JP6646864B2 - Method for producing plate-like alumina particles - Google Patents

Description

  The present invention relates to plate-like alumina particles having a high aspect ratio and a plate-like shape and containing molybdenum in the particles, and a method for producing the same.

  Alumina particles, which are inorganic fillers, are used for various purposes. In particular, plate-like alumina particles are used in a wide range of thermal conductive fillers, high-brightness pigments, cosmetics, abrasives, conductive powder base materials, resin film lubricants, and particularly have low cohesiveness, There is a need for high aspect ratio plate-like alumina particles having high dispersion.

  Various methods are conventionally known as a method for producing plate-like alumina particles. For example, Patent Literature 1 discloses a method of adding a mineralizer such as aluminum fluoride in a calcining step of a raw material. As a method for producing alumina particles by a hydrothermal synthesis method, for example, a method described in Patent Document 2 is known. However, it is difficult for these methods to control the particle size, particularly to produce plate-like alumina having a high aspect ratio. In addition, there is a problem of agglomeration such that a plurality of the obtained plate-like alumina particles overlap or twins are formed.

  In recent years, there have been various reports on the production of plate-like alumina particles having a controlled size and shape. For example, Patent Literature 3 discloses a plate-like member having a diameter of 0.2 to 15 μm and an aspect ratio of 15 to 50 under a hydrothermal condition of 350 ° C. or more and a pressure of 50 to 200 atm using phosphate ions as a shape controlling agent. A method for producing alumina particles is disclosed. Such an aspect ratio may not provide sufficient functions for applications such as cosmetics and high-brightness pigments, and the hydrothermal method requires high temperatures, high pressures, special equipment, and high manufacturing costs. There is.

  Patent Document 4 discloses that zinc oxide is used as a crystal controlling agent and calcined at a temperature of 1000 ° C. or more in the presence of a sulfate as a high-temperature flux to have a thickness of 0.1 to 0.5 μm and an average particle diameter of Has a thickness of 15 to 25 [mu] m and an aspect ratio of 50 to 250. Since the obtained plate-like alumina particles have a high aspect, they have excellent properties as a pearlescent pigment. However, the plate-like alumina obtained by this method tends to agglomerate. For example, after sintering, the sulfate as a flux is removed, and then stirred in a 0.5% sulfuric acid solution at a temperature of 60 ° C. for 48 hours. It is necessary to disperse the agglomeration. In addition, there is a problem that a large amount of sulfate is used as a flux, and a fired product cannot be easily taken out as a solid powder from a firing container after firing, which makes industrialization difficult.

JP-B-35-6977 JP-B-37-7750 JP-A-9-59018 Japanese Patent No. 4825264

An object of the present invention is to provide a plate-like alumina particle having a low agglomeration property and a high aspect ratio having a high dispersibility and a method for producing the same.

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, by firing an aluminum compound in the presence of a molybdenum compound and a shape controlling agent, the particle shape is a polygonal plate shape, and the thickness is reduced. 0.01 to 5 μm, the average particle diameter is 0.1 to 500 μm, the aspect ratio which is the ratio of the particle diameter to the thickness is 2 to 500, and plate-like alumina particles containing molybdenum in the particles are obtained. This led to the completion of the present invention.

  That is, the present invention is characterized in that it has a step of firing an aluminum compound in the presence of a molybdenum compound which is a fluxing agent using silicon or a compound containing a silicon atom or sodium or a compound containing a sodium atom as a shape controlling agent. It is intended to provide plate-like alumina particles.

  The present invention also provides a method for producing plate-like alumina particles, comprising: a step of reacting the aluminum compound and the molybdenum compound to form aluminum molybdate; and a step of decomposing the aluminum molybdate to obtain plate-like alumina particles. Is what you do.

  The present invention also provides a method for producing plate-like alumina particles, wherein the molar ratio of the aluminum atom in the aluminum compound to the molybdenum atom in the molybdenum compound is in the range of molybdenum / aluminum = 0.01 to 3.0. Is what you do.

  According to the present invention, plate-like alumina particles containing molybdenum in particles having high dispersibility and a high aspect ratio can be obtained. When the plate-like alumina particles are used as a thermally conductive filler, a high-brightness pigment, a cosmetic, an abrasive, a conductive powder base material, or a lubricant for a resin film, the effect can be maximized.

By adjusting the compounding ratio of the aluminum compound, the molybdenum compound, and the shape control agent used as the precursor, and the type and addition method of the shape control agent, the average particle diameter, thickness, and aspect ratio of the obtained plate-like alumina particles And the like can be controlled, and plate-like alumina particles having a particularly high aspect ratio can be obtained. Further, by using a molybdenum compound as a fluxing agent, the obtained plate-like alumina particles are alumina containing molybdenum in the particles, and have excellent self-shape and excellent dispersibility.

  In addition, the production method of the present invention is a simple step of simply baking solid powders together, and does not involve the discharge of solvents and waste liquids, expensive equipment, complicated processes, post-treatments, etc., and does not involve an environmental burden. Manufacturing method.

  In addition, ordinary alumina has a neutral isoelectric point at the zeta potential, and has a problem in dispersibility. However, the plate-like alumina obtained in the present invention is excellent in dispersibility because the isoelectric point of the zeta potential is shifted to the acidic side as compared with normal alumina by containing molybdenum.

3 is a scanning electron micrograph of the plate-like alumina particles obtained in Example 1. 3 is a powder XRD chart of the plate-like alumina particles obtained in Example 1. 6 is a scanning electron micrograph of the plate-like alumina particles obtained in Example 3. 9 is a scanning electron micrograph of the plate-like alumina particles obtained in Example 4. 9 is a scanning electron micrograph of the plate-like alumina particles obtained in Example 6. 9 is a scanning electron micrograph of particles of plate-like alumina obtained in Example 7.

Hereinafter, embodiments for carrying out the present invention will be described in detail.

<Plate alumina particles>
The plate-like alumina particles according to this embodiment include molybdenum in the particles and have a polygonal plate shape. Further, as long as the effects of the present invention are not impaired, impurities from a raw material or a shape controlling agent may be included. The plate-like alumina particles may further contain an organic compound or the like.

“Plate shape” in the present invention indicates that the aspect ratio obtained by dividing the average particle diameter by the thickness is 2 or more. In the present specification, a value measured using a scanning electron microscope (SEM) is adopted as the “thickness of plate-like alumina particles”. Further, “particle diameter of plate-like alumina particles” means an arithmetic mean value of a maximum length and a minimum length of a distance between two points on a contour line of the plate, and the value is a scanning electron microscope ( (SEM) shall be used. The value of the “average particle diameter” means a value obtained by measuring the particle diameter of arbitrary 100 plate-like alumina particles from an image obtained by a scanning electron microscope (SEM).

  The plate-like alumina particles preferably have a thickness of 0.01 to 5 μm, an average particle diameter of 0.1 to 500 μm, and an aspect ratio, which is a ratio of the particle diameter to the thickness, of 2 to 500. It is preferable that the aspect ratio of the plate-like alumina particles is 2 or more, since the plate-like alumina particles can have two-dimensional compounding characteristics. If the aspect ratio of the plate-like alumina particles is 500 or less, the mechanical strength is excellent. More preferably, the thickness is 0.03 to 3 μm, the average particle diameter is 0.5 to 100 μm, and the aspect ratio, which is the ratio of the particle diameter to the thickness, is 10 to 300. An aspect ratio of from 10 to 300 is preferable because the resulting pigment has high brightness.

In the plate-like alumina particles of the present invention, the thickness thereof, the average particle diameter, the aspect ratio, and the like, the molybdenum compound, the aluminum compound, and the use ratio of the shape control agent, the type of the shape control agent, the shape control agent and the aluminum compound Can be controlled by selecting the existence state of

The plate-like alumina particles according to the present invention may be obtained based on any production method as long as molybdenum is contained in the particles, but the aspect ratio is higher and the dispersibility is higher. It is preferable to obtain by firing an aluminum compound in the presence of a molybdenum compound and a shape controlling agent, from the viewpoint of excellent and more excellent productivity. That is, in the plate-like alumina particles according to the present invention, when the molybdenum compound reacts with the aluminum compound at a high temperature to form aluminum molybdate, the aluminum molybdate further decomposes to alumina and molybdenum oxide at a higher temperature. In addition, the molybdenum compound is more easily obtained by incorporating it into the plate-like alumina particles. Molybdenum oxide can be sublimated, recovered, and reused. Hereinafter, this manufacturing method is referred to as a flux method. This flux method will be described later in detail.

The shape controlling agent plays an important role in plate crystal growth. In the molybdenum oxide flux method generally performed, molybdenum oxide is selectively adsorbed on the [113] plane of the α crystal of alumina, and the crystal component is hardly supplied to the [113] plane. Therefore, polyhedral particles based on a hexagonal double pyramid are formed. The present invention uses a shape controlling agent to suppress the selective adsorption of molybdenum oxide, which is a flux agent, on the [113] plane. Can be formed. By using a molybdenum compound as a fluxing agent, plate-like alumina particles containing molybdenum and having a high α crystallization ratio, particularly having an α crystallization ratio of 90% or more, can be formed more easily.

By utilizing molybdenum, the plate-like alumina particles can have excellent dispersibility, mechanical strength, and high thermal conductivity because alumina has a high α crystallinity and has an automorphic shape.

Further, since the plate-like alumina particles of the present invention contain molybdenum, the isoelectric point of the zeta potential is shifted to the acidic side as compared with ordinary alumina, so that the dispersibility is excellent. In addition, it may be possible to use the properties of molybdenum contained in the plate-like alumina particles for applications of oxidation reaction catalysts and optical materials.

[alumina]
`` Alumina '' according to the present invention is aluminum oxide, is not particularly limited as long as molybdenum is included in the particles, for example, γ, δ, θ, κ, even transition alumina of various crystal forms such as δ, Alternatively, alumina hydrate may be contained in the transition alumina, but it is basically preferable to be in the α-crystal form in view of more excellent mechanical strength or thermal conductivity.

[molybdenum]
Molybdenum has a catalytic function and an optical function. Further, by utilizing molybdenum, plate-like alumina particles having a high aspect ratio and excellent dispersibility can be produced in a production method as described later.

The molybdenum is not particularly limited, but includes molybdenum metal, molybdenum oxide, a partially reduced molybdenum compound, and the like, in addition to molybdenum metal.

  The form in which molybdenum is contained is not particularly limited, and may be contained in a form that adheres to the surface of the plate-like alumina particles, or may be contained in a form that is partially substituted with aluminum in the alumina crystal structure. Or a combination of these.

  The content of molybdenum in the plate-like alumina particles of the present invention is preferably 10% by mass or less in terms of molybdenum trioxide, and more preferably by adjusting the firing temperature, the firing time, and the sublimation rate of the molybdenum compound. Is 0.001 to 8% by mass, and more preferably 0.01 to 5% by mass or less. When the content of molybdenum is 10% by mass or less, it is preferable because the quality of the α single crystal of alumina is improved.

[Organic compound]
In one embodiment, the plate-like alumina particles may include an organic compound. The organic compound exists on the surface of the plate-like alumina particles and has a function of adjusting the surface properties of the plate-like alumina particles. For example, plate-like alumina particles containing an organic compound on the surface improve affinity with a resin, so that the function of the plate-like alumina particles as a filler can be maximized.

  Organic compounds include, but are not limited to, organic silanes, phosphonic acids, and polymers.

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

As the phosphonic acid, for example, 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 dodecylbenzenesulfonic 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, polycyclohexyl (meth) acrylate, polyt-butyl (meth) acrylate, polyglycidyl (meth) Acrylate and polypentafluoropropyl (meth) acrylate; and polymers such as general-purpose polystyrene, polyvinyl chloride, polyvinyl acetate, epoxy resin, polyester, polyimide, and polycarbonate.

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

  The content form of the organic compound is not particularly limited, and may be connected to alumina by a covalent bond, or may be coated with alumina.

  The content of the organic compound is preferably 20% by mass or less, more preferably 10 to 0.01% by mass, based on the mass of the plate-like alumina particles. When the content of the organic compound is 20% by mass or less, it is preferable because physical properties derived from the plate-like alumina particles can be easily obtained.

<Method for producing plate-like alumina particles>
The method for producing the plate-like alumina particles is not particularly limited, and a known technique can be appropriately applied.However, from the viewpoint of suitably controlling alumina having a high α crystallization ratio at a relatively low temperature, preferably A production method by a flux method using a molybdenum compound can be applied.

  More specifically, a preferred method for producing plate-like alumina particles includes a step of firing an aluminum compound in the presence of a molybdenum compound and a shape controlling agent.

[Firing step]
The firing step is a step of firing the aluminum compound in the presence of the molybdenum compound and the shape controlling agent.

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

  According to the flux method described in detail below, since the shape of the raw material aluminum compound is hardly reflected in the shape of the plate-like alumina particles of the present invention, for example, there is a spherical shape, an amorphous shape, and an aspect. Any structure (wire, fiber, ribbon, tube, etc.), sheet, etc. can be suitably used.

  Similarly, since the particle diameter of the aluminum compound is hardly reflected on the plate-like alumina particles of the present invention according to the flux method described in detail below, the solid of the aluminum compound from several nm to several hundred μm is preferably used. Can be used.

  The specific surface area of the aluminum compound is not particularly limited. Since the molybdenum compound works effectively, it is preferable that the specific surface area is large. However, any material having any specific surface area can be used as a raw material by adjusting the firing conditions and the amount of the molybdenum compound used.

  Further, the aluminum compound may be composed of only the aluminum compound or a composite of the aluminum compound and the organic compound. For example, an organic / inorganic composite obtained by modifying an aluminum compound with an organic silane, an aluminum compound composite on which a polymer is adsorbed, or the like can be suitably used. When these composites are used, the content of the organic compound is not particularly limited, but from the viewpoint of efficiently producing plate-like alumina particles, the content is preferably 60% by mass or less, and 30% by mass or less. It is more preferable that the content is not more than mass%.

(Shape control agent)
In order to form the plate-like alumina particles of the present invention, it is essential to use a shape controlling agent. The shape controlling agent plays an important role in plate growth of alumina by firing the alumina compound in the presence of the molybdenum compound.

The state of the shape controlling agent is not particularly limited as long as it can contact the aluminum compound. For example, a physical mixture of a shape controlling agent and an aluminum compound, a complex in which the shape controlling agent is uniformly or locally present on or inside the aluminum compound, and the like can be suitably used.

Further, the shape controlling agent may be added to the aluminum compound, but may be contained as an impurity in the aluminum compound.

The type of the shape controlling agent is not particularly limited as long as molybdenum oxide can suppress selective adsorption to the [113] plane of α-alumina and form a plate-like form during high-temperature firing in the presence of a molybdenum compound. . It is preferable to use a metal compound other than a molybdenum compound and an aluminum compound in terms of higher aspect ratio, more excellent dispersibility, and more excellent productivity, silicon or a compound containing a silicon atom or a compound containing sodium or a sodium atom. It is more preferable to use

The silicon or the compound containing a silicon atom is not particularly limited, and a known compound can be used. Specific examples of silicon or a compound containing a silicon atom include metal silicon, organic silane, silicon resin, silica fine particles, silica gel, mesoporous silica, SiC, mullite, etc .; artificial silicon compounds, such as biosilica. Can be Among these, it is preferable to use an organic silane, a silicon resin, and silica fine particles from the viewpoint of more uniformly forming and mixing with an aluminum compound. Note that silicon or a compound containing a silicon atom may be used alone or in combination of two or more.

  The shape of silicon or a compound containing a silicon atom is not particularly limited, and for example, a sphere, an amorphous, a structure having an aspect (a wire, a fiber, a ribbon, a tube, or the like), a sheet, or the like can be preferably used.

  The amount of silicon or a compound containing a silicon atom is not particularly limited, but is preferably 0.0001 to 1 mol, more preferably 0.001 to 0.5 mol, per 1 mol of aluminum metal in the aluminum compound. Is more preferable. It is preferable that the amount of silicon or a compound containing a silicon atom be in the above range because plate-like alumina particles having a high aspect ratio and excellent dispersibility can be easily obtained.

The sodium or a compound containing a sodium atom is not particularly limited, and a known compound can be used. Specific examples of sodium or a compound containing a sodium atom include sodium carbonate, sodium molybdenum, sodium oxide, sodium sulfate, sodium hydroxide, sodium nitrate, sodium chloride, and metallic sodium. Of these, sodium carbonate, sodium molybdate, sodium oxide, and sodium sulfate are preferably used from the viewpoint of industrial availability and ease of handling. Note that sodium or a compound containing a sodium atom may be used alone or in combination of two or more.

The shape of sodium or the compound containing a sodium atom is not particularly limited, and for example, spherical, amorphous, aspect-like structures (wires, fibers, ribbons, tubes, and the like), sheets, and the like can be suitably used.

The amount of sodium or the compound containing a sodium atom is not particularly limited, but is preferably 0.0001 to 2 mol, and more preferably 0.001 to 1 mol, per 1 mol of aluminum metal in the aluminum compound. More preferred. When the amount of sodium or the compound containing a sodium atom is in the above range, plate-like alumina particles having a high aspect ratio and excellent dispersibility are easily obtained, which is preferable.

(Molybdenum compound)
As will be described later, the molybdenum compound has a flux function for α-crystal growth of alumina at a relatively low temperature.
The molybdenum compound is not particularly limited, molybdenum oxide, a compound containing molybdenum metal acid radical anions consisting of binding with oxygen (MoO _x ^n-) and the like.

The compound containing the acid radical anion (MoO _x ^n-), is not particularly limited, molybdate, sodium molybdate, potassium molybdate, lithium _{molybdate, H 3 PMo 12 O 40,} H 3 SiMo 12 O 40, NH ₄ Mo ₇ O ₁₂ , molybdenum disulfide and the like can be mentioned.

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

  Of the above molybdenum compounds, it is preferable to use molybdenum oxide from the viewpoint of cost. Further, the above molybdenum compounds may be used alone or in combination of two or more.

  The amount of the molybdenum compound used is not particularly limited, but is preferably 0.01 to 3.0 mol, and more preferably 0.03 to 0.7 mol, per mol of the aluminum metal in the aluminum compound. More preferred. When the amount of the molybdenum compound used is in the above range, plate-like alumina particles having a high aspect ratio and excellent dispersibility are easily obtained, which is preferable.

(Fired)
The plate-like alumina particles of the present invention can be obtained, for example, by firing an aluminum compound in the presence of a molybdenum compound and a shape controlling agent. As described above, this manufacturing method is called a flux method. When the aluminum compound is calcined in the presence of the molybdenum compound, the molybdenum compound reacts with the aluminum compound at a high temperature to form aluminum molybdate, which is further decomposed into alumina and molybdenum oxide at a higher temperature, By growing α-alumina plate-like crystals in the presence of the shape controlling agent, plate-like alumina particles can be easily obtained. The obtained plate-like alumina particles contain molybdenum in the particles, and have a polygonal plate shape, a thickness of 0.01 to 5 μm, an average particle diameter of 0.1 to 500 μm, and The aspect ratio, which is the ratio of the particle diameters, is 2 to 500.

  The firing method is not particularly limited, and can be performed by a known and commonly used method. If the firing temperature exceeds 700 ° C., the aluminum compound reacts with the molybdenum compound to form aluminum molybdate. Further, when the firing temperature is 900 ° C. or higher, aluminum molybdate is decomposed, and plate-like alumina particles are formed by the action of the shape control agent. Further, the plate-like alumina particles are obtained by incorporating a molybdenum compound into the aluminum oxide particles when the aluminum molybdate is decomposed to become alumina and molybdenum oxide.

  Further, when firing, the states of the aluminum compound, the shape controlling agent, and the molybdenum compound are not particularly limited, as long as the molybdenum compound and the shape controlling agent are present in the same space where they can act on the aluminum compound. Specifically, simple mixing of mixing a powder of a molybdenum compound, a shape controlling agent and an aluminum compound, mechanical mixing using a pulverizer or the like, or mixing using a mortar or the like may be used. Alternatively, the mixing may be performed in a wet state.

There is no particular limitation on the conditions of the firing temperature, and the firing temperature is appropriately determined depending on the average particle diameter, aspect ratio, dispersibility, etc. of the target plate-like alumina particles of the present invention. Normally, the firing temperature may be 900 ° C. or higher, which is the highest temperature at which aluminum molybdate (Al ₂ (MoO ₄ ) ₃ ) is decomposed.

  Generally, in order to control the shape of α-alumina obtained after firing, it is necessary to perform high-temperature firing at 2000 ° C. or higher, which is close to the melting point of α-alumina, but from the viewpoint of burden on the firing furnace and fuel cost, There are major issues for industrial use.

  The production method of the present invention can be carried out even at a high temperature such as exceeding 2000 ° C., but even at a temperature much lower than the melting point of α-alumina of 1600 ° C. or less, regardless of the shape of the precursor, α Α-alumina having a plate-like shape having a high crystallization rate and a high aspect ratio can be formed.

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

  Regarding the firing time, it is preferable to raise the temperature to the predetermined maximum temperature in a range of 15 minutes to 10 hours, and to hold the temperature at the maximum firing temperature in a range of 5 minutes to 30 hours. In order to efficiently form the plate-like alumina particles, it is more preferable that the firing holding time is about 10 minutes to 15 hours.

  The firing atmosphere is not particularly limited as long as the effects of the present invention can be obtained.However, for example, an oxygen-containing atmosphere such as air or oxygen, or an inert atmosphere such as nitrogen or argon is preferable, and in consideration of cost. Is more preferably an air atmosphere.

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

[Molybdenum removal process]
The method for producing plate-like alumina particles may further include a molybdenum removing step of removing at least a portion of molybdenum as needed after the firing step.

  As described above, since molybdenum involves sublimation during firing, the content of molybdenum contained in the plate-like alumina particles can be controlled by controlling the firing time, the firing temperature, and the like.

  Molybdenum can adhere to the surface of the plate-like alumina particles. The molybdenum can be removed by washing with water, an aqueous ammonia solution, an aqueous sodium hydroxide solution, or an acidic aqueous solution.

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

[Organic compound layer forming step]
In one embodiment, the method for producing plate-like alumina particles may further include an organic compound layer forming step. The organic compound layer forming step is usually performed after the firing step or after the molybdenum removing step.

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

  As the organic compound that can be used for forming the organic compound layer, those described above can be used.

  Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. Unless otherwise specified, “%” represents “% by mass”.

[Shape analysis of plate-like alumina particles by scanning electron microscope]
The sample was fixed to a sample support with double-sided tape, and it was observed with a Keyence surface observation device VE-9800.

[Composition analysis of plate-like alumina particles by X-ray fluorescence]
About 100 mg of the sample was placed on filter paper, covered with a PP film, and subjected to X-ray fluorescence measurement (ZSX100e / Rigaku Corporation).

[Analysis by X-ray diffraction (XRD) method]
The prepared sample is placed on a holder for measurement sample, and set on a wide-angle X-ray diffractometer [Rint-Ultma, manufactured by Rigaku Corporation], Cu / Kα ray, 40 kV / 30 mA, scan speed 1.0 ° / min. The measurement was performed under the conditions of a scanning range of 5 to 80 °.

[Firing method]
The firing was performed in a firing furnace apparatus equipped with an AMF-2P type temperature controller for a ceramic electric furnace ARF-100K manufactured by Asahi Rika Seisakusho Co., Ltd.

[Measurement of zeta potential]
Using a Zetasizer Nano ZSP (Malvern), the zeta potential was measured.
After diluting the sample 3000 times with pure water, pH titration was performed using 0.1N HCl, 0.01N HCl, and 0.1N NaOH.

Example 1 <Production of plate-like alumina particles>
5 g of activated alumina (manufactured by Wako Pure Chemical Industries, Ltd., average particle size: 45 μm) and 0.01 g of silica nanoparticles (KE-P10, manufactured by Nippon Shokubai Co., average particle size: 0.1 to 0.2 μm) And 5 g of molybdenum trioxide (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed in a mortar to obtain 10.01 g of the mixture. The obtained mixture was put into a crucible and fired in a ceramic electric furnace at 1100 ° C. for 3 hours. Most of the molybdenum oxide sublimated, and after the temperature was lowered, the crucible was taken out to obtain 5.1 g of a blue powder.

  The obtained powder was confirmed by SEM observation to have a polygonal shape, a thickness of 500 nm, an average particle diameter of 10 μm, and an aspect ratio of 20 (FIG. 1). Further, no twins or aggregates in which a plurality of plates overlapped were observed by SEM observation, and it was confirmed that the particles were plate-shaped particles suggesting excellent dispersibility. Further, when XRD measurement was performed, a sharp scattering peak derived from α-alumina appeared, and no alumina crystal system peak other than the α crystal structure was observed (FIG. 2). From the results of the fluorescent X-ray quantitative analysis, it was confirmed that the obtained particles contained 1.38% of molybdenum in terms of molybdenum trioxide.

In addition, 4 g of the obtained blue powder is dispersed in 4 mL of 10% aqueous ammonia, and the dispersion is stirred at room temperature (25 to 30 ° C.) for 3 hours. After removing the aqueous ammonia by filtration, washing with water and drying are performed. As a result, molybdenum remaining on the particle surface was removed to obtain 3.9 g of powder. The obtained powder was subjected to fluorescent X-ray quantitative evaluation measurement. As a result, it was confirmed that the amount of molybdenum in the powder was 0.84% by mass in terms of molybdenum trioxide, and the particles were alumina particles containing molybdenum. did.
The zeta potential was measured, and it was found that the isoelectric point of the obtained alumina particles was pH 5.3.

Example 2 <Production of plate-like alumina particles>
The experiment was performed in the same manner as in Example 1 except that the amount of the silica nanoparticles used was changed to 0.5 g, and 5.4 g of a blue powder was obtained. The obtained powder was confirmed by SEM observation to have a polygonal shape, a thickness of 250 nm, an average particle diameter of 8 μm, and an aspect ratio of 32. Further, no twins or aggregates in which a plurality of plates overlapped were observed by SEM observation, and it was confirmed that the particles were plate-shaped particles suggesting excellent dispersibility. Further, when the XRD measurement was performed, a sharp scattering peak derived from α-alumina appeared, and no alumina crystal system peak other than the α crystal structure was observed. From the results of the fluorescent X-ray quantitative analysis, it was confirmed that the obtained particles contained 1.04% of molybdenum in terms of molybdenum trioxide. Further, after removing molybdenum remaining on the particle surface in the same manner as in Example 1, the amount of molybdenum was 0.93% by mass in terms of molybdenum trioxide in quantitative X-ray fluorescence evaluation measurement, and the particle contained molybdenum. It was confirmed that the particles were alumina particles.
Also, the zeta potential was measured, and it was found that the isoelectric point of the obtained alumina particles was pH 5.5.

Example 3 <Production of plate-like alumina particles>
An experiment was conducted in the same manner as in Example 1 except that the amount of molybdenum trioxide used was changed to 1.25 g, and 5.0 g of a blue powder was obtained. SEM observation confirmed that the obtained powder had a polygonal shape, a thickness of 250 nm, an average particle diameter of 20 μm, and an aspect ratio of 80 (FIG. 3). Further, no twins or aggregates in which a plurality of plates overlapped were observed by SEM observation, and it was confirmed that the particles were plate-shaped particles suggesting excellent dispersibility. Further, when the XRD measurement was performed, a sharp scattering peak derived from α-alumina appeared, and no alumina crystal system peak other than the α crystal structure was observed. From the result of the fluorescent X-ray quantitative analysis, it was confirmed that the obtained particles contained 0.59% of molybdenum in terms of molybdenum trioxide. Further, after removing molybdenum remaining on the particle surface in the same manner as in Example 1, the amount of molybdenum was 0.50% by mass in terms of molybdenum trioxide in quantitative X-ray fluorescence evaluation measurement, and the particle contained molybdenum. It was confirmed that the particles were alumina particles.
Further, the zeta potential was measured, and it was found that the isoelectric point of the obtained alumina particles was pH 5.4.

Example 4 <Production of plate-like alumina particles>
20 g of boehmite (manufactured by Daimei Chemical Co., Ltd., average particle size: 1 μm) containing 0.04% of silicon and 2 g of molybdenum trioxide (manufactured by Wako Pure Chemical Industries, Ltd.) are mixed in a mortar, and 25 g of the mixture is mixed. Obtained. The obtained mixture was put in a crucible and fired in a ceramic electric furnace at 1100 ° C. for 10 hours. Most of the molybdenum oxide sublimated, and after cooling, the crucible was taken out to obtain 17.0 g of a blue powder.

The obtained powder was confirmed by SEM observation to have a polygonal shape, a thickness of 600 nm, an average particle diameter of 30 μm, and an aspect ratio of 50 (FIG. 4). Further, no twins or aggregates in which a plurality of plates overlapped were observed by SEM observation, and it was confirmed that the particles were plate-shaped particles suggesting excellent dispersibility. Further, when the XRD measurement was performed, a sharp scattering peak derived from α-alumina appeared, and no alumina crystal system peak other than the α crystal structure was observed. Further, from the result of the fluorescent X-ray quantitative analysis, it was confirmed that the obtained particles contained 0.50% of molybdenum in terms of molybdenum trioxide. Further, after removing the molybdenum remaining on the particle surface in the same manner as in Example 1, the amount of molybdenum was 0.43% by mass in terms of molybdenum trioxide in a fluorescent X-ray quantitative evaluation measurement, and the particle contained molybdenum. It was confirmed that the particles were alumina particles.
Also, the zeta potential was measured, and it was found that the isoelectric point of the obtained alumina particles was pH 5.5.

Example 5 <Production of plate-like alumina particles>
20 g of aluminum hydroxide containing 0.31% by weight of Na ₂ O (manufactured by Showa Denko KK, average particle size 0.9 μm) and 1.5 g of molybdenum trioxide (manufactured by Wako Pure Chemical Industries, Ltd.) Mixing in a mortar gave 21.5 g of the mixture. The obtained mixture was put in a crucible and fired in a ceramic electric furnace at 1100 ° C. for 10 hours. Most of the molybdenum oxide sublimated, and after the temperature was lowered, the crucible was taken out to obtain 13 g of a blue powder.

It was confirmed by SEM observation that the obtained powder had a polygonal shape, a thickness of 1.5 μm, an average particle diameter of 3.5 μm, and an aspect ratio of 2.3. Further, since no twins or aggregates in which a plurality of plates overlapped were observed by SEM observation, it was confirmed that the particles were plate-shaped particles suggesting excellent dispersibility. Further, when the XRD measurement was performed, a sharp scattering peak derived from α-alumina appeared, and no alumina crystal system peak other than the α crystal structure was observed. Further, from the result of the fluorescent X-ray quantitative analysis, it was confirmed that the obtained particles contained 1.39% of molybdenum in terms of molybdenum trioxide. After the molybdenum remaining on the particle surface was removed in the same manner as in Example 1, the amount of molybdenum was 0.90% by mass in terms of molybdenum trioxide, and the particle contained molybdenum in X-ray fluorescence quantitative evaluation measurement. It was confirmed that the particles were alumina particles.
The zeta potential was measured, and it was found that the isoelectric point of the obtained alumina particles was pH 5.6.

Example 6 <Production of plate-like alumina particles>
30 g of aluminum hydroxide (manufactured by Showa Denko KK, average particle size 4.0 μm, SiO ₂ content 0.01% by weight) treated with acrylic silane and 19 g of molybdenum trioxide (manufactured by Wako Pure Chemical Industries, Ltd.) Was mixed in a mortar to obtain 49.5 g of the mixture. The obtained mixture was put in a crucible and fired in a ceramic electric furnace at 1100 ° C. for 10 hours. Most of the molybdenum oxide sublimated, and after cooling, the crucible was taken out to obtain 19.3 g of a blue powder.

The obtained powder was confirmed by SEM observation to have a thickness of 400 nm, an average particle diameter of 8 μm, and an aspect ratio of 20 (FIG. 5). Further, no twins or aggregates in which a plurality of plates overlapped were observed by SEM observation, and it was confirmed that the particles were plate-shaped particles suggesting excellent dispersibility. Further, when XRD measurement was performed, a sharp scattering peak derived from α-alumina appeared, and no alumina crystal system peak other than the α crystal structure was observed. From the results of the fluorescent X-ray quantitative analysis, it was confirmed that the obtained particles contained 0.66% of molybdenum in terms of molybdenum trioxide. After the molybdenum remaining on the particle surface was removed in the same manner as in Example 1, the amount of molybdenum was 0.57% by mass in terms of molybdenum trioxide as determined by quantitative X-ray fluorescence evaluation measurement, and the particles contained molybdenum. It was confirmed that the particles were alumina particles.
Also, the zeta potential was measured, and it was found that the isoelectric point of the obtained alumina particles was pH 5.6.

Example 7 <Production of plate-like alumina particles>
4 g of aluminum hydroxide (manufactured by Showa Denko KK, average particle size 1 μm), 0.5 g of sodium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.), and 1 g of molybdenum oxide (manufactured by Wako Pure Chemical Industries, Ltd.) Was mixed in a mortar to obtain 5.5 g of the mixture. The obtained mixture was put into a crucible and fired in a ceramic electric furnace at 1100 ° C. for 5 hours. After cooling, the crucible was taken out and washed with water to obtain 2.1 g of powder.

Observation by SEM confirmed that the obtained powder did not contain agglomerates, had a hexagonal plate shape, a thickness of 1.5 μm, an average particle diameter of 4 μm, and an aspect ratio of 2.7 (FIG. 6). Further, when the XRD measurement was performed, a sharp scattering peak derived from α-alumina appeared, and no alumina crystal system peak other than the α crystal structure was observed. Further, from the result of the fluorescent X-ray quantitative analysis, it was confirmed that the obtained particles contained molybdenum at 0.22% in terms of molybdenum trioxide. Further, after removing the molybdenum remaining on the particle surface in the same manner as in Example 1, the amount of molybdenum was 0.2% by mass in terms of molybdenum trioxide, and the particle contained molybdenum in quantitative X-ray fluorescence evaluation measurement. It was confirmed that the particles were alumina particles.
Also, the zeta potential was measured, and it was found that the isoelectric point of the obtained alumina particles was pH 5.5.

Example 8 <Production of plate-like alumina particles>
An experiment was performed in the same manner as in Example 7, except that the amount of sodium carbonate used was changed to 1 g. After cooling, the crucible was taken out and washed with water to obtain 2.6 g of powder. The obtained powder was confirmed by SEM observation to be free of aggregates, having a thickness of 50 nm, an average particle diameter of 600 nm, and an aspect ratio of 12. Further, when XRD measurement was performed, a scattering peak derived from transition alumina appeared in addition to α-alumina, and it was confirmed that the α crystal structure and the transition alumina crystal structure coexist. Also, from the result of the fluorescent X-ray quantitative analysis, it was confirmed that the obtained particles contained 0.16% of molybdenum in terms of molybdenum trioxide. Further, after removing the molybdenum remaining on the particle surface in the same manner as in Example 1, the amount of molybdenum was 0.15% by mass in terms of molybdenum trioxide in the fluorescent X-ray quantitative evaluation measurement, and the particle contained molybdenum. It was confirmed that the particles were alumina particles.
The zeta potential was measured, and it was found that the isoelectric point of the obtained alumina particles was pH 5.4.

Example 9 <Production of plate-like alumina particles>
20 g of aluminum hydroxide (average particle size, <1 μm) and 6.5 g of sodium molybdate (manufactured by Wako Pure Chemical Industries, Ltd.) were mixed in a mortar to obtain 26.5 g of a mixture. The obtained mixture was put in a crucible and fired in a ceramic electric furnace at 1100 ° C. for 10 hours. Most of the molybdenum oxide sublimated, and after cooling, the crucible was taken out and washed with water to obtain 12.5 g of powder. The obtained powder was confirmed by SEM observation to be plate-shaped particles having a thickness of 900 nm, an average particle diameter of 13 μm, and an aspect ratio of 14.4, without any agglomerates. Further, after removing the molybdenum remaining on the particle surface in the same manner as in Example 1, the amount of molybdenum was 0.2% by mass in terms of molybdenum trioxide, and the particle contained molybdenum in quantitative X-ray fluorescence evaluation measurement. It was confirmed that the particles were alumina particles.
The zeta potential was measured, and it was found that the isoelectric point of the obtained alumina particles was pH 5.7.

Comparative Example 1
An experiment was performed in the same manner as in Example 1 except that molybdenum trioxide was not used. After cooling, the crucible was taken out to obtain 39 g of white powder. The obtained powder was found to be alumina particles having an amorphous particle diameter of 45 μm similar to that of the precursor by SEM observation. Since molybdenum trioxide as a fluxing agent was not used, plate-like alumina particles could not be formed.
The zeta potential was measured, and it was found that the isoelectric point of the obtained alumina particles was pH 7.4.

  The plate-like alumina having a high aspect ratio of the present invention is not agglomerated and the isoelectric point is shifted to acidic, so that excellent dispersibility can be expected. It can be suitably used for high-gloss pigments, lubricants, conductive powder base materials, ceramic materials, and the like.

Claims (2)

In the presence of a molybdenum compound and a shape controlling agent, obtained by calcining an aluminum compound, a method for producing plate-like alumina particles characterized by containing molybdenum in the particles ,
The shape controlling agent is silicon or a compound containing a silicon atom, or sodium or a compound containing a sodium atom,
When the shape controlling agent is silicon or a compound containing a silicon atom, the amount used is 0.0001 to 1 mol, relative to 1 mol of the aluminum atom metal of the aluminum compound, or the shape controlling agent is sodium or When the compound contains a sodium atom, the amount used is 0.001 to 2 moles per mole of the aluminum atom metal of the aluminum compound.
Molybdenum compound is a compound containing molybdenum oxide or acid radical anion (MoOx ^n-), the amount used relative to aluminum atoms metal 1 mole of aluminum compound is 0.001 to 3.0 mol,
A method for producing plate-like alumina particles, wherein firing is performed in an oxygen-containing atmosphere or an inert atmosphere at a firing temperature of 700 to 1600 ° C., a heating time of 15 minutes to 10 hours, and a holding time at the highest firing temperature of 5 minutes to 30 hours . A step of reacting the aluminum compound and the molybdenum compound at a temperature higher than 700 ° C. and lower than 900 ° C. to form aluminum molybdate;
The step of decomposing the aluminum molybdate at 900 ° C. or higher to obtain plate-like alumina particles containing molybdenum in the particles,
The method for producing plate-like alumina particles according to claim 1, comprising: