JP7790249B2 - Near-infrared absorbing fiber, textile product, and method for producing near-infrared absorbing fiber - Google Patents

Description

The present invention relates to near-infrared absorbing fibers, textile products, and methods for producing near-infrared absorbing fibers.

A variety of cold weather clothing, interior goods, and leisure items with enhanced thermal insulation have been devised and put into practical use. There are two main methods for increasing thermal insulation.

The first method is to physically increase the air space in cold weather clothing, for example by controlling the weaving and knitting structure or by making the fibers used hollow or porous, thereby reducing the dissipation of heat generated by the human body and maintaining heat retention.

The second method, for example in the case of cold weather clothing, involves chemically or physically processing the entire garment or the fibers that make up the garment, thereby actively storing heat and improving its heat retention, such as by radiating the heat generated by the human body back toward the body or by converting some of the sunlight received by the garment into heat.

The first method mentioned above has been to increase the number of air pockets in the clothing, make the fabric thicker, use a finer weave, or darken the color. Examples of this include sweaters and other winter clothing. Another example is winter sportswear, which has a layer of padding between the outer and inner layers, with the thickness of the air layer in the padding maintaining warmth. However, padding makes the clothing heavy and bulky, which can be problematic for sportswear that require ease of movement. To address these problems, the second method mentioned above, which actively and effectively utilizes heat generated internally or from the outside, has begun to be adopted in recent years.

One known method for implementing this second approach is to vapor-deposit metals such as aluminum or titanium onto the lining of clothing, and then reflect the radiant heat emitted from the body onto the metal-deposited surface, thereby actively preventing heat dissipation. However, these methods not only require considerable costs to vapor-deposit metal onto clothing, but also result in poor yields due to uneven deposition, which ultimately increases the price of the product itself.

Another proposed method for implementing the second method involves kneading ceramic particles such as alumina, zirconia, or magnesia into the fibers themselves, and utilizing the far-infrared radiation and light-to-heat properties of these inorganic particles, i.e., actively incorporating external energy.

For example, Patent Document ¹ discloses a heat-radiating fiber containing one or more types of inorganic fine particles such as silica or barium sulfate that have heat-radiating properties and contain at least one type of metal or metal ion with a thermal conductivity of 0.3 kcal/m²·sec·°C or more.

Patent Document 2 discloses a heat-retaining composite fiber comprising a thermoplastic polymer A having a melting point of 110°C or higher and a thermoplastic polymer B having a melting point of 15 to 50°C, a cooling crystallization temperature of 40°C or lower, and a heat of crystallization of 10 mJ/mg or higher, the fiber containing 0.1 to 20% by weight of ceramic microparticles capable of emitting far-infrared rays, and the fiber surface being covered with polymer A.

Patent Document 3 proposes an infrared-absorbing processed textile product in which an infrared absorber made of a specific amino compound, an optional ultraviolet absorber, and a binder resin containing various stabilizers are dispersed and fixed.

Patent Document 4 proposes a near-infrared absorbing processing method for cellulosic fiber structures, which involves dyeing a dye selected from direct dyes, reactive dyes, naphthol dyes, and vat dyes that has greater absorption in the near-infrared region than black dyes in combination with other dyes, resulting in a fabric with a spectral reflectance of 65% or less in the near-infrared absorption range of 750 to 1500 nm.

In Patent Documents 5 to 7, the inventors propose fibers containing tungsten oxide microparticles or composite tungsten oxide microparticles on the surface and/or inside, and textile products obtained by processing such fibers.

Japanese Patent Application Publication No. 11-279830 Japanese Patent Application Publication No. 5-239716 Japanese Patent Application Publication No. 8-3870 Japanese Patent Application Publication No. 9-291463 Japanese Patent Application Laid-Open No. 2006-132042 International Publication No. 2018/235839 International Publication No. 2019/054476

K. Machida, M. Okada, and K. Adachi, "Excitations of free and localized electrons at nearby energies in reduced cesium tungsten bronze nanocrystals," Journal of Applied Physics, Vol. 125, 103103 (2019) S. Yoshio and K. Adachi, "Polarons in reduced cesium tungsten bronzes studied using the DFT+U method," Materials Research Express, Vol. 6, 026548 (2019) S. F. Solodovnikov, N.V. Ivannikova, Z.A. Solodovnikova, E.S. Zolotova, "Synthesis and X-ray diffraction study of potassium, rubidium, and cesium polytungstates with defect pyrochlore and hexagonal tungsten bronze structures," Inorganic Materials, Vol. 34, 845-853 (1998) S. Nakakura, A. F. Arif, K. Machida, K. Adachi, T. Ogi, Cationic defect engineering for controlling the infrared absorption of hexagonal cesium tungsten bronze nanoparticles, Inorg. Chem., 58, 9101-9107 (2019)

In the heat-emitting fiber disclosed in Patent Document 1, which contains inorganic fine particles such as silica containing metals and other elements that have heat-emitting properties, the amount of inorganic fine particles added to the fiber is large. This increases the specific gravity of the fiber, making clothing heavier and making it extremely difficult to disperse the fine particles uniformly during melt spinning.

As mentioned above, there is also a known technology in which metals such as aluminum or titanium are attached to fibers through processes such as adhesion or vapor deposition to impart a radiation-reflecting effect and improve heat retention. However, because adhesion or vapor deposition processes significantly change the color of the fibers, their applications have sometimes been limited. Furthermore, there are various problems associated with vapor deposition processes, such as increased costs, the occurrence of vapor deposition spots due to handling of the fabric in the preparation process before vapor deposition, and reduced heat retention due to the vapor-deposited metal falling off due to friction during washing or wearing.

According to the applicant's investigations, the tungsten oxide microparticles or composite tungsten oxide microparticles disclosed in, for example, Patent Documents 5 to 7, are materials that exhibit high transmittance and low absorbance for visible light, yet low transmittance and high absorbance for light in the near-infrared region. For this reason, fibers containing composite tungsten oxide microparticles are particularly promising for applications such as cold weather clothing. However, because they preferentially absorb long-wavelength visible light, i.e., red light, they are colored blue, and the blue color intensity increases as the amount of microparticles added increases. As a result, fibers containing these microparticles as a near-infrared absorbing component, and textile products obtained by processing these fibers, are colored blue, making it difficult to color them in yellows or light colors other than blue, which are complementary to blue, by adding other pigments. Therefore, there has been a demand for fibers containing composite tungsten oxide with excellent near-infrared absorption properties, and that can be colored in a more neutral color tone that can be colored in complementary or light colors.

Therefore, one aspect of the present invention aims to provide near-infrared absorbing fibers that contain near-infrared absorbing particles containing composite tungsten oxide and can be made to have a more neutral color tone.

In one aspect of the invention, a fiber;
and near-infrared absorbing particles disposed at one or more locations selected from the surface and the interior of the fiber,
the near-infrared absorbing particles contain cesium tungstate,
The cesium tungstate has a pseudo-hexagonal crystal structure that is modulated to one or more types selected from orthorhombic, rhombohedral, and cubic crystals, and contains one or more types of additive components selected from O , OH, OH2 _, and OH3 _;
The cesium tungstate is represented by the general formula _CsxWyOz , and in a ternary composition diagram with Cs, W, _and O at _the vertices, the composition is within the region surrounded by four straight lines: x = 0.6y, z = 2.5y, y = 5x, and _Cs2O : _WO3 = m:n (m and n are integers).

One aspect of the present invention is to provide near-infrared absorbing fibers that contain near-infrared absorbing particles containing composite tungsten oxide and can be made to have a more neutral color tone.

FIG. 1A is a Cs-WO composition diagram with Cs, W, and O at the vertices. FIG. 1B is an enlarged view of a portion of the Cs-WO composition diagram with Cs, W, and O at the vertices. FIG. 2 shows powder XRD diffraction patterns of the near-infrared absorbing particles produced in Examples 1 to 6 and Comparative Examples 1 and 2. FIG. 3 shows powder XRD diffraction patterns of the near-infrared absorbing particles produced in Examples 9 to 14. FIG. 4 shows a transmission electron microscope bright-field image, a selected area electron diffraction image, and a high angle electron diffraction dark-field (HAADF) image of the near-infrared absorbing particles prepared in Example 1. FIG. 5 is an illustration of a near-infrared absorbing particle having a coating. FIG. 6 is an explanatory diagram of the structure of the near-infrared absorbing fiber.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and various modifications and substitutions can be made to the following embodiments without departing from the scope of the present invention.
[Near-infrared absorbing fiber]
The near-infrared absorbing fiber and textile product according to the present embodiment will be described in the following order: [1] near-infrared absorbing particles; [2] a method for producing near-infrared absorbing particles; [3] a near-infrared absorbing particle dispersion; [4] near-infrared absorbing fiber; [5] a method for producing near-infrared absorbing fiber; and [6] a textile product.
[1] Near-infrared absorbing particles As will be described later, the near-infrared absorbing fiber of this embodiment contains near-infrared absorbing particles. Therefore, the near-infrared absorbing particles will be described first.

The near-infrared absorbing particles contain cesium tungstate, which is a composite tungsten oxide. The near-infrared absorbing particles of this embodiment may also be composed of cesium tungstate. However, even in this case, the inclusion of inevitable impurities is not excluded.
(1) Cesium Tungstate Cesium tungstate (cesium polytungstate) can have a pseudo-hexagonal crystal structure that is modified to one or more types selected from orthorhombic, rhombohedral, and cubic crystals. Specifically, such cesium tungstate can have one or more types of crystal structure selected from orthorhombic, rhombohedral, and cubic crystals that are modified pseudo-hexagonal structures that are partially modified from hexagonal alkali tungsten bronze structures.

The transmission color and light absorption of cesium-doped hexagonal tungsten bronze particles, which have conventionally been used as near-infrared absorbing particles, are determined by the imaginary part of the dielectric function (ε ₂ ) and the band structure.

In the visible light energy range (1.6 eV to 3.3 eV), cesium-doped hexagonal tungsten bronze (hereinafter also referred to as Cs-HTB) has a sufficiently large band gap that light absorption in the visible light range is essentially suppressed. In addition, tungsten dd-d orbital electronic transitions and oxygen p-p orbital electronic transitions are forbidden by the Fermi golden rule, reducing the probability of electronic transitions. These two effects result in small values of _ε2 at wavelengths in the visible light range. Since _ε2 represents the absorption of photons by electrons, a small _ε2 at wavelengths in the visible light range results in visible light transmittance. However, it has recently been revealed that absorption due to band-edge transitions exists near the shortest wavelengths in the visible light range (blue wavelengths), and that localized surface plasmon resonance (LSPR) absorption and polaronic electronic transition absorption exist near the longest wavelengths in the red wavelength range (Non-Patent Document 1). As a result, light transmittance is limited in each case.

As mentioned above, the band gap of Cs-HTB is large enough that the band edge transition exceeds the energy of blue wavelength light, resulting in blue transmittance. Conversely, at red wavelengths, Cs-HTB has a large number of conduction electrons, resulting in strong LSPR absorption and polaronic absorption, and the base of this absorption extends into the red wavelengths, resulting in low red transmittance. Therefore, the transmitted color of a Cs-HTB nanoparticle-dispersed film appears blue due to the balance between these two.

In other words, to neutralize the blue transmission color of Cs-HTB, all you need to do is increase the absorption on the blue side and increase the transmission on the red side.

Strengthening the blue absorption of Cs-HTB can be achieved, for example, by shifting the absorption position of the band edge transition to lower energy. Shifting the absorption position of the band edge transition to lower energy corresponds to narrowing the band gap of Cs-HTB. Therefore, this can be achieved by selecting a material with a slightly smaller band gap.

The red absorption of Cs-HTB can be weakened by reducing the concentration of surface plasmon resonance electrons or polaron-bound electrons.

Based on the above considerations, the inventors of the present invention conducted various studies on cesium tungsten oxide, an oxide containing cesium (Cs) and tungsten (W), and continued to improve the material by also conducting band structure calculations based on first-principles calculations. As a result, they discovered that when the conventional hexagonal crystal structure is modified to an orthorhombic, rhombohedral, or cubic pseudo-hexagonal structure through changes in the microstructure, the band structure changes and the number of free and bound electrons changes, resulting in a change in color.

Here, the pseudo-hexagonal structure modulated to one or more types selected from orthorhombic, rhombohedral, and cubic crystals refers to a pseudo-hexagonal crystal modulated by inserting Cs-rich faces regularly or randomly into the prism faces or base faces of a hexagonal crystal. Note that a Cs-rich face is synonymous with a face lacking W or O. As will be described later, O, OH, _OH2 , and _OH3 ions can substitute for the Cs site, and the introduction of these ions into the prism faces or base faces can promote modulation to a pseudo-hexagonal structure, similar to Cs.

Orthorhombic, rhombohedral, and cubic crystal structures can be identified, for example, by electron diffraction. For example, they can be distinguished by noting the symmetry of the diffraction spots when the electron beam is incident along the c-axis, i.e., when the electron beam is incident from the (0001) direction.

In a hexagonal crystal, the diffraction spots of the three types of prism planes, (10-10), (01-10), and (1-100), appear at the same distance from the incident spot within the reciprocal lattice plane. In other words, the hexagonal crystal has the same crystal plane spacing. Note that the above-mentioned same distance includes distances that can be considered the same within the error range of electron diffraction spot distance measurement. For this reason, a hexagonal crystal produces an electron diffraction pattern that is hexagonally symmetric, i.e., invariant to a 60° rotation.

In an orthorhombic crystal, one type of prism surface spot appears closer to the incident spot than the other two types of prism surface spots. In other words, in an orthorhombic crystal, only one type of prism surface has a long crystal plane spacing.

In a rhombohedral crystal, the three types of prism surface spots each have a different crystal plane spacing.

Cubic crystals have the same hexagonal symmetry pattern as hexagonal crystals, but cubic symmetry can be easily identified by observing from other crystal zone axis directions.

In XRD powder patterns, pseudohexagonal crystals are often considered to be a mixed pattern of orthorhombic and hexagonal crystals, or a mixed pattern of rhombohedral and hexagonal crystals, or a mixed pattern of cubic and hexagonal crystals, but due to the insertion of the planar lattice defects mentioned above, the positions and intensities of the diffraction peaks change slightly.

One method for obtaining a pseudo-hexagonal crystal structure modulated to one or more types selected from the above-mentioned orthorhombic, rhombohedral, and cubic crystals is to add one or more types of additive components selected from O, OH, OH ₂ , and OH _3. Therefore, in the near infrared absorbing particles of the present embodiment, the cesium tungstate preferably contains one or more types of additive components selected from O, OH, OH ₂ , and OH ₃ .

The one or more additive components selected from O, OH, _OH2 , and _OH3 are preferably present at one or more positions selected from hexagonal windows and cavities present in hexagonal tunnels that penetrate the c-axis direction of a hexagon formed by _six WO6 octahedra that constitute the hexagonal alkali tungsten bronze structure of a cesium tungstate crystal, and triangular cavities formed by three _WO6 octahedra.

The hexagonal tunnel has two voids: a large hexagonal cavity and a hexagonal window. The hexagonal window is the second largest void in the hexagonal crystal after the hexagonal cavity and is surrounded by six oxygen atoms that make up the _WO6 octahedron. The hexagonal window is adjacent to the Cs ions located in the hexagonal cavity above and below in the c-axis direction. The trigonal cavity is the next largest void after the hexagonal window and penetrates the hexagonal crystal in the c-axis direction. One or more ions selected from O, OH, _OH2 , and _OH3 can enter the hexagonal cavity by replacing Cs, but they will also invade the hexagonal window if there is a sufficient amount of Cs or if there is a large amount of invaded moisture. In some cases, they invade the trigonal cavity at the bottom or the cavities on the prism surface in parallel with the hexagonal window void, replacing Cs. The addition of the above-mentioned additive components creates defects on the base and prism surfaces, and in this process, the crystal structure shifts from hexagonal to orthorhombic, rhombohedral, and then to cubic, narrowing the band gap and reducing the conduction band electron concentration. Therefore, compared to Cs-HTB, cesium tungstate with a pseudo-hexagonal crystal structure can enhance absorption on the blue side and transmittance on the red side, thereby neutralizing blue-based transmitted colors.

In this case, the orthorhombic, rhombohedral, and cubic crystals can also be considered pseudo-hexagonal crystals, which have atomic arrangements similar to those of hexagonal tungsten bronze, but which have a different symmetry from hexagonal crystals. To avoid strictness and describe it roughly, the orthorhombic crystal in this case is one in which hexagonal symmetry is broken by regularly or randomly inserting faces with missing W and O atoms into one of the three prism faces of a hexagonal crystal. Therefore, in an orthorhombic crystal, only one prism face has a long interplanar spacing. Utilizing this, modulation to an orthorhombic crystal can be easily identified, for example, by the (0001) electron diffraction pattern.

In this case, a rhombohedron is formed by inserting a plane that accepts excess Cs into the base of a hexagonal crystal, i.e., a plane lacking W and O, and systematically displacing the stacking in the c-axis direction of the base, thereby breaking the hexagonal symmetry. In this case, the excess Cs plane involves expansion in the direction perpendicular to the plane as well as displacement on the plane, resulting in changes in the prism plane spacing and the c-axis lattice constant. Therefore, in a rhombohedron, all three prism planes have different spacings. Utilizing this, modulation to a rhombohedron can be easily identified, for example, by the (0001) electron diffraction pattern.

Furthermore, when the three axes of the rhombohedron intersect at 90 degrees, it becomes a cubic crystal. Such a cubic crystal has a pyrochlore structure, and a typical composition thereof is CsW ₂ O ₆ .

Therefore, the voids corresponding to the above-mentioned hexagonal windows, hexagonal cavities, and trigonal cavities are also present in orthorhombic, rhombohedral, and cubic crystals. Therefore, the hexagonal windows, hexagonal cavities, and trigonal cavities in the cesium tungstate contained in the near-infrared absorbing particles of this embodiment also refer to the corresponding voids in orthorhombic, rhombohedral, and cubic crystals (pyrochlore phase).

Hereinafter, a structural example of the method for producing near-infrared absorbing particles of this embodiment will be described, mainly taking as an example the case of hexagonal windows as sites or voids into which O, OH, OH ₂ , and OH ₃ can be substituted or penetrated.

One method for obtaining orthorhombic, rhombohedral, or cubic crystals in which one or more ions selected from O, OH, _OH2 , and _OH3 are present in the hexagonal window is to crystallize the cesium tungstate in saturated water vapor during crystallization during synthesis. Generally, in a Cs-HTB structure, the ionic radius of Cs is slightly larger than the hexagonal cavity, making it difficult for Cs to move. Therefore, once crystallized into a hexagonal crystal, it becomes difficult to diffuse and insert oxygen atoms or the like into the hexagonal window by subsequent heat treatment or the like. Therefore, a method has been devised in which the atmosphere is filled with saturated water vapor before the cesium tungstate crystallizes, and water molecules and O, OH, and _OH3 ions derived from the water molecules are inserted into the hexagonal window simultaneously with the crystallization of the cesium tungstate. For this reason, as will be described later, the method for producing near-infrared absorbing particles of this embodiment preferably includes a step of introducing water vapor at a heating temperature close to the crystallization temperature of the cesium tungstate and crystallizing the cesium tungstate in an atmosphere containing water vapor. When near-infrared absorbing fibers are produced using the near-infrared absorbing particles synthesized through the above steps, or near-infrared absorbing particles that have been further heat-treated in a reducing atmosphere as necessary, the blueness of the color tone can be reduced while the near-infrared absorbing effect is sufficiently maintained, i.e., a neutral color tone can be achieved.

On the other hand, once hexagonal cesium tungstate crystals have been produced, heating the cesium tungstate in a water vapor atmosphere or holding and heating it in a high-temperature, high-humidity environment will not have the effect of neutralizing the above-mentioned transmitted color. This is because elements with a large ionic radius, such as Cs, inhibit the diffusion of oxygen atoms and other atoms through hexagonal tunnels, so once the crystal has crystallized into a hexagonal crystal, subsequent heat treatment makes it difficult for oxygen atoms and other atoms to diffuse into the hexagonal windows of the voids. Therefore, the heat treatment in water vapor described above must be carried out during the initial crystallization process during synthesis.

When heating in an atmosphere containing water vapor during crystallization, it is also possible to simultaneously mix in a reducing gas such as hydrogen gas and crystallize in a reducing gas atmosphere. Furthermore, if the crystals have been crystallized in a water vapor atmosphere, they can be further heated at a high temperature of 500°C to 950°C in an atmosphere containing a reducing gas such as hydrogen gas, or in an inert gas atmosphere. In either case, near-infrared absorbing particles with a neutralized transmitted color and a high near-infrared absorption effect can be obtained. By heating at 500°C or higher, the arrangement of equilibrium atomic positions, such as an orthorhombic crystal structure containing defects, progresses sufficiently, enhancing the near-infrared absorption effect. Furthermore, by heating at 950°C or lower, the speed of crystal structure change can be maintained at an appropriate level, and the crystal state and electronic state can be easily controlled to an appropriate level. Note that if the heating temperature is higher than 950°C and, for example, excessive reduction occurs, lower oxides such as W metal and _WO2 may be generated, which is undesirable from this perspective.

During the initial crystallization by heating with water vapor, O, OH, _OH2 , and _OH3 are incorporated, forming one or more crystal types selected from orthorhombic, rhombohedral, and cubic (pyrochlore phase) crystals that are microscopically modified from hexagonal crystals. By heat-treating these in atmospheres with various degrees of reduction, one or more crystal structures selected from orthorhombic, rhombohedral, and cubic crystals with different amounts and distributions of lattice defects are generated.

The cesium tungstate contained in the near-infrared absorbing particles of this embodiment may have lattice defects of Cs, W, and O. The reason why lattice defects of Cs, W, and O are introduced into the cesium tungstate will be explained below.

In compositions near the hexagonal _{Cs0.33WO3 structure} , crystal stability is determined by a trade-off between structural stability resulting from high crystal symmetry and stability in charge balance, where charge transfer between elements results in overall charge neutrality. For example, the charge-neutral _2Cs2O.11WO3 = _Cs4W11O35 is considered _a thermodynamically stable phase, but when heated in a reducing atmosphere, it easily changes into the hexagonal _{Cs0.32WO3 - y structure} with high crystal symmetry ₍ Non-Patent Document 2). _{Cs0.32WO3 -y} is _a metastable structure with high crystal symmetry, while _Cs4W11O35 is _a stable composition in terms of charge balance. However _{, Cs4W11O35} has poor symmetry in the atomic arrangement within the crystal. For example _, in the model proposed by Solodovnikov (Non-Patent Document 3), in the hexagonal arrangement of _WO6 octahedra, the same as in hexagonal tungsten bronze, planes with missing W and O atoms are inserted at a b/8 pitch in the hexagonal (1,1,-2,0) plane (= orthorhombic (010) plane) of the orthorhombic unit cell, resulting in an orthorhombic crystal as a whole. In other words, the Cs, W, and O defects were inevitably introduced to locally satisfy both the crystal structure and charge balance, and have actually been observed recently using TEM and XRD (Non-Patent Document 4).

In the near-infrared absorbing particles of this embodiment, in orthorhombic, rhombohedral, or cubic crystals where O, OH, _OH2 , or _OH3 is incorporated into the hexagonal window, hexagonal cavity, or trigonal cavity, the local charge balance is disturbed, further modifying the crystal microstructure. Specifically, H ⁺ and _H3O ⁺ are introduced into the crystal during the process of introducing moisture-derived components. These ions compete with Cs ⁺ and W6 ⁺ in the crystal, resulting in Cs or W vacancies to achieve local charge neutrality. As a result, lattice defects including Cs or W vacancies are introduced. O, OH, _OH2 , and _OH3 may invade not only the hexagonal window but also the trigonal cavity. Furthermore, OH2 and OH3 may be substituted with an alkali element (Cs) in the hexagonal cavity. When _OH2 and _OH3 are substituted with charge-neutral _OH2 , the electrons emitted by the originally present alkali ion (Cs ⁺ ) are lost, resulting in a decrease in the conduction band electrons of the crystal.

Among the cesium tungstates having a pseudo-hexagonal crystal structure modulated to one or more types selected from orthorhombic, rhombohedral, and cubic crystals, those that have excellent near-infrared absorption properties and visible light transmittance have a specified composition.

Here, Figure 1A shows a ternary composition diagram 10 with Cs-W-O as the three vertices. Figure 1B shows an enlarged view of a region 11 in the ternary composition diagram 10 of Figure _1A , with _CsWO3 , _W2O3 , and _WO4 as the vertices. It should be noted that this diagram is not a phase diagram showing the thermodynamic equilibrium phase, but rather _a convenient composition diagram showing the range of compositions in this system. Therefore, _CsWO3 , _W2O3 , _WO4 , etc. are compositions shown for convenience, and it is not intended to state whether these are actually compounds that can be obtained.

The cesium tungstate contained in the near-infrared absorbing particles of this embodiment is _preferably represented _by the general formula _CsxWyOz , and has a composition within a region surrounded by four lines: x = 0.6y, z = 2.5y, y = 5x, and _Cs2O : _WO3 = m:n (m and n are integers) in a ternary composition diagram with Cs, W, and O as the vertices. Specifically, in the ternary composition diagrams shown in Figures 1A and 1B, the composition is preferably within region 16 surrounded by line 12 satisfying x = 0.6y, line 13 satisfying z = 2.5y, line 14 satisfying y = 5x, and line 15 satisfying _Cs2O : _WO3 = m:n (m and n are integers). Region 16 also includes points on lines 12 to 15. Also, a line 15 satisfying Cs ₂ O:WO ₃ =m:n (m and n are integers) is a line connecting Cs ₂ O and WO ₃ in the ternary composition diagram 10 as shown in FIG. 1A.

In the above ternary composition diagram, when x > 0.6y, cesium tungstate has a tetragonal-based crystal structure, and the near-infrared absorption effect is lost. Furthermore, when z < 2.5y, cesium tungstate has a hexagonal-based structure with lower oxides of W mixed in, significantly impairing its near-infrared absorption effect and visible light transmittance. When y > 5x, cesium tungstate has a crystal structure called intergrowth, in which _WO3 is mixed into the hexagonal substructure, and the near-infrared absorption effect is lost. Furthermore, if the cesium tungstate falls on the O-rich side to the right of line 15, where _Cs2O : _WO3 is an integer ratio, no near-infrared absorption effect can be obtained. Therefore, it is preferable that the cesium tungstate satisfy the aforementioned range.

The cesium tungstate contained in the near-infrared absorbing particles of this embodiment may have defects in each of the elements cesium, tungsten, and oxygen, but the atomic ratio of cesium to tungsten (x/y) may be any value in the range of 0.2 to 0.6. That is, the near-infrared absorbing particles of this embodiment preferably have partial defects in one or more elements selected from Cs and W that constitute the cesium _tungstate crystal, and x and y in the general _{formula CsxWyOz} preferably satisfy the relationship 0.2≦x/y≦0.6.

Cesium and tungsten supply electrons to the crystal, so by setting x/y to 0.2 or greater, near-infrared absorption can be enhanced. Furthermore, by setting x/y to 0.2 or greater, a hexagonal crystal structure or a crystal structure with a modulated hexagonal crystal structure can be achieved. When x/y exceeds 0.33, Cs ions no longer fit into the hexagonal cavity and begin to occupy the trigonal cavity as well, resulting in modulation of the prism faces and bases, gradually transforming locally into an orthorhombic, rhombohedral, or cubic pyrochlore layered structure. Furthermore, when x/y exceeds 0.6, the crystal structure changes to a tetragonal Cs ₂ W ₃ O ₁₀ , significantly impairing visible light transmittance and reducing usefulness.

The near infrared absorbing particles of the present embodiment can have defects in at least a part of W in the WO ₆ octahedra constituting the crystal based on a hexagonal cesium tungsten bronze structure Cs _0.33 WO _3. The W defects are introduced as planar defects mainly on the hexagonal prism faces or base faces, but since the ionic repulsion of the atomic rows on both sides of the defect plane increases the interplanar spacing, the crystal symmetry changes from hexagonal to orthorhombic, rhombohedral, or cubic.

The near-infrared absorbing particles of this embodiment can have vacancies in at least some of the O atoms in the WO ₆ octahedra that constitute the cesium tungstate crystal, based on the hexagonal alkali tungsten bronze structure CsW ₃ O _9. These O vacancies are introduced randomly, and the vacancies can supply localized electrons to the system, thereby enhancing the near-infrared absorption function. It is known that in the known hexagonal tungsten bronze Cs _0.32 WO _3-y , y = 0.46 or up to 15% of all lattice sites of O atoms that constitute the octahedra (Non-Patent Document 3). If the vacancy amount exceeds 0.5, the crystal becomes unstable, generating a heterophase and decomposing. The cesium tungstate Cs _x W _y O _z contained in the near-infrared absorbing particles of this embodiment can contain O vacancies in an amount corresponding to a maximum z/y = 2.5. However, it should be noted that when excess O, OH, OH ₂ , or OH ₃ is introduced into voids such as the hexagonal window, the identified value of O obtained by chemical analysis includes these excess amounts.

The cesium tungstate contained in the near-infrared absorbing particles of this embodiment may have a portion of the Cs replaced with an additional element. In this case, the additional element is preferably one or more selected from Na, Tl, In, Li, Be, Mg, Ca, Sr, Ba, Al, and Ga.

These additive elements have electron donating properties and assist in donating electrons to the conduction band of the W—O octahedral framework at the Cs site.
(2) Moisture and Heat Resistance of Near-Infrared Absorbing Particles The near-infrared absorbing particles of this embodiment exhibit improved moisture and heat resistance compared to cesium-doped hexagonal tungsten bronze. This effect is reasonable considering that a portion of the near-infrared absorbing particles of this embodiment contains one or more selected from orthorhombic, rhombohedral, and cubic (pyrochlore) phases modulated by interstitial substitution with O, OH, _OH2 , and _OH3 . In other words, humidity and moisture degradation of cesium-doped hexagonal tungsten bronze is essentially a substitution reaction between Cs and water molecules. However, when the cavities and windows of the hexagonal tunnels, which are the main oxygen diffusion pathways, are filled with Cs, O, OH, _OH2 , and _OH3 , this substitution reaction is significantly slowed down. Therefore, the near-infrared absorbing particles of this embodiment not only suppress the loss of near-infrared absorbing function in a high-humidity environment, but also slow down the degradation reaction mediated by atmospheric moisture in a high-temperature heat resistance test at normal humidity, thereby improving moisture and heat resistance.
(3) Average Particle Size of Near-Infrared Absorbing Particles The average particle size of the near-infrared absorbing particles of this embodiment is not particularly limited, but is preferably 0.1 nm or more and 200 nm or less. This is because, by setting the average particle size of the near-infrared absorbing particles to 200 nm or less, localized surface plasmon resonance is more significantly expressed, thereby particularly improving the near-infrared absorption characteristics, i.e., particularly suppressing the solar transmittance. Furthermore, by setting the average particle size of the near-infrared absorbing particles to 0.1 nm or more, the near-infrared absorbing particles can be easily produced industrially. Furthermore, the particle size is closely related to the color of the near-infrared absorbing fiber. In the particle size range where Mie scattering is dominant, the smaller the particle size, the less scattering of short wavelengths in the visible light region. Therefore, while increasing the particle size has the effect of suppressing the blue color tone, an average particle size exceeding 200 nm suppresses the generation of surface plasmons and reduces LSPR absorption. Therefore, by setting the average particle size of the near-infrared absorbing particles to 200 nm or less, the color of the near-infrared absorbing fiber can be made particularly neutral while maintaining a certain level of LSPR absorption.

Furthermore, if the average particle size of the near-infrared absorbing particles is 200 nm or less, it is possible to prevent clogging of the filter, thread breakage, and other problems during the spinning and drawing processes used to produce the near-infrared absorbing fiber. Furthermore, by setting the average particle size of the near-infrared absorbing particles to 200 nm or less, it becomes easier to uniformly mix and disperse the near-infrared absorbing particles in the spinning raw material for the near-infrared absorbing fiber.

Here, the average particle size of the near-infrared absorbing particles can be determined from the median diameter of multiple near-infrared absorbing particles measured from a transmission electron microscope image, or from the dispersed particle size measured using a particle size measuring device based on the dynamic light scattering method of the dispersion liquid.

In particular, when applying to applications where transparency in the visible light region is important, it is preferable to further consider reducing scattering using near-infrared absorbing particles. When such scattering reduction is important, it is particularly preferable that the average particle size of the near-infrared absorbing particles be 30 nm or less.

The average particle size refers to the particle size at 50% of the cumulative value in the particle size distribution, and the same meaning is used throughout this specification. The particle size distribution can be measured to calculate the average particle size by directly measuring the particle size of each particle using, for example, a transmission electron microscope. The average particle size can also be measured using a particle size measuring device based on the dynamic light scattering method of the dispersion, as described above.
(4) Optional Configuration of Near-Infrared Absorbing Particles Near-infrared absorbing particles may be surface-treated for purposes such as surface protection, improved durability, oxidation prevention, and improved water resistance. The specific content of the surface treatment is not particularly limited. For example, as shown in FIG. 5 , the near-infrared absorbing particles of this embodiment may have a coating 51 on a surface 50A of a near-infrared absorbing particle 50. Specifically, the surface of the near-infrared absorbing particle 50 may be coated with a coating 51 of a compound containing one or more atoms selected from Si, Ti, Zr, Al, and Zn. That is, the near-infrared absorbing particles may have a coating of the above-mentioned compound. In this case, examples of the compound containing one or more atoms selected from Si, Ti, Zr, Al, and Zn include one or more selected from oxides, nitrides, carbides, and the like.

5 merely schematically illustrates the shape of the near-infrared absorbing particle, and is not limited to such a shape. For example, the near-infrared absorbing particle 50 may be irregularly shaped instead of spherical. The coating 51 does not need to completely cover the surface 50A of the near-infrared absorbing particle 50, and may be disposed so as to cover only a portion of the surface 50A. Furthermore, the thickness of the coating 51 may vary depending on the location on the surface 50A of the near-infrared absorbing particle 50.
[2] Manufacturing method of near-infrared absorbing particles Next, a configuration example of the manufacturing method of near-infrared absorbing particles of this embodiment will be described. Since the manufacturing method of near-infrared absorbing particles of this embodiment can manufacture the near-infrared absorbing particles described above, the description will be omitted.

The method for producing near-infrared absorbing particles is not particularly limited, and any method can be used as long as it can produce near-infrared absorbing particles that satisfy the above-mentioned properties. Here, one configuration example of the method for producing near-infrared absorbing particles will be described.
(1) First Heat Treatment Step The method for producing near infrared absorbing particles of the present embodiment can include, for example, the following steps.

A first heat treatment process in which a compound raw material containing Cs and W is heated at 400°C or higher and 650°C or lower in an atmosphere containing water vapor or an atmosphere containing water vapor and a reducing gas.

In the first heat treatment step, cesium tungstate can be crystallized by heating at a temperature of 400°C or higher and 650°C or lower.

However, in order to make cesium tungstate a pseudohexagonal crystal, it is preferable to contain sufficient water vapor in the atmosphere when the cesium tungstate crystallizes, i.e., when the _WO6 units form hexagonal crystals with Cs. During this crystallization process, Cs is mainly incorporated into the hexagonal cavities, while water molecules or their decomposition products, _OH3 ⁺ , ^OH- , and ^O2- , are mainly incorporated into the hexagonal windows. When the composition contains a relatively large amount of Cs or water molecules, Cs or water molecules, etc., are also incorporated into the trigonal cavities.

The compound raw material containing Cs and W can be a mixture of a compound raw material containing Cs and a compound raw material containing W. The compound raw material containing Cs and W can be any material containing Cs and W, and can be, for example _, a mixture of _Cs2CO3 and _WO3 .

However, the purpose of the crystallization process in the first heat treatment step is to incorporate water molecules, OH, O, etc. into the crystals during crystallization. For this reason, it is preferable not to use cesium tungsten oxide that already forms a hexagonal crystal structure, such as crystal powder of nCs ₂ O·mWO ₃ (n and m are integers, 3.6≦m/n≦9.0), as a compound raw material containing Cs and W. It is also preferable not to use cesium tungstate using other methods such as the sol-gel method or complex polymerization method, non-equilibrium cesium tungstate obtained by gas phase synthesis, powder by thermal plasma method, or powder by electron beam melting as a compound raw material containing Cs and W. This is because in raw materials that already form a hexagonal crystal structure, Cs inhibits the diffusion of oxygen atoms, etc., making it difficult for water molecules, etc. to be incorporated into the crystals. In other words, it is preferable not to use cesium tungstate having a hexagonal crystal structure as a compound raw material containing Cs and W.

The supply of water vapor during the crystallization process in the first heat treatment step is preferably achieved by, for example, supplying superheated water vapor into a heating furnace. Superheated water vapor is high-enthalpy water vapor that has been heated to a temperature of 100°C or higher by further heating saturated water vapor vaporized at 100°C. It may be supplied together with a carrier gas. When the carrier gas is an inert gas, an atmosphere close to oxygen-free is created. Superheated water vapor may be supplied at 400°C or higher, at which point crystallization becomes active, but it is preferable to supply it from a temperature sufficiently low before crystallization begins. A mixture of superheated water vapor and an inert gas, or a mixture of superheated water vapor, an inert gas, and a reducing gas such as hydrogen, may also be supplied. When a reducing gas is mixed, the rate of hexagonal crystal arrangement tends to increase, and even if the same orthorhombic, rhombohedral, or cubic crystals are used, different microscopic defect structures may be obtained.

In the first heat treatment step, heating may be performed in an atmosphere that does not contain water vapor, such as an inert atmosphere, before or after crystallization of the cesium tungstate.

The method for producing near infrared ray absorbing particles of the present embodiment may further include an optional step.
(2) Second Heat Treatment Step The method for producing near infrared absorbing particles of the present embodiment may also have a second heat treatment step of heating at a temperature of 500° C. or more and 950° C. or less in an atmosphere containing a reducing gas after the first heat treatment step.

The second heat treatment step is, for example, a step of heating and reducing the material powder that has undergone the first heat treatment step at a temperature of 500°C to 950°C. This step serves to anneal and stabilize the orthorhombic, rhombohedral, and cubic crystals with defect structures, while also removing some of the oxygen in the WO ₆ octahedra through high-temperature reduction. The reduction and removal of the octahedral oxygen generates bound electrons on adjacent W atoms, resulting in a structural treatment that enhances near-infrared absorption properties.

When performing a thermal reduction treatment, it is preferable to perform it under a stream of reducing gas. The reducing gas can be a mixed gas containing a reducing gas such as hydrogen and one or more inert gases selected from nitrogen, argon, etc. It is also possible to use a combination of heating in a water vapor atmosphere or vacuum atmosphere or other mild heating and reduction conditions.

The second heat treatment process can also consist of multiple processes, and after heating in the reducing gas atmosphere, heating can also be carried out in an inert gas atmosphere.

In the second heat treatment step, when partial removal of oxygen from the WO _6- octahedron is not intended, heating can be performed in an inert gas atmosphere instead of the reducing gas atmosphere within the above temperature range. That is, the second heat treatment step can be performed in an inert gas atmosphere or a reducing gas atmosphere at a temperature of 500° C. to 950° C.

As mentioned above, the method for producing near-infrared absorbing particles of this embodiment is not particularly limited. Various methods can be used to produce near-infrared absorbing particles as long as they can produce a predetermined structure, including a defective microstructure.

The near-infrared absorbing particles may be produced by synthesizing a tungstate by a solid phase method, a liquid phase method, or a gas phase method in an atmosphere in which water molecules coexist.
(3) Pulverization Step As described above, the near infrared absorbing particles are preferably pulverized into fine particles. Therefore, the method for producing near infrared absorbing particles may include a pulverization step of pulverizing the powder obtained by the first heat treatment step and the second heat treatment step.

The specific means for pulverizing and micronizing the particles is not particularly limited, and various means capable of mechanically pulverizing the particles can be used. A dry pulverization method using a jet mill or the like can be used as a mechanical pulverization method. Furthermore, mechanical pulverization may be performed in a solvent during the process of obtaining the near-infrared absorbing particle dispersion liquid described below.

If necessary, further sieving or the like can be carried out.
(4) Coating Step As described above, the surface of the near infrared absorbing particle may be coated with a compound containing one or more types of atoms selected from Si, Ti, Zr, Al, and Zn. Therefore, the method for producing the near infrared absorbing particle may further include, for example, a coating step of coating the near infrared absorbing particle with a compound containing one or more types of atoms selected from Si, Ti, Zr, Al, and Zn.

In the coating step, specific conditions for coating the surfaces of the near infrared absorbing particles are not particularly limited. For example, a coating step may be included in which an alkoxide or the like containing one or more metals selected from the above metal group is added to the near infrared absorbing particles to be coated, and a film is formed on the surfaces of the near infrared absorbing particles.
[3] Near-infrared absorbing particle dispersion liquid Next, a configuration example of the near-infrared absorbing particle dispersion liquid of this embodiment will be described.

The near-infrared absorbing particle dispersion of this embodiment can also be used, for example, when producing near-infrared absorbing fibers, as described below.

The near-infrared absorbing particle dispersion of this embodiment can contain the near-infrared absorbing particles described above and a liquid medium that is one or more selected from water, organic solvents, oils and fats, liquid resins, and liquid plasticizers. The near-infrared absorbing particle dispersion preferably has a configuration in which near-infrared absorbing particles are dispersed in a liquid medium.

As mentioned above, the liquid medium can be one or more selected from water, organic solvents, oils and fats, liquid resins, and liquid plasticizers.

A variety of organic solvents can be selected, including alcohols, ketones, esters, hydrocarbons, and glycols. Specific examples of the solvent include one or more selected from alcohol-based solvents such as isopropyl alcohol, methanol, ethanol, 1-propanol, isopropanol, butanol, pentanol, benzyl alcohol, diacetone alcohol, and 1-methoxy-2-propanol; ketone-based solvents such as dimethyl ketone, acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; ester-based solvents such as 3-methyl-methoxy-propionate and butyl acetate; glycol derivatives such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol isopropyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol methyl ether acetate, and propylene glycol ethyl ether acetate; amides such as formamide, N-methylformamide, dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone; aromatic hydrocarbons such as toluene and xylene; and halogenated hydrocarbons such as ethylene chloride and chlorobenzene.

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

Examples of oils and fats that can be used include one or more selected from the following: 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; non-drying oils such as olive oil, coconut oil, palm oil, and dehydrated castor oil; fatty acid monoesters obtained by direct esterification of vegetable oil fatty acids with monoalcohols; ethers; and petroleum-based solvents such as Isopar® E, Exxor® Hexane, Heptane, E, D30, D40, D60, D80, D95, D110, and D130 (all manufactured by ExxonMobil).

The liquid resin may be one or more selected from the group consisting of liquid acrylic resin, liquid epoxy resin, liquid polyester resin, liquid urethane resin, etc.

Examples of liquid plasticizers that can be used include liquid plasticizers for plastics.

The components contained in the near-infrared absorbing particle dispersion are not limited to the near-infrared absorbing particles and liquid medium described above. The near-infrared absorbing particle dispersion can also contain other optional components as needed.

For example, the pH of the near-infrared absorbing particle dispersion may be adjusted by adding an acid or alkali to the dispersion as needed.

In addition, in order to further improve the dispersion stability of the near-infrared absorbing particles in the near-infrared absorbing particle dispersion liquid described above and to prevent the dispersed particle size from becoming coarse due to re-aggregation, various surfactants, coupling agents, etc. can also be added to the near-infrared absorbing particle dispersion liquid as dispersants.

The dispersant, such as the surfactant or coupling agent, can be selected according to the application, but it is preferable that the dispersant have one or more functional groups selected from an amine-containing group, a hydroxyl group, a carboxyl group, and an epoxy group. These functional groups adsorb to the surface of the near-infrared absorbing particles to prevent aggregation and have the effect of uniformly dispersing the near-infrared absorbing particles, for example, in an infrared shielding film formed using the near-infrared absorbing particles. It is even more preferable that the dispersant be a polymeric dispersant having one or more functional groups (functional groups) selected from the above functional groups in the molecule.

Suitable commercially available dispersants that can be used include SOLSPERSE 3000, SOLSPERSE 9000, SOLSPERSE 11200, SOLSPERSE 13000, SOLSPERSE 13240, SOLSPERSE 13650, SOLSPERSE 13940, SOLSPERSE 16000, SOLSPERSE 17000, SOLSPERSE 18000, SOLSPERSE 20000, SOLSPERSE 21000, SOLSPERSE 24000SC, SOLSPERSE 24000GR, SOLSPERSE 26000, SOLSPERSE 27000, SOLSPERSE 28000, and SOLSPERSE 29000, all manufactured by Lubrizol Japan Co., Ltd. PERSE31845, SOLSPERSE32000, SOLSPERSE32500, SOLSPERSE32550, SOLSPERSE32600, SOL SPERSE33000, SOLSPERSE33500, SOLSPERSE34750, SOLSPERSE35100, SOLSPERSE35200, SO LSPERSE36600, SOLSPERSE37500, SOLSPERSE38500, SOLSPERSE39000, SOLSPERSE41000, S OLSPERSE41090, SOLSPERSE53095, SOLSPERSE55000, SOLSPERSE56000, SOLSPERSE76500, etc.;
Disperbyk-101, Disperbyk-103, Disperbyk-107, Disperbyk-108, Disperbyk-109, Disperbyk-110, Disperbyk-111, Disperbyk-112, Disperbyk-116, Disperbyk-130, Disperbyk-140 manufactured by BYK Japan Co., Ltd. Disperbyk-142, Disperbyk-145, Disperbyk-154, Disperbyk-161, Disperbyk-162, Disperbyk-163, D isperbyk-164, Disperbyk-165, Disperbyk-166, Disperbyk-167, Disperbyk-168, Disperbyk-170, Di superbyk-171, Disperbyk-174, Disperbyk-180, Disperbyk-181, Disperbyk-182, Disperbyk-183, Dis perbyk-184, Disperbyk-185, Disperbyk-190, Disperbyk-2000, Disperbyk-2001, Disperbyk-2020, D isperbyk-2025, Disperbyk-2050, Disperbyk-2070, Disperbyk-2095, Disperbyk-2150, Disperbyk-2 155, Anti-Terra-U, Anti-Terra-203, Anti-Terra-204, BYK-P104, BYK-P104S, BYK-220S, BYK-6919, etc.;
EFKA4008, EFKA4046, EFKA404 manufactured by BASF Japan Ltd.
7, EFKA4015, EFKA4020, EFKA4050, EFKA4055, EFKA4060, EFKA4080, EFKA4300, EFKA4330, EFKA44
00, EFKA4401, EFKA4402, EFKA4403, EFKA4500, EFKA4510, EFKA4530, EFKA4550, EFKA4560, EFKA4585, EFKA4800, EFKA5220, EFKA6 230, JONCRYL67, JONCRYL678, JONCRYL586, JONCRYL611, JONCRYL680, JONCRYL682, JONCRYL690, JONCRYL819, JONCRYL-JDX5050, etc.;
Examples include one or more selected from Ajisper PB-711, Ajisper PB-821, Ajisper PB-822, and the like, all of which are manufactured by Ajinomoto Fine-Techno Co., Ltd.

The method for dispersing near-infrared absorbing particles in a liquid medium is not particularly limited, as long as it can disperse the near-infrared absorbing particles in the liquid medium. In this case, it is preferable to disperse the near-infrared absorbing particles so that their average particle size is 200 nm or less, and more preferably so that they are 0.1 nm to 200 nm. This is because a small average particle size reduces the scattering of light in the visible light region with wavelengths of 400 nm to 780 nm due to geometric scattering or Mie scattering. As a result of this reduced light scattering, for example, a near-infrared absorbing particle dispersion obtained using the near-infrared absorbing particle dispersion liquid of this embodiment, in which near-infrared absorbing particles are dispersed in a resin or the like, can be prevented from appearing like frosted glass and losing its clear transparency. That is, when the average particle size is 200 nm or less, the light scattering mode weakens from the geometric scattering or Mie scattering mode and shifts to the Rayleigh scattering mode. In the Rayleigh scattering region, scattered light is proportional to the sixth power of the dispersed particle size, so as the dispersed particle size decreases, scattering decreases and transparency improves. Furthermore, when the average particle size is 100 nm or less, scattered light is extremely reduced, which is preferable.

Examples of methods for dispersing near-infrared absorbing particles in a liquid medium include dispersion methods using devices such as bead mills, pole mills, sand mills, paint shakers, and ultrasonic homogenizers. Among these, grinding and dispersing using a media agitation mill such as a bead mill, pole mill, sand mill, or paint shaker that uses media (beads, poles, or Ottawa sand) is preferred from the perspective of shortening the time required to achieve the desired average particle size. By using a media agitation mill, the near-infrared absorbing particles are dispersed in the liquid medium, and at the same time, the particles are further atomized due to collisions between the near-infrared absorbing particles and between the media, resulting in the near-infrared absorbing particles being dispersed in a finer particle size. In other words, the particles are subjected to a grinding-dispersion process.

The dispersion state of the near-infrared absorbing particles in the near-infrared absorbing particle dispersion obtained using the near-infrared absorbing particle dispersion of this embodiment, in which the near-infrared absorbing particles are dispersed in a solid medium such as a resin, does not result in aggregation of particles with a particle size greater than the average particle size of the near-infrared absorbing particles in the dispersion, as long as the dispersion is added to the solid medium using a known method.

Furthermore, if the average particle size of the near-infrared absorbing particles is 0.1 nm or more and 200 nm or less, it is possible to prevent the near-infrared absorbing particle dispersion and its molded product (plate, sheet, etc.) from being grayish in color with a monotonically decreasing transmittance.

The content of the near-infrared absorbing particles in the near-infrared absorbing particle dispersion liquid of this embodiment is not particularly limited, but is preferably, for example, 0.01% by mass or more and 80% by mass or less. This is because a sufficient solar radiation absorptivity can be exhibited by setting the content of the near-infrared absorbing particles to 0.01% by mass or more. Also, by setting the content to 80% by mass or less, the near-infrared absorbing particles can be uniformly dispersed in the dispersion medium.
[4] Near-infrared absorbing fiber The near-infrared absorbing fiber according to this embodiment will be described.

FIG. 6 is a schematic diagram of a near-infrared absorbing fiber of this embodiment. FIG. 6 is a schematic cross-sectional view of a near-infrared absorbing fiber 60 taken along a plane passing through the central axis CA of a fiber 61. As shown in FIG. 6, the near-infrared absorbing fiber 60 of this embodiment contains fibers 61 and near-infrared absorbing particles 62 disposed at one or more locations selected from the surface 61A and the interior 61B of the fibers 61. Note that FIG. 6 is a schematic diagram illustrating an example in which the near-infrared absorbing particles 62 are disposed on both the surface 61A and the interior 61B of the fibers 61, but this is not a limitation. The near-infrared absorbing particles 62 may be disposed on only one of the surface 61A and the interior 61B of the fibers 61. Furthermore, while the near-infrared absorbing particles 62 are depicted as spherical particles in FIG. 6, the shape of the near-infrared absorbing particles 62 is not limited to this shape and may have any shape.
(1) Near-infrared absorbing particles The near-infrared absorbing fiber of this embodiment can contain the near-infrared absorbing particles described above. Since the near-infrared absorbing particles have already been described, a description thereof will be omitted here.

The amount of near-infrared absorbing particles contained in the near-infrared absorbing fiber of this embodiment is not particularly limited, but because the near-infrared absorbing ability per unit weight of the near-infrared absorbing particles is extremely high, a usage amount of about 1/4 to 1/10 of that of ITO or ATO can achieve the same near-infrared absorbing effect. Specifically, the near-infrared absorbing fiber of this embodiment preferably contains the near-infrared absorbing particles in a proportion of, for example, 0.001% by mass or more and 80% by mass or less, based on the solid content of the fiber. Furthermore, from the perspective of the weight of the near-infrared absorbing fiber and raw material costs, the near-infrared absorbing fiber of this embodiment more preferably contains the near-infrared absorbing particles in a proportion of 0.005% by mass or more and 50% by mass or less, based on the solid content of the fiber.

By including near-infrared absorbing particles in a proportion of 0.001% by mass or more relative to the solid content of the fiber, a sufficient near-infrared absorbing effect can be obtained even if the fabric is thin. Furthermore, by including near-infrared absorbing particles in a proportion of 80% by mass or less relative to the solid content of the fiber, deterioration of spinnability due to clogging of the filter, thread breakage, etc. during spinning can be avoided, and a proportion of 50% by mass or less is even more preferable. Furthermore, by including near-infrared absorbing particles in a proportion of 80% by mass or less relative to the solid content of the fiber, the content of the near-infrared absorbing particles can be reduced, so the physical properties of the fiber are not impaired.
(2) Fibers Various fibers can be selected depending on the application of the near-infrared absorbing fiber, and can contain one or more types selected from the fiber group consisting of synthetic fibers, semi-synthetic fibers, natural fibers, regenerated fibers, and inorganic fibers. The fibers can be any of a single type of fiber, a blend, a doubling, and a mixed yarn obtained by mixing fibers. Therefore, the fibers can be any fiber selected from the above fiber group, a blend containing one or more types of fibers selected from the above fiber group, a doubling containing one or more types of fibers selected from the above fiber group, or a mixed yarn obtained by mixing one or more types of fibers selected from the above fiber group.

In consideration of the ease with which the near-infrared absorbing particles can be incorporated into the fibers and the durability of heat retention, the fibers preferably contain synthetic fibers, and more preferably are made of synthetic fibers.
(2-1) Type of fiber (synthetic fiber)
As the synthetic fiber, for example, one or more types selected from polyurethane fibers, polyamide fibers, acrylic fibers, polyester fibers, polyolefin fibers, polyvinyl alcohol fibers, polyvinylidene chloride fibers, polyvinyl chloride fibers, polyether ester fibers, etc. can be suitably used.

Examples of polyamide fibers include nylon, nylon 6, nylon 66, nylon 11, nylon 610, nylon 612, aromatic nylon, and aramid.

Examples of acrylic fibers include polyacrylonitrile, acrylonitrile-vinyl chloride copolymer, and modacrylic.

Examples of polyester fibers include polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, and polyethylene naphthalate.

Examples of polyolefin fibers include polyethylene, polypropylene, and polystyrene.

Examples of polyvinyl alcohol-based fibers include vinylon.

Examples of polyvinylidene chloride fibers include vinylidene.

Examples of polyvinyl chloride fibers include polyvinyl chloride.

Examples of polyetherester fibers include Rexe and Success.
(semi-synthetic fiber)
As the semi-synthetic fiber, for example, one or more types selected from cellulose-based fibers, protein-based fibers, chlorinated rubber, hydrochloric rubber, etc. can be suitably used.

Examples of cellulosic fibers include acetate, triacetate, and acetate oxide.

Examples of protein-based fibers include Promix.
(natural fibers)
As the natural fiber, for example, one or more types selected from plant fibers, animal fibers, mineral fibers, etc. can be suitably used.

Examples of plant fibers include cotton, kapok, flax, hemp, jute, Manila hemp, sisal, New Zealand hemp, ramie, palm, rush, and wheat straw.

Animal fibers include, for example, wool such as sheep's wool, goat's hair, mohair, cashmere, alpaca, angora, camel, and vicuna, as well as silk, down, and feathers.

Examples of mineral fibers include asbestos.
(regenerated fiber)
As the regenerated fiber, for example, one or more types selected from cellulose-based fibers, protein-based fibers, alginate fibers, rubber fibers, chitin fibers, and mannan fibers can be suitably used.

Examples of cellulosic fibers include rayon, viscose rayon, cupro, polynosic, and cuprammonium rayon.

Examples of protein fibers include casein fiber, peanut protein fiber, corn protein fiber, soy protein fiber, and regenerated silk.
(inorganic fibers)
As the inorganic fiber, for example, one or more types selected from metal fiber, carbon fiber, and silicate fiber can be suitably used.

Examples of metal fibers include metal fibers, gold thread, silver thread, and heat-resistant alloy fibers.

Examples of silicate fibers include glass fibers, slag fibers, and rock fibers.
(2-2) Regarding the Shape of the Fiber The cross-sectional shape of the fiber is not particularly limited, and examples thereof include one or more types selected from a circular, triangular, hollow, flat, Y-shaped, star-shaped, and sheath-core type. The near-infrared absorbing particles can be contained in one or more locations selected from the surface and the interior of the fiber in various forms. For example, in the case of a sheath-core type, the near-infrared absorbing particles may be contained in the core or sheath of the fiber. Furthermore, the shape of the fiber may be a filament (long fiber) or a staple (short fiber).
(3) Additives The near-infrared absorbing fiber of the present embodiment may contain additives such as antioxidants, flame retardants, deodorizers, insect repellents, antibacterial agents, and ultraviolet absorbers depending on the purpose, within the range that does not impair the performance of the fiber.

The near-infrared absorbing fiber of this embodiment may also contain particles of a far-infrared emitting material capable of emitting far-infrared rays.

Particles of far-infrared emitting material can be placed at one or more locations selected from the surface and interior of the fiber.

The far-infrared radiating material may be one or more _selected from metal oxides such as _ZrO2 , SiO2, _TiO2 , _Al2O3 , _MnO2 , _MgO , _Fe2O3 , and _CuO , carbides such as ZrC, SiC, and TiC, and nitrides such as _ZrN , _Si3N4 , and AlN.

The cesium tungstate contained in the near-infrared absorbing particles has the property of absorbing solar energy with a wavelength of 0.3 μm or more and 3 μm or less, and particularly selectively absorbs the near-infrared region around the wavelength range of 0.9 μm or more and 2.2 μm or less, and converts it to heat or re-radiates it. Meanwhile, the particles of the far-infrared emitting material have the ability to receive the energy absorbed by the cesium tungstate, a near-infrared absorbing material, convert this energy into thermal energy with a wavelength of mid- to far-infrared, and radiate it. For example, _ZrO2 particles convert the energy absorbed by the cesium tungstate into thermal energy with a wavelength of 2 μm or more and 20 μm or less, and radiate it. Therefore, when the particles of the far-infrared emitting material capable of emitting far-infrared rays and the above-mentioned near-infrared absorbing particles coexist inside or on the surface of the fiber, the solar energy absorbed by the near-infrared absorbing particles is efficiently consumed inside or on the surface of the fiber, resulting in more effective heat retention.

The content of the far-infrared emitting material particles is not particularly limited, but is preferably 0.001% by mass or more and 80% by mass or less relative to the solid content of the fiber. This is because a content of 0.001% by mass or more can obtain a sufficient thermal energy radiation effect even if the fabric is thin. Furthermore, by setting the content ratio of the far-infrared emitting material to 80% by mass or less, it is possible to more reliably avoid a decrease in spinnability of the near-infrared absorbing fiber due to clogging of the filter, yarn breakage, etc. during spinning.
[5] Manufacturing method of near-infrared absorbing fiber Next, a manufacturing method of the near-infrared absorbing fiber of the present embodiment will be described. According to the manufacturing method of the near-infrared absorbing fiber of the present embodiment, the near-infrared absorbing fiber already described can be manufactured, and therefore, the description of the matters already described will be omitted.

The method for producing the near-infrared absorbing fiber of this embodiment is not particularly limited, and may include, for example, a step of disposing near-infrared absorbing particles at one or more locations selected from the surface and interior of the fiber. Since the near-infrared absorbing particles described above can be used as the near-infrared absorbing particles, further explanation will be omitted here.

In the above-mentioned placement process, there are no particular limitations on the method for placing near-infrared absorbing particles at one or more locations selected from the surface and interior of the fiber.

For example, the following methods (a) to (d) can be mentioned.

(a) A method in which near-infrared absorbing particles are directly mixed into the raw polymer of synthetic fibers and then spun.

(b) A method in which a masterbatch is produced in advance by incorporating a high concentration of near-infrared absorbing particles into a portion of the raw polymer, and this is then diluted to the desired concentration before spinning.

(c) A method in which near-infrared absorbing particles are uniformly dispersed in a raw material monomer or oligomer solution in advance, and the desired raw material polymer is synthesized using this dispersion, while the near-infrared absorbing particles are uniformly dispersed in the raw material polymer and then spun.

(d) A method in which near-infrared absorbing particles are attached to the surface of fibers obtained by prior spinning using a binder or the like.

We will now briefly explain the manufacturing methods for the masterbatches used in methods (a) and (b) above.

The method for producing the masterbatch is not particularly limited. For example, first, a near-infrared absorbing particle dispersion, thermoplastic resin powder or pellets, and, if necessary, other additives are uniformly melt-mixed using a mixer or kneader while removing the solvent, such as a liquid medium. This operation allows for the preparation of a mixture in which the near-infrared absorbing particles are uniformly dispersed in the thermoplastic resin.

Examples of mixers include a Riboblender, tumbler, Nauta mixer, Henschel mixer, super mixer, and planetary mixer. Examples of kneading machines include a Banbury mixer, kneader, roll, kneader-ruder, single-screw extruder, and twin-screw extruder.

The method for producing a mixture of near-infrared absorbing particles and resin is not limited to the above method. For example, after preparing a near-infrared absorbing particle dispersion, the solvent, such as the liquid medium of the dispersion, may be removed by a known method, and the resulting powder may be uniformly melt-mixed with thermoplastic resin powder or pellets, and, if necessary, other additives, to produce a mixture in which the near-infrared absorbing particles are uniformly dispersed in the thermoplastic resin. Alternatively, a method may be used in which the near-infrared absorbing particle powder is directly added to the thermoplastic resin and then uniformly melt-mixed.

A masterbatch containing near-infrared absorbing particles can be obtained by kneading a mixture of near-infrared absorbing particles obtained by the method described above and a thermoplastic resin in a vented single-screw or twin-screw extruder and processing it into pellets.

Here, we will explain the above methods (a) to (d) that can be applied to the placement process using specific examples.

Method (a): For example, we will explain the case where polyester fibers are used as the fibers.

A near-infrared absorbing particle dispersion is added to polyethylene terephthalate resin pellets, which are a thermoplastic resin, and the mixture is mixed uniformly in a blender. The solvent, such as the liquid medium, is then removed. The mixture from which the solvent has been removed is melt-kneaded in a twin-screw extruder to obtain a near-infrared absorbing particle-containing masterbatch. This near-infrared absorbing particle-containing masterbatch can be melt-mixed near the melting temperature of the resin and spun, for example, using various known methods. As mentioned above, the masterbatch can also be prepared by methods other than those described above.

Method (b): A masterbatch containing near-infrared absorbing particles is prepared by a method such as that described in method (a). Then, the masterbatch and a target amount of a masterbatch made of polyethylene terephthalate without added near-infrared absorbing particles are melt-mixed at a desired mixing ratio near the melting temperature of the resin, and the mixture is spun according to a known method.

Method (c): For example, we will explain the case where urethane fibers are used as the fibers.

A polymeric diol containing near-infrared absorbing particles is reacted with an organic diisocyanate in a twin-screw extruder to synthesize an isocyanate-terminated prepolymer, which is then reacted with a chain extender to produce a polyurethane solution (raw polymer). This polyurethane solution is then spun using known methods.

Method (d): For example, we will explain the case where near-infrared absorbing particles are attached to the surface of natural fibers.

First, a treatment liquid is prepared by mixing near-infrared absorbing particles, one or more binder resins selected from acrylic, epoxy, urethane, and polyester, and a solvent such as water.

Next, natural fibers are immersed in the prepared treatment solution, or the natural fibers are impregnated with the prepared treatment solution by padding, printing, spraying, or other methods, and then dried. This allows the near-infrared absorbing particles to adhere to the natural fibers. Furthermore, method (d) can be applied to semi-synthetic fibers, regenerated fibers, inorganic fibers, or blends, doubling, or mixed fibers thereof, in addition to the natural fibers mentioned above.

When carrying out methods (a) to (d), the dispersion method for dispersing the near-infrared absorbing particles in the dispersion medium is not particularly limited, and any method that can uniformly disperse the near-infrared absorbing particles in the liquid, i.e., the dispersion medium, can be used. For example, methods such as a medium stirring mill, ball mill, sand mill, and ultrasonic dispersion can be suitably applied. Note that the near-infrared absorbing particle dispersion liquid described above can be used as a dispersion of the near-infrared absorbing particles in the dispersion medium.

When dispersing the near-infrared absorbing particles, it is preferable to set the dispersion process conditions so that, when the XRD peak intensity of the (220) plane of a silicon powder standard sample (640c, manufactured by NIST) is taken as 1, the ratio of the XRD peak top intensity of the near-infrared absorbing particles is 0.13 or greater. By doing so, the near-infrared absorbing fiber according to this embodiment can exhibit particularly excellent optical properties.

Furthermore, the dispersion medium for the near-infrared absorbing particles is not particularly limited and can be selected according to the fibers to be mixed. For example, one or more types selected from various common organic solvents such as alcohols, ethers, esters, ketones, and aromatic compounds, and water can be used.

Furthermore, when attaching or mixing near-infrared absorbing particles with fibers or the polymer that serves as their raw material, the dispersion of near-infrared absorbing particles may be mixed directly with the fibers or the polymer that serves as their raw material. If necessary, the pH may be adjusted by adding an acid or alkali to the dispersion of near-infrared absorbing particles, and various surfactants, coupling agents, etc. may also be added to further improve the dispersion stability of the near-infrared absorbing particles.

As explained above, the near-infrared absorbing fiber according to this embodiment can efficiently absorb near-infrared rays from sunlight and the like by disposing near-infrared absorbing particles inside or on the surface of the fiber, thereby providing a fiber with excellent heat retention properties.

The near-infrared absorbing fiber of this embodiment also has good weather resistance, excellent transparency, and is low-cost, and the near-infrared absorbing particles have a neutral color tone. Therefore, the design of textile products using the near-infrared absorbing fiber of this embodiment is not impaired, and it can be colored in complementary or light colors, and basic physical properties of the fiber such as strength and elongation can be avoided from being impaired. As a result, the near-infrared absorbing fiber of this embodiment can be used in a variety of applications, such as textile products that require heat retention, such as cold weather clothing, sports clothing, stockings, curtains, and other industrial textile products, and can be colored in complementary or light colors.

In the near-infrared absorbing fiber of this embodiment, the near-infrared absorbing particles are preferably contained uniformly inside and on the surface of the fiber. By containing near-infrared absorbing particles uniformly inside and on the surface of the near-infrared absorbing fiber of this embodiment, even when the content of near-infrared absorbing particles is small, the fiber can efficiently absorb near-infrared rays contained in sunlight, etc., and provide excellent heat retention properties.

Furthermore, in the near-infrared absorbing fiber of this embodiment, it is preferable that the near-infrared absorbing particles and the particles of the far-infrared emitting material described above are uniformly contained within and on the surface of the fiber. By uniformly containing the near-infrared absorbing particles and the particles of the far-infrared emitting material described above within and on the surface of the near-infrared absorbing fiber of this embodiment, even when the content of the near-infrared absorbing particles is small, it is possible to efficiently absorb and utilize the near-infrared rays contained in sunlight, etc., and provide a fiber with particularly excellent heat retention properties.

Incidentally, "uniformly contained" means that the near-infrared absorbing particles and the like are contained inside or on the surface of the fiber in a state where they are not aggregated and formed into clumps.
[6] Textile product The textile product of this embodiment can contain the near-infrared absorbing fiber described above. Specifically, the textile product of this embodiment can be obtained by processing the near-infrared absorbing fiber described above and can contain the near-infrared absorbing fiber described above. Note that the textile product of this embodiment can also be made of the near-infrared absorbing fiber described above.

The textile product of this embodiment includes the near-infrared absorbing fiber described above, which has good weather resistance, excellent transparency, and is low cost, and the near-infrared absorbing particles have a neutral color tone. This allows the textile product to be colored in complementary or light colors without compromising the design of the textile product, and also avoids compromising the basic physical properties of the fiber, such as strength and elongation.

The present invention will be specifically described below with reference to examples, although the present invention is not limited to the following examples.
(Evaluation method)
First, the evaluation methods used in the following examples and comparative examples will be described.
(chemical analysis)
The obtained near-infrared absorbing particles were chemically analyzed by atomic absorption spectrometry (AAS) for Cs and by inductively coupled plasma optical emission spectrometry (ICP-OES) for W (tungsten). A light element analyzer (ON-836) manufactured by LECO was used for O.
(X-ray diffraction measurement)
The X-ray diffraction measurement was carried out by powder XRD measurement using Cu-Kα radiation with a Spectris X'Pert-PRO/MPD device.

[Example 1]
(Production and Evaluation of Near-Infrared Absorbing Particles)
_A total of 20 g of cesium carbonate ( _Cs2CO3 ) and tungsten trioxide ( _WO3 ) were weighed, mixed, and kneaded to a molar ratio of _Cs2CO3 : _WO3 = ₁ :6, and the resulting mixture was placed in a carbon boat and dried in air at 110°C for 12 hours. This yielded a cesium tungsten oxide precursor powder, which is a compound raw material containing Cs and W.

The cesium tungsten oxide precursor powder was placed on an alumina boat and placed in a heating muffle furnace. While flowing a mixed gas of superheated steam and nitrogen gas at a volume ratio of 50:50, the temperature was raised to 550°C and maintained for 1 hour. In Table 1, this mixed gas is represented as 50% N ₂ -50% superheated H ₂ O. Next, the gas supplied was changed to 100% nitrogen gas by volume. While flowing nitrogen gas, the temperature was maintained at 550°C for 0.5 hours, after which the temperature was raised and maintained at 800°C for 1 hour. The temperature was then lowered to room temperature, yielding a slightly greenish white powder (first heat treatment step).

The X-ray powder diffraction pattern of this white powder was identified as Cs ₄ W ₁₁ O ₃₅ (ICDD 00-51-1891).

Next, this white powder was placed in a carbon boat and placed in a tubular furnace, heated in a 1 vol% H ₂ -Ar gas flow (represented as 1% H ₂ -Ar in Table 1), and reduced by holding at 550°C for 1 hour. Next, the gas supplied was changed to 100 vol% Ar gas, and the temperature was held at 550°C for 30 minutes while flowing Ar gas. Subsequently, the temperature was raised to 800°C and heated for 1 hour, and then cooled to room temperature to obtain a pale blue powder A (second heat treatment step).

The XRD powder pattern of Powder A obtained here, as shown in Figure 2, showed a broad two-phase mixture pattern with a hexagonal _Cs0.32WO3 primary phase and _{an orthorhombic Cs4W11O35} secondary phase. Chemical analysis of Powder A determined a molar Cs/W ratio of 0.33. The composition ratios of other components are shown in Table _2. The XRD powder pattern in this case contained a mixture of diffraction lines from both _{hexagonal Cs0.32WO3} and _{orthorhombic Cs4W11O35} , but _{the Cs4W11O35} diffraction line exhibited slight deviations from the ideal position and intensity. _No data matching this diffraction pattern was found in the _ICDD database.

When this powder was observed under a transmission electron microscope (Hitachi High-Tech Corporation HF-2200), fine particles 40 were observed, as shown in Figure 4(A). As shown in the selected-area electron diffraction pattern in Figure 4(B), the crystals of each fine particle were observed as a single-phase structure, rather than a mixed structure consisting of two separated phases, hexagonal and orthorhombic. The electron diffraction pattern shown in Figure 4(B) corresponds to the [0001] crystal zone of the hexagonal crystal, and the diffraction spots indicate the plane indices when considered as hexagonal. When the corresponding plane spacings were calculated from the nearest diffraction spots in the three directions, only the (01-10) plane spacing was found to be 3.88 Å, significantly larger than the values for the other two directions, 3.48 Å and 3.43 Å, indicating a deviation from precise hexagonal symmetry. Note that, while in crystallography, negative indices are usually indicated by a bar above the number, for convenience of description, a minus sign is placed before the number in this specification.

Figure 4(C), on the other hand, is an atomic image captured using the STEM-HAADF method (high-angle-scattering dark-field observation in scanning electron mode). With the HAADF method, the higher the atomic number and the greater the atomic density in the projection direction, the brighter and more intense the atomic spot obtained. Therefore, when combined with the projection plane information of the [0001] crystal zone, the atomic species in the image can be identified. The most intense spot in Figure 4(C) is a W atom, but it is aligned along the (01-10) plane; in a hexagonal crystal, a similar arrangement is not observed along the equivalent (1-100) or (10-10) planes. The streaks observed in the (01-10) spot direction in Figure 4(C) indicate that many planar defects (W and O vacancies) have been inserted only in the (01-10) plane, which is interpreted as increasing the interplanar spacing of the (01-10) plane. In a hexagonal crystal, almost no defects are introduced into the (01-10), (1-100), and (10-10) planes, which intersect at 60°. However, it can be seen that many planar defects have been inserted only into the (01-10) plane, causing it to lose its hexagonal symmetry and become orthorhombic. The regular spots indicated by arrows 41 in Figure 4(B) show that these W-defect planes have been introduced at a periodicity of approximately 3.88 Å. As described above, it has been determined that these near-infrared absorbing particles are single-crystal particles of cesium tungstate with a pseudo-hexagonal crystal structure that has been modified into an orthorhombic crystal.

Furthermore, when the obtained near-infrared absorbing particle powder was irradiated with 25 W Al-Kα X-rays using X-ray photoelectron spectroscopy (Ulvac-Phi XPS-Versa Probe II) and the excited photoelectrons were observed, it was found that the O1s peak near 530.45 eV had a shoulder on the high-energy side. The component near 532.80 eV was assumed to be due to H ₂ O, and peak separation revealed that it contained a large amount of OH ₂ . Furthermore, thermal desorption spectroscopy confirmed that OH and OH ₂ were released from the crystals during heating in the temperature range of 500°C to 700°C. These observation results suggest that OH and OH ₂ are contained in the cesium tungstate of Powder A, and considering the voids in the pseudohexagonal crystals elongated in the uniaxial direction, it is inferred that they have penetrated into the window voids of the hexagonal tunnel. It is thought that water and its decomposition products were introduced into the crystals by crystallization in superheated steam, and the H ⁺ and H ₃ O ⁺ ions generated at that time competed with the positive W ions, leading to the partial desorption of the W ions.
(Near-infrared absorbing fibers, production and evaluation of textile products)

10% by mass of the prepared Powder A, 10% by mass of an acrylic polymer dispersant having an amine-containing functional group (hereinafter referred to as "Dispersant A"), and 80% by mass of toluene as a solvent were weighed out. These weighed materials were placed in a glass container along with 0.3 mm diameter silica beads, and dispersed and pulverized for 1 hour using a paint shaker to obtain Dispersion A.

Toluene was removed from Dispersion A using a spray dryer, yielding a near-infrared absorbing particle dispersion powder according to Example 1. The obtained near-infrared absorbing particle dispersion powder was added to polyethylene terephthalate resin pellets, which are a thermoplastic resin, and the mixture was uniformly mixed in a blender. The mixture was then melt-kneaded and extruded in a twin-screw extruder, and the extruded strands were cut into pellets to obtain a masterbatch containing 40% by mass of near-infrared absorbing particles, which are a near-infrared absorbing component.

The above masterbatch was melt-spun and then drawn to produce a polyester multifilament yarn, which is the near-infrared absorbing fiber of Example 1. The obtained near-infrared absorbing fiber contained 40% by mass of near-infrared absorbing particles, the same as the masterbatch. The obtained near-infrared absorbing fiber had a structure in which polyethylene terephthalate fibers were combined with near-infrared absorbing particles disposed on the surface and inside of the fibers. The polyester multifilament yarns produced in the other examples below also had the same structure.

The average particle size of near-infrared absorbing particles contained in the near-infrared absorbing polyester multifilament yarn was calculated to be 30 nm using an image processing device based on transmission electron microscope images. The particle size of each particle is the diameter of the circumscribed circle of the particle, and the average particle size was calculated as the median diameter in the particle size distribution measured for 100 particles.

The resulting polyester multifilament yarn was cut to produce polyester staple, which was then used to manufacture spun yarn. This spun yarn was then used to obtain a knitted product, the textile product of Example 1, which has heat-retaining properties. The solar reflectance of the knitted product sample was adjusted to 8%. Adjustment of the solar reflectance of the knitted product sample to 8% was performed in all of the examples and comparative examples described below.

The spectral characteristics of the produced knitted fabric were measured using a Hitachi spectrophotometer to measure the transmittance and reflectance of light with wavelengths of 200 to 2100 nm, and the solar absorptance was calculated in accordance with JIS A 5759 (2019). The solar absorptance was calculated from the formula: solar absorptance (%) = 100% - solar transmittance (%) - solar reflectance (%). The calculated solar absorptance was 51.1%. Furthermore, the color index of the knitted fabric was calculated from the reflectance, resulting in L ^* = 88, a ^* = -2, and b ^* = 9, confirming that the blue color was very weak and the fabric had a neutral tone.

The results are shown in Table 3. Table 3 also lists the results obtained in Examples 2 to 14 and Comparative Examples 1 and 2, which will be described later.

Next, the temperature-raising effect on the backside of the knitted fabric was measured as follows. In an environment of 20°C and 60% RH, a solar-like spectrum lamp (solar simulator XL-03E50 modified, manufactured by Seric Co., Ltd.) was irradiated from a distance of 30 cm from the knitted fabric, and the temperature of the backside of the fabric was measured at regular intervals (0 seconds, 30 seconds, 60 seconds, 180 seconds, 360 seconds, and 600 seconds) using a radiation thermometer (HT-11, manufactured by Minolta Co., Ltd.).

The results are shown in Table 4. Table 4 also shows the results obtained in Examples 2 to 14 and Comparative Examples 1 and 2, which will be described later.
[Example 2]
(Production and Evaluation of Near-Infrared Absorbing Particles)
The cesium tungsten oxide precursor powder produced in Example 1 was placed on an alumina boat and placed in a heating muffle furnace, and the temperature was raised to 150°C while flowing 100% by volume of nitrogen gas. The gas supplied here was changed to a gas containing superheated steam, hydrogen gas, and nitrogen gas in a volume ratio of 50:1:49 (represented as 1% H ₂ -49% N ₂ -50% superheated H ₂ O in Table 1), and the temperature was raised to 550°C while flowing this mixed gas and maintained at that temperature for 1 hour. The temperature was then lowered to room temperature, yielding a light blue powder B (first heat treatment step).

The X-ray powder diffraction pattern of this powder, as shown in Figure 2, shows broad diffraction lines, _with hexagonal _Cs0.32WO3 as the main phase, but _also a pattern of a mixture of diffraction lines from _{orthorhombic Cs4W11O35} and pyrochlore phase ( _Cs2O ) _0.44W2O6 as _heterophases . The diffraction lines of this pyrochlore phase are broad, and the reflection positions _are slightly shifted. It is believed that oxygen from water, OH, _OH2 , and _OH3 are incorporated into the pyrochlore cavities. The (111) plane of the cubic pyrochlore phase has hexagonal symmetry similar to the basal plane of a hexagonal crystal, and the pyrochlore cavities correspond to the voids between the hexagonal and trigonal cavities in a hexagonal crystal. In other examples, small amounts of pyrochlore phase reflections were often observed in the XRD powder patterns.

When one particle of this powder was observed under a transmission electron microscope from the (0001) direction, the position of the prism surface spot that appeared in the electron diffraction image was short and accompanied by a weak streak. This indicated that the hexagonal crystals were orthorhombic crystals modulated by prism surface defects.

Chemical analysis of Powder B showed that Cs/W=0.32. The composition ratios of other components are shown in Table 2.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product were obtained and evaluated in the same manner as in Example 1, except that Powder B was used. The evaluation results are shown in Tables 3 and 4.
[Example 3]
(Production and Evaluation of Near-Infrared Absorbing Particles)
The light blue powder B obtained in Example 2 was spread on a carbon boat and held at 550°C for 2 hours in a 1% by volume _H2 -Ar gas flow. Next, the gas supplied was changed to 100% by volume nitrogen gas, and the boat was held at 550°C for 0.5 hours while flowing nitrogen gas, after which the temperature was increased and held at 800°C for 1 hour. The temperature was then lowered to room temperature, and light blue powder C was obtained (second heat treatment step).

Chemical analysis of Powder C revealed a Cs/W ratio of 0.31, in terms of the ratio of amounts of substance. The composition ratios of other components are shown in Table 2.

As shown in Figure 2, the X-ray powder diffraction pattern of Powder C had broader diffraction lines compared to Examples ₁ and ₂ , and showed a pattern in which the diffraction lines of _{hexagonal Cs0.32WO3 and orthorhombic Cs4W11O35 were mixed. However, the diffraction line position and intensity of Cs4W11O35 did not completely} match the ICDD data.

When one particle of this powder was observed under a transmission electron microscope from the (0001) direction, the position of the prism surface spot that appeared in the electron diffraction image was short and accompanied by a weak streak, indicating that the hexagonal crystal was an orthorhombic crystal modulated by prism surface defects.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product were obtained and evaluated in the same manner as in Example 1, except that Powder C was used. The evaluation results are shown in Tables 3 and 4.
[Example 4]
(Production and Evaluation of Near-Infrared Absorbing Particles)
The pale blue powder B obtained in Example 2 was spread on a carbon boat, heated in a 100% by volume Ar gas flow, and held at 800° C. for 1 hour. Thereafter, the temperature was lowered to room temperature, and a pale blue powder D was obtained.

The X-ray powder diffraction pattern of Powder D had broad diffraction lines as shown in Figure 2 _{, and showed a pattern in which the diffraction lines of hexagonal Cs0.32WO3 and orthorhombic Cs4W11O35 were mixed. The diffraction line positions and intensities of Cs4W11O35 did not completely match the ICDD data} .

When one particle of this powder was observed under a transmission electron microscope from the (0001) direction, the position of the prism surface spot appearing in the electron diffraction image was short and accompanied by a weak streak. This indicated that the hexagonal crystals were orthorhombic crystals modulated by prism surface defects.

Chemical analysis of Powder D showed that Cs/W=0.33. The composition ratios of other components are shown in Table 2.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product were obtained and evaluated in the same manner as in Example 1, except that Powder D was used. The evaluation results are shown in Tables 3 and 4.
[Example 5]
(Production and Evaluation of Near-Infrared Absorbing Particles)
The pale blue powder B obtained in Example 2 was spread on a carbon boat and heated to 800°C in a 100% by volume Ar gas flow. Then, the gas supplied was changed to 1% by volume H ₂ -Ar, and the temperature was maintained at 800°C for 10 minutes in the gas flow. The temperature was then lowered to room temperature, and pale blue powder E was obtained.

The X-ray powder diffraction pattern of Powder E had broad diffraction lines as shown in Figure 2 _{, and showed a pattern in which the diffraction lines of hexagonal Cs0.32WO3 and orthorhombic Cs4W11O35 were mixed. The diffraction line positions and intensities of Cs4W11O35 did not completely match the ICDD data} .

When one particle of this powder was observed under a transmission electron microscope from the (0001) direction, the position of the prism surface spot appearing in the electron diffraction image was short and accompanied by a weak streak. This indicated that the hexagonal crystals were orthorhombic crystals modulated by prism surface defects.

Chemical analysis of Powder E showed that Cs/W=0.32. The composition ratios of other components are shown in Table 2.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knitted product were obtained and evaluated in the same manner as in Example 1, except that Powder E was used. The evaluation results are shown in Tables 3 and 4.
[Example 6]
(Production and Evaluation of Near-Infrared Absorbing Particles)
The pale blue powder B obtained in Example 2 was spread on a carbon boat and held at 500°C for 30 minutes in a 1% by volume _H2 -Ar gas flow. Next, the gas supplied was changed to 100% by volume nitrogen gas, and the boat was held at 550°C for 30 minutes while flowing nitrogen gas, and then the temperature was further increased to 800°C and held for 1 hour. The temperature was then lowered to room temperature, and pale blue powder F was obtained.

The X-ray powder diffraction pattern of Powder F had broad diffraction lines as shown in Figure 2 _{, and showed a pattern in which the diffraction lines of hexagonal Cs0.32WO3 and orthorhombic Cs4W11O35 were mixed. The diffraction line positions and intensities of Cs4W11O35 did not completely match the ICDD data} .

When one particle of this powder was observed under a transmission electron microscope from the (0001) direction, the position of the prism surface spot appearing in the electron diffraction image was short and accompanied by a weak streak. This indicated that the hexagonal crystals were orthorhombic crystals modulated by prism surface defects.

Chemical analysis of Powder F showed that Cs/W=0.31. The composition ratios of other components are shown in Table 2.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product were obtained and evaluated in the same manner as in Example 1, except that Powder F was used. The evaluation results are shown in Tables 3 and 4.
[Example 7]
_A total of 20 g of cesium carbonate ( _Cs2CO3 ) and tungsten trioxide ( _WO3 ) were weighed, mixed, and kneaded to a molar ratio of _Cs2CO3 : _WO3 = 1:10, and the resulting mixture was placed in a carbon boat and dried in air at 110°C for 12 hours. This yielded a cesium tungsten oxide precursor powder, _a compound raw material containing Cs and W.

Then, the first heat treatment step was carried out under the same conditions as in Example 2, except that the above-mentioned cesium tungsten oxide precursor powder was used.

The powder obtained in the first heat treatment step was spread on a carbon boat and heated to 800°C in a 100% by volume Ar gas flow. Then, the gas supplied was changed to a 1% by volume H ₂ -Ar gas flow, and the temperature was maintained at 800°C for 10 minutes while the gas was flowing, and then the temperature was lowered to room temperature to obtain a light blue powder G.

The X-ray powder diffraction pattern of Powder G had broad diffraction lines and showed a pattern in which the diffraction lines of hexagonal Cs _0.20 WO ₃ (ICDD 0-083-1333) and orthorhombic Cs ₄ W ₁₁ O ₃₅ were mixed. The diffraction line positions and intensities of Cs ₄ W ₁₁ O ₃₅ did not completely match the ICDD data.

When one particle of this powder was observed under a transmission electron microscope from the (0001) direction, the position of the prism surface spot appearing in the electron diffraction image was short and accompanied by a weak streak. Therefore, the hexagonal crystal was identified as an orthorhombic crystal modulated by prism surface defects.

Chemical analysis of Powder G showed that Cs/W=0.20. The composition ratios of other components are shown in Table 2.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product were obtained and evaluated in the same manner as in Example 1, except that Powder G was used. The evaluation results are shown in Tables 3 and 4.
[Example 8]
_A total of 20 g of cesium carbonate ( _Cs2CO3 ) and tungsten trioxide ( _WO3 ) were weighed, mixed, and kneaded to a molar ratio of _Cs2CO3 : _WO3 = 3:10, and the resulting mixture was placed in a carbon boat and dried in air at 110°C for 12 hours. This yielded a cesium tungsten oxide precursor powder, _a compound raw material containing Cs and W.

Then, the first heat treatment step was carried out under the same conditions as in Example 2, except that the above-mentioned cesium tungsten oxide precursor powder was used.

The powder obtained in the first heat treatment step was spread on a carbon boat and heated to 800°C in a 100% by volume Ar gas flow. Then, the gas supplied was changed to 1% by volume H ₂ -Ar, and the temperature was maintained at 800°C for 10 minutes while the gas was flowing, and then the temperature was lowered to room temperature to obtain light blue powder H.

The X-ray powder diffraction pattern of Powder H had broad diffraction lines, _{with rhombohedral Cs6W11O36} and _Cs8.5W15O48 as the main phases, mixed with small amounts of diffraction lines from _{hexagonal Cs0.32WO3 and tetragonal Cs2W3O10 .} However _, the _diffraction line positions and _intensities of _{Cs6W11O36 and Cs8.5W15O48} did not completely match _the ICDD data.

When one particle of this powder was observed under a transmission electron microscope from the (0001) direction, the positions of the prism surface spots appearing in the electron diffraction pattern were found to differ by more than the experimental error range for all three particles. This indicated that the powder was primarily composed of rhombohedral crystals in which hexagonal crystals were modulated by basal defects.

Chemical analysis of Powder H showed that Cs/W=0.59. The composition ratios of other components are shown in Table 2.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product were obtained and evaluated in the same manner as in Example 1, except that Powder H was used. The evaluation results are shown in Tables 3 and 4.
[Example 9]
_A total of 20 g of cesium carbonate ( _Cs2CO3 ) and tungsten trioxide ( _WO3 ) were weighed, mixed, and kneaded to a molar ratio of _Cs2CO3 : _WO3 = 2:11, and the resulting mixture was placed in a carbon boat and dried in air at 110°C for 12 hours. This yielded a cesium tungsten oxide precursor powder, _a compound raw material containing Cs and W.

Then, the first heat treatment step was carried out under the same conditions as in Example 2, except that the above-mentioned cesium tungsten oxide precursor powder was used, and light green Powder I was obtained.

The X-ray powder diffraction pattern of Powder I had broad diffraction lines as shown in Figure ₃ , with the _pyrochlore phase ( _Cs2O ) _0.44W2O6 as the main phase, and showed a pattern mixed with some diffraction lines from _{hexagonal Cs0.32WO3 and orthorhombic Cs4W11O35} . However _{, the diffraction line positions and intensities of (Cs2O)0.44W2O6 and Cs4W11O35 did not completely} match _the ICDD data.

Transmission electron microscope observation of this powder revealed a cubic electron diffraction pattern.

Chemical analysis of Powder I showed that Cs/W=0.36. The composition ratios of other components are shown in Table 2.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product were obtained and evaluated in the same manner as in Example 1, except that Powder I was used. The evaluation results are shown in Tables 3 and 4.
[Example 10]
(Production and Evaluation of Near-Infrared Absorbing Particles)
Powder I prepared in Example 9 was spread on a carbon boat and heated to 800°C while flowing 100% by volume of Ar gas. Then, the gas supplied was changed to 1% by volume of H ₂ -Ar, and the boat was maintained at 800°C for 10 minutes while flowing this gas, and then cooled to room temperature to obtain light blue powder J.

The X-ray powder diffraction pattern of this powder, as shown in Figure ₃ , showed a pattern containing a mixture of diffraction lines _from hexagonal _Cs0.32WO3 , _{orthorhombic Cs4W11O35} , _{rhombohedral Cs6W11O36 ,} and _{Cs8.5W15O48 .} However, _the diffraction line positions and _intensities of _{Cs4W11O35 , Cs6W11O36 , and Cs8.5W15O48} did not completely match _{the ICDD} data.

When one particle of this powder was observed under a transmission electron microscope from the (0001) direction, the positions of the prism surface spots appearing in the electron diffraction pattern were found to differ by more than the experimental error range for all three particles. This indicated that the powder was primarily composed of rhombohedral crystals in which hexagonal crystals were modulated by basal defects.

Chemical analysis of Powder J showed that Cs/W=0.36. The composition ratios of other components are shown in Table 2.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product were obtained and evaluated in the same manner as in Example 1, except that Powder J was used. The evaluation results are shown in Tables 3 and 4.
[Example 11]
(Production and Evaluation of Near-Infrared Absorbing Particles)
Powder I prepared in Example 9 was spread on a carbon boat and held in a 1% by volume H ₂ -Ar gas flow at 500°C for 30 minutes. Then, the gas supplied was changed to 100% by volume nitrogen gas, and the boat was held at 800°C for 1 hour while the nitrogen gas was flowing, and then cooled to room temperature to obtain light blue powder K.

The X-ray powder diffraction pattern of this powder, as shown in Figure ₃ , showed a pattern containing a mixture of diffraction lines _from hexagonal _Cs0.32WO3 , _{orthorhombic Cs4W11O35} , _{rhombohedral Cs6W11O36 ,} and _{Cs8.5W15O48 .} However, _the diffraction line positions and _intensities of _{Cs4W11O35 , Cs6W11O36 , and Cs8.5W15O48} did not completely match _{the ICDD} data.

When one particle of this powder was observed under a transmission electron microscope from the (0001) direction, the positions of the prism surface spots appearing in the electron diffraction pattern were found to differ by more than the experimental error range for all three particles. This indicated that the powder was primarily composed of rhombohedral crystals in which hexagonal crystals were modulated by basal defects.

Chemical analysis of the powder K showed that Cs/W=0.35. The composition ratios of the other components are shown in Table 2.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product were obtained and evaluated in the same manner as in Example 1, except that Powder K was used. The evaluation results are shown in Tables 3 and 4.
[Example 12]
_A total of 20 g of cesium carbonate ( _Cs2CO3 ) and tungsten trioxide ( _WO3 ) were weighed, mixed, and kneaded to a molar ratio of _Cs2CO3 : _WO3 = ₁ :5, and the resulting mixture was placed in a carbon boat and dried in air at 110°C for 12 hours. This yielded a cesium tungsten oxide precursor powder, a compound raw material containing Cs and W.

The precursor powder was then placed on an alumina boat in a heating muffle furnace and heated to 150°C while flowing 100% nitrogen gas by volume. The gas supplied was then changed to a mixture of superheated steam, hydrogen gas, and nitrogen gas in a volume ratio of 50:1:49. While flowing this mixed gas, the temperature was raised to 550°C and maintained at this temperature for 1 hour. The temperature was then lowered to room temperature, yielding light blue powder L (first heat treatment step).

The X-ray powder diffraction pattern of Powder L, as shown in Figure 3 _, had broad diffraction lines, with the _pyrochlore phase ( _Cs2O ) _0.44W2O6 as the main phase, and showed a pattern in which diffraction lines from _{hexagonal Cs0.32WO3 and orthorhombic Cs4W11O35} were mixed in slightly. However _{, the diffraction line positions and intensities of (Cs2O)0.44W2O6 and Cs4W11O35 did not completely match the} ICDD data.

Transmission electron microscope observation of this powder revealed a cubic electron diffraction pattern.

Chemical analysis of Powder L showed that Cs/W=0.40. The composition ratios of other components are shown in Table 2.
(Production and evaluation of near-infrared absorbing fibers)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product were obtained and evaluated in the same manner as in Example 1, except that Powder L was used. The evaluation results are shown in Tables 3 and 4.
[Example 13]
(Production and Evaluation of Near-Infrared Absorbing Particles)
The powder L prepared in Example 12 was spread on a carbon boat and heated to 800°C while flowing 100% by volume of Ar gas. Then, the gas supplied was changed to 1% by volume of H ₂ -Ar, and the boat was kept at 800°C for 10 minutes while flowing this gas, and then cooled to room temperature to obtain a light blue powder M.

The X-ray powder diffraction pattern of this powder, as shown in Figure ₃ , showed a pattern containing a mixture of diffraction lines _from hexagonal _Cs0.32WO3 , _{orthorhombic Cs4W11O35} , _{rhombohedral Cs6W11O36 ,} and _{Cs8.5W15O48 .} However _{, the} diffraction line positions and _intensities of _{Cs4W11O35 , Cs6W11O36 , and Cs8.5W15O48} did not completely match _the ICDD data.

When one particle of this powder was observed under a transmission electron microscope from the (0001) direction, the positions of the prism surface spots appearing in the electron diffraction pattern were found to differ by more than the experimental error range for all three particles. This indicated that the powder was primarily composed of rhombohedral crystals in which hexagonal crystals were modulated by basal defects.

Chemical analysis of Powder M showed that Cs/W=0.42. The composition ratios of other components are shown in Table 2.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product were obtained and evaluated in the same manner as in Example 1, except that Powder M was used. The evaluation results are shown in Tables 3 and 4.
[Example 14]
The powder L prepared in Example 12 was spread on a carbon boat and held in a 1 vol% H ₂ -Ar gas flow at 500°C for 30 minutes. Then, the gas supply was changed to 100 vol% Ar, and the boat was held at 550°C for 30 minutes while the gas was flowing. The temperature was then further increased to 800°C and held for 1 hour, and the temperature was then lowered to room temperature to obtain a light blue powder N.

The X-ray powder diffraction pattern of this powder, as shown in Figure ₃ , showed a pattern containing a mixture of diffraction lines _from hexagonal _Cs0.32WO3 , _{orthorhombic Cs4W11O35} , _{rhombohedral Cs6W11O36 ,} and _{Cs8.5W15O48 .} However, _the diffraction line positions and _intensities of _{Cs4W11O35 , Cs6W11O36 , and Cs8.5W15O48} did not completely match _{the ICDD} data.

When one particle of this powder was observed under a transmission electron microscope from the (0001) direction, the positions of the prism surface spots appearing in the electron diffraction pattern were found to differ by more than the experimental error range for all three particles. This indicated that the powder was primarily composed of rhombohedral crystals in which hexagonal crystals were modulated by basal defects.

Chemical analysis of Powder N showed that Cs/W=0.42. The composition ratios of other components are shown in Table 2.
(Near-infrared absorbing fibers, production and evaluation of textile products)
A near-infrared absorbing particle dispersed powder, a masterbatch, a polyester multifilament yarn, and a knitted product were obtained and evaluated in the same manner as in Example 1, except that Powder N was used. The evaluation results are shown in Tables 3 and 4.
[Comparative Example 1]
(Production and Evaluation of Near-Infrared Absorbing Particles)
The cesium tungsten oxide precursor powder obtained in Example 1 was placed in a carbon boat, heated to 850°C in a tubular furnace in the atmosphere, and held for 20 hours. The temperature was then lowered to room temperature and crushed and mixed in a grinder. The resulting mixture was then heated again to 850°C in the atmosphere and held for ₂₀ hours. The temperature was _then lowered to room temperature, yielding a very slightly greenish white powder i. The X-ray powder diffraction pattern of this powder i, as shown in Figure 2, was identified as a single phase _{of Cs4W11O35 (ICDD 0-51-1891), with a trace of Cs6W11O36 mixed in .} Chemical analysis of powder i indicated a Cs/W ratio of 0.36. The composition ratios of the other components are shown in Table 2.

(Production and evaluation of near-infrared absorbing fibers)
A near-infrared absorbing particle-dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product according to Comparative Example 1 were obtained and evaluated in the same manner as in Example 1, except that the white powder i obtained in Comparative Example 1 was used instead of the powder A according to Example 1. The evaluation results are shown in Tables 3 and 4.
[Comparative Example 2]
The cesium tungsten oxide precursor powder obtained in Example 1 was placed in a carbon boat and held at 550°C for 2 hours under a 1% by volume _H2 gas stream with _N2 as a carrier. The stream was then changed to 100% by volume _N2 and held for 1 hour. The temperature was then increased to 800°C and held for 1 hour, and the powder was slowly cooled to room temperature to obtain powder II. Powder II was dark blue in color. The X-ray powder diffraction pattern of this powder II, as shown in Figure 2, was identified as a _single -phase _Cs0.32WO3 (ICDD 0-81-1244), a hexagonal cesium tungsten oxide. Chemical analysis of powder II showed a Cs/W ratio of 0.34. The composition ratios of other components are shown in Table 2.

(Production and evaluation of near-infrared absorbing fibers)
A near-infrared absorbing particle-dispersed powder, a masterbatch, a polyester multifilament yarn, and a knit product according to Comparative Example 2 were obtained and evaluated in the same manner as in Example 1, except that Powder ii obtained in Comparative Example 2 was used instead of Powder A according to Example 1. The evaluation results are shown in Tables 3 and 4.

The XRD powder patterns of the powders prepared in Examples 1 to 7 all showed a mixed _phase pattern of hexagonal _{Cs0.32WO3 and orthorhombic Cs4W11O35} , but the intensity ratios and positions of the diffraction lines deviated from the ICDD data, which is thought to be due to the influence of irregular planar defects inserted into the prism surfaces. The (0001) electron diffraction pattern showed an increase in the interplanar spacing of one of the prism surface spots, confirming modulation of the crystal structure to orthorhombic. Furthermore, the XRD powder patterns of the powders produced in Examples 8 to 14 all _showed a mixture of hexagonal _{Cs0.32WO3 and rhombohedral Cs6W11O36 , Cs8.5W15O48} , or pyrochlore phase ( _Cs2O ) _{0.44W2O6 . However} , the diffraction line positions and intensity distributions of the _rhombohedral and pyrochlore _phases deviated from the ICDD data. The (0001) electron diffraction patterns for all three types of prism surface spots were accompanied by a change in interplanar spacing, confirming a modulation of the crystal structure to rhombohedral. Furthermore, the powders identified as having a pyrochlore phase pattern by XRD also showed a cubic electron diffraction pattern. In other words, it was confirmed that the cesium tungstates contained in the powders produced in Examples 1 to 14 have a pseudohexagonal crystal structure.

It was also confirmed that the textile products using the near-infrared absorbing fibers produced in Examples 1 to 14, which included near-infrared absorbing particles containing cesium tungstate satisfying the predetermined composition, all had a color tone b ^* satisfying the relationship of b ^* ≧0, and had a very weak blue color and a neutral color tone.

In contrast, the near-infrared absorbing particles contained in the near-infrared absorbing fibers of Comparative Examples 1 and 2 do not contain cesium tungsten oxide that satisfies the specified composition.

The textile product using the near-infrared absorbing fiber produced in Comparative Example 1 exhibited a neutral color tone, but had a low solar absorptance of 12.4%. It was also confirmed that the temperature rise on the backside of the textile product of Comparative Example 1 when irradiated with light from a solar-like spectrum lamp shown in Table 4 was lower than in Examples 1 to 14. This is thought to be due to the low solar absorptance of the near-infrared absorbing particles contained in the near-infrared absorbing fiber used in Comparative Example 1.

Furthermore, it can be seen that the textile product using the near-infrared absorbing fiber produced in Comparative Example 2 has a color tone b ^* of b ^* <0, and a bluish tinge is clearly recognized. In other words, it was confirmed that the textile product does not have a neutral color tone.

10 Ternary composition diagram 11, 16 Regions 12 to 15 Line 40 Particle 41 Arrows 50, 62 Near-infrared absorbing particle 50A Surface 51 Coating 60 Near-infrared absorbing fiber 61 Fiber 61A Surface 61B Interior CA Central axis

Claims (17)

Fiber and
and near-infrared absorbing particles disposed at one or more locations selected from the surface and the interior of the fiber,
the near-infrared absorbing particles contain cesium tungstate,
The cesium tungstate has a pseudo-hexagonal crystal structure that is modulated to one or more types selected from orthorhombic, rhombohedral, and cubic crystals, and contains one or more types of additive components selected from O , OH, OH2 _, and OH3 _;
The cesium tungstate is a near-infrared absorbing fiber represented by the general formula Cs _x W _y O _z , and has a composition within the region surrounded by four straight lines x = 0.6y, z = 2.5y, y = 5x, and Cs ₂ O:WO ₃ = m:n (m and n are integers) in a ternary composition diagram with Cs, W, and O as the vertices. 2. The near-infrared absorbing fiber according to claim 1 , wherein the additive component is present at one or more positions selected from hexagonal windows, hexagonal cavities, and trigonal cavities formed by WO ₆ octahedra of the cesium tungstate crystal. The cesium tungstate crystal has a partial deficiency in one or more elements selected from Cs and W,
_3. The near-infrared absorbing fiber according to claim 1 , wherein x and y _in the general formula _CsxWyOz satisfy the relationship 0.2≦x/y≦0.6. 4. The near-infrared absorbing fiber according to claim 1 , wherein the WO ₆ octahedron constituting the cesium tungstate crystal has defects in some of its O atoms. 5. The near-infrared absorbing fiber according to claim 1, wherein a portion of Cs in the cesium tungstate is substituted with an additional element, and the additional element is one or more elements selected from the group consisting of Na, Tl, In, Li, Be, Mg, Ca, Sr, Ba, Al, and Ga. 6. The near-infrared absorbing fiber according to claim 1 , wherein the near-infrared absorbing particles have an average particle size of 0.1 nm or more and 200 nm or less. 7. The near-infrared absorbing fiber according to claim 1 , wherein the surface of the near-infrared absorbing particle is coated with a compound containing one or more types of atoms selected from Si, Ti, Zr, Al, and Zn. 8. The near-infrared absorbing fiber according to claim 1 , wherein the content of the near-infrared absorbing particles is 0.001% by mass or more and 80% by mass or less with respect to the solid content of the fiber. It also contains particles of far-infrared emitting material,
the particles of the far-infrared emitting material are disposed at one or more locations selected from the surface and the interior of the fiber;
9. The near-infrared absorbing fiber according to claim 1 , wherein the content of the particles of the far-infrared emitting substance is 0.001% by mass or more and 80% by mass or less based on the solid content of the fiber. 10. The near-infrared absorbing fiber according to any one of claims 1 to 9, wherein the fiber is any fiber selected from a fiber group consisting of synthetic fibers, semi-synthetic fibers, natural fibers, regenerated fibers, and inorganic fibers; a blended yarn containing one or more types of fibers selected from the fiber group; a doubled yarn containing one or more types of fibers selected from the fiber group; or a mixed yarn containing one or more types of fibers selected from the fiber group. 11. The near-infrared absorbing fiber according to claim 10, wherein the synthetic fiber is at least one type selected from the group consisting of polyurethane fibers, polyamide fibers, acrylic fibers, polyester fibers, polyolefin fibers, polyvinyl alcohol fibers, polyvinylidene chloride fibers, polyvinyl chloride fibers, and polyether ester fibers. 12. The near-infrared absorbing fiber according to claim 10 , wherein the semi-synthetic fiber is one or more fibers selected from the group consisting of cellulose-based fibers, protein-based fibers, chlorinated rubber, and hydrochloric rubber. 13. The near-infrared absorbing fiber according to claim 10 , wherein the natural fiber is at least one type selected from the group consisting of plant fibers, animal fibers, and mineral fibers. 14. The near-infrared absorbing fiber according to claim 10 , wherein the regenerated fiber is one or more fibers selected from the group consisting of cellulose-based fibers, protein-based fibers, alginate fibers, rubber fibers, chitin fibers, and mannan fibers. 15. The near-infrared absorbing fiber according to claim 10 , wherein the inorganic fiber is at least one type selected from the group consisting of metal fiber, carbon fiber, and silicate fiber. A textile product comprising the near-infrared absorbing fiber according to any one of claims 1 to 15 . a disposing step of disposing near-infrared absorbing particles at one or more locations selected from the surface and the interior of the fiber,
the near-infrared absorbing particles contain cesium tungstate,
The cesium tungstate has a pseudo-hexagonal crystal structure that is modulated to one or more types selected from orthorhombic, rhombohedral, and cubic crystals, and contains one or more types of additive components selected from O , OH, OH2 _, and OH3 _;
The cesium tungstate is represented by the general _{formula CsxWyOz} , _and has a composition within the region surrounded by four straight lines x = 0.6y, z = 2.5y, y = 5x, and _Cs2O : _WO3 = m:n (m and n are integers) in a ternary composition diagram with Cs, W, and O as the vertices.