Near-infrared-absorbing fiber and fiber product

Abstract

The present invention addresses the problem of providing a near-infrared-absorbing fiber in which a residual organic solvent is reduced.　A near-infrared-absorbing fiber (20) according to the present invention includes a fiber (21) and composite tungsten oxide particles (22). The composite tungsten oxide particles (22) are modified with a nonionic polymer dispersant, and are displaced in at least one portion of the fiber (21) selected from the surface (21A) and the interior (21B) thereof.

Description

Near-infrared absorbing fibers and textile products

[0001] This invention relates to near-infrared absorbing fibers and textile products.

[0002] Traditionally, various winter clothing, interior furnishings, and leisure goods designed to enhance cold protection have been devised and put into practical use.

[0003] There are broadly two ways to improve the effectiveness of cold protection.

[0004] The first method involves, for example, controlling the structure of the weave or knit of the winter clothing, or making the fibers used hollow or porous, thereby physically increasing the air layer in the winter clothing and reducing the dissipation of heat generated from the human body to the outside, thereby improving its ability to keep warm.

[0005] The second method involves, for example, applying chemical or physical processing to the entire winter clothing or the fibers that make up the winter clothing to radiate heat generated from the human body back to the body, or to convert a portion of the sunlight received by the winter clothing into heat. The second method is an active method of storing heat and improving the cold-weather protection.

[0006] As described above, the first method has involved increasing the amount of air in the garment, making the fabric thicker, making the weave finer, or making the color darker. For example, winter clothing such as sweaters falls under the first method. Also, for example, in winter sports clothing that uses the first method, padding is placed between the outer and inner layers, and the thickness of the air layer of the padding enhances the cold-weather protection. However, the addition of padding makes the clothing heavy and bulky, which is problematic for sports clothing where ease of movement is required. To resolve these problems, in recent years, the second method described above, which involves actively and effectively utilizing the heat generated inside the garment or product, or the heat from the outside of the garment or product, has begun to be adopted.

[0007] One known method for implementing the second method described above involves depositing metals such as aluminum or titanium onto the lining of clothing, thereby actively preventing heat dissipation by reflecting the radiant heat emitted from the body onto the metal-deposited surface. However, these methods incur considerable costs due to the metal deposition process on the clothing, and yields are poor due to uneven deposition, ultimately leading to higher prices for the clothing products themselves.

[0008] Furthermore, as an alternative to implementing the second method, a method has been proposed in which ceramic particles such as alumina, zirconia, and magnesia are kneaded into the fibers themselves. Specifically, by kneading ceramic particles into the fibers, a method has been proposed that utilizes the far-infrared radiation effect and the effect of converting light into heat that these ceramic particles possess, that is, a method that actively incorporates external energy.

[0009] For example, Patent Document 1 states that the thermal conductivity is 0.3 kcal / m 2 A heat-radiating fiber is disclosed, characterized by containing one or more inorganic fine particles having heat-radiating properties, each containing at least one metal and metal ion with a temperature of sec·°C or higher.

[0010] Furthermore, Patent Document 2 discloses an infrared-absorbing processed fiber product obtained by dispersing and fixing a binder resin containing an infrared absorbent made of an amino compound.

[0011] Furthermore, Patent Document 3 discloses a method for processing cellulosic fiber structures to absorb near-infrared rays, in which the spectral reflectance of the fabric in the range of 750 to 1500 nm is 65% or less, by dyeing with a dye selected from among direct dyes, reactive dyes, naphthol dyes, and vat dyes that has the characteristic of absorbing more in the near-infrared region than black dyes, in combination with other dyes.

[0012] Furthermore, the applicant of the present application proposed a boride microparticle-containing fiber containing boride microparticles in Patent Document 4. In addition, the inventors of the present invention proposed a near-infrared absorbing fiber containing tungsten oxide microparticles and / or composite tungsten oxide microparticles on its surface and / or inside in Patent Document 5.

[0013] Japanese Unexamined Patent Publication No. 11-279830 Japanese Unexamined Patent Publication No. 8-3870 Japanese Unexamined Patent Application No. 9-291463 Unexamined Japanese Patent Application No. 2005-9024 Unexamined Japanese Patent Application No. 2006-132042

[0014] For example, the near-infrared absorbing fiber disclosed in Patent Document 5 is said to have good weather resistance, efficiently absorb heat rays from sunlight and other sources with a small amount of additive, and has excellent transparency so as not to impair the design of textile products, and can provide a low-cost fiber with heat retention properties.

[0015] However, the near-infrared absorbing fiber disclosed in Patent Document 5 requires a dispersion containing an organic solvent during its manufacturing process, which leads to the problem of organic solvent residue remaining on the composite tungsten oxide particles, etc. In some cases, it is necessary to reduce the amount of residual organic solvent in near-infrared absorbing fibers, so there has been a demand for near-infrared absorbing fibers with reduced organic solvent residue.

[0016] Therefore, one aspect of the present invention aims to provide near-infrared absorbing fibers with reduced residual organic solvents.

[0017] A near-infrared absorbing fiber according to one aspect of the present invention comprises a fiber and composite tungsten oxide particles, wherein the composite tungsten oxide particles are modified with a nonionic polymer dispersant, and the composite tungsten oxide particles are arranged in one or more selected portions from the surface and interior of the fiber.

[0018] According to one aspect of the present invention, near-infrared absorbing fibers with reduced residual organic solvents can be provided.

[0019] Figure 1 is an explanatory diagram of a high-frequency plasma reactor. Figure 2 is an explanatory diagram of a near-infrared absorbing fiber according to one embodiment of the present disclosure.

[0020] Specific examples of near-infrared absorbing fibers and textile products according to one embodiment of this disclosure (hereinafter referred to as "this embodiment") will be described below with reference to the drawings. However, the present invention is not limited to these examples and is intended to be shown by the claims, and all modifications within the meaning and scope of the equivalents of the claims are intended to be included.

[0021] [Near-infrared absorbing fiber] The near-infrared absorbing fiber according to this embodiment may include a fiber and composite tungsten oxide particles. That is, the near-infrared absorbing fiber of this embodiment is a fiber containing composite tungsten oxide particles as a near-infrared absorbing component.

[0022] A model for implementing a near-infrared absorbing fiber according to one aspect of this disclosure will be described in the following order: [1] composite tungsten oxide particles, and [2] near-infrared absorbing fiber.

[0023] [1] Composite Tungsten Oxide Particles The following describes composite tungsten oxide particles and a dispersion of composite tungsten oxide particles used to manufacture near-infrared absorbing fibers by incorporating the composite tungsten oxide particles into various fibers. Specifically, the following will be described in order: [1-1] Composite Tungsten Oxide Particles, [1-2] Method for Manufacturing Composite Tungsten Oxide Particles, and [1-3] Dispersion of Composite Tungsten Oxide Particles. [1-1] Composite Tungsten Oxide Particles Hereafter, the composite tungsten oxide particles will be described in order: (1) Crystal structure, (2) Average particle size and crystallite size, (3) Composition of composite tungsten oxide particles, and (4) Surface coating of composite tungsten oxide particles.

[0024] (1) The composite tungsten oxide contained in the crystalline structure composite tungsten oxide particles may take the form of hexagonal, tetragonal, or cubic tungsten bronze structures, but it is effective as a near-infrared absorbing material regardless of which structure it takes. For this reason, the crystalline structure of the composite tungsten oxide contained in the composite tungsten oxide particles used in the near-infrared absorbing fiber of this embodiment is not particularly limited.

[0025] The absorption position of light in the near-infrared region of composite tungsten oxides tends to change depending on the crystal structure. Specifically, the absorption position in the near-infrared region shifts to longer wavelengths in tetragonal crystals compared to cubic crystals, and shifts even further to longer wavelengths in hexagonal crystals than in tetragonal crystals. In addition, in conjunction with this variation in absorption position, the absorption of light in the visible light region is lowest in hexagonal crystals, followed by tetragonal crystals, and highest in cubic crystals.

[0026] Based on the above findings, the crystal structure of the composite tungsten oxide contained in the composite tungsten oxide particles may be selected to absorb and transmit light in a predetermined wavelength range depending on the application. For example, when used in applications where it is required to transmit more light in the visible light region and absorb more light in the near-infrared region, it is preferable to use hexagonal tungsten bronze as the composite tungsten oxide contained in the composite tungsten oxide particles. For this reason, the composite tungsten oxide contained in the composite tungsten oxide particles may have a hexagonal crystal structure. When the composite tungsten oxide has a hexagonal crystal structure, the transmittance of light in the visible light region of the composite tungsten oxide is improved, and the absorption rate of light in the near-infrared region is improved. In a hexagonal crystal structure, WO ６ The structure consists of six octahedrons formed by a single unit, which combine to form a hexagonal void (tunnel). Element M is placed within this void to form a single unit, and a large number of these units are assembled together.

[0027] Regarding composite tungsten oxide particles, in order to obtain the effect of improving the transmittance of light in the visible light region and improving the absorption rate of light in the near-infrared region, it is preferable that the composite tungsten oxide contains the above-mentioned unit structure, but it is sufficient that it contains the unit structure, and it does not need to be crystalline. The above-mentioned unit structure is WO ６ This refers to a structure that includes a hexagonal void formed by the aggregation of six octahedrons, each formed as a unit, and in which element M is placed.

[0028] When cations of element M are added and present in the hexagonal voids, the light absorption rate in the near-infrared region is particularly improved. Generally, when an element M with a large ionic radius is added, it is easier to form a hexagonal crystal. Therefore, specifically, for example, it is preferable to add one or more selected from Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, as it is easier to form a hexagonal crystal.

[0029] Furthermore, among these elements M with a large ionic radius, when adding one or more elements selected from Na, K, Rb, Cs, Ba as element M, the composite tungstate is more likely to adopt a hexagonal crystal structure. Among them, in composite tungstate oxide particles containing composite tungsten added with one or more elements selected from Cs, Rb as element M, the light absorption rate in the near-infrared region can be made particularly high, and the light transmittance in the visible light region can also be made particularly high. That is, when element M contains one or more elements selected from Cs, Rb, it is possible to achieve both high performance in terms of the light absorption rate in the near-infrared region and the light transmittance in the visible light region while achieving compatibility.

[0030] It is also possible to select and combine two or more elements as element M for use. In this case, even when at least one of the two or more elements contained in element M is selected from one or more selected from Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, and the rest are elements other than the above elements, it may also form a hexagonal crystal.

[0031] Composite tungstate oxide particles are represented by the general formula M ｘ WO ｙ When the composite tungstate oxide particles have a uniform crystal structure, the addition amount of element M, which is the added element, is preferably 0.1 ≦ x ≦ 1.0, more preferably 0.2 ≦ x ≦ 0.5, still more preferably 0.25 ≦ x ≦ 0.39, and particularly preferably x = 0.33. This is because theoretically, when y = 3, x = 0.33, and it is considered that element M is arranged in all of the hexagonal voids. A typical example is Cs ０．３３ WO ３ 、Cs ０．０３ Rb ０．３０ WO３ , Rb ０．３３ WO ３ _K ０．３３ WO ３ Ba ０．３３ WO ３ These are some examples.

[0032] (2) Average particle diameter and crystallite diameter (2-1) Average particle diameter The average particle diameter of the composite tungsten oxide particles is not particularly limited, but it is preferable that the average particle diameter is 100 nm or less. Excellent near-infrared absorption characteristics can be exhibited if the average particle diameter is in the range of 100 nm or less. From the viewpoint of exhibiting particularly excellent near-infrared absorption characteristics, it is more preferable that the average particle diameter of the composite tungsten oxide particles is 10 nm or more and 100 nm or less, even more preferably 10 nm or more and 80 nm or less, particularly preferably 10 nm or more and 60 nm or less, and most preferably 10 nm or more and 40 nm or less.

[0033] Here, the average particle diameter is the average value of the diameters of individual, non-aggregated composite tungsten oxide particles. Specifically, it is the average particle diameter of the composite tungsten oxide particles contained in a composite tungsten oxide particle dispersion obtained by dispersing composite tungsten oxide particles in a solid medium such as a resin.

[0034] The average particle diameter does not include the diameter of aggregates of composite tungsten oxide particles and is therefore different from the dispersed particle diameter.

[0035] The average particle size is measured and calculated from electron microscope images of the composite tungsten oxide particles.

[0036] To measure the average particle diameter of composite tungsten oxide particles contained in a composite tungsten oxide particle dispersion, a thinned sample of the dispersion obtained by cross-sectional processing can be used. Then, 100 composite tungsten oxide particles can be selected from the transmission electron microscope image of the thinned sample, and the particle diameter of the selected particles can be measured using an image processing device, and the average value can be calculated. The average value is the arithmetic mean, which is the sum of the particle diameters of the 100 composite tungsten oxide particles divided by the number of particles, 100. Furthermore, the particle diameter of each composite tungsten oxide particle represents the diameter equivalent to a circle. That is, the particle diameter of each composite tungsten oxide particle measured using the thinned sample can be considered the diameter of a circle with the same area (cross-sectional area) as each composite tungsten oxide particle.

[0037] For cross-sectional processing to obtain thin sections for evaluation, a microtome, cross-section polisher, focused ion beam (FIB) apparatus, etc., can be used. The average particle size of the composite tungsten oxide particles contained in the composite tungsten oxide particle dispersion is the average value of the particle sizes of the composite tungsten oxide particles dispersed in the solid medium that serves as the matrix.

[0038] (2-2) Crystallite size The crystallite size of the composite tungsten oxide particles is not particularly limited, but from the viewpoint of exhibiting particularly excellent near-infrared absorption characteristics, the crystallite size of the composite tungsten oxide particles is preferably, for example, 10 nm to 100 nm, more preferably 10 nm to 80 nm, even more preferably 10 nm to 60 nm, and most preferably 10 nm to 40 nm. By setting the crystallite size of the composite tungsten oxide particles to 10 nm to 100 nm, particularly excellent near-infrared absorption characteristics can be exhibited.

[0039] The crystallite size of the composite tungsten oxide particles contained in the composite tungsten oxide particle dispersion obtained after the crushing, grinding, or dispersion treatments described later can be maintained even after volatile components, etc., are removed from the composite tungsten oxide particle dispersion. For example, the crystallite size of the composite tungsten oxide particles contained in the composite tungsten oxide particle dispersion can be maintained even in composite tungsten oxide particles obtained by removing the liquid medium, etc., from the composite tungsten oxide particle dispersion. Furthermore, the crystallite size of the composite tungsten oxide particles contained in the composite tungsten oxide particle dispersion can also be maintained in the composite tungsten oxide particle dispersion obtained using the composite tungsten oxide particle dispersion.

[0040] (3) Composition of composite tungsten oxide particles The composite tungsten oxide particles have the general formula M ｘ WO ｙ It is preferable that the compound tungsten oxide represented by [formula] is included.

[0041] Furthermore, while the composite tungsten oxide particles may consist solely of the above-mentioned composite tungsten oxide, this does not exclude the possibility of unavoidable impurities being present.

[0042] The above general formula M ｘ WO ｙ The composite tungsten oxide shown is described below.

[0043] General formula M ｘ WO ｙ The elements M, x, and y within the composite tungsten oxide particles, along with their crystal structure, are closely related to the free electron density of the composite tungsten oxide particles and significantly influence the near-infrared absorption properties.

[0044] Generally, tungsten trioxide (WO ３ ) Because there are no effective free electrons present, it has low near-infrared absorption characteristics.

[0045] The inventors of this invention have discovered that by adding element M to tungsten trioxide to form a composite tungsten oxide, free electrons are generated in the composite tungsten oxide, and absorption characteristics originating from these free electrons are exhibited in the near-infrared region. In particular, they have found that the above composite tungsten oxide is effective as a near-infrared absorbing material that absorbs near-infrared light around a wavelength of 1000 nm, and that the composite tungsten oxide maintains a chemically stable state and is effective as a near-infrared absorbing material with excellent weather resistance.

[0046] In the above general formula, the element M represented by M preferably contains one or more elements selected from Li (lithium), Na (sodium), K (potassium), Rb (rubidium), Cs (cesium), Fr (francium), Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium), and Ra (radium). This is because the inclusion of one or more elements selected from Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, and Ra in element M makes it easier for the composite tungsten oxide particles to adopt a hexagonal crystal structure, particularly increasing the transmittance of light in the visible light region and also increasing the absorption rate of light in the near-infrared region. It is more preferable that element M contains one or more elements selected from Na, K, Rb, Cs, and Ba. It is even more preferable that element M contains one or more elements selected from Cs and Rb. Furthermore, in the general formula, W represents tungsten, O represents oxygen, and x may be 0.1 ≤ x ≤ 1.0, 0.2 ≤ x ≤ 0.5, or 0.25 ≤ x ≤ 0.39. y may also be 2.0 ≤ y < 4.0.

[0047] In particular, if element M contains one or more elements selected from Na, K, Rb, Cs, and Ba, the composite tungsten oxide is more likely to adopt a hexagonal crystal structure. If element M contains one or more elements selected from Cs and Rb, the composite tungsten oxide is especially likely to adopt a hexagonal crystal structure. As a result, it is particularly preferable because it increases the transmittance of light in the visible light region and absorbs light in the near-infrared region, converting it into heat. Element M may be formed from only one or more elements selected from Na, K, Rb, Cs, and Ba, or from only one or more elements selected from Cs and Rb.

[0048] It is also possible to select and combine two or more elements as element M. In this case, even if at least one of the two or more elements contained in element M is selected from Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, and Ra, and the remaining elements are other elements, a hexagonal crystal may still be formed.

[0049] In the general formula above, regarding the value of x which indicates the amount of element M added, if the value of x is 0.1 or greater, a sufficient amount of free electrons is generated, and particularly high near-infrared absorption characteristics can be obtained. Furthermore, the more element M is added, the greater the supply of free electrons and the higher the near-infrared absorption characteristics, but this effect saturates when the value of x is around 1. Also, if the value of x is 1 or less, the formation of an impurity phase in the composite tungsten particles can be avoided, so it is preferable that x is 1.0 or less.

[0050] The value of y, which represents the amount of oxygen in the above general formula, is preferably 2.0 ≤ y < 4.0, more preferably 2.2 ≤ y ≤ 3.5, even more preferably 2.6 ≤ y ≤ 3.0, and particularly preferably 2.7 ≤ y ≤ 3.0. If the value of y, which represents the amount of oxygen, is 2.0 or greater, then the composite tungsten oxide particles will contain unintended WO ２ This method avoids the appearance of the crystalline phase and provides chemical stability as a material, making it a particularly effective near-infrared absorbing material.

[0051] Tungsten oxide (WO ｙIn this case, by setting y, which represents the amount of oxygen, to less than 3, a particularly sufficient amount of free electrons can be generated to enhance the absorption and reflection characteristics in the near-infrared region. ｘ WO ｙ Even in composite tungsten oxides represented as WO ｙ The same mechanism as that used for tungsten oxide is at work. However, in the case of composite tungsten oxides, even when the value of y, which indicates the amount of oxygen, is y = 3.0 or when y, which indicates the amount of oxygen, is in excess and exceeds 3.0, near-infrared absorption characteristics can be obtained because of the supply of free electrons due to the addition of element M. For this reason, y may be y < 4.0 or y ≤ 3.5.

[0052] If the value of y is 3.0 or less, the required amount of free electrons is generated in the tungsten oxide, resulting in an even more efficient near-infrared absorbing material. For this reason, y may be 3.0 or less.

[0053] (4) Surface coating of composite tungsten oxide particles In order to improve the weather resistance of composite tungsten oxide particles, the composite tungsten oxide particles may have a surface coating on the surface of the particles containing a compound that contains one or more elements selected from silicon, zirconium, titanium, and aluminum. As examples of surface coating materials, the compounds containing the elements listed above are basically transparent and their addition does not reduce the visible light transmittance of the composite tungsten oxide particles, and therefore does not impair the design of the fibers. Furthermore, it is preferable that these compounds are oxides. The oxides of these compounds have high far-infrared radiation ability and also have the ability to receive the energy absorbed by the composite tungsten oxide particles, convert that energy into thermal energy in the mid- and far-infrared wavelengths, and radiate it. Therefore, the oxides of these compounds are also effective for the heat retention effect of the fibers. The coating method is not particularly limited, but for example, it is possible to coat the surface of the composite tungsten oxide particles by adding the alkoxide of the above metal to a solution in which the composite tungsten oxide particles are dispersed.

[0054] [1-2] Method for Manufacturing Composite Tungsten Oxide Particles The method for manufacturing composite tungsten oxide particles described above is not particularly limited. Composite tungsten oxide particles can be manufactured using, for example, a thermal plasma method or a solid-phase reaction method. Various properties of composite tungsten oxide particles, such as crystallite size, can be easily controlled by the conditions under which the composite tungsten oxide particles are manufactured. For this reason, for example, preliminary tests can be conducted to select manufacturing conditions in order to produce composite tungsten oxide particles with desired properties. Examples of the above manufacturing conditions include the temperature (firing temperature) when producing the composite tungsten oxide particles, the production time (firing time), the production atmosphere (firing atmosphere), the form of the precursor raw material, the annealing treatment after production, and the doping of impurity elements.

[0055] The following describes an example of a method for producing composite tungsten oxide particles.

[0056] Methods for producing composite tungsten oxide particles include the thermal plasma method, in which starting materials are introduced into a thermal plasma, and the solid-phase reaction method, in which starting materials are heat-treated. Composite tungsten oxide particles synthesized by the thermal plasma method or the solid-phase reaction method can be dispersed or crushed and dispersed as needed.

[0057] The following will explain the processes in the following order: (1) thermal plasma method, (2) solid-phase reaction method, and (3) pulverization and dispersion treatment.

[0058] (1) Thermal Plasma Method The thermal plasma method will be explained in the following order: (1-1) Raw materials used in the thermal plasma method, and (1-2) The thermal plasma method and its conditions.

[0059] (1-1) When synthesizing composite tungsten oxide particles used in the thermal plasma method by the thermal plasma method, a mixed powder of a tungsten source containing tungsten and an element M source containing element M can be used as a raw material. Examples of tungsten sources include elemental tungsten and tungsten compounds. Examples of element M sources include elemental M and element M compounds.

[0060] Examples of tungsten compounds include tungstic acid (H ２ WO ４), one or more selected from ammonium tungstate, tungsten hexachloride, tungsten oxide hydrate, etc. may be used.

[0061] As a hydrate of tungsten oxide, for example, a hydrated powder of tungsten oxide obtained by dissolving tungsten hexachloride in alcohol, adding water to hydrolyze it, and then drying the solvent can also be used.

[0062] Furthermore, one or more of the oxides, hydroxides, nitrates, sulfates, chlorides, and carbonates of element M may be used as the element M compound.

[0063] When mixing starting materials to produce composite tungsten oxide particles, if the starting materials are in solution form, each element contained in the starting materials can be easily and uniformly mixed. For this reason, the tungsten source and at least one of the element M source may be mixed after being in solution form, such as an aqueous solution.

[0064] Therefore, for example, with respect to the tungsten source and the element M source, the composition ratio of the tungsten element and element M is such that, for example, the general formula M described above is used ｘ WO ｙ The mixture may be wet-mixed to satisfy the requirements. Then, by drying the resulting mixture, a mixture of the tungsten source and the element M source, for example, a mixed powder of a tungsten compound and an element M compound, is obtained.

[0065] Furthermore, the tungsten source and the element M source may be mixed using a dry process.

[0066] The resulting mixed powder can be used as a raw material for the thermal plasma method.

[0067] The mixed powder obtained by mixing can also be used as a raw material for the thermal plasma method after the first stage of calcination in an atmosphere of either an inert gas alone or a mixed gas of an inert gas and a reducing gas.

[0068] As raw materials for the thermal plasma method, not only the first-stage calcination but also calcined powder obtained after multiple stages of calcination may be used. Specifically, for example, the first-stage calcination may be carried out in a mixed gas atmosphere of inert gas and reducing gas. Then, the calcined material obtained in the first-stage calcination may be further calcined in the second stage in an inert gas atmosphere, and the calcined powder obtained from the second stage of calcination may be used as the raw material for the thermal plasma method.

[0069] In other words, the mixed powder obtained by mixing can be used as is as a raw material for the thermal plasma method, or the calcined powder obtained after one-stage calcination or multiple-stage calcination can be used as a raw material for the thermal plasma method.

[0070] (1-2) Thermal plasma method and its conditions As the thermal plasma used for the production of composite tungsten oxide particles, any of the candidate plasmas selected from the group consisting of, for example, DC arc plasma, high-frequency plasma, microwave plasma, and low-frequency AC plasma may be used. Also, as the thermal plasma used for the production of infrared absorbing particles, a superposition of two or more plasmas selected from the above candidate group may be used. As the thermal plasma, any of the plasmas selected from plasmas generated by an electrical method of applying a magnetic field to a DC plasma, plasmas generated by irradiation with a high-power laser, and plasmas generated by a high-power electron beam or ion beam may be used.

[0071] However, in any case of thermal plasma used, it is preferable that the thermal plasma has a high-temperature region of 10,000 K to 15,000 K, and in particular, that the plasma can control the generation time of fine particles.

[0072] When raw materials are supplied into a thermal plasma with a high-temperature region, they instantly evaporate in the high-temperature region. The evaporated raw materials then condense as they reach the plasma tail flame, and are rapidly cooled and solidified outside the plasma flame to produce composite tungsten oxide particles.

[0073] The synthesis method will be explained using Figure 1 as an example, with reference to the case where a high-frequency plasma reactor is used.

[0074] The high-frequency plasma reactor 10 shown in Figure 1 has a water-cooled quartz double tube 11 and a reaction vessel 12 connected to the water-cooled quartz double tube 11. A vacuum evacuation device 13 is also connected to the reaction vessel 12.

[0075] A plasma generation gas supply port 14 is provided above the water-cooled quartz double tube 11.

[0076] The water-cooled quartz double tube 11 is configured to supply a sheath gas for generating high-frequency plasma and protecting the quartz tube along its inner wall, and a sheath gas inlet 15 is provided on the upper flange of the water-cooled quartz double tube 11.

[0077] A water-cooled copper coil 16 for generating high-frequency plasma is arranged around the water-cooled quartz double tube 11.

[0078] A raw material powder carrier gas supply port 17 is provided near the plasma generation gas supply port 14, and is connected by piping to a raw material powder supply device 18 that supplies raw material powder.

[0079] For example, composite tungsten oxide particles can be manufactured using the following procedure.

[0080] First, the reaction system, consisting of the water-cooled quartz double tube 11 and the reaction vessel 12, is evacuated to approximately 0.1 Pa (approximately 0.001 Torr) using the vacuum evacuation device 13. After evacuating the reaction system, it is filled with argon gas to create an argon gas flow system at 1 atmosphere.

[0081] Subsequently, argon gas, a mixture of argon and helium (Ar-He mixture gas), and a mixture of argon and nitrogen (Ar-N) gas are added to the reaction vessel 12 as plasma gases. ２ One of the gases selected from the mixed gases is introduced at a flow rate of 30 L / min to 45 L / min. Meanwhile, an Ar-He mixed gas is introduced as a sheath gas flowing just outside the plasma region at a flow rate of 60 L / min to 70 L / min.

[0082] Then, an alternating current is applied to a water-cooled copper coil 16, which is a high-frequency coil arranged around the water-cooled quartz double tube 11, to generate a thermal plasma using a high-frequency electromagnetic field (frequency 4 MHz). At this time, the plate power is set to 30 kW or more and 40 kW or less.

[0083] Furthermore, a mixed powder of element M source and tungsten source, or calcined powder obtained by calcining the mixed powder, can be supplied from the raw material powder carrier gas supply port 17. The raw material powder can be introduced into the thermal plasma at a rate of 25 g / min to 50 g / min using argon gas supplied from the gas supply device 19 as a carrier gas at a rate of 6 L / min to 98 L / min, and the reaction can be carried out for a predetermined time. After the reaction, the generated composite tungsten oxide particles accumulate in the reaction vessel 12 and can be recovered.

[0084] The carrier gas flow rate and raw material supply rate significantly affect the generation time of composite tungsten oxide particles. Therefore, it is preferable to set the carrier gas flow rate to 6 L / min or more and 98 L / min or less, and the raw material supply rate to 25 g / min or more and 50 g / min or less.

[0085] Furthermore, it is preferable to set the plasma gas flow rate to 30 L / min or more and 45 L / min or less, and the sheath gas flow rate to 60 L / min or more and 70 L / min or less. The plasma gas has the function of maintaining a thermal plasma region having a high-temperature part of 10,000 K or more and 15,000 K or less, and the sheath gas has the function of cooling the inner wall surface of the quartz torch in the reaction vessel and preventing the melting of the quartz torch. At the same time, since the plasma gas and sheath gas affect the shape of the plasma region, the flow rates of these gases are important parameters for controlling the shape of the plasma region. The higher the plasma gas flow rate and sheath gas flow rate, the more the shape of the plasma region extends in the direction of gas flow, and the gentler the temperature gradient of the plasma tail flame. As a result, the generation time of the composite tungsten oxide particles is extended, and composite tungsten oxide particles with good crystallinity can be generated.

[0086] After synthesizing composite tungsten oxide particles obtained by the thermal plasma method, depending on the crystallite size and average particle size of the obtained composite tungsten oxide particles, pulverization and dispersion treatments described later can also be performed. When manufacturing composite tungsten oxide particles by the thermal plasma method, the average particle size, crystallite size, and properties such as the a-axis length and c-axis length of the lattice constants of the composite tungsten oxide particles can be controlled by appropriately selecting the plasma conditions and subsequent pulverization and dispersion treatment conditions.

[0087] (2) Solid-phase reaction method The solid-phase reaction method will be explained in the following order: (2-1) Raw materials used in the solid-phase reaction method, and (2-2) Firing conditions in the solid-phase reaction method.

[0088] (2-1) When synthesizing composite tungsten oxide particles used in the solid-phase reaction method by the solid-phase reaction method, a mixed powder of a tungsten source containing tungsten and an element M source containing element M can be used as raw materials. Examples of tungsten sources include elemental tungsten and tungsten compounds. Examples of element M sources include elemental M and element M compounds.

[0089] As the tungsten compound and element M compound can be the same raw materials as those described for the thermal plasma method, their explanation will be omitted.

[0090] Furthermore, the raw material may include a compound containing one or more impurity elements selected from Si, Al, and Zr (hereinafter also referred to as "impurity element compound"). The impurity element compound does not react with the composite tungsten oxide in the subsequent calcination process and suppresses the crystal growth of the composite tungsten oxide, thereby preventing crystal coarsening. The compound containing the impurity element is preferably one or more selected from oxides, hydroxides, nitrates, sulfates, chlorides, and carbonates, with colloidal silica and colloidal alumina being more preferred. The compound containing the impurity element may have a particle size of, for example, 500 nm or less. The particle size here refers to the average particle size measured by dynamic light scattering.

[0091] When mixing starting materials to produce composite tungsten oxide particles, if the starting materials are in solution form, each element contained in the starting materials can be easily and uniformly mixed. For this reason, the tungsten source and at least one of the element M source may be mixed after being in solution form, such as an aqueous solution.

[0092] Therefore, regarding the tungsten source and the element M source, the tungsten element and element M are given a desired composition ratio, for example, the general formula M described above ｘ WO ｙ Wet mixing may be used to satisfy the requirements. If impurity element compounds are included as raw materials, wet mixing can be performed so that the amount of impurity element compounds is 0.5% by mass or less. Then, by drying the resulting mixture, a mixed powder of element M source and tungsten source, or a mixed powder of element M source and tungsten source containing impurity element compounds, can be obtained.

[0093] (2-2) Sintering conditions in the solid-phase reaction method The sintering conditions are not particularly limited, but a mixed powder of element M source and tungsten source, or a mixed powder of element M source and tungsten source containing impurity element compounds, can be sintered in, for example, one step. Sintering may be carried out, for example, under an atmosphere of inert gas alone or a mixed gas atmosphere of inert gas and reducing gas. Sintering may also be carried out in multiple steps, for example, sintering may be carried out under a mixed gas atmosphere of inert gas and reducing gas, and then sintering may be carried out again under an inert gas atmosphere. Furthermore, sintering may be carried out in two or more steps while changing the atmosphere and temperature conditions.

[0094] The firing temperature is preferably close to the temperature at which the composite tungsten oxide particles begin to crystallize. Specifically, for example, the firing temperature is preferably 1000°C or lower, more preferably 850°C or lower, and even more preferably in a temperature range of 500°C to 850°C.

[0095] The reducing gas is not particularly limited, but H ２ Hydrogen can be suitably used as a reducing gas. ２ When using it, the concentration can be appropriately selected according to the calcination temperature and the amount of starting material, and is not particularly limited. H is used as the reducing gas. ２When using this method, H in the mixed gas of inert gas and reducing gas ２ The concentration of is preferably 20% by volume or less, more preferably 10% by volume or less, and even more preferably 7% by volume or less. If the concentration of the reducing gas is 20% by volume or less, WO that does not have solar radiation absorption function will be rapidly reduced. ２ This is because it prevents the formation of certain substances. At this time, by controlling these firing conditions, it is also possible to control the average particle size and crystallite size of the composite tungsten oxide particles.

[0096] H as a reducing gas ２ When using this method, H in the mixed gas of inert gas and reducing gas ２ The concentration can be, for example, preferably 0.1% by volume or more, more preferably 1% by volume or more. H is used as the reducing gas. ２ When using this method, H in the mixed gas of inert gas and reducing gas ２ The concentration may be, for example, 0.1% by volume or more and 20% by volume or less, 0.1% by volume or more and 10% by volume or less, or 1% by volume or more and 7% by volume or less.

[0097] (3) Composite tungsten oxide particles obtained by synthesis methods such as the pulverization and dispersion thermal plasma method or the solid-phase reaction method may aggregate, causing, for example, the dispersed particle size or average particle size of the composite tungsten oxide particles to fall outside the desired range.

[0098] Thus, if the characteristics of the obtained composite tungsten oxide particles, such as particle size, are not within the desired range, the composite tungsten oxide particles can be added to a liquid medium and subjected to crushing, grinding, or dispersion treatments. After crushing or grinding and dispersion treatments, the liquid medium can be removed by drying, and the composite tungsten oxide particles can be recovered.

[0099] As for the drying equipment, one or more types selected from the following are preferably used, but are not limited to these, as they are capable of performing one or more operations selected from heating and reduced pressure, and are easy to mix and recover particles with. These include air dryers, universal mixers, ribbon mixers, vacuum fluidized bed dryers, vibrating fluidized bed dryers, freeze dryers, Ribocones, rotary kilns, spray dryers, Palcon dryers, etc.

[0100] [1-3] Composite Tungsten Oxide Particle Dispersion A composite tungsten oxide particle dispersion (hereinafter also referred to as "dispersion") used to manufacture near-infrared absorbing fibers by incorporating composite tungsten oxide particles into various fibers will be described below.

[0101] A dispersion of composite tungsten oxide particles may include a liquid medium and composite tungsten oxide particles.

[0102] Water can be used as the liquid medium.

[0103] The composite tungsten oxide particle dispersion may also contain dispersants, coupling agents, surfactants, etc., as needed.

[0104] A dispersion of composite tungsten oxide particles can be prepared by grinding and dispersing the composite tungsten oxide particles, which are the raw materials, along with a liquid medium and any dispersants added as needed, using a media stirring mill.

[0105] In a composite tungsten oxide particle dispersion, it is preferable that the composite tungsten oxide particles are dispersed in a liquid medium. Furthermore, it is preferable that the dispersed particles of the composite tungsten oxide have a particle diameter of 1 nm or more and 200 nm or less.

[0106] The amount of composite tungsten oxide particles contained in the composite tungsten oxide particle dispersion is not particularly limited, but may be, for example, 0.01% by mass or more and 80% by mass or less.

[0107] The following will be explained regarding the composite tungsten oxide particle dispersion: (1) liquid medium, (2) nonionic polymer dispersant, (3) grinding and dispersion method, (4) dispersed particle size, and (5) binder and other additives.

[0108] (1) The liquid medium used in the composite tungsten oxide particle dispersion can be water from the viewpoint of reducing environmental impact. For this reason, the composite tungsten oxide particle dispersion of this embodiment can also be called a water dispersion. By using water as the liquid medium, the residual organic solvent in the composite tungsten oxide particles of the near-infrared absorbing fiber manufactured using the composite tungsten oxide particle dispersion can be reduced or even eliminated.

[0109] (2) In order to further improve the dispersion stability of composite tungsten oxide particles in a nonionic polymer dispersant composite tungsten oxide particle dispersion and to avoid coarsening of the dispersed particle size due to re-aggregation, the composite tungsten oxide particle dispersion may contain a dispersant.

[0110] Dispersants that are water-soluble and can surface-coat tungsten oxide particles include nonionic, anionic, and cationic dispersants. Here, it is necessary to consider the compatibility between the resin and the dispersant when forming a masterbatch. Of these, nonionic dispersants can maintain the dispersion state of the particles when forming a masterbatch with polyamide resins. For example, when using anionic or cationic dispersants, composite tungsten oxide particles are difficult to disperse.

[0111] The composite tungsten oxide particle dispersion preferably contains a nonionic polymer dispersant as a dispersant that does not ionize when dissolved in water. As the nonionic polymer dispersant, a polymer dispersant containing one or more selected from pyrrolidone groups, amide groups, and hydroxyl groups may be used. These functional groups adsorb to the surface of the composite tungsten oxide particles by forming bonds such as hydrogen bonds, preventing aggregation and allowing for uniform dispersion of the composite tungsten oxide particles even when used in near-infrared fibers.

[0112] Furthermore, since the nonionic polymer dispersant used in the present invention is water-soluble, it is possible to disperse composite tungsten oxide particles in water in a composite tungsten oxide particle dispersion using water, without using an organic solvent in the liquid medium, which was previously difficult.

[0113] Examples of nonionic polymer dispersants include one or more selected from polyvinylpyrrolidone, polyvinyl alcohol, and the like.

[0114] Polyvinylpyrrolidone can be represented by the following chemical formula (1).

[0115] Polyvinyl alcohol can be represented by the following chemical formula (2).

[0116] The average molecular weight of the nonionic polymer dispersant is not particularly limited, but may be, for example, 1,000 to 400,000, or 5,000 to 200,000.

[0117] In this specification, average molecular weight refers to the weight-average molecular weight measured by the GPC (Gel Permeation Chromatography) method and calculated using a calibration curve based on standard polystyrene.

[0118] The amount of nonionic polymer dispersant added can be selected depending on the type of other polymer dispersants and composite tungsten oxide particles, as well as the specific surface area of ​​the composite tungsten oxide particles, and is not particularly limited.

[0119] For example, the amount of nonionic polymer dispersant added may be 0.1 parts by mass or more and 150 parts by mass or less per 100 parts by mass of composite tungsten oxide particles. That is, the aqueous dispersion of this embodiment may contain nonionic polymer dispersant in a proportion of 0.1% by mass or more and 150% by mass or less when the content of composite tungsten oxide particles is 100 parts by mass. In the aqueous dispersion of this embodiment, by adding 0.1 parts by mass or more and 150 parts by mass or less of nonionic polymer dispersant per 100 parts by mass of composite tungsten oxide particles, a particularly good dispersion state can be achieved for the composite tungsten oxide particles. The amount of nonionic polymer dispersant added may be 0.1 parts by mass or more and 100 parts by mass or less per 100 parts by mass of composite tungsten oxide particles. From the viewpoint of improving the dispersibility of composite tungsten oxide particles, the amount of nonionic polymer dispersant added may be 20 parts by mass or more per 100 parts by mass of composite tungsten oxide particles. Therefore, the amount of nonionic polymer dispersant added may be 20 parts by mass or more and 150 parts by mass or 20 parts by mass or more and 100 parts by mass per 100 parts by mass of composite tungsten oxide particles.

[0120] When the near-infrared absorbing fibers of this embodiment are manufactured using an aqueous dispersion, the nonionic polymer dispersant may also be present in the fibers, and depending on the amount of nonionic polymer dispersant added, it may affect the affinity of the fibers to water. By setting the amount of nonionic polymer dispersant added to the aqueous dispersion to 150 parts by mass or less per 100 parts by mass of composite tungsten oxide particles, the effect on the affinity of the fibers to water can be reduced, for example. Therefore, by setting the amount of nonionic polymer dispersant added to the aqueous dispersion to 150 parts by mass or less per 100 parts by mass of composite tungsten oxide particles, the fibers can exhibit the desired water-repellent effect when treated with a water-repellent finish.

[0121] In this embodiment, the composite tungsten oxide particle dispersion is modified with a nonionic polymer dispersant on the surface of the composite tungsten oxide particles, thus improving dispersibility even when water is used as the dispersion medium. Therefore, it can be used in the production of near-infrared absorbing fibers containing composite tungsten oxide particles.

[0122] Since the composite tungsten oxide particle dispersion of this embodiment does not require the addition of an organic solvent, the content of organic solvents can be reduced. For example, low-boiling point solvents such as toluene and MIBK can be reduced to 0.1% by mass or less, 0.01% by mass or less, or even 0% by mass. In other words, it can be reduced to below the detection limit.

[0123] (3) Grinding and Dispersion Method A suitable method for dispersing the composite tungsten oxide particles into a dispersion is one that allows for uniform dispersion of the composite tungsten oxide particles in the dispersion without aggregation.

[0124] Examples of grinding and dispersion methods include grinding and dispersion processes using devices such as bead mills, ball mills, sand mills, paint shakers, and ultrasonic homogenizers. Among these, grinding and dispersion using media stirring mills such as bead mills, ball mills, sand mills, and paint shakers, which utilize media such as beads, balls, and Ottawa sand, is preferable because it requires less time to achieve the desired dispersed particle size.

[0125] The grinding and dispersion process using a media stirring mill simultaneously disperses the composite tungsten oxide particles into the dispersion liquid and further micronizes them through collisions between the particles and collisions between the media and the composite tungsten oxide particles. Therefore, the composite tungsten oxide particles can be dispersed into even finer particles. In other words, the composite tungsten oxide particles can be ground and dispersed.

[0126] In the case of finely ground and dispersed composite tungsten oxide particles, the grinding and dispersion processing conditions can be adjusted so that the crystallite size is preferably 10 nm to 100 nm, more preferably 10 nm to 80 nm, even more preferably 10 nm to 60 nm, and most preferably 10 nm to 40 nm, in order to exhibit excellent infrared absorption properties.

[0127] (4) Dispersed particle size The dispersed particle size of the composite tungsten oxide particles in the dispersion of composite tungsten oxide particles is preferably 800 nm or less, more preferably 200 nm or less, even more preferably 10 nm to 200 nm, and particularly preferably 10 nm to 100 nm. This is because particles of composite tungsten oxide with a dispersed particle size of 800 nm or less do not completely absorb light due to scattering and have transparency. Furthermore, if the dispersed particle size of the composite tungsten oxide particles is 200 nm or less, light in the visible light region is not scattered by geometric scattering or Mie scattering, so haze is reduced and visible light transmittance can be increased. Furthermore, in the Rayleigh scattering region, scattered light is reduced inversely proportional to the sixth power of the particle size, so as the dispersed particle size decreases, the scattering of light is reduced and transparency is improved.Therefore, when the dispersed particle size is 200 nm or less, scattered light is very little, and as a result, discoloration caused by composite tungsten oxide particles is less likely to occur in textile materials such as clothing.

[0128] Here, we will briefly explain the particle size of the dispersed composite tungsten oxide particles in a dispersion of composite tungsten oxide particles. The dispersed particle size refers to the particle size of the individual composite tungsten oxide particles dispersed in the solvent, as well as the particle size of aggregated particles formed by the aggregation of the composite tungsten oxide particles. This can be measured using various commercially available particle size analyzers. For example, the dispersed particle size of the composite tungsten oxide particles can be measured by taking a sample of the dispersion of composite tungsten oxide particles and measuring the sample using the ELS-8000 manufactured by Otsuka Electronics Co., Ltd., which is based on the principle of dynamic light scattering.

[0129] The composite tungsten oxide particle dispersion may contain composite tungsten oxide particles in an amount of 0.01% to 80% by mass. This is because a composite tungsten oxide particle dispersion with a composite tungsten oxide particle content of 0.01% to 80% by mass exhibits excellent liquid stability. When appropriate liquid media, dispersants, coupling agents, and surfactants are selected, the dispersion will not gel or particle sedimentation will not occur for more than six months even when placed in a constant temperature bath at 40°C, and the dispersed particle size can be maintained, for example, within a range of 200 nm or less.

[0130] It should be noted that the particle size of the composite tungsten oxide particle dispersion may differ from the particle size of the composite tungsten oxide particles dispersed in the yarn or other materials constituting the near-infrared absorbing fibers. This is because the composite tungsten oxide particles may aggregate in the composite tungsten oxide particle dispersion. Furthermore, when manufacturing or processing the yarn or other materials constituting the near-infrared absorbing fibers using the composite tungsten oxide particle dispersion, the composite tungsten oxide particles may be loosened and the aggregation may be undone. However, the smaller the particle size of the composite tungsten oxide particle dispersion, the smaller the particle size of the dispersed near-infrared absorbing fibers tends to be. Therefore, controlling the particle size of the composite tungsten oxide particle dispersion is important for controlling the properties of the near-infrared absorbing fibers obtained in subsequent processes.

[0131] The particle size of the composite tungsten oxide particles can be selected according to their intended use. First, for applications where transparency must be maintained, it is preferable to have a particle size of 800 nm or less. This is because particles with a particle size of 800 nm or less do not completely absorb light due to scattering, resulting in a faint blue tint, while maintaining visibility in the visible light region and efficiently maintaining transparency. When transparency in the visible light region is particularly important, it is preferable to further consider scattering by the particles.

[0132] It should be noted that the dispersed particle diameter of the composite tungsten oxide particles mentioned above is a concept that includes the diameter of the aggregates of the composite tungsten oxide particles, and is a different concept from the average particle diameter of the composite tungsten oxide particles described previously.

[0133] When prioritizing the reduction of light scattering by particles, that is, when prioritizing the design properties such as dyeability of near-infrared absorbing fibers containing composite tungsten oxide particles and textile products using them, the dispersed particle diameter is preferably 200 nm or less, more preferably 10 nm to 200 nm, and even more preferably 10 nm to 100 nm. This is because, if the dispersed particle diameter is small, the scattering of light in the visible light region due to geometric scattering or Mie scattering is reduced, and as a result, the composite tungsten oxide particles can efficiently absorb near-infrared light while maintaining transparency. In other words, when the dispersed particle diameter is 200 nm or less, geometric scattering or Mie scattering is reduced, and the Rayleigh scattering region is reached. In the Rayleigh scattering region, scattered light is proportional to the sixth power of the dispersed particle diameter, so as the dispersed particle diameter decreases, scattering is reduced and transparency improves. Near-infrared absorbing components containing composite tungsten oxide particles absorb light in the near-infrared region, particularly around 900 nm to 2200 nm wavelengths, resulting in a transmission color that is often blue to green. Therefore, transparency can be ensured by reducing the dispersion particle size of the composite tungsten oxide particles to 200 nm or less. However, if transparency is a priority, the dispersion particle size is preferably 150 nm or less, more preferably 100 nm or less. From the viewpoint of avoiding light scattering, a smaller dispersion particle size is preferable, but industrial manufacturing is easy if the dispersion particle size is 10 nm or larger.

[0134] Furthermore, if the dispersed particle size is 200 nm or less, it is possible to avoid a decrease in spinnability due to clogging of the filter or breakage of the yarn during subsequent fiber-making processes such as spinning and drawing. Also, if the dispersed particle size is large, even if spinning can be performed, problems such as breakage of the yarn may occur during the drawing process, and it may also be difficult to uniformly mix and disperse the particles in the spinning raw material. From this viewpoint as well, it is preferable that the dispersed particle size is 200 nm or less.

[0135] Near-infrared absorbing films manufactured by dispersing composite tungsten oxide particles in or on a suitable medium can absorb sunlight, particularly near-infrared light, more efficiently than films manufactured by dry methods or by CVD or spray methods, without relying on optical interference effects. Furthermore, near-infrared absorbing films manufactured by dispersing composite tungsten oxide particles in or on a suitable medium can simultaneously transmit visible light. Note that films manufactured by dry methods refer to films produced by vacuum deposition methods such as sputtering, vapor deposition, ion plating, and chemical vapor deposition (CVD). Therefore, the near-infrared absorbing fibers of this embodiment, containing composite tungsten oxide particles, can efficiently absorb near-infrared light and generate heat.

[0136] (5) The dispersed powder can also be obtained by evaporating water from the dispersed powder composite tungsten oxide particle dispersion. That is, the dispersed powder composite tungsten oxide particle dispersion can also be obtained by coating the surface with a nonionic polymer dispersant.

[0137] The specific method for evaporating water from the dispersion is not particularly limited; for example, one or more methods selected from natural drying in the atmosphere, heat drying using a dryer, vacuum drying in a vacuum atmosphere, spray drying, etc., can be used. Furthermore, when preparing the dispersion powder, multiple methods for evaporating water from the dispersion can be combined and carried out in multiple stages as needed.

[0138] The dispersed powder obtained from the composite tungsten oxide particle dispersion may contain residual moisture from the aqueous dispersion. However, it is preferable that the moisture content of the dispersed powder be low. Specifically, it may be 8% by mass or less, 6% by mass or less, or 5% by mass or less. By keeping the moisture content of the dispersed powder at 8% by mass or less, the moisture can be further reduced by heating during the melting and kneading process in masterbatch formation, thereby keeping the moisture content of the masterbatch low.

[0139] While it is preferable for the dispersion powder of this embodiment to have a low moisture content, it is difficult to completely eliminate moisture from the dispersion powder considering cost and productivity. For this reason, the dispersion powder of this embodiment may contain moisture, and the moisture content of the dispersion powder of this embodiment may be, for example, 0.1% by mass or more, 0.5% by mass or more, or 1% by mass or more.

[0140] The moisture content of the dispersed powder in this embodiment may be 0.1% by mass or more and 8% by mass or less, 0.5% by mass or more and 6% by mass or less, or 1% by mass or more and 5% by mass or less. In this specification, the moisture content of the dispersed powder can be calculated by heating the dispersed powder sample at 125°C for 10 minutes and considering the decrease in mass after heating compared to before heating as being due to the moisture contained in the dispersed powder. For example, when heating at 125°C for 10 minutes, if the mass of the dispersed powder sample before heating is W1 and the mass of the dispersed powder sample after heating is W2, the moisture content can be calculated as follows: Moisture content = (W1 - W2) ÷ W1 × 100.

[0141] (6) Binders and other additives

[0142] Furthermore, to improve the near-infrared absorption properties of the composite tungsten oxide particle dispersion or the near-infrared absorbing fibers, the dispersion may also contain further near-infrared absorbing particles.

[0143] Near-infrared absorbing particles are, for example, those with the general formula XB ｍ Examples include one or more particles selected from borides, ATO, and ITO, represented by (where X is a metallic element selected from alkaline earth elements or rare earth elements containing yttrium, B is boron, and m satisfies 4 ≤ m ≤ 6.3). The proportion of near-infrared absorbing particles in the dispersion can be appropriately selected according to the required near-infrared absorption characteristics, etc., and is not particularly limited.

[0144] Alkaline earth elements include Ca (calcium), Sr (strontium), Ba (barium), and Ra (radium). Rare earth elements include Sc (scandium), Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium).

[0145] Furthermore, in order to adjust the color tone of the composite tungsten oxide particle dispersion and the near-infrared absorbing fibers, the dispersion may also contain known inorganic pigments such as carbon black and iron oxide, as well as known organic pigments.

[0146] The composite tungsten oxide particle dispersion may contain known ultraviolet absorbers, known organic infrared absorbers, or phosphorus-based color inhibitors.

[0147] The dispersion may further contain particles capable of emitting far-infrared radiation. Examples of particles capable of emitting far-infrared radiation include ZrO ２ SiO ２ , TiO ２ Al ２ O ３ MnO ２ , MgO, Fe ２ O ３ Metal oxides such as CuO, carbides such as ZrC, SiC, and TiC, ZrN, Si ３ N ４ Examples include nitrides such as AlN.

[0148] [2] Near-infrared absorbing fibers [2-1] Near-infrared absorbing fibers The near-infrared absorbing fibers according to this embodiment will be described below.

[0149] Figure 2 shows a schematic diagram of the near-infrared absorbing fiber of this embodiment. Figure 2 schematically shows a cross-sectional view of the near-infrared absorbing fiber 20 in a plane passing through the central axis CA of the fiber 21. As shown in Figure 2, the near-infrared absorbing fiber 20 of this embodiment may include the fiber 21 and composite tungsten oxide particles 22.

[0150] The arrangement of the composite tungsten oxide particles 22 is not particularly limited, but the composite tungsten oxide particles 22 can be arranged in one or more selected portions from the surface 21A and interior 21B of the fiber 21, for example. Figure 2 is a schematic diagram showing an example in which the composite tungsten oxide particles 22 are arranged on both the surface 21A and interior 21B of the fiber 21, but the invention is not limited to this configuration. The composite tungsten oxide particles 22 may be arranged on only one of the surface 21A and interior 21B of the fiber 21. In addition, although the composite tungsten oxide particles 22 are depicted as spherical particles in Figure 2, the shape of the composite tungsten oxide particles 22 is not limited to this configuration and can have any shape.

[0151] The following describes the components contained in the near-infrared absorbing fiber of this embodiment.

[0152] (1) Fibers (1-1) Types of Fibers The fibers contained in the near-infrared absorbing fibers of this embodiment can be selected in various ways depending on the application and are not particularly limited. Preferably, the fibers are one or more types selected from a group of fibers consisting of synthetic fibers, semi-synthetic fibers, natural fibers, regenerated fibers, and inorganic fibers, and mixed yarns made by blending, plying, or filamenting two or more types of fibers selected from the above fiber group. That is, fibers selected from the above fiber group can be used, and fibers selected from the above mixed yarns can also be used.

[0153] In particular, considering the ease with which composite tungsten oxide particles can be incorporated into the interior of the fibers, and the long-lasting heat retention, it is preferable that the fibers include synthetic fibers, and more preferably that they are composed of synthetic fibers.

[0154] If the fibers include synthetic fibers, the fibers contained in the near-infrared absorbing fibers of this embodiment may be made solely of synthetic fibers, or they may contain one or more fibers from the group consisting of synthetic fibers, semi-synthetic fibers, natural fibers, regenerated fibers, and inorganic fibers. If the fibers also contain fibers other than synthetic fibers, the fibers may consist of one or more fibers selected from synthetic fibers and one or more fibers selected from the above-mentioned group, such as blended yarns, plywoods, or mixed fibers.

[0155] The following describes each type of fiber.

[0156] (1-1-1) Synthetic Fibers The synthetic fibers are not particularly limited, but for example, one or more selected from polyurethane fibers, polyamide fibers, acrylic fibers, polyester fibers, polyolefin fibers, polyvinyl alcohol fibers, polyvinylidene chloride fibers, polyvinyl chloride fibers, polyether ester fibers, etc., can be suitably used.

[0157] Examples of polyamide fiber materials include nylon, nylon 6, nylon 66, nylon 11, nylon 610, nylon 612, aromatic nylon, and aramid.

[0158] Examples of acrylic fiber materials include polyacrylonitrile, acrylonitrile-vinyl chloride copolymer, and modacrylic.

[0159] Examples of polyester fiber materials include polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, and polyethylene naphthalate.

[0160] Examples of materials for polyolefin fibers include polyethylene, polypropylene, and polystyrene.

[0161] Examples of materials for polyvinyl alcohol-based fibers include vinylon.

[0162] Examples of materials for polyvinylidene chloride fibers include vinylidene.

[0163] Examples of materials for polyvinyl chloride fibers include polyvinyl chloride.

[0164] Examples of polyether ester fiber materials include Lexe and Success.

[0165] (1-1-2) Semi-synthetic fibers The semi-synthetic fibers are preferably one or more selected from, for example, cellulose fibers, protein fibers, chlorinated rubber, hydrochloric acid rubber, etc.

[0166] Examples of materials for cellulose fibers include acetate, triacetate, and acetate oxide.

[0167] Examples of protein-based fiber materials include Promix.

[0168] (1-1-3) Natural Fibers: It is preferable that the natural fibers are one or more types selected from, for example, plant fibers, animal fibers, mineral fibers, etc.

[0169] Examples of plant fiber materials include cotton, kapok, flax, hemp, jute, Manila hemp, sisal, New Zealand hemp, oak, palm, rush, and straw.

[0170] Examples of animal fiber materials include wool such as sheep's wool, goat's wool, mohair, cashmere, alpaca, angora, camel, and vicuña, as well as silk, down, and feathers.

[0171] Examples of mineral fiber materials include asbestos.

[0172] (1-1-4) Regenerated Fibers The regenerated fibers are preferably one or more selected from, for example, cellulose fibers, protein fibers, algin fibers, rubber fibers, chitin fibers, mannan fibers, etc.

[0173] Examples of cellulose fiber materials include rayon, viscose rayon, cupro, polynosic, and copper ammonia rayon.

[0174] Examples of protein-based fibers include casein fiber, peanut protein fiber, corn protein fiber, soy protein fiber, and regenerated silk.

[0175] (1-1-5) Inorganic Fibers As inorganic fibers, one or more types selected from, for example, metal fibers, carbon fibers, silicate fibers, etc., can be used.

[0176] Examples of metal fibers include metal fibers, gold threads, silver threads, and heat-resistant alloy fibers.

[0177] Examples of silicate fibers include glass fibers, slag fibers, and rock fibers.

[0178] (1-2) Fiber shape The cross-sectional shape of the fiber is not particularly limited, but examples include one or more types selected from circular, triangular, hollow, flattened, Y-shaped, star-shaped, core-sheath type, etc.

[0179] The inclusion and arrangement of composite tungsten oxide particles in the fiber are not particularly limited. For example, if the cross-sectional shape of the fiber is core-sheath type, the composite tungsten oxide particles may be included in either the core or the sheath of the fiber. Furthermore, the shape of the fiber is not particularly limited; it may be a filament (long fiber) or a staple (short fiber).

[0180] (2) Composite tungsten oxide particles The near-infrared absorbing fiber of this embodiment may contain composite tungsten oxide particles.

[0181] Since the composite tungsten oxide particles originate from the composite tungsten oxide particle dispersion described above, they can have a nonionic polymer dispersant on their surface. That is, the composite tungsten oxide particles may be modified with a nonionic polymer dispersant. In one aspect of this disclosure, since the composite tungsten oxide particle dispersion uses water as the liquid medium, residual organic solvents caused by the dispersion can be reduced, or even eliminated.

[0182] The content of the nonionic polymer dispersant in the near-infrared absorbing fiber of this embodiment is not particularly limited, but is preferably 20% by mass or less, and more preferably 10% by mass or less. By limiting the amount of nonionic polymer dispersant contained in the near-infrared absorbing fiber to 20% by mass or less, the influence of the nonionic polymer dispersant on the function imparted to the near-infrared absorbing fiber is reduced, making it easier for the near-infrared absorbing fiber to exhibit the desired function.

[0183] The nonionic polymer dispersant contained in the near-infrared absorbing fiber of this embodiment is preferably 20% by mass or less, and more preferably 10% by mass or less. By limiting the amount of nonionic polymer dispersant contained in the near-infrared absorbing fiber to 20% by mass or less, the influence of the nonionic polymer dispersant on the function imparted to the near-infrared absorbing fiber is reduced, making it easier for the near-infrared absorbing fiber to exhibit the desired function.

[0184] The nonionic polymer dispersant contained in the near-infrared absorbing fiber of this embodiment can be more than 0% by mass. Therefore, the near-infrared absorbing fiber of this embodiment may contain more than 0% by mass and 20% by mass or more than 0% by mass and 10% by mass or less of the nonionic polymer dispersant.

[0185] Furthermore, the statement that the composite tungsten oxide particles do not contain residual organic solvents means that they were not intentionally added, and does not exclude the possibility of unintentional contamination during the manufacturing process.

[0186] The content of composite tungsten oxide particles contained in the near-infrared absorbing fiber of this embodiment is not particularly limited, but may be, for example, 0.001% by mass or more and 80% by mass or less relative to the solid content of the fiber. Furthermore, considering the weight and raw material cost of the near-infrared absorbing fiber containing composite tungsten oxide particles, the content of composite tungsten oxide particles in the near-infrared absorbing fiber of this embodiment may be 0.005% by mass or more and 50% by mass or less, 0.005% by mass or more and 30% by mass or less, or even 0.005% by mass or more and 20% by mass or less, 0.005% by mass or more and 10% by mass or less, or 0.005% by mass or more and 5% by mass or less, relative to the solid content of the fiber.

[0187] By setting the content of composite tungsten oxide particles in the near-infrared absorbing fiber of this embodiment to 0.001% by mass or more, sufficient near-infrared radiation can be absorbed and heat generation can be obtained even with a thin fabric. By setting the content of composite tungsten oxide particles in the near-infrared absorbing fiber of this embodiment to 80% by mass or less, it is possible to avoid a decrease in spinnability due to clogging of the filter or breakage of the yarn during the spinning process.

[0188] By increasing the content of composite tungsten oxide particles in near-infrared absorbing fibers to 0.001% by mass or more, the heat generation effect when absorbing near-infrared rays can be particularly enhanced. Furthermore, by reducing the content of composite tungsten oxide particles in near-infrared absorbing fibers to 80% by mass or less, the strength of the near-infrared absorbing fibers can be increased. By increasing the strength of the near-infrared absorbing fibers, it is possible to particularly prevent the fabric from tearing due to pulling or needle pressure during sewing, and to prevent seams from unraveling. In addition, it is possible to prevent tearing due to friction when the fabric is made, increase the firmness and resilience of the fabric, and prevent deformation and wrinkles.

[0189] Near-infrared absorbing fibers and general-purpose fibers (fibers that do not contain composite tungsten oxide particles) can be used in combination, and the two can be integrated into a single yarn during the twisting process. This allows the near-infrared absorbing fibers to possess the performance characteristics of the fibers while also providing the durability and flexibility of the general-purpose fibers. Furthermore, it can reduce costs.

[0190] Since the preferred composition, average particle size, crystallite size, etc., for composite tungsten oxide particles have already been explained, we will omit further explanation here.

[0191] (3) Additives and particles of far-infrared emitting material The near-infrared absorbing fiber of this embodiment may contain one or more additives selected from antioxidants, flame retardants, deodorants, insecticides, antibacterial agents, ultraviolet absorbers, etc., as long as it does not impair the performance of the fiber.

[0192] The near-infrared absorbing fiber according to this embodiment may contain, in addition to composite tungsten oxide particles, particles of far-infrared emitting material (hereinafter also referred to as "far-infrared particles") which are particles capable of emitting far-infrared rays, arranged and contained in one or more selected portions from the surface and interior of the fiber. Examples of far-infrared particles include ZrO ２ SiO ２ , TiO ２ Al ２ O ３ MnO ２ , MgO, Fe ２ O ３ Metal oxides such as CuO, carbides such as ZrC, SiC, and TiC, ZrN, Si３ N ４ Particles containing one or more types selected from nitrides such as AlN can be used.

[0193] Composite tungsten oxide particles have the property of absorbing solar energy with wavelengths between 0.3 μm and 3 μm, and in particular selectively absorb light in the near-infrared region with wavelengths between 0.9 μm and 2.2 μm, converting it into heat or re-radiating it.

[0194] In contrast, far-infrared particles have the ability to receive energy absorbed by composite tungsten oxide particles, convert that energy into thermal energy in the mid- and far-infrared wavelength range, and radiate it. For example, ZrO ２ The particle can convert the received energy into thermal energy with a wavelength of 2 μm to 20 μm and radiate it.

[0195] Therefore, when far-infrared particles coexist with composite tungsten oxide particles within or on the surface of the fiber, the solar energy absorbed by the composite tungsten oxide can be efficiently converted into far-infrared rays on or inside the near-infrared absorbing fiber, resulting in more effective heat generation.

[0196] When the near-infrared absorbing fiber of this embodiment contains far-infrared particles, the amount of far-infrared particles is not particularly limited, but it is preferably, for example, 0.001% by mass or more and 80% by mass or less relative to the fiber solids.

[0197] By setting the far-infrared particle content in the near-infrared absorbing fiber of this embodiment to 0.001% by mass or more, a sufficient thermal energy radiation effect can be obtained even with a thin fabric. By setting the far-infrared particle content in the near-infrared absorbing fiber of this embodiment to 80% by mass or less, it is possible to avoid a decrease in spinnability due to clogging of the filter or breakage of the yarn during the spinning process.

[0198] (4) Characteristics of near-infrared absorbing fibers As described above, the near-infrared absorbing fibers according to this embodiment contain composite tungsten oxide particles as near-infrared absorbing components in the fibers.

[0199] The near-infrared absorbing fiber according to this embodiment can efficiently absorb near-infrared rays from sunlight and other sources with the inclusion of a small amount of composite tungsten oxide particles, making it possible to provide a near-infrared absorbing fiber with excellent heat retention properties. Furthermore, the near-infrared absorbing fiber according to this embodiment has excellent weather resistance and transparency and is low cost. Moreover, since the amount of composite tungsten oxide particles added can be reduced in the near-infrared absorbing fiber according to this embodiment, the design of the textile product itself is not impaired, and the basic physical properties of the fiber, such as strength and elongation, are not compromised.

[0200] As a result, the near-infrared absorbing fiber according to this embodiment can be used in a variety of applications, such as textile products for cold weather protection, sportswear, stockings, curtains, and other industrial textile products.

[0201] [2-2] Method for Manufacturing Near-Infrared Absorbing Fibers The method for manufacturing near-infrared absorbing fibers according to this embodiment will now be described. As the near-infrared absorbing fibers described above can be manufactured according to the method for manufacturing near-infrared absorbing fibers according to this embodiment, the matters already described will be omitted from the explanation.

[0202] The method for producing near-infrared absorbing fibers according to this embodiment may include a near-infrared absorbing fiber manufacturing step for preparing near-infrared absorbing fibers containing fibers and composite tungsten oxide particles.

[0203] Since the composite tungsten oxide particles and fibers have already been explained, we will omit the explanation here.

[0204] In the near-infrared absorbing fiber manufacturing process, specifically, for example, composite tungsten oxide particles can be placed on the surface of the fiber and at one or more selected locations within the fiber.

[0205] The method for arranging the composite tungsten oxide particles at one or more selected locations on the surface and inside of the fiber is not particularly limited. For example, any of the following methods (a) to (d) can be used: (a) A method of mixing composite tungsten oxide particles into a raw material polymer of synthetic fibers and spinning the fibers. (b) A method of preparing a masterbatch containing a high concentration of composite tungsten oxide particles in a portion of the raw material polymer in advance, and then diluting the masterbatch to a predetermined concentration before spinning. (c) A method of preparing a dispersion solution in which composite tungsten oxide particles are dispersed in a raw material monomer or oligomer solution, and then synthesizing the target raw material polymer using the dispersion solution while simultaneously dispersing the composite tungsten oxide particles in the raw material polymer, and then spinning the fibers. (d) A method of attaching composite tungsten oxide particles to the surface of a fiber obtained by spinning in advance using a binder or the like.

[0206] Here, we will further explain the methods (a) to (d) described above with specific examples. However, the resins used are not limited to the following examples. Method (a): We will explain using the case where polyester fibers are used as the fibers.

[0207] First, a dispersion of composite tungsten oxide particles is added to polyethylene terephthalate resin pellets, which are a thermoplastic resin, and uniformly mixed in a blender. Then, the dispersion medium, such as a liquid medium, is removed. The mixture from which the dispersion medium has been removed is melt-kneaded in a twin-screw extruder to obtain a masterbatch containing composite tungsten oxide particles. The obtained masterbatch containing composite tungsten oxide particles is melt-mixed at or near the melting temperature of the resin, and near-infrared absorbing fibers can be produced by spinning, for example, by various known methods.

[0208] The method for manufacturing the masterbatch described above is not particularly limited. For example, a mixture in which composite tungsten oxide particles are dispersed in a thermoplastic resin can be prepared by first melt-mixing a dispersion of composite tungsten oxide particles, granular or pelletized thermoplastic resin, and other additives as needed, using a kneader while removing the dispersion medium.

[0209] When mixing raw materials, one or more types of mixers selected from, for example, a ribo blender, tumbler, Nauter mixer, Henschel mixer, super mixer, planetary mixer, etc., can be used. Furthermore, when melting and mixing the resulting mixture of raw materials, one or more types of kneaders selected from, for example, a Banbury mixer, kneader, roll mixer, kneader-ruder, single-screw extruder, twin-screw extruder, etc., can be used.

[0210] The method for preparing a mixture in which composite tungsten oxide particles are dispersed in a resin is not limited to the above-described form.

[0211] For example, after preparing a dispersion of composite tungsten oxide particles, the dispersion medium, such as the liquid medium of the dispersion, is first removed by a known method. Then, the powder (dispersed powder) obtained by removing the dispersion medium is uniformly melt-mixed with granular or pelletized thermoplastic resin and, if necessary, other additives to produce a mixture in which composite tungsten oxide particles are dispersed in thermoplastic resin. Alternatively, to produce a mixture in which composite tungsten oxide particles are dispersed in thermoplastic resin, a method can be used in which the composite tungsten oxide particles are directly added to the thermoplastic resin and melt-mixed.

[0212] In this embodiment, when a dispersion using water as the liquid medium is used for the masterbatch, some of the residual moisture in the dispersed powder of the raw materials to be melted and kneaded evaporates, and the remainder remains in the masterbatch. The moisture content of the masterbatch is preferably low, and may be 0.8% by mass or less, or 0.6% by mass or less.

[0213] While a low moisture content in the masterbatch is preferable, it may be 0.0001% by mass or more from the viewpoint of cost and productivity. Therefore, the moisture content of the masterbatch may be 0.0001% by mass or more and 0.8% by mass or less, or 0.0001% by mass or more and 0.6% by mass or less.

[0214] When spinning using a masterbatch, the moisture content can be further reduced by keeping the masterbatch dry.

[0215] The moisture content of the masterbatch may be evaluated by the Karl Fischer method, with a heating temperature of 160°C.

[0216] A masterbatch containing composite tungsten oxide particles can be obtained by kneading a mixture of composite tungsten oxide particles obtained by the above method and a thermoplastic resin in a vented uniscrew or twin-screw extruder and processing it into pellets. Method (b): A masterbatch containing composite tungsten oxide particles is prepared using a method similar to that in (a). Then, near-infrared absorbing fibers can be produced by melt-mixing this masterbatch and a masterbatch made of polyethylene terephthalate resin without composite tungsten oxide particles at a desired mixing ratio near the melting temperature of the resin and spinning them according to a known method. Method (c): For example, the case in which urethane fibers are used as the fibers will be explained.

[0217] A polymeric diol containing composite tungsten oxide particles is reacted with an organic diisocyanate in a twin-screw extruder to synthesize an isocyanate-terminated prepolymer. A chain extender is then reacted with this prepolymer to produce a polyurethane solution (raw polymer). Near-infrared absorbing particles can be produced by spinning this polyurethane solution according to various known methods. Method (d): For example, the case in which composite tungsten oxide particles are attached to the surface of a natural fiber will be explained.

[0218] First, a processing solution is prepared by mixing a composite tungsten oxide particle dispersion according to one aspect of this disclosure with one or more binder resins selected from acrylic, epoxy, urethane, and polyester, and a solvent such as water.

[0219] Next, the natural fibers are immersed in the prepared treatment solution, or the prepared treatment solution is impregnated into the natural fibers by padding, printing, or spraying, and then dried. This allows infrared-absorbing particles to be attached to the natural fibers. Method (d) can be applied to synthetic fibers, semi-synthetic fibers, regenerated fibers, inorganic fibers, or blends, synthetic yarns, or blended fibers thereof, in addition to the natural fibers described above.

[0220] Furthermore, the method for preparing the composite tungsten oxide particle dispersion that can be used when carrying out the methods (a) to (d) described above is not particularly limited, and for example, the composite tungsten oxide particle dispersion can be prepared by the method described above.

[0221] When attaching and mixing composite tungsten oxide particles to fibers or polymers that serve as their raw materials, the dispersion of composite tungsten oxide particles can also be directly mixed with the fibers or polymers.

[0222] Here, we will explain the content of composite tungsten oxide particles in the near-infrared absorbing fiber of this embodiment.

[0223] The near-infrared absorption capacity per unit weight of the composite tungsten oxide particles in the near-infrared absorbing fiber of this embodiment is very high, so it can exert its effect with about one-quarter to one-tenth the amount used compared to ITO or ATO. Specifically, the content of composite tungsten oxide particles contained on the surface or inside the fiber is preferably, for example, 0.001% by mass or more and 80% by mass or less relative to the solid content of the fiber. Furthermore, considering the mass of the fiber and raw material costs after the addition of composite tungsten oxide particles, the content of composite tungsten oxide particles in the near-infrared absorbing fiber of this embodiment may be 0.005% by mass or more and 50% by mass or less, 0.005% by mass or more and 30% by mass or less, or even 0.005% by mass or more and 20% by mass or less, 0.005% by mass or more and 10% by mass or less, or 0.005% by mass or more and 5% by mass or less.

[0224] If the content of composite tungsten oxide particles in the near-infrared absorbing fiber of this embodiment is 0.001% by mass or more, a sufficient near-infrared absorption effect can be obtained even with a thin fabric. Furthermore, if the content of composite tungsten oxide particles in the near-infrared absorbing fiber of this embodiment is 80% by mass or less, a decrease in spinnability due to clogging of the filter or breakage of the yarn can be avoided during the spinning process.

[0225] Furthermore, from the viewpoint of maintaining the physical properties of the fibers, it is preferable to have a low content of composite tungsten oxide particles. From this viewpoint, it is even more preferable that the content of composite tungsten oxide particles be 50% by mass or less.

[0226] The near-infrared absorbing fiber of this embodiment can use a composite tungsten oxide particle dispersion according to one aspect of the present disclosure as a raw material, thereby reducing the content of organic solvents. The near-infrared absorbing fiber of this embodiment can have a residual organic solvent content of, for example, 5% by mass or less, or even 0% by mass.

[0227] The residual organic solvent here refers to the content ratio of organic solvents originating from the liquid medium of the composite tungsten oxide particle dispersion. [Textile Products] The textile products of this embodiment are made by processing the near-infrared absorbing fibers described above and may include the near-infrared absorbing fibers according to one aspect of this disclosure. The textile products of this embodiment may consist of the near-infrared absorbing fibers described above, or they may contain the near-infrared absorbing fibers of this embodiment and other fibers.

[0228] The amount of composite tungsten oxide particles contained in textile products is 0.02 g / m² per unit area of ​​the textile product. ２ The above is preferable, and 0.03 g / m ２ The above is even more preferable, 0.04 g / m ２ The above is more preferable. The content of composite tungsten oxide particles per unit area of ​​the textile product is 0.02 g / m². ２ By doing so, a sufficient heat-generating effect can be expected when textile products absorb near-infrared rays.

[0229] The amount of composite tungsten oxide particles contained in textile products is 1.0 g / m² per unit area of ​​the textile product. ２ The following may also be true: 0.6 g / m ２ The following is also acceptable: The content of composite tungsten oxide particles per unit area of ​​the textile product is 1.0 g / m². ２ By doing the following, color changes caused by composite tungsten oxides can be reduced. This prevents the development of vivid colors such as yellow and orange in textile products, thereby enhancing their design appeal.

[0230] Therefore, the amount of the composite tungsten oxide particles contained in the textile product may be 0.02 g / m or more and 1.0 g / m or less per unit area of the textile product. ２ or more and 1.0 g / m ２ or less, and may also be 0.03 g / m ２ or more and 1.0 g / m ２ or less, and may also be 0.04 g / m ２ or more and 1.0 g / m ２ or less, and may also be 0.04 g / m ２ or more and 0.6 g / m ２ or less.

[0231] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. [1] Regarding the evaluation method (crystal structure, crystallite size) For the measurement of the crystal structure and crystallite size of the composite tungsten oxide particles obtained in the following examples and comparative examples, the composite tungsten oxide particles obtained by removing the liquid medium from the composite tungsten oxide particle dispersion were used.

[0232] In measuring the crystal structure and crystallite size of the composite tungsten oxide particles, the X-ray diffraction pattern of the composite tungsten oxide particles was measured. The measurement of the X-ray diffraction pattern was performed by the powder X-ray diffraction method (θ-2θ method) using a powder X-ray diffractometer (X'Pert-PRO / MPD manufactured by PANalytical Co., Ltd.). Then, the crystal structure of the composite tungsten oxide contained in the composite tungsten oxide particles was specified from the obtained X-ray diffraction pattern, and the crystallite size was calculated using the Rietveld method. [2] Regarding the conditions and results of the examples and comparative examples [Example 1] 39.9 g of water was dissolved with Cs ２ CO ３ 17.7 g, and this was added to H ２ WO ４ 82.3 g, and the mixture was dried in a vacuum dryer while stirring. The obtained dried powder was calcined at a temperature of 550°C for 1 hour in a 5% by volume H ２ gas atmosphere with N ２ gas as a carrier, and then calcined at 800°C for 1 hour in a N ２ gas atmosphere to obtain particles a. The composition of particles a was Cs ０．３３ WO ２．４５The measured powder X-ray diffraction pattern was hexagonal Cs ０．３ WO ３ The X-ray diffraction pattern matched that of the sample, confirming that it has a hexagonal crystal structure.

[0233] Next, particles a were weighed in a ratio of 15% by mass and water in a ratio of 73% by mass. The weighed material was ground and dispersed for 6 hours in a paint shaker containing 0.3 mmφ ZrO2 beads to prepare a composite tungsten oxide particle dispersion (Solution A). The crystallite size of the composite tungsten oxide particles in Solution A was measured to be 32.2 nm.

[0234] Next, polyvinylpyrrolidone (average molecular weight 45,000), a nonionic polymer dispersant, was added to solution A at a concentration of 12% by mass relative to particle a, and the mixture was held for 10 hours while stirring. This procedure yielded an aqueous dispersion containing composite tungsten oxide particles treated with the nonionic polymer dispersant (hereinafter also referred to as "solution A1"). Subsequently, water was removed from solution A1 using a large vacuum grinder to obtain a composite tungsten oxide particle dispersion powder (dispersion powder A). The moisture content of dispersion powder A after drying at 125°C for 10 minutes using a heating and drying type moisture meter MX-50 (manufactured by A&D Co., Ltd.) was 4.7% by mass.

[0235] The obtained dispersed powder A was added to polyethylene terephthalate resin powder (PET), a thermoplastic resin, so that the composite tungsten oxide particle concentration was 1.0% by mass, and the mixture was uniformly mixed in a blender. The resulting mixture was then melt-kneaded and extruded in a twin-screw extruder, and the extruded strands were cut in a pelletizer to obtain a masterbatch. At this time, the moisture content of the obtained masterbatch, measured by the Karl Fischer method (heating temperature 160°C), was 0.38% by mass. The masterbatch was melt-spun and then drawn to produce the polyester multifilament yarn according to Example 1.

[0236] Furthermore, the composite tungsten oxide particles in the near-infrared absorbing fibers obtained in this example and in Examples 2 to 10 below do not contain residual organic solvents and are modified with a nonionic polymer dispersant. In addition, in all of the near-infrared absorbing fibers obtained in Examples 1 to 10, the composite tungsten oxide particles are arranged in one or more selected portions on the surface and inside of the fiber.

[0237] The obtained polyester multifilament yarn was cut to produce polyester staples, which were used to manufacture spun yarn. This spun yarn was then used to obtain a knitted product sample, which is a near-infrared absorbing fiber according to Example 1. The solar reflectance of the prepared knitted product sample was adjusted to 8%. The adjustment of the solar reflectance to 8% in the knitted product sample was performed in all of the examples and comparative examples described later.

[0238] The spectral characteristics of the fabricated knit product samples were measured using a Hitachi U-4100 spectrophotometer to determine the transmittance and reflectance of light in the wavelength range of 200 nm to 2100 nm. The solar absorptance was calculated according to JIS A 5759:2016. The solar absorptance was calculated using the following formula (1).

[0239] The calculated solar absorptance was 49.5%. The measurement results for the knitted product sample are shown in Table 1. In Table 1, the "Particle content per unit area" column for the "Knitted Product Sample" shows the amount of composite tungsten oxide particles contained per unit area of ​​the knitted product sample. Table 1 also includes the measurement results for Examples 2 to 10 and Comparative Example 2, which will be described later.

[0240] Next, the temperature rise effect on the reverse side of the fabric of the prepared knitted product sample was measured as follows.

[0241] In an environment of 20°C and 60% RH, a solar spectrum approximation lamp (Solar Simulator XL-03E50 modified, manufactured by Celic Co., Ltd.) was irradiated from a distance of 30 cm from the fabric of the knitted product sample. Then, the temperature of the back surface of the fabric before irradiation and 10 minutes after the start of irradiation was measured with a radiation thermometer (HT-11, manufactured by Minolta Co., Ltd.). The measurement results are shown in the column of "Fabric Temperature" in Table 1. The value shown in the column of "Before Irradiation" is the temperature of the back surface of the fabric before irradiation, and the value shown in the column of "10 Minutes After Irradiation" is the temperature of the back surface of the fabric 10 minutes after the start of irradiation. In addition, Table 1 also describes the measurement results related to Examples 2 to 10 and Comparative Example 2 described later. [Example 2] 16.5 g of water was dissolved with ２ CO ３ 8.8 g, and this was added to ２ WO ４ 50 g and dried with a vacuum dryer while stirring. The obtained dry powder was calcined at a temperature of 570°C for 1 hour in a 5% by volume ２ H ２ gas atmosphere with ２ gas as a carrier, and then calcined at 800°C for 1 hour in a 1% by volume air atmosphere with ２ gas as a carrier, and further calcined at 820°C for 0.5 hour in a ０．３３ WO ２．８６ gas atmosphere to obtain particles b. The composition of particles b was ０．３ WO ３ from chemical analysis, and it was confirmed to have a hexagonal crystal structure because the measured powder X-ray diffraction pattern matched the X-ray diffraction pattern of hexagonal

[0242] Using the same procedure and conditions as in Example 1 except for using particles b, a polyester multifilament yarn, which is a near-infrared absorbing fiber according to Example 2, and a knitted product sample were obtained and evaluated. The crystallite diameter of the composite tungsten oxide particles was 32.5 nm. The moisture content of the dispersion powder obtained using particles b was 4.9% by mass when dried at 125°C for 10 minutes with a heat drying type moisture meter MX-50. The moisture content of the masterbatch produced using this dispersion powder, measured by the Karl Fischer method (heating temperature 160°C), was 0.40% by mass.

[0243] The evaluation results are shown in Table 1. The solar absorptivity of the prepared knitted product sample was 48.4%. [Example 3] 39.9 g of water and Cs ２ CO ３ Dissolve 17.7g and add H ２ WO ４ It was added to 82.3g and dried in a vacuum dryer while stirring to obtain dried powder c.

[0244] A hybrid plasma reactor was used, which superimposed DC plasma and high-frequency plasma. The reaction system was evacuated to approximately 0.1 Pa (approximately 0.001 torr) using a vacuum pump, and then completely replaced with argon gas to create a flow system at 1 atmosphere. Subsequently, 8 L / min of argon gas was flowed from the plasma generation gas supply port to generate DC plasma. The DC power input at this time was 6 kW. Furthermore, 40 L / min of argon gas and 3 L / min of hydrogen gas were flowed spirally along the inner wall of the water-cooled quartz tube from the sheath gas supply port as gases for high-frequency plasma generation and protection of the quartz tube, and high-frequency plasma was generated. The high-frequency power input at this time was 45 kW. After generating the hybrid plasma in this way, a mixed gas of 3 L / min of argon gas and 0.15 L / min of oxygen gas was used as a carrier gas, and the obtained dried powder c was supplied into the plasma at a rate of 2 g / min from the raw material powder supply device. As a result, the raw material instantly evaporated, condensed in the plasma tail flame, and was pulverized to obtain particle c. Chemical analysis of particle c revealed that its composition is Cs ０．３１ WO ３．２１ The measured powder X-ray diffraction pattern was hexagonal Cs ０．３ WO ３ The X-ray diffraction pattern matched that of the sample, confirming that it has a hexagonal crystal structure.

[0245] Except for using particle c, polyester multifilament yarn and knit product samples, which are near-infrared absorbing fibers according to Example 3, were obtained and evaluated using the same procedure and conditions as in Example 1. The crystallite size of the composite tungsten oxide particles was 24.6 nm. The moisture content of the dispersed powder obtained using particle c was 4.5% by mass when dried at 125°C for 10 minutes using a heating and drying type moisture meter MX-50. The moisture content of the masterbatch produced using this dispersed powder, measured by the Karl Fischer method (heating temperature 160°C), was 0.37% by mass.

[0246] The evaluation results are shown in Table 1. The solar absorptivity of the knitted product sample was 47.7%. [Example 4] When preparing the raw materials, Rb ２ CO ３ and H ２ WO ４ Except for setting the Rb / W molar ratio to 0.33, the same procedure and conditions as in Example 1 were used to obtain particle d, which is a composite tungsten oxide particle according to Example 4. Chemical analysis revealed that the composition of particle d is Rb ０．３３ WO ２．４５ The measured powder X-ray diffraction pattern was hexagonal Rb ０．３３ WO ３ The X-ray diffraction pattern matched that of the sample, confirming that it has a hexagonal crystal structure.

[0247] Except for using particle d, polyester multifilament yarn and knit product samples, which are near-infrared absorbing fibers according to Example 4, were obtained and evaluated using the same procedure and conditions as in Example 1. The crystallite size of the composite tungsten oxide fine particles was 32.5 nm. The moisture content of the dispersed powder obtained using particle d was 4.6% by mass when dried at 125°C for 10 minutes using a heat-drying type moisture meter MX-50. The moisture content of the masterbatch produced using this dispersed powder, measured by the Karl Fischer method (heating temperature 160°C), was 0.36% by mass.

[0248] The evaluation results are shown in Table 1. The solar absorptivity of the knitted product sample was 47.9%. [Example 5] When preparing the masterbatch, dispersion powder A was added to polyethylene terephthalate resin powder, which is a thermoplastic resin, so that the composite tungsten oxide particle concentration was 0.3% by mass. Except for the above, polyester multifilament yarn, which is a near-infrared absorbing fiber according to Example 5, and knitted product samples were obtained and evaluated under the same conditions and procedures as Example 1. The crystallite size of the composite tungsten oxide particles was 32.5 nm. The moisture content of the masterbatch produced in Example 5, measured by the Karl Fischer method (heating temperature 160°C), was 0.37% by mass.

[0249] The evaluation results are shown in Table 1. The solar absorptivity of the knitted product sample was 22.3%. [Example 6] When preparing the masterbatch, dispersion powder A was added to polyethylene terephthalate resin powder, which is a thermoplastic resin, so that the composite tungsten oxide particle concentration was 0.6% by mass. Except for the above, polyester multifilament yarn, which is a near-infrared absorbing fiber according to Example 6, and knitted product samples were obtained under the same conditions and procedures as Example 1, and these were evaluated. The crystallite size of the composite tungsten oxide particles was 32.5 nm. The moisture content of the masterbatch produced in Example 6, measured by the Karl Fischer method (heating temperature 160°C), was 0.37% by mass.

[0250] The evaluation results are shown in Table 1. The solar radiation absorptivity of the knitted product sample was 33.7%. [Example 7] Except for using acrylic resin powder as the thermoplastic resin, acrylic multifilament yarn, which is a near-infrared absorbing fiber according to Example 7, and knitted product samples were obtained and evaluated under the same conditions and procedures as in Example 1. The moisture content of the masterbatch produced in Example 7, measured by the Karl Fischer method (heating temperature 160°C), was 0.37% by mass.

[0251] The evaluation results are shown in Table 1. The solar radiation absorptivity of the knitted product sample was 49.3%. [Example 8] Except for using polyurethane resin powder as the thermoplastic resin, polyurethane multifilament yarn, which is a near-infrared absorbing fiber according to Example 8, and knitted product samples were obtained and evaluated under the same conditions and procedures as in Example 1. The moisture content of the masterbatch produced in Example 8, measured by the Karl Fischer method (heating temperature 160°C), was 0.37% by mass.

[0252] The evaluation results are shown in Table 1. The solar radiation absorptivity of the knitted product sample produced was 49.4%. [Example 9] In Example 1, dispersion powder A was added to polybutylene terephthalate resin powder (PBT), a thermoplastic resin, so that the composite tungsten oxide particle concentration was 3.0% by mass, and the mixture was uniformly mixed in a blender. Next, the obtained mixture was melt-kneaded and extruded in a twin-screw extruder, and the extruded strands were cut in a pelletizer to obtain the first masterbatch. The first masterbatch and polyethylene terephthalate resin pellets (PET), a thermoplastic resin, were added so that the composite tungsten oxide particle concentration was 0.1% by mass, and the mixture was uniformly mixed in a blender. Next, the obtained mixture was melt-kneaded and extruded in a twin-screw extruder, and the extruded strands were cut in a pelletizer to obtain the second masterbatch. The second masterbatch was melt-spun, followed by drawing, to produce the polyester multifilament yarn according to Example 9. Except for the points mentioned above, polyester multifilament yarn, which is a near-infrared absorbing fiber according to Example 9, and knit product samples were obtained and evaluated under the same conditions and procedures as in Example 1. The moisture content of the second masterbatch, measured by the Karl Fischer method (heating temperature 160°C), was 0.37% by mass.

[0253] The evaluation results are shown in Table 1. The solar radiation absorptivity of the knitted product sample was 20.9%. [Example 10] When preparing an aqueous dispersion containing composite tungsten oxide particles treated with a nonionic polymer dispersant, polyvinylpyrrolidone (average molecular weight 45,000) was added at a concentration of 13.5% by mass relative to particle a. Except for the above, polyester multifilament yarn, which is a near-infrared absorbing fiber according to Example 10, and knitted product samples were obtained and evaluated under the same conditions and procedures as Example 9. The moisture content of the dispersion powder produced in Example 10 was 4.7% by mass when dried at 125°C for 10 minutes using a heat-drying type moisture meter MX-50. The moisture content of the second masterbatch produced in Example 10, measured by the Karl Fischer method (heating temperature 160°C), was 0.37% by mass.

[0254] The evaluation results are shown in Table 1. The solar radiation absorptivity of the knitted product sample was 20.3%. [Comparative Example 1] An attempt was made to produce polyester multifilament yarn, which is a near-infrared absorbing fiber according to Comparative Example 1, under the same conditions and procedures as in Example 1, except that polyvinylpyrrolidone was not used when preparing the dispersion. However, breakage occurred frequently, and yarn production was not achieved. [Comparative Example 2] Polyester multifilament yarn, which is a near-infrared absorbing fiber according to Comparative Example 2, and knitted product samples were obtained under the same conditions and procedures as in Example 1, except that composite tungsten oxide particles and polyvinylpyrrolidone were not used, and were evaluated.

[0255] The evaluation results are shown in Table 1. The solar radiation absorptivity of the knitted product sample produced was 6.2%. [Comparative Example 3] Instead of polyvinylpyrrolidone, a nonionic polymer dispersant, a carboxylic acid-based anionic polymer dispersant was used. Except for the above, an attempt was made to produce polyester multifilament yarn, which is a near-infrared absorbing fiber according to Comparative Example 3, under the same conditions and procedures as in Example 1, but breakage occurred frequently and yarn production was not achieved. [Comparative Example 4] Cetyltrimethylammonium chloride was added to the dispersion (Solution A) prepared in Example 1 at a ratio of 10% by mass relative to the composite tungsten oxide particles, and the mixture was held for 6 hours while stirring. Through the above operation, an aqueous dispersion (Solution N1) containing composite tungsten oxide particles surface-modified with cetyltrimethylammonium chloride, an ammonium salt that is a cationic dispersant, was obtained.

[0256] Water was removed from liquid N1 using a large vacuum grinder to obtain a composite tungsten oxide particle dispersion powder (hereinafter also referred to as "dispersion powder N").

[0257] A masterbatch was prepared under the same conditions and procedure as in Example 1, except that dispersed powder N was used.

[0258] Visual inspection of the masterbatch obtained in Comparative Example 4 revealed significant color unevenness, and it was determined that the dispersibility of the composite tungsten oxide particles was poor, so the near-infrared absorbing fibers were not produced. [Reference Example] In Example 1, polyvinylpyrrolidone was added at a concentration of 11% by mass relative to particle a. Except for the above, the dispersion according to the Reference Example was prepared in the same manner as in Example 1.

[0259] However, during the masterbatch manufacturing process, some of the composite tungsten oxide particles aggregated. While this did not pose a problem in product manufacturing, it resulted in slight color unevenness, and therefore, near-infrared absorbing fibers were not produced. It has been confirmed that the above aggregation can be reduced by adjusting the amount of composite tungsten oxide particles added and the melting and kneading conditions during masterbatch manufacturing.

[0260] [Evaluation] According to the results shown in Table 1, it was confirmed that the solar radiation absorptance of the knit product samples of Examples 1 to 10 was 20% or more. In addition, when a test was conducted on the temperature rise effect on the back surface of the fabric, the fabric temperature of Examples 1 to 10 increased by 20°C or more, confirming excellent heat generation properties.

[0261] On the other hand, Comparative Examples 1, 3, and 4 did not result in the production of polyester multifilament yarn, and it was confirmed that the solar radiation absorptivity of the knitted product sample of Comparative Example 2 was low, at 7% or less. Furthermore, it was confirmed that Comparative Example 2 had poor heat generation properties, with a fabric temperature increase of 12°C or less.

[0262] Examples of embodiments of the present disclosure are as follows:

[0263] <1> A near-infrared absorbing fiber comprising a fiber and composite tungsten oxide particles, wherein the composite tungsten oxide particles are modified with a nonionic polymer dispersant, and the composite tungsten oxide particles are arranged in one or more selected portions from the surface and interior of the fiber.

[0264] <2> The near-infrared absorbing fiber according to <1>, wherein the fiber contains a synthetic fiber, and the synthetic fiber is one or more selected from polyurethane fiber, polyamide fiber, acrylic fiber, polyester fiber, polyolefin fiber, polyvinyl alcohol fiber, polyvinylidene chloride fiber, polyvinyl chloride fiber, and polyether ester fiber.

[0265] <3> The near-infrared absorbing fiber according to <1> or <2>, wherein the content of the composite tungsten oxide particles is 0.001% by mass or more and 80% by mass or less relative to the solid content of the fiber.

[0266] <4> A near-infrared absorbing fiber according to any one of <1> to <3>, wherein particles of far-infrared emitting material are further arranged on one or more portions selected from the surface and interior of the fiber, and the content of the particles of far-infrared emitting material is 0.001% by mass or more and 80% by mass or less with respect to the solid content of the fiber.

[0267] <5> A near-infrared absorbing fiber according to any one of <1> to <4>, wherein the amount of residual organic solvent is 5% by mass or less.

[0268] <6> The near-infrared absorbing fiber according to any one of <1> to <5>, wherein the average particle diameter of the composite tungsten oxide particles is 10 nm or more and 100 nm or less.

[0269] <7> The near-infrared absorbing fiber according to any one of <1> to <6>, wherein the crystallite size of the composite tungsten oxide particles is 10 nm or more and 100 nm or less.

[0270] <8> The composite tungsten oxide particles are of the general formula M ｘ WO ｙ A near-infrared absorbing fiber according to any one of <1> to <7>, containing a composite tungsten oxide represented by (element M includes one or more elements selected from Na, K, Rb, Cs, and Ba, satisfying 0.1 ≤ x ≤ 1.0 and 2.0 ≤ y < 4.0).

[0271] <9> The near-infrared absorbing fiber according to <8>, wherein the element M contains one or more elements selected from Cs and Rb.

[0272] <10> The near-infrared absorbing fiber according to any one of <1> to <9>, wherein the fiber is one or more selected from a group of fibers consisting of synthetic fibers, semi-synthetic fibers, natural fibers, regenerated fibers, and inorganic fibers, and a mixed yarn made by blending, plying, or blending two or more types of fibers selected from the group of fibers.

[0273] <11> A textile product containing a near-infrared absorbing fiber as described in any of <1> to <10>.

[0274] This application claims priority based on Japanese Patent Application No. 2024-181314, filed with the Japan Patent Office on 16 October 2024, and Japanese Patent Application No. 2025-060804, filed with the Japan Patent Office on 1 April 2025, and the entire contents of Japanese Patent Application No. 2024-181314 and Japanese Patent Application No. 2025-060804 are incorporated herein by reference.

[0275] 10 High-frequency plasma reactor 11 Water-cooled quartz double tube 12 Reaction vessel 13 Vacuum exhaust system 14 Plasma generation gas supply port 15 Sheath gas inlet 16 Water-cooled copper coil 17 Raw material powder carrier gas supply port 18 Raw material powder supply device 19 Gas supply device 20 Near-infrared absorbing fiber 21 Fiber 21A Surface 21B Interior 22 Composite tungsten oxide particles CA Central axis

Claims

1. A near-infrared absorbing fiber comprising a fiber and composite tungsten oxide particles, wherein the composite tungsten oxide particles are modified with a nonionic polymer dispersant, and the composite tungsten oxide particles are arranged in one or more selected portions from the surface and interior of the fiber.

2. The near-infrared absorbing fiber according to claim 1, wherein the fiber contains synthetic fibers, and the synthetic fibers are one or more selected from polyurethane fibers, polyamide fibers, acrylic fibers, polyester fibers, polyolefin fibers, polyvinyl alcohol fibers, polyvinylidene chloride fibers, polyvinyl chloride fibers, and polyether ester fibers.

3. The near-infrared absorbing fiber according to claim 1 or claim 2, wherein the content of the composite tungsten oxide particles is 0.001% by mass or more and 80% by mass or less relative to the solid content of the fiber.

4. The near-infrared absorbing fiber according to any one of claims 1 to 3, wherein particles of far-infrared emitting material are further arranged on one or more portions selected from the surface and interior of the fiber, and the content of the particles of far-infrared emitting material is 0.001% by mass or more and 80% by mass or less relative to the solid content of the fiber.

5. The near-infrared absorbing fiber according to any one of claims 1 to 4, wherein the amount of residual organic solvent is 5% by mass or less.

6. The near-infrared absorbing fiber according to any one of claims 1 to 5, wherein the average particle diameter of the composite tungsten oxide particles is 10 nm or more and 100 nm or less.

7. The near-infrared absorbing fiber according to any one of claims 1 to 6, wherein the crystallite size of the composite tungsten oxide particles is 10 nm or more and 100 nm or less.

8. The composite tungsten oxide particles are of general formula M ｘ WO ｙ A near-infrared absorbing fiber according to any one of claims 1 to 7, containing a composite tungsten oxide represented by (element M comprises one or more elements selected from Na, K, Rb, Cs, and Ba, satisfying 0.1 ≤ x ≤ 1.0 and 2.0 ≤ y < 4.0).

9. The near-infrared absorbing fiber according to claim 8, wherein the element M comprises one or more elements selected from Cs and Rb.

10. The near-infrared absorbing fiber according to any one of claims 1 to 9, wherein the fiber is one or more selected from a group of fibers consisting of synthetic fibers, semi-synthetic fibers, natural fibers, regenerated fibers, and inorganic fibers, and from a blend of two or more fibers selected from the group of fibers, a blended yarn, or a mixed yarn.

11. A textile product comprising a near-infrared absorbing fiber according to any one of claims 1 to 10.

Images