JP2001064538A - Yellow-colored powder and preparation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vivid yellow-colored powder having a high functionality and preferably a sufficient color value, and provide a preparation process thereof which does not use a process via hydrolysis of metal alkoxides, requires no expensive metal alkoxide, highly inflammable organic solvent, preparation facility nor explosion-proof facility, allows easy control of temperature and moisture and inexpensively yields products in general. SOLUTION: This yellow-colored powder has a coated film on the surface of a substrate particle, wherein at least one layer of the coated film is formed via a reaction of a metal salt in an aqueous solvent, and shows a reflective spectrum having its peak at a wavelength of from 380 to 500 nm. Furthermore, preferably, at least one layer of the coated film is formed as an aggregate of crystalline fine particles having voids.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a yellow powder and a method for producing the same, and more specifically, to produce it by an inexpensive and safe method without using expensive raw materials or dangerous organic solvents. The present invention relates to a yellow powder used for various purposes such as ink, filler for plastic/paper, toner, ink for inkjet printer, and a method for producing the same.

[0002]

2. Description of the Related Art The present inventors have previously used powder particles as a base material in order to provide a powder having not only the properties that only one powder particle has but also another property and having a composite function. As a result, the inventors invented a powder having a metal oxide film or the like with a uniform thickness of 0.01 to 20 μm on the surface thereof (Japanese Patent Laid-Open No. H06-69242).
-228604 publication). Further, the present inventors have further improved the above-mentioned powder, and invented not only the metal oxide film but also a powder having a plurality of layers of the metal oxide film and the metal film alternately (see Japanese Patent Application Laid-Open No. Hei 7 (1999)-58). -90310).

In order to produce these powders, it is necessary to provide a plurality of metal oxide films having a uniform thickness on the surface of the substrate. For that purpose, the metal oxide or its precursor is prepared from the aqueous solution of the metal salt. Since it is difficult to precipitate the metal compound which is the body, the present inventors have dispersed the above-mentioned substrate in a metal alkoxide solution and hydrolyzed the metal alkoxide to form a metal oxide film on the substrate. By developing a method for producing the metal oxide film, it becomes possible to form a thin metal oxide film having a uniform thickness, and in particular, it becomes possible to form a multilayer metal oxide film. In addition, the inventors of the present invention control the combination of substances of the multilayer film, the refractive index, and the film thickness of the powder having a multilayer film coating such as a metal oxide film on the surface of the powder particles as a base. It was found that by adjusting the reflected light interference waveform of the multilayer film, a colored powder such as a pigment can be obtained (WO96/2).
8269).

Further, the inventors of the present invention have based on the above-mentioned technology.
An attempt was made to establish a technology for obtaining a desired colored powder having a specific color tone, specifically, a condition range for developing the color of a film-coated powder exhibiting a vivid yellow color. For example, yellow is one of the three primary colors,
It is also an important pigment that psychologically gives people a warm feeling, a bright feeling, and a healthy feeling. It is of great industrial significance to obtain a pigment powder having such a yellow color tone and having a specific function. As a result of study from such a viewpoint, the present inventors have formed a plurality of coating films in which a coating film having a large refractive index and a coating film having a small refractive index are laminated next to each other on the surface of the substrate particles, and the coating film having a thickness of 550 to 850 nm is formed. It has been found that a yellowish powder can be obtained by setting the conditions of the base particles and the coating film so as to show a reflection spectrum having a peak between them (JP-A No. 11-12488).

[0005]

However, in the yellow powder described in JP-A-11-12488, the coating layer on the surface of the base particles is formed by the hydrolysis reaction of the metal alkoxide. Met.
In the film formation method by the hydrolysis reaction of metal alkoxide, it is necessary to use an organic solvent having high flammability as a solvent and an expensive metal alkoxide as a raw material. Further, in order to use an organic solvent having high flammability, the manufacturing facility must be an explosion-proof facility and the temperature and humidity must be controlled strictly, and the price of the product manufactured using it is naturally expensive as a whole. Further, in the case of the yellow powder, the reflectance is insufficient only by providing the base particles with a multi-layered coating layer relating to optical interference, and thus a dark color tone such as ocher is obtained. Therefore, it is necessary to increase the light reflectance by providing a metallic silver film between the multilayer coating and the base particles. Therefore, expensive metallic silver has to be used, and there is a problem that the manufacturing cost is further increased.

Therefore, an object of the present invention is to overcome the above-mentioned drawbacks of the prior art, and without using a method by hydrolysis of metal alkoxide, without using expensive metal silver and metal alkoxide or a highly flammable organic solvent. The manufacturing facility does not require explosion-proof equipment, the temperature and humidity can be easily controlled, and the product price is high. is there.
A further object of the present invention is to provide a bright yellow-colored powder having sufficient brightness and a method for producing the same.

[0007]

[In the formula, N=n+iκ (i represents a complex number) n: Refractive index of substance constituting film d: Film thickness m: Natural number λ: Peak wavelength of reflection spectrum of powder (where λ is 550 ~850 nm) κ: attenuation coefficient]

(3) The yellow powder as described in (1) above, wherein the coating film on the surface of the base particles is a multilayer film. (4) The yellow colored powder as described in (3) above, wherein each of the multilayer films is formed by a reaction of a metal salt in an aqueous solvent. (5) The yellow powder as described in (3) above, wherein each of the multilayer films satisfies the condition of the following formula. Nd=mλ/4 [In the formula, N=n+iκ (i represents a complex number) n: Refractive index of substance constituting film d: Film thickness m: Natural number λ: Peak wavelength of reflection spectrum of powder ( However, λ is 550 to 850 nm) κ: Attenuation coefficient]

(6) At least one layer of the coating film on the surface of the base particles is constituted as an aggregate of crystallized fine particles having voids, (1)
The yellow powder as described. (7) The coating film formed as an aggregate of crystallized fine particles having voids can impart lightness by scattering and reflection of light generated between the surface of the crystallized fine particles and voids. (7) The yellow powder as described in (6) above. (8) A dense coating film composed of ultrafine particles capable of closing the voids on the surface is provided on the surface of the coating film formed as an aggregate of crystallized fine particles having voids. The yellow powder as described in (6) above. (9) The yellow powder as described in (6) above, wherein the coating film formed as an aggregate of crystallized fine particles having voids is a high refractive index film. (10) The yellow powder as described in (8) above, wherein the dense film is a silica film.

(11) The coating film, which is formed as an aggregate of crystallized fine particles, brings the crystallized fine particles onto the surface of the base powder in a liquid in which the crystallized fine particles and the base powder are dispersed. The yellow powder as described in (6) above, which is formed by adhering. (12) The coating film formed as an aggregate of crystallized fine particles having voids forms solid phase fine particles in a reaction solution for forming the coating film, and the solid phase fine particles are coated with the solid phase fine particles. The yellow powder as described in (6) above, which is formed by firing after being incorporated into a film. (13) The yellow powder as described in (12) above, wherein the reaction solution is an aqueous solution. (14) Before performing the firing, the coating film in which the solid phase fine particles are incorporated is coated with ultrafine particles capable of forming a dense film that closes voids on the surface of the coating film. (12) The yellow powder as described in (12) above.

(15) In the method for producing a yellow powder by forming a coating film on the surface of base particles, the powder obtained has a reflection spectrum having a peak between 550 and 850 nm. A method for producing a yellow powder, which comprises forming at least one layer of a coating film by a reaction of a metal salt in an aqueous solvent. (16) The method for producing a yellow powder according to (15), wherein the coating film formed by the reaction of a metal salt in an aqueous solvent is formed so as to satisfy the condition of the following formula. Nd=mλ/4 [In the formula, N=n+iκ (i represents a complex number) n: Refractive index of the substance constituting the film d: Film thickness m: Natural number λ: Peak wavelength of the reflection spectrum of the powder ( However, λ is 550 to 850 nm) κ: Attenuation coefficient] (17) The method for producing a yellow powder as described in (15) above, wherein the coating film formed on the surface of the base particles is a multilayer film. (18) The above-mentioned (17), wherein each of the multilayer films is formed by a reaction of a metal salt in an aqueous solvent.
A method for producing the yellow powder as described. (19) The method for producing a yellow powder according to (17), wherein each of the multilayer films is formed so as to satisfy the condition of the following formula. Nd=mλ/4 [In the formula, N=n+iκ (i represents a complex number) n: Refractive index of substance constituting film d: Film thickness m: Natural number λ: Peak wavelength of reflection spectrum of powder ( However, λ is 550 to 850 nm) κ: Attenuation coefficient]

(20) The yellow powder as described in (15) above, wherein at least one layer of the coating film formed on the surface of the base particles is constituted as an aggregate of crystallized fine particles having voids. Production method. (21) The coating film, which is formed as an aggregate of crystallized fine particles having voids, is formed so that lightness can be imparted by scattering and reflection of light generated between the surface of the crystallized fine particles and voids. A method for producing a yellow powder according to (20) above. (22) A dense film of ultrafine particles capable of closing the voids on the surface is formed on the surface of the coating film formed as an aggregate of crystallized fine particles having voids, (20) A method for producing the yellow powder as described. (23) The method for producing a yellow powder according to (20), wherein the coating film formed as an aggregate of crystallized fine particles having voids is a high refractive index film.

(24) The method for producing a yellow powder according to (22), wherein the dense film is a silica film. (25) The coating film formed as an aggregate of crystallized fine particles is added with a film-forming substance in a liquid in which the crystallized fine particles and the base powder are dispersed, and the crystallized fine particles are added to the base powder. The white powder as described in (20) above, which is formed by adhering to the body surface. (26) The coating film, which is formed as an aggregate of crystallized fine particles having voids, is formed into solid phase fine particles in a reaction solution for forming the coating film, and the solid phase fine particles are used as the coating film. The method for producing a yellow color powder as described in (20) above, wherein the yellow color powder is formed by incorporating it into the interior and firing it. (27) The method for producing a yellow powder according to (26), wherein the reaction solution is an aqueous solution. (28) coating the coating film in which the solid phase fine particles are incorporated with ultrafine particles capable of forming a dense film that closes voids on the surface of the coating film before performing the baking (26) The method for producing a yellow colored powder as described in (26) above.

During the film-forming reaction, the yellow color powder of the present invention can suppress the deposition of a solid phase that does not form a film by the following operations and actions, and a film having a uniform thickness can be formed on the surface of the substrate particles. It can be formed with a thickness of.
By using a buffer solution as the reaction solvent and adjusting the pH to a certain level, the effect of acid or alkali is moderated,
Corrosion of the substrate surface is prevented; ultrasonic dispersion not only improves the dispersibility of the substrate particles, especially the magnetic substance such as magnetite powder, but also improves the diffusibility of the coating components.
Prevents the adhesion of the coatings to each other and improves the dispersibility of the coated magnetic particles; suppresses the precipitation of solid phase that does not form a coating by precipitating the coating components at an appropriate reaction speed. Due to the above-mentioned comprehensive action, the electric charge on the surface of the film-coated powder can be kept constant, and the function of the electric double layer can provide dispersed particles without aggregation of the film-coated powder. In order to make the best use of the function of the electric double layer, the pH differs depending on the combination of the substance of the substrate and the kind of the metal compound formed in the liquid by the film forming reaction, and it is preferable to avoid the isoelectric point of both. Further, at least one layer of the coating film on the surface of the base particles is a film composed of an aggregate of crystallized fine particles and crystallized fine particles having voids between the crystallized fine particles (hereinafter, also simply referred to as a crystallized fine particle constituent film). By increasing the refractive index difference between the surface of the crystallized fine particles and the voids, scattering reflection of light is caused, the reflection effect is enhanced, and a functional powder of yellow color tone having excellent brightness is provided. It became possible to do.

According to the present invention, due to the above mechanism of action, despite the use of the water-soluble raw material, the film-coated powders do not agglomerate or stick to each other even when the magnetic substance is used as the substrate, and preferable film thickness control It was possible to easily produce a film-coated powder capable of Further, by using water as a solvent, it is possible to obtain an effect that a film can be formed at a lower manufacturing cost than the alkoxide method.

FIG. 1 is a cross-sectional view of an example of a yellow colored powder of the present invention having a crystallized fine particle constituting film 2 on the surface of a base particle 1, and FIG. 2 is a crystal of the yellow colored powder of FIG. FIG. 3 is an enlarged cross-sectional view of a film 2 for forming fine particles. 1 and 2
As shown in FIG. 3, the crystallized fine particle constituting film 2 has voids between the crystallized fine particles 3 so that
The difference in refractive index between the surface and the voids is increased to cause light scattering and reflection, whereby a powder having high brightness can be obtained. The stronger the scattering reflection is, the more light the powder is. It is preferable that the crystallized fine particles 3 contained in the film 2 have a high refractive index and that the particle diameters are not uniform. The brightness can be adjusted by the amount and particle size of the crystallized fine particles in the film. However, depending on the particle size, scattering and interference may occur at the same time, and due to the interference, a hue other than yellow may be exhibited. In particular, when the obtained film-coated powder has a strong opal-like monochromatic spectrum color, the crystallized particle diameter in the film is uniform with a certain size (about 1/4 to 1 wavelength of light wavelength). Therefore, it is considered that the crystallized fine particles cause interference, and the film thickness is designed in consideration of the interference reflection.

In this case, the particle size of the crystallized fine particles in the film is preferably 1 to 500 nm, more preferably 10 to 500 nm.
300 nm, more preferably 10 to 250 nm
The range is. If the particle size is less than 1 nm, the color of the underlying substrate particles may appear as it is, even if it becomes a film, because it transmits light. On the other hand, when it is larger than 500 nm, the interference coloring occurs due to the reflected light of a plurality of particles, or the film becomes brittle and peels off easily, which is not preferable. Further, the crystallized fine particles in the film can be distinguished by the shape such as grain boundaries even if they are in contact with other fine particles or the film.

On the other hand, one layer of the above-mentioned crystallized fine particle constituent film,
The preferred thickness range depends on the size of the base particles. 0.05 μ when the base particles are 0.1 μm to 1 μm
.mu.m to 0.5 .mu.m and the substrate particles are 1 .mu.m to 10 .mu.m, the value of 0.
05 μm to 2 μm, 0.0 when the substrate particles are 10 μm or more
It is preferably 5 μm to 3 μm. Further, the preferable thickness range of the total film thickness of the crystallized fine particle constituent film also differs depending on the size of the particles serving as the substrate. Base particle is 0.1μ
m-1 μm, 0.1 μm-3 μm, base particles 1 μm
10 μm to 0.1 μm to 5 μm, the base particles are 10 μm
When it is m or more, it is preferably 0.1 μm to 10 μm.

Further, as shown in FIG. 2, the yellow-colored powder of the present invention has ultrafine particles 4 capable of closing the voids on the surface of the film 2 composed of crystallized fine particles 3 having voids. It is preferable to have a dense coating film (hereinafter also simply referred to as a dense film) configured by. For example, when the yellow powder having the above-mentioned crystallized fine particle constituting film as the outermost layer is used as the pigment powder such as toner or paint, the resin of the toner or the vehicle of the paint enters into the voids and the crystallized fine particles are generated. The difference in the refractive index between the surface of 3 and the voids is reduced to weaken the scattered reflection of light, and as a result, the brightness is also reduced. The dense film described above is suitable for preventing the decrease in brightness as described above.

Japanese Patent Application Laid-Open No. 4-269804 discloses a colored powder having a coating layer of inorganic pigment particles on the surface.
It is filled with a mixture of a surface treatment agent and a resin, and unlike the yellow powder of the present invention, does not cause scattered reflection, but is colored to a desired color by the color of the pigment particles themselves. is there. Moreover, this Japanese Patent Laid-Open No. 4-26
In the colored powder described in Japanese Patent Publication No. 9804, the pigment particles may not be sufficiently fixed on the surface of the base particles. In that case, the pigment particles adhering to the substrate are separated in the mixed liquid of the solvent and the resin, so that they may not be applicable to paints and the like.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The yellow color powder of the present invention will be described in detail below. The yellow-colored powder of the present invention is a multi-layered film-coated powder which further has, on the surface of the base particles, not only the above-mentioned crystallized fine particle-constituting film but also a film consisting of other components capable of transmitting light. As the light-transmitting coating film having a low refractive index, when the metal hydroxide film or the metal oxide film is formed into a plurality of layers by the reaction of a metal salt or the like, the above-mentioned coating film (coating the base particles A special function can be given by adjusting the thickness of each layer (the layer of the film that participates in optical interference). For example, an alternating coating film having a different refractive index is provided on the surface of the base particles so as to satisfy the following formula (1):
Providing an appropriate thickness and number of alternating films having a thickness d corresponding to an integer m times a quarter of the wavelength of visible light lying between 550 and 850 nm and the refractive index n of the material forming the coating, 5
Light of wavelength λ between 50 and 850 nm (using Fresnel interference reflection) is reflected or absorbed. nd=mλ/4 (1)

Utilizing this action, a film having a film thickness and a refractive index satisfying the formula (1) for the target wavelength of 550 to 850 nm is formed on the surface of the substrate particles, Furthermore, by coating a film having a different refractive index on it once or more alternately, 5
A film having a reflection peak between 50 and 850 nm is formed. At this time, the order of the materials for film formation is determined as follows. First, when the refractive index of the core substrate is high, the first layer is preferably a film having a low refractive index, and in the opposite case, the first layer is preferably a film having a high refractive index.

The film thickness is measured by controlling a change in optical film thickness, which is a product of film refractive index and film thickness, as a reflection waveform with a spectrophotometer or the like. Design the film thickness of each layer. For example, if the peak position of the reflection waveform of each unit coating film forming the multilayer film is precisely adjusted to the range of 550 to 850 nm, a yellow-based monochromatic colored powder can be obtained without using a dye or a pigment.

However, in the case of an actual substrate, the particle size of the substrate,
It is necessary to design considering the shape, the phase shift at the interface between the film substance and the substrate particle substance, and the peak shift due to the wavelength dependence of the refractive index. For example, when the shape of the substrate particles is a parallel plate shape, the Fresnel interference due to the parallel film formed on the particle plane is designed under the condition that n in the above formula (1) is replaced with N in the following formula (2). To do. In particular, when the metal film is included even when the substrate has a parallel plate shape, the attenuation coefficient κ is included in the refractive index N of the metal of the formula (2). In the case of a transparent oxide (dielectric), κ is very small and can be ignored. N=n+iκ (i represents a complex number) (2) If this attenuation coefficient κ is large, the phase shift at the interface between the film substance and the substrate substance becomes large, and further, interference due to the phase shift occurs in all layers of the multilayer film. Affects optimum film thickness.

As a result, the peak position shifts even if only the geometrical film thickness is adjusted, and the color becomes light, especially when coloring in the yellow color system. In order to prevent this, the effect of the phase shift on all films is taken into consideration, and it is designed in advance by computer simulation to optimize the combination of film thicknesses. Furthermore, there is a phase shift due to the oxide layer on the surface of the substrate and a peak shift due to the wavelength dependence of the refractive index. To correct these, use a spectrophotometer, etc.
The reflection peak is the target wavelength and the target wavelength is 550 to 8
It is necessary to find the optimum conditions for the range of 50 nm.

The interference of a film formed on a curved surface such as spherical powder occurs similarly to a flat plate, and basically follows the Fresnel's interference principle. Therefore, the coloring method can also be designed in the yellow color system. However, in the case of a curved surface, the incident angle of light to each film, the reflection angle, the curvature of each film, etc. are different and a phase shift occurs accordingly, and the light incident on the powder and causing a complex interference .. These interference waveforms are almost the same as the flat plate when the number of films is small. However, as the total number increases, the interference inside the multilayer becomes more complicated. Also in the case of a multilayer film, the reflection spectral curve can be designed in advance by computer simulation so as to optimize the combination of film thicknesses based on Fresnel interference. In particular, in the case of forming a film on the surface of the base particles, the influence of the phase shift on the surface of the base particles and all the films is taken into consideration, and the combination of the film thicknesses is optimized in advance by computer simulation. Furthermore, the peak shift due to the oxide layer on the surface of the substrate particles and the peak shift due to the wavelength dependence of the refractive index are taken into consideration.
In actual sample production, refer to the designed spectral curve,
In order to correct these in the actual film, the reflection peak in a spectrophotometer or the like is 550 to 850 nm as the final target film number.
Optimum conditions must be found while changing the film thickness so that the target wavelength in the range is.

Interference occurs due to the multilayer film even when the powder of irregular shape is colored, and the basic film design is carried out with reference to the conditions of the interference multilayer film of spherical powder. The peak position of each unit coating film that constitutes the above-mentioned multilayer film can be adjusted by the film thickness of each layer, and the film thickness depends on the raw material under the coating forming conditions for forming a solid phase component such as a metal oxide on the surface of the base particles. By controlling the composition, the solid phase deposition rate, the amount of substrate, etc., the film thickness can be accurately controlled, a film having a uniform thickness can be formed, and a desired yellow color system can be colored. As described above, the reflection peak and the absorption bottom are 5 in the final target film number.
By changing the film forming conditions such as the film forming solution so as to obtain the target wavelength in the range of 50 to 850 nm and finding the optimum conditions, a yellowish powder can be obtained. In addition, the color development due to the interference of the multilayer film can be adjusted by controlling the combination of the substances forming the multilayer film and the film thickness of each unit film. This allows the powder to be vividly colored in a desired yellow color system without using a dye or pigment.

The yellow powder and the method for producing the same according to the present invention will be described in detail below. In the yellow colored powder of the present invention and the method for producing the same, the base particles on which the metal oxide film or the like is formed are not particularly limited,
It may be an inorganic substance containing a metal, an organic substance, a magnetic substance, a dielectric substance, a conductor or an insulator. If the substrate is metal, iron, nickel, chromium, titanium, aluminum, etc.
Although any metal may be used, when utilizing its magnetism, it is preferable to be magnetic such as iron. These metals may be alloys, and when they have the above magnetism, it is preferable to use a ferromagnetic alloy. Also,
When the powder substrate is a metal compound, typical examples thereof include the above-mentioned metal oxides. Examples include iron, nickel, chromium, titanium, aluminum, silicon and the like, calcium, magnesium. Oxides such as barium and barium, or composite oxides thereof may be used. Furthermore, examples of metal compounds other than metal oxides include metal nitrides, metal carbides, metal sulfides, metal fluorides, metal carbonates, metal phosphates, metal silicides, and the like.

Further, as the base particles, other than metal,
It is a semi-metal or non-metal compound, particularly an oxide, a carbide or a nitride, and silica, glass beads or the like can be used. Other inorganic substances include inorganic hollow particles such as shirasu balloon (hollow silicate particles), fine carbon hollow spheres (crecassphere), fused alumina bubbles, aerosil, white carbon, silica fine hollow spheres, calcium carbonate fine hollow spheres, Mica such as calcium carbonate, perlite, talc, bentonite, synthetic mica, muscovite, kaolin and the like can be used.

Resin particles are preferred as the organic material. Specific examples of the resin particles include cellulose powder, cellulose acetate powder, polyamide, epoxy resin, polyester, melamine resin, polyurethane, vinyl acetate resin, silicon resin, acrylic ester, methacrylic ester, styrene, ethylene, propylene and these. Examples thereof include spherical or crushed particles obtained by polymerization or copolymerization of the derivative of. Particularly preferred resin particles are spherical acrylic resin particles obtained by polymerization of acrylic acid or methacrylic acid ester.

The shape of the substrate is, for example, isotropic bodies such as spheres, subspheres, regular polyhedrons, cuboids, spheroids, rhombohedra, plates, needles (cylindrical prisms) and other polyhedrons, and further crushing. It is also possible to use a completely amorphous powder such as a thing. These substrates are not particularly limited in particle size,
It is preferably in the range of 0.01 μm to several mm. Also,
The specific gravity of the base particles used is in the range of 0.1 to 10.5, but in view of fluidity and floating property, it is 0.1 to 10.5.
It is preferably 5.5, more preferably 0.1 to 2.8. If the specific gravity of the substrate is less than 0.1, the buoyancy in the liquid is too large, and the film must be multi-layered or extremely thick, which is uneconomical. On the other hand, when it exceeds 10.5, the film for floating becomes thick, which is also uneconomical.

In the present invention, as described above, the powder base particles are coated with a plurality of coating layers having different refractive indexes, and the coating layers are coated by appropriately selecting the refractive index and the layer thickness. A powder that is colored yellow due to the interference color and exhibits a specific interference reflection peak in a region other than the visible light region can be obtained. As described above, the metal hydroxide film or the metal oxide film is deposited on the surface of the substrate particles by the reaction of the metal salt. However, a buffer solution is used as a solvent for the solid phase deposition reaction, and the solution is kept at a certain pH. Precipitate at an appropriate rate.

In the present invention, the metal used as the metal salt is iron, nickel, chromium, titanium, zinc, aluminum, cadmium, zirconium, silicon, tin, lead,
Other than lithium, indium, neodymium, bismuth, cerium and antimony, calcium, magnesium, barium and the like can be mentioned. Examples of salts of these metals include salts of sulfuric acid, nitric acid, hydrochloric acid, oxalic acid, carbonic acid and carboxylic acids. Furthermore, chelate complexes of the above metals are also included. The kind of the metal salt used in the present invention is selected according to the properties to be imparted to the surface of the substrate and the means applied in the production.

A film of a metal oxide or the like formed of these metal salts may be formed in a plurality of layers, and if necessary, a metal oxide or the like formed by hydrolysis of a metal alkoxide may be formed on the film of the metal oxide or the like. It is also possible to form a film by another film forming method. In this way, a multi-layered film can be formed on the base particles, and at that time, by setting the forming conditions so that the thickness of each layer has a predetermined thickness, the desired characteristics can be obtained. In addition, it is possible to obtain a multi-layered film of metal oxide or the like by using a metal salt which is an inexpensive raw material with a simple operation. In particular, it is an important advantage that a multi-layer film-coated powder can be obtained without using an expensive metal alkoxide as a raw material.

In the method for producing the yellow powder of the present invention, the multilayer coating film may be produced as a continuous process,
Further, each coating film can be manufactured by various methods such as manufacturing one layer at a time, or combining single-layer manufacturing and multi-layer continuous manufacturing. The particle size of the film-coated powder according to the present invention is not particularly limited and may be appropriately adjusted depending on the purpose, but is usually in the range of 0.01 μm to several mm.

In the present invention, the thickness of the metal oxide film formed at one time can be in the range of 5 nm to 10 μm, which can be made thicker than the conventional forming method. As the total thickness of the metal oxide film formed by dividing into a plurality of times, in the case of the color magnetic powder described above,
In order to form a metal oxide film having a high reflectance due to the interference, the range of 10 nm to 20 μm is preferable, and the range of 20 nm to 5 μm is more preferable.
The range of 0.02 to 2.0 μm is preferable for interference reflection of visible light with a particularly thin film thickness such as a limited particle size.

The yellow powder of the present invention is as described above.
An aqueous solvent having a constant pH is used as a film-forming reaction solvent, and at the same time, a film-coating reaction is formed by a film-forming reaction on the surface of a substrate under ultrasonic dispersion conditions. In the present invention, in order to keep the film-forming reaction constant, a buffer solution is added to an aqueous solvent to prepare a buffer solution, or a buffer solution prepared in advance is used. Further, at the time of the film forming reaction, a film raw material other than the buffer solution is added to form the film. When the film is formed by adding the film-forming raw material, if the pH changes greatly, in order to prevent this,
It is desirable to add a buffer solution. In the present invention, the constant pH means that the pH is within ±2 of a predetermined pH, preferably within ±1, and more preferably within ±0.5.

Various systems may be used for the buffer solution, and the system is not particularly limited, but first, it is important that the substrate particles can be sufficiently dispersed, and at the same time, a metal hydroxide or a metal oxide film coated on the surface of the substrate is coated. It is necessary to select the powder so that it can be dispersed by the action of the electric double layer and the condition that the dense coating film can be formed by the gentle dropping reaction described above. Therefore, the method for producing the film-coated powder of the present invention is different from the conventional method of neutralization by the reaction of a metal salt solution, deposition by the isoelectric point, or decomposition by heating to deposit.

Next, for particles that are difficult to disperse due to attraction between particles such as magnetic force, it is desirable to carry out film formation after ultrasonic irradiation and sufficiently disperse, or to form a film while performing ultrasonic irradiation. As the ultrasonic dispersion conditions, various ultrasonic oscillators can be used, for example, a water tank of an ultrasonic cleaner can be used, and there is no particular limitation. However, the conditions of the ultrasonic dispersion of the present invention vary depending on the size of the oscillator, the shape and size of the reaction vessel, the amount of reaction solution, the volume, the amount of substrate particles, etc. Appropriate conditions may be selected. The buffer solution used in the present invention depends on the solid phase component to be precipitated, and is not particularly limited, but includes Tris type, boric acid type, glycine type, succinic acid type, lactic acid type, acetic acid type, tartaric acid type, hydrochloric acid. A system etc. are mentioned.

Next, as an example, a method of forming an alternating multilayer film of a metal oxide having a high refractive index and a metal oxide having a low refractive index will be specifically described. First, when forming a film of titanium oxide or zirconium oxide, the base particles are immersed in a buffer solution of acetic acid/sodium acetate or the like and dispersed by ultrasonic oscillation, and titanium sulfate that is a metal salt of titanium or zirconium is , Zirconium sulfate or the like as a raw material, an aqueous solution of these metal salts is slowly dropped into the reaction system,
It can be carried out by depositing the produced metal hydroxide or metal oxide around the base particles. During this dropping reaction, the pH is maintained at the pH of the buffer solution (5.4). After the reaction is completed, this powder is subjected to solid-liquid separation, washed and dried, and then heat treated. Vacuum drying as the drying means,
Any of natural drying may be used. It is also possible to use a device such as a spray dryer in an inert atmosphere. In addition,
When the film to be coated is titanium oxide, the formation of titanium oxide is shown by the following reaction formula. Ti(SO ₄ ) ₂ +2H ₂ O → TiO ₂ +4H ₂ (SO
_{4) 2} TiO ₂ content of titanyl sulfate is 5 g / liter to 18
It is preferably 0 g/liter, more preferably 10 g/liter to 160 g/liter. If it is less than 5 g/l, it takes a long time to form a film, and the amount of powder to be processed is reduced, which is uneconomical. If it exceeds 180 g/l, the diluent causes hydrolysis during addition and does not become a film forming component. , Both are unsuitable.

Subsequently, when forming a film of silicon dioxide or aluminum oxide, KCl/H ₃ BO ₃
The above titania-coated particles are dipped and dispersed in a buffer solution in which NaOH is added to the system, and sodium silicate, which is a metal salt of silicon or aluminum, or aluminum chloride is used as a raw material, and an aqueous solution of these metal salts is reacted. It can be carried out by slowly dropping it into the system and depositing the produced metal hydroxide or metal oxide around the base particles. During the dropping reaction, the pH is the pH of the buffer solution.
It is held at (9.0). After the reaction is completed, this powder is subjected to solid-liquid separation, washed and dried, and then heat treated. By this operation, by repeating the operation of forming two layers of metal oxide films having different refractive indexes on the surface of the base particles, powder having a multi-layer metal oxide film on the surface thereof can be obtained. In addition,
When the film to be coated is silicon dioxide, the formation of silicon dioxide is shown in the reaction scheme below. Na ₂ Si _X O _2X+1 +H ₂ O → XSiO ₂ +2Na ⁺ +
2OH ^-

Next, the yellow powder of the present invention has
The crystallized fine particle constituting film may be made of any substance as long as it can scatter and reflect light and increase the brightness, but it is preferably made of a substance having a high refractive index. The substance having a high refractive index is not particularly limited, but oxides such as titanium oxide (titania), zirconium oxide, bismuth oxide, cerium oxide, antimony oxide, and indium oxide can be used, have a high refractive index, and are widely used. Most preferred is titanium oxide (titania).

As a method for forming the crystallized fine particle constituting film as described above, a method of solid phase precipitation in a film forming reaction liquid phase is used. Specifically, the inventors of the present invention have previously proposed JP-A-6-228604 and JP-A-7-903.
No. 10 and WO 96/28269, the solid phase deposition method (metal alkoxide method) by hydrolysis of metal alkoxide in an organic solvent, and the specification attached to Japanese Patent Application No. 9-298717. The solid phase precipitation method (aqueous method) by the reaction from the metal salt in the aqueous solution described in 1) and the like can be mentioned. In this case, in the film-forming reaction solution, the rate at which the solid phase fine particles are deposited in the reaction solution is higher than the rate at which the film of the deposits grows on the surface of the substrate particles (linear growth rate).
The reaction solution concentration, the added catalyst amount, and the base particle dispersion amount are adjusted. As described above, the solid phase fine particles deposited in the film forming reaction solution are adhered to the surfaces of the base particles to form a coating film composed of the solid phase fine particles.

At this point, the solid phase fine particles incorporated into the film are amorphous, voids between the solid phase fine particles are not formed, no scattering and reflection of light occurs, and the mechanical strength of the film is low. Is also very low. Therefore, the coating film composed of the solid phase fine particles is fired. By this firing, the amorphous solid phase fine particles are crystallized, and voids are also formed between the crystallized fine particles to form the crystallized fine particle constituent film that scatters and reflects the light.

In order to form the crystallized fine particle constituent film, the aqueous method is easier than the above-mentioned metal alkoxide method to make the relationship between the linear growth rate and the solid phase deposition rate preferable. Therefore, it is preferable. Further, the metal alkoxide method requires an expensive metal alkoxide as a raw material and a relatively expensive and dangerous organic solvent as a reaction solvent. For this reason, the manufacturing equipment, equipment, etc. must be explosion-proof specifications, and the cost performance becomes worse. From this point as well, the aqueous method is preferable to the metal alkoxide method.

The firing may be carried out after forming a coating film composed of the solid phase fine particles, and the coating film is further formed on the coating film as a crystallized fine particle constituting film. In that case, it is desirable from the viewpoint of the film strength of the obtained yellow-colored powder to carry out after coating with ultrafine particles capable of forming a dense film for closing the voids on the surface. Firing is 300
It is preferable to carry out at about 1200°C.

In addition to the method of forming ultrafine particles that scatter and reflect visible light in a liquid by adjusting the solid phase deposition rate, existing particles can be used. That is, in the buffer solution, the base particles and the crystallized ultrafine particles of silica or titania are sufficiently dispersed uniformly in the buffer solution, and then a solution of the raw material for coating the film such as silica or titania on the surface is dropped. , By optimizing the solid phase deposition rate so that only the film is formed, the solid phase films deposited on the surfaces of both the base particles and the crystallized ultrafine particles adhere to each other during stirring, and the base particles are Covered with crystallized ultrafine particles.

The powder thus formed is 300 to 1
By firing at 200° C., the particles of the crystallized ultrafine particles are covered with a film (particles having a fine particle film), the scattering ultrafine particles have a high refractive index, and the particle size of the visible light scattering ultrafine particles is The particle size is preferably such that the scattering power is maximized. Especially in titania, 0.2 to 0.3 μm
The particle size is preferably. When the refractive index of the substrate particles is smaller than that of the crystallized ultrafine particles, a film having a high refractive index is directly formed on the substrate particles, or after the outermost layer is formed into a film having a high refractive index, the fine particle film is formed. You may form. On the contrary, if the refractive index of the base particles is larger than that of the crystallized ultrafine particles, the fine particle film is formed of a film having a low refractive index. In that case, the outermost layer of the base particles is also a low refractive index film. Is preferred to maximize scatter.

In the yellow powder of the present invention, the crystallized fine particle constituting film may have two or more layers. In that case, it is preferable that a light-transmitting coating film having a low refractive index is present between the two layers of the crystallized fine particle constituent films. The light-transmitting coating film having a low refractive index is not particularly limited, and examples thereof include those made of metal compounds, organic substances and the like.

Examples of the metal compound include metal oxides, metal sulfides, metal selenides, metal tellurides, and metal fluorides. More specifically, zinc oxide, aluminum oxide, cadmium oxide, titanium oxide,
Zirconium oxide, tantalum oxide, silicon oxide, antimony oxide, neodymium oxide, lanthanum oxide, bismuth oxide, cerium oxide, tin oxide, magnesium oxide, lithium oxide, lead oxide, cadmium sulfide, zinc sulfide, antimony sulfide, cadmium selenide, tellurium. Cadmium chloride, calcium fluoride, sodium fluoride, trisodium aluminum fluoride, lithium fluoride, magnesium fluoride and the like can be preferably used.

The method for forming the metal compound film will be described below. As a film forming method, a vapor deposition method such as a PVD method, a CVD method or a spray drying method can be used to directly deposit the particles on the surface of the base particles. However, the above-mentioned Japanese Patent Laid-Open No. 6-22 proposed by the present inventors has been proposed.
The metal alkoxide method described in 8604, JP 7-90310 A or WO 96/28269, and the aqueous method described in Japanese Patent Application No. 9-298717 are preferable. In this case, unlike the film formation of the crystallized fine particle constituent film described above, the linear growth rate is set higher than the solid phase deposition rate, and the reaction conditions are adjusted so that an amorphous uniform film is formed.

The organic substance is not particularly limited, but is preferably a resin. Specific examples of the resin include cellulose, cellulose acetate, polyamide, epoxy resin, polyester, melamine resin, polyurethane, vinyl acetate resin, silicon resin, acrylic ester, methacrylic ester, styrene, ethylene, propylene and derivatives thereof. Examples thereof include polymers and copolymers. (1) When forming an organic material film (resin film), a. A method of forming a resin film on the particles by dispersing the base particles in a liquid phase and performing emulsion polymerization (polymerization method in the liquid phase); b. Film forming method in vapor phase (CVD)
(PVD) or the like is adopted.

An example of producing a yellow-colored powder of the present invention having a multi-layered film on base particles is shown below. For example, if the base particles are made of a substance having a high refractive index, a light-transmitting film having a low refractive index is provided thereon,
Further, a high-refractive-index particle constituent film is further provided thereon, and a low-refractive-index light-transmitting film is further provided thereon in sequence and alternately. If the base particles have a low refractive index, a high refractive index particle constituent film is formed thereon, a low refractive index light-transmissive film is formed thereon, and a high refractive index particle constituent film is formed thereon. And sequentially provide.

Next, the raw materials used in the present invention, especially the metal salt, will be explained. As a raw material used for forming a film having a high refractive index, titanium oxide film, titanium halide, sulfate, etc., zirconium oxide film,
Zirconium halide, sulfate, carboxylate,
For cerium oxide film such as oxalate and chelate complex,
Cerium halides, sulfates, carboxylates, oxalates, etc. For bismuth oxide films, bismuth halides, nitrates, carboxylates, etc., for indium oxide films, indium halides, sulfates, etc. Etc. are preferred.
Further, as a raw material used for forming a film having a low refractive index, for a silicon oxide film, sodium silicate, water glass, a halide of silicon, an organosilicon compound such as an alkyl silicate and a polymer thereof, etc. , For aluminum oxide film,
For magnesium oxide films such as aluminum halides, sulfates and chelate complexes, magnesium sulfates and halides are preferred. In the case of a titanium oxide film, for example, mixing titanium chloride with titanium chloride has the effect of forming a rutile-type titanium oxide film having a high refractive index at a lower temperature.

A more complete oxide film can be manufactured by controlling the reaction temperature at the time of coating so as to be suitable for the kind of each metal salt. When the film forming reaction (solid layer deposition reaction) on the surface of the substrate in the aqueous solvent is too slow, the reaction system can be heated to accelerate the solid layer deposition reaction. However, if the heat treatment for heating is excessive, the reaction rate is too fast, and the supersaturated solid layer does not form a film but precipitates in an aqueous solution to form gel or fine particles, which makes it difficult to control the film thickness.

After the coating film is manufactured, the gradient washing is repeated while adding distilled water to remove the electrolyte, and then heat treatment such as drying and firing is performed to remove the water contained in the solid phase to completely remove the electrolyte. It is preferable to use an oxide film. Further, by heat-treating the powder after film formation in a rotary tube furnace or the like, sticking can be prevented and dispersed particles can be obtained. To form a hydroxide film or an oxide film and heat-treat it, heat treatment may be performed every time each layer is coated, or heat treatment may be performed last after the target multilayer film is completed. The heat treatment conditions vary depending on the reaction system, but the heat treatment temperature is 200 to 1300° C., preferably 400 to
It is 1100°C. If the temperature is lower than 200°C, salts and water may remain, and if the temperature is higher than 1300°C, the film and the substrate may react with each other to become another substance, both of which are unsuitable. The heat treatment time is 0.1 to 100 hours, preferably 0.5 to 50 hours.

[0056]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited by these examples. [Example 1] (Yellow colorization of magnetite powder particles,
Aqueous two-layer coating) (Formation of first-layer silica film) (1) Preparation of buffer solution In 1 liter of water, 0.4M potassium chloride reagent and 0.4M boric acid are dissolved to prepare buffer solution. It was set to 1. 0.4 M sodium hydroxide was dissolved in 1 liter of water to prepare buffer solution 2. 250 ml of the buffer solution 1 and 115 ml of the buffer solution 2 were mixed and homogenized to prepare buffer solution 3. (2) Aqueous sodium silicate solution (water glass solution) A sodium silicate reagent is diluted with pure water to obtain Na ₂ SiO ₃
The concentration was adjusted so that the content was 10 wt %.

(3) Silica film 50 g of spherical magnetite powder (average particle size 2.3 μm)
2,200 ml of the previously prepared buffer solution
Put it in a mixed solution of 770 ml of pure water and 28 kHz, 60
Ultrasonic waves are applied in a 0 W ultrasonic bath, and further dispersed in a buffer solution containing magnetite powder with stirring. To this was added 670 ml (40 ml/min) of an aqueous sodium silicate solution prepared in advance, and the reaction was gradually decomposed to deposit a silica film on the surface. After the addition of the aqueous sodium silicate solution was completed, the reaction was continued for another 2 hours to react all unreacted raw materials. After the film formation reaction,
The slurry containing the silica film powder is repeatedly decanted with sufficient water and washed. After washing, the silica film-forming powder was put in a vat, separated by sedimentation, the upper liquid was discarded, and then dried in a dryer at 150° C. for 8 hours to obtain a silica-coated magnetite powder A ₁ . Obtained silica-coated magnetite powder A
_The film thickness of the silica coating film of ₁ was 109 nm.

(Formation of second layer titania film) (1) Preparation of buffer solution 0.3 M acetic acid, 0.
9M sodium acetate was dissolved to give buffer solution 4. (2) Titanium Sulfate Aqueous Solution Titanium sulfate was added with water so that the concentration of TiO _{2 in} the aqueous solution was 12 g/liter, and dissolved to prepare a titanium sulfate aqueous solution.

(3) Titania film formation: To 4.0 g of A ₁ obtained, 220 ml of a buffer solution was prepared, and while A ₁ was ultrasonically dispersed in the solution, it was sufficiently dispersed in an ultrasonic dispersion tank. Thereafter, while maintaining the temperature of the liquid at 50° C. to 55° C., 65 ml of a titanium sulfate aqueous solution prepared in advance was gradually added dropwise at 0.5 (ml/min). After the dropping, the reaction was continued for 3 hours to deposit the unreacted titania raw material. Then, the solid phase fine particles deposited in the liquid are fixed on the surface A ₁ of the base particle, and further, the surface is covered with the ultrafine particles having a smaller particle size than the solid phase fine particles fixed on the surface of the base particle. It was

(4) Washing and Drying After completion of the film formation reaction, decantation with pure water was performed to remove unreacted components, excess sulfuric acid and sulfuric acid formed by the reaction,
Solid-liquid separation was performed, and after drying with a vacuum dryer, dried powder was obtained.
The obtained dry powder is heated in a rotary tube furnace at 650° C. for 3 hours.
By performing overheat treatment (calcination) for 0 minutes, silica/titania-coated magnetite powder A ₂ having a smooth surface was obtained. The two-layer film-coated powder A ₂ is yellow and its magnetization at 1 kOe is 38e.
It was mu/g. The thickness of the titania coating film of the obtained silica/titania-coated magnetite powder A ₂ was 65 nm. The reflection peak of this two-layer film coating was 598 nm, and the reflectance at that peak wavelength was 40%. Table 1 shows each refractive index, the film thickness, the peak wavelength of the spectral reflection curve of the coated powder and the reflectance at the peak wavelength of the first and second layers. Table 2 shows the measured values of the final coated powder in the L ^* , a ^* , and b ^* standard color system.

[0061]

[Table 1]

[0062]

[Table 2]

The peak wavelength of the spectral reflection curve of the coating powder of the coating film, the reflectance at that peak wavelength, the refractive index of the coating film, the film thickness and the L ^* , a ^* , b ^* standard color system. The value of was measured by the following method. 1) As for the spectral reflection curve, a powder sample was packed in a glass holder with a spectrophotometer with an integrating sphere manufactured by JASCO Corporation, and the reflected light was measured. The measuring method was according to JIS Z8723 (1988). 2) The refractive index and the film thickness were evaluated by obtaining the spectral reflection curve measurement results of the samples having different film thicknesses prepared under different conditions by fitting with the curve of the instrument calculation based on the interference equation. 3) L ^* , a ^* , and b ^* values are TC-8 manufactured by Tokyo Denshoku Co., Ltd.
Using a 600A type colorimetric color difference meter, JISZ8722 (19
The results of color measurement based on 82) are displayed in the L ^* , a ^* , b ^* standard color system defined by CIE (International Association for Certification).

[Example 2] (Yellow coloring of magnetite powder particles, water-based three-layer coating) (1st layer silica film formation) As in Example 1, buffer solutions 1 and 2 and an aqueous sodium silicate solution (water Glass solution)
Was prepared. (1) Silica film 15 g of spherical magnetite powder (average particle size 2.3 μm)
Put in 680 ml of buffer solution prepared in advance,
Ultrasonic waves are applied in an ultrasonic bath of 26 kHz and 600 W, and further dispersed in a buffer solution containing magnetite powder with stirring. Similarly, 203 ml of an aqueous sodium silicate solution prepared in advance (40 ml/
Min) and gradually decomposed by reaction to deposit a silica film on the surface. After the addition of the aqueous sodium silicate solution was completed, the reaction was continued for another 2 hours to react all unreacted raw materials. After the film forming reaction is completed, the slurry containing the silica film forming powder is repeatedly decanted with sufficient water and washed. After washing, put the silica film powder in a vat, settle and separate, discard the upper liquid, then dry in a dryer at 150°C for 8 hours in air, heat treat at 500°C for 30 minutes in a nitrogen atmosphere, and coat with silica. Magnetite powder B ₁ was obtained.

(Second Layer Titania Film Forming) (1) Titania Film Forming In the same manner as in Example 1, the buffer solution 4 and the titanium sulfate aqueous solution were prepared and prepared in advance. Obtained B ₁ ,
To 4.0 g, 250 ml of buffer solution and 250 ml of pure water
And ultrasonically dispersing B ₁ in the solution, and thoroughly dispersing in an ultrasonic dispersion tank, and then maintaining the temperature of the solution at 60° C., 67 g of an aqueous titanium sulfate solution prepared in advance. Is gradually added dropwise at a constant rate of 1.5 ml/min. At the time of dropping, fine particles in the liquid were initially deposited, but were fixed on the surface of the core powder, and the surface was covered with the deposited fine particles having a particle size of 0.01 to 0.5 micron.

(2) Washing and Drying After completion of the film forming reaction, decantation with pure water was performed to remove unreacted components, excess sulfuric acid and sulfuric acid formed by the reaction,
Solid-liquid separation was performed, and after drying with a vacuum dryer, dried powder was obtained.
The obtained dry powder is heated in a rotary tube furnace at 650° C. for 3 hours.
By performing overheat treatment (calcination) for 0 minutes, silica/titania-coated magnetite powder B ₂ was obtained. The color of B ₂ obtained was red-white, and the reflection peak of this two-layer film coating was 722 nm. The surface of this B ₂ was slightly uneven, and a convex portion of titania fine particles was also partially seen.

(Formation of third layer silica film) (when the surface of the film is enclosed by a silica thin film) As in Example 1, buffer solutions 1 and 2 and an aqueous sodium silicate solution (water glass solution) were prepared in advance. It was (1) Silica film formation 15 g of titania/silica-coated powder B ₂ was added to 80 ml of a buffer solution prepared in advance, the dropping rate of the silica raw material solution was the same as in the case of the first layer coating, and the dropping amount was changed. A film was formed at 19 ml and reacted for 2 hours until there were no unreacted substances. After the film forming reaction is completed, the slurry containing the silica film forming powder is repeatedly decanted with sufficient water and washed. After washing, put the silica film powder in a vat, separate it by sedimentation, discard the upper liquid, and dry it in air in a dryer.
Dry at 50°C for 8 hours, and then in a nitrogen atmosphere at 500°C for 30 hours.
It was heat treated for minutes to obtain a silica-coated magnetite powder B ₃ . This three-layer film-coated powder B ₃ was pale yellow, and its magnetization at 1 kOe was 34 emu/g. The thickness of the titania coating film of the obtained silica/titania-coated magnetite powder B ₃ was 72 nm. The reflection peak of this three-layer film coating is 60
It was 4 nm and the reflectance at the peak wavelength was 47%. Table 3 shows each refractive index, the film thickness, the peak wavelength of the spectral reflection curve of the coated powder and the reflectance at the peak wavelength of the first to third layers. In addition, L ^* , a ^* , b of the final coated powder
^* Table 2 shows the measured values in the standard color system.

[0068]

[Table 3]

[Example 3] (Yellow coloring of magnetite powder particles, water-based 4-layer coating) (First layer silica film formation) As in Example 1, buffer solutions 1, 2 and 3 and an aqueous solution of sodium silicate were prepared. (Water glass solution) was prepared. (1) Silica film 40 g of granular (octahedral-like) magnetite powder (average particle size 0.7 μm) was placed in a previously prepared mixed solution of 1,460 ml of buffer solution and 500 ml of pure water, and 2
Ultrasonic waves are applied in an ultrasonic bath of 8 kHz and 600 W, and further dispersed in a buffer solution containing magnetite powder with stirring. 400 ml of an aqueous sodium silicate solution (40 ml/
Min) and gradually decomposed by reaction to deposit a silica film on the surface. After the addition of the aqueous sodium silicate solution was completed, the reaction was continued for another 2 hours to react all unreacted raw materials. After the film forming reaction is completed, the slurry containing the silica film forming powder is repeatedly decanted with sufficient water and washed. After washing, the silica film-forming powder was placed in a vat, separated by sedimentation, and the upper liquid was discarded, followed by drying in a dryer at 150° C. for 8 hours to obtain silica-coated magnetite powder C ₁ .

(Formation of second layer titania film) Buffer solution 4 was prepared and prepared in the same manner as in Example 1. (1) Titanium Sulfate Aqueous Solution Water was added to titanium sulfate so that the concentration of TiO _{2 in} the aqueous solution was 60 g/liter, and the solution was prepared to give a titanium sulfate aqueous solution. (2) Titania Film Preparation 500 ml of a buffer solution was prepared for 20 g of C ₁ obtained, and while C ₁ was ultrasonically dispersed in the solution, the temperature of the liquid was sufficiently dispersed in an ultrasonic dispersion tank. While maintaining the temperature at 40°C to 50°C, 220 ml of an aqueous titanium sulfate solution prepared in advance was gradually added dropwise at 0.5 (ml/min). At the same time, 32 ml of 1.0 mol/liter titanium sulfate aqueous solution prepared in advance was added at a dropping rate (0.5 ml/liter).
min) was gradually added dropwise. After the dropping, the reaction was continued for 3 hours to deposit the unreacted titania raw material. (2) Washing and drying By decanting with pure water to remove unreacted components, excess sulfuric acid and sulfuric acid formed by the reaction, solid-liquid separation is performed,
After drying with a vacuum dryer, a dry powder was obtained. The obtained dry powder was subjected to a heat treatment at 650° C. for 30 minutes in a rotary tube furnace to obtain silica-titania-coated magnetite powder C ₂ having a substantially smooth surface. The two-layer film-coated powder C ₂ was yellow and its magnetization at 1 kOe was 38 emu/g.
The reflection peak of this two-layer film coating was 672 nm.

(Formation of third layer silica film) Powder silica/
Titanium-coated magnetite powder C _{2 (} 15 g) was placed in a previously prepared mixed solution of 600 ml of buffer solution and 200 ml of pure water, and ultrasonic waves were applied in an ultrasonic bath of 28 kHz and 600 W, and a buffer containing magnetite powder was further added. Disperse in solution with stirring. The sodium silicate aqueous solution 160 which was also prepared in advance
ml (40 ml/min) to gradually decompose the reaction,
A silica film was deposited on the surface. After the addition of the aqueous sodium silicate solution was completed, the reaction was continued for another 2 hours to react all unreacted raw materials. After completion of the film forming reaction, the slurry containing the silica/titania film forming powder is repeatedly decanted with sufficient water and washed. After washing, put the silica film powder in a vat, separate it by sedimentation, discard the upper liquid, and dry it in air in a dryer.
It was dried at 50° C. for 8 hours to obtain silica/titania-coated magnetite powder C ₃ .

(Formation of Fourth Layer Titania Film) A buffer solution 4 similar to that of Example 1 and a 60 g/liter titanium sulfate aqueous solution similar to that of the above second layer were prepared and prepared in advance. (1) Titania film formation To 20 g of C ₃ obtained, 510 ml of a buffer solution was prepared, and while C ₃ was ultrasonically dispersed in the solution, it was sufficiently dispersed in an ultrasonic dispersion tank, and then the temperature of the liquid While maintaining the temperature at 40°C to 50°C, 220 ml of an aqueous titanium sulfate solution prepared in advance was gradually added dropwise at 0.5 (ml/min). At the same time, 36 ml of a 1.0 mol/liter solution prepared in advance was gradually added dropwise at (0.5 ml/min). After the dropping, the reaction was continued for 3 hours to deposit the unreacted titania raw material.

(Washing/Drying) By decantation with pure water, unreacted components, excess sulfuric acid and sulfuric acid formed by the reaction were removed, solid-liquid separation was performed, and dried in a vacuum dryer to obtain a dry powder. The resulting dry powder was placed in a rotary tube furnace for 6
Superheat treatment was performed at 50° C. for 30 minutes to obtain silica/titania-coated magnetite powder C ₄ having a substantially smooth surface. This four-layer film-coated powder C ₄ was yellow and its magnetization at 1 kOe was 17 emu/g. The thickness of the titania coating film of the obtained silica/titania-coated magnetite powder C ₄ was 65 n.
It was m. The reflection peak of this 4-layer film coating is 598 nm.
And the reflectance at that peak wavelength was 50%.
Table 4 shows the respective refractive indexes, the film thicknesses, the peak wavelengths of the spectral reflection curves of the coated powders and the reflectances at the peak wavelengths of the first to fourth layers. In addition, L ^* , a ^* , b ^{* of} the final coated powder C ₄
Table 2 shows the measured values in the standard color system.

[0074]

[Table 4]

[Example 4] (Yellow coloring of magnetite powder particles, coating with 5 layers of water system) (Formation of first layer silica film) A buffer solution was prepared in the same manner as in Example 1. (1) Silica film 50 g of granular (octahedral) magnetite powder (average particle size: 0.7 micron) was placed in a previously prepared mixed solution of buffer solution 1, 460 ml and pure water 500 ml, and 2
Ultrasonic waves are applied in an ultrasonic bath of 8 kHz and 600 W, and further dispersed in a buffer solution containing magnetite powder with stirring. 400 ml of an aqueous sodium silicate solution (40 ml/
Min) and gradually decomposed by reaction to deposit a silica film on the surface. After the addition of the aqueous sodium silicate solution was completed, the reaction was continued for another 2 hours to react all unreacted raw materials. After the film forming reaction is completed, the slurry containing the silica film forming powder is repeatedly decanted with sufficient water and washed. After washing, the silica film-forming powder was put in a vat, separated by sedimentation, and the upper liquid was discarded, followed by drying in a dryer at 150° C. for 8 hours to obtain silica-coated magnetite powder D ₁ .

(Formation of second layer titania film) A buffer solution 4 similar to that in Example 1 and a 60 g/liter titanium sulfate aqueous solution similar to Example 3 were prepared and prepared in advance. (1) Titania film formation 830 ml of a buffer solution was prepared for 20 g of D ₁ obtained, and while ultrasonically dispersing D ₁ in the solution, sufficiently disperse in an ultrasonic dispersion tank and then the temperature of the liquid. While maintaining the temperature at 55°C to 60°C, 235 ml of an aqueous titanium sulfate solution prepared in advance was gradually added dropwise at 0.5 (ml/min). At the same time, 33 ml of a 1.0 mol/liter solution prepared in advance was gradually added dropwise at (0.5 ml/min). After the dropping, the reaction was continued for 3 hours to deposit the unreacted silica raw material on the surface of D ₁ . (2) Washing and drying By decanting with pure water to remove unreacted components, excess sulfuric acid and sulfuric acid formed by the reaction, solid-liquid separation is performed,
After drying with a vacuum dryer, a dry powder was obtained. The obtained dry powder was subjected to a heat treatment at 650° C. for 30 minutes in a rotary tube furnace to obtain silica/titania-coated magnetite powder D ₂ having a substantially smooth surface. This two-layer film coating was pale yellow and its magnetization at 1 kOe was 36 emu/g. This 2
The reflection peak of the layer coating was 647 nm.

(Third layer silica film formation) 37 g of silica/titania-coated magnetite powder D ₂ was placed in a previously prepared mixed solution of buffer solution 1, 460 ml and pure water 500 ml, and ultrasonic waves of 28 kHz and 600 W were applied. Ultrasonic waves are applied in a bath and further dispersed in a buffer solution containing magnetite powder with stirring. 400 ml of sodium silicate aqueous solution prepared in advance
(40 ml/min), and the reaction was gradually decomposed to deposit a silica film on the surface. After the addition of the aqueous sodium silicate solution was completed, the reaction was continued for another 2 hours to react all unreacted raw materials. After the film forming reaction is completed, the slurry containing the silica film forming powder is repeatedly decanted with sufficient water and washed. After washing, put silica/titania film-making powder in a vat,
After separating by sedimentation and discarding the upper liquid, 150
After drying at 8° C. for 8 hours, silica/titania-coated magnetite powder D ₃ was obtained.

(Formation of fourth layer titania film) Buffer solution 4 as in Example 1 and 60 g/liter titanium sulfate aqueous solution as in Example 3 were prepared and prepared in advance. (1) Titania film formation 830 ml of a buffer solution was prepared for 20 g of D ₃ obtained, and while thoroughly dispersing D ₃ in the solution in an ultrasonic dispersion tank, the temperature of the liquid While maintaining the temperature at 55°C to 60°C, 235 ml of an aqueous titanium sulfate solution prepared in advance was gradually added dropwise at 0.5 (ml/min). At the same time, 36 ml of a 1.0 mol/liter solution prepared in advance was gradually added dropwise at (0.5 ml/min). After the dropping, the reaction was continued for 3 hours to deposit an unreacted silica raw material on the surface of D ₃ . (4) Washing and drying By decanting with pure water to remove unreacted components, excess sulfuric acid and sulfuric acid formed by the reaction, solid-liquid separation is performed,
After drying with a vacuum dryer, a dry powder was obtained. The obtained dry powder was subjected to a heat treatment in a rotary tube furnace at 650° C. for 30 minutes to obtain a silica/titania-coated magnetite powder D ₄ having a substantially smooth surface.

(Fifth Layer Silica Film Formation) To 37 g of the magnetite powder D ₄ coated with silica/titania was added a previously prepared mixed solution of 1,460 ml of buffer solution and 500 ml of pure water, and the mixture was heated at 28 kHz and 600 W or more. Ultrasonic waves are applied in a sonic bath and further dispersed in a buffer solution containing magnetite powder with stirring. 40m of sodium silicate solution prepared in advance
1 (40 ml/min), and the reaction was gradually decomposed to deposit a silica film on the surface. After the addition of the aqueous sodium silicate solution was completed, the reaction was continued for another 2 hours to react all unreacted raw materials. After the film forming reaction is completed, the slurry containing the silica film forming powder is repeatedly decanted with sufficient water and washed. After washing, put the silica/titania film-forming powder in a vat, settle and separate, discard the upper liquid, then dry in a dryer at 150°C for 8 hours in air, and in a nitrogen atmosphere at 500°C.
Heat treatment was performed for 30 minutes to obtain silica/titania-coated magnetite powder D ₅ . The five-layer film-coated powder D ₅ is pale yellow,
The magnetization at 1 kOe was 16 emu/g. The thickness of the titania coating film of the obtained silica/titania-coated magnetite powder D ₅ was 13 nm. The reflection peak of this 5-layer film coating was 598 nm, and the reflectance at that peak wavelength was %. Table 5 shows each refractive index of each of the first to fifth layers, the film thickness, the peak wavelength of the spectral reflection curve of the coated powder, and the reflectance at the peak wavelength. Table 2 shows the measured values of the final coated powder in the L ^* , a ^* , and b ^* standard color system.

[0080]

[Table 5]

[Example 5] (Yellow coloring of magnetite powder particles, water-based 4-layer coating, use of existing titania particles) (First layer silica film formation) As in Example 1, buffer solutions 1, 2 and Aqueous sodium silicate solution (water glass solution)
Was prepared. (1) Silica film 15 g of spherical magnetite powder (average particle size 2.3 μm)
Put in 680 ml of buffer solution prepared in advance,
Ultrasonic waves are applied in an ultrasonic bath of 26 kHz and 600 W, and further dispersed in a buffer solution containing magnetite powder with stirring. Similarly, 203 ml of an aqueous sodium silicate solution prepared in advance (40 ml/
Min) and gradually decomposed by reaction to deposit a silica film on the surface. After the addition of the aqueous sodium silicate solution was completed, the reaction was continued for another 2 hours to react all unreacted raw materials. After the film forming reaction is completed, the slurry containing the silica film forming powder is repeatedly decanted with sufficient water and washed. After washing, put the silica film powder in a vat, settle and separate, discard the upper liquid, and then dry in a dryer at 150°C for 8 hours in air and heat treat at 500°C for 30 minutes in a nitrogen atmosphere to coat silica. Magnetite powder E ₁ was obtained.

(Second Layer Titania Film Forming) (1) Titania Film Forming In the same manner as in Example 1, the buffer solution 4 and the titanium sulfate aqueous solution were prepared and prepared in advance. The obtained E ₁ ,
To 4.0 g, 250 ml of buffer solution and 250 ml of pure water
67 g of titanium sulfate aqueous solution prepared in advance while maintaining the temperature of the solution at 60° C. after sufficiently dispersing E ₁ in the solution in an ultrasonic dispersion tank while ultrasonically dispersing E ₁ in the solution. Is gradually added dropwise at a constant rate of 1.5 ml/min. At the time of dropping, fine particles in the liquid were initially deposited, but were fixed on the surface of the core powder, and the surface was covered with the deposited fine particles having a particle size of 0.01 to 0.5 micron.

(2) Washing and Drying After completion of the film formation reaction, decantation with pure water was performed to remove unreacted components, excess sulfuric acid and sulfuric acid formed by the reaction,
Solid-liquid separation was performed, and after drying with a vacuum dryer, dried powder was obtained.
The obtained dry powder is heated in a rotary tube furnace at 650° C. for 3 hours.
By performing overheat treatment (calcination) for 0 minutes, silica/titania-coated magnetite powder E ₂ was obtained. The color of E ₂ obtained was red-white, and the reflection peak of this two-layer film coating was 722 nm. The surface of this E ₂ was slightly uneven, and a convex portion of titania fine particles was also partially seen.

(Third-layer silica dense film formation) (when the film surface is confined by a silica thin film) As in Example 1, buffer solutions 1 and 2 and an aqueous sodium silicate solution (water glass solution) were prepared in advance. went. (1) Silica film formation Titania/silica-coated powder E _{2 (} 15 g) was placed in 80 ml of a buffer solution prepared in advance, the dropping rate of the silica raw material solution was the same as in the case of the first layer coating, and the dropping amount was changed. A film was formed with a volume of 19 ml, and reacted for 2 hours until there were no unreacted substances. After the film forming reaction is completed, the slurry containing the silica film forming powder is repeatedly decanted with sufficient water and washed. After washing, put the silica film powder in a vat, separate it by sedimentation, discard the upper liquid, and dry it in air in a dryer.
Dry at 50°C for 8 hours, and then in a nitrogen atmosphere at 500°C for 30 hours.
It was heat treated for minutes to obtain silica-coated magnetite powder E ₃ . This three-layer film-coated powder E ₃ was pale yellow and its magnetization at 1 kOe was 38 emu/g. The thickness of the titania coating film of the obtained silica/titania-coated magnetite powder E ₃ was 72 nm. The reflection peak of this three-layer film coating is 60
It was 4 nm and the reflectance at the peak wavelength was 47%.

(Fourth Layer Crystallized Fine Particle Constitution Film (Scattering Film)
Film-forming) A buffer solution 4 and an aqueous titanium sulfate solution were prepared and prepared in the same manner as in Example 1. To 10 g of the obtained E _{3, 7} g of titanium oxide crystal ultrafine particles (CR-5 manufactured by Ishihara Sangyo Co., Ltd.) was added to 800 g of the solution 3 described above.
It was added to ml and well dispersed. The container containing this suspension is placed in a water tank of a 200 W, 28 kHz ultrasonic cleaning tank (US-6 type, manufactured by Inai Morieidou Co., Ltd.) and stirred. At the same time as stirring was started, ultrasonic waves were oscillated and dispersed. Next, 1
40 ml of 0% by weight sodium silicate aqueous solution 30 ml
The solution was dropped at a dropping rate of 1 minute/minute, and the reaction was gradually decomposed to deposit a silica film on the surface. After the dropwise addition of the sodium silicate aqueous solution, the reaction was continued for 2 hours to react all unreacted raw materials.

After the film forming reaction was completed, the slurry containing the silica film forming powder was repeatedly decanted with sufficient ion exchange water and washed. After the washing operation, the silica film-forming powder was put in a vat, precipitated and separated, and the upper liquid was discarded.
After drying at 0° C. for 8 hours, heat treatment was performed in air at 500° C. for 30 minutes to obtain silica-coated magnetite powder E ₄ .

(Fifth layer silica dense film formation) 37 g of magnetite powder D ₄ coated with silica/titania was added to 1,460 ml of a buffer solution prepared in advance and 500 m of pure water.
1 of the mixed solution, ultrasonic waves are applied in an ultrasonic bath of 28 kHz and 600 W, and further dispersed in a buffer solution containing magnetite powder while stirring. Sodium silicate solution 1 prepared in advance
It was added at 4 ml (4 ml/min) and gradually decomposed by reaction to deposit a silica film on the surface. After the addition of the aqueous sodium silicate solution was completed, the reaction was continued for another 2 hours to react all unreacted raw materials. After the film forming reaction is completed, the slurry containing the silica film forming powder is repeatedly decanted with sufficient water,
Wash. After washing, put the silica/titania film-forming powder in a vat, settle and separate, discard the upper liquid, and then dry in a dryer at 150°C for 8 hours in air, and then at 500°C for 3 hours in a nitrogen atmosphere.
Heat treated for 0 minutes Silica/titania coated magnetite powder E ₅
Got The five-layer film-coated powder E ₅ had a pale yellow color and its magnetism was 18 emu/g at 1 kOe. The thickness of the silica film of the obtained silica/titania-coated magnetite powder E ₅ was 9 nm. The reflection peak of this 5-layer film coating is 604 nm, and the reflectance at the peak wavelength is 91%.
Met. Table 6 shows each refractive index of each of the first to fifth layers, the film thickness, the peak wavelength of the spectral reflection curve of the coated powder, and the reflectance at the peak wavelength. In addition, L ^{* of} the final coated powder,
Table 2 shows the measured values in the a ^* and b ^* standard color system.

[0088]

[Table 6]

As is clear from Table 2, all the yellow color powders of the examples according to the present invention had a high L ^* value according to the standard color system, a high brightness and a vivid yellow color. Especially, since the powder of Example 5 used the existing fine particles as the fine particles of the crystallized fine particle constituting film, the particle size of the fine particles was relatively large and the scattering reflection was large, and satisfactory results were obtained.

[0090]

As described above, the yellow powder and the method for producing the same according to the present invention have a coating film on the surface of base particles, and at least one layer of the coating film is formed with crystallization fine particles. By forming a layer composed of an aggregate of crystallized fine particles having voids between the crystallized fine particles, the difference in the refractive index between the surface of the crystallized grains and the voids is increased to cause scattering reflection of light and a reflection effect. It has become possible to provide a functional powder having excellent brightness. In addition to the method of forming ultrafine particles that scatter and reflect visible light in a liquid by adjusting the solid phase deposition rate when forming the crystallized ultrafine particle constituent film, the existing particles are incorporated into the film. By forming a film, the crystallized ultrafine particles contained in the film tend to have a relatively large particle size, so that the degree of scattering reflection also increases and a yellow powder having a higher brightness can be obtained.

Further, the yellow colored powder of the present invention can be formed into a film at a lower manufacturing cost than that of the alkoxide method by using water as a solvent in the film forming reaction in the manufacturing method, and has high flammability. The effect of not using an organic solvent, requiring no explosion-proof equipment in the manufacturing facility, and easily controlling temperature and humidity can be obtained. In addition to possessing these excellent functions, when a magnetic substance, conductor or dielectric is used as the substrate, it reacts due to external factors such as an electric field and a magnetic field to exert additional effects such as moving force, rotation, movement and heat generation. It has a function of emitting light, and for example, when a magnetic material is applied as a substrate, it can be applied as a pigment for color magnetic toner or color magnetic ink.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an example of a yellow powder of the present invention.

FIG. 2 is an enlarged cross-sectional view of a crystallized fine particle constituent film 2 included in the yellow powder of FIG.

[Explanation of symbols]

1 Base particle 2 Crystallized fine particle constituent film 3 Crystallized fine particle 4 Ultra fine particle

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kiyoshi Hoshino 8th Hirai, Hinode-cho, Nishitama-gun, Tokyo 1st Iron Mining Co., Ltd. (72) Katsuto Nakatsuka 4-3 Moiwadai, Taihaku-ku, Sendai, Miyagi Prefecture No. 5 1403 F term (reference) 4J037 AA04 AA05 AA09 AA10 AA14 AA18 AA19 AA22 AA25 AA26 AA27 AA29 AA30 CA05 CA14 CA16 CA18 CA20 CA29 DD02 DD05 DD08 EA03 EA03 EE03 FE02 BA24JE07 FF21 FF21 FF02 FF02 FF02 FF02 FF03 FF16 FF02 FF02 FF02 FF02 FF02 FF02 FF02 FF02 FF02 FF02 FF02 FF02 FF03 FF02

Claims (28)

[Claims] 1. A substrate particle has a coating film on the surface thereof, and at least one layer of the coating film is formed by a reaction of a metal salt in an aqueous solvent, and has a peak between 550 and 850 nm. A yellow powder characterized by exhibiting a reflection spectrum having 2. The yellow colored powder according to claim 1, wherein the coating film formed by the reaction of the metal salt in an aqueous solvent satisfies the condition of the following formula. N
d=mλ/4 [In the formula, N=n+iκ (i represents a complex number) n: Refractive index of the substance constituting the film d: Film thickness m: Natural number λ: Peak wavelength of the reflection spectrum of the powder ( However, λ is 550 to 850 nm) κ: Attenuation coefficient] 3. The yellow powder according to claim 1, wherein the coating film on the surface of the base particles is a multilayer film. 4. The yellow powder according to claim 3, wherein each of the multilayer films is formed by a reaction of a metal salt in an aqueous solvent. 5. The yellow colored powder according to claim 3, wherein each of the multilayer films satisfies the condition of the following formula. Nd=mλ/4 [In the formula, N=n+iκ (i represents a complex number) n: Refractive index of substance constituting film d: Film thickness m: Natural number λ: Peak wavelength of reflection spectrum of powder ( However, λ is 550 to 850 nm) κ: Attenuation coefficient] 6. The yellow powder according to claim 1, wherein at least one layer of the coating film on the surface of the base particles is constituted as an aggregate of crystallized fine particles having voids. .. 7. The coating film formed as an aggregate of crystallized fine particles having voids is capable of imparting lightness by scattering and reflection of light generated between the surface of the crystallized fine particles and voids. The yellow colored powder according to claim 6, wherein the yellow colored powder is present. 8. A dense coating film composed of ultrafine particles capable of closing the voids on the surface is provided on the surface of the coating film formed as an aggregate of crystallized fine particles having voids. The yellow powder according to claim 6, which is characterized in that. .. 9. The yellow powder according to claim 6, wherein the coating film formed as an aggregate of crystallized fine particles having voids is a high refractive index film. 10. The yellow powder according to claim 8, wherein the dense film is a silica film. 11. The coating film formed as an aggregate of crystallized fine particles adheres the crystallized fine particles to the surface of the base powder in a liquid in which the crystallized fine particles and the base powder are dispersed. 7. The yellow colored powder according to claim 6, which is formed by: 12. The coating film formed as an aggregate of crystallized fine particles having voids forms solid phase fine particles in a reaction solution for forming the coating film, and the solid phase fine particles are formed into 7. The yellow powder according to claim 6, which is formed by firing after being incorporated into the coating film. 13. The yellow powder according to claim 12, wherein the reaction solution is an aqueous solution. 14. Before the firing, the coating film in which the solid phase fine particles are incorporated is coated with ultrafine particles capable of forming a dense film that closes voids on the surface of the coating film. The yellow powder according to claim 12, characterized in that 15. A method for producing a yellow powder by forming a coating film on the surface of substrate particles, wherein the powder obtained has a reflection spectrum having a peak between 550 and 850 nm. A method for producing a yellow powder, comprising forming at least one layer of a covering film by a reaction of a metal salt in an aqueous solvent. 16. The method for producing a yellow color powder according to claim 15, wherein the coating film formed by the reaction of a metal salt in an aqueous solvent is formed so as to satisfy the condition of the following formula. .. Nd=mλ/4 [In the formula, N=n+iκ (i represents a complex number) n: Refractive index of substance constituting film d: Film thickness m: Natural number λ: Peak wavelength of reflection spectrum of powder ( However, λ is 550 to 850 nm) κ: Attenuation coefficient] 17. The method for producing a yellow color powder according to claim 15, wherein the coating film formed on the surface of the base particles is a multilayer film. 18. The method for producing a yellow powder according to claim 17, wherein each of the multilayer films is formed by a reaction of a metal salt in an aqueous solvent. 19. The method according to claim 17, wherein each of the multilayer films is formed so as to satisfy the condition of the following formula.
A method for producing the yellow powder as described. Nd=mλ/4 [In the formula, N=n+iκ (i represents a complex number) n: Refractive index of substance constituting film d: Film thickness m: Natural number λ: Peak wavelength of reflection spectrum of powder ( However, λ is 550 to 850 nm) κ: Attenuation coefficient] 20. The method for producing a yellow powder according to claim 15, wherein at least one layer of the coating film formed on the surface of the base particles is constituted as an aggregate of crystallized fine particles having voids. .. 21. The coating film formed as an aggregate of crystallized fine particles having voids is formed so that lightness can be imparted by scattering reflection of light generated between the surface of the crystallized fine particles and voids. 21. The method for producing a yellow powder according to claim 20, which is characterized in that. 22. A dense film is formed on the surface of the coating film formed as an aggregate of crystallized fine particles having voids, with ultrafine particles capable of closing the voids on the surface. 20. The method for producing a yellow powder according to 20. 23. The method for producing a yellow powder according to claim 20, wherein the coating film formed as an aggregate of crystallized fine particles having voids is a high refractive index film. 24. The method for producing a yellow powder according to claim 22, wherein the dense film is a silica film. 25. A film-forming substance is added to a liquid in which the crystallized fine particles and a base powder are dispersed, and the coating film formed as an aggregate of crystallized fine particles The white powder according to claim 20, which is formed by adhering it to the surface of the base powder. 26. The coating film, which is formed as an aggregate of crystallized fine particles having voids, is formed into solid phase fine particles in a reaction solution for forming the coating film, and the solid phase fine particles are coated with the solid phase fine particles. 21. The method for producing a yellow color powder according to claim 20, wherein the yellow color powder is formed by firing after being incorporated into the covering film. 27. The method for producing a yellow powder according to claim 26, wherein the reaction solution is an aqueous solution. 28. Before the firing, the coating film in which the solid phase fine particles are incorporated is coated with ultrafine particles capable of forming a dense film that closes voids on the surface of the coating film. 27. The method for producing a yellow powder according to claim 26, wherein