Method for producing composite tungsten oxide particles

Abstract

To provide a method for producing composite tungsten oxide particles by which equipment with a low introduction cost can be used and the number of steps is small.SOLUTION: A method for producing composite tungsten oxide particles represented by the general formula MxWyOz (0.001≤x / y≤1, 2.2≤z / y≤3.0) is provided. The method for producing composite tungsten oxide particles comprises an aerosol forming step of forming an aerosol containing a mixed raw material powder of a W source raw material powder, which is a tungsten source, and an M source raw material powder, which is a source of an M element, which are objects to be treated, and a heat treatment step in which the aerosol is carried by a carrier gas while being heat-treated at a temperature of 1000°C or higher and 1350°C or lower, with the carrier gas being air.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing composite tungsten oxide particles. [Background technology]

[0002] Various near-infrared shielding technologies have been proposed to date that have good visible light transmittance and reduce solar radiation transmittance while maintaining transparency. Among these, near-infrared shielding technologies that use inorganic conductive fine particles have the advantages of superior near-infrared shielding properties compared to other technologies, low cost, radio wave transmittance, and high weather resistance.

[0003] For example, Patent Document 1 discloses an infrared-shielding material particle dispersion in which infrared-shielding material particles are dispersed in a medium, and the infrared-shielding material particles are represented by the general formula M x W y O z (wherein M is one or more elements selected from H, He, alkali metals, alkaline earth metals, rare earth elements, 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, and I; W is tungsten; O is oxygen; and 0.001≦x / y≦1, 2.2≦z / y≦3.0), as well as a technique related to a method for producing the infrared-shielding microparticles. Patent Document 1 also discloses an example of producing an infrared-shielding film that is a thin-film dispersion of infrared-shielding material microparticles.

[0004] According to Patent Document 1, it is possible to prepare a dispersion of infrared-shielding material particles that has excellent optical properties, such as more efficient shielding of sunlight, particularly light in the near-infrared region, while at the same time maintaining transmittance in the visible light region, etc. Therefore, application of the infrared-shielding particle dispersion disclosed in Patent Document 1 to various applications such as window glass has been studied.

[0005] Various studies have been conducted on methods for producing composite tungsten oxide particles that are useful as near-infrared shielding materials.

[0006] For example, the inventor of Patent Document 1 has reported in Non-Patent Document 1 that Cs 0.32 proposed a method for synthesizing WO nanoparticles. However, the synthesis method disclosed in Non-Patent Document 1 required a pulverization process to produce nanoparticles due to the large particle size. This could potentially increase the number of process steps.

[0007] Non-patent document 2 describes Cs produced by hydrothermal synthesis. x A method for synthesizing WO3 has been disclosed. However, the hydrothermal synthesis method requires a synthesis time of several tens of hours or more. In addition, the hydrothermal synthesis method has the problem of requiring many steps, such as post-treatment processes.

[0008] Non-Patent Document 3 discloses a synthesis method based on inductively coupled thermal plasma technology. However, this synthesis method requires the introduction of an inductively coupled thermal plasma device, which increases costs.

[0009] Patent document 2 describes the chemical formula K x Cs y WO z A process for preparing potassium-cesium-tungsten bronze solid solution particles of the formula: where x+y≦1 and 2≦z≦3, comprising combining a suitable tungsten source with potassium and cesium salts to form a powder mixture, and exposing the powder mixture to a plasma torch under a reducing atmosphere, preferably supplied by a sheath gas comprising a hydrogen / noble gas mixture, is disclosed.

[0010] However, Patent Document 2 also requires the use of plasma, which increases costs due to the need to introduce a plasma device. Patent Document 2 also discloses that the manufacturing method disclosed in Patent Document 2 may result in the inclusion of metallic tungsten as an impurity.

[0011] As shown in Non-Patent Document 4, a method has been proposed in which an aerosolized raw material is supplied to a flame field. This raw material powder supply method easily increases productivity and eliminates the effects of the solvent contained in the raw material. It simultaneously solves the problems of "the low droplet formation rate (less than 3 g / hr on a lab scale) due to the use of an ultrasonic atomizer" and "the need for latent heat to vaporize and remove the solvent." However, the method described in Non-Patent Document 4 involves a combustion reaction to form a flame field, which results in the contamination of water and carbon as by-products. This leaves the problem of "by-products contained in the solvent and raw material being mixed into the crystals, resulting in poor infrared absorption characteristics." Another problem is the need for devices to form a flame field, supply the raw material to the flame field, and recover the product. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] International Publication No. 2005 / 037932 [Patent Document 2] Special Publication No. 2012-532822 [Non-patent literature]

[0013] [Non-Patent Document 1] Takeda Hiromitsu, 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 [Non-patent document 2] Guo Chongshen, et al., "Novel synthesis of homogenous CsxWO3nanorods with excellent NIR shielding properties by a water controlled-release solvothermal process." Journal of Materials Chemistry,2010, Vol.20, Issue38, P.8227-8229. [Non-patent document 3] Mamak Marc, et al., "Thermal plasma synthesis of tungsten bronze nanoparticles for near infra-red absorption applications." Journal of Materials Chemistry, 2010, Vol.20, Issue44, P.9855-9857. [Non-patent document 4] Hidayat, Darmawan, et al. "Preparation of size-controlled tungsten oxide nanoparticles and evaluation of their adsorption performance." Materials Research Bulletin 45.2 (2010): 165-173. Summary of the Invention [Problem to be solved by the invention]

[0014] As described above, composite tungsten oxide particles are useful as near-infrared shielding materials. There is a need for a method for producing composite tungsten oxide particles at low cost and with fewer steps.

[0015] However, the conventionally disclosed methods for producing composite tungsten oxide particles have had problems such as the need for the introduction of special, expensive equipment and the need for many steps, as described above.

[0016] In view of the above-mentioned problems of the conventional art, an object of one aspect of the present invention is to provide a method for producing composite tungsten oxide particles that can use equipment with low installation costs and that requires a small number of steps. [Means for solving the problem]

[0017] In one aspect of the invention, compounds of general formula M x W y O z (However, the M element is an alkali metal. Genus wherein W is tungsten, O is oxygen, and 0.001≦x / y≦1, 2.2≦z / y≦3.0), an aerosol forming step of forming an aerosol containing a mixed raw material powder of a W source raw material powder serving as a tungsten source and an M element source raw material powder serving as an M element source, which are objects to be processed; a heat treatment step of heat-treating the aerosol at 1000°C or higher and 1350°C or lower while transporting the aerosol with a carrier gas, The present invention provides a method for producing composite tungsten oxide particles, wherein the carrier gas is air. [Effects of the Invention]

[0018] One aspect of the present invention provides a method for producing composite tungsten oxide particles that can use equipment with low installation costs and that requires fewer steps. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is an explanatory diagram of a composite material production apparatus that can be suitably used when producing composite tungsten oxide particles according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is an explanatory diagram of the reduction treatment device. [Figure 3] FIG. 3 shows the temperature profile in the pipe of the reaction section in Example 1. [Figure 4] FIG. 4 shows XRD profiles of the composite tungsten oxide particles obtained in Examples 1 and 2 and Comparative Examples 1 to 4. [Figure 5] FIG. 5 shows the content ratio of each phase in the composite tungsten oxide particles obtained in Examples 1 and 2 and Comparative Examples 1 to 4. [Figure 6] FIG. 6 is a diagram showing the change in lattice constant of the CWO phase of the composite tungsten oxide particles obtained in Examples 1 and 2 and Comparative Examples 1 to 4. [Figure 7] FIG. 7 shows the permeation profiles of the dispersions in which the composite tungsten oxide particles obtained in Example 2, Comparative Example 3, and Comparative Example 4 were dispersed. DETAILED DESCRIPTION OF THE INVENTION

[0020] Specific examples of the method for producing composite tungsten oxide particles according to one embodiment of the present disclosure (hereinafter referred to as "the present embodiment") will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0021] Hereinafter, one example of the method for producing composite tungsten oxide particles of this embodiment will be described.

[0022] The method for producing the composite tungsten oxide particles of the present embodiment is a method for producing a tungsten oxide particle containing a compound of the general formula M x W y O z The method for producing composite tungsten oxide particles represented by the formula (1) can include the following aerosol formation step and heat treatment step.

[0023] The M element in the above general formula can be one or more elements selected from alkali metals, alkaline earth metals, rare earth elements, 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, and I. Furthermore, W represents tungsten, O represents oxygen, and x, y, and z preferably satisfy the relationships 0.001≦x / y≦1 and 2.2≦z / y≦3.0, respectively.

[0024] In the aerosol forming step, an aerosol containing a mixed raw material powder of a W source raw material powder serving as a tungsten source and an M element source raw material powder serving as an M element source can be formed as the object to be processed.

[0025] In the heat treatment step, the aerosol formed in the aerosol formation step can be heat treated at 1000° C. or higher and 1350° C. or lower while being transported by a carrier gas.

[0026] The carrier gas used in the heat treatment step may be air. (1) Composite tungsten oxide particles First, the composite tungsten oxide particles produced by the method for producing composite tungsten oxide particles of this embodiment will be described. (About the composition) The composite tungsten oxide contained in the composite tungsten oxide particles has the general formula M x W y O z The composite tungsten oxide particles of this embodiment can contain, in addition to the composite tungsten oxide represented by the above general formula, inevitable impurities that are mixed in during the manufacturing process. For this reason, the composite tungsten oxide particles of this embodiment can contain, in addition to the composite tungsten oxide represented by the above general formula M x W y O z The term "tungsten oxide" refers to particles containing a composite tungsten oxide represented by the formula:

[0027] The composite tungsten oxide can have a tungsten bronze-type crystal structure, such as a tetragonal, cubic, or hexagonal crystal structure. The crystal structure of the composite tungsten oxide contained in the composite tungsten oxide particles obtained by the method for producing composite tungsten oxide particles of this embodiment is not particularly limited, and can have one or more crystal structures selected from a tetragonal, cubic, and hexagonal crystal structure.

[0028] However, when the composite tungsten oxide has a hexagonal crystal structure, the transmittance of the composite tungsten oxide particles in the visible light region and the absorption of light in the near-infrared region are particularly improved, which is preferable. For this reason, the composite tungsten oxide particles preferably contain a composite tungsten oxide with a hexagonal crystal structure.

[0029] Furthermore, when one or more elements selected from Cs, Rb, K, Tl, Ba, and In are used as the M element, it becomes easier to form a hexagonal crystal. For this reason, it is preferable that the M element contains one or more elements selected from Cs, Rb, K, Tl, Ba, and In. In particular, it is more preferable that the M element contains Cs, and it is even more preferable that the M element is Cs.

[0030] Here, the arrangement of the M element when the composite tungsten oxide has a hexagonal crystal structure will be described.

[0031] An octahedron formed by a unit of W and six O atoms, i.e., an octahedron with O atoms at the vertices and a W atom in the center, is assembled into six octahedrons to form hexagonal voids (tunnels) composed of O atoms. An M element is then placed in the void to form one unit, and many of these units are assembled to form a hexagonal crystal structure. When a 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, more preferably 0.33, in terms of the value of x / y. When z / y=3, the value of x / y is 0.33, which is thought to result in the M element being placed in all of the hexagonal voids.

[0032] Similarly, when z / y=3, the cubic and tetragonal composite tungsten oxides each have an upper limit to the amount of M element added due to their structure, and the maximum amount of M element added per mole of tungsten is 1 mole in the case of a cubic crystal, and about 0.5 moles in the case of a tetragonal crystal. Note that the maximum amount of M element added per mole of tungsten in the case of a tetragonal crystal varies depending on the type of M element, but as mentioned above, the amount that is easy to industrially produce is about 0.5 moles. However, these structures are difficult to simply define, and the ranges are examples that show particularly basic ranges, so the present invention is not limited to these.

[0033] Furthermore, by adding even a trace amount of element M, free electrons are generated in the composite tungsten oxide, and the desired infrared absorption effect can be achieved. For this reason, it is preferable that x / y satisfy the relationship 0.001≦x / y≦1.

[0034] Furthermore, composite tungsten oxide has a composition in which an element M is added to tungsten trioxide (WO3). Since tungsten trioxide does not contain effective free electrons, the ratio of oxygen to 1 mole of tungsten must be less than 3 in order to achieve infrared absorption. However, in composite tungsten oxide, the addition of element M generates free electrons, enabling the infrared absorption effect to be achieved. Therefore, the ratio of oxygen to 1 mole of tungsten can be set to 3 or less. However, the crystalline phase of WO2 may absorb or scatter light in the visible light region, potentially reducing the absorption of light in the near-infrared region. Therefore, from the viewpoint of suppressing the generation of WO2, it is preferable that the ratio of oxygen to 1 mole of tungsten be greater than 2.

[0035] Therefore, it is preferable to satisfy the above-mentioned condition 2.2≦z / y≦3.0. (About particle size) The particle size of the composite tungsten oxide particles produced by the method for producing composite tungsten oxide particles of the present embodiment is not particularly limited, and can be selected depending on the intended use, etc.

[0036] For example, when used in applications where transparency must be maintained, it is preferable for the particle diameter to be 800 nm or less. This is because particles with a diameter of 800 nm or less do not completely block light due to scattering, and can maintain high visibility in the visible light range while efficiently maintaining transparency. In particular, when transparency in the visible light range is important, it is preferable to further consider scattering by the particles.

[0037] When emphasis is placed on reducing scattering caused by such particles, the particle size is preferably 200 nm or less, and more preferably 100 nm or less.

[0038] This is because a small particle size reduces scattering of light in the visible light region with wavelengths of 400 nm to 780 nm due to geometric scattering or Mie scattering, which can prevent the infrared-shielding film from looking like frosted glass and losing clear transparency. Furthermore, when the particle size is 200 nm or less, the geometric scattering or Mie scattering is reduced, and the film enters the Rayleigh scattering region. In the Rayleigh scattering region, scattered light decreases in proportion to the sixth power of the particle size, so scattering decreases with decreasing particle size, improving transparency. Furthermore, a particle size of 100 nm or less is preferable because scattered light is significantly reduced. From the viewpoint of avoiding light scattering, a small particle size is preferred.

[0039] Therefore, the particle size of the composite tungsten oxide particles produced by the method for producing composite tungsten oxide particles of this embodiment can be selected according to the intended use.For example, as described above, when it is required to maintain high visibility in the visible light region, the particle size is preferably 800 nm or less, more preferably 200 nm or less, and even more preferably 100 nm or less.The lower limit of the particle size of the composite tungsten oxide particles produced by the method for producing composite tungsten oxide particles of this embodiment is not particularly limited, but can be, for example, 1 nm or more.

[0040] The particle diameter of the composite tungsten oxide particles obtained by the method for producing composite tungsten oxide particles of the present embodiment can be determined by observing the particles with, for example, an SEM or TEM, and determining the diameter of the smallest circumscribing circle that circumscribes the particle.

[0041] The particle size of the resulting composite tungsten oxide particles can be selected by adjusting, for example, the size of the aerosol formed in the aerosol forming step described below, the heat treatment temperature in the heat treatment step, and the like.

[0042] Infrared-shielding materials containing composite tungsten oxide particles obtained by the method for producing composite tungsten oxide particles of the present embodiment largely absorb light in the near-infrared region, particularly light with a wavelength around 1000 nm, and therefore many of them have a transmitted color tone ranging from bluish to greenish. (2) Manufacturing method of composite tungsten oxide particles Next, the method for producing the composite tungsten oxide particles of this embodiment will be specifically described.

[0043] The method for producing composite tungsten oxide particles in this embodiment is a powder supply type pyrolysis method (solid spray pyrolysis method) in which a mixed raw material powder is converted into an aerosol, and heated while being transported by a carrier gas, causing the powder to sublimate and precipitate a composite tungsten oxide, thereby obtaining the desired composite tungsten oxide particles.

[0044] Therefore, the method for producing composite tungsten oxide particles of this embodiment can include an aerosol formation step of aerosolizing a mixed raw material powder obtained by mixing a W source raw material powder serving as a tungsten source with an M element source raw material powder serving as an M element source, and can further include a heat treatment step of conveying and supplying the aerosol with a carrier gas and performing a heat treatment at 1000°C or higher and 1350°C or lower. (Aerosol formation process) In the aerosol forming step, the aerosol is formed from a mixed raw material powder obtained by mixing a W source raw material powder serving as a tungsten source and an M element source raw material powder serving as an M element source, which are the objects to be processed. Note that "serving as a tungsten source" and "serving as an M element source" mean that tungsten and the M element can be supplied, respectively.

[0045] The aerosol forming step may be performed by any device capable of forming a dispersion of the mixed raw material powder and supplying it into the airflow, and the specific means are not particularly limited. For example, the aerosol forming unit provided in the composite material manufacturing apparatus that can be used in the composite tungsten oxide manufacturing method of this embodiment can be composed of a stirring unit such as a rotating brush or stirring blade, and a powder supply unit including a piston or screw feeder that sends the mixed raw material powder to the stirring unit. The mixed raw material powder supplied from the powder supply unit is dispersed into particles that make up the powder in the stirring unit, and an aerosol can be generated from the mixed raw material powder by sending each particle into a carrier gas. The stirring unit allows the rotation speed of the brush or stirring blade to be selected so that the mixed raw material powder can be dispersed into particles, and it is preferable to rotate it at a high speed.

[0046] In particular, since an aerosol with little particle aggregation can be stably formed, a rotating brush can be suitably used in the stirring section, and a configuration in which mixed raw material powder loaded in a reservoir is supplied to the stirring section by a piston can be suitably used in the powder supply section.

[0047] In such an aerosol forming unit, the powder concentration in the aerosol changes depending on the transport speed of the powder loaded in the reservoir, for example, the movement speed of the piston.

[0048] The tungsten source is not particularly limited, and tungsten salts or the like can be used, and for example, H2WO4 and ammonium paratungstate can be preferably used.

[0049] In H2WO4, the elements other than tungsten are H (hydrogen) and O (oxygen), and the elements other than tungsten are discharged outside the system in the heat treatment process described below. For this reason, by using H2WO4 as the W source raw material powder, which is the tungsten source, composite tungsten oxide particles can be obtained with reduced impurity contamination, and therefore it is preferably used.

[0050] The M element source raw material powder can be, for example, a powder of a salt containing the element M. The type of salt containing the element M is not particularly limited, but for example, one or more types selected from carbonates, acetates, nitrates, hydroxides, etc. of the element M can be used.

[0051] For example, when the M element is cesium, one or more selected from carbonates, acetates, nitrates, hydroxides, etc. can be used, with carbonates being particularly preferred.

[0052] The ratio of the M element to 1 mole of tungsten in the resulting composite tungsten oxide, i.e., the doping amount, is determined by the mixing ratio of the W source raw material powder and the M element source raw material powder when forming the raw material mixed powder. Therefore, the doping amount can be controlled by adjusting the amount of the W source raw material powder and the amount of the M element source raw material powder, for example.

[0053] The mixed raw material powder may be a mixed raw material powder obtained by physically mixing the W source raw material powder and the M element source raw material powder, or may be a mixed raw material powder obtained by dissolving the W source raw material powder and the M element source raw material powder in a solvent such as water to form a solution, mixing them, and then removing the solvent from the solution by drying, etc. In cases where it is particularly required to suppress variation in the composition of the obtained composite tungsten oxide particles, a mixed raw material powder obtained by dissolving the W source raw material powder and the M element source raw material powder in a solution, mixing them, and then removing the solvent from the solution by drying, etc. may be preferable.

[0054] The particle size of the mixed raw material powder dispersed in the aerosol forming process is not particularly limited, but the particle diameter is preferably 100 μm or less, more preferably 10 μm or less, and even more preferably 3 μm or less. By making the particle diameter 100 μm or less, it is possible to more reliably sublimate the inside of the particle. Note that the particle size of the mixed raw material powder dispersed in the aerosol forming process is preferably 100 nm or more. The particle diameter of the mixed raw material powder can be measured in the same manner as the particle diameter of the composite tungsten oxide particles described above.

[0055] The aerosol formed in the aerosol forming step can be transported, for example, by a carrier gas and subjected to the heat treatment step. (Heat treatment process) In the heat treatment step, the workpiece is heat treated at a temperature of 1000°C or higher and 1350°C or lower.

[0056] The mixed powder material containing the W-source powder and the M-element source powder, which is the material to be treated, is thought to evaporate and be completely decomposed to the atomic level during heating to 1000°C or higher and 1350°C or lower. It is thought that clusters are then formed, and composite tungsten oxide particles are formed through a condensation process as composite tungsten oxide. The heat treatment temperature is more preferably 1200°C or higher and 1350°C or lower, and even more preferably 1250°C or higher and 1350°C or lower.

[0057] It is believed that tungsten and the M element react with each other during the decomposition of the W source raw material powder and the M element source raw material powder, or at higher temperatures, to form a composite tungsten oxide.

[0058] Therefore, in order to sufficiently advance the decomposition of the W source raw material powder and the M element source raw material powder and to suppress the incorporation of impurities into the composite tungsten oxide, it is preferable to perform the heat treatment at a temperature equal to or higher than the decomposition temperature of the W source raw material powder and the M element source raw material powder in the heat treatment step. The decomposition of the W source raw material powder and the M element source raw material powder is thought to normally occur at 500°C or lower. Therefore, in the heat treatment step, the aerosol, which is the object to be treated, can be heat treated at 500°C or higher.

[0059] According to the studies of the present inventors, the heat treatment temperature also affects the particle size of the resulting composite tungsten oxide particles. Further studies by the present inventors have shown that as the heat treatment temperature increases, the particle size of the resulting composite tungsten oxide particles tends to decrease.

[0060] This is presumably because, when the heat treatment temperature is increased, thermal energy is used to sublimate the generated composite tungsten oxide particles, causing the particles to burst due to sublimation, resulting in particles with a fine particle size.

[0061] 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 aim is to obtain particularly fine nanoparticles, it is preferable to heat treat the workpiece at 1000° C. or higher in the heat treatment step.

[0062] In the heat treatment step, the upper limit of the temperature is 1350° C. If the heat treatment temperature exceeds 1350° C., a different phase such as metallic W may occur.

[0063] The aerosol is transported by a carrier gas to an electric furnace or the like, where the above-mentioned heat treatment step can be carried out. Therefore, the time for the heat treatment step can be adjusted by controlling, for example, the flow rate of the carrier gas.

[0064] The time required for the heat treatment step is not particularly limited and can be selected arbitrarily.

[0065] As described above, the mixed powder material containing the W-source powder and the M-element powder, which is the material to be treated, evaporates during heating to the heat treatment temperature and is decomposed into atoms. Then, clusters are formed, and the composite tungsten oxide is formed through a condensation process as the composite tungsten oxide.

[0066] In the heat treatment step, air can be used as a carrier gas. By using air as a carrier gas, it is possible to suppress the incorporation of different phases, which are inevitable impurities, into the composite tungsten oxide particles obtained after the heat treatment step and after the reduction treatment step described below. In other words, it is possible to increase the content of the composite tungsten oxide that contributes to infrared absorption, and to obtain composite tungsten oxide particles with excellent infrared shielding performance.

[0067] The flow rate of the carrier gas may be any flow rate that can form and maintain an aerosol in the aerosol forming section of the composite material production apparatus described below, and can be adjusted appropriately depending on the size of the composite material production apparatus used to produce the composite tungsten oxide particles, etc. (cooling process) The composite tungsten oxide particles produced in this embodiment can be recovered not immediately after heat treatment but through a cooling step in which cooling gas is supplied to cool them. The cooling step is an optional step, and the method for producing composite tungsten oxide particles of this embodiment does not need to include the cooling step. In the method for producing composite tungsten oxide particles of this embodiment, the heat treatment temperature is relatively high, at 1000°C or higher and 1350°C or lower. Therefore, by cooling in the cooling step, the product heated by the heat treatment and the high-temperature gas can be cooled to stop the reaction and suppress the generation of heterogeneous phases.

[0068] The specific operation of the cooling step is not particularly limited, but the product produced in the heat treatment step may be introduced into a container to which a cooling gas at room temperature is supplied. Note that a cooling gas at room temperature means a cooling gas that is in equilibrium with the ambient temperature without heating or cooling, and for example, a gas at 5°C to 35°C can be used. In particular, in the cooling step, it is preferable to supply the cooling gas to the product obtained in the heat treatment step from multiple directions, i.e., from two or more directions. This is because supplying the cooling gas to the product obtained in the heat treatment step from two or more directions allows for particularly rapid cooling and suppresses the generation of heterogeneous phases.

[0069] The cooling gas is preferably a mixed gas of an inert gas and O2. As the inert gas, a rare gas such as Ar or N2 can be used. In consideration of cost, N2 is preferably used as the inert gas. Therefore, a mixed gas of N2 and O2 can be suitably used as the cooling gas. The cooling gas preferably has an oxygen concentration of 1% by volume or more and 5% by volume or less.

[0070] By including O2 in the cooling gas, the reduction reaction that has progressed during the heat treatment process can be actively stopped, which in turn can particularly suppress the formation of heterogeneous phases. (Reduction treatment process) Particles obtained through a heat treatment process, specifically composite tungsten oxide particles, may not exhibit infrared absorption properties. Therefore, the inventors of the present invention have conducted research and found that by further performing a reduction treatment process in which the composite tungsten oxide particles obtained through the heat treatment process are subjected to a reduction treatment, the composite tungsten oxide particles can more reliably exhibit infrared absorption properties.

[0071] Therefore, the method for producing composite tungsten oxide particles of this embodiment preferably includes a reduction treatment step in which the obtained particles are reduced in an atmosphere containing a reducing gas after the heat treatment step. Note that, when the cooling step described above is carried out after the heat treatment step, the reduction treatment step can be carried out after the cooling step.

[0072] The conditions for the reduction treatment are not particularly limited, but it is preferable to select the conditions for the reduction treatment so that when the composite tungsten oxide particles after the reduction treatment are analyzed by X-ray diffraction pattern, metallic tungsten and the like do not precipitate.

[0073] In the reduction treatment step, the composite tungsten oxide particles obtained after the heat treatment step can be reduced by raising and lowering the temperature in a reducing atmosphere containing a reducing gas, that is, by performing heat treatment.

[0074] During the reduction treatment step, the composite tungsten oxide particles may be stirred or left to stand, and the handling of the composite tungsten oxide particles during the reduction treatment step can be selected appropriately, but it is preferable to select handling conditions so as not to cause precipitation of metallic tungsten.

[0075] The temperature of the reduction treatment (reduction treatment temperature) is preferably higher than 400°C and lower than 700°C, more preferably 500°C or higher and lower than 700°C, and even more preferably 600°C or higher and lower than 700°C. After the temperature is raised from room temperature to the reduction treatment temperature, it can be lowered again to room temperature. Here, room temperature refers to the temperature before the temperature rise begins or after the temperature drop, and means the ambient temperature or a temperature close to the ambient temperature.

[0076] By setting the reduction temperature to above 400°C, the reduction process of the composite tungsten oxide particles can be advanced and the infrared absorption properties can be more reliably exhibited. In addition, by setting the temperature to below 700°C, the reduction of the composite tungsten oxide particles to metallic tungsten can be prevented.

[0077] The reducing atmosphere is preferably an atmosphere of a mixed gas of an inert gas such as argon and a reducing gas such as H2 gas (hydrogen gas), and the reducing gas is preferably H2 gas.

[0078] When H2 gas is used as the reducing gas, the content of H2 gas in the reducing atmosphere can be selected appropriately, but the content of H2 gas is preferably in the range of 0.1% by volume to 10% by volume, more preferably 2% by volume to 10% by volume. Care must be taken when reduction is performed in an atmosphere containing only a reducing gas, as the reduction reaction may proceed excessively and metallic tungsten may precipitate.

[0079] The reduction treatment time is preferably 30 minutes or more, including the total time from temperature increase to temperature decrease. There is no particular upper limit to the reduction treatment time, and it is preferable to select it by conducting a preliminary test or the like so that the reduction does not proceed excessively. Here, the total time from temperature increase to temperature decrease means the time from starting temperature increase from room temperature, reaching the reduction treatment temperature, and cooling to room temperature. During this time, the composite tungsten oxide particles are preferably placed in the reducing atmosphere described above.

[0080] Although the mechanism of the reduction process is not clear, the composite tungsten oxide particles obtained after the cooling process were confirmed by X-ray diffraction patterns, such as CsW 1.6 O6 phase, Cs2O phase, etc. 0.32 It is also possible to convert the heterophase, which does not contribute much to infrared absorption properties, into the target phase capable of exhibiting infrared absorption properties by carrying out the reduction treatment step, thereby making it possible to obtain composite tungsten oxide particles with particularly excellent infrared absorption properties.

[0081] Furthermore, according to the research of the inventors of the present invention, the composite tungsten oxide particles obtained after the cooling step may contain two types of composite tungsten oxide crystal phases. Specifically, they may contain two crystal structures: a first crystal structure having an a-axis lattice constant of 7.400 Å to 7.405 Å and a c-axis lattice constant of 7.680 Å to 7.700 Å, and a second crystal structure having an a-axis lattice constant of 7.415 Å to 7.420 Å and a c-axis lattice constant of 7.600 Å to 7.620 Å. However, by performing a reduction treatment step, these two types of crystal structure phases can be converted into composite tungsten oxide particles containing a single-phase composite tungsten oxide having a crystal structure with excellent infrared absorption properties.

[0082] That is, composite tungsten oxide particles with excellent infrared absorption properties can also be prepared via the above two crystal structures. (3)Composite material manufacturing equipment An example of the configuration of a composite material production apparatus that can be suitably used in the method for producing composite tungsten oxide particles of this embodiment will be described below.

[0083] FIG. 1 is a diagram schematically illustrating a composite material manufacturing apparatus 10. As shown in FIG.

[0084] The composite material manufacturing apparatus 10 can have an aerosol formation section 11, a transport section 21, a reaction section 31, a cooling section 41, and a recovery section 51. When the cooling step described above is not performed, the composite material manufacturing apparatus 10 can be configured without the cooling section 41, with the reaction section 31 and the recovery section 51 connected to each other. Even when the composite material manufacturing apparatus 10 has the cooling section 41, the cooling step can be avoided by not supplying a cooling gas to the cooling section 41, and the target substance can be recovered in the recovery section 51.

[0085] (Aerosol formation part) The aerosol generating section 11 includes an aerosol generating tube 12, a stirring section 14, and a powder supply section 16 that supplies mixed raw material powder to the stirring section 14. The aerosol generating tube is tubular and includes an opening 13 that connects to the stirring section 14. The stirring section 14 includes a rotating brush 15. The brush 15 is disposed at the opening 13 so as to be exposed to the aerosol generating tube 12. Alternatively, a stirring blade may be used instead of the brush.

[0086] The powder supply unit 16 can have a raw material reservoir 17 for storing the mixed raw material powder, and a piston 18 for sending the mixed raw material powder to the stirring unit 14. The supply rate of the mixed raw material powder can be controlled by the movement speed of the piston 18. A known screw feeder or the like can also be used instead of the piston.

[0087] Furthermore, the aerosol generating pipe 12 can also be provided with a function of supplying carrier gas to the composite material manufacturing apparatus 10 by connecting a regulator 19 that controls the flow rate of carrier gas supplied from the outside.

[0088] (Transportation Department) The transport unit 21 can be provided between the aerosol formation unit 11 and the reaction unit 31. Specifically, the aerosol generation tube 12 can be connected to the transport unit 21 on the downstream side of the carrier gas, and the transport unit 21 can be connected to the piping 32 of the reaction unit 31. The transport unit 21 can supply the aerosol from the aerosol generation tube 12 to the piping 32.

[0089] (Reaction section) The heat treatment step described above can be carried out in the reaction section 31. For this purpose, the reaction section 31 can have, for example, a heat-resistant pipe 32 and a heater 33 for heating the pipe 32, as shown in Fig. 1. By heating the pipe 32 with the heater 33 and supplying and transporting an aerosol of the mixed raw material powder into the pipe 32, the aerosol can be heated in the heat treatment step without coming into contact with a flame or the like. This makes it possible to suppress the inclusion of impurities, by-products, and the like.

[0090] For example, ceramic piping can be used as the piping 32. From the viewpoint of preventing the inclusion of impurities, it is preferable to use a furnace tube made of Al2O3 with high purity. To reduce the cost of the furnace tube, mullite or the like can also be used.

[0091] The length L32 of the pipe 32 of the reaction section 31 is not particularly limited, and is preferably selected so that heating can be performed up to the predetermined temperature in the heat treatment step and sufficient time for the heat treatment step can be ensured.

[0092] The length L32 of the pipe 32 in the reaction section 31 is preferably 1 m or more from the viewpoint of heating to a predetermined temperature and ensuring sufficient time for the heat treatment step. Although there is no particular upper limit to the length of the pipe 32, an excessively long length requires a large amount of carrier gas and also increases the size of the apparatus, so that the length is preferably 5 m or less.

[0093] Furthermore, the diameter D32 of the pipe 32 is not particularly limited, but is preferably 1 cm or more from the viewpoint of productivity. The upper limit of the diameter D32 of the pipe 32 is not particularly limited, but it is preferably selected so that the temperature difference between the center and the wall portion does not become excessively large, and the diameter D32 of the pipe 32 is preferably, for example, 20 cm or less.

[0094] The diameter D32 of the pipe 32 means the inner diameter of the pipe 32.

[0095] The pipe 32 of the reaction section 31 usually has a temperature gradient along its longitudinal direction. For example, the temperature is low at the reaction section inlet 32A side and increases toward the reaction section outlet 32B.

[0096] Therefore, it is preferable to set various conditions so that a temperature region with a temperature of 1000° C. or higher can be formed in the vicinity of the reaction section outlet 32B.

[0097] Furthermore, particularly when the workpiece is heat-treated at a temperature of 1000°C or higher in the heat treatment step described above, it is preferable to set various conditions so that a temperature region where the temperature is 1000°C or higher can be formed near the reaction section outlet 32B. Furthermore, when the heat treatment time at a temperature of 1000°C or higher is set to 1 second or longer in the heat treatment step, it is preferable to set various conditions so that the time the workpiece passes through the temperature region of 1000°C or higher in the reaction section 31 is 1 second or longer. Specifically, for example, it is preferable to measure the temperature distribution in the pipe 32 in advance and adjust the supply rate of the carrier gas, etc.

[0098] The product of the heat treatment may be optionally recovered through a cooling step in which a cooling gas is supplied to cool the product after the heat treatment, rather than being recovered immediately after the heat treatment. The optional cooling step may be performed in the cooling section 41.

[0099] The cooling unit 41 may include a cooling vessel 42, a cooling gas inlet pipe 44 for introducing cooling gas, and a thermocouple 45. The cooling vessel 42 includes a connector 43, which is connected to the reactor outlet 32B and can receive high-temperature gas discharged from the reactor 31. Furthermore, it is preferable to keep the length L43 between the reactor outlet 32B and the cooling vessel 42 as short as possible. The length L43 of the connector 43 is at most 20 cm, preferably 10 cm, and more preferably 7 cm. To prevent carrier gas leakage from the joint between the reactor outlet 32B and the connector 43, the joint is preferably sealed with a commercially available heat-resistant ceramic adhesive primarily composed of ceramics such as alumina. A cooling gas supply means (not shown) can be connected to the cooling gas inlet pipe 44. While FIG. 1 shows an example in which one cooling gas inlet pipe 44 is provided, this configuration is not limited thereto. For example, two or more cooling gas inlet pipes 44 may be provided surrounding the connector 43. For example, cooling gas inlet pipes can be arranged around the periphery of the connecting part 43 at 120° intervals so that cooling gas can be introduced from three directions toward the high-temperature gas heated in the reaction part 31 and introduced from the connecting part 43. By providing multiple cooling gas inlet pipes in this way and supplying cooling gas from multiple directions, the products of the heat treatment process contained in the high-temperature gas (discharge gas) can be cooled quickly and efficiently. This particularly helps to suppress the generation of heterogeneous phases.

[0100] For example, the temperature inside the cooling vessel 42 may be measured by the thermocouple 45 described above, and the supply rate of the cooling rate, the temperature, etc. may be controlled.

[0101] In the recovery section 51, the composite tungsten oxide particles cooled in the cooling section 41 can be recovered. The configuration of the recovery section 51 is not particularly limited and can be selected depending on the particle size of the composite tungsten oxide particles to be produced, etc. As the recovery section 51, for example, various filters 52 can be used. Alternatively, an electrostatic collector can be used. A valve 61 and a pump 62 can be provided downstream of the recovery section 51. (reduction treatment device) In the reduction treatment device, the reduction treatment step described above can be carried out.

[0102] The reduction treatment device is not particularly limited as long as it is configured to be able to carry out the reduction treatment step described above. For example, it may include a container for storing the composite tungsten oxide particles obtained by the composite material production device described above, a gas pipe for supplying a mixed gas into the container to create a reducing atmosphere inside the container, and a heat source for heating the container.

[0103] Alternatively, a mixed gas that creates a reducing atmosphere in the container may be introduced into the container and then exhausted, and the composite tungsten oxide particles to be treated may be placed under a gas flow of the mixed gas. In this case, a gas supply pipe and an exhaust pipe may be provided as gas pipes so that such a gas flow can be formed.

[0104] Furthermore, a stirring blade or the like may be used in combination to stir the composite tungsten oxide particles in the container.

[0105] FIG. 2 is a diagram showing a schematic configuration example of a reduction treatment device, and shows a cross section taken along a plane passing through the central axis of a reaction tube 71 of a reduction treatment device 70.

[0106] The reduction treatment device 70 is a horizontal tubular furnace, and can be used by attaching a gas inlet pipe (not shown) to one port 71A of a reaction tube 71 and a gas exhaust pipe (not shown) to the other port 71B of the tubular furnace. Then, by supplying a mixed gas that forms a reducing atmosphere from the one port 71A side, the inside of the reaction tube 71 can be made into a reducing atmosphere.

[0107] A heater 72 can be provided around the reaction tube 71, and the composite tungsten oxide particles can be placed in a ceramic container 73 such as a boat and placed at a position corresponding to the heater 72 inside the reaction tube 71 of the tubular furnace.

[0108] Using this reduction treatment device 70, a reduction treatment can be performed on composite tungsten oxide particles 74 placed in a container 73 by creating a reducing atmosphere inside a reaction tube 71 and heating to a desired temperature with a heater 72.

[0109] According to the method for producing composite tungsten oxide particles of the present embodiment described above, it is possible to use equipment with low installation costs, such as an aerosol forming unit and a heater, and the number of steps can be reduced, thereby making it possible to easily produce composite tungsten oxide particles. [Example]

[0110] The present invention will be explained below by giving specific examples, but the present invention is not limited to these examples. (1) Evaluation method (1-1) Powder X-ray Diffraction The composite tungsten oxide particles obtained in the following examples and comparative examples were subjected to powder X-ray diffraction pattern (XRD pattern) measurement using a powder X-ray diffractometer (manufactured by Bruker, model: D2 PHASER). The powder X-ray diffraction pattern measurement was performed using CuKα radiation as the radiation source, with a tube voltage of 40 kV and a tube current of 30 mA. (1-2) Optical properties of dispersion The optical properties of the ink, which is a dispersion of composite tungsten oxide particles, were measured using a spectrophotometer (U-4100 manufactured by Hitachi, Ltd.). (2) Examples and Comparative Examples (2-1) Examples 1 and 2, Comparative Examples 1 to 4 [Example 1] In Example 1, composite tungsten oxide particles were synthesized by solid spray pyrolysis. The synthesis method will be described.

[0111] Using the composite material manufacturing apparatus 10 shown in FIG. 1, Cs 0.32 WO particles were produced and evaluated. Specific conditions are explained below. The composite material production apparatus 10 is equipped with a cooling section 41, but no cooling gas is introduced from the cooling gas inlet pipe 44; instead, the cooling gas inlet pipe 44 is used to connect the reaction section 31 and the recovery section 51.

[0112] 1 includes an aerosol-forming section 11, a transporting section 21, a reaction section 31, a cooling section 41, and a collection section 51. The aerosol-forming section 11, the transporting section 21, the reaction section 31, the cooling section 41, and the collection section 51 are connected by piping.

[0113] The aerosol forming unit 11 includes an aerosol generating tube 12, a stirring unit 14, and a powder supply unit 16 that supplies mixed raw material powder to the stirring unit 14. The aerosol generating tube 12 is tubular and includes an opening 13 that connects to the stirring unit 14. The stirring unit 14 includes a rotating brush 15. The brush 15 is disposed at the opening 13 so as to be exposed to the aerosol generating tube 12.

[0114] The powder supply unit 16 is composed of a raw material reservoir 17 for storing the mixed raw material powder, and a piston 18 for sending the mixed raw material powder to the stirring unit.

[0115] Furthermore, the aerosol generating pipe 12 is connected to a regulator 19 that controls the flow rate of the carrier gas supplied from a carrier gas tank (not shown), and also has the function of supplying the carrier gas to the composite material manufacturing apparatus 10.

[0116] First, a tungsten oxide powder represented by H2WO4 was prepared as a W source raw material powder.

[0117] Furthermore, cesium carbonate (manufactured by Sigma-Aldrich Co.) was prepared as a raw material powder of the M element source. The cesium carbonate was dissolved in water and used as an aqueous solution.

[0118] The Cs2CO3 aqueous solution and H2WO4 powder were mixed so that the ratio of the amounts of substances was Cs / W = 0.33, and then dried at 100°C for 12 hours to obtain a mixed raw material powder. When the mixed raw material powder was examined with an SEM, it was found to be a powder with a particle size of 1 μm or more and 2 μm or less.

[0119] (Aerosol formation process) In the aerosol generating section 11, the mixed raw material powder was extruded from the powder supplying section 16 at a supply rate of 2 g / hr toward the brush 15, which was rotating at a high speed of 1000 rpm or more. The mixed raw material powder dispersed in the carrier gas by the brush 15 became an aerosol. The aerosol was transported to the reaction section 31 via the transporting section 21. That is, the aerosol formed in the aerosol generating step was supplied to the heat treatment step.

[0120] The flow rate of the carrier gas was set to 10 L / min to sufficiently disperse the mixed raw material powder.

[0121] Air (air gas) was used as the carrier gas.

[0122] The reaction section 31 was equipped with a ceramic pipe 32, and a cylindrical pipe having a length L32 of 1.5 m and a diameter D32 of 13 mm was used as the pipe 32. The diameter D32 means the inner diameter of the pipe 32.

[0123] The reaction section 31 was configured to be heated from the outside of the pipe 32 by a heater 33, and the temperature was set so that it increased from the reaction section inlet 32A toward the reaction section outlet 32B.

[0124] A bag filter was placed as the filter 52 in the recovery section 51, and the resulting composite tungsten oxide particles were recovered.

[0125] Composite tungsten oxide particles were produced under the above conditions.

[0126] In Example 1, the furnace temperature in the reaction section 31 was set to 1300° C. That is, in the heat treatment step, the supplied aerosol was heated to 1300° C. and heat-treated at 1300° C. The heat treatment time at a heat treatment temperature of 1000° C. or higher was 0.8 seconds.

[0127] 3 shows the temperature profile in the reaction section 31. The position on the horizontal axis indicates the distance from the reaction section inlet 32A, and the temperature profile is measured along the central axis of the pipe 32. [Example 2] In Example 2, the composite tungsten oxide particles obtained in Example 1 were subjected to reduction treatment at 500°C for 1 hour in a mixed gas atmosphere of 3% by volume H / Ar (reduction treatment step). The reduction treatment was performed using the reduction treatment device 70 shown in Figure 2. [Comparative Example 1] In Comparative Example 1, nitrogen (N2) gas was used as the carrier gas in the aerosol forming step and the heat treatment step. Except for the above points, synthesis was carried out in the same manner as in Example 1. Comparative Example 2 In Comparative Example 2, a 0.5% by volume H / Ar gas containing 0.5% by volume hydrogen gas and the remainder Ar gas was used as the carrier gas in the aerosol-forming step and the heat-treating step. Except for the above, synthesis was carried out in the same manner as in Example 1. Comparative Example 3 In Comparative Example 3, the powder synthesized in Comparative Example 1 was subjected to the same reduction treatment as in Example 2 to synthesize the powder. Comparative Example 4 In Comparative Example 4, the powder synthesized in Comparative Example 2 was subjected to the same reduction treatment as in Example 2 to synthesize the powder.

[0128] The recovered composite tungsten oxide particles were evaluated.

[0129] 4(A) and 4(B) show the XRD measurement results for Examples 1 and 2 and Comparative Examples 1 to 4. Under all conditions, the main phase contained Cs 0.32 The WO3 phase was confirmed.

[0130] In Examples 1 and 2 and Comparative Examples 1 to 4, the mixed raw material powder was heated in a dispersed state as an aerosol in the heat treatment process, so that Cs 0.32 It was confirmed that the thermal decomposition reaction proceeded up to the WO3 phase.

[0131] 4(A) shows the XRD measurement results of the composite tungsten oxide particles synthesized in Example 1, in which the furnace temperature was set to 1300°C and air was used as the carrier gas, Comparative Example 1, in which nitrogen was used as the carrier gas, and Comparative Example 2, in which 0.5% by volume of H2 / Ar was used as the carrier gas. 0.32 The peak of the WO3 phase was confirmed.

[0132] FIG. 4(B) shows the results of XRD measurement of the composite tungsten oxide particles obtained in Example 2 and Comparative Examples 3 and 4, which are experimental examples in which the products obtained in Example 1 and Comparative Examples 1 and 2 were further subjected to reduction treatment. 0.32 The peak of the WO3 phase was confirmed.

[0133] 5(A) shows the proportions of components contained in the composite tungsten oxide particles synthesized in Example 1, which used air as the carrier gas, Comparative Example 1, which used nitrogen as the carrier gas, and Comparative Example 2, which used 0.5% by volume of H / Ar as the carrier gas, all at a furnace temperature of 1300° C. The proportions of each component were calculated by the Rietveld method from the measured XRD diffraction patterns.

[0134] The synthesized composite tungsten oxide particles contain (CsO) 0.44 The proportion of W2O6 was highest in Comparative Example 2, which used 0.5% by volume of H2 / Ar as the carrier gas, and lowest in Example 1, which used air as the carrier gas. 0.32 The proportion of the WO3-A phase was also the highest in Comparative Example 2 and the lowest in Example 1. On the other hand, the Cs content of the composite tungsten oxide particles was 0.32 The proportion of the WO3-B phase was the highest in Example 1.

[0135] Cs 0.32 WO3-A phase, and Cs 0.32 Although the lattice constant of the WO3-B phase is different, it is a composite tungsten oxide and exhibits infrared absorption properties. 0.44W2O6 becomes a heterophase that does not exhibit infrared absorption characteristics. Therefore, it was confirmed that by using air as a carrier gas in the heat treatment process, composite tungsten oxide particles can be obtained in which the generation and incorporation of heterophases is suppressed.

[0136] 5B shows the proportions of components contained in the composite tungsten oxide particles obtained in Example 2 and Comparative Examples 3 and 4, which are experimental examples in which the composite tungsten oxide particles obtained in Example 1 and Comparative Examples 1 and 2 were subjected to reduction treatment. 0.44 The W2O6 content was highest in Comparative Example 4, in which the composite tungsten oxide particles obtained in Comparative Example 2 were reduced using 0.5% by volume of H2 / Ar as the carrier gas. 0.32 The WO3-D phase was also precipitated.

[0137] Cs 0.32 WO3-C phase, and Cs 0.32 Although the lattice constant of the WO3-D phase is different, it is a composite tungsten oxide and exhibits infrared absorption properties. 0.44 W2O6 becomes a heterophase that does not exhibit infrared absorption characteristics. Therefore, even when a further reduction treatment is performed after the heat treatment process, it was confirmed that by using air as a carrier gas in the heat treatment process, composite tungsten oxide particles can be obtained in which the generation and incorporation of heterophases is suppressed.

[0138] 6 shows the change in lattice constant due to reduction treatment of the composite tungsten oxide particles obtained in Examples 1 and 2 and Comparative Examples 1 to 4. The lattice constant was calculated by Rietveld analysis.

[0139] The composite tungsten oxide particles obtained in Example 1, Comparative Example 1, and Comparative Example 2, which were not subjected to a reduction treatment step, contain two types of composite tungsten oxides with different lattice constants as described above, and therefore are plotted in Region A and Region B in Figure 6. It was confirmed that by performing a reduction treatment, a composite tungsten oxide consisting of approximately one phase was formed, as indicated by the arrow in Figure 6.

[0140] The composite tungsten oxide particles obtained in Example 1 contained Cs 0.32 WO3-A phase and Cs 0.32 It contains the WO3-B phase, but as shown in Example 2, it can be converted to Cs by reduction treatment. 0.32 It was confirmed that the WO3-C phase was formed.

[0141] The optical properties of inks, which were dispersions of the composite tungsten oxide particles obtained in Example 2 and Comparative Examples 3 and 4, were evaluated. Inks were prepared as dispersions using 2% by mass of the composite tungsten oxide particles obtained in Example 2 and Comparative Examples 3 and 4, with the remainder consisting of methyl isobutyl ketone as a dispersion medium. The inks were prepared by dispersing and pulverizing the composite tungsten oxide particles and dispersion medium using 0.3 mm diameter ZrO2 beads in a paint shaker for 120 minutes. The dispersion medium was added to the resulting inks to adjust the transmittance at a wavelength of 600 nm to approximately 80%, and then the optical properties were evaluated. The results are shown in Figure 7.

[0142] 7, it can be seen that the ink using the composite tungsten oxide particles of Example 2 has a lower transmittance in the infrared region than the inks using the composite tungsten oxide particles of Comparative Examples 3 and 4. This indicates that the above-described method for producing composite tungsten oxide particles is a synthesis method suitable for synthesizing infrared-shielding material particles.

Claims

1. General formula M ｘ W ｙ O ｚ (wherein M element is one or more elements selected from alkali metals, W is tungsten, O is oxygen, and 0.001≦x / y≦1, 2.2≦z / y≦3.0), an aerosol forming step of forming an aerosol containing a mixed raw material powder of a W source raw material powder serving as a tungsten source and an M element source raw material powder serving as an M element source, which are objects to be processed; a heat treatment step of heat-treating the aerosol at 1000°C or higher and 1350°C or lower while transporting the aerosol with a carrier gas, The method for producing composite tungsten oxide particles, wherein the carrier gas is air.

2. 2. The method for producing composite tungsten oxide particles according to claim 1, wherein the M element is Cs.

Images