TW202142490A - Plate-shaped alumina particles and manufacturing method of plate-shaped alumina particles including aluminum compounds, molybdenum compounds, potassium compounds, and silicon or silicon compounds - Google Patents

Abstract

A plate-shaped alumina particle which has a longitudinal diameter of 30 [mu]m or more, a thickness of 3 [mu]m or more, and an aspect ratio of 2 to 50, and contains molybdenum. A manufacturing method of plate-shaped alumina particles, which includes: mixing the following compounds to form a mixture: when the total amount of raw materials obtained by conversion of oxides is set to 100% by mass, aluminum compounds containing 10% by mass or more of aluminum in terms of Al2O3, molybdenum compounds containing 20% by mass or more of molybdenum in terms of MoO3, potassium compounds containing 1% by mass or more of potassium in terms of K2O, and silicon or silicon compounds containing 1% by mass or less of silicon in terms of SiO2; and calcining the mixture.

Description

Tabular alumina particles and method for producing tabular alumina particles

The present invention relates to a method for producing plate-shaped alumina particles and plate-shaped alumina particles.

Alumina particles as inorganic fillers are used in various applications. Among them, the plate-shaped alumina particles are particularly excellent in thermal properties, optical properties, etc., compared with spherical alumina particles, and further improvement in performance is required.

In recent years, researches on the synthesis of inorganic materials for learning from nature or biology have been actively carried out. Among them, the flux method is a method that effectively utilizes the wisdom of nature to create crystals (minerals) and precipitates crystals from solutions of inorganic compounds or metals at high temperatures. The characteristics of the flux method include the ability to grow crystals at a temperature far below the melting point of the target crystal, the growth of crystals with very few defects, and the ability to control the particle shape.

Previously, there has been reported a technology for producing α-alumina by such a flux method. For example, Patent Document 1 describes an invention related to a macrocrystal of α-alumina, which is essentially a small hexagonal plate-like single crystal, and the coarse crystal of α-alumina is characterized by: The diameter of the small plate is 2 μm-20 μm, the thickness is 0.1 μm-2 μm, and the ratio of the diameter to the thickness is 5-40. Patent Document 1 describes that the α-alumina can be produced from transition alumina or hydrated alumina and a flux. It is stated that the flux used at this time has a melting point of 800° C. or less, contains chemically bonded fluorine, and melts transitional alumina or hydrated alumina in a molten state.

When manufacturing tabular alumina, a method for manufacturing tabular alumina using silicon or a silicon compound containing silicon as a crystallization control agent is known (Patent Document 2). The technique of Patent Document 3 relates to octahedral alumina with a large particle size. [Prior Art Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 03-131517 [Patent Document 2] Japanese Patent Laid-Open No. 2016-222501 [Patent Document 3] International Publication No. 2018/112810

[The problem to be solved by the invention] However, with regard to the conventional plate-like alumina particles shown in Patent Document 1 to Patent Document 3, the brilliance when observed with the naked eye is insufficient, and there is room for improvement in optical characteristics.

The present invention has been made in view of such facts, and its subject is to provide plate-shaped alumina particles having excellent brightness. [Means to solve the problem]

The inventors of the present invention conducted diligent studies in order to solve the above-mentioned problems, and as a result, discovered that plate-shaped alumina particles having a predetermined shape are excellent in brightness, and completed the present invention. That is, the present invention proposes the following means in order to solve the above-mentioned problems. (1) A plate-shaped alumina particle having a long diameter of 30 μm or more, a thickness of 3 μm or more, an aspect ratio of 2 to 50, and containing molybdenum. (2) The plate-shaped alumina particles as described in (1) above, which further contain silicon. (3) The tabular alumina particles described in (2) above, wherein in X-ray Photoelectron Spectroscopy (XPS) analysis, the molar ratio of Si to Al [Si]/[Al ] Is 0.001 or more. (4) The tabular alumina particles described in any one of (1) to (3), wherein the diffraction peak value obtained by X-Ray Diffraction (XRD) analysis is The crystallite diameter of the (104) plane calculated from the half-value width of the peak corresponding to the (104) plane is 150 nm or more. (5) The tabular alumina particles as described in any one of (1) to (4), wherein the half value of the peak corresponding to the (113) plane of the diffraction peak obtained by XRD analysis The crystallite diameter of the (113) plane calculated by the width is 200 nm or more. (6) The plate-shaped alumina particles described in any one of (1) to (5) above have a hexagonal plate shape. (7) The plate-shaped alumina particles as described in any one of (1) to (6), which are single crystals. (8) A method for producing plate-shaped alumina particles, wherein the plate-shaped alumina particles are the plate-shaped alumina particles as described in any one of (1) to (7), wherein the oxide When the total amount of raw materials obtained by conversion is set to 100% by mass, 10% by mass or more of aluminum compounds _{in terms of Al 2} O _{3 and} 20% by mass or more of molybdenum _{compounds in terms of MoO 3} , K ₂ O converted to 1% by mass or more of potassium compounds containing potassium, and SiO ₂ converted to less than 1% by mass of silicon or silicon compounds containing silicon are mixed to form a mixture; The mixture is simmered. (9) The method for producing plate-shaped alumina particles as described in (8), wherein the mixture further contains an yttrium compound containing yttrium element. [Effects of the invention]

According to the present invention, it is possible to provide a plate-shaped alumina particle having a predetermined shape and excellent glossiness.

Hereinafter, a method for producing plate-shaped alumina particles and plate-shaped alumina particles according to an embodiment of the present invention will be described in detail.

＜Plate Alumina Particles＞ Regarding the shape of the plate-like alumina particles of the embodiment, the long diameter is 30 μm or more, the thickness is 3 μm or more, and the aspect ratio is 2-50. As described later, the crystalline form is preferably α-type (preferably α-alumina). In addition, the plate-shaped alumina particles of the embodiment contain molybdenum. Furthermore, as long as the effect of the present invention is not impaired, the plate-shaped alumina particles of the embodiment may contain impurities derived from raw materials and the like. Furthermore, the plate-shaped alumina particles may further include organic compounds and the like.

The plate-shaped alumina particles of the embodiment can have excellent brightness by having the above-mentioned shape. The conventional plate-shaped alumina particles shown in Patent Document 1 to Patent Document 3 do not satisfy the requirements of the aforementioned major diameter, thickness, and aspect ratio. Therefore, the previous alumina particles may not be plate-shaped or have a small particle size, and therefore lack the sense of brightness. In addition, the octahedral alumina particles shown in Patent Document 3 are significantly inferior in brightness when compared with the plate-shaped alumina particles of the embodiment of the present invention with approximately the same particle size. It can be presumed that the reason is that the octahedral alumina does not totally reflect the incident light like a plate, but reflects on several surfaces (causes random reflection).

Since the plate-shaped alumina particles of the embodiment of the present invention are plate-shaped and have a large particle size, it is considered that the reflection surface of light is large and can exhibit strong brightness. In addition, the "particle size" in this specification shall be a value that takes into consideration the major diameter and thickness. The so-called "brightness" refers to the height of the visible state of the flickering light generated by the light reflected by the alumina particles.

The "plate shape" in the present invention means that the aspect ratio obtained by dividing the long diameter of the alumina particles by the thickness is 2 or more. Furthermore, in this specification, the "thickness of alumina particles" is set as the arithmetic average of the following thicknesses: According to the image obtained by scanning electron microscope (SEM), at least 50 randomly selected alumina particles are measured. Measure the resulting thickness. "Long diameter of alumina particles" is set as the arithmetic average of the following long diameters: The length obtained by measuring at least 50 randomly selected tabular alumina particles based on the image obtained by scanning electron microscope (SEM) path. The "major diameter" is the maximum length among the distances between two points on the outline of the alumina particles.

Regarding the shape of the plate-like alumina particles of the embodiment, the major axis is 30 μm or more, the thickness is 3 μm or more, and the ratio of the major axis to the thickness, that is, the aspect ratio is 2-50. When the long diameter of the plate-shaped alumina particles is 30 μm or more, an excellent brilliance can be exhibited. When the thickness of the plate-shaped alumina particles is 3 μm or more, an excellent brilliance can be exerted, and the mechanical strength can be excellent. If the aspect ratio of the plate-shaped alumina particles is 2 or more, they can exhibit excellent brightness and can have two-dimensional blending characteristics. When the aspect ratio of the plate-shaped alumina particles is 50 or less, the mechanical strength can be excellent. The plate-shaped alumina particles of the embodiment can have more excellent brightness, mechanical strength, and two-dimensional configuration characteristics by making the shape or size more uniform. Therefore, the long diameter is preferably 50 μm to 200 μm, and the thickness is relatively large. It is preferably 5 μm to 60 μm, and the ratio of the major axis to the thickness, that is, the aspect ratio, is preferably 3 to 30.

Regarding the shape of the preferred alumina particles, the conditions of thickness, average particle size, and aspect ratio may be arbitrarily combined within the range of the plate shape.

The plate-shaped alumina particles of the embodiment may be in the shape of a circular plate or an elliptical plate. However, in terms of optical properties, handling properties, and ease of manufacture, the particle shape is preferably polygonal such as hexagonal to octagonal. The plate shape is more preferably a hexagonal plate shape in terms of exhibiting particularly excellent brilliance.

Here, the hexagonal plate-shaped alumina particles refer to the following particles: the aspect ratio is 2 or more, and the number of sides (including the longest side) with a length of 0.6 or more relative to the length 1 of the longest side is 6 , And the total length of the sides whose length is 0.6 or more with respect to the length 1L of the outer circumference is 0.9L or more. Furthermore, in terms of the observation conditions of the particles, when it is clear that the side is not linear due to the gaps in the particle, the side can be corrected to be a straight line for measurement. Similarly, when the portion corresponding to the corner of the hexagon is slightly rounded, the corner can be corrected to the intersection of the straight lines for measurement. In the hexagonal plate-shaped aluminum oxide particles, the aspect ratio is preferably 3 or more. In the hexagonal plate-shaped aluminum oxide particles, the long diameter is preferably 50 μm or more.

Regarding the plate-like alumina particles of the embodiment, the proportion of the hexagonal plate-like particles relative to 100% of the total number of plate-like alumina particles is preferably 30% or more by number. The regular light reflection brought about by the shape can further exert the brightness, so it is particularly preferably 80% or more.

The crystallite diameter of the (104) plane of the plate-shaped alumina particles of the embodiment is preferably 150 nm or more, more preferably in the range of 200 nm to 700 nm, and still more preferably in the range of 300 nm to 600 nm. Here, the size of the crystal domain of the (104) plane is equivalent to the crystallite diameter of the (104) plane. The larger the crystallite diameter, the larger the light reflection surface, and it is considered that high brightness can be exerted. In addition, the crystallite diameter of the (104) plane of the plate-shaped alumina particles can be controlled by appropriately setting the conditions of the manufacturing method described later. In addition, in this specification, the value of the "crystallite diameter of the (104) plane" adopts the following value: According to the peak value attributable to the (104) plane measured by X-ray diffraction (XRD) (at 2θ=35.2 degrees around) The half-value width of the peak appearing), and the value calculated using the Scherrer equation.

In addition, the crystallite diameter of the (113) plane of the plate-shaped alumina particles of the embodiment is preferably 200 nm or more, more preferably in the range of 250 nm to 1000 nm, and still more preferably in the range of 300 nm to 500 nm. Here, the size of the crystal domain of the (113) plane corresponds to the crystallite diameter of the (113) plane. The larger the crystallite diameter, the larger the light reflection surface, and it is considered that high brightness can be exerted. In addition, the crystallite diameter of the (113) plane of the plate-shaped alumina particles can be controlled by appropriately setting the conditions of the manufacturing method described later. In addition, in this specification, the value of the "crystallite diameter of the (113) plane" adopts the following value: Based on the peak value attributable to the (113) plane measured using X-ray diffraction (XRD) (at 2θ=43.4 degrees around) The half-value width of the peak appearing), and the value calculated using the Scherrer equation.

The XRD analysis is performed under the same conditions as the measurement conditions described in the examples described later or under interchangeable conditions that can obtain the same measurement results.

The plate-shaped alumina particles of the embodiment are preferably single crystals. The so-called single crystal refers to crystal grains containing a single composition that are neatly arranged in a unit lattice. If it is a good crystal, it will be transparent and produce reflected light in most cases. If a part of the crystal is in a stepped shape or shrinks at an acute angle, it can be presumed to be a polycrystal in which a plurality of crystal components overlap. The single crystal measurement of particles is carried out under the same conditions as the measurement conditions described in the examples described later or under interchangeable conditions that can obtain the same measurement results. The fact that the plate-like alumina particles are single crystals means that the particles are of high quality, and it can be presumed that they are also excellent in brightness.

The thickness, long diameter, aspect ratio, shape, crystallite diameter, etc. of the plate-shaped alumina particles of the embodiment can be selected by the use ratio of aluminum compound, molybdenum compound, potassium compound, silicon or silicon compound, and metal compound in the raw materials described below. Wait to control.

Regarding the α-alumina-based tabular alumina particles of the embodiment, as long as the long diameter is 30 μm or more, the thickness is 3 μm or more, the aspect ratio is 2 to 50, and they contain molybdenum, they can be obtained based on any manufacturing method. However, in terms of the ability to produce plate-shaped alumina particles with a higher aspect ratio and excellent brightness, it is preferably obtained by sintering the aluminum compound in the presence of a molybdenum compound, a potassium compound, a silicon or a silicon compound . In addition, although it will be described later, it is more preferably obtained by sintering an aluminum compound in the presence of a molybdenum compound, a potassium compound, silicon or a silicon compound, or a metal compound. The metal compound may be used in combination or not, but by using it in combination, crystallization control can be performed more simply. As the metal compound, in order to further favorably advance crystal growth so that the obtained α-type plate-like alumina particles are uniform in crystal shape, size, etc., a yttrium compound can be used.

In the manufacturing method, the molybdenum compound can be used as a flux. In this specification, below, the manufacturing method using a molybdenum compound as a flux may be referred to simply as the "flux method". The flux method will be described in detail later. Furthermore, by the sintering, the molybdenum compound and the potassium compound react to form potassium molybdate. At the same time, the molybdenum compound reacts with the aluminum compound to form aluminum molybdate. Then, in the presence of potassium molybdate, the aluminum molybdate is decomposed, and the crystal grows in the presence of silicon or silicon compound, thereby obtaining a large particle size and a Plate-shaped alumina particles. That is, when alumina particles are produced via an intermediate of aluminum molybdate, if potassium molybdate is present, alumina particles with a large particle size can be obtained. In addition, it is considered that the molybdenum compound is incorporated in the plate-shaped alumina particles when crystal growth is performed. The flux method shown above is a kind of flux slow cooling method, and it is considered that crystal growth occurs in potassium molybdate in the liquid phase. Furthermore, potassium molybdate can also be easily recovered and reused by washing with an inorganic alkali aqueous solution such as water, ammonia water, sodium hydroxide aqueous solution, or potassium aqueous solution.

In the production of the tabular alumina particles, by effectively using molybdenum compounds, potassium compounds, silicon or silicon compounds, the alumina particles have a high α crystal rate and self-shape, so excellent dispersibility and mechanical properties can be achieved. Strength and brightness.

The shape of the plate-shaped alumina particles can be controlled according to the usage ratio of molybdenum compound, potassium compound, silicon or silicon compound, etc., in particular, it can be controlled according to the usage ratio of molybdenum compound and silicon or silicon compound. The amount of molybdenum and the amount of silicon contained in the plate-shaped alumina particles, and the preferred use ratio of each raw material will be described in detail later.

[Alumina] The "alumina" contained in the plate-shaped alumina particles of the embodiment is alumina (aluminium oxide), for example, it may be transition alumina of various crystal forms such as γ, δ, θ, κ, and δ, or may be Alumina hydrate is included in the transition alumina, but in terms of more excellent mechanical strength and brightness, it is basically preferably an α crystal form (α type). The α crystal form is the dense crystal structure of alumina, which is beneficial to improve the mechanical strength or brightness of the tabular alumina of the present invention.

The closer the α crystallization rate is to 100%, the easier it is to exhibit the original properties of the α crystal form, which is preferable. The alpha crystallization rate of the plate-shaped alumina particles of the embodiment is, for example, 90% or more, preferably 95% or more, and more preferably 99% or more.

[molybdenum] In addition, the plate-shaped alumina particles of the embodiment contain molybdenum. The molybdenum is derived from a molybdenum compound used as a flux.

Molybdenum has catalytic and optical functions. In addition, by effectively using molybdenum, in a manufacturing method as described below, it is possible to produce a product with a long diameter of 30 μm or more, a thickness of 3 μm or more, an aspect ratio of 2 to 50, and containing molybdenum and having excellent brightness. Plate-shaped alumina particles. Furthermore, by increasing the amount of molybdenum used, it is easy to obtain hexagonal plate-shaped alumina particles with a large particle size and crystallite diameter, and there is a tendency that the obtained alumina particles are more excellent in brightness. In addition, it can be applied to applications of oxidation reaction catalysts and optical materials by utilizing the characteristics of molybdenum contained in the plate-shaped alumina particles.

The molybdenum is not particularly limited. In addition to molybdenum metal, molybdenum oxide or a part of reduced molybdenum compounds, and the like are also included. Although it is considered that molybdenum is contained in the plate-shaped alumina particles in the form of _{MoO 3 , in addition to MoO 3} , it may be contained in the plate-shaped alumina particles in the form of _{MoO 2 or MoO.}

The content of molybdenum is not particularly limited, and it may be included in a form that adheres to the surface of the plate-shaped alumina particles, may be included in a form in which a part of aluminum in the crystal structure of alumina is substituted, or a combination of these.

The content of molybdenum relative to 100% by mass of the tabular alumina particles of the embodiment is preferably 10% by mass or less in terms of molybdenum trioxide, and it is more preferable by adjusting the sintering temperature, sintering time, and sublimation rate of the molybdenum compound It is 0.1% by mass to 5% by mass, and more preferably 0.3% by mass to 1% by mass. If the content of molybdenum is 10% by mass or less, the alpha single crystal quality of alumina is improved, which is preferable. If the content of molybdenum is 0.1% by mass or more, the shape of the obtained plate-like alumina particles improves the brightness, which is preferable.

The content of molybdenum can be determined by X-Ray Fluorescence (XRF) analysis. The XRF analysis is carried out under the same conditions as the measurement conditions described in the examples described later or under interchangeable conditions that can obtain the same measurement results.

[Silicon] The plate-shaped alumina particles of the embodiment may further contain silicon. The silicon is derived from silicon or silicon compounds used as raw materials. By effectively using silicon, in a manufacturing method as described later, it is possible to manufacture a plate with a long diameter of 30 μm or more, a thickness of 3 μm or more, and an aspect ratio of 2 to 50, containing silicon, and having excellent brilliance. Alumina particles. Furthermore, by reducing the amount of silicon used to a certain extent, it is easy to obtain hexagonal plate-shaped alumina particles with a large particle size and crystallite diameter, and the obtained alumina particles tend to have more excellent brightness. The preferred amount of silicon used will be described later.

The plate-shaped alumina particles of the embodiment may contain silicon on the surface layer. Here, the “surface layer” means that the distance from the surface of the plate-shaped alumina particles of the embodiment is within 10 nm. This distance corresponds to the detection depth of XPS used for measurement in the embodiment.

In the plate-shaped alumina particles of the embodiment, silicon may be eccentrically present in the surface layer. Here, the term "biased in the surface layer" refers to a state in which the mass of silicon per unit volume in the surface layer is greater than the mass of silicon per unit volume other than the surface layer. As shown in the following examples, it can be determined that the silicon bias is present on the surface layer by comparing the results of the surface analysis using XPS and the overall analysis using XRF.

The silicon contained in the tabular alumina particles of the embodiment may be silicon alone or silicon in a silicon compound. The plate-shaped alumina particles of the embodiment may include _{at least one selected from the group consisting of Si, SiO 2} and SiO as silicon or a silicon compound, and may also include the substance on the surface layer. It is preferable that the plate-shaped alumina particles of the embodiment do not substantially contain mullite.

Since the plate-shaped alumina particles of the embodiment contain silicon in the surface layer, Si can be detected by XPS analysis. The value of the molar ratio [Si]/[Al] of Si to Al obtained in the XPS analysis of the plate-shaped alumina particles of the embodiment is preferably 0.001 or more, more preferably 0.01 or more, and still more preferably 0.02 or more. Regarding the surface of the plate-shaped alumina particles, the entire surface may be covered with silicon or a silicon compound, or at least a part of the surface of the plate-shaped alumina particles may be covered with silicon or a silicon compound.

The upper limit of the value of the molar ratio [Si]/[Al] in the XPS analysis is not particularly limited, and is preferably 0.4 or less, more preferably 0.11 or less, and still more preferably 0.06 or less.

The value of the molar ratio [Si]/[Al] of Si to Al obtained in the XPS analysis of the tabular alumina particles of the embodiment is preferably 0.001 or more and 0.4 or less, more preferably 0.01 or more and 0.11 or less, More preferably, it is 0.02 or more and 0.06 or less.

The value of the molar ratio [Si]/[Al] obtained in the XPS analysis is that the amount of Si contained in the surface layer of the plate-shaped alumina particles in the range is appropriate, and they are plate-shaped and have a large particle size , Brightness is more excellent and better.

XPS analysis is carried out under the same conditions as the measurement conditions described in the examples described later or under interchangeable conditions that can obtain the same measurement results.

Since the plate-shaped alumina particles of the embodiment contain silicon, Si can be detected by XRF analysis. The molar ratio [Si]/[Al] of Si relative to Al obtained in the XRF analysis of the tabular alumina particles of the embodiment is preferably 0.0003 or more and 0.01 or less, more preferably 0.0005 or more and 0.0025 or less, more preferably It is 0.0006 or more and 0.001 or less.

The molar ratio [Si]/[Al] value obtained by the XRF analysis is the appropriate amount of Si in the tabular alumina particles within the range, and is tabular and has a large particle size, and is bright More excellent and better.

The plate-shaped alumina particles of the embodiment include silicon corresponding to the silicon or silicon compound used in the production method. The content of silicon relative to 100% by mass of the tabular alumina particles of the embodiment is preferably 10% by mass or less in terms of silicon dioxide, more preferably 0.001% to 3% by mass, and still more preferably 0.01% to 1% by mass , Particularly preferably 0.03% by mass to 0.3% by mass. The content of silicon is suitable for the Si content of the plate-shaped alumina particles in the above-mentioned range, and the plate-shaped aluminum oxide particles have a large particle size and are more excellent in brightness, which is preferable.

The XRF analysis is carried out under the same conditions as the measurement conditions described in the examples described later or under interchangeable conditions that can obtain the same measurement results.

(Inevitable impurities) The plate-shaped alumina particles may contain unavoidable impurities.

The inevitable impurities are those derived from potassium compounds and metal compounds used in the production, existing in the raw materials, or inevitably mixed into the plate-shaped alumina particles during the production process, and refer to the original Impurities that are not necessary but are trace amounts and do not affect the characteristics of the plate-shaped alumina particles.

The inevitable impurities are not particularly limited, and examples thereof include potassium, magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, cerium, and sodium. These unavoidable impurities may be contained alone, or two or more kinds may be contained.

The content of the inevitable impurities in the plate-shaped alumina particles is preferably 10,000 ppm or less, more preferably 1,000 ppm or less, and still more preferably 10 ppm to 500 ppm relative to the mass of the plate-shaped alumina particles.

(Other atoms) Other atoms are those that are intentionally added to the plate-shaped alumina particles for the purpose of imparting mechanical strength, electrical functions, or magnetic functions within a range that does not hinder the effects of the present invention.

There are no particular limitations on other atoms, and examples include zinc, manganese, calcium, strontium, and yttrium. These other atoms may be used alone, or two or more of them may be used in combination.

The content of other atoms in the plate-shaped alumina particles is preferably 5% by mass or less, and more preferably 2% by mass or less with respect to the mass of the plate-shaped alumina particles.

[Organic Compound] In one embodiment, the plate-shaped alumina particles may also include an organic compound. The organic compound is present on the surface of the plate-shaped alumina particles and has a function of adjusting the surface physical properties of the plate-shaped alumina particles. For example, since the plate-shaped alumina particles containing an organic compound on the surface increase the affinity with resin, the function of the plate-shaped alumina particles as a filler can be expressed to the maximum.

The organic compound is not particularly limited, and examples thereof include organosilane, alkylphosphonic acid, and polymers.

Examples of the organosilanes include methyltrimethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyl Alkyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, pentyltrimethoxysilane, hexyltrimethoxysilane, and other alkyl trimethyl groups with a carbon number of 1 to 22 Oxysilanes or alkyltrichlorosilanes; 3,3,3-trifluoropropyltrimethoxysilane, (tridecafluoro-1,1,2,2-tetrahydrooctyl)trichlorosilanes; benzene Trimethoxysilane, phenyltriethoxysilane, p-chloromethylphenyltrimethoxysilane, p-chloromethylphenyltriethoxysilane, etc.

Examples of the phosphonic acid include methylphosphonic acid, ethylphosphonic acid, propylphosphonic acid, butylphosphonic acid, pentylphosphonic acid, hexylphosphonic acid, heptylphosphonic acid, octylphosphonic acid, and decylphosphonic acid. Phosphonic acid, dodecyl phosphonic acid, octadecyl phosphonic acid, 2-ethylhexyl phosphonic acid, cyclohexyl methyl phosphonic acid, cyclohexyl ethyl phosphonic acid, benzyl phosphonic acid, phenyl phosphonic acid, Dodecylbenzenephosphonic acid.

As the polymer, for example, poly(meth)acrylates can be suitably used. Specifically, polymethyl (meth)acrylate, polyethyl (meth)acrylate, polybutyl (meth)acrylate, polybenzyl (meth)acrylate, poly(meth)cyclohexyl acrylate, Poly(tert-butyl)(meth)acrylate, poly(meth)glycidyl(meth)acrylate, poly(meth)acrylate pentafluoropropyl, etc. In addition, examples include: general-purpose polystyrene, polyvinyl chloride, polyethylene Acetate, epoxy, polyester, polyimide, polycarbonate and other polymers.

In addition, the organic compound may be contained alone, or two or more kinds may be contained.

There are no particular restrictions on the form of the organic compound, and it may be linked to alumina by a covalent bond, or it may be coated with alumina.

The content of the organic compound relative to the mass of the plate-shaped alumina particles is preferably 20% by mass or less, and more preferably 10% by mass to 0.01% by mass. If the content of the organic compound is 20% by mass or less, the physical properties derived from the plate-shaped alumina particles can be easily expressed, which is preferable.

<Method for manufacturing plate-shaped alumina particles> The method for producing the plate-shaped alumina particles of the embodiment is not particularly limited, and a known technique can be appropriately applied. From the viewpoint that the alumina having a high α crystallization rate can be appropriately controlled at a relatively low temperature, it is more Preferably applicable: a manufacturing method using a flux method using a molybdenum compound.

In more detail, a preferable manufacturing method of the plate-shaped alumina particles includes a step of sintering the aluminum compound in the presence of a molybdenum compound, a potassium compound, a silicon or a silicon compound (the sintering step). The sintering step may be a step of sintering the mixture obtained in the step (mixing step) of obtaining a mixture of objects to be sintered. The mixture preferably further contains the metal compound described later. As the metal compound, an yttrium compound is preferred.

[Mixing Step] The mixing step is a step of mixing raw materials such as aluminum compound, molybdenum compound, potassium compound, silicon or silicon compound to form a mixture. Hereinafter, the content of the mixture will be described.

(Aluminum compound) The aluminum compound is a raw material of the plate-shaped alumina particles of the embodiment.

The aluminum compound is not particularly limited as long as it becomes alumina particles by heat treatment, and examples include metallic aluminum, aluminum sulfide, aluminum nitride, aluminum fluoride, aluminum chloride, aluminum bromide, and iodide. Aluminum, aluminum sulfate, aluminum sulfate, aluminum potassium sulfate, aluminum ammonium sulfate, aluminum nitrate, aluminum aluminate, aluminum silicate, aluminum phosphate, aluminum lactate, aluminum laurate, aluminum stearate, aluminum oxalate, aluminum acetate, alkali Aluminium acetate, alumina propionate, aluminum butadiene oxide, aluminum hydroxide, boehmite, pseudo-boehmite, transition alumina (γ-alumina, δ-alumina, θ-alumina, etc.), α-alumina , Mixed alumina with two or more crystalline phases, etc. Among these, it is preferable to use transition alumina, boehmite, pseudo-boehmite, aluminum hydroxide, aluminum chloride, aluminum sulfate, aluminum nitrate and these hydrates, and more preferably to use transition alumina, soft water Bauxite, fake boehmite, aluminum hydroxide. In the case of obtaining α-alumina as plate-shaped alumina particles, as the raw material, it is preferable to use alumina that does not substantially contain α-alumina, for example, a relatively inexpensive transition containing γ-alumina as a main component. Alumina. As described above, by sintering the raw material, plate-shaped alumina particles of a specific shape or size different from the shape or size of the raw material are obtained in the form of a product.

Furthermore, the aluminum compound may be used alone, or two or more of them may be used in combination.

Commercially available aluminum compounds can be used, or they can be prepared by themselves.

In the case of self-preparation of aluminum compounds, for example, alumina hydrate or transition alumina with high structural stability at high temperatures can be prepared by neutralization of aluminum in an aqueous solution. In more detail, the alumina hydrate may be prepared by neutralizing an acidic aqueous solution of aluminum with an alkali, and the transition alumina may be prepared by heat-treating the obtained alumina hydrate. Furthermore, the alumina hydrate or transition alumina obtained by this has high structural stability at high temperatures. Therefore, if sintered in the presence of a molybdenum compound and a potassium compound, a plate-like oxidation with a large particle size can be obtained. The tendency of aluminum particles.

The shape of the aluminum compound is not particularly limited, and any of spherical, amorphous, aspect ratio structures (threads, fibers, ribbons, tubes, etc.), sheets, etc., can be suitably used.

The average particle size of the aluminum compound is also not particularly limited, and is preferably 5 nm to 10,000 μm.

In addition, aluminum compounds can form organic compounds and complexes. Examples of the composite include an organic/inorganic composite obtained by modifying an aluminum compound with organosilane, an aluminum compound composite to which a polymer is adsorbed, and a composite coated with an organic compound. In the case of using these composites, the content of the organic compound is not particularly limited, but it is preferably 60% by mass or less, and more preferably 30% by mass or less.

The molar ratio of the molybdenum element of the molybdenum compound to the aluminum element of the aluminum compound (molybdenum element/aluminum element) is preferably 0.01 to 3.0, more preferably 0.1 to 1.0. In order to achieve good productivity and allow crystal growth to proceed appropriately, More preferably, it is 0.30 to 0.70. If the molar ratio (molybdenum element/aluminum element) is within the above range, plate-shaped alumina particles having a large particle size can be obtained, which is preferable.

(Molybdenum compound) The molybdenum compound is not particularly limited, and examples thereof include metallic molybdenum, molybdenum oxide, molybdenum sulfide, lithium molybdate, sodium molybdate, potassium molybdate, calcium molybdate, ammonium molybdate, and H ₃ PMo ₁₂ O ₄₀ , H ₃ SiMo ₁₂ O ₄₀ and other molybdenum compounds. At this time, the molybdenum compound contains isomers. For example, the molybdenum oxide may be molybdenum (IV) dioxide (MoO ₂ ) or molybdenum trioxide (VI) (MoO ₃ ). In addition, potassium molybdate has _{a structural formula of K 2} Mo _n O _3n+1 , and n may be 1, or 2, or 3. Among these, molybdenum trioxide, molybdenum dioxide, ammonium molybdate, and potassium molybdate are preferred, and molybdenum trioxide is more preferred.

Furthermore, the molybdenum compound may be used alone, or two or more of them may be used in combination.

In addition, since potassium molybdate (K ₂ Mo _n O _3n+1 , n=1 to 3) contains potassium, it may also have a function as a potassium compound described later.

(Potassium compound) The potassium compound is not particularly limited, and examples thereof include potassium chloride, potassium chlorite, potassium chlorate, potassium sulfate, potassium hydrogen sulfate, potassium sulfite, potassium hydrogen sulfite, potassium nitrate, potassium carbonate, potassium hydrogen carbonate, potassium acetate, Potassium oxide, potassium bromide, potassium bromate, potassium hydroxide, potassium silicate, potassium phosphate, potassium hydrogen phosphate, potassium sulfide, potassium hydrogen sulfide, potassium molybdate, potassium tungstate, etc. At this time, the potassium compound contains isomers similarly to the case of the molybdenum compound. Among these, potassium carbonate, potassium bicarbonate, potassium oxide, potassium hydroxide, potassium chloride, potassium sulfate, potassium molybdate are preferably used, and potassium carbonate, potassium bicarbonate, potassium chloride, and potassium sulfate are more preferably used. , Potassium molybdate.

Furthermore, the potassium compound may be used alone, or two or more of them may be used in combination.

In addition, similarly to the above, since potassium molybdate contains molybdenum, it may also have a function as the molybdenum compound.

Regarding water-soluble potassium compounds, such as potassium molybdate, which are used as raw materials or are produced in the reaction of the heating process during sintering, they do not vaporize even in the sintering temperature range, and can be used for simmering. It is easy to recycle by cleaning after burning, so the amount of molybdenum compound released out of the burning furnace can also be reduced, and the production cost can also be greatly reduced.

The molar ratio (molybdenum element/potassium element) of the molybdenum element of the molybdenum compound to the potassium element of the potassium compound is preferably 5 or less, more preferably 0.01 to 3, and further preferably 0.5 to 1.5 in order to further reduce the production cost. If the molar ratio (molybdenum element/potassium element) is within the above range, plate-shaped alumina particles with a large particle size can be obtained, which is preferable.

(Silicon or silicon compound) The silicon or the silicon compound containing silicon is not particularly limited, and known ones can be used. Specific examples of silicon or silicon compounds include synthetic silicon compounds such as metallic silicon, organosilane, silicon resin, silica particles, silica gel, mesoporous silica, SiC, and mullite; biosilica And other natural silicon compounds. Among these, it is preferable to use organosilane, silicon resin, or silicon oxide fine particles from the viewpoint that the compound and the aluminum compound can be formed more uniformly and mixed. Furthermore, silicon or silicon compound may be used alone, or two or more of them may be used in combination.

The addition rate of the silicon compound relative to the mass conversion value of the aluminum atom in the aluminum compound is preferably 0.01% by mass to 1% by mass, and more preferably 0.03% by mass to 0.4% by mass. When the addition rate of the silicon compound is within the above-mentioned range, plate-shaped alumina particles having a thick thickness and excellent brightness can be obtained, which is preferable.

The molar ratio of the silicon element of the silicon compound to the aluminum element of the aluminum compound (silicon element/aluminum element) is preferably 0.0001 to 0.01, more preferably 0.0002 to 0.005, and still more preferably 0.0003 to 0.003. If the molar ratio (molybdenum element/potassium element) is within the above range, plate-shaped alumina particles with a large particle size can be obtained, which is preferable.

The shape of silicon or a silicon compound containing silicon is not particularly limited. For example, spherical, amorphous, aspect ratio structures (threads, fibers, ribbons, tubes, etc.), sheets, etc. can be suitably used.

(Metal compound) As described later, the metal compound may have a function of promoting the crystal growth of alumina. The metal compound can be used during sintering as needed. Furthermore, since the metal compound has a function of promoting the crystal growth of α-alumina, it is not essential for the production of the plate-shaped alumina particles of the present invention.

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

Examples of the group II metal compounds include magnesium compounds, calcium compounds, strontium compounds, and barium compounds.

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

Furthermore, the metal compound refers to oxides, hydroxides, carbonates, and chlorides of metal elements. For example, if it is an yttrium compound, yttrium oxide (Y ₂ O ₃ ), yttrium hydroxide, and yttrium carbonate are mentioned. Among these, the metal compound is preferably an oxide of a metal element. Furthermore, these metal compounds include isomers.

Among these, preferred are metal compounds of period 3 elements, metal compounds of period 4 elements, metal compounds of period 5 elements, metal compounds of period 6 elements, and more preferably metal compounds of period 4 elements, The metal compound of the element of the fifth period is more preferably the metal compound of the element of the fifth period. Specifically, it is preferable to use a magnesium compound, a calcium compound, an yttrium compound, and a lanthanum compound, and it is more preferable to use a magnesium compound, a calcium compound, and an yttrium compound, and it is especially preferable to use an yttrium compound.

The addition rate of the metal compound is preferably 0.02% by mass to 20% by mass, and more preferably 0.1% by mass to 20% by mass relative to the mass conversion value of aluminum atoms in the aluminum compound. If the addition rate of the metal compound is 0.02% by mass or more, the crystal growth of α-alumina containing molybdenum can be suitably performed, which is preferable. On the other hand, if the addition rate of the metal compound is 20% by mass or less, plate-shaped alumina particles with a low content of impurities derived from the metal compound can be obtained, which is preferable.

[yttrium] In the case where the aluminum compound is sintered in the presence of the yttrium compound as a metal compound, in the sintering step, crystal growth further suitably proceeds to produce α-alumina and a water-soluble yttrium compound. At this time, the water-soluble yttrium compound is likely to be locally present on the surface of the α-alumina as the plate-shaped alumina particles, and therefore, water, alkaline water, these warmed liquids, etc. are used for washing as necessary. This can remove yttrium compounds from the plate-shaped alumina particles.

The aluminum compound, the amount of molybdenum compound, potassium compound and silicon or a silicon compound is not particularly limited, but is preferably: to make the total amount in terms of the resulting oxide starting material as 100 mass%, Al ₂ O to ₃ in terms of 10% by mass or more aluminum compounds, in terms of MoO ₃ to 20 mass% of molybdenum compound, in terms of K ₂ O to less than 1% by mass of the potassium compound, and in terms of SiO ₂ is less than 1% by mass of silicon or a silicon compound is mixed to prepare a mixture; and the mixture is sintered. In terms of being able to further increase the content of the hexagonal plate-shaped alumina, it is more preferable that when the total amount of raw materials obtained by conversion of oxides is 100% by mass, it can be calculated as Al ₂ O ₃ 20% by mass or more and 70% by mass or less of aluminum compounds, 30% by mass or more and 80% by mass or less of molybdenum compounds _{in terms of MoO 3} , and 5 mass% or more and 30% by mass or less of potassium in _{terms of K 2 O} The compound and silicon or silicon compound of 0.001% by mass or more and 0.3% by mass or less in _{terms of SiO 2 are mixed to prepare a mixture; and the mixture is sintered.} It is further preferred that when the total amount of the raw material obtained by conversion of oxides is 100% by mass, it can be calculated as 25% by mass or more and 40% by mass or less _{in Al 2} O _{3 as aluminum compounds, and as MoO 3} as 45 mass% or more and 70 mass% or less of molybdenum compounds, 10 mass% or more and 20 mass% or less of potassium compounds _{in terms of K 2} O, and 0.01 mass% or more and 0.1 mass% or less in _{terms of SiO 2} Silicon or silicon compounds are mixed to form a mixture; and the mixture is sintered. In order to maximize the content of the hexagonal plate-shaped alumina and further appropriately advance the crystal growth, it is particularly preferred that when the total amount of raw materials obtained by conversion of oxides is 100% by mass, Al ₂ O _{3 is} calculated as 35% by mass or more and 40% by mass or less of aluminum compounds, in terms of MoO _{3 is} calculated as 45% by mass or more and 65% by mass or less of molybdenum compounds, in terms of K ₂ O is 10% by mass or more, and 20% by mass or less of potassium compound and 0.02% by mass or more and 0.08% by mass or less of silicon or silicon compound _{in terms of SiO 2 are mixed to prepare a mixture; and the mixture is sintered.}

By blending various compounds within the above range, it is possible to produce plate-shaped alumina particles having a large particle size and having more excellent brightness. In particular, by setting the tendency to increase the usage of molybdenum and to reduce the usage of silicon to a certain extent, the particle size and crystallite diameter can be further increased, and hexagonal plate-shaped alumina particles can be easily obtained. By blending various compounds in the more preferable range, hexagonal plate-shaped alumina particles can be easily obtained, the content rate can be further increased, and the obtained alumina particles tend to be more excellent in brightness.

In the case where the mixture further contains the yttrium compound, the amount of the yttrium compound used is not particularly limited, but it is preferable that when the total amount of the raw materials obtained by the oxide conversion is 100% by mass, Y _{2 may be mixed} O _{3 is} calculated as 5 mass% or less of yttrium compound. More preferably, when the total amount of raw materials in terms of oxides is 100% by mass, a yttrium compound that is 0.01% by mass or more and 3% by mass or less in _{terms of Y 2} O _{3 may be mixed.} In order to allow crystal growth to proceed more appropriately, it is more preferable that when the total amount of raw materials obtained by conversion of oxides is 100% by mass, a mixture of 0.1% by mass or more and 1% by mass or less in _{terms of Y 2} O _{3 may be mixed} Yttrium compound.

The aluminum compound, molybdenum compound, potassium compound, silicon or silicon compound, and metal compound are used so that the total amount of each oxide converted does not exceed 100% by mass.

[Bring step] The firing step of the embodiment is a step of firing an aluminum compound in the presence of a molybdenum compound, a potassium compound, and a silicon or silicon compound. The sintering step may also be a step of sintering the mixture obtained in the mixing step.

The plate-shaped alumina particles of the embodiment can be obtained, for example, by sintering an aluminum compound in the presence of a molybdenum compound, a potassium compound, and a silicon or silicon compound. As described above, this manufacturing method is called the flux method.

The flux method is classified as a solution method. The so-called flux method is, in more detail, a method of showing eutectic crystal growth using a crystal-fluxing two-component system state diagram. The mechanism of the flux method is presumed to be as follows. That is, when the mixture of the solute and the flux is heated, the solute and the flux become a liquid phase. At this time, since the flux is a flux, in other words, since the solute-flux two-component system state diagram shows a eutectic type, the solute melts at a temperature lower than its melting point to form a liquid phase. In this state, if the flux evaporates, the concentration of the flux decreases. In other words, the melting point lowering effect of the solute caused by the flux is reduced, and the evaporation of the flux becomes the driving force to cause the crystal growth of the solute (assistance Flux evaporation method). Furthermore, solutes and fluxes can also cause solute crystal growth by cooling the liquid phase (slow cooling method).

The flux method has the following advantages: crystal growth can be carried out at a temperature far below the melting point, crystal structure can be precisely controlled, and polyhedral crystals with self-shape can be formed.

In the production of alumina particles by the flux method using a molybdenum compound as a flux, the mechanism is not necessarily clear, but it is presumed to be based on the following mechanism, for example. That is, when the aluminum compound is sintered in the presence of the molybdenum compound, first, aluminum molybdate is formed. At this time, it can be understood from the above description that the aluminum molybdate grows alumina crystals at a temperature lower than the melting point of alumina. Then, for example, by evaporating the flux, aluminum molybdate is decomposed, and crystal growth proceeds, whereby alumina particles can be obtained. That is, the molybdenum compound functions as a flux and produces alumina particles via an intermediate of aluminum molybdate.

Here, if a potassium compound and a silicon or a silicon compound are used in combination in the flux method, it is possible to produce plate-shaped alumina particles with a large particle size. In more detail, when a molybdenum compound and a potassium compound are used in combination, first, the molybdenum compound and the potassium compound react to form potassium molybdate. At the same time, the molybdenum compound reacts with the aluminum compound to form aluminum molybdate. Then, for example, in the presence of potassium molybdate, aluminum molybdate is decomposed, and crystal growth proceeds in the presence of silicon or a silicon compound, thereby obtaining aluminum oxide particles having a large particle size and a plate shape. That is, when alumina particles are produced via an intermediate of aluminum molybdate, if potassium molybdate is present, alumina particles with a large particle size can be obtained.

That is, although the reason is not clear, compared with the case of obtaining aluminum oxide particles based on aluminum molybdate, a larger particle size can be obtained in the case of obtaining aluminum oxide particles based on aluminum molybdate in the presence of potassium molybdate. Of alumina particles.

In addition, silicon or a silicon compound plays an important role in the growth of plate crystals as a shape control agent. In the molybdenum oxide flux method that is generally performed, molybdenum oxide is selectively adsorbed on the (113) face of the α crystal of alumina, and it is difficult to supply the crystal component to the (113) face, and the (001) or (006) face can be completely suppressed. Appears, thus forming a polyhedral particle with a six-sided two-hammer type as the base. In the manufacturing method of the embodiment, by using silicon or a silicon compound to suppress molybdenum oxide as a fluxing agent from selectively adsorbing crystalline components on the (113) plane, a dense (001) plane developed and thermodynamically most stable can be formed. The plate-like morphology of the crystalline structure of a hexagonal lattice.

In addition, the above-mentioned mechanism is only a guesser, and even a case where the effect of the present invention is obtained by a mechanism different from the above-mentioned mechanism is included in the technical scope of the present invention.

The composition of the potassium molybdate is not particularly limited, and it usually contains a molybdenum atom, a potassium atom, and an oxygen atom. As the structural formula, it is preferably represented by K ₂ Mo _n O _3n+1 . At this time, n is not particularly limited, and if it is in the range of 1 to 3, the growth of alumina particles can be promoted to function effectively, which is preferable. In addition, potassium molybdate may contain other atoms, and examples of the other atoms include sodium, magnesium, silicon, and the like.

In one embodiment of the present invention, the sintering can be carried out in the presence of a metal compound. That is, in the sintering, the metal compound may be used together with the molybdenum compound and the potassium compound. In this way, alumina particles with a larger particle size can be produced. The mechanism is not necessarily clear, but it is presumed to be based on the following mechanism, for example. That is, it is believed that the presence of metal compounds during the crystal growth of alumina particles can prevent or inhibit the formation of alumina crystal nuclei and/or promote the diffusion of aluminum compounds required for the growth of alumina crystals, in other words, prevent The function of excessively generating crystal nuclei and/or increasing the diffusion rate of the aluminum compound can obtain alumina particles with a large particle size. In addition, the above-mentioned mechanism is only a guesser, and even a case where the effect of the present invention is obtained by a mechanism different from the above-mentioned mechanism is included in the technical scope of the present invention.

The sintering temperature is not particularly limited, but the maximum sintering temperature is preferably 700°C or higher, more preferably 900°C or higher, further preferably 900°C to 2000°C, particularly preferably 900°C to 1000°C. If the sintering temperature is 700°C or higher, the flux reaction proceeds appropriately. Therefore, if the sintering temperature is 900°C or higher, the plate-like crystal growth of the alumina particles proceeds appropriately, which is more preferable.

The state of the aluminum compound, molybdenum compound, potassium compound, silicon or silicon compound, and metal compound at the time of sintering is not particularly limited, as long as these are mixed. Examples of the mixing method include simple mixing of mixed powders, mechanical mixing using a pulverizer or mixer, and mixing using a mortar or the like. At this time, the obtained mixture may be in a dry state or a wet state, but from the viewpoint of cost, it is preferably in a dry state.

The sintering time is also not particularly limited, but it is preferably from 0.1 hour to 1000 hours. From the viewpoint of efficiently forming alumina particles, it is more preferably from 1 hour to 100 hours. If the sintering time is 0.1 hour or more, alumina particles with a large particle size can be obtained, which is preferable. On the other hand, if the sintering time is within 1000 hours, the manufacturing cost can be reduced, which is preferable.

The environment for sintering is also not particularly limited. For example, an oxygen-containing environment such as air or oxygen, or an inert gas environment such as nitrogen or argon is preferable, from the viewpoint of the safety of the implementer or the durability of the furnace. , More preferably a non-corrosive oxygen-containing environment or nitrogen environment, and even more preferably an air environment from the viewpoint of cost.

The pressure during sintering is also not particularly limited, and it may be under normal pressure, under pressure, or under reduced pressure. The heating device is not particularly limited, but it is preferable to use a sintering furnace. Examples of the sintering furnace that can be used at this time include tunnel furnaces, roller hearth furnaces, rotary kilns, muffle furnaces, and the like.

[Cooling step] The manufacturing method of the present invention may also include a cooling step. This cooling step is a step of cooling the alumina that has undergone crystal growth in the sintering step.

The cooling rate is not particularly limited, and is preferably 1°C/hour to 1000°C/hour, more preferably 5°C/hour to 500°C/hour, and still more preferably 50°C/hour to 100°C/hour. If the cooling rate is 1°C/hour or more, the manufacturing time can be shortened, which is preferable. On the other hand, if the cooling rate is 1000° C./hour or less, the sintered container is less likely to be broken due to thermal shock and can be used for a long time, so it is preferable.

The cooling method is not particularly limited, and it can be left to cool naturally, or a cooling device can also be used.

[Post-processing steps] The manufacturing method of the present invention may also include a post-processing step. This post-processing step is a step of removing the flux. The post-treatment step can be performed after the sintering step, can also be performed after the cooling step, or can be performed after the sintering step and the cooling step. In addition, it can be repeated more than twice as necessary.

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

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

At this time, the molybdenum content can be controlled by appropriately changing the concentration, usage amount, cleaning location, cleaning time, etc. of the water, ammonia aqueous solution, sodium hydroxide aqueous solution, and acidic aqueous solution used.

In addition, as a method of high-temperature treatment, a method of raising the temperature to the sublimation point or boiling point or higher of the auxiliary solvent can be cited.

[Crushing step] Regarding the sintered product, the plate-shaped alumina particles sometimes aggregate and do not satisfy the range of the particle size suitable for the present invention. Therefore, the plate-shaped alumina particles may also be pulverized as necessary to satisfy the particle size range suitable for the present invention.

The method of pulverizing the burnt material is not particularly limited, and the prior known methods such as ball mills, jaw crushers, jet mills, disc mills, Spectromills, grinders, mixer mills, etc. can be used. The crushing method.

[Grading Steps] Regarding the plate-shaped alumina particles, in order to adjust the average particle diameter and improve the fluidity of the powder, or to suppress the increase in viscosity when blended in the binder for forming the matrix, it is preferable to perform classification treatment. The so-called "grading process" refers to the operation of grouping particles according to their size.

The classification may be either wet or dry. From the viewpoint of productivity, dry classification is preferred. In dry classification, in addition to classification using a sieve, there are also wind classification based on the difference between centrifugal force and fluid resistance. From the standpoint of classification accuracy, wind classification is preferred, and the Coanda effect can be used ( Coanda effect) airflow classifier, cyclone airflow classifier, forced vortex centrifugal classifier, semi-free vortex centrifugal classifier and other classifiers.

The pulverization step or the classification step may be performed at a desired stage including before and after the organic compound layer forming step described later. By selecting the presence or absence of these pulverization or classification, or the selection of these conditions, for example, the average particle diameter of the obtained plate-shaped alumina particles can be adjusted.

Regarding the tabular alumina particles of the present invention or the tabular alumina particles obtained by the production method of the present invention, they can easily exhibit their original properties, have better handling properties, and are used when dispersed in a dispersion medium. In this case, from the viewpoint that the dispersibility is more excellent, the one with less aggregation or the one without aggregation is preferable. In the method for producing plate-shaped alumina particles, if the pulverization step or the classification step can be omitted to obtain the less agglomerated or non-agglomerated ones, the steps are not required, and the production can be produced with high productivity and has the target excellent properties. The platy alumina is therefore preferred.

[Organic Compound Layer Formation Step] In one embodiment, the method of manufacturing the plate-shaped alumina particles may further include an organic compound layer forming step. The organic compound layer formation step is usually performed after the sintering step or the molybdenum removal step.

The method of forming the organic compound layer is not particularly limited, and a known method can be appropriately adopted. For example, a method in which plate-shaped alumina particles containing molybdenum are brought into contact with a liquid containing an organic compound and dried.

Furthermore, as the organic compound that can be used to form the organic compound layer, those described above can be used. [Example]

Next, examples are shown to further describe the present invention in detail, but the present invention is not limited to the following examples.

＜＜Production of plate-shaped alumina particles＞＞ <Example 1>

Use a mortar to mix 50 g of transitional alumina (with γ-alumina as the main component; the same below), 0.025 g of silica (manufactured by Kanto Chemical Co., Ltd.), and 67 g of molybdenum trioxide (Sun Mining Co., Ltd.) Company manufacture), 32 g of potassium carbonate (manufactured by Kanto Chemical Co., Ltd.), and 0.25 g of yttrium oxide (manufactured by Kanto Chemical Co., Ltd.) were mixed to obtain a mixture. The obtained mixture was put in a crucible, heated to 1000° C. at 5° C./min using a ceramic electric furnace, and kept at 1000° C. for 24 hours for sintering. Then, after cooling to room temperature under the condition of 5°C/min, the crucible was taken out to obtain 136 g of light blue powder.

Then, 136 g of the obtained light blue powder was washed with about 1% sodium hydroxide aqueous solution. Then, pure water washing was performed while continuing the filtration under reduced pressure. Drying was performed at 110°C to obtain 47 g of plate-shaped alumina particles containing α-alumina as light blue powder.

Table 1 shows the blending amounts (g) and blending ratios of transition alumina, silica, molybdenum trioxide, potassium carbonate, and yttrium oxide in the mixture. "Mo/Al molar ratio" means the molar ratio of the molybdenum element of the molybdenum compound to the aluminum element of the aluminum compound (molybdenum element/aluminum element). "Mo/K molar ratio" means the molar ratio of the molybdenum element of the molybdenum compound to the potassium element of the potassium compound (molybdenum element/potassium element). The " _{addition amount to Al 2} O ₃ " of the silicon compound indicates the addition rate of the silicon compound relative to the mass conversion value of aluminum atoms in the aluminum compound. The "addition amount of the yttrium compound to Al ₂ O ₃ " means the addition rate of the yttrium compound relative to the mass conversion value of aluminum atoms in the aluminum compound.

<Example 2～Example 7> In Example 1, the blending amounts of transition alumina, molybdenum trioxide, potassium carbonate, silicon dioxide, and yttrium oxide were changed as shown in Table 1, except that the same procedure as in Example 1 was carried out to produce α-alumina. Of platy alumina particles.

Furthermore, the yttrium compound was removed by washing from the plate-shaped alumina particles produced by using the yttrium compound as the metal compound in combination, but no yttrium compound was detected.

[Table 1] Example Comparative example 1 2 3 4 5 6 7 1 2 Real deployment Transition alumina Al ₂ O ₃ 50 50 80 80 65 80 50 50 - Aluminum hydroxide Al(OH) ₃ - - - - - - - - 77 Molybdenum trioxide MoO ₃ 67 67 108 108 58 150 45 67 50 Potassium Carbonate K ₂ CO ₃ 32 32 51 51 28 72 twenty two 32 - Silicon dioxide SiO ₂ 0.025 0.05 0.2 0.4 0.16 0.2 0.2 - 0.1 Yttrium oxide Y ₂ O ₃ 0.25 0.25 0.4 0.4 0.32 0.4 - 0.25 - ratio Molybdenum compound Mo/Al Moerby 0.47 0.47 0.47 0.47 0.32 0.66 0.32 0.47 0.35 Potassium compounds Mo/K Moerby 1 1 1 1 1 1 1 1 - Silicon compound Addition of Al ₂ O ₃ (mass%) 0.05 0.1 0.25 0.5 0.25 0.25 0.1 - 0.2 Yttrium compound Addition of Al ₂ O ₃ (mass%) 0.5 0.5 0.5 0.5 0.5 0.5 0 0.5 - *In the table, the actual blended value represents grams (g).

<Comparative example 1> Use a mortar to mix 50 g of transitional alumina, 67 g of molybdenum trioxide (manufactured by Sun Mining Co., Ltd.), 32 g of potassium carbonate (manufactured by Kanto Chemical Co., Ltd., deer 1 grade), and 0.25 g of yttrium oxide ( Kanto Chemical Co., Ltd.) is mixed to obtain a mixture. The obtained mixture was put in a crucible, heated to 1000° C. at 5° C./min using a ceramic electric furnace, and kept at 1000° C. for 24 hours for sintering. Then, after cooling to room temperature under the condition of 5°C/min, the crucible was taken out to obtain 136 g of light blue powder.

Then, 136 g of the obtained light blue powder was washed with about 1% sodium hydroxide aqueous solution. Then, pure water washing was performed while continuing the filtration under reduced pressure. Drying was performed at 110°C to obtain 48 g of polyhedral alumina as a light blue powder.

When the XRD measurement was performed, a sharp peak scattering derived from α-alumina appeared, and no alumina crystal system peaks other than the α crystal structure were observed, and it was confirmed that it was a plate-shaped alumina having a dense crystal structure. Furthermore, based on the result of fluorescent X-ray quantitative analysis, it was confirmed that the obtained particles contained 0.2% of molybdenum in terms of molybdenum trioxide.

＜Comparative example 2＞ Use a mortar to mix 77.0 g of aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd., with an average particle size of 10 μm), 0.1 g of silicon dioxide (manufactured by Kanto Chemical Co., Ltd., special grade) and 50.0 g of molybdenum trioxide (sun Miner Co., Ltd.) is mixed to obtain a mixture. The obtained mixture was put in a crucible, and sintered at 1100°C for 10 hours in a ceramic electric furnace. After cooling, take out the crucible to obtain 52 g of light blue powder. Use a mortar to disintegrate the obtained powder until it passes through a 106 μm sieve.

Then, 52.0 g of the obtained light blue powder was dispersed in 150 mL of 0.5% ammonia water, and the dispersed solution was stirred at room temperature (25°C ~ 30°C) for 0.5 hours, and then the ammonia water was removed by filtration , And washed with water and dried to remove the molybdenum remaining on the particle surface to obtain 51.2 g of blue powder.

When the XRD measurement was performed, a sharp peak scattering derived from α-alumina appeared, and no alumina crystal system peaks other than the α crystal structure were observed, and it was confirmed that it was a plate-shaped alumina having a dense crystal structure. Furthermore, based on the result of fluorescent X-ray quantitative analysis, it was confirmed that the obtained particles contained 1.39% molybdenum in terms of molybdenum trioxide.

This comparative example 1 is an example equivalent to Example 1 of Japanese Patent Laid-Open No. 2016-222501 listed in the form of Patent Document 2.

＜＜Evaluation＞＞ The powders produced in Examples 1 to 7 and Comparative Examples 1 to 2 were used as samples, and the following evaluations were performed. The measurement method is shown below.

[Measurement of the long diameter L of the plate-shaped alumina] The average value of 50 long diameters measured using a scanning electron microscope (SEM) is used as the long diameter L (μm).

[Measurement of Thickness D of Plate Alumina] The average value obtained by measuring the thickness of 50 pieces using a scanning electron microscope (SEM) is used as the thickness D (μm).

[Aspect Ratio L/D] The aspect ratio is calculated using the following formula. Aspect ratio=Long diameter of slab alumina L/thickness D of slab alumina

[Evaluation of the shape of tabular alumina] The shape of the alumina particles is confirmed based on the image obtained using a scanning electron microscope (SEM). In the case of 100% of the total number of alumina particles whose shape is confirmed, if 5% or more hexagonal plate-shaped particles are observed by the number, it is assumed that there is a hexagonal plate-shaped oxidation. Aluminum particles ("+", "++").

[XRD analysis] Place the sample in a 0.5 mm depth measurement sample holder, fill it flatly with a certain load, and set it on a wide-angle X-ray diffraction (XRD) device (Rint-Ultma manufactured by RIGAKU Co., Ltd.) ), measured under the conditions of Cu/Kα radiation, 40 kV/30 mA, scanning speed of 2 degrees/min, and scanning range of 10 degrees to 70 degrees.

[Analysis of the amount of Si in the surface layer of tabular alumina particles] Using an X-ray photoelectron spectroscopy (XPS) device Quantera SNM (ULVAC-PHI), the produced sample was pressed and fixed on a double-sided tape, and the composition was analyzed under the following conditions. . X-ray source: monochromatic AlKα, beam diameter 100 μmΦ, output 25 W . Measurement: area measurement (1000 μm square), n=3 . Charge correction: C1s=284.8 eV

The [Si]/[Al] obtained from the results of the XPS analysis was defined as the amount of Si in the surface layer of the plate-shaped alumina particles.

[Analysis of the amount of Si contained in tabular alumina particles] Using a fluorescent X-ray (XRF) analysis device PrimusIV (manufactured by RIGAKU Co., Ltd.), approximately 70 mg of the prepared sample was taken on a filter paper, covered with a polypropylene (PP) film, and analyzed for composition.

Let [Si]/[Al] determined from the XRF analysis result be the amount of Si in the plate-shaped alumina particles.

The amount of silicon obtained from the XRF analysis result was obtained by conversion of silicon dioxide (mass%) to 100% by mass of the tabular alumina particles.

[Analysis of the amount of Mo contained in tabular alumina] Using a fluorescent X-ray analysis device PrimusIV (manufactured by Rigaku Co., Ltd.), approximately 70 mg of the prepared sample was taken on the filter paper, covered with a PP film, and analyzed for composition.

The amount of molybdenum determined from the XRF analysis result was determined by conversion (mass %) of molybdenum trioxide with respect to 100% by mass of the tabular alumina particles.

[Crystalline Diameter] Use SmartLab (manufactured by RIGAKU Co., Ltd.) as an X-ray diffraction device, use a high-intensity/high-resolution crystal analyzer (CALSA) as a detector, and use PDXL as an analysis software To perform the measurement. At this time, the measurement method is the 2θ/θ method, and the analysis is based on the half-value width of the peaks appearing near 2θ=35.2° ([104] plane) and 2θ=43.4° ([113] plane), and using Scherer (Scherrer) formula to calculate. Furthermore, as the measurement conditions, it is assumed that the scanning speed is 0.05 degrees/min, the scanning range is 5 degrees to 70 degrees, the step is 0.002 degrees, and the standard width of the device is 0.027° (Si).

[Single crystal measurement] A single crystal X-ray structure analysis device Xtalab P200 (manufactured by Rigaku) was used to perform structural analysis of plate-shaped α alumina. The measurement conditions and various software used in the analysis are described below. . Device: Xtalab P200 manufactured by Rigaku (Detector: PIRATUS 200K). Measurement conditions: ray source Mo Kα (λ=0.7107 Å) X-ray output: 50 kV-24 mA Blowing gas: N ₂ , 25°C Camera length: 30 mm. Measurement software: CrystalClear. Image processing software: CrysAlis Pro. Structural analysis software: olex2, SHELX

The structure of the measurement results was analyzed, and the image-processed screen was visually inspected, and those with no deformation and regular arrangement were evaluated as single crystals.

[Evaluation of Brightness] The powder was visually observed and evaluated based on the following criteria. ◎...The reflection of strong light originating from the flicker of the powder can be confirmed. ×...The reflection of light originating from the flicker of the powder cannot be confirmed.

[Analysis of alpha rate] Place the prepared sample in a 0.5 mm depth measurement sample holder, fill it flatly with a certain load, and set it in a wide-angle X-ray diffraction device (Rint-Ultma manufactured by RIGAKU Co., Ltd.) ), measured under the conditions of Cu/Kα radiation, 40 kV/30 mA, scanning speed of 2 degrees/min, and scanning range of 10 degrees to 70 degrees. The α-alumina and transition alumina's strongest peak height ratio was used to obtain the α-alumina ratio.

Table 2 shows the formula (100% by mass as a whole) in terms of oxide conversion of the raw material compound and the evaluation results.

[Table 2] Oxide conversion Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Comparative example 1 Comparative example 2 formula Al ₂ O ₃ 37.07 37.07 36.93 36.89 46.80 29.61 46.84 37.08 50.1 MoO ₃ 49.68 49.67 49.85 49.80 41.76 55.52 42.16 49.69 49.8 K ₂ O 13.05 13.05 12.95 12.93 11.09 14.65 10.82 13.05 - SiO ₂ 0.02 0.04 0.09 0.18 0.12 0.07 0.19 - 0.1 Y ₂ O ₃ 0.19 0.19 0.18 0.18 0.23 0.15 - 0.19 - L[μm] 80 88 85 67 80 95 84 65 10.1 D[μm] 20 15 11 7 9 12 13 65 0.5 Aspect ratio L/D 4 6 8 10 9 8 6 1 20 Six-sided plate ++ ++ + + + ++ + - - XPS Moerby [Si]/[Al] 0.0220 0.0288 0.0439 0.0804 0.0459 0.0432 0.0224 ND 0.11 XRF Moerby [Si]/[Al] 0.00062 0.00086 0.00182 0.00303 0.00180 0.00189 0.00087 ND 0.002 XRF SiO ₂ (mass%) 0.06 0.1 0.21 0.35 0.22 0.2 0.1 ND 0.21 XRF MoO ₃ (mass%) 0.4 0.44 0.92 1.61 0.88 0.92 0.42 0.2 1.39 (104) face crystallite diameter [nm] 515 543 374 188 240 386 538 260 125 (113) face crystallite diameter [nm] 371 687 321 250 216 353 664 314 159 Single crystal ○ ○ ○ ○ ○ ○ ○ ○ ※1 Brightness ◎ ◎ ◎ ◎ ◎ ◎ ◎ X X ※1: Cannot be measured

The SEM image of the plate-shaped alumina particles of Example 1 is shown in FIG. 1.

It was confirmed that the powders obtained in Examples 1 to 7 and Comparative Examples 1 to 2 had the thickness, average particle diameter, and aspect ratio described in Table 2 above.

Regarding the particle shape, the image obtained from a plurality of SEM images from an arbitrary field of view of the sample was observed. In Table 2, among those who "have" six-sided plate-shaped particles, the ratio of the observed six-sided plate-shaped particles relative to the total number of plate-shaped alumina particles 100% is calculated as 80% or more. Expressed as "++" for those who observe 30% or more as "+". In Examples 1 to 7, hexagonal plate-shaped alumina particles were confirmed.

In the above-mentioned Examples 1 to 7, it was confirmed that as the molar ratio of [Mo]/[Al] increases, the proportion of hexagonal plate-like particles increases, and as the amount of silicon compound increases, the hexagonal The proportion of plate-shaped particles is reduced. Furthermore, it was confirmed that the addition amount range of the silicon compound to include a large number of hexagonal plate-shaped particles varies according to the [Mo]/[Al] molar ratio.

When the powders obtained in Examples 1 to 7 and Comparative Examples 1 to 2 were subjected to XRD measurement, sharp peak scattering derived from α-alumina was observed, and no oxidation other than the α crystal structure was observed. The peak of the aluminum crystal system was confirmed to be tabular alumina having a dense crystal structure. Therefore, it was confirmed that the gelatinization rate of the powders obtained in Examples 1 to 7 and Comparative Examples 1 to 2 was 90% or more.

In the above-mentioned Examples 1 to 7, since the alpha conversion rate was 90% or more, the reflection of strong light that the raw material did not have was confirmed.

Furthermore, when performing single crystal X-ray analysis, structural analysis was performed on the measurement results obtained in Examples 1 to 7, and the image processed screen was visually inspected. As a result, it was confirmed that there was no distortion and regular arrangement. It was confirmed that the particles were single crystals.

In the aforementioned Examples 1 to 7, the plate-like alumina crystals are not only α-type, but also single crystals or hexagonal plate-like crystals with a high content rate, which has strong powder-derived scintillation. The reflection of light confirmed the excellent brightness.

In addition, according to XRD analysis, in the powders obtained in Examples 1 to 7, the presence of mullite was not confirmed.

According to the comparison between Example 1 to Example 7 and Comparative Example 1 to Comparative Example 2, it can be seen that the plates of Examples 1 to 7 having a major diameter of 30 μm or more, a thickness of 3 μm or more, and an aspect ratio of 2 to 50 Compared with the alumina particles of Comparative Example 1 to Comparative Example 2 that do not satisfy this requirement, the shaped alumina particles are superior in brightness.

According to the comparison between Examples 1 to 7 and Comparative Example 1, it can be seen that _{the plate-shaped alumina particles of Examples 1 to 7 manufactured using SiO 2} as a raw material have an aspect ratio of 2 or more and are plate-shaped. _{In contrast, the aluminum oxide particles of Comparative Example 1 produced by not blending SiO 2} in the raw material had an aspect ratio of less than 2 and did not have a plate-like structure. In addition, it can be seen that in Examples 1 to 6, the input amount _{of SiO 2 as a raw material was gradually increased, thereby increasing the aspect ratio.} The plate-shaped alumina particles of Examples 1 to 7 having an aspect ratio of 2 or more are excellent in brightness.

In addition, according to the comparison between Example 1 to Example 7 and Comparative Example 2, it can be seen that the crystallite diameter of the (104) plane is 150 nm or more or the crystallite diameter of the (113) plane is 200 nm or more. The plate-shaped alumina particles of Example 7 are superior in brightness compared to the alumina particles of Comparative Example 2 which does not satisfy this requirement.

According to the comparison between Example 1 to Example 6 and Comparative Example 1 to Comparative Example 2, it can be seen that: Examples made by using Al ₂ O ₃ , MoO ₃ , K ₂ CO ₃ , SiO ₂ and Y ₂ O _{3 in the raw materials} Compared with the alumina particles of Comparative Examples 1 to 2 produced without using these compounds, the plate-shaped alumina particles of 1 to Example 6 are plate-shaped, have a large particle size and crystallite diameter, and are excellent in brightness.

Furthermore, when referring to Examples 1 to 6, it can be seen that in Examples 1 to 2 and Example 6, the amount of molybdenum oxide used as the raw material is increased, and the amount of SiO _{2 used} as the raw material is reduced. The tendency of the amount of use makes it easy to obtain hexagonal plate-shaped alumina particles, and can obtain hexagonal plate-shaped alumina particles having a larger particle size and crystallite diameter and exhibiting particularly excellent brightness.

It was confirmed by XPS analysis and XRF analysis that Si and Mo derived from these raw material compounds are present in the manufactured tabular alumina particles. In addition, Si and Mo of the raw material compounds are contained in the particles according to the amount used. Propensity.

The configurations and combinations of these in the above-described embodiments are just an example, and additions, omissions, substitutions, and other changes to the configurations can be made without departing from the scope of the present invention. In addition, the present invention is not limited by each embodiment but only by the scope of a claim. [Industrial availability]

According to the present invention, it is possible to provide a plate-shaped alumina particle that has a predetermined shape and has a higher brightness than the conventional plate-shaped alumina particle.

none

FIG. 1 is a scanning electron microscope (Scanning Electron Microscope, SEM) image of plate-shaped alumina particles obtained in Examples.

Claims (9)

A plate-shaped alumina particle having a long diameter of 30 μm or more, a thickness of 3 μm or more, an aspect ratio of 2 to 50, and containing molybdenum. The plate-shaped alumina particles according to claim 1, which further contain silicon. The plate-shaped alumina particles according to claim 2, wherein in X-ray photoelectron spectroscopy analysis, the molar ratio [Si]/[Al] of Si to Al is 0.001 or more. The plate-shaped alumina particles according to claim 1, wherein the microstructure of the (104) plane is calculated from the half-value width of the peak corresponding to the (104) plane of the diffraction peak obtained by X-ray diffraction analysis The crystal diameter is 150 nm or more. The plate-shaped alumina particles according to claim 1, wherein the microstructure of the (113) plane is calculated from the half-value width of the peak corresponding to the (113) plane of the diffraction peak obtained by X-ray diffraction analysis The crystal diameter is 200 nm or more. The plate-shaped alumina particles according to claim 1 have a hexagonal plate shape. The plate-shaped alumina particles according to claim 1, which are single crystals. A method for producing plate-shaped alumina particles, wherein the plate-shaped alumina particles are the plate-shaped alumina particles according to claim 1, wherein when the total amount of raw materials obtained by conversion of oxides is set to 100% by mass, mixing Aluminum compounds containing aluminum at 10% by mass or more in terms of Al ₂ O ₃ , molybdenum compounds containing molybdenum at 20% by mass or more in _{terms of MoO 3} , and 1 mass% or more in _{terms of K 2 O} A potassium compound containing potassium element, and silicon or a silicon compound containing silicon element less than 1% by mass _{in terms of SiO 2 are made into a mixture; and the mixture is sintered.} The method for producing plate-shaped alumina particles according to claim 8, wherein the mixture further contains an yttrium compound containing yttrium element.

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