Spherical magnesium oxide, its manufacturing method, resin filler, and resin composition

Abstract

To provide spherical magnesium oxide with high sphericity, excellent moisture resistance and resin fillability, and a method for producing the same.SOLUTION: The present invention provides a spherical magnesium oxide obtained by firing magnesium carbonate. The spherical magnesium oxide is characterized by having a cumulative 50% particle size (D50) in a range of 1 to 200 μm as a volume reference by laser diffraction scattering particle size distribution measurement and a sphericity read from a SEM photograph of 1.00 to 1.20.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to spherical magnesium oxide having high sphericity and excellent moisture resistance, a method for producing the same, a resin filler containing the spherical magnesium oxide, and a resin composition containing the same. [Background technology]

[0002] Magnesium oxide has excellent electrical insulation, thermal conductivity, and heat resistance, and is used in a variety of industrial applications, including as a refractory raw material, heater insulating material, abrasive, rubber vulcanization accelerator, and paint and ink pigment. It is also used as a resin filler to impart properties such as heat resistance to resins. Patent Document 1 describes the use of magnesium oxide to impart gas barrier properties to resin films used in food packaging and other applications. Patent Document 2 describes the use of magnesium oxide as a white pigment added to resins. Patent Document 3 describes the use of magnesium oxide to improve the light resistance of resins. Patent Document 4 describes the use of magnesium oxide to improve the thermal conductivity of epoxy resins. However, when incorporated into resins, magnesium oxide is highly hygroscopic, and hydration with atmospheric moisture can cause problems such as cracks due to volume expansion of the filler. Therefore, there is a need for magnesium oxide with excellent moisture resistance that does not cause these problems even with long-term use. Furthermore, when magnesium oxide is used as a resin filler, high loading capacity into resin compositions is also required to achieve excellent performance.

[0003] When magnesium oxide is used as a resin filler, it needs to have good packing properties and moisture resistance. Patent Document 5 proposes a method for producing spherical magnesium oxide with high sphericity and excellent packing properties by spray-drying magnesium hydroxide having a certain range of lithium content, granulating the resulting granules, and then firing the granules. Patent Document 6 proposes a method for producing spherical magnesium oxide with high sphericity, excellent packing properties, and moisture resistance by spray-drying a dispersion of magnesium oxide in which the contents of boron and iron are adjusted to certain ranges, granulating the resulting granules, and then firing the granules. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-131494 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-101614 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-227725 [Patent Document 4] Japanese Patent Application Publication No. 2017-186578 [Patent Document 5] Japanese Patent Application Publication No. 2016-088838 [Patent Document 6] Japanese Patent Application Publication No. 2018-131378 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although the above-mentioned methods can produce spherical magnesium oxide with high moisture resistance and excellent fillability in resin, they require a special granulation process such as spray drying, which results in a multi-stage production process, resulting in increased costs. Furthermore, when producing granules with a small particle size by spray drying, nozzles and the like tend to clog, and the granules tend to adhere to the piping of the device during spray drying, resulting in poor yield. Therefore, an object of the present invention is to develop a production method that does not necessarily require a granulation process such as spray drying, thereby providing spherical magnesium oxide with high sphericity, moisture resistance, and excellent fillability in resin. [Means for solving the problem]

[0006] In order to solve the above problems, the present inventors have conducted extensive research into methods for producing spherical magnesium oxide, and have found that when magnesium carbonate is used as a precursor to magnesium oxide, it is possible to produce spherical magnesium oxide without necessarily requiring a special granulation process such as spray drying, and to obtain spherical magnesium oxide that has high sphericity, excellent moisture resistance, and excellent fillability into resin.

[0007] That is, the present invention relates to magnesium oxide obtained by firing spherical magnesium carbonate, and the volume-based cumulative 50% particle diameter (D 50 ) is in the range of 1 to 200 μm, and the sphericity as read from an SEM photograph is 1.00 to 1.20.

[0008] The present invention also provides a resin filler containing the spherical magnesium oxide.

[0009] The present invention also provides a resin composition containing the resin filler.

[0010] The present invention also provides a method for producing spherical magnesium oxide, which comprises a step of calcining spherical magnesium carbonate particles to obtain spherical magnesium oxide. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide spherical magnesium oxide having high sphericity, excellent moisture resistance, and excellent fillability into resin, by a production method that does not necessarily require a granulation step such as spray drying. [Brief explanation of the drawings]

[0012] [Figure 1] 1 shows an SEM photograph of the spherical magnesium oxide of Example 1. [Figure 2] 1 shows an SEM photograph of spherical magnesium oxide of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] The spherical magnesium oxide of the present invention is magnesium oxide obtained by firing spherical magnesium carbonate, and has a volume-based cumulative 50% particle diameter (D 50 ) is in the range of 1 to 200 μm, and the sphericity as read from the SEM photograph is 1.00 to 1.20.

[0014] In the magnesium oxide of the present invention, the cumulative 50% particle diameter (D 50 ) can be set in the range of 1 to 200 μm, preferably 5 to 100 μm, and more preferably 10 to 50 μm.

[0015] In the magnesium oxide of the present invention, the sphericity, which can be read from an SEM photograph and which affects moisture resistance and fillability into a resin, can be 1.00 to 1.20, preferably 1.00 to 1.15, and more preferably 1.00 to 1.10. In the present invention, the lengths of the major axis and minor axis passing through the center of the particle are measured for 100 particles in an electron micrograph taken using a scanning electron microscope (SEM), the ratio of the major axis to the minor axis is calculated, and the average value is taken as the sphericity.

[0016] In the magnesium oxide of the present invention, the BET specific surface area is, for example, 0.01 to 1.00 m 2 / g, preferably 0.05 to 0.80 m 2 / g, more preferably 0.10 to 0.60 m 2 / g.

[0017] In the present invention, the boron content of magnesium oxide is not particularly limited, but is, for example, less than 10 ppm, preferably less than 9 ppm, and more preferably less than 8 ppm. When the boron content is low, the deterioration of the properties of magnesium oxide is suppressed, and high properties can be imparted when blended with a resin. In addition, ppm in the specification means ppm by mass unless otherwise specified.

[0018] In the present invention, the lithium content of the magnesium oxide is not particularly limited, but is, for example, less than 15 ppm, preferably less than 10 ppm, and more preferably less than 5 ppm. When the lithium content is low, the deterioration of the insulating properties of the magnesium oxide is suppressed. Furthermore, since the elution into the resin is reduced, the deterioration of the performance of the final product can be prevented.

[0019] In the present invention, the calcium content of the magnesium oxide is not particularly limited, but from the viewpoint of, for example, sphericity and moisture resistance, it is preferably less than 700 ppm, more preferably less than 600 ppm, and particularly preferably less than 500 ppm.

[0020] In the present invention, the total content of silicon, aluminum, phosphorus, chlorine, bromine, titanium, and iron in the magnesium oxide is not particularly limited, but from the viewpoint of sphericity, it is, for example, preferably 500 to 12,000 ppm, more preferably 500 to 10,000 ppm, and particularly preferably 500 to 8,000 ppm.

[0021] The spherical magnesium oxide of the present invention is obtained by calcining spherical magnesium carbonate, and may be produced by any process other than calcining spherical magnesium carbonate. For example, the following production method can be referred to as an example. 1) reacting a magnesium source with a carbonate source to obtain a magnesium carbonate slurry; 2) obtaining spherical magnesium carbonate particles from the magnesium carbonate slurry; 3) The spherical magnesium carbonate particles are calcined to obtain the desired spherical magnesium oxide. This production method uses magnesium carbonate as a precursor to magnesium oxide. Magnesium carbonate slurry can be easily agglomerated by maintaining it under appropriate temperature conditions, which is preferable because it can produce spherical magnesium carbonate particles without necessarily relying on a spray drying method. The target spherical magnesium oxide can be obtained by calcining this.

[0022] The magnesium source may be, for example, an aqueous magnesium salt solution, magnesium hydroxide, magnesium oxide, etc. Among these, it is preferable to use an aqueous magnesium salt solution. The magnesium salt in the aqueous magnesium salt solution is not particularly limited, and may be selected from, for example, magnesium chloride, magnesium nitrate, magnesium sulfate, magnesium acetate, and combinations thereof.

[0023] The carbonate source may be, for example, an aqueous carbonate solution or carbon dioxide gas. Among these, it is preferable to use an aqueous carbonate solution. The carbonate in the aqueous carbonate solution is not particularly limited, and may be selected from, for example, sodium carbonate, potassium carbonate, ammonium carbonate, and combinations thereof.

[0024] For example, when an aqueous solution of magnesium salt is used as the magnesium source and an aqueous solution of carbonate is used as the carbon dioxide source to produce magnesium carbonate, the magnesium salt concentration of the aqueous solution of magnesium salt is preferably 1 to 30 mass %, and the carbonate concentration of the aqueous solution of carbonate is preferably 1 to 30 mass %. The reaction between the aqueous solution of magnesium salt and the aqueous solution of carbonate may be carried out, for example, by the reaction of [Mg 2+ ]:[CO3 2- The ion concentration ratio of [amount of ion] can be 1.2:1 to 1:1.5.

[0025] After reacting the magnesium source with the carbonate source, spherical magnesium carbonate particles are obtained from the resulting magnesium carbonate slurry. The method for obtaining spherical magnesium carbonate particles from the magnesium carbonate slurry is not particularly limited, and the spherical magnesium carbonate particles can be obtained from the magnesium carbonate slurry by a common method such as spray drying, but it is preferred, for example, to aggregate magnesium carbonate into spherical particles in the magnesium carbonate slurry, followed by filtration, washing with water, and drying.

[0026] Specifically, magnesium carbonate obtained by reacting a magnesium source with a carbonate source is heated to a temperature of, for example, 60 to 100°C and maintained for 0.1 to 5 hours, and the volume-based cumulative 50% particle diameter (D 50 ) can be agglomerated into spheres having a diameter of, for example, 1 to 200 μm, 5 to 120 μm, or 10 to 70 μm, and a sphericity of, for example, 1.00 to 1.30, 1.00 to 1.25, or 1.00 to 1.20. The spherically agglomerated magnesium carbonate slurry is then processed into spherical magnesium carbonate particles by a method commonly used in the art. The method for obtaining spherical magnesium carbonate particles from the spherical magnesium carbonate slurry is not particularly limited, but for example, the spherical magnesium carbonate particles can be obtained by filtering the spherical magnesium carbonate slurry, washing with water, and drying it. Alternatively, the spherical magnesium carbonate particles can also be obtained by using a spray drying method.

[0027] The magnesium carbonate particles obtained by the above production method may be any of anhydrous magnesium carbonate, normal magnesium carbonate, and basic magnesium carbonate, but are preferably basic magnesium carbonate.

[0028] The obtained spherical magnesium carbonate particles are fired in an air atmosphere to form magnesium oxide. The firing conditions for the magnesium carbonate particles are not particularly limited as long as they are within a range in which magnesium carbonate can be thermally decomposed to magnesium oxide, but for example, the temperature is preferably 1000°C to 1800°C, more preferably 1100°C to 1700°C, and particularly preferably 1200°C to 1600°C. The firing time depends on the firing temperature, but is preferably 0.5 to 10 hours, for example. If the firing temperature is less than 1000°C, the particles will not be sufficiently sintered, and if it exceeds 1800°C, the particles will sinter together and form coarse aggregates, so the temperature is adjusted to be within the above range.

[0029] Furthermore, in the above-mentioned production method, by adding at least one compound selected from the group consisting of silicon compounds, aluminum compounds, boron compounds, phosphorus compounds, halogen compounds, titanium compounds, and iron compounds to magnesium carbonate, mixing them, and firing them, it is possible to stably obtain spherical magnesium oxide that has excellent moisture resistance, maintains its spherical shape, has high sphericity, and has a smooth surface. The timing of adding the compound may be before firing the spherical magnesium carbonate particles, and specifically, for example, it can be added to a) the magnesium source (e.g., an aqueous magnesium salt solution) and / or the carbonate source (e.g., an aqueous carbonate solution), b) the magnesium carbonate slurry (including spherical magnesium carbonate slurry), or c) the spherical magnesium carbonate particles. After addition, these are thoroughly mixed.

[0030] The total amount of the compounds added is determined so that the amount of the compounds contained in the spherical magnesium carbonate particles immediately before firing is preferably 0.01 to 5.0 mass%, more preferably 0.05 to 3.0 mass%, and particularly preferably 0.1 to 3.0 mass%, relative to the spherical magnesium carbonate particles immediately before firing (not including the compounds). Therefore, the actual amount added is determined so that the amount of the compounds contained in the spherical magnesium carbonate particles immediately before firing is within the above range.

[0031] Among the above compounds, at least one selected from the group consisting of silicon compounds, aluminum compounds, boron compounds, phosphorus compounds, halogen compounds, and titanium compounds is preferred. At least one selected from the group consisting of silicon compounds, aluminum compounds, boron compounds, and titanium compounds is more preferred. At least one selected from the group consisting of silicon compounds, aluminum compounds, and titanium compounds is also preferred.

[0032] Examples of usable silicon compounds include silicon oxide and silicates. Examples of silicon oxide include crystalline silica, amorphous fumed silica, and colloidal silica. Examples of silicates include sodium silicate, magnesium silicate, potassium silicate, and calcium silicate.

[0033] Examples of aluminum compounds that can be used include aluminum hydroxide, aluminum oxide, aluminum carbonate, aluminum chloride, aluminum nitrate, aluminum acetate, and aluminum sulfate.

[0034] As the boron compound, for example, boric acid, boron oxide, boron hydroxide, boron nitride, boron carbide, ammonium borate, etc. can be used.

[0035] Examples of phosphorus compounds that can be used include phosphoric acid, phosphates, etc. Examples of phosphates include magnesium phosphate, sodium phosphate, potassium phosphate, and ammonium phosphate.

[0036] Examples of halogen compounds that can be used include chlorides, fluorides, bromides, and iodides. Examples of chlorides include sodium chloride, potassium chloride, and magnesium chloride.

[0037] Examples of titanium compounds include titanium oxide (anatase type, rutile type), titanium chloride, titanium hydroxide, titanium bromide, titanium fluoride, and magnesium titanate.

[0038] Examples of iron compounds include iron (II) oxide, iron (III) oxide, iron tetroxide, iron hydroxide, iron chloride, iron nitride, iron bromide, and iron fluoride.

[0039] It is also preferable to control the boron content of the spherical magnesium oxide after final firing to less than 10 ppm, the lithium content to less than 15 ppm, and the calcium content to less than 700 ppm.

[0040] The method for reducing the boron content, lithium content, and calcium content is not particularly limited, and known processes can be used, such as repulp washing in which the precursor magnesium carbonate cake is reslurried and filtered, followed by repeated water washing, pretreatment of an aqueous magnesium salt solution with an adsorbent, or adjustment of the temperature rise profile during firing, or a combination of these processes. Furthermore, the contents of the above elements can also be controlled low by selecting raw materials that do not contain these elements and appropriately managing the possibility of their inclusion in the manufacturing process.

[0041] In the manufacturing method of the present invention, even when boron is added as described above, most of the boron volatilizes during firing as long as the amount added is within the above-mentioned range. Therefore, by appropriately managing the raw materials, manufacturing process, etc., the boron content of the spherical magnesium oxide after final firing can be controlled to a low level as described above.

[0042] The spherical magnesium oxide of the present invention is characterized by having sufficient moisture resistance even without surface treatment, but can also be surface-treated using a known method to further improve moisture resistance. When surface-treating the spherical magnesium oxide of the present invention, the surface treatment agent used is not particularly limited, but examples that can be used include colloidal silica, silane-based coupling agents, titania sol, titanate-based coupling agents, phosphorus compounds, alumina sol, aluminate-based coupling agents, and zirconium-based coupling agents.

[0043] Examples of silane coupling agents include vinyltrichlorosilane, vinyltrialkoxysilane, glycidoxypropyltrialkoxysilane, and methacryloxypropylmethyldialkoxysilane.

[0044] Examples of titanate coupling agents include tetraisopropyl titanate, tetra-normal-butyl titanate, tetraoctyl titanate, tetrastearyl titanate, isopropyl triisostearoyl titanate, tetraoctyl bis(ditridecyl phosphite) titanate, and bis(dioctyl pyrophosphate)oxyacetate titanate.

[0045] The phosphorus compound is not particularly limited as long as it is a compound that can react with magnesium oxide to form a magnesium phosphate compound, and examples thereof include phosphoric acid, phosphates, and acidic phosphate esters. These may be used alone or in combination of two or more. Examples of acidic phosphate esters include isopropyl acid phosphate, 2-ethylhexyl acid phosphate, oleyl acid phosphate, methyl acid phosphate, ethyl acid phosphate, propyl acid phosphate, butyl acid phosphate, lauryl acid phosphate, and stearyl acid phosphate.

[0046] Examples of the aluminate coupling agent include aluminum isopropylate, monosec-butoxyaluminum diisopropylate, aluminum sec-butylate, aluminum ethylacetoacetate diisopropylate, aluminum tris(ethylacetoacetate), and aluminum alkylacetoacetate diisopropylate.

[0047] Examples of zirconium-based coupling agents include normal propyl zirconate and normal butyl zirconate.

[0048] The spherical magnesium oxide of the present invention has high sphericity, excellent moisture resistance, and excellent fillability into resins, and therefore can be suitably blended into resins as a filler and is useful as a resin filler, such as a thermally conductive filler, a heat-resistant filler, a gas-barrier filler, or a light-resistant filler, and is particularly suitable as a thermally conductive filler.

[0049] Resins that can be used in the present invention include, for example, thermosetting resins and thermoplastic resins. Thermosetting resins are not particularly limited, but examples thereof include phenolic resins, urea resins, melamine resins, alkyd resins, polyester resins, epoxy resins, diallyl phthalate resins, polyurethane resins, and silicone resins. Thermoplastic resins are not particularly limited, but examples thereof include polyamide resins, polyacetal resins, polycarbonate resins, polybutylene terephthalate resins, polyolefin resins, polysulfone resins, polyamideimide resins, polyetherimide resins, polyarylate resins, polyphenylene sulfide resins, polyether ether ketone resins, fluororesins, and liquid crystal polymers.

[0050] The amount of spherical magnesium oxide blended in the resin composition of the present invention is not particularly limited and may be appropriately determined depending on the properties required of the resin composition, but as an example, the amount of spherical magnesium oxide used may be in the range of 0.1 to 100 parts by mass per 100 parts by mass of resin.

[0051] The resin composition containing the spherical magnesium oxide of the present invention can be used in various fields depending on the properties of the resin. [Example]

[0052] The present invention will be described in detail with reference to the following examples, but these examples are not intended to limit the present invention in any way.

[0053] <Measurement and evaluation methods> (1) Measurement method of element content The elemental content was measured by ICP atomic emission spectrometry. The measurement sample was added to acid and completely dissolved, and then the content of each element was measured using an ICP measurement device (PS3520 VDD, Hitachi High-Tech Science Corporation). In Table 1 below, when the content of each element was below the detection limit, it was expressed as a trace amount (<1 ppm).

[0054] (2) Measurement method for BET specific surface area The BET specific surface area was measured by a gas adsorption method (BET method) using nitrogen gas using a specific surface area measuring device (Macsorb, manufactured by Mountech Co. Ltd.).

[0055] (3) Volume-based cumulative 50% particle size (D 50 ) Measurement sample 0.1 x 10 -3 kg was precisely weighed, dispersed in 40 mL of methanol, and measured using a laser diffraction scattering particle size distribution analyzer (MT3300, manufactured by Nikkiso Co., Ltd.).

[0056] (4) Sphericity and surface smoothness as seen in SEM photographs A scanning electron microscope (SEM) (JSM6510LA, manufactured by JEOL Ltd.) was used. The major and minor axes passing through the center of 100 particles in the electron micrographs were measured, and the ratio of the major axis to the minor axis was calculated. The average value was used as the sphericity. The surface condition of the spherical magnesium oxide in the electron micrographs taken with the scanning electron microscope (SEM) was evaluated as follows: ◯: a smooth surface with almost no fine particles present on the surface of the spherical magnesium oxide; △: a smooth surface with multiple fine particles present on the surface of the spherical magnesium oxide, or a surface with almost no fine particles present but with an uneven, non-smooth surface; and ×: a rough surface with multiple fine particles present on the surface of the spherical magnesium oxide, and with an uneven, non-smooth surface.

[0057] (5) Moisture resistance evaluation by constant temperature and humidity test The moisture resistance of the spherical magnesium oxide was evaluated based on the mass increase rate in a constant temperature and humidity test. The thermo-hygrostat used was THN040FA manufactured by Advantec Toyo Co., Ltd. The mass increase rate was determined after 10 g of spherical magnesium oxide was exposed to an environment of 85°C and 85% RH for 168 hours using the thermo-hygrostat.

[0058] Example 1 Magnesium nitrate hexahydrate (special grade, manufactured by Kanto Chemical Co., Ltd.) was dissolved in ion-exchanged water to prepare an approximately 20% by mass aqueous solution of magnesium nitrate. Potassium carbonate (special grade, manufactured by Kanto Chemical Co., Ltd.) was dissolved in ion-exchanged water to prepare an approximately 15% by mass aqueous solution of potassium carbonate. [Mg 2+ ]:[CO3 2- Magnesium carbonate was synthesized by reacting an aqueous magnesium nitrate solution with an aqueous potassium carbonate solution so that the ion concentration ratio of [Ion concentration ratio] was 1:1. After the reaction, the magnesium carbonate slurry was heated to 90°C and held for 1 hour to prepare a spherical magnesium carbonate slurry. Then, silicon dioxide (special grade, manufactured by Kanto Chemical Co., Ltd.) was added in an amount of 0.5 mass% relative to the magnesium carbonate and mixed. After filtration, washing with water, and drying, spherical magnesium carbonate particles were obtained. The obtained spherical magnesium carbonate particles were fired in an electric furnace at 1500°C for 1 hour to obtain spherical magnesium oxide particles. The particle diameter (D 50 ) was 21.3 μm and the sphericity was 1.10.

[0059] <Example 2> Spherical magnesium oxide was obtained in the same manner as in Example 1, except that the amount of silicon dioxide added was 1.0 mass % relative to the amount of magnesium carbonate. The particle diameter (D 50 ) was 21.5 μm and the sphericity was 1.11.

[0060] Example 3 Spherical magnesium oxide was obtained in the same manner as in Example 1, except that aluminum oxide (Kanto Chemical Co., Ltd., special grade) was added in an amount of 0.5 mass % relative to the magnesium carbonate instead of silicon dioxide. The particle diameter (D 50 ) was 20.5 μm and the sphericity was 1.10.

[0061] Example 4 Spherical magnesium oxide was obtained in the same manner as in Example 1, except that boric acid (special grade, manufactured by Kanto Chemical Co., Ltd.) was added in an amount of 0.5 mass % relative to the magnesium carbonate instead of silicon dioxide. The particle diameter (D 50 ) was 22.0 μm and the sphericity was 1.10.

[0062] <Example 5> Spherical magnesium oxide was obtained in the same manner as in Example 1, except that titanium oxide (Kanto Chemical Co., Ltd., anatase type, Shika Grade 1) was added in an amount of 0.5 mass % relative to the magnesium carbonate instead of silicon dioxide. The particle diameter (D 50 ) was 21.8 μm and the sphericity was 1.11.

[0063] <Comparative Example 1> Magnesium oxide particles were obtained in the same manner as in Example 1, except that silicon dioxide was not added. The particle diameter (D 50 ) was 21.3 μm and the sphericity was 1.11.

[0064] <Result> The above measurements and evaluations were carried out on the spherical magnesium oxides of Examples 1 to 5 and Comparative Example 1. The results are shown in Table 1 below.

[0065] [Table 1]

[0066] As is clear from Table 1, the spherical magnesium oxides of Examples 1 to 5 had high sphericity and excellent moisture resistance.

[0067] This indicates that the spherical magnesium oxide of the present invention has high sphericity and excellent moisture resistance, and is therefore useful as an excellent resin filler. [Industrial Applicability]

[0068] The spherical magnesium oxide of the present invention has high sphericity and excellent moisture resistance, and is therefore useful as an excellent resin filler.

Claims

1. A particle size distribution measurement method using a laser diffraction scattering method, which measures the cumulative 50% particle size (D ５０ ) is in the range of 1 to 200 μm, the sphericity as read from an SEM photograph is 1.00 to 1.20, and the boron content is less than 10 ppm.

2. 2. The spherical magnesium oxide according to claim 1, having a lithium content of less than 15 ppm.

3. Cumulative 50% particle diameter (D ５０ 3. The spherical magnesium oxide according to claim 1, wherein the particle size is in the range of 5 to 100 μm.

4. BET specific surface area: 0.01 to 1.00 m ２ The spherical magnesium oxide according to any one of claims 1 to 3, wherein the molecular weight of the spherical magnesium oxide is 1 / g.

5. A resin filler containing the spherical magnesium oxide according to any one of claims 1 to 4.

6. A resin composition containing the resin filler according to claim 5.

7. The method includes a step of calcining the spherical magnesium carbonate particles to obtain spherical magnesium oxide, A method for producing spherical magnesium oxide, comprising adding at least one compound selected from the group consisting of silicon compounds, aluminum compounds, boron compounds, phosphorus compounds, halogen compounds, titanium compounds and iron compounds before firing, The spherical magnesium carbonate particles have a sphericity of 1.00 to 1.30, and the spherical magnesium oxide particles have a sphericity of 1.00 to 1.

20.

8. 8. The method for producing spherical magnesium oxide according to claim 7, wherein the total amount of the silicon compound, aluminum compound, boron compound, phosphorus compound, halogen compound, titanium compound and iron compound added is 0.01 to 5.0 mass% based on the spherical magnesium carbonate particles immediately before firing.

9. reacting a magnesium source with a carbonate source to obtain a magnesium carbonate slurry; obtaining spherical magnesium carbonate particles from the magnesium carbonate slurry; The method for producing spherical magnesium oxide according to claim 7 or 8, further comprising:

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