JP7515148B2 - Inorganic decorative product exhibiting structural color, its manufacturing method, and dispersion liquid used therein - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies. (1) Published on the website of the proceedings of KISTEC Innovation Hub 2019 in EBINA on October 4, 2019. (2) Presented at KISTEC Innovation Hub 2019 in EBINA on October 31, 2019.

The present invention relates to an inorganic decorative product exhibiting structural color and a manufacturing method thereof. More specifically, the present invention relates to an inorganic decorative product made of an inorganic material, which has excellent heat resistance, mechanical strength, abrasion resistance, etc., and which is capable of continuously expressing structural color over a wide area. The present invention also relates to a manufacturing method thereof that is low cost and has a low environmental impact, and that can rapidly form a multi-layered periodic structure and obtain an inorganic decorative product exhibiting structural color in a short period of time.

Light is a type of electromagnetic wave, and the wavelength of light that is visible to humans is said to be approximately 380 to 780 nm. It is known that when a periodic structure is formed on the order of several hundred nanometers, which is the same scale as the wavelength of visible light, light of specific wavelengths in the visible range overlap and are strongly reflected due to the reflection and refraction of light by the periodic structure, resulting in the appearance of color. Colors that appear due to such microstructures are called structural colors or play of colors, and can be seen in natural gemstones such as opals, and in living things such as morpho butterflies and peacocks.

It is also possible to artificially obtain substances that exhibit structural color. For example, if spherical particles with diameters of several hundred nanometers are created and arranged in a highly regular pattern, the particle aggregate will form a periodic structure and exhibit structural color. Such particle aggregates have a structure and color similar to that of the natural gemstone opal, and so are called artificial opals, including those made from materials other than silicon oxide, the main component of opal. In research and development of artificial opals, polymer particles such as latex, which have a uniform particle size and are easy to form periodic structures with, are often created and used.

For example, it has been reported that when a liquid in which uniformly sized polymer particles are dispersed in a silica sol is coated on ceramics or glass and fired at 500°C, a ceramic product exhibiting structural color is obtained (Non-Patent Document 1). Due to the highly uniform particle size of the polymer particles, the polymer particles self-organize into a regular arrangement when the solvent in the dispersion liquid evaporates, making it possible to directly coat the dispersion liquid on a ceramic substrate and produce structural color.

Ceramics, metals, and other inorganic products are widely used as daily necessities, building materials, structural materials, etc., taking advantage of their excellent characteristics such as heat resistance, mechanical strength, abrasion resistance, and weather resistance. Depending on the application, decoration using various techniques is required to improve the aesthetic appearance. In particular, there is a strong demand in the field of ceramics for the expression of structural colors, which can achieve an aesthetic appearance similar to that of the national treasure "Yohen Tenmoku."

On the other hand, the organic polymer particles used in Non-Patent Document 1 have disadvantages such as low heat resistance, weak mechanical strength, susceptibility to wear, and deterioration over time. Coating the surface of inorganic products such as ceramics and metals with artificial opals made of organic materials is undesirable because it results in the formation of a surface coating layer that is inferior in performance to the main body, limiting the fields of use of the inorganic products. Artificial opals made of stable inorganic materials will not disappear like polymer particles even when fired at temperatures of 600°C or higher, and will exhibit high strength, hardness, wear resistance, chemical stability, corrosion resistance, weather resistance, etc., derived from covalent bonds, ionic bonds, and metallic bonds that bond atoms three-dimensionally.

For example, "Created Opal" manufactured by Kyocera Corporation is known as an artificial opal made of silicon oxide microparticles (e.g., Non-Patent Document 2), and is used in the field of jewelry because it exhibits beautiful structural colors similar to those of the natural gemstone opal.

There is also a type of bone china known in the art in which artificial opal particles (bulk body) made of fine silicon oxide particles, like created opal, are dispersed in a glaze layer, i.e., a glass layer, and attached to the base (Patent Document 1). By using this technology and making the surface glass layer transparent, it is possible to fix gem-like artificial opal to the base, resulting in beautiful ceramics that show the structural color unique to artificial opal.

Other examples of inorganic products that have a microstructure formed on the surface to produce structural or interference colors include ceramics in which a thin film of heavy metals such as lead or silver is formed on the surface by reduction firing (Patent Document 2), and ceramics in which a microstructure is formed on the surface by the deposition of fine compounds due to chemical reactions or the etching action of the gas by firing in the presence of chlorine- or fluorine-based gas (for example, Patent Document 3).

JP 2011-73948 A JP 2005-82438 A JP 2011-6290 A

Surface Technology, Surface Finishing Society of Japan, 2010, vol.61, No.11, p.754-756 Ceramics, Ceramic Society of Japan, 2009, vol.44, No.7, p.540-542

However, although artificial opal, an inorganic material, exhibits beautiful structural colors similar to those of the natural gemstone opal and has excellent properties such as heat resistance, mechanical strength, and abrasion resistance, it cannot necessarily be said that it has been actively used in fields other than jewelry. The reason for this is that it is difficult to control the particle size and microstructure of inorganic particles. In order to produce structural colors, it is necessary to produce fine particles on the order of several hundred nanometers with uniform particle sizes and arrange them in a highly regular pattern to form a periodic structure.

For polymer particles such as latex produced by emulsion polymerization, both nucleation and particle growth are easy to control, and technology has been established to make even fine particles uniform in particle size. On the other hand, for inorganic materials, even silicon oxide fine particles, for which technology for controlling particle size is relatively well established, require special technology and a long time. For example, Non-Patent Document 2 notes that Kyocera Corporation's "Created Opal" requires 13 months for the entire manufacturing process, and that the company is the only one that has successfully synthesized it on a commercial basis.

In addition, the bone china of Patent Document 1 uses bulk artificial opals, and since the artificial opals are scattered, it is not possible to form a continuous colored area over a wide area. In the same document, it is stated that the preferable diameter of the artificial opal bulk is up to 0.5 mm, and the area of each scattered area is less than 0.2 ^mm2 at most. Furthermore, it is not possible to express a gradation of structural color, and it is not possible to attach artificial opals with different structural colors in the same area. Therefore, there is a problem in that the expression technique by structural color is extremely limited. In addition, there is also a problem in that a large amount of glaze and high-temperature firing are required to disperse and hold the thick artificial opals in the glaze layer, which results in high manufacturing costs and environmental load.

Furthermore, the ceramics in which a thin film is formed on the surface using heavy metals as described in Patent Document 2 have issues such as the heavy metals being harmful to the human body and having a high environmental impact, high material costs, only being able to produce color through interference effects or light absorption by metal elements, and aging due to oxidation. Also, the ceramics in which a microstructure is formed on the surface using a gas-phase reaction with gas as described in Patent Document 3 have issues such as the difficulty of producing the intended multicolored colors in the intended areas and of giving thickness to the periodic structure that produces the structural color, making reproduction extremely difficult. Using these techniques may produce the finest, aesthetically pleasing works of art, but they are not suitable for industrial products that require product safety, stability, and reproducibility in production.

The present invention has been made in consideration of the above background technology and the problems associated with it, and aims to provide an inorganic decorative product that is made of an inorganic material and has excellent properties such as heat resistance, mechanical strength, and abrasion resistance, and that is capable of continuously expressing an aesthetically pleasing structural color consisting of a multi-layered periodic structure over a wide area. Another aim is to provide a low-cost, low-environmental-impact manufacturing method that can quickly form a multi-layered periodic structure by arranging inorganic fine particles in a highly regular manner, and can obtain an inorganic decorative product exhibiting structural color in a short period of time.

As a result of intensive research by the inventors to solve the above problems, they have found that the optimal method is to directly form an aggregate in which inorganic particles are arranged in a highly regular manner on the surface of an inorganic substrate and then bond them with a glass phase. They have also found that by precipitating inorganic particles by liquid phase synthesis under conditions suitable for the nucleation and grain growth of the inorganic particles, preparing a dispersion containing the inorganic particles and a component that will become the glass phase for bonding them, and directly coating this on an inorganic substrate, it is possible to continuously form a periodic structure in which inorganic particles are arranged in a regular manner over a wide area in a drying time of several tens of seconds. Further research into the structure and manufacturing method has led to the completion of the present invention.

That is, the present invention is an inorganic decorative article that includes an aggregate of approximately spherical inorganic fine particles, an inorganic base material that serves as a base, and a glass phase that serves as a bonding material, in which the inorganic fine particles are arranged in an approximately regular pattern on the surface of the inorganic base material to form an aggregate, the inorganic fine particle aggregate is bonded to any region of the surface of the inorganic base material by the glass phase, and the inorganic decorative article has a region in which a structural color derived from the particle size and regular arrangement of the inorganic fine particles is expressed.

The inorganic decorative product of the present invention is composed of inorganic materials, has excellent heat resistance, mechanical strength, hardness, abrasion resistance, chemical stability, corrosion resistance, and weather resistance, and exhibits a structural color with excellent aesthetics derived from a multi-layered periodic structure. Since this structural color is produced from the periodic structure formed by inorganic fine particles, unlike interference colors produced by thin films, it is possible to produce a homogeneous color over a wide area without being affected by the unevenness of the base material. In addition, it can be produced using silicon oxide, which is the most abundant solid material in the earth's crust, and does not need to contain transition metals such as rare metals as in conventional pigments, making it possible to reduce material costs, human toxicity, and environmental impact.

The present invention also relates to the inorganic decorative article, in which the inorganic particles and the glass phase that serves as the bonding material have the same chemical composition. By forming the inorganic particles and the glass phase from the same raw material and giving them the same chemical composition, a regular arrangement of the inorganic particles over a long period is formed, and the unique coloring characteristic of structural color, which "changes color depending on the viewing angle," can be more prominently and stably expressed.

Furthermore, the present invention relates to the inorganic decorative article, in which an aggregate of inorganic fine particles is bonded to an inorganic base material with a portion of the aggregate exposed on the surface. This structure makes it possible to exhibit the unique feature that the structural color changes or disappears when wet with liquid, and the original structural color is revealed when the liquid is removed by evaporation or the like. This phenomenon originates from a mechanism in which the effects of light refraction, reflection, diffraction, scattering, etc. change when liquid penetrates into the periodic structure formed by the inorganic fine particles or into the interior of the porous inorganic fine particles, and is a phenomenon that cannot be achieved with general pigments that are based on the principle of light absorption, but can only be achieved with structural colors.

The present invention also relates to the inorganic decorative article, in which the structural color is continuously expressed over an area of ^0.2 mm2 or more, a plurality of types of inorganic fine particle aggregates that express structural colors are formed in the same area, and a plurality of colors derived from the inorganic fine particle aggregates are developed when visually observed from the same angle, and the inorganic base material has a curved surface portion and the inorganic fine particle aggregate is bonded to any area of the curved surface portion. The structural color of the present invention is continuously expressed over a wide area including the curved surface, different colors are developed depending on the observation angle, gradation is expressed by the thickness of the periodic structure formed by the inorganic fine particles, and a plurality of colors can be overlapped to develop in the same area of the inorganic decorative article.

The present invention further relates to the inorganic decorative article, in which the number-average diameter of the primary particles of the inorganic fine particles is 150 to 350 nm, the inorganic fine particles are porous and the measured value of the specific surface area of the inorganic fine particles by nitrogen gas adsorption method is at least twice the calculated value calculated from the density and the particle size by observation with a scanning electron microscope, the inorganic fine particles are silicon oxide, and the inorganic base material is ceramic. These structures can further enhance the above-mentioned features of the inorganic decorative article and its structural color of the present invention.

The present invention also relates to an inorganic decorative product that is one selected from the group consisting of tableware and its parts, ornaments and its parts, parts of writing implements, housings and parts of portable information and communication devices, building materials for interior and exterior use, bodies and parts of transport equipment, and stone products for gardens and cemeteries. These finished products or semi-finished products of the present invention have the above-mentioned structural color that is excellent in aesthetics and various properties, and have high commercial value.

The present invention further provides a method for producing the inorganic decorative product, which includes the steps of precipitating inorganic fine particles by liquid-phase synthesis to prepare a dispersion containing the inorganic fine particles and unreacted raw material components, and coating any area on the surface of an inorganic substrate with the dispersion, followed by drying and firing. This production method can stably produce inorganic decorative products with coloring that emphasizes the characteristic of structural color, which "changes color depending on the viewing angle." As a result, this new and unprecedented decorative technique is expected to be useful not only for arts and crafts and decorative items, but also for applications requiring high decorativeness and design.

The present invention also relates to a method for producing the inorganic decorative product, which includes the steps of preparing a dispersion of the inorganic fine particles and the inorganic binder by adding an inorganic binder after precipitating inorganic fine particles by liquid phase synthesis, and coating any area on the surface of an inorganic substrate with the dispersion, followed by drying and firing. With this production method, it is possible to obtain an inorganic decorative product with a color similar to that of conventional pigments, which "does not change color depending on the viewing angle." This makes it possible to use abundant resources such as silicon oxide as a raw material as an alternative technology to conventional pigments, and to achieve rare metal-free production.

The manufacturing method of the present invention described above can rapidly and continuously form a periodic structure in which inorganic fine particles are regularly arranged over a wide area in a drying time of several tens of seconds, requires a small amount of inorganic binder to be added, and can be fired in air at a relatively low temperature.

The inorganic decorative product of the present invention is made of inorganic materials and has excellent properties such as heat resistance, mechanical strength, and abrasion resistance, and can continuously express aesthetic structural colors derived from its multilayer periodic structure over a wide area.
In addition, the method for manufacturing inorganic decorative items of the present invention can form a periodic structure in which inorganic microparticles are regularly arranged in a short period of time, and can produce inorganic decorative items that exhibit aesthetically pleasing structural colors at low cost.
The structural color exhibited by the inorganic decorative product of the present invention can be a color that changes depending on the viewing angle, which is unique to structural colors, or a color that does not change depending on the viewing angle like conventional pigments, and the color of the structural color can be controlled by the manufacturing method.

1 is an external image of the ceramics produced by spray coating in Example 1. 1 is an enlarged image of a surface of ceramic produced by spray coating in Example 1, observed by a scanning electron microscope. 1 is an external image showing the change in color tone when the ceramic produced by brush painting in Example 2 is wetted with water and dried. 1 is an external image of ceramics produced by brush painting in Example 3. 13 is an external image showing the change in color tone when the ceramic produced by brush painting in Example 3 is wetted with water. 11 shows enlarged images of the surfaces of test pieces prepared by changing the amount of ammonia water added in Example 4, observed by a scanning electron microscope. 1 is an external image 1 of the ceramics produced by brush painting in Example 5. 2 is an external image 2 of the ceramics produced by brush painting in Example 5. 1 is an observation image of the surface of a test piece in which silicon oxide fine particles prepared in Example 6 are completely covered with a glass phase.

The inorganic decorative product and the manufacturing method thereof of the present invention will be described in detail below. Note that the structure, characteristics, composition, manufacturing method, etc. that are not described here may be the same or substantially the same as those known to those skilled in the art.

In addition, in the present invention, "approximately" is not limited to being strictly identical, but is a concept that includes errors and deformations that do not lose their identity. For example, "approximately spherical" is not limited to being strictly spherical, but includes cases that can be regarded as being the same as a sphere.

The chemical composition of the inorganic fine particles used in the present invention includes silicon oxide, aluminum oxide, titanium oxide, iron oxide, magnesium oxide, calcium oxide, manganese oxide, cobalt oxide, copper oxide, zinc oxide, yttrium oxide, zirconium oxide, palladium oxide, silver oxide, and composite oxides thereof, silicon nitride, aluminum nitride, titanium nitride, silicon carbide, sialon ceramics, calcium carbonate, calcium phosphate, apatite compounds, carbon, feldspars such as alkali feldspar and plagioclase, clays such as kaolinite, montmorillonite, smectite, allophane, zeolite, and layered double hydroxides, and metals such as platinum, gold, silver, copper, iron, titanium, steel, and various alloys.

Among these, oxides or metals whose surfaces are covered with oxides are preferred from the viewpoint of stability in the atmosphere, and silicon oxide, aluminum oxide, aluminum silicate, or chemical compositions containing small amounts of alkali or alkaline earth metals are more preferred from the viewpoint of cost and environmental friendliness. From the viewpoint of particle size controllability and refractive index uniformity, silicon oxide and aluminum oxide, which are oxides of a single composition, are even more preferred. The use of silicon oxide, which is the same material as opals, is the most preferred because it can be described as a feature that it is the same material as natural gemstones and is an abundant resource.

The inorganic fine particles are arranged in a generally regular pattern on the surface of the inorganic substrate to form an aggregate. This aggregate of inorganic fine particles may be any aggregate in which a plurality of inorganic fine particles are arranged in a generally regular pattern and maintain a certain shape, and is an aggregate in which inorganic fine particles are assembled by physicochemical forces. Specifically, in the manufacturing method described below, an example is an aggregate in which inorganic fine particles are arranged in a regular pattern in a self-organizing manner in the process of coating the surface of the inorganic substrate with a dispersion of highly dispersed inorganic fine particles and then drying.

In the present invention, even if partial cracks, defects, or fallen particles are found in the inorganic fine particle aggregate under magnified observation, as long as the aggregate is capable of continuously expressing the desired structural color under visual observation, it is considered to be arranged in a substantially regular pattern and can be regarded as being the same as an aggregate that is arranged in a precisely regular pattern.

In the manufacturing method described below, the inorganic fine particle aggregates can be formed in any region of the inorganic substrate surface by adjusting the shape and area to be coated with the dispersion liquid. In the present invention, the term "any region" refers to any region in a plan view direction that is within a part or entire range of the inorganic substrate surface and can be formed by coating with the dispersion liquid at the discretion of the producer. The region in which the inorganic fine particle aggregates are formed may be one or more. In order to continuously express the structural color over a wide area, the area of each region in which the inorganic fine particle aggregates are formed is preferably 0.2 ^mm2 or more.

The thickness of the inorganic fine particle aggregate can be formed to any thickness by adjusting the coating method, liquid amount, and number of times. In order to form a multi-layered periodic structure and to produce a structural color that is clearly visible to the naked eye, the thickness after firing is preferably 800 nm or more, and more preferably 1000 nm or more. The number of layers is preferably 2 to 3 layers or more, and more preferably 4 to 5 layers or more. The thicker the layer, the clearer the structural color will be, and a thinner layer is advantageous in terms of recoating and cost. The thickness is set taking into consideration abrasion resistance, peeling resistance, etc.

The inorganic fine particle aggregates are bonded to any region of the inorganic substrate surface by the glass phase present in the gaps. In the manufacturing method described below, when a dispersion containing inorganic fine particles and unreacted raw material components is used, the inorganic fine particles are bonded by the reaction of the remaining unreacted raw material components during firing to form chemical bonds. In this case, the inorganic fine particles and the glass phase that serves as the bonding material are formed from the same starting material and have the same chemical composition. In the present invention, "having the same chemical composition" means that the types of constituent elements of the inorganic compounds that form the inorganic fine particles and the glass phase that serves as the bonding material are the same.

By using unreacted raw material components as a bonding material, there is no need to add additives to the dispersion liquid that disrupt the periodic arrangement of the inorganic fine particles. This makes it easier to form a regular arrangement of inorganic fine particles over a long period, so that the color produced by regular reflected light becomes more dominant than the color produced by scattered reflected light, enhancing the unique coloring characteristic of structural colors, which "change color depending on the viewing angle."

On the other hand, when a dispersion containing inorganic particles and an inorganic bonding agent is used, the glass phase that bonds the inorganic particles is formed by melting the added inorganic bonding agent during firing. It is most preferable that the glass phase is colorless and transparent. A dark glass phase is also preferable from the viewpoint of interposing it between the periodic structure of the inorganic particles and emphasizing the structural color expressed by the aggregate of inorganic particles as a background color. When an inorganic bonding agent is added, the glass phase formed by melting the inorganic bonding agent partially disrupts the regular arrangement of the inorganic particles, so that the color due to scattered reflected light becomes dominant over that due to regular reflected light, and it is possible to achieve color development similar to that of conventional pigments, in which the color does not change depending on the viewing angle.

By bonding the inorganic fine particle aggregates while leaving some exposed to the surface, rather than covering the entire aggregate with the glass phase, it is possible to impart the unique property of changing or disappearing color when wet with liquid, as described above, and reappearing the original structural color when the liquid is removed. In this form, the fine particles are bonded together with the glass phase intervening in the gaps between them, and it is presumed that a small number of glass phase-covered areas are scattered like islands on the outermost surface. If a large number of glass phase-covered areas are scattered like islands, they will scatter light, giving the appearance a whitish appearance and marring the aesthetics, so the amount of inorganic bonding agent that forms the glass phase is adjusted to balance the bonding strength and aesthetics.

On the other hand, by bonding the inorganic fine particle aggregates while covering them entirely with the glass phase, the properties such as the change or disappearance of the structural color due to the liquid penetration described above are lost, and light energy is lost due to scattering and absorption, but properties such as abrasion resistance, peel resistance, and stain resistance can be improved.

In the present invention, the inorganic fine particle aggregates form a multi-layered periodic structure, and the structural color resulting from the particle size and regular arrangement of the inorganic fine particles can be continuously expressed over a wide area. In the present invention, "continuous" means continuity that can be recognized by the human eye, and is considered continuous even if there are discontinuous areas in the target area that cannot be recognized by the human eye. The area in which the structural color is continuously expressed is preferably ^0.2 mm2 or more. In the production method described below, the structural color can be expressed in any area by adjusting the shape and area to be coated with the dispersion. The area in which the structural color is expressed may be one or more places.

Here, the wavelength of light of the structural color exhibited by the periodic structure can be predicted using the following Bragg-Snell equation.
λ=2(d/m)(n ² −sin ² θ) ^0.5
When the above Bragg-Snell formula is applied to the inorganic decorative product of the present invention, λ is the wavelength (nm) of light that reinforces the surface layer of the inorganic decorative product to which inorganic fine particles are bonded by light interaction, d is the periodic distance (nm) of the periodic structure determined by the diameter of the inorganic fine particles, m is an integer, n is the refractive index of the surface layer, and θ is the observation angle from the normal to the inorganic decorative product surface. In other words, the structural color that appears and is observed in the inorganic decorative product depends on the particle size of the inorganic fine particles, the refractive index of the inorganic fine particle aggregate, and the observation angle.

In this specification, the term "particle size" refers to the diameter of a primary particle when it is approximated as a sphere. Spherical particles form a periodic structure characterized by a short periodic distance due to the particles being densely packed, so there is a high possibility that there are multiple wavelengths of light in the visible range that satisfy the Bragg-Snell equation. In other words, in a periodic structure formed by densely packed spherical particles, different colors can be observed depending on the observation angle θ. The characteristic of observing different colors depending on the observation angle is a unique characteristic of structural color that is not seen in general pigments that are based on the principle of light absorption, and for this reason it is preferable to use spherical particles.

Even if the particle surface has ultra-fine irregularities, if the appearance in a magnified image observed under an electron microscope can be approximated to a sphere, it is considered to be approximately spherical and is within the scope of the present invention. On the other hand, since it is difficult to develop structural color derived from regular arrangement and therefore periodic structure in oblong particles, they are not within the scope of the present invention. In the present invention, the boundary between a sphere and an oblong spheroid is the value of the major axis divided by the minor axis of 1.3, and particles with this value of 1.3 or less are considered to be approximately spherical.

The inorganic particles may be solid, hollow, or porous, as they are capable of expressing a structural color according to their refractive index. If the inorganic particles are solid or hollow, when a portion of the aggregate is exposed on the surface of the inorganic decorative item, liquid such as water will penetrate into the gaps between the inorganic particles, changing the effects of light refraction, reflection, diffraction, scattering, etc., and the structural color will exhibit a unique characteristic of changing or disappearing depending on the difference in refractive index between the inorganic particles and the liquid. In addition, if the inorganic particles are porous, the liquid will penetrate into the gaps between the inorganic particles and into the pores of the inorganic particles at the same time, causing the structural color to disappear regardless of the refractive index of the liquid used.

The color change caused by liquid penetration returns to the original color when the liquid is removed by evaporation or other means. This characteristic is not seen in general pigments that use light absorption as a principle, and is unique to structural colors. The degree of porosity of inorganic fine particles can be evaluated by measuring the specific surface area. If the measured value of the specific surface area using the nitrogen gas adsorption method is larger than the calculated value calculated from the density and particle size observed under a scanning electron microscope, it can be judged to be porous, and the larger it is, the higher the porosity can be evaluated to be. The more porous it is, the more pronounced the characteristic of disappearance of structural color due to liquid penetration will be, so the measured value of the specific surface area should preferably be at least twice the calculated value, and more preferably at least three times.

In the case of porous silicon oxide microparticles, the structural color that appears due to the periodic structure is purple at a diameter of about 150 nm, and as the particle size increases, it exhibits blue-purple, blue, blue-green, green, yellow-green, yellow, orange, and red on the long wavelength side. When the particle size becomes larger than this, the constructive color under the condition of m = 1 and the constructive color under the condition of m = 2 mix together, exhibiting reddish purple and even blue-purple.

When the particle size becomes larger, the constructive colors under m=1 enter the near-infrared region and cannot be detected by human photoreceptor cells, while under m=2 they exhibit constructive purple and blue colors, followed by blue-green and green colors. As can be seen from the Bragg-Snell formula above, the constructive colors under m=2 are colors with constructive wavelengths where the optical path difference, calculated as the length to account for the effects of refraction, is twice the wavelength of light. The refractive index differs depending on the chemical composition and porosity of the inorganic particles, but beautiful colors are produced under m=1 conditions, so the particle size of the inorganic particles is preferably in the range of 150 to 350 nm, where beautiful structural colors are produced, and more preferably in the range of 150 to 300 nm.

The inorganic substrates used in the present invention include ceramics such as porcelain, various tiles, glass, carbon, and silicon; natural stones such as marble, Oya stone, and granite; and metals such as iron, steel, aluminum, titanium, gold, silver, copper, platinum, and various alloys. Composite materials combining multiple inorganic materials may also be used. In the case of substrates such as carbon that disappear when fired in air, and substrates such as silicon and metals that oxidize when fired in air, firing is performed in an inert atmosphere, vacuum atmosphere, or reducing atmosphere.

If the surface of the inorganic substrate is porous and the coated inorganic particle dispersion liquid penetrates into the interior, a base layer may be provided on the surface of the inorganic substrate by pretreatment. For example, a glassy base layer may be provided by coating with a glaze containing an inorganic bonding agent described below and firing it. In addition, the structural color expressed by the aggregate of inorganic particles may be emphasized by making the base layer a dark color as the background color. The inorganic substrate that serves as the base may be either manufactured in-house or outsourced. For example, the inorganic substrate may be manufactured in-house by kneading and molding inorganic materials, followed by drying and firing, or a finished or semi-finished product manufactured outsourced may be prepared separately.

The inorganic decorative product of the present invention is an inorganic product made of inorganic materials, on which an inorganic decorative layer that exhibits structural color is laminated in any region. It includes both products such as ceramic arts and ornaments that are themselves beautiful and are objects of appreciation, and semi-finished products such as parts and building materials that are incorporated to decorate other objects or structures. Specific examples include daily necessities such as tableware, vases, cooking utensils, writing implements, and tools, and their parts; ornaments such as jewelry, accessories, and watches, and their parts; portable information and communication devices such as mobile phones and smartphones; display panels, housings and parts of electrical appliances; furniture components such as tables, desks, and shelves; fixtures and building materials such as roofs, walls, floors, windows, and doors; components of housing facilities such as baths, toilets, kitchens, and washbasins; frames, bodies, and interior and exterior parts of transportation equipment such as bicycles, motorcycles, automobiles, trains, and airplanes; stone processed products such as monuments, lanterns, and gravestones; ceramic arts and crafts.

Next, the manufacturing method of the present invention differs from the conventional technology in that a dispersion containing inorganic fine particles and a component that will become a glass phase that bonds them is prepared, and this dispersion is directly coated on the surface of the inorganic substrate and dried, directly forming a periodic structure in which the inorganic fine particles are regularly arranged on the surface of the inorganic substrate, and then the substrate is fired. In order to obtain a highly dispersed dispersion, it is preferable to prepare the inorganic fine particles by liquid phase synthesis and use them as they are without going through an aggregation process, and it is preferable to coat them in a highly dispersed state.

For example, gas-phase synthesis can also be used to obtain particles with uniform particle size, but the particles recovered from gas-phase synthesis tend to be somewhat aggregated, and it is difficult to completely disperse these particles in liquid to obtain monodispersed particles, or to control the degree of aggregation. For this reason, liquid-phase synthesis is used in the present invention. Examples of liquid-phase synthesis include the alkoxide method, which uses alkoxides as raw materials, the precipitation method, which precipitates particles from a solution, and the hydrothermal synthesis method, which dissolves sparingly soluble salts under high-temperature and high-pressure conditions to precipitate particles.

Among these, the alkoxide method is preferred because of its excellent controllability of particle size. Examples of alkoxides used as raw materials include alkoxides of silicon, titanium, aluminum, magnesium, zirconium, etc. Among these, tetramethyl orthosilicate and tetraethyl orthosilicate are preferred because the reaction rate is easily controlled and the raw materials are inexpensive.

In the above liquid phase synthesis, in order to obtain a dispersion of inorganic fine particles with a uniform particle size, it is necessary to generate nuclei of inorganic fine particles quickly and uniformly. Therefore, the faster the stirring speed and catalyst addition speed during liquid phase synthesis, the better. In the nucleation and particle growth steps of liquid phase synthesis, the synthesis reaction may be promoted by applying external energy using ultrasound or a vibrator, and the synthesis rate may be controlled by heating or cooling the liquid from which the particles are precipitated.

In liquid-phase synthesis, the raw materials that form the inorganic fine particles may not be completely reacted, and some raw material components may be intentionally left unreacted to prepare a dispersion containing inorganic fine particles and unreacted raw material components. In this case, the unreacted raw material components remaining in the gaps between the inorganic fine particles form chemical bonds during firing to form a glass phase that bonds the inorganic fine particles. The reaction rate in liquid-phase synthesis can be controlled by adjusting the nucleation reaction and particle growth reaction rates of the starting raw materials for the inorganic fine particles, for example, by adjusting the reagent concentration, catalyst compounding ratio, temperature, pressure, concentration, stirring speed, solubility parameter, and reaction time. As mentioned above, this manufacturing method can stably produce inorganic decorative products with coloring that emphasizes the characteristic of structural color, which "changes color depending on the viewing angle."

On the other hand, after the raw materials that form the inorganic particles in the liquid phase synthesis have been sufficiently reacted, an appropriate amount of inorganic bonding agent may be added to prepare a dispersion containing inorganic particles and the inorganic bonding agent. In this case, the glass phase that bonds the inorganic particles is formed when the added inorganic bonding agent melts as it is fired. With this manufacturing method, it is possible to obtain inorganic decorative products with color development similar to that of conventional pigments, in that the color does not change depending on the viewing angle.

The inorganic bonding agent used is one that melts during firing and forms a glass phase that bonds inorganic particles. Substances that contain fine amorphous silicon oxide as the main component, and solid-solution elements such as aluminum, boron, lead, and phosphorus, and alkali and alkaline earth metals such as lithium, sodium, potassium, magnesium, calcium, strontium, and barium, can be used. As long as they do not interfere with the development of the structural color, colored metal elements such as iron, copper, manganese, cobalt, chromium, nickel, gold, tin, titanium, and zirconium may also be included. It is most preferable that the glass phase formed by the inorganic bonding agent is colorless and transparent, but a dark glass phase is also preferable from the viewpoint of emphasizing the structural color as a background color.

Since the inorganic bonding agent is added to a highly dispersed dispersion of inorganic fine particles, it must be thoroughly mixed in the coating liquid before preparation. This makes it possible to bond inorganic fine particles to the surface of the inorganic substrate even with a small amount of inorganic bonding agent and a relatively low firing temperature. Conditions vary depending on the type of inorganic bonding agent used, the firing temperature, the particle size of the inorganic fine particles to be bonded, etc., but under optimal conditions, adding an inorganic bonding agent in an amount equal to half the weight of the inorganic fine particles makes it possible to bond inorganic fine particles to the surface of the inorganic substrate even when fired in air at 900°C. Here, bonding refers to a state in which the particles do not come off even when rubbed with a finger.

The more the amount of inorganic bonding agent added, the stronger the bonding strength becomes, but if a discontinuous glass phase is present on the outermost surface, the light is scattered and the appearance becomes whitish, which impairs the aesthetics. The amount of inorganic bonding agent added is preferably half to the same amount as the weight of the inorganic particles, in a form in which the inorganic particle aggregate is bonded to the inorganic base material with a part of it exposed on the surface and which exhibits characteristics such as the change or disappearance of the structural color due to the liquid penetration described above. However, if the bonding strength is important, the amount may be two to three times the weight of the inorganic particles.
In the above manufacturing method, after forming a periodic structure by regularly arranging inorganic microparticles on the surface of the inorganic substrate, a topcoat liquid containing an inorganic bonding agent can be applied thereon and fired to produce a form in which the entire inorganic microparticle aggregate is covered with a glass phase.

Methods for coating the dispersion include dip coating, in which the inorganic substrate is immersed in the dispersion, coating with a brush or writing brush, spray coating by spraying, and, in addition, when the shape of the inorganic substrate is smooth, bar coating or spin coating can be used. Unlike conventional techniques, the present invention allows the inorganic substrate to be directly coated with the dispersion to form a periodic structure, so that structural color can be continuously expressed over any large area. In addition, even if the inorganic substrate includes a curved surface, it can be coated uniformly, and it is possible to coat the entire surface of the inorganic substrate, or to coat by spraying to scatter structural color coloring regions. A coating method suitable for the intended color expression can be selected from the above methods, and multiple coating methods may be combined.

When inorganic fine particle dispersions with different particle sizes and refractive indices are coated on the same area of an inorganic substrate by spraying or other methods, multiple structural colors can be produced in the same area even when observed from the same angle. There is no limit to the type and number of structural colors to be coated, and the combinations are arbitrary. For example, it is possible to produce different structural colors and paint them separately even when the particle size difference of inorganic fine particles is large, or when the particle size difference is small, such as about 10 nm. It is also possible to express color gradations due to structural colors by controlling the thickness of the inorganic fine particle aggregate to be coated. The thickness can be controlled by adjusting the coating method, liquid amount, and number of times, and the thickness of the coating layer can be selected arbitrarily according to the shade of the structural color to be expressed.

In the manufacturing method of the present invention, the inorganic fine particles are regularly arranged to form a periodic structure during the process of evaporating the solvent in the dispersion liquid, which allows the appearance of structural color. The solvent may be evaporated at room temperature, or may be heated at 50 to 300°C. Evaporation may be promoted by blowing air on the substrate, or by preheating the inorganic substrate. The solvent of the dispersion liquid contains water and alcohol, and examples of the alcohol used in the present invention include methanol, ethanol, propanol, butanol, ethylene glycol, and glycerin, as well as higher alcohols such as lauryl alcohol, oleyl alcohol, and linolyl alcohol. These alcohols may be used in combination.

To control the evaporation rate, acetone, methyl ethyl ketone, toluene, xylene, benzene, phenol, n-hexane, formic acid, acetic acid, methyl acetate, ethyl acetate, dibutyl phthalate, acetonitrile, dimethylformamide, etc. may be added, or a combination of these may be added. A surfactant may also be added to improve the dispersion stability of the inorganic fine particles or improve the wettability of the inorganic substrate surface. The surfactant used may be any of an anionic surfactant, cationic surfactant, amphoteric surfactant, and nonionic surfactant. Multiple ionic surfactants may be combined, or an ionic surfactant and a nonionic surfactant may be combined.

Furthermore, in order to adhere inorganic fine particles or inorganic bonding agents to the inorganic substrate or to adjust the viscosity of the dispersion, carboxymethylcellulose, methylcellulose or salts thereof, latex, natural rubber, glue, dextrin, etc. may be added. These may also be used in combination.

The inorganic decorative product and its manufacturing method of the present invention will be specifically described below with reference to examples and comparative examples. In addition, in order to supplement the explanation of the color and color development, color photographs corresponding to Figures 1, 3, 4, 5, 7, 8, and 9 are attached to the application for submission on the same date as this application. Note that the present invention is not limited to these examples, etc., and various modifications are possible within the scope of the technical concept of the present invention.

[Example 1]
5.0 to 6.5 g of tetraethyl orthosilicate was mixed into an aqueous ethanol solution (20 g ethanol, 5 g water), and 1 mol/L ammonia water was added while stirring at room temperature to obtain a dispersion of silicon oxide fine particles. The amount of ammonia water added was 5.0 to 6.5 mL corresponding to the amount of tetraethyl orthosilicate. 0.125 g of an inorganic binder containing silicon oxide as the main component and trace amounts of Al, K, Fe, etc. was added to 5 g of this dispersion, stirred, dispersed in an ultrasonic cleaner, and then coated on the ceramic surface using a spray. In order to adjust the thickness, the coating was performed partially multiple times. In addition, dispersions prepared under conditions with different amounts of tetraethyl orthosilicate were coated on the same area of the ceramic surface. This was dried at 80°C for several tens of seconds, and then fired at 900°C in an air atmosphere for 1 hour.

A digital photograph of the appearance of the obtained ceramics is shown in Figure 1. Continuous structural coloring was observed over a wide area of several ^cm2 including curved surfaces, and it was also possible to overlay two colors in the same area. The color could be controlled by the synthesis conditions of the silicon oxide microparticles, with 5.0 g of tetraethyl orthosilicate showing purple, 5.5 g showing blue, and 6.5 g showing yellow-green. The coating layer did not peel off even when rubbed with a finger. In the thickly coated areas, the color clearly differed depending on the observation angle.

Next, magnified images of the obtained ceramic surface observed by scanning electron microscope are shown in Figures 2(a) and (b). At the observation point (a), it was found that spherical particles with a diameter of about 215 nm were packed and arranged regularly to form a periodic structure. At the observation point (b), a small number of areas covered with a glass phase were scattered like islands, and the arrangement of the spherical particles was partially disordered. Since spherical particles were observed in the scanning electron microscope image, which mainly observes surface irregularities by electron beam irradiation, it was found that the top layer of the inorganic particle aggregate was exposed on the ceramic surface without being covered by the glass layer formed by the inorganic binder.

[Example 2]
A ceramic piece with a pattern drawn on its surface was obtained under the same conditions as in Example 1, except that the dispersion was partially applied using a brush. As shown in Figures 3(a) to (d), the structural color of the obtained ceramic piece disappeared when it was wetted with water, and the original structural color was revealed when it was dried. This phenomenon is considered to be due to the penetration of water into the aggregates of fine particles exposed on the ceramic surface and into the interior of the fine particles.

This is supported by the fact that the specific surface area of the silicon oxide microparticles of the obtained sample measured by the nitrogen adsorption method was about three times that calculated from the density of amorphous silicon oxide (2.2 g/ ^cm3 ) and the particle size observed by a scanning electron microscope, indicating that the silicon oxide microparticles are porous. Note that the particle size of the silicon oxide microparticles was calculated as an average value from the observation images of 10 particles with relatively clear boundaries in high magnification observation.

[Example 3]
Pottery with Roman letters drawn on the surface was obtained under the same conditions as in Example 1, except that the amount of tetraethyl orthosilicate (TEOS) was 5.5 to 8.0 g, the amount of ammonia water added was 5.5 to 8.0 mL, and the dispersion was partially applied using a brush. As shown in Figures 4(a) and (b), the color of K drawn with silicon oxide fine particles synthesized under the condition of 5.5 g of TEOS was blue. Similarly, 6.0 g of I was green, 6.5 g of S was yellow-green, 7.0 g of T was red, 7.5 g of E was purple, and 8.0 g of C was blue. 7.5 g of E and 8.0 g of C were slightly whitish in color.

The coating layer did not peel off even when rubbed with a finger. The color did not change depending on the viewing angle. The particle size of the fine particles was measured in the same way as in Example 1, and the blue color was 230 nm for 5.5 g of TEOS, the green color was 270 nm for 6.0 g, the yellow-green color was 290 nm for 6.5 g, the red color was 310 nm for 7.0 g, the purple color was 350 nm for 7.5 g, and the blue color was 370 nm for 8.0 g. It was found that when only a single dispersion liquid with an inorganic binder added is used as in this example, the color is similar to that of conventional pigments, which are a constant color that does not change depending on the viewing angle.

In addition, when the surface was wetted with water in the same manner as in Example 2, the blue color of K under the TEOS 5.5 g condition changed to green, and the blue color of C under the 8.0 g condition disappeared, as shown in Figures 5 (a) and (b). Both returned to their original colors when the water evaporated and they dried. Furthermore, when the specific surface area value after firing was measured in the same manner as in Example 2, the fine particles under the 5.5 g condition had a value of 11.9 ^m2 /g, which was consistent with the calculated value calculated from the density and particle size. The fine particles under the 8.0 g condition had a value of 16.0 ^m2 /g, which was approximately 2.2 times larger than the calculated value.

Under the 5.5 g condition, the measured and calculated values for the specific surface area matched, so it is believed that solid spheres were formed. When wetted with water, the refractive index around the microparticles changed from 1.00 (air) to 1.33 (water), meaning the difference in refractive index between the microparticles and their surroundings changed, causing the discoloration. On the other hand, the microparticles under the 8.0 g condition were highly porous, allowing water to penetrate deep into the particles, and the refractive index in the coating layer became uniform, which is thought to be why the color disappeared.

[Example 4]
A dispersion of silicon oxide fine particles was prepared by adding 5.0 to 7.0 mL of ammonia water to 7.0 g of tetraethyl orthosilicate without adding any inorganic binder. This dispersion was applied to ceramic pieces with a brush to obtain three types of test pieces with different amounts of ammonia water added. The other conditions were the same as in Example 1.

From the scanning electron microscope images of the test piece surface shown in Figures 6 (a) to (c), it was found that the smaller the amount of ammonia water added, the smaller the diameter of the microparticles and the more a glass phase was formed to fill the gaps between the particles. When each coating layer was rubbed with a finger, the test piece with 7.0 mL of ammonia water added was able to withstand light pressure but peeled off when rubbed with strong pressure, while the test pieces with 6.0 mL and 5.0 mL of ammonia water added did not peel off even when rubbed with strong pressure.

[Comparative Example 1]
A test piece was obtained under the same conditions as in Example 4, except that the amount of ammonia water added was 8.0 mL per 7.0 g of tetraethyl orthosilicate. This coating layer was clearly peeled off even when rubbed with a weak force.
The results of Example 4 and Comparative Example 1 show that by preparing a dispersion of silicon oxide microparticles in which the reaction has not progressed completely and the TEOS component remains unreacted, and then applying this to the surface of a substrate and then baking it, the silicon oxide microparticles can be regularly and firmly bonded to the substrate surface in a glass phase, even without the addition of an inorganic bonding agent.

[Example 5]
A dispersion of silicon oxide fine particles was prepared by adding 7.0 mL of ammonia water to 7.0 g of tetraethyl orthosilicate without adding any inorganic binder. This dispersion was applied to the surface of ceramics with a brush and fired at 950°C for 1 hour to obtain ceramics with a pattern on the surface. Other conditions were the same as in Example 1.

As shown in the external photographs in Figures 7 and 8, different colors were observed, including yellow-green, yellow, orange, and red, even though a single dispersion liquid was used. When the same area was observed while tilting the ceramic, red was observed at an observation angle close to vertical, and when tilted further, orange and yellow were observed, and yellow-green was also seen. In other words, the characteristic of structural color, which "changes color depending on the viewing angle," was clearly demonstrated. No peeling was observed even when the coating layer was rubbed hard with a finger. The reason why the characteristic of structural color is so pronounced is thought to be that by using unreacted TEOS components as a bonding agent, there is no need to add extra additives that disrupt the arrangement of silicon oxide particles, and the particles are regularly arranged over a long period, resulting in the coloring caused by regular reflection light becoming dominant.

[Example 6]
A dispersion of silicon oxide particles prepared under the same conditions as in Example 5 was applied to a ceramic piece with a brush and dried at 80°C for several tens of seconds. A drop (about 0.03g) of a dispersion prepared by adding 0.8g of the inorganic binder used in Example 1 to 6g of a 1% methylcellulose aqueous solution was dropped onto the applied surface, and the piece was fired at 900°C for 1 hour to obtain a test piece in which the color-developing layer made of silicon oxide particles was completely covered with a glass phase. As shown in the enlarged digital microscope photograph in Figure 9, the appearance of a blue-purple structural color was observed even in the part of the surface completely covered with the glass phase. No peeling was observed even when the coating layer was rubbed with strong force.

The inorganic decorative product of the present invention is made of inorganic materials, has excellent heat resistance, mechanical strength, hardness, abrasion resistance, chemical stability, corrosion resistance, and weather resistance, and exhibits structural colors with excellent aesthetics derived from a multi-layered periodic structure. Depending on the application and design, it is possible to make the color change unique to structural colors, which changes depending on the viewing angle, or to make the color change like general pigments, which does not change depending on the viewing angle, and this can be controlled. The structural colors of the present invention are colored due to microstructures, unlike general pigments that use light absorption by transition metals, and therefore can be expressed using inorganic fine particles such as silicon oxide and aluminum oxide, which are rare metal-free, inexpensive, hazardous to the human body, and have low environmental impact.

The structural color of the present invention can also exhibit the unique feature that the color changes or disappears when wet with liquid, and returns to the original color when the liquid is removed by evaporation or the like. Furthermore, the manufacturing method of the present invention can continuously and quickly form a periodic structure in which inorganic fine particles are regularly arranged over a wide area, requires a small amount of inorganic binder to be added, and can be fired in air at a relatively low temperature, resulting in low manufacturing costs and a small environmental impact.

In other words, the inorganic decorative products and the manufacturing method of the present invention can be used in daily necessities and their parts, such as tableware, vases, cooking utensils, writing implements, and tools; decorative items and their parts, such as jewelry, accessories, and watches; portable information and communication devices, such as mobile phones and smartphones; display panels, housings and parts, furniture components, such as tables, desks, and shelves, fixtures and building materials, such as roofs, walls, floors, windows, and doors; components for housing facilities, such as baths, toilets, kitchens, and washbasins; frames, bodies, and interior and exterior parts of transportation equipment, such as bicycles, motorcycles, automobiles, trains, and airplanes; stone products, such as monuments, lanterns, and gravestones; ceramics and crafts; and it is expected that the inorganic decorative products and the manufacturing method thereof will contribute to the development of various industrial fields.

Claims (11)

An inorganic decorative article having a region in which a structural color resulting from the particle size and regular arrangement of approximately spherical inorganic fine particles of silicon oxide is expressed,
the region where the structural color is expressed is composed of the inorganic fine particles, an inorganic base material which is a substrate, and an inorganic bonding material which bonds them together,
the inorganic bonding material is silicon oxide in a glass phase and has the same chemical composition as the inorganic fine particles;
the inorganic fine particles are arranged in a substantially regular pattern on the surface of the inorganic base material and are bonded to each other by the inorganic bonding material present in the gaps between the fine particles to form a multi-layered aggregate of inorganic fine particles;
the inorganic fine particle aggregate is bonded to a part or the entire area of a surface of the inorganic base material by the inorganic bonding material present in the gap between the inorganic fine particles and the inorganic base material,
The weight of the inorganic bonding material is in the range of half to the same amount as the weight of the inorganic fine particles,
The structural color is continuously expressed over an area of ^0.2 mm2 or more ,
the inorganic fine particle aggregate is bonded to the inorganic base material in a state where a part of the aggregate is exposed on a surface thereof,
The inorganic decorative article, wherein the inorganic microparticles are porous and the specific surface area measured by a nitrogen gas adsorption method is at least twice the value calculated from the density of silicon oxide and the particle size observed by a scanning electron microscope. 2. The inorganic decorative article according to claim 1, wherein a plurality of types of inorganic fine particle aggregates exhibiting structural colors are formed in the same region, and the inorganic decorative article has a region in which a plurality of colors originating from the inorganic fine particle aggregates are exhibited at the same observation angle. 3. The inorganic decorative article according to claim 1 , wherein the inorganic base material has a curved surface portion, and the inorganic fine particle aggregate is bonded to a part or the entire area of the curved surface portion. 4. The inorganic decorative article according to claim 1 , wherein the number average particle diameter of the primary particles of the inorganic fine particles is 150 to 370 nm. 5. The inorganic decorative article according to claim 1, wherein the inorganic base material is ceramic. 6. The inorganic decorative item according to claim 1, which is one selected from the group consisting of tableware and its parts, ornaments and its parts, parts of writing instruments, housings and parts of portable information and communication devices, building materials for interior and exterior use, bodies and parts of transportation equipment, and stone products for gardens and cemeteries. a step of preparing a dispersion containing inorganic fine particles of silicon oxide having a roughly spherical shape by an alkoxide method using a silicon alkoxide as a raw material, the dispersion not being reacted completely with the alkoxide, leaving unreacted components, the dispersion containing the inorganic fine particles and the unreacted components, the weight of the unreacted components being half to three times the weight of the inorganic fine particles ;
a step of coating a part or the whole area of a surface of an inorganic substrate with the dispersion liquid obtained in the previous step and drying the coating, thereby forming a multi-layer aggregate of inorganic fine particles on the surface of the inorganic substrate, in which the inorganic fine particles are arranged in a substantially regular pattern;
and baking the inorganic base material on which the inorganic fine particle aggregates have been formed, causing the remaining unreacted components to react and form an inorganic bonding material, bonding the inorganic fine particles together and the inorganic fine particles and the inorganic base material together with the inorganic bonding material, thereby bonding the inorganic fine particle aggregates to a part or all of the area of the inorganic base material surface.
A method for producing an inorganic decorative article having a region in which a structural color resulting from the particle size and regular arrangement of the inorganic fine particles is expressed . In the step of preparing a dispersion liquid containing inorganic fine particles and unreacted components, an inorganic binder mainly composed of amorphous silicon oxide is further added and mixed to prepare a dispersion liquid containing the inorganic fine particles, the unreacted components and the inorganic binder, the weight of the unreacted components and the inorganic binder being half to three times the weight of the inorganic fine particles ;
8. The method for producing an inorganic decorative product according to claim 7 , wherein in the step of bonding the aggregate of inorganic fine particles to a part or the entire area of the surface of the inorganic base material, the inorganic bonding agent is further melted by firing to form an inorganic bonding material. A dispersion liquid containing substantially spherical inorganic fine particles of silicon oxide and unreacted components remaining after the silicon alkoxide, which is a raw material of the inorganic fine particles, has not completely reacted,
The weight of the unreacted components is in the range of half to three times the weight of the inorganic fine particles,
The dispersion liquid, in which the inorganic microparticles are arranged in a substantially regular pattern and bonded together by an inorganic bonding material formed from the unreacted components to form a multilayer inorganic microparticle aggregate, exhibits a structural color resulting from the particle size and regular arrangement of the inorganic microparticles. The dispersion according to claim 9 , wherein the inorganic fine particles have a number average particle diameter of primary particles of 150 to 370 nm. 11. A method for producing a dispersion according to claim 9 or 10, comprising the step of: in a reaction for precipitating approximately spherical inorganic fine particles of silicon oxide by an alkoxide method using a silicon alkoxide as a raw material, not completely reacting the alkoxide to leave unreacted components, thereby preparing a dispersion containing the inorganic fine particles and the unreacted components, wherein the weight of the unreacted components is half to three times the weight of the inorganic fine particles .