JP2022171034A - Composite particles and manufacturing method of the composite particles - Google Patents

Abstract

To provide composite particles having an inorganic coating composed of a molybdenum compound and capable of exhibiting good properties.SOLUTION: Composite particles comprise alumina particles containing molybdenum (Mo) and an inorganic coating formed on the surface of the alumina particles and composed of molybdenum oxide, and the ratio of the amount of MoO3 to the amount of Al2O3 at the surface of the alumina particles ([MoO3]/[Al2O3]×100)XPS is equal to or more than 15.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to composite particles and a method for producing the composite particles, and more particularly to composite particles in which alumina particles are provided with an inorganic coating.

Alumina is excellent in mechanical strength such as abrasion resistance, chemical stability, thermal conductivity, heat resistance, etc., so it has many uses such as pigments, paints, coatings, abrasives, electronic materials, and 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 Reference 1).

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

Molybdenum trioxide (MoO ₃ ) is widely used in catalysts, optical materials, pigments, ceramics and glass manufacturing additives, semiconductors, and the like. The present applicant found that nano-MoO ₃ can be synthesized by quenching MoO ₃ vapor, and disclosed this technology (Patent Document 3).

JP 2008-238057 A JP 2016-222501 A WO2018/003481

However, in the adsorbent of Patent Document 1, the particle size of alumina and the structural positional relationship between the inert carrier of alumina and molybdenum trioxide are unknown. There is still room for improvement. Moreover, the adsorbent of Patent Document 1 adsorbs metallic mercury in exhaust gas, and its application is limited.
In addition, neither of Patent Documents 2 and 3 has knowledge about composite particles having alumina particles and a coating portion composed of molybdenum oxide and their characteristics.

The present invention has been made in view of such circumstances, and provides a composite particle having an inorganic coating portion composed of molybdenum oxide and capable of exhibiting excellent properties, and a method for producing the composite particle. for the purpose.

As a result of intensive research by the present inventors to solve the above problems, when a molybdenum compound is further added to alumina particles containing molybdenum and fired, the alumina particles are easily coated with molybdenum oxide, and on the surface of the alumina particles The inventors have found that molybdenum oxide can be unevenly distributed, and have completed the present invention. In addition, the combination of alumina particles containing molybdenum and molybdenum oxide unevenly distributed on the surface of the alumina particles provided, for example, a very low pH in an aqueous solvent. It can be expected to exhibit various properties such as functions and oxidation catalyst functions.

That is, the present invention provides the following means.
[1] including alumina particles and an inorganic coating portion provided on the surface of the alumina particles and composed of molybdenum oxide,
Ratio of _MoO3 amount to _Al2O3 amount _on the surface of the alumina particles obtained by X-ray photoelectron spectroscopy (XPS) analysis ₍ [ _MoO3 ]/[ _Al2O3 ] × 100) _XPS is 15 or more is a composite particle.

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

[3] The composite particles according to [1] or [2] above, wherein the alumina particles have an α crystallization rate of 90% or more.

[4] The composite particles according to any one of [1] to [3] above, wherein the alumina particles contain molybdenum.

[5] 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. The composite particle according to any one of [4].

[6] The composite particles according to [1] above, wherein the alumina particles further contain silicon and/or germanium.

[7] The composite particles according to [6] above, wherein the alumina particles contain mullite in a surface layer.

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

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

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

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

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

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

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

ADVANTAGE OF THE INVENTION According to this invention, the composite particle which has the inorganic coating part comprised with molybdenum oxide and can express favorable various characteristics can be provided.

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

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<Composite particles>
A composite particle according to the present embodiment includes alumina particles and an inorganic coating portion provided on the surface of the alumina particles and made of molybdenum oxide. The composite particles of this embodiment may have any shape such as plate-like, house-of-cards, polyhedral, and the like. From the viewpoint of making the most of the anisotropy of the composite particles, the composite particles preferably have, for example, a plate-like shape. When the composite particles are plate-like, the alumina particles also have a plate-like shape. Hereinafter, in the present embodiment, alumina particles having a plate-like shape are also referred to as "plate-like alumina particles", "plate-like alumina particles", or simply "alumina particles".

<Plate-like alumina particles>
The term "plate-like" as used in the present invention means that the aspect ratio obtained by dividing the average particle diameter of the alumina particles by the thickness is 2 or more. In this specification, the "thickness of alumina particles" is the arithmetic of the thickness measured for at least 50 plate-like alumina particles randomly selected from images obtained by a scanning electron microscope (SEM). Average value. The "average particle size of alumina particles" is a value calculated as a volume-based median diameter _D50 from a volume-based cumulative particle size distribution measured by a laser diffraction particle size measuring device.

In the alumina particles, the conditions of thickness, particle diameter and aspect ratio shown below can be combined in any way as long as they are tabular. Also, the upper limit and lower limit of the numerical ranges exemplified in these conditions can be freely combined.

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

The plate-like alumina particles preferably have an average particle diameter (D ₅₀ ) of 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 (D ₅₀ ) equal to or less than the above upper limit value are suitable for use as a filler, and when used as a functional filler, antibacterial, antiviral, etc., expressed by the inorganic coating portion. Various characteristics can be exhibited sufficiently. In addition, since alumina particles having an average particle diameter (D ₅₀ ) equal to or larger than the above lower limit have low cohesiveness, they are excellent in dispersibility when used as a resin filler.

The plate-like alumina particles preferably have an aspect ratio of 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 two-dimensional blending characteristics can be obtained. When the aspect ratio is 5 or more, the above characteristics can be exhibited more, which is preferable.

The plate-like alumina particles may have a circular plate-like shape or an elliptical plate-like shape, but the particle shape is preferably, for example, a polygonal plate-like shape from the viewpoint of handleability and ease of production.

The plate-like alumina particles may be obtained based on any production method, but a molybdenum compound (preferably Furthermore, it is preferably obtained by firing an aluminum compound in the presence of a potassium compound) and a shape control agent. At least one selected from the group consisting of silicon, silicon compounds, and germanium compounds is preferably used as the shape control agent. It is more preferable to use silicon or a silicon compound containing elemental silicon as the shape control agent, since it serves as a supplier of Si for mullite, which will be described later.
In the manufacturing method described above, the molybdenum compound is used as a fluxing agent. In this specification, this manufacturing method using a molybdenum compound as a fluxing agent may be simply referred to as "fluxing method". The flux method will be described in detail later. By such firing, the molybdenum compound reacts with the aluminum compound at a high temperature to form aluminum molybdate, and when this aluminum molybdate further decomposes into alumina and molybdenum oxide at a higher temperature, the molybdenum compound forms a plate. It is believed that the particles are incorporated into the alumina particles. Molybdenum oxide can also be sublimated, recovered and reused.
In the case where the plate-like alumina particles contain mullite in the surface layer, in this process, silicon or a compound containing silicon atoms mixed as a shape control agent reacts with an aluminum compound via molybdenum to form mullite. It is considered to be formed on the surface layer of the plate-like alumina particles. Regarding the formation mechanism of mullite in more detail, on the surface of the alumina plate, the formation of Mo--O--Si through the reaction of molybdenum and Si atoms and the formation of Mo--O--Al through the reaction of molybdenum and Al atoms occur. It is believed that mullite having Si--O--Al bonds is formed while Mo is eliminated by high-temperature firing.
Molybdenum oxide not incorporated into the plate-like alumina particles is preferably recovered by sublimation and reused.
In the present specification, fluxing agents that can be sublimated in the production method described below are called fluxing agents, and shapes that cannot be sublimated are called shape controlling agents.

In the production of the plate-like alumina particles, by utilizing molybdenum and a shape control agent, the plate-like alumina particles have a high α-crystal rate and have an idiomorphic shape, resulting in excellent dispersibility, mechanical strength, and high thermal conductivity. It is possible to realize sexuality.

When the plate-like alumina particles contain mullite in the surface layer, the amount of mullite generated on the surface layer of the plate-like alumina particles can be controlled by the proportion of the molybdenum compound and the shape control agent used. It can be controlled by the ratio of silicon used or silicon compound containing silicon element used. A preferred value for the amount of mullite formed on the surface layer of the plate-like alumina particles and a preferred usage ratio of the raw materials will be described in detail later.

The plate-like alumina particles are plate-like alumina particles having an aspect ratio of 5 to 500 from the viewpoint of further manifestation of the above-mentioned characteristics, and solid ²⁷ Al NMR analysis shows that at a static magnetic field strength of 14.1 T. The longitudinal relaxation time T1 for the peak of hexacoordinated aluminum at 30 ppm is preferably ₅ seconds or more.

That the longitudinal relaxation time T1 is ₅ seconds or longer means that the crystallinity of the plate-like alumina particles is high. It has been reported that when the longitudinal relaxation time in the solid state is large, the crystallinity is high and the symmetry of the crystal is good (Previous report: Kitagawa Susumu et al. Publishing Co., Ltd., p80-82).

In the plate-like alumina particles, the longitudinal relaxation time T1 is preferably ₅ seconds or longer, more preferably 6 seconds or longer, and even more preferably 7 seconds or longer.
In the plate-like alumina particles of the embodiment, the _upper limit of the longitudinal relaxation time T1 is not particularly limited. 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. may

In the plate-like alumina particles, it is preferable that the 4-coordinated aluminum peak at 60 to 90 ppm at a static magnetic field strength of 14.1 T is not detected in solid-state ²⁷ Al NMR analysis. Such plate-like alumina particles are considered to be less likely to break or fall off due to the distortion of crystal symmetry due to the inclusion of crystals with different coordination numbers, and tend to be more excellent in shape stability. .

Conventionally, the degree of crystallinity of inorganic substances is generally evaluated based on the results of XRD analysis or the like. However, as a result of investigations by the present inventors, it was found that the crystallinity of alumina particles can be evaluated by using the longitudinal relaxation time T1 as _an index, thereby obtaining analysis results with higher accuracy than conventional XRD analysis. rice field. The plate-like alumina particles according to the embodiment have a large longitudinal relaxation time T1 of ₅ seconds or more, and it can be said that the crystallinity of the alumina particles is high. That is, the plate-like alumina particles according to the embodiment probably have high crystallinity, so that irregular reflection on the crystal plane is suppressed, light reflection is improved, and it is considered to be excellent in brilliance.

Furthermore, the present inventors have found that 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 are very well correlated. In particular, in plate-like alumina particles having an average particle diameter of 10 μm or less and an aspect ratio of 30 or _less , the value of longitudinal relaxation time T1, the shape retention rate of plate-like alumina particles, and the processing stability of the resin composition Correlation appears remarkably. The above plate-like alumina particles having a longitudinal relaxation time T1 of ₅ seconds or more have good processing stability when mixed with a resin to produce a resin composition, and can be easily processed into a desired shape. It also has the advantage of being Since the plate-like alumina particles as described above have _a long value of the longitudinal relaxation time T1, the crystallinity is enhanced. Therefore, since the crystallinity of alumina is high, the strength of the particles is high, and when the resin and plate-like alumina particles are mixed in the production process of the resin composition, it is thought that the plate is unlikely to break, and furthermore, probably Since alumina has high crystallinity, the surface of the particles has few irregularities, and it is considered that the adhesion with the resin is excellent. Due to these factors, the plate-like alumina particles as described above are considered to have good processing stability of the resin composition. Therefore, according to the composite particles having the plate-like alumina particles as described above, the original performance of the plate-like alumina particles and the inorganic coating portion can be satisfactorily exhibited even when blended in a resin composition.

The shape retention rate can be evaluated as follows.
(Shape retention rate)
66% by mass of alumina particles and 34% by mass of polyphenylene sulfite resin (PPS resin, LR-100G manufactured by DIC) are blended to prepare a total of 5 kg of mixture. Using a twin-screw extruder with a screw diameter of 40 mm and L/D=45, 5 kg of the mixture is melt-kneaded under conditions of a feed rate of 15 kg/h, an extruder temperature of 320° C., and a screw rotation speed of 150 rpm. The strands obtained after melt-mixing are cut with a pelletizer to obtain pellets having a major diameter of 3 mm and a length of 5 mm. 5 g of pellets are collected, placed in a crucible, and heated at 700° C. for 3 hours to incinerate the pellets. The average particle diameter D ₅₀ (μm) of the ashed powdery sample is measured with a laser diffraction particle size distribution meter, and the obtained value is defined as the average particle diameter after extrusion kneading. Separately from the above sample, 3 g of a sample before extrusion kneading (before blending with the polyphenylene sulfite resin) was prepared, the average particle diameter D ₅₀ (μm) was measured in the same manner, and the obtained value was used as the value before extrusion kneading. Let it be the average particle size.
The shape retention rate (%) of the powder is determined by (average particle size after extrusion kneading/average particle size before extrusion kneading×100).
In samples with low crystallinity, the alumina particles are destroyed by melt-kneading with an extruder, the fine-grained component increases, and the average particle size becomes smaller than before kneading (the value of the shape retention rate decreases).

The processing stability can be evaluated, for example, by the following method.
(processing stability)
66% by mass of alumina particles and 34% by mass of polyphenylene sulfite resin (PPS resin, manufactured by DIC, LR-100G) were blended to prepare a mixture of 5 kg in total. Using a twin-screw extruder with a screw diameter of 40 mm and L/D=45, 5 kg of the mixture is melt-kneaded under conditions of a feed rate of 15 kg/h, an extruder temperature of 320° C., and a screw rotation speed of 150 rpm. If the diameter of the strand coming out of the die is not stable and causes surging, or if unevenness or streaks are observed on the strand surface due to foaming or foreign matter, etc., the processing stability is evaluated as poor, and the above phenomenon is observed. If there is none, it can be evaluated that the processing stability is good.

Compared with spherical alumina particles, it has been difficult to obtain plate-like alumina particles with high crystallinity. This is probably because plate-like alumina particles, unlike spherical alumina particles, need to be biased in the direction of crystal growth during the production process.
On the other hand, the above plate-like alumina particles satisfying the value of the longitudinal relaxation time T1 have _a plate-like shape and high crystallinity. Therefore, it is very useful because it has the advantages of plate-like alumina particles, such as excellent thermal conductivity, and further enhances the shape retention rate and processing stability of the resin composition.

The pH of the isoelectric point of the plate-like alumina particles is, for example, in the range of 2-6, preferably in the range of 2.5-5, and more preferably in the range of 3-4. Plate-like alumina particles having an isoelectric point pH within the above range have a high electrostatic repulsion force, and by themselves can enhance the dispersion stability when blended in the medium to be dispersed as described above. Modification by surface treatment such as a coupling treatment agent intended to improve performance becomes easier.

The pH value of the isoelectric point was measured using a zeta potential measurement device (Zetasizer Nano ZSP, manufactured by Malvern), and 20 mg of a sample and 10 mL of a 10 mM KCl aqueous solution were treated with Awatori Rentaro (ARE-310, manufactured by Thinky). ) in the stirring/defoaming mode for 3 minutes, and the supernatant left to stand for 5 minutes is used as a measurement sample. (applied voltage 100 V, Monomodl mode), and the pH at the isoelectric point at which the potential is zero is evaluated.

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 a density of It is more preferably 3.80 g/cm ³ or more and 4.10 g/cm ³ or less.
The density was measured using a dry automatic densitometer (Accupic II1330 manufactured by Micromeritics) after pretreatment of plate-like alumina particles at 300°C for 3 hours at a measurement temperature of 25°C with helium as a carrier gas. It can be measured under the conditions used as

[alumina]
The “alumina” contained in the plate-like alumina particles is aluminum oxide, for example, transition alumina of various crystal forms such as γ, δ, θ, κ, etc., or alumina hydrate in the transition alumina Although it may contain, it is basically preferable to be in the α crystal form (α type) in terms of better mechanical strength or thermal conductivity. The α-crystal form is a dense crystal structure of alumina, which is advantageous for improving the mechanical strength or thermal conductivity of plate-like alumina.
It is preferable that the α crystallization rate is as close as possible to 100%, since the original properties of the α crystal form are likely to be exhibited. The α crystallization rate of the plate-like alumina particles is, for example, 90% or more, preferably 95% or more, more preferably 99% or more.

[Silicon/Germanium]
The plate-like alumina particles of this embodiment may contain silicon and/or germanium.
The silicon or germanium may be derived from silicon, silicon compounds and/or germanium compounds that can be used as shape control agents. By utilizing these properties, plate-like alumina particles having excellent luster can be produced in the production method described later.

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

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

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

Si can be detected in the plate-like alumina particles by XRF analysis when silicon or a silicon compound containing elemental silicon is used as the shape control agent. In the plate-like alumina particles, 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, It is more preferably 0.02 or less.
In addition, 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 0.005 or more. is more preferred.
In the plate-like alumina particles, the molar ratio of Si to Al [Si]/[Al] obtained by XRF analysis is, for example, 0.003 or more and 0.04 or less, and 0.004 or more and 0.035 or less. is preferred, and 0.005 or more and 0.02 or less is more preferred.
The value of the molar ratio [Si] / [Al] obtained by the XRF analysis is within the above range. The plate-like alumina particles satisfy the above (006/113) ratio value, and the brightness is more preferable. As a result, a plate-like shape is formed satisfactorily. In addition, deposits are less likely to adhere to the surface of the plate-like alumina particles, resulting in excellent quality. These deposits are considered to be two SiO ₂ grains, and are considered to be generated due to excess Si when the formation of mullite on the surface layer of the plate-like alumina particles reaches a saturated state.
When using plate-like alumina particles with a larger particle diameter, the plate-like alumina particles have a molar ratio of Si to Al [Si]/[Al] obtained by XRF analysis of 0.0003 or more and 0.01 is 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 content of silicon with respect 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, and still more preferably 0.01 to 4% by mass in terms of silicon dioxide. %, more preferably 0.3 to 2.5% by mass, particularly preferably 0.6 to 2.5% by mass.
When plate-like alumina particles having a larger particle size are used, the content of silicon with respect to 100% by mass of plate-like alumina particles is preferably 10% by mass or less, more preferably 0.1% by mass, in terms of silicon dioxide. 001 to 3% by mass, more preferably 0.01 to 1% by mass, and particularly preferably 0.03 to 0.3% by mass.

(Mullite)
The plate-like alumina particles of embodiments may contain mullite. By including mullite in the surface layer of the plate-like alumina particles, it is speculated that the selectivity of the molybdenum compound constituting the inorganic coating portion is improved, and the inorganic coating portion can be efficiently formed on the plate-like alumina particles.
When mullite is contained in the surface layer of the plate-like alumina particles, it significantly reduces the wear of equipment. "Mullite" which the plate-like alumina particles may contain in the surface layer is a composite oxide of Al and Si and is represented by Al _X Si _Y O _z , but the values of x, y and z are not particularly limited. A more preferred range is Al ₂ Si ₁ O ₅ to Al ₆ Si ₂ O ₁₃ . In addition, the XRD peak intensities of Al _2.85 Si ₁ O _6.3 , Al ₃ Si ₁ O _6.5 , Al _3.67 Si ₁ O _7.5 and Al ₄ are confirmed in Examples described later. It contains Si ₁ O ₈ or Al ₆ Si ₂ O ₁₃ . _The plate _- like _{alumina particles are Al2.85Si1O6.3} , _{Al3Si1O6.5 , Al3.67Si1O7.5 , Al4Si1O8 , and Al6Si2O} At least one compound selected from the group consisting of ₁₃ may be included in the surface layer. Here, the term "surface layer" refers to a layer within 10 nm from the surface of the plate-like alumina particles. This distance corresponds to the detection depth of XPS used for measurement in the example.
Mullite is preferably unevenly distributed in the surface layer of the plate-like alumina particles. Here, "unevenly distributed in the surface layer" means a state in which the mass of mullite per unit volume in the surface layer is larger than the mass of mullite per unit volume in the other layers than the surface layer. The fact that mullite is unevenly distributed in the surface layer can be determined by comparing the results of the surface analysis by XPS and the overall analysis by XRF, as shown in Examples described later.

Moreover, the mullite of the surface layer may form a mullite layer, or may be in a state in which mullite and alumina are mixed. At the interface between mullite and alumina in the surface layer, mullite and alumina may be in physical contact, or mullite and alumina may form chemical bonds such as Si--O--Al.

(germanium)
The plate-like alumina particles of the embodiment may contain germanium. Moreover, the plate-like alumina particles may contain germanium in the surface layer.
Although it varies depending on the raw material used, the plate-like alumina particles are germanium or germanium compounds such as Ge, GeO ₂ , GeO, GeCl ₂ , GeBr ₄ , GeI ₄ , GeS ₂ , AlGe, GeTe, GeTe _{3 and} As ₂ . , GeSe, GeS ₃ As, SiGe, Li ₂ Ge, FeGe, SrGe, GaGe, and the like, and at least one selected from the group consisting of oxides thereof, etc., and the surface layer contains the above substance. You can stay.
The "germanium or germanium compound" contained in the plate-like alumina particles and the "raw material germanium compound" used as the raw material shape control agent may be the same type of germanium compound. For example, GeO ₂ may be detected in plate-like alumina particles produced by addition of raw GeO ₂ .

When germanium or a germanium compound is contained in the surface layer of the plate-like alumina particles, significant wear reduction of equipment is realized. Here, the term "surface layer" refers to a layer within 10 nm from the surface of the plate-like alumina particles.
It is preferable that the plate-like alumina particles have germanium or a germanium compound unevenly distributed in the surface layer. Here, "unevenly distributed in the surface layer" refers to a state in which the mass of germanium or germanium compound per unit volume in the surface layer is larger than the mass of germanium or germanium compound per unit volume in the other than the surface layer. Whether germanium or a germanium compound is unevenly distributed in the surface layer can be determined by comparing the results of the surface analysis by XPS and the overall analysis by XRF.

The plate-like alumina particles contain germanium corresponding to the raw material germanium compound used in the production method. The content of germanium with respect 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, and still more preferably 0.01 in terms of germanium dioxide. 4% by mass, particularly preferably 0.1 to 3.0% by mass. The germanium content can be determined by XRF analysis.
The XRF analysis shall be carried out under the same conditions as the measurement conditions described in Examples below, or under conditions compatible with the same measurement results.

The germanium or germanium compound in the surface layer may form a layer, or may be in a state in which germanium or germanium compound and alumina are mixed. The interface between germanium or germanium compound and alumina in the surface layer may be in a state where germanium or germanium compound and alumina are in physical contact, and germanium or germanium compound and alumina are chemically bonded such as Ge-O-Al. may form

[molybdenum]
The plate-like alumina particles of this embodiment contain molybdenum. Further, the plate-like alumina particles preferably contain molybdenum in their surface layers. It is presumed that this improves the selectivity of the molybdenum compound forming the inorganic coating portion, and enables efficient formation of the inorganic coating portion on the plate-like alumina particles.

The molybdenum may be derived from the molybdenum compound used as the fluxing agent in the method for producing alumina particles, which will be described later.

By utilizing molybdenum, plate-like alumina particles having a plate-like shape and high crystallinity and a high aspect ratio can be produced in the production method described below.

By increasing the amount of molybdenum used, it is possible to obtain plate-like alumina particles having an appropriate particle size and containing molybdenum in the alumina surface layer, and to form an inorganic coating on the surface of the obtained plate-like alumina particles. It is advantageous to form 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, by utilizing the properties of molybdenum contained in the plate-like alumina particles, it may be possible to apply them to applications such as oxidation reaction catalysts and optical materials.

The molybdenum is not particularly limited, but includes molybdenum metal, molybdenum oxide, partially reduced molybdenum compounds, molybdates, and the like. The molybdenum compound may be contained in the plate-like alumina particles in any of the possible polymorphs or in combination, and may be contained in the plate-like alumina particles as α-MoO ₃ , β-MoO ₃ , MoO ₂ , MoO, molybdenum cluster structures, etc. may be

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

In the present embodiment, the ratio of the _MoO3 amount to the _Al2O3 amount of the plate-like alumina particles obtained by X-ray fluorescence (XRF) analysis ₍ [ _MoO3 ]/[ _Al2O3 ] _x 100) _XRF is , is preferably 1 or more. ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF is more preferably 10 or more, still more preferably 15 or more, and particularly preferably 20 or more. ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF is, for example, the content of Al ₂ O ₃ with respect to 100% by mass of plate-like alumina particles, and the content of MoO ₃ with respect to 100% by mass of plate-like alumina particles. is the ratio of This makes it possible to improve the brilliance of the alumina particles and enhance the oxidation catalytic function of molybdenum oxide.

The content of molybdenum with respect to 100% by mass of plate-like alumina particles obtained by XRF analysis is preferably 1% by mass or less in terms of molybdenum trioxide, and the firing temperature, firing time, and molybdenum compound sublimation rate are adjusted. By doing so, it is more preferably 0.001 to 1% by mass, still 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 α single crystal quality of alumina.

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

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 improved in the method for producing alumina particles described later.

The potassium is not particularly limited, but includes potassium metal, potassium oxide, partially reduced potassium compounds, and the like.

The form in which potassium is contained is not particularly limited, and even if it is contained in the form of adhering to the surface of the plate-like alumina of the plate-like alumina particles, it is contained in the form of being substituted for part of aluminum in the crystal structure of alumina. or a combination thereof.

The content of potassium with respect to 100% by mass of the alumina particles obtained by XRF analysis is preferably 0.01% by mass or more in terms of potassium oxide (K ₂ O), and is 0.01 to 1.0 mass. %, more preferably 0.03 to 0.5% by mass, and particularly preferably 0.05 to 0.3% by mass. Alumina particles having a potassium content within the above range are preferable because they have a polyhedral shape and suitable values such as average particle diameter.

(other atoms)
The other atoms mean those intentionally added to the alumina particles for the purpose of imparting mechanical strength, electricity, or magnetism to the extent that the effects of the present invention are not impaired.

Other atoms include, but are not limited to, zinc, manganese, calcium, strontium, yttrium, and the like. 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, more preferably 2% by mass or less, relative to the mass of the alumina particles.

[Inevitable impurities]
Alumina particles may contain unavoidable impurities.

Unavoidable impurities are derived from metal compounds used in production, are present in raw materials, or are inevitably mixed into alumina particles in the production process, and are originally unnecessary, but in trace amounts. It means an impurity that does not affect the properties of alumina particles.

Inevitable impurities include, but are not limited to, magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, cerium, sodium, and the like. These unavoidable impurities may be contained singly or in combination of two or more.

The content of inevitable impurities in the alumina particles is preferably 10000 ppm or less, more preferably 1000 ppm or less, and even more preferably 10 to 500 ppm, relative to the mass of the alumina particles.

<Inorganic coating>
The inorganic coating part coats at least part of the surface of the alumina particles, and preferably comprises an inorganic coating layer covering at least part of the surface of the alumina particles.
The inorganic coating is provided on the surfaces of the alumina particles as described above. "On the surface of the alumina particle" means outside the surface of the alumina particle. Therefore, the inorganic coating portion formed on the outer surface of the alumina particles is clearly distinguished from the surface layer containing mullite and germanium formed on the inner surface of the alumina particles.

The inorganic coating is composed of molybdenum oxide. Molybdenum oxide includes, for example, MoO ₃ , MoO ₂ and MoOx (x=2-3).

The shape of the molybdenum oxide forming the inorganic coating portion is not particularly limited, but may be, for example, spherical, needle-like, polyhedral, disk-like, hollow, porous, or other particulate shape. The average particle diameter of the particles composed of the particulate molybdenum compound is, for example, preferably 1 nm or more and 500 nm or less, more preferably 5 nm or more and 200 nm or less. Molybdenum oxide may be crystalline or amorphous.

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

In the composite particles 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 particles ([ _MoO3 ]/[Al ₂ O ₃ ]×100) _XPS is 15 or more. ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XPS is, for example, the content of Al ₂ O ₃ with respect to 100% by mass of plate-like alumina particles and the content of MoO ₃ with respect to 100% by mass of plate-like alumina particles. ratio. ([MoO ₃ ]/[Al ₂ O ₃ ]×100) When _XPS is 15 or more, molybdenum oxide is unevenly distributed on the surface of the composite particles, and various properties such as antibacterial and high viral functions by molybdenum oxide are efficiently and can be fully demonstrated.

From the viewpoint of further enhancing the above properties, ([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 the present embodiment, molybdenum oxide is preferably unevenly distributed on the surfaces of the alumina particles. Here, "unevenly distributed on the surface" refers to a state in which the mass of molybdenum oxide per unit volume on the surface is larger than the mass of molybdenum oxide per unit volume on other than the surface. The uneven distribution of molybdenum oxide on the surface can be determined by comparing the results of the surface analysis by XPS and the overall analysis by XRF.

For example, (1) the ratio of the amount of _MoO3 to the amount of _{Al2O3 on} the surface of the plate-like alumina particles obtained by X-ray photoelectron spectroscopy (XPS) analysis ₍ [ _MoO3 ]/[ _Al2O3 ] × 100) The _XPS is 15 or more, and ( ₂ ) the ratio of the _MoO3 amount to the _Al2O3 amount of the plate-like alumina particles ([ _MoO3 ]/[ _{Al2O 3} ]×100) _XRF is 1 or more, and (3) ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XPS is ([MoO ₃ ]/[Al ₂ O ₃ ]×100) It is preferably greater than the _XRF . As a result, various properties of molybdenum oxide, such as antibacterial properties, high virus function, and oxidation catalyst function, can be exhibited more effectively.

[Organic compound layer on composite particle surface]
In one embodiment, the composite particle may have an organic compound layer on its surface. The organic compound forming the organic compound layer exists on the surface of the composite particles and has the function of adjusting the surface physical properties of the composite particles. For example, since composite particles having an organic compound on their surface have improved affinity with resin, the function of the composite particles as a filler can be maximized.

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

Examples of the organic silanes include methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, iso-propyltrimethoxysilane, iso-propyltrimethoxysilane, and iso-propyltrimethoxysilane. Alkyltrimethoxysilane or alkyltrichlorosilanes having 1 to 22 carbon atoms in the alkyl group such as ethoxysilane, pentyltrimethoxysilane, hexyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, trideca fluoro-1,1,2,2-tetrahydrooctyl)trichlorosilanes, phenyltrimethoxysilane, phenyltriethoxysilane, p-chloromethylphenyltrimethoxysilane, p-chloromethylphenyltriethoxysilane and the like.

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, dodecylbenzenephosphonic acid.

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

In addition, the said organic compound may be contained independently, or may contain 2 or more types.

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

The content of the organic compound is preferably 20% by mass or less, more preferably 10% by mass or more and 0.01% by mass or less, relative to the mass of the alumina particles. When the content of the organic compound is 20% by mass or less, it is preferable because physical properties derived from the composite particles can be easily exhibited.

In the composite particles configured as described above, the pH of a dispersion (0.1% by mass) obtained by dispersing the composite particles in water is preferably less than 5.0, and preferably 4.5 or less. more preferred. If the pH of the aqueous dispersion is less than 5.0, antibacterial activity and high viral activity can be further enhanced.

<Method for producing composite particles>
Next, the details of the method for producing composite particles according to the present embodiment will be exemplified. The method for producing composite particles according to the present embodiment is not limited to the method for producing composite particles described below.

In the method for producing composite particles according to the present embodiment, 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 is fired. Then, a step of producing alumina particles, and a second mixture containing the alumina particles and a molybdenum compound containing a molybdenum element are fired to form an inorganic coating portion composed of molybdenum oxide on the surface of the alumina particles. and the step of Hereinafter, a method for producing composite particles using plate-like alumina particles will be described as an example of the method for producing composite particles according to the present embodiment.

<Method for producing plate-like alumina particles>
The method for producing the plate-like alumina particles constituting the composite particles is not particularly limited, and known techniques can be applied as appropriate, but alumina having a high α crystallization rate at a relatively low temperature can be suitably controlled. From the point of view, a manufacturing method by a flux method using a molybdenum compound can be preferably applied.

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

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

(aluminum compound)
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. Examples include 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. Physical forms such as diameter and specific surface area are not particularly limited.

According to the flux method described in detail below, the shape of the aluminum compound may be, for example, spherical, amorphous, aspected structure (wire, fiber, ribbon, tube, etc.), sheet, etc. can be used.

Similarly, according to the flux method described in detail below, a solid aluminum compound having a particle size of several nanometers to several hundreds of micrometers can be suitably used.

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

Further, the aluminum compound may consist of only an aluminum compound, or may be a composite of an aluminum compound and an organic compound. For example, an organic/inorganic composite obtained by modifying an aluminum compound with an organic silane, an aluminum compound composite with a polymer adsorbed thereon, and the like can be suitably used. When using these composites, the content of the organic compound is not particularly limited, but from the viewpoint of efficiently producing plate-like alumina particles, the content is preferably 60% by mass or less. % or less is more preferable.

(Shape control agent)
Shape control agents can be used to form platey alumina particles according to embodiments. The shape control agent plays an important role in the platelet crystal growth of alumina by sintering the alumina compound in the presence of the molybdenum compound.

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

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

Shape control agents play an important role in platelet crystal growth. In the molybdenum oxide flux method, molybdenum oxide reacts with an aluminum compound to form aluminum molybdate, and then the change in chemical potential in the process of decomposition of this aluminum molybdate is the driving force for crystallization. Hexagonal bipyramidal polyhedral particles with well-developed automorphic faces (113) are formed. In the manufacturing method of the embodiment, the shape control agent is localized near the particle surface during the α-alumina growth process, and as a result, the growth of the automorphic plane (113) is significantly inhibited. It is thought that the growth of the crystal orientation becomes faster, the (001) plane or the (006) plane grows, and a plate-like morphology can be formed. By using a molybdenum compound as a fluxing agent, plate-like alumina particles containing molybdenum with a high α crystallization rate can be formed more easily.

It should be noted that the mechanism described above is only a guess, and even if the effects of the present invention are obtained by a mechanism different from the above mechanism, it is included in the technical scope of the present invention.

The type of shape control agent is selected from the group consisting of silicon, silicon compounds, and germanium compounds from the viewpoint that plate-like alumina particles having a higher aspect ratio, better dispersibility, and higher productivity can be produced. It is preferable to use at least one of the Silicon or a silicon compound and a germanium compound can be used in combination. It is preferable to use silicon or a silicon compound containing elemental silicon as the shape control agent from the viewpoint of being a supplier of Si for mullite and capable of efficiently producing mullite. In addition, it is preferable to use a germanium compound as the shape control agent from the viewpoint that plate-like alumina particles having a higher aspect ratio and a larger particle diameter can be produced than when silicon or a silicon compound is used.
By the flux method using silicon or a silicon compound as a shape control agent, plate-like alumina particles containing mullite in the surface layer can be easily produced.
Plate-like alumina particles containing germanium or a germanium compound can be easily produced by the flux method using the starting material germanium compound as the shape control agent.

• Silicon or Silicon Compound Silicon or a silicon compound containing a silicon element is not particularly limited, and known compounds can be used. Specific examples of silicon or silicon compounds containing elemental silicon include artificially synthesized silicon compounds such as metallic silicon, organic silane, silicon resin, silica fine particles, silica gel, mesoporous silica, SiC, and mullite; and natural silicon compounds such as biosilica. mentioned. Of these, organic silanes, silicon resins, and fine silica particles are preferably used from the viewpoint of more uniform formation of composites and mixtures with aluminum compounds. Silicon or a silicon compound containing a silicon element may be used alone or in combination of two or more. In addition, it may be used in combination with other shape control agents as long as the effects of the present invention are not impaired.

The shape of silicon or a silicon compound containing silicon element is not particularly limited, and for example, spherical, amorphous, structures with aspect (wires, fibers, ribbons, tubes, etc.), sheets, etc. can be suitably used.

- Germanium compound The raw material 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. Note that the raw material germanium compounds may be used alone, or two or more of them may be used in combination. In addition, it may be used in combination with other shape control agents as long as the effects of the present invention are not impaired.

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

(molybdenum compound)
As will be described later, the molybdenum compound imparts a flux function to the α-crystal growth of alumina at relatively low temperatures.
Examples of the molybdenum compound include, but are not limited to, molybdenum oxide and compounds containing an acid root anion (MoO _x ⁿ⁻ ) consisting of a bond between molybdenum metal and oxygen.

The acid radical anion (MoO _x ⁿ⁻ )-containing compound is not particularly limited, but 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 , molybdenum disulfide and the like.

It is also possible to include silicon in the molybdenum compound, in which case the silicon containing molybdenum compound acts as both a fluxing agent and a shape control agent.

Among the molybdenum compounds described above, it is preferable to use molybdenum oxide from the viewpoint of ease of sublimation and cost. Moreover, the above molybdenum compounds may be used alone or in combination of two or more.

Further, since potassium molybdate (K ₂ Mon O _3n+1 , _n =1 to 3) contains potassium, it can also function as a potassium compound to be described later. In the production method of the embodiment, using potassium molybdate as a fluxing agent is synonymous with using a molybdenum compound and a potassium compound as fluxing agents.

(potassium compound)
A potassium compound may be used in combination with the shape control agent.
Potassium compounds include, but are not limited to, potassium chloride, potassium chlorite, potassium chlorate, potassium sulfate, potassium hydrogensulfate, potassium sulfite, potassium hydrogensulfite, potassium nitrate, potassium carbonate, potassium hydrogencarbonate, 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 and the like. At this time, the potassium compound includes isomers as in the case of the molybdenum compound. Among these, potassium carbonate, potassium hydrogen carbonate, potassium oxide, potassium hydroxide, potassium chloride, potassium sulfate, and potassium molybdate are preferably used, and potassium carbonate, potassium hydrogen carbonate, potassium chloride, potassium sulfate, and potassium molybdate are preferably used. It is more preferable to use

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

A potassium compound contributes to the efficient formation of mullite on the alumina surface layer. Also, the potassium compound contributes to the efficient formation of the germanium-containing layer on the alumina surface layer.

It is also preferable to use the potassium compound together with the molybdenum compound as a fluxing agent.

Among the above, potassium molybdate contains molybdenum, so it can also function as the molybdenum compound described above. When potassium molybdate is used as a fluxing agent, the same effect can be obtained as when molybdenum compounds and potassium compounds are used as fluxing agents.

A water-soluble potassium compound such as potassium molybdate does not vaporize even in the sintering temperature range and can be easily recovered by washing after sintering. The amount of molybdenum compound discharged out of the kiln is also reduced, and the production cost can be greatly reduced.

When a molybdenum compound and a potassium compound are used as a fluxing agent, the molar ratio of the molybdenum element in the molybdenum compound to the potassium element in the potassium compound (molybdenum element/potassium element) is preferably 5 or less, and is 0.01 to 3. is more preferable, and 0.5 to 1.5 is even more preferable because the production cost can be further reduced. When the molar ratio (molybdenum element/potassium element) is within the above range, plate-like alumina particles having a large particle size can be obtained, which is preferable.
(metal compound)
The metal compound can have a function of promoting crystal growth of alumina, as described later. The metal compound may optionally be used during firing. Note that the metal compound has a function of promoting the crystal growth of α-alumina, so 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, and the like.

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

The metal compounds mentioned above mean oxides, hydroxides, carbonates and chlorides of metal elements. For example, yttrium compounds include yttrium oxide (Y ₂ O ₃ ), yttrium hydroxide, and yttrium carbonate. Among these, the metal compound is preferably an oxide of a metal element. These metal compounds include isomers.

Among these, metal compounds of the 3rd period element, metal compounds of the 4th period element, metal compounds of the 5th period element, and metal compounds of the 6th period element are preferable. It is more preferably a metal compound of a 5th period element, and more preferably a metal compound of a 5th period element. Specifically, magnesium compounds, calcium compounds, yttrium compounds, and lanthanum compounds are preferably used, magnesium compounds, calcium compounds, and yttrium compounds are more preferably used, and yttrium compounds are particularly preferably used.

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

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

The amount of the aluminum compound, molybdenum compound, silicon or silicon compound, germanium compound, potassium compound, etc. used is not particularly limited. can be calcined.
1) Aluminum compound of preferably 50% by mass or more, more preferably 70% by mass or more and 99% by mass or less, still more preferably 80% by mass or more and 94.5% by mass or less of aluminum compound in terms of Al ₂ O ₃ When,
a molybdenum compound of preferably 40% by mass or less, more preferably 0.5% by mass or more and 20% by mass or less, still more preferably 1% by mass or more and 7% by mass or less of a molybdenum compound, in terms of _MoO3 ;
Preferably 0.1% by mass or more and 10% by mass or less of silicon, silicon compound or germanium compound, more preferably 0.5% by mass or more and less than 7% by mass of silicon, silicon compound or germanium in terms of _SiO2 or _GeO2 a compound, 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.

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 silicon or a silicon compound and a germanium compound may be used in combination.
When a germanium compound is used as a shape control agent, it is preferably 0.4% by mass or more and less than 1.5% by mass, more preferably 0.4% by mass or more and less than 1.5% by mass in terms of GeO ₂ when the total amount of raw materials converted to oxides is 100% by mass. A germanium compound of 0.7% by mass or more and 1.2% by mass or less may be added to the first mixture.

The raw material composition (mass%) conditions described above may be freely combined for each raw material, and the lower limit and upper limit of 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 is preferably 5 in terms of K ₂ O when the total amount of raw materials converted to oxides is 100% by mass. A potassium compound can be mixed in an amount of not more than 0.01% by mass and not more than 3% by mass, more preferably not less than 0.05% by mass and not more than 1% by mass.
Potassium molybdate formed by reaction with the molybdenum compound by using the potassium compound exerts an effect of Si diffusion and is thought to contribute to promotion of mullite formation on the surface of the plate-like alumina particles.
Similarly, due to the use of a potassium compound, potassium molybdate formed by reaction with the molybdenum compound exerts the effect of raw material germanium diffusion and contributes to promoting the formation of germanium or germanium compounds on the surface of the plate-like alumina particles.
A water-soluble potassium compound such as potassium molybdate does not vaporize even in the sintering temperature range and can be easily recovered by washing after sintering. The amount of molybdenum compound discharged out of the kiln is also reduced, and the production cost can be greatly reduced.

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 generated in the course of firing using molybdenum compounds and potassium compounds, which are inexpensive and readily available, as raw materials, for example. Here, the case where a molybdenum compound and a potassium compound are used as a fluxing agent, and the case where a compound containing molybdenum and potassium is used as a fluxing agent are both combined, and the case where a molybdenum compound and a potassium compound are used as a fluxing agent is taken as an example. explain.

The numerical ranges of the amount of each of the raw materials described above can be appropriately combined within a range in which the total content thereof does not exceed 100% by mass.

[Baking process]
The firing step is a step of firing the aluminum compound in the presence of the molybdenum compound and the shape control agent. The firing step may be a step of firing the first mixture obtained in the mixing step.

Plate-like alumina particles are obtained, for example, by firing an aluminum compound in the presence of a molybdenum compound and a shape control agent. As described 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 eutectic phase diagram of the crystal-flux binary system. The mechanism of the flux method is presumed to be as follows. That is, when a mixture of solute and flux is heated, the solute and flux become liquid phase. At this time, since the flux is a flux, in other words, the phase diagram of the solute-flux binary system shows a eutectic type, so the solute melts at a temperature lower than its melting point and forms a liquid phase. becomes. When the flux is evaporated in this state, the concentration of the flux decreases. evaporation method). The solute and flux can also cause crystal growth of the solute by cooling the liquid phase (slow cooling method).

The flux method has advantages such as being able to grow crystals at a temperature much lower than the melting point, being able to precisely control the crystal structure, and being able to form polyhedral crystals having an ephemeral shape.

In the production of α-alumina particles by the flux method using a molybdenum compound as a flux, the mechanism is not necessarily clear, but it is presumed, for example, as follows. That is, firing an aluminum compound in the presence of a molybdenum compound first forms aluminum molybdate. At this time, the aluminum molybdate grows α-alumina crystals at a temperature lower than the melting point of alumina, as understood from the above description. Then, for example, alumina particles can be obtained by decomposing aluminum molybdate, evaporating flux, etc., and accelerating crystal growth. 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 used as a fluxing agent, the mechanism is not necessarily clear, but it is presumed, for example, as follows. First, a molybdenum compound and an aluminum compound react to form aluminum molybdate. Then, for example, aluminum molybdate decomposes into molybdenum oxide and alumina, and at the same time, the molybdenum compound containing molybdenum oxide obtained by decomposition reacts with a potassium compound to form potassium molybdate. The plate-like alumina particles according to the embodiment can be obtained by crystal growth of alumina in the presence of the molybdenum compound containing potassium molybdate.

The method for firing the first mixture is not particularly limited, and can be carried out by a known and commonly used method.

In the step of producing the alumina particles, it is preferable to calcine the first mixture at, for example, 900° C. or higher. When the firing temperature exceeds 700°C, the aluminum compound and the molybdenum compound react to form aluminum molybdate. Furthermore, when the firing temperature reaches 900° C. or higher, the aluminum molybdate is decomposed to form tabular alumina particles by the action of the shape control agent. In the plate-like alumina particles, it is considered that the molybdenum compound is incorporated into the aluminum oxide particles when the aluminum molybdate decomposes to form alumina and molybdenum oxide.
Also, when the firing temperature reaches 900° C. or higher, it is believed that the molybdenum compound (for example, molybdenum trioxide) obtained by decomposition of aluminum molybdate reacts with the potassium compound to form potassium molybdate.
Furthermore, when the firing temperature is 1000 ° C. or higher, Al ₂ O ₃ and SiO ₂ on the surface of the plate-like alumina particles react with each other with the crystal growth of the plate-like alumina particles in the presence of molybdenum, forming mullite with high efficiency. it is conceivable that.
Similarly, when the firing temperature is 1000° C. or higher, in the presence of molybdenum, along with the crystal growth of the plate-like alumina particles, the Al ₂ O ₃ on the surface of the plate-like alumina particles reacts with the Ge compound, resulting in highly efficient germanium dioxide and Ge It is thought that a compound or the like having —O—Al is formed.

The states of the aluminum compound, the shape control agent, and the molybdenum compound are 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, it may be simple mixing of powders of a molybdenum compound, a shape control agent and an aluminum compound, mechanical mixing using a grinder or the like, mixing using a mortar or the like, and dry conditions. , may be mixed in a wet state.

The firing temperature conditions are not limited to the above, and the above-mentioned (006/113) ratio value, average particle diameter, aspect ratio, formation of mullite, and the above longitudinal relaxation time T of the target plate-like alumina particles It is appropriately determined depending on the value of ₁ , dispersibility, and the like. Generally, the firing temperature of the first mixture is preferably 900° C. or higher, which is the decomposition temperature of aluminum molybdate (Al ₂ (MoO ₄ ) ₃ ). C. or more is _more preferable, and 1200.degree.

In general, when trying 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. There is a big problem in order to use it industrially.

The production method of the present embodiment can be carried out even at a high temperature exceeding 2000 ° C., but even at a temperature of 1600 ° C. or lower, which is considerably lower than the melting point of α-alumina, regardless of the shape of the precursor. It is possible to form α-alumina having a plate-like shape with a high α crystallization rate and a high aspect ratio.

According to the present embodiment, even under conditions where the maximum firing temperature is 900 to 1600° C., plate-like alumina particles having a high aspect ratio and an α crystallization ratio of 90% or more can be efficiently formed at low cost. Firing at a maximum temperature of 950 to 1500°C is more preferable, firing at a maximum temperature of 1000 to 1400°C is more preferable, and firing at a maximum temperature of 1200 to 1400°C is most preferable.

As for the firing time of the first mixture, it is preferable that the heating time to the predetermined maximum temperature is in the range of 15 minutes to 10 hours, and the holding time at the maximum firing temperature is in the range of 5 minutes to 30 hours. In order to efficiently form the plate-like alumina particles, it is more preferable that the firing and holding time is about 10 minutes to 15 hours.
By selecting conditions of a maximum temperature of 1000 to 1400° C. and a sintering holding time of 10 minutes to 15 hours, dense α-crystalline polygonal tabular alumina particles can be easily obtained without agglomeration.
By selecting the 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 a 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 effect of the present invention can be obtained, but 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 from the viewpoint of cost. Air atmosphere is more preferable when considering.

An apparatus for firing is not necessarily limited, and a so-called firing furnace can be used. The firing furnace is preferably made of a material that does not react with the sublimated molybdenum oxide, and it is preferable to use a firing furnace with a high degree of airtightness so as to efficiently use the molybdenum oxide.

The alumina particles are preferably obtained by firing an aluminum compound in the presence of a molybdenum compound and a shape control agent, or in the presence of a molybdenum compound, a shape control agent, a potassium compound and a metal oxide.

That is, a preferred method for producing alumina particles includes a step (firing step) of firing an aluminum compound in the presence of a molybdenum compound and a shape control agent, or in the presence of a molybdenum compound, a shape control agent and a potassium compound. The first mixture preferably further contains the above metal compound. A yttrium compound is preferable as the metal compound.

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 in the process of decomposition of this aluminum molybdate becomes the driving force for crystallization. Therefore, hexagonal bipyramidal polyhedral particles with well-developed automorphic faces (113) are formed. The shape control agent is localized in the vicinity of the grain surface during the growth process of α-alumina, and as a result, the growth of the automorphic plane (113) is significantly inhibited, and as a result, the growth of the crystal orientation in the plane direction is relatively inhibited. It is presumed that the (001) plane or (006) plane can grow and form a plate-like morphology. Therefore, by using a molybdenum compound as a fluxing agent, plate-like alumina particles containing molybdenum with a high α-crystallization ratio can be formed more easily.

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

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 the production time can be shortened. On the other hand, when the cooling rate is 1000° C./hour or less, the firing container is less likely to crack due to heat shock and can be used for a long time, which is preferable.

The cooling method is not particularly limited, and natural cooling or a cooling device may be used.

[Post-treatment 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 of removing the fluxing agent. The post-treatment step may be performed after the firing step described above, after the cooling step described above, or after the firing step and the cooling step. Moreover, you may repeat twice or more as needed.

Post-treatment methods include washing and high temperature treatment. These can be performed in combination.

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

At this time, the molybdenum content can be controlled by appropriately changing the concentrations and amounts of the water, ammonia aqueous solution, sodium hydroxide aqueous solution, and acidic aqueous solution used, as well as the cleaning sites, cleaning time, and the like.

Moreover, as a method of high-temperature treatment, there is a method of raising the temperature above the sublimation point or boiling point of the flux.

[Pulverization process]
In some cases, the calcined product aggregates plate-like alumina particles and does not satisfy the particle size range suitable for the present invention. Therefore, the plate-like alumina particles may be pulverized so as to satisfy the particle size range suitable for the present invention, if necessary.
The method of pulverizing the fired product is not particularly limited, and conventionally known pulverizing methods such as ball mill, jaw crusher, jet mill, disc mill, spectromill, grinder and mixer mill can be applied.

[Classification process]
The plate-like alumina particles are preferably classified in order to adjust the average particle size and improve the fluidity of the powder, or to suppress the increase in viscosity when blended with the binder for forming the matrix. . "Classification" refers to an operation of grouping particles according to their size.
Classification may be either wet or dry, but dry classification is preferred from the viewpoint of productivity. Dry classification includes classification by sieve, air classification based on the difference between centrifugal force and fluid drag force, etc., but from the viewpoint of classification accuracy, air classification is preferable. It can be carried out using a classifier such as a swirling airflow classifier, a forced vortex centrifugal classifier, and a semi-free vortex centrifugal classifier.
The pulverization process and the classification process described above can be performed at necessary stages including before and after the organic compound layer forming process described below. For example, the average particle size of the obtained plate-like alumina particles can be adjusted by the presence or absence of pulverization and classification and the selection of conditions for them.

The plate-like alumina particles of the embodiment, or the plate-like alumina particles obtained by the production method of the embodiment, are less agglomerated or not agglomerated, and tend to exhibit their inherent properties, and are more excellent in handleability themselves. It is preferable from the viewpoint of being more excellent in dispersibility when it is used by dispersing it in a medium to be dispersed. In the method for producing plate-like alumina particles, if particles with less aggregation or no aggregation can be obtained without performing the pulverization step or classification step described above, there is no need to perform the steps on the left, and the intended excellent properties can be obtained. It is preferable because the plate-like alumina having can be produced with high productivity.

[Inorganic coating portion forming step]
Next, an inorganic coating is formed on the surface of the plate-like alumina particles obtained above. In the present 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 is not particularly limited, but examples thereof include a vapor phase method and a liquid phase method.

As the molybdenum compound, the same molybdenum compound as the molybdenum compound mixed in the first mixture can be used. For example, molybdenum oxide, containing an acid root anion (MoO _x ⁿ⁻ ) consisting of a bond between molybdenum metal and oxygen compound.

The method of firing the second mixture is not particularly limited, and can be carried out by a known and commonly used method. For example, it is preferable to bake the second mixture at 750°C or higher and lower than 1100°C. When 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. Molybdenum oxide can be sufficiently adhered to the surface. 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 in which plate-like alumina particles are dispersed is prepared, and if necessary, the pH of the dispersion is adjusted and heated, and then a metal oxide such as molybdenum oxide is added to the dispersion. Drop the aqueous solution. At this time, it is preferable to keep the pH constant with an alkaline aqueous solution. Thereafter, the dispersion liquid is stirred for a predetermined time, filtered, washed and dried to obtain powder. As a result, an inorganic coating composed of an oxide such as molybdenum oxide is formed on the surface of the plate-shaped alumina particles.

Moreover, in this step, an inorganic coating layer may be formed so as to cover at least part of the surface of the plate-like alumina particles. In this case, for example, particles composed of a molybdenum compound are aggregated to form a layer.

[Organic compound layer forming step]
In the present embodiment, the method for producing a composite particle may further include 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) after the inorganic coating portion forming step. . The organic compound layer forming step is usually performed after the baking step of the second mixture or after the post-treatment step.

A method for forming the organic compound layer is not particularly limited, and a known method can be appropriately employed. For example, there is 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.

Examples of organic compounds that can be used to form the organic compound layer include organic silane compounds. The organosilane compound may be linked to at least part or all of the silicon atoms on the surface of the plate-like alumina particles and/or the inorganic silicon compound by covalent bonds through a reaction, and not only a part of the alumina but also the entirety of the alumina undergoes the above reaction. It may be covered with a substance. Immersion deposition or chemical vapor deposition (CVD) can be used to provide the alumina surface.

The amount of the organic silane compound used is preferably 20% by mass or less, based on silicon atoms, relative to the mass of the silicon atoms or the inorganic silicon compound contained on the surface of the plate-like alumina particles, and is preferably 10 to 0.01. % by mass is more preferred. When the amount of the organic silane compound used is 20% by mass or less, physical properties derived from the alumina particles can be easily exhibited, which is preferable.

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 filler surface modification method, for example, a spray method using a fluid nozzle, a shearing force method, or the like. Dry methods such as agitation, ball mills and mixers, and wet methods such as water-based or organic solvent-based methods can be employed. It is desirable that the treatment using a shearing force is performed to such an extent that the alumina particles used in the embodiment are not destroyed.

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

<Resin composition>
As 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 thermosetting resins and thermoplastic resins.

The resin composition can be cured to obtain a cured product of the resin composition, and cured and molded to obtain a molded product of the resin composition. For molding, the resin composition can be appropriately subjected to a treatment such as melting or kneading. The molding method includes compression molding, injection molding, extrusion molding, foam molding, and the like. Among them, extrusion molding with an extruder is preferable, and extrusion molding with a twin-screw extruder is more preferable.
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 for 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 and a resin. Since the composite particles described above can be used as the composite particles, the description thereof is omitted here.

The composite particles may be surface-treated.

Moreover, the composite particles to be used may be used alone or in combination of two or more.

Furthermore, 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 30 to 80% by mass with respect to 100% by mass of the resin composition. is more preferred. When 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, when the content of the composite particles is 95% by mass or less, a resin composition having excellent moldability can be obtained, which is preferable.
When the resin composition is used as a coating agent, paint, etc., 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 It is preferably 0.1 to 80% by mass, more preferably 1 to 50% by mass, and even more preferably 3 to 30% by mass based on 100% by mass of the solid content.

(resin)
The resin is not particularly limited, and includes 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. Specifically, 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 Resins, polycarbonate resins, polyacetal resins, polyethylene terephthalate resins, polyphenylene oxide resins, polyphenylene sulfide resins, polysulfone resins, polyethersulfone resins, polyetheretherketone resins, polyarylsulfone resins, thermoplastic polyimide resins, thermoplastic urethane resins, polyamino Bismaleimide resin, polyamideimide resin, polyetherimide resin, bismaleimide triazine resin, polymethylpentene resin, fluorinated resin, liquid crystal polymer, olefin-vinyl alcohol copolymer, ionomer resin, polyarylate resin, acrylonitrile-ethylene-styrene copolymers, acrylonitrile-butadiene-styrene copolymers, acrylonitrile-styrene copolymers, and the like.

The thermosetting resin is a resin that can be changed to be substantially insoluble and infusible when cured by means of heat, radiation, or a catalyst, and is generally used as a molding material. Known and commonly used resins used for the above can be used. Specifically, novolac-type phenolic resins such as phenolic novolak resins and cresol novolak resins; unmodified resol-phenolic resins, resol-type phenolic resins such as oil-modified resol-phenolic resins modified with tung oil, linseed oil, walnut oil, etc. Phenol resin; bisphenol type epoxy resin such as bisphenol A epoxy resin and bisphenol F epoxy resin; novolac type epoxy resin such as fatty chain modified bisphenol type epoxy resin, novolak epoxy resin, cresol novolak epoxy resin; Epoxy resins such as chol-type epoxy resins; Resins having a triazine ring such as urea resins and melamine resins; Vinyl resins such as (meth)acrylic resins and vinyl ester resins: Unsaturated polyester resins, bismaleimide resins, polyurethane resins , diallyl phthalate resin, silicone resin, resin having a benzoxazine ring, cyanate ester resin, and the like.

The above resins may be used alone or in combination of two or more. At this time, 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. may

The resin content is preferably 5 to 90% by mass, more preferably 10 to 70% by mass, based on 100% by mass of the resin composition. A resin content of 5% by mass or more is preferable because excellent moldability can be imparted to the resin composition. On the other hand, when the resin content is 90% by mass or less, it is preferable because high thermal conductivity can be obtained as a compound by molding.

(curing agent)
A curing agent may be mixed with the resin composition, if necessary. The curing agent is not particularly limited, and known ones can be used.

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

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

Examples of the amide-based compound include dicyandiamide and a polyamide resin synthesized from a dimer of linolenic acid and ethylenediamine.

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

Examples of the phenol-based compound include polyhydric resins represented by phenol novolak resin, cresol novolak resin, aromatic hydrocarbon formaldehyde resin-modified phenol resin, dicyclopentadiene phenol addition type resin, phenol aralkyl resin (Zyloc resin), and resorcinol novolak resin. Polyhydric phenol novolac resins synthesized from hydroxy compounds and formaldehyde, naphthol aralkyl resins, trimethylolmethane resins, tetraphenylolethane resins, naphthol novolac resins, naphthol-phenol co-condensed novolak resins, naphthol-cresol co-condensed novolak resins, biphenyl Modified phenolic resin (polyhydric phenol compound with phenolic nucleus linked with bismethylene group), biphenyl-modified naphthol resin (polyhydric naphthol compound with phenolic nucleus linked with bismethylene group), aminotriazine-modified phenolic resin (with melamine, benzoguanamine, etc.) polyhydric phenol compounds in which phenol nuclei are linked) and alkoxy group-containing aromatic ring-modified novolac resins (polyhydric phenol compounds in which phenol nuclei and alkoxy group-containing aromatic rings are linked with formaldehyde).

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

(Curing accelerator)
A curing accelerator may be mixed with the resin composition, if necessary.

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

Examples of the curing accelerator include, but are not particularly limited to, phosphorus compounds, tertiary amines, imidazoles, organic acid metal salts, Lewis acids, amine complex salts, and the like.

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

(Curing catalyst)
A curing catalyst may be mixed with the resin composition, if necessary.

The curing catalyst has a function of advancing the curing reaction of the epoxy group-containing compound instead of the curing agent.

The curing catalyst is not particularly limited, and known and commonly used thermal polymerization initiators and active energy ray polymerization initiators can be used.

In addition, a curing catalyst may be used independently or may be used in combination of 2 or more type.

(Viscosity modifier)
A viscosity modifier may be mixed in the resin composition as needed.

A viscosity modifier has the function of adjusting the viscosity of the composition.

The viscosity modifier is not particularly limited, and organic polymers, polymer particles, inorganic particles and the like can be used.

In addition, a viscosity modifier may be used individually or may be used in combination of 2 or more types.

(Plasticizer)
A plasticizer may be mixed in the resin composition as needed.

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

The plasticizer is not particularly limited, and phthalates, adipates, phosphates, trimellitates, polyesters, polyolefins, polysiloxanes and the like can be used.

In addition, the above plasticizers may be used alone or in combination of two or more.

[Mixing process]
The resin composition according to the present embodiment is obtained by mixing the composite particles, the resin, and, if necessary, other compounds. The mixing method is not particularly limited, and is mixed by a known and commonly used method.

When the resin is a thermosetting resin, as a general method for mixing the thermosetting resin and the composite particles, etc., a predetermined blending amount of the thermosetting resin, the composite particles, and, if necessary, other components are mixed. After sufficiently mixing with a mixer or the like, the mixture is kneaded with a triple roll or the like to obtain a fluid composition in liquid form. Further, as a method for mixing the thermosetting resin and the composite particles in another embodiment, after sufficiently mixing a predetermined amount of the thermosetting resin, the composite particles, and, if necessary, other components with a mixer or the like, , a mixing roll, an extruder, or the like, followed by cooling to obtain a solid composition.
Regarding the mixed state, when a curing agent, a catalyst, or the like is blended, the curable resin and the blend thereof should be sufficiently uniformly mixed, but it is more preferable that the composite particles are uniformly dispersed and mixed.

When the resin is a thermoplastic resin, a general method for mixing the thermoplastic resin and the composite particles is to mix the thermoplastic resin, the composite particles, and optionally other ingredients in a tumbler, Henschel mixer, or the like. After pre-mixing using various mixers, a method of melt-kneading with a mixer such as a Banbury mixer, a roll, a Brabender, a single-screw kneading extruder, a twin-screw kneading extruder, a kneader, or a mixing roll can be used. The melt-kneading temperature is not particularly limited, but is usually in the range of 100 to 320°C.

A coupling agent may be externally added to the resin composition, since the fluidity of the resin composition and the fillability of the composite particles and the like can be further enhanced. By externally adding a coupling agent, the adhesion between the resin and the composite particles is further enhanced, the interfacial thermal resistance between the resin and the composite particles is reduced, and the thermal conductivity of the resin composition can be improved. .

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

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

Molybdenum oxide, which constitutes the inorganic coating portion of the composite particles, is excellent in antibacterial properties, high virus resistance, and oxidation catalyst function. Further, the plate-like alumina particles constituting the composite particles are excellent in mechanical properties, and the molybdenum oxide contained in the plate-like alumina particles is excellent in oxidation catalyst function and the like. 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 for thermally conductive materials. Since the plate-like alumina particles contained in the resin composition are excellent in the thermal conductivity of the resin composition, the resin composition can also be used as an insulating heat-dissipating member. As a result, it is possible to improve the heat dissipation function of the device, which contributes to the reduction in size and weight of the device and the enhancement of its performance.

<Method for producing cured product>
According to one embodiment of the present invention, a method for producing a cured product is provided. The production method includes curing the resin composition produced above.

Although the curing temperature is not particularly limited, it is preferably 20 to 300°C, more preferably 50 to 200°C.

Although the curing time is not particularly limited, it is preferably 0.1 to 10 hours, more preferably 0.2 to 3 hours.

The shape of the cured product varies depending on the intended use, and can be appropriately designed by those skilled in the art.

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

In addition, in the resin composition, the method for producing the resin composition, and the cured product described above, composite particles having a plate-like shape are used. .

Examples of the present invention are described below. The invention is not limited to the following examples.

<Example 1>
First, alumina particles were produced as the base of the composite particles. Aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd., average particle size 1 to 2 μm) 120 g (90% by weight in terms of oxide of Al ₂ O ₃ ) and molybdenum trioxide (manufactured by Taiyo Koko) 7.8 g (MoO ₃ 9% by mass in terms of oxide) and 0.78 g of silicon dioxide (manufactured by Kanto Kagaku Co., Ltd., special grade) (1% by mass 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 a rate of 5° C./min in a ceramic electric furnace, and fired at 1100° C. for 5 hours. After that, the temperature was lowered to room temperature at 5° C./min, and the crucible was taken out to obtain 79.0 g of plate-like alumina A powder.

9. Dispersing 10.0 g of the powder of the obtained alumina particles A in 50 mL of ethanol, stirring the dispersion at room temperature (25 to 30° C.) for 3 hours, filtering to remove the ethanol, and drying. 9 g of powder of alumina particles B1 were obtained.

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

<Example 2>
Except that 2 g of the powder of alumina particles B1 after washing with ethanol and 0.4 g of molybdenum trioxide (molybdenum trioxide synthesized in Example 1 of WO 2021/060375) were mixed to obtain a mixture. obtained 2.2 g of powder of composite particles in the same manner as in Example 1.

<Example 3>
Except that 5 g of powder of alumina particles B1 after washing with ethanol and 0.5 g of molybdenum trioxide (molybdenum trioxide synthesized in Example 1 of WO 2021/060375) were mixed to obtain a mixture. obtained 5.15 g of powder of composite particles in the same manner as in Example 1.

<Example 4>
Except that 5 g of powder of alumina particles B1 after washing with ethanol and 0.25 g of molybdenum trioxide (molybdenum trioxide synthesized in Example 1 of WO 2021/060375) were mixed to obtain a mixture. obtained 5.0 g of powder of composite particles in the same manner as in Example 1.

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

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

<Comparative Example 1>
As Comparative Example 1, a powder of alumina particles A before being washed with ethanol was obtained by the same manufacturing method as in Example 1.
A SEM image of the resulting powder is shown in FIG. The magnification of FIG. 3 is 2000 times. It was confirmed by SEM observation that the alumina particles A had a polygonal shape, a thickness of 400 nm, and a particle size distribution measurement of _D50 of 5 μm and an aspect ratio of 12.5. Furthermore, when XRD measurement was performed, a sharp scattering peak derived from α-alumina appeared, no alumina crystal system peak other than the α crystal structure was observed, and it was confirmed 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 washing with ethanol was obtained by the same manufacturing method as in Example 1.

<Comparative Example 3>
As Comparative Example 3, alumina particles B2 in a state after being washed with water were obtained by the same manufacturing method as in Example 1. Example 1 A powder of 9.8 g of alumina particles B2 was prepared in the same manner as in Example 1, except that 10.0 g of the obtained powder of alumina particles A was dispersed in 50 mL of water to prepare a dispersion liquid. got

≪Evaluation≫
[Measurement of length L of alumina particles]
Using a laser diffraction particle size analyzer (SALD-7000, manufactured by Shimadzu Corporation), 1 mg of alumina powder was diluted to 18 g in total with an aqueous solution of sodium hexametaphosphate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) prepared to 0.2 wt%. Then, this was measured as a sample, and the average particle diameter _D50 value (μm) was determined and defined as the major diameter L.

[Measurement of thickness D of alumina particles]
Using a scanning electron microscope (SEM), the average value obtained by measuring the thickness of 50 pieces was adopted as the thickness D (μm).

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

[XRF analysis]
Using an X-ray fluorescence (XRF) analyzer (Rigaku, Primus IV), about 70 mg of the powder of the prepared sample was placed on a filter paper, covered with a PP film, and subjected to composition analysis.
The amount of Al ₂ O ₃ ([Al ₂ O ₃ ]), the amount of SiO ₂ ([SiO ₂ ]) and the amount of MoO ₃ ([MoO ₃ ]) were obtained by X-ray fluorescence (XRF) analysis, and the Al ₂ of the alumina particles The ratio of MoO ₃ amount to O ₃ amount ([MoO ₃ ]/[Al ₂ O ₃ ]×100) was obtained by _XRF .

[XPS analysis]
Using an X-ray photoelectron spectroscopy (XPS) device (Quantera SXM manufactured by ULVAC-PHI), the prepared sample (composite particles) was press-fixed on a double-sided tape, and composition analysis was performed under the following conditions.
・X-ray source: monochromatic AlKα, beam diameter 100 μmφ, output 25 W
・Measurement: area measurement (1000 μm square), n=3
・Electrification correction: C1s = 284.8 eV
The amount of Al ₂ O ₃ ([Al ₂ O ₃ ]), the amount of SiO ₂ ([SiO ₂ ]) and the amount of MoO ₃ ([MoO ₃ ]) were obtained by X-ray photoelectron spectroscopy (XPS) analysis, and the surface of the alumina particles The ratio of _MoO3 amount to _Al2O3 amount at ₍ [ _MoO3 ]/[ _Al2O3 ] _x 100) _XPS was obtained.

[pH measurement of aqueous dispersion]
A dispersion was prepared by dispersing 0.1 g of the powder of each composite particle obtained in Examples 1 to 6 and Comparative Examples 1 to 3 in 9.9 mL of water, and a pH measurement device (LAQUA act portable type manufactured by HORIBA Scientific) was used. D-71), the pH of each dispersion was measured. Table 1 shows the results.

First, SEM observation images of the composite particles obtained in Examples 1 and 4 are shown in FIGS. 1 and 2, respectively. The magnifications of FIGS. 1 and 2 are 1000 times and 2000 times, respectively. From FIGS. 1 and 2, it was confirmed that the composite particles of Examples 1 and 4 were tabular.

Further, from the results of Table 1, the ratio of the _MoO3 amount to the _Al2O3 amount _on the surface of the alumina particles ([ _MoO3 ]/[ _Al2O3 ] _x 100) _XPS was 47, and the surface of the alumina particles It was found that a large amount of molybdenum oxide as an inorganic coating was present in the coating. Furthermore, ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF is 43, and the amount of molybdenum oxide present on the surface of the alumina particles is greater than the amount of molybdenum oxide present throughout the alumina particles. I found out.

In Example ₂ , the ratio of the amount of _MoO3 to the amount of _Al2O3 on the surface of the alumina particles ([ _MoO3 ]/[ _Al2O3 ]×100) _XPS was ₃₂ . It was found that a large amount of molybdenum oxide was present on the surface of the particles. In addition, ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF is 23, and the amount of molybdenum oxide present on the surface of the alumina particles is greater than the amount of molybdenum oxide present throughout the alumina particles. I found out.

Also in Example ₃ , the ratio of the amount of _MoO3 to the amount of _{Al2O3 on} the surface of the alumina particles ([ _MoO3 ]/[ _Al2O3 ]×100) _XPS was 27. It was found that a large amount of molybdenum oxide was present on the surface of the particles. In addition, ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF is 21, and the amount of molybdenum oxide present on the surface of the alumina particles is greater than the amount of molybdenum oxide present throughout the alumina particles. I found out.

In Example 4, the ratio of the amount of _MoO3 to the amount of _{Al2O3 on} the surface of the alumina particles ₍ [ _MoO3 ]/[ _Al2O3 ] × 100) _XPS was 24, and many Molybdenum oxide was found to be present. In particular, ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF is 4, and the amount of molybdenum oxide present on the surface of the alumina particles is significantly higher than the amount of molybdenum oxide present throughout the alumina particles. It turns out there are many.

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, and many Molybdenum oxide was found to be present. In particular, ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF is 1.2, and the amount of molybdenum oxide present on the surface of the alumina particles is greater than the amount of molybdenum oxide present throughout the alumina particles. It turned out to be a lot.

Also in Example 6, the ratio of the _MoO3 amount to the _Al2O3 amount _on the surface of the alumina particles ([ _MoO3 ]/[ _Al2O3 ] _x 100) _XPS was 19, and many Molybdenum oxide was found to be present. In particular, ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF is 1.3, and the amount of molybdenum oxide present on the surface of the alumina particles is greater than the amount of molybdenum oxide present throughout the alumina particles. It turned out to be a lot.

Further, the dispersion liquids in which the composite particles of Examples 1 to 6 were dispersed had a pH of 3.9 to 4.8, indicating a low pH.

On the other hand, in Comparative Example 1, the ratio ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XPS of the amount of MoO ₃ to the amount of Al ₂ O ₃ on the surface of the alumina particles was 13. It was a smaller value than either of In addition, ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF was 0.6, which was smaller than any of Examples 1-6.

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 ]×100) _XPS was 8. It was a smaller value than any of Examples 1-6. In addition, ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF was 0.7, which was smaller than any of Examples 1-6.

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 ]×100) _XPS was ₂ . It was a smaller value than any of Examples 1-6. In addition, ([MoO ₃ ]/[Al ₂ O ₃ ]×100) _XRF was 0.3, which was smaller than any of Examples 1-6.

Further, the dispersion liquids in which the alumina particles of Comparative Examples 1 to 3 were dispersed had pH values of 5.0 to 6.8, which were higher than those of Examples 1 to 6.

Claims (14)

Alumina particles and an inorganic coating portion provided on the surface of the alumina particles and composed of molybdenum oxide,
Ratio of _MoO3 amount to _Al2O3 amount _on the surface of the alumina particles obtained by X-ray photoelectron spectroscopy (XPS) analysis ₍ [ _MoO3 ]/[ _Al2O3 ] × 100) _XPS is 15 or more is a composite particle. Ratio of _MoO3 amount to _Al2O3 amount of the alumina particles ₍ [ _MoO3 ]/[ _Al2O3 ]×100) obtained by X _- ray fluorescence (XRF) analysis _XRF 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 . 3. The composite particles according to claim 1, wherein the alumina particles have an α crystallization rate of 90% or more. Composite particles according to any one of claims 1 to 3, wherein the alumina particles comprise molybdenum. 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. 2. The composite particle according to item 1. 2. Composite particles according to claim 1, wherein the alumina particles further comprise silicon and/or germanium. 7. The composite particles according to claim 6, wherein the alumina particles contain mullite in a surface layer. A composite particle comprising the composite particle according to any one of claims 1 to 7. A first mixture containing an aluminum compound containing an aluminum element and a molybdenum compound containing a molybdenum element, or an aluminum compound containing an aluminum element, a molybdenum compound containing a molybdenum element, and the shape of alumina particles are controlled. calcining a first mixture containing a shape control agent for producing alumina particles;
firing a second mixture containing the alumina particles and a molybdenum compound containing a molybdenum element to form an inorganic coating portion composed of the molybdenum compound on the surface of the alumina particles;
A method for producing composite particles, comprising: 10. The method for producing composite particles according to claim 9, wherein the molybdenum compound is molybdenum oxide. The method for producing composite particles according to claim 10, wherein in the step of forming the inorganic coating portion, the second mixture is fired at 750°C or higher and lower than 1100°C. The method for producing composite particles according to claim 10, wherein in the step of producing the alumina particles, the first mixture is fired at 900°C or higher. The composite particle according to any one of claims 9 to 12, wherein the shape control agent is composed of one or more selected from silicon, a silicon compound containing a silicon element, and a germanium compound containing a germanium element. manufacturing method. The method for producing composite particles according to any one of claims 9 to 13, wherein the first mixture further contains a potassium compound containing potassium element.

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