WO2024090211A1 - Black particles - Google Patents

Black particles Download PDF

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Publication number
WO2024090211A1
WO2024090211A1 PCT/JP2023/036939 JP2023036939W WO2024090211A1 WO 2024090211 A1 WO2024090211 A1 WO 2024090211A1 JP 2023036939 W JP2023036939 W JP 2023036939W WO 2024090211 A1 WO2024090211 A1 WO 2024090211A1
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black particles
silica
particles
less
structural color
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PCT/JP2023/036939
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French (fr)
Japanese (ja)
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雄介 荒井
敏行 増井
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Ａｇｃ株式会社
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Publication of WO2024090211A1 publication Critical patent/WO2024090211A1/en

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G45/00—Compounds of manganese
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09C—TREATMENT OF INORGANIC MATERIALS, OTHER THAN FIBROUS FILLERS, TO ENHANCE THEIR PIGMENTING OR FILLING PROPERTIES ; PREPARATION OF CARBON BLACK  ; PREPARATION OF INORGANIC MATERIALS WHICH ARE NO SINGLE CHEMICAL COMPOUNDS AND WHICH ARE MAINLY USED AS PIGMENTS OR FILLERS
    • C09C1/00—Treatment of specific inorganic materials other than fibrous fillers; Preparation of carbon black

Definitions

  • the present invention relates to black particles, and more specifically to transition metal oxide-based black particles.
  • Structural color is a coloring phenomenon resulting from the spectrum of a microstructure close to the wavelength of light. Unlike coloring caused by dyes or pigments, there is no discoloration due to the absorption of ultraviolet light, and the coloring will continue forever unless the microstructure that causes the coloring phenomenon disappears. Materials with such structural coloring properties can achieve vivid coloring without using heavy metals such as mercury or chromium, so they have a small environmental impact and can meet the needs for safety and security, and are expected to be applied to new pigments. In particular, structural coloring materials using silica (silicon dioxide, SiO 2 ), which does not contain components that are harmful to the human body or have a high environmental impact, and has excellent heat resistance, have attracted attention.
  • structural coloring materials using silica including spherical colloidal crystals formed from silica particles of uniform particle size, and structural color films in which silica particles are deposited on the surface of an electrode by electrophoresis (hereafter collectively referred to as structural color silica). These materials are expected to find industrial applications because they can easily produce structural colors by self-arranging silica particles.
  • the color of structurally colored silica is due to Bragg reflection in a colloidal crystal structure in which silica particles are arranged, but it is known that the saturation of the color is reduced by various types of light scattering that occur in addition to Bragg reflection (scattering by particles, multiple scattering on the surface of the bulk, etc.). For this reason, a method is known in which black particles (such as carbon black nanoparticles, graphene, melanin, etc.) are added to primary silica particles in structurally colored silica to remove unnecessary scattered light and increase saturation.
  • black particles such as carbon black nanoparticles, graphene, melanin, etc.
  • Patent Document 1 describes a composite metal oxide mainly composed of Cu, Mn, and Al.
  • Non-Patent Document 1 reports a research example in which heat-resistant, environmentally friendly black particles are applied to structural color silica.
  • Non-Patent Document 2 reports black particles mainly composed of Cu as black particles containing Cu.
  • structurally colored silica which develops structural colors through self-arrangement, has the problem that the bonding strength between primary particles is weak, and the application of external force easily causes the structure to collapse and color to be lost.
  • structurally colored silica can be strengthened by heat treating it at a temperature of 600°C or higher. This is thought to be due to the formation of necks between the primary silica particles, and strength can be further increased by increasing the heat treatment temperature, and according to non-patent document 3, it is known that high structural robustness can be achieved by heat treatment at a temperature of 900°C or higher.
  • Non-Patent Document 1 reports on the change in color development due to heat treatment for structural color silica using carbon black, cobalt black, Fe3O4 , calcium manganate , and lanthanum manganate as black particles.
  • structural color silica to which carbon black and Fe3O4 have been added discolors due to heat treatment at 400°C or higher, and it is reported that calcium manganate, although thermally stable up to 1200°C by itself, discolors when used in structural color silica due to heat treatment at 700°C or higher.
  • the present invention aims to provide black particles that are environmentally friendly, have excellent heat resistance, and have good blackness when used in structural color silica without discoloration even when heat treated at 800°C or higher.
  • transition metal oxides with a double perovskite structure containing strontium, tantalum, and manganese as the main phase can produce novel black particles that are environmentally friendly, heat resistant, and have a high degree of blackness, making them suitable for structural color silica, leading to the completion of the present invention.
  • the present invention relates to the following: (1) Black particles made of a transition metal oxide containing at least strontium, tantalum, and manganese and substantially no chromium, cobalt, or nickel, and having a double perovskite structure as a main phase. (2) The black particles according to (1) above, which are made of a transition metal oxide having a double perovskite structure as a main phase and represented by the general formula ( CaxSr1 -x ) 2TaMnO6 (wherein x is 0 ⁇ x ⁇ 0.7). (3) The black particles according to (1) or (2), wherein the black particles have a lightness index L * value of 25 or less in the CIE1976 L * a * b * color system.
  • the black particles according to (6) above, wherein the black particles in the structural color silica have a number-based cumulative 10% particle diameter D10 of 1.5 ⁇ m or less and a number-based cumulative 50% particle diameter D50 of 3 ⁇ m or less.
  • the present invention can provide black particles that combine environmental friendliness, heat resistance, and blackness.
  • the black particles of the present invention can be used as black particles for structural color silica, which are suitable for improving the color development and strength of structural color silica particles and structural color pigments and coatings that contain structural color silica particles.
  • FIG. 1 is a diagram showing powder X-ray diffraction patterns of the black particles of Examples 1 and 3 to 6.
  • the black particles of the present invention are made of a transition metal oxide that contains at least strontium, tantalum, and manganese, and is substantially free of chromium, cobalt, and nickel, and has a double perovskite structure as its main phase.
  • the transition metal oxide constituting the black particles of the present invention contains at least strontium, tantalum, and manganese.
  • the transition metal oxide has a double perovskite structure ( A2B'B " O6 ) as the main phase of the crystal structure, in which A contains at least strontium, B' contains manganese, B" contains tantalum, and O contains oxygen.
  • the transition metal oxide has the above structure, so that the crystal does not denature at high temperatures, and even when used in structural color silica, it does not react with silica at high temperatures, improving heat resistance, suppressing discoloration even at high temperatures of 800°C or higher, and maintaining blackness.
  • the transition metal oxide constituting the black particles of the present invention may have a double perovskite structure represented by the general formula ( CaxSr1 -x ) 2TaMnO6 (wherein x is 0 ⁇ x ⁇ 0.7).
  • Structural color silica containing black particles made of transition metal oxides containing calcium is prone to neck formation between primary silica particles by heating, so that it is possible to increase the strength at a temperature lower than 800°C.
  • x is preferably 0 ⁇ x ⁇ 0.7, more preferably 0 ⁇ x ⁇ 0.5, and most preferably 0 ⁇ x ⁇ 0.3.
  • the crystal structure is a double perovskite structure
  • the maximum peak in the powder X-ray diffraction pattern is attributable to a double perovskite structure consisting of strontium, tantalum and manganese.
  • the amount of calcium is preferably in a range in which no peaks attributed to Ca2MnTaO6 appear.
  • the fact that the double perovskite structure is the main phase can also be confirmed by the fact that the transition metal oxide contains 80 mol % or more of the double perovskite structure.
  • the black particles of the present invention are desirably composed only of a double perovskite structure containing at least strontium, tantalum, and manganese, but other elements or other phases may be included as long as the crystal structure of the double perovskite structure can be maintained and the desired effect of the present invention is not impaired.
  • Such other elements include, for example, calcium, barium, niobium, antimony, etc.
  • other phases include, for example, Sr 2 Ta 2 O 7 , Ca 2 Ta 2 O 7 , etc.
  • the black particles of the present invention may be inevitably mixed with impurities derived from various raw materials, but do not substantially contain chromium (Cr), cobalt (Co) and nickel (Ni). "Substantially” means excluding the case where they are inevitably contained from other blended components unintentionally. Even if Cr, Co and Ni are contained as impurities, it is preferable that the content of Cr 6+, which is particularly a safety concern, is 10 mass ppm or less. It is also preferable that unreacted residues of the raw materials are not contained as much as possible, and it is particularly preferable that the content of Cr 6+ , which is a safety concern, is 1 mass ppm or less in the black particles.
  • composition and impurity amount of transition metal oxides can be measured by ICP emission spectroscopy, energy dispersive X-ray spectroscopy, X-ray fluorescence analysis, etc.
  • the blackness of the black particles of the present invention is represented by the CIE1976 L * a * b * color system, in which lightness is represented by L * , red to green by a * (positive is reddish, negative is greenish), and yellow to blue by b * (positive is yellowish, negative is blueish), and the smaller L * is and the closer a * and b * are to 0, the better the blackness is.
  • the L * value, a * value and b * value can be calculated from measurements made with a general color difference meter or spectrum measurements made with a visible/ultraviolet spectrophotometer.
  • the black particles of the present invention preferably have a lightness index L * value of 25 or less. If the L * value is 25 or less, when used in structurally colored silica, the arrangement structure of the primary silica particles is maintained within a range in which the structural color can be expressed, while unnecessary scattered light is removed, thereby improving saturation.
  • the L * value is more preferably 24 or less, even more preferably 23 or less, particularly preferably 21 or less, even more preferably 20 or less, and most preferably 19 or less.
  • the a * and b * values of the black particles of the present invention are preferably -3 or more and 3 or less.
  • cool colors such as blue and green are suppressed, and when they are 3 or less, warm colors such as red and yellow are suppressed.
  • the a * and b * values are more preferably -2.8 or more, even more preferably -2.6 or more, and more preferably 2.8 or less, and even more preferably 2.6 or less.
  • the achromaticity C * calculated from the a * and b * values by the following formula (1) is preferably 0 to 5, more preferably 0 to 4, particularly preferably 0 to 3, and most preferably 0 to 2.
  • C * represents the degree of coloring, with C * of 0 being achromatic and the higher C * being the greater the coloring. If C * exceeds 5, the blackness tends to be insufficient.
  • C * ⁇ (a * ) 2 + (b * ) 2 ⁇ 1/2 ... (1)
  • the black particles of the present invention can be produced by a method of mixing raw materials in a wet or dry manner, firing the raw materials, and then crushing them. From the viewpoint of production costs, it is preferable to produce the black particles by a method of mixing raw materials, firing, and pulverizing them, but the black particles of the present invention have a feature that a single-phase double perovskite structure can be easily obtained by dry mixing and then firing.
  • strontium compound, calcium compound, tantalum compound, and manganese compound used as starting materials may be in the form of their respective oxides, hydroxides, carbonates, etc.
  • strontium compounds include SrCO3 , SrO, Sr(OH) 2 , etc.
  • calcium compounds include CaCO3 , CaO, Ca(OH) 2 , etc.
  • tantalum compounds include Ta2O5 , Ta2O5 ( H2O ) 5 , Ta2 ( OC2H5 ) 10 , etc.
  • manganese compounds include Mn2O3 , MnO2 , Mn( OH ) 2 , etc.
  • the starting materials are weighed out to obtain a predetermined composition in a stoichiometric ratio.
  • the starting materials are then mixed.
  • Mixing can be performed by a known method.
  • a wet mill using a grinding media such as a wet ball mill, wet bead mill, wet sand grinder mill, or media stirring mill, or a wet mill without grinding media such as a stirring mill, disk mill, in-line mill, or jet mill, can be used.
  • a dry disperser such as a dry jet mill, hammer mill, dry bead mill, impeller mill, or dry ball mill can be used.
  • the mixing time and number of passes can be set appropriately according to the capacity of the equipment, and when using grinding media, the media diameter and media packing rate can also be adjusted appropriately.
  • grinding media such as alumina and zirconia can be used.
  • an agate mortar instead of mixing with a grinder, an agate mortar can be used for simplicity.
  • any solvent can be used as the dispersion medium.
  • examples include water and alcohol, but it is preferable to use water.
  • a dispersant may be added during wet mixing, and for example, a polymer dispersant such as a polyoxyalkylene-based or polycarboxylic acid-based dispersant may be used.
  • the amount of dispersant added may be adjusted as appropriate.
  • the mixture may be filtered, dried, spray-dried, etc. as necessary. Granulation or molding may also be performed as necessary.
  • the mixed raw materials are fired using known equipment.
  • firing equipment include electric furnaces and rotary kilns.
  • the firing is preferably carried out in an air atmosphere at a temperature in the range of 1200 to 1500°C, and can be adjusted as appropriate based on the results of powder X-ray diffraction and particle size distribution measurement of the particles after firing and crushing.
  • the firing temperature is preferably 1200°C or higher, more preferably 1250°C or higher, even more preferably 1300°C or higher, particularly preferably 1350°C or higher, and most preferably 1400°C or higher.
  • it is preferably 1500°C or lower, and most preferably 1450°C or lower.
  • the firing time can be set appropriately, but firing for a period between 3 and 12 hours makes it easier to obtain a transition metal oxide having the aforementioned crystalline phase.
  • the firing time is preferably 3 hours or more, more preferably 4 hours or more, particularly preferably 5 hours or more, and most preferably 6 hours or more.
  • the firing time is preferably 12 hours or less, more preferably 11 hours or less, even more preferably 10 hours or less, particularly preferably 9 hours or less, and most preferably 8 hours or less.
  • the black particles after firing may be crushed or pulverized as necessary.
  • the aforementioned dry grinder or ultrasonic disperser is used for crushing and pulverization. After crushing and pulverization, the particles can be classified as necessary to obtain the desired particle size.
  • the size of the black particles of the present invention is preferably in the range of 10 nm to 20 ⁇ m in particle diameter.
  • the particle diameter is 10 nm or more, it is easy to mix uniformly with the silica primary particles when forming the structural color silica, and the effect of improving saturation relative to the amount added is good.
  • the particle diameter is 20 ⁇ m or less, it is unlikely that the desired effect will not be obtained because the particles are not included in the structure of the structural color silica, and the effect of reducing the angle dependency of color development can be expected by moderately disturbing the arrangement of the silica primary particles.
  • the particle diameter is more preferably 40 nm or more, even more preferably 60 nm or more, even more preferably 80 nm or more, particularly preferably 100 nm or more, and more preferably 18 ⁇ m or less, even more preferably 16 ⁇ m or less, and particularly preferably 14 ⁇ m or less.
  • the black particles of the present invention preferably have a cumulative 50% particle diameter D 50 based on volume of 5 ⁇ m or less.
  • the 50% particle diameter D 50 is 5 ⁇ m or less, the desired effect is rarely not obtained because the particles are not included in the structure of the structural color silica when forming the structural color silica, and the effect of reducing the angle dependency of color development can be expected by moderately disturbing the arrangement of the primary silica particles.
  • the 50% particle diameter D 50 is preferably 100 nm or more, and when the 50% particle diameter D 50 is 100 nm or more, the effect of improving saturation relative to the amount added is good.
  • the 50% particle diameter D 50 is preferably 100 nm to 5 ⁇ m
  • the lower limit is more preferably 125 nm or more, even more preferably 150 nm or more, and particularly preferably 175 nm or more
  • the upper limit is more preferably 4 ⁇ m or less, more preferably 3.5 ⁇ m or less, and particularly preferably 3 ⁇ m or less.
  • the black particles of the present invention preferably have a cumulative 10% particle diameter D10 based on volume of 2 ⁇ m or less. If the 10 % particle diameter D10 is 2 ⁇ m or less, the occurrence of color unevenness between particles due to the number of black particles per structural color silica becoming non-uniform when forming structural color silica can be suppressed.
  • the 10% particle diameter D10 is preferably 20 nm or more, and if the 10% particle diameter D10 is 20 nm or more, it is easy to mix uniformly with the silica primary particles when synthesizing structural color silica.
  • the 10% particle diameter D10 is preferably 20 nm to 2 ⁇ m
  • the lower limit is more preferably 50 nm or more, even more preferably 75 nm or more, and particularly preferably 100 nm or more
  • the upper limit is more preferably 1.8 ⁇ m or less, more preferably 1.6 ⁇ m or less, and particularly preferably 1.4 ⁇ m or less.
  • the black particles of the present invention preferably have a cumulative 90% particle diameter D 90 based on volume of 1 ⁇ m to 15 ⁇ m.
  • the 90% particle diameter D 90 is 1 ⁇ m or more, the effect of improving saturation relative to the amount added is good, and when it is 15 ⁇ m or less, it is unlikely that the particles will not be incorporated into the structure of the structural color silica and the desired effect will not be obtained, and the effect of reducing the angle dependency of color development can be expected by moderately disturbing the arrangement of the primary silica particles.
  • the 90% particle diameter D 90 is more preferably 2 ⁇ m or more, even more preferably 3 ⁇ m or more, particularly preferably 4 ⁇ m or more, and more preferably 14 ⁇ m or less, even more preferably 13 ⁇ m or less, and particularly preferably 12 ⁇ m or less.
  • the particle size and particle size distribution of the black particles can be measured using a known particle size distribution measuring device.
  • An example of a particle size distribution measuring device is Microtrac's "MT3000II" (product name).
  • the black particles of the present invention are preferably used for structural color silica.
  • the structural color silica containing the black particles of the present invention has excellent heat resistance, and does not discolor even when heat-treated at a high temperature of 800° C. or more, and can improve the color development of the structural color silica.
  • the structural color silica is composed of primary silica particles and the black particles of the present invention.
  • the primary silica particles are preferably made of silica (SiO 2 ) and have a spherical shape.
  • the sphericity which is a measure of how close the shape of an object is to a perfect sphere, is preferably 80% or more.
  • the spherical shape of the primary silica particles makes it possible to realize a periodic structure sufficient to express structural colors through aggregation, self-arrangement, etc.
  • the sphericity is more preferably 83% or more, further preferably 85% or more, and particularly preferably 87% or more. The higher the sphericity, the more preferable it is, and 100% is the most preferable.
  • the sphericity is determined by measuring 100 of the primary silica particles constituting one particle of any structural color silica in a photographic projection obtained by photographing structural color silica with a scanning electron microscope (SEM). For each of the 100 primary silica particles, the circumscribed circle diameter (DL) and the inscribed circle diameter (DS) are measured, and the ratio (DS/DL) of the inscribed circle diameter (DS) to the circumscribed circle diameter (DL) is calculated, and the average value expressed as a percentage is taken as the sphericity. If the number of primary silica particles constituting one particle of structural color silica is less than 100, the particle diameter of all primary silica particles visible in the SEM image of one particle of structural color silica is measured to determine the sphericity.
  • the primary silica particles constituting the structural color silica of the present invention must be selected to have an appropriate particle size depending on the desired color development, but in order to achieve color development in the visible light range, the particle size is preferably in the range of 100 to 1000 nm. If the particle size is 100 nm or more, color development due to light interference, diffraction, scattering, etc. based on the arrangement of the primary silica particles is obtained, and if it is 1000 nm or less, the particle size of the structural color silica is easy to adjust.
  • the particle size of the primary silica particles is more preferably 110 nm or more, even more preferably 120 nm or more, and particularly preferably 130 nm or more.
  • the particle size is more preferably 900 nm or less, even more preferably 800 nm or less, and particularly preferably 700 nm or less.
  • the cumulative 50% particle size D 50 based on the number of primary silica particles in the structural color silica should be selected from particle sizes appropriate for the desired color development.
  • the ratio D 50 / ⁇ d of D 50 [nm] to the dominant wavelength ⁇ d [nm] of the desired color development of the structural color silica is preferably in the range of 0.30 to 0.60.
  • D 50 / ⁇ d is more preferably 0.33 or more, even more preferably 0.34 or more, particularly preferably 0.35 or more, and more preferably 0.55 or less, even more preferably 0.50 or less, and particularly preferably 0.47 or less.
  • the cumulative 10% particle diameter D10 based on the number of primary silica particles in the structural color silica is preferably 100 nm or more from the viewpoint of preventing adverse effects on the human body.
  • the particle size distribution of the primary silica particles in the structural color silica can be measured using a particle size distribution meter or by observation with a SEM.
  • An example of a particle size distribution meter is "Nanotrack" (product name) by Microtrack.
  • the particle size distribution is determined by measuring 100 of the primary silica particles constituting one particle of any structural color silica by SEM observation.
  • the particle size distribution is determined by measuring the particle size of all primary silica particles visible in the SEM image of one particle of structural color silica.
  • the range of the particle size (D 50 ) of the primary silica particles for obtaining a desired color is as follows.
  • the particle size of the primary silica particles constituting the structural color silica is preferably in the range of 150 to 235 nm, more preferably in the range of 180 to 230 nm, and even more preferably in the range of 190 to 225 nm.
  • the particle size of the primary silica particles that make up the structural color silica is in the range of 235 to 265 nm.
  • the particle size is more preferably in the range of 240 to 260 nm, and even more preferably in the range of 245 to 255 nm.
  • the particle diameter of the primary silica particles that make up the structural color silica is in the range of 265 to 320 nm.
  • the particle diameter is more preferably in the range of 270 to 315 nm, and even more preferably in the range of 275 to 310 nm.
  • the cumulative 50% particle diameter D 50 based on the number of black particles in the structural color silica is preferably 3 ⁇ m or less. If the 50% particle diameter D 50 is 3 ⁇ m or less, the desired effect is rarely not obtained because the particles are not included in the structure of the structural color silica, and the effect of reducing the angle dependency of color development can be expected by moderately disturbing the arrangement of the primary silica particles.
  • the 50% particle diameter D 50 is preferably 50 nm or more, and if the 50% particle diameter D 50 is 50 nm or more, the effect of improving saturation relative to the amount added is good.
  • the 50% particle diameter D 50 is preferably 50 nm to 3 ⁇ m
  • the lower limit is more preferably 75 nm or more, even more preferably 100 nm or more, and particularly preferably 125 nm or more
  • the upper limit is more preferably 2.8 ⁇ m or less, more preferably 2.6 ⁇ m or less, and particularly preferably 2.4 ⁇ m or less.
  • the cumulative 10% particle diameter D10 based on the number of black particles in the structural color silica is preferably 1.5 ⁇ m or less.
  • the 10% particle diameter D10 is preferably 20 nm or more, and when the 10% particle diameter D10 is 20 nm or more, it is easy to mix uniformly with the silica primary particles when synthesizing the structural color silica.
  • the 10% particle diameter D10 is preferably 20 nm to 1.5 ⁇ m
  • the lower limit is more preferably 50 nm or more, even more preferably 75 nm or more, and particularly preferably 100 nm or more
  • the upper limit is more preferably 1.2 ⁇ m or less, more preferably 0.8 ⁇ m or less, and particularly preferably 0.4 ⁇ m or less.
  • the black particles have a cumulative 10% particle size D10 based on the number of particles in the structural color silica of 1.5 ⁇ m or less, and a cumulative 50% particle size D50 of 3 ⁇ m or less.
  • the cumulative 90% particle diameter D 90 based on the number of black particles in the structural color silica is preferably 400 nm to 20 ⁇ m. If the 90% particle diameter D 90 is 400 nm or more, the effect of improving saturation relative to the amount added is good, and if it is 20 ⁇ m or less, it is unlikely that the desired effect will not be obtained because it is not incorporated into the structure of the structural color silica, and the effect of reducing the angle dependency of color development can be expected by moderately disturbing the arrangement of the primary silica particles.
  • the 90% particle diameter D 90 is more preferably 520 nm or more, even more preferably 650 nm or more, particularly preferably 800 nm or more, and more preferably 12 ⁇ m or less, even more preferably 10 ⁇ m or less, and particularly preferably 8 ⁇ m or less.
  • the particle size distribution of the black particles in the structural color silica can be measured by a particle size distribution meter or SEM observation, as described above.
  • SEM observation the particle size of 100 randomly selected black particles is measured to determine the particle size. If the number of black particles is small compared to the number of primary silica particles and it is difficult to confirm 100 black particles in SEM observation, it is sufficient to measure a possible number of particles of 10 or more for convenience. If no black particles are found on the surface of the structural color silica, the structural color silica 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 by the diameter of the circumscribed circle of the particle.
  • the ratio s/d of the cumulative 10% particle diameter s ( D10 ) of the black particles to the 50% particle diameter d ( D50 ) of the silica primary particles is preferably 0.5 or less. If the size of the black particles is too large relative to the silica primary particles, the arrangement of the structural color silica is too much disrupted, and there is a risk that the structural color will not be generated.
  • the ratio s/d is 0.5 or less, the black particles are dispersed in the structure without disrupting the arrangement of the structural color silica, and unnecessary scattered light can be efficiently suppressed to improve saturation.
  • the ratio s/d is more preferably 0.45 or less, more preferably 0.4 or less, and from the viewpoint of the efficiency of absorbing scattered light, it is preferably 0.01 or more, more preferably 0.05 or more.
  • N Si of primary silica particles present on the surface of any 10 pieces of structural color silica and the average number N BL of black particles satisfy the following relational formula (2).
  • N Si ⁇ 10 ⁇ (a/d) 2 ⁇ N BL (2) (In formula (2), d is the cumulative 50% particle diameter D50 based on the number of silica primary particles, and a is the cumulative 50% particle diameter D50 based on the number of black particles.)
  • the content ratio of primary silica particles to black particles in the structural color silica is preferably 50:50 to 98:2, calculated as a mass ratio of oxides.
  • the ratio is more preferably 55:45 to 95:5, more preferably 60:40 to 90:10, and particularly preferably 65:35 to 85:15, for primary silica particles to black particles.
  • Structural color silica can be produced, for example, by forming colloidal crystals or by forming an electrodeposition film using an electrodeposition method.
  • One method for forming colloidal crystals is to disperse an aqueous phase containing dispersed silica primary particles and black particles in a non-water-soluble organic liquid to form an oil-in-water emulsion, and then to remove the dispersant by repeating drying and solvent replacement one or more times to obtain structurally colored silica in which the primary particles are aggregated.
  • the primary particles self-align in the aggregation process to form a colloidal crystal structure with a periodic structure, which produces the structural color.
  • an electrodeposited film is prepared according to a conventional method, and then the film is peeled off to obtain structurally colored silica.
  • a sol solution in which primary silica particles are dispersed in a water-soluble solvent is mixed with black particles to prepare a primary particle dispersion, and then the anode and cathode are immersed in an electrolytic cell that stores the primary particle dispersion, and direct current electrolysis is performed in this state.
  • the electrodeposited film is peeled off from the anode, and a structurally colored silica thin film is obtained by crushing or cutting. When producing particulate structurally colored silica by electrodeposition, the obtained structurally colored silica thin film can be crushed and classified.
  • Examples 1 to 5 are examples, and Examples 6 to 8 are comparative examples.
  • Example 1 The starting materials shown in Table 1 were weighed out in a stoichiometric ratio, dry-mixed in an agate mortar for 30 minutes, and then placed in an alumina boat and fired in an electric furnace at 1400° C. for 6 hours in air. After firing, the mixture was coarsely crushed in the agate mortar for about 1 minute to obtain black particles.
  • the obtained black particles were used to prepare structurally colored silica.
  • 1.0 g of a dispersion sol of primary silica particles having a cumulative 50% particle diameter D50 of 220 nm based on volume and 0.1 g of the black particles prepared above were mixed with pure water, and the mixture was subjected to ultrasonic treatment for 3 minutes using an ultrasonic cleaner (US-13KS manufactured by SND Co., Ltd.)
  • the mixture was gently dropped onto a PFA petri dish using a micropipette, and was left to stand until the solvent was completely evaporated and the dish was dried.
  • the obtained dried body was divided into two, and one was heat-treated at 800° C. for 2 hours in an air atmosphere to obtain structurally colored silica.
  • Example 2 The preparation of structurally colored silica was carried out in the same manner as in Example 1, except that the ultrasonic treatment time was 30 minutes.
  • Examples 3 to 6 The same procedure as in Example 1 was repeated, except that the starting materials were changed as shown in Table 1 to obtain black particles.
  • Example 7 The starting materials shown in Table 1 were weighed out in a stoichiometric ratio, dry-mixed in an agate mortar for 30 minutes, then placed in an alumina boat and fired in an electric furnace in air at 1200° C. for 6 hours. After firing, the mixture was coarsely crushed in the agate mortar for about 5 minutes to obtain black particles. Using the obtained black particles, structurally colored silica was obtained in the same manner as in Example 1.
  • Example 8 The starting materials shown in Table 1 were weighed out in a stoichiometric ratio, dry-mixed in an agate mortar for 30 minutes, then placed in an alumina boat and fired in an electric furnace in air at 1000° C. for 10 hours. After firing, the mixture was coarsely crushed in the agate mortar for about 5 minutes to obtain black particles. Using the obtained black particles, structurally colored silica was obtained in the same manner as in Example 1.
  • Black particle size distribution ( D10 , D50 , D90 )
  • the particle size distribution was measured using a Microtrac MT3000II.
  • the black particles were placed in pure water and dispersed for 3 minutes using an ultrasonic cleaner (US-13KS manufactured by SND Corporation) for Examples 1 and 3 to 8, and for 30 minutes using an ultrasonic cleaner for Example 2, and then measurements were performed for 30 seconds with a particle refractive index of 2.16 and a solvent refractive index of 1.333. From this, the cumulative 10% particle size D 10 , cumulative 50% particle size D 50 and cumulative 90% particle size D 90 on a volume basis were determined. The results are shown in Table 1.
  • XRD pattern of black particles The black particles of Examples 1 and 3 to 6 were subjected to X-ray diffraction.
  • X-ray diffraction an Ultima IV manufactured by Rigaku Corporation was used, and the measurement conditions were Cu-K ⁇ radiation, tube voltage 40 kV, tube current 40 mA, scanning speed 2 ⁇ : 6°/min, sampling width 0.02°. The results are shown in Figure 1.
  • the peaks indicated by the symbol “ ⁇ ” are diffraction peaks derived from a double perovskite structure ( Sr2MnTaO6 ) consisting of strontium, tantalum, and manganese
  • the peaks indicated by the symbol “ ⁇ " are diffraction peaks derived from a double perovskite structure ( Ca2MnTaO6 ) consisting of calcium, tantalum, and manganese.
  • the black particles of Examples 1 to 5 are excellent in environmental friendliness since they do not contain Cr, Co, or Ni, which are harmful to the environment and human body, and are excellent in heat resistance since they are black particles produced by firing at 1400°C in the atmosphere, and have a good blackness with a small lightness L * , which is an index of blackness, of 20 or less.
  • L * which is an index of blackness, of 20 or less.
  • the color change in the structurally colored silica is small even after heat treatment at 800°C, so they are also suitable for increasing strength by heat treatment.
  • they can be finely divided to a particle size distribution suitable for structurally colored silica by a simple crushing treatment in an ultrasonic cleaner for about 3 minutes, so they are suitable as black particles for structurally colored silica.

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Abstract

The present invention provides black particles that are environmentally friendly and heat-resistant, do not discolor even upon heat treatment at 800°C or higher when used in structural color silica, and have excellent blackness. Black particles according to the present invention are composed of a transition metal oxide that contains at least strontium, tantalum, and manganese, the transition metal oxide being substantially free of chromium, cobalt, and nickel, and having a double perovskite structure as the main phase.

Description

黒色粒子Black Particles
　本発明は、黒色粒子に関し、さらに詳しくは、遷移金属酸化物系黒色粒子に関する。 The present invention relates to black particles, and more specifically to transition metal oxide-based black particles.
　現在、広く用いられている色材には、耐薬品性、対候性、耐水性の低い色材も多く、長時間紫外線にさらされることなどによって退色が生じる色材も存在する。無機顔料は、退色しにくく対候性に優れたものが多いが、毒性の高い重金属を使用した化合物を含むものもあり、規制などにより使用用途の限られる場合もある。 Many of the colorants currently in widespread use have poor chemical, weather, and water resistance, and some fade when exposed to UV rays for long periods of time. Many inorganic pigments are resistant to fading and have excellent weather resistance, but some contain compounds that use highly toxic heavy metals, and their uses may be limited by regulations.
　構造色は光線の波長に近い微細構造による分光に由来する発色現象をいい、色素や顔料による発色とは異なり、紫外線の吸収による脱色がなく、発色現象をもたらす微細構造が消失しない限り、永久に発色し続ける。このような構造発色性を持つ材料は、水銀やクロム等の重金属を用いることなく鮮やかな発色を実現できるため、環境負荷が小さく、安全安心を求めるニーズに対応でき、新しい顔料への応用が期待される。特に人体への有害性や環境負荷の高い成分を含まず、耐熱性にも優れた、シリカ（二酸化ケイ素、ＳｉＯ２）を用いた構造発色性材料が注目されている。 Structural color is a coloring phenomenon resulting from the spectrum of a microstructure close to the wavelength of light. Unlike coloring caused by dyes or pigments, there is no discoloration due to the absorption of ultraviolet light, and the coloring will continue forever unless the microstructure that causes the coloring phenomenon disappears. Materials with such structural coloring properties can achieve vivid coloring without using heavy metals such as mercury or chromium, so they have a small environmental impact and can meet the needs for safety and security, and are expected to be applied to new pigments. In particular, structural coloring materials using silica (silicon dioxide, SiO 2 ), which does not contain components that are harmful to the human body or have a high environmental impact, and has excellent heat resistance, have attracted attention.
　シリカを用いた構造発色性材料は種々提案がされているが、粒径のそろったシリカ微粒子により形成された球状コロイド結晶や、電気泳動法により電極表面にシリカ微粒子を堆積させた構造色膜（以降、これらを総称して構造色シリカと呼称する）は、シリカ粒子を自己配列させることで簡単に構造色を発現できることから工業的な応用が期待されている。 Various structural coloring materials using silica have been proposed, including spherical colloidal crystals formed from silica particles of uniform particle size, and structural color films in which silica particles are deposited on the surface of an electrode by electrophoresis (hereafter collectively referred to as structural color silica). These materials are expected to find industrial applications because they can easily produce structural colors by self-arranging silica particles.
　構造色シリカにおける発色は、シリカ微粒子が配列したコロイド結晶構造におけるブラッグ反射によるものであるが、ブラッグ反射に加えて生じる各種の光散乱（微粒子による散乱、バルク体表面における多重散乱等）によって発色の彩度が低減することがわかっている。このため、構造色シリカではシリカ一次粒子に加えて黒色粒子（例えばカーボンブラックナノ粒子やグラフェン、メラニン等）を添加することで不要な散乱光を除去し高彩度化させる手法が知られている。 The color of structurally colored silica is due to Bragg reflection in a colloidal crystal structure in which silica particles are arranged, but it is known that the saturation of the color is reduced by various types of light scattering that occur in addition to Bragg reflection (scattering by particles, multiple scattering on the surface of the bulk, etc.). For this reason, a method is known in which black particles (such as carbon black nanoparticles, graphene, melanin, etc.) are added to primary silica particles in structurally colored silica to remove unnecessary scattered light and increase saturation.
　しかしこれらの有機系の黒色粒子は熱分解により消色してしまう。このため、有機系黒色粒子を用いた構造色シリカは高温環境下で発色を維持できない。そのため、耐熱性の構造色シリカの実現には、無機系の黒色粒子の利用が考えられる。 However, these organic black particles lose their color due to thermal decomposition. For this reason, structurally colored silica that uses organic black particles cannot maintain its color in high-temperature environments. Therefore, the use of inorganic black particles is considered to realize heat-resistant structurally colored silica.
　ＣｒやＣｏといった環境負荷の高い成分を含まず、Ｆｅ３Ｏ４等の金属酸化物のように熱処理によって変色することのない耐熱性の優環境性黒色粒子として、例えば、特許文献１には、Ｃｕ，Ｍｎ，Ａｌを主成分とする複合金属酸化物が記載されている。また、非特許文献１には、構造色シリカにおいて耐熱性の優環境性黒色粒子を適用した研究例が報告されている。また、Ｃｕを含む黒色粒子として、非特許文献２には、Ｃｕを主成分とする黒色粒子が報告されている。 As heat-resistant, environmentally friendly black particles that do not contain components with high environmental impact such as Cr and Co and do not discolor due to heat treatment like metal oxides such as Fe3O4 , for example, Patent Document 1 describes a composite metal oxide mainly composed of Cu, Mn, and Al. In addition, Non-Patent Document 1 reports a research example in which heat-resistant, environmentally friendly black particles are applied to structural color silica. In addition, Non-Patent Document 2 reports black particles mainly composed of Cu as black particles containing Cu.
　また、自己配列させることで構造色を発現させる構造色シリカでは、一次粒子間の結合力が弱いため、外力を加えることで簡単に構造が崩れてしまい発色を失うという課題があるが、構造色シリカを６００℃以上の温度で熱処理することで高強度化できる。これはシリカ一次粒子間のネック形成によって高強度化すると考えられ、熱処理温度を高くすることでより高強度化し、非特許文献３によれば９００℃以上の温度での熱処理によって高い構造堅牢性を実現することが知られている。 Furthermore, structurally colored silica, which develops structural colors through self-arrangement, has the problem that the bonding strength between primary particles is weak, and the application of external force easily causes the structure to collapse and color to be lost. However, structurally colored silica can be strengthened by heat treating it at a temperature of 600°C or higher. This is thought to be due to the formation of necks between the primary silica particles, and strength can be further increased by increasing the heat treatment temperature, and according to non-patent document 3, it is known that high structural robustness can be achieved by heat treatment at a temperature of 900°C or higher.
日本国特開２０１５－９８５０９号公報Japanese Patent Publication No. 2015-98509
　非特許文献１では、カーボンブラック、コバルトブラック、Ｆｅ３Ｏ４、マンガン酸カルシウムおよびマンガン酸ランタンを黒色粒子として用いた構造色シリカに関して熱処理による発色の変化を報告している。非特許文献１によると、４００℃以上の熱処理によってカーボンブラック及びＦｅ３Ｏ４を添加した構造色シリカでは変色が生じ、マンガン酸カルシウムについても、単体では１２００℃まで熱的に安定であるにもかかわらず、構造色シリカに用いると７００℃以上の熱処理で変色してしまうことが報告されている。
　また、発明者らの検討によれば、特許文献１や非特許文献２に記載の複合酸化物のように、主成分に銅を含む無機黒色粒子を構造色シリカに用いると、８００℃の熱処理により構造色シリカが消色してしまうという課題があることが分かった。また、固相反応法で作製した非特許文献１に記載の黒色粒子は、シリカ一次粒子に対して均一に分散できるような粒度分布に調整しにくく、最終的な構造色の発色が均一になりにくいという課題もあることがわかった。 Non-Patent Document 1 reports on the change in color development due to heat treatment for structural color silica using carbon black, cobalt black, Fe3O4 , calcium manganate , and lanthanum manganate as black particles. According to Non-Patent Document 1, structural color silica to which carbon black and Fe3O4 have been added discolors due to heat treatment at 400°C or higher, and it is reported that calcium manganate, although thermally stable up to 1200°C by itself, discolors when used in structural color silica due to heat treatment at 700°C or higher.
Furthermore, according to the inventors' study, it was found that when inorganic black particles containing copper as a main component are used for structurally colored silica, such as the composite oxides described in Patent Document 1 and Non-Patent Document 2, there is a problem that the structurally colored silica is discolored by heat treatment at 800° C. In addition, it was found that the black particles described in Non-Patent Document 1, which are produced by the solid-phase reaction method, are difficult to adjust to a particle size distribution that allows them to be uniformly dispersed in the silica primary particles, and there is also a problem that the final structural color is difficult to develop uniformly.
　そこで、本発明は、環境性に優れ耐熱性を有し、構造色シリカに用いた際に８００℃以上の熱処理でも変色することなく、良好な黒色度を有する、黒色粒子を提供することを課題とする。 The present invention aims to provide black particles that are environmentally friendly, have excellent heat resistance, and have good blackness when used in structural color silica without discoloration even when heat treated at 800°C or higher.
　発明者らは上記課題に鑑み検討したところ、ストロンチウムとタンタルとマンガンを含むダブルペロブスカイト構造を主相とする遷移金属酸化物は、環境性と耐熱性を有し、さらに黒色度が高く、構造色シリカに好適である新規な黒色粒子を実現できることを見出し、本発明を完成させるに至った。 The inventors conducted research in light of the above problems and discovered that transition metal oxides with a double perovskite structure containing strontium, tantalum, and manganese as the main phase can produce novel black particles that are environmentally friendly, heat resistant, and have a high degree of blackness, making them suitable for structural color silica, leading to the completion of the present invention.
　本発明は、下記に関するものである。
（１）少なくともストロンチウムとタンタルとマンガンを含み、クロム、コバルト、ニッケルを実質的に含まない、ダブルペロブスカイト構造を主相とする遷移金属酸化物からなる黒色粒子。
（２）一般式（ＣａｘＳｒ１－ｘ）２ＴａＭｎＯ６（式中、ｘは０≦ｘ≦０．７）で表される、ダブルペロブスカイト構造を主相とする遷移金属酸化物からなる、前記（１）に記載の黒色粒子。
（３）前記黒色粒子は、ＣＩＥ１９７６Ｌ＊ａ＊ｂ＊表色系における明度指数Ｌ＊値が２５以下である、前記（１）又は（２）に記載の黒色粒子。
（４）前記黒色粒子は、体積基準による累積１０％粒径Ｄ１０が２μｍ以下である、前記（１）～（３）のいずれか１つに記載の黒色粒子。
（５）前記黒色粒子は、体積基準による累積５０％粒径Ｄ５０が５μｍ以下である、前記（１）～（４）のいずれか１つに記載の黒色粒子。
（６）構造色シリカ用の黒色粒子である、前記（１）～（５）のいずれか１つに記載の黒色粒子。
（７）前記構造色シリカ中において、前記黒色粒子の個数基準による累積１０％粒径Ｄ１０が１．５μｍ以下であり、累積５０％粒径Ｄ５０が３μｍ以下となる、前記（６）に記載の黒色粒子。 The present invention relates to the following:
(1) Black particles made of a transition metal oxide containing at least strontium, tantalum, and manganese and substantially no chromium, cobalt, or nickel, and having a double perovskite structure as a main phase.
(2) The black particles according to (1) above, which are made of a transition metal oxide having a double perovskite structure as a main phase and represented by the general formula ( CaxSr1 -x ) 2TaMnO6 (wherein x is 0≦x≦0.7).
(3) The black particles according to (1) or (2), wherein the black particles have a lightness index L * value of 25 or less in the CIE1976 L * a * b * color system.
(4) The black particles according to any one of (1) to (3), wherein the black particles have a cumulative 10% particle diameter D10 based on volume of 2 μm or less.
(5) The black particles according to any one of (1) to (4), wherein the black particles have a cumulative 50% particle diameter D50 based on volume of 5 μm or less.
(6) The black particles according to any one of (1) to (5), which are black particles for structural color silica.
(7) The black particles according to (6) above, wherein the black particles in the structural color silica have a number-based cumulative 10% particle diameter D10 of 1.5 μm or less and a number-based cumulative 50% particle diameter D50 of 3 μm or less.
　本発明によれば、環境性と耐熱性、黒色度を兼ね備えた黒色粒子を提供できる。また、本発明の黒色粒子は、構造色シリカ粒子及び構造色シリカ粒子を含む構造色顔料・塗膜の発色改善と高強度化に好適な、構造色シリカ用の黒色粒子として用いることができる。 The present invention can provide black particles that combine environmental friendliness, heat resistance, and blackness. In addition, the black particles of the present invention can be used as black particles for structural color silica, which are suitable for improving the color development and strength of structural color silica particles and structural color pigments and coatings that contain structural color silica particles.
図１は、例１、例３～例６の黒色粒子における粉末Ｘ線回折パターンを示す図である。FIG. 1 is a diagram showing powder X-ray diffraction patterns of the black particles of Examples 1 and 3 to 6.
　以下、本発明について説明するが、以下の説明における例示によって本発明は限定されない。 The present invention will be described below, but the present invention is not limited to the examples given below.
　本発明の黒色粒子は、少なくともストロンチウムとタンタルとマンガンを含み、クロム、コバルト及びニッケルを実質的に含まない、ダブルペロブスカイト構造を主相とする遷移金属酸化物からなるものである。 The black particles of the present invention are made of a transition metal oxide that contains at least strontium, tantalum, and manganese, and is substantially free of chromium, cobalt, and nickel, and has a double perovskite structure as its main phase.
＜遷移金属酸化物の結晶構造＞
　本発明の黒色粒子を構成する遷移金属酸化物は、少なくともストロンチウムとタンタルとマンガンを含む。結晶構造はダブルペロブスカイト構造（Ａ２Ｂ′Ｂ″Ｏ６）を主相とし、前記式中、Ａは少なくともストロンチウムを含み、Ｂ′はマンガン、Ｂ″はタンタルを含み、Ｏは酸素である遷移金属酸化物である。遷移金属酸化物が前記構造をとることで結晶が高温で変性することなく、構造色シリカに用いても高温でもシリカと反応することがないため、耐熱性が向上し、８００℃以上の高温下でも変色が抑えられ黒色度が保たれる。 <Crystal structure of transition metal oxide>
The transition metal oxide constituting the black particles of the present invention contains at least strontium, tantalum, and manganese. The transition metal oxide has a double perovskite structure ( A2B'B " O6 ) as the main phase of the crystal structure, in which A contains at least strontium, B' contains manganese, B" contains tantalum, and O contains oxygen. The transition metal oxide has the above structure, so that the crystal does not denature at high temperatures, and even when used in structural color silica, it does not react with silica at high temperatures, improving heat resistance, suppressing discoloration even at high temperatures of 800°C or higher, and maintaining blackness.
　また、本発明の黒色粒子を構成する遷移金属酸化物は、一般式（ＣａｘＳｒ１－ｘ）２ＴａＭｎＯ６（式中、ｘは０≦ｘ≦０．７）で表される、ダブルペロブスカイト構造であってもよい。カルシウムを含む遷移金属酸化物からなる黒色粒子を含む構造色シリカは、加熱によるシリカ一次粒子間でネック形成がされやすくなるため、８００℃よりも低い温度での高強度化が可能となる。前記一般式において、ｘが大きくなることで構造色シリカを高強度化するための熱処理温度を低温化できる一方で、黒色度が悪化する傾向があるので、ｘは０≦ｘ≦０．７であることが好ましく、０≦ｘ≦０．５がより好ましく、０≦ｘ≦０．３が最も好ましい。 The transition metal oxide constituting the black particles of the present invention may have a double perovskite structure represented by the general formula ( CaxSr1 -x ) 2TaMnO6 (wherein x is 0≦x≦0.7). Structural color silica containing black particles made of transition metal oxides containing calcium is prone to neck formation between primary silica particles by heating, so that it is possible to increase the strength at a temperature lower than 800°C. In the general formula, as x increases, the heat treatment temperature for increasing the strength of the structural color silica can be lowered, but the blackness tends to deteriorate, so x is preferably 0≦x≦0.7, more preferably 0≦x≦0.5, and most preferably 0≦x≦0.3.
　結晶構造がダブルペロブスカイト構造であることは、粉末Ｘ線回折により確認できる。Ｃｕ－Ｋαを線源とする粉末Ｘ線回折において、ストロンチウムとタンタルとマンガンからなるダブルペロブスカイト構造は、概ねブラッグ角２θ＝２２．５°，３２°，４６°，５１．５°，５７°，６７°，７６°付近に回折ピークを示す。なお、これらのピーク位置は組成により±２°程度の範囲内で変動し得る。例えばストロンチウムの一部がイオン半径の小さいカルシウムに置換されると、回折角は高角度側にシフトする。 The fact that the crystal structure is a double perovskite structure can be confirmed by powder X-ray diffraction. In powder X-ray diffraction using Cu-Kα as the radiation source, a double perovskite structure consisting of strontium, tantalum, and manganese shows diffraction peaks approximately at Bragg angles 2θ = 22.5°, 32°, 46°, 51.5°, 57°, 67°, and 76°. Note that the positions of these peaks can vary within a range of about ±2° depending on the composition. For example, when part of the strontium is replaced by calcium, which has a smaller ionic radius, the diffraction angle shifts to the higher angle side.
　本発明において、「ダブルペロブスカイト構造を主相とする」とは、粉末Ｘ線回折パターン中の最大ピークがストロンチウムとタンタルとマンガンからなるダブルペロブスカイト構造に帰属されることを意味する。ここで、このダブルペロブスカイト構造のメインピークは２θ＝３２°付近のピークであり、このメインピークの強度に対して、ほかのピークの強度が０．２以下であるような結晶構造であることが好ましい。
　また、カルシウム量が多くなるに従い、上述の回折ピーク以外のＣａ２ＭｎＴａＯ６に帰属されるピークが出現するが、本発明の黒色粒子を構成する遷移金属酸化物ではＣａ２ＭｎＴａＯ６に帰属されるピークが現れない範囲のカルシウム量であることが好ましい。 In the present invention, "having a double perovskite structure as a main phase" means that the maximum peak in the powder X-ray diffraction pattern is attributable to a double perovskite structure consisting of strontium, tantalum and manganese. Here, the main peak of this double perovskite structure is a peak near 2θ=32°, and it is preferable that the crystal structure has an intensity of the other peaks that is 0.2 or less relative to the intensity of this main peak.
Furthermore, as the amount of calcium increases, peaks other than the above-mentioned diffraction peaks attributed to Ca2MnTaO6 appear. However, in the transition metal oxide constituting the black particles of the present invention, the amount of calcium is preferably in a range in which no peaks attributed to Ca2MnTaO6 appear.
　また、ダブルペロブスカイト構造を主相とすることは、遷移金属酸化物中にダブルペロブスカイト構造が８０モル％以上含まれることからも確認できる。本発明の黒色粒子は、少なくともストロンチウムとタンタルとマンガンを含むダブルペロブスカイト構造のみからなることが望ましいが、ダブルペロブスカイト構造の結晶構造を維持でき、本発明の所望の効果を損なわない限り、他の元素又は他の相が含まれていてもよい。 The fact that the double perovskite structure is the main phase can also be confirmed by the fact that the transition metal oxide contains 80 mol % or more of the double perovskite structure. The black particles of the present invention are desirably composed only of a double perovskite structure containing at least strontium, tantalum, and manganese, but other elements or other phases may be included as long as the crystal structure of the double perovskite structure can be maintained and the desired effect of the present invention is not impaired.
　このような他の元素としては、例えば、カルシウム、バリウム、ニオブ、アンチモン等が挙げられる。また、他の相としては、例えば、Ｓｒ２Ｔａ２Ｏ７、Ｃａ２Ｔａ２Ｏ７等が挙げられる。 Such other elements include, for example, calcium, barium, niobium, antimony, etc. Also, other phases include, for example, Sr 2 Ta 2 O 7 , Ca 2 Ta 2 O 7 , etc.
　本発明の黒色粒子は、不可避的に各種原料由来の不純物が混入してもよいが、クロム（Ｃｒ）、コバルト（Ｃｏ）及びニッケル（Ｎｉ）は実質的には含まない。「実質的に」とは意図せずに他の配合成分から不可避的に含有される場合を除くことを意味する。Ｃｒ、Ｃｏ及びＮｉは不純物として含有している場合でも黒色粒子中に１質量％以下であることが好ましく、特に安全性に懸念があるＣｒ６＋の含有量は１０質量ｐｐｍ以下であることが好ましい。原料の未反応残差もできるだけ含有していないことが好ましく、特に黒色粒子中に１質量％以下であるのが好ましい。 The black particles of the present invention may be inevitably mixed with impurities derived from various raw materials, but do not substantially contain chromium (Cr), cobalt (Co) and nickel (Ni). "Substantially" means excluding the case where they are inevitably contained from other blended components unintentionally. Even if Cr, Co and Ni are contained as impurities, it is preferable that the content of Cr 6+, which is particularly a safety concern, is 10 mass ppm or less. It is also preferable that unreacted residues of the raw materials are not contained as much as possible, and it is particularly preferable that the content of Cr 6+ , which is a safety concern, is 1 mass ppm or less in the black particles.
　なお、遷移金属酸化物の組成及び不純物量は、ＩＣＰ発光分光分析法やエネルギー分散型Ｘ線分光法、蛍光Ｘ線分析法等により測定できる。 The composition and impurity amount of transition metal oxides can be measured by ICP emission spectroscopy, energy dispersive X-ray spectroscopy, X-ray fluorescence analysis, etc.
＜黒色度＞
　本発明の黒色粒子の黒色度は、ＣＩＥ１９７６Ｌ＊ａ＊ｂ＊表色系によって表わされる。この表色系においては、明度がＬ＊、赤～緑がａ＊（正が赤味、負が緑味）、黄～青がｂ＊（正が黄味、負が青味）で表わされ、Ｌ＊が小さく，ａ＊、ｂ＊がいずれも０に近いほど黒色度に優れる。
　Ｌ＊値、ａ＊値およびｂ＊値は、一般的な色彩色差計による測定値または可視紫外分光光度計によるスペクトル測定結果などから算出できる。 <Blackness>
The blackness of the black particles of the present invention is represented by the CIE1976 L * a * b * color system, in which lightness is represented by L * , red to green by a * (positive is reddish, negative is greenish), and yellow to blue by b * (positive is yellowish, negative is blueish), and the smaller L * is and the closer a * and b * are to 0, the better the blackness is.
The L * value, a * value and b * value can be calculated from measurements made with a general color difference meter or spectrum measurements made with a visible/ultraviolet spectrophotometer.
　本発明の黒色粒子は、明度指数Ｌ＊値が２５以下であることが好ましい。Ｌ＊値が２５以下であれば構造色シリカに用いた際に、シリカ一次粒子の配列構造を構造色が発現できる範囲に維持しつつ不要な散乱光を除去して彩度を向上させられる。Ｌ＊値は２４以下であることがより好ましく、２３以下がさらに好ましく、２１以下が特に好ましく、２０以下が殊更に好ましく、１９以下が最も好ましい。 The black particles of the present invention preferably have a lightness index L * value of 25 or less. If the L * value is 25 or less, when used in structurally colored silica, the arrangement structure of the primary silica particles is maintained within a range in which the structural color can be expressed, while unnecessary scattered light is removed, thereby improving saturation. The L * value is more preferably 24 or less, even more preferably 23 or less, particularly preferably 21 or less, even more preferably 20 or less, and most preferably 19 or less.
　また、本発明の黒色粒子のａ＊値およびｂ＊値はそれぞれ、－３以上３以下であることが好ましい。黒色粒子のａ＊値およびｂ＊値がそれぞれ－３以上であると、青味や緑味といった寒色系の色味が抑えられ、３以下であると赤身や黄色みといった暖色系の色味が抑えられる。ａ＊値およびｂ＊値はそれぞれ、－２．８以上であるのがより好ましく、－２．６以上がさらに好ましく、また、２．８以下であるのがより好ましく、２．６以下がさらに好ましい。 The a * and b * values of the black particles of the present invention are preferably -3 or more and 3 or less. When the a * and b * values of the black particles are -3 or more, cool colors such as blue and green are suppressed, and when they are 3 or less, warm colors such as red and yellow are suppressed. The a * and b * values are more preferably -2.8 or more, even more preferably -2.6 or more, and more preferably 2.8 or less, and even more preferably 2.6 or less.
　また、ａ＊値およびｂ＊値から下記式（１）により算出される無彩色度Ｃ＊は０～５であることが好ましく、０～４がより好ましく、０～３が特に好ましく、０～２が最も好ましい。Ｃ＊は色付きの度合いを表し、Ｃ＊が０の場合は無彩色であり、Ｃ＊が大きいほど色付きが大きい。Ｃ＊が５を超えると、黒色度が不十分となる傾向がある。
　　Ｃ＊＝｛（ａ＊）２＋（ｂ＊）２｝１／２　・・・（１） The achromaticity C * calculated from the a * and b * values by the following formula (1) is preferably 0 to 5, more preferably 0 to 4, particularly preferably 0 to 3, and most preferably 0 to 2. C * represents the degree of coloring, with C * of 0 being achromatic and the higher C * being the greater the coloring. If C * exceeds 5, the blackness tends to be insufficient.
C * = {(a * ) 2 + (b * ) 2 } 1/2 ... (1)
＜黒色粒子の製造方法＞
　本発明の黒色粒子は原料を湿式または乾式で混合後に焼成しその後解砕する手法により製造できる。製造コストの観点から原料混合～焼成、粉砕による手法で作製することが好ましいが、本発明の黒色粒子は、乾式混合後に焼成することで容易に単相のダブルペロブスカイト構造を得ることができる特徴を有する。また、特にＣａ量の少ないストロンチウムとタンタルとマンガンを含むダブルペロブスカイト構造を主相とする遷移金属酸化物の場合、焼成後の解砕で容易に微細な黒色粒子を得ることができるため、特に構造色シリカ用の黒色粒子として好適である。 <Method of manufacturing black particles>
The black particles of the present invention can be produced by a method of mixing raw materials in a wet or dry manner, firing the raw materials, and then crushing them. From the viewpoint of production costs, it is preferable to produce the black particles by a method of mixing raw materials, firing, and pulverizing them, but the black particles of the present invention have a feature that a single-phase double perovskite structure can be easily obtained by dry mixing and then firing. In addition, in the case of a transition metal oxide having a double perovskite structure as the main phase, which contains strontium, tantalum, and manganese with a small amount of Ca, in particular, fine black particles can be easily obtained by crushing after firing, so that it is particularly suitable as black particles for structural color silica.
　出発原料として用いるストロンチウム化合物、カルシウム化合物、タンタル化合物、マンガン化合物は、それぞれの酸化物、水酸化物、炭酸塩等を用いてもよい。
　ストロンチウム化合物としては、例えば、ＳｒＣＯ３、ＳｒＯ、Ｓｒ（ＯＨ）２等が挙げられる。カルシウム化合物としては、例えば、ＣａＣＯ３、ＣａＯ、Ｃａ（ＯＨ）２等が挙げられる。タンタル化合物としては、例えば、Ｔａ２Ｏ５、Ｔａ２Ｏ５(Ｈ２Ｏ)５、Ｔａ２(ＯＣ２Ｈ５)１０等が挙げられる。マンガン化合物としては、例えば、Ｍｎ２Ｏ３、ＭｎＯ２、Ｍｎ(ＯＨ)２等が挙げられる。 The strontium compound, calcium compound, tantalum compound, and manganese compound used as starting materials may be in the form of their respective oxides, hydroxides, carbonates, etc.
Examples of strontium compounds include SrCO3 , SrO, Sr(OH) 2 , etc. Examples of calcium compounds include CaCO3 , CaO, Ca(OH) 2 , etc. Examples of tantalum compounds include Ta2O5 , Ta2O5 ( H2O ) 5 , Ta2 ( OC2H5 ) 10 , etc. Examples of manganese compounds include Mn2O3 , MnO2 , Mn( OH ) 2 , etc.
　これらの出発原料を化学量論比で所定の組成となるよう秤量する。続いて、前記出発原料を混合する。混合手法は公知の方法で行うことができ、例えば湿式混合であれば、湿式ボールミル、湿式ビーズミル、湿式サンドグラインダーミル、媒体攪拌ミル等の粉砕メディアを用いる湿式粉砕機や、攪拌ミル、ディスクミル、インラインミル、ジェットミル等の粉砕メディアを用いない湿式粉砕機を用いることができる。乾式混合であれば、乾式ジェットミル、ハンマーミル、乾式ビーズミル、インペラーミル、乾式ボールミル等の乾式分散機が用いられる。 These starting materials are weighed out to obtain a predetermined composition in a stoichiometric ratio. The starting materials are then mixed. Mixing can be performed by a known method. For example, for wet mixing, a wet mill using a grinding media such as a wet ball mill, wet bead mill, wet sand grinder mill, or media stirring mill, or a wet mill without grinding media such as a stirring mill, disk mill, in-line mill, or jet mill, can be used. For dry mixing, a dry disperser such as a dry jet mill, hammer mill, dry bead mill, impeller mill, or dry ball mill can be used.
　混合時間やパス回数などは、設備の能力に合わせて適宜設定すればよく、粉砕メディアを用いる際のメディア径、メディア充填率も適宜調整してよい。粉砕メディアにはアルミナやジルコニアなどの公知のものを用いてよい。また粉砕機による混合に代えて簡易的にはメノウ乳鉢を用いて混合してもよい。 The mixing time and number of passes can be set appropriately according to the capacity of the equipment, and when using grinding media, the media diameter and media packing rate can also be adjusted appropriately. Known grinding media such as alumina and zirconia can be used. Also, instead of mixing with a grinder, an agate mortar can be used for simplicity.
　湿式で混合する際の分散媒には任意の溶媒が用いられる。例えば、水、アルコール等が挙げられるが、水を用いるのが好ましい。 When mixing in a wet state, any solvent can be used as the dispersion medium. Examples include water and alcohol, but it is preferable to use water.
　本発明では、湿式混合の際に分散剤を添加してもよく、例えば、ポリオキシアルキレン系、ポリカルボン酸系等の高分子分散剤を用いてよい。分散剤の添加量は適宜調整してよい。 In the present invention, a dispersant may be added during wet mixing, and for example, a polymer dispersant such as a polyoxyalkylene-based or polycarboxylic acid-based dispersant may be used. The amount of dispersant added may be adjusted as appropriate.
　湿式で混合した場合は、必要に応じてろ過、乾燥、噴霧乾燥等をしてもよい。また、必要に応じて造粒や成形をしてもよい。 If the mixture is wet mixed, it may be filtered, dried, spray-dried, etc. as necessary. Granulation or molding may also be performed as necessary.
　混合後の原料は公知の装置を用いて焼成する。焼成装置としては例えば、電気炉やロータリーキルンなどが挙げられる。 The mixed raw materials are fired using known equipment. Examples of firing equipment include electric furnaces and rotary kilns.
　焼成は大気雰囲気下、１２００～１５００℃の範囲で実施するのが好ましく、焼成・解砕後の粒子の粉末Ｘ線回折結果や粒度分布測定結果をもとに適宜調整できる。焼成温度は結晶性を維持するために、１２００℃以上が好ましく、１２５０℃以上がより好ましく、１３００℃以上がさらに好ましく、１３５０℃以上が特に好ましく、１４００℃以上が最も好ましい。一方で省エネルギーの観点から１５００℃以下であることが好ましく、１４５０℃以下であることが最も好ましい。 The firing is preferably carried out in an air atmosphere at a temperature in the range of 1200 to 1500°C, and can be adjusted as appropriate based on the results of powder X-ray diffraction and particle size distribution measurement of the particles after firing and crushing. In order to maintain crystallinity, the firing temperature is preferably 1200°C or higher, more preferably 1250°C or higher, even more preferably 1300°C or higher, particularly preferably 1350°C or higher, and most preferably 1400°C or higher. On the other hand, from the viewpoint of energy conservation, it is preferably 1500°C or lower, and most preferably 1450°C or lower.
　焼成時間は適宜設定できるが、３～１２時間の範囲で焼成すると前述する結晶相を有する遷移金属酸化物が得られやすい。焼成時間は確実な反応の完結の観点から３時間以上が好ましく、４時間以上がより好ましく、５時間以上が特に好ましく、６時間以上が最も好ましい。一方で省エネルギーの観点から１２時間以下が好ましく、１１時間以下がより好ましく、１０時間以下がさらに好ましく、９時間以下が特に好ましく、８時間以下が最も好ましい。 The firing time can be set appropriately, but firing for a period between 3 and 12 hours makes it easier to obtain a transition metal oxide having the aforementioned crystalline phase. From the viewpoint of ensuring the completion of the reaction, the firing time is preferably 3 hours or more, more preferably 4 hours or more, particularly preferably 5 hours or more, and most preferably 6 hours or more. On the other hand, from the viewpoint of energy saving, the firing time is preferably 12 hours or less, more preferably 11 hours or less, even more preferably 10 hours or less, particularly preferably 9 hours or less, and most preferably 8 hours or less.
　焼成後の黒色粒子は必要に応じて解砕・粉砕してもよい。解砕・粉砕には前述の乾式粉砕機や、超音波分散機が用いられる。解砕・粉砕後、必要に応じて分級をすることで、所望の粒子径に揃えられる。 The black particles after firing may be crushed or pulverized as necessary. The aforementioned dry grinder or ultrasonic disperser is used for crushing and pulverization. After crushing and pulverization, the particles can be classified as necessary to obtain the desired particle size.
＜物性＞
　本発明の黒色粒子の大きさは、粒子径が１０ｎｍ～２０μｍの範囲であるのが好ましい。粒子径が１０ｎｍ以上であると、構造色シリカを形成する際にシリカ一次粒子と均一に混合することが容易であるとともに、添加量に対する彩度向上の効果が良好である。また、粒子径が２０μｍ以下であると、構造色シリカの構造内に入れずに所望の効果が得られなくなることが少なく、適度にシリカ一次粒子の配列を乱すことで発色の角度依存性を低減させる効果が期待できる。粒子径は、４０ｎｍ以上であるのがより好ましく、６０ｎｍ以上がさらに好ましく、８０ｎｍ以上が一層好ましく、１００ｎｍ以上が特に好ましく、また、１８μｍ以下であるのがより好ましく、１６μｍ以下がさらに好ましく、１４μｍ以下が特に好ましい。 <Physical Properties>
The size of the black particles of the present invention is preferably in the range of 10 nm to 20 μm in particle diameter. When the particle diameter is 10 nm or more, it is easy to mix uniformly with the silica primary particles when forming the structural color silica, and the effect of improving saturation relative to the amount added is good. Also, when the particle diameter is 20 μm or less, it is unlikely that the desired effect will not be obtained because the particles are not included in the structure of the structural color silica, and the effect of reducing the angle dependency of color development can be expected by moderately disturbing the arrangement of the silica primary particles. The particle diameter is more preferably 40 nm or more, even more preferably 60 nm or more, even more preferably 80 nm or more, particularly preferably 100 nm or more, and more preferably 18 μm or less, even more preferably 16 μm or less, and particularly preferably 14 μm or less.
　本発明の黒色粒子は、体積基準による累積５０％粒径Ｄ５０が、５μｍ以下であるのが好ましい。５０％粒径Ｄ５０が５μｍ以下であると、構造色シリカを形成する際に構造色シリカの構造内に入れずに所望の効果が得られなくなることが少なく、適度にシリカ一次粒子の配列を乱すことで発色の角度依存性を低減させる効果が期待できる。５０％粒径Ｄ５０は１００ｎｍ以上であるのが好ましく、５０％粒径Ｄ５０が１００ｎｍ以上であると添加量に対する彩度向上の効果が良好である。すなわち、５０％粒径Ｄ５０は、１００ｎｍ～５μｍであるのが好ましく、下限は１２５ｎｍ以上であるのがより好ましく、１５０ｎｍ以上がさらに好ましく、１７５ｎｍ以上が特に好ましく、また、上限は４μｍ以下であるのがより好ましく、３．５μｍ以下がさらに好ましく、３μｍ以下が特に好ましい。 The black particles of the present invention preferably have a cumulative 50% particle diameter D 50 based on volume of 5 μm or less. When the 50% particle diameter D 50 is 5 μm or less, the desired effect is rarely not obtained because the particles are not included in the structure of the structural color silica when forming the structural color silica, and the effect of reducing the angle dependency of color development can be expected by moderately disturbing the arrangement of the primary silica particles. The 50% particle diameter D 50 is preferably 100 nm or more, and when the 50% particle diameter D 50 is 100 nm or more, the effect of improving saturation relative to the amount added is good. That is, the 50% particle diameter D 50 is preferably 100 nm to 5 μm, the lower limit is more preferably 125 nm or more, even more preferably 150 nm or more, and particularly preferably 175 nm or more, and the upper limit is more preferably 4 μm or less, more preferably 3.5 μm or less, and particularly preferably 3 μm or less.
　本発明の黒色粒子は、体積基準による累積１０％粒径Ｄ１０が、２μｍ以下であるのが好ましい。１０％粒径Ｄ１０が２μｍ以下であると、構造色シリカを形成する際に構造色シリカ毎の黒色粒子数が不均一となることによる粒子間での色ムラ発生を抑制できる。１０％粒径Ｄ１０は２０ｎｍ以上であるのが好ましく、１０％粒径Ｄ１０が２０ｎｍ以上であると構造色シリカを合成する際にシリカ一次粒子と均一に混合することが容易にできる。すなわち、１０％粒径Ｄ１０は、２０ｎｍ～２μｍであるのが好ましく、下限は５０ｎｍ以上であるのがより好ましく、７５ｎｍ以上がさらに好ましく、１００ｎｍ以上が特に好ましく、また、上限は１．８μｍ以下であるのがより好ましく、１．６μｍ以下がさらに好ましく、１．４μｍ以下が特に好ましい。 The black particles of the present invention preferably have a cumulative 10% particle diameter D10 based on volume of 2 μm or less. If the 10 % particle diameter D10 is 2 μm or less, the occurrence of color unevenness between particles due to the number of black particles per structural color silica becoming non-uniform when forming structural color silica can be suppressed. The 10% particle diameter D10 is preferably 20 nm or more, and if the 10% particle diameter D10 is 20 nm or more, it is easy to mix uniformly with the silica primary particles when synthesizing structural color silica. That is, the 10% particle diameter D10 is preferably 20 nm to 2 μm, the lower limit is more preferably 50 nm or more, even more preferably 75 nm or more, and particularly preferably 100 nm or more, and the upper limit is more preferably 1.8 μm or less, more preferably 1.6 μm or less, and particularly preferably 1.4 μm or less.
　本発明の黒色粒子は、体積基準による累積９０％粒径Ｄ９０が、１μｍ～１５μｍであるのが好ましい。９０％粒径Ｄ９０が１μｍ以上であると添加量に対する彩度向上の効果が良好であり、１５μｍ以下であると構造色シリカの構造内に入れずに所望の効果が得られなくなることが少なく、適度にシリカ一次粒子の配列を乱すことで発色の角度依存性を低減させる効果が期待できる。９０％粒径Ｄ９０は、２μｍ以上であるのがより好ましく、３μｍ以上がさらに好ましく、４μｍ以上が特に好ましく、また、１４μｍ以下であるのがより好ましく、１３μｍ以下がさらに好ましく、１２μｍ以下が特に好ましい。 The black particles of the present invention preferably have a cumulative 90% particle diameter D 90 based on volume of 1 μm to 15 μm. When the 90% particle diameter D 90 is 1 μm or more, the effect of improving saturation relative to the amount added is good, and when it is 15 μm or less, it is unlikely that the particles will not be incorporated into the structure of the structural color silica and the desired effect will not be obtained, and the effect of reducing the angle dependency of color development can be expected by moderately disturbing the arrangement of the primary silica particles. The 90% particle diameter D 90 is more preferably 2 μm or more, even more preferably 3 μm or more, particularly preferably 4 μm or more, and more preferably 14 μm or less, even more preferably 13 μm or less, and particularly preferably 12 μm or less.
　黒色粒子の粒径及び粒度分布は、公知の粒度分布測定計で測定できる。粒度分布測定計は、例えば、マイクロトラック社の「ＭＴ３０００ＩＩ」（商品名）等が挙げられる。 The particle size and particle size distribution of the black particles can be measured using a known particle size distribution measuring device. An example of a particle size distribution measuring device is Microtrac's "MT3000II" (product name).
＜構造色シリカへの利用＞
　本発明の黒色粒子は、構造色シリカに好適に用いられる。本発明の黒色粒子を含有した構造色シリカは、優れた耐熱性を有し、８００℃以上の高温で熱処理したときにも変色することなく、構造色シリカの発色性を向上できる。 <Use in structurally colored silica>
The black particles of the present invention are preferably used for structural color silica. The structural color silica containing the black particles of the present invention has excellent heat resistance, and does not discolor even when heat-treated at a high temperature of 800° C. or more, and can improve the color development of the structural color silica.
　構造色シリカは、シリカ一次粒子と本発明の黒色粒子を含んで構成される。 The structural color silica is composed of primary silica particles and the black particles of the present invention.
　シリカ一次粒子はシリカ（ＳｉＯ２）より構成され、その形状は真球形状であるのが好ましい。対象物の形状がどの程度真球に近いかを示す尺度である真球度は、８０％以上であるのが好ましい。シリカ一次粒子が真球形状であることで、集積・自己配列等によって構造色を発現させるに足る周期構造を実現できる。
　真球度は、８３％以上であることがより好ましく、８５％以上がさらに好ましく、８７％以上が特に好ましく、また、真球度が高ければ高いほど好ましく、１００％であることが最も好ましい。 The primary silica particles are preferably made of silica (SiO 2 ) and have a spherical shape. The sphericity, which is a measure of how close the shape of an object is to a perfect sphere, is preferably 80% or more. The spherical shape of the primary silica particles makes it possible to realize a periodic structure sufficient to express structural colors through aggregation, self-arrangement, etc.
The sphericity is more preferably 83% or more, further preferably 85% or more, and particularly preferably 87% or more. The higher the sphericity, the more preferable it is, and 100% is the most preferable.
　なお、真球度は、走査型電子顕微鏡（ＳＥＭ）により構造色シリカを写真撮影して得られる写真投影図における任意の構造色シリカの１粒子を構成するシリカ一次粒子から任意の１００個を測定して求める。任意の１００個のシリカ一次粒子について、それぞれその外接円の径（ＤＬ）と、内接円の径（ＤＳ）とを測定し、外接円の径（ＤＬ）に対する内接円の径（ＤＳ）の比（ＤＳ／ＤＬ）を算出した平均値をパーセント表示したものを真球度とする。構造色シリカの１粒子を構成するシリカ一次粒子の個数が１００個に満たない場合は、構造色シリカの１粒子のＳＥＭ画像で視認できる全てのシリカ一次粒子の粒径を測定して求める。 The sphericity is determined by measuring 100 of the primary silica particles constituting one particle of any structural color silica in a photographic projection obtained by photographing structural color silica with a scanning electron microscope (SEM). For each of the 100 primary silica particles, the circumscribed circle diameter (DL) and the inscribed circle diameter (DS) are measured, and the ratio (DS/DL) of the inscribed circle diameter (DS) to the circumscribed circle diameter (DL) is calculated, and the average value expressed as a percentage is taken as the sphericity. If the number of primary silica particles constituting one particle of structural color silica is less than 100, the particle diameter of all primary silica particles visible in the SEM image of one particle of structural color silica is measured to determine the sphericity.
　本発明の構造色シリカを構成するシリカ一次粒子は所望する発色により適切な粒子径のものを選択する必要があるが、可視光域での発色を実現する上では、粒子径が１００～１０００ｎｍの範囲であるのが好ましい。粒子径が１００ｎｍ以上であると、シリカ一次粒子の配列に基づく光の干渉、回折、散乱などによる発色が得られ、１０００ｎｍ以下であると、構造色シリカの粒子径の調整がしやすい。シリカ一次粒子の粒子径は、発色に悪影響する可能性のあるレイリー散乱の抑制や人体に対する悪影響が無いという観点から、１１０ｎｍ以上であるのがより好ましく、１２０ｎｍ以上がさらに好ましく、１３０ｎｍ以上が特に好ましい。また、発色に悪影響する可能性のあるミー散乱を抑制し、構造色シリカの形成時に良好な配列を実現させるという観点から、粒子径は、９００ｎｍ以下であるのがより好ましく、８００ｎｍ以下がさらに好ましく、７００ｎｍ以下が特に好ましい。 The primary silica particles constituting the structural color silica of the present invention must be selected to have an appropriate particle size depending on the desired color development, but in order to achieve color development in the visible light range, the particle size is preferably in the range of 100 to 1000 nm. If the particle size is 100 nm or more, color development due to light interference, diffraction, scattering, etc. based on the arrangement of the primary silica particles is obtained, and if it is 1000 nm or less, the particle size of the structural color silica is easy to adjust. From the viewpoint of suppressing Rayleigh scattering that may adversely affect color development and having no adverse effects on the human body, the particle size of the primary silica particles is more preferably 110 nm or more, even more preferably 120 nm or more, and particularly preferably 130 nm or more. In addition, from the viewpoint of suppressing Mie scattering that may adversely affect color development and achieving good arrangement when forming the structural color silica, the particle size is more preferably 900 nm or less, even more preferably 800 nm or less, and particularly preferably 700 nm or less.
　構造色シリカ中のシリカ一次粒子の個数基準による累積５０％粒径Ｄ５０は、所望する発色により適切な粒子径のものを選択する必要がある。本発明においては、所望する構造色シリカの発色の主波長λｄ［ｎｍ］に対するＤ５０［ｎｍ］の比Ｄ５０／λｄの範囲が０．３０～０．６０であるのが好ましい。Ｄ５０／λｄが上記範囲内であると、粒子間距離の調節や媒質の屈折率を調整することにより所望の色を得やすくなる。Ｄ５０／λｄは０．３３以上であるのがより好ましく、０．３４以上がさらに好ましく、０．３５以上が特に好ましく、また、０．５５以下であるのがより好ましく、０．５０以下がさらに好ましく、０．４７以下が特に好ましい。 The cumulative 50% particle size D 50 based on the number of primary silica particles in the structural color silica should be selected from particle sizes appropriate for the desired color development. In the present invention, the ratio D 50 /λ d of D 50 [nm] to the dominant wavelength λ d [nm] of the desired color development of the structural color silica is preferably in the range of 0.30 to 0.60. When D 50 /λ d is within the above range, it is easy to obtain the desired color by adjusting the interparticle distance or the refractive index of the medium. D 50 / λ d is more preferably 0.33 or more, even more preferably 0.34 or more, particularly preferably 0.35 or more, and more preferably 0.55 or less, even more preferably 0.50 or less, and particularly preferably 0.47 or less.
　また、構造色シリカ中のシリカ一次粒子の個数基準による累積１０％粒径Ｄ１０は、人体への悪影響を防ぐ観点から１００ｎｍ以上であることが好ましい。 Moreover, the cumulative 10% particle diameter D10 based on the number of primary silica particles in the structural color silica is preferably 100 nm or more from the viewpoint of preventing adverse effects on the human body.
　構造色シリカにおけるシリカ一次粒子の粒径分布は、粒度分布測定計を用いたり、ＳＥＭによる観察により測定できる。粒度分布測定計は、例えば、マイクロトラック社の「ナノトラック」（商品名）等が挙げられる。ＳＥＭ観察を行う場合は、ＳＥＭ観察で任意の構造色シリカの１粒子を構成するシリカ一次粒子から任意の１００個を測定して求める。構造色シリカの１粒子を構成するシリカ一次粒子の個数が１００個に満たない場合は、構造色シリカの１粒子のＳＥＭ画像で視認できる全てのシリカ一次粒子の粒径を測定して求める。
　なお、シリカ一次粒子は、構造色シリカの形状や陰影によって粒径を正確に把握しにくいため、画像処理ソフトウェアＩｍａｇｅＪを用いて画像処理し、評価するのが好ましい。 The particle size distribution of the primary silica particles in the structural color silica can be measured using a particle size distribution meter or by observation with a SEM. An example of a particle size distribution meter is "Nanotrack" (product name) by Microtrack. When performing SEM observation, the particle size distribution is determined by measuring 100 of the primary silica particles constituting one particle of any structural color silica by SEM observation. When the number of primary silica particles constituting one particle of structural color silica is less than 100, the particle size distribution is determined by measuring the particle size of all primary silica particles visible in the SEM image of one particle of structural color silica.
In addition, since it is difficult to accurately grasp the particle size of the primary silica particles due to the shape and shade of the structural color silica, it is preferable to perform image processing and evaluation using image processing software ImageJ.
　所望の発色を得るためのシリカ一次粒子の粒子径（Ｄ５０）の範囲の一例は以下のとおりである。
　本発明の構造色シリカによって青色を発色させたい場合は、構造色シリカを構成するシリカ一次粒子の粒子径を１５０～２３５ｎｍの範囲とするのが好ましい。粒子径は、より好ましくは１８０～２３０ｎｍの範囲であり、さらに好ましくは１９０～２２５ｎｍの範囲である。 An example of the range of the particle size (D 50 ) of the primary silica particles for obtaining a desired color is as follows.
When blue color is desired to be produced by the structural color silica of the present invention, the particle size of the primary silica particles constituting the structural color silica is preferably in the range of 150 to 235 nm, more preferably in the range of 180 to 230 nm, and even more preferably in the range of 190 to 225 nm.
　また、本発明の構造色シリカによって緑色を発色させたい場合は、構造色シリカを構成するシリカ一次粒子の粒子径を２３５～２６５ｎｍの範囲とするのが好ましい。粒子径は、より好ましくは２４０～２６０ｎｍの範囲であり、さらに好ましくは２４５～２５５ｎｍの範囲である。 If you want to produce a green color using the structural color silica of the present invention, it is preferable that the particle size of the primary silica particles that make up the structural color silica is in the range of 235 to 265 nm. The particle size is more preferably in the range of 240 to 260 nm, and even more preferably in the range of 245 to 255 nm.
　そしてまた、本発明の構造色シリカによって赤色を発色させたい場合は、構造色シリカを構成するシリカ一次粒子の粒子径を２６５～３２０ｎｍの範囲とするのが好ましい。粒子径は、より好ましくは２７０～３１５ｎｍの範囲であり、さらに好ましくは２７５～３１０ｎｍの範囲である。 Furthermore, if it is desired to produce a red color using the structural color silica of the present invention, it is preferable that the particle diameter of the primary silica particles that make up the structural color silica is in the range of 265 to 320 nm. The particle diameter is more preferably in the range of 270 to 315 nm, and even more preferably in the range of 275 to 310 nm.
　構造色シリカ中の黒色粒子の個数基準による累積５０％粒径Ｄ５０は、３μｍ以下であるのが好ましい。５０％粒径Ｄ５０が３μｍ以下であると、構造色シリカの構造内に入れずに所望の効果が得られなくなることが少なく、適度にシリカ一次粒子の配列を乱すことで発色の角度依存性を低減させる効果が期待できる。５０％粒径Ｄ５０は、５０ｎｍ以上であるのが好ましく、５０％粒径Ｄ５０が５０ｎｍ以上であると添加量に対する彩度向上の効果が良好である。すなわち、５０％粒径Ｄ５０は、５０ｎｍ～３μｍであるのが好ましく、下限は７５ｎｍ以上であるのがより好ましく、１００ｎｍ以上がさらに好ましく、１２５ｎｍ以上が特に好ましく、また、上限は２．８μｍ以下であるのがより好ましく、２．６μｍ以下がさらに好ましく、２．４μｍ以下が特に好ましい。 The cumulative 50% particle diameter D 50 based on the number of black particles in the structural color silica is preferably 3 μm or less. If the 50% particle diameter D 50 is 3 μm or less, the desired effect is rarely not obtained because the particles are not included in the structure of the structural color silica, and the effect of reducing the angle dependency of color development can be expected by moderately disturbing the arrangement of the primary silica particles. The 50% particle diameter D 50 is preferably 50 nm or more, and if the 50% particle diameter D 50 is 50 nm or more, the effect of improving saturation relative to the amount added is good. That is, the 50% particle diameter D 50 is preferably 50 nm to 3 μm, the lower limit is more preferably 75 nm or more, even more preferably 100 nm or more, and particularly preferably 125 nm or more, and the upper limit is more preferably 2.8 μm or less, more preferably 2.6 μm or less, and particularly preferably 2.4 μm or less.
　構造色シリカ中の黒色粒子の個数基準による累積１０％粒径Ｄ１０は、１．５μｍ以下であるのが好ましい。１０％粒径Ｄ１０が１．５μｍ以下であると、構造色シリカ毎の黒色粒子数が不均一となることによる粒子間での色ムラ発生を抑制できる。１０％粒径Ｄ１０は、２０ｎｍ以上であるのが好ましく、１０％粒径Ｄ１０が２０ｎｍ以上であると構造色シリカを合成する際にシリカ一次粒子と均一に混合することが容易にできる。すなわち、１０％粒径Ｄ１０は、２０ｎｍ～１．５μｍであるのが好ましく、下限は５０ｎｍ以上であるのがより好ましく、７５ｎｍ以上がさらに好ましく、１００ｎｍ以上が特に好ましく、また、上限は１．２μｍ以下であるのがより好ましく、０．８μｍ以下がさらに好ましく、０．４μｍ以下が特に好ましい。 The cumulative 10% particle diameter D10 based on the number of black particles in the structural color silica is preferably 1.5 μm or less. When the 10% particle diameter D10 is 1.5 μm or less, the occurrence of color unevenness between particles due to the number of black particles being non-uniform for each structural color silica can be suppressed. The 10% particle diameter D10 is preferably 20 nm or more, and when the 10% particle diameter D10 is 20 nm or more, it is easy to mix uniformly with the silica primary particles when synthesizing the structural color silica. That is, the 10% particle diameter D10 is preferably 20 nm to 1.5 μm, the lower limit is more preferably 50 nm or more, even more preferably 75 nm or more, and particularly preferably 100 nm or more, and the upper limit is more preferably 1.2 μm or less, more preferably 0.8 μm or less, and particularly preferably 0.4 μm or less.
　なお、本発明において、黒色粒子は、構造色シリカ中において、個数基準による累積１０％粒径Ｄ１０が１．５μｍ以下であり、かつ累積５０％粒径Ｄ５０が３μｍ以下となるのが好ましい。 In the present invention, it is preferable that the black particles have a cumulative 10% particle size D10 based on the number of particles in the structural color silica of 1.5 μm or less, and a cumulative 50% particle size D50 of 3 μm or less.
　構造色シリカ中の黒色粒子の個数基準による累積９０％粒径Ｄ９０は、４００ｎｍ～２０μｍであるのが好ましい。９０％粒径Ｄ９０が４００ｎｍ以上であると添加量に対する彩度向上の効果が良好であり、２０μｍ以下であると構造色シリカの構造内に入れずに所望の効果が得られなくなることが少なく、適度にシリカ一次粒子の配列を乱すことで発色の角度依存性を低減させる効果が期待できる。９０％粒径Ｄ９０は、５２０ｎｍ以上であるのがより好ましく、６５０ｎｍ以上がさらに好ましく、８００ｎｍ以上が特に好ましく、また、１２μｍ以下であるのがより好ましく、１０μｍ以下がさらに好ましく、８μｍ以下が特に好ましい。 The cumulative 90% particle diameter D 90 based on the number of black particles in the structural color silica is preferably 400 nm to 20 μm. If the 90% particle diameter D 90 is 400 nm or more, the effect of improving saturation relative to the amount added is good, and if it is 20 μm or less, it is unlikely that the desired effect will not be obtained because it is not incorporated into the structure of the structural color silica, and the effect of reducing the angle dependency of color development can be expected by moderately disturbing the arrangement of the primary silica particles. The 90% particle diameter D 90 is more preferably 520 nm or more, even more preferably 650 nm or more, particularly preferably 800 nm or more, and more preferably 12 μm or less, even more preferably 10 μm or less, and particularly preferably 8 μm or less.
　なお、構造色シリカにおける黒色粒子の粒径分布は、上記と同様に、粒度分布測定計や、ＳＥＭによる観察により測定できる。ＳＥＭ観察を行う場合は、無作為に選択した黒色粒子１００個の粒径を測定して求める。黒色粒子の数がシリカ一次粒子の数と比べて少なく、ＳＥＭ観察において１００個の黒色粒子を確認することが困難な場合は、便宜上１０粒子以上の可能な数で測定を行なえばよい。また、構造色シリカ表面に黒色粒子が見られない場合は、構造色シリカに外力を加えて破損させる等して破断面を形成させ、破断面上に存在する黒色粒子を持って測定をしてよい。なお粒径は、粒子の外接円の直径を用いる。 The particle size distribution of the black particles in the structural color silica can be measured by a particle size distribution meter or SEM observation, as described above. When performing SEM observation, the particle size of 100 randomly selected black particles is measured to determine the particle size. If the number of black particles is small compared to the number of primary silica particles and it is difficult to confirm 100 black particles in SEM observation, it is sufficient to measure a possible number of particles of 10 or more for convenience. If no black particles are found on the surface of the structural color silica, the structural color silica 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 by the diameter of the circumscribed circle of the particle.
　本発明において、構造色シリカにおけるシリカ一次粒子の個数基準による累積５０％粒径Ｄ５０をｄ、黒色粒子の個数基準による累積１０％粒径Ｄ１０をｓとしたとき、シリカ一次粒子の５０％粒径ｄ（Ｄ５０）に対する黒色粒子の累積１０％粒径ｓ（Ｄ１０）の比ｓ／ｄは、０．５以下であることが好ましい。シリカ一次粒子に対する黒色粒子の大きさが大きすぎると、構造色シリカの配列を崩し過ぎてしまい、構造色が発生しなくなる虞がある。前記比ｓ／ｄが０．５以下であることで、構造色シリカの配列を崩すことなく黒色粒子が構造内に分散し、不要な散乱光を効率よく抑制して彩度を向上できる。前記比ｓ／ｄは０．４５以下であるのがより好ましく、０．４以下がさらに好ましく、また、散乱光を吸収する効率の観点から、０．０１以上であるのが好ましく、０．０５以上がより好ましい。 In the present invention, when the cumulative 50% particle diameter D50 based on the number of silica primary particles in the structural color silica is d and the cumulative 10% particle diameter D10 based on the number of black particles is s, the ratio s/d of the cumulative 10% particle diameter s ( D10 ) of the black particles to the 50% particle diameter d ( D50 ) of the silica primary particles is preferably 0.5 or less. If the size of the black particles is too large relative to the silica primary particles, the arrangement of the structural color silica is too much disrupted, and there is a risk that the structural color will not be generated. When the ratio s/d is 0.5 or less, the black particles are dispersed in the structure without disrupting the arrangement of the structural color silica, and unnecessary scattered light can be efficiently suppressed to improve saturation. The ratio s/d is more preferably 0.45 or less, more preferably 0.4 or less, and from the viewpoint of the efficiency of absorbing scattered light, it is preferably 0.01 or more, more preferably 0.05 or more.
　ただし、黒色粒子が構造色シリカ表面に多く存在しすぎると発色が阻害されてしまうため、任意の構造色シリカ１０個の表面に存在するシリカ一次粒子の平均個数ＮＳｉと黒色粒子の平均個数ＮＢＬとが下記の関係式（２）を満たすことが好ましい。
　ＮＳｉ≧１０×（ａ／ｄ）２×ＮＢＬ　　・・・（２）
（式（２）中、ｄはシリカ一次粒子の個数基準による累積５０％粒径Ｄ５０、ａは黒色粒子の個数基準による累積５０％粒径Ｄ５０である。） However, if too many black particles are present on the surface of the structural color silica, color development is inhibited, so it is preferable that the average number N Si of primary silica particles present on the surface of any 10 pieces of structural color silica and the average number N BL of black particles satisfy the following relational formula (2).
N Si ≧10×(a/d) 2 ×N BL (2)
(In formula (2), d is the cumulative 50% particle diameter D50 based on the number of silica primary particles, and a is the cumulative 50% particle diameter D50 based on the number of black particles.)
　構造色シリカ中のシリカ一次粒子と黒色粒子の含有比は、酸化物換算の質量比で、シリカ一次粒子：黒色粒子が５０：５０～９８：２であることが好ましい。シリカ一次粒子と黒色粒子の含有比が前記範囲であると、構造色シリカの強度及び耐熱性の向上と、構造色の発現との両立を達成できる。前記比は、シリカ一次粒子：黒色粒子で５５：４５～９５：５であるのがより好ましく、６０：４０～９０：１０がさらに好ましく、６５：３５～８５：１５が特に好ましい。 The content ratio of primary silica particles to black particles in the structural color silica is preferably 50:50 to 98:2, calculated as a mass ratio of oxides. When the content ratio of primary silica particles to black particles is within the above range, it is possible to achieve both improved strength and heat resistance of the structural color silica and the expression of structural color. The ratio is more preferably 55:45 to 95:5, more preferably 60:40 to 90:10, and particularly preferably 65:35 to 85:15, for primary silica particles to black particles.
　構造色シリカは、例えば、コロイド結晶を形成する方法、電着法により電着膜を形成する方法等により作製できる。 Structural color silica can be produced, for example, by forming colloidal crystals or by forming an electrodeposition film using an electrodeposition method.
　コロイド結晶を形成する方法では、例えばシリカ一次粒子と黒色粒子を分散させた水相を、非水溶性の有機液体中に分散させて水中油型エマルションを形成させた後、乾燥と溶媒置換を一回以上繰り返すことで分散媒を除去し、一次粒子が凝集した構造色シリカを得る方法が挙げられる。この方法では、凝集工程で一次粒子が自己配列することで、周期構造を持ったコロイド結晶構造が形成され、構造色を発現する。 One method for forming colloidal crystals is to disperse an aqueous phase containing dispersed silica primary particles and black particles in a non-water-soluble organic liquid to form an oil-in-water emulsion, and then to remove the dispersant by repeating drying and solvent replacement one or more times to obtain structurally colored silica in which the primary particles are aggregated. In this method, the primary particles self-align in the aggregation process to form a colloidal crystal structure with a periodic structure, which produces the structural color.
　電着法により作製する方法では、従来公知の方法に従い電着膜を作製し、その後膜を剥離することで構造色シリカを得ることができる。シリカ一次粒子を水溶性溶媒に分散させたゾル溶液と黒色粒子を混合して一次粒子分散液を調整した後、一次粒子分散液を貯留した電解槽に陽極及び陰極を浸漬し、この状態で直流電解を行う。これにより、陽極の表面に電着膜が形成される。電着膜を陽極から剥離し、粉砕又は切断等により構造色シリカ薄膜を得る。電着法により粒子状の構造色シリカを作製する場合は、得られた構造色シリカ薄膜を粉砕、分級すればよい。 In the electrodeposition method, an electrodeposited film is prepared according to a conventional method, and then the film is peeled off to obtain structurally colored silica. A sol solution in which primary silica particles are dispersed in a water-soluble solvent is mixed with black particles to prepare a primary particle dispersion, and then the anode and cathode are immersed in an electrolytic cell that stores the primary particle dispersion, and direct current electrolysis is performed in this state. This forms an electrodeposited film on the surface of the anode. The electrodeposited film is peeled off from the anode, and a structurally colored silica thin film is obtained by crushing or cutting. When producing particulate structurally colored silica by electrodeposition, the obtained structurally colored silica thin film can be crushed and classified.
　以下、本発明を実施例により詳しく説明するが、本発明はこれらに限定されるものではない。例１～例５は実施例、例６～例８は比較例である。 The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Examples 1 to 5 are examples, and Examples 6 to 8 are comparative examples.
（例１）
１．黒色粒子の作製
　表１に記載の出発原料を化学量論比で秤量し、メノウ乳鉢にて３０分間乾式混合後にアルミナボートに入れ、電気炉を用いて大気中１４００℃で６時間焼成した。焼成後、メノウ乳鉢で１分程度粗粉砕し、黒色粒子を得た。 (Example 1)
The starting materials shown in Table 1 were weighed out in a stoichiometric ratio, dry-mixed in an agate mortar for 30 minutes, and then placed in an alumina boat and fired in an electric furnace at 1400° C. for 6 hours in air. After firing, the mixture was coarsely crushed in the agate mortar for about 1 minute to obtain black particles.
２．構造色シリカの作製
　得られた黒色粒子を用いて構造色シリカを作製した。
　体積基準による累積５０％粒径Ｄ５０が２２０ｎｍのシリカ一次粒子分散ゾル１．０ｇと上記作製した黒色粒子０．１ｇを純水と混合し、混合液を超音波洗浄機（株式会社エスエヌディ製ＵＳ－１３ＫＳ）を用いて３分間超音波処理した。これをＰＦＡシャーレ上にマイクロピペットを用いて静かに滴下し、そのまま溶媒が完全に揮散し乾燥するまで静置した。
　得られた乾燥体を二つに分け、片方を大気雰囲気下８００℃で２時間熱処理して構造色シリカを得た。 2. Preparation of structurally colored silica The obtained black particles were used to prepare structurally colored silica.
1.0 g of a dispersion sol of primary silica particles having a cumulative 50% particle diameter D50 of 220 nm based on volume and 0.1 g of the black particles prepared above were mixed with pure water, and the mixture was subjected to ultrasonic treatment for 3 minutes using an ultrasonic cleaner (US-13KS manufactured by SND Co., Ltd.) The mixture was gently dropped onto a PFA petri dish using a micropipette, and was left to stand until the solvent was completely evaporated and the dish was dried.
The obtained dried body was divided into two, and one was heat-treated at 800° C. for 2 hours in an air atmosphere to obtain structurally colored silica.
（例２）
　構造色シリカの作製において、超音波処理の時間を３０分とした以外は、例１と同様に行った。 (Example 2)
The preparation of structurally colored silica was carried out in the same manner as in Example 1, except that the ultrasonic treatment time was 30 minutes.
（例３～例６）
　例１において、出発原料を表１のとおりに変更して黒色粒子を得た以外は、例１と同様に行った。 (Examples 3 to 6)
The same procedure as in Example 1 was repeated, except that the starting materials were changed as shown in Table 1 to obtain black particles.
（例７）
　表１に記載の出発原料を化学量論比で秤量し、メノウ乳鉢にて３０分間乾式混合後にアルミナボートに入れ、電気炉を用いて大気中１２００℃で６時間焼成した。焼成後、メノウ乳鉢で５分程度粗粉砕し、黒色粒子を得た。
　得られた黒色粒子を用いて、例１と同様にして構造色シリカを得た。 (Example 7)
The starting materials shown in Table 1 were weighed out in a stoichiometric ratio, dry-mixed in an agate mortar for 30 minutes, then placed in an alumina boat and fired in an electric furnace in air at 1200° C. for 6 hours. After firing, the mixture was coarsely crushed in the agate mortar for about 5 minutes to obtain black particles.
Using the obtained black particles, structurally colored silica was obtained in the same manner as in Example 1.
（例８）
　表１に記載の出発原料を化学量論比で秤量し、メノウ乳鉢にて３０分間乾式混合後にアルミナボートに入れ、電気炉を用いて大気中１０００℃で１０時間焼成した。焼成後、メノウ乳鉢で５分程度粗粉砕し、黒色粒子を得た。
　得られた黒色粒子を用いて、例１と同様にして構造色シリカを得た。 (Example 8)
The starting materials shown in Table 1 were weighed out in a stoichiometric ratio, dry-mixed in an agate mortar for 30 minutes, then placed in an alumina boat and fired in an electric furnace in air at 1000° C. for 10 hours. After firing, the mixture was coarsely crushed in the agate mortar for about 5 minutes to obtain black particles.
Using the obtained black particles, structurally colored silica was obtained in the same manner as in Example 1.
＜評価法＞
　例１～８の黒色粒子及び構造色シリカについて行った評価方法を以下に示す。 <Evaluation method>
The evaluation methods carried out for the black particles and structural color silica of Examples 1 to 8 are shown below.
（黒色粒子の粒径分布（Ｄ１０、Ｄ５０、Ｄ９０））
　粒径分布測定はマイクロトラック社のＭＴ３０００ＩＩを用いて行った。黒色粒子を純水中に入れ、例１、３～８は超音波洗浄機（株式会社エスエヌディ製ＵＳ－１３ＫＳ）を用いて３分間、例２については超音波洗浄機を用いて３０分間分散させた後に、粒子屈折率を２．１６、溶媒屈折率を１．３３３として、測定時間３０秒で測定を実施した。これにより、体積基準による累積１０％粒径Ｄ１０、累積５０％粒径Ｄ５０及び累積９０％粒径Ｄ９０を求めた。結果を表１に示す。 (Black particle size distribution ( D10 , D50 , D90 ))
The particle size distribution was measured using a Microtrac MT3000II. The black particles were placed in pure water and dispersed for 3 minutes using an ultrasonic cleaner (US-13KS manufactured by SND Corporation) for Examples 1 and 3 to 8, and for 30 minutes using an ultrasonic cleaner for Example 2, and then measurements were performed for 30 seconds with a particle refractive index of 2.16 and a solvent refractive index of 1.333. From this, the cumulative 10% particle size D 10 , cumulative 50% particle size D 50 and cumulative 90% particle size D 90 on a volume basis were determined. The results are shown in Table 1.
（黒色粒子および構造色シリカの明度Ｌ＊及び色度ａ＊、ｂ＊）
　明度Ｌ＊及び色度ａ＊、ｂ＊は紫外可視分光光度計（日本分光株式会社製Ｖ－６７０）による拡散反射率スペクトル測定結果をもとに、ＪＩＳ　Ｚ８７８１－４：２０１３に記載の方法に従い算出した。黒色粒子の黒色度は明度Ｌ＊および無彩色度Ｃ＊により評価した。
　Ｃ＊は式（１）により算出した。結果を表１に示す。
　　Ｃ＊＝｛（ａ＊）２＋（ｂ＊）２｝１／２　・・・（１） (Lightness L * and chromaticity a * , b * of black particles and structural color silica)
The lightness L * and chromaticity a * , b * were calculated based on the diffuse reflectance spectrum measurement results using an ultraviolet-visible spectrophotometer (V-670 manufactured by JASCO Corporation) according to the method described in JIS Z8781-4: 2013. The blackness of the black particles was evaluated based on the lightness L * and achromaticity C * .
C * was calculated by formula (1). The results are shown in Table 1.
C * = {(a * ) 2 + (b * ) 2 } 1/2 ... (1)
（構造色シリカの耐熱性（ΔＬ））
　構造色シリカの熱処理前後における色の変化（ΔＬ）を測定した。上記「２．構造色シリカの作製」で得た、構造色シリカ乾燥体と８００℃で２時間乾燥した熱処理後の構造色シリカそれぞれの明度（Ｌ＊）を測定し、熱処理後の構造色シリカの明度から構造色シリカ乾燥体の明度を差し引いてその差を求めた。結果を表１に示す。ΔＬが１５以上は耐熱性がないと判断した。 (Heat resistance (ΔL) of structural color silica)
The color change (ΔL) of the structural color silica before and after heat treatment was measured. The lightness (L*) of the structural color silica dried body and the structural color silica after heat treatment dried at 800° C. for 2 hours obtained in the above " 2. Preparation of structural color silica" was measured, and the lightness of the structural color silica dried body was subtracted from the lightness of the structural color silica after heat treatment to obtain the difference. The results are shown in Table 1. It was determined that ΔL of 15 or more was not heat resistant.
（黒色粒子のＸＲＤパターン）
　例１，３～６の黒色粒子について、Ｘ線回折を行った。
　Ｘ線回折には、（株）リガク製Ｕｌｔｉｍａ　ＩＶを用い、測定条件はＣｕ－Ｋα線使用、管電圧４０ｋＶ、管電流４０ｍＡ、走査速度２θ：６°／分、サンプリング幅０．０２°とした。
　結果を図１に示す。図１中、記号「◆」で示したピークがストロンチウムとタンタルとマンガンからなるダブルペロブスカイト構造（Ｓｒ２ＭｎＴａＯ６）に由来する回折ピークであり、記号「▼」がカルシウムとタンタルとマンガンからなるダブルペロブスカイト構造（Ｃａ２ＭｎＴａＯ６）に由来する回折ピークである。 (XRD pattern of black particles)
The black particles of Examples 1 and 3 to 6 were subjected to X-ray diffraction.
For the X-ray diffraction, an Ultima IV manufactured by Rigaku Corporation was used, and the measurement conditions were Cu-Kα radiation, tube voltage 40 kV, tube current 40 mA, scanning speed 2θ: 6°/min, sampling width 0.02°.
The results are shown in Figure 1. In Figure 1, the peaks indicated by the symbol "♦" are diffraction peaks derived from a double perovskite structure ( Sr2MnTaO6 ) consisting of strontium, tantalum, and manganese, and the peaks indicated by the symbol "▼ " are diffraction peaks derived from a double perovskite structure ( Ca2MnTaO6 ) consisting of calcium, tantalum, and manganese.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　図１より、例１，３～６はＣａ量が増えるにしたがってブラッグ角２θ＝３２°付近の回折ピークが小さくなった。
　表１の結果より、例１～例５の黒色粒子は、環境や人体に有害なＣｒ，Ｃｏ，Ｎｉを含まないことから環境性に優れ、大気中１４００℃で焼成して作製した黒色粒子であることから耐熱性にも優れており、黒色度の指標である明度Ｌ＊が２０以下と小さく、良好な黒色度を有することが分かった。また、構造色シリカに用いた際に８００℃の熱処理によっても構造色シリカにおける色の変化が小さいことから、熱処理による高強度化にも好適である。また、超音波洗浄機で３分間程度の簡易的な解砕処理で構造色シリカに好適な粒径分布まで微細化できることから、構造色シリカ用の黒色粒子として好適であることが分かった。 1, in Examples 1 and 3 to 6, the diffraction peak near the Bragg angle 2θ=32° became smaller as the Ca content increased.
From the results in Table 1, the black particles of Examples 1 to 5 are excellent in environmental friendliness since they do not contain Cr, Co, or Ni, which are harmful to the environment and human body, and are excellent in heat resistance since they are black particles produced by firing at 1400°C in the atmosphere, and have a good blackness with a small lightness L * , which is an index of blackness, of 20 or less. In addition, when used in structurally colored silica, the color change in the structurally colored silica is small even after heat treatment at 800°C, so they are also suitable for increasing strength by heat treatment. In addition, they can be finely divided to a particle size distribution suitable for structurally colored silica by a simple crushing treatment in an ultrasonic cleaner for about 3 minutes, so they are suitable as black particles for structurally colored silica.
　本発明を詳細にまた特定の実施形態を参照して説明したが、本発明の精神と範囲を逸脱することなく様々な変更や修正を加えられることは当業者にとって明らかである。本出願は、２０２２年１０月２８日出願の日本特許出願（特願２０２２－１７３５８１）に基づくものであり、その内容はここに参照として取り込まれる。 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 present invention. This application is based on a Japanese patent application (Patent Application No. 2022-173581) filed on October 28, 2022, the contents of which are incorporated herein by reference.

Claims (7)

  1. 　少なくともストロンチウムとタンタルとマンガンを含み、クロム、コバルト及びニッケルを実質的に含まない、ダブルペロブスカイト構造を主相とする遷移金属酸化物からなる黒色粒子。 Black particles made of transition metal oxides with a double perovskite structure as the main phase, containing at least strontium, tantalum, and manganese, and substantially free of chromium, cobalt, and nickel.
  2. 　一般式（ＣａｘＳｒ１－ｘ）２ＴａＭｎＯ６（式中、ｘは０≦ｘ≦０．７）で表される、ダブルペロブスカイト構造を主相とする遷移金属酸化物からなる、請求項１に記載の黒色粒子。 2. The black particles according to claim 1, which are made of a transition metal oxide having a double perovskite structure as a main phase , and which is represented by the general formula ( CaxSr1 -x ) 2TaMnO6 (wherein x is 0≦x≦0.7).
  3. 　前記黒色粒子は、ＣＩＥ１９７６Ｌ＊ａ＊ｂ＊表色系における明度指数Ｌ＊値が２５以下である、請求項１又は２に記載の黒色粒子。 The black particles according to claim 1 or 2, wherein the black particles have a lightness index L * value of 25 or less in the CIE 1976 L* a * b * color system.
  4. 　前記黒色粒子は、体積基準による累積１０％粒径Ｄ１０が２μｍ以下である、請求項１又は２に記載の黒色粒子。 The black particles according to claim 1 or 2, wherein the black particles have a cumulative 10% particle diameter D10 based on volume of 2 μm or less.
  5. 　前記黒色粒子は、体積基準による累積５０％粒径Ｄ５０が５μｍ以下である、請求項１又は２に記載の黒色粒子。 The black particles according to claim 1 or 2, wherein the black particles have a cumulative 50% particle diameter D50 based on volume of 5 μm or less.
  6. 　構造色シリカ用の黒色粒子である、請求項１又は２に記載の黒色粒子。 The black particles according to claim 1 or 2, which are black particles for structural color silica.
  7. 　前記構造色シリカ中において、前記黒色粒子の個数基準による累積１０％粒径Ｄ１０が１．５μｍ以下であり、累積５０％粒径Ｄ５０が３μｍ以下となる、請求項６に記載の黒色粒子。 The black particles according to claim 6, wherein the black particles in the structural color silica have a cumulative 10% particle diameter D10 of 1.5 μm or less and a cumulative 50% particle diameter D50 of 3 μm or less based on the number of particles.
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