Composite particles and method for producing composite particles

Abstract

Disclosed is a composite particle including an alumina particle and an inorganic coating layer provided on the surface of the alumina particle. The alumina particle contains molybdenum (Mo), and the inorganic coating layer contains a composite metal oxide.

Description

Technical Field

[0001] This invention relates to composite particles and methods for producing composite particles. In particular, this invention relates to composite particles comprising alumina particles having a coating.

[0002] Priority is claimed to international application No. PCT / CN2021 / 071384, filed on January 13, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] Alumina particles, used as inorganic fillers, are employed in various applications. Among them, lamellar alumina particles, which have a high aspect ratio, exhibit particularly superior thermal and optical properties compared to spherical alumina particles. Therefore, further improvements in the performance of lamellar alumina particles are desired.

[0004] In related technologies, various lamellar alumina particles with shape characteristics (e.g., specific main dimensions or thicknesses) are known; such characteristics are designed to improve the aforementioned inherent properties and dispersibility of lamellar alumina particles (Patent Documents 1 and 2). Furthermore, production methods for controlling the shape of lamellar alumina particles to increase their aspect ratio are known. Examples of production methods include a method of hydrothermal synthesis by adding a phosphoric acid compound as a shape control agent (Patent Document 3); and a method of calcination by adding fluorosilicates (Patent Document 4).

[0005] In addition, there is a known method for producing sheet alumina in which silicon or a silicon compound containing elemental silicon is used as a crystallinity control agent (Patent Document 5).

[0006] As coated alumina particles, alumina particles with zirconium oxide nanoparticles uniformly covered on their surface are known; alumina particles can be obtained by covering the surface of alumina particles with an average particle size of 0.1 μm or more with zirconium oxide nanoparticles with an average particle size of less than 100 nm (Patent Document 6).

[0007] In addition, other coated particles are known to include a composite powder comprising a matrix powder and spherical barium sulfate particles with a number average particle size of 0.5 to 5.0 μm, which are adhered to the surface of the matrix powder in the form of protrusions; the coating rate of the spherical barium sulfate particles is 10 to 70% relative to the surface area of ​​the matrix powder (Patent Document 7).

[0008] In addition, as the composite oxide-coated particles, the following blue-green pigments are known: a substrate of flaky fine powder is coated with a metal composite oxide including oxides of magnesium, calcium, cobalt, and titanium, and the weight of the coating layer is 5 to 70 weight percent based on the total weight of the pigment, and the powder is selected from powders such as mica, talc, kaolin, sericite, and synthetic mica (Patent Document 8).

[0009] In addition, other composite metal oxide-coated particles are as follows. There is known a flaky alumina pigment in which a colored composite metal oxide that has reacted with the surface is present on the surface of flaky alumina (Patent Document 9). The following wurtzite-type inorganic pigments are known: among those having a wurtzite-type structure of main particles such as ZnO, ZnO 1-x (0 < x < 1), ZnS, GaN, Bn, or SiC, there is present a wurtzite-type compound having a composition different from that of the particle (Patent Document 10).

[0010] [Citation List]

[0011] [Patent Document]

[0012] [Patent Document 1]

[0013] Japanese Unexamined Patent Application Publication No. 2003-192338

[0014] [Patent Document 2]

[0015] Japanese Unexamined Patent Application Publication No. 2002-249315

[0016] [Patent Document 3]

[0017] Japanese Unexamined Patent Application Publication No. 9-59018

[0018] [Patent Document 4]

[0019] Japanese Unexamined Patent Application Publication No. 2009-35430

[0020] [Patent Document 5]

[0021] Japanese Unexamined Patent Application Publication No. 2016-222501

[0022] [Patent Document 6]

[0023] Japanese Unexamined Patent Application Publication No. 2005-306635

[0024] [Patent Document 7]

[0025] Japanese Unexamined Patent Application Publication No. 2004-300080

[0026] [Patent Document 8]

[0027] Japanese Unexamined Patent Application Publication No. 4-28771

[0028] [Patent Document 9]

[0029] Japanese Unexamined Patent Application Publication No. 7-331110

[0030] [Patent Document 10]

[0031] Japanese Unexamined Patent Application Publication No. 2003-221524 Summary of the Invention

[0032] The problem the invention aims to solve

[0033] However, none of the patent documents 1 to 7 disclose coated alumina particles having a coating that includes a composite metal oxide.

[0034] Patent Document 8 states that a non-aluminum substrate is coated with a metal composite oxide comprising oxides of magnesium, calcium, cobalt, and titanium, wherein the weight of the coating layer is 5 to 70% by weight based on the total weight of the pigment. Therefore, the resulting blue-green pigment exhibits high strength and saturation, as well as good safety and stability. However, Patent Document 8 does not disclose coated alumina particles having a coating layer comprising the composite metal oxide.

[0035] Patent Document 9 states that a coloring composite metal oxide, which has reacted with the aluminum oxide on the surface of the flake-shaped alumina, is present, thus the resulting flake-shaped alumina pigment has excellent coating properties and high-temperature stability. However, Patent Document 9 does not disclose coated alumina particles having a coating layer comprising a composite metal oxide containing more than one metal other than aluminum.

[0036] Patent Document 10 states that a wurtzite-type compound with a composition different from that of the main particles exists on the surface of the main particles having a wurtzite-type structure. Therefore, the resulting wurtzite-type inorganic pigment is non-toxic, has excellent high-temperature stability, and high saturation. However, Patent Document 10 does not disclose coated alumina particles having a coating layer including a composite metal oxide.

[0037] The present invention has been made in view of the above circumstances, and the object of the present invention is to provide composite particles in which the selectivity of the coating material is improved, and to provide a method for producing the composite particles.

[0038] Solution for solving the problem

[0039] The inventors diligently conducted research to achieve the above-mentioned objectives and thus discovered that when molybdenum is present in the surface region of alumina particles used as the host to form composite particles, the alumina particles can be coated with an inorganic coating layer comprising a composite metal oxide containing any of various multiple metal species, thereby significantly improving the selectivity of the coating material. Therefore, the inventors completed the present invention. Furthermore, with the combination of molybdenum present in the alumina particles and other multiple metal species present in the inorganic coating layer, applications of the composite particles in various fields are anticipated, such as the field of catalysts. Specifically, the present invention provides the following means for achieving the above-mentioned objectives.

[0040] [1] A composite particle comprising alumina particles and an inorganic coating disposed on the surface of the alumina particles, the alumina particles comprising molybdenum (Mo) and the inorganic coating comprising a composite metal oxide.

[0041] [2] According to the composite particles described in [1], the composite metal oxide includes metal oxides of two or more metals selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al).

[0042] [3] According to the composite particles described in [1], the composite metal oxide includes a first metal oxide and a second metal oxide, wherein the first metal oxide is a metal oxide selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co) and manganese (Mn), and the second metal oxide is a metal oxide selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co) and manganese (Mn), and the second metal oxide is different from the first metal oxide.

[0043] [4] The composite particles according to [1] further comprise silicon (Si) and / or germanium (Ge).

[0044] [5] The composite particles according to [4], wherein the alumina particles contain mullite in the surface layer of the alumina particles.

[0045] [6] The composite particles according to any one of [1] to [5], wherein the composite particles have one of a plate shape, a spherical shape and a polyhedral shape.

[0046] [7] The composite particles according to any one of [1] to [6], wherein the composite particles have a sheet-like shape, a thickness of 0.01 μm or more and 5 μm or less, an average particle size of 0.1 μm or more and 500 μm or less, and an aspect ratio of 2 or more and 500 or less.

[0047] [8] A coating formulation, ink or molded article comprising any of the composite particles described in any one of [1] to [7].

[0048] [9] A method for producing composite particles, the method comprising the following steps:

[0049] Alumina particles are produced by sintering a mixture containing an aluminum compound and a molybdenum compound, or by sintering a mixture containing an aluminum compound, a molybdenum compound, and a shape control agent for controlling the shape of the alumina particles; and

[0050] An inorganic coating containing composite metal oxides is formed on the surface of alumina particles.

[0051]

[10] The method for producing composite particles according to [9], wherein the shape control agent comprises one or more selected from silicon, silicon compounds containing elemental silicon, and germanium compounds containing elemental germanium.

[0052]

[11] The method for producing composite particles according to [9] or

[10] , wherein the mixture further comprises a potassium compound containing elemental potassium.

[0053]

[12] The method for producing composite particles according to [9] includes composite metal oxides of two or more metals selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al).

[0054]

[13] According to the method for producing composite particles described in [9], the composite metal oxide includes a first metal oxide and a second metal oxide, wherein the first metal oxide is a metal oxide selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co) and manganese (Mn), and the second metal oxide is a metal oxide selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co) and manganese (Mn), and the second metal oxide is different from the first metal oxide.

[0055]

[14] According to the method for producing composite particles described in [9], in which, when forming an inorganic coating, a metal inorganic salt containing at least one metal other than aluminum (Al) is contacted with alumina particles, and then the metal inorganic salt deposited on the alumina particles is converted into a composite metal oxide.

[0056]

[15] According to the method for producing composite particles described in [9], wherein

[0057] The formation of the inorganic coating layer includes a first transformation step and a second transformation step.

[0058] In the first conversion step, a first metal inorganic salt containing at least one metal other than aluminum (Al) is contacted with alumina particles, and then the first metal inorganic salt deposited on the alumina particles is converted into a metal oxide.

[0059] In the second conversion step, a second metal inorganic salt is contacted with metal oxide and / or alumina particles. The second metal inorganic salt contains at least one different metal other than aluminum (Al) and is different from the metal used in the first conversion step. Then, the metal oxide and / or the second metal inorganic salt is converted into a composite metal oxide.

[0060] Using the present invention, composite particles in which the selectivity of the coating material is improved are provided. Attached Figure Description

[0061] [ Figure 1 ]

[0062] Figure 1 The image shown is an electron microscope image of the composite particles obtained in Example 3, illustrating an example of the construction of composite particles according to an embodiment of the present invention.

[0063] [ Figure 2 ]

[0064] Figure 2 yes Figure 1 The magnified image of the composite particles shown.

[0065] [ Figure 3 ]

[0066] Figure 3 yes Figure 1 A magnified image of the surface of the composite particles shown.

[0067] [ Figure 4 ]

[0068] Figure 4 The image shown is an electron microscope image of the composite particles obtained in Example 6, illustrating an example of the construction of composite particles according to an embodiment of the present invention.

[0069] [ Figure 5 ]

[0070] Figure 5 yes Figure 4 The magnified image of the composite particles shown.

[0071] [ Figure 6 ]

[0072] Figure 6 yes Figure 4 A magnified image of the surface of the composite particles shown.

[0073] [ Figure 7 ]

[0074] Figure 7 The image shown is an electron microscope image of the composite particles obtained in Example 12, illustrating an example of the construction of composite particles according to an embodiment of the present invention.

[0075] [ Figure 8 ]

[0076] Figure 8 yes Figure 7 The enlarged view of the composite particles shown.

[0077] [ Figure 9 ]

[0078] Figure 9 yes Figure 7 A magnified image of the surface of the composite particles shown.

[0079] [ Figure 10 ]

[0080] Figure 10 The image shown is an electron microscope image of the composite particles obtained in Example 14, illustrating an example of the construction of composite particles according to an embodiment of the present invention.

[0081] [ Figure 11 ]

[0082] Figure 11 yes Figure 10 The magnified image of the composite particles shown.

[0083] [ Figure 12 ]

[0084] Figure 12 yes Figure 10 A magnified image of the surface of the composite particles shown.

[0085] [ Figure 13 ]

[0086] Figure 13 The image shows an electron microscope image of the composite particles obtained in Comparative Example 1.

[0087] [ Figure 14 ]

[0088] Figure 14 yes Figure 13 The magnified image of the composite particles shown.

[0089] [ Figure 15 ]

[0090] Figure 15 yes Figure 13 The magnified image of the composite particles shown. Detailed Implementation

[0091] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0092] [First Implementation Plan]

[0093] [Composite Particles]

[0094] The composite particles according to the first embodiment include alumina particles and an inorganic coating layer disposed on the surface of the alumina particles. The alumina particles contain molybdenum (Mo). The inorganic coating layer contains a composite metal oxide. The alumina particles of the embodiment have a plate-like shape, and the composite particles also have a plate-like shape. In the following, in this embodiment, alumina particles having a plate-like shape will also be referred to as "plate-like alumina particles," "plate-like alumina," or simply "alumina particles."

[0095] [Flake-shaped alumina particles]

[0096] As used in this invention, the term "flaky" refers to having an aspect ratio of 2 or greater. The aspect ratio is a proportion obtained by dividing the average particle size of the alumina particles by the thickness of the alumina particles. Note that in this specification, "thickness of the alumina particles" is the arithmetic mean of the measured thicknesses of at least 50 flaky alumina particles randomly selected from images obtained using a scanning electron microscope (SEM). Furthermore, "average particle size of the alumina particles" is the median diameter D based on the volume-based cumulative particle size distribution measured by a laser diffraction particle size analyzer. 50 The calculated value.

[0097] In alumina particles, the properties described below—thickness, particle size, and aspect ratio—can be any combination of various types, provided that the alumina particles have a plate-like shape. Furthermore, the upper and lower limits of the numerical ranges for the properties mentioned as examples can be freely combined with each other.

[0098] The thickness of the flake-shaped alumina particles is preferably 0.01 μm or more and 5 μm or less, more preferably 0.03 μm or more and 5 μm or less, even more preferably 0.1 μm or more and 5 μm or less, even more preferably 0.3 μm or more and 3 μm or less, and even more preferably 0.5 μm or more and 1 μm or less.

[0099] When using flaky alumina particles with a large particle size, the thickness is preferably greater than or equal to 3 μm, more preferably 5 μm or more and 60 μm or less.

[0100] When the thickness is any of the above-mentioned thicknesses, the alumina particles have a high aspect ratio and excellent mechanical strength, therefore, such a thickness is preferred.

[0101] The average particle size (D) of the flaky alumina particles50 Preferably, the micrometer is 0.1 μm or more and 500 μm or less, more preferably 0.5 μm or more and 100 μm or less, and even more preferably 1 μm or more and 50 μm or less.

[0102] When using flaky alumina particles with a large particle size, the average particle size (D) 50 The average particle size is preferably greater than or equal to 10 μm, more preferably greater than or equal to 20 μm, even more preferably greater than or equal to 22 μm, even more preferably greater than or equal to 25 μm, and particularly preferably greater than or equal to 31 μm. There is no particular upper limit on the average particle size. For example, the average particle size (D) of the lamellar alumina particles in this embodiment is... 50 The size of the material is 10 μm or more and 500 μm or less, more preferably 20 μm or more and 300 μm or less, even more preferably 22 μm or more and 100 μm or less, even more preferably 25 μm or more and 100 μm or less, and particularly preferably 31 μm or more and 50 μm or less.

[0103] When the average particle size (D) 50 When the average particle size (D) is greater than or equal to the lower limit, alumina particles have a large area of ​​light-reflecting surface, therefore, alumina particles exhibit particularly excellent luminescent properties. Furthermore, when the average particle size (D) is greater than or equal to the lower limit, alumina particles possess a large area of ​​light-reflecting surface, thus exhibiting particularly excellent luminescent properties. 50 When the alumina content is less than or equal to the upper limit, alumina particles are suitable as fillers.

[0104] The aspect ratio of the flaky alumina particles, i.e., the ratio of average particle size to thickness, is preferably 2 or more and 500 or less, more preferably 5 or more and 500 or less, even more preferably 15 or more and 500 or less, even more preferably 10 or more and 300 or less, even more preferably 17 or more and 300 or less, and even more preferably 33 or more and 100 or less. When the aspect ratio is greater than or equal to 2, the flaky alumina particles can have two-dimensional mixing characteristics, therefore, such an aspect ratio is preferred. When the aspect ratio is less than or equal to 500, the flaky alumina particles have excellent mechanical strength, therefore, such an aspect ratio is preferred. When the aspect ratio is greater than or equal to 15, the flaky alumina particles can form highly luminescent pigments, therefore, such an aspect ratio is preferred.

[0105] When using flaky alumina particles with a large particle size, the aspect ratio, which is the ratio of average particle size to thickness, is preferably 2 or more and 50 or less, and more preferably 3 or more and 30 or less.

[0106] Flake-shaped alumina particles can have a circular or elliptical flake shape, but for operability and ease of production, it is preferred that the particle shape be, for example, a polygonal flake shape.

[0107] Flaky alumina particles can be obtained using any production method. From the viewpoint of achieving higher aspect ratio, higher dispersion, and higher productivity, flaky alumina particles are preferably obtained by calcining an aluminum compound in the presence of a molybdenum compound (preferably a potassium compound) and a shape control agent. Suitable shape control agents used are at least one selected from the group consisting of silicon, silicon compounds, and germanium compounds. More preferably, the shape control agent is silicon or a silicon compound containing elemental silicon, because in this case, the shape control agent can be a source of Si from mullite, which will be described later.

[0108] In this production method, a molybdenum compound is used as a fluxing agent. In this specification, the production method using a molybdenum compound as a fluxing agent will be simply referred to as the "flux method." The flux method will be described in detail later. Note that during firing, the molybdenum compound and the aluminum compound react with each other at high temperatures to form aluminum molybdate, and subsequently, it is presumed that the molybdenum compound is introduced into the flake-like alumina particles as the aluminum molybdate decomposes into alumina and molybdenum oxide at even higher temperatures. The sublimated molybdenum oxide can be recovered and recycled.

[0109] Note that when mullite is present in the surface layer of the flaky alumina particles, the following process may occur during the above process: silicon or a silicon-containing compound, acting as a shape control agent, reacts with a molybdenum-aluminum compound, resulting in the formation of mullite in the surface layer of the flaky alumina particles. More specifically, the mechanism of mullite formation is presumed to be as follows: in the flaky surface of alumina, molybdenum and Si atoms react with each other to form Mo-O-Si, and molybdenum and Al atoms react with each other to form Mo-O-Al. During high-temperature firing, Mo is removed, and mullite with Si-O-Al bonds is formed.

[0110] Preferably, the molybdenum oxide that was not introduced into the flake alumina particles is recovered by sublimation and recycled. In this case, the amount of molybdenum oxide adhering to the surface of the flake alumina can be reduced, and therefore, when the flake alumina is dispersed in a dispersion medium (examples of which include organic binders such as resins and inorganic binders such as glass), the unintentional introduction of molybdenum oxide into the binder can be prevented, and thus the inherent properties of the flake alumina can be maximized.

[0111] Note that in this specification, regarding the production method described later, materials with sublimable properties are referred to as fluxes, and materials that are not sublimable are referred to as shape control agents.

[0112] The use of molybdenum and shape control agents in the production of flake alumina particles enables the alumina particles to have a highly α-crystalline euhedral shape, thus exhibiting excellent dispersibility, mechanical strength, and high thermal conductivity.

[0113] When the surface layer of the flake-shaped alumina particles contains mullite, the amount of mullite formed in the surface layer of the flake-shaped alumina particles can be controlled by the ratio of molybdenum compound to shape control agent. Specifically, the amount of mullite can be controlled by the ratio of silicon or a silicon compound containing elemental silicon used as a shape control agent. Preferred values ​​for the amount of mullite formed in the surface layer of the flake-shaped alumina particles and preferred ratios of the raw materials will be described in detail later.

[0114] From the viewpoint of improving luminescence properties, it is preferable that the sheet-like alumina particles have the following characteristics: the sheet-like alumina particles have an aspect ratio of 5 to 500, and the sheet-like alumina particles are subjected to solid-state treatment under a static magnetic field strength of 14.1 T. 27 In Al NMR analysis, the longitudinal relaxation time T1 associated with the peaks of hexacoordinate aluminum in the range of 10–30 ppm is greater than or equal to 5 seconds.

[0115] A longitudinal relaxation time T1 greater than or equal to 5 seconds indicates that the lamellar alumina particles have high crystallinity. Reported knowledge suggests that a long solid-state longitudinal relaxation time indicates good crystal symmetry and high crystallinity (reported in Susumu Kitagawa et al., Japan Society of Coordination Chemistry selection 4, “Takakushuno yoeki oyobi kotai NMR (Multinuclear Solution and Solid NMR)”, published by Sankyo Shuppan Co., Ltd., pp. 80-82).

[0116] The longitudinal relaxation time T1 of the flaky alumina particles is preferably greater than or equal to 5 seconds, more preferably greater than or equal to 6 seconds, and even more preferably greater than or equal to 7 seconds.

[0117] For the sheet-like alumina particles in this embodiment, there is no particular upper limit on the longitudinal relaxation time T1. For example, the upper limit can be less than or equal to 22 seconds, less than or equal to 15 seconds, or less than or equal to 12 seconds.

[0118] Examples of the numerical range of the longitudinal relaxation time T1 mentioned above can 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.

[0119] Solid-state reaction of sheet-like alumina particles under a static magnetic field strength of 14.1 T 27 In Al NMR analysis, it is preferable that no peak of tetracoordinated aluminum is detected in the 60–90 ppm range. In this case, it is presumed that the lamellar alumina particles are less likely to experience the damage or shedding caused by crystal symmetry deformation that can occur when crystals with different coordination numbers are present; therefore, lamellar alumina particles tend to have higher shape stability.

[0120] In existing technologies, the crystallinity of inorganic materials is typically evaluated based on results such as XRD analysis. However, the inventors have conducted research and discovered that by using the longitudinal relaxation time T1 as an evaluation index of the crystallinity of alumina particles, more accurate analytical results can be obtained than those obtained through XRD analysis in existing technologies. The lamellar alumina particles of the embodiment have a long longitudinal relaxation time T1 of 5 seconds or more; therefore, it can be inferred that the alumina particles have high crystallinity. That is, it is speculated that in the lamellar alumina particles of the embodiment, due to the high crystallinity, diffuse reflection from the crystal planes may be suppressed, thus improving light reflection, resulting in excellent luminescent properties of the lamellar alumina particles.

[0121] Furthermore, the inventors have discovered a very strong correlation between the longitudinal relaxation time T1 of the lamellar alumina particles, the shape retention rate, and the processing stability of the resin composition. In particular, when the average particle size of the lamellar alumina particles is 10 μm or less and the aspect ratio is 30 or less (e.g., Examples 1 and 2), the correlation between the longitudinal relaxation time T1 of the lamellar alumina particles, the shape retention rate, and the processing stability of the resin composition is significantly observed. Lamellar alumina particles with a longitudinal relaxation time T1 greater than or equal to 5 seconds, such as the lamellar alumina particles described above, also have the advantage that, when the resin composition is produced by mixing the lamellar alumina particles with resin, the resin composition exhibits good processing stability and can therefore be easily processed into the desired shape. The lamellar alumina particles described above, with their high long longitudinal relaxation time T1 value, exhibit enhanced crystallinity. Therefore, it is speculated that because the particles possess high strength due to the high crystallinity of alumina, the flakes are less prone to breakage when resin and flake alumina particles are mixed together during the production of the resin composition. Furthermore, because the particles may have almost no unevenness on their surface due to the high crystallinity of alumina, the particles exhibit excellent adhesion to the resin. It is speculated that, due to these factors, the flake alumina particles described above possess good processing stability of the resin composition. For example, even when flake alumina particles are mixed into the resin composition, the flake alumina particles described above advantageously exhibit the inherent properties of flake alumina particles.

[0122] In existing technologies, it is more difficult to obtain highly crystalline alumina particles with flaky shapes compared to spherical alumina particles. This is presumably because, unlike spherical alumina particles, flaky alumina particles inevitably exhibit inhomogeneity in the direction of crystal growth during the production process.

[0123] In contrast, for example, those lamellar alumina particles that satisfy the longitudinal relaxation time T1 value, despite their lamellar shape, exhibit high crystallinity. Therefore, lamellar alumina particles are very useful because, while possessing the advantages of lamellar alumina particles, such as exhibiting high thermal conductivity, they also have enhanced shape retention and enhanced processing stability of the resin composition.

[0124] Furthermore, the lamellar alumina particles of this embodiment have a ratio I(006) / I(113) determined by X-ray diffraction measurements using Cu-Kα radiation, which is the ratio of the peak intensity I(006) corresponding to 2θ = 41.6 ± 0.3 degrees on the (006) plane to the peak intensity I(113) corresponding to 2θ = 43.3 ± 0.3 degrees on the (113) plane (hereinafter, the ratio I(006) / I(113) will be abbreviated as "(006 / 113) ratio"). The (006 / 113) ratio is preferably 0.2 or more and 30 or less, more preferably 1 or more and 20 or less, even more preferably 3 or more and 10 or less, and particularly preferably 7.5 or more and 10 or less. In these cases, for example, the average particle size (D) of the lamellar alumina particles is... 50 ) greater than or equal to 10 μm and thickness greater than or equal to 0.1 μm.

[0125] It is understood that a high (006 / 113) ratio indicates a high proportion of the (006) facet relative to the (113) facet. Therefore, the alumina particles are plate-like alumina particles in which the crystal faces corresponding to the (006) facet orientation have been significantly developed. Plate-like alumina particles exhibit high luminescence properties even when the mass of each particle is small because the large area developed on the top or bottom surface of the plate-like alumina particles leads to increased visibility of reflected light reflected from the top or bottom surface. In addition, the formation of crystal faces corresponding to the (113) facet orientation is suppressed.

[0126] The isoelectric point pH of the lamellar alumina particles is, for example, in the range of 2 to 6. The isoelectric point pH is preferably in the range of 2.5 to 5, and more preferably in the range of 3 to 4. When the isoelectric point pH of the lamellar alumina particles is within any of the above ranges, the lamellar alumina particles exhibit high electrostatic repulsion. Therefore, when lamellar alumina particles are added to a dispersion medium, such as those described above, the lamellar alumina particles themselves can exhibit enhanced dispersion stability, thus promoting further performance improvement through surface treatment using coupling agents or the like.

[0127] The isoelectric point pH value can be obtained as follows. To measure the zeta potential, a zeta potential analyzer (Zetasizer Nano ZSP from Malvern) was used. 20 mg of sample and 10 mL of 10 mM KCl aqueous solution were stirred for 3 minutes in an Awatori Rentaro (ARE-310, from Thinky Corporation) in stirring / defoaming mode, and the mixture was allowed to stand for 5 minutes. The resulting supernatant was used as the measurement sample. The zeta potential was measured up to pH 2 using an automatic titrator with the addition of 0.1 N HCl (applied voltage 100 V, single-mode mode). Therefore, the pH value at the isoelectric point, where the potential is zero, was evaluated.

[0128] For example, the density of flaky alumina particles is 3.70 g / cm³. 3 Above and 4.10 g / cm 3 The following density is preferred: 3.72 g / cm³. 3 Above and 4.10 g / cm 3 Hereinafter, more preferably, the density is 3.80 g / cm³. 3 Above and 4.10 g / cm 3 the following.

[0129] Density was measured as follows: The flaky alumina particles were pretreated at 300°C for 3 hours. Subsequently, the density was measured using a Micromeritics AccuPyc II 1330 dry-type automatic density meter under conditions including a measurement temperature of 25°C and the use of helium as the carrier gas.

[0130] [Alumina]

[0131] The alumina present in the lamellar alumina particles is an aluminum oxide, and can be any of various types of transition alumina having crystal forms such as γ, δ, θ, or κ, and transition alumina may include alumina hydrates. However, generally speaking, for the sake of higher mechanical strength or higher thermal conductivity, it is preferred that the alumina be in the α-crystal form (α-type). The α-crystal form is a dense crystalline structure of alumina, and therefore, it is advantageous for improving the mechanical strength or thermal conductivity of the lamellar alumina.

[0132] Preferably, the α-crystallinity is as close to 100% as possible, because in this case, the inherent properties of the α-crystal form can be readily expressed. The α-crystallinity of the lamellar alumina particles is, for example, greater than or equal to 90%. The α-crystallinity is preferably greater than or equal to 95%, and more preferably greater than or equal to 99%.

[0133] [Silicon and Germanium]

[0134] The sheet-like alumina particles in this embodiment may contain silicon (Si) and / or germanium (Ge).

[0135] Silicon and / or germanium can be derived from silicon, silicon compounds, and / or germanium compounds that can be used as shape control agents. By utilizing any of these, sheet-like alumina particles with excellent luminescent properties can be produced in the production method described later.

[0136] [silicon]

[0137] The sheet-like alumina particles of this embodiment may contain silicon. The sheet-like alumina particles of this embodiment may contain silicon in the surface layer.

[0138] As used herein, the term "surface layer" refers to a region within a 10 nm range on the surface of the lamellar alumina particles in this embodiment. This distance corresponds to the probe depth of the XPS used for measurement in the embodiments.

[0139] In lamellar alumina particles, silicon can be localized in the surface layer. As used herein, "localized in the surface layer" means that the mass of silicon per unit volume in the surface layer is greater than the mass of silicon per unit volume in the rest of the particle. Localized silicon in the surface layer can be determined by comparing the results of surface analysis performed by XPS with the results of global analysis performed by XRF.

[0140] The silicon that may be included in the sheet-like alumina particles may be elemental silicon or silicon present in silicon compounds. The sheet-like alumina particles may contain at least one of the following as silicon or silicon compounds: mullite, Si, SiO2, SiO, and aluminum silicate formed by reaction with alumina; any of these substances may be included in the surface layer. Mullite will be described later.

[0141] When silicon or silicon compounds containing elemental silicon are used as shape control agents, Si can be detected from lamellar alumina particles by XRF analysis. In the lamellar alumina particles, the molar ratio [Si] / [Al], which is the ratio of the number of moles of Si to the number of moles of Al determined by XRF analysis, is, for example, less than or equal to 0.04. The molar ratio [Si] / [Al] is preferably less than or equal to 0.035, and more preferably less than or equal to 0.02.

[0142] Furthermore, there are no particular restrictions on the value of the molar ratio [Si] / [Al], and it is, for example, greater than or equal to 0.003. This value is preferably greater than or equal to 0.004, and more preferably greater than or equal to 0.005.

[0143] In the flaky alumina particles, the molar ratio [Si] / [Al], which is the ratio of the number of moles of Si to the number of moles of Al as determined by XRF analysis, is, for example, 0.003 or more and 0.04 or less. The molar ratio [Si] / [Al] is preferably 0.004 or more and 0.035 or less, and more preferably 0.005 or more and 0.02 or less.

[0144] When the molar ratio [Si] / [Al] determined by XRF analysis of the lamellar alumina particles is within any of the aforementioned ranges, the aforementioned ratio (006 / 113) is satisfied, thereby obtaining more favorable luminescent properties and advantageously forming a lamellar shape. Furthermore, adhering objects are unlikely to adhere to the surface of the lamellar alumina particles, thus achieving excellent quality. It is speculated that the adhering objects are SiO2 particles, which are believed to originate from excess Si generated when the formation of mullite in the surface layer of the lamellar alumina particles has reached its maximum level.

[0145] When using flaky alumina particles with a large particle size, the molar ratio of the flaky alumina particles [Si] / [Al], which is the ratio of the number of moles of Si to the number of moles of Al as determined by XRF analysis, is preferably 0.0003 or more and 0.01 or less, more preferably 0.0005 or more and 0.0025 or less, and even more preferably 0.0006 or more and 0.001 or less.

[0146] The flake-shaped alumina particles may contain silicon corresponding to the silicon or silicon compounds containing elemental silicon used in the production method of the flake-shaped alumina particles. The silicon content, calculated as silica, is preferably less than or equal to 10% by mass relative to the total mass of 100% by mass of the flake-shaped alumina particles; more preferably 0.001 to 5% by mass, even more preferably 0.01 to 4% by mass, even more preferably 0.3 to 2.5% by mass, and particularly preferably 0.6 to 2.5% by mass.

[0147] When the silicon content is within any of the above-mentioned ranges, the above-mentioned ratio (006 / 113) is satisfied, thereby obtaining more favorable luminescent properties and advantageously forming a sheet-like shape. Furthermore, it is presumed that the adhering material as SiO2 particles is unlikely to adhere to the surface of the sheet-like alumina particles, thus obtaining excellent quality.

[0148] When using flaky alumina particles with a large particle size, the silicon content, calculated as silica, is preferably less than or equal to 10% by mass relative to the total mass of 100% by mass of flaky alumina particles; more preferably 0.001 to 3% by mass, even more preferably 0.01 to 1% by mass, and particularly preferably 0.03 to 0.3% by mass.

[0149] [Mullite]

[0150] The flake-shaped alumina particles of this embodiment may contain mullite. It is inferred that the presence of mullite in the surface layer of the flake-shaped alumina particles improves the selectivity of the inorganic material that can form the inorganic coating layer, thus enabling the effective formation of the inorganic coating layer on the flake-shaped alumina particles.

[0151] The presence of mullite in the surface layer of the lamellar alumina particles leads to a significant reduction in device wear. Mullite, which can be present in the surface layer of the lamellar alumina particles, is a composite oxide of Al and Si, denoted by AlxSiyOz, where there are no particular limitations on the values ​​of x, y, and z. A more preferred range is Al2Si1O5 to Al6Si2O. 13 Note that the XRD peak intensities identified in the examples described later are Al. 2.85 Si1O 6.3 Al3Si1O 6.5 Al 3.67 Si1O 7.5 Al4Si1O8 and Al6Si2O 13 The XRD peak intensity. Flaky alumina particles can include Al-selected particles in the surface layer. 2.85 Si1O 6.3 Al3Si1O 6.5 Al3 .67 Si1O 7.5Al4Si1O8 and Al6Si2O 13 At least one compound from the group consisting of. As used herein, the term "surface layer" refers to a region within a 10 nm range of the surface of the lamellar alumina particles. This distance corresponds to the probe depth of the XPS used for measurement in the examples.

[0152] In the flaky alumina particles, it is preferred that mullite is locally present in the surface layer. As used herein, the expression "locally present in the surface layer" means that the mass of mullite per unit volume in the surface layer is greater than the mass of mullite per unit volume in the remaining portion excluding the surface layer.

[0153] Furthermore, the mullite in the surface layer can be in the form of a mullite layer or a state where mullite and alumina coexist. Regarding the interface between mullite and alumina in the surface layer, mullite and alumina can be in physical contact with each other, or they can form chemical bonds, such as Si-O-Al.

[0154] [germanium]

[0155] The flake-shaped alumina particles of this embodiment may contain germanium. The flake-shaped alumina particles may contain germanium in the surface layer.

[0156] The flake-shaped alumina particles may contain germanium or germanium compounds, which may vary depending on the raw materials used. For example, the germanium or germanium compound is at least one of the group consisting of compounds of Ge, such as GeO2, GeO, GeCl2, GeBr4, GeI4, GeS2, AlGe, GeTe, GeTe3, GeAs2, GeSe, GeS3As, SiGe, Li2Ge, FeGe, SrGe, and GaGe, and oxides of any of these; any of these substances may be present in the surface layer.

[0157] Note that germanium or germanium compounds that may be included in the flake-shaped alumina particles and the germanium compound used as a shape control agent as a raw material may be the same type of germanium compound. For example, GeO2 can be detected in flake-shaped alumina particles produced by adding GeO2 as a raw material.

[0158] The presence of germanium or germanium compounds in the surface layer of the lamellar alumina particles leads to a significant reduction in device wear. As used herein, the term "surface layer" refers to the region within 10 nm of the surface of the lamellar alumina particles.

[0159] In the flaky alumina particles, it is preferred that germanium or germanium compounds are locally present in the surface layer. As used herein, the expression "locally present in the surface layer" means a state in which the mass of germanium or germanium compounds per unit volume in the surface layer is greater than the mass of germanium or germanium compounds per unit volume in the remaining portion excluding the surface layer. The local presence of germanium or germanium compounds in the surface layer can be confirmed by comparing the results of surface analysis performed by XPS with the results of global analysis performed by XRF.

[0160] The flake-shaped alumina particles contain germanium corresponding to the germanium compound used in the production method of the flake-shaped alumina particles. The germanium content, calculated as germanium dioxide, is preferably less than or equal to 10% by mass relative to the total mass of 100% by mass of the flake-shaped alumina particles; more preferably 0.001 to 5% by mass, even more preferably 0.01 to 4% by mass, and particularly preferably 0.1 to 3.0% by mass. When the germanium content is within any of the above-mentioned ranges, the amount of germanium or germanium compound is suitable, thus satisfying the above-mentioned (006 / 113) ratio, thereby obtaining more favorable luminescent properties. Therefore, such a content is preferred. The germanium content can be determined by XRF analysis.

[0161] XRF analysis will be performed under the same measurement conditions as those listed in the Examples section described later, or under compatible conditions under which the same measurement results can be obtained.

[0162] Furthermore, the germanium or germanium compound in the surface layer can be in the form of a layer, or in a state where germanium or germanium compound coexists with aluminum oxide. Regarding the interface between the germanium or germanium compound and aluminum oxide in the surface layer, the germanium or germanium compound and aluminum oxide can be in physical contact with each other, or the germanium or germanium compound and aluminum oxide can form chemical bonds, such as Ge-O-Al.

[0163] [molybdenum]

[0164] The flake-shaped alumina particles of this embodiment contain molybdenum. Preferably, the flake-shaped alumina particles contain molybdenum in the surface layer. It is inferred that in this case, the selectivity of the inorganic material that can form the inorganic coating is improved, and therefore, the inorganic coating can be effectively formed on the flake-shaped alumina particles.

[0165] Molybdenum can be derived from molybdenum compounds used as fluxes in the production methods of alumina particles described later.

[0166] Molybdenum possesses catalytic and optical properties. Furthermore, when using molybdenum, it is possible to produce sheet-like alumina particles with high crystallinity and excellent luminescent properties, despite their flaky shape, using the production methods described later.

[0167] When the amount of molybdenum is increased, the particle size and (0.06 / 113) ratio tend to be satisfied, thus further enhancing the luminescent properties of the resulting alumina particles. Furthermore, the use of molybdenum promotes mullite formation, thereby enabling the production of lamellar alumina particles with high aspect ratio and excellent dispersibility. Moreover, the properties of molybdenum contained in the lamellar alumina particles can be utilized to apply them in applications such as catalysts for oxidation reactions and optical materials.

[0168] Examples of molybdenum include, but are not limited to, molybdenum metal, molybdenum oxide, partially reduced molybdenum compounds, and molybdates. Lamellar alumina particles may contain one or more polymorphs of molybdenum compounds, or combinations thereof. For example, lamellar alumina particles may contain any and more of α-MoO3, β-MoO3, MoO2, MoO, and molybdenum cluster structures.

[0169] There are no particular restrictions on the form in which molybdenum exists, and any of the following forms are possible: molybdenum adhering to the surface of flaky alumina particles; molybdenum partially replacing aluminum in the crystal structure of alumina; and combinations of these forms.

[0170] The molybdenum content, calculated as molybdenum trioxide and determined by XRF analysis, is preferably less than or equal to 10% by mass relative to the total mass of 100% by mass of flake-shaped alumina particles; more preferably 0.001 to 5% by mass, even more preferably 0.01 to 5% by mass, and particularly preferably 0.1 to 1.5% by mass. This can be achieved by adjusting the firing temperature, firing time, and / or the sublimation rate of the molybdenum compound. When the molybdenum content is less than or equal to 10% by mass, the quality of the α-crystals of alumina is improved. Therefore, such a content is preferred.

[0171] When using flaky alumina particles with a large particle size, the molybdenum content, calculated as molybdenum trioxide, is preferably less than or equal to 10% by mass relative to the total mass of the flaky alumina particles of this embodiment, which is taken as 100% by mass; this content is more preferably 0.1 to 5% by mass, and even more preferably 0.3 to 1% by mass, which can be achieved by adjusting the firing temperature, firing time and / or the sublimation rate of the molybdenum compound.

[0172] The molybdenum content can be determined by XRF analysis. The XRF analysis will be performed under the same conditions as those listed in the Examples section below, or under compatible conditions that will yield the same measurement results.

[0173] In addition, the Mo content on the surface of alumina particles can be analyzed using an X-ray photoelectron spectroscopy (XPS) instrument as described above.

[0174] Potassium

[0175] Flaky alumina particles may also contain potassium.

[0176] Potassium can be potassium derived from potassium that can be used as a flux in the production method of alumina particles described later.

[0177] In the alumina particle production method described later, the particle size of the alumina particles can be appropriately improved when potassium is used.

[0178] Examples of potassium include, but are not limited to, potassium metal, potassium oxide, and partially reduced potassium compounds.

[0179] There are no particular restrictions on the form in which potassium exists, and any of the following forms are possible: potassium adhering to the surface of the lamellar alumina particles; potassium partially replacing aluminum in the crystal structure of alumina; and combinations of these forms.

[0180] The potassium content, calculated as potassium oxide (K₂O) and determined by XRF analysis, is preferably greater than or equal to 0.01% by mass relative to the total mass of 100% alumina particles; more preferably 0.01 to 1.0% by mass, even more preferably 0.03 to 0.5% by mass, and particularly preferably 0.05 to 0.3% by mass. When the potassium content is within any of the above-mentioned ranges, the alumina particles have a polyhedral shape and an average particle size with an appropriate value. Therefore, such a potassium content is preferred.

[0181] [Other elements]

[0182] Other elements are intentionally added to the alumina particles to a degree that does not impair the effects of the invention. The purpose of addition is to impart mechanical strength or electrical and / or magnetic properties.

[0183] Examples of other elements include, but are not limited to, zinc, manganese, calcium, strontium, and yttrium. These other elements may be used alone or in combination of two or more.

[0184] The content of other elements in the alumina particles is preferably less than or equal to 5% by mass, and more preferably less than or equal to 2% by mass, relative to the mass of the alumina particles.

[0185] [Contains impurities]

[0186] Alumina particles may contain contaminated impurities.

[0187] Contributing impurities are those originating from the metal compounds used in production, those present in the raw materials, and / or those unintentionally introduced into the alumina particles during production. Contributing impurities are actually unnecessary; however, since they exist in trace amounts, they do not affect the properties of the alumina particles.

[0188] Examples of incidental impurities include, but are not limited to, magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, cerium, and sodium. One of these incidental impurities may be present alone, or two or more of them may be present.

[0189] The content of impurities in the alumina particles, relative to the mass of the alumina particles, is preferably less than or equal to 10,000 ppm, more preferably less than or equal to 1,000 ppm, and even more preferably 10 to 500 ppm.

[0190] [Inorganic Coating]

[0191] An inorganic coating layer covers at least a portion of the surface of the alumina particles. Preferably, the inorganic coating layer is formed by an inorganic coating layer covering at least a portion of the surface of the alumina particles. In other words, at least a portion of the surface of the composite particles is covered with an inorganic coating layer, and preferably, at least a portion of the surface of the composite particles is covered with an inorganic coating layer.

[0192] As described above, the inorganic coating is disposed on the surface of the alumina particles. The statement "on the surface of the alumina particles" means "on the outer side of the surface of the alumina particles." Therefore, the inorganic coating formed on the outer side of the surface of the alumina particles will be clearly distinguished from the surface layer formed on the inner side of the surface of the alumina particles, which may contain mullite and / or germanium.

[0193] The inorganic chemical species forming the inorganic coating can be large relative to the alumina particles. However, it is preferable that the inorganic chemical species are small relative to the alumina particles, because in this case, an inorganic coating with the desired coating weight (or coating thickness) can be readily provided according to the purpose. For example, micron-sized alumina particles and inorganic chemical species smaller than 150 nm can be used in combination. The inorganic coating containing inorganic chemical species smaller than the alumina particles can be formed on the outer surface of the alumina particles as follows: A small amount of inorganic chemical species can be used to form an inorganic coating on a portion of the alumina surface in such a way that the substrate alumina particles are clearly visible from the outside. Alternatively, a large amount of inorganic chemical species can be used to form an inorganic coating on the surface of the alumina particles in the form of a layer of inorganic species in such a way that the substrate alumina particles are not visible from the outside. The shape of the inorganic chemical species forming the inorganic coating is not limited. For example, it is preferable that the shape is spherical or polyhedral, because in this shape, a dense coating can be formed with a minimal amount of inorganic chemicals, thereby easily covering the substrate.

[0194] The composite particles of the present invention are formed from molybdenum-containing alumina particles and an inorganic coating layer formed from one or more inorganic chemical species. The composite particles exhibit superior properties that cannot be achieved by a simple mixture of alumina particles and inorganic chemical species. Regarding the composite particles of the present invention, when micron-sized molybdenum-containing alumina particles and non-aggregated inorganic chemical species below 150 nm are used in combination, the interaction between the two is enhanced, for example, through intermolecular forces and, in some cases, local chemical reactions, resulting in particularly significant superior properties. For example, higher coating properties can be obtained, a more uniform inorganic coating layer can be easily obtained, and the resulting inorganic coating layer is less prone to delamination from the alumina particles. In this respect, the contribution of molybdenum present in the alumina particles can also be expected. For example, discrete nanoscale particles of inorganic chemical species can be obtained by mechanically pulverizing micron-sized inorganic chemical species; however, in this case, reaggregation occurs immediately, etc., thus making processing for use difficult. When using alumina particles that do not contain molybdenum or aggregated inorganic chemical species, the two merely form a simple mixture, and this mixture does not exhibit properties such as those of the composite particles of the present invention. In the case of the composite particle production method of the present invention described later, composite particles with high coating efficiency can be easily produced.

[0195] The inorganic coating layer of this embodiment comprises, or preferably is formed of, a composite metal oxide. In this specification, the term "composite metal oxide" refers to a metal oxide containing two or more metals. Composite metal oxides are generally classified as follows (i) to (iii): (i) a mixture of a metal oxide containing two or more metals (a first compound) and a metal oxide containing one metal (a second compound); (ii) a metal oxide containing two or more metals (a first compound); and (iii) a mixture of a metal oxide containing two or more metals (a first compound) and a metal oxide containing two or more metals (a second compound).

[0196] Examples of mixture (i) include, but are not limited to, metal oxides of two or more metals selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al), and mixtures of metal oxides of metals selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), and manganese (Mn). Specific examples of mixtures include mixtures of aluminum-cobalt oxide and iron oxide, mixtures of aluminum-cobalt oxide and titanium oxide, mixtures of cobalt-iron oxide and iron oxide, mixtures of zinc-iron oxide and zinc oxide, mixtures of zinc-titanium oxide and zinc oxide, mixtures of nickel-titanium oxide and nickel oxide, and mixtures of manganese-iron oxide and iron oxide.

[0197] The mixture (i) may include multiple metal oxides (first compound) comprising two or more metals, and additionally or optionally, may include multiple metal oxides (second compound) of metals selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co) and manganese (Mn).

[0198] Examples of compound (ii) include, but are not limited to, metal oxides of two or more metals selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). Specific examples of such compounds include nickel-iron oxide, nickel-titanium oxide, and manganese-iron oxide.

[0199] Examples of mixture (iii) include, but are not limited to, mixtures of a first metal oxide and a second metal oxide. The first metal oxide is a metal oxide selected from two or more metals, namely iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). The second metal oxide is a metal oxide selected from two or more metals, namely iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). The second metal oxide differs from the first metal oxide. Specific examples of mixtures include mixtures of cobalt-titanium oxide and aluminum-cobalt oxide.

[0200] The mixture (iii) may include multiple (three or more) metal oxides selected from two or more metals, namely iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al).

[0201] There are no particular limitations on the shape of the composite oxide forming the inorganic coating. For example, the shape can be particulate, such as spherical, needle-like, polyhedral, disk-like, hollow, or porous. The average particle size of the particulate composite oxide is preferably 1 nm or more and 500 nm or less, and more preferably 5 nm or more and 200 nm or less. The particles of the composite oxide can be crystalline or amorphous.

[0202] When the inorganic coating is an inorganic coating layer, the thickness of the inorganic coating layer formed on the surface of the alumina particles is preferably 20 nm or more and 400 nm or less, more preferably 30 nm or more and 300 nm or less, and particularly preferably 30 nm or more and 200 nm or less.

[0203] Inorganic coatings can be formed from one or more layers. When an inorganic coating is formed from two or more layers, the two or more layers can be formed from different corresponding materials.

[0204] For example, when the inorganic coating is formed by a first layer disposed on the surface of alumina particles and a second layer disposed on the first layer, the thickness of the first layer is preferably 10 nm or more and 200 nm or less, more preferably 15 nm or more and 150 nm or less, and particularly preferably 15 nm or more and 100 nm or less. Furthermore, the thickness of the second layer is preferably 10 nm or more and 200 nm or less, more preferably 15 nm or more and 150 nm or less, and particularly preferably 15 nm or more and 150 nm or less.

[0205] [The organic compound layer on the surface of the composite particles]

[0206] In one embodiment, the composite particles may include an organic compound layer on their surface. The organic compound forming the organic compound layer is present on the surface of the composite particles and functions to modulate the physical properties of the composite particle surface. For example, when the composite particles contain organic compounds on their surface, the composite particles have an improved affinity for resins, thus maximizing the performance of the alumina particles as a filler.

[0207] Examples of organic compounds include, but are not limited to, organosilanes, alkylphosphonic acids, and polymers.

[0208] Examples of organosilanes include alkyltrimethoxysilanes and alkyltrichlorosilanes in which the alkyl group has 1 to 22 carbon atoms, such as methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, pentyltrimethoxysilane, and hexyltrimethoxysilane, trimethoxy(3,3,3-trifluoropropyl)silane, (tridecylfluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane, phenyltrimethoxysilane, phenyltriethoxysilane, p-(chloromethyl)phenyltrimethoxysilane, and p-(chloromethyl)phenyltriethoxysilane.

[0209] Examples of phosphonic acids include methylphosphonic acid, ethylphosphonic acid, propylphosphonic acid, butylphosphonic acid, pentylphosphonic acid, hexylphosphonic acid, heptylphosphonic acid, octylphosphonic acid, decylphosphonic acid, dodecylphosphonic acid, octadecylphosphonic acid, 2-ethylhexylphosphonic acid, cyclohexylmethylphosphonic acid, cyclohexylethylphosphonic acid, benzylphosphonic acid, phenylphosphonic acid, and dodecylphenylphosphonic acid.

[0210] Suitable examples of polymers include poly(meth)acrylates. Specifically, examples of polymers include poly(meth)acrylate, poly(meth)acrylate, poly(meth)acrylate, poly(meth)acrylate, poly(benzyl)acrylate, poly(cyclohexyl)acrylate, poly(tert-butyl)acrylate, poly(glycidyl)methacrylate, and poly(pentafluoropropyl)methacrylate, and further examples include general-purpose polymers such as polystyrene, polyvinyl chloride, polyvinyl acetate, epoxy resins, polyesters, polyimides, and polycarbonates.

[0211] Note that one of the above-mentioned organic compounds may exist alone, or two or more of them may exist.

[0212] There are no particular restrictions on the form in which the organic compound exists. The organic compound can be covalently bonded to alumina and / or to materials that can cover alumina and / or an inorganic coating.

[0213] The content of organic compounds relative to the mass of alumina particles is preferably less than or equal to 20% by mass, and more preferably more than 0.01% by mass and less than 10% by mass. When the content of organic compounds is less than or equal to 20% by mass, the physical properties obtained from composite particles can be readily exhibited; therefore, such a content is preferred.

[0214] [Production method of composite particles]

[0215] An example of the method for producing composite particles according to the first embodiment will now be described in detail. The method for producing composite particles according to this embodiment is not limited to the method for producing composite particles described below.

[0216] The method for producing composite particles according to this embodiment includes the steps of producing alumina particles by sintering a mixture comprising an aluminum compound containing elemental aluminum, a molybdenum compound containing elemental molybdenum, and a shape control agent for controlling the shape of alumina particles; and forming an inorganic coating layer comprising composite metal oxides on the surface of the alumina particles.

[0217] [Production method of flake-shaped alumina particles]

[0218] There are no particular limitations on the production method for the composite alumina particles, and any known technology can be appropriately employed. Preferably, a production method based on a flux method utilizing molybdenum compounds can be used, because in this case, alumina with high α-crystallinity can be appropriately produced at relatively low temperatures.

[0219] More specifically, a preferred method for producing flaky alumina particles includes a step of calcining an aluminum compound in the presence of a molybdenum compound and a shape control agent (calcination step). The calcination step may be a step of calcining a mixture produced from a step of obtaining a mixture to be calcined (mixing step).

[0220] [Mixed Steps]

[0221] The mixing step involves combining an aluminum compound, a molybdenum compound, and a shape control agent to form a mixture. Preferably, the mixture also contains a potassium compound. Details of the mixture will be described below.

[0222] [Aluminum compounds]

[0223] Aluminum compounds are the raw materials for the flaky alumina particles of this embodiment. There are no particular limitations on the aluminum compounds, provided that they are converted to alumina during heat treatment. Examples of aluminum compounds include aluminum chloride, aluminum sulfate, basic aluminum acetate, aluminum hydroxide, boehmite, pseudoboehmite, transition alumina (e.g., γ-alumina, δ-alumina, and θ-alumina), α-alumina, and mixed alumina having two or more crystalline phases. There are no particular limitations on the physical form, such as shape, particle size, and specific surface area, of any of these aluminum compounds used as precursors.

[0224] In the fluxing method, which will be described in detail later, the shape of the aluminum compound can be any suitable shape, including spherical shapes, amorphous shapes, structural shapes with high aspect ratios (e.g., wires, fibers, strips, and tubes), and sheet shapes.

[0225] Similarly, in the fluxing method, which will be described in detail later, the aluminum compound can be a suitable solid aluminum compound, and its particle size can be in the range of a few nanometers to hundreds of micrometers.

[0226] Furthermore, there are no particular limitations on the specific surface area of ​​the aluminum compound. A high specific surface area is preferred because the molybdenum compound functions effectively in this case. However, by adjusting the firing conditions and / or the amount of molybdenum compound used, aluminum compounds with any specific surface area can be used as raw materials.

[0227] Furthermore, the aluminum compound can be a compound comprising only aluminum, or it can be a composite material comprising both aluminum and an organic compound. Suitable examples include organic-inorganic composite materials obtained by modifying the aluminum compound with an organosilane, and composite materials comprising an aluminum compound comprising a polymer adsorbed thereon. When using composite materials such as those described above, there is no particular limitation on the content of the organic compound. From the viewpoint of efficiently producing flake-shaped alumina particles, it is preferred that the content is less than or equal to 60% by mass; more preferably, the content is less than or equal to 30% by mass.

[0228] [Shape control agent]

[0229] Shape control agents can be used to form the lamellar alumina particles of this embodiment. When aluminum compounds are calcined in the presence of molybdenum compounds, shape control agents play an important role in the growth of lamellar crystals of alumina.

[0230] There are no particular restrictions on the state in which the shape control agent is present. Examples of suitable materials include those in which the shape control agent is physically mixed with the aluminum compound; and composite materials in which the shape control agent is uniformly or locally present on the surface or within the aluminum compound.

[0231] In addition, shape control agents can be added to aluminum compounds and / or exist as impurities in aluminum compounds.

[0232] Shape control agents play a crucial role in the growth of lamellar crystals. In the molybdenum oxide flux method, molybdenum oxide reacts with aluminum compounds to form aluminum molybdate. Then, during the decomposition of aluminum molybdate, a change in chemical potential occurs, which is the driving force for crystallization; thus, hexagonal bipyramidal polyhedral particles with developing euhedral facets (113) are formed. In the production method according to this embodiment, it is presumed that because the shape control agent is locally present in the region near the particle surface during α-alumina growth, the growth of the euhedral facets (113) is significantly suppressed. As a result, the growth of crystal orientation in the facet direction becomes relatively rapid, leading to the growth of (001) or (006) facets and thus forming a lamellar morphology. The use of molybdenum compounds as flux promotes the formation of lamellar alumina particles containing molybdenum and possessing high α-crystallinity.

[0233] Note that the above mechanism is based on speculation only. Therefore, if the effects of the present invention are produced by a mechanism different from the above mechanism, such cases are also included within the technical scope of the present invention.

[0234] Regarding the type of shape control agent, from the viewpoint of producing flake-shaped alumina particles with higher aspect ratio and higher dispersibility, and providing higher productivity, it is preferable to use at least one selected from the group consisting of silicon, silicon compounds, and germanium compounds. Silicon or silicon compounds can be used in combination with germanium compounds. Silicon or silicon compounds containing elemental silicon can be the Si source for mullite, thus enabling efficient production of mullite; in this respect, it is preferable to use silicon or silicon compounds containing elemental silicon as the shape control agent. When using germanium compounds, compared to using silicon or silicon compounds, flake-shaped alumina particles with higher aspect ratio and larger particle size can be produced; in this respect, it is preferable to use germanium compounds as the shape control agent.

[0235] When silicon or silicon compounds are used as shape control agents in the above fluxing method, flake-shaped alumina particles containing mullite in the surface layer can be easily produced.

[0236] In the above fluxing method, when using a germanium compound as a shape control agent, it is easy to produce sheet-like alumina particles containing germanium or germanium compounds.

[0237] [Silicon or silicon compounds]

[0238] There are no particular limitations on silicon or silicon compounds containing elemental silicon, and they can be known materials. Specific examples of silicon or silicon compounds containing elemental silicon include silicon metal; artificial / synthetic silicon compounds, such as organosilanes, organosilicon resins, silica microparticles, silica gel, mesoporous silica, SiC, and mullite; and natural silicon compounds, such as bio-silicon. Preferably, one or more of organosilanes, organosilicon resins, and silica microparticles are used because these materials can be combined and mixed more uniformly with the aluminum compound. Note that silicon or silicon compounds containing elemental silicon can be used alone, or two or more of silicon and silicon compounds can be used in combination. Furthermore, one or more other shape control agents can be used, provided that the effects of the invention are not impaired.

[0239] There are no particular limitations on the shape of silicon or silicon compounds containing elemental silicon, and suitable examples of shapes include spherical shapes, amorphous shapes, structural shapes with high aspect ratios (e.g., wires, fibers, strips, and tubes), and sheet shapes.

[0240] [Germanium compounds]

[0241] There are no particular limitations on the germanium compound used as the shape control agent, and it can be any known material. Specific examples of germanium compounds include germanium metal, germanium dioxide, germanium monoxide, germanium tetrachloride, and organogermanium compounds having Ge-C bonds. Note that a single germanium compound can be used, or two or more germanium compounds can be used in combination. Furthermore, one or more other shape control agents can be used, provided that the effects of the invention are not impaired.

[0242] There are no particular restrictions on the shape of the raw material germanium, and suitable examples of shapes include spherical shapes, amorphous shapes, structural shapes with high aspect ratios (e.g., wires, fibers, strips and tubes) and sheet shapes.

[0243] [Molybdenum compounds]

[0244] As will be described later, molybdenum compounds act as fluxes in the growth of α-crystals of alumina. Examples of molybdenum compounds include, but are not limited to, molybdenum oxides and anions containing an acidic group (MoO) in which molybdenum metal is bonded to oxygen. x n- ) compounds.

[0245] Anions containing acidic groups (MoO) x n- Examples of compounds including, but not limited to, molybdic acid, sodium molybdate, potassium molybdate, lithium molybdate, and H3PMo 12 O 40 H3SiMo 12 O 40 NH4Mo7O 12 And molybdenum disulfide.

[0246] Molybdenum compounds can contain silicon, and in this case, the silicon-containing molybdenum compound is used both as a flux and as a shape control agent.

[0247] Of the molybdenum compounds mentioned above, molybdenum oxide is preferred from the viewpoints of cost and ease of sublimation. One of the molybdenum compounds may be used alone, or two or more may be used in combination.

[0248] Potassium molybdate (K2Mo) n O 3n+1 (n = 1 to 3) contains potassium, and therefore can also have the functions of potassium compounds described below. In the production method of this embodiment, "using potassium molybdate as a flux" has the same meaning as "using molybdenum compound and potassium compound as flux".

[0249] [Potassium compounds]

[0250] Potassium compounds can be used in conjunction with shape control agents.

[0251] Examples of potassium compounds include, but are not limited to, potassium chloride, potassium chlorite, potassium chlorate, potassium sulfate, potassium bisulfate, potassium sulfite, potassium bisulfite, potassium nitrate, potassium carbonate, potassium bicarbonate, potassium acetate, potassium oxide, potassium bromide, potassium bromate, potassium hydroxide, potassium silicate, potassium phosphate, potassium hydrogen phosphate, potassium sulfide, potassium hydrogen sulfide, potassium molybdate, and potassium tungstate. As described herein, potassium compounds include isomers, such as in the case of molybdenum compounds. Preferably, one or more of potassium carbonate, potassium bicarbonate, potassium oxide, potassium hydroxide, potassium chloride, potassium sulfate, and potassium molybdate are used, and more preferably, one or more of potassium carbonate, potassium bicarbonate, potassium chloride, potassium sulfate, and potassium molybdate are used.

[0252] One of the potassium compounds mentioned above can be used alone, or two or more of them can be used in combination.

[0253] Potassium compounds facilitate the effective formation of mullite on the surface layer of alumina. Furthermore, potassium compounds contribute to the effective formation of germanium-containing layers on the surface layer of alumina.

[0254] Furthermore, it is preferred that potassium compounds be used together with molybdenum compounds as fluxes.

[0255] Among the potassium compounds mentioned above, potassium molybdate contains molybdenum, and therefore can also possess the functions of the aforementioned molybdenum compounds. Using potassium molybdate as a flux produces effects similar to those produced by using molybdenum compounds and potassium compounds as fluxes.

[0256] The potassium compound used as the raw material to be loaded, or the potassium compound formed in the reaction during the heating process of firing, can be a water-soluble potassium compound, such as potassium molybdate. In this case, since potassium molybdate does not evaporate even within the firing temperature range and can be easily recovered by washing after firing, the amount of molybdenum compound released outside the firing furnace is reduced, and production costs are significantly lowered.

[0257] When using molybdenum compounds and potassium compounds as fluxes, the molar ratio of elemental molybdenum in the molybdenum compound to elemental potassium in the potassium compound (elemental molybdenum / elemental potassium) is preferably less than or equal to 5, and more preferably 0.01 to 3; even more preferably, this molar ratio is 0.5 to 1.5, because in this case, production costs can be further reduced. When the molar ratio (elemental molybdenum / elemental potassium) is within any of the above-mentioned ranges, flake-like alumina particles with large particle size can be obtained, therefore, such a molar ratio is preferred.

[0258] [Metallic compounds]

[0259] As described below, the metal compound can promote the crystal growth of alumina. The metal compound can be used for sintering as needed. Note that while the metal compound can promote the growth of α-alumina crystals, it is not essential for the production of the sheet-like alumina particles of this invention.

[0260] There are no particular limitations on the metal compound, but it is preferably a metal compound containing at least one metal selected from the group consisting of metals of Group II and Group III.

[0261] Examples of metal compounds containing at least one Group II metal include magnesium compounds, calcium compounds, strontium compounds, and barium compounds.

[0262] Examples of metal compounds containing at least one group III metal include scandium compounds, yttrium compounds, lanthanum compounds, and cerium compounds.

[0263] Note that, as described above, the term "metal compound" refers to oxides, hydroxides, carbonates, and chlorides of any metallic element. For example, yttrium compounds include yttrium oxide (Y₂O₃), yttrium hydroxide, and yttrium carbonate. Among the aforementioned metal compounds, oxides of the metallic element are preferred. Note that, as stated herein, metal compounds include isomers.

[0264] Among the aforementioned metal compounds, compounds of period 3, period 4, period 5, and period 6 metals are preferred; compounds of period 4 and period 5 metals are more preferred; and compounds of period 5 metals are even more preferred. Specifically, one or more of magnesium compounds, calcium compounds, yttrium compounds, and lanthanum compounds are preferred; one or more of magnesium compounds, calcium compounds, and yttrium compounds are more preferred; and yttrium compounds are particularly preferred.

[0265] The addition ratio of the metal compound relative to the amount of elemental aluminum in the aluminum compound is preferably 0.02 to 20% by mass, and more preferably 0.1 to 20% by mass. When the addition ratio of the metal compound is greater than or equal to 0.02% by mass, the crystal growth of molybdenum-containing α-alumina can be appropriately carried out, and therefore, such an addition ratio is preferred. On the other hand, when the addition ratio of the metal compound is less than or equal to 20% by mass, flaky alumina particles with a low content of impurities derived from the metal compound can be obtained, and therefore, such an addition ratio is preferred.

[0266] [yttrium]

[0267] When aluminum compounds are calcined in the presence of yttrium compounds used as metallic compounds, crystal growth is more suitable during the calcination step, thus forming α-alumina and water-soluble yttrium compounds. In this case, the water-soluble yttrium compounds readily exist locally on the surface of α-alumina, i.e., lamellar alumina particles; therefore, yttrium compounds can be removed from the lamellar alumina particles by washing with water, alkaline water, or a liquid obtained by heating any of these, as needed.

[0268] There are no particular limitations on the amount of aluminum compounds, molybdenum compounds, silicon or silicon compounds, germanium compounds, and potassium compounds, etc. For example, the following mixtures can be calcined, based on the total mass of the raw materials (calculated as oxides) as 100% by mass:

[0269] 1) A mixture of an aluminum compound, a molybdenum compound, and a silicon or silicon compound, or a germanium compound, wherein the amount of the aluminum compound, calculated as Al2O3, is preferably greater than or equal to 50% by mass, more preferably 70% by mass and less than 99% by mass, and even more preferably 80% by mass and less than 94.5% by mass; the amount of the molybdenum compound, calculated as MoO3, is preferably less than or equal to 40% by mass, more preferably 0.5% by mass and less than 20% by mass, and even more preferably 1% by mass and less than 7% by mass; and the amount of the silicon or silicon compound, or the germanium compound, calculated as SiO2 or GeO2, is preferably 0.1% by mass and less than 10% by mass, more preferably 0.5% by mass and less than 7% by mass, and even more preferably 0.8% by mass and less than 4% by mass.

[0270] From the viewpoint of obtaining flaky alumina particles with a large particle size, it is preferable to use a molybdenum compound in the mixture in an amount of 7% by mass or more and 40% by mass or less calculated as MoO3; more preferably, the amount is 9% by mass or more and 30% by mass or less, and even more preferably 10% by mass or more and 17% by mass or less.

[0271] From the viewpoint of obtaining flaky alumina particles with a large particle size, it is preferable to use silicon or silicon compound, or germanium compound, in the mixture in an amount of 0.4% by mass or more and less than 10% by mass calculated as SiO2 and / or GeO2; more preferably, this amount is 0.5% by mass or more and less than 10% by mass, and particularly preferably 1% by mass or more and less than 3% by mass.

[0272] The silicon or silicon compound and / or germanium compound used as a shape control agent may be silicon or silicon compound, or germanium compound.

[0273] Regarding shape control agents, silicon or silicon compounds may be used exclusively, germanium compounds may be used exclusively, or a combination of silicon or silicon compounds and germanium compounds may be used.

[0274] When using germanium compounds as shape control agents, the amount of germanium compounds contained in the mixture, calculated as GeO2, is preferably 0.4% by mass or more and less than 1.5% by mass, and more preferably 0.7% by mass or more and less than 1.2% by mass, based on the total mass of the raw materials taken as 100% by mass (calculated as oxides).

[0275] The above conditions for raw material quantity (mass%) can be freely combined for the raw materials, and the lower and upper limits of each raw material quantity (mass%) can also be freely combined.

[0276] By using various compounds within any of the above-mentioned ranges, sheet-like alumina particles that satisfy the above (006 / 113) ratio and thus have excellent luminescent properties can be readily produced.

[0277] When the mixture also contains potassium compounds, there is no particular limitation on the amount of potassium compounds used, and the amount of potassium compounds in the mixture, calculated as K2O, based on the total mass of the raw materials taken as 100% by mass (calculated as oxides), is preferably less than or equal to 5% by mass, more preferably 0.01% by mass or more and 3% by mass or less, and even more preferably 0.05% by mass or more and 1% by mass or less.

[0278] It is speculated that, in the case of using potassium compounds, potassium molybdate, which is formed by reacting with molybdenum compounds, has the effect of diffusing Si, thus helping to promote the formation of mullite on the surface of flaky alumina particles.

[0279] Similarly, it is speculated that, in the case of using potassium compounds, potassium molybdate formed by reacting with molybdenum compounds has the effect of diffusing the raw material germanium, and thus helps to promote the inclusion of germanium or germanium compounds in the surface of the flake-shaped alumina particles.

[0280] The potassium compound used as the raw material to be loaded, or the potassium compound formed in the reaction during the heating process of firing, can be a water-soluble potassium compound, such as potassium molybdate. In this case, since potassium molybdate does not evaporate even within the firing temperature range and can be easily recovered by washing after firing, the amount of molybdenum compound released outside the firing furnace is reduced, and production costs are significantly lowered.

[0281] In the fluxing method, molybdenum compounds and potassium compounds are preferred as fluxes.

[0282] Note that during the firing process, compounds containing molybdenum and potassium can be produced, for example, by using low-cost and readily available molybdenum and potassium compounds as raw materials, to produce fluxing agents. In this document, examples are described as illustrative of the use of molybdenum and potassium compounds as fluxing agents, including both examples using molybdenum and potassium compounds as fluxing agents and examples using compounds containing molybdenum and potassium as fluxing agents.

[0283] From the viewpoint of obtaining flaky alumina particles with even larger particle sizes, the following mixture can be used, wherein the amounts of aluminum compound, molybdenum compound, potassium compound, and silicon or silicon compound are preferably as follows, based on the total mass (in oxides) of the raw materials taken as 100% by mass:

[0284] 2) A mixture of aluminum compound, molybdenum compound, potassium compound and silicon or silicon compound, wherein the amount of aluminum compound is greater than or equal to 10% by mass as Al2O3, the amount of molybdenum compound is greater than or equal to 20% by mass as MoO3, the amount of potassium compound is greater than or equal to 1% by mass as K2O, and the amount of silicon or silicon compound is less than 1% by mass as SiO2.

[0285] From the viewpoint of increasing the content of hexagonal sheet alumina, it is more preferable to use the following mixture, the amount of which is based on the total mass of the raw materials taken as 100% by mass (calculated as oxides).

[0286] 3) A mixture of aluminum compound, molybdenum compound, potassium compound and silicon or silicon compound, wherein the amount of aluminum compound is 20% by mass and less than 70% by mass as Al2O3, the amount of molybdenum compound is 30% by mass and less than 80% by mass as MoO3, the amount of potassium compound is 5% by mass and less than 30% by mass as K2O, and the amount of silicon or silicon compound is 0.001% by mass and less than 0.3% by mass as SiO2.

[0287] From the viewpoint of increasing the content of hexagonal sheet alumina, it is even more preferable to use the following mixture, the amount of which is based on the total mass of the raw materials taken as 100% by mass (calculated as oxides).

[0288] 4) A mixture of aluminum compound, molybdenum compound, potassium compound and silicon or silicon compound, wherein the amount of aluminum compound is 25% by mass and less than 40% by mass as Al2O3, the amount of molybdenum compound is 45% by mass and less than 70% by mass as MoO3, the amount of potassium compound is 10% by mass and less than 20% by mass as K2O, and the amount of silicon or silicon compound is 0.01% by mass and less than 0.1% by mass as SiO2.

[0289] To maximize the content of hexagonal sheet alumina and enable crystal growth to proceed more appropriately, the following mixture is particularly preferred, the amount of which is based on the total mass (calculated as oxides) of the raw materials taken as 100% by mass.

[0290] 5) A mixture of aluminum compound, molybdenum compound, potassium compound and silicon or silicon compound, wherein the amount of aluminum compound is 35% by mass and less than 40% by mass as Al2O3, the amount of molybdenum compound is 45% by mass and less than 65% by mass as MoO3, the amount of potassium compound is 10% by mass and less than 20% by mass as K2O, and the amount of silicon or silicon compound is 0.02% by mass and less than 0.08% by mass as SiO2.

[0291] When the various compounds are included in any of the above-mentioned ranges, it is possible to produce sheet-like alumina particles with large particle size and high luminescence properties. In particular, when the amount of molybdenum used tends to increase and the amount of silicon used tends to decrease to a certain extent, the particle size and crystallite diameter can be increased, and hexagonal sheet-like alumina particles can be easily produced; and when the various compounds are included in any of the above-mentioned more preferred ranges, hexagonal sheet-like alumina particles tend to be easier to produce, and their content tends to be further increased, and the luminescence properties of the resulting alumina particles tend to be even higher.

[0292] When the mixture further includes a yttrium compound, the amount of the yttrium compound is not particularly limited; it is preferable to mix the yttrium compound in an amount of less than or equal to 5% by mass, and more preferably in an amount of 0.01% by mass and less than 3% by mass, based on the total mass of the raw materials (calculated as oxides) as 100% by mass, in order to enable crystal growth to proceed more appropriately. It is even more preferable to mix the yttrium compound in an amount of 0.1% by mass and less than 1% by mass, based on Y2O3, based on the total mass of the raw materials (calculated as oxides) as 100% by mass.

[0293] The amount of raw materials used can be appropriately combined within the range that the total content of the raw materials does not exceed 100% by mass.

[0294] [Firing Steps]

[0295] The firing step is the process of firing an aluminum compound in the presence of a molybdenum compound and a shape control agent. The firing step can also be the process of firing a mixture obtained from the mixing step.

[0296] Flaky alumina particles can be obtained, for example, by calcining an aluminum compound in the presence of a molybdenum compound and a shape control agent. As described above, this production method is called the fluxing process.

[0297] Flux methods are classified as solution methods. More specifically, flux methods utilize instances where the crystal-flux binary phase diagram is eutectic to grow crystals. The mechanism of flux methods is presumably as follows: Specifically, when a mixture of solute and flux is heated, the solute and flux form a liquid phase. In this case, since the flux is the fluxing agent, that is, the solute-flux binary phase diagram is eutectic, the solute melts at a temperature below its melting point to form a liquid phase. When the flux evaporates in this state, the flux concentration decreases, i.e., the flux's effect on lowering the solute's melting point decreases. Therefore, flux evaporation serves as the driving force for solute crystal growth (flux evaporation method). Note that solute crystal growth can also be caused by cooling the liquid phase of solute and flux (slow cooling method).

[0298] Flux methods have advantages. For example, crystal growth can be achieved at temperatures far below the melting point; the crystal structure can be precisely controlled; and polyhedral crystal bodies with euhedral shapes can be formed.

[0299] The mechanism for producing α-alumina particles using a fluxing method with molybdenum compounds as fluxes is not entirely clear. However, for example, the mechanism is hypothesized as follows: Specifically, when an aluminum compound is calcined in the presence of a molybdenum compound, aluminum molybdate is first formed. In this case, α-alumina crystals grow from aluminum molybdate at a temperature below the melting point of alumina, as can be understood from the description above. Then, for example, the crystal growth is accelerated by the decomposition of aluminum molybdate and the evaporation of the flux, thus alumina particles can be obtained. That is, a molybdenum compound is used as a flux, and α-alumina particles are produced from aluminum molybdate as an intermediate product.

[0300] When potassium compounds are used as fluxes, the mechanism for producing α-alumina particles via the flux method is not necessarily clear. However, for example, the mechanism is presumed to be as follows: First, a molybdenum compound and an aluminum compound react with each other to form aluminum molybdate. Then, for example, aluminum molybdate decomposes into molybdenum oxide and aluminum oxide, and the molybdenum compound containing the molybdenum oxide produced by the decomposition reacts with a potassium compound to form potassium molybdate. Alumina crystals grow in the presence of the molybdenum compound containing potassium molybdate, thus obtaining the flaky alumina particles of this embodiment.

[0301] By using the above-described fluxing method, flaky alumina particles that satisfy the above (006 / 113) ratio and therefore possess excellent luminescent properties can be produced.

[0302] There are no particular restrictions on the firing method; any known common method can be used. When the firing temperature exceeds 700°C, aluminum compounds react with molybdenum compounds to form aluminum molybdate. Furthermore, when the firing temperature reaches above 900°C, aluminum molybdate decomposes and, under the action of a shape control agent, forms lamellar alumina particles. Additionally, it is speculated that when aluminum molybdate decomposes into alumina and molybdenum oxide, molybdenum compounds are introduced into the aluminum oxide particles within the lamellar alumina particles.

[0303] Furthermore, it is speculated that when the firing temperature reaches above 900°C, molybdenum compounds (e.g., molybdenum trioxide) produced by the decomposition of aluminum molybdate react with potassium compounds to form potassium molybdate.

[0304] Furthermore, it is speculated that when the firing temperature reaches above 1000℃, the crystals of the flaky alumina particles grow in the presence of molybdenum, and the Al2O3 and SiO2 on the surface of the flaky alumina particles react with each other to form mullite with high efficiency.

[0305] Similarly, it is speculated that when the firing temperature reaches above 1000°C, the crystals of the lamellar alumina particles grow in the presence of molybdenum, and the Al2O3 and Ge compounds on the surface of the lamellar alumina particles react with each other to form germanium dioxide and / or compounds containing Ge-O-Al with high efficiency.

[0306] Furthermore, during firing, the states of the aluminum compound, shape control agent, and molybdenum compound are not particularly restricted, and it is sufficient that the aluminum compound, shape control agent, and molybdenum compound exist in the same space so that the molybdenum compound and shape control agent can act on the aluminum compound. Specifically, any of the following can be used: simple mixing of powders of molybdenum compound, shape control agent, and aluminum compound together; mechanical mixing using a grinder or the like; and mixing using a mortar and pestle or the like; and either dry mixing or wet mixing can be used.

[0307] There are no particular restrictions on the firing temperature, and it is appropriately determined taking into account the aforementioned (006 / 113) ratio, average particle size, aspect ratio, mullite formation, longitudinal relaxation time T1, and dispersibility of the target lamellar alumina particles. Generally, regarding the firing temperature, the highest temperature is preferably higher than or equal to 900°C, which is the decomposition temperature of aluminum molybdate (Al2(MoO4)3), more preferably higher than or equal to 1000°C, at which mullite and germanium compounds can be formed efficiently, and even more preferably higher than or equal to 1200°C, at which lamellar alumina particles with a longitudinal relaxation time T1 greater than or equal to 5 seconds (with high crystallinity) can be easily obtained.

[0308] Generally, controlling the shape of the α-alumina produced by firing requires high-temperature firing at or above 2000°C, close to the melting point of α-alumina. However, industrial applications of such high-temperature firing present significant challenges in terms of furnace load and fuel costs.

[0309] The production method of this embodiment can even be carried out at high temperatures above 2000°C; however, even at temperatures below 1600°C, which is much lower than the melting point of α-alumina, the production method can form α-alumina with a sheet-like shape having high α-crystallinity and high aspect ratio, regardless of the shape of the precursor.

[0310] According to one embodiment of the present invention, even at the highest firing temperature of 900 to 1600°C, lamellar alumina particles with a high aspect ratio and an α-crystallinity of over 90% can be formed efficiently and at low cost. Firing at a maximum temperature of 950 to 1500°C is more preferred, firing at a maximum temperature of 1000 to 1400°C is even more preferred, and firing at a maximum temperature of 1200 to 1400°C is most preferred.

[0311] Regarding the firing time, it is preferable to raise the temperature to the predetermined maximum temperature within the range of 15 minutes to 10 hours, and to hold the maximum firing temperature for 5 minutes to 30 hours. For the effective formation of flake-shaped alumina particles, a firing holding time of approximately 10 minutes to 15 hours is more preferable.

[0312] By selecting a maximum temperature of 1000 to 1400°C and a firing holding time of 10 minutes to 15 hours, it is easy to obtain alumina particles with a dense α-crystal structure and a polygonal lamellar shape, while suppressing the formation of aggregates.

[0313] By selecting a maximum temperature of 1200 to 1400°C and a firing holding time of 10 minutes to 15 hours, it is easy to obtain flaky alumina particles with a longitudinal relaxation time T1 greater than or equal to 5 seconds (with high crystallinity).

[0314] There are no particular limitations on the atmosphere used for firing, provided that the effects of the present invention are achieved. For example, oxygen-containing atmospheres such as air and oxygen, as well as inert atmospheres such as nitrogen, argon, and carbon dioxide, are preferred, and an air atmosphere is more preferred when cost is taken into account.

[0315] The equipment used for firing is not necessarily limited, and a so-called firing furnace can be used. Preferably, the firing furnace is formed of a material that does not react with sublimated molybdenum oxide, and even more preferably, an airtight firing furnace is used to efficiently utilize the molybdenum oxide.

[0316] When alumina particles are to be obtained, it is preferable to obtain alumina particles by calcining 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.

[0317] In other words, a preferred method for producing alumina particles includes a step of calcining an aluminum compound in the presence of a molybdenum compound and a shape control agent, or in the presence of a molybdenum compound, a shape control agent, and a potassium compound (calcination step). Preferably, the mixture also includes the metal compound as described above. Preferably, the metal compound is a yttrium compound.

[0318] In the fluxing method using molybdenum compounds, molybdenum oxide reacts with aluminum compounds to form aluminum molybdate. Then, during the decomposition of aluminum molybdate, a change in chemical potential occurs, which is the driving force for crystallization; thus, hexagonal bipyramidal polyhedral particles with developing euhedral faces (113) are formed. It can be inferred that in the production method according to this embodiment, since the shape control agent is locally present in the region near the particle surface during α-alumina growth, the growth of the euhedral faces (113) is significantly suppressed. As a result, the growth of crystal orientation in the facet direction becomes relatively rapid, leading to the growth of (001) or (006) faces and thus forming a plate-like morphology. Therefore, using molybdenum compounds as a flux promotes the formation of plate-like alumina particles containing molybdenum and having high α-crystallinity.

[0319] [Cooling Steps]

[0320] When using molybdenum and potassium compounds as fluxes, the method for producing alumina particles may include a cooling step. The cooling step is a step of cooling the alumina produced by crystal growth achieved in the firing step. More specifically, the cooling step may be a step of cooling a liquid-phase composition comprising alumina and flux obtained from the firing step.

[0321] 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 greater than or equal to 1°C / hour can shorten production time, and therefore is preferred. On the other hand, when the cooling rate is less than or equal to 1000°C / hour, the crucible used for firing is less prone to cracking due to thermal shock, and therefore can be used for a longer period; therefore, such a cooling rate is preferred.

[0322] There are no particular restrictions on the methods used for cooling, and cooling can be achieved through natural cooling or by using a cooling device.

[0323] [Post-processing steps]

[0324] The method for producing flaky alumina particles according to this embodiment may include a post-treatment step. The post-treatment step comprises processing the flaky alumina particles and removing the flux. The post-treatment step may be performed after the firing step, after the cooling step, or after both the firing and cooling steps. If necessary, the post-treatment step may be repeated more than twice.

[0325] Examples of post-treatment methods include washing and high-temperature treatment. These can be combined.

[0326] There are no particular restrictions on the washing method, and washing can be carried out using water, ammonia solution, sodium hydroxide solution or acidic solution to remove flux.

[0327] In this case, the molybdenum content can be controlled by appropriately changing the concentration and amount of water, ammonia solution, sodium hydroxide solution or acidic solution to be used, the area to be washed, and / or the washing time.

[0328] Examples of methods for high-temperature processing include heating to achieve a temperature higher than or equal to the sublimation temperature or boiling point temperature of the flux.

[0329] [Grinding Step]

[0330] In some cases, the calcined product may comprise aggregates of flaky alumina particles, which may not achieve the particle size range suitable for the present invention. Therefore, the flaky alumina particles can be pulverized as needed to obtain the particle size range suitable for the present invention.

[0331] There are no particular restrictions on the method of pulverizing the calcined product. Any known pulverizing method can be used, such as ball mills, jaw crushers, spray mills, disc mills, SpectroMills, grinding mills, or mixing mills.

[0332] [Particle size classification steps]

[0333] Preferably, the flaky alumina particles undergo particle size classification. The purpose of particle size classification is to adjust the average particle size to improve powder flowability or suppress the viscosity increase that may occur when the flaky alumina particles are added to the binder used to form the matrix. The term "particle size classification" refers to the operation of screening particles by particle size.

[0334] Particle size classification can be wet or dry, but from a productivity point of view, dry classification is preferred. Dry classification can be classification using sieves, or it can be, for example, air classification, in which classification is achieved by using the difference between centrifugal force and fluid resistance. From the point of view of classification accuracy, air classification is preferred, and air classification can be performed using a classifier, such as an air classifier utilizing the Coanda effect, a rotary air classifier, a forced vortex centrifugal classifier, or a semi-free vortex centrifugal classifier.

[0335] The aforementioned pulverization and particle size classification steps can be performed at stages where these steps are required, including stages before and after the organic compound layer formation step, which will be described later. The average particle size of the resulting flaky alumina particles can be adjusted by choosing whether to perform pulverization and / or particle size classification and / or by selecting conditions, for example.

[0336] Preferably, the flaky alumina particles of this embodiment and the flaky alumina particles produced by the production method of this embodiment have few or no aggregates. This is because their inherent properties can be readily manifested in this case, their operability is enhanced, and they exhibit enhanced dispersibility when used by dispersing the flaky alumina particles in a dispersion medium. In the production method of flaky alumina particles, these steps are unnecessary if flaky alumina particles with few or no aggregates can be produced without the aforementioned pulverization and / or particle size classification steps. In this case, the target flaky alumina with excellent properties can be produced with high productivity, and therefore, this is preferred.

[0337] [Steps for forming an inorganic coating]

[0338] Next, an inorganic coating layer comprising a composite metal oxide is formed on the surface of the flake-like alumina particles obtained as described above. There are no particular limitations on the method for forming this layer. Examples of such methods include liquid-phase methods and gas-phase methods.

[0339] As inorganic chemical types that can form inorganic coatings, any of the aforementioned inorganic chemical types can be used.

[0340] The inorganic coating formation step includes, for example, contacting a metal inorganic salt containing at least one metal other than aluminum (Al) with flake-shaped alumina particles, and then converting the metal inorganic salt deposited on the flake-shaped alumina particles into a composite metal oxide.

[0341] Alternatively, the inorganic coating formation step may include other processes, including a first conversion step and a second conversion step. In the first conversion step, a first metallic inorganic salt containing at least one metal other than aluminum (Al) is contacted with lamellar alumina particles, and then the first metallic inorganic salt deposited on the lamellar alumina particles is converted into a metal oxide or a composite metal oxide (hereinafter also referred to as "metal oxide, etc."); subsequently, in the second conversion step, a second metallic inorganic salt is contacted with the metal oxide, etc. and / or the lamellar alumina particles, the second metallic inorganic salt containing at least one different metal other than aluminum (Al) and different from the metal used in the first conversion step; then the metal oxide and / or the second metallic inorganic salt is converted into a composite metal oxide.

[0342] The formation of a coating containing a composite metal oxide on alumina particles can be accomplished as follows: A liquid medium dispersion of molybdenum-containing alumina particles can be mixed with the composite metal oxide itself or its dispersion, and the mixture can be filtered and dried. When it is desirable to enhance the interaction between the alumina particles and the composite metal oxide, thereby enabling the formation of particularly superior properties, for example, when it is desirable, as described above, to enhance the coating properties, to achieve a more uniform inorganic coating, and / or to reduce the likelihood of the resulting inorganic coating delaminating from the alumina particles, the inorganic coating can preferably be formed as follows: A solution of a first inorganic metal salt, which is soluble in a liquid medium and serves as a precursor to a metal oxide, can be mixed with molybdenum-containing alumina particles or its liquid medium dispersion to ensure sufficient contact between the dissolved molecular form of the first inorganic metal salt and the molybdenum-containing alumina particles. The first inorganic metal salt, deposited on the alumina particles and having a very small particle size of less than or equal to 150 nm, can then be converted into a metal oxide, etc. Furthermore, preferably, a solution of a second inorganic metal salt that is soluble in a liquid medium can be mixed with alumina particles on which metal oxides or the like have already formed, or with a dispersion in a liquid medium, to ensure sufficient contact between the dissolved molecular form of the second inorganic metal salt and the metal oxides or / or molybdenum-containing alumina particles. Then, the second inorganic metal salt, deposited on the metal oxides or / or molybdenum-containing alumina particles and having a very small particle size of less than or equal to 150 nm, can be converted into metal oxides or the like. Furthermore, filtration and / or drying can be performed if necessary. If the conversion of the first inorganic metal salt to metal oxides or / or the second inorganic metal salt to metal oxides or the like cannot be easily completed due to low temperature or pH changes, firing can be performed if necessary. In this case, strong interactions between the alumina particles and the composite metal oxides, which are not present in simple mixtures, can be exhibited, and therefore, the particularly significant superior properties described above can be easily exhibited. For the firing conditions of the step forming the inorganic coating layer, the optimal conditions can be appropriately selected and adopted with reference to the conditions described above for alumina particles.

[0343] For example, a firing temperature of 600 to 1200°C can be selected as the firing conditions for converting the first inorganic metal salt into a metal oxide, etc. Similarly, a firing temperature of 600 to 1200°C can be selected as the firing conditions for converting the second inorganic metal salt into a metal oxide, etc. The conversion of the first inorganic metal salt to a metal oxide, etc., and the conversion of the second inorganic metal salt to a metal oxide, etc., can occur simultaneously; for example, firing can be performed at a temperature of 600 to 1200°C.

[0344] Regarding the liquid-phase method, an example is as follows: A dispersion in which flake-like alumina particles are dispersed is prepared. The dispersion is then pH-adjusted and heated as needed. Subsequently, an aqueous solution of a first metal inorganic salt, such as cobalt sulfate, is added dropwise to the dispersion. In this case, it is preferable to maintain the pH at a constant level using an alkaline aqueous solution. The dispersion is then stirred for a predetermined time, and the resulting product is filtered, washed, and dried to obtain a powder. In this way, a first inorganic coating layer formed by a metal oxide, such as cobalt oxide, is formed on the surface of the alumina particles having a flake-like shape.

[0345] Next, a dispersion in which the sheet-like alumina particles on which the first inorganic coating has been formed are dispersed is prepared. The dispersion is then pH-adjusted and heated as needed. Subsequently, an aqueous solution of a second inorganic metal salt, such as ferric chloride, is added dropwise to the dispersion. In this case, it is preferable to maintain the pH at a constant level using an acidic aqueous solution. The dispersion is then stirred for a predetermined time, and the result is filtered, washed, and dried to obtain a powder. In this way, a second inorganic coating, formed of, for example, aluminum-cobalt oxide and iron oxide, is formed on the surface of the sheet-like alumina particles.

[0346] Inorganic coatings can be formed from any other composite metal oxides, examples of which include aluminum-cobalt oxide, aluminum-zinc oxide, aluminum-cobalt and iron oxide, aluminum-cobalt and titanium oxide, cobalt-iron oxide and iron oxide, zinc-iron oxide and zinc oxide, zinc-titanium oxide and zinc oxide, nickel-titanium oxide and nickel oxide, and manganese-iron oxide and iron oxide.

[0347] Alternatively, the inorganic coating may be formed of nickel-iron oxide, nickel-titanium oxide, or manganese-iron oxide, or the inorganic coating may be formed of cobalt-titanium oxide and aluminum-cobalt oxide.

[0348] In this step, the inorganic coating can be formed in such a way that it covers at least a portion of the surface of the flake-shaped alumina particles. In this case, for example, the layer is formed when the particles, formed of composite metal oxides, are aggregated together.

[0349] [Steps for forming organic compound layers]

[0350] In one embodiment, the method for producing flake alumina particles may further include an organic compound layer forming step, performed after the inorganic coating layer forming step, to form an organic compound layer on the surface of the inorganic coating layer (also referred to as the "surface of the composite particles"). Typically, the organic compound layer forming step is performed after the firing step or after a post-treatment step.

[0351] There are no particular limitations on the method for forming the organic compound layer, and known methods can be appropriately employed. Examples of methods include those in which a liquid containing an organic compound is contacted with molybdenum-containing flake-shaped alumina particles and then dried.

[0352] Note that the organic compounds that can be used to form the organic compound layer can be, for example, organosilanes.

[0353] [Organosilanes]

[0354] When the lamellar alumina particles contain silicon atoms and / or inorganic silicon compounds, the surface modification effects described above can be expected compared to when the lamellar alumina particles do not contain silicon atoms or inorganic silicon compounds. Furthermore, a reaction product of an organosilane compound and alumina particles containing silicon atoms and / or inorganic silicon compounds can be formed and used. Lamellar alumina particles that are a reaction product of lamellar alumina particles and organosilane compounds are preferred over lamellar alumina particles containing silicon atoms and / or inorganic silicon compounds because the lamellar alumina particles that are a reaction product have a better affinity for the matrix due to the reaction of silicon atoms and / or inorganic silicon compounds locally present on the surface of the lamellar alumina particles with the organosilane compound.

[0355] Examples of organosilane compounds include alkyltrimethoxysilanes and alkyltrichlorosilanes in which the alkyl group has 1 to 22 carbon atoms, such as methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, pentyltrimethoxysilane, and hexyltrimethoxysilane, trimethoxy(3,3,3-trifluoropropyl)silane, (tridecylfluoro-1,1,2,2-tetrahydrooctyl)trichlorosilane, phenyltrimethoxysilane, phenyltriethoxysilane, p-(chloromethyl)phenyltrimethoxysilane, p-(chloromethyl)phenyltriethoxysilane, such as γ-glycidyl etheroxypropyltrimethoxysilane, γ-glycidyl Epoxysilanes such as etheroxypropyltriethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; aminosilanes such as γ-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-aminopropyltrimethoxysilane, and γ-ureopropyltriethoxysilane; mercaptosilanes such as 3-mercaptopropyltrimethoxysilane; vinylsilanes such as p-styryltrimethoxysilane, vinyltrichlorosilane, vinyltri(β-methoxyethoxy)silane, vinyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane; and polymeric silanes that can be epoxy-based, amino-based, or vinyl-based. Note that one or more of the above-mentioned organosilane compounds may exist alone.

[0356] As a result of the reaction, sufficiently, organosilane compounds are covalently bonded to at least some or all of the silicon atoms and / or inorganic silicon compounds on the surface of the lamellar alumina particles. Not only a portion, but the entirety of the alumina can be covered by the reaction products. Methods that can be used to provide organosilane compounds to the alumina surface include application by impregnation and chemical vapor deposition (CVD).

[0357] The amount of organosilane compound, calculated in terms of silicon atoms, is preferably less than or equal to 20% by mass, and more preferably 10 to 0.01% by mass, relative to the mass of silicon atoms and / or inorganic silicon compounds present on the surface of the flake-shaped alumina particles. When the amount of organosilane compound is less than or equal to 20% by mass, the physical properties obtained from the alumina particles can be readily exhibited, therefore, such an amount is preferred.

[0358] The reaction between the organosilane compound and the alumina particles containing silicon atoms and / or inorganic silicon compounds can be accomplished using any known common method for modifying the filler surface. For example, a spray method using a fluid nozzle, a dry method using shear force stirring, a ball mill, or a mixer, or a wet method, such as an aqueous or organic solvent system, can be employed. It is desirable to use a shear force method in a manner that prevents the alumina particles used in the embodiments from being damaged.

[0359] The temperature in the dry process or the post-treatment drying temperature in the wet process should be appropriately specified according to the type of organosilane compound, so that the temperature is within a range that does not cause thermal decomposition of the organosilane compound. For example, when processing with organosilane compounds such as those described above, the temperature is preferably between 80°C and 150°C.

[0360] [Resin Composition]

[0361] In one embodiment, a resin composition comprising a resin and the composite particles of the above embodiments is provided. Examples of resins include, but are not limited to, thermosetting resins and thermoplastic resins.

[0362] The resin composition can be cured to form a cured product of the resin composition. The resin composition can be cured and shaped to form a molded article of the resin composition. For molding, the resin composition can suitably undergo more than one treatment, such as melting and kneading. Examples of molding methods include compression molding, injection molding, extrusion molding, and foam molding. In particular, extrusion molding using extrusion equipment is preferred, and extrusion molding using twin-screw extrusion equipment is more preferred.

[0363] When a resin composition is used as a coating agent or in a coating formulation, a coating film containing a cured product of the resin composition can be formed by applying the resin composition to the coating target.

[0364] [Production method of resin composition]

[0365] According to one embodiment of the present invention, a method for producing a resin composition is provided.

[0366] The production method includes the step of mixing the resin with the composite particles of the above-described embodiment. The flake-shaped alumina particles to be used can be the aforementioned flake-shaped alumina particles; therefore, their description is omitted here.

[0367] Note that the composite particles to be used can be composite particles that have undergone surface treatment.

[0368] In addition, one type of composite particle can be used alone, or two or more types of composite particles can be used in combination.

[0369] In addition, composite particles can be used in combination with one or more other fillers (such as fillers for alumina, spinel, boron nitride, aluminum nitride, magnesium oxide and magnesium carbonate).

[0370] The content of composite particles relative to the total mass of the resin composition taken as 100% by mass is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, and even more preferably 30 to 80% by mass. When the content of composite particles is greater than or equal to 5% by mass, the high thermal conductivity of the composite particles can be effectively exhibited, and therefore, such a content is preferred. On the other hand, when the content of composite particles is less than or equal to 95% by mass, a resin composition with excellent formability can be obtained, and therefore, such a content is preferred.

[0371] When the resin composition is used as a coating agent or in a coating formulation, from the viewpoint of being able to exhibit excellent luminescent properties and promote the formation of a coating film, it is preferable that the content of the composite particles is 0.1 to 95% by mass relative to the total mass of 100% by mass of the solids based on the resin composition; more preferably, the content is 1 to 50% by mass, and even more preferably 3 to 30% by mass.

[0372] [Resin]

[0373] Examples of resins include, but are not limited to, thermoplastic resins and thermosetting resins.

[0374] There are no particular limitations on the thermoplastic resin; any known common thermoplastic resin used as molding material, etc., can be used. Specific examples include polyethylene resin, polypropylene resin, polymethyl methacrylate resin, polyvinyl acetate resin, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, polyvinyl chloride resin, polystyrene resin, polyacrylonitrile resin, polyamide resin, polycarbonate resin, polyacetal resin, polyethylene terephthalate resin, polyphenylene ether resin, polyphenylene sulfide resin, polysulfone resin, polyethersulfone resin, polyetheretherketone resin, polyallyl sulfone resin, thermoplastic polyimide resin, thermoplastic polyurethane resin, polyaminobismaleimide resin, polyamide-imide resin, polyetherimide resin, bismaleimide triazine resin, polymethylpentene resin, fluorinated resin, liquid crystal polymer, olefin-vinyl alcohol copolymer, ionomer resin, polyarylate resin, acrylonitrile-ethylene-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, and acrylonitrile-styrene copolymer.

[0375] Thermosetting resins are resins that, when cured by means such as heating, radiation, or the use of a catalyst, possess the property of becoming substantially insoluble and infusible. Typically, thermosetting resins can be any known common thermosetting resin used as a molding material, etc. Specific examples include phenolic resins, such as phenolic varnish-type phenolic resins and methyl phenolic resins; examples of phenolic varnish-type phenolic resins including phenolic resins and cresol phenolic resins; examples of methyl phenolic resins including unmodified methyl phenolic resins and oil-modified methyl phenolic resins modified with tung oil, linseed oil, or walnut oil, etc.; and epoxy resins, such as bisphenol-type epoxy resins, aliphatic chain-modified bisphenol-type epoxy resins, phenolic epoxy resins, biphenyl-type epoxy resins, and polyalkylene glycol-type epoxy resins. Resins, including examples of bisphenol-type epoxy resins such as bisphenol A type epoxy resins and bisphenol F type epoxy resins, examples of phenolic-type epoxy resins such as phenolic type epoxy resins and cresol-phenolic type epoxy resins; urea-formaldehyde resins; resins containing triazine rings, such as melamine resins; vinyl resins, such as (meth)acrylic resins and vinyl ester resins; unsaturated polyester resins; bismaleimide resins; polyurethane resins; diallyl phthalate resins; silicone resins; resins containing benzoxazine rings; and cyanate ester resins.

[0376] One of the above-mentioned resins can be used alone, or two or more of them can be used in combination. In this case, two or more thermoplastic resins can be used, two or more thermosetting resins can be used, or one or more thermoplastic resins and one or more thermosetting resins can be used.

[0377] The resin content relative to the total mass of the resin composition taken as 100% by mass is preferably 5 to 90% by mass, and more preferably 10 to 70% by mass. When the resin content is greater than or equal to 5% by mass, the resin composition can be endowed with excellent formability, and therefore such a content is preferred. On the other hand, when the resin content is less than or equal to 90% by mass, the compound obtained by molding has high thermal conductivity, and therefore such a content is preferred.

[0378] [Curing agent]

[0379] As needed, the resin composition may include a curing agent mixed therewith.

[0380] There are no particular restrictions on the curing agent, and it can be any known curing agent.

[0381] Specific examples include amine compounds, amide compounds, acid anhydride compounds, and phenolic compounds.

[0382] Examples of amine compounds include diaminodiphenylmethane, diethylenetriamine, triethylenetetramine, diaminodiphenyl sulfone, isophorone diamine, imidazole, BF3-amine complexes, and guanidine derivatives.

[0383] Examples of amide compounds include dicyandiamide and polyamide resins synthesized from linolenic acid dimer and ethylenediamine.

[0384] Examples of anhydride compounds include phthalic anhydride, trimellitic anhydride, pyromellitic anhydride, maleic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylnadic anhydride, hexahydrophthalic anhydride, and methylhexahydrophthalic anhydride.

[0385] Examples of phenolic compounds include phenolic resins, cresol resins, aromatic hydrocarbon formaldehyde resins modified with phenolic resins, dicyclopentadienol adduct resins, and phenol aralkyl resins (neophenolic resins). Resins) are polyphenolic resins, represented by resorcinol phenolic resin, naphthol aralkyl resin, trimethylolmethane resin, tetraphenol ethane resin, naphthol phenolic resin, naphthol-phenol cocondensed phenolic resin, naphthol-cresol cocondensed phenolic resin, biphenyl modified phenolic resin (a polyphenolic compound in which the phenol core is interconnected by a diemine), biphenyl modified naphthol resin (a polynaphthol compound in which the phenol core is interconnected by a diemine), as well as polyhydroxy phenolic compounds such as aminotriazine modified phenolic resin (a polyphenolic compound in which the phenol core is interconnected by melamine or benzoguanamine) and alkoxy aromatic ring modified phenolic resin (a polyphenolic compound in which the phenol core and the alkoxy aromatic ring are interconnected by formaldehyde).

[0386] One of the above-mentioned curing agents can be used alone, or two or more of them can be used in combination.

[0387] [Curing Accelerator]

[0388] As needed, the resin composition may contain a curing accelerator mixed therewith.

[0389] When the composition is to be cured, the curing accelerator has the function of promoting curing.

[0390] Examples of curing accelerators include, but are not limited to, phosphorus-containing compounds, tertiary amines, imidazoles, metal salts of organic acids, Lewis acids, and amine complex salts.

[0391] One of the above-mentioned curing accelerators can be used alone, or two or more of them can be used in combination.

[0392] [Cure catalyst]

[0393] Depending on the requirements, the resin composition may contain a curing catalyst mixed therewith.

[0394] Curing catalysts can replace curing agents to promote the curing reaction of epoxy-containing compounds.

[0395] Examples of curing catalysts include, but are not limited to, known common thermal polymerization initiators and photochemical radiation polymerization initiators.

[0396] Note that a single curing catalyst can be used, or two or more curing catalysts can be used in combination.

[0397] Viscosity modifier

[0398] As needed, the resin composition may contain a viscosity modifier mixed therewith.

[0399] Viscosity modifiers have the function of modifying the viscosity of a composition.

[0400] Examples of viscosity modifiers include, but are not limited to, organic polymers, polymer particles, and inorganic particles.

[0401] Note that a single viscosity modifier can be used, or two or more viscosity modifiers can be used in combination.

[0402] [Plasticizer]

[0403] As needed, the resin composition may contain a plasticizer mixed therewith.

[0404] Plasticizers improve the processability, flexibility, and weather resistance of thermoplastic synthetic resins.

[0405] Examples of plasticizers include, but are not limited to, phthalates, adipates, phosphates, trimellitates, polyesters, polyolefins, and polysiloxanes.

[0406] Note that one of the plasticizers mentioned above can be used alone, or two or more of them can be used in combination.

[0407] [Mixed Steps]

[0408] The resin composition of this embodiment can be obtained by mixing composite particles, resin, and one or more other components that may be added as needed. There are no particular limitations on the mixing method; any known common method can be used.

[0409] When the resin is a thermosetting resin, a common method for mixing the thermosetting resin and composite particles together is as follows: A predetermined amount of thermosetting resin, composite particles, and one or more other components added as needed are thoroughly mixed together in a mixer or similar apparatus. Subsequently, the mixture is kneaded in a three-roll mill or similar apparatus to obtain a flowing liquid composition. Alternatively, in another embodiment, the method for mixing the thermosetting resin and composite particles together is as follows: A predetermined amount of thermosetting resin, composite particles, and one or more other components added as needed are thoroughly mixed together in a mixer or similar apparatus. Subsequently, the mixture is melt-kneaded in a mixing roller mill or extrusion equipment or similar apparatus, and then cooled to obtain a solid composition. Regarding the mixing state, when a curing agent and / or catalyst are added, it is sufficient for the additives and curable resin to be sufficiently and uniformly mixed together; however, it is preferable that the composite particles are also uniformly dispersed and mixed therein.

[0410] When the resin is a thermoplastic resin, a common method for mixing the thermoplastic resin and composite granules together is as follows. For example, using any type of mixer, such as a drum mixer or Henschel mixer, the thermoplastic resin, composite granules, and one or more other components added as needed are pre-mixed together. Subsequently, the mixture is melt-kneaded in a mixer such as a Banbury mixer, roller mill, Brabender mixer, single-screw kneading and extrusion equipment, twin-screw kneading and extrusion equipment, kneader, or mixing roller mill. Note that there are no particular limitations on the melt-kneading temperature, and it is generally in the range of 100 to 320°C.

[0411] Coupling agents can be added to resin compositions because they enhance the flowability and filling properties of fillers such as composite particles in the resin composition. Note that adding a coupling agent further enhances the adhesion between the resin and the composite particles and reduces the interfacial thermal resistance between them, thus improving the thermal conductivity of the resin composition.

[0412] A single coupling agent can be used alone, or two or more coupling agents can be used in combination.

[0413] There is no particular limitation on the amount of coupling agent added, and it is preferably 0.01 to 5% by mass relative to the resin, and more preferably 0.1 to 3% by mass.

[0414] In one embodiment, the resin composition is used as a thermally conductive material.

[0415] Because the composite particles contained in the resin composition exhibit excellent thermal conductivity, the resin composition is preferably used as an insulating and heat-dissipating component. Therefore, the heat dissipation properties of the device can be improved, thereby enabling a reduction in device size and weight as well as enhanced performance.

[0416] Because the composite particles contained in the resin composition have excellent luminescent properties, the resin composition is suitable for use as a coating agent and in coating formulations.

[0417] [Production method of cured products]

[0418] In one embodiment of the present invention, a method for producing a cured product is provided. The method includes curing a resin composition produced as described above.

[0419] There are no particular limitations on the curing temperature, but it is preferably 20–300°C, and more preferably 50–200°C.

[0420] There is no particular limitation on the curing time, but it is preferably 0.1 to 10 hours, and more preferably 0.2 to 3 hours.

[0421] The shape of the cured product can vary depending on the desired application and can be appropriately designed by those skilled in the art.

[0422] In the above-described resin composition, the method for producing the resin composition, and the cured product, composite particles with a sheet-like shape are used; alternatively, composite particles with a polyhedral shape, as described below, may be used.

[0423] The aforementioned inorganic coating is formed on the sheet-like alumina particles; alternatively, the inorganic coating can be formed on polyhedral alumina particles. Specifically, the composite particles can have a polyhedral shape; that is, the composite particles can include alumina particles with a polyhedral shape and an inorganic coating comprising a composite metal oxide disposed on the surface of the alumina particles. In this case, the method for producing the composite particles can be similar to the method described above, except that different methods are used for producing alumina particles with a polyhedral shape.

[0424] Alumina particles, as polyhedral particles, can be readily loaded into resin compositions; in this respect, such alumina particles are advantageous. For example, in the fluxing method described in detail below, when a molybdenum compound is used as a flux, polyhedral particles that are substantially close to spherical particles can be obtained, and these near-spherical polyhedral particles are an advantageous form because loading can be easily accomplished when the particles are loaded into the resin composition. Specifically, the area of ​​the largest flat surface is less than or equal to one-eighth of the area of ​​the structure; in particular, particles in which the area of ​​the largest flat surface is less than or equal to one-sixteenth of the area of ​​the structure can be suitably obtained.

[0425] Furthermore, it is speculated that when the alumina particles are polyhedral, surface-to-surface contact occurs when the particles come into contact with each other in the resin composition, which contributes to high thermal conductivity. As a result, higher thermal conductivity can be obtained compared to the case of spherical particles, provided that the filling rate is the same in both cases.

[0426] Furthermore, in conventional fluxing methods using large amounts of flux, the aluminum oxides that can be obtained have a hexagonal bipyramidal shape, i.e., a shape with acute angles. Therefore, a problem with aluminum oxides is that they can damage equipment, for example, when producing resin compositions including composite particles as described in the embodiments. In contrast, the aluminum oxides used in this embodiment do not have a hexagonal bipyramidal shape, and are therefore less likely to cause problems such as damage to the equipment. Moreover, since the aluminum oxides of this embodiment are essentially polyhedra with eight or more faces, thus having a near-spherical shape, they are less likely to cause problems such as damage to the equipment.

[0427] [Example]

[0428] The invention will now be described in more detail with reference to embodiments. It should be noted that the invention is not limited to the embodiments described below.

[0429] [Example 1]

[0430] Flaky alumina was produced as the main component of a composite particle. A mixture was obtained by combining 100 g (65 wt% as oxide (Al₂O₃)) of commercially available aluminum hydroxide (average particle size 1–2 μm), 6.5 g (9.0 wt% as oxide (MoO₃)) of molybdenum trioxide (manufactured by Taiyo Koko Co., Ltd.), and 0.65 g (0.9 wt% as oxide (SiO₂)) of silica (premium grade, manufactured by Kanto Chemical Co., Inc.) in a mortar. The resulting mixture was placed in a crucible and heated to 1200 °C at 5 °C / min in a ceramic furnace, and then held at 1200 °C for 10 hours. Firing was performed in this manner. Subsequently, the crucible was cooled to room temperature at 5 °C / min and then removed. Thus, 67.0 g of a light blue powder was obtained. The obtained powder was ground in a mortar until the particles could pass through a 2 mm sieve.

[0431] Subsequently, 65.0 g of the obtained light blue powder was dispersed in 250 mL of 0.25% ammonia water, and the dispersion was stirred at room temperature (25–30 °C) for 3 hours. The resulting product was then passed through a 106 μm sieve and filtered to remove the ammonia water, followed by washing with water and drying to remove residual molybdenum on the particle surface. Thus, 60.0 g of light blue powder was obtained. Therefore, D was prepared...50 Flaky alumina particles with a value of 28 μm.

[0432] SEM analysis confirmed that the obtained powder consisted of lamellar alumina particles with a polygonal, sheet-like shape and very few aggregates, thus exhibiting excellent workability. Furthermore, XRD measurements revealed narrow scattering peaks for α-alumina, while no peaks were observed in alumina crystalline systems outside the α-crystal structure. Therefore, lamellar alumina with a dense crystalline structure was confirmed. Additionally, quantitative X-ray fluorescence analysis confirmed that the obtained particles contained 0.61% molybdenum (calculated as molybdenum trioxide).

[0433] Next, add 15g of D 50 Alumina flakes with a micrometer diameter of 28 μm were dispersed in 150 mL of water to obtain a dispersion. The pH of the dispersion was adjusted to 11.4 using 1 mol NaOH, while the temperature was adjusted to 65 °C. While stirring the dispersion, 100 g of 14.1% CoSO4 solution (theoretical coverage: 20%) was added dropwise to the dispersion over a period of 4.5 hours. Simultaneously, the pH of the dispersion was maintained at 11.4 using 80 g of 5% NaOH aqueous solution. After the addition of the CoSO4 solution, the dispersion was stirred for another 4 hours, and the resulting dispersion was filtered and washed. Next, it was calcined at 1200 °C for 2 hours. Thus, 18.3 g of powder coated with cobalt oxide flakes of alumina was obtained. The composite particles were blue in color.

[0434] [Example 2]

[0435] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0436] In addition, 18.3g of powder coated with flake-shaped alumina particles forming a first layer of cobalt oxide was obtained by using a production method similar to that in Example 1.

[0437] Next, 5g of the obtained powder was dispersed in 50mL of water to obtain a dispersion. The pH of the dispersion was adjusted to 1.8 using 1mol HCl, and the temperature of the dispersion was adjusted to 70°C over 2.5 hours. While stirring the dispersion, 26.2g of 5% TiCl4 solution was added dropwise (theoretical coverage: 10%). Simultaneously, the pH of the dispersion was maintained at 1.8 using 47.3g of 5% NaOH aqueous solution. After the addition of TiCl4 solution, the dispersion was stirred for another 4 hours, and the resulting dispersion was filtered and washed. Next, it was calcined at 600°C for 2 hours. Thus, 5.4g of a sample of sheet-like alumina particles coated with a second layer of alumina-cobalt oxide and titanium oxide was obtained. The composite particles were blue in color.

[0438] [Example 3]

[0439] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0440] Except for the following differences, a sample of 5.4 g of flake-shaped alumina particles coated with cobalt-iron oxide and iron(III) oxide was obtained in a manner similar to that of Example 2. The differences are as follows: for the formation of the first layer, 93.8 g of 8.1% FeCl3 solution was used, the FeCl3 solution was added dropwise for no more than 4.5 hours, and the pH of the dispersion was maintained at 2.7 using 112.5 g of NaOH aqueous solution; and for the formation of the second layer, 14.8 g of 14.1% CoSO4 solution was used, the CoSO4 solution was added dropwise for no more than 2.1 hours, the pH of the dispersion was maintained at 11.4 using 11.9 g of NaOH aqueous solution, and the firing temperature was changed to 700°C. The composite particles were black in color.

[0441] [Example 4]

[0442] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0443] Except for the following differences, 5.4 g of alumina particle sample coated with nickel-iron oxide was obtained in a manner similar to that of Example 3. The difference lies in that, for the formation of the second layer, 26.5 g of 11.9% NiCl2 solution was used, the NiCl2 solution was added dropwise over a period of less than 2 hours, and the pH of the dispersion was maintained at 10.5 using 21.2 g of NaOH aqueous solution. The composite particles were brown in color.

[0444] [Example 5]

[0445] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0446] Except for the following differences, a sample of 5.5 g of flaky alumina particles coated with zinc-iron oxide and zinc oxide was obtained in a manner similar to that of Example 3. The differences were that, for the formation of the second layer, 15.6 g of 11.9% ZnCl2 solution was used, the ZnCl2 solution was added dropwise over a period of less than 2 hours, the pH of the dispersion was maintained at 7 using 21.8 g of NaOH aqueous solution, and the calcination temperature was changed to 600°C. The composite particles were light brown in color.

[0447] [Example 6]

[0448] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0449] Except for the following differences, a sample of 5.4 g of sheet-like alumina particles coated with zinc-titanium oxide and zinc oxide was obtained in a manner similar to that of Example 2. The differences are as follows: for the formation of the first layer, 20 g of sheet-like alumina particles and 237.4 g of 5% TiCl4 solution were used, with the TiCl4 solution added at a time of less than 5.8 hours, and the pH of the dispersion was maintained at 1.8 using 280.6 g of NaOH aqueous solution; and for the formation of the second layer, 15.64 g of 11.9% ZnCl2 solution was used, with the ZnCl2 solution added at a time of less than 2 hours, and the pH of the dispersion was maintained at 7 using 21.8 g of NaOH aqueous solution. The composite particles were white in color.

[0450] [Example 7]

[0451] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0452] Except for the following differences, a sample of 5.5 g of flake-shaped alumina particles coated with cobalt-titanium oxide and aluminum-cobalt oxide was obtained in a manner similar to that of Example 6. The differences were that, for the formation of the second layer, 14.8 g of 14.1% CoSO4 solution was used, the CoSO4 solution was added dropwise over a period of less than 2.1 hours, the pH of the dispersion was maintained at 11.4 using 11.9 g of NaOH aqueous solution, and the calcination temperature was changed to 800 °C. The composite particles were light green in color.

[0453] [Example 8]

[0454] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0455] Except for the following differences, 5.0 g of alumina particle sample coated with nickel-titanium oxide was obtained in a manner similar to that of Example 6. The differences were that for the formation of the first layer, the TiCl4 solution was added at a rate of 2.5 hours or less; for the formation of the second layer, 2.7 g of 11.9% NiCl2 solution was used, the NiCl2 solution was added at a rate of 0.25 hours or less, the pH of the dispersion was maintained at 10.5 using 2.2 g of NaOH aqueous solution, and the calcination temperature was changed to 700°C. The composite particles were light yellow in color.

[0456] [Example 9]

[0457] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0458] Except for the following differences, a sample of 5.2 g of sheet-like alumina particles coated with nickel-titanium oxide was obtained in a manner similar to that of Example 8. The difference is that 14.1 g of NiCl2 solution was used for the formation of the second layer, and the dropping time of the NiCl2 solution was changed to less than 1 hour. The composite particles were light yellow in color.

[0459] [Example 10]

[0460] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0461] Except for the following differences, a sample of 5.5 g of sheet-like alumina particles coated with nickel-titanium oxide and nickel oxide was obtained in a manner similar to that of Example 8. The difference is that 26.5 g of NiCl2 solution was used for the formation of the second layer, and the dropping time of the NiCl2 solution was changed to less than 2 hours. The composite particles were light yellow in color.

[0462] [Example 11]

[0463] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0464] Except for the following differences, a sample of 6.2 g of flake-shaped alumina particles coated with nickel-titanium oxide and nickel oxide was obtained in a manner similar to that of Example 8. The differences are that, for the formation of the first layer, 20 g of flake-shaped alumina particles and 237.4 g of TiCl4 solution were used, and the dropping time of the TiCl4 solution was changed to 5.8 hours or less; and for the formation of the second layer, 47.2 g of NiCl2 solution was used, and the dropping time of the NiCl2 solution was changed to 3.4 hours or less. The composite particles were yellow in color.

[0465] [Example 12]

[0466] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0467] Except for the following differences, a sample of 5.5 g of flake-like alumina particles coated with aluminum-cobalt oxide and iron(III) oxide was obtained in a manner similar to that of Example 2. The difference lies in that, for the formation of the second layer, 13.9 g of 8.1% FeCl3 solution was used, the FeCl3 solution was added dropwise over a period of less than 2 hours, and the pH of the dispersion was maintained at 2.7 using 16.7 g of NaOH aqueous solution. The composite particles were black in color.

[0468] [Example 13]

[0469] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0470] Except for the following differences, a sample of 17.6 g of flake-shaped alumina particles coated with aluminum-zinc oxide was obtained in a manner similar to that of Example 1. The differences are that, for the formation of the first layer, 15.6 g of 11.9% ZnCl2 solution was used, the ZnCl2 solution was added dropwise over a period of less than 2.1 hours, and the pH of the dispersion was maintained at 2.7 using 16.7 g of NaOH aqueous solution. The composite particles were white in color.

[0471] [Example 14]

[0472] D was prepared using a production method similar to that in Example 1. 50 Flaky alumina particles with a value of 28 μm.

[0473] Except for the following differences, a sample of 5.2 g of flake-shaped alumina particles coated with manganese-iron oxide was obtained in a manner similar to that of Example 2. The differences are as follows: for the formation of the first layer, 5 g of flake-shaped alumina particles and 34.1 g of 8.1% FeCl3 solution were used, with the FeCl3 solution added at a rate of less than 2.5 hours, and the pH of the dispersion was maintained at 2.7 using 41.0 g of NaOH aqueous solution; and for the formation of the second layer, 12.65 g of 10.0% MnCl2·4H2O solution was used, with the MnCl2·4H2O solution added at a rate of less than 1 hour, the pH of the dispersion was maintained at 8.0 using 13.9 g of NaOH aqueous solution, and the calcination temperature was changed to 800°C under a nitrogen atmosphere. The composite particles were dark brown in color.

[0474] (Comparative Example 1)

[0475] Except for the following differences, in a manner similar to Example 4, 5.2 g of a sample of flaky alumina particles coated with iron(III) oxide and nickel oxide was obtained by using FeCl3 solution to form the first layer and NiCl2 solution to form the second layer. The difference lies in the use of D... 50 Commercially available alumina particles with a particle size of 30 μm (trade name A-SF-60, manufactured by Zhengzhou Research Institute of Chalco); and for the formation of the first layer, the NiCl2 solution dropping time was changed to less than 1.7 hours. The composite particles are brown in color.

[0476] (Comparative Example 2)

[0477] Except for the following differences, in a manner similar to Example 7, 5.36 g of a sample of flaky alumina particles coated with cobalt oxide and titanium oxide was obtained by using TiCl4 solution to form the first layer and CoSO4 solution to form the second layer. The difference lies in the use of D... 50 The above-mentioned commercially available alumina particles have a particle size of 30 μm. The composite particles are light green in color.

[0478] (Comparative Example 3)

[0479] Except for the following differences, in a manner similar to Example 5, 5.0 g of a sample coated with polyhedral alumina particles covered with alumina and zinc oxide was obtained by using FeCl3 solution to form the first layer and ZnCl2 solution to form the second layer. The difference lies in the use of D... 50 The above-mentioned commercially available alumina particles have a particle size of 30 μm. The composite particles are light brown in color.

[0480] (Comparative Example 4)

[0481] Except for the following differences, in a manner similar to Example 6, 5.4 g of a sample coated with polyhedral alumina particles covered with alumina and zinc oxide was obtained by using a TiCl4 solution to form the first layer and a ZnCl2 solution to form the second layer. The difference lies in the use of D... 50 The above-mentioned commercially available alumina particles have a particle size of 30 μm. The composite particles are white in color.

[0482] (Comparative Example 5)

[0483] Except for the following differences, in a manner similar to Example 9, 4.7 g of a sample coated with polyhedral alumina particles was obtained by using TiCl4 solution to form the first layer and NiCl2 solution to form the second layer. The difference lies in the use of D... 50 The above-mentioned commercially available alumina particles have a particle size of 30 μm. The composite particles are light yellow in color.

[0484] [Table 1]

[0485]

[0486] [Table 2]

[0487]

[0488] [Table 3]

[0489]

[0490] [evaluate]

[0491] The powders prepared in Examples 1-14 and Comparative Examples 1-5, which were used as test samples, were evaluated as follows. The measurement methods are described below.

[0492] [Measurement of the major diameter L of alumina particles]

[0493] 1 mg of alumina powder was dispersed in a 0.2 wt% sodium hexametaphosphate aqueous solution (manufactured by FUJIFILM Wako PureChemical Corporation) to make a total dispersion of 18 g. This was used as a sample, and the sample was measured using a laser diffraction particle size analyzer (SALD-7000, manufactured by Shimadzu Corporation). Therefore, the average particle size D was determined. 50 The value (μm) is assigned and designated as the major axis L.

[0494] [Measurement of the thickness D of alumina particles]

[0495] The thickness of 50 particles was measured using a scanning electron microscope (SEM), and the average value of the measurements was taken and designated as the thickness D (μm).

[0496] Aspect Ratio (L / D)

[0497] The aspect ratio can be obtained using the following equation.

[0498] Aspect Ratio = (Large Diameter L of Alumina Particle / Thickness D of Alumina Particle)

[0499] [Analysis of Mo content on the surface of alumina particles]

[0500] The prepared test samples were pressed and fixed onto double-sided adhesive tape, and their composition was analyzed using an X-ray photoelectron spectroscopy (XPS) instrument (Quantera SXM, manufactured by Ulvac-PHI, Inc.) under the following conditions.

[0501] -X-ray source: Monochromatic AlKα; beam diameter is The output is 25W.

[0502] - Measurement: The analysis area is 1000 μm square; and n = 3

[0503] -Charging calibration: C1s = 284.8eV

[0504] Based on the results of XPS analysis, the [Mo] / [Al] value was determined and designated as the Mo content on the surface of the alumina particles. A Mo content greater than or equal to 0.0005 was considered to indicate the presence of Mo on the surface of the alumina particles, while a Mo content less than 0.0005 was considered to indicate the absence of Mo on the surface of the alumina particles.

[0505] [Evaluation of the covering layer]

[0506] The obtained composite particles were placed and loaded into a measurement sample holder with a depth of 0.5 mm, allowing the composite particles to flatten under a given load. The sample holder was placed in a wide-angle X-ray diffractometer (Ultima IV (for XRD measurements), manufactured by Rigaku Corporation), and measurements were performed under the following conditions: Cu-Kα radiation; 40 kV-40 mA; scan rate of 2 / min; scan range of 10 to 70°. The composition of the composite oxide layer was determined based on the obtained peak pattern. A rating of A (“Acceptable”) was given if one or more composite metal oxides containing two or more metals were present in the inorganic coating of the obtained composite particles, and a rating of B (“Unacceptable”) was given if no composite metal oxides were present in the inorganic coating.

[0507] The powders obtained in Examples 1-14 were confirmed to have the particle size (D) shown in Table 1 or Table 2. 50 The values ​​for thickness and aspect ratio were also considered. The powders obtained in Comparative Examples 1-5 were confirmed to have the particle size values ​​(D) shown in Table 3. 50 ).

[0508] Figures 1 to 3 The image shows the sheet-like alumina particles of Example 3 obtained by SEM detection. Figure 1 , Figure 2 and Figure 3 The magnification factors are 500×, 2000×, and 50000×, respectively.

[0509] like Figures 1 to 3 As shown, it was confirmed that the surface of the sheet-like alumina in Example 3 was covered with cobalt-iron oxide (CoFe2O4) and iron(III) oxide (Fe2O3) in the form of particles.

[0510] Figures 4 to 6 Images of the sheet-like alumina particles of Example 6 obtained by SEM analysis are shown. Figure 4 , Figure 5 and Figure 6 The magnification factors are 500×, 2000×, and 50000×, respectively.

[0511] like Figures 4 to 6As shown, it is confirmed that the surface of the sheet-like alumina in Example 6 is covered with granular zinc oxide-titanium oxide (ZnTiO3) and zinc oxide (ZnO).

[0512] Figures 7 to 9 Images of the sheet-like alumina particles of Example 12 obtained by SEM analysis are shown. Figure 7 , Figure 8 and Figure 9 The magnification factors are 500×, 2000×, and 50000×, respectively.

[0513] like Figures 7 to 9 As shown, it is confirmed that the surface of the sheet-like alumina in Example 12 is covered with particulate alumina-cobalt (CoAl2O4) and iron(III) (Fe2O3).

[0514] Figures 10-12 Images of the flaky alumina particles of Example 14 obtained by SEM analysis are shown. Figure 10 , Figure 11 and Figure 12 The magnification factors are 500×, 2000×, and 50000×, respectively.

[0515] like Figures 10 to 12 As shown, it is confirmed that the surface of the sheet-like alumina in Example 14 is covered with manganese-iron oxide (MnFe2O4) in the form of particles.

[0516] also, Figures 13 to 15 Images of the flaky alumina particles of Comparative Example 1 obtained by SEM detection are shown. Figure 13 , Figure 14 and Figure 15 The magnification factors are 500×, 2000×, and 50000×, respectively.

[0517] like Figures 13 to 15 As shown, it was confirmed that the surface of the sheet-like alumina in Comparative Example 1 was covered with granular iron(III) (Fe2O3) and nickel oxide (NiO).

[0518] In addition, using D 50 In the composite particles of Examples 1 to 14, which contain 28 μm lamellar alumina particles, Mo and Si were confirmed to be present on the surface of the lamellar alumina. Furthermore, in the inorganic coatings of the composite particles obtained in each example, one or more of the composite metal oxides shown in Table 1 or Table 2 were present. Therefore, it was found that when Mo is present on the surface of the lamellar alumina, an inorganic coating containing composite metal oxides can be formed on the lamellar alumina. In particular, it was found that under the conditions of Examples 2 to 12 and 14, during the formation of the second layer, an inorganic coating containing the composite metal oxides shown in Table 1 or Table 2 could be formed at a relatively low firing temperature of 600–800 °C.

[0519] On the other hand, when using D 50 In Comparative Example 1, the composite particles of commercially available lamellar alumina particles with a particle size of 30 μm were confirmed by XRD measurement to have an α-crystal structure. Furthermore, it was confirmed that neither Mo nor Si was present on the surface of the lamellar alumina. Additionally, although an inorganic coating formed from iron(III) oxide and nickel oxide was obtained, an inorganic coating containing nickel-iron oxide was not obtained.

[0520] Using D 50 In Comparative Example 2, the composite particles of commercially available lamellar alumina particles with a particle size of 30 μm were confirmed by XRD measurement to have an α-crystal structure. Furthermore, it was confirmed that neither Mo nor Si was present on the surface of the lamellar alumina. Additionally, although an inorganic coating formed from cobalt oxide and titanium oxide was obtained, an inorganic coating containing cobalt oxide-titanium oxide was not obtained.

[0521] Using D 50 In Comparative Example 3, the composite particles of commercially available lamellar alumina particles with a particle size of 30 μm were confirmed by XRD measurement to have an α-crystal structure. Furthermore, it was confirmed that neither Mo nor Si was present on the surface of the lamellar alumina. Additionally, while an inorganic coating formed from alumina and zinc oxide was obtained, an inorganic coating containing zinc oxide-iron was not obtained.

[0522] Using D 50 In Comparative Example 4, the composite particles of commercially available lamellar alumina particles with a particle size of 30 μm were confirmed by XRD measurement to have an α-crystal structure. Furthermore, it was confirmed that neither Mo nor Si was present on the surface of the lamellar alumina. Additionally, while an inorganic coating formed from alumina and zinc oxide was obtained, an inorganic coating containing zinc oxide-titanium was not obtained.

[0523] Using D 50 In Comparative Example 5, the composite particles of commercially available lamellar alumina particles with a particle size of 30 μm were confirmed by XRD measurement to have an α-crystal structure. Furthermore, it was confirmed that neither Mo nor Si was present on the surface of the lamellar alumina. Additionally, although an inorganic coating formed from alumina was obtained, an inorganic coating containing nickel-titanium oxide was not obtained.

[0524] Industrial availability

[0525] The composite particles of this invention are alumina particles that exhibit high selectivity for the coating material, thus making them suitable for a wide range of applications. For example, the composite particles can be used in printing inks, paint formulations, automotive coatings, industrial coatings, thermally conductive fillers, cosmetic materials, abrasives, high-luminescence pigments, lubricants, matrix materials for conductive powders, and ceramic materials.

Claims

1. A composite particle comprising alumina particles and an inorganic coating layer disposed on the surface of the alumina particles, the alumina particles comprising molybdenum (Mo) and silicon (Si), and the inorganic coating layer comprising a composite metal oxide. The inorganic coating layer is formed by two or more layers. The composite metal oxide is a metal oxide containing two or more metals. The formation of the inorganic coating layer includes a first conversion step and a second conversion step. In the first conversion step, a first metal inorganic salt containing at least one metal other than aluminum (Al) is contacted with the alumina particles, and then the first metal inorganic salt deposited on the alumina particles is converted into a metal oxide. In the second conversion step, a second metal inorganic salt is contacted with the metal oxide and / or the alumina particles, the second metal inorganic salt comprising at least one different metal other than aluminum (Al) and different from the metal used in the first conversion step, and then the metal oxide and / or the second metal inorganic salt is converted into the composite metal oxide.

2. The composite particles according to claim 1, wherein the composite metal oxide comprises metal oxides of two or more metals selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al).

3. The composite particles according to claim 1, wherein the composite metal oxide comprises a first metal oxide and a second metal oxide, the first metal oxide being a metal oxide selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), and manganese (Mn), and the second metal oxide being a metal oxide selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), and manganese (Mn), wherein the second metal oxide is different from the first metal oxide.

4. The composite particles according to claim 1, wherein the alumina particles further comprise germanium (Ge).

5. The composite particles according to claim 4, wherein the alumina particles contain mullite in the surface layer of the alumina particles.

6. The composite particles according to any one of claims 1 to 5, wherein the composite particles have one of a sheet-like shape, a spherical shape, and a polyhedral shape.

7. The composite particles according to any one of claims 1 to 5, wherein the composite particles have a sheet-like shape, a thickness of 0.01 μm or more and 5 μm or less, an average particle size of 0.1 μm or more and 500 μm or less, and an aspect ratio of 2 or more and 500 or less.

8. A coating formulation, ink, or molded article comprising composite particles according to any one of claims 1 to 7.

9. A method for producing composite particles, the method comprising the following steps: The alumina particles are produced by sintering a mixture comprising an aluminum compound containing elemental aluminum, a molybdenum compound containing elemental molybdenum, and a shape control agent for controlling the shape of the alumina particles. and An inorganic coating layer comprising a composite metal oxide is formed on the surface of the alumina particles. The shape control agent comprises one or more silicon compounds selected from silicon and elemental silicon. The composite metal oxide is a metal oxide containing two or more metals. The formation of the inorganic coating layer includes a first conversion step and a second conversion step. In the first conversion step, a first metal inorganic salt containing at least one metal other than aluminum (Al) is contacted with the alumina particles, and then the first metal inorganic salt deposited on the alumina particles is converted into a metal oxide. In the second conversion step, a second metal inorganic salt is contacted with the metal oxide and / or the alumina particles, the second metal inorganic salt comprising at least one different metal other than aluminum (Al) and different from the metal used in the first conversion step, and then the metal oxide and / or the second metal inorganic salt is converted into the composite metal oxide.

10. The method for producing composite particles according to claim 9, wherein the shape control agent further comprises a germanium compound containing element germanium.

11. The method for producing composite particles according to claim 9 or 10, wherein the mixture further comprises a potassium compound containing elemental potassium.

12. The method for producing composite particles according to claim 9, wherein the composite metal oxide comprises metal oxides of two or more metals selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), manganese (Mn) and aluminum (Al).

13. The method for producing composite particles according to claim 9, wherein the composite metal oxide comprises a first metal oxide and a second metal oxide, the first metal oxide being a metal oxide selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), and manganese (Mn), and the second metal oxide being a metal oxide selected from iron (Fe), titanium (Ti), zinc (Zn), nickel (Ni), cobalt (Co), and manganese (Mn), and the second metal oxide being different from the first metal oxide.

14. The method for producing composite particles according to claim 9, wherein, During the formation of the inorganic coating, a metal inorganic salt containing at least one metal other than aluminum (Al) is contacted with the alumina particles, and then the metal inorganic salt deposited on the alumina particles is converted into the composite metal oxide.

Images