Magnesium oxide granules and production method therefor

Abstract

The purpose of the present invention is to provide magnesium oxide granules having high particle redispersibility and excellent handleability, and a production method therefor.　The present invention is magnesium oxide granules composed of magnesium oxide particles having a magnesium oxide purity of 99.9 mass% or higher, wherein the strength of the granules as measured in accordance with JIS R 1639-5:2007 is 0.10-1.50 MPa.

Description

Magnesium oxide granules and method for producing the same

[0001] This invention relates to magnesium oxide granules and a method for producing the same.

[0002] Magnesium oxide possesses excellent properties such as heat resistance, thermal conductivity, and electrical insulation, and is widely used in various fields, including as a filler, refractory material, ceramic material, target material, and catalyst. It is also used in pharmaceuticals, nutritional supplements, and food additives, such as laxatives and mineral supplements.

[0003] For example, in filler applications, magnesium oxide is mixed with resins and other materials to improve thermal conductivity and heat resistance, and studies have been conducted to improve the packing and dispersibility of magnesium oxide in resins and other materials. Patent Document 1 discloses that the dispersibility of magnesium oxide in resins and rubbers can be improved by controlling the average particle size, BET specific surface area, and sieve residue with a mesh size of 45 μm. Patent Document 2 discloses that the packing rate in resins can be increased by using magnesium oxide powder having two peaks in its particle size distribution.

[0004] However, because these magnesium oxides are in powder form, they present handling problems such as adhesion to equipment and scattering / dusting, resulting in poor workability. Therefore, there was a need to develop magnesium oxide that is easier to handle and has superior handling properties.

[0005] Japanese Patent Publication No. 2016-106160 Japanese Patent Publication No. 2018-172541

[0006] As mentioned above, powdered magnesium oxide presents handling problems. Therefore, the inventors conceived of producing magnesium oxide in granular form to improve handling. Here, magnesium oxide granules for filler applications require not only high handling properties, such as minimal generation of fine powder during handling, but also high particle redispersibility when filling resins, etc. However, no such magnesium oxide granules have existed to date. Therefore, the object of the present invention is to provide magnesium oxide granules with high particle redispersibility and excellent handling properties, and a method for producing the same.

[0007] While conducting various studies to solve the above-mentioned problems, the inventors unexpectedly discovered that by controlling the strength of the magnesium oxide granules within a predetermined range, they could obtain magnesium oxide granules that exhibit high particle redispersibility, generate less fine powder during handling, and have excellent handling properties, thus completing the present invention. The gist of the present invention is as follows.

[0008] [1] Magnesium oxide granules composed of magnesium oxide particles with a purity of 99.9% by mass or higher, wherein the granule intensity measured in accordance with JIS R 1639-5:2007 is 0.10 to 1.50 MPa.

[0009] [2] Magnesium oxide granules of [1], wherein the cumulative 50% particle size of the granules is 10 to 150 μm.

[0010] [3] Magnesium oxide granules of [1] or [2], wherein the cumulative 50% particle size of the magnesium oxide particles is 0.1 to 5.0 μm.

[0011] [4] The BET specific surface area of ​​the granules is 1 to 100 m² ２ Magnesium oxide granules of any of [1] to [3], in a quantity of / g.

[0012] [5] Cumulative 50% particle size of granules (granule D ５０ ) and the cumulative 10% particle size of magnesium oxide particles (particle D １０ ) and cumulative 90% particle size (particle D ９０ In relation to ) Granule D ５０ / (particle D９０ -Particle D １０ Magnesium oxide granules of any of [1] to [4], wherein the ratio is between 10 and 100.

[0013] [6] A method for producing magnesium oxide granules, comprising the steps of: reacting an aqueous magnesium salt solution with an alkali source to obtain a magnesium hydroxide slurry, then filtering, washing with water and drying to obtain magnesium hydroxide; calcining the magnesium hydroxide to obtain magnesium oxide particles; and granulating the magnesium oxide particles to form magnesium oxide granules, wherein the magnesium oxide particles have a magnesium oxide purity of 99.9% by mass or more, and the magnesium oxide granules have a granular strength of 0.10 to 1.50 MPa as measured in accordance with JIS R 1639-5:2007.

[0014] Furthermore, any two or more of the configurations described in [1] to [6] above can be selected and combined.

[0015] According to the present invention, magnesium oxide granules with excellent redispersibility and handling properties can be provided. These magnesium oxide granules are useful and can be suitably used in various applications such as fillers, refractory raw materials, ceramic raw materials, various target material raw materials, catalysts, pharmaceuticals, nutritional functional foods, and food additives.

[0016] The magnesium oxide granules of the present invention are composed of magnesium oxide particles with a magnesium oxide purity of 99.9% by mass or higher, and the granule intensity measured in accordance with JIS R 1639-5:2007 is 0.10 to 1.50 MPa.

[0017] The magnesium oxide granules of the present invention are composed of magnesium oxide particles with a primary particle purity of 99.9% by mass or higher. By controlling the strength of the magnesium oxide granules within a predetermined range, specifically, within the range of 0.10 to 1.50 MPa as measured in accordance with JIS R 1639-5:2007, magnesium oxide granules with excellent redispersibility and handling properties can be obtained. Granules refer to granulated products formed by aggregating and bonding primary particles.

[0018] In the present invention, the strength of magnesium oxide granules refers to the crushing strength (crushing strength) (MPa) measured in a measurement in accordance with JIS R 1639-5:2007. In the present invention, the strength of the magnesium oxide granules is 0.10 to 1.50 MPa, preferably 0.15 to 1.40 MPa, more preferably 0.20 to 1.30 MPa. If the strength of the granules is higher than 1.50 MPa, redispersion becomes difficult, and the granules cannot be uniformly dispersed in a resin or solvent. If the strength of the granules is lower than 0.10 MPa, the granules easily collapse, fine powder is likely to be generated during handling, and handling properties deteriorate.

[0019] Furthermore, the shape of the magnesium oxide granules is preferably spherical. Being spherical provides excellent fluidity and facilitates handling. The sphericity of the magnesium oxide granules is, for example, 1.00 to 1.40, preferably 1.00 to 1.30, more preferably 1.00 to 1.25. In the present invention, sphericity is obtained by measuring the lengths of the major axis and minor axis passing through the center of 20 granules in an electron micrograph captured using a scanning electron microscope (SEM), calculating the ratio of major axis / minor axis, and computing the average value thereof.

[0020] In the present invention, the cumulative 50% particle diameter of the magnesium oxide granules is, for example, 10 to 150 µm, preferably 20 to 120 µm, more preferably 40 to 100 µm. In the present invention, the cumulative 50% particle diameter of the magnesium oxide granules is the volume-based cumulative 50% particle diameter (D ５０ ) obtained by laser diffraction scattering particle size distribution measurement.

[0021] Furthermore, it is desirable that the granules have a uniform size. In the particle size distribution measurement described below, the volume-based cumulative 90% particle diameter (D ９０ ) and the volume-based cumulative 10% particle diameter (D １０ ), the ratio D ９０ / D １０ is preferably 5.0 or less.

[0022] In the present invention, the BET specific surface area of the magnesium oxide granules is, for example, 1 to 100 m ２ / g, preferably 3 to 80 m ２ / g, more preferably 5 to 70 m ２ / g. When the BET specific surface area is greater than 100 m ２ / g, the cohesive force between the magnesium oxide particles constituting the granules becomes strong, making it difficult to control the strength of the granules. When the BET specific surface area is less than 1 m ２ / g, the reactivity of magnesium oxide decreases, which makes it necessary to add a large amount of magnesium oxide granules to improve the performance of the resin.

[0023] In the present invention, the magnesium oxide particles constituting the magnesium oxide granules are preferably in the form of a polyhedron having 6 to 14 faces, such as a cube, a rectangular parallelepiped, an octahedron, or a tetradecahedron. When the magnesium oxide particles have a polyhedral shape, the contact surfaces between the particles increase during granulation, which makes it easy to control the strength of the granules within a predetermined range. In addition, the polyhedral shape of the magnesium oxide particles can reduce voids between particles generated during filling when used as a ceramic raw material, for example, so a dense molded body can be obtained. Furthermore, for example, when used as a resin filler, the contact surface between particles increases, so the effect of improving the thermal conductivity of the resin can be further enhanced.

[0024] In the present invention, the purity of the magnesium oxide particles constituting the magnesium oxide granules is 99.9% by mass or more, preferably 99.95% by mass or more, and more preferably 99.99% by mass or more. Here, the purity of magnesium oxide is expressed as a value obtained by subtracting the content (% by mass) of impurities contained in magnesium oxide from 100%. When the purity of the magnesium oxide particles is 99.9% by mass or more, the magnesium oxide particles tend to easily obtain a polyhedral shape, which is preferable because, for example, the effect of improving thermal conductivity can be obtained. In addition, when the purity of the magnesium oxide particles is 99.9% by mass or more, the magnesium oxide particles can be suitably used in applications requiring high purity.

[0025] The magnesium oxide particles constituting the magnesium oxide granules of the present invention have a purity of 99.9% by mass or more, and may contain, for example, calcium (Ca), aluminum (Al), silicon (Si), iron (Fe), chlorine (Cl) and the like as impurities.

[0026] When the magnesium oxide particles of the present invention contain calcium (Ca), the Ca content is, for example, 100 ppm or less, preferably 50 ppm or less, and more preferably 30 ppm or less. In the present specification, ppm means mass ppm unless otherwise specified.

[0027] When the magnesium oxide particles of the present invention contain aluminum (Al), the Al content is, for example, 50 ppm or less, preferably 30 ppm or less, and more preferably 20 ppm or less.

[0028] When the magnesium oxide particles of the present invention contain silicon (Si), the Si content is, for example, 50 ppm or less, preferably 30 ppm or less, and more preferably 20 ppm or less.

[0029] When the magnesium oxide particles of the present invention contain iron (Fe), the Fe content is, for example, 50 ppm or less, preferably 30 ppm or less, and more preferably 20 ppm or less.

[0030] In the present invention, the magnesium oxide particles constituting the magnesium oxide granules may contain, for example, chlorine (Cl). Cl is an element that affects the particle growth and sinterability of magnesium oxide. When the Cl content is 1 to 100 ppm, for example, polyhedral magnesium oxide particles are easily obtained. Further, for example, when granulating into magnesium oxide granules by a method such as spray drying, it becomes easy to control the strength of the magnesium oxide granules. Therefore, when the magnesium oxide particles of the present invention contain chlorine (Cl), the Cl content is, for example, 1 to 100 ppm, preferably 11 to 80 ppm, and more preferably 15 to 50 ppm.

[0031] In the present invention, the cumulative 50% particle size of the magnesium oxide particles constituting the magnesium oxide granules is, for example, 0.1 to 5.0 μm, preferably 0.2 to 4.0 μm, more preferably 0.3 to 3.0 μm, and particularly preferably 0.4 to 2.0 μm. If the cumulative 50% particle size of the magnesium oxide particles is outside the range of 0.1 to 5.0 μm, it becomes difficult to control the strength of the granules. Also, if the cumulative 50% particle size is smaller than 0.1 μm, the efficiency of granule production decreases. In the present invention, the cumulative 50% particle size of the magnesium oxide particles is the volume-based cumulative 50% particle size (D) measured by laser diffraction scattering particle size distribution measurement. ５０ ) refers to the cumulative 90% particle size (D ９０ ) and cumulative 10% particle size (D １０ The same applies to ).

[0032] In the present invention, the cumulative 50% particle size of magnesium oxide granules (granule D ５０ ) and the cumulative 10% particle size (particle D) of the magnesium oxide particles that make up the magnesium oxide granules １０ ) and cumulative 90% particle size (particle D ９０ In relation to ) Granule D ５０ / (particle D ９０ -Particle D １０ ) is, for example, 10 to 100, preferably 15 to 90, and more preferably 20 to 80. Granule D ５０ / (particle D ９０ -Particle D １０ When the ratio is between 10 and 100, the affinity of the magnesium oxide granules to the resin and solvent is adjusted to an optimal range, making it easier to uniformly disperse the magnesium oxide granules throughout the resin and solvent when mixing and kneading them, which is preferable.

[0033] Here, "Granule D" ５０ / (particle D ９０ -Particle D １０ The reason why controlling the ratio between 10 and 100 optimizes the affinity of magnesium oxide granules for resins, etc., is not limited to that theory, but for example, granule D ５０ , particle D ９０ , and particle D １０It is presumed that this is because, by setting the relationship to the above range, the interparticle voids within the magnesium oxide granules are adjusted to ensure appropriate penetration into the granules of resins and other materials.

[0034] The magnesium oxide granules of the present invention can be produced using known methods.

[0035] For example, first, an aqueous solution of magnesium salt is used as a raw material, and an alkali source is added to this aqueous solution to react and form a magnesium hydroxide slurry.

[0036] The magnesium salt aqueous solution is not particularly limited, but for example, it can be selected from magnesium chloride, magnesium nitrate, magnesium sulfate, and magnesium acetate and used as an aqueous solution.

[0037] The alkali source is not particularly limited, but can be selected from, for example, calcium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia, and used as an aqueous solution or slurry.

[0038] The resulting magnesium hydroxide slurry may be subjected to hydrothermal treatment at 100-180°C for 0.1-2.0 hours to increase the purity of the magnesium.

[0039] Next, the obtained magnesium hydroxide slurry is filtered, washed with water, and dried to obtain magnesium hydroxide. Then, magnesium oxide particles are obtained by calcining this magnesium hydroxide in the atmosphere.

[0040] The calcination conditions for magnesium hydroxide are not particularly limited as long as they are within the range of thermal decomposition to magnesium oxide, but the calcination temperature is preferably 600 to 1400°C, more preferably 700 to 1300°C, and particularly preferably 800 to 1200°C. If the calcination temperature exceeds 1400°C, the particles tend to sinter and form coarse aggregates, making subsequent granulation difficult. The calcination time is preferably 0.5 to 5.0 hours.

[0041] The particle size of magnesium oxide particles before granulation can be adjusted by known methods. For example, it can be adjusted by controlling the reaction temperature and reaction rate during the magnesium hydroxide manufacturing process, and by controlling the calcination temperature and time when the magnesium hydroxide is calcined. Alternatively, the calcined magnesium oxide can be adjusted by crushing it using a crusher such as a jaw crusher, gyratory crusher, cone crusher, impact crusher, roll crusher, roller mill, jet mill, hammer mill, pin mill, rotary mill, vibratory mill, planetary mill, or ball mill.

[0042] Next, the obtained magnesium oxide particles are formed into magnesium oxide granules (granulation step) to obtain the desired magnesium oxide granules. This granulation step can be performed using wet granulation methods such as spray drying, or dry granulation methods such as compression granulation or briquette granulation.

[0043] When granulation is performed using a wet granulation method, for example, granulation can be carried out using spray drying as described below.

[0044] First, a magnesium oxide dispersion is prepared by dispersing magnesium oxide particles in a solvent. The dispersion method is not particularly limited, but a stirrer, ultrasonic device, ball mill, bead mill, etc., can be used. The solvent used for dispersion is not particularly limited, but known organic solvents such as methanol, ethanol, propanol, butanol, pentanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monoethyl ether, diethylene glycol monomethyl ether, dipropylene glycol monoethyl ether, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, glycerin, trimethylolpropane, pentaerythritol, acetone, formic acid, acetic acid, propionic acid, tetrahydrofuran, and toluene can be used.

[0045] While the spray drying method is not particularly limited as a wet granulation method, magnesium oxide granules can be obtained by spraying a magnesium oxide dispersion from a rotating disk or nozzle using a spray dryer or the like and drying it.

[0046] Here, the strength of the magnesium oxide granules can be controlled by adjusting the concentration of the dispersion, the supply rate of the dispersion, the rotation speed of the atomizer, the drying temperature, etc., during spray drying. In addition, the particle size and sphericity of the magnesium oxide granules can also be controlled by adjusting the concentration of the dispersion, the supply rate of the dispersion, the rotation speed of the atomizer, the drying temperature, etc., during spray drying.

[0047] The concentration of the dispersion during spray drying is preferably adjusted so that the magnesium oxide particles make up 10 to 70% by mass. If the dispersion concentration is lower than 10% by mass, the strength of the resulting granules tends to be lower, and production efficiency is poor. If the dispersion concentration is higher than 70% by mass, the viscosity of the dispersion increases, making it difficult to supply the dispersion to the spray dryer stably and thus difficult to produce granules stably.

[0048] The drying temperature during spray drying is preferably between 70°C and 200°C. If the drying temperature is lower than 70°C, drying will be insufficient, solvent will tend to remain, and it will be difficult to control the strength of the granules. If the drying temperature is higher than 200°C, drying will proceed rapidly, or magnesium oxide particles may grow or aggregate unintentionally, making it difficult to control the strength of the granules and making it difficult to obtain the strength within the range of the present invention.

[0049] The supply rate of the dispersion liquid and the rotation speed of the atomizer during spray drying should be adjusted as appropriate according to the processing capacity of the spray dryer.

[0050] When granulating using a dry granulation method, granulation can be performed using methods such as extrusion granulation, compression granulation, and rolling granulation. For example, in the case of compression granulation, the strength of the granules can be adjusted by controlling the raw material supply speed, roller rotation speed, roll pressure, etc.

[0051] Furthermore, after granulation using these methods, the magnesium oxide granules may be sized using a vibrating sieve.

[0052] The BET specific surface area of ​​magnesium oxide granules can be adjusted by known methods. For example, it can be adjusted by controlling the reaction temperature and reaction rate during the magnesium hydroxide manufacturing process, and by controlling the calcination temperature and time when the magnesium hydroxide is subsequently calcined. Alternatively, in the granulation process, for example, in the wet granulation method, it can be adjusted by controlling the dispersion concentration, dispersion supply rate, atomizer rotation speed, drying temperature, etc. In the dry granulation method, for example, it can be adjusted by controlling the raw material supply rate, roller rotation speed, roll pressure, etc.

[0053] The magnesium oxide granules of the present invention can be manufactured without using additives such as binders, for example, by the manufacturing method described above. Therefore, the magnesium oxide granules of the present invention do not contain binders (for example, organic binders such as surfactants, fatty acids, polysaccharides such as carboxymethylcellulose, polyethylene glycol, polyacrylic acid, and starch, amorphous silicates, inorganic binders such as smectite).

[0054] In the present invention, the purity of the magnesium oxide particles constituting the magnesium oxide granules is 99.9% by mass or higher. However, the purity of the magnesium oxide particles can be adjusted by known methods, for example, by selecting high-purity raw materials and / or by removing impurity elements during the manufacturing process. The removal of impurity elements can be carried out, for example, by hydrothermal treatment of the magnesium hydroxide slurry, or by physically washing or chemically separating impurities in a wet manner. By adjusting the purity of the magnesium oxide to a high level, it becomes easier to obtain polyhedral particles.

[0055] Furthermore, if magnesium oxide particles contain chlorine (Cl), the Cl content can be adjusted by known methods. For example, Cl can be added or removed during the manufacturing process so that the Cl content in the magnesium oxide falls within a predetermined range. Cl can be added, for example, to magnesium hydroxide slurry or magnesium hydroxide before calcination, either wet or dry. Cl can be removed, for example, by physical removal in a wet manner or by chemical separation.

[0056] Furthermore, the magnesium oxide granules of the present invention can be surface-treated by known methods to enhance their affinity for resins and solvents. Surface treatment may be performed before or after the granulation process. The surface treatment agent used is not particularly limited, but for example, silane-based coupling agents, titanate-based coupling agents, aluminate-based coupling agents, higher fatty acids, etc., can be used. These may be used individually or in combination of two or more.

[0057] Examples of silane coupling agents include vinyl-based ones such as vinyltrimethoxysilane and vinyltriethoxysilane; epoxy-based ones such as 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, and γ-glycidoxypropyltriethoxysilane; methacrylic-based ones such as γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, and γ-methacryloxypropyltriethoxysilane; acrylic-based ones such as γ-acryloxypropyltrimethoxysilane; amino-based ones such as γ-aminopropyltrimethoxysilane and γ-aminopropyltriethoxysilane; and mercapto-based ones such as γ-mercaptopropylmethyldimethoxysilane and γ-mercaptopropyltrimethoxysilane.

[0058] Examples of titanate-based coupling agents include tetraisopropyl titanate, tetran-butyl titanate, tetraoctyl titanate, tetrastearyl titanate, isopropyl triisostearoyl titanate, tetraoctylbis(ditridecylphosphite) titanate, and bis(dioctyl pyrophosphate) oxyacetate titanate.

[0059] Examples of aluminate-based coupling agents include aluminum isopropylate, monosec-butoxyaluminum diisopropylate, aluminum sec-butyrate, aluminum ethyl acetacetate diisopropylate, aluminum tris(ethyl acetacetate), and aluminum alkyl acetacetate diisopropylate.

[0060] Examples of higher fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, erucic acid, and linoleic acid.

[0061] The magnesium oxide granules of the present invention have excellent redispersibility and handling properties, and can therefore be widely used in various applications where such properties are required. For example, they can be used in applications such as fillers, refractory raw materials, ceramic raw materials, various target material raw materials, catalysts, pharmaceuticals, nutritional functional foods, and food additives, and are preferably used in filler applications (e.g., resin fillers).

[0062] The present invention will be described in detail by the following embodiments, but these embodiments do not limit the present invention in any way.

[0063] <Measurement Method and Evaluation Method> (1) Method for Measuring the Strength of Magnesium Oxide Granules The strength of magnesium oxide granules was measured by crushing strength (MPa) in accordance with JIS R 1639-5:2007. Specifically, to prevent any bias in the size of the granules, the granules were sieved using a sieve with mesh openings before and after the granule size as a pretreatment, and then 20 granules without any bias in shape were selected. For the 20 selected granules, a micro-compression tester (MCT-510, manufactured by Shimadzu Corporation) was used with a flat compression terminal with a tip dimension of 100 μm (material: upper part: diamond, lower part: SiC plate), and measurements were taken at a maximum test force of 19.6 mN and a loading speed of 0.1 mN / s at a temperature of 24°C and a humidity of 50%. The crushing strength (MPa) was calculated from the pressure at which the granules crushed using the following formula. The strength of the magnesium oxide granules was defined as the average of the crush strengths (MPa) of 20 granules. The granule diameter is the arithmetic mean of the major axis diameter and minor axis diameter. σ = α × P / (π × d ２ ) Here, σ: crushing strength (MPa) α: coefficient (2.48) P: test pressure at crushing (N) d: granule diameter measured using an optical microscope (μm)

[0064] (2) Method for measuring the sphericity of magnesium oxide granules The sphericity of magnesium oxide granules was measured using a scanning electron microscope (SEM) (JSM6510LA, manufactured by JEOL Ltd.). Magnesium oxide granules were photographed with the SEM, and for 20 randomly selected magnesium oxide granules, the lengths of the major axis and minor axis passing through the center of the granule were measured, the ratio of major axis to minor axis was calculated, and the average value was taken as the sphericity.

[0065] (3) Method for measuring the cumulative 50% particle size of magnesium oxide granules The cumulative 50% particle size of magnesium oxide granules was measured using a laser diffraction scattering particle size distribution analyzer MT3300 (manufactured by Nikkiso Co., Ltd.). 0.1 g of magnesium oxide granules and 40 mL of methanol were placed in a 100 mL beaker, lightly mixed, and then placed in the particle size distribution analyzer to measure the particle size distribution. The volume-based cumulative 50% particle size (D) of the sample was measured. ５０ The cumulative 50% particle size of magnesium oxide granules was defined as (D) based on the volume of the sample. １０ ), cumulative 90% particle diameter (D ９０ ) was calculated similarly.

[0066] (4) Method for measuring the BET specific surface area of ​​magnesium oxide granules The BET specific surface area of ​​magnesium oxide granules was measured using a specific surface area measuring device (Macsorb, manufactured by Mountain Tech Co., Ltd.) by gas adsorption method (BET method) using nitrogen gas. Prior to measurement, the granules were subjected to a heating and degassing treatment at 150°C for 15 minutes under a nitrogen atmosphere.

[0067] (5) Method for measuring the purity of magnesium oxide particles The purity of magnesium oxide particles was calculated by measuring the content of impurity elements in the magnesium oxide and subtracting the total content of these elements from 100% by mass (mass%).

[0068] The Cl content in magnesium oxide was measured using a spectrophotometer. Magnesium oxide particles prior to the granulation process were completely dissolved in acid, and then diluted with ultrapure water to prepare the sample for measurement. The Cl content in this sample was measured using a spectrophotometer (UV-2550, Shimadzu Corporation).

[0069] The content of various impurity elements, excluding Cl, in magnesium oxide was measured using an ICP emission spectrometer. Magnesium oxide particles prior to the granulation process were completely dissolved in acid, and then diluted with ultrapure water to prepare the sample for measurement. The content of various impurity elements in this sample was measured using an ICP emission spectrometer (PS3520 VDD, manufactured by Hitachi High-Tech Science Corporation).

[0070] (6) Method for measuring the cumulative 50% particle size of magnesium oxide particles The cumulative 50% particle size of magnesium oxide particles constituting the magnesium oxide granules was measured using a laser diffraction scattering particle size distribution analyzer MT3300 (manufactured by Nikkiso Co., Ltd.). 0.1 g of magnesium oxide particles before the granulation process and 40 mL of methanol were placed in a 100 mL beaker, and after thorough dispersion treatment using an ultrasonic homogenizer US-300T (manufactured by Nippon Seiki Seisakusho Co., Ltd.) at 300 W for 3 minutes, the mixture was placed in the particle size distribution analyzer and the particle size distribution was measured. The cumulative 50% particle size (D) of the sample was measured based on volume. ５０ The cumulative 50% particle size of magnesium oxide particles was defined as (D) based on the volume of the sample. １０), cumulative 90% particle diameter (D ９０ ) was calculated similarly.

[0071] (7) Evaluation Method for the Handling Properties of Magnesium Oxide Granules The handling properties of magnesium oxide granules were evaluated by determining the pulverization rate using a Rotap-type sieve shaker. As JIS standard test sieves (conform to JIS Z8801-1), a total of seven sieves with mesh sizes of 150 μm, 106 μm, 90 μm, 75 μm, 53 μm, 45 μm, and 25 μm were used. The sieves were stacked on a receiving tray in order from the smallest mesh size to the largest mesh size, and 50 g of the sample was placed on top and the lid was closed. This was set in a Rotap-type sieve shaker (manufactured by Iida Seisakusho) and shaken for 1 hour under the conditions of rotation speed (shaking rate): 290 rpm and impact rate (beats): 165 rpm. After 1 hour, the weight of the sample accumulated in the receiving tray was measured and the pulverization rate was calculated using the following formula, and the handling properties were evaluated from the pulverization rate. Powdering rate (%) = Weight of sample accumulated in the tray (g) ÷ Weight of sample before sieving and shaking (g) × 100 (%)

[0072] (Evaluation criteria for handling performance) ○: Powdering rate less than 5% ×: Powdering rate 5% or more

[0073] (8) Method for Evaluating the Redispersibility of Magnesium Oxide Granules The redispersibility of magnesium oxide granules was evaluated by determining the sieve pass rate after redispersion treatment. A dispersion was prepared by placing 3 g of the sample and 50 mL of methanol in a 100 mL beaker and performing redispersion treatment at 300 W for 1 minute using an ultrasonic homogenizer US-300T (manufactured by Nippon Seiki Seisakusho Co., Ltd.). This dispersion was then passed through a sieve with a mesh size of 10 μm. The sample remaining on the sieve was dried at 100 °C for 1 hour, and its weight was measured. The sieve pass rate was calculated using the following formula, and the redispersibility was evaluated from the sieve pass rate. Sieve pass rate (%) = (Sample weight before redispersion treatment (g) - Sample weight remaining on the sieve (g)) ÷ Sample weight before redispersion treatment (g) × 100 (%)

[0074] (Criteria for evaluating redispersion) ○: Sieve pass rate of 95% or higher ×: Sieve pass rate of less than 95%

[0075] (9) Method for Evaluating the Affinity of Magnesium Oxide Granules The affinity of magnesium oxide granules to resins and solvents was evaluated by measuring the sedimentation time when they were added to the surface of the solvent (ethanol). Specifically, 100 mL of ethanol at 25°C was placed in a 100 mL beaker and allowed to stand, after which 5 g of the sample was added to the surface of the ethanol. The time from when the sample was placed on the surface of the liquid until the entire sample was submerged (settled) was measured as the sedimentation time. The affinity was evaluated from the measured sedimentation time. Here, the affinity of magnesium oxide granules should be within an appropriate range; if it is too high or too low, it is undesirable for the granules to be uniformly dispersed throughout the resin, etc.

[0076] (Affinity Evaluation Criteria) ○: Sedimentation time 10 seconds or more and 30 seconds or less ×: Sedimentation time less than 10 seconds or more than 30 seconds. If the sample does not sink from the liquid surface, it is marked as ×.

[0077] <Example 1> Magnesium chloride (reagent) was dissolved in deionized water to prepare an aqueous magnesium chloride solution of approximately 3.5 mol / L. An aqueous sodium hydroxide solution was added and reacted to obtain a magnesium hydroxide slurry so that the reaction rate of magnesium chloride was 90 mol%. The obtained magnesium hydroxide slurry was subjected to hydrothermal treatment at 140°C for 1 hour in an autoclave, then filtered, washed with water, and dried to obtain magnesium hydroxide. The obtained magnesium hydroxide was calcined at 1200°C for 1 hour to obtain magnesium oxide particles. At this time, the obtained magnesium oxide particles were polyhedral in shape. Next, in order to granulate the magnesium oxide particles and form magnesium oxide granules, the obtained magnesium oxide particles were dispersed in an organic solvent to obtain a magnesium oxide slurry with a magnesium oxide concentration of 45% by mass. After dispersion treatment for 4 hours using a ball mill, spray drying was performed using a spray dryer device (Okawara Chemical Machinery Co., Ltd. COC-20 type) under conditions of atomizer rotation speed of 7,500 rpm and drying temperature of 150°C to obtain magnesium oxide granules.

[0078] <Example 2> Magnesium oxide granules were obtained by the same method as in Example 1, except that the concentration of the magnesium oxide slurry was 60% by mass and the spray drying temperature was 120°C.

[0079] <Example 3> Magnesium oxide granules were obtained by the same method as in Example 1, except that the concentration of the magnesium oxide slurry was 40% by mass and the spray drying temperature was 160°C.

[0080] <Comparative Example 1> Magnesium oxide granules were obtained by the same method as in Example 1, except that the concentration of the magnesium oxide slurry was 10% by mass and the atomizer rotation speed was 8,500 rpm.

[0081] <Comparative Example 2> Magnesium oxide granules were obtained by the same method as in Example 1, except that the concentration of the magnesium oxide slurry was 70% by mass and the spray drying temperature was 300°C.

[0082] The obtained magnesium oxide granules were subjected to the above measurements and evaluations. The results are shown in Tables 1 and 2.

[0083]

[0084]

[0085] As is clear from Tables 1 and 2, the magnesium oxide granules of Examples 1 to 3 exhibited excellent handling and redispersibility. In other words, magnesium oxide granules (Examples 1 to 3) with a granular strength within a predetermined range (0.10 to 1.50 MPa) exhibited excellent handling and redispersibility.

[0086] On the other hand, the magnesium oxide granules of Comparative Examples 1 and 2, whose strength was not within the specified range, exhibited poor handling or redispersibility.

[0087] This revealed that the magnesium oxide granules of the present invention are excellent in both handling and redispersibility.

[0088] Furthermore, based on the results in Tables 1 and 2, "Granule D ５０ / (particle D ９０ -Particle D １０ It was found that magnesium oxide granules in which the ) value is controlled within a predetermined range (10 to 100) have a preferred affinity for resins and the like compared to magnesium oxide granules that are not controlled in this way.

[0089] According to the present invention, magnesium oxide granules with excellent redispersibility and handling properties can be provided. These magnesium oxide granules are useful and can be suitably used in various applications such as fillers, refractory raw materials, ceramic raw materials, various target material raw materials, catalysts, pharmaceuticals, nutritional functional foods, and food additives.

Claims

1. Magnesium oxide granules composed of magnesium oxide particles with a purity of 99.9% by mass or higher, wherein the granule intensity measured in accordance with JIS R 1639-5:2007 is 0.10 to 1.50 MPa.

2. Magnesium oxide granules according to claim 1, wherein the cumulative 50% particle size of the granules is 10 to 150 μm.

3. Magnesium oxide granules according to claim 1 or 2, wherein the cumulative 50% particle size of the magnesium oxide particles is 0.1 to 5.0 μm.

4. The BET specific surface area of ​​the granules is 1 to 100 m². ２ Magnesium oxide granules according to claim 1 or 2, wherein the amount is / g.

5. Cumulative 50% particle size of granules (granule D ５０ ) and the cumulative 10% particle size of magnesium oxide particles (particle D １０ ) and cumulative 90% particle size (particle D ９０ In relation to ) Granule D ５０ / (particle D ９０ -Particle D １０ Magnesium oxide granules according to claim 1 or 2, wherein the ratio is 10 or more and 100 or less.

6. A method for producing magnesium oxide granules, comprising the steps of: reacting an aqueous magnesium salt solution with an alkali source to obtain a magnesium hydroxide slurry, then filtering, washing with water and drying to obtain magnesium hydroxide; calcining the magnesium hydroxide to obtain magnesium oxide particles; and granulating the magnesium oxide particles to form magnesium oxide granules, wherein the magnesium oxide particles have a magnesium oxide purity of 99.9% by mass or more, and the magnesium oxide granules have a granular strength of 0.10 to 1.50 MPa as measured in accordance with JIS R 1639-5:2007.

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