JP7302811B2 - Light-absorbing particles, light-absorbing particle dispersion, and method for producing light-absorbing particles - Google Patents

Description

The present invention relates to light-absorbing particles, light-absorbing particle dispersions, and methods for producing light-absorbing particles.

Materials with the property of absorbing light are collectively referred to as light absorbing materials. The above-mentioned light means, for example, light in the range of ultraviolet light to visible light to near-infrared light, specifically electromagnetic waves having a wavelength of approximately 200 to 3000 nm.

Among them, near-infrared absorbing materials are one field of light-absorbing materials whose applications are expanding in recent years. Near-infrared absorbing particles are light-absorbing materials that strongly absorb light in the near-infrared region with a wavelength in the range of approximately 700 to 2500 nm. It is widely used in fields such as filters and thermal insulation materials for agriculture, and research and development is underway.

Various materials have been proposed as near-infrared absorbing materials.

For example, Patent Document 1 discloses an infrared-absorbing synthetic resin molded product obtained by molding a transparent resin containing tin oxide fine powder in a dispersed state into various shapes, and a transparent synthetic resin containing tin oxide fine powder in a dispersed state. An infrared-absorbing synthetic resin molded product has been proposed in which a resin is molded in the form of a sheet or a film, which is laminated on a transparent synthetic resin substrate.

In Patent Document 2, Sn, Ti, Si, Zn, Zr, Fe, Al, Cr, Co, Ce, In, Ni, Ag, Cu, Pt, Mn, and Ta are inserted between at least two sheets of plate glass facing each other. , W, V, Mo metals, oxides of the metals, nitrides of the metals, sulfides of the metals, dopes of Sb or F to the metals, or at least two of these Laminated glass has been proposed which has an intermediate film layer in which a composite of the above is dispersed.

In Patent Document 3, the applicant of this patent discloses ruthenium oxide fine particles, titanium nitride fine particles, tantalum nitride fine particles, titanium silicide fine particles, molybdenum silicide fine particles, lanthanum boride fine particles, iron oxide fine particles, and iron oxide hydroxide (III). A coating liquid for a permselective membrane and a permselective membrane characterized by dispersing at least one type of fine particles are disclosed.

However, the near-infrared absorbing materials that are heat ray shielding structures such as the infrared absorbing synthetic resin molded products disclosed in Patent Documents 1 to 3 all have heat ray shielding performance when high visible light transmittance is required. was not sufficient.

For example, as a specific numerical example of the heat ray shielding performance of the heat ray shielding structures disclosed in Patent Documents 1 to 3, visible light transmittance calculated based on JIS R 3106 (in this specification, simply When the "visible light transmittance" is 70%, the solar radiation transmittance similarly calculated based on JIS R 3106 (in this specification, sometimes simply referred to as "solar transmittance") is 70%. ) exceeded 50%.

Therefore, the applicant of the present patent has proposed an infrared shielding material fine particle dispersion in which infrared shielding material fine particles are dispersed in a medium, wherein the infrared shielding material fine particles have the general formula M _x W _y O _z (where M is 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, 0.001≦x/y≦1, 2.2≦z/y≦3.0). Composite tungsten oxide microparticles are contained, the composite tungsten oxide microparticles include at least one type of microparticles having a hexagonal, tetragonal, or cubic crystal structure, and the particle diameter of the infrared shielding material microparticles Patent Document 4 discloses a heat ray shielding dispersion characterized in that the is 1 nm or more and 800 nm or less.

As disclosed in Patent Document 4, a heat ray shielding dispersion using composite tungsten oxide fine particles represented by the general formula M _x W _y O _z exhibits high heat ray shielding performance, and has a visible light transmittance of 70%. was improved to less than 50%. In particular, the heat ray shielding fine particle dispersion using composite tungsten oxide fine particles with a hexagonal crystal structure, which employs at least one element selected from specific elements such as Cs, Rb, and Tl as the element M, has excellent heat ray shielding performance. , and the solar transmittance when the visible light transmittance was 70% was improved to below 37%.

JP-A-2-136230 JP-A-8-259279 JP-A-11-181336 WO2005/037932

K. Adachi, et al., Chromatic instabilities in cesium-doped tungsten bronze nanoparticles, J. Appl. Phys. 114, 194304 (2013)

However, the fine particles of composite tungsten oxide, which are the fine particles of the infrared shielding material disclosed in Patent Document 4, are either the particles themselves, the dispersion liquid containing the particles, or the dispersion at high temperature or high humidity, or both. When kept for a long time in a high-temperature, high-humidity environment that satisfies The decolorization phenomenon is a deterioration phenomenon of the light-absorbing particles under high temperature and high humidity. It means a phenomenon in which the color of the light-absorbing particles as seen by the human eye changes.

When such a decolorization phenomenon occurs, the appearance of materials and instruments using the light-absorbing particles is impaired, and the near-infrared shielding ability is sometimes lowered, which is a problem.

Therefore, in view of the above-described problems of the prior art, it is an object of one aspect of the present invention to provide light-absorbing particles that suppress the occurrence of the decoloring phenomenon.

In order to solve the above problems, in one aspect of the present invention,
Light absorbing particles comprising hexagonal tungsten bronze,
The tungsten bronze has the general formula: M _x WO _y (wherein the element M contains at least one selected from K, Rb, Cs, and Tl, and 0.1 ≤ x ≤ 0.5, 2.2 ≤ y ≤ 3.0),
Substitution ions having a larger ionic radius than oxygen ions (O ²⁻ ) are arranged on the surface,
The replacement ions provide light-absorbing particles comprising one or more ions selected from S ^2- , Se ^2- , Te ^2- , P ^3- , As ^3- and Sb ^3- .

According to one aspect of the present invention, it is possible to provide light-absorbing particles that suppress the occurrence of decolorization.

1 is a schematic plan view of the crystal structure of tungsten bronze having hexagonal crystals; FIG. FIG. 10 is an explanatory diagram of a structural model set in Example 10 and Comparative Example 2;

A light-absorbing particle, a light-absorbing particle dispersion, and a method for producing light-absorbing particles according to an embodiment of the present disclosure (hereinafter referred to as "this embodiment") will be described below with reference to the drawings. The present invention is not limited to these exemplifications, but is indicated by the scope of the claims, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

The light-absorbing particles, the method for producing the light-absorbing particles, the light-absorbing particle dispersion, the method for producing the light-absorbing particle dispersion, and application examples of the light-absorbing particles will be described below in order.
1. Light-Absorbing Particles A configuration example of the light-absorbing particles of the present embodiment will be described below.

The light absorbing particles of this embodiment can comprise hexagonal tungsten bronze.
The tungsten bronze can be represented by the general formula: M _x WO _y . The element M preferably contains at least one selected from K, Rb, Cs, and Tl and satisfies 0.1≦x≦0.5 and 2.2≦y≦3.0.
In the light-absorbing particles of the present embodiment, substitution ions having an ion radius larger than that of oxygen ions (O ²⁻ ) are arranged on the surfaces of the light-absorbing particles, and the substitution ions are group 15 elements and group 16 elements. , and one or more elements selected from Group 17 elements.

The inventors of the present invention have extensively studied a method for suppressing the decolorization phenomenon in light-absorbing particles containing tungsten bronze having a hexagonal crystal structure.

As described above, the decolorization phenomenon is a deterioration phenomenon of light-absorbing particles under high temperature and high humidity conditions. Specifically, when the light-absorbing particles themselves, a dispersion containing the light-absorbing particles, or a dispersion is kept in a high-temperature and high-humidity environment for a long time, the light transmittance of the light-absorbing particles in the visible region changes significantly. or a phenomenon in which the light absorbing ability in the near-infrared region is reduced and the color of the light absorbing particles as seen by the human eye changes. The high-temperature and high-humidity environment means an environment that satisfies either one of high temperature and high humidity, or both.

In the decolorization phenomenon, the element M, which is a doping element such as cesium, is detached from the crystal structure of the tungsten bronze contained in the light-absorbing particles, and the element M is partially missing in tungsten bronze or amorphous tungsten oxide. It has been reported that the

Based on the above findings, the inventors of the present invention proceeded with further studies. In the crystal structure 10 of tungsten bronze represented by M _{x WO y} shown in FIG. It is arranged in the interatomic cavity that exists through the entire crystal along the c-axis direction, which is perpendicular to the . The element M can relatively easily replace water molecules present in the surrounding environment. When the oxidation-reduction potential of the surrounding environment is near neutral, the entry and exit of water molecules and the element M, which is the doping element, are antagonistic, and the reaction does not proceed in one net direction. Emission of the element M and oxidation of the tungsten oxide proceed in one direction, leading to deterioration and discoloration. That is, the moisture resistance stability of element M depends on the pH and oxidation-reduction potential of the surrounding environment. This mechanism is the same for the decoloring phenomenon in a high-temperature environment in the normal atmosphere.

As a result of further research based on this knowledge, in order to prevent the element M from desorbing from the particle surface, steric hindrance is introduced to the particle surface, and the water molecules in the atmosphere and the element M on the particle surface We arrived at a completely new idea of interfering with the interaction between The inventors of the present invention conducted a test based on this idea, and found that at least part of the oxygen groups (O ^2- ) or hydroxyl groups (OH ^- ) present on the surface of the light-absorbing particles were converted to oxygen ions (O ^2- ). We found that the steric hindrance on the surface of the light-absorbing particles can be increased by substituting with substitution ions having larger ionic radii than the ions. The light-absorbing particles in which at least part of the oxygen groups or hydroxyl groups present on the surface of the particles have been substituted with substituted ions are more stable in a high-temperature and high-humidity environment than conventional light-absorbing particles in which the surface is not substituted. can be improved and the occurrence of the decolorization phenomenon can be suppressed, and the present invention has been completed.

The light absorbing particles of this embodiment can comprise hexagonal tungsten bronze. The tungsten bronze contained in the light-absorbing particles of the present embodiment is preferably tungsten bronze represented by the general formula M _x WO _y .

Element M in the above general formula is preferably one or more elements selected from Cs, Rb, K, Tl, In, Ba, Li, Ca, Sr, Fe, Sn, Al, Cu and Na. , at least one selected from K, Rb, Cs, and Tl. More preferably, the element M contains one or more selected from Cs and Rb, even more preferably the element M contains Cs, and most preferably the element M is Cs.

In the general formula, x indicating the content of the element M preferably satisfies 0.1≦x≦0.5, and more preferably satisfies 0.15≦x≦0.5. Moreover, y, which indicates the content of oxygen, preferably satisfies 2.2≦y≦3.0.

In the light-absorbing particles of the present embodiment, at least part of the oxygen groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ) present on the surface of the particles, that is, some or all of the oxygen groups or hydroxyl groups are replaced with oxygen ions (O ^2- ) can have a configuration substituted with substitution ions having a larger ionic radius than ). Therefore, the light-absorbing particles of this embodiment can have a structure in which substitution ions are arranged on the surfaces of the particles.

Although the substitution ion is not particularly limited, ions containing one or more elements selected from group 15 elements, group 16 elements, and group 17 elements can be preferably used.

Particles containing tungsten bronze and substitution of oxygen groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ) on the particle surface are described below.
(a) Particles Containing Tungsten Bronze In the general formula M _x WO _y representing tungsten bronze, W represents tungsten and O represents oxygen. Further, since the element M in the above general formula has already been described, the description thereof is omitted here.

By containing the tungsten bronze, the light-absorbing particles of the present embodiment can suppress the transmission of light in the infrared region, particularly the near-infrared region, and can exhibit heat ray shielding ability. In addition, the tungsten bronze has an absorption coefficient for light in the visible region that is much smaller than that for light in the near-infrared region. Even when the transmission of light in the visible region is sufficiently suppressed, high transmittance to light in the visible region can be maintained. The light absorbing particles of this embodiment can also be made of tungsten bronze.

The tungsten bronze contained in the light-absorbing particles according to this embodiment is represented by the general formula M _x WO _y as described above, and has a composition in which the element M is added to tungsten oxide (WO _y ).

According to studies by the inventors of the present invention, tungsten oxide (WO _y ) also has infrared absorption properties. However, in the case of tungsten oxide, for example, tungsten trioxide (WO ₃ ) does not have effective free electrons, so it has little absorption/reflection characteristics in the near-infrared region. Here, by setting the value of y, which is the ratio of oxygen to tungsten in tungsten oxide (WO _y ), to less than 3, free electrons are generated in the tungsten oxide to form efficient infrared absorbing particles. be able to. On the other hand, the crystalline phase of _WO2 absorbs and scatters light in the visible region, which may impair the transparency of visible light.

Therefore, in the case of tungsten oxide, the value of y in the chemical formula represented by WO _y satisfies 2.2≦y<3.0, thereby suppressing the formation of the WO ₂ crystal phase and increasing the efficiency. It can be a good infrared absorbing particle.

In tungsten oxide, the so-called “Magneli phase”, which has a composition ratio where the value of y is expressed by 2.45≦y<3.0, is chemically stable and absorbs light in the near-infrared region. Since it also has good properties, it can be used more preferably as an infrared absorbing particle.

In the tungsten bronze containing the light-absorbing particles and the light-absorbing particle dispersion liquid of the present embodiment, by adding the element M to the tungsten oxide, free electrons are generated in the tungsten bronze, and are free in the near-infrared region. A stronger electron-derived absorption characteristic develops. As a result, tungsten bronze exhibits particularly high properties as an infrared absorbing material that absorbs light in the near-infrared region, that is, near-infrared rays.

Tungsten bronze can be made into a more efficient infrared absorbing material by controlling the amount of oxygen described in tungsten oxide and adding an element M that generates free electrons in combination. When the control of the oxygen content and the addition of the element M that generates the free electrons are used in combination, in the general formula M _x WO _y representing tungsten bronze, 0.1 ≤ x ≤ 0.5, 2.2 ≤ y It is preferable to satisfy the relationship ≦3.0.

Here, the value of x indicating the amount of the element M added in the general formula of the tungsten bronze described above will be described. When the value of x is 0.1 or more, a sufficient amount of free electrons are generated and the desired infrared absorption effect can be obtained, which is preferable. As the amount of the element M added increases, the supply amount of free electrons increases and the infrared absorption efficiency increases, but the effect is saturated when the value of x is about 0.5. In addition, it is preferable that the value of x is 0.5 or less because it is possible to avoid the generation of an impurity phase in the infrared absorbing material.

Next, the value of y indicating the control of the oxygen amount will be explained. Regarding the value of y, in the infrared absorbing material represented by M _x WO _y , in addition to the mechanism similar to that of tungsten oxide (WO _y ) described above, the above-described element M There is a supply of free electrons depending on the amount of added. Therefore, 2.2≤y≤3.0 is preferable. In particular, as described for the Magneli phase of tungsten oxide, 2.45≦y≦3.0 is more preferable from the viewpoint of chemical stability.

The crystal structure of the tungsten bronze contained in the tungsten bronze particles is not particularly limited, and tungsten bronze of any crystal structure can be contained. However, when the tungsten bronze contained in the light-absorbing particles has a hexagonal crystal structure, the transmittance of the particles in the visible region and the absorption of light in the near-infrared region are particularly improved, which is preferable.

FIG. 1 shows a schematic plan view of the crystal structure of tungsten bronze having such a hexagonal crystal structure. As described above, in FIG. 1, _six WO ₆ octahedrons 12 formed by 6 units of WO are aggregated to form a hexagonal cavity. Then, the element M11 is placed in the gap to form one unit, and many of these one units are assembled to form a hexagonal crystal structure.

In this way, when the tungsten bronze contains a unit structure in which six octahedra formed of WO ₆ units are aggregated to form hexagonal voids, and the element M is arranged in the voids, light in the visible region can particularly improve the transmittance of the light and the absorption of light in the near-infrared region. It should be noted that the entire light-absorbing particles need not be composed of crystalline tungsten bronze having the structure shown in FIG. The effect of improving the absorption of light in the region can be obtained. As a result, the light absorbing particles as a whole may be crystalline or amorphous.

When an element M having a large ionic radius is added as the element M of tungsten bronze, the hexagonal crystal described above is likely to be formed. Specifically, when one or more of Cs, Rb, K, and Tl are added as the element M, hexagonal crystals are likely to be formed. Therefore, the element M preferably contains one or more of Cs, Rb, K, and Tl, and more preferably one or more of Cs, Rb, K, and Tl. In order to form a hexagonal crystal, even if the element M is an element other than these elements, it is sufficient if the element M can be present in the hexagonal voids formed by the WO ₆ units. It is not limited to the case of adding.

When the crystal structure of the tungsten bronze contained in the light-absorbing particles is a uniform hexagonal crystal structure, it is more preferable that the value of x, which indicates the amount of the element M added, satisfies 0.20≦x≦0.50. More preferably, 25≦x≦0.40 is satisfied. As described above, the value of y preferably satisfies 2.2≤y≤3.0. When y=3.0, the value of x becomes 0.33, so it is considered that the element M is arranged in all the hexagonal voids.

The crystal structure of the tungsten bronze contained in the light-absorbing particles of this embodiment is not particularly limited as described above. For example, it may contain tungsten bronzes of different crystal structures at the same time.

However, as described above, hexagonal tungsten bronze can increase the transmittance of light in the visible region and the absorbance of light in the near-infrared region. Therefore, the tungsten bronze contained in the light-absorbing particles of the present embodiment preferably has a hexagonal crystal system.

Further, when one or more selected from, for example, Cs and Rb is used as the element M, the crystal structure of the tungsten bronze tends to be hexagonal as described above. Furthermore, the transmittance of light in the visible region is high, while the transmittance of light in the infrared region, particularly the near-infrared region, is low. greater contrast with Therefore, it is more preferable that the element M of the general formula M _x WO _y representing tungsten bronze contains one or more selected from Cs and Rb. In particular, when the element M contains Cs, the weather resistance of the tungsten bronze is further enhanced, so it is even more preferable that the element M contains Cs, and it is particularly preferable that the element M is Cs.

The particle size of the light-absorbing particles according to this embodiment is not particularly limited, and can be arbitrarily selected. For example, it can be selected based on the application of the light-absorbing particles of the present embodiment, the degree of absorption of light in the near-infrared region required by the purpose of use, productivity, and the like. The average particle size of the light-absorbing particles of the present embodiment is preferably 1 nm or more and 500 nm or less, more preferably 1 nm or more and 100 nm or less.

This is because if the average particle size of the light absorbing particles is 500 nm or less, the light absorbing particles can exhibit strong absorption of light in the near-infrared region, and if the average particle size is 1 nm or more, industrial production is easy.

However, when the light-absorbing particles of the present embodiment are used for, for example, heat ray shielding applications, by making the particle diameter of the light-absorbing particles fine, visible light with a wavelength of 400 nm to 780 nm due to Mie scattering and Rayleigh scattering caused by the light-absorbing particles Light scattering in the region can be suppressed. As a result, it is possible to prevent the light-absorbing particle dispersion containing the light-absorbing particles of the present embodiment and the dispersion prepared by using the dispersion from becoming frosted glass and failing to obtain clear transparency. preferable.

By suppressing the scattering of the light, the transparency to light in the visible region can be ensured, and the transparency of the light absorbing material using the light absorbing particles of the present embodiment can be particularly enhanced. When the average particle diameter of the light-absorbing particles is 200 nm or less, the geometric scattering or Mie scattering is reduced, resulting in a Rayleigh scattering region. In the Rayleigh scattering region, the scattered light is proportional to the sixth power of the diameter of the dispersed particles. Therefore, as the diameter of the dispersed particles decreases, the scattering decreases and the transparency improves. Further, when the average particle diameter is 100 nm or less, the above-described scattered light is extremely reduced, which is preferable.

The dispersion state of the light-absorbing particles in the light-absorbing particle dispersion in which the light-absorbing particles are dispersed in the resin or the like obtained by using the dispersion liquid containing the light-absorbing particles of the present embodiment is known to those skilled in the art of the dispersion liquid in the resin or the like. As long as the adding method of (1) is carried out, the light-absorbing particles in the dispersion do not agglomerate beyond the average particle size. When the average particle size of the light absorbing particles is 1 nm or more and 100 nm or less, the light absorbing particle dispersion produced using the dispersion liquid containing the light absorbing particles and the molded article thereof (plate, sheet, etc.) are monotonous. It is preferable because it is possible to avoid becoming a grayish one with a decrease in transmittance.

From the above point of view, the average particle diameter of the light-absorbing particles of the present embodiment is more preferably 100 nm or less, and even more preferably 40 nm or less, as described above.

When the average particle diameter of the light-absorbing particles is 40 nm or less, the scattering of light due to Mie scattering and Rayleigh scattering of the particles is sufficiently suppressed, and the visibility of light in the visible region is maintained, and at the same time, the transparency is efficiently maintained. can be done. Especially when used in applications requiring transparency, the average particle size of the light absorbing particles is particularly preferably 30 nm or less in order to further suppress scattering.

The average particle size of the light-absorbing particles means the particle size at 50% of the integrated value in the particle size distribution determined by the dynamic light scattering method, for example, for the dispersion liquid of the light-absorbing particles. Hereinafter, the term "average particle size" in the present specification has the same meaning.

As described above, from the viewpoint of avoiding scattering of light, it is preferable that the average particle size of the light-absorbing particles is small. However, the average particle diameter of the light-absorbing particles in the present embodiment is 1 nm, because it may facilitate handling when manufacturing the light-absorbing particle dispersion or may prevent aggregation in the light-absorbing particle dispersion. It is preferable that it is above.

Of the properties described above, the transmittance of light in the near-infrared region and the transmittance of light in the visible region depend on the substitution of oxygen groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ) on the surface of the light-absorbing particles, which will be described later. It was found that optical properties such as transmittance hardly changed.
(b) Substitution of Oxygen Groups (O ²⁻ ) or Hydroxyl Groups (OH ⁻ ) on the Surface of Light Absorbing Particles Tungsten bronze literally belongs to oxides, and as described in (a) particles containing tungsten bronze, basically It is preferably crystalline rather than amorphous. In a particle containing a crystalline oxide, the crystal unit lattice is repeated inside the particle, while the crystal is naturally interrupted at the particle surface, that is, at the interface with other substances or vacuum, and as a result , a surface relaxation layer, and the like. In many cases, in this surface structure present in particles containing crystalline oxides, oxygen groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ) among the elements constituting the crystals are present at the surface of the particles. . It has been clarified that even in light-absorbing particles containing tungsten bronze, oxygen groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ) are present on the surface of the particles. In ordinary light-absorbing particles in which the ions on the surface of the particles are not substituted, whether oxygen groups or hydroxyl groups are present depends on the surrounding environment, such as hydrogen ion concentration, temperature, and surface adsorption in the surrounding liquid. It depends on the organic molecules and the like, and in some cases oxygen groups and hydroxyl groups may coexist on the same particle surface.

As described above, in the light-absorbing particles of the present embodiment, substitution ions, which are ions that have a larger ionic radius than oxygen ions (O ²⁻ ) and increase steric hindrance on the surface of the light-absorbing particles, cause the light-absorbing particles to be sterically hindered. At least part of the surface oxygen groups and hydroxyl groups can be substituted. The replacement ions are ions containing one or more elements selected from group 15 elements, group 16 elements, and group 17 elements, for example. In addition, the light-absorbing particles of the present embodiment in which the oxygen groups and hydroxyl groups are substituted with the above-mentioned substituted ions have improved stability in a high-temperature and high-humidity environment compared to conventional light-absorbing particles that are not substituted, It is possible to suppress the occurrence of the decoloring phenomenon.

^As the replacement ^ions , ions containing ^one or more elements selected from the ^above -described predetermined element group can be preferably used ^. It is more preferable to contain at least one type of ion selected from the ion group of ⁻ , Sb ³⁻ , Cl ⁻ , Br ⁻ and I ⁻ .

This is because when the substituted ions include one or more ions selected from the group of ions such as S ^2- described above, the light-absorbing particles having the substituted ions on the surface of the particles are decolored under a high-temperature and high-humidity environment. This is because it is possible to particularly suppress the occurrence of All of the ions included in the group of ions such as S ²⁻ have an ionic radius that is particularly larger than that of oxygen ions (O ²⁻ ), so that the steric hindrance on the surface of the light-absorbing particles can be further increased. As a result, desorption of the element M and oxidation of the tungsten element due to moisture can be suppressed, and the decolorization phenomenon of the light-absorbing particles can be particularly suppressed.

Substituting ions more preferably include one or more ions selected from S ²⁻ , P ³⁻ , Cl ⁻ , Br ⁻ , and I ⁻ from the viewpoints of material availability and ease of handling.

A plurality of different types of ions can be used at the same time as the substitution ions arranged on the particle surfaces of the light-absorbing particles of this embodiment.

Although there is no particular limitation on the specific form of the substitution ions on the surface of the light-absorbing particles, the substitution ions on the surface of the light-absorbing particles are S ²⁻ , SH ⁻ , Se ²⁻ , SeH ⁻ , Te ²⁻ , It is preferably present in one or more forms selected from TeH ⁻ , PH ²⁻ , PH ₂ ⁻ , AsH ₂ ⁻ , SbH ₂ ⁻ , Cl ⁻ , Br ⁻ and I ⁻ . Substitution ions in these forms are relatively easy to introduce as monovalent anions in place of oxygen groups (O ²⁻ ) and hydroxyl groups (OH ⁻ ) in the surface relaxation layer, and are stable after introduction. is also high. Above all, from the viewpoint of material availability, ease of handling, etc., the substitution ion on the particle surface of the light-absorbing particles is one selected from SH ⁻ , PH ₂ ⁻ , Cl ⁻ , Br ⁻ and I ⁻ . It is more preferable to exist in the above forms.

Elements and ions present on the surface of the light-absorbing particles can be detected by any method. As a method for confirming the presence of elements, a method of heating and detecting degassing by infrared absorption spectroscopy, etc., elemental mapping by high-sensitivity TEM-EDX, detection by EELS using a high-resolution transmission microscope, etc. can be used. can be done.

Specific ionic forms of the elements present on the surface of the light absorbing particles: O ²⁻ , OH ⁻ , S ²⁻ , SH ⁻ , Se ²⁻ , SeH ⁻ , Te ²⁻ , TeH ⁻ , PH ^{2 −} , PH ₂ ⁻ , AsH ₂ ⁻ , SbH ₂ ⁻ , Cl ⁻ , Br ⁻ , and I ⁻ can be arbitrarily selected from known methods such as Raman spectroscopy, FT-IR method, and NMR method. can. Among them, the detection of functional groups by the FT-IR method using the KBr tablet method is preferably used because it is possible to analyze functional groups even with a small amount of sample and is excellent in accuracy and reproducibility. can.
2. Method for Producing Light-Absorbing Particles A configuration example of the method for producing light-absorbing particles according to the present embodiment will be described.

The method for producing light-absorbing particles of the present embodiment relates to a method for producing light-absorbing particles containing hexagonal tungsten bronze. Obtainable.
The tungsten bronze can be represented by the general formula: M _x WO _y . The element M preferably contains at least one selected from K, Rb, Cs, and Tl and satisfies 0.1≦x≦0.5 and 2.2≦y≦3.0.
According to the method for producing light-absorbing particles of the present embodiment, at least part of the oxygen groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ) existing on the surface of the light-absorbing particles are replaced with oxygen ions (O ²⁻ ). can be replaced with a replacement ion having an ionic radius larger than As a result, a structure in which substitution ions having an ionic radius larger than that of oxygen ions (O ²⁻ ) are arranged on the surface of the light absorbing particles can be obtained. The replacement ions can be ions containing one or more elements selected from group 15 elements, group 16 elements, and group 17 elements.

Element M in the above general formula is preferably one or more elements selected from Cs, Rb, K, Tl, In, Ba, Li, Ca, Sr, Fe, Sn, Al, Cu and Na. , at least one selected from K, Rb, Cs, and Tl. In particular, the element M more preferably contains one or more selected from Cs and Rb, more preferably Cs, and particularly preferably Cs.

The average particle size of the light-absorbing particles obtained by the method for producing light-absorbing particles according to the present embodiment is not particularly limited, and can be arbitrarily selected. It is more preferably 1 nm or more and 100 nm or less, and further preferably 1 nm or more and 40 nm or less. Especially when used in applications requiring transparency, the average particle size of the light absorbing particles is particularly preferably 30 nm or less in order to further suppress scattering.

In the method for producing light-absorbing particles of the present embodiment, the substitution ions are particularly those of S ²⁻ , Se ²⁻ , Te ²⁻ , P ³⁻ , As ³⁻ , Sb ³⁻ , Cl ⁻ , Br ⁻ and I ^{− .} More preferably, it contains one or more ions selected from the group of ions. Substituting ions more preferably include one or more ions selected from S ²⁻ , P ³⁻ , Cl ⁻ , Br ⁻ , and I ⁻ from the viewpoints of material availability and ease of handling.

Although the specific form of the above-mentioned substituted ions is not particularly limited, the substituted ions are S ²⁻ , SH ⁻ , Se ²⁻ , SeH ⁻ , Te ²⁻ , TeH ⁻ , PH ²⁻ , PH ₂ ⁻ , AsH ₂ ⁻ , SbH ₂ ⁻ , Cl ⁻ , Br ⁻ and I ⁻ . Above all, from the viewpoint of material availability, ease of handling, etc., the substitution ion on the particle surface of the light-absorbing particles is one selected from SH ⁻ , PH ₂ ⁻ , Cl ⁻ , Br ⁻ and I ⁻ . It is more preferable to exist in the above forms.

According to the method for producing light absorbing particles of the present embodiment, the light absorbing particles described above can be produced. Therefore, some of the items already explained will be omitted.

The steps that the method for producing light-absorbing particles of the present embodiment can preferably have will be described below.
(A) Substitution step In the method for producing light-absorbing particles of the present embodiment, oxygen groups (O ^2- ) or at least part of the hydroxyl groups (OH ⁻ ) are replaced with replacement ions having a larger ionic radius than oxygen ions (O ^2- ).

The tungsten bronze can be represented by the general formula: M _x WO _y . The element M preferably contains at least one selected from K, Rb, Cs, and Tl and satisfies 0.1≦x≦0.5 and 2.2≦y≦3.0.

As described above, the replacement ions can be ions containing one or more elements selected from group 15 elements, group 16 elements, and group 17 elements. Since the preferred replacement ions have already been described, the description is omitted here.

In the substitution step, a specific method for substituting at least a portion, ie, a portion or all, of the oxygen groups or hydroxyl groups present on the surface of the particles with substitution ions is not particularly limited. For example, particles to be substituted containing oxygen groups or hydroxyl groups on the surface can be mixed with a solution containing substitution ions and dried to effect substitution with substitution ions. Substitution with substitution ions can also be carried out by exposing the particles to be substituted to a gas containing the element corresponding to the substitution ions. In particular, the latter replacement by exposing the particles to be replaced to the gas is preferable because the oxygen groups and the like on the surface of the particles to be replaced can be efficiently replaced with replacement ions.

Thus, the replacement step can include, for example, an exposure step of exposing particles containing hexagonal tungsten bronze to a gas containing one or more elements selected from group 15 elements, group 16 elements, and group 17 elements. can.

In such an exposure step, the particles to be substituted having oxygen groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ) present on the surface are treated with a gas containing an element corresponding to the substituted ion, such as sulfur, sulfur dioxide, sulfur trioxide, and hydrogen sulfide. can be exposed to a gas comprising one or more selected from In this case, oxygen groups and hydroxyl groups present on the surfaces of the particles to be substituted can be substituted with sulfur groups (S ²⁻ ) and thiol groups (SH ⁻ ).

As described above, the replacement ions can contain one or more elements selected from group 15 elements, group 16 elements, and group 17 elements. You can choose the type. In the exposure step, for example, in addition to the above sulfur-based materials, PH ₃ , phosphorus trichloride, phosphorus pentachloride, Cl ₂ , HCl, thionyl chloride, orysanyl chloride, triphosgene, Br ₂ , HBr, A gas containing one or more selected from I ₂ , HI, and the like can be used.

The conditions of the replacement treatment in the exposure step, such as the type of gas, gas concentration, flow rate, treatment temperature, treatment time, etc., are the elements and ions to be replaced, the amount of particles to be replaced, the average particle size, the type of tungsten bronze, i.e. It can be selected according to the type and amount of the element M, the amount of oxygen deficiency (oxygen defect), and the like.

For example, a mixed gas of hydrogen sulfide and argon can be used to replace oxygen groups and hydroxyl groups present on the surface of particles with sulfur groups (S ²⁻ ) and thiol groups (SH ⁻ ). The hydrogen sulfide concentration in the mixed gas used is preferably 5 ppm or more and 10000 ppm or less, the flow rate is preferably 0.1 L / min or more and 3 L / min or less, and the treatment temperature is 150 ° C. or more and 400 ° C. or less. and the treatment time is preferably 30 minutes or more and 2 hours or less.

The particles to be substituted are preferably sufficiently dried before being subjected to the exposure step.

As described above, the replacement method with replacement ions in the replacement step is not limited to the exposure step, and any method can be selected.

On the surface of the light absorbing particles obtained after the substitution step, at least part of the oxygen groups and the like are substituted with substitution ions. It can be preferably used as the light-absorbing particles of the present embodiment.

Since the above tungsten bronze and replacement ions have already been described, the description is omitted here.
(B) Pulverization Step, Isolation Step The method for producing light-absorbing particles of the present embodiment may optionally include the following pulverization step and isolation step prior to the replacement step.
A pulverization step of pulverizing particles containing hexagonal tungsten bronze in a liquid medium to pulverized particles having an average particle size of 1 nm or more and 100 nm or less.
An isolation step for isolating the ground particles from the liquid medium.

The light-absorbing particles produced by the method for producing light-absorbing particles of the present embodiment are preferably finely divided into fine particles. In particular, it is preferable that fine particles having a particle size suitable for use in a light-absorbing particle dispersion or the like are finally obtained before performing the replacement step described above.

Even if at least part of the oxygen groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ) on the surface of the particles are substituted with substituted ions in the substitution step, this is the case when the grain refinement step is further performed after the substitution step. , the comminution of the primary particles will expose new surfaces. This is because the newly exposed surface consists of unsubstituted oxygen groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ).

In the pulverization step, the specific means for pulverizing the particles containing hexagonal tungsten bronze is not particularly limited, and various means capable of pulverizing to the target particle size can be used. As a mechanical pulverization method, a dry pulverization method using a jet mill or the like can be used. However, when pulverization to a finer particle size is required, it is preferable to perform wet pulverization using a paint shaker, a wet bead mill device, or the like. For this reason, in the pulverization step, as described above, wet pulverization is preferably performed in a liquid medium until pulverized particles having a desired average particle size are obtained.

When wet pulverization is performed using a liquid medium as described above in the pulverization step, the method for producing light-absorbing particles of the present embodiment can further include an isolation step. In the isolation step, ground particles can be isolated from the liquid medium to obtain ground particles having a desired average particle size. Any method can be used to isolate the ground particles from the liquid medium, and can include a combination of steps such as drying, centrifugation, and filtering of agglomerated particles. The pulverized particles obtained in the isolation step can be subjected to, for example, the replacement step described above, and the pulverized particles can be used as the particles containing tungsten bronze mentioned in the replacement step.

For example, when particles having a desired average particle size are obtained as particles containing tungsten bronze, they can be subjected to the replacement step described above without carrying out the pulverization step or the like.
(C) Raw Material Particle Production Step The method for producing light-absorbing particles according to the present embodiment may further include a raw material particle production step for producing raw material particles, that is, particles containing tungsten bronze, if necessary.

The method for producing the raw material particles used in the raw material particle production process is not particularly limited, and various methods capable of obtaining a predetermined composition can be used. Methods for producing raw material particles include a method of synthesizing in a reducing gas stream, a solid phase reduction reaction method, a method of oxidizing tungsten bronze obtained by a solid phase reaction/liquid phase method/gas phase method using an oxygen-containing gas, Alternatively, a method of reduction treatment using a stream of reducing gas, a method of reducing _WO3 in a molten alkali halide, and the like can be used.

Hereinafter, configuration examples of the raw material particle manufacturing process will be described for each method of manufacturing the raw material particles.
(Synthesis method in reducing gas stream)
As a method for producing raw material particles in the raw material particle production process, for example, a synthesis method in a reducing gas stream can be used. In this case, the raw material particle manufacturing process can have the following heating process.

In the heating step, a raw material mixture containing the elements M and W and having an atomic ratio a (M/W) between the element M (M) and W satisfying 0.1 ≤ a ≤ 0.5 is heated to a reducing A solid-phase reaction can be performed by heating at a solid-phase reaction temperature of 400° C. or higher and 650° C. or lower in a gas stream.

Elements that can be suitably used as the element M have already been described, and therefore descriptions thereof are omitted here. In addition, a can be selected according to the composition of the target tungsten bronze, and can take the same preferable range as x when the tungsten bronze is explained.

It is preferable that the raw material particle production step further includes a homogenization step in which heat treatment is performed at a temperature higher than the solid phase reaction temperature in the heating step, for example, 700° C. or higher and 900° C. or lower.

As raw materials for the heating step, for example, an M ₂ CO ₃ aqueous solution containing a carbonate of the element M and H ₂ WO ₄ (tungstic acid) can be used. In addition, when the element M contains a plurality of elements, a plurality of corresponding M ₂ CO ₃ aqueous solutions can also be used.

The raw material mixture to be subjected to the heating step is an aqueous solution of M ₂ CO ₃ and H ₂ WO ₄ mixed and kneaded at a ratio of a (M/W), which is the atomic number ratio, to 0.1 ≤ a ≤ 0.5. obtained by doing Moreover, it is preferable to dry the raw material mixture in the atmosphere in order to reduce the water content before the heating step.

In the heating step, the raw material mixture is heated at a solid-phase reaction temperature of 400° C. or higher and 650° C. or lower in a stream of reducing gas to cause a solid-phase reaction, whereby tungsten bronze M _a WO _3-b can be prepared. .

The reaction formula in the heating step when a=0.33 is represented by the following formula.
0.165 _M2CO3 + _H2WO4 + _{( 0.165} +b) _H2
→ 0.165 CO ₂ ↑ + (1.165 + b) H ₂ O ↑ + M _0.33 WO _3-b
In the homogenization step, heat treatment can be performed at a temperature higher than the solid phase reaction temperature in the heating step, for example, 700° C. or higher and 900° C. or lower. The homogenization step is preferably carried out under an inert gas atmosphere such as nitrogen or argon.
(Solid phase reduction reaction method)
A solid-phase reduction reaction method can also be used as a method for producing raw material particles in the raw material particle production process.

In this case, the raw material particle production step can include a heating/reduction step of heating the raw material mixture at 750° C. or higher and 950° C. or lower in a vacuum atmosphere or an inert gas atmosphere.

As the raw material mixture, one selected from WO ₃ , one or more selected from M ₂ CO ₃ and M ₂ WO ₄ , simple tungsten, and tungsten oxide having an O/W atomic ratio of less than 3 The atomic number ratio M/W between the elements M and W can be set to 0.1≦a≦0.5.

Elements that can be suitably used as the element M have already been described, and therefore descriptions thereof are omitted here. In addition, a can be selected according to the composition of the target tungsten bronze, and can take the same preferable range as x when the tungsten bronze is explained.

In the case of heating in a vacuum or in an inert gas atmosphere so as to realize a stoichiometry of the composition including oxygen in a closed system reaction between the raw materials, it is preferable that the raw materials contain a reducing component. . Specifically, as described above, in addition to WO ₃ as a raw material and one or more selected from M ₂ CO ₃ and M ₂ WO ₄ as a reducing component, simple tungsten and O/W atoms It is preferable to use one or more tungsten oxides having a number ratio of less than 3 (for example, one or more selected from W, WO ₂ and WO _2.72 ).

Then, each component of the raw materials is weighed, mixed, and heated at 750° C. or higher and 950° C. or lower in a vacuum or in an inert gas atmosphere to perform a heating and reduction step to synthesize M _a WO _3-b. be able to. Heating may be performed by vacuum sealing in a quartz tube, heating in a vacuum firing furnace, or heating in an inert gas atmosphere such as nitrogen. In addition, when using an inert gas, it can also heat under an inert gas stream. An ideal reaction formula when using WO ₃ , M ₂ WO ₄ and tungsten elemental W as raw materials is represented by the following formula.
(a/2) M ₂ WO ₄ + (1−2a/3) WO ₃ + (a/6) W=M _a WO ₃
However, although oxygen stoichiometry should be achieved by solid-state reactions between the raw materials, oxygen vacancies are usually introduced to produce M _a WO _3-b . The reason for this lies in M ₂ CO ₃ and M ₂ WO ₄ which are one of the raw materials. M ₂ CO ₃ and M ₂ WO ₄ tend to absorb moisture and deliquescence at room temperature during weighing. If the solid-phase reaction is carried out as it is, the moisture mixed in according to the humidity in the atmosphere evaporates and acts as a reducing agent, so M _a WO _3-b having oxygen deficiency is produced.

Since M _a WO _3-b is very easily reduced, preparation of samples with very few or no oxygen vacancies requires ingenuity. In this case, the raw material M ₂ WO ₄ is preferably weighed in a dry environment in a glove box and handled so as not to absorb moisture. For example, when heating in a vacuum firing furnace, the heating is performed at 750° C. or higher and 950° C. or lower, but if the vacuum holding time at high temperature is long, such as exceeding several days, the reduction of M _a WO _3-b proceeds, A fully reduced state, for example b of 0.46, may occur. Furthermore, when a crucible made of carbon material is used, reduction may progress at the portion in contact with carbon.

Thus, the hygroscopicity of the raw materials M ₂ CO ₃ and M ₂ WO ₄ and the conditions of the heat treatment in the heating/reduction process are important factors that affect the amount of oxygen deficiency in the obtained M _a WO _3-b. be. Therefore, in order to control the amount b of oxygen deficiency in M _a WO _3-b to a particularly low value, it is preferable to pay sufficient attention to the raw materials, atmospheric humidity, vacuum holding time, crucible material, and the like.
(Method of oxidizing or reducing tungsten bronze)
Examples of a method for producing raw material particles in the raw material particle production process include a method of oxidizing tungsten bronze using an oxidizing gas and a method of reducing treatment using a reducing gas.

In this case, the raw material particle production step includes forming tungsten bronze represented by the general formula M _a WO _3-b (0.1≦a≦0.5, 0<b≦0.46) including An annealing step can be performed in which the substrate is placed in a crucible made of a reducing material and annealed at 300° C. or higher and 650° C. or lower in an atmosphere of an oxidizing gas.

In addition, in the raw material particle production process, tungsten bronze represented by the general formula: M _a WO _3-b (0.1≦a≦0.5, 0<b≦0.46) including oxygen deficiency An annealing step of annealing at 300° C. or higher and 650° C. or lower in a gas atmosphere can be included.

Elements that can be suitably used as the element M have already been described, and therefore descriptions thereof are omitted here. Also, a can be selected according to the composition of the target tungsten bronze, and can be within the same preferable range as x described for the tungsten bronze.

In the method of oxidizing tungsten bronze, tungsten bronze having more oxygen vacancies than the desired tungsten bronze is heated in an oxidizing gas atmosphere to reduce the amount of oxygen vacancies to the desired value.

An oxygen-containing gas can be used as the oxidizing gas. Although the amount of oxygen in the oxygen-containing gas is not particularly limited, it preferably contains 18 vol % or more and 100 vol % or less of oxygen. As the oxidizing gas, it is preferable to use the atmosphere (air) or oxygen gas, for example.

In addition, in the method of reducing the tungsten bronze, a tungsten bronze having less oxygen vacancies than the desired tungsten bronze is heated in a reducing gas atmosphere to increase the amount of oxygen vacancies to a desired value. In addition, when performing a reduction process, it is preferable to perform under the air current of reducing gas.

As the reducing gas, a mixed gas containing a reducing gas such as hydrogen and an inert gas can be used.

In addition, the manufacturing method of the tungsten bronze which is subjected to oxidation treatment or reduction treatment of the tungsten bronze is not particularly limited.

For example, a thermal plasma method can be used as a method of manufacturing tungsten bronze.

When synthesizing tungsten bronze by the thermal plasma method, a mixed powder of a tungsten compound and an element M compound can be used as a raw material.

Examples of the tungsten compound include tungstic acid (H ₂ WO ₄ ), ammonium tungstate, tungsten hexachloride, tungsten hydrate obtained by adding water to tungsten hexachloride dissolved in alcohol, hydrolyzing it, and then evaporating the solvent; It is preferably one or more selected from.

Moreover, as the element M compound, it is preferable to use one or more selected from oxides, hydroxides, nitrates, sulfates, chlorides, and carbonates of the element M.

An aqueous solution containing the above-mentioned tungsten compound and the above-mentioned element M compound is prepared so that a (M/W), which is the atomic number ratio of the element M (M) and W, matches the composition of the target tungsten bronze. Wet mix as follows. Then, by drying the obtained mixture, a mixed powder of the element M compound and the tungsten compound is obtained. The mixed powder can be used as a raw material for the thermal plasma method.

In addition, tungsten bronze obtained by performing one-step firing on the mixed powder in an inert gas alone or in a mixed gas atmosphere of an inert gas and a reducing gas is used as a raw material for the thermal plasma method. You can also In addition, in the first stage, it is fired in a mixed gas atmosphere of an inert gas and a reducing gas, and the fired product in the first stage is fired in an inert gas atmosphere in the second stage. Tungsten bronze obtained by subjecting the mixed powder to sintering in stages can also be used as a raw material for the thermal plasma method.

The thermal plasma used in the thermal plasma method is not particularly limited. At least one selected from plasma generated by an electrical method in which a magnetic field is applied to the plasma, plasma generated by irradiation with a high-power laser, plasma generated by a high-power electron beam or ion beam, and the like can be applied.

However, whichever thermal plasma is used, it is preferable that the thermal plasma has a high temperature portion of 10,000 to 15,000 K, and it is particularly preferable that the plasma is capable of controlling the generation time of fine particles.

The raw material supplied into the thermal plasma having the high temperature portion instantly evaporates in the high temperature portion. Then, the vaporized raw material is condensed in the process of reaching the plasma trailing flame and is rapidly cooled and solidified outside the plasma flame, thereby producing tungsten bronze.

Furthermore, as a method for producing tungsten bronze, a known compound synthesis method such as a hydrothermal synthesis method may be used.
3. Light-absorbing particle dispersion liquid The light-absorbing particle dispersion liquid of the present embodiment is a liquid medium comprising the light-absorbing particles described above and at least one selected from water, organic solvents, oils, liquid resins, and liquid plasticizers for plastics. , wherein the light absorbing particles are dispersed in a liquid medium.

The light-absorbing particle dispersion liquid is a liquid in which the above-described light-absorbing particles are dispersed in a liquid medium as a solvent.

As the liquid medium, as described above, one or more selected from water, organic solvents, fats and oils, liquid resins, and liquid plasticizers for plastics can be used.

Various organic solvents such as alcohol, ketone, hydrocarbon, glycol, and water can be selected as the organic solvent. Specifically, alcohol solvents such as isopropyl alcohol, methanol, ethanol, 1-propanol, isopropanol, butanol, pentanol, benzyl alcohol, diacetone alcohol, 1-methoxy-2-propanol; dimethyl ketone, acetone, methyl ethyl ketone, Ketone solvents such as methyl propyl ketone, methyl isobutyl ketone, cyclohexanone and isophorone; ester solvents such as 3-methyl-methoxy-propionate and butyl acetate; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol isopropyl ether, propylene glycol derivatives such as glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol methyl ether acetate and propylene glycol ethyl ether acetate; formamide, N-methylformamide, dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone amides; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as ethylene chloride and chlorobenzene;

However, among these, organic solvents with low polarity are preferred, particularly isopropyl alcohol, ethanol, 1-methoxy-2-propanol, dimethyl ketone, methyl ethyl ketone, methyl isobutyl ketone, toluene, propylene glycol monomethyl ether acetate, n-butyl acetate, and the like. is more preferred. These solvents can be used singly or in combination of two or more.

Examples of fats and oils include drying oils such as linseed oil, sunflower oil, and tung oil, semi-drying oils such as sesame oil, cottonseed oil, rapeseed oil, soybean oil, and rice bran oil, and non-drying oils such as olive oil, coconut oil, palm oil, and dehydrated castor oil. , Fatty acid monoesters obtained by directly esterifying vegetable oil fatty acids and monoalcohols, ethers, Isopar (registered trademark) E, Exol (registered trademark) Hexane, Heptane, E, D30, D40, D60, D80, D95, D110, One or more selected from petroleum solvents such as D130 (manufactured by ExxonMobil) can be used.

As the liquid resin, for example, one or more selected from liquid acrylic resin, liquid epoxy resin, liquid polyester resin, and liquid urethane resin can be used.

As the plasticizer, for example, a liquid plasticizer for plastics or the like can be used.

Further, if necessary, an acid or an alkali may be added to adjust the pH of the dispersion.

In order to further improve the dispersion stability of the light-absorbing particles in the above-described light-absorbing particle dispersion and to avoid coarsening of the dispersed particle diameter due to reaggregation, various surfactants, coupling agents, and polymer dispersions are added. A dispersant or the like can also be added as a dispersant.

The dispersant can be selected according to the application, but includes amine-containing groups, hydroxyl groups, carboxyl groups, carboxylic acid esters, phosphoric acid groups, phosphoric acid esters, sulfonic acid groups, sulfonic acid esters, thiol groups, and epoxy groups. It is preferable to have one or more selected from groups as functional groups. The dispersing agent having any of the above functional groups adsorbs to the surface of the light absorbing particles, prevents aggregation of the light absorbing particles, and is a light absorbing particle dispersion such as a dispersion or an infrared shielding film formed using the same. Since the light-absorbing particles can be more uniformly dispersed therein, it can be preferably used.

Furthermore, the dispersant preferably has a main chain composed of acrylic, styrene, urethane, polyethylene, polyester, or polyethyleneimine, or a main chain composed of a copolymer of two or more types selected from these structures. . This is because the dispersant having any of the main chains described above prevents aggregation of the light-absorbing particles due to steric hindrance, is compatible with the ink solvent and resin, and more uniformly disperses the light-absorbing particles in the resin. This is because it is possible. Among them, when the main chain is polyester or polyethyleneimine, the main chain structure has a structure having an adsorptive property for the light-absorbing particles. It is more preferable because the light-absorbing particles can be more uniformly dispersed in the light-absorbing particle dispersion such as an infrared shielding film.

Moreover, it is also preferable to use two or more kinds of dispersants in combination as necessary.

Specific examples of the dispersant having any of the above functional groups include, for example, a styrene-acrylic copolymer dispersant having a carboxyl group as a functional group, an acrylic dispersant having an amine-containing group as a functional group, A polyester-based dispersant having a phosphoric acid group as a functional group, a urethane-based dispersant having an amine-containing group, and the like can be mentioned. Acrylic resins (acrylic dispersants) having functional groups such as carboxyl groups can also be used.

A dispersant having an amine-containing functional group preferably has a molecular weight Mw of 2,000 to 200,000 and an amine value of 5 to 100 mgKOH/g. Dispersants having carboxyl groups preferably have a molecular weight Mw of 2,000 to 200,000 and an acid value of 1 to 50 mgKOH/g.

The amount of the dispersant added is not particularly limited, but for example, it is preferably added in an amount of 10 parts by mass or more and 1000 parts by mass or less, and 30 parts by mass or more and 400 parts by mass or less with respect to 100 parts by mass of the light absorbing particles. It is more preferable to add so that

If the amount of the dispersing agent added is within the above range, the light absorbing particles can be more reliably dispersed in the dispersion liquid or the light absorbing particle dispersion such as an infrared shielding film formed using the same, and the obtained resin can be improved. This is because there is no adverse effect on physical properties.

Commercially available dispersants that can be suitably used for the light-absorbing particles of the present embodiment include ADEKA CORPORATION ADEKA COL® TS-230E, CS-141E, CS-1361E, PS-984, and PS-440E. , PS-807, NOF Polystar (registered trademark) OM, OMR, OMP, A-1060, SMX-1H, OMA, OMA-500, Marialim (registered trademark) AKM-0531, AKM-1511-60, AFB -1521, AAB-0851, AWS-0851, HKM-50A, Nymeen (registered trademark) L-201, L-202, Marproof (registered trademark) G-0150M, G-0115S, G-0250S, G-0130S- P, G-1010S, Ajinomoto Ajisper (registered trademark) PB-711, PB-821, PB-822, PB-881, PN-411, PA-111, Kusumoto Kasei Co., Ltd. Disparon (registered trademark) 1210, 2150 , KS-860, KS-873N, 7004, 1830, 1850, 1860, DA-1401, PW-36, DN-900, DA-1200, DA-550, DA-7301, DA-325, DA-375, DA -234, Lubrizol SOLSPERSE® 3000, 5000, 9000, 11200, 12000, 13240, 13350, 13940, 16000, 17000, 18000, 20000, 21000, 22000, 24000SC, 24000GR, 26000, 27000, 28000, 5 3095, 54000, 55000, 56000, 71000, 76500, Solplus (registered trademark) D510, D520, D530, D540, L300, L400, K200, K210, K500, C800, C825, DP310, DP320, DP330, R700, Mitsubishi Chemical Corporation Dianal (registered trademark) BR- 52, 73, 87, 105, 106, 116, Reseda (registered trademark) GP-301 manufactured by Toagosei Co., Ltd., Alfon (registered trademark) UF-5022, UF-5080, UC-3000, UC-3910, UC-3920, UG-4030, UG-4040, UG-4070, Disperbyk (registered trademark) manufactured by BYK Chemie 101, 108, 102, 103, 106, 109, 110, 111, 112, 116, 130, 140, 142, 145, 160, 161, 162, 163, 164, 166, 167, 168, 170, 171, 174, 180, 181, 182, 183, 184, 185, 187, 190, 191, 192, 193, 194, 2000, 2010, 2020, 2025, 2050, 2070, 2090, 2091, 2095, 2096, 2150, 2155, 2163, 2164, BYK (registered trademark) P104, P104S, P105, 154, 9076, P9077, 220S, W980, W985, EFKA manufactured by BASF ( Registered trademark) 2020, 2025, 2720, 3030, 3031, 3236, 4008, 4009, 4010, 4015, 4020, 4046, 4047, 4050, 4055, 4060, 4080, 4300, 4310, 4400, 4401, 4402, 4403, 451 0 , 4520, 4550, 4560, 4570, 4580, 4590, 6230, 7414, 8215, Joncryl (registered trademark) J-67, J-586, J-587, J-611, J-680, J-690, J -810, JDX-C3000, JDX-C3020 and the like.

The average particle diameter of the light-absorbing particles in the light-absorbing particle dispersion liquid of the present embodiment is preferably 1 nm or more and 500 nm or less, more preferably 1 nm or more and 100 nm or less, and further preferably 1 nm or more and 40 nm or less. preferable. Especially when used in applications requiring transparency, the average particle size of the light absorbing particles is particularly preferably 30 nm or less in order to further suppress scattering.

The reason why the above range is suitable has already been explained in the description of the light-absorbing particles, so the explanation is omitted here.

The content of the light-absorbing particles in the light-absorbing particle dispersion of the present embodiment is not particularly limited, and the required transmittance of light in the visible region, the transmittance of light in the infrared region, particularly the near-infrared region, etc. can be selected arbitrarily according to Although the content of the light-absorbing particles in the light-absorbing particle dispersion of the present embodiment is not particularly limited, it is preferably, for example, 0.01% by mass or more and 80% by mass or less. This is because a sufficient solar transmittance can be exhibited by setting the content of the light-absorbing particles to 0.01% by mass or more. Moreover, it is because it can be uniformly dispersed in the dispersion medium by making it 80% by mass or less.
4. Method for Producing Light-Absorbing Particle Dispersion A method for producing the light-absorbing particles of the present embodiment is not particularly limited, and can include, for example, a dispersing step of dispersing the light-absorbing particles described above in a liquid medium.

In addition, according to the method for producing a light-absorbing particle dispersion liquid of the present embodiment, the above-described light-absorbing particle dispersion liquid can be produced, so the explanation of some of the matters already explained will be omitted.

In the dispersing step, the method for dispersing the light absorbing particles in the liquid medium is not particularly limited as long as the method can disperse the light absorbing particles in the liquid medium.

Examples of the method of dispersing the light-absorbing particles in a liquid medium include dispersing methods using devices such as a bead mill, ball mill, sand mill, paint shaker, and ultrasonic homogenizer. Among them, dispersing with a medium stirring mill such as a bead mill, ball mill, sand mill, or paint shaker using medium media (beads, balls, Ottawa sand) is a viewpoint of shortening the time required to obtain the desired average particle size. preferred from

However, a dispersing method that accompanies strong pulverization due to collision and shearing force of the medium during dispersing is not preferable. This is because when the particles substituted with substitution ions are pulverized, a new surface is exposed by the pulverization of the primary particles of the light-absorbing particles, and the new surface is of course exposed to oxygen that is not substituted. This is because it is composed of groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ).

Therefore, when a dispersion is produced by a medium agitating mill using medium media, it is preferable to select conditions so as not to accompany strong pulverization due to collision and shear force of the medium media. More specifically, for example, beads made of a material with low hardness are used, beads of the same material with a smaller particle size are used, and the shaking frequency of the paint shaker device is lowered. In the case of a ball mill or a wet bead mill, it is preferable to select conditions such as lowering the number of revolutions per unit time.
5. Application Examples of Light-Absorbing Particles Using the light-absorbing particles and the light-absorbing particle dispersion described above, for example, a light-absorbing particle dispersion can be obtained.

The light-absorbing particle dispersion of this embodiment can have a form in which the light-absorbing particles are dispersed in a solid medium such as a resin. The shape and the like of the light-absorbing particle dispersion are not particularly limited, and can be any shape, for example, a film shape. That is, the light-absorbing particle dispersion of the present embodiment can be a film in which light-absorbing particles are dispersed in a solid medium such as resin, for example.

The method for producing the light-absorbing particle dispersion of the present embodiment is not particularly limited. For example, first, a resin is added to the light-absorbing particle dispersion of the present embodiment and dissolved to obtain a resin-added light-absorbing particle dispersion. be able to. Next, the light-absorbing particle dispersion containing the resin is poured into a mold of any shape, or coated on a substrate that transmits visible light, such as sheet glass or a resin substrate, and then the resin is added. It can be obtained by solidifying the added light-absorbing particle dispersion. A light absorbing particle dispersion can also be obtained by kneading the light absorbing particle dispersion according to this embodiment into a resin.

The resin used for the light-absorbing particle dispersion is not particularly limited, but for example, UV curable resin, thermosetting resin, electron beam curable resin, room temperature curable resin, thermoplastic resin, etc. can be selected depending on the purpose. Specifically, polyethylene resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl alcohol resin, polystyrene resin, polypropylene resin, ethylene vinyl acetate copolymer, polyester resin, polyethylene terephthalate resin, fluorine resin, polycarbonate resin, acrylic resin , polyvinyl butyral resin, and ionomer resin. These resins may be used singly or in combination.

The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples.

First, the evaluation method in each example below will be described.
(X-ray diffraction measurement)
The X-ray diffraction measurement was carried out by powder XRD measurement using a Cu-Kα ray with an X'Pert-PRO/MPD apparatus from Spectris.

Measurement was performed at a scan speed of 0.095° (2θ)/sec and a number of measurement points of 5555 points/90° in the range of the angle 2θ of 10° or more and 100° or less.
(visible light transmittance, solar transmittance)
The visible light transmittance and solar transmittance of the light absorbing particles were measured according to ISO 9050:2003 and JIS R 3106:1998. Specifically, the transmittance was measured using a spectrophotometer U-4100 manufactured by Hitachi, Ltd., and calculated by multiplying by a coefficient corresponding to the spectrum of sunlight. In measuring the transmittance, the measurement is performed at intervals of 5 nm in the wavelength range of 300 nm or more and 2500 nm or less. The measurement procedure is detailed in Example 1 below.
(Average particle size)
The average particle size was measured using a particle size distribution meter.

Specifically, the particle size distribution of the diluted solution of the dispersion was measured using a particle size distribution meter (Nanotrack UPA-150 manufactured by Nikkiso Co., Ltd.), and the particle size at an integrated value of 50% was determined as the average particle size. The measurement principle of the used particle size distribution meter is based on the dynamic light scattering method.
(Detection of surface functional groups)
An FT-IR device (FT/IR-6000 manufactured by JASCO Corporation) was used to confirm the specific ionic form of the elements present on the surface of the light-absorbing particles. A known KBr tablet method was adopted as a method for measuring the powder sample.
(Evaluation of Discoloration Phenomenon)
The decolorization phenomenon of the light-absorbing particles was evaluated based on the optical properties of the light-absorbing particle dispersion. Specifically, dispersions prepared in the following Examples and Comparative Examples were placed in a glass test tube and sealed with a glass stopper, and then placed in a constant temperature bath set at 70 ° C. for 100 hours as a weather resistance test. placed. Then, the visible light transmittance of the dispersion liquid was measured before and after the weather resistance test, and the amount of change in the visible light transmittance was calculated. It was judged that the smaller the amount of change in visible light transmittance before and after the weather resistance test, the more the decoloring phenomenon was suppressed.

The manufacturing conditions of the light-absorbing particles and the light-absorbing particle dispersion in each example and comparative example will be described below.
[Example 1]
(1) Raw Material Particle Production Process A cesium carbonate (Cs ₂ CO ₃ ) aqueous solution and tungstic acid (H ₂ WO ₄ ) as raw materials are mixed, and x (Cs/ A raw material mixture was prepared by weighing, mixing, and kneading such that W) was 0.33. The raw material mixture was then dried in the air at 110° C. for 12 hours. The raw material mixture (precursor) after drying was spread thinly and evenly on a quartz boat, heated and held at 600° C. for 1 hour under a 2 vol % H ₂ /98 vol % N ₂ stream (heating step).

Next, after holding at 600 ° C. for 1 hour under a 100 vol% N ₂ gas stream, the temperature is raised to 800 ° C., held at 800 ° C. for 1 hour and homogenized to obtain raw material particles of tungsten bronze powder (hereinafter referred to as " A tungsten bronze powder A” was obtained (homogenization step).

As a result of XRD measurement of the obtained blue powder, JCPDS card No. 81-1224 and identified as Cs _0.3 WO ₃ .
(2) Pulverization Step, Isolation Step Next, 5% by mass of tungsten bronze powder A and 95% by mass of pure water were weighed. These were loaded into a paint shaker containing 0.3 mmφ ZrO ₂ beads, and pulverized and dispersed for 10 hours to prepare a dispersion liquid (pulverization step). Here, the average particle size of the light absorbing particles in the dispersion was measured with a particle size distribution meter and found to be 22.5 nm.

The dispersion is subjected to a centrifugal separator (12000 rpm, 30 minutes) to sediment the particles, followed by solid-liquid separation by vacuum filtration, followed by drying and pulverizing tungsten bronze powder (hereinafter referred to as "tungsten bronze powder A'"). described) was isolated (isolation step).
(3) Substitution step The pulverized tungsten bronze powder A' was dried in an oven at 110°C for 24 hours. The dried tungsten bronze powder A' was placed in a quartz boat and heated to 300° C. in a vacuum atmosphere in a tubular furnace. Then, hydrogen sulfide gas (concentration of hydrogen sulfide: 500 ppm) using argon as a carrier gas was passed at a mixed gas flow rate of 1 L/min for 1 hour.

After that, the gas supply was stopped, the temperature was naturally lowered to room temperature, and the sample was taken out. As a result, light-absorbing particles (hereinafter referred to as light-absorbing particles A) in which at least part of the oxygen groups or hydroxyl groups on the particle surface were substituted with sulfur groups (S ²⁻ ) were obtained.

The functional groups on the particle surfaces of the tungsten bronze powder A' and the light-absorbing particles A were analyzed with an FT-IR device. As a result, infrared absorption corresponding to the sulfur group (S ^2- ) was confirmed in the light-absorbing particles A. On the other hand, when the tungsten bronze powder A' before the substitution step was subjected to the same analysis, infrared absorption corresponding to hydroxyl groups and oxygen groups was confirmed, but infrared absorption corresponding to sulfur groups was not confirmed. rice field. Therefore, it can be confirmed that at least part of the oxygen groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ) present on the surface of the light-absorbing particles A are certainly substituted with sulfur groups (S ²⁻ ). rice field.
(4) Preparation of light-absorbing particle dispersion Next, 10% by mass of light-absorbing particles A and Disperbyk-110 manufactured by BYK Chemie as a dispersant (a polyester polymer dispersant having a group containing a phosphoric acid group as a functional group 10 mass % of the dispersing agent (hereinafter abbreviated as "dispersant a") and 80 mass % of methyl isobutyl ketone (MIBK) as a liquid medium were weighed. These were placed in a paint shaker containing 0.3 mm diameter glass beads and dispersed for 6 hours to obtain a light-absorbing particle dispersion (hereinafter referred to as "dispersion A"). Here, when the average particle size of the light absorbing particles in the dispersion liquid A was measured with a particle size distribution meter, it was 21.5 nm.

Dispersion A was diluted with MIBK so that the concentration of the light-absorbing particles was 0.10% to obtain a diluted solution. A spectroscopic cell made of quartz glass with an optical path length of 1 mm (hereinafter simply referred to as "spectroscopic cell") was filled with MIBK, and a baseline measurement of the spectrophotometer was performed. Next, a diluted solution of dispersion A was placed in the same spectroscopic cell, and the spectral transmittance was measured. Visible light transmittance (VLT), solar transmittance (ST) were calculated or read from the transmittance profile, resulting in VLT=85.0% and ST=47.3%.

After the weather resistance test was performed on the dispersion, the spectral transmittance of the diluted liquid was measured in the same manner as before the weather resistance test, and the VLT was calculated to be VLT=86.1%. Therefore, the change in VLT before and after weathering was calculated to be 1.1%.

Table 1 summarizes the above evaluation results.
[Examples 2 to 5]
Examples 2 to 5 were carried out in the same manner as in Example 1, except that the conditions (gas used, concentration in carrier gas, temperature, time) of the replacement step for tungsten bronze powder A' were changed to those shown in Table 1. was obtained.

In addition, PH ₂ ^- in Example 2, Cl ^- (chlorine ion) in Example 3, Br ^- (bromine ion) in Example 4, and I ^- (iodine ion) in Example 5, the surface of the tungsten bronze powder A' Substitution treatment of the oxygen group or hydroxyl group present in was performed. The particles obtained by each treatment are hereinafter referred to as light-absorbing particles B (Example 2), light-absorbing particles C (Example 3), light-absorbing particles D (Example 4), and light-absorbing particles E (Example 5). ) respectively.

Functional groups on the surface of the light-absorbing particles B, C, D and E were analyzed by an FT-IR device. As a result, the infrared absorption corresponding to the PH ₂ ^- group in the light absorbing particles B, the Cl ^- group in the light absorbing particles C, the Br ^- group in the light absorbing particles D, and the I ^- group in the light absorbing particles E, respectively. were confirmed respectively. Therefore, at least part of the oxygen groups or hydroxyl groups present on the surfaces of the light absorbing particles B, C, D and E are certainly substituted with PH ₂ ^-groups , Cl ^-groups , Br ^-groups and I ^-groups , respectively. I was able to confirm that

In the same manner as in Example 1 except that the light absorbing particles B, C, D and E were used instead of the light absorbing particles A, the light absorbing particle dispersion liquids of Examples 2 to 5 (hereinafter referred to as dispersion liquids respectively) B, Dispersion C, Dispersion D and Dispersion E) were obtained. Here, the average particle size of the light-absorbing particles in the dispersions B, C, D and E was measured by a particle size distribution meter, and the results are shown in Table 1.

Visible light transmittance, solar transmittance, VLT after weather resistance test, VLT before and after weather resistance test were measured in the same manner as in Example 1 except that dispersions B, C, D and E were used instead of dispersion A. was measured and calculated.

Table 1 summarizes the above evaluation results.
[Example 6]
(1) Raw material particle manufacturing process Rubidium carbonate (Rb ₂ CO ₃ ) aqueous solution and tungstic acid (H ₂ WO ₄ ) as raw materials are mixed, and x (Rb/W ) was 0.33, a raw material mixture was prepared by weighing, mixing and kneading. The raw material mixture was then dried in the air at 110° C. for 12 hours. The raw material mixture (precursor) after drying was spread thinly and evenly on a quartz boat, heated and held at 580° C. for 1 hour under a 2 vol % H ₂ /98 vol % N ₂ stream (heating step).

Next, after being held at 600 ° C. for 1 hour under a 100 vol% N ₂ gas stream, the temperature is raised to 800 ° C. and held at 800 ° C. for 1 hour for homogenization. Tungsten bronze powder (hereinafter referred to as tungsten bronze Powder F) was obtained (homogenization step).

As a result of XRD measurement of the obtained blue powder, JCPDS card No. 72-6572, identifying Rb _0.333 WO ₃ .
(2) Pulverization Step, Isolation Step Next, 5% by mass of tungsten bronze powder F and 95% by mass of pure water were weighed. These were loaded into a paint shaker containing 0.3 mmφ ZrO ₂ beads, and pulverized and dispersed for 9 hours to prepare a dispersion liquid (pulverization step). Here, the average particle size of the light absorbing particles in the dispersion was measured with a particle size distribution meter and found to be 23.8 nm.

The dispersion is subjected to a centrifugal separator (12000 rpm, 30 minutes) to sediment the particles, followed by solid-liquid separation by vacuum filtration, followed by drying and pulverizing tungsten bronze powder (hereinafter referred to as "tungsten bronze powder F'"). described) was isolated (isolation step).
(3) Substitution Step The pulverized tungsten bronze powder F' was dried in an oven at 110°C for 24 hours. The dried tungsten bronze powder F′ was placed in a quartz boat and heated to 300° C. in a vacuum atmosphere in a tubular furnace. Then, hydrogen sulfide gas (concentration of hydrogen sulfide: 500 ppm) using argon as a carrier gas was passed at a mixed gas flow rate of 1 L/min for 1 hour.

After that, the gas supply was stopped, the temperature was naturally lowered to room temperature, and the sample was taken out. As a result, light-absorbing particles (hereinafter referred to as light-absorbing particles F) having surface hydroxyl groups replaced with thiol groups (SH ⁻ ) were obtained.

The functional groups on the particle surfaces of the tungsten bronze powder F' and the light-absorbing particles F were analyzed with an FT-IR device. As a result, in the light-absorbing particles F, infrared absorption corresponding to thiol groups (SH ⁻ ) was confirmed. On the other hand, when the same analysis was performed on the tungsten bronze powder F' before performing the substitution step, infrared absorption corresponding to hydroxyl groups and oxygen groups was confirmed, but infrared absorption corresponding to thiol groups was not confirmed. rice field. Therefore, it was confirmed that at least part of the hydroxyl groups or oxygen groups present on the surface of the light-absorbing particles F were certainly substituted with thiol groups (SH ⁻ ).
(4) Preparation of light-absorbing particle dispersion liquid (hereinafter referred to as "dispersion liquid") in the same manner as in Example 1 except that light-absorbing particle F was used instead of light-absorbing particle A. F”) was obtained. Here, when the average particle size of the light absorbing particles in the dispersion liquid F was measured by a particle size distribution meter, the results were as shown in Table 1.

Visible light transmittance, solar transmittance, VLT after the weather resistance test, and changes in VLT before and after the weather resistance test were measured and calculated in the same manner as in Example 1 except that the dispersion liquid F was used instead of the dispersion liquid A. .

Table 1 summarizes the above evaluation results.
[Example 7]
Using the light-absorbing particles A prepared in Example 1, a dispersion was prepared using water as the solvent.

Specifically, 10% by mass of light absorbing particles A and 90% by mass of pure water as a liquid medium were weighed. These were placed in a paint shaker containing 0.3 mm diameter glass beads and subjected to dispersion treatment for 5 hours to obtain a light absorbing particle dispersion (hereinafter referred to as "dispersion G"). Here, when the average particle size of the light absorbing particles in the dispersion liquid G was measured with a particle size distribution meter, it was 20.9 nm.

The dispersion G was diluted with pure water so that the concentration of the light-absorbing particles was 0.10% to obtain a diluted solution. The same spectroscopic cell as that used in Example 1 was filled with pure water, and the baseline measurement of the spectrophotometer was performed. Thereafter, in the same manner as in Example 1 except that dispersion G was used instead of dispersion A, the visible light transmittance, solar transmittance, VLT after the weather resistance test, and changes in VLT before and after the weather resistance test were measured. and calculated.

The evaluation results are summarized in Table 1.
[Example 8]
Using the light-absorbing particles A prepared in Example 1, a dispersion was prepared using toluene as a solvent.
Specifically, 10% by mass of light-absorbing particles A and Mitsubishi Chemical Dianal BR-116 as a dispersant (acrylic polymer dispersant having a carboxyl group as a functional group. Hereinafter referred to as "dispersant b" ) and 82% by mass of toluene as a liquid medium were weighed. These were placed in a paint shaker containing 0.3 mmφ glass beads and dispersed for 6 hours to obtain a light-absorbing particle dispersion (hereinafter abbreviated as “dispersion H”). Here, the average particle size of the light absorbing particles in the dispersion liquid H was measured with a particle size distribution meter and found to be 21.5 nm.

Dispersion H was diluted with toluene so that the concentration of the light-absorbing particles was 0.10% to prepare a diluted solution. The same spectroscopic cell as used in Example 1 was filled with toluene and a baseline measurement of the spectrophotometer was performed. Thereafter, in the same manner as in Example 1 except that dispersion H was used instead of dispersion A, the visible light transmittance, solar transmittance, VLT after the weather resistance test, and changes in VLT before and after the weather resistance test were measured. and calculated.

The evaluation results are summarized in Table 1.
[Example 9]
Using the light-absorbing particles A prepared in Example 1, a dispersion was prepared using methyl ethyl ketone (MEK) as a solvent.

Specifically, 10% by mass of light-absorbing particles A and Disperbyk-163 manufactured by BYK-Chemie Co., Ltd. as a dispersant (a urethane polymer dispersant having a tertiary amine group as a functional group. Hereinafter referred to as "dispersant c" ), and 84% by mass of MEK, which is a 6% by mass liquid medium, were weighed. These were placed in a paint shaker containing 0.3 mmφ glass beads and dispersed for 6 hours to obtain a light-absorbing particle dispersion (hereinafter referred to as “dispersion I”). Here, the average particle diameter of the light absorbing particles in the dispersion liquid I was measured with a particle size distribution meter and found to be 21.3 nm.

Dispersion I was diluted with MEK so that the concentration of the light-absorbing particles was 0.10% to prepare a diluted solution. The same spectroscopic cell used in Example 1 was filled with MEK and a spectrophotometer baseline measurement was taken. Thereafter, in the same manner as in Example 1 except that Dispersion I was used instead of Dispersion A, visible light transmittance, solar transmittance, VLT after weather resistance test, and change in VLT before and after weather resistance test were measured. and calculated.

The evaluation results are summarized in Table 1.
[Comparative Example 1]
A particle dispersion liquid (referred to as dispersion liquid α) was obtained in the same manner as in Example 1, except that the tungsten bronze powder A' before the substitution step used in Example 1 was used instead of the light absorbing particles A. rice field. Here, the average particle size of the light absorbing particles in the dispersion α was measured with a particle size distribution meter and found to be 21.9 nm.

Visible light transmittance, solar transmittance, VLT after weather resistance test, and change in VLT before and after weather resistance test were measured and calculated in the same manner as in Example 1 except that dispersion liquid α was used instead of dispersion liquid A. bottom.

The evaluation results are summarized in Table 1.

（実施例１～９ならびに比較例１の評価）
比較例１に係るタングステンブロンズ粒子は、粒子の表面に存在する酸素基や水酸基が置換されておらず、置換イオンを有していない。その結果、可視光透過率に対して日射透過率が低いという、赤外線吸収材料として好ましい光学特性を有してはいるものの、耐候性試験前後での可視光透過率変化が大きい、すなわち大きな消色現象が見られた。

(Evaluation of Examples 1 to 9 and Comparative Example 1)
In the tungsten bronze particles according to Comparative Example 1, oxygen groups and hydroxyl groups present on the surface of the particles are not substituted, and do not have substituted ions. As a result, although it has favorable optical properties as an infrared absorbing material, that is, the solar transmittance is low relative to the visible light transmittance, the change in visible light transmittance before and after the weather resistance test is large, that is, the color is greatly decolored. phenomenon was observed.

On the other hand, the light-absorbing particles according to Examples 1 to 9 are light-absorbing particles containing hexagonal tungsten bronze, and the tungsten bronze has the general formula: M _x WO _y (where the element M is at least K, Rb , Cs, and Tl, represented by 0.1≦x≦0.5, 2.2≦y≦3.0), and oxygen ions (O ²⁻ ) on the surface of the particles. Substitution ions having a large ionic radius are arranged, and the substitution ions are ions containing one or more elements selected from group 15, group 16, and group 17 elements. As a result, the tungsten bronze particles according to Comparative Example 1 exhibited favorable optical characteristics as an infrared absorbing material, such as a low solar transmittance relative to the visible light transmittance, and a change in the visible light transmittance before and after the weather resistance test. It was confirmed that the excellent weather resistance in which the decoloring phenomenon was suppressed was exhibited.
[Example 10]
In order to microscopically compare and study the effect of substitution ions, a structural model 20 consisting of a Cs _0.33 WO ₃ surface and water molecules was created, and by first-principles molecular dynamics calculations, Cs desorbed. estimated the activation energy required for A calculation model is shown in FIG.

The structural model 20 _shown in _FIG . O atoms 213 located on the surface shown were modified with H atoms 214 to make them monovalent. As is clear from the above chemical formula, the surface model 21 is a model of light-absorbing particles containing hexagonal tungsten bronze.

Further, two O atoms 213A and 213B located on the surface indicated by the dotted line A were replaced with sulfur atoms. That is, a model was used in which substitution ions containing a sulfur element were arranged on the surface of the light-absorbing particles.

A large number of water molecules 22 are arranged on this surface model 21 to simulate a high-humidity environment and an aqueous solution environment. Calculated by calculation. A plane wave basis first-principles calculation software VASP is used for the first-principles calculation, and the Cs atoms located on the surface of the surface model 21 are given a velocity in the z direction, which is the direction perpendicular to the surface, that is, the dotted line A, and the Cs atoms was reproduced. The moving speed of the Cs atoms in the z-direction was set to 0.7 Å/ps, and the process was traced until the Cs atoms desorbed from the initial positions by 3 Å or more. The activation energy was calculated using the slow growth simulation formula shown below.

上記式中の、ξは反応座標であり、Ｃｓ原子のz座標を反応座標として選定した。その結果、硫黄で置換した構造の活性化エネルギーは１．２ｅＶと比較例２で検討した構造モデルの場合よりも大きく、Ｃｓ原子が脱離しにくいことが確認された。

In the above formula, ξ is the reaction coordinate, and the z coordinate of the Cs atom was selected as the reaction coordinate. As a result, it was confirmed that the activation energy of the structure substituted with sulfur was 1.2 eV, which was larger than that of the structural model studied in Comparative Example 2, and that the Cs atoms were less likely to detach.

That is, it was confirmed that by replacing the oxygen ions on the surface of the light-absorbing particles with the replacement ions containing the sulfur element, the detachment of the element M becomes difficult, that is, the occurrence of the decoloring phenomenon can be suppressed.
[Comparative Example 2]
The desorption energy of Cs atoms was calculated in the same manner as in Example 10, except that the O atoms 213A and 213B located on the surface were not replaced with sulfur. As a result, the energy required for desorption of Cs atoms was as small as 1.0 eV.

Claims (13)

Light absorbing particles comprising hexagonal tungsten bronze,
The tungsten bronze has the general formula: M _x WO _y (wherein the element M contains at least one selected from K, Rb, Cs, and Tl, and 0.1 ≤ x ≤ 0.5, 2.2 ≤ y ≤ 3.0),
Substitution ions having a larger ionic radius than oxygen ions (O ²⁻ ) are arranged on the surface,
The light absorbing particles, wherein the replacement ions include one or more ions selected from S ²⁻ , Se ²⁻ , Te ²⁻ , P ³⁻ , As ³⁻ and Sb ³⁻ . the replacement ions are one or more selected from S ²⁻ , SH ⁻ , Se ²⁻ , SeH ⁻ , Te ²⁻ , TeH ⁻ , PH ²⁻ , PH ₂ ⁻ , AsH ₂ ⁻ , SbH ₂ ⁻ 2. A light absorbing particle according to claim 1 , present in the form 3. The light- absorbing particle according to claim 1, wherein said element M consists of Cs. 4. The light absorbing particles according to any one of claims 1 to 3 , having an average particle size of 1 nm or more and 100 nm or less. a light-absorbing particle according to any one of claims 1 to 4 ;
and a liquid medium that is one or more selected from water, organic solvents, fats and oils, liquid resins, and liquid plasticizers for plastics,
A light-absorbing particle dispersion liquid in which the light-absorbing particles are dispersed in the liquid medium. 6. The light-absorbing particle dispersion liquid according to claim 5 , wherein the content of the light-absorbing particles is 0.01% by mass or more and 80% by mass or less. For particles containing hexagonal tungsten bronze and having an average particle size of 1 nm or more and 100 nm or less, at least part of the oxygen groups (O ²⁻ ) or hydroxyl groups (OH ⁻ ) present on the surface of the particles is replaced with oxygen. a replacement step of replacing the ion (O ²⁻ ) with a replacement ion having a larger ionic radius;
The tungsten bronze has the general formula: M _x WO _y (wherein the element M contains at least one selected from K, Rb, Cs, and Tl, and 0.1 ≤ x ≤ 0.5, 2.2 ≤ y ≤ 3.0),
A method for producing light-absorbing particles, wherein the substituted ions include one or more ions selected from S ²⁻ , Se ²⁻ , Te ²⁻ , P ³⁻ , As ³⁻ and Sb ³⁻ . 8. The method of claim 7 , wherein the replacing step comprises exposing the particles containing the tungsten bronze to a gas containing one or more elements selected from group 15 elements, group 16 elements, and group 17 elements. A method for producing light-absorbing particles according to claim 1. Before the replacement step,
a pulverizing step of pulverizing the particles containing the hexagonal tungsten bronze in a liquid medium to pulverized particles having an average particle size of 1 nm or more and 100 nm or less;
9. The method for producing light-absorbing particles according to claim 7 , further comprising an isolation step of isolating said pulverized particles from said liquid medium. After the substitution step, light-absorbing particles comprising the hexagonal tungsten bronze are obtained,
10. The method for producing light-absorbing particles according to any one of claims 7 to 9 , wherein the substitution ions are arranged on the surfaces of the light-absorbing particles. the replacement ions are one or more selected from S ²⁻ , SH ⁻ , Se ²⁻ , SeH ⁻ , Te ²⁻ , TeH ⁻ , PH ²⁻ , PH ₂ ⁻ , AsH ₂ ⁻ , SbH ₂ ⁻ 11. A method for producing light-absorbing particles according to any one of claims 7 to 10 , wherein the particles are present in a form. 12. The method for producing light-absorbing particles according to any one of claims 7 to 11 , wherein the element M comprises Cs. The method for producing light-absorbing particles according to any one of claims 10 to 12 , wherein the light-absorbing particles have an average particle size of 1 nm or more and 100 nm or less.

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