JP7635628B2 - Composite particles and method for producing the same - Google Patents

Description

The present invention relates to composite particles and a method for producing the composite particles, and in particular to composite particles in which an inorganic coating portion is provided on an alumina particle.

Alumina has many applications due to its excellent mechanical strength including abrasion resistance, chemical stability, thermal conductivity, and heat resistance, and is used in a wide range of areas, including pigments, paints, coatings, abrasives, electronic materials, heat dissipation fillers, optical materials, cosmetics, and biomaterials. As a prior art, for example, an adsorbent for metallic mercury in exhaust gas is disclosed in which 5 atom% or more of molybdenum trioxide or tungsten trioxide is supported on an inert carrier such as silica, titania, alumina, or zirconia (Patent Document 1).

The present applicant has discovered that by using _MoO3 as a fluxing agent and adding silica or germanium, it is possible to produce plate-like α-alumina with a narrow particle size and particle size distribution, and has disclosed this technology (Patent Document 2).

In addition, molybdenum trioxide (MoO ₃ ) is widely used as a catalyst, optical material, pigment, additive for manufacturing ceramics and glass, semiconductor, etc. The applicant of the present invention discovered that nano-MoO ₃ can be synthesized by quenching MoO ₃ vapor, and has disclosed this technology (Patent Document 3).

JP 2008-238057 A JP 2016-222501 A International Publication No. 2018/003481

However, in the adsorbent of Patent Document 1, the particle size of alumina and the structural positional relationship between the inactive alumina carrier and molybdenum trioxide are unclear, and there is still room for improvement in order to enhance the various properties exhibited by molybdenum trioxide. In addition, the adsorbent of Patent Document 1 adsorbs metallic mercury in exhaust gas, and its applications are limited.
Furthermore, neither Patent Documents 2 nor 3 discloses any knowledge about composite particles having alumina particles and a coating portion made of molybdenum oxide, nor about the characteristics thereof.

The present invention was made in consideration of these circumstances, and aims to provide composite particles that have an inorganic coating made of molybdenum oxide and can exhibit various favorable characteristics, and a method for producing the composite particles.

As a result of intensive research to solve the above problems, the inventors discovered that adding a molybdenum compound to alumina particles containing molybdenum and then firing the mixture makes it easier to coat the alumina particles with molybdenum oxide, and allows the molybdenum oxide to be unevenly distributed on the surfaces of the alumina particles, thus completing the present invention. In addition, by combining alumina particles containing molybdenum with molybdenum oxide unevenly distributed on the surfaces of the alumina particles, a very low pH is obtained in, for example, an aqueous solvent, and various properties derived from molybdenum oxide, including antibacterial and antiviral functions and oxidation catalyst functions, can be expected to be expressed.

That is, the present invention provides the following means.
[1] Alumina particles; and an inorganic coating portion formed on the surface of the alumina particles and composed of molybdenum oxide,
Composite particles, wherein the ratio of the amount of _{MoO3 to the amount of Al2O3 on} the surface of _the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) obtained by _X -ray photoelectron spectroscopy ( _XPS ) analysis is 15 or more.

[2] The ratio of the amount of _MoO3 to _the amount of _Al2O3 of the alumina particles ([ _MoO3 ]/ _{[ Al2O3} ] x 100) obtained by X-ray fluorescence ( _XRF ) analysis is 1 or more;
The composite particle according to the above [1], wherein ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XPS is greater than ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF .

[3] The composite particles described in [1] or [2] above, in which the alumina particles have an alpha crystallization rate of 90% or more.

[4] The composite particles described in any one of [1] to [3] above, in which the alumina particles contain molybdenum.

[5] The composite particles described in any one of [1] to [4] above, in which the alumina particles have a plate shape, a thickness of 0.01 μm or more and 5 μm or less, an average particle diameter of 0.1 μm or more and 500 μm or less, and an aspect ratio of 2 or more and 500 or less.

[6] The composite particles described in [1] above, in which the alumina particles further contain silicon and/or germanium.

[7] The composite particles described in [6] above, in which the alumina particles contain mullite in the surface layer.

[8] A composite particle comprising the composite particle described in any one of [1] to [7] above.

[9] A step of producing alumina particles by calcining a first mixture containing an aluminum compound containing an aluminum element and a molybdenum compound containing a molybdenum element, or a first mixture containing an aluminum compound containing an aluminum element, a molybdenum compound containing a molybdenum element, and a shape control agent for controlling the shape of alumina particles;
a step of firing a second mixture containing the alumina particles and a molybdenum compound containing elemental molybdenum to form an inorganic coating portion composed of a molybdenum compound on the surface of the alumina particles;
A method for producing composite particles, comprising:

[10] The method for producing composite particles described in [9] above, wherein the molybdenum compound is molybdenum oxide.

[11] The method for producing composite particles described in [10] above, in which the second mixture is fired at 750°C or higher and lower than 1100°C in the step of forming the inorganic coating portion.

[12] The method for producing composite particles described in [10] above, in which the first mixture is fired at 900°C or higher in the step of producing the alumina particles.

[13] The method for producing composite particles described in any one of [9] to [12] above, wherein the shape control agent is composed of one or more selected from silicon, a silicon compound containing silicon element, and a germanium compound containing germanium element.

[14] The method for producing composite particles described in any one of [9] to [13] above, wherein the first mixture further contains a potassium compound containing potassium element.

The present invention provides composite particles that have an inorganic coating made of molybdenum oxide and can exhibit various favorable properties.

FIG. 1 is a scanning electron microscope image showing the composite particle obtained in Example 1 as an example of the configuration of the composite particle according to an embodiment of the present invention. FIG. 2 is a scanning electron microscope image showing the composite particle obtained in Example 4 as an example of the configuration of the composite particle according to an embodiment of the present invention. FIG. 3 is a scanning electron microscope image showing alumina particles obtained in Comparative Example 1 as an example of the configuration of a comparative example of the present invention.

The following describes in detail an embodiment of the present invention with reference to the drawings.

<Composite particles>
The composite particle according to this embodiment includes an alumina particle and an inorganic coating portion formed on the surface of the alumina particle and composed of molybdenum oxide. The composite particle according to this embodiment may have any shape, such as a plate shape, a card house shape, or a polyhedron. From the viewpoint of making the most of the anisotropy of the composite particle, it is preferable that the composite particle has, for example, a plate shape. When the composite particle is formed in a plate shape, the alumina particle also has a plate shape. Hereinafter, in this embodiment, the alumina particle having a plate shape is also referred to as a "plate-shaped alumina particle", "plate-shaped alumina", or simply "alumina particle".

<Plate-shaped alumina particles>
In the present invention, "plate-like" refers to an aspect ratio of 2 or more, calculated by dividing the average particle size of the alumina particles by the thickness. In this specification, the "thickness of the alumina particles" refers to the arithmetic average value of thicknesses measured for at least 50 plate-like alumina particles randomly selected from an image obtained by a scanning electron microscope (SEM). In addition, the "average particle size of the alumina particles" refers to a value calculated as the volume-based median diameter _D50 from the volume-based cumulative particle size distribution measured by a laser diffraction particle size measurement device.

For alumina particles, the thickness, particle size, and aspect ratio conditions shown below can be combined in any way as long as they are plate-shaped. In addition, the upper and lower limit values of the numerical ranges exemplified for these conditions can be freely combined.

The plate-like alumina particles preferably have a thickness of 0.01 μm or more and 5 μm or less, more preferably 0.03 μm or more and 5 μm or less, more preferably 0.1 μm or more and 5 μm or less, more preferably 0.3 μm or more and 3 μm or less, and even more preferably 0.5 μm or more and 1 μm or less.

The average particle diameter (D ₅₀ ) of the plate-like alumina particles is preferably 0.1 μm or more and 500 μm or less, more preferably 0.5 μm or more and 50 μm or less, and even more preferably 1 μm or more and 20 μm or less.
Alumina particles having an average particle diameter ( _D50 ) of the above upper limit or less are suitable for use as a filler, and when used as a functional filler, they can fully exhibit the various properties such as antibacterial and antiviral properties exhibited by the inorganic coating portion. Furthermore, alumina particles having an average particle diameter ( _D50 ) of the above lower limit or more have low agglomeration properties and therefore excellent dispersibility when used as a resin filler.

The aspect ratio of the plate-like alumina particles, which is the ratio of particle diameter to thickness, is preferably 2 or more and 500 or less, more preferably 5 or more and 100 or less, and even more preferably 10 or more and 50 or less. When the aspect ratio of the plate-like alumina particles is 2 or more, it is preferable because it can have two-dimensional blending characteristics, and when the aspect ratio of the plate-like alumina particles is 500 or less, it is preferable because it has excellent mechanical strength. When the aspect ratio is 5 or more, the above-mentioned characteristics can be more effectively exhibited, and this is preferable.

The plate-like alumina particles may be circular or elliptical, but it is preferable that the particle shape be, for example, polygonal, from the standpoint of ease of handling and manufacturing.

The plate-like alumina particles may be obtained based on any manufacturing method, but it is preferable to obtain them by firing an aluminum compound in the presence of a molybdenum compound (preferably further a potassium compound) and a shape control agent, in terms of a higher aspect ratio, better dispersibility, and better productivity. The shape control agent is preferably at least one selected from the group consisting of silicon, a silicon compound, and a germanium compound. Since the shape control agent is a source of Si for mullite described later, it is more preferable to use silicon or a silicon compound containing silicon element.
In the above manufacturing method, the molybdenum compound is used as a fluxing agent. In the present specification, this manufacturing method using a molybdenum compound as a fluxing agent may be simply referred to as the "flux method". The flux method will be described in detail later. It is considered that, after the molybdenum compound reacts with the aluminum compound at high temperature by the firing to form aluminum molybdate, the aluminum molybdate is further decomposed into alumina and molybdenum oxide at a higher temperature, and the molybdenum compound is taken into the plate-like alumina particles. The molybdenum oxide is sublimated, recovered, and can be reused.
In addition, when the plate-like alumina particles contain mullite in the surface layer, it is considered that in this process, the silicon or silicon atom-containing compound blended as a shape control agent reacts with the aluminum compound via molybdenum to form mullite in the surface layer of the plate-like alumina particles. More specifically, the mechanism of mullite formation is that on the alumina plate surface, the reaction of molybdenum with Si atoms results in the formation of Mo-O-Si, and the reaction of molybdenum with Al atoms results in the formation of Mo-O-Al, and high-temperature firing is performed to remove Mo and form mullite having Si-O-Al bonds.
Molybdenum oxide that is not incorporated into the plate-like alumina particles is preferably recovered by sublimation and reused.
In this specification, a material that has the property of being sublimable in the manufacturing method described below is called a fluxing agent, and a material that cannot be sublimated is called a shape control agent.

By utilizing molybdenum and a shape control agent in the production of the plate-like alumina particles, the plate-like alumina particles have a high alpha crystal rate and are idiomorphic, which allows them to achieve excellent dispersibility, mechanical strength, and high thermal conductivity.

When the plate-like alumina particles contain mullite in the surface layer, the amount of mullite formed in the surface layer of the plate-like alumina particles can be controlled by the proportions of the molybdenum compound and the shape control agent used, and in particular by the proportions of silicon or silicon-containing silicon compounds used as the shape control agent. The preferred amount of mullite formed in the surface layer of the plate-like alumina particles and the preferred proportions of the raw materials used will be described in detail later.

From the viewpoint of further exhibiting the above-mentioned various properties, the plate-like alumina particles are preferably plate-like alumina particles having an aspect ratio of 5 to 500, and a longitudinal relaxation time _T1 for a hexacoordinate aluminum peak of 10 to 30 ppm at a static magnetic field strength of 14.1 T being 5 seconds or longer in solid-state ^27Al NMR analysis.

The longitudinal relaxation time _T1 of 5 seconds or more means that the plate-like alumina particles have high crystallinity. It has been reported that a long longitudinal relaxation time in the solid state means that the crystal has good symmetry and high crystallinity (previously reported: Kitagawa Susumu et al., "Society of Coordination Chemistry Selections 4: Solution and Solid NMR of Polynuclear Species," Sankyo Publishing Co., Ltd., pp. 80-82).

In the plate-like alumina particles, the longitudinal relaxation time _T1 is preferably 5 seconds or more, more preferably 6 seconds or more, and even more preferably 7 seconds or more.
In the plate-like alumina particles according to the embodiment, the upper limit of the longitudinal relaxation time _T1 is not particularly limited, but may be, for example, 22 seconds or less, 15 seconds or less, or 12 seconds or less.
An example of the numerical range of the longitudinal relaxation time _T1 exemplified above may be 5 seconds or more and 22 seconds or less, 6 seconds or more and 15 seconds or less, or 7 seconds or more and 12 seconds or less.

The plate-like alumina particles preferably exhibit no detectable peak of 4-coordinate aluminum at 60 to 90 ppm in solid-state ²⁷ Al NMR analysis at a static magnetic field strength of 14.1 T. Such plate-like alumina particles are considered to be less susceptible to breakage or falling off due to distortion of crystal symmetry caused by the inclusion of crystals with different coordination numbers, and tend to have better shape stability.

Conventionally, the degree of crystallinity of inorganic substances is generally evaluated by the results of XRD analysis and the like. However, the inventors have found that, by using the longitudinal relaxation time _T1 as an index for evaluating the crystallinity of alumina particles, more accurate analysis results can be obtained than with conventional XRD analysis. The plate-like alumina particles according to the embodiment have a long longitudinal relaxation time _T1 of 5 seconds or more, and the crystallinity of the alumina particles is high. That is, the plate-like alumina particles according to the embodiment are probably highly crystallinity-prohibiting diffuse reflection on the crystal surface, improving light reflection, and providing excellent brilliance.

Furthermore, the present inventors have found that the value of the longitudinal relaxation time _T1 is highly correlated with the shape retention rate of the plate-like alumina particles and the processing stability of the resin composition. In particular, in the case of plate-like alumina particles having an average particle diameter of 10 μm or less and an aspect ratio of 30 or less, the correlation between the value of the longitudinal relaxation time _T1 , the shape retention rate of the plate-like alumina particles, and the processing stability of the resin composition is significantly expressed. The above-mentioned plate-like alumina particles having the longitudinal relaxation time _T1 of 5 seconds or more have the advantage that they have good processing stability and are easy to process into a desired shape when blended with a resin to produce a resin composition. The above-mentioned plate-like alumina particles have a long value of the longitudinal relaxation time _T1 , so that the crystallinity is enhanced. Therefore, it is considered that the strength of the particles is high due to the high crystallinity of alumina, and when the resin and the plate-like alumina particles are mixed in the manufacturing process of the resin composition, the plate is unlikely to break, and further, it is considered that the particle surface has few irregularities due to the high crystallinity of alumina, and therefore has excellent adhesion to the resin. Due to these factors, it is believed that the above-mentioned plate-like alumina particles have good processing stability in the resin composition. Therefore, according to the composite particles having the above-mentioned plate-like alumina particles, even when they are blended in a resin composition, the inherent performance of the plate-like alumina particles and the inorganic coating portion is well exhibited.

The shape retention rate can be evaluated as follows.
(shape retention rate)
Alumina particles 66% by mass and polyphenylene sulfite resin (PPS resin, DIC LR-100G) 34% by mass are mixed to prepare a total of 5 kg of mixture. 5 kg of the mixture is melt-kneaded using a twin-screw extruder with a screw diameter of 40 mm and L/D=45 under the conditions of a feed rate of 15 kg/h, an extruder temperature of 320°C, and a screw rotation speed of 150 rpm. The strand obtained after melt-kneading is cut with a pelletizer to obtain pellets with a major axis of 3 mm and a length of 5 mm. 5 g of the pellets are collected, placed in a crucible, and heated under the conditions of 700°C for 3 hours to incinerate the pellets. The average particle diameter D ₅₀ (μm) of the incinerated powder sample is measured using a laser diffraction particle size distribution analyzer, and the obtained value is taken as the average particle diameter after extrusion kneading. Separately from the above sample, 3 g of a sample before extrusion kneading (before being mixed with polyphenylene sulfite resin) is prepared and the average particle diameter D ₅₀ (μm) is similarly measured, and the obtained value is regarded as the average particle diameter before extrusion kneading.
The shape retention rate (%) of the powder is calculated by (average particle size after extrusion kneading/average particle size before extrusion kneading×100).
It is believed that in samples with low crystallinity, the alumina particles are destroyed by melt kneading in the extruder, the fine particle components increase, and the average particle size becomes smaller than before kneading (the shape retention value decreases).

The processing stability can be evaluated, for example, by the following method.
(Processing stability)
A total of 5 kg of a mixture was prepared by blending 66% by mass of alumina particles and 34% by mass of polyphenylene sulfite resin (PPS resin, manufactured by DIC, LR-100G). 5 kg of the mixture was melt-kneaded using a twin-screw extruder with a screw diameter of 40 mm and L/D=45 under the conditions of a feed rate of 15 kg/h, an extruder temperature of 320°C, and a screw rotation speed of 150 rpm. A strand that had an unstable diameter coming out of the die and caused surging, or a strand surface with unevenness or streaks due to foaming or foreign matter, etc., was evaluated as having poor processing stability, and a strand that did not exhibit the above phenomena was evaluated as having good processing stability.

Conventionally, it has been difficult to obtain plate-shaped alumina particles with high crystallinity compared to spherical alumina particles, which is believed to be because, unlike spherical alumina particles, plate-shaped alumina particles require a bias in the direction of crystal growth during the production process.
In contrast, the plate-like alumina particles satisfying the longitudinal relaxation time _T1 have a plate-like shape but are highly crystalline, and therefore have the advantages of plate-like alumina particles, such as excellent thermal conductivity, while also improving the shape retention and processing stability of the resin composition, making them extremely useful.

The pH of the isoelectric point of the plate-like alumina particles is, for example, in the range of 2 to 6, preferably in the range of 2.5 to 5, and more preferably in the range of 3 to 4. Plate-like alumina particles with an isoelectric point pH within the above range have a high electrostatic repulsion force, which can increase the dispersion stability when blended with the above-mentioned dispersion medium, and also makes it easier to modify the surface by a coupling treatment agent or the like in order to further improve performance.

The pH value of the isoelectric point is obtained by measuring the zeta potential with a zeta potential measuring device (Malvern, Zetasizer Nano ZSP), stirring 20 mg of sample and 10 mL of 10 mM KCl aqueous solution for 3 minutes with a foam remover (Thinky, ARE-310) in stirring/defoaming mode, leaving the supernatant to stand for 5 minutes as the measurement sample, adding 0.1 N HCl to the sample with an automatic titrator, and measuring the zeta potential in the range up to pH = 2 (applied voltage 100 V, Monomodl mode), and evaluating the pH of the isoelectric point where the potential becomes zero.

The plate-like alumina particles have, for example, a density of 3.70 g/cm ³ or more and 4.10 g/cm ³ or less, preferably a density of 3.72 g/cm ³ or more and 4.10 g/cm ³ or less, and more preferably a density of 3.80 g/cm ³ or more and 4.10 g/cm ³ or less.
The density can be measured using a dry automatic density meter (Micromeritics' Accupypic II1330) at a measurement temperature of 25°C and helium as a carrier gas after pretreatment of the plate-like alumina particles at 300°C for 3 hours.

[alumina]
The "alumina" contained in the plate-like alumina particles is aluminum oxide, and may be transition alumina of various crystal forms such as γ, δ, θ, κ, etc., or may contain alumina hydrate in the transition alumina, but is basically preferably in the α crystal form (α type) in terms of superior mechanical strength or thermal conductivity. The α crystal form is a dense crystal structure of alumina, and is advantageous for improving the mechanical strength or thermal conductivity of the plate-like alumina.
The α-crystallinity ratio is preferably as close to 100% as possible, since the inherent properties of the α-crystal form are more easily exhibited. The α-crystallinity ratio of the plate-like alumina particles is, for example, 90% or more, preferably 95% or more, and more preferably 99% or more.

[Silicon and Germanium]
The platelet alumina particles of this embodiment may contain silicon and/or germanium.
The silicon or germanium may be derived from silicon, a silicon compound, and/or a germanium compound that can be used as a shape control agent. By utilizing these, it is possible to produce plate-like alumina particles having excellent brilliance in the production method described below.

(silicon)
The plate-like alumina particles according to the present embodiment may contain silicon. The plate-like alumina particles according to the present embodiment may contain silicon in the surface layer.
Here, the "surface layer" refers to a region within 10 nm from the surface of the plate-like alumina particle according to the present embodiment. This distance corresponds to the detection depth of the XPS used for measurement in the examples.

The plate-like alumina particles may have silicon unevenly distributed in the surface layer. Here, "distributed unevenly in the surface layer" refers to a state in which the mass of silicon per unit volume in the surface layer is greater than the mass of silicon per unit volume outside the surface layer. The fact that silicon is unevenly distributed in the surface layer can be determined by comparing the results of a surface analysis by XPS and a total analysis by XRF.

The silicon contained in the plate-like alumina particles may be silicon alone or silicon in a silicon compound. The plate-like alumina particles may contain at least one selected from the group consisting of mullite, Si, SiO ₂ , SiO, and aluminum silicate produced by reacting with alumina as silicon or a silicon compound, and may contain the above-mentioned substance in the surface layer. Mullite will be described later.

When silicon or a silicon compound containing silicon is used as a shape control agent, the plate-like alumina particles can have Si detected by XRF analysis. The molar ratio of Si to Al of the plate-like alumina particles, [Si]/[Al], obtained by XRF analysis, is, for example, 0.04 or less, preferably 0.035 or less, and more preferably 0.02 or less.
The value of the molar ratio [Si]/[Al] is not particularly limited, but is, for example, 0.003 or more, preferably 0.004 or more, and more preferably 0.005 or more.
The molar ratio of Si to Al, [Si]/[Al], of the plate-like alumina particles obtained by XRF analysis is, for example, 0.003 or more and 0.04 or less, preferably 0.004 or more and 0.035 or less, and more preferably 0.005 or more and 0.02 or less.
The plate-like alumina particles having the molar ratio [Si]/[Al] within the above range obtained by the XRF analysis satisfy the above (006/113) ratio value, have better brilliance, and have a good plate-like shape. In addition, deposits are less likely to adhere to the surface of the plate-like alumina particles, and are excellent in quality. The deposits are thought to be _SiO2 particles, and are generated due to excess Si when the generation of mullite on the surface layer of the plate-like alumina particles becomes saturated.
When using plate-like alumina particles having a larger particle size, the molar ratio of Si to Al, [Si]/[Al], obtained by XRF analysis, of the plate-like alumina particles is preferably 0.0003 or more and 0.01 or less, more preferably 0.0005 or more and 0.0025 or less, and more preferably 0.0006 or more and 0.001 or less.

The plate-like alumina particles may contain silicon corresponding to the silicon or silicon compound containing elemental silicon used in the production method thereof. The silicon content relative to 100 mass% of the plate-like alumina particles, calculated as silicon dioxide, is preferably 10 mass% or less, more preferably 0.001 to 5 mass%, even more preferably 0.01 to 4 mass%, still more preferably 0.3 to 2.5 mass%, and particularly preferably 0.6 to 2.5 mass%.
When using plate-like alumina particles having a larger particle size, the silicon content relative to 100 mass% of the plate-like alumina particles, calculated as silicon dioxide, is preferably 10 mass% or less, more preferably 0.001 to 3 mass%, even more preferably 0.01 to 1 mass%, and particularly preferably 0.03 to 0.3 mass%.

(Mullite)
The plate-like alumina particles of the embodiment may contain mullite. It is presumed that the inclusion of mullite in the surface layer of the plate-like alumina particles improves the selectivity of the molybdenum compound constituting the inorganic coating portion, and allows the inorganic coating portion to be efficiently formed on the plate-like alumina particles.
Mullite is contained in the surface layer of the plate-like alumina particles, and thus a significant reduction in wear of the equipment is achieved. The "mullite" that may be contained in _{the surface layer of the plate-like alumina particles is a composite oxide of Al and Si and is expressed as AlXSiYOz, but there is no particular limit to the values of x, y, and z. A more preferred range is Al2Si1O5 to Al6Si2O13 . Note that the XRD peak intensity confirmed in the} examples described below is that _{containing Al2.85Si1O6.3 , Al3Si1O6.5 , Al3.67Si1O7.5} , _{Al4Si1O8 , or Al6Si2O13 .} The plate- _like alumina particles _may contain at least one compound selected from the group consisting _{of Al2.85Si1O6.3} , _{Al3Si1O6.5 , Al3.67Si1O7.5 , Al4Si1O8 ,} and _Al6Si2O13 in the surface layer. Here, the "surface layer" refers to within _{10 nm} from the surface of the _plate - _like alumina particles. This distance corresponds to the detection depth of the XPS used for measurement in the examples.
The plate-like alumina particles preferably have mullite unevenly distributed in the surface layer. Here, "distributed unevenly in the surface layer" refers to a state in which the mass of mullite per unit volume in the surface layer is greater than the mass of mullite per unit volume in the rest of the surface layer. The uneven distribution of mullite in the surface layer can be determined by comparing the results of surface analysis by XPS and overall analysis by XRF, as shown in the examples described later.

The mullite in the surface layer may form a mullite layer, or may be a mixture of mullite and alumina. The interface between the mullite and alumina in the surface layer may be in a state where the mullite and alumina are in physical contact with each other, or the mullite and alumina may form a chemical bond such as Si-O-Al.

(germanium)
The plate-like alumina particles according to the embodiment may contain germanium. Also, the plate-like alumina particles may contain germanium in a surface layer.
Although it depends on the raw materials used, the plate-like alumina particles may contain at least one germanium or germanium compound selected from the group consisting of compounds such as Ge, _GeO2 , GeO, _GeCl2 , _GeBr4 , _GeI4 , _GeS2 , AlGe, GeTe _{, GeTe3} , _As2 , GeSe, _GeS3As , SiGe, _Li2Ge , FeGe, SrGe, GaGe, etc., and oxides thereof, and may contain the above-mentioned substances in the surface layer.
In addition, the "germanium or germanium compound" contained in the plate-like alumina particles and the "raw material germanium compound" used as a shape control agent of the raw material may be the same type of germanium compound. For example, _GeO2 may be detected in the plate-like alumina particles produced by adding _GeO2 to the raw material.

When germanium or a germanium compound is contained in the surface layer of the plate-like alumina particles, a significant reduction in wear of the equipment is achieved. Here, the "surface layer" refers to the area within 10 nm from the surface of the plate-like alumina particles.
The plate-like alumina particles preferably have germanium or a germanium compound unevenly distributed in the surface layer. Here, "distributed unevenly in the surface layer" refers to a state in which the mass of germanium or a germanium compound per unit volume in the surface layer is greater than the mass of germanium or a germanium compound per unit volume in the other part of the surface layer. The uneven distribution of germanium or a germanium compound in the surface layer can be determined by comparing the results of a surface analysis by XPS and a total analysis by XRF.

The plate-like alumina particles contain germanium corresponding to the raw germanium compound used in the production method thereof. The germanium content relative to 100% by mass of the plate-like alumina particles is preferably 10% by mass or less, more preferably 0.001 to 5% by mass, even more preferably 0.01 to 4% by mass, and particularly preferably 0.1 to 3.0% by mass, calculated as germanium dioxide. The germanium content can be determined by XRF analysis.
The XRF analysis should be carried out under the same measurement conditions as those described in the Examples below, or under compatible conditions that give the same measurement results.

The germanium or germanium compound in the surface layer may form a layer, or may be in a state where germanium or germanium compound and alumina are mixed. The interface between the germanium or germanium compound in the surface layer and alumina may be in a state where the germanium or germanium compound and alumina are in physical contact with each other, or the germanium or germanium compound and alumina may form a chemical bond such as Ge-O-Al.

[molybdenum]
The plate-like alumina particles of this embodiment contain molybdenum. In addition, the plate-like alumina particles preferably contain molybdenum in their surface layers. This is believed to improve the selectivity of the molybdenum compound that constitutes the inorganic coating portion, and to allow the inorganic coating portion to be efficiently formed on the plate-like alumina particles.

The molybdenum may be derived from a molybdenum compound used as a fluxing agent in the method for producing alumina particles described below.

By utilizing molybdenum, it is possible to produce plate-shaped alumina particles with high crystallinity and a high aspect ratio, despite their plate-like shape, using the manufacturing method described below.

By using a large amount of molybdenum, it is possible to obtain plate-like alumina particles having an appropriate particle size and containing molybdenum on the alumina surface layer, and this is also advantageous for forming an inorganic coating on the surface of the obtained plate-like alumina particles. Furthermore, the use of molybdenum promotes the formation of mullite, making it possible to produce plate-like alumina particles with a high aspect ratio and excellent dispersibility. In addition, the properties of the molybdenum contained in the plate-like alumina particles can be utilized to apply them to applications such as oxidation reaction catalysts and optical materials.

The molybdenum is not particularly limited, and in addition to molybdenum metal, it includes molybdenum oxide, partially reduced molybdenum compounds, molybdates, etc. The molybdenum compound may be contained in the plate-like alumina particles in any of its possible polymorphic forms or in combination, and may be contained in the plate-like alumina particles as α-MoO ₃ , β-MoO ₃ , MoO ₂ , MoO, a molybdenum cluster structure, etc.

The form in which molybdenum is contained is not particularly limited, and it may be contained in a form in which it is attached to the surface of the plate-like alumina particles, or in a form in which it is substituted for part of the aluminum in the crystal structure of the alumina, or it may be a combination of these.

In this embodiment, the ratio of the amount of _MoO3 to the amount of _Al2O3 of the plate-like alumina particles obtained by X- _ray fluorescence (XRF) analysis ([ _MoO3 ]/ _{[ Al2O3} ] x 100) is preferably 1 or more. ([ _MoO3 ]/[ _Al2O3 ] x 100) _XRF is more preferably 10 or more, even more preferably _{15 or more, and particularly preferably 20 or more. ([MoO3]/[Al2O3] x 100) XRF is , for example} , the ratio of the content of _Al2O3 relative to 100% by mass of the plate- _like alumina particles to the content of _MoO3 relative to 100% by mass of the plate _- like alumina particles. This can improve the brilliance of the alumina particles while enhancing the oxidation catalyst function of molybdenum oxide.

The molybdenum content relative to 100% by mass of the plate-like alumina particles obtained by XRF analysis is preferably 1% by mass or less, calculated as molybdenum trioxide, and by adjusting the firing temperature, firing time, and sublimation rate of the molybdenum compound, it is more preferably 0.001 to 1% by mass, even more preferably 0.01 to 0.9% by mass, and particularly preferably 0.1 to 0.8% by mass. A molybdenum content of 1% by mass or less is preferable because it improves the alpha single crystal quality of the alumina.

[potassium]
The plate-like alumina particles may further contain potassium.

The potassium may be derived from potassium that can be used as a fluxing agent in the method for producing alumina particles described below.
By utilizing potassium, the particle size of the alumina particles can be appropriately increased in the method for producing alumina particles described below.

The potassium is not particularly limited, but includes potassium metal, potassium oxide, partially reduced potassium compounds, etc.

The form in which potassium is contained is not particularly limited, and it may be contained in a form in which it is attached to the surface of the tabular alumina of the plate-like alumina particles, or it may be contained in a form in which it is substituted for part of the aluminum in the crystal structure of the alumina, or it may be a combination of these.

The potassium content relative to 100 mass% of the alumina particles obtained by XRF analysis is preferably 0.01 mass% or more, more preferably 0.01 to 1.0 mass%, even more preferably 0.03 to 0.5 mass%, and particularly preferably 0.05 to 0.3 mass%, calculated as potassium oxide ( _{K 2} O) relative to 100 mass% of the alumina particles. Alumina particles having a potassium content within the above range are preferred because they have a polyhedral shape and have suitable values such as an average particle size.

(other atoms)
The other atoms refer to those that are intentionally added to the alumina particles for the purpose of imparting mechanical strength or electrical or magnetic functionality, within the scope of not impairing the effects of the present invention.

Other atoms include, but are not limited to, zinc, manganese, calcium, strontium, yttrium, etc. These other atoms may be used alone or in combination of two or more.

The content of other atoms in the alumina particles is preferably 5% by mass or less, and more preferably 2% by mass or less, based on the mass of the alumina particles.

[Inevitable impurities]
The alumina particles may contain unavoidable impurities.

Inevitable impurities are impurities that originate from metal compounds used in production, are present in raw materials, or are inevitably mixed into alumina particles during the manufacturing process. Although they are not actually necessary, they are present in trace amounts and do not affect the properties of the alumina particles.

Examples of unavoidable impurities include, but are not limited to, magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, cerium, sodium, etc. These unavoidable impurities may be contained alone or in combination of two or more kinds.

The content of unavoidable impurities in the alumina particles is preferably 10,000 ppm or less, more preferably 1,000 ppm or less, and even more preferably 10 to 500 ppm, relative to the mass of the alumina particles.

<Inorganic coating part>
The inorganic coating portion coats at least a portion of the surface of the alumina particle, and is preferably constituted by an inorganic coating layer coating at least a portion of the surface of the alumina particle.
As described above, the inorganic coating portion is provided on the surface of the alumina particle. "On the surface of the alumina particle" means the outside of the surface of the alumina particle. Therefore, the inorganic coating portion formed on the outside of the surface of the alumina particle is clearly distinguished from the surface layer containing mullite or germanium formed on the inside of the surface of the alumina particle.

The inorganic coating portion is made of molybdenum oxide, such as MoO ₃ , MoO ₂ , and MoOx (x=2 to 3).

The shape of the molybdenum oxide constituting the inorganic coating portion is not particularly limited, but may be particulate, such as spherical, acicular, polyhedral, discoidal, hollow, or porous. The average particle size of the particles composed of the particulate molybdenum compound is preferably, for example, 1 nm or more and 500 nm or less, and more preferably 5 nm or more and 200 nm or less. The molybdenum oxide may be crystalline or amorphous.

When the inorganic coating portion is an inorganic coating layer, the thickness of one layer of the inorganic coating layer formed on the surface of the alumina particle is preferably 0.1 nm or more and 100 nm or less, preferably 1 nm or more and 50 nm or less, and particularly preferably 3 nm or more and 20 nm or less.

In the composite particle having the inorganic coating portion, the ratio of the amount of _MoO3 to the amount of _Al2O3 on the surface of the plate- _like alumina particle obtained by X-ray photoelectron spectroscopy ( _XPS ) analysis ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS is 15 or more. ([ _MoO3 ]/[ _Al2O3 ] x ₁₀₀ ) _XPS is, for example, the ratio of the content of _Al2O3 relative to 100% by mass of _the plate-like alumina particle to the content of _MoO3 relative to 100% by mass of the plate- _like alumina particle. When ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS is 15 or more, molybdenum oxide is unevenly distributed on the surface of the composite particle, and various properties such as antibacterial and antiviral functions of molybdenum oxide can be efficiently and sufficiently exhibited.

From the viewpoint of further improving the above-mentioned various properties, the ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XPS is preferably 20 or more, more preferably 25 or more, and even more preferably 30 or more.

In the composite particles of this embodiment, it is preferable that the molybdenum oxide is unevenly distributed on the surface of the alumina particles. Here, "distributed unevenly on the surface" refers to a state in which the mass of molybdenum oxide per unit volume on the surface is greater than the mass of molybdenum oxide per unit volume outside the surface. The uneven distribution of molybdenum oxide on the surface can be determined by comparing the results of surface analysis by XPS and overall analysis by XRF.

For example, _it is preferable that (1) the ratio of the amount of _{MoO3 to the amount of Al2O3 on} the surface of the plate-like _alumina particle obtained by X-ray photoelectron spectroscopy (XPS) analysis ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS is 15 or more, (2) the ratio of the amount of _MoO3 to the amount of _Al2O3 in the plate- _like alumina particle obtained by X-ray fluorescence (XRF) analysis ([ _MoO3 ]/[ _Al2O3 ] x 100) _XRF is 1 or more, and (3) ([ _MoO3 ]/ _{[ Al2O3} ] x 100 _{) XPS} is larger than ([ _MoO3 ]/[ _Al2O3 ] x 100) _XRF . This allows the various properties _of molybdenum oxide, such as antibacterial properties, antiviral properties, and oxidation catalyst properties, to be more effectively exhibited.

[Organic Compound Layer on the Surface of Composite Particles]
In one embodiment, the composite particle may have an organic compound layer on its surface. The organic compound constituting the organic compound layer is present on the surface of the composite particle and has the function of adjusting the surface properties of the composite particle. For example, the composite particle having an organic compound on its surface improves the affinity with the resin, and therefore the function of the composite particle as a filler can be maximized.

Organic compounds include, but are not limited to, organosilanes, alkylphosphonic acids, and polymers.

The organic silanes include alkyltrimethoxysilanes or alkyltrichlorosilanes having an alkyl group with 1 to 22 carbon atoms, such as methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, iso-propyltrimethoxysilane, iso-propyltriethoxysilane, pentyltrimethoxysilane, and hexyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilanes, phenyltrimethoxysilane, phenyltriethoxysilane, p-chloromethylphenyltrimethoxysilane, and p-chloromethylphenyltriethoxysilanes.

Examples of the phosphonic acid include methylphosphonic acid, ethylphosphonic acid, propylphosphonic acid, butylphosphonic acid, pentylphosphonic acid, hexylphosphonic acid, heptylphosphonic acid, octylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, octadecylphosphonic acid, 2_ethylhexylphosphonic acid, cyclohexylmethylphosphonic acid, cyclohexylethylphosphonic acid, benzylphosphonic acid, phenylphosphonic acid, and dodecylbenzenephosphonic acid.

As the polymer, for example, poly(meth)acrylates can be suitably used. Specific examples include polymethyl(meth)acrylate, polyethyl(meth)acrylate, polybutyl(meth)acrylate, polybenzyl(meth)acrylate, polycyclohexyl(meth)acrylate, polyt-butyl(meth)acrylate, polyglycidyl(meth)acrylate, polypentafluoropropyl(meth)acrylate, etc., and also include general-purpose polymers such as polystyrene, polyvinyl chloride, polyvinyl acetate, epoxy resin, polyester, polyimide, polycarbonate, etc.

The organic compounds may be contained alone or in combination of two or more.

The form in which the organic compound is contained is not particularly limited, and it may be linked to the alumina by a covalent bond, or it may be coated with the alumina or the material of the inorganic coating portion.

The content of the organic compound is preferably 20% by mass or less, and more preferably 10% by mass or more and 0.01% by mass or less, relative to the mass of the alumina particles. A content of the organic compound of 20% by mass or less is preferable because it makes it easier to express the physical properties derived from the composite particles.

In the composite particles configured as described above, the pH of the dispersion (0.1% by mass) in which the composite particles are dispersed in water is preferably less than 5.0, and more preferably 4.5 or less. If the pH of the aqueous dispersion is less than 5.0, the antibacterial activity and antiviral activity can be further increased.

<Method of Manufacturing Composite Particles>
Next, the method for producing the composite particles according to the present embodiment will be illustrated in detail, but the method for producing the composite particles according to the present embodiment is not limited to the method for producing the composite particles described below.

The method for producing composite particles according to this embodiment includes a step of producing alumina particles by firing a first mixture containing an aluminum compound containing an aluminum element, a molybdenum compound containing a molybdenum element, and a shape control agent for controlling the shape of the alumina particles, and a step of firing a second mixture containing the alumina particles and a molybdenum compound containing a molybdenum element to form an inorganic coating portion composed of molybdenum oxide on the surface of the alumina particles. Below, a method for producing composite particles using plate-shaped alumina particles will be described as an example of the method for producing composite particles according to this embodiment.

<Method of producing plate-like alumina particles>
The method for producing the plate-like alumina particles that constitute the composite particles is not particularly limited, and known techniques can be applied as appropriate. From the viewpoint of being able to suitably control alumina having a high α crystallization rate at a relatively low temperature, a production method using a flux method that utilizes a molybdenum compound can be preferably applied.

More specifically, a preferred method for producing plate-shaped alumina particles includes a step of calcining an aluminum compound in the presence of a molybdenum compound and a shape control agent (calcination step). The calcination step may be a step of calcining a mixture obtained in a step of obtaining a mixture to be calcined (mixing step).

[Mixing process]
The mixing step is a step of mixing an aluminum compound, a molybdenum compound, and a shape control agent to obtain a first mixture. The first mixture preferably further contains a potassium compound. The contents of the first mixture will be described below.

(Aluminum Compounds)
The aluminum compound is a raw material for the plate-like alumina particles of the present embodiment, and is not particularly limited as long as it becomes alumina by heat treatment. For example, aluminum chloride, aluminum sulfate, basic aluminum acetate, aluminum hydroxide, boehmite, pseudo-boehmite, transition alumina (γ-alumina, δ-alumina, θ-alumina, etc.), α-alumina, mixed alumina having two or more crystal phases, etc. can be used, and the physical form, such as the shape, particle size, and specific surface area, of these aluminum compounds as precursors is not particularly limited.

According to the flux method described in detail below, the aluminum compound can be suitably used regardless of its shape, for example, spherical, amorphous, aspected structures (wires, fibers, ribbons, tubes, etc.), sheets, etc.

Similarly, the particle size of the aluminum compound can be suitably adjusted to a range from a few nm to a few hundred μm using the flux method described in detail below.

The specific surface area of the aluminum compound is not particularly limited. Since the molybdenum compound acts effectively, a larger specific surface area is preferable, but by adjusting the firing conditions and the amount of molybdenum compound used, any specific surface area can be used as a raw material.

The aluminum compound may be composed of only the aluminum compound, or may be a complex of the aluminum compound and an organic compound. For example, an organic/inorganic complex obtained by modifying an aluminum compound with an organic silane, or an aluminum compound complex adsorbing a polymer, may be suitably used. When using these complexes, there are no particular restrictions on the content of the organic compound, but from the viewpoint of efficiently producing plate-like alumina particles, the content is preferably 60% by mass or less, and more preferably 30% by mass or less.

(Shape control agent)
To form the plate-like alumina particles according to the embodiment, a shape control agent can be used, which plays an important role in the growth of plate-like crystals of alumina by calcining an alumina compound in the presence of a molybdenum compound.

The state in which the shape control agent is present is not particularly limited, and for example, a physical mixture of the shape control agent and the aluminum compound, or a complex in which the shape control agent is present uniformly or locally on the surface or inside of the aluminum compound, etc. can be suitably used.

A shape control agent may be added to the aluminum compound, or may be included in the aluminum compound as an impurity.

The shape control agent plays an important role in the growth of plate-like crystals. In the molybdenum oxide flux method, molybdenum oxide reacts with an aluminum compound to form aluminum molybdate, and then the change in chemical potential during the decomposition of this aluminum molybdate serves as the driving force for crystallization, forming hexagonal bipyramidal polyhedral particles with well-developed idiomorphic faces (113). In the manufacturing method of the embodiment, the shape control agent is localized near the particle surface during the α-alumina growth process, significantly inhibiting the growth of the idiomorphic faces (113), resulting in relatively fast growth of the crystal orientation in the face direction, and the (001) or (006) face growing, which is believed to form a plate-like shape. By using a molybdenum compound as a flux agent, it is possible to more easily form molybdenum-containing plate-like alumina particles with a high α crystallization rate.

The above mechanism is merely speculative, and even if the effects of the present invention are achieved through a mechanism different from the above mechanism, it is still within the technical scope of the present invention.

As for the type of shape control agent, it is preferable to use at least one selected from the group consisting of silicon, silicon compounds, and germanium compounds, from the viewpoint of being able to produce plate-like alumina particles with a higher aspect ratio, better dispersibility, and better productivity. Silicon or silicon compounds and germanium compounds can be used in combination. From the viewpoint of being a supplier of Si for mullite and being able to efficiently produce mullite, it is preferable to use silicon or silicon compounds containing silicon as the shape control agent. In addition, it is preferable to use germanium compounds as the shape control agent, from the viewpoint of being able to produce plate-like alumina particles with a higher aspect ratio and a larger particle size than when silicon or silicon compounds are used.
By the above-mentioned flux method using silicon or a silicon compound as the shape control agent, plate-like alumina particles containing mullite on the surface layer can be easily produced.
By the above-mentioned flux method using a raw germanium compound as a shape control agent, plate-like alumina particles containing germanium or a germanium compound can be easily produced.

Silicon or silicon compound Silicon or silicon-containing silicon compounds are not particularly limited, and known compounds can be used. Specific examples of silicon or silicon-containing silicon compounds include artificially synthesized silicon compounds such as metal silicon, organosilane, silicon resin, silica fine particles, silica gel, mesoporous silica, SiC, and mullite; and natural silicon compounds such as biosilica. Among these, organosilane, silicon resin, and silica fine particles are preferably used from the viewpoint of forming a more uniform composite or mixture with an aluminum compound. Silicon or silicon-containing silicon compounds may be used alone or in combination of two or more. In addition, they may be used in combination with other shape control agents as long as the effect of the present invention is not impaired.

The shape of silicon or silicon compounds containing elemental silicon is not particularly limited, and for example, spherical, amorphous, aspected structures (wires, fibers, ribbons, tubes, etc.), sheets, etc. can be suitably used.

Germanium Compound The raw germanium compound used as the shape control agent is not particularly limited, and known compounds can be used. Specific examples of the raw germanium compound include germanium metal, germanium dioxide, germanium monoxide, germanium tetrachloride, and organic germanium compounds having a Ge-C bond. The raw germanium compound may be used alone or in combination of two or more kinds. Furthermore, it may be used in combination with other shape control agents as long as the effect of the present invention is not impaired.

The shape of the raw germanium compound is not particularly limited, and for example, spherical, amorphous, aspected structures (wires, fibers, ribbons, tubes, etc.), sheets, etc. can be suitably used.

(Molybdenum Compounds)
The molybdenum compound provides a fluxing function for the alpha crystal growth of alumina at relatively low temperatures, as will be described below.
The molybdenum compound is not particularly limited, but examples thereof include molybdenum oxide and compounds containing an acid radical anion (MoO _x ⁿ⁻ ) consisting of a bond between molybdenum metal and oxygen.

The compound containing the acid radical anion (MoO _x ⁿ⁻ ) is not particularly limited, but examples thereof include molybdic acid, sodium molybdate, potassium molybdate, lithium molybdate, H ₃ PMo ₁₂ O ₄₀ , H ₃ SiMo ₁₂ O ₄₀ , NH ₄ Mo ₇ O ₁₂ , and molybdenum disulfide.

It is also possible for the molybdenum compound to contain silicon, in which case the silicon-containing molybdenum compound acts as both a flux agent and a shape control agent.

Among the above-mentioned molybdenum compounds, it is preferable to use molybdenum oxide, which is easy to sublimate and is also cost-effective. The above-mentioned molybdenum compounds may be used alone or in combination of two or more kinds.

In addition, potassium molybdate (K _{2 Mon} O _3n+1 , n=1 to 3) contains potassium and can therefore function as a potassium compound, which will be described later. In the manufacturing method of the embodiment, the use of potassium molybdate as a fluxing agent is synonymous with the use of a molybdenum compound and a potassium compound as fluxing agents.

(Potassium compounds)
A potassium compound may be further used in combination with the shape control agent.
The potassium compound is not particularly limited, but includes potassium chloride, potassium chlorite, potassium chlorate, potassium sulfate, potassium hydrogen sulfate, potassium sulfite, potassium hydrogen sulfite, potassium nitrate, potassium carbonate, potassium hydrogen carbonate, potassium acetate, potassium oxide, potassium bromide, potassium bromate, potassium hydroxide, potassium silicate, potassium phosphate, potassium hydrogen phosphate, potassium sulfide, potassium hydrogen sulfide, potassium molybdate, potassium tungstate, etc. In this case, the potassium compound includes isomers, as in the case of molybdenum compounds. Among these, it is preferable to use potassium carbonate, potassium hydrogen carbonate, potassium oxide, potassium hydroxide, potassium chloride, potassium sulfate, and potassium molybdate, and it is more preferable to use potassium carbonate, potassium hydrogen carbonate, potassium chloride, potassium sulfate, and potassium molybdate.

The above potassium compounds may be used alone or in combination of two or more.

Potassium compounds contribute to the efficient formation of mullite on the alumina surface layer. Potassium compounds also contribute to the efficient formation of a germanium-containing layer on the alumina surface layer.

It is also preferable to use potassium compounds together with molybdenum compounds as fluxing agents.

Of the above, potassium molybdate contains molybdenum, and therefore can also function as the molybdenum compound described above. When potassium molybdate is used as a fluxing agent, it can exert the same effect as when a molybdenum compound and a potassium compound are used as fluxing agents.

As potassium compounds used when raw materials are charged or generated in a reaction during the heating process during calcination, water-soluble potassium compounds such as potassium molybdate do not vaporize even at the calcination temperature range and can be easily recovered by washing after calcination, which reduces the amount of molybdenum compounds released outside the calcination furnace and allows for a significant reduction in production costs.

When a molybdenum compound and a potassium compound are used as a fluxing agent, the molar ratio of the molybdenum element of the molybdenum compound to the potassium element of the potassium compound (molybdenum element/potassium element) is preferably 5 or less, more preferably 0.01 to 3, and even more preferably 0.5 to 1.5, in order to further reduce production costs. When the molar ratio (molybdenum element/potassium element) is within the above range, it is preferable because plate-like alumina particles having a large particle size can be obtained.
(Metal Compounds)
The metal compound can have a function of promoting the crystal growth of alumina, as described below. The metal compound can be used during firing as desired. Note that since the metal compound has a function of promoting the crystal growth of α-alumina, it is not essential for the production of the plate-like alumina particles according to the present invention.

The metal compound is not particularly limited, but preferably contains at least one selected from the group consisting of Group II metal compounds and Group III metal compounds.

Examples of the Group II metal compounds include magnesium compounds, calcium compounds, strontium compounds, barium compounds, etc.

Examples of the Group III metal compounds include scandium compounds, yttrium compounds, lanthanum compounds, and cerium compounds.

The above-mentioned metal compounds refer to oxides, hydroxides, carbonates, and chlorides of metal elements. For example, yttrium compounds include yttrium oxide (Y ₂ O ₃ ), yttrium hydroxide, and yttrium carbonate. Of these, the metal compounds are preferably oxides of metal elements. These metal compounds include isomers.

Among these, metal compounds of period 3, period 4, period 5, and period 6 are preferred, metal compounds of period 4 and period 5 are more preferred, and metal compounds of period 5 are even more preferred. Specifically, magnesium compounds, calcium compounds, yttrium compounds, and lanthanum compounds are preferred, magnesium compounds, calcium compounds, and yttrium compounds are more preferred, and yttrium compounds are particularly preferred.

The addition rate of the metal compound is preferably 0.02 to 20 mass% relative to the mass equivalent value of aluminum atoms in the aluminum compound, and more preferably 0.1 to 20 mass%. When the addition rate of the metal compound is 0.02 mass% or more, the crystal growth of α-alumina containing molybdenum can proceed favorably, which is preferable. On the other hand, when the addition rate of the metal compound is 20 mass% or less, it is preferable because plate-like alumina particles with a low content of impurities derived from the metal compound can be obtained.

[yttrium]
When an aluminum compound is calcined in the presence of an yttrium compound as a metal compound, crystal growth proceeds more favorably in the calcination step, and α-alumina and a water-soluble yttrium compound are produced. At this time, since the water-soluble yttrium compound is likely to be localized on the surface of the α-alumina, which is a plate-like alumina particle, if necessary, the yttrium compound can be removed from the plate-like alumina particles by washing with water, alkaline water, or a liquid obtained by warming these.

The amounts of the above-mentioned aluminum compound, molybdenum compound, silicon or silicon compound, germanium compound, potassium compound, and the like used are not particularly limited. For example, when the total amount of the raw materials calculated as oxide is taken as 100 mass %, the following first mixture is fired.
1) An aluminum compound having an amount of preferably ₅₀ % by mass or _more , more preferably 70% by mass or more and 99% by mass or less, and even more preferably 80% by mass or more and 94.5% by mass or less, calculated as Al 2 O 3 ;
In terms of _MoO3 , preferably 40% by mass or less of a molybdenum compound, more preferably 0.5% by mass or more and 20% by mass or less of a molybdenum compound, and even more preferably 1% by mass or more and 7% by mass or less of a molybdenum compound;
Silicon, a silicon compound, or a germanium compound, preferably 0.1% by mass or more and 10% by mass or less, in terms of _SiO2 or _GeO2 , more preferably 0.5% by mass or more and less than 7% by mass of silicon, a silicon compound, or a germanium compound, and even more preferably 0.8% by mass or more and 4% by mass or less of silicon, a silicon compound, or a germanium compound,
The first mixture was mixed with the above.

The silicon, silicon compound and/or germanium compound of the shape control agent may be silicon or a silicon compound, or may be a germanium compound.
As the shape control agent, only silicon or a silicon compound may be used, only a germanium compound may be used, or only a combination of silicon or a silicon compound and a germanium compound may be used.
In the case of using a germanium compound as the shape control agent, when the total amount of the raw materials calculated as oxide is taken as 100 mass %, the first mixture may contain preferably 0.4 mass % or more and less than 1.5 mass %, and more preferably 0.7 mass % or more and 1.2 mass % or less of the germanium compound calculated as _GeO2 .

The above raw material composition (mass%) conditions may be freely combined for each raw material, and the lower and upper limits for each raw material composition (mass%) may also be freely combined.

When the first mixture further contains the above potassium compound, the amount of the potassium compound used is not particularly limited, but when the total amount of the raw materials calculated as oxide is taken as 100 mass%, the potassium compound can be mixed in an amount of preferably 5 mass% or less, more preferably 0.01 mass% or more and 3 mass% or less, and even more preferably 0.05 mass% or more and 1 mass% or less, calculated as _K2O .
It is believed that potassium molybdate formed by the reaction of the potassium compound with the molybdenum compound has an effect of diffusing Si and contributes to the promotion of the formation of mullite on the surfaces of the plate-like alumina particles.
Similarly, it is believed that the use of a potassium compound causes potassium molybdate formed by reaction with a molybdenum compound to have an effect on the diffusion of the starting germanium, and contribute to promoting the formation of germanium or germanium compounds on the surface of the plate-like alumina particles.
As the potassium compound used when the raw materials are charged or generated in a reaction during the temperature rise process during calcination, a water-soluble potassium compound, for example, potassium molybdate, does not vaporize even in the calcination temperature range and can be easily recovered by washing after calcination. This reduces the amount of molybdenum compounds released outside the calcination furnace, and also enables a significant reduction in production costs.

In the flux method, it is also preferable to use a molybdenum compound and a potassium compound as fluxing agents.
The compound containing molybdenum and potassium as a fluxing agent can be produced, for example, in the firing process using a molybdenum compound and a potassium compound, which are cheaper and easier to obtain, as raw materials. Here, the case where a molybdenum compound and a potassium compound are used as fluxing agents will be described as an example, combining the case where a molybdenum compound and a potassium compound are used as fluxing agents and the case where a compound containing molybdenum and potassium is used as fluxing agents.

The numerical ranges for the amounts of each of the above raw materials used can be appropriately combined as long as their total content does not exceed 100% by mass.

[Firing process]
The calcination step is a step of calcining an aluminum compound in the presence of a molybdenum compound and a shape control agent, and may be a step of calcining the first mixture obtained in the mixing step.

Plate-shaped alumina particles can be obtained, for example, by calcining an aluminum compound in the presence of a molybdenum compound and a shape control agent. As mentioned above, this manufacturing method is called the flux method.

The flux method is classified as a solution method. More specifically, the flux method is a crystal growth method that utilizes the fact that the crystal-flux two-component phase diagram shows a eutectic type. The mechanism of the flux method is assumed to be as follows. That is, when a mixture of solute and flux is heated, the solute and flux become liquid phase. In this case, since the flux is a flux, in other words, since the solute-flux two-component phase diagram shows a eutectic type, the solute melts at a temperature lower than its melting point and forms a liquid phase. If the flux is evaporated in this state, the concentration of the flux decreases, in other words, the effect of the flux in lowering the melting point of the solute is reduced, and the evaporation of the flux becomes the driving force for the crystal growth of the solute (flux evaporation method). Note that the solute and flux can also cause crystal growth of the solute by cooling the liquid phase (slow cooling method).

The flux method has the advantages of allowing crystal growth at temperatures much lower than the melting point, allowing precise control of the crystal structure, and allowing the formation of euhedral polyhedral crystals.

The mechanism of the production of α-alumina particles by the flux method using a molybdenum compound as a flux is not entirely clear, but it is presumed to be due to the following mechanism, for example. That is, when an aluminum compound is fired in the presence of a molybdenum compound, aluminum molybdate is first formed. At this time, as can be understood from the above explanation, the aluminum molybdate grows α-alumina crystals at a temperature lower than the melting point of alumina. Then, for example, through the decomposition of aluminum molybdate and the evaporation of the flux, the crystal growth is accelerated, and alumina particles can be obtained. That is, the molybdenum compound functions as a flux, and α-alumina particles are produced via an intermediate called aluminum molybdate.

In the production of α-alumina particles by the flux method when a potassium compound is further used as a fluxing agent, the mechanism is not necessarily clear, but it is presumed to be, for example, due to the following mechanism. First, a molybdenum compound reacts with an aluminum compound to form aluminum molybdate. Then, for example, the aluminum molybdate decomposes to form molybdenum oxide and alumina, and at the same time, the molybdenum compound containing molybdenum oxide obtained by the decomposition reacts with a potassium compound to form potassium molybdate. Alumina crystals grow in the presence of the molybdenum compound containing potassium molybdate, and thus plate-like alumina particles according to the embodiment can be obtained.

The method for firing the first mixture is not particularly limited and can be any known or commonly used method.

In the step of producing the alumina particles, the first mixture is preferably fired at, for example, 900° C. or higher. When the firing temperature exceeds 700° C., the aluminum compound reacts with the molybdenum compound to form aluminum molybdate. Furthermore, when the firing temperature reaches 900° C. or higher, the aluminum molybdate decomposes and forms plate-like alumina particles due to the action of the shape control agent. In addition, in the plate-like alumina particles, it is believed that the aluminum molybdate decomposes to form alumina and molybdenum oxide, and the molybdenum compound is incorporated into the aluminum oxide particles.
Furthermore, when the baking temperature is 900° C. or higher, it is believed that a molybdenum compound (for example, molybdenum trioxide) obtained by decomposition of aluminum molybdate reacts with a potassium compound to form potassium molybdate.
Furthermore, when the firing temperature is 1000° C. or higher, in the presence of molybdenum, the crystals of the plate-like alumina particles grow and Al ₂ O ₃ and SiO ₂ on the surfaces of the plate-like alumina particles react with each other, forming mullite with high efficiency.
Similarly, when the firing temperature reaches 1000°C or higher, in the presence of molybdenum, the crystals of the plate-like alumina particles grow, and the Al ₂ O ₃ on the surface of the plate-like alumina particles reacts with the Ge compound to form germanium dioxide, compounds having Ge-O-Al, and the like with high efficiency.

In addition, the state of the aluminum compound, shape control agent, and molybdenum compound during firing is not particularly limited, as long as the molybdenum compound and the shape control agent are present in the same space where they can act on the aluminum compound. Specifically, they may be simply mixed by mixing powders of the molybdenum compound, the shape control agent, and the aluminum compound, mechanically mixed using a grinder, or mixed using a mortar, and may be mixed in a dry or wet state.

The firing temperature conditions are not limited to the above, and are appropriately determined depending on the (006/113) ratio value, average particle size, aspect ratio, formation of mullite, the longitudinal relaxation time _T1 value, dispersibility, etc. of the target plate-like alumina particles. Usually, the firing temperature of the first mixture is preferably 900°C or higher, which is the decomposition temperature of aluminum molybdate ( _Al2 ( _MoO4 ) ₃ ), more preferably 1000°C or higher at which mullite or germanium compounds are formed with high efficiency, and more preferably 1200°C or higher at which plate-like alumina particles with the longitudinal relaxation time _T1 of 5 seconds or more (high crystallinity) can be easily obtained.

In general, to control the shape of α-alumina obtained after firing, it is necessary to perform high-temperature firing at 2000°C or higher, which is close to the melting point of α-alumina. However, there are major issues with industrial use in terms of the burden on the firing furnace and fuel costs.

The manufacturing method of this embodiment can be carried out at high temperatures exceeding 2000°C, but even at temperatures below 1600°C, which is significantly lower than the melting point of α-alumina, it is possible to form α-alumina that has a high α-crystallization rate and a plate-like shape with a high aspect ratio, regardless of the shape of the precursor.

According to this embodiment, even when the maximum firing temperature is 900 to 1600°C, plate-shaped alumina particles with a high aspect ratio and an alpha crystallization rate of 90% or more can be formed efficiently at low cost. Firing at a maximum temperature of 950 to 1500°C is more preferable, firing at a maximum temperature in the range of 1000 to 1400°C is even more preferable, and firing at a maximum temperature of 1200 to 1400°C is most preferable.

Regarding the calcination time of the first mixture, it is preferable to raise the temperature to the predetermined maximum temperature in a range of 15 minutes to 10 hours, and to hold the calcination maximum temperature for a range of 5 minutes to 30 hours. In order to efficiently form plate-like alumina particles, it is more preferable that the calcination holding time is about 10 minutes to 15 hours.
By selecting conditions of a maximum temperature of 1000 to 1400° C. and a firing holding time of 10 minutes to 15 hours, dense α-crystal polygonal plate-like alumina particles are easily obtained without being easily agglomerated.
By selecting conditions of a maximum temperature of 1200 to 1400° C. and a firing holding time of 10 minutes to 15 hours, plate-like alumina particles having the longitudinal relaxation time T ₁ of 5 seconds or more (high crystallinity) can be easily obtained.

The firing atmosphere is not particularly limited as long as the effects of the present invention can be obtained. For example, an oxygen-containing atmosphere such as air or oxygen, or an inert atmosphere such as nitrogen, argon, or carbon dioxide is preferable, and an air atmosphere is more preferable when cost is taken into consideration.

The calcination device is not necessarily limited, and a so-called calcination furnace can be used. The calcination furnace is preferably made of a material that does not react with the sublimated molybdenum oxide, and it is preferable to use a highly airtight calcination furnace so that the molybdenum oxide is efficiently utilized.

The above-mentioned alumina particles are preferably obtained by calcining an aluminum compound in the presence of a molybdenum compound and a shape control material, or in the presence of a molybdenum compound, a shape control material, a potassium compound, and a metal oxide.

That is, a preferred method for producing alumina particles includes a step of calcining an aluminum compound in the presence of a molybdenum compound and a shape control material, or in the presence of a molybdenum compound, a shape control material, and a potassium compound (calcination step). It is preferable that the first mixture further contains the above-mentioned metal compound. As the metal compound, a yttrium compound is preferable.

In the flux method using a molybdenum compound, molybdenum oxide reacts with an aluminum compound to form aluminum molybdate, and then the change in chemical potential during the decomposition of this aluminum molybdate is the driving force for crystallization, resulting in the formation of hexagonal bipyramidal polyhedral particles with well-developed idiomorphic faces (113). It is presumed that the shape control agent is localized near the particle surface during the α-alumina growth process, significantly inhibiting the growth of the idiomorphic faces (113), resulting in relatively rapid growth of the crystal orientation in the face direction, and the (001) or (006) face growing to form a plate-like shape. Therefore, by using a molybdenum compound as a flux agent, it is possible to more easily form molybdenum-containing plate-like alumina particles with a high α crystallization rate.

[Cooling process]
When a molybdenum compound and a potassium compound are used as fluxing agents, the method for producing alumina particles may include a cooling step. The cooling step is a step of cooling the alumina crystal-grown in the firing step. More specifically, the cooling step may be a step of cooling a composition containing the alumina obtained by the firing step and the fluxing agent in a liquid phase.

The cooling rate is not particularly limited, but is preferably 1 to 1000°C/hour, more preferably 5 to 500°C/hour, and even more preferably 50 to 100°C/hour. A cooling rate of 1°C/hour or more is preferable because it can shorten the manufacturing time. On the other hand, a cooling rate of 1000°C/hour or less is preferable because the firing container is less likely to crack due to heat shock and can be used for a long time.

There are no particular limitations on the cooling method, and the material may be cooled naturally or using a cooling device.

[Post-processing process]
The method for producing plate-like alumina particles according to the embodiment may include a post-treatment step. The post-treatment step is a post-treatment step for the plate-like alumina particles, and is a step for removing a fluxing agent. The post-treatment step may be performed after the above-mentioned firing step, after the above-mentioned cooling step, or after the firing step and the cooling step. In addition, the post-treatment step may be repeated two or more times as necessary.

Post-treatment methods include washing and high-temperature treatment, which may be combined.

The cleaning method is not particularly limited, but it can be removed by washing with water, an aqueous ammonia solution, an aqueous sodium hydroxide solution, or an acidic aqueous solution.

In this case, the molybdenum content can be controlled by appropriately changing the concentration and amount of water, ammonia water solution, sodium hydroxide water solution, and acidic water solution used, as well as the cleaning area and cleaning time.

Another high-temperature treatment method is to raise the temperature above the sublimation or boiling point of the flux.

[Crushing process]
In the fired product, the plate-like alumina particles may aggregate and may not satisfy the particle size range suitable for the present invention. Therefore, the plate-like alumina particles may be pulverized as necessary to satisfy the particle size range suitable for the present invention.
The method for pulverizing the fired product is not particularly limited, and any conventionally known pulverizing method such as a ball mill, a jaw crusher, a jet mill, a disk mill, a spectromill, a grinder, or a mixer mill can be used.

[Classification process]
The plate-like alumina particles are preferably classified to adjust the average particle size and improve the powder flowability, or to suppress an increase in viscosity when mixed with a binder to form a matrix. "Classification" refers to an operation of classifying particles into groups based on their size.
The classification may be either wet or dry, but from the viewpoint of productivity, dry classification is preferred. Dry classification includes classification by sieving, as well as wind classification, which classifies based on the difference between centrifugal force and fluid drag, but from the viewpoint of classification accuracy, wind classification is preferred, and can be performed using a classifier such as an air classifier utilizing the Coanda effect, a swirling air classifier, a forced vortex centrifugal classifier, or a semi-free vortex centrifugal classifier.
The above-mentioned pulverization step and classification step can be carried out at any stage required, including before or after the organic compound layer forming step described later. Depending on whether or not the pulverization or classification is carried out and the selection of the conditions therefor, for example, the average particle size of the obtained plate-like alumina particles can be adjusted.

The plate-like alumina particles of the embodiment, or the plate-like alumina particles obtained by the manufacturing method of the embodiment, are preferably those with little or no agglomeration, as they are more likely to exhibit their inherent properties, are easier to handle, and have better dispersibility when dispersed in a dispersion medium. In the manufacturing method of plate-like alumina particles, if particles with little or no agglomeration can be obtained without performing the above-mentioned crushing and classification steps, there is no need to perform the steps, and plate-like alumina having the desired excellent properties can be manufactured with high productivity, which is preferable.

[Inorganic coating forming process]
Next, an inorganic coating portion is formed on the surface of the plate-like alumina particles obtained above. In this embodiment, the second mixture containing the alumina particles and the molybdenum compound containing the molybdenum element is fired to form the inorganic coating portion composed of the molybdenum compound. The method for forming the inorganic coating portion is not particularly limited, but examples thereof include a gas phase method and a liquid phase method.

As the molybdenum compound, the same molybdenum compound as that mixed in the first mixture can be used, and examples thereof include molybdenum oxide and a compound containing an acid radical anion (MoO _x ⁿ⁻ ) formed by a bond between molybdenum metal and oxygen.

The method for firing the second mixture is not particularly limited, and can be any known or conventional method. For example, it is preferable to fire the second mixture at 750°C or higher and lower than 1100°C. If the firing temperature is 750°C or higher, firing can be performed at a temperature equal to or higher than the sublimation temperature of molybdenum oxide, and if the firing temperature is lower than 1100°C, excessive sublimation of molybdenum oxide can be suppressed, and as a result, molybdenum oxide can be sufficiently attached to the surface of the alumina particles. From the viewpoint of the above effects, the firing temperature of the second mixture is more preferably 1100°C or lower, and even more preferably 1000°C or lower.

In the liquid phase method, for example, a dispersion liquid in which plate-shaped alumina particles are dispersed is prepared, and the pH of the dispersion liquid is adjusted and heated as necessary, and then an aqueous solution of a metal oxide such as molybdenum oxide is dropped into the dispersion liquid. At this time, it is preferable to maintain the pH constant with an alkaline aqueous solution. The dispersion liquid is then stirred for a predetermined time, filtered, washed, and dried to obtain a powder. As a result, an inorganic coating portion composed of an oxide such as molybdenum oxide is formed on the surface of the plate-shaped alumina particles.

In addition, in this process, an inorganic coating layer may be formed so as to cover at least a portion of the surface of the plate-like alumina particles. In this case, for example, a layer is formed in which particles composed of a molybdenum compound are aggregated together.

[Organic compound layer formation process]
In the present embodiment, the method for producing the composite particle may further include, after the inorganic coating portion forming step, an organic compound layer forming step of forming an organic compound layer on the surface of the inorganic coating portion (also referred to as the composite particle surface). The organic compound layer forming step is usually performed after the baking step of the second mixture or after the post-treatment step.

The method for forming the organic compound layer is not particularly limited, and any known method can be used as appropriate. For example, a method in which a liquid containing an organic compound is brought into contact with plate-like alumina particles containing molybdenum oxide and then dried can be mentioned.

An example of an organic compound that can be used to form the organic compound layer is an organosilane compound. The organosilane compound only needs to be covalently bonded to at least some or all of the silicon atoms and/or inorganic silicon compounds on the surface of the plate-like alumina particles through a reaction, and the alumina may be entirely, not just partially, covered with the reactant. The method of providing the alumina surface may be attachment by immersion or chemical vapor deposition (CVD).

The amount of the organosilane compound used is preferably 20% by mass or less, and more preferably 10 to 0.01% by mass, based on the mass of silicon atoms or inorganic silicon compounds contained on the surface of the plate-like alumina particles. When the amount of the organosilane compound used is 20% by mass or less, it is preferable because it is easy to express the physical properties derived from the alumina particles.

The reaction between the alumina particles containing silicon atoms and/or inorganic silicon compounds and the organic silane compound can be carried out by a known and commonly used method for modifying the surface of fillers, such as a spray method using a fluid nozzle, a dry method using stirring with shear force, a ball mill, a mixer, or a wet method using a water-based or organic solvent-based system. It is desirable to carry out the treatment using shear force to the extent that the alumina particles used in the embodiment are not destroyed.

The system temperature in the dry method or the drying temperature after treatment in the wet method is appropriately determined according to the type of organosilane compound within the range where it does not thermally decompose. For example, when treating with the organosilane compounds described above, a temperature of 80 to 150°C is desirable.

<Resin Composition>
In one embodiment, a resin composition containing a resin and the composite particles of the embodiment is provided. The resin is not particularly limited, and examples thereof include a thermosetting resin and a thermoplastic resin.

The resin composition can be cured to form a cured product of the resin composition, and can be cured and molded to form a molded product of the resin composition. For molding, the resin composition can be appropriately subjected to treatments such as melting and kneading. Examples of molding methods include compression molding, injection molding, extrusion molding, and foam molding. Among them, extrusion molding using an extrusion molding machine is preferred, and extrusion molding using a twin-screw extruder is more preferred.
When the resin composition is used as a coating agent, paint, or the like, the resin composition can be applied to an object to be coated to form a coating film having a cured product of the resin composition.

<Method of producing resin composition>
According to one embodiment of the present invention, a method for producing a resin composition is provided.

The manufacturing method includes a step of mixing composite particles with a resin. As the composite particles may be any of those described above, a detailed description is omitted here.

The above composite particles may be surface-treated.

The composite particles used may be of one type or a combination of two or more types.

Furthermore, the composite particles may be used in combination with other fillers (alumina, spinel, boron nitride, aluminum nitride, magnesium oxide, magnesium carbonate, etc.).

The content of the composite particles is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, and even more preferably 30 to 80% by mass, based on 100% by mass of the resin composition. If the content of the composite particles is 5% by mass or more, the high thermal conductivity of the composite particles can be efficiently exhibited, which is preferable. On the other hand, if the content of the composite particles is 95% by mass or less, a resin composition with excellent moldability can be obtained, which is preferable.
When the resin composition is used as a coating agent, paint, or the like, from the viewpoint of exhibiting excellent oxidation catalyst function, antibacterial and antiviral functions and facilitating the formation of a coating film, the content of the composite particles is preferably 0.1 to 80 mass%, more preferably 1 to 50 mass%, and even more preferably 3 to 30 mass%, relative to 100 mass% of the solid content of the resin composition.

(resin)
The resin is not particularly limited, and examples thereof include thermoplastic resins and thermosetting resins.

The thermoplastic resin is not particularly limited, and known and commonly used resins used for molding materials and the like can be used. Specific examples include polyethylene resin, polypropylene resin, polymethyl methacrylate resin, polyvinyl acetate resin, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, polyvinyl chloride resin, polystyrene resin, polyacrylonitrile resin, polyamide resin, polycarbonate resin, polyacetal resin, polyethylene terephthalate resin, polyphenylene oxide resin, polyphenylene sulfide resin, polysulfone resin, polyether sulfone resin, polyether ether ketone resin, polyaryl sulfone resin, thermoplastic polyimide resin, thermoplastic urethane resin, polyamino bismaleimide resin, polyamide imide resin, polyether imide resin, bismaleimide triazine resin, polymethyl pentene resin, fluorinated resin, liquid crystal polymer, olefin-vinyl alcohol copolymer, ionomer resin, polyarylate resin, acrylonitrile-ethylene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene copolymer, etc.

The thermosetting resin is a resin that has the property of becoming substantially insoluble and infusible when hardened by means of heating, radiation, a catalyst, or the like, and generally, any well-known and commonly used resin used in molding materials, etc. may be used. Specifically, phenolic resins include novolac-type phenolic resins such as phenol novolac resin and cresol novolac resin; phenolic resins such as unmodified resol phenolic resin and oil-modified resol phenolic resin modified with tung oil, linseed oil, walnut oil, etc.; bisphenol-type epoxy resins such as bisphenol A epoxy resin and bisphenol F epoxy resin; novolac-type epoxy resins such as fatty chain-modified bisphenol-type epoxy resin, novolac epoxy resin, cresol novolac epoxy resin; epoxy resins such as biphenyl-type epoxy resin and polyalkylene glycol-type epoxy resin; resins having a triazine ring such as urea resin and melamine resin; vinyl resins such as (meth)acrylic resin and vinyl ester resin; unsaturated polyester resin, bismaleimide resin, polyurethane resin, diallyl phthalate resin, silicone resin, resin having a benzoxazine ring, cyanate ester resin, etc.

The above-mentioned resins may be used alone or in combination of two or more. In this case, two or more thermoplastic resins may be used, two or more thermosetting resins may be used, or one or more thermoplastic resins and one or more thermosetting resins may be used.

The resin content is preferably 5 to 90% by mass, and more preferably 10 to 70% by mass, relative to 100% by mass of the resin composition. A resin content of 5% by mass or more is preferable because it can impart excellent moldability to the resin composition. On the other hand, a resin content of 90% by mass or less is preferable because it can be molded into a compound that has high thermal conductivity.

(Hardening agent)
If necessary, a curing agent may be mixed into the resin composition. The curing agent is not particularly limited, and any known curing agent may be used.

Specific examples include amine compounds, amide compounds, acid anhydride compounds, and phenol compounds.

Examples of the amine compounds include diaminodiphenylmethane, diethylenetriamine, triethylenetetramine, diaminodiphenylsulfone, isophoronediamine, imidazole, BF ₃ -amine complexes, and guanidine derivatives.

Examples of the amide-based compounds include dicyandiamide, polyamide resins synthesized from a dimer of linoleic acid and ethylenediamine, etc.

Examples of the acid anhydride compounds include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride.

The phenolic compounds include phenol novolac resin, cresol novolac resin, aromatic hydrocarbon formaldehyde resin modified phenol resin, dicyclopentadiene phenol addition type resin, phenol aralkyl resin (Zylok resin), polyhydric phenol novolac resin synthesized from polyhydric hydroxy compounds such as resorcinol novolac resin and formaldehyde, naphthol aralkyl resin, trimethylol methane resin, tetraphenylol ethane resin, naphthol novolac resin, naphthol-phenol co-condensed novolac resin, naphthol- Examples of polyhydric phenol compounds include cresol co-condensed novolac resin, biphenyl-modified phenol resin (a polyhydric phenol compound in which the phenol nucleus is linked by a bismethylene group), biphenyl-modified naphthol resin (a polyhydric naphthol compound in which the phenol nucleus is linked by a bismethylene group), aminotriazine-modified phenol resin (a polyhydric phenol compound in which the phenol nucleus is linked by melamine, benzoguanamine, etc.), and alkoxy-group-containing aromatic ring-modified novolac resin (a polyhydric phenol compound in which the phenol nucleus and the alkoxy-group-containing aromatic ring are linked by formaldehyde).

The above-mentioned hardeners may be used alone or in combination of two or more.

(Cure Accelerator)
If necessary, a curing accelerator may be mixed into the resin composition.

The curing accelerator has the function of accelerating the curing of the composition.

The curing accelerator is not particularly limited, but examples thereof include phosphorus compounds, tertiary amines, imidazoles, organic acid metal salts, Lewis acids, and amine complex salts.

The above-mentioned curing accelerators may be used alone or in combination of two or more.

(Curing catalyst)
If necessary, a curing catalyst may be mixed into the resin composition.

The curing catalyst acts in place of the curing agent to promote the curing reaction of the compound having an epoxy group.

There are no particular limitations on the curing catalyst, and any known, commonly used thermal polymerization initiator or active energy ray polymerization initiator can be used.

The curing catalysts may be used alone or in combination of two or more.

(Viscosity modifier)
A viscosity modifier may be mixed into the resin composition, if necessary.

The viscosity modifier functions to adjust the viscosity of the composition.

Viscosity regulators are not particularly limited, and organic polymers, polymer particles, inorganic particles, etc. can be used.

The viscosity modifiers may be used alone or in combination of two or more.

(Plasticizer)
A plasticizer may be mixed into the resin composition, if necessary.

Plasticizers have the function of improving the processability, flexibility, weather resistance, etc. of thermoplastic synthetic resins.

The plasticizer is not particularly limited, and examples that can be used include phthalates, adipates, phosphates, trimellitates, polyesters, polyolefins, polysiloxanes, etc.

The above-mentioned plasticizers may be used alone or in combination of two or more.

[Mixing process]
The resin composition according to the present embodiment can be obtained by mixing the composite particles, the resin, and, if necessary, other ingredients. There is no particular limitation on the mixing method, and the mixture can be mixed by a known, commonly used method.

When the resin is a thermosetting resin, a typical method for mixing the thermosetting resin with the composite particles, etc., is to thoroughly mix a predetermined amount of the thermosetting resin, the composite particles, and other components as necessary with a mixer, etc., and then knead with a three-roll mill, etc., to obtain a fluid liquid composition. In another embodiment, a method for mixing the thermosetting resin with the composite particles is to thoroughly mix a predetermined amount of the thermosetting resin, the composite particles, and other components as necessary with a mixer, etc., and then melt-knead with a mixing roll, extruder, etc., and then cool to obtain a solid composition.
Regarding the mixed state, when a curing agent, catalyst, etc. are blended, it is sufficient that the curable resin and the blended material are mixed sufficiently uniformly, but it is more preferable that the composite particles are also uniformly dispersed and mixed.

When the resin is a thermoplastic resin, a typical method for mixing the thermoplastic resin with the composite particles, etc., is to premix the thermoplastic resin, the composite particles, and, if necessary, other components using various mixers such as a tumbler or Henschel mixer, and then melt-knead using a mixer such as a Banbury mixer, roll, Brabender, single-screw kneading extruder, twin-screw kneading extruder, kneader, or mixing roll. The temperature for melt-kneading is not particularly limited, but is usually in the range of 100 to 320°C.

A coupling agent may be added to the resin composition because it can further improve the fluidity of the resin composition and the filler loading of the composite particles. By adding a coupling agent to the resin, the adhesion between the resin and the composite particles can be further improved, the interfacial thermal resistance between the resin and the composite particles can be reduced, and the thermal conductivity of the resin composition can be improved.

The above-mentioned coupling agents may be used alone or in combination of two or more.

The amount of coupling agent added is not particularly limited, but is preferably 0.01 to 5% by mass, and more preferably 0.1 to 3% by mass, relative to the mass of the resin.

The molybdenum oxide constituting the inorganic coating portion of the composite particle has excellent antibacterial properties, antiviral properties, and oxidation catalyst function. In addition, the plate-like alumina particles constituting the composite particle have excellent mechanical properties, and the molybdenum oxide contained in the plate-like alumina particles has excellent oxidation catalyst function, etc. Therefore, the resin composition is suitably used as a coating agent, paint, etc. that can impart one or more of the above functions and physical properties.

The resin composition can also be used as a thermally conductive material. The plate-like alumina particles contained in the resin composition provide excellent thermal conductivity to the resin composition, so the resin composition can also be used as an insulating heat dissipation material. This can improve the heat dissipation function of the device, contributing to making the device smaller, lighter, and more powerful.

<Method of producing the cured product>
According to one embodiment of the present invention, there is provided a method for producing a cured product, which comprises curing the resin composition produced as described above.

There are no particular limitations on the curing temperature, but it is preferably 20 to 300°C, and more preferably 50 to 200°C.

There are no particular limitations on the curing time, but it is preferably 0.1 to 10 hours, and more preferably 0.2 to 3 hours.

The shape of the cured product will vary depending on the desired application and can be designed appropriately by those skilled in the art.

In this embodiment, the alumina particles are plate-like alumina particles, and the composite particles also have a plate shape, but this is not limited thereto, and the alumina particles may be polyhedral alumina particles, and the composite particles may have a polyhedral shape.

In addition, in the above-mentioned resin composition, the method for producing the resin composition, and the cured product, composite particles having a plate-like shape are used, but this is not limited thereto, and composite particles having a polyhedral shape may also be used.

The following describes examples of the present invention. The present invention is not limited to the following examples.

Example 1
First, alumina particles were produced as the base of the composite particles. 120 g of aluminum hydroxide (manufactured by Nippon Light Metals Co., Ltd., average particle size 1-2 μm) (90% by weight in terms of oxide of Al ₂ O ₃ ), 7.8 g of molybdenum trioxide (manufactured by Taiyo Koko Co., Ltd.) (9% by weight in terms of oxide of MoO ₃ ), and 0.78 g of silicon dioxide (manufactured by Kanto Chemical Co., Ltd., special grade) (1% by weight in terms of oxide of SiO ₂ ) were mixed in a mortar to obtain a mixture. The obtained mixture was placed in a crucible, heated to 1100°C at 5°C/min in a ceramic electric furnace, and held at 1100°C for 5 hours to perform firing. After that, the temperature was lowered to room temperature at 5°C/min, and the crucible was removed to obtain 79.0 g of a powder of plate-shaped alumina A.

10.0 g of the obtained alumina particle A powder was dispersed in 50 mL of ethanol, and the dispersion was stirred at room temperature (25-30°C) for 3 hours, after which the ethanol was removed by filtration and the mixture was dried to obtain 9.9 g of alumina particle B1 powder.

2 g of the obtained alumina particle B1 powder was mixed with 0.8 g of molybdenum trioxide (molybdenum trioxide synthesized in Example 1 of WO 2021/060375) to obtain a mixture. The obtained mixture was placed in a crucible and heated to 800°C at 5°C/min in a ceramic electric furnace, and then held at 800°C for 5 hours for firing. After that, the temperature was lowered to room temperature at 5°C/min, and the crucible was removed to obtain 2.5 g of composite particle powder.

Example 2
2.2 g of composite particle powder was obtained by the same method as in Example 1, except that 2 g of alumina particle B1 powder after washing with ethanol was mixed with 0.4 g of molybdenum trioxide (molybdenum trioxide synthesized in Example 1 of WO 2021/060375).

Example 3
5.15 g of composite particle powder was obtained by the same method as in Example 1, except that 5 g of alumina particle B1 powder after washing with ethanol was mixed with 0.5 g of molybdenum trioxide (molybdenum trioxide synthesized in Example 1 of WO 2021/060375).

Example 4
5.0 g of composite particle powder was obtained by the same method as in Example 1, except that 5 g of alumina particle B1 powder after washing with ethanol was mixed with 0.25 g of molybdenum trioxide (molybdenum trioxide synthesized in Example 1 of WO 2021/060375).

Example 5
A mixture was obtained by mixing 5 g of the powder of alumina particles B1 after washing with ethanol with 1.0 g of molybdenum trioxide (manufactured by Taiyo Koko Co., Ltd.). The mixture was placed in a crucible and heated to 900° C. at a rate of 5° C./min in a ceramic electric furnace, and then fired by holding at 900° C. for 5 hours. The temperature was then lowered to room temperature at a rate of 5° C./min, and the crucible was removed to obtain 5.15 g of composite particle powder.

Example 6
A mixture was obtained by mixing 5 g of the powder of alumina particles B1 after washing with ethanol with 1.0 g of molybdenum trioxide (manufactured by Taiyo Koko Co., Ltd.). The mixture was placed in a crucible and heated to 1000°C at a rate of 5°C/min in a ceramic electric furnace, and then fired by holding at 1000°C for 5 hours. The temperature was then lowered to room temperature at a rate of 5°C/min, and the crucible was removed to obtain 5.10 g of composite particle powder.

<Comparative Example 1>
As Comparative Example 1, a powder of alumina particles A in a state before being washed with ethanol was obtained by the same production method as in Example 1.
The SEM image of the obtained powder is shown in Figure 3. The magnification of Figure 3 is 2000 times. SEM observation confirmed that the shape of the alumina particles A was polygonal, the thickness was 400 nm, and the particle size distribution measurement confirmed that _D50 was 5 μm and the aspect ratio was 12.5. Furthermore, when XRD measurement was performed, a sharp scattering peak derived from α-alumina appeared, and no alumina crystal system peaks other than the α crystal structure were observed, confirming that the α crystallization rate was 99% or more.

<Comparative Example 2>
As Comparative Example 2, a powder of alumina particles B1 in a state after being washed with ethanol was obtained by the same production method as in Example 1.

<Comparative Example 3>
As Comparative Example 3, alumina particles B2 in a state after washing with water were obtained by the same production method as in Example 1. 9.8 g of alumina particles B2 powder was obtained by the same production method as in Example 1, except that a dispersion liquid was prepared by dispersing 10.0 g of the alumina particles A powder obtained in Example 1 in 50 mL of water.

Evaluation
[Measurement of major axis L of alumina particles]
Using a laser diffraction particle size measurement device (Shimadzu Corporation, SALD-7000), 1 mg of alumina powder was diluted with a 0.2 wt % aqueous solution of sodium hexametaphosphate (Fuji Film Wako Pure Chemical Industries, Ltd.) to a total of 18 g, and this was used as a sample for measurement to determine the average particle size _D50 value (μm), which was taken as the major axis L.

[Measurement of thickness D of alumina particles]
The thickness of 50 pieces was measured using a scanning electron microscope (SEM), and the average value was used as the thickness D (μm).

[Aspect ratio L/D]
The aspect ratio was calculated using the following formula.
(Aspect ratio)=(long diameter L of alumina particle/thickness D of alumina particle)

[XRF Analysis]
About 70 mg of the powder of the prepared sample was placed on filter paper and covered with a PP film, and a composition analysis was performed using an X-ray fluorescence (XRF) analyzer (Rigaku Corporation, Primus IV).
The amount _{of Al2O3} ( _{[ Al2O3} ]), the amount of _SiO2 ([ _SiO2 ]) and the amount of _MoO3 ([ _MoO3 ]) were obtained by _XRF analysis, and the ratio of the amount of _MoO3 to the _amount of _Al2O3 in _the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) was calculated.

[XPS analysis]
The prepared sample (composite particles) was press-fixed onto double-sided tape and subjected to composition analysis using an X-ray photoelectron spectroscopy (XPS) device (Quantera SXM, manufactured by ULVAC-PHI, Inc.) under the following conditions.
X-ray source: Monochromatic AlKα, beam diameter 100 μmφ, output 25 W
Measurement: Area measurement (1000 μm square), n = 3
Charge correction: C1s = 284.8 eV
The amount _{of Al2O3} ( _{[ Al2O3} ]), the amount _{of SiO2} ([ _SiO2 ]), and the amount of _MoO3 ([ _MoO3 ]) were obtained by X-ray photoelectron spectroscopy (XPS) analysis, and the ratio of the _amount of MoO3 to the amount of _Al2O3 on the surface of the alumina _particles ([ _MoO3 ]/[ _Al2O3 ] _× 100) was _determined .

[pH Measurement of Aqueous Dispersion]
0.1 g of each of the composite particle powders obtained in Examples 1 to 6 and Comparative Examples 1 to 3 was dispersed in 9.9 mL of water to prepare a dispersion, and the pH of each dispersion was measured using a pH measuring device (LAQUA act portable type D-71, manufactured by HORIBA Scientific Co., Ltd.). The results are shown in Table 1.

First, SEM images of the composite particles obtained in Examples 1 and 4 are shown in Figures 1 and 2, respectively. The magnifications of Figures 1 and 2 are 1000x and 2000x, respectively. Figures 1 and 2 confirm that the composite particles of Examples 1 and 4 are plate-shaped.

Furthermore, from the results in Table 1, it was found that the ratio of _the amount of _MoO3 to the amount of _Al2O3 on the surface of the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS was 47, indicating that a large amount of molybdenum oxide was present as an inorganic coating on the surface of _the alumina particles. Furthermore, the ([ _MoO3 ]/ _{[ Al2O3} ] x 100) _XRF was 43, indicating that the amount of molybdenum oxide present on the surface of the alumina particles was greater than the amount of molybdenum oxide present in the entire alumina particles.

In Example 2, the ratio of the amount of _MoO3 to the amount _{of Al2O3} on the surface of the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS was 32, which indicated that a large amount of molybdenum oxide was present on the surface of _the alumina particles, similar to Example 1. In addition, the ratio of ([ _MoO3 ]/[ _Al2O3 ] x 100) _XRF was 23, which indicated that the amount of molybdenum oxide present on the surface of the alumina particles was greater than the amount of molybdenum oxide present in _the entire alumina particles.

In Example 3, the ratio of the amount of _MoO3 to the amount _{of Al2O3} on the surface of _the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS was 27, which indicated that a large amount of molybdenum oxide was present on the surface of _the alumina particles, as in Example 1. In addition, the ([ _MoO3 ]/[ _Al2O3 ] x 100) _XRF was 21, which indicated that the amount of molybdenum oxide present on the surface of the alumina particles was greater than the amount of molybdenum oxide present in the entire alumina particles.

In Example 4, the ratio of the amount of _MoO3 to the amount _{of Al2O3} on the surface of _the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS was 24, indicating that a large amount of molybdenum oxide was present on the surface of the alumina particles. In particular, _{the ([MoO3]/[Al2O3] x 100) XRF was 4 ,} indicating that the amount of molybdenum oxide present on the surface of the alumina particles was significantly greater than the amount of molybdenum oxide present in the entire alumina particles.

In Example 5, the ratio of the amount of _MoO3 to the amount _{of Al2O3} on the surface of _the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS was 22, indicating that a large amount of molybdenum oxide was present on the surface of the alumina particles. In particular, the ratio of ([ _MoO3 ]/[ _Al2O3 ] x ₁₀₀ ) _XRF was 1.2, indicating that the amount of molybdenum oxide present on the surface of the alumina particles was significantly greater than the amount of molybdenum oxide present in the entire alumina particles.

In Example 6, the ratio of the amount of _MoO3 to _the amount of _Al2O3 on the surface of _the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS was 19, indicating that a large amount of molybdenum oxide was present on the surface of the alumina particles. In particular, the ratio of ([ _MoO3 ]/[ _Al2O3 ] x ₁₀₀ ) _XRF was 1.3, indicating that the amount of molybdenum oxide present on the surface of the alumina particles was significantly greater than the amount of molybdenum oxide present in the entire alumina particles.

The dispersions containing the composite particles of Examples 1 to 6 had a low pH of 3.9 to 4.8.

On the other hand, in Comparative Example 1, the ratio of the amount of _MoO3 to _the amount of _Al2O3 on the surface of _the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS was 13, a smaller value than any of Examples 1 to 6. In addition, _the ratio of ([ _MoO3 ]/[ _Al2O3 ] x 100) _XRF was 0.6, a smaller value than any of Examples 1 to 6.

In Comparative Example 2, the ratio of the amount of _MoO3 to the amount _{of Al2O3} on the surface of _the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS was 8, which was a smaller value than any of Examples 1 to 6, similar to Comparative Example 1. In addition, the ratio of ([ _MoO3 ] _/ [ _Al2O3 ] x 100) _XRF was 0.7, which was a smaller value than any of Examples 1 to 6.

In Comparative Example 3, the ratio of the amount of _MoO3 to the amount _{of Al2O3} on the surface of _the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) _XPS was 2, which was a smaller value than any of Examples 1 to 6, similar to Comparative Example 1. In addition, the ratio of ([ _MoO3 ] _/ [ _Al2O3 ] x 100) _XRF was 0.3, which was also a smaller value than any of Examples 1 to 6.

The dispersions in which the alumina particles of Comparative Examples 1 to 3 were dispersed had a pH of 5.0 to 6.8, which was higher than any of the values in Examples 1 to 6.

Claims (10)

The inorganic coating material includes alumina particles and an inorganic coating portion formed on a surface of the alumina particles and composed of molybdenum oxide,
The alumina particles contain silicon and/or germanium and further contain mullite in a surface layer,
Composite particles, wherein the ratio of the amount of _{MoO3 to the amount of Al2O3 on} the surface of _the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) obtained by _X -ray photoelectron spectroscopy (XPS) analysis is 15 or more. The ratio of the amount of _MoO3 to _the amount of _Al2O3 in _the alumina particles ([ _MoO3 ]/[ _Al2O3 ] x 100) obtained by X-ray fluorescence (XRF) analysis is 1 or more;
_2. The composite particle of claim 1, wherein ([ _MoO3 ]/ _{[ Al2O3} ] x 100) XPS is greater than ([ _MoO3 ]/[ _Al2O3 ] x 100) XRF. The composite particles according to claim 1 or 2, wherein the alumina particles have an alpha crystallization rate of 90% or more. The composite particles according to any one of claims 1 to 3, wherein the alumina particles contain molybdenum. The composite particles according to any one of claims 1 to 4, wherein the alumina particles have a plate shape, a thickness of 0.01 μm or more and 5 μm or less, an average particle diameter of 0.1 μm or more and 500 μm or less, and an aspect ratio of 2 or more and 500 or less. a step of producing alumina particles having mullite on a surface layer by firing a first mixture containing an aluminum compound containing an aluminum element, a molybdenum compound containing a molybdenum element, and a shape control agent for controlling the shape of the alumina particles, the shape control agent being composed of one or more selected from silicon, a silicon compound containing a silicon element, and a germanium compound containing a germanium element ;
a step of firing a second mixture containing the alumina particles and a molybdenum compound containing elemental molybdenum to form an inorganic coating portion composed of a molybdenum compound on the surface of the alumina particles;
A method for producing composite particles, comprising: The method for producing composite particles according to claim 6 , wherein the molybdenum compound is molybdenum oxide. The method for producing composite particles according to claim 7 , wherein the second mixture is fired at 750° C. or higher and lower than 1100° C. in the step of forming the inorganic coating portion. The method for producing composite particles according to claim 7 , wherein the first mixture is fired at 900° C. or higher in the step of producing the alumina particles. The method for producing composite particles according to any one of claims 6 to 9 , wherein the first mixture further contains a potassium compound containing potassium element.