JP7707718B2 - Near infrared absorbing fiber, fiber 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.

Various cold weather clothing, interior decorations, and leisure items with enhanced thermal insulation have been devised and put to practical use. There are two main methods for increasing the thermal insulation effect.

The first method is to physically increase the amount of air in the 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 is to improve the thermal insulation of cold-weather clothing by actively storing heat, for example by subjecting the entire garment or the fibers that make up the garment to chemical or physical processing, so that the heat generated by the human body is radiated back to the human 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 layers in the clothing, make the fabric thicker, make the mesh finer, or make the color darker. For example, clothing worn in winter, such as sweaters, is an example of clothing that uses the first method. Also, for example, clothing that has been commonly used for winter sports has padding between the outer and inner layers, and the thickness of the air layer in the padding maintains heat retention. However, the padding makes the clothing heavy and bulky, which is inconvenient for sports that require ease of movement. To solve these problems, the second method mentioned above, which actively and effectively utilizes heat generated inside or from outside, has begun to be used in recent years.

One method of implementing the second method is to deposit a metal such as aluminum or titanium onto the lining of clothing, and reflect the radiant heat from inside the body onto the metal-deposited surface, thereby actively preventing the dissipation of heat. However, these methods not only require considerable costs to deposit metal onto clothing, but also result in poor yields due to uneven deposition, which ultimately leads to an increase in the price of the product itself.

As another method of implementing the second method, a method has been proposed in which ceramic particles such as alumina, zirconia, or magnesia are kneaded into the fibers themselves, and the far-infrared radiation effect and light-to-heat conversion effect of these ceramic particles are utilized, i.e., a method of actively taking in external energy.

For example, Patent Document 1 describes a heat radiating fiber that contains one or more types of inorganic fine particles having heat radiating properties, which contain at least one of metals and metal ions having a thermal conductivity of 0.3 Kcal/ ^m2 ·sec·° C. or more. Examples of inorganic fine particles having heat radiating properties include silica and barium sulfate.

Patent Document 2 describes a heat-retaining composite fiber that is made of 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 crystallization heat of 10 mJ/mg or higher, contains ceramic microparticles having far-infrared radiation capability in an amount of 0.1 to 20% by weight based on the fiber weight, and the fiber surface is covered with polymer A.

Patent document 3 describes an infrared absorbing processed textile product in which a binder resin containing an infrared absorbing agent made of at least one amino compound represented by a specific general formula is dispersed and fixed in the textile product.

Patent Document 4 describes a near-infrared absorbing processing method for a cellulose-based fiber structure in which a dye selected from direct dyes, reactive dyes, naphthol dyes, and vat dyes, which has greater absorption in the near-infrared region than black dyes, is combined with other dyes to achieve a near-infrared absorbing level of 65% or less in the spectral reflectance of the fabric in the range of 750 to 1500 nm.

In Patent Documents 5 to 7, the applicant of the present application has selected tungsten oxide microparticles and/or composite tungsten oxide microparticles as materials that have high transmittance and low absorbance for visible light but low transmittance and high absorbance for light in the near-infrared region, and has proposed fibers containing these microparticles as near-infrared absorbing components, as well as textile products made from such fibers. Despite their light color, the above-mentioned fibers and textile products absorb the near-infrared rays of sunlight and convert them into heat, have moisture retention, and are highly designable, capable of being colored in a variety of colors by adding other pigments.

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 JP 2006-132042 A International Publication No. 2018/235839 International Publication No. 2019/054476

K. Adachi and T. Asahi, "Activation of plasmons and polarons in solar control cesium tungsten bronze and reduced tungsten oxide nanoparticles," Journal of Material Research, Vol. 27, 965-970 (2012) S. Yoshio and K. Adachi, "Polarons in reduced cesium tungsten bronzes studied using the DFT+U method," Materials Research Express, Vol. 6, 026548 (2019) 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. 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) M. Okada, K. Ono, S. Yoshio, H. Fukuyama and K. Adachi, "Oxygen vacancies and pseudo Jahn-Teller destabilization in cesium-doped hexagonal tungsten bronzes," Journal of American Ceramic Society, Vol. 102, 5386-5400 (2019) S. Yoshio, M. Okada, K. Adachi, "Destabilization of Pseudo Jahn-Teller Distortion in Cesium-doped Hexagonal Tungsten Bronzes", J. Appl. Phys., vol. 124, 063109-1-8 (2018)

In particular, the tungsten oxide microparticles or composite tungsten oxide microparticles disclosed in Patent Documents 5 to 7 are materials that have high transmittance and low absorptance for visible light, but low transmittance and high absorptance for light in the near-infrared region. For this reason, fibers containing composite tungsten oxide microparticles and the like are particularly promising fibers for applications such as cold weather clothing.

However, the composite tungsten oxide microparticles, etc., preferentially absorb long-wavelength visible light, i.e., red light, and are therefore colored blue, with the blue color increasing as the amount of the microparticles added increases. As a result, fibers containing composite tungsten oxide microparticles, etc., as a near-infrared absorbing component, and textile products obtained by processing such fibers, are colored blue, and it may be difficult to color them in light colors other than blue or yellow, which are complementary colors of blue, by adding other pigments. For this reason, there has been a demand for fibers that contain composite tungsten oxide with excellent near-infrared absorbing properties and that can be colored in a more neutral color tone that can be colored in complementary colors or light colors.

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

In one aspect of the invention, a fiber and
Near infrared absorbing particles,
The near infrared absorbing particles contain cesium tungsten oxide represented by a general formula Cs _x W _1-y O _3-z (0.2≦x≦0.4, 0<y≦0.4, 0<z≦0.46) and having an orthorhombic or hexagonal crystal structure ;
The cesium tungsten oxide has linear or planar defects in one or more faces selected from the (010) face of an orthorhombic crystal, the {100} face which is a prism face of a hexagonal crystal, and the (001) face which is a basal face of a hexagonal crystal .

In one aspect of the present invention, it is possible to provide near-infrared absorbing fibers that contain near-infrared absorbing particles containing composite tungsten oxide and can have a more neutral color tone.

FIG. 1 is an explanatory diagram of the crystal structure of cesium tungsten oxide. FIG. 2 shows the energy band structure of cesium tungsten oxide. FIG. 3 is the dielectric function of cesium tungsten oxide. FIG. 4 is an electron beam diffraction image taken from the c-axis direction of Powder A' obtained in Experimental Example 1-1. FIG. 5 is an electron beam diffraction image of the [001] _HEX zone axis of the pseudohexagonal particles of Powder A obtained in Experimental Example 1-1. FIG. 6 is a STEM-HAADF image observed from the [221] zone axis of the pseudohexagonal particles of Powder A obtained in Experimental Example 1-1. FIG. 7 is an electron beam diffraction image of the [001] _HEX zone axis of the pseudohexagonal particles of Powder B obtained in Experimental Example 1-2. FIG. 8 is an electron beam diffraction image of the [001] _HEX zone axis of the pseudohexagonal particles of Powder C obtained in Experimental Example 1-3.

Hereinafter, the form for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiment, and various modifications and substitutions can be made to the following embodiment without departing from the scope of the present invention.
[Near infrared absorbing fiber]
The near infrared absorbing fiber of the present embodiment will be described in the following order: [1] near infrared absorbing particles and a method for producing the near infrared absorbing particles, [2] near infrared absorbing particle dispersion, [3] near infrared absorbing fiber, and [4] method for producing the near infrared absorbing fiber.
[1] Near infrared absorbing particles and method for producing near infrared absorbing particles (near infrared absorbing particles)
The transmitted color of cesium-doped hexagonal tungsten bronze particles, which have traditionally been used as near-infrared absorbing particles, is determined by the imaginary part of its dielectric function (ε ₂ ) (the experimentally obtained ε ₂ is given in Non-Patent Document 1) and its band structure (Non-Patent Document 2).

In the visible light energy region (1.6 eV to 3.3 eV), cesium-doped hexagonal tungsten bronze (hereinafter abbreviated as Cs-HTB) has a sufficiently large band gap. In addition, since the d-d orbital electronic transition of tungsten is forbidden by the Fermi golden rule, the probability of electronic transition is small, and ε ₂ takes a small value. Since ε ₂ represents the absorption of photons by electrons, visible light transmittance occurs if ε ₂ is small at visible wavelengths. However, in the vicinity of the blue wavelength, which has the shortest wavelength in the visible light region, absorption due to band-to-band transition exists, and in the vicinity of the red wavelength, which has the longest wavelength, localized surface plasmon resonance (LSPR) absorption and polaronic electronic transition absorption exist (Non-Patent Document 3). For this reason, the light transmittance is restricted in each case.

As mentioned above, the band gap of Cs-HTB is large enough that the interband transition exceeds the energy of blue wavelength light, resulting in high blue transmittance. Conversely, on the red wavelength side, Cs-HTB has many conduction electrons, so LSPR absorption and polaronic absorption are strong, and at the same time, the absorption wavelength approaches the red wavelength side, resulting in low transmittance. Therefore, the transmitted color of a Cs-HTB particle dispersion film, etc. appears blue.

In other words, to neutralize the blue transmission color of Cs-HTB, it is necessary to strengthen the absorption on the blue side and the transmission on the red side, but to do this, it is preferable to shift the absorption position of the interband transition to lower energy and also to weaken the LSPR absorption and polaronic absorption and shift them to the lower energy side.

To weaken LSPR absorption and polaronic absorption, it is effective to reduce the amount of free and bound electrons contained in the material.

The increase in blue absorption is achieved by using materials with different energy band structures with lower band gaps, while the red transmission can be controlled by increasing or decreasing the amount of cesium ions (Cs ⁺ ) and oxygen vacancies (V _O ), which are sources of free and bound electrons.

Based on the above considerations, the inventors of the present invention have conducted various studies on cesium tungsten oxide, which is an oxide containing cesium (Cs) and tungsten (W), and have found that when near-infrared absorbing particles containing cesium tungsten oxide obtained by reducing crystal powder of cesium tungsten oxide precursor nCs ₂ O.mWO ₃ (n, m are integers, 3.6≦m/n≦9.0) containing Cs and W are used, the color tone of the near-infrared absorbing particle dispersion such as a transmission membrane in which the particles are dispersed and the near-infrared absorbing particle dispersion liquid are also reduced in blue and neutralized.In addition, it has been found that the near-infrared absorbing fiber containing such near-infrared absorbing particles can also have a more neutral color tone.

The near infrared absorbing particles are considered to have been produced by starting from a compound having a narrower band gap than hexagonal Cs-HTB and low blue transmittance, reducing the compound to gradually increase _V2O , gradually increasing the LSPR absorption and polaronic absorption within an allowable range, and optimizing the red transmittance, thereby neutralizing the color tone.

In the above cesium tungsten oxide precursor _nCs2O.mWO3 containing Cs, the charges of the positive elements _Cs and W are neutralized by O, making it a non _- conductor. In compounds along _{the WO3-Cs2O line ,} such _{as Cs2W7O22 , Cs6W20O63} , _{Cs2W6O19 , Cs4W11O35 , Cs6W11O36 , and Cs2W3O10 ,} the valences are balanced, so _{the Fermi energy E F exists} between _{the valence} band and the conduction band, making it a non-conductor. When the Cs/W ratio (molar ratio) is 0.2 or more, in order to incorporate Cs, which has a large ionic radius, the basic skeleton formed by the W-O octahedron has a hexagonally symmetric structure with large hexagonal gaps, or a crystal structure in which planar defects including W vacancies (tungsten vacancies) have been introduced into the atomic arrangement of a hexagonal or cubic crystal (pyrochlore structure) with large hexagonal gaps, reducing the symmetry to an orthorhombic or monoclinic crystal.

For example, in the case of 2Cs ₂ O.11WO ₃ , in the model of Solodovnikov 1998 (Non-Patent Document 4), in a hexagonal arrangement of W-O octahedra similar to hexagonal tungsten bronze, a plane in which W and O are missing is inserted at a pitch of b/8 of the orthorhombic unit cell on the hexagonal (110) plane (=orthorhombic (010) plane), resulting in an orthorhombic crystal as a whole. These cesium tungsten oxide precursors nCs ₂ O.mWO ₃ (n, m are integers, 3.6≦m/n≦9.0) have a narrower band gap than Cs-HTB, and therefore have low blue transmittance. However, when this is heated and reduced, the whole gradually changes to the hexagonal crystal structure of tungsten bronze, and in the process, the band structure changes, the band gap widens, and the blue absorption weakens, resulting in stronger blue transmittance. In addition, at this time, as the reduction proceeds, electrons are gradually injected into the conduction band, causing the material to become a conductor, and the band gap gradually widens due to the Burstein-Moss effect, so that the blue transmission becomes even stronger.

When the orthorhombic crystals become hexagonal crystals by heating and reduction, the planar defects including W vacancies in the orthorhombic crystals gradually disappear, and a hexagonal crystal framework of W-O octahedra is formed. Planar defects including W vacancies exist on the (010) _ORTH plane, but this plane is taken over by the hexagonal prism plane {100} _HEX , that is, [(100) _HEX , (010) _HEX , (110) _HEX ], so that with heating and reduction, the crystal gradually becomes a hexagonal crystal with defects on the {100} _HEX plane. At this time, the hexagonal crystal deviates from perfect hexagonal symmetry because it contains defects on the {100} _HEX plane, and can be said to be in a pseudo-hexagonal state. In this way, with heating and reduction, the crystal structure changes from an orthorhombic crystal to a pseudo-hexagonal crystal and then to a hexagonal crystal. At this time, it is believed that the planar defects of the (010) _ORTH plane, including W vacancies contained in the orthorhombic crystal, are inherited by planar defects of the {100} _HEX plane, gradually decrease, and finally disappear.

The electronic structure also changes with the change in the crystal structure during heating and reduction. The disappearance of W vacancies results in the injection of a large amount of electrons into the material. In the orthorhombic crystal, the outer shell electrons of Cs are used to neutralize O, resulting in overall charge neutrality, but when the W vacancies are reduced to form a pseudo-hexagonal crystal, six outer shell electrons per W atom are used to neutralize O, and the outer shell electrons of Cs enter the W-5d orbital at the bottom of the conduction band and become free electrons. These free electrons absorb near-infrared light through LSPR absorption. On the other hand, heating and reduction simultaneously has the effect of generating V 2 _O. The generation of V 2 _O proceeds at random sites. When V _{2 O} is generated, the W atoms on both sides of it become overcharged, and localized electrons bound to W ⁵⁺ are generated (Non-Patent Document 2). These localized electrons transition to vacancies above the conduction band, resulting in polaronic absorption, but some are excited to free electron orbitals, resulting in LSPR absorption (Non-Patent Document 3). The absorption by these free electrons and bound electrons both has a peak wavelength in the near infrared region, so the absorption base falls on the red wavelength, and therefore the red transmittance is reduced. As the amount of free electrons and bound electrons increases, i.e., the degree of reduction increases, the LSPR absorption and polaronic absorption wavelengths shift to higher wavelengths and the amount of absorption increases, so the red transmittance decreases.

Therefore, by reducing crystal powder of cesium tungsten oxide precursor nCs ₂ O.mWO ₃ (n and m are integers, 3.6≦m/n≦9.0) and adjusting the degree of reduction, it is possible to neutralize the bluish transmitted color.

The near infrared absorbing particles of the present embodiment described above can be produced by heating a crystal powder of a cesium tungsten oxide precursor _nCs2O.mWO3 containing Cs and _W in a reducing atmosphere at 650° C. to 950° C. In the formula of the cesium tungsten oxide, n and m are integers, and preferably satisfy 3.6≦m/n≦9.0.

That is, as the near-infrared absorbing particles, particles obtained by heating and reducing a crystal powder _of a cesium tungsten oxide precursor _nCs2O.mWO3 (n and m are integers, 3.6≦m/n≦9.0) containing cesium and tungsten in an atmosphere of a reducing gas at 650°C or higher and 950°C or lower can be used.

In order for all or part of the tungsten oxide to become hexagonal tungsten bronze by heating and reduction, the value of m/n must be in the range of 3.6≦m/n≦9.0 as described above. If it is less than 3.6, the tungsten oxide will become a cubic pyrochlore phase after heating and reduction, and will be strongly colored and will not absorb near-infrared rays. If it is more than 9.0, the tungsten oxide will separate into hexagonal tungsten bronze and tungsten trioxide after heating and reduction, and the near-infrared absorbing effect will be significantly reduced. The tungsten oxide precursor is more preferably Cs ₄ W ₁₁ O ₃₅ , which has m/n=5.5. That is, it is more preferable to use particles obtained by heating and reducing a tungsten oxide precursor containing a Cs ₄ W ₁₁ O ₃₅ phase as the main phase in a reducing gas atmosphere at 650° C. or more and 950° C. or less as the near-infrared absorbing particles. By obtaining near-infrared absorbing particles by high-temperature reduction of Cs ₄ W ₁₁ O ₃₅ , when the near-infrared absorbing particles are dispersed, a large near-infrared absorbing effect can be obtained while having a transmitted color with a suppressed bluish tint. Note that the main phase referred to here means the phase that is contained in the largest amount by mass ratio.

As described above, the heating temperature when reducing cesium tungsten oxide is preferably 650°C or higher and 950°C or lower. By setting the temperature at 650°C or higher, the structural change from orthorhombic to hexagonal can be sufficiently promoted, and the near-infrared absorption effect can be enhanced. In addition, by setting the temperature at 950°C or lower, the speed of the crystal structure change can be appropriately maintained, and it is possible to easily control the crystal state and electronic state to an appropriate state. Note that if the heating temperature is higher than 950°C and reduction proceeds too far, lower oxides such as W metal and _WO2 may be generated, which is not preferable from this viewpoint.

The near infrared absorbing particles of this embodiment can contain cesium tungsten oxide represented by the general formula Cs _x W _1-y O _3-z (0.2≦x≦0.4, 0<y≦0.4, 0<z≦0.46) and having an orthorhombic or hexagonal crystal structure. The near infrared absorbing particles can also simultaneously contain cesium tungsten oxide having an orthorhombic crystal structure and cesium tungsten oxide having a hexagonal crystal structure.

When the cesium tungsten oxide contained in the near-infrared absorbing particles satisfies the above general formula, the degree of W vacancy and oxygen vacancy _Vo are within an appropriate range, and when the cesium tungsten oxide is dispersed to form a near-infrared absorbing particle dispersion, a near-infrared absorbing fiber, or the like, the transmitted color can be made to have a more neutral tone while suppressing the solar transmittance.

The near-infrared absorbing particles may also be made of the above composite tungsten oxide. However, even in this case, this does not exclude the inclusion of unavoidable impurities that may be mixed in during the manufacturing process, etc.

Conventionally known near-infrared absorbing tungsten bronzes have a hexagonal crystal structure. On the other hand, the composite tungsten oxide of the near-infrared absorbing particles of this embodiment can have an orthorhombic or hexagonal crystal structure. Here, hexagonal crystals also include pseudo-hexagonal crystals.

The cesium tungsten oxide, which is a composite tungsten oxide contained in the near-infrared absorbing particles, preferably has linear or planar defects on one or more faces selected from the (010) face of an orthorhombic crystal, the {100} face which is a prism face of a hexagonal crystal, and the (001) face which is the base face of a hexagonal crystal. The above defects include stacking faults due to the misalignment of the faces, and the arrangement and atomic positions of Cs atoms and W atoms within the faces, and therefore often streaks are present in the electron diffraction spots. The {100} face which is a prism face of the hexagonal crystal means the (100) face, the (010) face, and the (110) face. The defects, i.e., lattice defects, of the composite tungsten oxide are accompanied by at least W defects, specifically partial W defects, and these W defects cause electron deficiencies in the crystal, which, as described above, is one of the essential causes that act to neutralize the blue tone.

Cesium tungsten oxide has defects, which can include tungsten vacancies as described above.

In addition, a part of the O in the W-O octahedron, i.e., the WO ₆ octahedron, constituting the orthorhombic or hexagonal crystal, which is the basic structure of cesium tungsten oxide, may further have a defect. Such a defect may be a random defect. This octahedral oxygen vacancy V ₀ may be introduced randomly as described above, and it is known that in the known hexagonal tungsten bronze Cs _0.32 WO _3-y , the vacancy reaches y=0.46 or a maximum of 15% of all O lattice points (Non-Patent Document 5). In the general formula Cs _x W _1-y O _3-z representing the cesium tungsten oxide contained in the near infrared absorbing particle of this embodiment, V ₀ may be contained in an amount of up to z=0.46. That is, z may be 0.46 or less.

The lattice constant of cesium tungsten oxide corresponds to the amount of defects in the crystal lattice, or the composition, and the crystallinity. Variations are observed in the a-axis value with respect to these variables, but the c-axis value corresponds relatively well to the amount of lattice defects or the optical properties. As a result, the cesium tungsten oxide contained in the near-infrared absorbing particles of this embodiment preferably has a c-axis length in hexagonal crystal equivalent of 7.560 Å or more and 7.750 Å or less. By setting the c-axis length in hexagonal crystal equivalent of cesium tungsten oxide within the above range, the near-infrared absorbing effect is sufficiently improved, and the visible light transmittance is particularly improved. Note that when cesium tungsten oxide is a hexagonal crystal, no conversion is necessary, and the c-axis length in the hexagonal crystal becomes the c-axis length in hexagonal crystal equivalent.

When the diffraction pattern of the sample is measured by X-ray powder diffraction method, the cesium tungsten oxide contained in the near infrared absorbing particles of this embodiment is often identified as a mixed phase of orthorhombic and hexagonal. For example, when the raw material Cs ₄ W ₁₁ O ₃₅ is reduced, it is identified as a mixed phase of orthorhombic Cs ₄ W ₁₁ O ₃₅ and hexagonal Cs _0.32 WO _3. In this case, the lattice constants of each phase can be obtained by Rietveld analysis or the like, and these can be converted into values converted into hexagonal crystals. As already explained, the orthorhombic crystal is a hexagonal crystal with a lattice defect plane, so the lattice constant of the orthorhombic crystal can be converted into the lattice constant of the hexagonal crystal by an appropriate lattice correspondence model. If the correspondence of the lattice change between the orthorhombic and hexagonal crystals is assumed to be the Solodovnikov 1998 model (Non-Patent Document 4), the geometric relationship for this model extracts the relationship of 4a _orth ² +b _orth ² =64a _hex ² =64b _hex ² and c _orth =c _hex , and these formulas can be used to obtain the lattice constants converted to hexagonal crystals. Note that a _orth , b _orth , and c _orth in the above formulas mean the lengths of the a-axis, b-axis, and c-axis of the orthorhombic crystal. Also, a _hex , b _hex , and c _hex mean the lengths of the a-axis, b-axis, and c-axis of the hexagonal crystal.

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

The above added elements have electron donating properties and assist in donating electrons to the conduction band of the W-O octahedral framework at the Cs site.

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 making the average particle size of the near-infrared absorbing particles 200 nm or less, the localized surface plasmon resonance is more prominently expressed, and the near-infrared absorbing characteristics can be particularly enhanced, that is, the solar radiation transmittance can be particularly suppressed. In addition, by making the average particle size of the near-infrared absorbing particles 0.1 nm or more, it can be easily manufactured industrially. In addition, the particle size is closely related to the color of the near-infrared absorbing particle dispersion, which is a dispersion transmission film in which the near-infrared absorbing particles are dispersed, and in the particle size range in which Mie scattering is dominant, the smaller the particle size, the less scattering of short wavelengths in the visible light region. Therefore, if the particle size is increased, it has the effect of particularly suppressing the blue tone, but if it exceeds 100 nm, the haze of the film due to light scattering becomes large enough to be not negligible, and if it exceeds 200 nm, in addition to the increase in the haze of the film, the generation of surface plasmons is suppressed, and the LSPR absorption may be excessively small.

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

When applied to applications in which transparency in the visible light region is particularly important, for example when it is required to particularly suppress the effect on the color tone of the near-infrared absorbing fiber, it is preferable to further consider the reduction in scattering by the near-infrared absorbing particles. When the reduction in scattering is important, it is particularly preferable that the average particle size of the near-infrared absorbing particles is 30 nm or less.

In addition, the near-infrared absorbing particles may be surface-treated for the purpose of surface protection, improving durability, preventing oxidation, improving water resistance, and the like. The specific content of the surface treatment is not particularly limited, but for example, the surface of the near-infrared absorbing particles of this embodiment may be coated with a compound containing one or more types of atoms selected from Si, Ti, Zr, Al, and Zn. In this case, examples of the compound containing one or more types of atoms (elements) selected from Si, Ti, Zr, Al, and Zn include one or more types selected from oxides, nitrides, carbides, and the like.

Here, we explain the band structures of cesium tungsten oxide and cesium tungsten oxide precursors.

As explained above, it was shown that a solar radiation shading material _with a more neutral transmitted color can be obtained by reducing _nCs2O.mWO3 (n and m are integers, 3.6≦m/n≦9.0) at high temperatures. During high-temperature reduction, electrons are injected into the conduction band due to hexagonal crystallization including the disappearance of W vacancies and the generation of _VO , which is thought to be the source of near-infrared absorption. This change in electronic structure is supported by first-principles calculations.

FIG. 1(a) shows the crystal structure of Cs ₄ W ₁₁ O _35. FIG. 1(b) shows the crystal structure of Cs ₄ W ₁₂ O ₃₆ , which is Cs _0.33 WO _3. In FIG. 1(a) and FIG. 1(b), cesium 11 and oxygen 12 are shown. The same type of atoms are hatched with the same pattern. Tungsten is arranged in an octahedron formed by oxygen 12, so it is not shown in FIG. 1(a) and FIG. 1(b). FIG. 1(b) shows a structure in which the axis of Cs _0.33 WO ₃ is reoriented in an orthorhombic system so that it can be compared with Cs ₄ W ₁₁ O ₃₅ in FIG. 1(a).

The structure of Cs ₄ W ₁₁ O ₃₅ in FIG. 1(a) is a structure in which W and O are regularly missing in the crystal structure of Cs ₄ W ₁₂ O ₃₆ in FIG. 1(b).

The band structures of the cesium tungsten oxides having the crystal structures shown in Figures 1(a) and 1(b) are shown in Figures 2(a) and 2(b), respectively. _The band structures of _Cs4W11O36 , which is missing one W _{atom based on Cs4W12O36 in} Figure 1(b), and _{Cs6W17O54 ,} which is missing one W atom and has _a cell size 1.5 times larger in the _b -axis direction, are shown in Figures 2(c) and 2(d) _, respectively.

The band structures of Cs ₄ W ₁₁ O ₃₅ and Cs ₄ W ₁₂ O ₃₆ shown in Figures 2(a) and 2(b) are similar, but the Fermi energy (E _F ) is located in the band gap for the former and at the bottom of the conduction band for the latter. Therefore, Cs ₄ W ₁₁ O ₃₅ is an insulator, and Cs ₄ W ₁₂ O ₃₆ is a conductor. In Cs ₄ W ₁₁ O ₃₅ , one W and one O are missing in the unit cell compared to Cs ₄ W ₁₂ O _36. It is interpreted that in Cs ₄ W ₁₂ O ₃₆ , which is full of W and O, a hexagonal WO ₃ network is formed, and Cs electrons are injected into the W-5d orbital to make it a conductor (Non-Patent Document 6).

Cs ₄ W ₁₁ O ₃₆ in FIG. 2C has a structure in which one W is removed from Cs ₄ W ₁₂ O ₃₆ in FIG. 2B.

Cs ₆ W ₁₇ O ₅₄ in FIG. 2(d), ie, 3Cs ₂ O.17WO ₃ , has a structure in which one W is removed from Cs ₄ W ₁₂ O ₃₆ in FIG. 2(b), ie, Cs ₆ W ₁₈ O ₅₄ , while maintaining charge neutrality.

The amount of W vacancy decreases in the order of Figure 2(a), Figure 2(d), and Figure 2(b), but E _F increases sequentially toward the bottom of the conduction band, which supports the idea that W electrons are injected into the W-5d orbital, increasing the number _{of conduction electrons and increasing the near-infrared absorption. A detailed calculation example has already been reported for the case where O is missing from Cs4W12O36 ,} and it is known that the number _of free electrons and localized electrons increases significantly as localized orbitals are introduced at the bottom of the conduction band (Non-Patent Document 2).

In the experimentally obtained pseudo-hexagonal crystal (an intermediate structure in the middle of the phase transition between orthorhombic and hexagonal crystals), the electronic state is considered to be a mixture of the above elements. That is, with reduction, electrons are gradually injected into the conduction band due to the hexagonal crystallization including the disappearance of W vacancies and the generation of _VO , and the Fermi energy E _F rises from the band gap to the bottom of the conduction band.

Based on these band structures, the dielectric function including the Drude term was calculated, and the results are shown in Figure 3. Focusing on the position of ε ₁ = 0 in the dielectric function ε ₁ shown in Figure 3(b), it can be seen that the shielded plasma frequency (Ω _SP ) increases in the order of Cs ₄ W ₁₁ O ₃₅ , Cs ₆ W ₁₇ O ₅₄ , Cs ₄ W ₁₂ O ₃₆ , and Cs ₄ W ₁₂ O _35. It is expected that the near-infrared absorption increases in this order, and this tendency coincides with the observed results.

From the dielectric function _ε2 plot shown in Figure 3(a), it can be seen that _ε2 in the visible region is generally small for cesium tungsten oxide. At 3.3 eV in the blue region shown by dotted line 31, the absorption of _Cs4W11O35 and _{Cs6W17O54 , which have} narrow band gaps, is _large due to the band- _to -band transition. On the other hand, at 1.6 eV in the red region shown by dotted line 32, it can be seen that the absorption of _Cs4W12O35 is large due to the influence of the base _of the surface _plasmon absorption. It is expected that the transmitted light in the red region decreases in the order of decreasing _ΩSP . The reason why the blueness of the cesium tungsten oxide contained in the near-infrared absorbing particles that can be suitably used for the near-infrared absorbing fiber of the present embodiment is reduced compared to the conventionally used cesium tungsten oxide is believed to be because the use of nCs ₂ O.mWO ₃ (3.6≦m/n≦9.0) with vacancies of W and O as a raw material results in the formation of a Cs _0.33 W _1-y O _3-z phase containing W vacancies, and the absorption on the high energy side is increased. By adjusting the high-temperature reduction of nCs ₂ O.mWO ₃ (3.6≦m/n≦9.0), the band gap and the amount of electrons injected into the conduction band are adjusted, and the bluish color tone can be adjusted. It was also confirmed that the near-infrared absorbing effect at that time is maintained at a relatively high level.
(Method for producing near infrared absorbing particles)
The method for producing the near infrared ray absorbing particles of the present embodiment is not particularly limited, and any method can be used as long as it can produce near infrared ray absorbing particles that satisfy the above-mentioned characteristics. Here, one configuration example of the method for producing the near infrared ray absorbing particles will be described.

The method for producing near-infrared absorbing particles of this embodiment can include, for example, the following steps:

A cesium tungsten oxide precursor synthesis step of synthesizing a cesium tungsten oxide precursor, which is a tungstate salt containing cesium.
A heating and reducing step of heating and reducing the cesium tungsten oxide precursor in a reducing gas atmosphere at 650° C. or more and 950° C. or less.

Each step will be described below.
(1) Cesium tungsten oxide precursor synthesis step In the cesium tungsten oxide precursor synthesis step, a tungstate containing cesium, i.e., a cesium tungstate precursor which is a cesium tungstate, can be synthesized. When the cesium tungsten oxide precursor has already been synthesized, the method for producing near infrared ray absorbing particles of the present embodiment can also start with a heating reduction step.

In addition, the cesium tungsten oxide precursor, which is cesium tungstate, is preferably a crystal powder _{of nCs2O.mWO3} (n, m are integers, 3.6≦m/n≦9.0 ₎ . As the cesium tungstate oxide precursor, which is cesium _tungstate , it is more _preferable to use a stable cesium tungstate. As the stable cesium tungstate, one or more types selected from _Cs4W11O35 , _{Cs2W6O19 , Cs6W20O63} , _{Cs2W7O22 , Cs6W11O36 , etc.} are listed. In particular, it is more preferable that _the cesium tungsten oxide precursor is a cesium _tungsten oxide precursor containing a _{Cs4W11O35 phase} as _{the main} phase.

These cesium tungstates can be prepared, for example, by firing a raw material powder mixture containing cesium and tungsten in air at 700°C to 1000°C. The method for producing cesium tungstate is not limited to the above, and other methods such as the sol-gel method and complex polymerization method can also be used.

Furthermore, as the cesium tungstate used as the starting material, a non-equilibrium tungstate obtained by gas phase synthesis or the like may be used. This includes powder obtained by a thermal plasma method and powder obtained by electron beam melting.
(2) Heat Reduction Step The above-mentioned cesium tungsten oxide precursor as the starting material, specifically, for example, cesium tungstate having one or more crystal structures selected from orthorhombic, monoclinic, and pseudohexagonal, can be subjected to a heat reduction step.

In the heating and reducing step, the above-mentioned cesium tungsten oxide precursor can be heated and reduced at 650°C or higher and 950°C or lower in an atmosphere of a reducing gas. By carrying out the heating and reducing step, near-infrared absorbing particles containing cesium tungsten oxide of the desired composition can be obtained.

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

The method for producing near infrared ray absorbing particles of the present embodiment is not particularly limited to the above-mentioned form. As the method for producing near infrared ray absorbing particles, various methods that can form a predetermined structure including a defective microstructure can be used. As the method for producing near infrared ray absorbing particles, a method of reducing a tungstate obtained by a solid phase method, a liquid phase method, or a gas phase method, a method of reducing _WO3 in a molten alkali halide, etc. can be mentioned.

The method for producing near infrared ray absorbing particles may further include any optional steps.
As described above, the near infrared absorbing particles are preferably finely divided into particles. Therefore, the method for producing near infrared absorbing particles may include a grinding step of grinding the powder obtained by the heating and reducing step.

The specific means for pulverizing and pulverizing is not particularly limited, and various means capable of mechanical pulverization can be used. As a mechanical pulverization method, a dry pulverization method using a jet mill or the like can be used. In addition, mechanical pulverization may be performed in a solvent in the process of obtaining a near-infrared absorbing particle dispersion liquid described later. In this case, since the near-infrared absorbing particles are dispersed in a liquid medium in the pulverization process, it can also be called a pulverization and dispersion process.
(4) Coating step As described above, the surface of the near infrared absorbing particle may be coated with a compound containing one or more 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 atoms selected from Si, Ti, Zr, Al, and Zn.

In the coating step, specific conditions for coating the near infrared ray absorbing particles are not particularly limited. For example, an alkoxide or the like containing one or more atoms selected from the above atomic group (metal group) can be added to the near infrared ray absorbing particles to be modified, thereby forming a coating on the surface of the near infrared ray absorbing particles.
[2] 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, which will be described later.

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.

As the organic solvent, various types can be selected, such as alcohols, ketones, hydrocarbons, and glycols. Specific examples of the solvent include alcohol solvents such as isopropyl alcohol, methanol, ethanol, 1-propanol, isopropanol, butanol, pentanol, benzyl alcohol, diacetone alcohol, and 1-methoxy-2-propanol; ketone solvents such as dimethyl ketone, acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone; ester 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 in particular, 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 more preferred. These organic solvents can be used alone or in combination of two or more.

As the fats and oils, for example, one or more selected from 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 directly esterifying fatty acids of vegetable oils with monoalcohols, ethers, and petroleum-based solvents such as Isopar (registered trademark) E, Exxor (registered trademark) Hexane, Heptane, E, D30, D40, D60, D80, D95, D110, and D130 (all manufactured by ExxonMobil) can be used.

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.

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

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 any other components added thereto as necessary.

For example, an acid or alkali may be added to the near-infrared absorbing particle dispersion liquid as necessary to adjust the pH of the dispersion liquid.

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 dispersion 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 has 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 even in an infrared shielding film formed using the near-infrared absorbing particles. A polymer dispersant having one or more functional groups (groups of functional groups) in the molecule is more preferable.

Suitable commercially available dispersants include Solsperse (registered trademark) 9000, 12000, 17000, 20000, 21000, 24000, 26000, 27000, 28000, 32000, 35100, 54000, and 250 (manufactured by Lubrizol Japan Co., Ltd.), and EFKA (registered trademark) 4008, 4009, 4010, 4015, and 4046.
, 4047, 4060, 4080, 7462, 4020, 4050, 4055, 4400, 4401, 4402, 4403, 4300, 4320, 4330, 4340, 6220, 6225, 6700, 6780, 6782, 8503 (manufactured by F-Ka Additives), Ajisper (registered trademark) PA111, PB821, PB822, PN411, Famex L-12 (manufactured by Ajinomoto Fine-Techno Co., Ltd.), DisperBYK (registered trademark) 101, 102, 106, 108, 111, 116, 130, 140, 142, 145, 161, 162, 163, 164, 166, 167, 168, 170, 171, 174, 180, 182, 192, 193, 2000, 2001, 2020, 2025, 2050, 2070, 2155, 2164, 220S, 300, 306, 320, 322, 325, 330, 340, 350, 377, 378, 380N, 410, 425, 430 (manufactured by Pick Chemi Japan Co., Ltd.), Disparlon (registered trademark) 1751N, 1831, 1850, 1860, 1934, DA-400N, DA-703-50, DA-725, DA-705, DA-7301, DN-900, NS-5210, NVI-8514L (manufactured by Kusumoto Chemicals Co., Ltd.), Arfon (registered trademark) UC-3000, UF-5022, UG-4010, UG-4035, UG-4070 (manufactured by Toagosei Co., Ltd.), and the like can be mentioned as one or more types selected therefrom.

The method of dispersing the near-infrared absorbing particles in the liquid medium is not particularly limited as long as it is a method that can disperse the near-infrared absorbing particles in the liquid medium. In this case, it is preferable that the near-infrared absorbing particles can be dispersed so that the average particle size is 200 nm or less, and it is more preferable that the near-infrared absorbing particles can be dispersed so that the average particle size is 0.1 nm or more and 200 nm or less.

Methods for dispersing near-infrared absorbing particles in a liquid medium include, for example, dispersion methods using devices such as a bead mill, a ball mill, a sand mill, a paint shaker, and an ultrasonic homogenizer. Among these, from the viewpoint of shortening the time required to obtain the desired average particle size, it is preferable to perform crushing and dispersion using a media agitation mill such as a bead mill, a ball mill, a sand mill, or a paint shaker that uses a medium media (beads, poles, Ottawa sand). By performing crushing-dispersion processing using a media agitation mill, the near-infrared absorbing particles are dispersed in a liquid medium, and at the same time, the near-infrared absorbing particles are also atomized due to collisions between the near-infrared absorbing particles and collisions of the medium media with the near-infrared absorbing particles, and the near-infrared absorbing particles can be dispersed in a more atomized form. In other words, the near-infrared absorbing particles are subjected to crushing-dispersion processing.

As described above, the average particle size of the near-infrared absorbing particles is preferably 0.1 nm or more and 200 nm or less. This is because a small average particle size reduces scattering of light in the visible light region with wavelengths of 400 nm or more and 780 nm or less due to geometric scattering or Mie scattering. As a result of reducing such light scattering, for example, a near-infrared absorbing particle dispersion obtained by 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 becomes like cloudy glass, and it is possible to avoid the loss of clear transparency. That is, when the average particle size is 200 nm or less, the light scattering becomes weaker in the geometric scattering or Mie scattering mode and becomes a Rayleigh scattering mode. In the Rayleigh scattering region, the scattered light is proportional to the sixth power of the dispersed particle size, so that the scattering is reduced and the transparency is improved as the dispersed particle size decreases. And, when the average particle size is 100 nm or less, the scattered light becomes very small, which is preferable.

By the way, the dispersion state of the near-infrared absorbing particles in the near-infrared absorbing particle dispersion obtained by 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, will not aggregate to a level greater than the average particle size of the near-infrared absorbing particles in the dispersion, as long as a known method for adding the dispersion to the solid medium is used.

In addition, 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 body (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 of the present 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 making the content of the near-infrared absorbing particles 0.01% by mass or more. Also, by making the content 80% by mass or less, the near-infrared absorbing particles can be uniformly dispersed in the dispersion medium.
[3] Near-infrared absorbing fiber The near-infrared absorbing fiber according to this embodiment will be described.

The near-infrared absorbing fiber of the present embodiment can include fibers and near-infrared absorbing particles. The near-infrared absorbing particles can be the above-mentioned near-infrared absorbing particles. For this reason, the near-infrared absorbing particles can include cesium tungsten oxide represented by the general formula Cs _x W _1-y O _3-z (0.2≦x≦0.4, 0<y≦0.4, 0<z≦0.46) and having an orthorhombic or hexagonal crystal structure.

As described above, the near-infrared absorbing fiber of this embodiment only needs to contain fibers and near-infrared absorbing particles, and the arrangement of the near-infrared absorbing particles is not particularly limited, but it is preferable that the near-infrared absorbing particles are arranged in one or more parts selected from the surface and the interior of the fiber.

The near-infrared absorbing fiber of this embodiment can be prepared by dispersing the near-infrared absorbing particles obtained by the synthesis method described above in an appropriate medium and incorporating the dispersion into one or more parts selected from, for example, the surface and the interior of the fiber.

Hereinafter, the members contained in the near infrared absorbing fiber of this embodiment will be described.
(1) Fibers (1-1) Types of Fibers

The fibers contained in the near-infrared absorbing fiber of this embodiment can be selected from various types depending on the application, and are not particularly limited. For example, the fibers can be one or more types selected from a fiber group consisting of synthetic fibers, semi-synthetic fibers, natural fibers, regenerated fibers, and inorganic fibers, and a mixed yarn obtained by blending, doubling, or mixing two or more types of fibers selected from the above fiber group. In other words, fibers selected from the above fiber group can be used, and fibers selected from the above mixed yarn can also be used.

Among these, in consideration of the ease of incorporating the near infrared absorbing particles inside the fibers and the durability of heat retention, the fibers preferably contain synthetic fibers, and more preferably are made of synthetic fibers.
(1-1-1) Synthetic Fibers The synthetic fibers are not particularly limited, but 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, and the like can be suitably used.

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

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, polystyrene, etc.

An example of a polyvinyl alcohol fiber is vinylon.

Examples of polyvinylidene chloride fibers include vinylidene.

Examples of polyvinyl chloride fibers include polyvinyl chloride.

Examples of polyetherester fibers include Lexe and Success.
(1-1-2) Semi-synthetic fiber As the semi-synthetic fiber, for example, one or more types selected from cellulosic fibers, protein-based fibers, chlorinated rubber, hydrochloric rubber, etc. can be used.

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

An example of a protein-based fiber is Promix.
(1-1-3) Natural Fibers As the natural fibers, for example, one or more types selected from vegetable fibers, animal fibers, mineral fibers, etc. can be used.

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

Examples of animal fibers include wool, silk, down, feathers, etc., such as sheep's wool, goat hair, mohair, cashmere, alpaca, angora, camel, and vicuna.

Examples of mineral fibers include asbestos.
(1-1-4) Regenerated Fibers As the regenerated fibers, for example, one or more types selected from cellulose-based fibers, protein-based fibers, alginate fibers, rubber fibers, chitin fibers, mannan fibers, and the like can be used.

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

Examples of protein-based fibers include casein fiber, peanut protein fiber, corn protein fiber, soy protein fiber, and regenerated silk.
(1-1-5) Inorganic Fibers As the inorganic fibers, for example, one or more types selected from metal fibers, carbon fibers, silicate fibers, etc. can be used.

Examples of metal fibers include metal fibers, gold threads, silver threads, heat-resistant alloy fibers, etc.

Examples of silicate fibers include glass fibers, slag fibers, and rock fibers.
(1-2) Fiber Shape The cross-sectional shape of the fiber is not particularly limited, and may be, for example, one or more types selected from the group consisting of circular, triangular, hollow, flat, Y-shaped, star-shaped, and sheath-core type.

The inclusion and arrangement of the near infrared absorbing particles in the fiber is not particularly limited. For example, when the cross-sectional shape of the fiber is a core-sheath type, the near infrared absorbing particles may be contained in the core part of the fiber or in the sheath part. In addition, the shape of the fiber is not particularly limited, and may be a filament (long fiber) or a staple (short fiber).
(2) Near-infrared absorbing particles As the near-infrared absorbing particles, the above-mentioned near-infrared absorbing particles can be used. Since the near-infrared absorbing particles have already been described, the 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 and can be selected according to the properties required of the near-infrared absorbing fiber.

However, the near-infrared absorbing ability per unit mass of the near-infrared absorbing particles mentioned above is very high, so compared to ITO or ATO, the same near-infrared absorbing effect can be achieved with only one-fourth to one-tenth the amount used.

The proportion of near-infrared absorbing particles contained in the near-infrared absorbing fiber of this embodiment is not particularly limited and can be selected as desired depending on the performance required of the near-infrared absorbing fiber. For example, the near-infrared absorbing fiber of this embodiment preferably contains near-infrared absorbing particles in a proportion of 0.001% by mass or more and 80% by mass or less, and more preferably 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 containing the near-infrared absorbing particles at a ratio of 0.001% by mass or more relative to the solid content of the fiber, even if the fabric containing the near-infrared absorbing fiber is thin, a sufficient near-infrared absorbing effect can be obtained. Also, by containing the near-infrared absorbing particles at a ratio of 80% by mass or less relative to the solid content of the fiber, it is possible to more reliably avoid a decrease in spinnability due to clogging of the filter or thread breakage when spinning the near-infrared absorbing fiber. Also, by making the content of the near-infrared absorbing particles 80% by mass or less, it is possible to more reliably avoid a loss of physical properties of the fiber.
(3) Far-infrared emitting substance, additives The near-infrared absorbing fiber of the present embodiment may be composed only of the above-mentioned fiber and near-infrared absorbing particles, but may further contain any optional components, for example, far-infrared emitting substances and additives described below according to the purpose. Note that even when the near-infrared absorbing fiber is composed only of the fiber and near-infrared absorbing particles as described above, it does not exclude the inclusion of unavoidable components and the like mixed in during the manufacturing process.
(3-1) Far-infrared emitting material The far-infrared emitting material is a material capable of emitting far-infrared rays, and is preferably in the form of particles. That is, far-infrared emitting material particles can be suitably used as the far-infrared emitting material.

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

Examples of far-infrared emitting materials include 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 tungsten oxide contained in the near-infrared absorbing particles has the property of absorbing solar energy with wavelengths of 0.3 μm or more and 3 μm or less, and in particular 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.

On the other hand, the particles of the far-infrared radiation material have the ability to receive the energy absorbed by the cesium tungsten oxide, which is a near-infrared absorbing material, convert this energy into heat energy of mid-to-far-infrared wavelengths, and radiate it. For example, _ZrO2 particles convert this energy into heat energy with a wavelength of 2 μm or more and 20 μm or less, and radiate it. Therefore, by coexisting the far-infrared radiation material capable of radiating far-infrared rays and the near-infrared absorbing particles described above 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, and more effective heat retention is achieved.

The content of the far-infrared emitting material is not particularly limited and can be selected according to the performance required for the near-infrared absorbing fiber. The near-infrared absorbing fiber of this embodiment preferably contains the far-infrared emitting material in a ratio of, for example, 0.001% by mass or more and 80% by mass or less relative to the solid content of the fiber. This is because, by setting the content ratio of the far-infrared emitting material to 0.001% by mass or more, a sufficient thermal energy radiation effect can be obtained even if the fabric containing the near-infrared absorbing fiber is thin. In addition, by setting the content ratio of the far-infrared emitting material to 80% by mass or less, the near-infrared absorbing fiber can be more reliably prevented from decreasing in spinnability due to clogging of the filter, thread breakage, etc., during spinning.
(3-2) Additives Examples of additives include antioxidants, flame retardants, deodorants, insect repellents, antibacterial agents, ultraviolet absorbers, etc. The additives can be contained and used within the range that does not impair the performance of the near infrared absorbing fiber.
[4] Manufacturing method of near-infrared absorbing fiber The manufacturing method of the near-infrared absorbing fiber of the present embodiment will be described. Since the manufacturing method of the near-infrared absorbing fiber of the present embodiment can manufacture the near-infrared absorbing fiber described above, the description of the matters already described will be omitted.

The method for producing a near-infrared absorbing fiber of this embodiment can include a near-infrared absorbing fiber production step for preparing a near-infrared absorbing fiber containing a fiber and a near-infrared absorbing fiber.

The near-infrared absorbing particles and fibers have already been described, and therefore will not be described here. The near-infrared absorbing particles can contain, for example, cesium tungsten oxide represented by the general formula Cs _x W _1-y O _3-z (0.2≦x≦0.4, 0<y≦0.4, 0<z≦0.46) and having an orthorhombic or hexagonal crystal structure, as described above.

In the near-infrared absorbing fiber manufacturing process, specifically, for example, near-infrared absorbing particles can be placed in one or more locations selected from the surface and interior of the fiber.

There is no particular limitation on the method for disposing near-infrared absorbing particles at one or more locations selected from the surface and interior of the fiber. For example, any of the following methods (a) to (d) can be used.

(a) A method of mixing near-infrared absorbing particles into the raw polymer of synthetic fibers and spinning them.

(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 the masterbatch is diluted and adjusted to the desired concentration at the time of spinning before being spun.

(c) A method in which near-infrared absorbing particles are dispersed in a raw material monomer or oligomer solution to prepare a dispersion solution in advance. The dispersion solution is then used to synthesize the desired raw material polymer, and the near-infrared absorbing particles are 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.

Here, we will further explain the above methods (a) to (d) by providing specific examples.

Method (a):
An example in which polyester fibers are used as the fibers will be described.

First, the near-infrared absorbing particle dispersion is added to polyethylene terephthalate resin pellets, which is a thermoplastic resin, and the mixture is mixed uniformly in a blender, after which the solvent is removed. The mixture from which the solvent has been removed is melt-kneaded in a twin-screw extruder to obtain a master batch containing near-infrared absorbing particles. The resulting master batch is melt-mixed near the melting temperature of the resin, and can be spun, for example, by various known methods to produce near-infrared absorbing fibers.

The method for producing the masterbatch is not particularly limited. For example, a near-infrared absorbing particle dispersion, powder or pellets of a thermoplastic resin, and other additives as necessary are first melt-mixed using a kneader while removing the solvent, to prepare a mixture in which the near-infrared absorbing particles are dispersed in the thermoplastic resin.

The kneading machine is not particularly limited, but may be one or more types selected from mixers such as a ribo blender, tumbler, Nauter mixer, Henschel mixer, super mixer, planetary mixer, Banbury mixer, kneader, roll, kneader ruder, single screw extruder, twin screw extruder, etc.

The method for preparing the mixture in which near-infrared absorbing particles are dispersed in the resin is not limited to the above form.

For example, after preparing a near-infrared absorbing particle dispersion, first remove the dispersion medium from the dispersion by a known method. Then, the powder obtained by removing the dispersion medium, powder particles or pellets of a thermoplastic resin, and other additives as necessary, are uniformly melt-mixed to produce a mixture in which near-infrared absorbing particles are dispersed in a thermoplastic resin. In addition, a method of directly adding near-infrared absorbing particles to a thermoplastic resin and melt-mixing the particles can also be used to produce a mixture in which near-infrared absorbing particles are dispersed in a thermoplastic resin.

The mixture of near-infrared absorbing particles obtained by the above-mentioned method and a thermoplastic resin is kneaded in a vented single-screw or twin-screw extruder and processed into pellets to obtain a master batch containing near-infrared absorbing particles.

Method (b):
A master batch containing near-infrared absorbing particles is prepared by utilizing a method similar to that of (a), etc. Then, the master batch and a master batch made of polyethylene terephthalate to which no near-infrared absorbing particles have been added are melt-mixed at a desired mixing ratio near the melting temperature of the resin, and spun according to a known method, whereby a near-infrared absorbing fiber can be produced.

Method (c):
For example, a case where urethane fibers are used as the fibers will be described.

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). The polyurethane solution is spun according to various known methods to produce near-infrared absorbing particles.

Method (d):
For example, a case where near-infrared absorbing particles are attached to the surface of natural fibers will be described.
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, the 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 the like, and then dried. This allows the near-infrared absorbing particles to be attached to the natural fibers. And the method (d) can be applied to semi-synthetic fibers, regenerated fibers, inorganic fibers, or blends, doubling yarns, and mixed fibers thereof, in addition to the natural fibers mentioned above.

The method for preparing the near-infrared absorbing particle dispersion that can be used when carrying out the above-mentioned methods (a) to (d) is not particularly limited, and for example, the near-infrared absorbing particle dispersion can be prepared by the method already described.

In dispersing the near-infrared absorbing particles, it is preferable to set the conditions of the dispersion process so that when the value of 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, specifically the contained cesium tungsten oxide, is 0.13 or more. By performing the dispersion process so as to satisfy the above conditions and preparing near-infrared absorbing fibers using the obtained dispersion, the optical properties of the near-infrared absorbing fibers can be particularly improved.

The dispersion medium of the near-infrared absorbing particle dispersion is not particularly limited and can be selected according to the fibers to be mixed. For example, various common organic solvents such as alcohols, ethers, esters, ketones, and aromatic compounds, as well as water, can be suitably used.

When attaching or mixing near-infrared absorbing particles to fibers or the polymers that are the raw materials thereof, the near-infrared absorbing particle dispersion can be mixed directly with the fibers or the polymers that are the raw materials thereof. If necessary, the pH can be adjusted by adding an acid or alkali to the near-infrared absorbing particle dispersion, and various surfactants, coupling agents, etc. can be added to further improve the dispersion stability of the near-infrared absorbing particles.

As described above, the near-infrared absorbing fiber of this embodiment contains fibers and near-infrared absorbing particles, and the near-infrared absorbing particles have a neutral color tone. Therefore, it is possible to make the near-infrared absorbing fiber have a neutral color tone. In addition, since the near-infrared absorbing particles contain cesium tungsten oxide, the near-infrared absorbing fiber of this embodiment can be a fiber with excellent heat retention. As a result, the design of the textile product using the near-infrared absorbing fiber is not impaired, and it can be colored in complementary or light colors.

The near infrared absorbing fiber of this embodiment can be used for various applications such as textile products requiring heat retention, such as cold weather clothing, sports clothing, stockings, curtains, and other industrial textile products.
[Textile products]
The textile product of the present embodiment is obtained by processing the near-infrared absorbing fiber described above, and may contain the near-infrared absorbing fiber described above. The textile product of the present embodiment may also be composed of the near-infrared absorbing fiber described above.

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

First, the method for evaluating near infrared ray absorbing particles in the following experimental examples will be described.
(chemical analysis)
Chemical analysis of the obtained near-infrared absorbing particles was performed by atomic absorption spectrometry (AAS) for Cs and by inductively coupled plasma optical emission spectrometry (1CP-OES) for W (tungsten). In addition, O was analyzed by a light element analyzer (LECO, model ON-836) in which the sample was melted in He gas and the CO gas reacted with the carbon in the crucible was quantified by IR absorption spectroscopy. In the following Experimental Examples 1-1 to 1-13, powders that are near-infrared absorbing particles containing cesium tungsten composite oxides having W deficiencies were obtained. Therefore, for Powders A to M, which are near-infrared absorbing particles obtained in Experimental Examples 1-1 to 1-13, it has been confirmed that the composition ratios obtained by multiplying the composition ratio when W is 1 by a value corresponding to the W deficiency determined by TEM observation or the like all satisfy the general formula Cs _x W _1-y O _3-z (0.2≦x≦0.4, 0<y≦0.4, 0<z≦0.46).
(X-ray diffraction measurement)
X-ray diffraction measurements were performed using a Spectris X'Pert-PRO/MPD instrument (Cu-Kα)
The measurement was carried out by powder XRD measurement using a line.

The diffraction angle was calibrated using a standard sample (NIST640e) before the measurements. The obtained XRD diffraction pattern was then subjected to Rietveld analysis to determine the lattice constant of the crystal phase. In Table 1, the identified crystal phase is indicated in the pattern column of the XRD column, and "orthorhombic + hexagonal" means that orthorhombic and hexagonal crystals are included. "Orthorhombic" means that orthorhombic crystals are included, and "hexagonal" means that hexagonal crystals are included.

In the case of a mixed phase of orthorhombic and hexagonal, the lattice constant for each phase was obtained. The lattice constant of the orthorhombic crystal was converted to the lattice constant of the hexagonal crystal by the following lattice correspondence model. The correspondence of the change in the lattice between the orthorhombic crystal and the hexagonal crystal was calculated using the formula 4a _orth ² +b _orth ² =64a _hex ² =64b _hex ² , c _orth =c _hex extracted from the model of Solodovnikov 1998 (Non-Patent Document 4). In addition, a _orth , b _orth , and c _orth in the above formula mean the lengths of the a-axis, b-axis, and c-axis of the orthorhombic crystal. In addition, a _hex , b _hex , and c _hex mean the lengths of the a-axis, b-axis, and c-axis of the hexagonal crystal.
[Experimental Example 1]
Near infrared absorbing particles for use in Experimental Example 2 described later were produced and evaluated.
[Experimental Example 1-1]
Cesium carbonate ( _Cs2CO3 ) and tungsten trioxide ( _WO3 ) were weighed, mixed, and kneaded to a molar ratio of _Cs2CO3 : _WO3 = 2:11 _{, and} the resulting kneaded mixture was placed in a carbon boat and heated twice in a tubular furnace in the atmosphere at 850°C for 20 hours to obtain Powder A', which was a very lightly greenish white powder. Note that when heating, the powder was taken out once after heating at 850°C for 20 hours, pulverized and mixed, and then reheated under the same conditions.

The resulting white powder, Powder A', was evaluated as follows.

The X-ray powder diffraction pattern identified the material as mostly single phase Cs ₄ W ₁₁ O ₃₅ (ICDD 00-51-1891), with a trace of Cs ₆ W ₁₁ O ₃₆ .

The lattice constants were measured to be a = 14.6733 Å, b = 52.3841 Å, and c = 7.7424 Å, which are very close to the values of a = 14.6686 Å, b = 52.3971 Å, and c = 7.7356 Å reported by Solodovnikov (Non-Patent Document ₄ ). Chemical analysis of the white powder gave _Cs0.36WO3.18 , which is in close agreement with the weighed composition.

Next, TEM observation was performed on the obtained white powder, Powder A'. When a selected area electron diffraction pattern was taken, an orthorhombic spot pattern was obtained. Figure 4 shows the spot pattern taken from the c-axis direction of the orthorhombic crystal. A b/8 periodicity was observed in the b-axis direction, and the presence of missing planes of W and O was confirmed. In addition, the streaks running in the b-axis direction revealed the presence of some planar defects on the b-plane. This c-axis crystal zone axis spot pattern is close to 6-fold symmetry, but the angle between the (480) and (4-80) spots is 52.2°, which is deviated from 60° in the case of 6-fold symmetry, and it is believed that the deviation from 6-fold symmetry is due to the missing planes of W and O that fall into the b/8 period.

The obtained white powder, Cs ₄ W ₁₁ O ₃₅ powder, was spread thinly and evenly on a carbon boat, placed in a tubular furnace, and heated in an Ar gas stream from room temperature to 800°C. While maintaining the temperature at 800°C, the stream was switched to a mixture of 1 vol% H ₂ gas (hereinafter, vol% is simply written as %) with Ar gas as a carrier, and reduced for 5 minutes, after which the H ₂ gas was stopped and the mixture was gradually cooled to 100°C using only the Ar gas stream, after which the Ar gas stream was stopped and the mixture was gradually cooled to room temperature, and powder A was taken out. The color of the taken-out powder A was light blue.

The XRD pattern of Powder A showed a two-phase mixed pattern of orthorhombic and hexagonal. The lattice constants of each phase were determined by the Rietveld method, and the orthorhombic phase had a = 14.6609 Å, b = 52.4040 Å, and c = 7.7419 Å (equivalent values for hexagonal phase were a = 7.5062 Å, c = 7.7419 Å), and the hexagonal phase had a = 7.4170 Å, c = 7.5752 Å. It was confirmed that the c-axis values for both phases were in the range of 7.560 Å ≦ c ≦ 7.750 Å.

Next, TEM observation of powder A was performed, and orthorhombic and pseudohexagonal particles were observed.

Here, an electron beam diffraction image of the pseudo-hexagonal particles is shown in Fig. 5. The pseudo-hexagonal particles exhibited a diffraction pattern close to that of a hexagonal crystal, as shown by the electron beam diffraction image of the [001] _HEX crystal zone axis in Fig. 5. The interplanar angle between (200) _HEX and (110) _HEX was measured to be 59.2°, a value close to that of a hexagonal crystal.

Powder A was then observed in STEM-HAADF mode (STEM: scanning transmission electron microscopy, HAADF: high-angle annular dark field).

Figure 6 shows a HAADF image observed from the [221] zone axis of a pseudohexagonal grain. In the HAADF mode, atomic particles are observed with brightness proportional to the atomic number and the probability of the atoms existing in the projection direction, so the linear region along (110) _HEX that appears dark in Figure 6 was identified as a vacancy of W, which has the largest atomic number. By observing from a different direction, it was confirmed that the trace of such a W vacancy region spreads in a planar manner on (110) _HEX . In addition, some of the traces with low contrast are thought to be linearly contracted.

In this experimental example, the heat reduction treatment was performed for 5 minutes, which is shorter than the time required for other experimental examples described later. In the initial stage of reduction at high temperature, W defects in the orthorhombic (010) _ORTH contracted, and a structural transition occurred to a pseudo-hexagonal crystal. Many W-deficient regions in the process of contracting were observed on the {100} _HEX plane of the pseudo-hexagonal crystal.
[Experimental Example 1-2]
The Cs ₄ W ₁₁ O ₃₅ powder, which is the powder A' obtained in Experimental Example 1-1, was spread thinly and evenly on a carbon boat, placed in a tubular furnace, and heated in an Ar gas stream from room temperature to 800°C. While maintaining the temperature at 800°C, the stream was switched to a mixture of 1% H ₂ gas with Ar gas as a carrier, and reduced for 15 minutes, after which the H ₂ gas was stopped and the mixture was gradually cooled to 100°C using only the Ar gas stream, after which the Ar gas stream was stopped and the mixture was gradually cooled to room temperature, and the powder B was taken out. The color of the powder B taken out was blue.

The XRD pattern of Powder B showed a two-phase mixed pattern of orthorhombic and hexagonal. The lattice constants of each phase were determined by the Rietveld method, and the orthorhombic phase had a = 14.6576 Å, b = 52.4315 Å, and c = 7.7412 Å (the hexagonal equivalent values were a = 7.5088 Å, c = 7.7412 Å), and the hexagonal phase had a = 7.4122 Å, c = 7.5940 Å. The c-axis values for both were 7.
It was confirmed that the range of c was 560 Å≦c≦7.750 Å.

Next, TEM observation of Powder B revealed orthorhombic and pseudo-hexagonal particles, as in the case of Powder A obtained in Experimental Example 1-1. The pseudo-hexagonal particles showed a diffraction pattern close to that of a hexagonal crystal, as shown in the electron beam diffraction image of the [001] _HEX crystal zone axis in Figure 7. The interplanar angle between (200) _HEX and (110) _HEX was measured to be 59.5°, a value close to that of a hexagonal crystal.
[Experimental Example 1-3]
The Cs ₄ W ₁₁ O ₃₅ powder, which is the powder A' obtained in Experimental Example 1-1, was spread thinly and evenly on a carbon boat, placed in a tubular furnace, and heated in an Ar gas stream from room temperature to 800°C. While maintaining the temperature at 800°C, the stream was switched to a mixture of 1% H ₂ gas with Ar gas as a carrier, and reduced for 30 minutes, after which the H ₂ gas was stopped and the mixture was gradually cooled to 100°C using only the Ar gas stream, after which the Ar gas stream was stopped and the mixture was gradually cooled to room temperature, and the powder C was taken out. The color of the taken out powder C was dark blue.

The XRD pattern of Powder C showed a two-phase mixed pattern of orthorhombic and hexagonal. The lattice constants of each phase were determined using the Rietveld method, and the orthorhombic phase had a = 14.6649 Å, b = 52.4010 Å, c = 7.7451 Å (equivalent values for hexagonal phase were a = 7.5064 Å, c = 7.7451 Å), and the hexagonal phase had a = 7.4076 Å, c = 7.6107 Å. It was confirmed that the c-axis values for both phases were in the range of 7.560 Å ≦ c ≦ 7.750 Å.

Next, TEM observation of Powder C revealed orthorhombic and pseudo-hexagonal particles, similar to the case of Powder A obtained in Experimental Example 1-1. The pseudo-hexagonal particles showed a hexagonal diffraction pattern, as shown in the electron beam diffraction image of the [001] zone axis in Figure 8. The interplanar angle between (200) _HEX and (110) _HEX was measured to be 60.0°, which is a value for a hexagonal crystal.
[Experimental Examples 1-4 to 1-7]
Powders D, E, F, and G were produced by subjecting the Cs ₄ W ₁₁ O ₃₅ powder, which is Powder A' obtained in Experimental Example 1-1, to a reduction treatment for a reduction time of 35 to 90 minutes as shown in Table 1. Powders D to G all had a deep blue color and had XRD lattice constants as shown in the table.

As shown in Table 1, in Experimental Example 1-4, an orthorhombic phase was also observed, and the c-axis length calculated as a hexagonal phase was 7.7440 Å (Experimental Example 1-4).
[Experimental Examples 1-8 to 1-11]
The heating temperature and reduction time when the Cs ₄ W ₁₁ O ₃₅ powder, which is the powder A' obtained in Experimental Example 1-1, was subjected to the heating and reduction treatment were changed as shown in Table 1. Specifically, in Experimental Example 1-8, the heating and reduction were performed for 120 minutes at 650°C, in Experimental Example 1-9, for 60 minutes at 700°C, in Experimental Example 1-10, for 10 minutes at 900°C, and in Experimental Example 1-11, for 20 minutes at 950°C. Except for the above points, the powders H, I, J, and K were prepared in the same manner as the powder A of Experimental Example 1-1. Light blue, blue, dark blue, and dark blue powders were obtained, respectively. The lattice constants obtained from the XRD patterns of the obtained powders were as shown in Table 1.

As shown in Table 1, in Experimental Examples 1-8 and 1-9, an orthorhombic phase was also observed, and the c-axis lengths converted to hexagonal were 7.7428 Å (Experimental Example 1-8) and 7.7471 Å (Experimental Example 1-9).
[Experimental Example 1-12]
Cesium carbonate and tungsten trioxide were mixed in a molar ratio _{of Cs2CO3} : _WO3 = 3:11, spread thinly and evenly on a carbon boat, placed in a tube furnace, and heated at _{850°C for 5 hours to obtain a very slightly greenish white powder. The main phase of this white powder was identified as Cs6W11O36 ( ICDD1-70-632} ), but _it was a mixed _phase with _Cs4W11O35 .

The obtained white powder was heat-treated in a 1% H ₂ —N ₂ gas flow at 800° C. for 30 minutes to obtain a deep blue powder L.

The XRD pattern of Powder L showed a two-phase mixed pattern of orthorhombic and hexagonal. The lattice constants obtained from the XRD pattern of Powder L are shown in Table 1. As described above, an orthorhombic phase was also observed, and the c-axis length converted to a hexagonal phase was 7.7449 Å.
[Experimental Example 1-13]
Cesium carbonate and tungsten trioxide were mixed in a molar ratio of Cs ₂ CO ₃ :WO ₃ = 1:6, spread thinly and evenly on a carbon boat, placed in a tube furnace, and heated at 850°C for 5 hours to obtain a very slightly greenish white powder. The main phase of this white powder was identified as Cs ₄ W ₁₁ O ₃₅ , but it was a mixed phase with Cs ₂ W ₆ O ₁₉ (ICDD00-045-0522).

The obtained white powder was heat-treated in a 1% H ₂ —N ₂ gas flow at 800° C. for 30 minutes to obtain a deep blue powder M.

The XRD pattern of Powder M showed a two-phase mixed pattern of orthorhombic and hexagonal crystals. The lattice constants obtained from the XRD pattern of Powder M are shown in Table 1. An orthorhombic phase was also observed, and the c-axis length converted to hexagonal crystals was 7.7466 Å.

As shown in the above Experimental Examples 1-1 to 1-13, when white Cs ₄ W ₁₁ O ₃₅ powder, Cs ₆ W ₁₁ O _{36 powder} , and Cs ₄ W ₁₁ O ₃₅ powder containing Cs ₂ W ₆ O ₁₉ were reduced at high temperature, the color of the powder gradually changed from light blue to blue and then to dark blue.

Furthermore, the _{Cs4W11O35 phase} contains lattice defects including _W vacancies and is orthorhombic. It was confirmed that when this phase is reduced at high temperatures, the lattice defects including W vacancies are reduced or eliminated, and the orthorhombic crystals change to hexagonal crystals.

It has been confirmed that the cesium tungsten oxide contained in Powders A to M obtained in Experimental Examples 1-1 to 1-13 all has W deficiencies and O deficiencies.
[Experimental Example 2]
Near infrared absorbing fibers were produced using the near infrared absorbing particles produced in Experimental Example 1, and were evaluated.

Experimental Examples 2-1 to 2-13 are working examples, and Experimental Examples 2-14 and 2-15 are comparative examples.
[Experimental Example 2-1]
10% by mass of the powder A prepared in Experimental Example 1-1, 10% by mass of an acrylic polymer dispersant having an amine-containing functional group (hereinafter abbreviated as "dispersant a"), and 80% by mass of toluene as a solvent were weighed out. These weighed materials were placed in a glass container together with silica beads having a diameter of 0.3 mm, and dispersed and pulverized for 1 hour using a paint shaker to obtain a dispersion A, which is a near-infrared absorbing particle dispersion.

Here, the average particle size of the near-infrared absorbing particles in dispersion A (dispersed particle size measured using an ELS-8000 manufactured by Otsuka Electronics Co., Ltd., a particle size measuring device based on dynamic light scattering) was measured to be 28.2 nm.

Toluene was removed from dispersion A using a spray dryer to obtain a near-infrared absorbing particle dispersion powder according to Experimental Example 2-1. The obtained near-infrared absorbing particle dispersion powder was added to polyethylene terephthalate resin pellets, which is a thermoplastic resin, and mixed uniformly 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 master batch containing 40% by weight of near-infrared absorbing particles, which are a near-infrared absorbing component.

The master batch according to Experimental Example 2-1 was melt-spun together with a polyester master batch using the raw polymer, followed by drawing to produce the polyester multifilament yarn according to Experimental Example 2-1. At this time, the cesium tungsten oxide particles, which are near-infrared absorbing particles, were melt-spun with the raw polymer so that the content was 10 mass% of the solid content of the fiber. The average particle size of the cesium tungsten oxide particles at this time was calculated to be 27 nm using an image processing device using a transmission electron microscope image. The particle size of each particle is the diameter of the circumscribed circle of the particle, and the average particle size is calculated as the average particle size measured for 100 particles. The polyester resin used in the polyester master batch is polyethylene terephthalate resin.

The obtained polyester multifilament yarn was cut to produce polyester staples, which were then used to manufacture spun yarn. The knitted product of Experimental Example 2-1, which has heat-retaining properties, was then obtained using this spun yarn.

The solar reflectance of the knitted product samples was adjusted to 8%. The solar reflectance of the knitted product samples was adjusted to 8% in all of the experimental examples 2-2 to 2-15 described below.

The spectral characteristics of the produced knitted product were measured using a spectrophotometer manufactured by Hitachi Ltd. to measure the transmittance and reflectance of light with a wavelength of 200 nm or more and 2100 nm or less, and the solar absorptance was calculated according to JIS A 5759 (2016). The solar absorptance was calculated as follows: solar absorptance (%) = 100% - solar transmittance (%) - solar reflectance (%). The calculated solar absorptance was 51.1%. In addition, the color index of the knitted product was calculated from the reflectance, and it was found to be L ^* = 88, a ^* = -1, b ^* = 8, and it was confirmed that the blue color was very weak and the color tone was neutral.

The results are shown in Table 2. Table 2 also lists the results obtained in Experimental Examples 2-2 to 2-15, which will be described later.

Next, the temperature rise effect on the reverse side of the fabric of the knitted product was measured as follows.

In an environment of 20°C and 60% RH, a solar spectrum approximation lamp (solar simulator XL-03E50 modified by Ceric Co., Ltd.) was irradiated from a distance of 30 cm from the knitted product 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, 600 seconds) using a radiation thermometer (HT-11 manufactured by Minolta Co., Ltd.).

The results are shown in Table 3. Table 3 also shows the results obtained in Experimental Examples 2-2 to 2-15, which will be described later.
[Experimental Examples 2-2 to 2-13]
Near-infrared absorbing particle dispersion powders, masterbatches, polyester multifilament yarns as near-infrared absorbing fibers, and knitted products as textile products as per Experimental Examples 2-2 to 2-13 were obtained and evaluated in the same manner as in Experimental Example 2-1, except that Powder B to Powder M as per Experimental Examples 1-2 to 1-13 were used instead of Powder A as per Experimental Example 1-1. The evaluation results are shown in Tables 2 and 3.
[Experimental Example 2-14]
A near-infrared absorbing particle-dispersed powder, a master batch _{, a polyester multifilament} yarn, and a knit product according to Experimental Example 2-14 were obtained and evaluated in the same manner as in Experimental Example 2-1, except that the powder A' obtained in Experimental Example 1-1, namely, Cs4W11O35 powder, was used instead of the powder A according to Experimental Example 1-1. The evaluation results are shown in Tables 2 and 3.
[Experimental Example 2-15]
A raw material mixture was prepared by weighing, mixing, and kneading an aqueous solution of cesium carbonate (Cs ₂ CO ₃ ), tungstic acid (H ₂ WO ₄ ), and tungsten dioxide powder (WO ₂ ) to obtain a composition of Cs _{2 O.5WO} 3.4WO _2. After thorough mixing, the raw material mixture was thinly and evenly spread on a carbon boat and held at 550° C. for 60 minutes under a 1% H ₂ gas flow with N ₂ gas as a carrier, then changed to a 100% N ₂ flow and held for 1 hour, then heated to 800° C. and held for 1 hour, and slowly cooled to room temperature to obtain powder O. The color of powder O was dark blue. As a result of chemical analysis, the composition Cs _0.33 WO _2.74 was obtained.

The XRD pattern of Powder O showed a single hexagonal phase. Rietveld analysis gave the lattice parameters a = 7.4088 Å and c = 7.6033 Å. The c-axis lattice parameter was within the desired range.

Next, TEM observation was performed, but no particularly noticeable lattice defects were found. STEM atomic image observation also showed no noticeable lattice defects, and no W deficiencies were found.

A near infrared absorbing particle dispersion powder, a master batch, a polyester multifilament yarn, and a knit product according to Experimental Example _2-15 were obtained and evaluated in the same manner as in Experimental Example 2-1, except that the _Cs0.33WO2.74 powder was used instead of the powder A according to Experimental Example 1-1. The evaluation results are shown in Tables 2 and 3.

According to the results shown in Table 2, it was confirmed that the near infrared absorbing fibers of Experimental Examples 2-1 to 2-13, which contain near infrared absorbing particles containing cesium tungsten oxide represented by the general formula Cs _x W _1-y O _3-z (0.2≦x≦0.4, 0<y≦0.4, 0<z≦0.46) and having an orthorhombic or hexagonal crystal structure, had a very weak blue color and a neutral color tone. In other words, it was confirmed that the near infrared absorbing fibers of these Experimental Examples contain near infrared absorbing particles containing a composite tungsten oxide and can be made to have a more neutral color tone.

In contrast, the near-infrared absorbing particles contained in the near-infrared absorbing fibers of Experimental Examples 2-14 and 2-15 do not contain cesium tungsten oxide that satisfies the above general formula.

In addition, it is found that the near infrared absorbing fiber of Experimental Example 2-15 has a negative b ^* value and a bluish tinge is clearly recognized. In other words, it was confirmed that the near infrared absorbing fiber of Experimental Example 2-15 cannot be made to have a neutral color tone.

Although the near-infrared absorbing fiber of Experimental Example 2-14 was able to have a neutral color tone, as is clear from the results in Tables 2 and 3, it was confirmed that the solar radiation absorptance was poor and the effect of increasing the temperature of the textile product was also insufficient. Therefore, it was confirmed that the near-infrared absorbing fiber of Experimental Example 2-14 does not have sufficient properties as a near-infrared absorbing fiber.

Claims (17)

Fibers and
Near infrared absorbing particles,
The near infrared absorbing particles contain cesium tungsten oxide represented by a general formula Cs _x W _1-y O _3-z (0.2≦x≦0.4, 0<y≦0.4, 0<z≦0.46) and having an orthorhombic or hexagonal crystal structure ;
A near-infrared absorbing fiber, wherein the cesium tungsten oxide has linear or planar defects in one or more faces selected from the (010) face of an orthorhombic crystal, the {100} face which is a prism face of a hexagonal crystal, and the (001) face which is a base face of a hexagonal crystal . 2. The near infrared absorbing fiber according to claim 1 , wherein the cesium tungsten oxide has defects, the defects including tungsten vacancies. 3. The near infrared absorbing fiber according to claim 1 , wherein the cesium tungsten oxide has a c-axis length in hexagonal equivalent of 7.560 Å or more and 7.750 Å or less. 4. The near infrared absorbing fiber according to claim 1 , wherein a part of O in the WO _6- octahedron constituting the cesium tungsten oxide crystal is deficient. A part of Cs in the cesium tungsten oxide is replaced by an additive element,
5. The near infrared absorbing fiber according to claim 1 , wherein the additive element is at least one 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. The near infrared absorbing fiber according to claim 1 , wherein the near infrared absorbing particles are contained in an amount of 0.001% by mass or more and 80% by mass or less based on the solid content of the fiber. The fiber further includes a far-infrared emitting material 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 far-infrared emitting substance is contained in an amount of 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 one or more types selected from a fiber group consisting of synthetic fibers, semi-synthetic fibers, natural fibers, regenerated fibers, and inorganic fibers, and a mixed yarn obtained by blending, doubling , or mixing two 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 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 at least one selected from the group consisting of cellulose-based fiber, protein-based fiber, 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 vegetable fibers, animal fibers, and mineral fibers. 14. The near infrared absorbing fiber according to claim 10 , wherein the regenerated fiber is one or more types 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 near-infrared absorbing fiber production process for preparing a near-infrared absorbing fiber containing fibers and near-infrared absorbing particles,
The near infrared absorbing particles contain cesium tungsten oxide represented by a general formula Cs _x W _1-y O _3-z (0.2≦x≦0.4, 0<y≦0.4, 0<z≦0.46) and having an orthorhombic or hexagonal crystal structure ;
The method for producing a near-infrared absorbing fiber, wherein the cesium tungsten oxide has linear or planar defects in one or more faces selected from the (010) face of an orthorhombic crystal, the {100} face which is a prism face of a hexagonal crystal, and the (001) face which is a basal face of a hexagonal crystal.