a medium such as a resin that transmits visible light. , a technique related to a method for manufacturing the infrared shielding material fine particles, etc. is disclosed. Patent Document 1 also discloses an example of an infrared shielding film that is a thin film-like infrared shielding material fine particle dispersion.

According to Patent Document 1, an infrared shielding material fine particle dispersion having excellent optical properties such as more efficiently shielding sunlight, particularly light in the near-infrared region and at the same time maintaining transmittance in the visible light region is produced. It is said that this will be possible. For this reason, it is being considered to apply the infrared shielding material fine particle dispersion disclosed in Patent Document 1 to various uses such as window glass.

Various studies have been made on methods for producing composite tungsten oxide particles useful as near-infrared shielding materials.

For example, the inventor of Patent Document 1 proposed Cs _0.32 WO ₃ nanoparticles by solid phase method in Non-Patent Document 1.

Patent Document 2 describes a process for preparing nano-sized potassium-cesium-tungsten bronze solid solution particles represented by the chemical formula K _x Cs _y WO _z , where x+y≦1 and 2≦z≦3. Yes, the process involves combining a suitable tungsten source with a potassium salt and a cesium salt to form a powder mixture and exposing the powder mixture to a plasma torch under a reducing atmosphere, preferably where the reducing atmosphere is hydrogen/dilute. A process is disclosed that is supplied by a sheath gas consisting of a gas mixture. According to the manufacturing method disclosed in Patent Document 2, it is also disclosed that metallic tungsten is mixed as an impurity.

By the way, according to Non-Patent Document 2, Cs _0.32 WO ₃ particles, known as one of the photochromic materials, have the property of becoming more bluish when exposed to strong UV (ultraviolet) irradiation (hereinafter referred to as UV coloring). phenomenon). In addition, according to Non-Patent Document 2, it is also reported that after the UV coloring phenomenon, when stored in a dark place, the original light blue color gradually returns. The above-mentioned UV coloring phenomenon has emerged as an issue for the widespread use of composite tungsten oxide particles. Under these circumstances, research has been conducted to reduce the UV coloring phenomenon.

Non-Patent Document 3 describes that by adding tetraethyl orthosilicate and a UV absorbing agent (UV-absorbing agent; UVA) to Cs _0.32 WO ₃ particles of composite tungsten oxide particles, SiO ₂ , UVA, CWO It is disclosed that a composite material has been synthesized.

Furthermore, in Non-Patent Document 4, using a melt blending process, Cs _0.32 WO ₃ particles are kneaded into an inert polymer to suppress the generation of protons present near the surface of the Cs _0.32 WO ₃ particles. This is disclosed.

Patent Document 3 discloses a technique in which composite tungsten oxide fine particles and a coloring inhibitor are used together.

The methods disclosed in Non-Patent Documents 3 and 4 and Patent Document 3 are intended to reduce the UV coloring phenomenon by combining composite tungsten oxide particles with a UV absorber, etc. The properties of the _0.32 WO ₃ particles themselves have not improved.

On the other hand, according to Non-Patent Document 2, the mechanism of this coloring phenomenon is similar to the mechanism reported in WO ₃ , and when Cs _0.32 WO ₃ nanoparticles are exposed to strong ultraviolet light, the resin It is proposed that this is caused by protons contained in Cs _0.32 WO ₃ particles entering Cs vacancy sites on the surface of the Cs 0.32 WO 3 particles, forming a H _x WO ₃ layer.

Hiromitsu Takeda, and Kenji Adachi, "Near infrared absorption of tungsten oxide nanoparticle dispersions." Journal of the American Ceramic Society,2007 , Vol.90, Issue 12, P.4059-4061 Adachi, K., Ota, Y., Tanaka, H., Okada, M., Oshimura, N., & Tofuku, A. (2013). Chromatic instabilities in cesium-doped tungsten bronze nanoparticles. Journal of Applied Physics, 114 (19), 194304. Zeng, Xianzhe, et al. "The preparation of a high performance near-infrared shielding CsxWO3/SiO2 composite resin coating and research on its optical stability under ultraviolet illumination." Journal of Materials Chemistry C 3.31 (2015): 8050-8060. Zhou, Yijie, et al. "CsxWO3 nanoparticle-based organic polymer transparent foils: low haze, high near infrared-shielding ability and excellent photochromic stability." Journal of Materials Chemistry C 5.25 (2017): 6251-6258. Sato, Yohei, Masami Terauchi, and Kenji Adachi. "High energy-resolution electron energy-loss spectroscopy study on the near-infrared scattering mechanism of Cs0. 33WO3 crystals and nanoparticles." Journal of Applied Physics 112.7 (2012): 074308.

Patent No. 4096205 Special Publication No. 2012-532822 JP2008-208274A

As described above, composite tungsten oxide particles represented by the general formula M _x W _y O _z are useful as a near-infrared shielding material. However, this composite tungsten oxide particle, which is a photochromic material, is colored blue by UV irradiation, and this coloring phenomenon has become an issue for widespread use.

In view of the above problems of the prior art, one aspect of the present invention aims to provide composite tungsten oxide particles that are less likely to be colored when irradiated with ultraviolet rays.

In one aspect of the present invention to solve the above problems,
A compound represented by the general formula M _x W _y O _z (where M element is cesium , W is tungsten, O is oxygen, 0.001≦x/y≦1, 2.2≦z/y≦3.0) Tungsten oxide particles,
The particle size is 800 nm or less,
The defect rate of the M element site is 10% or less in a range from the surface of the composite tungsten oxide particle to a depth of 3 nm,
The composite tungsten oxide particles include a composite tungsten oxide with a hexagonal crystal structure,
The present invention provides composite tungsten oxide particles having an a-axis lattice constant of 7.39 Å or more and 7.42 Å or less, and a c-axis lattice constant of 7.58 Å or more and 7.65 Å or less.

According to one aspect of the present invention, it is possible to provide composite tungsten oxide particles that are not easily colored when irradiated with ultraviolet rays.

FIG. 1 is a schematic diagram of a composite material manufacturing apparatus that can be suitably used in the method for manufacturing composite tungsten oxide particles of the present embodiment. FIG. 2 is a schematic diagram of a reduction treatment apparatus that can be suitably used in the method for manufacturing composite tungsten oxide particles of the present embodiment. 2 shows the temperature distribution measurement results of the reaction section of the composite material manufacturing apparatus used in Example 1. An X-ray diffraction pattern of composite tungsten oxide particles according to Example 1. TEM image of composite tungsten oxide particles obtained in Example 1. Particle size distribution of composite tungsten oxide particles obtained in Example 1. High-angle angular dark-field images and contrast intensity at [010] incidence of the composite tungsten oxide particles obtained in Example 1. High-angle angular dark-field images and contrast intensity at [010] incidence of the composite tungsten oxide particles obtained in Example 1. Transmission profiles of resin cured films of composite tungsten oxide particles obtained in Example 1 and Comparative Example 1 before and after UV irradiation. Figure 2 shows the time change in total light transmittance of the resin cured films of composite tungsten oxide particles obtained in Example 1 and Comparative Example 1 before and after UV irradiation due to UV irradiation. The amount of change (ΔABS) in the absorbance ABS of the resin cured film of the composite tungsten oxide particles obtained in Example 1 and Comparative Example 1 before and after UV irradiation. TEM image of composite tungsten oxide particles after pulverization according to Comparative Example 1. Particle size distribution of composite tungsten oxide particles after pulverization according to Comparative Example 1.

A specific example of composite tungsten oxide particles according to an embodiment of the present disclosure (hereinafter referred to as "this embodiment") will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is indicated by the scope of the claims, and is intended to include all changes within the meaning and scope equivalent to the scope of the claims.
[Composite tungsten oxide particles]
An example of the structure of the composite tungsten oxide particles of this embodiment will be described below.

The composite tungsten oxide particles of this embodiment relate to composite tungsten oxide particles represented by the general formula M _x W _y O _z .

M element in the above general formula is an alkali metal, an alkaline earth metal, a rare earth element, Mg, Zr, Cr, Mn, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, Al, Ga, In, Tl, Si, Ge, Sn, Pb, Sb, B, F, P, S, Se, Br, Te, Ti, Nb, V, Mo, Ta, Re, Be, It can be one or more elements selected from Hf, Os, Bi, and I. Further, W represents tungsten, O represents oxygen, and x, y, and z satisfy 0.001≦x/y≦1 and 2.2≦z/y≦3.0, respectively.

The composite tungsten oxide particles of this embodiment have a particle diameter of 800 nm or less, and the defect rate of M element sites in a range from the surface of the composite tungsten oxide particles to a depth of 3 nm is 10% or less. Can be done.

The composite tungsten oxide contained in the composite tungsten oxide particles is expressed by the general formula M _x W _y O _z as described above. Since the M element, W, O, and x, y, and z in the formula have already been described, their explanation will be omitted here.

The crystal structure of the composite tungsten oxide contained in the composite tungsten oxide particles of this embodiment is not particularly limited, and can have one or more types of crystal structures selected from tetragonal, cubic, and hexagonal.

However, it is preferable that the composite tungsten oxide has a hexagonal crystal structure because the transmittance of the composite tungsten oxide particles to light in the visible light range and the absorption of light in the near-infrared range are particularly improved. Therefore, it is preferable that the composite tungsten oxide particles include a composite tungsten oxide having a hexagonal crystal structure. The composite tungsten oxide particles can also be composed of a composite tungsten oxide having a hexagonal crystal structure. When one or more selected from Cs, Rb, K, Tl, Ba, and In is used as the M element, it becomes easier to form a hexagonal crystal. For this reason, it is preferable that the M element of the tungsten oxide particles contains one or more types selected from Cs, Rb, K, Tl, Ba, and In. Note that the M element can also be composed of one or more selected from the elements listed above.

Here, a method of arranging the M element when the composite tungsten oxide has a hexagonal crystal structure will be explained.

An octahedron formed with W and six O atoms as a unit, that is, an octahedron with an O atom at the apex and a W atom in the center, is assembled to form a hexahedron composed of O atoms. A rectangular cavity (tunnel) is formed. Then, in the void, the M element is arranged to form one unit, and a large number of this one unit are aggregated to form a hexagonal crystal structure. When the composite tungsten oxide having a hexagonal crystal structure has a uniform crystal structure, the amount of M element added is preferably 0.2 or more and 0.5 or less in x/y value, and more preferably 0.33. It is. When z/y=3, since the value of x/y is 0.33, it is considered that the M element is arranged in all the hexagonal voids.

Similarly, when z/y = 3, each of the cubic and tetragonal composite tungsten oxides has an upper limit to the amount of M element added based on the structure, and the maximum amount of M element added to 1 mole of tungsten is is 1 mol in the case of cubic crystal, and about 0.5 mol in case of tetragonal crystal. In addition, the maximum amount of M element to be added to 1 mol of tungsten in the case of tetragonal crystal varies depending on the type of M element, but the amount that can be easily manufactured industrially is about 0.5 mol as described above. However, these structures are difficult to define simply, and the ranges are examples showing particularly basic ranges, so the present invention is not limited thereto.

Furthermore, by adding even a very small amount of M element, free electrons are generated within the composite tungsten oxide, and the desired infrared absorption effect can be obtained. Therefore, as described above, x/y preferably satisfies 0.001≦x/y≦1.

The composite tungsten oxide has a composition in which M element is added to tungsten trioxide (WO ₃ ). Since tungsten trioxide does not contain effective free electrons, it cannot exhibit an infrared absorption effect unless the ratio of oxygen to 1 mole of tungsten is less than 3. However, in the composite tungsten oxide, by adding the M element, free electrons are generated and an infrared absorption effect can be obtained. Therefore, the ratio of oxygen to 1 mole of tungsten can be 3 or less. However, the crystal phase of WO ₂ causes absorption and scattering of light in the visible light range, and there is a possibility that absorption of light in the near-infrared range may be reduced. Therefore, from the viewpoint of suppressing the generation of WO ₂ , the ratio of oxygen to 1 mole of tungsten is preferably greater than 2.

Therefore, it is preferable to satisfy 2.2≦z/y≦3.0 as described above.

The particle size of the composite tungsten oxide particles of this embodiment is not particularly limited, and can be selected depending on the purpose of use.

However, since the composite tungsten oxide particles of this embodiment can suppress coloring during UV irradiation, they can be suitably used in various applications requiring transparency. When used in applications requiring transparency, it is preferable that the particles have a particle diameter of 800 nm or less. Therefore, it is preferable that the composite tungsten oxide particles of this embodiment have a particle diameter of 800 nm or less.

This is because particles with a particle size of 800 nm or less do not completely block light due to scattering, and can maintain high visibility in the visible light region and at the same time efficiently maintain transparency. In particular, when emphasis is placed on transparency in the visible light region, it is preferable to further consider scattering by particles.

When placing emphasis on reducing scattering by such particles, the particle diameter of the composite tungsten oxide particles of this embodiment is preferably 200 nm or less, more preferably 100 nm or less.

This is because if the particle size is small, the scattering of light in the visible light range with a wavelength of 400 nm to 780 nm due to geometric scattering or Mie scattering is reduced, resulting in an infrared shielding film that resembles frosted glass, resulting in clear transparency. This is because it is possible to avoid not being able to obtain . When the particle diameter of the composite tungsten oxide particles becomes 200 nm or less, the geometrical scattering or Mie scattering is reduced and becomes a Rayleigh scattering region. This is because in the Rayleigh scattering region, scattered light is reduced in proportion to the sixth power of the particle diameter, so as the particle diameter decreases, scattering decreases and transparency improves. Further, when the particle diameter is 100 nm or less, the amount of scattered light is extremely reduced, which is preferable. From the viewpoint of avoiding light scattering, it is preferable that the particle size is small.

Therefore, the particle size of the composite tungsten oxide particles of this embodiment can be selected depending on the intended use. For example, when it is required to maintain high visibility in the visible light region as described above, the particle size is preferably 800 nm or less, more preferably 200 nm or less, and even more preferably 100 nm or less. preferable. Although the lower limit of the particle size of the composite tungsten oxide particles of this embodiment is not particularly limited, it can be, for example, 1 nm or more.

The particle diameter of the composite tungsten oxide particles of this embodiment can be determined by observing the particles using, for example, SEM or TEM and drawing the smallest circumscribed circle that circumscribes the particles.

Further, the average particle diameter of the composite tungsten composite oxide particles of this embodiment is preferably 5 nm or more and 800 nm or less, preferably 5 nm or more and 200 nm or less, and more preferably 30 nm or more and 50 nm or less.

This is because by setting the average particle diameter of the composite tungsten oxide particles to 800 nm or less, scattering of light in the visible light region can be particularly reduced.

However, it is difficult to make the average particle size of the composite tungsten oxide particles less than 5 nm, and productivity may decrease, so the average particle size of the composite tungsten composite oxide particles should be 5 nm or more. preferable.

The average particle diameter of composite tungsten oxide particles obtained by the method for manufacturing composite tungsten oxide particles of this embodiment can be calculated by the following procedure. First, composite tungsten oxide particles to be evaluated are observed using, for example, SEM or TEM, and 200 to 500 particles are randomly selected. Then, the diameter of the smallest circumscribed circle that circumscribes the selected particles is defined as the particle diameter of the selected particles, and the average value of the particle diameters of the selected particles is defined as the average particle diameter of the composite tungsten oxide particles. .

Although the method for manufacturing the composite tungsten oxide particles of this embodiment is not particularly limited, the composite tungsten oxide particles can be manufactured by, for example, the method for manufacturing composite tungsten oxide particles described below. When manufacturing composite tungsten oxide particles using such a method for manufacturing composite tungsten oxide particles, for example, by adjusting the size of droplets formed in the droplet formation step described below, the composite tungsten oxide particles obtained can be adjusted. The particle size and average particle size can be selected. Further, for example, by further carrying out a crushing treatment step, which will be described later, after the reduction treatment step, the particle diameter and average particle diameter of the resulting composite tungsten oxide particles can be selected.

Since the infrared shielding material containing the composite tungsten oxide particles of this embodiment largely absorbs light in the near-infrared region, particularly in the vicinity of a wavelength of 1000 nm, its transmitted color tone often ranges from blue to green.

The lattice constant of the composite tungsten oxide particles of this embodiment, specifically the composite tungsten oxide particles contained in the composite tungsten oxide particles, is not particularly limited, but the a-axis is 7.39 Å or more and 7.42 Å or less, the c-axis is preferably 7.58 Å or more and 7.65 Å or less, the a-axis is preferably 7.40 Å or more and 7.42 Å or less, and the c-axis is more preferably 7.58 Å or more and 7.63 Å or less.

This is because by setting the lattice constant of the composite tungsten oxide within the above range, a crystal structure free of W (tungsten) defects is formed.

The method for calculating the lattice constant is not particularly limited, and it can be calculated using the Rietveld method or the like from the powder X-ray diffraction pattern measured for the obtained composite tungsten oxide particles.

Note that the composite tungsten oxide particles of this embodiment may contain inevitable components such as, for example, an oxide of element M. In this case, it is preferable that the crystal phase of the composite tungsten oxide, that is, the lattice constant of the composite tungsten oxide phase, satisfies the above range.

Here, according to Non-Patent Document 2, the Cs defect sites on the surface of Cs _0.32 WO ₃ particles are caused by the crushing process for obtaining Cs _0.32 WO ₃ particles with a particle size of 20 nm to 40 nm. According to Non-Patent Document 2 and Non-Patent Document 5, the Cs atomic concentration near the outermost surface of Cs _0.32 WO ₃ particles subjected to the pulverization process, specifically, the Cs atomic concentration within several nm from the outermost surface of the particle (Cs atomic layer The Cs atomic concentration in the range of about 10 layers) is about 30 to 40% lower than the Cs atomic concentration inside the particle.

When such a Cs defect occurs, protons invade the Cs defect. Due to the intrusion of protons, the composite tungsten oxide particles are irradiated with UV light and colored blue. Therefore, based on this mechanism, it is thought that suppressing the generation of Cs-deficient sites leads to suppressing the UV coloring phenomenon.

Furthermore, according to the studies of the inventors of the present invention, not only the Cs _0.32 WO ₃ particles but also the composite tungsten oxide particles represented by the general formula M _x W _y O _z described above similarly It was confirmed that when the number of M element defects on the particle surface increases, it is more likely to be colored by UV irradiation.

Therefore, in the composite tungsten oxide particles of this embodiment, the defect rate of M element sites is set to 10% or less within a depth of 3 nm from the surface of the composite tungsten oxide particles. By suppressing the defect rate of the M element near the surface of the composite tungsten oxide particles, it is possible to suppress the composite tungsten oxide particles from being colored blue after being irradiated with UV. The lower limit of the defect rate of the M element site is not particularly limited, but since it is preferable that there be no defects, it can be set to, for example, 0% or more.

The defect rate of the M element site within a depth of 3 nm from the surface of the composite tungsten oxide particle can be calculated using the following formula (1) based on, for example, a HAADF-STEM image.

Cs defect rate (%) = [1-(number of Cs atoms at each cesium site in the measurement area)/(number of sites where cesium can enter in the measurement area)] x 100... (1)
In the above formula, (number of Cs atoms at each cesium site in the measurement region)/(number of sites in which cesium can enter in the measurement region) corresponds to the Cs occupancy. The Cs occupancy rate is the ratio of Cs present at the Cs site, and can be calculated from the magnitude of contrast intensity in the HAADF image. This occupancy rate can be calculated for each site. Since the total occupancy rate and missing rate are 100%, the missing rate can be determined by subtracting the obtained value from 100%.
[Method for manufacturing composite tungsten oxide particles]
Although the method for manufacturing the composite tungsten oxide particles of this embodiment is not particularly limited, composite tungsten oxide particles having a desired particle size are obtained from the viewpoint of suppressing defects in the M element contained in the composite tungsten oxide particles obtained. Therefore, a manufacturing method that does not require excessive pulverization is preferable.

The method for manufacturing composite tungsten oxide particles of this embodiment can include, for example, the following steps.

A droplet forming step of forming droplets of a raw material mixed solution containing a tungsten source and an M element source, which are objects to be processed.
A heat treatment process in which the object to be treated is heat treated at 500°C or higher.
A reduction treatment step in which the particles obtained in the heat treatment step are heat treated at 500° C. or higher in an atmosphere containing a reducing gas.
A crushing treatment process in which particles obtained through reduction treatment are crushed using a crushing device.

The method for producing composite tungsten oxide particles of the present embodiment involves supplying droplets containing a tungsten source and an M element source together with a gas flow to an atmosphere at a temperature higher than the thermal decomposition temperature of the raw materials, and causing evaporation of the solvent and thermal decomposition. This is a spray pyrolysis method to obtain composite tungsten oxide particles.

As described above, the method for producing composite tungsten oxide particles of the present embodiment includes a droplet forming step of forming droplets of a raw material mixed solution containing a tungsten source and an M element source, which are the objects to be treated. be able to. Further, it is possible to include a heat treatment step of heat treating the droplet, which is the object to be treated, at 500° C. or higher. These steps will be explained first.
(Droplet formation process)
In the droplet forming step, droplets of a raw material mixed solution containing a tungsten source and an M element source, which are objects to be processed, can be formed.

The specific means for forming droplets in the droplet forming step is not particularly limited. For example, a method of forming droplets of a solution containing a tungsten source and an M element source using a spray nozzle, or a method of forming droplets by irradiating a solution containing a tungsten source and an M element source with ultrasonic waves. , a method of forming droplets using a two-fluid nozzle, and a method of forming droplets using various atomizers including a centrifugal atomizer.

In particular, since fine droplets can be stably formed, it is preferable to form droplets by irradiating a solution containing a tungsten source and an M element source with ultrasonic waves. That is, a droplet forming method using ultrasonic waves can be suitably used.

Note that a solution containing a tungsten source and a solution containing an M element source are prepared separately, and for example, they are mixed immediately before being supplied to the droplet forming section (droplet forming means) or within the droplet forming section, and the solution containing the tungsten source is prepared separately. Preferably, a solution is formed containing a source of M element and a source of M element. That is, in the droplet forming step, it is preferable to mix a solution containing a tungsten source and a solution containing an M element source to form a raw material mixed solution. Subsequent to the formation of the raw material mixed solution, it is preferable to continuously form droplets using the raw material mixed solution.

The specific method of mixing both solutions in the droplet formation step is not particularly limited. For example, a solution containing a tungsten source and a solution containing an M element source are separately introduced into an ultrasonic spraying device (ultrasonic irradiation device) that is a droplet forming section, and both solutions are mixed in the device to mix raw materials. It is preferable to form a solution and form droplets. That is, in the droplet formation step, when droplets of the raw material mixture solution are formed using an ultrasonic atomizer, a solution containing a tungsten source and a solution containing an M element source are mixed in the ultrasonic atomizer. However, it is preferable to form a raw material mixed solution. In this way, by separately preparing a solution containing a tungsten source and a solution containing an M element source and mixing them in an ultrasonic atomizer, for example, the process from forming a raw material mixed solution to forming droplets can be performed. The time can be particularly shortened. Therefore, it is possible to particularly suppress the reaction between the tungsten source and the M element source due to the neutralization reaction, and the occurrence of precipitation in the raw material mixed solution.

The tungsten source is not particularly limited, and tungsten salts can be used, and for example, ammonium paratungstate can be preferably used. Ammonium paratungstate pentahydrate (ATP) can be represented, for example, by (NH ₄ ) ₁₀ (W ₁₂ O ₄₁ )·5H ₂ O.

In ammonium paratungstate, elements other than tungsten are N (nitrogen), H (hydrogen), and O (oxygen), and are discharged from the system in a temperature raising step or a heat treatment step, which will be described later. Therefore, by using it as a solute in a solution containing a tungsten source, it is possible to obtain composite tungsten oxide particles in which contamination with impurities is suppressed, so it can be preferably used.

Further, as the solution containing the tungsten source, an aqueous solution containing the tungsten source can be suitably used because of ease of handling. Therefore, water-soluble salts can be suitably used as the tungsten source. Ammonium paratungstate can be preferably used because it is easily dissolved in water and a solution containing a tungsten source can be easily formed using water as a solvent.

As the solution containing the M element source, for example, a solution of a salt containing the M element can be used. The type of salt of element M that is the source of element M is not particularly limited, but for example, one or more types selected from carbonates, acetates, nitrates, hydroxides, etc. of element M can be used.

As the solution containing the M element source, an aqueous solution containing the M element source can be suitably used from the viewpoint of ease of handling. Therefore, a water-soluble salt can be suitably used as the salt of element M.

For example, when the M element is cesium, one or more selected from carbonates, acetates, nitrates, hydroxides, etc. can be used, and carbonates can be particularly preferably used. This is because cesium carbonate is easily dissolved in water.

Note that the ratio of the M element to 1 mole of tungsten in the obtained composite tungsten oxide, that is, the doping amount, is determined by the ratio of the tungsten source and the M element source when forming the raw material mixed solution. Therefore, it can be controlled by, for example, the concentration of the solution containing the tungsten source or the concentration of the solution containing the M element source.

The concentration of the tungsten source contained in the solution containing the tungsten source is not particularly limited. For example, it is preferable that the tungsten concentration of the solution containing the tungsten source is 0.0015 mol/L or more and 12 mol/L or less. Such a concentration increases the productivity of particles obtained in the heat treatment step, making it possible to obtain particles with an average particle diameter of 800 nm or less, for example. By setting the tungsten concentration of the solution containing the tungsten source to 0.0015 mol/L or more, a sufficient amount of composite tungsten oxide particles can be produced per unit time, and a sufficient amount can be recovered using a filter, etc. This is because productivity can be increased. Further, by setting the tungsten concentration of the solution containing the tungsten source to 12 mol/L or less, only particles having an average particle diameter of 800 nm or less can be selectively obtained. This is also because it is possible to suppress the incorporation of coarse composite tungsten oxide particles, for example, several micrometers or more.

For example, when an aqueous ammonium paratungstate solution is used as a solution containing a tungsten source, the concentration of ammonium paratungstate is 0.000125 mol/L or more and 1 mol/L or less because ammonium paratungstate contains 12 tungstens in the molecule. is preferred.

Further, the concentration of the M element contained in the solution containing the M element source is not particularly limited, and the desired composition of the composite tungsten oxide particles to be manufactured and the concentration of the tungsten source contained in the solution containing the tungsten source etc. can be selected according to the following.

Any component other than the solution containing the tungsten source and the solution containing the M element source can be added to the raw material mixed solution. For example, ammonia can be added as a reducing agent in order to promote reduction of the composite tungsten oxide particles. When the above-mentioned ammonium paratungstate aqueous solution is used as the solution containing the tungsten source, the ammonia can be added to the ammonium paratungstate aqueous solution, for example.

Although the size of the droplet formed in the droplet forming step is not particularly limited, the diameter of the droplet is preferably 100 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. By setting the diameter of the droplets to 100 μm or less, it is possible to prevent the obtained composite tungsten oxide particles from becoming coarse and to obtain nanometer-order composite tungsten oxide particles. Note that the lower limit of the size of droplets formed in the droplet forming step is not particularly limited. However, it is difficult to form droplets that are too small, which may reduce productivity, so it is preferable that the droplet size is, for example, 1 μm or more.

The droplets formed in the droplet forming step can be transported by, for example, a carrier gas and subjected to a heat treatment step or a temperature raising step.
(Heat treatment process)
In the heat treatment process, the object to be treated can be heat treated at 500°C or higher.

The solvent contained in the droplets of the raw material mixture solution containing the tungsten source and the M element source, which are the objects to be processed, evaporates during the process of heating to 500° C., and the tungsten source and the M element source are further decomposed. Then, in the decomposition process, tungsten and the M element react to form a composite tungsten oxide.

When a droplet is heated in a heat treatment step or the like, if the solvent contained in the droplet is water, it is estimated that evaporation of the water occurs in a range of 50° C. or higher and 120° C. or lower. Further, it is estimated that the decomposition of the tungsten source and the M element source occurs, for example, in a range of 120° C. or higher and 500° C. or lower.

It is considered that a composite tungsten oxide is formed through the decomposition process of the tungsten source and the M element source, or through the reaction between tungsten and the M element at a higher temperature.

Therefore, in order to sufficiently progress the decomposition of the tungsten source and M element source and to suppress the contamination of impurities into the composite tungsten oxide, heat treatment is performed at a temperature higher than the decomposition temperature of the tungsten source and M element source in the heat treatment process. It is preferable. As mentioned above, it is thought that decomposition of the tungsten source and the M element source usually occurs at temperatures below 500°C. Therefore, in the heat treatment step, the droplet as the object to be treated can be heat treated at 500° C. or higher.

According to studies by the inventors of the present invention, the heat treatment temperature also affects the particle size of the composite tungsten oxide particles obtained. According to further studies by the inventors of the present invention, it has been found that as the heat treatment temperature increases, the particle size of the resulting composite tungsten oxide particles tends to become smaller.

An example will be described in which cesium-doped tungsten oxide particles are manufactured using an ammonium paratungstate aqueous solution as a tungsten source solution and a cesium carbonate aqueous solution as an M element source solution. In this case, when the heat treatment temperature was 500° C. or higher and lower than 1000° C., the particle diameter of the cesium-doped tungsten oxide particles ranged from 100 nm to less than 1 μm. Further, when the temperature is higher than 1000° C., the particle diameter of the cesium-doped tungsten oxide particles may become less than 100 nm.

This is presumed to be because when the heat treatment temperature becomes high, thermal energy is used to sublimate the generated composite tungsten oxide particles, and the particles burst due to sublimation, resulting in particles having a fine particle size.

It was confirmed that a similar tendency was observed in the production of composite tungsten oxide particles having other compositions. Therefore, in order to obtain composite tungsten oxide particles that are particularly fine nanoparticles, the heat treatment temperature is preferably 1000° C. or higher. That is, when the purpose is to obtain particularly fine nanoparticles, it is preferable that the object to be treated be heat treated at 1000° C. or higher in the heat treatment step.

The upper limit of the heat treatment temperature of the object to be treated in the heat treatment step is not particularly limited, but if the temperature is raised to an excessively high temperature, the cost of the heating device may increase, so it is preferably 1500° C. or lower.

In addition, when the purpose is to produce nanoparticle composite tungsten oxide particles with a particle size of less than 100 nm, in addition to heat-treating the object to be treated at a temperature of 1000°C or higher in the heat treatment process, a heat treatment temperature of 1000°C or higher is required. The heat treatment time is preferably 1 second or more, more preferably 3 seconds or more. By setting the heat treatment time to 1 second or more at a heat treatment temperature of 1000°C or higher, sufficient thermal energy is given to the generated composite tungsten oxide particles to sublimate them, and the particle size can be more reliably reduced, for example. This is because nanoparticles with a diameter of less than 100 nm can be obtained.

The upper limit of the heat treatment time at a heat treatment temperature of 1000°C or higher is not particularly limited, but if you try to make it too long, the size of the heat treatment furnace will increase, which may reduce productivity, or the precipitated powder may reach the filter. Otherwise, it may fall into the reaction section piping and cause a blockage. Therefore, the heat treatment time at a heat treatment temperature of 1000° C. or higher is preferably 100 seconds or less, for example.

The droplets formed in the droplet forming step can be transported to an electric furnace or the like by, for example, a carrier gas, and subjected to the above-described heat treatment step. Therefore, for example, by controlling the flow rate of the carrier gas, etc., the time of the heat treatment process can be adjusted.

Note that the method for manufacturing composite tungsten oxide particles of this embodiment may further include a temperature raising step before the heat treatment step.

The temperature raising step can be a step of raising the temperature of the droplet, which is the object to be processed, to 500° C., for example. Further, for example, in the case of nanoparticles having a particularly small particle size as described above, the temperature raising step can be a step of raising the temperature of the droplet, which is the object to be treated, to 1000°C.

After the temperature raising step, heat treatment can be performed in a heat treatment step. Note that in the heat treatment step, the temperature can be raised to a predetermined temperature as necessary.

The time required for the temperature raising step is not particularly limited and can be arbitrarily selected.

As mentioned above, the solvent contained in the droplets of the raw material mixture solution containing the tungsten source and M element source, which are the objects to be treated, evaporates during the heating process, and as the temperature rises, tungsten source or M element source decomposes. Then, in the decomposition process, tungsten and the M element react to form a composite tungsten oxide.
(Reduction treatment process)
Particles obtained through the heat treatment process, specifically composite tungsten oxide particles, sometimes do not exhibit infrared absorption characteristics. Therefore, the inventors of the present invention conducted a study and found that by further carrying out a reduction treatment step in which the composite tungsten oxide particles obtained through the heat treatment step are reduced, the composite tungsten oxide particles can be It has been found that absorption properties can be expressed.

Therefore, the method for producing composite tungsten oxide particles of the present embodiment can include a reduction treatment step in which the particles obtained in the heat treatment step are reduced in an atmosphere containing a reducing gas.

The conditions of the reduction treatment are not particularly limited, but when the composite tungsten oxide particles after the reduction treatment are analyzed by X-ray diffraction pattern, the crystal structure does not change before and after the reduction treatment process, and metal tungsten etc. is precipitated. It is preferable to select the conditions for the reduction treatment so as not to cause this.

In the reduction treatment step, the composite tungsten oxide obtained in the heat treatment step can be reduced by increasing and decreasing the temperature in a reducing atmosphere containing a reducing gas, that is, by performing heat treatment.

During the reduction treatment process, the composite tungsten oxide particles may be stirred or left standing, and the handling of the composite tungsten oxide particles during the reduction treatment process can be selected as appropriate, but it must be handled in such a way that metallic tungsten does not precipitate. It is preferable to select the conditions.

The temperature of the reduction treatment (reduction treatment temperature) can be 500°C or higher, preferably 500°C or higher and lower than 700°C, more preferably 550°C or higher and 650°C or lower, and even more preferably 550°C or higher and lower than 650°C. less than In addition, in the droplet formation step, when the raw material concentration is lowered, the resulting particle size becomes smaller. Since the particles having a smaller diameter are more easily reduced, the temperature in the reduction treatment step can be lowered than before. After raising the temperature from room temperature to the temperature for reduction treatment, the temperature can be lowered to room temperature again.

The reduction conditions can be determined from the optical properties of the composite tungsten oxide particles obtained.

By setting the temperature of the reduction treatment to 500° C. or higher, the reduction treatment can proceed on the composite tungsten oxide particles, and the infrared absorption characteristics can be more reliably exhibited. Further, by setting the temperature to be less than 700°C, reduction of the composite tungsten oxide particles to metallic tungsten can be suppressed.

The reducing atmosphere is preferably an atmosphere containing a mixed gas of an inert gas such as argon and a reducing gas such as H ₂ gas (hydrogen gas), and the reducing gas is preferably H ₂ gas.

When using _H2 gas as the reducing gas, the content of _H2 gas in the reducing atmosphere can be selected as appropriate, but the content of _H2 gas should be in the range of 0.1% to 10% by volume. It is preferably in the range of 2% or more and 10% or less. If reduction is performed in an atmosphere containing only a reducing gas, the reduction reaction may proceed excessively and metal tungsten may precipitate, so care must be taken.

The time required for the reduction treatment step is desirably 30 minutes or more in total from temperature rise to temperature fall. The upper limit of the time for the reduction treatment step is not particularly limited, and it is preferable to select it after conducting a preliminary test, for example, to prevent the reduction from proceeding excessively. In addition, the total time from temperature rise to temperature fall here means the time from starting temperature rise from room temperature until it cools down to room temperature after reaching the reduction treatment temperature. In addition, it is preferable that the composite tungsten oxide particles are placed under the above-mentioned reducing atmosphere for such a period of time.

By performing the reduction treatment step in this manner, it is possible to convert the unintended foreign phase of the composite tungsten oxide particles obtained after the heat treatment step into the intended composite tungsten oxide phase.

The method for manufacturing composite tungsten oxide particles of the present embodiment may further include any steps other than the droplet forming step, heat treatment step, and reduction treatment step described above. For example, it can further include a crushing process described below.
(Crushing process)
In the method for producing composite tungsten oxide particles of this embodiment, the particles obtained by the reduction treatment step can also be subjected to a crushing treatment. That is, the method for manufacturing composite tungsten oxide particles of the present embodiment can further include a crushing process of subjecting the particles obtained in the reduction process to crushing as described above.

The average particle diameter of the composite tungsten oxide particles obtained by the method for manufacturing composite tungsten oxide particles according to the present embodiment is, for example, 800 nm or less. However, the particles obtained by the reduction treatment step may be agglomerated. The reason that agglomeration may occur in the particles obtained after the reduction treatment process is because the nano-sized particles are synthesized by a gas phase method and collected in the form of a dry powder. This is thought to be due to the addition of thermal energy during the reduction process. It is known that composite tungsten oxide particles in a dispersed state exhibit particularly excellent transmission characteristics in the visible light region and particularly high absorption characteristics in the infrared region. Therefore, depending on the state of the particles obtained after the reduction treatment step, it is preferable to perform a weak crushing treatment to obtain dispersed nano-sized particles.

The crushing means used in the crushing process is not particularly limited, but examples include crushing methods using devices such as bead mills, ball mills, sand mills, paint shakers, and ultrasonic homogenizers. Among these, crushing with a media agitation mill such as a bead mill, ball mill, sand mill, paint shaker, etc. using media (beads, balls, Ottawa sand) shortens the time required to obtain the desired average particle size. Preferable from this point of view.

As mentioned above, the composite tungsten oxide synthesized by the solid-phase method requires pulverization for several hours or more using beads with a particle size of 0.3 mm, for example, in order to pulverize submicron-sized particles to nano-sized particles. Processing needs to be done. Generally, when beads with large particle diameters are used in crushing or crushing, the collision energy between the beads increases, which increases the energy received by the particles to be treated during crushing or crushing. Therefore, by using a medium with a large particle size, the particle size of the particles to be treated after crushing can be reduced. However, when such a medium with a large particle size is used, the particles to be treated may be damaged during crushing or pulverization, and the crystal structure of the substance constituting the particles to be treated may change. Furthermore, M element defects may be caused on the surface of the composite tungsten oxide particles.

On the other hand, in the method for producing composite tungsten oxide particles of the present embodiment, the composite tungsten oxide particles obtained after the reduction treatment step are already fine and are only aggregated with a weak force. Therefore, when carrying out the crushing treatment step in the method for producing composite tungsten oxide of the present embodiment, beads having a particle size of 10 μm or more and 500 μm or less, for example, can be suitably used as the crushing medium. Disintegration treatment can be performed using beads. This is because by using beads with a particle size of 500 μm or less as a crushing medium, it is possible to suppress changes in the crystal structure due to excessive energy being applied to the composite tungsten oxide particles. Further, by using beads having a particle size of 10 μm or more, the composite tungsten oxide particles can be sufficiently crushed to form nano-sized particles.

The material of the beads used as the crushing medium is not particularly limited, but it is preferably a material that can be separated from the composite tungsten oxide particles in the dispersion liquid due to the difference in specific gravity after the crushing process. Zirconia beads, ie, zirconia beads, can be suitably used.

Further, the time for the crushing treatment in the crushing step is not particularly limited, but is preferably, for example, 5 minutes or more and 1 hour or less. By setting the crushing time to one hour or less, excessive energy is applied to the composite tungsten oxide particles, which may change the crystal structure or cause M element defects on the particle surface. This is especially because it can be suppressed. Further, by setting the crushing time to 5 minutes or more, the composite tungsten oxide particles can be sufficiently crushed to form nano-sized particles.
[Composite material manufacturing equipment, reduction processing equipment]
A configuration example of a composite material manufacturing apparatus and a reduction treatment apparatus that can be suitably used in the method for manufacturing composite tungsten oxide particles of this embodiment will be described below.
(Composite material manufacturing equipment)
FIG. 1 is a diagram schematically showing a composite material manufacturing apparatus 10. As shown in FIG.

The composite material manufacturing apparatus 10 can include a droplet forming section 11, a transport section 12, a reaction section 13, and a recovery section 14, and can perform the droplet forming step, temperature raising step, and heat treatment step described above. It can be implemented.

In addition, as shown in FIG. 1, it is preferable that the droplet forming part 11, the transport part 12, the reaction part 13, and the collection part 14 be connected by piping.

Additional equipment can be connected to the droplet forming section 11 as necessary. For example, the droplet forming section 11 can be connected to a first storage section 151 that stores a solution containing a tungsten source, which is a raw material solution, and a second storage section 152 that stores a solution that contains an M element source. . Note that, for example, pumps 151A and 152A are provided in the piping between the first storage section 151 and the droplet formation section 11 and the piping between the second storage section 152 and the droplet formation section 11, respectively. Each solution can be configured to be supplied to the droplet forming section 11 at a desired flow rate. Further, a carrier gas tank 16 containing a carrier gas for transporting the droplets formed in the droplet forming section 11 to the transport section 12 or the like can be connected.

In the apparatus shown in FIG. The raw materials are mixed at the upper part of the chamber 11 to form a raw material mixed solution. Next, droplets are formed by the droplet forming section 11 using the formed raw material mixed solution.

Note that the droplet forming unit 11 shown in FIG. 1 is an example of an ultrasonic spraying device, and for example, the ultrasonic irradiation unit 111 irradiates the raw material mixed solution with ultrasonic waves to form droplets. .

As described above, the droplet forming section 11 can be connected to the carrier gas tank 16 filled with carrier gas, and the carrier gas is supplied to the droplet forming section 11 from the carrier gas tank 16 . The droplets formed in the droplet forming section 11 are transported by a carrier gas and supplied to the reaction section 13 via the transport section 12.

The transport unit 12 connects the droplet forming unit 11 and the reaction unit 13 and can supply droplets formed in the droplet forming unit 11 to the reaction unit 13. It is preferable to heat the droplets passing through the transport section 12 in advance so that the inside of the transport section 12 can be heated so that the temperature of the reaction section 13 does not drop. Specifically, for example, it is preferable to install a heater wrapped around the outside of the transport section 12 to maintain the temperature inside the transport section 12 at 30° C. or higher and 80° C. or lower.

In the reaction section 13, the above-mentioned temperature raising step and heat treatment step can be carried out. For this reason, the reaction section 13 can include, for example, a heat-resistant pipe 131 and a heater 132 that heats the pipe 131, as shown in FIG.

As the pipe 131, for example, a ceramic pipe can be used.

The length of the reaction section 13 is not particularly limited, and is preferably selected so that it can be heated to a predetermined temperature in the temperature raising step and the heat treatment step, and a sufficient time can be secured for the heat treatment step.

The length of the pipe 131 of the reaction section 13 is preferably 1 m or more from the viewpoint of heating to a predetermined temperature and ensuring sufficient time for the heat treatment step. The upper limit of the length of the piping 131 is not particularly limited, but if it is too long, a large amount of carrier gas will be required and the size of the device will also increase, so it is preferably 5 m or less.

Further, the diameter (inner diameter) of the pipe 131 is not particularly limited either, but from the viewpoint of productivity, it is preferably 2 cm or more. The upper limit of the diameter (inner diameter) of the pipe 131 is not particularly limited, but it is preferably selected so that the temperature difference between the center and the wall surface does not become excessively large, and the diameter of the pipe 131 is, for example, 20 cm or less. It is preferable that there be.

The piping 131 of the reaction section 13 usually has a temperature gradient along its longitudinal direction. For example, the temperature at the reaction section inlet 131A is low, and the temperature increases toward the reaction section outlet 131B.

Therefore, it is preferable to set various conditions so that a temperature region of 500° C. or higher can be formed near the reaction section outlet 131B.

In addition, especially when the object to be treated is heat-treated at a temperature of 1000°C or higher in the heat treatment process described above, various conditions are set so that a temperature region of 1000°C or higher can be formed near the reaction section outlet 131B. It is preferable to do so. In addition, in the heat treatment process, for example, when the heat treatment time at a temperature of 1000°C or more is set to 1 second or more, the time for the object to be processed to pass through the temperature region of 1000°C or higher in the reaction section 13 is 1 second or more. It is preferable to set various conditions so that Specifically, for example, it is preferable to measure the temperature distribution inside the pipe 131 in advance and adjust the supply rate of the carrier gas, etc.

In the recovery section 14, the composite tungsten oxide particles generated in the reaction section 13 can be recovered. The configuration of the recovery section 14 is not particularly limited, and can be selected depending on the particle size of the composite tungsten oxide particles to be manufactured. As the collection unit 14, various filters can be used, for example. Alternatively, an electrostatic collector can be used. Note that in order to prevent the liquid contained in the solution containing the tungsten source from precipitating in the recovery section 14, a heating means such as a heater may be placed around the recovery section 14 to heat it.

Preferably, the inside of the composite material manufacturing apparatus 10 is sealed, and the gas flow is configured such that gas flows from the carrier gas tank 16 into the droplet forming section 11 and flows out from the recovery section 14.
(reduction processing equipment)
In the reduction treatment apparatus, the reduction treatment process described above can be carried out.

The reduction treatment apparatus is not particularly limited as long as it is configured to be able to carry out the reduction treatment process described above. For example, a container that stores composite tungsten oxide particles that are particles obtained by the above-mentioned composite material manufacturing apparatus, a gas pipe that supplies a mixed gas to create a reducing atmosphere into the container, and a heat source that heats the container. All you have to do is prepare.

Note that it is also possible to introduce a mixed gas to create a reducing atmosphere into the container and exhaust it, and place the composite tungsten oxide particles, which are the objects to be treated, under the airflow of the mixed gas. In this case, a mixed gas supply pipe and an exhaust pipe may be provided as gas pipes so as to form such an air flow.

Further, a stirring blade or the like may be used in combination to stir the composite tungsten oxide particles in the container.

FIG. 2 is a diagram schematically showing a configuration example of a reduction treatment apparatus, and shows a cross-sectional view taken along a plane passing through the central axis of the reaction tube 21 of the reduction treatment apparatus 20. As shown in FIG.

The reduction treatment apparatus 20 is a horizontal tubular furnace, and can be used by attaching a gas inlet pipe (not shown) to one port 21A of the reaction tube 21 and a gas exhaust pipe (not shown) to the other port 21B of the tube furnace. . By supplying a mixed gas to create a reducing atmosphere from one port 21A side, a reducing atmosphere can be created in the reaction tube 21.

A heater 22 can be provided around the reaction tube 21, and the composite tungsten oxide particles are placed in a ceramic container 23 such as a boat and placed at a position corresponding to the heater 22 in the reaction tube 21 of the tube furnace. Can be placed.

By using the reduction processing apparatus 20, creating a reducing atmosphere in the reaction tube 21, and heating it to a desired temperature with the heater 22, the composite tungsten oxide particles 24 placed in the container 23 can be reduced.

According to the method for manufacturing composite tungsten oxide particles of the present embodiment described above, it is possible to use equipment with low installation cost, such as a droplet forming section and a heater. Furthermore, composite tungsten oxide particles, which are near-infrared absorbing particles, can be obtained directly without going through a long process such as pulverization, and the number of steps can be reduced. Therefore, composite tungsten oxide particles can be easily produced.

Furthermore, by performing the reduction treatment step, infrared absorption characteristics can be reliably expressed, and even if the composite tungsten oxide particles synthesized in the heat treatment step contain foreign phases, the foreign phases can be reduced and removed. Therefore, the method for manufacturing composite tungsten oxide particles of this embodiment has high industrial utility value.

The present invention will be described below with reference to specific examples, but the present invention is not limited to these examples.
[Example 1]
Using the composite material manufacturing apparatus 10 shown in FIG. 1 and the reduction treatment apparatus 20 shown in FIG. 2, Cs _0.32 WO ₃ particles were manufactured as composite tungsten oxide particles and evaluated. The specific conditions will be explained below.

The composite material manufacturing apparatus 10 shown in FIG. , the reaction section 13 and the recovery section 14 are connected by piping.

The droplet forming unit 11 includes a first storage unit 151 that stores a solution containing a tungsten source as a raw material solution, a second storage unit 152 that stores a solution containing an M element source, and a liquid formed in the droplet forming unit 11. A carrier gas tank 16 containing a carrier gas for transporting the droplets to the transport section 12 and the like was connected.

First, as a solution containing a tungsten source, ammonium paratungstate (ATP) represented by (NH ₄ ) ₁₀ (W ₁₂ O ₄₁ )·5H ₂ O (manufactured by Kanto Kagaku, purity: 88-90%), and ultra-pure A 1.25 mmol/L ammonium paratungstate aqueous solution was prepared using water. The ammonium paratungstate aqueous solution was placed in the first storage section 151 and was configured to be continuously supplied to the droplet forming section 11 connected to the first storage section 151 via piping by a pump 151A.

Further, as a solution containing an M element source, a 2.4 mmol/L cesium carbonate aqueous solution was prepared using cesium carbonate (manufactured by Sigma-Aldrich) and ultrapure water. The cesium carbonate aqueous solution was placed in the second storage section 152 and was configured to be continuously supplied to the droplet forming section 11 connected to the second storage section 152 via piping by a pump 152A.

Note that, as described above, each solution is supplied from the first storage section 151 and the second storage section 152 to the droplet formation section 11 at a constant flow rate via the piping by the pumps 151A and 152A, and the droplet formation section 11 Both solutions are mixed at the upper part of the chamber to form a raw material mixed solution. Then, the supply rate and the concentration of each solution were adjusted so that the ratio of the number of moles of cesium to 1 mole of tungsten in the raw material mixed solution formed in the droplet forming section 11 was 0.32. Specifically, each of the above solutions was supplied in equal amounts, that is, the same volume was supplied per unit time. As a result, the raw material mixed solution contained 0.625 mmol/L of ammonium paratungstate and 1.2 mmol/L of cesium carbonate.

A carrier gas tank 16 was connected to the droplet forming section 11, and an air cylinder was used as the carrier gas tank 16. During production of composite tungsten oxide particles, air gas was supplied as a carrier gas to the droplet forming section 11 at a flow rate of 4 L/min.

The droplet forming unit 11 is provided with an ultrasonic irradiation unit 111, which irradiates the raw material mixture solution formed in the droplet forming unit 11 with ultrasonic waves to form droplets with a diameter of 1 μm or more and 5 μm or less. The ultrasonic output was adjusted so that it could be formed. Note that as the droplet forming section 11, an ultrasonic nebulizer (manufactured by OMRON Healthcare Co., Ltd., model: NE-U17, ultrasonic transmission frequency: 1.7 MHz) was used.

A heater was placed outside the transport section 12 to keep the temperature inside the transport section 12 at 70°C.

The reaction section 13 was equipped with a pipe 131, which was a cylindrical ceramic pipe with a length of 1.3 m and an inner diameter of 28.5 mm.

The reaction section 13 was configured to be heated from the outside of the pipe 131 by a heater 132, and the temperature was set so that the temperature increased from the reaction section inlet 131A toward the reaction section outlet 131B.

In this example, the temperature of the heater 132 was set so that the maximum temperature near the reaction section outlet 131B was 1200°C. FIG. 3 shows the temperature distribution of the reaction section used in this example. FIG. 3 shows a temperature distribution curve obtained by measuring the temperature every 2 cm along the length of the pipe 131 using a thermocouple. Note that the temperature is also partially measured in the piping section between the piping 131 and the recovery section 14. In FIG. 3, the horizontal axis indicates the position (distance) x (cm) of the measurement point along the length direction of the pipe 131 from the reaction section inlet 131A, assuming that the position of the reaction section inlet 131A is 0. There is. Further, the vertical axis in FIG. 3 indicates the furnace temperature at each position in the length direction of the pipe 131.

As shown in FIG. 3, it was confirmed that the temperature distribution was formed such that the temperature gradually increased from the reaction section inlet 131A toward the reaction section outlet 131B, and that a temperature range of 1000°C or higher was also set. can.

A bag filter was disposed in the recovery section 14 so that the composite tungsten oxide particles formed after the temperature raising step and the heat treatment step were completed in the reaction section 13 could be recovered. In order to collect the powder in a dry state, the glass filter was sealed with glass fiber tape and heated to 120°C. Note that if the temperature is not heated, evaporated droplets may precipitate.

Composite tungsten oxide particles were manufactured under the above conditions.

Specifically, in the droplet forming section 11, droplets of a raw material mixed solution of an ammonium paratungstate aqueous solution and a cesium carbonate aqueous solution were formed (droplet forming step), and the furnace body temperature was set at 1200°C. The droplets were supplied to the reaction section 13 using a carrier gas, and a temperature raising step and a heat treatment step were performed. The inside of the pipe 131 of the reaction section 13 has the temperature distribution shown in FIG. 3, and since the flow rate of the carrier gas was set to 4 L/min, the temperature of the droplet was raised to 1000°C (heating step), and the droplet was heated to 1000°C. Heat treatment is performed for 3.0 seconds at the above heat treatment temperature (heat treatment step).

Next, the particles obtained after the heat treatment step were subjected to reduction treatment using the reduction treatment apparatus 20 shown in FIG. 2 at a reduction treatment temperature of 650° C. to obtain composite tungsten oxide particles (reduction treatment step).

The reduction treatment apparatus 20 is a horizontal tubular furnace, and the particles obtained after the heat treatment step are placed in a container 23, which is a ceramic boat, and the container 23 is heated to the highest temperature in the reaction tube 21, that is, the above-mentioned reduction treatment temperature. placed in a certain position.

A gas inlet pipe (not shown) was attached to one port 21A of the reaction tube 21, and a gas exhaust pipe (not shown) was attached to the other port 21B of the tube furnace. Then, by supplying a mixed gas containing argon, which is an inert gas, and H ₂ gas, which is a reducing gas, from one port 21A side, the inside of the reaction tube 21 was made into a reducing atmosphere. The content of H ₂ gas in the mixed gas was 5% by volume, and it was supplied so that the pressure inside the reaction tube was 0.08 MPa.

A heater 22 is provided around the reaction tube 21, and the temperature is raised from room temperature to 600°C. After the part where the container 23 is placed reaches the reduction treatment temperature, it is held for 1 hour, and then it is cooled to room temperature to perform the reduction. processed.

The composite tungsten oxide particles obtained after the reduction treatment step were crushed for 10 minutes using zirconia beads having a particle size of 50 μm (pulverization treatment step).

Specifically, first, 200 mg of composite tungsten oxide particles obtained after the reduction treatment step were prepared, and 12.5 mL of MIBK (specific gravity 0.8) as a dispersion medium and a dispersant (an amine-based dispersant with an acrylic skeleton, amine) were added. 48 mg/KOH) to disperse composite tungsten oxide particles. The mass concentration of composite tungsten oxide particles relative to MIBK in this dispersion is 2% by mass. Next, zirconia beads (manufactured by Daiken Kagaku Co., Ltd.) having a particle size of 50 μm were introduced into a 50 mL glass bottle and crushed using a paint shaker. The dispersion liquid after the crushing process was designated as the composite tungsten oxide particle dispersion liquid according to Example 1. Further, a part of the dispersion liquid was taken out and the dispersion medium was removed by drying to obtain composite tungsten oxide particles, which were analyzed as follows.

The XRD pattern of the obtained composite tungsten oxide particles is shown in FIG. It was confirmed that the composite tungsten oxide particles obtained from the XRD pattern can be expressed as Cs _0.32 WO ₃ . When the lattice constants of the Cs _0.32 WO ₃ phase, which is a composite tungsten oxide, were calculated by Rietveld analysis, the a-axis = 7.42 Å and the c-axis = 7.59 Å. Moreover, it was confirmed that the composite tungsten oxide contained in the obtained composite tungsten oxide particles had a hexagonal crystal structure.

It was confirmed that the particle diameter of the composite tungsten oxide particles of this example obtained by the crushing process was 28.6 nm. The composite tungsten oxide particles to be evaluated are observed using a TEM, and 200 particles are randomly selected. Then, the diameter of the smallest circumscribed circle circumscribing the selected particles was taken as the particle size of the selected particles, and the average value of the particle sizes of the selected particles was taken as the average particle size of the composite tungsten oxide particles. .

TEM images of the composite tungsten oxide particles after the crushing process are shown in FIGS. 5(A) and 5(B), and the particle size distribution is shown in FIG. 6, respectively. FIG. 5(B) corresponds to a partially enlarged view of FIG. 5(A).
(3) STEM image observation Figures 7 and 8 show high-angle angular dark-field images (HAADF) images observed using a JEOL STEM (model: JEM-ARM200F). Particle contrast in a HAADF image is proportional to the number of atoms in the particle and the number of atoms. Since the more heavy atoms are stacked, the brighter the contrast is, the brightest contrast and the second brightest contrast are W, the third brightest contrast is Cs, and it is thought that O cannot be confirmed.

FIG. 7(A) shows a HAADF-STEM image of Cs _0.32 WO ₃ particles, which are composite tungsten oxide particles obtained after the crushing process, at [010] incidence. That is, in FIG. 7(A), the integrated contrast of W atoms and Cs atoms is seen when the Cs _0.32 WO ₃ particles are viewed in the [010] incident direction. The rectangular region a-b in FIG. 7(A) is the Cs plane inside the particle, and the rectangular region c-d in FIG. 7(A) is the Cs plane of the second layer from the outermost surface. ) was defined as the Cs plane at the outermost surface of the particle.

FIG. 7(B) shows an image of the crystal structure in the same orientation as the grains shown in FIG. 7(A). In the crystal structure from this orientation, a plane in which only W is lined up (W plane) and a plane in which only Cs is lined up (Cs plane) are arranged alternately. Therefore, the state of Cs desorption can be evaluated from the contrast intensity of the Cs plane in the rectangular frame shown in FIG. 7(A). FIG. 7(D) shows the results of averaging the contrast intensity within a line width range of 1 nm in the Cs plane. FIG. 7(D) also shows the positions of a to f, a', and f' in FIG. 7(A).

In the contrast on the Cs plane inside the particle shown in a-b of FIG. 7(D), a clear peak derived from Cs was confirmed. The weak peaks between the Cs peaks originate from the contrast of W on the W plane. Furthermore, in the contrast of the Cs plane of the second layer from the outermost surface shown in c-d of FIG. 7(D), a clear Cs contrast equivalent to or higher than that inside the particle was confirmed in all ranges. In other words, Cs similar to that inside exists even in a region close to the surface at a depth of about 1 nm from the outermost surface. In the Cs contrast of the outermost surface of the particle shown in ef of FIG. 7(D), a weak peak derived from Cs was confirmed only in the region from e' to f'. That is, although the Cs on the outermost surface of the composite tungsten oxide particles obtained in Example 1 was partially deficient in Cs, in the inner region deeper than the second layer, Cs was present at a concentration equal to or higher than that inside.

A similar analysis was performed using the HAADF-STEM image of the present particle at [001] incidence shown in FIG. In this field of view, the brightest contrast corresponds to tungsten, and the second brightest contrast corresponds to cesium. a-b in Figure 8(A) is the Cs plane inside the particle, c-d in Figure 8(A) is the Cs plane of the second layer from the outermost surface, and e-f in Figure 8(A) is the particle. The outermost Cs plane was used.

FIG. 8(B) shows an image of the crystal structure in the same orientation as the grains shown in FIG. 8(A). FIG. 8(C) shows the result of averaging the contrast intensity within a line width range of 1 nm in the Cs plane. FIG. 8(C) also shows the positions of a to f and arrows in FIG. 8(A). From FIG. 8(A) and FIG. 8(C), it was confirmed that Cs exists at the same concentration as inside the particle from the inside to the surface depth of 1 nm, similarly to the [010] direction. However, in the outermost Cs/W layer, a slight decrease in contrast was observed as indicated by the arrow.

In the range from the surface of the composite tungsten oxide particles according to Example 1 to a depth of 3 nm, the defect rate of M element, that is, Cs element sites, was 8.2%.

Here, in this crystal system, Cs can ideally exist in an atomic weight ratio of up to 0.33 with respect to W. On the other hand, Cs present at the particle interface completely disappears from the Cs site while maintaining the W skeleton structure through a desorption process such as a crushing process. Therefore, the Cs deficiency rate was defined and calculated according to the following formula (1).

Cs deficiency rate = [1-(Number of Cs atoms at each cesium site in the measurement area)/(Number of sites in the measurement area where cesium can enter)] x 100... (1)
The Cs occupancy rate is the ratio of Cs present at the Cs site, and can be calculated from the magnitude of contrast intensity in the HAADF image. This occupancy rate can be calculated for each site. Since the occupancy rate and the missing rate totaled 100%, the obtained value was removed from 100% to obtain the missing rate.
(Optical properties of composite tungsten oxide particle dispersion)
The optical properties of the composite tungsten oxide particles obtained in Example 1 were evaluated using a cured resin film containing composite tungsten oxide particles, which is a composite tungsten oxide particle dispersion.

First, a UV curing resin (UV-3701 manufactured by Toagosei Co., Ltd.) was added to the above-mentioned composite tungsten oxide particle dispersion obtained after the crushing process in an amount of 5 parts by mass per 1 part by mass of the composite tungsten oxide particles. A coating solution was prepared by mixing in the following proportions.

The obtained coating solution was applied to a soda glass substrate (thickness 3 mm x 10 mm x 10 mm) on a tabletop bar coater (TC-3, Mitsui Electric Seiki), and then heated at 100°C for 1 minute to coat it in the coating solution. The organic solvent contained was dried and removed.

Furthermore, UV irradiation was performed for 1 minute using a UV conveyor device (ECS-401GX, manufactured by I-Graphic) to polymerize and harden the resin in the coating film, thereby producing the composite tungsten oxide particle dispersion according to Example 1. A cured film was prepared. A mercury lamp having a dominant wavelength of 365 nm was used as the UV source in the UV conveyor device. The thickness of the cured resin film according to Example 1 was adjusted using a bar coater so that the total light transmittance, which will be described later, was about 80%.

The total light transmittance of the cured resin film containing composite tungsten particles was measured using a haze meter (NDH 5000, manufactured by Nippon Denshoku Industries Co., Ltd.) based on ISO 13468-1:1996. Further, the haze of the same sample was determined using the same haze meter based on ISO 14782:1999. Furthermore, for the same sample, visible light transmission (VLT) was determined from the transmission profile (Transmittance; T) measured by ultraviolet-visible near-infrared spectroscopy in accordance with ISO 9050:2003.

The transmittance of each wavelength was determined, and the absorbance (ABS) was calculated from the transmittance. The transmittance at a wavelength of 550 nm is expressed as _T550nm , and the transmittance at a wavelength of 1300 nm is expressed as _T1300nm . Further, the absorbance (ABS) at a wavelength of 550 nm is expressed as ABS _{2.26 eV (550 nm)} , and the absorbance (ABS) at a wavelength of 1300 nm is expressed as ABS _{0.95 eV (1300 nm)} . Note that the energy of light at each wavelength, which is a subscript of absorbance, was calculated using the following equation (2).

E=hc/eλ...(2)
h: Planck constant c: speed of light e: elementary charge λ: wavelength The above evaluation results are shown in the column before UV irradiation in Table 1.
(Evaluation of changes in optical properties of cured resin film due to UV irradiation)
Further, the cured resin film was subjected to UV irradiation for 20 minutes from the coating film side to evaluate photochromic stability. The total light transmittance, haze, and visible light transmittance of the cured resin film after UV irradiation were determined. Furthermore, the transmittance of each wavelength was determined, and the absorbance (ABS) was calculated from the transmittance of each wavelength. The results are shown in the column 20 minutes after UV irradiation in Table 1.

The amount of change in ABS (absorbance) of the cured resin film due to UV irradiation at a wavelength of 550 nm and a wavelength of 1300 nm (ΔABS=ABS _{before UV irradiation} −ABS _{after UV irradiation} ) was calculated. The results are shown in Table 1. The amount of change in absorbance (ABS) at a wavelength of 550 nm before and after UV irradiation is expressed as ΔABS _{2.26 eV} , and the amount of change in absorbance (ABS) at a wavelength of 1300 nm before and after UV irradiation is expressed as ΔABS _{0.95 eV} .

FIG. 9A shows the transmission profile measured by ultraviolet-visible-near-infrared spectroscopy of the cured resin film according to Example 1 before UV irradiation and after 20 minutes of UV irradiation.

When performing the UV irradiation, the irradiation was once stopped 5 or 10 minutes after the start of UV irradiation, and the total light transmittance of the cured resin film was measured. FIG. 10 shows the change in total light transmittance depending on the UV irradiation time. According to the results shown in FIG. 10, it was confirmed that the decrease in total light transmittance due to UV irradiation could be suppressed compared to Comparative Example 1 described later. It was confirmed that the total light transmittance decreased slightly for about 5 minutes from the start of UV irradiation, but after that, it was confirmed that the total light transmittance hardly decreased and leveled off.

FIG. 11 shows the amount of change in ABS (absorbance) of the cured resin film according to Example 1 due to UV irradiation for 20 minutes (ΔABS=ABS _{before UV irradiation} −ABS _{after UV irradiation} ). It was confirmed that the cured resin film according to Example 1 had a smaller ΔABS over all wavelengths than Comparative Example 1, which will be described later. That is, it was confirmed that the composite tungsten oxide particles of Example 1 and the cured resin film containing them were able to suppress the UV coloring phenomenon.
[Comparative example 1]
Composite tungsten oxide particles according to Comparative Example 1 were synthesized and evaluated.

0.216 kg of Cs ₂ CO ₃ was dissolved in 0.330 kg of water, and the resulting solution was added to 1.000 kg of H ₂ WO ₄ and sufficiently stirred, followed by drying to obtain a dried product. The dried material was heated while supplying 5% H ₂ gas using N ₂ gas as a carrier, and baked at a temperature of 800° C. for 1 hour. Thereafter, a solid phase reaction method was further performed in which the material was fired at 800° C. for 2 hours in an N ₂ gas atmosphere to obtain a composite tungsten oxide. Prepare 1 g of the obtained composite tungsten oxide, mix it with 12.5 mL of MIBK (specific gravity 0.8), which is a dispersion medium, and 1 mL of a dispersant (amine-based dispersant with an acrylic skeleton, amine value 48 mg/KOH) to form a composite. Tungsten oxide particles were dispersed. Note that the mass concentration of composite tungsten oxide particles relative to MIBK in this dispersion is 10% by mass. Next, zirconia beads (manufactured by Daiken Kagaku Co., Ltd.) with a particle size of 0.3 mm were introduced into a 50 mL glass bottle, and crushed for 6 hours using a paint shaker to obtain a dispersion of composite tungsten oxide particles according to Comparative Example 1. I got it. The dispersion after pulverization was used as a composite tungsten oxide particle dispersion according to Comparative Example 1. Further, a part of the dispersion liquid was taken out and the dispersion medium was removed by drying to obtain composite tungsten oxide particles, which were analyzed as follows.

The particle size of the composite tungsten oxide according to Comparative Example 1 after pulverization was 16.1 nm.

FIG. 12 shows a TEM image of the composite tungsten oxide particles according to Comparative Example 1, and FIG. 13 shows the particle size distribution.

The defect rate of Cs element sites was 40.5% in the range from the surface of the composite tungsten oxide according to Comparative Example 1 to a depth of 3 nm.
(Optical properties of composite tungsten oxide particle dispersion)
The optical properties of the composite tungsten oxide particles obtained in Comparative Example 1 were evaluated using a cured resin film containing composite tungsten oxide particles, which is a composite tungsten oxide particle dispersion.

Specifically, a cured film of a resin containing composite tungsten oxide particles was produced in the same manner as in Example 1, except that the composite tungsten oxide particle dispersion according to Comparative Example 1 obtained after pulverization was used. The optical properties were evaluated. The evaluation results are shown in Table 1.
(Evaluation of changes in optical properties of cured resin film due to UV irradiation)
As in the case of Example 1, for the cured resin film according to Comparative Example 1, the total light transmittance, haze, and visible light transmittance after UV irradiation, as well as the amount of change in ABS due to UV irradiation, were calculated. The results are shown in the column 20 minutes after UV irradiation in Table 1.

Further, FIG. 9(B) shows the transmission profile measured by ultraviolet-visible-near-infrared spectroscopy of the cured resin film according to Comparative Example 1 before UV irradiation and after UV irradiation for 20 minutes. When compared with the case of Example 1, it can be confirmed that the transmittance in the near-infrared region after ultraviolet irradiation is lower than that of Example 1. This is considered to be because, in the cured resin film according to Comparative Example 1, more electrons are supplied to the 5d orbital of the W atom of Cs _0.32 WO ₃ after UV irradiation.

When performing the above UV irradiation, the irradiation was once stopped 5 minutes and 10 minutes after the start of UV irradiation, and the total light transmittance was measured. FIG. 10 shows changes in total light transmittance depending on UV irradiation time. According to FIG. 10, the total light transmittance of the cured resin film of Comparative Example 1 significantly decreased by about 4% in the first 5 minutes after starting UV irradiation, and continued to decrease thereafter. It could be confirmed.

FIG. 11 shows the amount of change in ABS (absorbance) with respect to light energy of the cured resin film according to Comparative Example 1 after 20 minutes of UV irradiation (ΔABS=ABS _{before UV irradiation} −ABS _{after UV irradiation} ). It was confirmed that the difference in absorbance (ΔABS) with respect to light energy in Comparative Example 1 had a first peak P ₁₃₁ at 0.98 eV and a second peak P ₁₃₂ at 1.51 eV. In addition, over a wide range of light energy from 0.5 eV to 2.3 eV, ΔABS is about 5 times that of the cured resin film of Example 1, and the amount of change in absorbance due to UV irradiation is large. It was confirmed that a UV coloring phenomenon occurred.

Claims (1)

A compound represented by the general formula M _x W _y O _z (where M element is cesium , W is tungsten, O is oxygen, 0.001≦x/y≦1, 2.2≦z/y≦3.0) Tungsten oxide particles,
The particle size is 800 nm or less,
The defect rate of the M element site is 10% or less in a range from the surface of the composite tungsten oxide particle to a depth of 3 nm,
The composite tungsten oxide particles include a composite tungsten oxide with a hexagonal crystal structure,
The composite tungsten oxide particles have an a-axis lattice constant of 7.39 Å or more and 7.42 Å or less, and a c-axis lattice constant of 7.58 Å or more and 7.65 Å or less.

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