Structures that exhibit structural color and paints containing said structures

Abstract

To provide a material that is color-developing, has heat-shielding properties, and is weather-resistant and durable. [Solution] A structure that exhibits structural color, comprising white spherical fine particles and black particles having a near-infrared solar reflectance of 50% or more; a paint containing the structure; and a laminate having a layer containing the structure.

Description

[Technical Field]

[0001] This invention relates to a structure that exhibits structural color and a paint containing the structure. [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. Specifically, it is a color produced by the interference of reflected and scattered light, without the absorption of light. Unlike color produced by dyes or pigments, structural color does not fade 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, meeting the need for safety and security, and are expected to have applications in new pigments.

[0004] For example, Patent Document 1 proposes photonic crystal particles in which the morphology and size are controllable and the color is not angle-dependent, wherein the outer surface of the photonic crystal particles consists of monodisperse colloidal microspheres stacked in a face-centered cubic periodic structure, the interior of the particles has a long-range disordered structure, and the gaps between the monodisperse colloidal microspheres are filled with nanoparticles of Fe3O4 nanoparticles, carbon black nanoparticles, graphene nanoparticles, or a mixture of these three, and the particle size of the Fe3O4 nanoparticles, carbon black nanoparticles, or graphene nanoparticles is 2 to 50 nm. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Chinese Patent Application Publication No. 105177714 Specification [Overview of the project] [Problems that the invention aims to solve]

[0006] As part of efforts to consider the global environment, one measure being considered to address global warming is to efficiently reflect the heat rays (near-infrared rays) in sunlight that directly hit roofs, rooftops, and balconies, thereby suppressing the rise in temperature inside buildings through insulation by coatings. For example, one could consider adding heat-shielding pigments to the coating, but pigments that can reflect near-infrared rays contained in sunlight and suppress temperature rise are generally white or black, and when used in building materials or cars, visibility, vividness of color, and diversity are required. Furthermore, applying a colored film on top of a coating made with white or black pigments may reduce the heat-shielding performance.

[0007] This invention has been made in view of the above circumstances, and aims to provide a material that is color-developing, has heat-shielding properties, and is weather-resistant and durable. [Means for solving the problem]

[0008] As a result of diligent research, the inventors of this invention have found that the above problem can be solved by using black particles with a near-infrared solar reflectance of 50% or more in a structure that exhibits structural color, which is composed of white particles and black particles, and have completed the present invention.

[0009] One aspect of the present invention relates to a structure that exhibits structural color, comprising white spherical fine particles and black particles having a near-infrared solar reflectance of 50% or more.

[0010] Another aspect of the present invention relates to a paint containing the above-mentioned structure.

[0011] Another aspect of the present invention relates to a laminate having a layer containing the above-mentioned structure. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a structure that exhibits a structural color that is color-developing, has heat-shielding properties, and is weather-resistant and durable. In the structure of the present invention, the color of the structure can be adjusted by changing the particle size of the white spherical microparticles, so there is no need to create different structures for each color, and costs can be reduced. [Modes for carrying out the invention]

[0013] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified and implemented as appropriate without departing from the spirit of the invention. Furthermore, the "~" indicating a numerical range is used to mean that the numbers written before and after it are included as the lower limit and upper limit.

[0014] The structure of the present invention contains white spherical microparticles and black particles having a near-infrared solar reflectance of 50% or more (hereinafter also referred to as "specific black particles"). Multiple white spherical microparticles (primary particles) and one or more specific black particles (primary particles) aggregate to form a structure, thereby exhibiting structural color. The structure of the present invention has improved strength due to the inclusion of black particles, and further improved color saturation due to the reduction of non-coherent scattered light. The near-infrared solar reflectance of the black particles is 50% or more, which increases the near-infrared reflectivity of the structure, thus exhibiting excellent heat shielding properties. Furthermore, due to the inclusion of white spherical microparticles, the structure exhibits various colors due to light interference, diffraction, and scattering based on the arrangement of white spherical microparticles within the structure, depending on the particle size of the white spherical microparticles.

[0015] The structure of a structure can be confirmed by observing it with a transmission electron microscope (TEM) or a scanning electron microscope (SEM). In the case of SEM observation, the structure can be confirmed by observing its surface and cross-section.

[0016] The structures of the present invention can take various forms, such as particulate (spherical, polyhedral, uneven, etc.), thin film, plate, cylindrical, or tubular, and can be made into various shapes depending on the application.

[0017] In the case of particulate matter, the structure can be secondary particles formed by the aggregation of white spherical microparticles and specific black particles, and it is often an aggregate of these secondary particles.

[0018] The particulate structure has an average particle size D 50The particle size is preferably 4 to 80 μm. When the average particle size of 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, resulting in a beautifully mixed appearance. 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.

[0019] 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.

[0020] The particulate structure preferably has 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 must be 1.0 or greater. On the other hand, if the aspect ratio is 5.0 or less, the particle orientation when the structural color particles are coated can be suppressed, and the angle dependence of the 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.

[0021] When the particulate structure is spherical, its sphericity is preferably 83% or higher. When the sphericity of the white spherical fine particles is 83% or higher, a dense periodic structure can be formed. A sphericity of 85% or higher is more preferable, 87% or higher is even more preferable, 90% or higher is particularly preferable, and the higher the sphericity, the better, so there is no particular upper limit, with 100% being the most preferable.

[0022] The sphericity is determined by measuring 100 arbitrary structural color particles in a photographic projection obtained by photographing the structure with a scanning electron microscope (SEM). For each of the 100 arbitrary 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 particles is less than 100, the particle size of the structural color particles visible in the SEM image is measured to determine the sphericity.

[0023] In the case of a thin film, the structure consists of a film formed by the aggregation of white spherical microparticles and specific black particles. The thickness of the thin film structure is not particularly limited, but is in the range of 0.1 to 1000 μm. The dimensions (long side, short side) of the thin film structure in plan view can be any size.

[0024] The structure of the present invention preferably has a total solar reflectance of 40% or more. A total solar reflectance of 40% or more improves heat shielding performance. The total solar reflectance is more preferably 41% or more, even more preferably 42% or more, and particularly preferably 43% or more. Furthermore, from the viewpoint of reflecting visible light and suppressing the cause of light pollution, the total solar reflectance is preferably 99% or less, more preferably 95% or less, even more preferably 90% or less, and particularly preferably 85% or less. In other words, the total solar reflectance of the structure is preferably in the range of 40 to 99%.

[0025] Furthermore, the structure of the present invention preferably has a near-infrared solar reflectance of 60% or more. When the near-infrared solar reflectance of the structure is 60% or more, it exhibits excellent heat shielding performance because the reflectance in the near-infrared region is high. The near-infrared solar reflectance is more preferably 61% or more, even more preferably 62% or more, and particularly preferably 63% or more. Since the heat shielding effect increases with higher near-infrared solar reflectance, there is no particular upper limit, but 100% is most preferable. In other words, the near-infrared solar reflectance of the structure is preferably in the range of 60 to 100%.

[0026] The total solar reflectance and near-infrared solar reflectance of the structure can be measured in accordance with JIS K5602 (2008). Specifically, when the structure is particulate, the structure is placed in a powder cell and measured by installing it in an ultraviolet-visible near-infrared spectrophotometer equipped with an integrating sphere. When the structure is other than particulate, the solar reflectance of the structure surface is directly measured.

[0027] The hue of the structure is represented by the CIE1976L * a * b * color system. In this color system, the lightness is L * , red to green is a * (positive is reddish, negative is greenish), yellow to blue is b * (positive is yellowish, negative is bluish). The L * value, a[[ID=2l]] * value and b * value can be calculated from measurement values by a general color difference meter or spectral measurement results by a visible ultraviolet spectrophotometer.

[0028] The structure of the present invention has a lightness L * a * b * represented by the color system in the range of 10 to 95. It is preferable that the L * value is 10 or more, and when the L * value is 95 or less, the color becomes darker, so the color development is good and it is suitable for paint applications. The L * value of the structure is preferably 10 or more, more preferably 15 or more, further preferably 20 or more, and preferably 95 or less, more preferably 90 or less, and further preferably 85 or less.

[0029] The structure of the present invention has an a * a * b * represented by the color system in the range of -1 or less or 1 or more. It is preferable that the a * value is -1 or less or 1 or more. When the a * value is -1 or less or 1 or more, the structure has a hue and high color development property. The a *The value is more preferably -60 to -1 or 1 to 60, and even more preferably -59 to -2 or 2 to 59.

[0030] The structure of the present invention is CIE1976L * a * b * b represented by the color system * It is preferable that the value is -1 or less or 1 or more. * If the value is -1 or less or 1 or more, the structure will have color and high color vibrancy. * The value is more preferably -60 to -1 or 1 to 60, and even more preferably -59 to -2 or 2 to 59.

[0031] In the present invention, when the structure is an aggregate of particles (secondary particles), the coefficient of variation (CV) of the particle size of the structure 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 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. In other words, the coefficient of variation (CV) of the particle size is preferably in the range of 10 to 80%.

[0032] The coefficient of variation (CV) of the particle size of the structure 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.

[0033] Next, we will explain each component that makes up the structure.

[0034] (Black particles) The structure of the present invention contains black particles (specific black particles) having a near-infrared solar reflectance of 50% or more. The inclusion of black particles in the structure improves its strength, enhances color saturation by reducing incoherent scattered light, and increases the near-infrared reflectivity of the structure due to the black particles having a near-infrared solar reflectance of 50% or more, thus exhibiting excellent heat shielding properties. From the viewpoint of further improving the heat shielding properties of the structure, the near-infrared solar reflectance of the specific black particles is more preferably 55% or more, and even more preferably 60% or more. Since a higher near-infrared solar reflectance increases the solar reflectance of the structure, there is no particular upper limit.

[0035] The near-infrared solar reflectance of black particles can be measured according to JIS K5602 (2008). Specifically, the particles are placed in a powder cell and measured using an ultraviolet-visible-near-infrared spectrophotometer equipped with an integrating sphere. When measuring black particles within a structure, the structure can be dismantled using a ball mill, bead mill, wet jet mill, etc., and the black particles can be separated by weight difference or other means to obtain an aggregate (powder) of black particles, which can then be measured.

[0036] The band gap of the black particles is preferably 1.6 eV or less, and more preferably 0 to 1.5 eV. When particles contain a metallic element that generates electric polarization, have a small band gap, and their absorption edge is above the visible light range, they become black particles that reflect near-infrared light. Examples of metallic elements that give such near-infrared reflectivity include transition metals such as vanadium (V), manganese (Mn), titanium (Ti), zinc (Zn), niobium (Nb), and bismuth (Bi), group 2 elements such as calcium (Ca), and lanthanides such as cerium (Ce) and gadolinium (Gd).

[0037] A specific composition of black particles with a near-infrared solar reflectance of 50% or more is, for example, Ce 0.80 Gd 0.20 VO4 (hereinafter also referred to as CGVO), Ca2Mn 0.85 Ti 0.15 Zn 0.08Examples include black particles such as O4 (hereinafter also referred to as CMTZO), CaTiMnO, MnBi, and LaMnO3.

[0038] Black particles with a near-infrared solar reflectance of 50% or more can be any known type, and can be produced by methods described, for example, T. Masui et al., RSC Advances, 2022, 12, 16570. and T. Masui et al., RSC Advances, 2019, 9, 38822. Commercially available products can also be used, such as "Black6340" and "Black6301" from Asahi Kasei Kogyo Co., Ltd., "Kikusui SP Power Thermo F", "Kikusui SP Power Thermo Si", "Thermo Factory Double One", and "Admacool Paint" from Kikusui Chemical Industry Co., Ltd., and "Typeque Black SG-101" from Ishihara Sangyo Co., Ltd.

[0039] Black particles with a near-infrared solar reflectance of 50% or more may inevitably contain impurities derived from various raw materials, but they shall not substantially contain chromium (Cr), cobalt (Co), and nickel (Ni). "Substantially" means excluding cases where they are unintentionally and inevitably present from other components. Even when Cr, Co, and Ni are present as impurities, it is preferable that they be present in the black particles at 1% by mass or less, and Cr in particular raises safety concerns. 6+ The content of is preferably 10 ppm by mass or less. It is also preferable that the unreacted residue of the raw materials is contained as little as possible, and in particular, it is preferable that it be 1% by mass or less in the black particles.

[0040] The composition and impurity levels of the black particles can be measured by methods such as ICP emission spectroscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence spectroscopy.

[0041] The blackness of black particles with a near-infrared solar reflectance of 50% or more is measured according to CIE1976L * a * b * Represented by a color system, L * It is small, a * , b *The closer these values ​​are to 0, the better the blackness.

[0042] Black particles with a near-infrared solar reflectance of 50% or more have a lightness index of L * The value should preferably be 25 or less. * If the value is 25 or less, the arrangement structure of the white spherical particles can be maintained within the range in which structural color can be expressed, while unwanted scattered light can be removed and saturation can be improved. * The value is more preferably 24 or less, even more preferably 23 or less, particularly preferably 21 or less, especially preferably 20 or less, and most preferably 19 or less.

[0043] Furthermore, black particles with a near-infrared solar reflectance of 50% or more * Value and b * The values ​​are preferably between -3 and 3. (Specific black particles a) * Value and b * If the values ​​are -3 or higher, cool colors such as blue and green are suppressed, and if they are 3 or lower, warm colors such as red and yellow are suppressed. * Value and b * Each value is more preferably -2.8 or greater, even more preferably -2.6 or greater, and more preferably 2.8 or less, and even more preferably 2.6 or less.

[0044] Also, a * Value and b * The achromaticity C is calculated from the value using the following formula (1). * It is preferably between 0 and 5, more preferably between 0 and 4, particularly preferably between 0 and 3, and most preferably between 0 and 2. * represents the degree of coloring, C * If it is 0, it is achromatic, C * The larger the size, the more intense the color. * When the value exceeds 5, the blackness tends to be insufficient. C * ={(a * ) 2 +(b * ) 2} 1 / 2 ...(1)

[0045] The size of the black particles having a near-infrared solar reflectance of 50% or more is preferably in the range of 0.01 to 100 μm in particle diameter. When the particle diameter is 0.01 μm or more, the mixability with white spherical fine particles is improved when fabricating the structure, allowing for uniform dispersion within the structure, and the effect of improving saturation in relation to the amount added is good. When the particle diameter is 100 μm or less, there is less chance of the desired effect not being obtained because the particles are not incorporated into the structure, and it is expected that the angle dependence of color development will be reduced by moderately disrupting the arrangement of the white spherical fine particles. The particle diameter is preferably 0.1 μm or more, more preferably 0.02 μm or more, even more preferably 0.03 μm or more, and also preferably 95 μm or less, more preferably 90 μm or less, and even more preferably 85 μm or less.

[0046] Black particles with a near-infrared solar reflectance of 50% or more have a cumulative 50% particle size D based on volume. 50 (Hereafter, average particle size D 50 Also called ( ), but preferably 0.05 to 40 μm. Average particle size D 50 When the particle size is 0.05 μm or larger, the effect of improving saturation relative to the amount added is good. When the particle size is 40 μm or smaller, there is less chance of the particle not being incorporated into the structure when forming the structure, resulting in a loss of the desired effect. Furthermore, by moderately disrupting the arrangement of white spherical particles, it is expected that the angle dependence of color development will be reduced. Average particle size D 50 The particle size is preferably 0.05 μm or larger, more preferably 0.08 μm or larger, even more preferably 0.10 μm or larger, and also preferably 40 μm or smaller, more preferably 30 μm or smaller, and even more preferably 20 μm or smaller.

[0047] Black particles with a near-infrared solar reflectance of 50% or more have a cumulative 10% particle size D based on volume. 10 It is preferable that the particle size is 0.01 to 0.1 μm. 10% particle size D 10 If the particle size is 0.01 μm or larger, it is possible to suppress the occurrence of color unevenness due to the non-uniform number of black particles in each structure. 10% particle size D 10 The particle size is preferably 0.02 μm or larger, and the 10% particle size D 10If the particle size is 0.03 μm or larger, it becomes easier to uniformly mix with the white spherical fine particles when synthesizing the structure. 10% particle size D 10 The particle size is preferably 0.01 μm or larger, more preferably 0.02 μm or larger, even more preferably 0.03 μm or larger, particularly preferably 0.04 μm or larger, most preferably 0.05 μm or larger, and also preferably 0.1 μm or smaller, more preferably 0.08 μm or smaller, even more preferably 0.07 μm or smaller, and particularly preferably 0.06 μm or smaller.

[0048] Black particles with a near-infrared solar reflectance of 50% or more have a cumulative 90% particle size D based on volume. 90 However, it is preferable that the particle size is between 0.04 and 100 μm. 90% particle size D 90 When the particle size is 0.04 μm or larger, the effect of improving saturation relative to the amount added is good, and when it is 100 μm or smaller, it is less likely that the desired effect will not be obtained because it is not incorporated into the structure of the material, and it is expected that the angle dependence of color development will be reduced by moderately disrupting the arrangement of white spherical particles. 90% particle size D 90 The particle size is preferably 0.04 μm or larger, more preferably 0.042 μm or larger, even more preferably 0.045 μm or larger, particularly preferably 0.050 μm or larger, and also preferably 100 μm or smaller, more preferably 98 μm or smaller, and even more preferably 96 μm or smaller.

[0049] The particle size and particle size distribution of the black particles within the structure can be confirmed by scanning electron microscopy (SEM) observation, for example, using a Hitachi S-4800 scanning electron microscope. Since it is difficult to accurately determine the particle size of the black particles due to the shape and shading of the structure, it is preferable to process and evaluate the image using the image processing software ImageJ.

[0050] Black particles having a near-infrared solar reflectance of 50% or more are preferably spherical in shape from the viewpoint of forming a uniform periodic structure. The sphericity of black particles having a near-infrared solar reflectance of 50% or more is preferably 80% or more, more preferably 83% or more, even more preferably 85% or more, particularly preferably 87% or more, and especially preferably 90% or more. Furthermore, the higher the sphericity, the better, so there is no particular upper limit, and 100% is the most preferable. Sphericity can be determined by the method described above.

[0051] The structure of the present invention may contain black particles other than black particles having a near-infrared solar reflectance of 50% or more, but other black particles are included such that the near-infrared solar reflectance of the entire black particle system is 50% or more when the near-infrared solar reflectance of the black particles is measured. Other black particles include carbon black, triiron tetroxide (Fe3O4), and heat-shielding pigments "Black6350" and "Black6310" manufactured by Asahi Chemical Industries, Ltd.

[0052] If other black particles are present, the preferred range of blackness, particle size, and particle size distribution for the other black particles is the same as that for black particles with a near-infrared solar reflectance of 50% or more.

[0053] To obtain the effects of the present invention, it is preferable that the black particles have a near-infrared solar reflectance of 50% or more in the entire black particle composition, that the composition contains 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and most preferably all black particles are black particles with a near-infrared solar reflectance of 50% or more (100% by mass).

[0054] The black particles are preferably contained in the structure in an amount of 1 to 50% by mass. When the black particle content in the structure is 1% by mass or more, the saturation of the color is enhanced and the strength of the structure can be maintained. Furthermore, when the black particle content in the structure is 50% by mass or less, the heat shielding properties can be improved. The black particle content is more preferably 3% by mass or more in the structure, even more preferably 5% by mass or more, even more preferably 45% by mass or less, and even more preferably 40% by mass or less.

[0055] (White spherical fine particles) The structure of the present invention contains spherical white microparticles. The whiteness of the white spherical microparticles is defined as CIE1976L * a * b * Represented by a color system, L * It is close to 100, a * , b * The closer each of these values ​​is to 0, the higher the degree of whiteness.

[0056] White spherical particles are L * A value of 80 or higher is preferable. * A value of 80 or higher results in more vibrant colors and improved saturation of the structure. * The value is more preferably 90 or higher, even more preferably 95 or higher, and most preferably 100.

[0057] Also, white spherical particles a * Value and b * The values ​​are preferably between -3 and 3. (a) of white spherical fine particles * Value and b * When the values ​​are -3 or higher, cool tones such as blue and green are suppressed, and when they are 3 or lower, warm tones such as red and yellow are suppressed, resulting in a clear white color and improved color rendering. * Value and b * Each value is more preferably -2.8 or greater, even more preferably -2.6 or greater, and more preferably 2.8 or less, and even more preferably 2.6 or less.

[0058] As the white spherical fine particles, particles composed of either an inorganic substance or an organic substance are preferably used.

[0059] Examples of inorganic materials include oxides containing at least one element selected from the group consisting of silicon (Si), titanium (Ti), zirconium (Zr), cerium (Ce), and aluminum (Al). Among these, oxides containing at least one element selected from the group consisting of silicon (Si), titanium (Ti), zirconium (Zr), and cerium (Ce) are more preferred. In particular, silica (SiO2) is harmless to the human body and has a low environmental impact, so it is preferable for the structure to contain silica particles.

[0060] Examples of organic substances include at least one polymer selected from the group consisting of polystyrene, polymethyl methacrylate, polycarbonate, polylactic acid, albumin, and polyethylene, as well as proteins. Among these, at least one polymer selected from the group consisting of polystyrene, polymethyl methacrylate, and polycarbonate is more preferred.

[0061] The sphericity of the white spherical particles is preferably 80% or higher. When the sphericity of the white spherical particles is 80% or higher, a periodic structure sufficient to exhibit structural color can be realized through aggregation, self-arrangement, 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. Furthermore, the higher the sphericity, the better, so there is no particular upper limit, and 100% is the most preferable. Sphericity can be determined by the method described above.

[0062] The white spherical fine particles need to be selected with an appropriate particle size according to the desired color development. However, in order to achieve color development in the visible light range, it is preferable that the particle size is in the range of 100 to 1000 nm. When the particle size is 100 nm or more, color development due to light interference, diffraction, scattering, etc. based on the arrangement of the white spherical fine particles can be obtained. When the particle size is 1000 nm or less, it becomes easier to form a closest packing structure with the black particles. From the viewpoints of suppressing Rayleigh scattering that may have an adverse effect on color development and having no adverse effect on the human body, the particle size of the white spherical fine particles is more preferably 110 nm or more, even more preferably 120 nm or more, and particularly preferably: 130 nm or more. Further, from the viewpoints of suppressing Mie scattering that may have an adverse effect on color development and realizing a good arrangement when aggregating with the black particles, the particle size of the white spherical fine particles is more preferably 900 nm or less, even more preferably 800 nm or less, and particularly preferably 700 nm or less.

[0063] The cumulative 50% particle size D based on the number standard of the white spherical fine particles 50 (Average particle size D 50 ) needs to be selected with an appropriate particle size according to the desired color development. However, from the viewpoint of achieving color development in the visible light range, it is preferably 100 to 500 nm. When the average particle size D 50 is 100 nm or more, color development due to light interference, diffraction, scattering, etc. based on the arrangement of the silica primary particles can be obtained. When the average particle size D 50 is 105 nm or more, it is more preferable, 110 nm or more is even more preferable, and 115 nm or more is particularly preferable. Also, it is more preferably 490 nm or less, even more preferably 480 nm or less, and particularly preferably 470 nm or less.

[0064] Incidentally, an example of the range of the average particle size D of the white spherical fine particles for obtaining the desired color development is as follows. 50 When it is desired to develop blue color with the structure of the present invention, it is preferable that the average particle size D of the white spherical silica fine particles constituting the structure is in the range of 150 to 235 nm. The average particle size D 50 is preferably in the range of 150 to 235 nm. The average particle size D 50is more preferably in the range of 180 to 230 nm, and even more preferably in the range of 190 to 225 nm. Also, when it is desired to develop a green color with the structure of the present invention, the average particle diameter D of the white spherical silica fine particles constituting the structure 50 is preferably in the range of 235 to 265 nm. The average particle diameter D 50 is more preferably in the range of 240 to 260 nm, and even more preferably in the range of 245 to 255 nm. And also, when it is desired to develop a red color with the structure of the present invention, the average particle diameter D of the silica primary particles constituting the structure 50 is preferably in the range of 265 to 320 nm. The average particle diameter D 50 is more preferably in the range of 270 to 315 nm, and even more preferably in the range of 275 to 310 nm.

[0065] The particle diameter and particle diameter distribution of the white spherical fine particles in the structure can be measured by observation with SEM or by dynamic light scattering (DLS). When performing SEM observation, 100 arbitrary white spherical fine particles in the structure are measured by SEM observation, image processing is performed using image processing software ImageJ, and evaluation is performed. When the number of white spherical fine particles in the structure is less than 100, the particle diameter of all the white spherical fine particles of one structure visible in the SEM image can be measured and obtained. When measuring by dynamic light scattering (DLS), for example, it is measured using a zeta potential / particle diameter / molecular weight measurement system.

[0066] The white spherical fine particles are usually aggregates of particles, but the polydispersity index thereof is preferably less than 10%. The polydispersity index is an index for evaluating the width of the particle diameter distribution. When the polydispersity index is less than 10%, the particle diameter distribution of the dispersion is said to be monodisperse. When the white spherical fine particles are monodisperse, the color development property of the structure is improved. The polydispersity index of the white spherical fine particles is preferably 7% or less, more preferably 3% or less, and even more preferably 1% or less. Since the smaller the polydispersity index, the narrower the particle size distribution, the lower limit is not particularly limited.

[0067] The polydispersion index can be measured using dynamic light scattering (DLS). When measuring using DLS, for example, a zeta potential, particle size, and molecular weight measurement system is used.

[0068] The white spherical particles are preferably contained in the structure in an amount of 50 to 99% by mass. If the content of white spherical particles in the structure is 50% by mass or more, the heat shielding properties can be improved, and if it is 99% by mass or less, the color saturation can be enhanced. The content of white spherical particles in the structure is more preferably 53% by mass or more, even more preferably 55% by mass or more, even more preferably 98.5% by mass or less, and even more preferably 98% by mass or less.

[0069] Furthermore, the ratio of black particles to white spherical particles in the structure is preferably 50:50 to 98:2 by mass, where white spherical particles:black particles. When the ratio of white spherical particles to black particles is within the above range, it is possible to achieve both improved strength and heat resistance of the structure and the appearance of structural color. The ratio is more preferably 55:45 to 95:5, even more preferably 60:40 to 90:10, and particularly preferably 65:35 to 85:15.

[0070] (binding agent) The structure of the present invention may have a binding agent between the particles. Examples of binding agents include polyvalent metal ions, and the inclusion of polyvalent metal ions strengthens the bonds between particles, thereby achieving excellent strength and heat resistance.

[0071] 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.

[0072] Polyvalent metal ions can be contained as hydroxides, oxides, or polyvalent metal salts. In the manufacturing process of the structure, 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 calcination process if the particles are calcined products. Examples of polyvalent metal salts include sulfates, nitrates, and carboxylates, and examples of their salts include sodium salts and potassium salts.

[0073] The polyvalent metal ion content in the structure is preferably 50 to 50,000 wtppm in terms of oxide. A polyvalent metal ion content of 50 wtppm or more can increase the bonding force between 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.

[0074] Furthermore, polyvalent metal ions in the structure can be measured by methods such as ICP emission spectroscopy, energy-dispersive X-ray spectroscopy, and X-ray fluorescence spectroscopy.

[0075] (Method of manufacturing a structure) Next, we will explain the manufacturing method of structures, using spherical particulate structures and thin film structures as examples.

[0076] <Spherical structure> Spherical particulate structures can be fabricated by methods that form spherical colloidal crystals. One method for forming spherical colloidal crystals involves dispersing an aqueous phase containing white spherical microparticles and black particles with a near-infrared solar reflectance of 50% or more in a water-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, thereby obtaining a structure in which the white spherical microparticles and black particles have aggregated. In this method, the white spherical microparticles and black particles self-align during the aggregation process, forming a colloidal crystal structure with a periodic structure and exhibiting structural color.

[0077] 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.

[0078] It is preferable to adjust the aqueous phase to be alkaline. When the aqueous phase is alkaline, the zeta potential of the white spherical fine particles increases and they disperse stably, so the black particles are incorporated into the structure and are less likely to fall off. This ensures that the color of the structure is maintained while improving the heat shielding properties. The pH of the aqueous phase is more preferably in the range of 8 to 13, and even more preferably in the range of 9 to 12. If the aqueous phase is acidic to neutral, the pH can be adjusted using, for example, ammonia water or sodium hydroxide solution.

[0079] 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.

[0080] The emulsion preferably 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.

[0081] The oil-in-water emulsion 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. The drying time is arbitrary, but for example, it is preferable to dry it at atmospheric pressure for 30 to 300 minutes.

[0082] In this invention, the dispersion medium may be removed and the remaining structure may be heat-treated (fired). Heat treatment creates necks (bonding parts) between primary particles in the range where structural color appears, thereby increasing the bonding between primary particles and increasing the mechanical strength of the structure. Here, by using heat-resistant black particles that can maintain their black color even after heat treatment, the saturation and brightness of the structure can be maintained even after heat treatment.

[0083] 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 white spherical fine 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.

[0084] The heat treatment time is not particularly limited as long as the neck can be formed, but considering manufacturing efficiency, it is preferable to perform the treatment for 0.5 to 4 hours, and more preferably for 1 to 3 hours. The heat treatment atmosphere can be appropriately selected depending on the type of black particles used and is not particularly limited, but the desired effect can be obtained by heat treatment in an atmospheric atmosphere.

[0085] <Thin film structure> Thin-film structures can be fabricated by electrodeposition. In the electrodeposition method, an electrodeposited film is fabricated on an electrode according to a conventionally known method, and then the electrodeposited film is peeled off to obtain a thin-film structure. For the production of the electrodeposited film, in this invention, a dispersion is prepared by mixing a sol solution in which white spherical fine particles are dispersed in a water-soluble solvent with black particles and optionally a binding agent. Then, the anode and cathode are immersed in an electrolytic cell containing the dispersion, and DC electrolysis is performed in this state. This forms an electrodeposited film on the surface of the anode. A SUS substrate, an ITO substrate, etc., can be used as the anode. A thin-film structure is obtained by peeling the electrodeposited film from the anode, but a laminate in which the thin-film structure is formed on the substrate (anode) may also be obtained. The thin-film structure produced by this method has 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 can be adjusted by the voltage during electrodeposition, the particle size distribution of the white spherical fine particles, the particle size distribution of the black particles, etc.

[0086] The inclusion of a binding agent strengthens the bonding between particles, thereby increasing the mechanical strength of the structure. 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.

[0087] As a solvent for dispersing the white spherical fine particles, for example, a water-soluble solvent can be used, and among these, 2-propanol (IPA) is preferred.

[0088] Thin-film structures can also be made into particulate matter by grinding and classification. Methods for grinding or cutting thin-film structures include, for example, jet mills, ball mills, vibrating ball mills, planetary mills, and bead mills, and the structure should be ground or cut until the desired particle size is achieved. Alternatively, thin-film structures can be obtained by dispersing spherical structures in a solvent to form a coating film.

[0089] (Application) The structure of the present invention has excellent color development and heat-shielding properties, making it suitable for a variety of applications. For example, it can be used as a pigment in various applications, such as paints for components exposed to outdoor environments, including automobiles, buildings, signs, and billboards; paints for everyday goods such as toys, stationery, and tableware; and colorants for cosmetics and food. In particular, because the structure of the present invention has excellent heat-shielding properties, it is suitable for use in paints for coating components exposed to outdoor environments.

[0090] When the structure of the present invention is used as a pigment in a paint, it is preferable that the structure be in particulate form from the viewpoint of dispersibility in the paint. Furthermore, the structure of the present invention may be used alone to form a single color, or by using two or more structures, a mixed structure color pigment can be obtained. By adjusting the particle size, mixing ratio, etc., of the structure particles used, pigments of various colors can be produced.

[0091] Furthermore, the present invention also provides a laminate having a layer containing the structure of the present invention, and examples of such laminates include a laminate in which a coating containing the structure of the present invention is applied to the surface of any object, and a laminate in which a thin film laminate is formed on a substrate.

[0092] As described above, the present invention includes the following configurations (1) to (14). (1) A structure that exhibits structural color, comprising white spherical particles and black particles having a near-infrared solar reflectance of 50% or more. (2) The average particle size D of the black particles 50 The structure described in (1) above, wherein the diameter is 0.05 to 40 μm. (3) The structure according to (1) or (2) above, wherein the black particles are substantially free of chromium, cobalt, and nickel. (4) The structure according to any one of (1) to (3) above, wherein the white spherical fine particles are made of an inorganic substance. (5) The structure according to (4), wherein the inorganic substance is an oxide containing at least one element selected from the group consisting of silicon, titanium, zirconium, and cerium. (6) The structure according to (5), wherein the inorganic substance is silica. (7) The structure according to any one of (1) to (3) above, wherein the white spherical fine particles are made of an organic substance. (8) The structure according to (7), wherein the organic substance is at least one polymer selected from the group consisting of polystyrene, polymethyl methacrylate, and polycarbonate. (9) The structure according to any one of (1) to (8) above, wherein the polydispersity index of the white spherical fine particles is less than 10%. (10) The average particle size D of the white spherical particles 50 A structure according to any one of (1) to (9) above, wherein the wavelength is 100 to 500 nm. (11) The structure according to any one of (1) to (10), wherein the structure is particulate. (12) The structure according to any one of (1) to (10), wherein the structure is in the form of a thin film. (13) A paint containing the structure described in any one of (1) to (12) above. (14) A laminate having a layer containing the structure described in any one of (1) to (12) above. [Examples]

[0093] 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. Furthermore, Examples 1-8 and 16-18 are examples, while Examples 9-15 and 19 are comparative examples.

[0094] The particles used in the example below are as follows:

[0095] <Black particles> • Black particles 1: Ce 0.80 Gd 0.20 VO4 (CGVO) According to the method described in T. Masui et al., RSC Advances, 2022, 12, 16570., Ce 0.80 Gd 0.20 VO4 (CGVO) was synthesized. CeO2, Gd2O3, and V2O5 were weighed out in a stoichiometric ratio of CeO2:Gd2O3:V2O5 = 0.8:0.1:0.5, mixed in a mortar, and then calcined at 900°C for 6 hours (heating increase of 5°C / min). SEM observation revealed particles with a size of 1-5 μm. The near-infrared solar reflectance was 76%, and the band gap was 1.69 eV.

[0096] • Black particles 2: Street2Mn 0.85 Ti 0.15 Zn 0.08 O4(CMTZO) According to the method described in T. Masui et al., RSC Advances, 2019, 9, 38822., Ca2Mn 0.85 Ti 0.15 Zn 0.08 O4(CMTZO) was synthesized. CaCO3, MnO2, TiO2, and ZnO were weighed out in a stoichiometric ratio of CaCO3:MnO2:TiO2:ZnO = 2:0.85:0.15:0.08, mixed in a mortar, and then calcined at 1200°C for 6 hours (heating increase of 5°C / min). SEM observation revealed particles with a size of 1-3 μm. The near-infrared solar reflectance was 67%, and the band gap was 1.77 eV.

[0097] • Black particles 3: Carbon black (CB) We used "Aqua-Black 162" (product name, average particle size listed in the catalog: 110 nm) manufactured by Tokai Carbon Co., Ltd. The near-infrared solar reflectance was 8.6%, and the band gap was 0 eV.

[0098] • Black particles 4: Iron tetroxide (Fe3O4) The product used was "S-SA4" (product name) manufactured by Toda Kogyo Co., Ltd. The average particle size (measured value) was 100 nm, the near-infrared solar reflectance was 9.6%, and the band gap was 0.1 eV.

[0099] <White particles> • White particles 1: Silica particles (SiO2) We used "Howtform Silbol" (product name) manufactured by Fuji Chemical Co., Ltd. Silica particles with average particle sizes of 200 nm, 260 nm, and 300 nm were prepared. The sphericity was 99%.

[0100] • White particles 2: Titanium dioxide particles (TiO2) The product used was "R-550" (product name, main treatment agents Al, Si) manufactured by Ishihara Sangyo Co., Ltd. The average particle size (measured value) was 240 nm, and the sphericity was 99%.

[0101] • White particles 3: Polystyrene particles (PS) Thermo Fisher Scientific Co., Ltd.'s "Standard Particles 100nm 3100A" (product name) was used. The average particle size (measured value) was 160nm, the SD (standard deviation) was 0.0163, and the sphericity was 100%.

[0102] <Evaluation Method> 1. Solar reflectance The near-infrared solar reflectance of black particles, and the near-infrared solar reflectance and total solar reflectance of the structures were measured using a V-670 spectrophotometer manufactured by JASCO Corporation. The black particles and spherical structures were placed in a powder cell and measured using the spectrophotometer. The thin-film laminates were measured directly using the spectrophotometer while they were formed on the substrate. Solar reflectance was measured at 0.5 nm intervals in the wavelength range of 300 to 2500 nm. Polytetrafluoroethylene powder was used as the baseline, and calculations were performed according to JIS K5602. Near-infrared solar reflectance is the solar reflectance in the near-infrared region with wavelengths of 780 to 2500 nm, while total solar reflectance is the solar reflectance across the entire wavelength range of 300 to 2500 nm. The details of the equipment, analysis software, and measurement conditions used for the measurement are as follows. [Measuring device] • Spectrophotometer "V-670" manufactured by JASCO Corporation • Integrating sphere attachment: ISN-923 [Analysis software] • "Spectra Manager Version 2" (included analysis software) manufactured by JASCO Corporation.

[0103] 2. Color coordinates (L * a * , b * ) L * value, a * Value and b * The values ​​were obtained using a Konica Minolta CR-400 colorimeter, CIE1976 L * a * b * Measurements were taken according to the color system.

[0104] 3. Average particle size D of black particles 50 The particle size of the black particles was measured using a Hitachi, Ltd. scanning electron microscope (SEM) "S-4800". The black particles were photographed at a magnification of 5000x, and the particle size was calculated from the obtained images using the image processing software "ImageJ".

[0105] 4. Average particle size D of white particles 50 and multivariance index The particle size and polydispersity index of the white particles were measured using the "ELS-Z" particle size measurement system manufactured by Otsuka Electronics Co., Ltd., by dynamic light scattering (DLS) method.

[0106] 5. Average particle size D of spherical structures 50 The particle size of the spherical structures fabricated in Examples 1-15 was measured using a Hitachi, Ltd. scanning electron microscope (SEM) "S-4800". The spherical structures were photographed at magnifications of 5000 to 10000x, and the particle size was calculated from the obtained images using the image processing software "ImageJ".

[0107] 6. Thickness of the thin-film structure The thickness of the thin-film structures prepared in Examples 16-19 was determined as follows: Each sample was embedded and cured in room-temperature curing epoxy resin NER-814 manufactured by Nissin EM Co., Ltd. After curing, the cross-section and surface of the sample were polished, and after Pt coating, the cross-section was processed by ion milling using Hitachi High-Technologies Corporation's E-3500. The thickness of the cross-sectioned sample was measured at a magnification of 10,000x using a scanning electron microscope (SEM) "S-4800" manufactured by Hitachi, Ltd.

[0108] <Test Example 1: Spherical Structure> (Example 1) An oil phase was prepared by stirring 98% by mass of hexadecane (manufactured by Nacalai Tesque Co., Ltd.) and 2% by mass of surfactant ("Span80" manufactured by Tokyo Chemical Industry Co., Ltd.) in a screw-top bottle. The average particle size D was measured as white particles. 50 0.75 g of 200 nm silica particles and 0.20 g of CGVO as black particles were weighed out and uniformly dispersed in water. A suspension was prepared by adding 28% aqueous ammonia (manufactured by Nacalai Tesque Co., Ltd.) to adjust the pH to 12, which served as the aqueous phase. 0.1 mL of the aqueous phase was added to 0.9 mL of the oil phase and mixed and stirred with a vortex mixer to form a W / O emulsion. The prepared W / O emulsion was transferred entirely to a petri dish, and the petri dish was placed on a hot plate set to 130°C. After evaporating the water and hexadecane over 300 minutes, the mixture was washed four times with water and then air-dried to obtain a spherical structure.

[0109] (Examples 2-15) A spherical structure was obtained in the same manner as in Example 1, except that the composition of black and white particles was changed as shown in Tables 1 and 2.

[0110] For the spherical structures obtained in Examples 1-15, the average particle size, solar reflectance (total solar reflectance, near-infrared solar reflectance), and color coordinates (L) were recorded. * a * , b * The following measurements were taken. The results are shown in Tables 1 and 2.

[0111] [Table 1]

[0112] [Table 2]

[0113] Examples 1-8 are L * a * , b * The values ​​indicated that the materials exhibited structural coloration. Examples 1-8 had a total solar reflectance of 40% or more and a near-infrared solar reflectance of 60% or more, demonstrating excellent heat shielding properties. In contrast, examples 9-13 did not exhibit structural coloration, and while examples 14 and 15 did exhibit structural coloration, both their total solar reflectance and near-infrared solar reflectance were low, resulting in insufficient heat shielding properties.

[0114] <Test Example 2: Thin-film structure> (Example 16) 2-Propanol (manufactured by Nacalai Tesque Co., Ltd.) contains white particles with an average particle size of D in 80 mL. 50 0.7 g of 200 nm silica particles were added, dispersed by ultrasonic irradiation, and then stirred with a vortex mixer to prepare a sol. -2 5 mL of mol / L magnesium nitrate aqueous solution (manufactured by Kishida Chemical Co., Ltd.) and 0.2 g of CGVO as black particles were added, and the mixture was stirred using an ultrasonic vortex to prepare an electrodeposited sol. An ITO substrate was placed in an electrodeposition sol solution and connected to a Kikusui Electronics Co., Ltd. DC power supply unit "PAN-110-3A". The electrodeposition conditions were set to cathode, 30V, and 5min, and electrophoresis was performed to form a thin film structure on the ITO substrate.

[0115] (Examples 17-19) A thin-film structure was formed in the same manner as in Example 16, except that the composition of black and white particles was changed as shown in Table 3.

[0116] For the thin-film structures obtained in Examples 16-19, the thickness, solar reflectance (total solar reflectance, near-infrared solar reflectance), and color coordinates (L) were recorded. * a * , b* The following was measured. The results are shown in Table 3.

[0117] [Table 3]

[0118] Examples 16-18 are L * a * , b * The material exhibited a coloration exceeding the specified value, displaying structural coloration, and had a total solar reflectance of 40% or more and a near-infrared solar reflectance of 60% or more, demonstrating excellent heat shielding properties. In contrast, Example 19 did not exhibit structural coloration, had a low near-infrared solar reflectance, and exhibited insufficient heat shielding properties.

Claims

1. A structure that exhibits structural color, containing white spherical particles and black particles with a near-infrared solar reflectance of 50% or more.

2. The average particle size D of the black particles ５０ The structure according to claim 1, wherein the particle size is 0.05 to 40 μm.

3. The structure according to claim 1 or 2, wherein the black particles are substantially free of chromium, cobalt, and nickel.

4. The structure according to claim 1 or 2, wherein the white spherical fine particles are made of an inorganic substance.

5. The structure according to claim 4, wherein the inorganic substance is an oxide containing at least one element selected from the group consisting of silicon, titanium, zirconium, and cerium.

6. The structure according to claim 5, wherein the inorganic substance is silica.

7. The structure according to claim 1 or 2, wherein the white spherical fine particles are made of an organic substance.

8. The structure according to claim 7, wherein the organic substance is at least one polymer selected from the group consisting of polystyrene, polymethyl methacrylate, and polycarbonate.

9. The structure according to claim 1 or 2, wherein the polydispersity index of the white spherical fine particles is less than 10%.

10. The average particle size D of the aforementioned white spherical particles ５０ The structure according to claim 1 or 2, wherein the wavelength is 100 to 500 nm.

11. The structure according to claim 1 or 2, wherein the structure is particulate.

12. The structure according to claim 1 or 2, wherein the structure is in the form of a thin film.

13. A paint comprising the structure described in claim 1 or 2.

14. A laminate having a layer containing the structure described in claim 1 or 2.

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