Amorphous tungsten oxide particles, ultraviolet blocking agent and method for producing the same

Abstract

Provided are tungsten oxide particles that do not absorb visible light or infrared light but can absorb ultraviolet light. The amorphous tungsten oxide particles contain iron. The general formula of the particles is W 1-X Fe X O 3ーY The particle may have a particle diameter of 0.4 μm or more and 40 μm or less, and the particle may have a ratio (A / B) of the average light absorption coefficient A for wavelengths of 315 nm or more and 400 nm or less to the average light absorption coefficient B for wavelengths of 450 nm or more and 1500 nm or less of 30 or more.

Description

[Technical Field]

[0001] The present invention relates to amorphous tungsten oxide particles, an ultraviolet blocking agent, and a method for producing the same. [Background technology]

[0002] The following materials have been proposed as materials having light absorption properties obtained by adding one or more elements to tungsten oxide. For example, Patent Document 1 (JP 2007-238353 A) describes a method for producing tungsten-containing oxide particles that improves UV resistance by preventing the tungsten oxide microparticles and composite tungsten oxide microparticles used from being colored by ultraviolet light and causing a change (decrease) in transmittance.

[0003] The tungsten-containing oxide particles described in Patent Document 1 are represented by the general formula W y O z (wherein W is tungsten, O is oxygen, and 2.2≦z / y≦2.999) or / and tungsten oxide fine particles represented by the general formula M x The composite tungsten oxide microparticles are characterized in that one or more elements selected from Cu, Fe, Mn, Ni, Co, Pt, Au, Ag, Na, In, Sn, Cs, and Rb or compounds thereof are further added to one or more microparticle crystals or / and the surface of the microparticles selected from composite tungsten oxide microparticles represented by WO3 (wherein M element is one or more elements selected from Cs, Rb, K, Tl, Ba, In, Li, Sn, Ca, Sr, and Na, W is tungsten, and O is oxygen; 0.001≦X≦1).

[0004] Patent Document 2 (JP 2020-169112 A) proposes light-absorbing particles that suppress the occurrence of the decolorization phenomenon. The light-absorbing particles described in Patent Document 2 are light-absorbing particles containing hexagonal tungsten bronze, and the tungsten bronze has the general formula: M x WO y(wherein element M contains at least one element selected from K, Rb, Cs, and Tl, and is represented by 0.1≦x≦0.5, 2.2≦y≦3.0), and oxygen ions (O 2- ) is placed, and the substitution ion is an ion containing one or more elements selected from the group consisting of group 15 elements, group 16 elements, and group 17 elements.

[0005] Patent Document 3 (JP 2021-075676 A) proposes a composite tungsten oxide microparticle dispersion and a composite tungsten oxide microparticle dispersion that have excellent infrared absorption properties and weather resistance while suppressing the blue tint to the extent that the b* value becomes positive.

[0006] The composite tungsten oxide microparticle dispersion described in Patent Document 3 contains composite tungsten oxide microparticles having a crystallite diameter of 25 nm or more and 85 nm or less, and a solid medium.

[0007] Patent Document 4 (WO 2022 / 209712) describes infrared absorbing particles that are pale blue in color and have excellent weather resistance and infrared absorbing properties.

[0008] The infrared absorbing particles described in Patent Document 4 are infrared absorbing particles containing composite tungsten oxide particles, and the composite tungsten oxide particles have a hexagonal crystal structure and are represented by the general formula M x W y O z (wherein M is one or more elements selected from Cs, Rb, K, Tl, Ba, Ca, Sr, and Fe, W is tungsten, O is oxygen, 0.25≦x / y≦0.39, 2.70≦z / y≦2.90).

[0009] Patent Document 5 (JP Patent Publication No. 2024-042596) describes a UV-C absorber that can absorb UV-C, a type of near-ultraviolet (UV) light, while preventing yellowing of wall materials and without causing blue discoloration due to photochromism, as well as a method for producing the base agent and an anti-yellowing paint.

[0010] Patent Document 5 describes a production method for the UV-C absorber, which comprises dissolving sodium tungstate in water, adding an acid to prepare an aqueous solution of sodium polytungstate having a pH of 3.5 to 7, and drying the prepared aqueous solution of sodium polytungstate to produce solid prepared sodium polytungstate. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-238353 [Patent Document 2] Japanese Patent Application Publication No. 2020-169112 [Patent Document 3] Japanese Patent Publication No. 2021-075676 [Patent Document 4] International Publication No. 2022 / 209712 [Patent Document 5] Japanese Patent Application Laid-Open No. 2024-042596 Summary of the Invention [Problem to be solved by the invention]

[0012] In recent years, the development of light-absorbing materials with light-absorbing properties has expanded, and they are widely used in applications such as window materials for buildings and vehicles, and solar radiation shielding materials. In particular, tungsten oxide particles have been developed that have the ability to absorb visible light or infrared light by adding elements, but it has not been sufficiently developed as an ultraviolet-shielding material that can block only ultraviolet light.

[0013] The tungsten oxide particles described in Patent Document 1 are a method for producing an infrared shielding material in which one or more elements selected from Cu, Fe, Mn, Ni, Co, Pt, Au, Ag, Na, In, Sn, Cs, and Rb, or compounds thereof, are present on the particle surface, thereby preventing coloration when irradiated with ultraviolet rays.

[0014] The tungsten oxide particles described in Patent Document 2 have oxygen ions (O 2- ) is placed in the ion radius of the ion atom, and the ion is 2- , Se 2- , Te 2- , P 3- , As 3- , Sb 3- This method suppresses the deterioration phenomenon of tungsten oxide particles at high temperatures and high humidity by containing one or more types of ions selected from the above.

[0015] The tungsten oxide particles described in Patent Document 3 are obtained by incorporating composite tungsten oxide microparticles having a crystallite diameter of 25 nm or more and 85 nm or less into a composite tungsten oxide microparticle dispersion and a composite tungsten microparticle dispersion liquid, thereby ensuring infrared absorption properties and weather resistance while suppressing the blueness of the particles.

[0016] The tungsten oxide particles described in Patent Document 4 have a hexagonal crystal structure and are represented by the general formula M x W y O z (wherein M is one or more elements selected from Cs, Rb, K, Tl, Ba, Ca, Sr, and Fe, W is tungsten, O is oxygen, and 0.25≦x / y≦0.39, 2.70≦z / y≦2.90) This provides excellent weather resistance and infrared absorption properties.

[0017] However, although the tungsten oxide particles disclosed in Patent Documents 1 to 5 are capable of absorbing visible light and infrared rays, they are not tungsten oxide particles that are capable of blocking only ultraviolet light without absorbing visible light and infrared rays.

[0018] The main object of the present invention is to provide tungsten oxide particles and cosmetics that do not absorb visible light and infrared light but can absorb ultraviolet light. Another object of the present invention is to provide amorphous tungsten oxide particles and cosmetics that can absorb ultraviolet light. [Means for solving the problem]

[0019] (1) According to one aspect, the amorphous tungsten oxide particles contain iron.

[0020] By adding elements to tungsten oxide particles, light absorption properties derived from the crystalline structure are expressed in the near-infrared region, and materials with absorption properties in various frequency bands have been developed. However, there has been insufficient development of an ultraviolet shielding material that can absorb only ultraviolet light while forming an amorphous structure by adding elements to tungsten particles. According to one aspect, amorphous tungsten oxide particles are obtained by adding iron to an aqueous solution of tungstate (sodium), which changes the crystal structure to an amorphous structure, allowing visible light and near-infrared light to pass through while absorbing only ultraviolet light. This results in tungsten oxide particles that block only ultraviolet light, and can be used in cosmetics, industrial paints, anti-aging materials, protective materials, etc.

[0021] (2) Amorphous tungsten oxide particles according to a second aspect of the present invention are amorphous tungsten oxide particles having the general formula: 1-X Fe X O 3-Y That's fine too.

[0022] In this general formula, the value X indicates the doping amount of Fe (iron) added to W (tungsten), and the value Y indicates the amount of oxygen vacancies of O (oxygen). This allows a preferable amorphous structure to be formed, and amorphous tungsten oxide particles can be obtained that do not absorb light in the visible and infrared regions and can preferably absorb only ultraviolet light.

[0023] (3) The amorphous tungsten oxide particles according to the third aspect of the present invention are the amorphous tungsten oxide particles according to the first aspect or the second aspect of the present invention, and in the general formula, the value X may be 0.05 or more and 0.4 or less, and the value Y may be 0.1 or less.

[0024] This allows for a more preferable amorphous structure, and more preferably, amorphous tungsten oxide particles that do not absorb visible or infrared light and can favorably absorb only ultraviolet light. Note that the value X (Fe doping amount) of quantitative analysis is preferably calculated by fluorescent X-ray quantitative measurement.

[0025] (4) The amorphous tungsten oxide particles according to a fourth aspect of the present invention are the tungsten oxide particles according to any one of the first to third aspects of the present invention, and may have a particle diameter of 0.40 μm or more and 40 μm or less.

[0026] This allows the particles to be free from coalescence and to form stable, independent amorphous tungsten oxide particles. The particle size referred to here can be calculated based on particle size distribution measurement using a laser diffraction scattering method.

[0027] Furthermore, since the particle diameter is relatively larger than the wavelength of visible light, scattering of visible light is unlikely to occur, and the particles grow stably into a spherical shape, making the particle surface smooth and unlikely to scatter visible light, so that a sufficient light absorption effect can be obtained in the ultraviolet range. Therefore, even when used in cosmetics, industrial paints, anti-deterioration materials, protective materials, etc., the unevenness of the coated surface is less noticeable and sufficient ultraviolet shielding effect can be achieved.

[0028] (5) The amorphous tungsten oxide particles according to a fifth aspect of the present invention are the amorphous tungsten oxide particles according to any one of the first to fourth aspects of the present invention, and may have a ratio (A / B) of 30 or more, where A is the average light absorption coefficient in the wavelength range of 315 nm or more and 400 nm or less, and B is the average light absorption coefficient in the wavelength range of 450 nm or more and 1500 nm or less.

[0029] This allows amorphous tungsten oxide particles to transmit visible light and infrared light while exhibiting excellent light absorption in the UVA region (315-400 nm).The light absorption coefficient value in this case can be calculated using the KM conversion formula. In particular, commonly used UV-blocking agents often use titanium oxide, which has an absorption edge in its band gap around 380 nm, but this has the problem of insufficient absorption of UVA light, which is problematic because UVA is not sufficiently absorbed by the ozone layer and the amount of UVA reaching the earth is greater than that of UVB. The amorphous tungsten oxide particles according to the fifth aspect of the present invention have an absorption edge at around 450 nm, and can sufficiently absorb ultraviolet rays in the UVA region, thereby exhibiting an excellent ultraviolet blocking effect.

[0030] (6) An ultraviolet blocking agent according to another aspect includes the amorphous tungsten oxide particles according to any one of the first to fifth aspects of the present invention.

[0031] This allows for the development of UV blocking agents, which are cosmetics with excellent sun protection and damage prevention capabilities. UVA (315-400 nm) in particular is more susceptible to sunburn than UVB (280-315 nm), and has been considered a problematic cause of darkening, wrinkles, and sagging skin. Cosmetics that comply with these other aspects can adequately absorb UVA rays, a problem posed by conventional UV blocking agents (such as titanium dioxide particles), and can be used to create sun care products with excellent sun protection and damage prevention capabilities. Furthermore, conventional UV blocking agents have the problem of causing significant light scattering, which makes unevenness on the surface (such as skin) that they are applied to more conspicuous. The amorphous tungsten oxide particles of the present invention have a smooth particle surface and cause less scattering of visible light, making unevenness on the surface (such as skin) that they are applied to less conspicuous, while still providing sufficient UV blocking effects. Furthermore, the particles of the present invention have a smooth surface and a spherical shape, which makes them excellent in coatability, allows for uniform coating, and prevents the coated surface from becoming rough. Therefore, it is possible to obtain a cosmetic product that has excellent applicability, makes unevenness of the applied surface less noticeable, and has sufficient ultraviolet shielding effect.

[0032] (7) A method for producing tungsten oxide particles according to still another aspect includes a preparation step of adding hydrochloric acid to an aqueous sodium tungstate solution to adjust the pH to an acidic range to obtain a preparation solution; a dialysis step of subjecting the preparation solution to electrodialysis to obtain a removal solution from which chloride ions have been removed; a precipitation step of adding iron chloride to the removal solution to obtain a precipitate solution; a precipitation step of precipitating tungsten oxide particles from the precipitation solution; and a washing step of washing the tungsten oxide particles obtained in the precipitation step with water.

[0033] This makes it possible to obtain tungsten oxide particles containing iron that can absorb ultraviolet light while transmitting visible light and near-infrared light.

[0034] (8) The method for producing tungsten oxide particles according to an eighth aspect of the present invention is a method for producing tungsten oxide particles according to yet another aspect, and the pH of the preparation liquid may be 0.5 to 5.

[0035] This allows the particles to be free from coalescence and to form stable, perfectly spherical tungsten oxide particles.

[0036] (9) The ninth aspect of the present invention relates to a method for producing tungsten oxide particles, which is the method for producing tungsten oxide particles according to the eighth aspect or the other aspect of the present invention, and in which more than 0.1 parts by weight and less than 7 parts by weight of iron chloride may be added to 100 parts by weight of the removal solution in the precipitation solution preparation step.

[0037] This allows the particles to be free from coalescence and to form stable, perfectly spherical tungsten oxide particles. [Brief explanation of the drawings]

[0038] [Figure 1]1 is a SEM photograph of amorphous tungsten oxide particles of Examples 1, 5, and 8. [Figure 2] 1 is a SEM photograph of amorphous tungsten oxide particles of Comparative Examples 1 to 4. [Figure 3] 1 shows SEM photographs of amorphous tungsten oxide particles of Comparative Examples 5 to 7 and Reference Example 1. [Figure 4] 1 shows the results of EDS measurement in Example 1. [Figure 5] 1 shows an SEM photograph and EDS measurement results of a cross section of an amorphous tungsten oxide particle of Example 1. [Figure 6] 1 shows the results of EDS measurement when the amount of iron chloride added is changed in the precipitation liquid preparation step of Example 1. [Figure 7] 1 shows the results of fluorescent X-ray measurement of amorphous tungsten oxide particles when the amount of iron chloride added is changed in the precipitation liquid preparation step of Example 1. [Figure 8] FIG. 2 is a particle size distribution diagram of tungsten oxide particles obtained in the examples. [Figure 9] 1 shows the results of X-ray diffraction measurements of Example 1 and Reference Example 1. [Figure 10] 1 shows the results of optical absorption measurement of Examples 1 and 6 and Reference Example 1, and the results of optical absorption measurement of tungsten oxide particles obtained by hydrothermal synthesis. [Figure 11] FIG. 1 is a schematic explanatory diagram for explaining an electrodialysis device. DETAILED DESCRIPTION OF THE INVENTION

[0039] The manufacturing method of this embodiment will be described in detail below. Preferred embodiments of the present invention are as follows, but the present invention is not limited thereto. Furthermore, at least a part of the configuration of each embodiment can be appropriately combined with a part of another embodiment without departing from the spirit and scope of the present invention.

[0040] (Method of manufacturing tungsten oxide particles) Hereinafter, a method for producing tungsten oxide particles according to an embodiment of the present invention will be described in detail. The method for producing tungsten oxide particles of this embodiment includes the following five steps. (1) Dissolution step: Sodium tungstate is dissolved in water to prepare an aqueous sodium tungstate solution. (2) Preparation step: An acid is added to the aqueous sodium tungstate solution obtained in the dissolution step, and the pH is adjusted to an acidic value to obtain a preparation solution. (3) Dialysis step: The prepared solution is dialyzed in an electrodialyzer until the concentration becomes 20 mS / cm or less to prepare a removal solution. (4) Precipitation liquid preparation step: Iron chloride is added to the removal solution to prepare a precipitate liquid. (5) Precipitation step: The precipitation liquid is left to stand at room temperature to allow natural precipitation. (6) Washing step: The precipitate obtained in the precipitation step is washed with water and then dried to obtain amorphous tungsten oxide particles. Each step will be described in detail below.

[0041] (melting process) An aqueous sodium tungstate solution is prepared by dissolving sodium tungstate in water. The concentration of sodium tungstate in the aqueous solution is preferably 0.01 mol / L or more and 0.9 mol / L or less, more preferably 0.05 mol / L or more and 0.7 mol / L or less, and even more preferably 0.1 mol / L or more and 0.5 mol / L or less. A concentration equal to or greater than the lower limit allows for sufficient particle size to be obtained, while a concentration equal to or less than the upper limit allows for a favorable precipitation rate and prevents incomplete precipitation. The temperature of the aqueous sodium tungstate solution in the dissolution step may be 20 to 25° C. The preferred pH of the aqueous sodium tungstate solution is about 8.5 to 8.8.

[0042] (Preparation process) The acid used in adjusting the pH may be either a strong acid or a weak acid, and may be an inorganic acid or an organic acid. Examples of inorganic acids include hydrochloric acid, sulfuric acid, and nitric acid, and examples of organic acids include citric acid, among which hydrochloric acid is preferably used. The use of hydrochloric acid prevents sodium polytungstate from precipitating in a polymorphic form, and amorphous tungsten oxide particles can be preferably precipitated. Furthermore, the use of hydrochloric acid removes unnecessary ions and the like from the removal solution after the dialysis step (desalting), allowing amorphous particles to be preferably formed. The lower limit of the pH of the prepared sodium tungstate aqueous solution is preferably 0.5 or higher, more preferably 2.0 or higher, and even more preferably 3.0 or higher. The upper limit of the pH is preferably 5.3 or lower, more preferably 5.0 or lower, and even more preferably 4.0 or lower. This allows for an optimal precipitation rate in the precipitation step, allowing for the preferred growth of spherical particles that are close to perfect spheres. Therefore, the particles are independent and stable without coalescence, resulting in highly uniform amorphous tungsten oxide particles.

[0043] (dialysis process) The preparation solution obtained in the preparation step is dialyzed using an electrodialyzer, whereby a solution in which excess chloride ions and sodium ions have been removed (desalted) can be obtained. As shown in Figure 11, the electrodialysis device is a device in which Na is introduced between a pair of electrodes. + A cation exchange membrane (molecular weight cutoff 300) that allows permeation of Cl - The deionization compartment and the concentration compartment are formed by alternately arranging anion exchange membranes (molecular weight cutoff 300) that are permeable to HCl and anion exchange membranes (molecular weight cutoff 300) that are permeable to HCl. The prepared aqueous sodium tungstate solution is introduced into this desalting compartment, and a current is passed through the pair of electrodes to carry out desalting until the electrical conductivity of the desalted solution becomes 20 mS / cm or less.

[0044] When the pH of the aqueous sodium tungstate solution in the adjustment step was changed, the amounts of chloride ions and sodium ions before and after electrodialysis were measured, and the results were as follows. [Table 1] From this result, it was confirmed that chloride ions were sufficiently removed by the dialysis process, and almost none remained in the removal solution.

[0045] (Precipitation liquid preparation process) A precipitate can be prepared by adding iron chloride to the removed solution obtained in the dialysis step. The iron chloride is preferably iron(III) chloride, which makes it possible to obtain particles with a perfect spherical shape. The amount of iron(III) chloride added relative to 100 parts by weight of the removal solution has a lower limit of 0.1 parts by weight, preferably 0.2 parts by weight or more, more preferably 1.0 parts by weight or more, and even more preferably 1.5 parts by weight or more, and an upper limit of less than 7.0 parts by weight, preferably 6.5 parts by weight or less, more preferably 6.0 parts by weight or less, and even more preferably 5.0 parts by weight or less. By setting the amount of iron chloride to the upper limit or less, particle formation can be performed favorably. By setting the amount of iron chloride to the lower limit or more, amorphous tungsten oxide particles can be reliably formed. It was confirmed that, within the range of more than 0.1 parts by weight and less than 1.0 parts by weight, the amount of precipitation (the amount of amorphous tungsten oxide particles formed) tends to increase with the amount of iron chloride added, while, within the range of 1.0 parts by weight or more, the amount of precipitation is independent of the chloride ion concentration.

[0046] (precipitation process) When a precipitation solution is prepared, iron-doped amorphous tungsten oxide particles are formed in the solution. By leaving the solution at room temperature, iron-doped amorphous tungsten oxide particles are formed, and these particles precipitate in the solution. Typically, precipitation begins about 10 minutes after preparation of the precipitation solution, but by leaving the solution at rest for a predetermined period of time or longer, the particles grow into a spherical shape. This example confirmed that using ferric chloride can cause problems with particle formation and growth, and that an excessively high chloride ion concentration can inhibit favorable particle formation and growth. Although the details of the mechanism by which iron-doped amorphous tungsten oxide particles are formed and grow are not clear, according to this production method, for example, polytungstic acid dissolved in the precipitation liquid and iron form a chelate, which randomly aggregates to form amorphous particles and precipitate. Furthermore, it is thought that when the precipitation liquid is allowed to stand, iron and polytungstic acid aggregate in a predetermined ratio, causing the amorphous particles to grow and become spherical. Therefore, in the precipitation step, it is preferable to allow the precipitation liquid to stand for a predetermined time or longer to allow natural precipitation to occur. The time for natural precipitation is preferably 9 hours or longer, and more preferably 15 hours or longer. This allows for the production of spherical amorphous tungsten oxide particles with a highly uniform particle size. In this case, it has been confirmed that the particles of this embodiment are uniformly doped with Fe at a predetermined ratio, regardless of the amount of iron chloride added in the precipitation liquid preparation process (see EDS cross-section measurement and Fe dependence measurement).

[0047] (Cleaning process) The precipitate obtained in the precipitation process is washed with distilled water, and the distilled water containing the precipitate is then centrifuged. This washing process is repeated multiple times until the electrical conductivity reaches 0.5 mS / cm or less, thereby removing impurities such as excess ions. The washed precipitate is then dried at 100°C to obtain powdered amorphous tungsten oxide particles.

[0048] (amorphous tungsten oxide particles) The amorphous tungsten oxide particles obtained in this embodiment have a particle size distribution width, as measured by a laser diffraction scattering method, of preferably 0.10 μm or more and 100 μm or less, more preferably 0.30 μm or more and 50 μm or less, and even more preferably 0.40 μm or more and 40 μm or less. 50 ) is preferably 1.0 μm or more and 10.0 μm or less, more preferably 2.0 μm or more and 7.0 μm or less, and even more preferably 3.0 μm or more and 5.0 μm or less.

[0049] The amorphous tungsten oxide particles obtained in this embodiment have the general formula W 1-X Fe X O 3ーY Here, the value X is the amount of Fe (iron) doped with W (tungsten), and the value Y is the amount of oxygen deficiency. As described below, from the results of EDS and XRF measurements, the value X is preferably 0.01 to 0.50, more preferably 0.05 to 0.40, and even more preferably 0.10 to 0.35. The value Y is preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.

[0050] The amorphous tungsten oxide particles obtained in this embodiment are characterized by having light absorption ability in the ultraviolet range and light transparency in the visible to infrared range. The average light absorption coefficient K in the ultraviolet range (250 nm to 380 nm) is preferably 3.2 or more, more preferably 3.5 or more, and even more preferably 4.0 or more. The average light absorption coefficient K in the visible and infrared range (450 nm to 1500 nm) is preferably 0.3 or less, more preferably 0.10 or less. Here, the light absorption coefficient K of the amorphous tungsten oxide particles obtained in this embodiment can be calculated from the light scattering coefficient S and light diffuse reflectance R of the particles using the KM transformation (Kubelka-Munk) formula. (Number 1) JPEG0007750575000003.jpg1538

[0051] Example 1 Sodium tungstate (manufactured by Nippon Inorganic Chemical Industry Co., Ltd.) was dissolved in distilled water to prepare a 0.5 mol / L aqueous solution of sodium tungstate. Next, hydrochloric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to the sodium tungstate aqueous solution obtained in the dissolution step using a pH meter (LAQUATwin manufactured by HORIBA Corporation) so that the pH was 3.5, thereby preparing a preparation solution. Next, the prepared solution was subjected to electrodialysis using an electrodialyzer (Micro Acilyzer (registered trademark) S3 manufactured by Astom) with an ion exchange membrane having a molecular weight cutoff of 300 (AC220 manufactured by SunActis) at 12 V until the molecular weight cutoff became 20 mS / cm or less, thereby obtaining a depleted solution. Next, 2 parts by weight of iron (III) chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added to 100 parts by weight of the removal solution to prepare a precipitate. The precipitate solution was allowed to stand at room temperature and natural precipitation was carried out for 15 hours. Next, the precipitate obtained in the precipitation step was washed with water and centrifuged (using a Kokusan H-9R) several times until the electrical conductivity became 0.5 mS / cm or less. The washed precipitate was then dried at 100°C to obtain powdered amorphous tungsten oxide particles.

[0052] Example 2 Amorphous tungsten oxide particles were obtained by carrying out the same steps as in Example 1, except that in the dissolution step, the concentration of the aqueous sodium tungstate solution was changed to 0.1 mol / L.

[0053] (Examples 3 and 4) Amorphous tungsten oxide particles were obtained by carrying out the same steps as in Example 1, except that the pH of the preparation solution was changed to 3.5 in the preparation step.

[0054] (Examples 5 and 6) Amorphous tungsten oxide particles were obtained by carrying out the same steps as in Example 1, except that in the preparation step, the pH of the adjusted sodium tungstate aqueous solution was changed to 0.5, 2.

[0055] Examples 7 to 9 Amorphous tungsten oxide particles were obtained by carrying out the same steps as in Example 1, except that in the precipitation liquid preparation step, the amount of iron chloride added was changed to 1 part by weight, 5 parts by weight, or 6 parts by weight per 100 parts by weight of the removal liquid.

[0056] (Comparative Example 1) The same steps as in Example 1 were carried out, except that the precipitation was carried out with stirring in the precipitation step, to obtain a precipitate.

[0057] (Comparative Example 2) The same steps as in Example 1 were carried out, except that in the precipitation step, precipitation was carried out while heating at 100°C, to obtain a precipitate.

[0058] (Comparative Example 3) A precipitate was obtained by carrying out the same steps as in Example 1, except that in the precipitation liquid preparation step, 7 parts by weight of iron chloride was added.

[0059] Comparative Example 4 In the precipitation step, the same steps as in Example 1 were carried out, except that the time for natural precipitation was changed to 3 hours or 8 hours, to obtain a precipitate.

[0060] (Comparative Example 5) In the dialysis step, the same steps as in Example 1 were carried out, except that the preparation solution was not subjected to dialysis, to obtain a precipitate.

[0061] (Comparative Example 6) In the preparation step, the same steps as in Example 1 were carried out except that the pH of the preparation solution was adjusted to 5.5, to obtain a precipitate.

[0062] (Comparative Example 7) The same steps as in Example 1 were carried out, except that in the dissolution step, the concentration of the aqueous sodium tungstate solution was adjusted to 1.0 mol / L, to obtain a precipitate.

[0063] (Reference example 1) The same steps as in Example 1 were carried out to obtain a precipitate, except that in the precipitation step, hydrothermal synthesis (TA-3 type manufactured by Taiatsu Glass Industry Co., Ltd.) was carried out at 120°C and 0.1 MPa for 4 hours instead of natural precipitation.

[0064] (SEM image taken) 1 to 3 show SEM images of the tungsten oxide particles obtained in the examples and comparative examples. The SEM images were taken using a field emission scanning electron microscope JSM7000F manufactured by JEOL Ltd. In the examples, perfectly spherical particles were formed, each particle being independent and stable (FIG. 1). On the other hand, in the comparative example, it was confirmed that the particle size was not uniform and the particles were incomplete and not perfectly spherical (Figs. 2 and 3). This confirmed that amorphous particles were reliably formed by dialyzing the precipitation solution at a predetermined pH and adding a predetermined amount of iron chloride. It was also confirmed that particle growth was reliably achieved and spherical particles were obtained by leaving the precipitation solution to stand for a predetermined period of time or longer in the precipitation step.

[0065] Example 1 had more spherical particles and less coalescence of particles than Examples 2 and 3, and as will be described later, had a larger mode diameter (FIG. 8). Furthermore, in the precipitation step, precipitation began earlier in Examples 2 and 3 than in Example 1. Therefore, by setting the pH and the amount of iron chloride added within the specified ranges, it is possible to obtain spherical particles that are preferably independent and stable. Furthermore, because the particle diameter is relatively larger than the wavelength of visible light and the particle surfaces are smooth and spherical, visible light is less likely to be scattered, allowing for sufficient light absorption effects in the ultraviolet range. Conventional ultraviolet screening agents have the problem of significant light scattering, making unevenness on the coated surface more noticeable. However, the amorphous tungsten oxide particles of Example 1 have smooth particle surfaces and little visible light scattering, making unevenness on the coated surface less noticeable and allowing for sufficient ultraviolet screening effects. Furthermore, because the particle surfaces are smooth and spherical, they have excellent applicability, can be applied uniformly, and can prevent the coated surface from becoming rough.

[0066] (shape evaluation test) After the drying process, the particles were visually inspected for shape using SEM images. Particles with uniform particle size and a perfectly spherical shape were rated as "Good", particles with a perfectly spherical shape were rated as "Good", particles with a perfectly spherical shape were rated as "Poor", and particles that were not perfectly spherical were rated as "Poor".

[0067] (particle size measurement) The average particle diameter D of the amorphous tungsten oxide obtained in Examples 1, 5, and 8 50 The measurement results (μm) are shown in Table 1. The average particle size was measured using MT3300II manufactured by Microtrackbell.

[0068] Table 2 shows the results of the above evaluation tests carried out on Examples 1 to 9, where the pH and the amount of iron (III) chloride added were changed.

[0069] [Table 2]

[0070] From the results in Table 1, it was confirmed that the amorphous tungsten oxide particles in Examples 1 to 9 were spherical. In addition, the average particle diameter (D 50 ) was 3.6 μm, and the average particle size (D50) of Examples 5 to 9 was 4.7 μm.

[0071] Table 3 shows the results of the shape evaluation test carried out on Comparative Examples 1 to 7 and Reference Example 1.

[0072] [Table 3]

[0073] As a result, it was found that the tungsten oxide particles were not perfectly spherical in Comparative Examples 1 to 7. Furthermore, in Comparative Example 3, perfectly spherical particles were not formed even when the amount of iron chloride added was 8 parts by weight and 9 parts by weight. In Comparative Examples 3 and 5, when a large amount of chlorine was added in the precipitation step, perfect spheres were not formed. As shown in Table 1, most of the chloride ions are removed in the dialysis step. Therefore, it is thought that by keeping the amount of iron chloride added in the precipitation solution preparation step below a predetermined value and suppressing the chloride ion concentration, particle growth is favorable and perfect spheres are formed.

[0074] Table 4 shows the results of measuring the pH of the precipitation liquid after adding iron chloride for Examples 1 and 9 and Comparative Examples 3 and 6.

[0075] [Table 4]

[0076] In Example 1 and Comparative Example 3, even when the pH of the precipitation solution was almost the same, the particle growth was insufficient when a large amount of iron chloride was added.Furthermore, in Example 1 and Comparative Example 6, even when the amount of iron chloride added was the same, the particle growth was insufficient when the pH of the precipitation solution was high.

[0077] (EDS qualitative analysis measurement) The results of elemental analysis by EDS measurement of the amorphous tungsten oxide particles obtained in Example 1 are shown in Figure 4 as a graph with the X-ray intensity (counts) on the vertical axis and the X-ray energy level (keV) on the horizontal axis. The analysis was performed using a JAMP-9500F manufactured by JEOL Ltd. As a result, no sodium or iron was detected, and only oxygen, tungsten, and iron were detected, confirming that the precipitate (particles) obtained in the precipitation process had sodium and chlorine removed and were amorphous tungsten oxide particles doped with iron.

[0078] (EDS: Fe distribution in particles) The amorphous tungsten oxide particles obtained in Example 1 were cut by ion milling (IB-09020CP manufactured by JEOL Ltd.), and EDS measurements were performed at five points on the cross section. The results are shown in FIG.

[0079] As a result, the tungsten, oxygen, and iron contents were approximately the same at all of the cross-sectional measurement points 1 to 5, confirming that the internal composition of the amorphous tungsten oxide particles was uniform and that iron was uniformly distributed within the particles.

[0080] (EDS: ferric chloride dependent) Figure 6 shows the results of EDS measurements of tungsten oxide particles when the amount of iron chloride added to the removal solution was changed. As a result of the measurement, it was confirmed that the content ratio of each atom number did not change when the amount of iron chloride added was changed from 1 to 10 parts by weight. Furthermore, EDS measurements have shown that the amorphous tungsten oxide particles of this embodiment contain approximately 18% tungsten, 7% iron, and 75% oxygen, and the general formula is approximately W 0.71 Fe 0.29 It was presumed to be O3.

[0081] (X-ray fluorescence measurement) Quantitative analysis using X-ray fluorescence was performed on the amorphous tungsten oxide particles of Examples 1 and 8 and when the amount of iron chloride added was varied. The analysis results are shown in Figure 7. The analysis measurements were performed using a wavelength dispersive X-ray fluorescence analyzer ZSPrimusIV manufactured by Rigaku Corporation. The analysis lines used were Fe-Kα for iron and W-Lα for tungsten.

[0082] As a result of the measurements, it was confirmed that in all cases where the amount of iron chloride added was in the range of 0.5 to 10 parts by weight (including Examples 1 and 8), the tungsten content was approximately 70% relative to 30% iron. Therefore, the chemical formula of amorphous tungsten oxide containing iron, assuming no oxygen vacancies, is W 0.65~0.90 Fe 0.10~0.35 This result was consistent with the EDS measurement results mentioned above. Furthermore, the results of the X-ray fluorescence measurements were the same even when the amount of iron chloride added was changed, confirming that particles identical to the above chemical formula are formed and grow regardless of the amount of iron chloride added in the precipitation solution preparation process.

[0083] (Particle size distribution measurement) Fig. 8(a) is a particle size distribution diagram for Examples 1, 2, and 3. Fig. 8(b) is a particle size distribution diagram for the cases where the natural precipitation time was 15 hours or 53 hours in Example 1. Particle size measurements were performed by a laser diffraction scattering method using an MT3300II manufactured by Microtrackbell.

[0084] As a result, the mode diameter of Example 1 was 4.6 μm, and the mode diameter of Examples 2 and 3 was 3.6 μm. It was confirmed that Example 1 had a high frequency of particles that had grown to large particle sizes, and that the particle size distribution was broadened toward the small particle size side. On the other hand, Examples 2 and 3 had a high frequency of particles that were smaller than Example 1, and some particles that had coalesced to a size of 10 μm or more were present. Comparing the time for natural precipitation of 15 hours and 53 hours, it was confirmed that particles with a highly uniform particle size were formed without bonding together after 15 hours.

[0085] (X-ray diffraction test) Fig. 9(a) shows the results of X-ray diffraction measurement of the tungsten oxide particles obtained in Example 1. Fig. 9(b) shows the results of X-ray diffraction measurement of the tungsten oxide particles obtained in Reference Example 1. The X-ray diffraction measurement was performed using a 9 kW X-ray source on a SmartLab (registered trademark) manufactured by Rigaku Corporation.

[0086] As a result, the X-ray diffraction pattern of the tungsten oxide particles obtained in Example 1 was a broad halo pattern, and it was therefore confirmed that the particles had an amorphous structure. Furthermore, in Reference Example 1, it was confirmed from the X-ray diffraction pattern that the particles were a composite of tungsten oxide having a hexagonal crystal structure and tungsten oxide having an amorphous structure.

[0087] (optical absorption measurement) Figure 10(a) shows the results of optical absorption measurement of the tungsten oxide particles obtained in Examples 1 and 2 and Reference Example 1. Figure 10(b) shows the results of optical absorption measurement of hexagonal tungsten oxide particles (undoped) obtained by hydrothermal synthesis, Cs-doped hexagonal tungsten oxide particles obtained by hydrothermal synthesis, and Na-doped hexagonal tungsten oxide particles obtained by hydrothermal synthesis (hereinafter referred to as the hydrothermally synthesized undoped product, the hydrothermally synthesized Cs-doped product, and the hydrothermally synthesized Na-doped product, respectively). Optical absorption measurements were performed using a JASCO V770 instrument with a powder sample 0.5 mm thick placed in a sample filling section φ5 mm, and calculations were performed using KM conversion.

[0088] As a result, it was confirmed that the hexagonal tungsten oxide particles (hydrothermally synthesized undoped product, hydrothermally synthesized Cs-doped product, and hydrothermally synthesized Na-doped product) had strong optical absorption in the ultraviolet and visible red to infrared ranges (Fig. 10(b)). On the other hand, it was confirmed that the iron-doped tungsten oxide particles (Example and Comparative Example) had strong optical absorption only in the ultraviolet range, with no absorption in the visible or infrared ranges (Fig. 10(a)).

[0089] Table 5 shows the results of calculating the average light absorption coefficient in the UVB region (wavelength 280 to 315 nm) in Figure 10, the average light absorption coefficient (A) in the UVA region (wavelength 315 to 400 nm), the average light absorption coefficient in the UVA to UVB region (wavelength 280 to 400 nm), the average light absorption coefficient (B) in the wavelength 450 to 1500 nm, and the value obtained by dividing the UVA absorption coefficient (A) by the visible and near-infrared absorption coefficient (B) for Examples 1 and 2, the hydrothermally synthesized Cs-doped product (hexagonal crystal), and the hydrothermally synthesized Na-doped product (hexagonal crystal).

[0090] [Table 5]

[0091] From the results in Table 5, it was confirmed that Example 1 is more suitable as an ultraviolet screening agent because it does not absorb infrared or visible light and absorbs ultraviolet light. In particular, the ratio (A / B) of the average light absorption coefficient (A) for wavelengths of 315 nm to 400 nm to the average light absorption coefficient (B) for wavelengths of 450 nm to 1500 nm is preferably 30 or more, more preferably 40 or more, and even more preferably 50 or more. This makes it possible to preferably block ultraviolet rays in the UVA region, which are irradiated to the ground in large amounts and cause significant damage to the skin.

[0092] Although the details are not clear, it is believed that the ultraviolet light absorption is due to tungsten oxide, and that the visible and infrared light absorption is due to plasmons and polarons. Therefore, it is speculated that iron-doped tungsten oxide particles act in some way to interfere with the formation of plasmons and polarons that occur in ordinary tungsten oxide particles, thereby eliminating visible and infrared light absorption. Furthermore, because this special effect is not due to the amorphous (crystalline structure), it is thought that it may be caused by a special interaction between iron and tungsten oxide.

Claims

1. The general formula is W １－Ｘ Fe Ｘ O ３ーＹ (wherein 0.01≦X≦0.5, Y≦0.1).

2. 2. The amorphous tungsten oxide particles according to claim 1, wherein the value X in the general formula is 0.05 or more and 0.4 or less, and the value Y is 0.1 or less.

3. 2. The amorphous tungsten oxide particles according to claim 1, wherein the ratio (A / B) of the average light absorption coefficient A for a wavelength of 315 nm or more and 400 nm or less to the average light absorption coefficient B for a wavelength of 450 nm or more and 1500 nm or less is 30 or more.

4. An ultraviolet blocking agent comprising the amorphous tungsten oxide particles according to claim 1.

5. a preparation step of adding hydrochloric acid to an aqueous sodium tungstate solution to adjust the pH to acidic to obtain a preparation solution; a dialysis step of subjecting the prepared solution to electrodialysis to obtain a solution from which chloride ions have been removed; a precipitation liquid preparation step of adding iron chloride to the removal solution to obtain a precipitation liquid; a precipitation step of precipitating tungsten oxide particles from the precipitation solution; a washing step of washing the tungsten oxide particles obtained in the precipitation step with water; The method for producing amorphous tungsten oxide particles according to claim 1, comprising:

6. The method for producing amorphous tungsten oxide particles according to claim 5, wherein the pH of the preparation solution is 0.5 to 5.

7. 7. The method for producing amorphous tungsten oxide particles according to claim 6, wherein more than 0.1 parts by weight and less than 7 parts by weight of iron chloride is added to 100 parts by weight of the removal solution in the precipitation solution preparation step.

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