Structural color pigment and method for preparing structural color pigment

Abstract

To provide structural color pigments that can be manufactured more inexpensively, and to provide a more inexpensive manufacturing method for such structural color pigments.SOLUTION: There is provided a structural color pigment comprising, in sequence, a flat substrate, a crystalline layer, and a nanorod layer containing multiple nanorods, wherein the crystalline layer contains metal oxides and the nanorod contains one or more selected from the group consisting of metal oxides, metal hydroxides, and metal oxide hydroxides, and an average tilt angle of the long axis of the nanorods is within the range of ±30 degrees relative to the plane of the flat substrate (0 degrees).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to structural color pigments and methods for preparing structural color pigments. [Background technology]

[0002] Structural colors are known to be produced by microscopic structures roughly smaller than the wavelength of light. Examples of structural colors in nature include the blue color of the Morpho butterfly, which is produced by the interference and diffraction of light caused by the shelf-like structures in its scales, and the iridescent color of the jewel beetle, which is produced by the interference of light caused by the multilayer structure of the membrane.

[0003] Structural colors have the advantage of being brighter or pearlescent than dyes made with ordinary pigments, making them superior in design. Furthermore, structural colors have the advantages of being less prone to fading and more weather-resistant than dyes made with ordinary pigments.

[0004] As an example of a structural color pigment, Patent Document 1 discloses a gold pigment based on a substrate coated with a metal oxide, which has a multilayer structure in which a first layer of titanium dioxide doped with carbon obtained by thermal decomposition of organic colloidal particles is followed by a layer of iron (III) oxide.

[0005] Furthermore, for example, Patent Document 2 discloses a structural color flake pigment comprising a core portion arrangement portion in which core portions, which are monodisperse resin particles with an average particle diameter of 100 to 850 nm, are regularly arranged, and a stationary phase that fixes the regular arrangement of the core portions, wherein the structural color flake pigment has a thickness of 1 to 30 μm, an aspect ratio of 1 to 250, and a refractive index difference between the core portions and the stationary phase of 0.01 or more. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 09-012919 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-024289 Summary of the Invention [Problem to be solved by the invention]

[0007] However, conventional structural color pigments are expensive, and there is a demand for structural color pigments that can be produced more inexpensively.

[0008] Therefore, an object of the present invention is to provide a structural color pigment that can be produced more inexpensively.

[0009] Another object of the present invention is to provide a method for producing such structural color pigments at lower cost. [Means for solving the problem]

[0010] The structural color pigment according to the present invention comprises, in order: A flat substrate; a crystalline layer; a nanorod layer comprising a plurality of nanorods; A structural color pigment having the formula: the crystalline layer includes a metal oxide; the metal oxide is an oxide of one or more metals selected from the group consisting of titanium, zinc, aluminum, zirconium, indium, tin, niobium, cerium, chromium, iron, magnesium, and cobalt; the nanorods comprise one or more selected from the group consisting of metal oxides, metal hydroxides, and metal oxide hydroxides; the metal of the metal oxide, metal hydroxide, and metal oxide hydroxide of the nanorods comprises one or more selected from the group consisting of iron, titanium, zinc, cobalt, aluminum, tin, chromium, zirconium, copper, and magnesium; The structural color pigment has an average tilt of the major axis of the nanorods within a range of ±30 degrees from the perpendicular (0 degrees) to the plane of the flat substrate.

[0011] In one embodiment of the structural color pigment according to the present invention, the metal oxide of the crystalline layer has a rutile structure.

[0012] In one embodiment of the structural color pigment according to the present invention, the metal oxide of the crystal layer has a refractive index of 1.3 or more and 3.0 or less, and the metal oxide constituting the nanorod layer has a refractive index of 1.3 or more and 3.0 or less.

[0013] In one embodiment of the structural color pigment according to the present invention, the nanorods have an average diameter of 10 nm or more and 80 nm or less, and an average height of 50 nm or more and 400 nm or less.

[0014] In one embodiment of the structural color pigment according to the present invention, the average maximum diameter of the structural color pigment is 3 μm or more and 50 μm or less, and the aspect ratio of the structural color pigment is 5 or more and 700 or less.

[0015] In one embodiment of the structural color pigment according to the present invention, the metal oxide of the crystalline layer is titanium dioxide, zinc oxide, tin-doped indium oxide, tin oxide (SnO2), or zirconium oxide, the nanorods comprise a metal oxide, and the metal oxide of the nanorods is iron oxide.

[0016] In one embodiment of the structural color pigment according to the present invention, when the mass of the crystal layer is M1 and the mass of the nanorod layer is M2, the proportion of M2 to the total of M1 and M2 is 10 to 80 mass %.

[0017] In one embodiment of the structural color pigment according to the present invention, the flat substrate is aluminum, mica, or alumina.

[0018] The method for preparing the structural color pigment according to the present invention is a method for preparing the structural color pigment, comprising the steps of: A step (1) of preparing a first laminate having a crystal layer provided on a flat surface of a flat substrate; (2) contacting the first laminate with a nanorod layer preparation solution to form a nanorod layer precursor on the outer surface of the crystal layer of the first laminate; (3) reacting the nanorod layer precursor to form a nanorod layer; Including, the crystalline layer comprises a metal oxide; the metal oxide is an oxide of one or more metals selected from the group consisting of titanium, zinc, aluminum, zirconium, indium, tin, niobium, cerium, chromium, iron, magnesium, and cobalt; the nanorod layer preparation solution contains one or more selected from the group consisting of metal oxides, metal hydroxides, and metal oxide hydroxides; the metal of the metal oxide, metal hydroxide, and metal oxide hydroxide of the nanorod layer preparation solution contains one or more metals selected from the group consisting of iron, titanium, zinc, cobalt, aluminum, tin, chromium, zirconium, copper, and magnesium; The nanorod layer preparation solution has a pH of 3.0 or higher.

[0019] In one embodiment of the preparation method according to the present invention, the step (3) comprises reacting the nanorod layer precursor at a temperature of 80° C. or less.

[0020] In one embodiment of the preparation method according to the invention, the metal oxide of the crystalline layer has a rutile structure. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a structural color pigment that can be produced more inexpensively. Furthermore, according to the present invention, it is possible to provide a method for producing such a structural color pigment more inexpensively. [Brief explanation of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram showing an example of a cross section perpendicular to the plane of a flat substrate of a structural color pigment according to the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an example of a cross section perpendicular to the plane of a flat substrate of another structural color pigment according to the present invention. [Figure 3] FIG. 3 is a schematic diagram showing an example of a cross section perpendicular to the plane of a flat substrate of another structural color pigment according to the present invention. [Figure 4] FIG. 4 is a schematic diagram showing an example of a cross section perpendicular to the plane of a flat substrate of another structural color pigment according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described. These descriptions are for the purpose of illustrating the present invention and are not intended to limit the present invention in any way.

[0024] In the present invention, two or more embodiments can be combined in any manner.

[0025] Unless otherwise specified, the materials, components, compounds, preparations, groups, crystals, crystal systems, crystal structures, refractive indices, shapes, nanorods, and solvents described herein may be used singly or in combination of two or more.

[0026] In this specification, unless otherwise specified, numerical ranges are intended to include the upper and lower limits of the range. For example, 10 to 80 nm means a range of 10 nm or more and 80 nm or less.

[0027] In the present invention, for the convenience of explanation, each step is numbered and expressed as step (1), etc., but these numbers are used to identify or distinguish each step and do not indicate the order of the steps.

[0028] The accompanying drawings are schematic diagrams given priority for facilitating understanding of the present invention, and therefore the scale of each layer, the number of nanorods, and the scale and shape of the structural color pigments in the drawings are not accurate.

[0029] Structural color pigments The structural color pigment according to the present invention is In order, A flat substrate; a crystalline layer; a nanorod layer comprising a plurality of nanorods; A structural color pigment having the formula: the crystalline layer includes a metal oxide; the metal oxide is an oxide of one or more metals selected from the group consisting of titanium, zinc, aluminum, zirconium, indium, tin, niobium, cerium, chromium, iron, magnesium, and cobalt; the nanorods comprise one or more selected from the group consisting of metal oxides, metal hydroxides, and metal oxide hydroxides; the metal of the metal oxide, metal hydroxide, and metal oxide hydroxide of the nanorods comprises one or more selected from the group consisting of iron, titanium, zinc, cobalt, aluminum, tin, chromium, zirconium, copper, and magnesium; The average tilt of the major axis of the nanorods is within the range of ±30 degrees from the perpendicular (0 degrees) to the plane of the flat substrate.

[0030] Fig. 1 is a schematic diagram showing an example of a cross section perpendicular to the plane of a flat substrate of a structural color pigment according to the present invention. In the example of Fig. 1, the structural color pigment 1 has, in order, a flat substrate 10, a crystal layer 20, and a nanorod layer 30. The nanorod layer 30 is composed of a plurality of nanorods 31. In the example of Fig. 1, the plurality of nanorods 31 are oriented perpendicular to the plane of the flat substrate 10.

[0031] Figure 2 is a schematic diagram showing an example of a cross section perpendicular to the plane of a flat substrate of another structural color pigment according to the present invention. In the example of Figure 2, the structural color pigment 1 has the same configuration as the structural color pigment 1 of Figure 1, except for the orientation of the nanorods 31. In the example of Figure 2, the multiple nanorods 31 are oriented at an angle of 30 degrees from the perpendicular to the plane of the flat substrate 10 (see the left side of Figure 2).

[0032] 3 is a schematic diagram showing an example of a cross section perpendicular to the plane of a flat substrate of another structural color pigment according to the present invention. In the example of FIG. 3, the structural color pigment 1 has, in order, a second nanorod layer 35, a second crystal layer 25, a flat substrate 10, a first crystal layer 20, and a first nanorod layer 30. The orientation of the nanorods 31 in the first nanorod layer 30 and the second nanorod layer 35 is the same as in FIG. 1.

[0033] Figure 4 is a schematic diagram showing an example of a cross section perpendicular to the plane of a flat substrate of another structural color pigment according to the present invention. In the example of Figure 4, the structural color pigment 1 has, in order, a second nanorod layer 35, a first crystal layer 20, a flat substrate 10, a first crystal layer 20, and a first nanorod layer 30. Unlike the structural color pigment 1 of Figure 3, the structural color pigment 1 of Figure 4 has the first crystal layer 20 covering the periphery (flat and side surfaces) of the flat substrate 10. The orientation of the nanorods 31 in the first nanorod layer 30 and the second nanorod layer 35 is the same as in Figure 1.

[0034] Hereinafter, each element of the structural color pigment according to the present invention will be illustrated and explained.

[0035] ·Flat base material The flat substrate is a substrate that serves as a base for the crystal layer. As the flat substrate, known scaly pigment or flake pigment substrates can be used. Examples of flat substrates include metal, glass, silica, kaolin, talc, and bismuth oxychloride. Examples of metals include aluminum, mica, and alumina (aluminum oxide). Other examples of flat substrates include the platelet-shaped non-metallic substrates described in JP-A-2018-507272. In one embodiment, the flat substrate is aluminum, mica, or alumina.

[0036] The shape of the flat substrate may be roughly flat, but does not have to be strictly flat. The shape of the flat substrate when viewed from a direction perpendicular to the largest opposing plane of the flat plate (hereinafter simply referred to as "plane") is not particularly limited, and may be a polygon such as a rectangle or hexagon, a circle, an ellipse, an irregular shape, or the like. The polygon may be roughly polygonal, for example, a polygon with rounded corners.

[0037] The planar dimension of the flat substrate is, for example, an average particle size of 3 μm or more and 60 μm or less, preferably an average particle size of 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 25 μm or less.

[0038] The thickness of the flat substrate, i.e., the dimension perpendicular to the plane, is, for example, 50 nm or more and 5000 nm or less, preferably 50 nm or more and 2000 nm or less, more preferably 100 nm or more and 1000 nm or less, and even more preferably 200 nm or more and 500 nm or less.

[0039] Crystal layer The crystalline layer contributes to the orientation of the nanorods and also serves to reflect light incident on the structural color pigment. The regular arrangement of atoms or atomic groups in the crystalline layer causes the nanorods to be arranged in a predetermined orientation on its surface (i.e., the surface of the crystalline layer opposite the flat substrate). In contrast, if an amorphous layer, rather than a crystalline layer, is present on the surface of the flat substrate, the nanorods will not be arranged in the predetermined orientation.

[0040] The crystalline layer includes a metal oxide, and the metal oxide is an oxide of one or more metals selected from the group consisting of titanium, zinc, aluminum, zirconium, indium, tin, niobium, cerium, chromium, iron, magnesium, and cobalt. Specific examples of metal oxides include titanium dioxide (rutile and anatase), zinc oxide, niobium oxide, iron oxide, aluminum oxide, zirconium oxide, indium oxide, tin oxide, cerium oxide, chromium oxide, iron oxide, magnesium oxide, and cobalt oxide. In one embodiment, the metal oxide of the crystalline layer includes titanium dioxide, zinc oxide, tin-doped indium oxide, tin oxide (SnO), or zirconium oxide. In another embodiment, the metal oxide of the crystalline layer is titanium dioxide, zinc oxide, tin-doped indium oxide, tin oxide (SnO), or zirconium oxide.

[0041] The crystal system of the metal oxide is not particularly limited, and examples thereof include tetragonal systems (SnO) such as rutile (TiO, SnO, CrO) and anatase (FeO); hexagonal systems (FeO, ZnO); trigonal systems (AlO, InO); cubic systems (MgO, FeO, FeO, CoO, CeO, InO, NbO); monoclinic systems (ZrO); and orthorhombic systems (CrO) such as brookite. In one embodiment, the metal oxide has a tetragonal structure. In another embodiment, the metal oxide has a rutile structure.

[0042] The refractive index of the metal oxide of the crystal layer is not particularly limited and can be adjusted as appropriate. In one embodiment, the refractive index of the metal oxide of the crystal layer is 1.3 or more, 1.4 or more, 1.5 or more, 1.6 or more, 1.7 or more, 1.8 or more, 1.9 or more, 2.0 or more, 2.1 or more, 2.2 or more, 2.3 or more, 2.4 or more, 2.5 or more, 2.6 or more, 2.7 or more, 2.8 or more, or 2.9 or more. In another embodiment, the refractive index of the metal oxide of the crystal layer is 3.0 or less, 2.9 or less, 2.8 or less, 2.7 or less, 2.6 or less, 2.5 or less, 2.4 or less, 2.3 or less, 2.2 or less, 2.1 or less, 2.0 or less, 1.9 or less, 1.8 or less, 1.7 or less, 1.6 or less, 1.5 or less, or 1.4 or less. In yet another embodiment, the refractive index of the metal oxide of the crystal layer is 1.3 or more and 3.0 or less.

[0043] The refractive index of the crystal layer is not particularly limited and can be adjusted appropriately. In one embodiment, the refractive index of the crystal layer is 1.3 or more, 1.4 or more, 1.5 or more, 1.6 or more, 1.7 or more, 1.8 or more, 1.9 or more, 2.0 or more, 2.1 or more, 2.2 or more, 2.3 or more, 2.4 or more, 2.5 or more, 2.6 or more, 2.7 or more, 2.8 or more, or 2.9 or more. In another embodiment, the refractive index of the crystal layer is 3.0 or less, 2.9 or less, 2.8 or less, 2.7 or less, 2.6 or less, 2.5 or less, 2.4 or less, 2.3 or less, 2.2 or less, 2.1 or less, 2.0 or less, 1.9 or less, 1.8 or less, 1.7 or less, 1.6 or less, 1.5 or less, or 1.4 or less. In yet another embodiment, the refractive index of the crystal layer is 1.3 or more and 3.0 or less.

[0044] The thickness of the crystal layer is not particularly limited and can be adjusted appropriately. The thickness of the crystal layer is, for example, 1 nm or more and 200 nm or less, preferably 10 nm or more and 100 nm or less, and more preferably 30 nm or more and 85 nm or less.

[0045] Nanorod layer The nanorod layer is a layer that contributes to the reflection of light incident on the structural color pigment through the orientation of multiple nanorods. The light reflected by the crystal layer and the nanorod layer interferes with each other, resulting in the appearance of structural color.

[0046] The nanorods contain one or more metals selected from the group consisting of metal oxides, metal hydroxides, and metal oxide hydroxides, and the metals of the metal oxides, metal hydroxides, and metal oxide hydroxides of the nanorods, i.e., the metal of the metal oxides, metal hydroxides, and metal oxide hydroxides, contain one or more metals selected from the group consisting of iron, titanium, zinc, cobalt, aluminum, tin, chromium, zirconium, copper, and magnesium.

[0047] Examples of metal oxides in the nanorods include iron(II) oxide, iron(III) oxide, titanium dioxide (rutile, anatase), zinc oxide, cobalt(II) oxide, cobalt(III) oxide, aluminum oxide, tin(II) oxide, tin(IV) oxide, chromium(II) oxide, chromium(III) oxide, chromium(IV) oxide, chromium(VI) oxide, zirconium(II) oxide, zirconium(IV) oxide, copper(I) oxide, copper(II) oxide, magnesium oxide, etc. In one embodiment, the metal oxide in the nanorods comprises iron oxide. In another embodiment, the metal oxide in the nanorods is iron oxide.

[0048] The metal oxide of the nanorods may or may not have a crystalline or crystalline structure.

[0049] Examples of metal hydroxides for nanorods include iron(II) hydroxide, iron(III) hydroxide, titanium hydroxide, zinc hydroxide, zirconium(II) hydroxide, zirconium(IV) hydroxide, tin hydroxide, chromium(II) hydroxide, chromium(III) hydroxide, aluminum hydroxide, magnesium hydroxide, iron hydroxide, cobalt(II) hydroxide, cobalt(III) hydroxide, and copper(II) hydroxide.

[0050] The metal oxide hydroxide of the nanorods may or may not have a crystalline system or structure.

[0051] The metal oxide hydroxide of the nanorods may be, for example, iron (III) hydroxide oxide.

[0052] In one embodiment, the nanorods comprise a metal oxide, and the metal oxide of the nanorods is iron oxide.

[0053] The refractive index of the nanorods is not particularly limited and can be adjusted as needed. In one embodiment, the refractive index of the nanorods is 1.3 or greater, 1.4 or greater, 1.5 or greater, 1.6 or greater, 1.7 or greater, 1.8 or greater, 1.9 or greater, 2.0 or greater, 2.1 or greater, 2.2 or greater, 2.3 or greater, 2.4 or greater, 2.5 or greater, 2.6 or greater, 2.7 or greater, 2.8 or greater, or 2.9 or greater. In another embodiment, the refractive index of the nanorods is 3.0 or less, 2.9 or less, 2.8 or less, 2.7 or less, 2.6 or less, 2.5 or less, 2.4 or less, 2.3 or less, 2.2 or less, 2.1 or less, 2.0 or less, 1.9 or less, 1.8 or less, 1.7 or less, 1.6 or less, 1.5 or less, or 1.4 or less. In yet another embodiment, the refractive index of the nanorods is 1.3 or greater and 3.0 or less.

[0054] The shape of the nanorod is not particularly limited as long as it is columnar, i.e., has a major axis and a minor axis. Furthermore, the shape of the nanorod may be roughly columnar, and does not have to be strictly columnar. Examples of the shape of the nanorod include a rectangular pillar and a cylindrical pillar. The rectangular pillar may be a right-angle pillar or an oblique pillar.

[0055] The dimensions of the nanorods are not particularly limited as long as they are columnar, i.e., have a major axis and a minor axis. The average diameter of the nanorods is, for example, 5 nm to 200 nm. The "average diameter of nanorods" refers to the average value of the diameter measurements of 100 randomly selected rods observed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0056] In one embodiment, the average diameter of the nanorods is 10 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm or more, or 150 nm or more. In another embodiment, the average diameter of the nanorods is 200 nm or less, 150 nm or less, 120 nm or less, 100 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, or 20 nm or less. In yet another embodiment, the average diameter of the nanorods is 10 nm or more to 120 nm or 18 nm or more to 80 nm.

[0057] The average height of the nanorods can be adjusted by, for example, varying the mass ratio of M1:M2, as described below, and reaction conditions (e.g., reaction time, temperature, and initial concentration of the M2 reactant). For example, when only the mass ratio of M1:M2 is varied, increasing the mass ratio of M2 can result in a higher average height of the nanorods.

[0058] The "average nanorod height" refers to the average height of the nanorods in the direction perpendicular to the plane of the crystalline layer from the part of the nanorod that is in contact with the crystalline layer, and is equal to the thickness of the nanorod layer. The average nanorod height refers to the average of height measurements taken at 20 random points measured by cross-sectional observation using a cross-sectional ion milling-scanning electron microscope (SEM) observation method.

[0059] In one embodiment, the average height of the nanorods is 50 nm or more, 100 nm or more, 150 nm or more, 160 nm or more, 170 nm or more, 180 nm or more, 190 nm or more, 200 nm or more, 210 nm or more, 220 nm or more, 230 nm or more, 240 nm or more, 250 nm or more, 300 nm or more, or 350 nm or more. In another embodiment, the average height of the nanorods is 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 240 nm or less, 230 nm or less, 220 nm or less, 210 nm or less, 200 nm or less, 190 nm or less, 180 nm or less, 170 nm or less, 160 nm or less, 150 nm or less, or 100 nm or less. In yet another embodiment, the average height of the nanorods is 50 nm or more and 400 nm or less.

[0060] Regarding the orientation of the nanorods, the average tilt of the nanorods' long axis is within a range of ±30 degrees from perpendicular (0 degrees) to the plane of the flat substrate. The average tilt of the nanorods' long axis is sufficient as long as it falls within this range; nanorods with tilts outside the range of 0 degrees to ±30 degrees may also exist. The average tilt of the nanorods' long axis is within a range of ±5 degrees, ±10 degrees, ±15 degrees, ±20 degrees, ±25 degrees, or ±30 degrees from perpendicular (0 degrees) to the plane of the flat substrate.

[0061] The refractive index of the nanorod layer is not particularly limited and can be adjusted as needed. In one embodiment, the refractive index of the metal oxide, metal hydroxide, or metal oxide hydroxide of the nanorods is 1.3 or greater, 1.4 or greater, 1.5 or greater, 1.6 or greater, 1.7 or greater, 1.8 or greater, 1.9 or greater, 2.0 or greater, 2.1 or greater, 2.2 or greater, 2.3 or greater, 2.4 or greater, 2.5 or greater, 2.6 or greater, 2.7 or greater, 2.8 or greater, or 2.9 or greater. In another embodiment, the refractive index of the metal oxide, metal hydroxide, or metal oxide hydroxide of the nanorod layer is 3.0 or less, 2.9 or less, 2.8 or less, 2.7 or less, 2.6 or less, 2.5 or less, 2.4 or less, 2.3 or less, 2.2 or less, 2.1 or less, 2.0 or less, 1.9 or less, 1.8 or less, 1.7 or less, 1.6 or less, 1.5 or less, or 1.4 or less. In yet another embodiment, the refractive index of the metal oxide, metal hydroxide, or metal oxide hydroxide of the nanorod layer is greater than or equal to 1.3 and less than or equal to 3.0.

[0062] In the structural color pigment according to the present invention, when the mass of the crystal layer is M1 and the mass of the nanorod layer is M2, M1 and M2 may be appropriately adjusted. In one embodiment, the proportion of M2 relative to the total of M1 and M2 is 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 70% by mass or more, or 80% by mass or more. In another embodiment, the proportion of M2 relative to the total of M1 and M2 is 80% by mass or less, 70% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, 45% by mass or less, 40% by mass or less, 30% by mass or less, or 20% by mass or less. In yet another embodiment, the proportion of M2 relative to the total of M1 and M2 is 10 to 80% by mass.

[0063] The dimensions of the structural color pigment may be adjusted as appropriate. In one embodiment, the average maximum diameter of the structural color pigment is 3 μm or more, 5 μm or more, 10 μm or more, 15 μm or more, 20 μm or more, 25 μm or more, 30 μm or more, 35 μm or more, 40 μm or more, or 45 μm or more. In another embodiment, the average maximum diameter of the structural color pigment is 50 μm or less, 45 μm or less, 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 10 μm or less, or 5 μm or less. In yet another embodiment, the average maximum diameter of the structural color pigment is 3 μm or more and 50 μm or less.

[0064] The average maximum diameter of structural color pigments is the mode measured for 100 randomly selected structural color pigment particles using a technique called "Dynamic Light Scattering (DLS) Particle Size Analyzer." This particle size analysis method provides information on the minimum, maximum, and average diameters of structural pigments.

[0065] The aspect ratio (major axis / minor axis) of the structural color pigment can be adjusted as appropriate. The "major axis" of the structural color pigment refers to the median between the minimum and maximum average diameters when the average value of the structural color pigment has a range, and refers to the average value when the average value of the structural color pigment is a single point. The "minor axis" of the structural color pigment refers to the thickness of the plate-shaped structural color pigment (i.e., the sum of the thicknesses of the layers that make up the structural color pigment, such as the plate substrate, crystal layer, and nanorod layer).

[0066] In one embodiment, the aspect ratio of the structural color pigment is 5 or more, 10 or more, 15 or more, 20 or more, 25 or more, 30 or more, 35 or more, 40 or more, 45 or more, 50 or more, 100 or more, 200 or more, 300 or more, 400 or more, 500 or more, or 600 or more. In another embodiment, the aspect ratio of the structural color pigment is 700 or less, 600 or less, 500 or less, 400 or less, 300 or less, 200 or less, 100 or less, 50 or less, 45 or less, 40 or less, 35 or less, 30 or less, 25 or less, 20 or less, 15 or less, or 10 or less. In yet another embodiment, the aspect ratio of the structural color pigment is 5 or more and 700 or less.

[0067] In one embodiment, the average maximum diameter of the structural color pigment is 3 μm or more and 50 μm or less, and the aspect ratio of the structural color pigment is 5 or more and 700 or less.

[0068] As described above, the layer structure of the structural color pigment may include, in order, a flat substrate, a crystal layer, and a nanorod layer, and may or may not include other layers. For example, as shown in FIG. 3, the structural color pigment 1 may include, in order, a second nanorod layer 35, a second crystal layer 25, a flat substrate 10, a first crystal layer 20, and a first nanorod layer 30. When the structural color pigment includes a first nanorod layer and a second nanorod layer, the material, refractive index, size, and orientation of the nanorods in each nanorod layer may be the same or different. Furthermore, when the structural color pigment includes a first crystal layer and a second crystal layer, the type, refractive index, and thickness of the metal oxide in each crystal layer may be the same or different.

[0069] 4, the structural color pigment 1 may have, in order, a second nanorod layer 35, a first crystal layer 20, a flat substrate 10, a first crystal layer 20, and a first nanorod layer 30. In other words, the crystal layer may cover the periphery of the flat substrate.

[0070] Although not shown, other layer configurations of structural color pigments include, for example, a four-layer configuration of a first flat substrate / a second flat substrate / a crystalline layer / a nanorod layer, in that order; or a four-layer configuration of a first flat substrate / a first crystalline layer / a second crystalline layer / a nanorod layer, in that order.

[0071] The uses of the structural color pigment are not particularly limited, and examples thereof include paints in which structural colors can be used. Examples of such paints include paints for vehicles such as automobiles and trains; interior or exterior paints for buildings such as houses, buildings, factories, bridges, and lighthouses; interior or exterior paints for structures such as embankments, roads, and dams; interior or exterior paints for ships; interior or exterior paints for aircraft; paints for home appliances; and paints for furniture.

[0072] Preparation method of structural color pigments The method for preparing the structural color pigment according to the present invention is a method for preparing the structural color pigment, comprising the steps of: A step (1) of preparing a first laminate having a crystal layer provided on a flat surface of a flat substrate; (2) contacting the first laminate with a nanorod layer preparation solution to form a nanorod layer precursor on the outer surface of the crystal layer of the first laminate; (3) reacting the nanorod layer precursor to form a nanorod layer; Including, the crystalline layer comprises a metal oxide; the metal oxide is an oxide of one or more metals selected from the group consisting of titanium, zinc, aluminum, zirconium, indium, tin, niobium, cerium, chromium, iron, magnesium, and cobalt; the nanorod layer preparation solution contains one or more selected from the group consisting of metal oxides, metal hydroxides, and metal oxide hydroxides; the metal of the metal oxide, metal hydroxide, and metal oxide hydroxide of the nanorod layer preparation solution contains one or more metals selected from the group consisting of iron, titanium, zinc, cobalt, aluminum, tin, chromium, zirconium, copper, and magnesium; The nanorod layer preparation solution has a pH of 3.0 or higher.

[0073] The structural color pigment obtained by the preparation method of the present invention is as described above, and the materials and configurations of the flat substrate, crystal layer, and nanorod layer are omitted.

[0074] ·Process (1) In step (1), a first laminate is prepared, in which a crystal layer is provided on the flat surface of a flat substrate. In step (1), a crystal layer is provided on at least one flat surface of the flat substrate, for example, by coating, immersion, or deposition. In step (1), a crystal layer may be provided on only one of the two flat surfaces of the flat substrate, or on both of the two flat surfaces.

[0075] The preparation method of the present invention may further include, for example, a step of providing a first crystalline layer on only one of the two flat surfaces of a flat substrate to prepare a first laminate, and then providing a second crystalline layer on the remaining flat surface of the flat substrate as a separate step. In this case, the means for providing the first crystalline layer and the second crystalline layer may be the same or different.

[0076] Furthermore, in step (1), a commercially available first laminate may be prepared. Examples of commercially available first laminates include Merck's "Xirallic (registered trademark) T50-10 Crystal Silver," "Xirallic (registered trademark) NXT F250-51 Cougar Red," and "Xirallic (registered trademark) NXT T250-23 Tigris Blue." "Xirallic (registered trademark) T50-10" has a composition in which aluminum oxide as a flat substrate is surrounded by rutile titanium dioxide and tin oxide (SnO) as crystalline layers. "Xirallic (registered trademark) NXT F250-51 Cougar Red" has a composition in which aluminum oxide as a flat substrate is surrounded by iron oxide as a crystalline layer. "Xirallic (registered trademark) NXT T250-23 Tigris Blue" has a composition in which aluminum oxide as a flat substrate is coated with rutile titanium dioxide and tin oxide (SnO2) as crystalline layers.

[0077] In one embodiment of the preparation method according to the invention, the metal oxide of the crystalline layer has a rutile structure.

[0078] The first laminate may be prepared as a solid first laminate or as a dispersion of the first laminate.

[0079] ·Process (2) In step (2), the first laminate is brought into contact with a nanorod layer preparation solution to form a nanorod layer precursor on the outer surface of the crystal layer of the first laminate.

[0080] The nanorod layer preparation liquid is a solution or dispersion containing nanorod raw materials. Examples of nanorod raw materials include water-soluble metal salts. The metal of the water-soluble metal salt is one or more metals selected from the group consisting of the metals contained in the nanorods, i.e., iron, titanium, zinc, cobalt, aluminum, tin, chromium, zirconium, copper, and magnesium. Examples of water-soluble metal salts include metal halides, such as iron chloride, titanium chloride, zinc chloride, cobalt chloride, aluminum chloride, tin chloride, chromium chloride, zirconium chloride, copper chloride, and magnesium chloride.

[0081] Examples of the nanorod layer preparation liquid include aqueous solutions of metal halides, and more specifically, examples include aqueous solutions of iron chloride, titanium chloride, zinc chloride, cobalt chloride, aluminum chloride, tin chloride, chromium chloride, zirconium chloride, copper chloride, magnesium chloride, etc. In one embodiment, the nanorod layer preparation liquid is one or more selected from the group consisting of aqueous solutions of iron chloride and tin chloride.

[0082] The concentration of the water-soluble metal salt in the nanorod layer preparation solution may be appropriately adjusted, for example, from 0.005 M to 1 M, preferably from 0.01 M to 0.25 M, and more preferably from 0.02 M to 0.1 M.

[0083] In one embodiment, the pH of the nanorod layer preparation solution is 3.0 or higher. The pH of the nanorod layer preparation solution is, for example, 3.0 or higher and 10.0 or lower. In another embodiment, the pH of the nanorod layer preparation solution is 3.0 or higher, 3.5 or higher, 4.0 or higher, 4.5 or higher, 5.0 or higher, 5.5 or higher, 6.0 or higher, 6.5 or higher, 7.0 or higher, 7.5 or higher, 8.0 or higher, 8.5 or higher, 9.0 or higher, or 9.5 or higher. In yet another embodiment, the pH of the nanorod layer preparation solution is 10.0 or lower, 9.5 or lower, 9.0 or lower, 8.5 or lower, 8.0 or lower, 7.5 or lower, 7.0 or lower, 6.5 or lower, 6.0 or lower, 5.5 or lower, 5.0 or lower, 4.5 or lower, 4.0 or lower, or 3.5 or lower.

[0084] In one embodiment, the pH of the nanorod layer preparation solution is 4.0 or less. In another embodiment, the pH of the nanorod layer preparation solution is 1.5 or more, 1.7 or more, 2.0 or more, 2.5 or more, 2.6 or more, 3.0 or more, or 3.5 or more. In yet another embodiment, the pH of the nanorod layer preparation solution is 4.0 or less, 3.5 or less, 3.0 or less, 2.5 or less, 2.1 or less, or 2.0 or less. In yet another embodiment, the pH of the nanorod layer preparation solution is 1.5 to 2.5 or 1.7 to 2.1.

[0085] The means for contacting the first laminate with the nanorod layer preparation liquid is not particularly limited, and examples thereof include coating, dropping, immersion, deposition, etc. Alternatively, the dispersion of the first laminate and the nanorod layer preparation liquid may be mixed.

[0086] The temperature when the first laminate is brought into contact with the nanorod layer preparation liquid (e.g., the temperature of the dispersion liquid of the first laminate) is, for example, 15 to 35°C, preferably 20 to 30°C, and more preferably 25°C.

[0087] The time for which the first laminate is brought into contact with the nanorod layer preparation solution is, for example, 10 to 90 minutes, and preferably 30 to 60 minutes.

[0088] In step (2), the nanorod layer preparation liquid is preferably added to the dispersion liquid of the first laminate over 1 to 5 minutes, and is preferably added all at once to maintain uniformity of nanorod growth.

[0089] By contacting the surface of the crystal layer of the first laminate with the nanorod layer preparation solution, the nanorod raw material contained in the nanorod layer preparation solution coats the surface of the crystal layer, and a nanorod layer precursor is formed on the surface of the crystal layer. The nanorod layer precursor is, for example, the water-soluble metal salt described above.

[0090] ·Process (3) In step (3), the nanorod layer precursor is reacted to form a nanorod layer.

[0091] The temperature at which the nanorod layer precursor is reacted may be adjusted as appropriate, and may be, for example, 5°C or higher and 80°C or lower, 15°C or higher and 80°C or lower, or 18°C ​​or higher and 75°C or lower.

[0092] In one embodiment of the method for preparing a structural color pigment according to the present invention, the step (3) comprises reacting the nanorod layer precursor at a temperature of 80° C. or less.

[0093] Furthermore, when reacting the nanorod layer precursor, it is preferable to slowly increase the temperature. The rate of temperature increase is, for example, 0.1 to 2.0°C / min, and preferably 0.5 to 1.0°C / min.

[0094] The time for reacting the nanorod layer precursor is, for example, 10 to 120 minutes, and preferably 30 to 90 minutes.

[0095] In one embodiment, the nanorod layer has a thickness of 50 nm or more, 100 nm or more, 150 nm or more, 160 nm or more, 170 nm or more, 180 nm or more, 190 nm or more, 200 nm or more, 210 nm or more, 220 nm or more, 230 nm or more, 240 nm or more, 250 nm or more, 300 nm or more, or 350 nm or more. In another embodiment, the nanorod layer has a thickness of 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 240 nm or less, 230 nm or less, 220 nm or less, 210 nm or less, 200 nm or less, 190 nm or less, 180 nm or less, 170 nm or less, 160 nm or less, 150 nm or less, or 100 nm or less. In yet another embodiment, the nanorod layer has a thickness of 50 nm or more and 400 nm or less.

[0096] In the preparation method of the present invention, for example, in step (2), a single or multiple nanorod layer precursors may be formed using a combination of multiple nanorod layer preparation solutions, and then in step (3), all of the formed nanorod layer precursors may be simultaneously reacted to form a single or multiple nanorod layers; or in the first step (2), a first nanorod layer precursor may be formed using a first nanorod layer preparation solution, and then in the second step (2), a second nanorod layer precursor may be formed using a second nanorod layer preparation solution, and then in step (3), the formed first and second nanorod layer precursors may be simultaneously reacted to form a single or multiple nanorod layers. Alternatively, in a first step (2), a first nanorod layer precursor may be formed using a first nanorod layer preparation solution, and then, in a first step (3), the first nanorod layer precursor is reacted to form a first nanorod layer. In a second step (2), a second nanorod layer precursor may be formed on the first nanorod layer using a second nanorod layer preparation solution, and then, in a second step (3), the second nanorod layer precursor is reacted to form a second nanorod layer.

[0097] ·Optional process The preparation method of the present invention may optionally include, after step (3), step (4) of separating the structural color pigment or the laminate comprising the flat substrate / crystal layer / nanorod layer (also referred to as the second laminate) from the reaction mixture.

[0098] The preparation method of the present invention may optionally include a step (5) of washing the structural color pigment or the second laminate after step (3) or step (4). The washing can be carried out, for example, with water.

[0099] The preparation method of the present invention may optionally include a step (6) of drying the structural color pigment or the second laminate after step (3), step (4), or step (5). The drying temperature may be, for example, 25 to 90° C. The drying time may be, for example, 30 to 180 minutes.

[0100] The preparation method of the present invention may optionally include step (7) of firing the structural color pigment or the second laminate after step (3), step (4), step (5), or step (6). The firing temperature may be, for example, 400 to 1100°C. The firing time may be, for example, 5 to 120 minutes, and preferably 15 to 60 minutes. [Example]

[0101] The present invention will be described in more detail below by way of examples, but these examples are intended to illustrate the present invention and are not intended to limit the present invention in any way.

[0102] The materials used in the examples are as follows: First laminate (flat substrate and crystalline layer) Merck, trade name "Xirallic (registered trademark) T50-10 Crystal Silver", a pigment having rutile-type titanium dioxide (IV) crystal layers on both surfaces of an aluminum oxide flat substrate, average maximum diameter: 22 μm, used in Examples 1 to 3 Merck's product name "Iriodin (registered trademark) Silver White" pigment having rutile-type titanium dioxide (IV) crystal layers on both surfaces of a synthetic mica flat substrate, average maximum diameter: 10 μm, used in Example 4 Synthetic mica substrate: Merck, trade name "Iriodin (registered trademark) Silver Pearl", average maximum diameter: 22 μm, used in Comparative Example 3 Natural mica substrate: Yamaguchi Mica Co., Ltd., used in Comparative Example 4

[0103] The devices and materials used in the examples are as follows: Tetraethoxysilane solution: Wako Pure Chemical Industries, Ltd., used without further purification

[0104] Example 1 200 parts by mass of "Xirallic (registered trademark) T50-10 Crystal Silver" was prepared as the first laminate in step (1). An aqueous iron chloride solution (nanorod layer preparation solution) was prepared by dissolving 540 parts of iron chloride in 400 mL of ion-exchanged water.

[0105] Next, in step (2), 200 parts by mass of "Xirallic (registered trademark) T50-10 Crystal Silver" was added to the aqueous iron chloride solution prepared in step (1), and the mixture was stirred at 25°C.

[0106] Next, in step (3), the mixture was stirred at 25° C. for 60 minutes. Then, the mixture was heated to 60° C. with stirring for 1.0 hour. The mixture was further stirred at 60° C. for 60 minutes to obtain a suspension.

[0107] Steps (4) to (7) were carried out as follows: The suspension was cooled to 25°C, filtered, and the obtained filter cake was washed with water. The filter cake was dried at 60°C for 180 minutes. The average maximum diameter of the obtained pigment was in the range of 15 to 22 μm, and the median of the average maximum diameters was 18 μm.

[0108] Examples 2 to 4 Except for changing the configurations of the flat substrate, the crystal layer, and the nanorod layer as shown in Table 1, the same steps as in Example 1 were carried out to obtain a structural color pigment.

[0109] Example 5 In step (1), a first laminate was prepared according to the procedure of Example 1 of WO 2018 / 034261. The first laminate had a layer structure of niobium pentoxide as the first layer, an aluminum oxide layer as the second layer, and a niobium pentoxide layer as the third layer. That is, the first laminate had niobium oxide crystal layers on both surfaces of an aluminum oxide flat substrate. Next, the steps were carried out in the same manner as in Example 1, except that the first laminate prepared in this manner was used. A structural color pigment was obtained. This structural color pigment exhibited a golden yellow structural color. The structural color pigment obtained in Example 5 had a nanorod layer, with an average nanorod long axis tilt of 0 degrees, an average nanorod diameter of 45 nm, an average nanorod height of 250 nm, an average maximum diameter of 22 μm, and an aspect ratio of 21.2.

[0110] Comparative Example 1 200 parts by mass of "Xirallic (registered trademark) T50-10 Crystal Silver" was added to 1300 mL of demineralized water and stirred. Then, the pH of the dispersion was adjusted to pH 2.6 and heated to 85°C. 570 parts of the same nanorod layer preparation solution as in Example 1 was added to the dispersion at 85°C. The mixture was then stirred for an additional 60 minutes to obtain a suspension. The pH of the suspension was then adjusted to pH 2.2. After that, 500 mL of a solution of SnCl4 having a concentration of 30 g / L of Sn was added to the suspension. The mixture was then stirred for an additional 120 minutes. Then, 1.42 g / cm3 of SnCl4 was added to the mixture. 3 750 parts by mass of an aqueous solution of iron chloride having a density of 1000 MPa was added. 60 minutes after the addition was completed, the suspension was filtered, and the resulting filter cake was washed. The filter cake was dried and calcined at 800 °C for 45 minutes.

[0111] Comparative Example 2 In Example 1, no nanorod layer was formed, and "Xirallic (registered trademark) T50-10 Crystal Silver" was used as the pigment as is.

[0112] Comparative Example 3 First, flat synthetic mica substrates were dispersed in water and vigorously stirred at room temperature to obtain flat substrate 1 (average maximum diameter: 10 μm). Next, the same steps as in Example 1 were carried out, except that flat substrate 1 was used instead of "Xirallic (registered trademark) T50-10 Crystal Silver" in Example 1, to obtain a comparative pigment.

[0113] Comparative Example 4 A natural mica substrate was dispersed in isopropanol while stirring. A 28% aqueous ammonia solution was added to this dispersion as a base catalyst. The dispersion was then stirred for 10 minutes. Next, a tetraethoxysilane solution was added dropwise to the dispersion while stirring. The solution was stirred for 15 hours. The solution was then filtered and washed twice with alcohol to obtain a comparative laminate (average maximum diameter: 22 μm) having amorphous silicon dioxide layers on both surfaces of an aluminum oxide flat substrate. Next, each step was carried out in the same manner as in Example 1, except that the obtained comparative laminate was used instead of "Xirallic (registered trademark) T50-10 Crystal Silver" in Example 1, to obtain a comparative pigment.

[0114] (Evaluation of structural color) The obtained structural color pigments and comparative pigments were visually observed, and the structural color and its color were evaluated. The structural color was evaluated according to the following criteria. The results are shown in Table 1. A: It has structural color B: There is structural color, but the coloring of the structural color is slight. C: No structural color

[0115] [Table 1]

[0116] According to the present invention, it is possible to provide a structural color pigment that can be produced more inexpensively. Furthermore, according to the present invention, it is possible to provide a method for producing such a structural color pigment more inexpensively. [Industrial Applicability]

[0117] According to the present invention, it is possible to provide a structural color pigment that can be produced more inexpensively. Furthermore, according to the present invention, it is possible to provide a method for producing such a structural color pigment more inexpensively. [Explanation of symbols]

[0118] 1: Structural color pigment 10: Flat base material 20: Crystal layer (first crystal layer) 25: Second crystal layer 30: Nanorod layer (first nanorod layer) 31: Nanorods 35: Second nanorod layer

Claims

1. In order, A flat substrate; a crystalline layer; a nanorod layer comprising a plurality of nanorods; A structural color pigment having the formula: the crystalline layer includes a metal oxide; the metal oxide is an oxide of one or more metals selected from the group consisting of titanium, zinc, aluminum, zirconium, indium, tin, niobium, cerium, chromium, iron, magnesium, and cobalt; the nanorods comprise at least one selected from the group consisting of metal oxides, metal hydroxides, and metal oxide hydroxides; the metal of the metal oxide, metal hydroxide, and metal oxide hydroxide of the nanorods comprises one or more selected from the group consisting of iron, titanium, zinc, cobalt, aluminum, tin, chromium, zirconium, copper, and magnesium; A structural color pigment, wherein the average tilt of the major axis of the nanorods is within a range of ±30 degrees from the perpendicular (0 degrees) to the plane of the flat substrate.

2. 2. The structural color pigment according to claim 1, wherein the metal oxide of the crystalline layer has a rutile structure.

3. the metal oxide of the crystal layer has a refractive index of 1.3 or more and 3.0 or less; 2. The structural color pigment according to claim 1, wherein the metal oxide constituting the nanorod layer has a refractive index of 1.3 or more and 3.0 or less.

4. The average diameter of the nanorods is 10 nm or more and 80 nm or less; The structural color pigment according to claim 1 , wherein the average height of the nanorods is 50 nm or more and 400 nm or less.

5. the average maximum diameter of the structural color pigment is 3 μm or more and 50 μm or less, 2. The structural color pigment according to claim 1, wherein the structural color pigment has an aspect ratio of 5 or more and 700 or less.

6. the metal oxide of the crystalline layer is titanium dioxide, zinc oxide, tin-doped indium oxide, or zirconium oxide; the nanorods comprise a metal oxide, and the metal oxide of the nanorods is iron oxide; The structural color pigment according to claim 1 .

7. 2. The structural color pigment according to claim 1, wherein the mass of the crystal layer is M1 and the mass of the nanorod layer is M2, and the ratio of M2 to the total of M1 and M2 is 10 to 80 mass%.

8. The structural color pigment according to claim 1 , wherein the flat substrate is aluminum, mica, or alumina.

9. 10. A method for preparing the structural color pigment of claim 1, comprising: A step (1) of preparing a first laminate having a crystal layer provided on a flat surface of a flat substrate; (2) contacting the first laminate with a nanorod layer preparation solution to form a nanorod layer precursor on the outer surface of the crystal layer of the first laminate; (3) reacting the nanorod layer precursor to form a nanorod layer; Including, the crystalline layer includes a metal oxide; the metal oxide is an oxide of one or more metals selected from the group consisting of titanium, zinc, aluminum, zirconium, indium, tin, niobium, cerium, chromium, iron, magnesium, and cobalt; the nanorod layer preparation solution contains one or more selected from the group consisting of metal oxides, metal hydroxides, and metal oxide hydroxides; the metal of the metal oxide, metal hydroxide, and metal oxide hydroxide of the nanorod layer preparation solution contains one or more metals selected from the group consisting of iron, titanium, zinc, cobalt, aluminum, tin, chromium, zirconium, copper, and magnesium; The pH of the nanorod layer preparation solution is 3.0 or more. method.

10. The method of claim 9 , wherein step (3) comprises reacting the nanorod layer precursor at a temperature of 80° C. or less.

11. The method of claim 9 , wherein the metal oxide of the crystalline layer has a rutile structure.

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