Structural color particles and structural color pigments containing structural color particles

Abstract

The present invention provides structural color particles that can be safely used on the human body and in the environment, and that have strength free of practical problems, and demonstrate heat resistance. These structural color particles have agglomerations of primary particles, which include spherical silica primary particles and black primary particles comprising silicon dioxide and an inorganic component other than carbon.

Description

[Technical Field]

[0001] This invention relates to structural color particles and structural color pigments containing structural color particles. [Background technology]

[0002] Structural color is a color phenomenon that originates from the spectral dispersion caused by microstructures close to the wavelength of light rays. Unlike color produced by dyes or pigments, it does not decolorize due to the absorption of ultraviolet light, and the color will persist indefinitely as long as the microstructures that cause the color phenomenon do not disappear.

[0003] Materials with this type of structural coloration can achieve vivid colors without using heavy metals such as mercury and chromium, thus having a low environmental impact and meeting the need for safety and security, and are expected to have applications in new pigments. In particular, structural coloration materials using silica (silicon dioxide, SiO2), which do not contain components that are harmful to the human body or have a high environmental impact, are attracting attention.

[0004] Various structural color-developing materials using silica have been proposed, and the present inventors have also proposed particulate and film-type structural color-developing materials. For example, Non-Patent Document 1 describes spherical colloidal crystals formed from silica nanoparticles, and mentions that the saturation can be increased by adjusting the particle size of the spherical colloidal crystals and by introducing a small amount of carbon black. Non-Patent Documents 2 to 4 also describe forming a structural color film by depositing silica nanoparticles on the electrode surface using electrophoresis. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] M. Sakai et al., “Monodisperse Silica Nanoparticle-Carbon Black Composite Microspheres as Photonic Pigments,” ACS Appl. Nano Mater., vol.3, no.7, pp.7047-7056, 2020. [Non-Patent Document 2] K. Katagiri et al., “Structural color coating films composed of an amorphous array of colloidal particles via electrophoretic deposition,” NPG Asia Mater., vol. 9, no. 3, pp. 1-4, 2017. [Non-Patent Document 3] K. Katagiri, et al., “Structurally colored coating films with tunable iridescence fabricated: Via cathodic electrophoretic deposition of silica particles,” RSC Adv., vol. 8, no. 20, pp. 10776-10784, 2018. [Non-Patent Document 4] K. Katagiri et al., “Robust structurally colored coatings composed of colloidal arrays prepared by the cathodic electrophoretic deposition method with metal cation additives,” ACS Appl. Mater. Interfaces, vol. 12, no. 36, pp. 40768-40777, 2020. [Overview of the project] [Problems that the invention aims to solve]

[0006] Conventional structural color-developing materials using silica can easily exhibit structural color by self-arranging silica particles. However, they lack sufficient strength, and the structure easily collapses when external force is applied, causing the structural color to be lost. The spherical colloidal crystal described in Non-Patent Literature 1 has the characteristic of suppressed angle dependence of color development, but its structure was easily collapsed when external stress was applied. Furthermore, the structural color film described in Non-Patent Document 2 sometimes collapsed when peeled off from the electrode. Furthermore, the structural color films described in Non-Patent Documents 3-4 have a high-strength structural color film formed on the electrode surface, but they have low heat resistance, and their structure collapses in high-temperature environments, causing them to lose their structural color.

[0007] Structural color-developing materials using silica are highly safe for the human body and have a reduced environmental impact, making them desirable for use in cosmetics and paints, with particulate structural color-developing materials being particularly in high demand. Such structural color particles are required to possess strength and heat resistance to withstand contact friction with other materials during manufacturing, as well as heating and pressurizing. Furthermore, they are desirable to possess the property of not fading even after prolonged outdoor use.

[0008] Therefore, the object of the present invention is to provide structural color particles that have sufficient strength for practical use, as well as heat resistance and weather resistance, and that can be used safely for the human body and the environment. [Means for solving the problem]

[0009] In view of the above problems, the inventors of the present invention conducted research and found that structural color particles, which consist of aggregates of primary particles including spherical silica primary particles and black primary particles made of inorganic components other than silicon dioxide and carbon, possess strength, heat resistance, and weather resistance, and thus completed the present invention.

[0010] The present invention relates to the following <1> ~ <14> This concerns... <1>Structural color particles formed by aggregation of a plurality of primary particles, wherein the primary particles include spherical silica primary particles and black primary particles composed of inorganic components other than silicon dioxide and carbon. <2>The cumulative 50% particle size D 50 of the silica primary particles based on the number standard is d, and the cumulative 50% particle size D 50 of the black primary particles based on the number standard is a. The structural color particles according to <1> above, wherein the ratio a / d of a to d is 1.0 or more and 10.0 or less. <3>The average number N Si of the silica primary particles present on the surfaces of any 10 structural color particles and the average number N BL of the black primary particles satisfy the following relational expression (1). The structural color particles according to <1> or <2> above. N Si ≧10×(a / d) 2 ×N BL ···(1) (In formula (1), d is the cumulative 50% particle size D 50 of the silica primary particles based on the number standard, and a is the cumulative 50% particle size D 50 of the black primary particles based on the number standard.) <4>The structural color particles according to any one of <1> to <3> above, having polyvalent metal ions as a binding aid between the grains of the plurality of primary particles. <5>The structural color particles according to any one of <1> to <4> above, wherein the average particle size of the structural color particles is 4 to 80 μm. <6>The structural color particles according to any one of <1> to <5> above, wherein the coefficient of variation (CV) of the particle size of the structural color particles is 10% or more. <7>The structural color particles according to any one of <1> to <6> above, wherein the shape of the structural color particles is at least one of a spherical shape and a polyhedral shape having at least two non-parallel opposing faces. <8>The structural color particles according to any one of <1> to <7> above, wherein the content ratio of the silica primary particles to the black primary particles is a mass ratio in terms of oxides, and silica primary particles:black primary particles is 50:50 to 98:2. <9> The structural color particles contain, in terms of oxides, 50 to 98% by mass of SiO2, 0 to 30% by mass of CaO, MgO, SrO, and BaO in total, 0 to 18% by mass of Li2O, Na2O, and K2O in total, and 2 to 50% by mass of transition metal elements. <1> ~ <8> Structural color particles as described in one of the following. <10> When the structural color particles are heat-treated at 800°C for 3 hours in an atmospheric environment, the difference in brightness before and after the heat treatment is 20 or less. <1> ~ <9> Structural color particles as described in one of the following. <11> When the structural color particles are subjected to a light-washing process at 2000 rpm for 1 minute using a rotational mixer, the difference in brightness before and after the light-washing process is 10 or less. <1> ~ <10> Structural color particles as described in one of the following. <12> When the aforementioned structural color particles are subjected to a weather resistance test by irradiating them with light of a specified intensity for 500 hours in accordance with the apparatus for exposure to artificial light (Method B) described in JIS K5101-9, the difference in brightness before and after the weather resistance test is 10 or less. <1> ~ <11> Structural color particles as described in one of the following. <13> The aforementioned <1> ~ <12> A structural color pigment containing structural color particles as described in any one of the following. <14> The aforementioned <1> ~ <12> A mixed structural color pigment containing two or more structural color particles as described in any one of the following. [Effects of the Invention]

[0011] According to the present invention, structural color particles with high strength and excellent heat resistance and weather resistance can be provided. Furthermore, the structural color particles of the present invention have low angle dependence and can be applied to various uses such as cosmetics and pigments. In addition, the structural color particles of the present invention are suitable for use in mixed colors. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 shows a scanning electron microscope (SEM) image of the structural color particles obtained in Example 1. [Figure 2] Figure 2 shows an optical microscope image of the structural color particles obtained in Example 1. [Modes for carrying out the invention]

[0013] The present invention will be described below, but the present invention is not limited by the examples in the following description. In this specification, "mass" is synonymous with "weight."

[0014] The structural color particles of the present invention are structural color particles formed by the aggregation of a plurality of primary particles, wherein the primary particles include spherical silica primary particles and black primary particles made of inorganic components other than silicon dioxide and carbon. In other words, the structural color particles of the present invention are secondary particles formed by the aggregation of primary particles.

[0015] Furthermore, the structural color particles of the present invention are often aggregates of the secondary particles described above, and each individual secondary particle (structural color particle) possesses the above-described structure.

[0016] The structure of structural color particles can be confirmed by transmission electron microscopy (TEM) or scanning electron microscopy (SEM). In the case of SEM observation, it can be confirmed by observing the surface and cross-section of the particles.

[0017] (Silica primary particles) The silica primary particles are composed of silica (SiO2). It is preferable that the silica primary particles are substantially free of impurities, but a small amount of alkali metal components may be present. If alkali metal components are intentionally included, the mass concentration of the alkali metal components is preferably 200 to 8000 ppm, more preferably 300 to 7000 ppm, even more preferably 500 to 6000 ppm, particularly preferably 800 to 5000 ppm, and most preferably 1000 to 4000 ppm. Here, the mass concentration of the alkali metal components is preferably 200 ppm or more, more preferably 300 ppm or more, even more preferably 500 ppm or more, particularly preferably 800 ppm or more, and most preferably 1000 ppm or more. Furthermore, the mass concentration of the alkali metal component is preferably 8000 ppm by mass or less, more preferably 7000 ppm by mass or less, even more preferably 6000 ppm by mass or less, particularly preferably 5000 ppm by mass or less, and most preferably 4000 ppm by mass or less.

[0018] The primary silica particles are perfectly spherical. The sphericity, a measure of how close an object's shape is to a perfect sphere, is preferably 80% or higher. The spherical shape of the primary silica particles allows for the realization of a periodic structure sufficient to produce structural color through aggregation, self-alignment, etc. The sphericity is more preferably 83% or higher, even more preferably 85% or higher, particularly preferably 87% or higher, and especially preferably 90% or higher. The higher the sphericity, the better, and 100% is most preferable.

[0019] The sphericity is determined by measuring 100 arbitrary silica primary particles that make up one structural color particle in a photographic projection obtained by photographing the structural color particle with a scanning electron microscope (SEM). For each of the 100 arbitrary silica primary particles, the diameter of its circumscribed circle (DL) and the diameter of its inscribed circle (DS) are measured, and the average value of the ratio of the inscribed circle diameter (DS) to the circumscribed circle diameter (DL) (circularity, DS / DL) is expressed as a percentage to determine the sphericity. If the number of silica primary particles that make up one structural color particle is less than 100, the sphericity is determined by measuring the particle size of all silica primary particles visible in the SEM image of one structural color particle.

[0020] The silica primary particles constituting the structural color particles of the present invention need to be selected with an appropriate particle size depending on the desired color development. However, for achieving color development in the visible light range, a particle size in the range of 100 to 1000 nm is preferable. When the particle size is 100 nm or more, color development is obtained due to light interference, diffraction, and scattering based on the arrangement of silica primary particles, and when it is 1000 nm or less, it is easier to adjust the particle size of the structural color particles. The particle size of the silica primary particles is more preferably 110 to 900 nm, even more preferably 120 to 800 nm, and particularly preferably 130 to 700 nm. From the viewpoint of suppressing Rayleigh scattering, which may adversely affect color development, and avoiding adverse effects on the human body, the particle size is more preferably 110 nm or more, even more preferably 120 nm or more, and particularly preferably 130 nm or more. Furthermore, from the viewpoint of suppressing Mie scattering, which may adversely affect color development, and achieving good alignment during secondary particle formation, the particle size of the silica primary particles is more preferably 900 nm or less, even more preferably 800 nm or less, and particularly preferably 700 nm or less.

[0021] Cumulative 50% particle size D based on the number of primary silica particles in structurally colored particles 50 Therefore, it is necessary to select a particle size appropriate for the desired color development. In this invention, the main wavelength λ of the desired structural color particles is used for color development. d D for [nm] 50 [nm] ratio D 50 / λ dIt is preferable that the range is 0.30 to 0.60. 50 / λ d If the above range is maintained, the desired color can be easily obtained by adjusting the interparticle distance or the refractive index of the medium. 50 / λ d It is more preferably 0.33 to 0.55, even more preferably 0.34 to 0.50, and particularly preferably 0.35 to 0.47. Here, D 50 / λ d It is preferably 0.30 or higher, more preferably 0.33 or higher, even more preferably 0.34 or higher, particularly preferably 0.35 or higher, and also preferably 0.60 or lower, more preferably 0.55 or lower, even more preferably 0.50 or lower, and particularly preferably 0.47 or lower.

[0022] Furthermore, the cumulative 10% particle size D is determined based on the number of primary silica particles in the structurally colored particles. 10 From the viewpoint of preventing adverse effects on the human body, it is preferable that the wavelength be 100 nm or greater.

[0023] The particle size distribution of primary silica particles in structurally colored particles can be measured using a particle size distribution analyzer or by observation with a scanning electron microscope (SEM). Examples of particle size distribution analyzers include Microtrac's "Nanotrac" (product name). When performing SEM observation, the particle size distribution is determined by measuring any 100 primary silica particles that make up one particle of a given structurally colored particle using SEM observation. If the number of primary silica particles that make up one structurally colored particle is less than 100, the particle size distribution can be determined by measuring the particle size of all primary silica particles visible in the SEM image of that single structurally colored particle. Furthermore, since the particle size of primary silica particles is difficult to determine accurately due to the shape and shading of structural color particles, it is preferable to use image processing software ImageJ to process and evaluate them.

[0024] If you want structural color particles with less angle dependence on color development, use the cumulative 10% particle size D based on the number of silica primary particles. 10 Cumulative 90% particle size D 90 Ratio D 90 / D 10It is preferable that the ratio is between 1.05 and 4.00. 90 / D 10 Because it falls within this range, the packing conditions when primary particles align have a periodicity sufficient to produce structural color, while also fluctuating slightly. Therefore, it is expected that the angle dependence will be mitigated to some extent while maintaining the coloration as structural color. Ratio D 90 / D 10 It is more preferably 1.10 to 3.00, even more preferably 1.10 to 2.50, particularly preferably 1.10 to 2.25, especially preferably 1.10 to 2.20, and most preferably 1.10 to 2.00.

[0025] The particle size (D) of the silica primary particles required to obtain the desired color 50 An example of the scope of ) is as follows: If you want to produce a blue color using the structural color particles of the present invention, it is preferable to set the particle size of the silica primary particles constituting the structural color particles to the range of 150 to 235 nm. More preferably, the particle size is in the range of 180 to 230 nm, and even more preferably, in the range of 190 to 225 nm.

[0026] Furthermore, if you want to produce a green color using the structural color particles of the present invention, it is preferable to set the particle size of the silica primary particles constituting the structural color particles to the range of 235 to 265 nm. More preferably, the particle size is in the range of 240 to 260 nm, and even more preferably, in the range of 245 to 255 nm.

[0027] Furthermore, if you want to produce a red color using the structural color particles of the present invention, it is preferable to set the particle size of the silica primary particles constituting the structural color particles to the range of 265 to 320 nm. More preferably, the particle size is in the range of 270 to 315 nm, and even more preferably, in the range of 275 to 310 nm.

[0028] (Black primary particles) The black primary particles constituting the structural color particles of the present invention consist of inorganic components other than silicon dioxide and carbon. By including black primary particles composed of inorganic components other than silicon dioxide and carbon, the strength of the structural color particles is improved, and the saturation of the color can be further enhanced by reducing non-coherent scattered light. In addition, by selecting heat-resistant black primary particles that do not discolor when used at high temperatures of 600°C or higher, it is possible to maintain the saturation and brightness of the color even in high-temperature environments.

[0029] As for black primary particles, L is normalized by the CIE. * a * b * In a color system, L * Value is 30 or less, C * It is preferable to select materials with a value of 10 or less. Furthermore, it is desirable that the material does not decompose, deform, or melt even at temperatures above 300°C. Examples of black primary particles include particles made from metal oxides such as Fe-Cr compounds (e.g., Black 6350 manufactured by Asahi Kasei Corporation), Mn-Bi compounds (e.g., Black 6301 manufactured by Asahi Kasei Corporation), cobalt black (Co3O4 or Cr-Fe-Co-Ni-O compounds), Cu(Fe,Mn)O4 (e.g., TM Black manufactured by Dainichi Seika Kogyo Co., Ltd.), Ti compounds (e.g., Tilack D manufactured by Ako Kasei Co., Ltd.), and Fe3O4. From an environmental perspective, it is preferable to use metal oxides that do not contain Co, Cr, or Ni, and contain at least one metal element selected from the group consisting of V, Mn, Fe, Cu, Zn, Mo, Nb, Ta, W, and lanthanides. Examples of such metal oxides include black pigments containing CaO-TiO2-MnO2 solid solution (e.g., MPT370 manufactured by Ishihara Sangyo Co., Ltd.), and black pigments described in Japanese Patent Publication No. 6592125 and the document "Synthesis and characterization of black pigments based on calcium manganese oxides for high near-infrared (NIR) reflectance" (R. Oka and T. Masui, RSC Advances, vol. 6, no. 93, pp.90952-90957, 2016).

[0030] The size of the black primary particles is preferably in the range of 10 nm to 20 μm in particle diameter. When the particle diameter is 10 nm or larger, it is easy to uniformly mix with the silica primary particles when synthesizing the structural color particles, and the effect of improving saturation with respect to the amount added is good. When the particle diameter is 20 μm or less, it is less likely that the desired effect will not be obtained because the particles are not incorporated into the structure of the structural color particles, and it is expected that the angle dependence of color development will be reduced by moderately disrupting the arrangement of the silica primary particles. The particle diameter of the black primary particles is more preferably 40 nm to 18 μm, even more preferably 60 nm to 16 μm, particularly preferably 80 nm to 14 μm, and most preferably 100 nm to 14 μm. Here, the particle size of the black primary particles is preferably 10 nm or larger, more preferably 40 nm or larger, even more preferably 60 nm or larger, even more preferably 80 nm or larger, particularly preferably 100 nm or larger, and also preferably 20 μm or smaller, more preferably 18 μm or smaller, even more preferably 16 μm or smaller, and particularly preferably 14 μm or smaller.

[0031] Cumulative 50% particle size D based on the number of black primary particles in structurally colored particles 50 The particle size is preferably 50-3000 nm. 50% particle size D 50 When the particle size is 50 nm or greater, the effect of improving saturation relative to the amount added is good. When it is 3000 nm or less, it is less likely that the desired effect will not be obtained because the particle is not incorporated into the structure of the structural color particles. By moderately disrupting the arrangement of silica primary particles, it is expected that the angle dependence of the color will be reduced. 50% particle size D 50 The wavelength is more preferably 75 to 2800 nm, even more preferably 100 to 2600 nm, and particularly preferably 125 to 2400 nm. Here, 50% particle size D 50 The wavelength is preferably 50 nm or more, more preferably 75 nm or more, even more preferably 100 nm or more, particularly preferably 125 nm or more, and also preferably 3000 nm or less, more preferably 2800 nm or less, even more preferably 2600 nm or less, and particularly preferably 2400 nm or less.

[0032] Cumulative 10% particle size D based on the number of black primary particles in structurally colored particles 10The particle size is preferably 20 to 1500 nm. 10% particle size D 10 If the particle size is 20 nm or larger, it is easy to uniformly mix structural color particles with silica primary particles when synthesizing them. If it is 1500 nm or smaller, it is possible to suppress the occurrence of color unevenness between particles due to the non-uniform number of black particles in each structural color particle. 10% particle size D 10 The particle size is more preferably 50-1200 nm, even more preferably 75-800 nm, and particularly preferably 100-400 nm. Here, 10% particle size D 10 The wavelength is preferably 20 nm or more, more preferably 50 nm or more, even more preferably 75 nm or more, particularly preferably 100 nm or more, and also preferably 1500 nm or less, more preferably 1200 nm or less, even more preferably 800 nm or less, and particularly preferably 400 nm or less.

[0033] Cumulative 90% particle size D based on the number of black primary particles in structurally colored particles 90 The particle size is preferably 400 nm to 20 μm. 90% particle size D 90 When the particle size is 400 nm or larger, the effect of improving saturation relative to the amount added is good. When it is 20 μm or smaller, it is less likely that the desired effect will not be obtained because it will not be incorporated into the structure of the structural color particles. By moderately disrupting the arrangement of silica primary particles, it is expected that the angle dependence of color development will be reduced. 90% particle size D 90 The particle size is more preferably 520 nm to 12 μm, even more preferably 650 nm to 10 μm, and particularly preferably 800 nm to 8 μm. Here, the 90% particle size D 90 The wavelength is preferably 400 nm or more, more preferably 520 nm or more, even more preferably 650 nm or more, particularly preferably 800 nm or more, and also preferably 20 μm or less, more preferably 12 μm or less, even more preferably 10 μm or less, and particularly preferably 8 μm or less.

[0034] The particle size distribution of black primary particles in structural color particles can be measured using a particle size analyzer or SEM observation, as described above. When performing SEM observation, the particle size of 100 randomly selected black primary particles is measured. If the number of black primary particles is small compared to the number of silica primary particles, and it is difficult to confirm 100 black primary particles in SEM observation, it is acceptable to measure a possible number of particles, 10 or more, for convenience. If no black primary particles are observed on the surface of the structural color particles, the structural color particles may be broken by applying an external force to form a fracture surface, and the black particles present on the fracture surface may be measured. The particle size is determined using the diameter of the circumscribed circle of the particle.

[0035] In the present invention, the cumulative 50% particle size D is determined based on the number of primary silica particles in the structural color particles. 50 D is the cumulative 50% particle size based on the number of black primary particles. 50 When a is the average particle size of silica primary particles, d(D 50 ) with respect to the average particle size a(D 50 The ratio a / d of ) is preferably 1.0 or more and 10.0 or less. When the ratio a / d is 1.0 or more, the strength and heat resistance of the structural color particles can be improved, and when it is 10.0 or less, black primary particles tend to be present on average among the structural color particles, making it easier to form a periodic structure of silica primary particles sufficient for structural color expression.

[0036] However, if too many black primary particles are present on the surface of structural color particles, the color development will be inhibited. Therefore, the average number of silica primary particles N on the surface of any 10 structural color particles is important. Si and the average number of black primary particles N BL It is preferable that the following relation (1) is satisfied. N Si ≥10 × (a / d) 2 ×N BL ...(1) (In equation (1), d is the cumulative 50% particle size D based on the number of primary silica particles) 50 , a is the cumulative 50% particle size D based on the number of black primary particles. 50 (That is the case.)

[0037] The structural color particles of the present invention only need to have the specific black primary particles described above, and the desired effect can be obtained regardless of whether or not the black primary particles are present on the surface of the particles. Average number of silica primary particles N Si and the average number of black primary particles N BL By satisfying the relationship in equation (1), it is possible to achieve excellent color development while further enhancing the strength and heat resistance of structural color particles.

[0038] The ratio of silica primary particles to black primary particles in structurally colored particles is preferably 50:50 to 98:2 in terms of oxide mass ratio. When the ratio of silica primary particles to black primary particles is within the above range, it is possible to achieve both improved strength and heat resistance of the structurally colored particles and the expression of structural color. The ratio is more preferably 55:45 to 95:5 for silica primary particles to black primary particles, even more preferably 60:40 to 90:10, and particularly preferably 65:35 to 85:15.

[0039] (binding agent) The structural color particles of the present invention may have polyvalent metal ions as binding aids between multiple primary particles. By including polyvalent metal ions, the bonds between primary particles become stronger, thereby achieving excellent strength and heat resistance.

[0040] Examples of polyvalent metal ions include Ca 2+ Mg 2+ Cu 2+ Ni 2+ Zn 2+ Ba 2+ Divalent metal ions such as Fe 3+ , Cr 3+ , Y 3+ and Al 3+ Examples of trivalent metal ions include Ca. 2+ Mg 2+ Zn 2+ Ba 2+ , Y 3+ and Al 3+ It is preferable that the following be included.

[0041] Polyvalent metal ions can be contained as hydroxides, oxides, or polyvalent metal salts. In the manufacturing process of structural color particles, polyvalent metal ions are added as polyvalent metal salts, exist as hydroxides during the particle formation stage, and are assumed to change to oxides during the firing process if the particles are fired products. Examples of polyvalent metal salts include sulfates, nitrates, and carboxylates, and examples of their salts include sodium salts and potassium salts.

[0042] The polyvalent metal ion content in structurally colored particles is preferably 50 to 50,000 wtppm in terms of oxides. A polyvalent metal ion content of 50 wtppm or more can increase the bonding force between primary particles, while a content of 50,000 wtppm or less does not affect the expression of structural color. A polyvalent metal ion content of 100 to 35,000 wtppm is more preferable, 200 to 25,000 wtppm is even more preferable, and 500 to 15,000 wtppm is particularly preferable. Here, the polyvalent metal ion content is preferably 50 wtppm or more, more preferably 100 wtppm or more, even more preferably 200 wtppm or more, particularly preferably 500 wtppm or more, and also preferably 50,000 wtppm or less, more preferably 35,000 wtppm or less, even more preferably 25,000 wtppm or less, and particularly preferably 15,000 wtppm or less.

[0043] Furthermore, polyvalent metal ions in structurally colored particles can be measured by methods such as ICP emission spectroscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence spectroscopy.

[0044] (Composition of structural color particles) In the present invention, it is preferable that the structural color particles contain 50 to 98% by mass of SiO2, 0 to 30% by mass of RO, 0 to 18% by mass of R2O, and 2 to 50% by mass of transition metal elements, in terms of oxides. Here, RO is the total amount of alkaline earth metal oxides consisting of CaO, MgO, SrO, and BaO, and R2O is the total amount of alkali metal oxides consisting of Li2O, Na2O, and K2O. Transition metal elements are elements located between Group 3 and Group 11 of the periodic table, such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, La, and Ce. When the content of each component is within the above range, both color development and intensity can be achieved. In structurally colored particles, it is more preferable that the SiO2 content is 55-95% by mass, the RO content is 0-25% by mass, the R2O content is 0-10% by mass, and the transition metal element content is 2-30% by mass, in terms of oxides.

[0045] (Physical properties) The structural color particles of the present invention preferably have an average particle size of 4 to 80 μm. When the average particle size of the structural color particles is 4 μm or more, structural color can be expressed, and when it is 80 μm or less, the graininess of each color is suppressed when structural color particles with different colors are mixed, and the colors appear to be mixed beautifully. The average particle size is more preferably 6 to 60 μm, even more preferably 8 to 45 μm, and particularly preferably 10 to 30 μm. Here, the average particle size is preferably 4 μm or more, more preferably 6 μm or more, even more preferably 8 μm or more, particularly preferably 10 μm or more, and also preferably 80 μm or less, more preferably 60 μm or less, even more preferably 45 μm or less, and particularly preferably 30 μm or less.

[0046] The average particle size is determined by taking SEM images of 100 structural color particles, taking the arithmetic mean of the major and minor axis lengths of each structural color particle as the particle size, and then taking the arithmetic mean of the particle sizes of the 100 structural color particles as the average particle size.

[0047] In the present invention, the coefficient of variation (CV) of the particle size of the structural color particles in the aggregate is preferably 10% or more. When the coefficient of variation (CV) of the particle size is 10% or more, it is easier to produce a more vivid color. The coefficient of variation (CV) of the particle size is more preferably 10 to 80%, even more preferably 15 to 80%, particularly preferably 20 to 70%, and most preferably 25 to 60%. Here, the coefficient of variation (CV) of the particle size is preferably 10% or more, more preferably 15% or more, even more preferably 20% or more, and particularly preferably 25% or more. Furthermore, from the viewpoint of maintaining the homogeneity of the texture when used as a pigment, it is preferably 80% or less, more preferably 70% or less, and even more preferably 60% or less.

[0048] The coefficient of variation (CV) of the particle size of structural color particles is the value obtained by dividing the standard deviation of the particle sizes of 100 structural color particles, as calculated above, by the arithmetic mean.

[0049] The shape of the structural color particles is preferably one of the following: spherical or polyhedral, with at least two faces that are not parallel to each other. When the structural color particles are spherical or polyhedral, the angle dependence of the color development is reduced, making them applicable to a wide variety of uses. Furthermore, "spherical" refers not only to literally spherical shapes in a geometric sense, but also to particles that have surface irregularities that inevitably occur during the manufacturing process of spherical particles, and particles whose cross-section, including the center of gravity, is not perfectly circular but distorted by the cut. In the case of polyhedral shapes, it is preferable that there are six or more planes, and more preferably eight or more planes.

[0050] The structural color particles of the present invention preferably have an aspect ratio of 1.0 to 5.0. Here, the aspect ratio is the value obtained by dividing the principal axis length by the secondary axis length when the shape of the structural color particles is approximated as an ellipse, so it is 1.0 or greater. On the other hand, if the aspect ratio is 5.0 or less, particle orientation when the structural color particles are coated can be suppressed, and the angle dependence of color development can be reduced. The aspect ratio is more preferably 1.01 to 4.6, even more preferably 1.05 to 4.2, and particularly preferably 1.1 to 3.8. For example, in cosmetic applications, from the viewpoint of a smooth feel when in contact with the skin and improved color development due to appropriate shape fluctuations, the aspect ratio is more preferably 1.01 or greater, even more preferably 1.05 or greater, particularly preferably 1.1 or greater, and also more preferably 4.6 or less, even more preferably 4.2 or less, and particularly preferably 3.8 or less.

[0051] The structural color particles of the present invention, when heat-treated at 800°C for 3 hours in an atmospheric environment, exhibit a difference in brightness (L) before and after heat treatment. * ab It is preferable that the difference (ΔL) between the two values ​​is 20 or less. If the difference in brightness before and after the heat treatment is 20 or less, it indicates that the degradation due to the heat treatment is small, resulting in structural color particles with high heat resistance. Brightness before and after heat treatment (L * ab The difference (ΔL) between ) is more preferably 15 or less, even more preferably 10 or less, particularly preferably 5 or less, and there is no particular lower limit, but it is most preferably 0.

[0052] Furthermore, when the structural color particles of the present invention are subjected to a lightning treatment at 2000 rpm for 1 minute using a rotational mixer, the lightness (L) before and after the lightning treatment is measured. * ab It is preferable that the difference (ΔL) between the two values ​​is 10 or less. When the difference in brightness before and after the aforementioned raikai treatment is 10 or less, it is understood that the strength is high and it is less susceptible to deterioration by grinding, thus resulting in structural color particles that are less affected by external forces, etc. Brightness before and after processing (L * abThe difference (ΔL) is more preferably 8 or less, still more preferably 6 or less, particularly preferably 4 or less, and the lower limit is not particularly limited, with 0 being most preferable.

[0053] In addition, when the structural color particles of the present invention are subjected to a weather resistance test by irradiating light with a specified illuminance for 500 hours in accordance with the apparatus (Method B) for exposing to artificial light described in JIS K5101-9, the lightness (L * ab ) difference (ΔL) before and after the weather resistance test is preferably 10 or less. When the difference in lightness before and after the weather resistance test is 10 or less, it can be seen that the color does not fade even under ultraviolet irradiation or a high-temperature environment, resulting in highly durable structural color particles. The difference in lightness (ΔL) before and after the weather resistance test * ab is more preferably 8 or less, still more preferably 6 or less, particularly preferably 4 or less, and the lower limit is not particularly limited, with 0 being most preferable.

[0054] Note that the difference in lightness (ΔL) in the above test is the absolute value of the difference before and after the test of lightness L * ab as defined in JIS Z8781-4, and L * ab can be calculated from measurement values by a general color difference meter or spectrum measurement results by a visible ultraviolet spectrophotometer, etc.

[0055] (Method for producing structural color particles) The structural color particles of the present invention can be produced, for example, by a method of forming spherical colloidal crystals, a method of forming an electrodeposited film by electrodeposition and then pulverizing it, or the like.

[0056] One method for forming spherical colloidal crystals involves dispersing a water phase containing silica primary particles and black primary particles in an insoluble organic liquid to form an oil-in-water emulsion. This emulsion is then removed by repeating drying and solvent replacement one or more times, resulting in structurally colored particles formed by the aggregation of primary particles. In this method, the primary particles self-align during the aggregation process, forming a colloidal crystal structure with a periodic structure and exhibiting structural color.

[0057] The aqueous phase of the emulsion mainly contains water as a solvent. This aqueous phase forms droplets within the emulsion, creating spherical structural color particles. Further additives such as water-soluble organic liquids and water-soluble resins may be added to the aqueous phase. The proportion of water in the aqueous phase is preferably 50-100% by mass, and more preferably 90-100% by mass.

[0058] The oil phase of the emulsion preferably contains an insoluble organic liquid that is incompatible with the aqueous phase component. Examples of insoluble organic liquids include aliphatic hydrocarbons such as n-hexane, isohexane, n-heptane, isoheptane, n-octane, isooctane, n-nonane, isononane, n-pentane, isopentane, n-decane, isodecane, n-dodecane, isododecane, pentadecane, hexadecane, or mixtures thereof such as paraffinic base oils, alicyclic hydrocarbons such as cyclopentane, cyclohexane, cyclohexene, or mixtures thereof such as naphthenic base oils, benzene, toluene, xylene, ethylbenzene, propylbenzene, Examples include aromatic hydrocarbons such as cumene, mesitylene, tetralin, and styrene; ethers such as propyl ether and isopropyl ether; esters such as ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, butyl lactate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, and butyl butyrate; vegetable oils such as palm oil, soybean oil, and rapeseed oil; and fluorinated solvents such as hydrofluorocarbons, perfluorocarbons, and perfluoropolyethers. Polyoxyalkylene glycols that become hydrophobic liquids at the reaction temperature can also be used. Examples include polypropylene glycol (molecular weight 1000 or more), polyoxyethylene-polyoxypropylene block copolymers with a proportion of oxyethylene units of less than 20% by mass and a cloud point (1% by mass aqueous solution) of 40°C or less, preferably 20°C or less. These may be used individually or in combination of two or more, as long as they form an oil phase as a single phase.

[0059] The emulsion contains a surfactant to enhance emulsification stability. The surfactant is preferably a nonionic surfactant. Examples of nonionic surfactants include the following: Sorbitan fatty acid esters: sorbitan monooleate, sorbitan monostearate, sorbitan monolaurate, Polyoxyethylene-polyoxypropylene copolymer surfactant, Polyoxyethylene sorbitan fatty acid ester surfactants: polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, Polyoxyethylene higher alcohol ether-based surfactants: polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene octylphenol ether, polyoxyethylene nonylphenol ether, Polyoxyethylene aliphatic ester surfactants: polyoxyethylene glycol monolaurate, polyoxyethylene glycol monostearate, polyoxyethylene glycol monooleate, Glycerin fatty acid ester-based surfactants: monoglyceride stearate, monoglyceride oleate. Furthermore, polyoxyethylene sorbitol fatty acid ester surfactants, sucrose fatty acid ester surfactants, polyglycerin fatty acid ester surfactants, polyoxyethylene hydrogenated castor oil surfactants, etc., may also be used. These may be used individually or in combination of two or more types.

[0060] The primary particle dispersion can be dried by known methods. It may be air-dried or heat-dried, and if heat is used, it is preferable to dry it at 40 to 200°C.

[0061] In this invention, the dispersion medium may be removed and the remaining structural color particles may be heat-treated (fired). Heat treatment creates necks (bonding parts) between primary particles in the range where structural color is expressed, thereby increasing the bonding strength between primary particles and increasing the mechanical strength of the structural color particles. By using heat-resistant black primary particles that can maintain their black color even after heat treatment, the saturation and brightness of the structural color particles can be maintained even after heat treatment.

[0062] The heat treatment method is not particularly limited and can be carried out by conventionally known methods. The heat treatment temperature is preferably 600 to 1200°C. If the heating temperature is 600°C or higher, sufficient neck bonding can be achieved, improving the bonding between primary particles, and if it is 1200°C or lower, deformation of black particles and excessive neck formation between silica primary particles can be prevented, maintaining the color. The heat treatment temperature is more preferably 650 to 1100°C, even more preferably 700 to 1100°C, particularly preferably 750 to 1000°C, and most preferably 800 to 1000°C. Here, the heat treatment temperature is preferably 600°C or higher, more preferably 650°C or higher, even more preferably 700°C or higher, even more preferably 750°C or higher, and particularly preferably 800°C or higher. Furthermore, the heat treatment temperature is preferably 1200°C or lower, more preferably 1100°C or lower, and even more preferably 1000°C or lower.

[0063] The heat treatment time is not particularly limited as long as the neck can be formed, but considering manufacturing efficiency, it is preferably 0.5 to 4 hours, and more preferably 1 to 3 hours. The heat treatment atmosphere can be appropriately selected depending on the type of black primary particles used, and is not particularly limited, but the desired effect can be obtained by heat treatment in an atmospheric atmosphere.

[0064] In the electrodeposition method, an electrodeposited film is prepared according to a conventionally known method, and then the film is peeled off, crushed, and classified to obtain structural color particles. In this invention, a binding agent is included in the primary particle dispersion for the preparation of the electrodeposited film. A primary particle dispersion is prepared by mixing a sol solution in which silica primary particles are dispersed in a water-soluble solvent, black primary particles, and an aqueous solution of the binding agent. Then, the anode and cathode are immersed in an electrolytic cell containing the primary particle dispersion, and DC electrolysis is performed in this state. As a result, an electrodeposited film is formed on the surface of the anode. The electrodeposited film is peeled off from the anode, and structural color particles are obtained by crushing or cutting, etc. The structural color particles produced by this method have the characteristic that the short-range order forms close packing that produces structural color, while the medium- and long-range order is disrupted and not regularly packed. The regularly packed nature of the medium- and long-range order is influenced by the voltage during electrodeposition, the particle size distribution of the silica primary particles, the particle size distribution of the black particles, etc.

[0065] The binding agent strengthens the bonds between primary particles, increasing the mechanical strength of the structural color particles. Furthermore, the inclusion of black primary particles helps maintain saturation and brightness.

[0066] Examples of binding aids include compounds (polyvalent metal salts) containing the polyvalent metal ions mentioned above, and the same applies to preferred compounds. By using compounds containing metal ions instead of resins, mechanical strength can be maintained even in high-temperature environments, and by particularly selecting polyvalent metal ions that do not discolor in high-temperature environments, saturation and brightness can be maintained even in high-temperature environments.

[0067] The amount of binding agent used is preferably 50 to 50,000 wtppm in oxide terms relative to the amount of SiO2 in the structural color particles. If the amount of binding agent used is 50 wtppm or more, the strength of the structural color particles can be improved, and if it is 50,000 wtppm or less, the strength can be increased without inhibiting the expression of structural color. The amount of binder used is more preferably 100 to 35,000 wtppm relative to the amount of SiO2 in the structural color particles, even more preferably 200 to 25,000 wtppm, and particularly preferably 500 to 15,000 wtppm. Here, the amount of binder used is preferably 50 wtppm or more relative to the amount of SiO2 in the structural color particles, more preferably 100 wtppm or more, even more preferably 200 wtppm or more, particularly preferably 500 wtppm or more, and also preferably 50,000 wtppm or less, more preferably 35,000 wtppm or less, even more preferably 25,000 wtppm or less, and particularly preferably 15,000 wtppm or less.

[0068] As a solvent for dispersing the silica primary particles, for example, a water-soluble solvent can be used, and among these, 2-propanol is preferred.

[0069] Methods for grinding or cutting the electrodeposited film include, for example, jet mills, ball mills, vibrating ball mills, planetary mills, bead mills, etc., and the film should be ground or cut until the desired particle size is reached.

[0070] (Application) The structural color particles of the present invention obtained by the above method have enhanced bonding between primary particles, possess heat resistance, and further reduce angle dependence due to the particle size distribution of silica primary particles, making them suitable for a variety of applications. For example, it can be used in cosmetics, food colorings, toys, stationery, tableware, automobiles, buildings, signs, and various other paints and pigments.

[0071] (Structural color pigments) The present invention also provides structural color pigments containing the structural color particles described above. Structural color pigments can be produced, for example, by dispersing the structural color particles of the present invention in a solvent. Examples of solvents include oils and resins commonly used in cosmetics, and fluorinated solvents. These should be selected appropriately depending on the application and usage conditions. The amount of structural color particles in the solvent is also arbitrary.

[0072] Furthermore, by using two or more types of structural color particles, a mixed structural color pigment can be obtained, and by adjusting the particle size, mixing ratio, etc., of the structural color particles used, pigments of various colors can be produced. [Examples]

[0073] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following description, common components are the same. Examples 1-5 and 7-11 are examples, while Examples 6 and 12 are comparative examples.

[0074] (Evaluation method) The evaluation methods used for structural color particles in Examples 1-12 are shown below.

[0075] <Particle size distribution of primary particles> The particle size distribution of the silica primary particles was determined by taking SEM images of one particle of any structural color particles at a magnification that allows discrimination of the constituent silica primary particles, and measuring the particle sizes of 100 arbitrary silica primary particles from the images using image processing software ImageJ. After setting the length per pixel using Set Scale from the scale bar of the taken SEM image, only the region where the silica primary particles were clearly imaged was selected by Crop. After binarizing the image, each particle was separated by the Watershed algorithm, and the major axis length (Major), circularity (Circularity, Circ.), and aspect ratio (AR) were determined using Analyze Particles. Also, the circularity obtained here expressed as a percentage was defined as the sphericity of the silica primary particles. Among the obtained results, the major axis length of the particles with a sphericity greater than 90% and less than 100% (Circ. greater than 0.9 and less than 1) and an AR of 1.1 or less was defined as the particle size of the silica primary particles, and the cumulative 10% particle size based on the number standard was D 10 The cumulative 50% particle size based on the number standard was D 50 The cumulative 90% particle size based on the number standard was D 90 and so on.

[0076] The particle size distribution of the black primary particles was determined by measuring the particle sizes of 100 randomly selected black primary particles. In SEM observation, particles other than the spherical silica primary particles present on the surface including the fracture surface of the structural color particles were regarded as black primary particles, and evaluation was carried out according to the following procedure using image processing software ImageJ. After setting the length per pixel using Set Scale from the scale bar of the SEM image showing the black primary particles, the circumcircle of the black primary particles was selected by circular range selection, and its diameter was taken as the particle size, and the cumulative 10% particle size based on the number standard was D 10 The cumulative 50% particle size based on the number standard was D 50 The cumulative 90% particle size based on the number standard was D 90 and so on. When the number of black particles is less than the number of primary silica particles, it may be difficult to identify 100 primary black particles using SEM observation. In such cases, for convenience, measurements were performed with a minimum of 10 particles.

[0077] <Particle size and coefficient of variation (CV) of structural color particles> The average particle size and aspect ratio of structural color particles were determined by taking SEM images of 100 randomly selected structural color particles and using the ImageJ image processing software to obtain the results using the following procedure. After setting the length per pixel using Set Scale from the scale bar of the captured SEM image, the region where the entire structural color particle was clearly visible was selected using Crop. After binarizing the image, the individual particles were separated using the Watershed algorithm as needed, and then the major axis length, minor axis length, and aspect ratio (AR) were determined using Analyze Particles. The arithmetic mean of the major and minor axis lengths of each structural color particle was defined as the particle size, the arithmetic mean of the particle sizes of 100 randomly selected structural color particles was defined as the average particle size, and the arithmetic mean of the AR was defined as the aspect ratio. Furthermore, the coefficient of variation (CV) of particle size was defined as the value obtained by dividing the standard deviation of particle size by the arithmetic mean.

[0078] <Number of silica primary particles and black primary particles on the structural color particle surface> The average number of silica primary particles present on the surface of 10 arbitrary structural color particles is N. Si and the average number of black primary particles N BL This was determined by the following method. SEM images showing the entire structure color particle in good condition were acquired, and the following procedure was used with the image processing software ImageJ. After setting the length per pixel using Set Scale from the scale bar of the acquired SEM image, the entire structure color particle to be measured was selected as a region using an appropriate method according to the shape of the structure color particle, and its area was measured. This area was then used to determine the average particle size d(D) of the silica primary particles measured by the method described above. 50 Using ), 3.14 × (1 / 2 × d) 2The number of primary silica particles present on the surface of a structurally colored particle was determined by dividing the calculated value by the cross-sectional area per primary silica particle. In addition, particles other than spherical primary silica particles present on the surface of the same structurally colored particle from which the primary silica particles were determined were counted as black primary particles. Perform this operation for any 10 structural color particles, and take the arithmetic mean of the obtained counts as N. Si , N BL N Si , N BL Therefore, we checked whether the following relation (1) was satisfied. N Si ≥10 × (a / d) 2 ×N BL ...(1) (In equation (1), d is the cumulative 50% particle size D based on the number of primary silica particles) 50 , a is the cumulative 50% particle size D based on the number of black primary particles. 50 (That is the case.)

[0079] <Main wavelength of structural color particles (λ d ), brightness (L * ab ) and hue angle (h)> The dominant wavelength λ of structural color particles d The dominant wavelength λ was calculated based on the diffuse reflectance spectrum measurement results obtained using a UV-Vis spectrophotometer (V-670, manufactured by JASCO Corporation), according to the method specified in JIS Z8781-3:2016. However, if the dominant wavelength cannot be calculated from the spectrum measurement results (when the intersection point of the line extended from the white point to the coordinates calculated from the spectrum measurement results and the outer edge of the chromaticity coordinate is located on the pure violet locus side rather than the monochromatic locus side), the wavelength at which the reflectance spectrum present in the visible range is maximum and highest was used as the dominant wavelength λ for convenience. d That's what I decided. Lightness (L * ab The value was calculated based on the diffuse reflectance spectrum measurement results, in accordance with the method described in JIS Z8781-4:2013. The hue angle (h) was calculated based on the diffuse reflectance spectrum measurement results, following the method described in JIS Z8781-5:2013. If the calculated value was negative, 360 was added to obtain the hue angle (h).

[0080] <Color change (Δh) of structural color particles with respect to angle> The color change of structural color particles with respect to angle was investigated using the following procedure. First, the fabricated structural color particles were placed without gaps on a white substrate in a circle with a diameter of 5 mm and a thickness of approximately 0.1 mm. This was then photographed under white light from directly above and at a 45-degree angle. The obtained image data was converted to HSB Stack using the image processing software ImageJ, and the structural color particle portion of the Hue image was selected to calculate the average hue value. The color change Δh with respect to angle was defined as the absolute value of the difference between the average hue values ​​at directly above and at a 45-degree angle multiplied by 360 / 255. Due to the characteristics of the color wheel, if the above Δh exceeded 180 even though the color change was not significant when the angle was changed visually for a red sample, the absolute value of the difference between the average hue values ​​was subtracted from 255 and then multiplied by 360 / 255 to obtain Δh. When Δh was 36 or less, the colors were evaluated as being in the same color family.

[0081] <Component analysis> The compositional analysis of structural color particles was performed by energy-dispersive X-ray spectroscopy. For the analysis of trace components at amounts less than 1 wt%, the concentration was calculated from a calibration curve prepared using standard solutions by ICP emission spectroscopy (Hitachi High-Tech Science Corporation, model number: SPS3100).

[0082] <Change in brightness (ΔL)> The change in brightness during heat treatment, lithotripsy treatment, and weathering tests was measured as follows. The change in brightness during heat treatment was observed when structural color particles were heat-treated at 800°C for 3 hours in an atmospheric environment, and the brightness (L) before and after heat treatment was measured. * ab The brightness difference (ΔL) was measured, and the difference was calculated. Materials with a brightness difference (ΔL) of 20 or less were evaluated as having heat resistance. The change in brightness during the light-scaling process was measured by performing the light-scaling process at 2000 rpm for 1 minute using a rotational mixer (THINKY Co., Ltd., Awatori Rentaro ARE-310), and comparing the brightness (L) before and after the light-scaling process. * ab The brightness difference (ΔL) was measured, and the difference was calculated. A difference of ΔL of 10 or less was evaluated as having intensity. The change in brightness in the weather resistance test was measured by irradiating the device for exposure to artificial light (Method B) described in JIS K5101-9 with light of a specified illuminance for 500 hours, and the change in brightness (L) before and after the weather resistance test was measured. * ab The brightness difference (ΔL) was measured, and the difference was calculated. Materials with a brightness difference (ΔL) of 10 or less were evaluated as having weather resistance. The brightness is defined as brightness L as specified in JIS Z8781-4. * ab Based on the diffuse reflectance spectrum measurement results using a UV-Vis spectrophotometer (V-670, manufactured by JASCO Corporation), the difference in brightness (ΔL) was calculated according to the method described in JIS Z8781-4:2013, and the difference in brightness (ΔL) was calculated as the brightness L before and after the test. * ab It was taken as the absolute value of the difference.

[0083] The structural color particles in Examples 1 to 6 were prepared below. Structural color particles in Examples 1 to 6 were prepared by colloidal crystal formation, and structural color particles in Examples 7 to 12 were prepared by electrophoresis.

[0084] (Example 1) The structural color particles in Example 1 were prepared by the following method. 1.8 g of silica particles with an average particle size of 200 nm and a sphericity of 90% or more, and 0.6 g of cobalt black were mixed with 7.69 g of pure water to prepare a uniformly dispersed aqueous solution. This solution was then mixed into 90 ml of a hexadecane solution containing 2 wt% sorbitan monooleate (Tokyo Chemical Industries, Span 80), stirred, and subjected to shear stress to form a W / O emulsion. The resulting emulsion solution was dried on a fluoropolymer (PFA) petri dish, then washed with hexane, dried again, and heat-treated at 900°C in air for 2 hours to obtain spherical structural color particles.

[0085] (Example 2) The structural color particles in Example 2 were prepared by the following method: 1.68 g of silica particles with an average particle size of 200 nm and a sphericity of 90% or more, and inorganic black particles (Ca2Mn 0.85 Ti 0.15 An aqueous solution was prepared by mixing 0.72 g of O4 with 7.69 g of pure water to create a uniformly dispersed solution. The inorganic black particles were synthesized using the method described in the literature "Synthesis and Characterization of Black Pigments Based on Calcium Manganese Oxides for High Near-Infrared (NIR) Reflectance" (R. Oka and T. Masui, RSC Advances, vol. 6, no. 93, pp. 90952-90957, 2016). The obtained aqueous solution was mixed with 90 ml of a hexadecane solution containing 2 wt% sorbitan monooleate (manufactured by Tokyo Chemical Industry Co., Ltd., Span 80), stirred, and subjected to shear stress to form a W / O emulsion. The resulting emulsion solution was dried on a PFA petri dish, then washed with hexane, dried again, and then heat-treated at 800°C in air for 2 hours to obtain spherical structurally colored particles.

[0086] (Example 3) The structural color particles in Example 3 were prepared by the following method. An aqueous solution was prepared by mixing 1.44 g of silica particles with an average particle size of 200 nm and a sphericity of 90% or more and 0.96 g of inorganic black particles (La2CuO4) with 7.69 g of pure water and dispersing them uniformly. The inorganic black particles were synthesized by the method described in the literature "Synthesis, characterization and optical band gap of La2CuO4 nanoparticles", Mater. Sci. Semicond. Process., vol. 16, no. 6, pp. 1517-1520, 2013. The obtained aqueous solution was mixed with 90 ml of a hexadecane solution containing 2 wt% sorbitan monooleate (manufactured by Tokyo Chemical Industry Co., Ltd., Span 80), stirred, and subjected to shear stress to form a W / O emulsion. The resulting emulsion solution was dried on a PFA petri dish, then washed with hexane, dried again, and then heat-treated at 800°C in air for 2 hours to obtain spherical structurally colored particles.

[0087] (Example 4) The structural color particles in Example 4 were prepared by the following method. 1.8 g of silica particles with an average particle size of 250 nm and a sphericity of 90% or more, and 0.6 g of cobalt black were mixed with 7.69 g of pure water to prepare a uniformly dispersed aqueous solution. This solution was then mixed into 90 ml of a hexadecane solution containing 2 wt% sorbitan monooleate (Tokyo Chemical Industries, Span 80), stirred, and subjected to shear stress to form a W / O emulsion. The resulting emulsion solution was dried on a PFA petri dish, then washed with hexane, dried again, and heat-treated at 800°C in air for 2 hours to obtain spherical structural color particles.

[0088] (Example 5) The structural color particles in Example 5 were prepared by the following method. 1.8 g of silica particles with an average particle size of 300 nm and a sphericity of 90% or more, and 0.6 g of cobalt black were mixed with 7.69 g of pure water to prepare a uniformly dispersed aqueous solution. This solution was then mixed into 90 ml of a hexadecane solution containing 2 wt% sorbitan monooleate (manufactured by Tokyo Chemical Industry Co., Ltd., Span 80), stirred, and subjected to shear stress to form a W / O emulsion. The resulting emulsion solution was dried on a PFA petri dish, then washed with hexane, dried again, and heat-treated at 650°C in air for 2 hours to obtain spherical structural color particles.

[0089] (Example 6) The structural color particles in Example 6 were prepared by the following method. 2.3 g of silica particles with an average particle size of 200 nm and a sphericity of 90% or more, and 0.01 g of carbon black (Aqua Black, manufactured by Tokai Carbon Co., Ltd.) were mixed with 7.69 g of pure water to prepare a uniformly dispersed aqueous solution. This solution was then mixed into 90 ml of a hexadecane solution containing 2 wt% sorbitan monooleate (Span 80, manufactured by Tokyo Chemical Industry Co., Ltd.), stirred, and subjected to shear stress to form a W / O emulsion. The resulting emulsion solution was dried on a PFA petri dish and then washed with hexane to obtain spherical structural color particles.

[0090] (Example 7) The structural color particles in Example 7 were prepared by the following method. Silica particles with an average particle size of 200 nm and a sphericity of 90% or more were washed by immersion in a solution (RCA solution) prepared by mixing 29% aqueous ammonium hydroxide, 30% aqueous hydrogen peroxide, and pure water in a 1:1:5 ratio. 0.7 g of these silica particles were then dispersed in 80 ml of 2-propanol. Immediately before electrophoresis, 0.6 ml of Fe3O4 suspension and 5 ml of Mg(NO3)2 aqueous solution (concentration: 105 mM / L) were added to this dispersion to prepare a uniformly dispersed raw material solution. The applied voltage was set to 30 V, and the film was deposited on a SUS substrate, which served as the cathode, for 5 minutes. The Fe3O4 suspension used was adjusted so that Fe3O4 accounted for 2.5 wt% of the total raw material solution. Subsequently, the film was peeled off the substrate with a polypropylene spatula and classified using a 300-mesh sieve to obtain polyhedral structural color particles.

[0091] (Example 8) The structural color particles in Example 8 were prepared by the following method. Silica particles with an average particle size of 200 nm and a sphericity of 90% or more were washed by immersion in an RCA solution, and 0.7 g of these silica particles were dispersed in 80 ml of 2-propanol. Immediately before electrophoresis, 0.6 g of cobalt black and 5 ml of Mg(NO3)2 aqueous solution (concentration: 105 mM / L) were added to this dispersion to prepare a uniformly dispersed raw material solution. The applied voltage was set to 30 V, and the film was deposited on a SUS substrate, which served as the cathode, for 5 minutes. After that, the film was peeled off the substrate with a polypropylene spatula and classified using a 300-mesh sieve to obtain polyhedral structural color particles.

[0092] (Example 9) The structural color particles in Example 9 were prepared by the following method. Silica particles with an average particle size of 200 nm and a sphericity of 90% or more were washed by immersion in RCA solution, and 0.7 g of these silica particles were dispersed in 80 ml of 2-propanol. Immediately before electrophoresis, 0.6 ml of Fe3O4 suspension and 5 ml of Mg(NO3)2 aqueous solution (concentration: 105 mM / L) were added to this dispersion to prepare a uniformly dispersed raw material solution. The applied voltage was set to 30 V, and the film was deposited on a SUS substrate, which served as the cathode electrode, for 5 minutes. The amount of Fe3O4 suspension was adjusted so that Fe3O4 accounted for 8.4 wt% of the total raw material solution. Subsequently, the film was peeled off the substrate with a polypropylene spatula and classified using a 300-mesh sieve to obtain polyhedral structural color particles.

[0093] (Example 10) The structural color particles in Example 10 were prepared by the following method. Silica particles with an average particle size of 200 nm and a sphericity of 90% or more were washed by immersion in RCA solution, and then 0.7 g of these silica particles were dispersed in 80 ml of 2-propanol. Immediately before electrophoresis, inorganic black particles ((Ca) were added to this dispersion. 0.99 Ce 0.01 A starting material solution was prepared by adding 0.6 ml of 2MnO4 suspension and 5 ml of Mg(NO3)2 aqueous solution (concentration: 105 mM / L) and dispersing them uniformly. In addition, inorganic black particles ((Ca 0.99 Ce 0.01The 2MnO4 (2MnO4) was prepared using the following procedure: CaCO3 (1.9907g), MnO2 (0.8733g), and CeO2 (0.0346g) powders were mixed in an agate mortar for 30 minutes, then placed in an alumina boat and fired at 1200°C in air for 6 hours. The resulting sintered body was ball-milled (zirconia balls, 50 rpm, 8 hours). The resulting inorganic black particles were adjusted to make up 2.0 wt% of the total raw material liquid and used. The applied voltage was set to 30V, and a film was deposited on a SUS substrate, which served as the cathode, for 5 minutes. The film was then peeled off the substrate using a polypropylene spatula and classified using a 300-mesh sieve to obtain polyhedral structural color particles.

[0094] (Example 11) The structural color particles in Example 11 were prepared by the following method. Silica particles with an average particle size of 200 nm and a sphericity of 90% or more were washed by immersion in RCA solution, and 0.7 g of these silica particles were dispersed in 80 ml of 2-propanol. Immediately before electrophoresis, 0.6 ml of a suspension of inorganic black particles (LaMnO3) and 5 ml of an aqueous solution of Mg(NO3)2 (concentration: 105 mM / L) were added to this dispersion to prepare a uniformly dispersed starting material solution. The inorganic black particles (LaMnO3) used were prepared using the following procedure: La2O3 (0.5398g) and Mn2O3 (0.2616g) powders were mixed in an agate mortar for 30 minutes, then placed in an alumina boat and fired at 1300°C in air for 6 hours. The resulting sintered body was then ground in a ball mill (zirconia balls, 50 rpm, 8 hours). The resulting inorganic black particles were adjusted to make up 2.0 wt% of the total raw material liquid and used. The applied voltage was set to 30V, and a film was deposited on a SUS substrate, which served as the cathode, for 5 minutes. The film was then peeled off the substrate using a polypropylene spatula and classified using a 300-mesh sieve to obtain polyhedral structural color particles.

[0095] (Example 12) The structural color particles in Example 12 were prepared by the following method. 2.3 g of silica particles with an average particle size of 300 nm and a sphericity of 90% or more, and 0.03 g of carbon black were mixed with 0.255 g of a 28% aqueous ammonia solution, 7.13 g of pure water, and 72.9 g of ethanol to prepare a uniformly dispersed raw material solution. The applied voltage was set to 80 V, and the solution was deposited on a copper plate (the anode) for 10 minutes. After peeling it off the substrate, it was classified using a 300-mesh sieve to obtain polyhedral structural color particles.

[0096] As an example of the structurally colored particles obtained, Figure 1 shows the SEM observation results of structurally colored particles from Example 1, and Figure 2 shows the optical microscope observation results of structurally colored particles from Example 1. Furthermore, Tables 1 and 2 show the results of measuring each physical property for structurally colored particles from Examples 1 to 12. Note that although carbon black was used as the black particle in Examples 6 and 12, the black particles could not be distinguished by SEM observation, therefore the particle size, a / d, and N of the black particles are not provided. Si , N BL We have not measured that.

[0097] [Table 1]

[0098] [Table 2]

[0099] The results in Tables 1 and 2 show that the structural color particles in Examples 1-5 and 7-11 exhibited small differences in brightness before and after treatment or testing in all three tests: heat treatment, lithotripsy treatment, and weathering test. These results indicate that these particles possess high strength and combine heat resistance and weather resistance.

[0100] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2021-130186, filed on August 6, 2021, the contents of which are incorporated herein by reference.

Claims

1. Structural color particles are formed by the aggregation of multiple primary particles, The primary particles include spherical silica primary particles and black primary particles consisting of inorganic components other than silicon dioxide and carbon. When the cumulative 50% particle size D50 based on the number of silica primary particles is denoted as d, and the cumulative 50% particle size D50 based on the number of black primary particles is denoted as a, the ratio of a to d, a / d, is 1.0 or more and 10.0 or less. The average number of silica primary particles N Si and the average number of black primary particles N BL present on the surface of 10 arbitrary structural color particles satisfy the following relationship (1): Structural color particles. N Si ≧10×(a / d) 2×N BL (1) (In formula (1), d is the cumulative 50% particle size D50 based on the number of primary silica particles, and a is the cumulative 50% particle size D50 based on the number of primary black particles.)

2. The structural color particle according to claim 1, wherein a polyvalent metal ion is provided as a binding aid between the plurality of primary particles.

3. The structural color particle according to claim 1, wherein the average particle size of the structural color particle is 4 to 80 μm.

4. The structural color particle according to claim 1, wherein the coefficient of variation (CV) of the particle size of the structural color particle is 10% or more.

5. The structural color particle according to claim 1, wherein the shape of the structural color particle is at least one of a spherical shape and a polyhedron shape having at least two faces that are not parallel to each other.

6. The structural color particle according to claim 1, wherein the content ratio of the silica primary particles to the black primary particles is 50:50 to 98:2 in terms of oxide mass ratio, where silica primary particles:black primary particles.

7. The aforementioned structural color particles, in terms of oxides, are SiO ２ 50-98% by mass of [unclear], 0-30% by mass of CaO, MgO, SrO and BaO in total, Li ２ O, Na ２ O and K ２ The structural color particles according to claim 1, comprising a total of 0 to 18% by mass of oxygen and 2 to 50% by mass of transition metal elements.

8. The structural color particles according to claim 1, wherein when the structural color particles are heat-treated at 800°C for 3 hours in an atmospheric environment, the difference in brightness before and after the heat treatment is 20 or less.

9. The structural color particles according to claim 1, wherein when the structural color particles are subjected to a light-washing process at 2000 rpm for 1 minute using a rotation-orbit mixer, the difference in brightness before and after the light-washing process is 10 or less.

10. The structural color particles according to claim 1, wherein when the structural color particles are subjected to a weather resistance test by irradiating them with light of a specified illuminance for 500 hours in accordance with the apparatus for exposure to artificial light (Method B) described in JIS K5101-9, the difference in brightness before and after the weather resistance test is 10 or less.

11. A structural color pigment comprising structural color particles according to any one of claims 1 to 10.

12. A mixed structural color pigment comprising two or more structural color particles according to any one of claims 1 to 10.

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