Magnesium oxide particles and method for producing the same

Abstract

The magnesium oxide particles of the present invention consist of spherical bodies having open pores in which a plurality of dead-burned magnesium oxide particles are partially fused together. The average particle diameter (D2) of the spherical bodies is 10-200 μm inclusive and the circularity of the projected image thereof is 0.7 or more. It is appropriate that the porosity within the spherical bodies, which is determined by image analysis, is 10-50% inclusive. It is also appropriate that the ratio D2 / D1 of the average particle diameter D2 of the spherical bodies to the particle diameter D1 converted from the BET specific surface area of the spherical bodies is 3-10 inclusive.

Description

[Technical Field]

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

[0002] One known application of magnesium oxide is as a thermally conductive filler. Patent Document 1 proposes spherical magnesium oxide particles with the aim of improving the packing properties of a thermally conductive filler made of magnesium oxide and thereby enhancing its thermal conductivity. Furthermore, needle-shaped magnesium oxide particles with a large aspect ratio have been proposed to enhance the effect of forming heat conduction paths (see Patent Document 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-088838 [Patent Document 2] Japanese Patent Publication No. 2020-152613 [Overview of the Initiative]

[0004] Spherical magnesium oxide particles, as described in Patent Document 1, exhibit excellent packing properties, and resin compositions highly filled with these particles exhibit high thermal conductivity. However, since magnesium oxide has a higher density than resin, resin compositions highly filled with magnesium oxide particles have the problem of having a high specific gravity. Furthermore, since spherical magnesium oxide particles, which are generally more expensive than resin, are used in large quantities, it is also economically disadvantageous.

[0005] Needle-shaped magnesium oxide particles with a high aspect ratio readily form heat conduction paths and, when filled into a resin, have the effect of increasing the rigidity of the resin composition. However, if high rigidity is not required for the resin composition, there is no need to use needle-shaped magnesium oxide particles, and needle-shaped magnesium oxide particles are generally brittle, which presents a challenge in terms of mixing them with resin.

[0006] Therefore, the object of the present invention is to provide magnesium oxide particles that are easier to knead with resin than needle-shaped magnesium oxide with a large aspect ratio, exhibit high thermal conductivity even without high filling of the resin, and as a result the specific gravity of the resin composition does not become excessively high.

[0007] As a result of diligent research to solve the aforementioned problems, the inventors of the present invention have found that granules produced using calcined magnesium oxide particles as a raw material are nearly spherical in shape, and that the structure containing heat conduction paths and voids within the granules results in high thermal conductivity and low apparent density, leading to the present invention.

[0008] In other words, the present invention consists of a spherical body having open pores formed by the partial fusion of multiple calcined magnesium oxide particles. The present invention provides magnesium oxide particles having an average particle diameter (D2) of 10 μm or more and 200 μm or less, and a circularity of the projected image of 0.7 or more.

[0009] Furthermore, the present invention includes a step of producing granules by granulating a raw material composition containing burnt magnesium oxide particles having an average particle diameter of 1.0 μm or more and 20.0 μm or less and a flux component into spherical shapes, The present invention provides a method for producing magnesium oxide particles, comprising the step of calcining the granulated material at a temperature of 900°C to 1700°C. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a scanning electron microscope image of the magnesium oxide particles obtained in Example 1. [Figure 2] Figure 2 shows a scanning electron microscope image of magnesium oxide particles obtained in Comparative Example 2. [Modes for carrying out the invention]

[0011] The present invention will be described below based on its preferred embodiments. This invention relates to magnesium oxide particles. The magnesium oxide particles of this invention are characterized by their low apparent density while utilizing the inherently high thermal conductivity of magnesium oxide. The low apparent density of the magnesium oxide particles of this invention is due to the presence of numerous voids within the particles. More specifically, the magnesium oxide particles of this invention are composed of spherical bodies with voids between particles, formed by the partial fusion of multiple calcined magnesium oxide particles. The primary particles of the magnesium oxide particles constituting these spherical bodies will be described below. In the following description, the term "particle" may refer to individual particles or to a powder, which is an aggregate of particles, depending on the context.

[0012] 1. Burned magnesium oxide particles The magnesium oxide particles of the present invention are composed of a fused body in which multiple calcined magnesium oxide particles are partially fused together. In the following description, the primary magnesium oxide particles refer to the individual particles that constitute a spherical body, surrounded by the partially fused grain boundaries and voids. The raw material particles refer to the particles used in the process of manufacturing the granulated product described later. The raw material particles preferably have an average particle diameter of 1.0 μm or more and 20.0 μm or more. An average particle diameter of 1.0 μm or more of the raw material particles suppresses the progress of sintering when the firing process described later is carried out, thereby leaving sufficient voids between the primary particles and making it easier to maintain the spherical shape of the particles after sintering. Furthermore, an average particle diameter of 20.0 μm or less of the raw material particles makes it easier to obtain magnesium oxide particles with a shape close to a perfect sphere after the firing process described later. From these viewpoints, the average particle diameter of the raw material particles is more preferably 3.0 μm or more and 15.0 μm or less, and even more preferably 5.0 μm or more and 10.0 μm or less. The BET specific surface area of the raw material particles is preferably 2.0 m 2 / g or less from the viewpoint of retaining voids after the firing described below, more preferably 0.09 m 2 / g or more and 1.8 m 2 / g or less, still more preferably 0.09 m 2 / g or more and 1.0 m 2 / g or less.

[0013] The average particle diameter of the raw material particles is the median diameter measured using the particle size distribution measuring device MT3300EX type manufactured by Microtrac Bell Corporation.

[0014] The main component of the raw material particles is magnesium oxide (MgO). It is desirable that the raw material particles are composed only of MgO, but if the purity thereof is 93% by mass or more, particularly 95% by mass or more, especially 97% by mass or more, the effects of the present invention can be sufficiently achieved. Therefore, it is acceptable that the raw material particles contain impurities within a range that does not impair the effects of the present invention. Examples of the impurities include calcium compounds, silicon compounds, aluminum compounds, iron compounds, boron compounds, and the like. The purity of magnesium oxide in the raw material particles is determined by the difference method of measuring the concentrations of impurities such as CaO, SiO2, Fe2O3, Al2O3, and B2O3 by ICP-AES and subtracting the measured value from 100%.

[0015] The raw material particles are preferably composed of a dead-burned magnesium oxide sintered body. Dead-burned magnesium oxide is magnesium oxide obtained by firing magnesium hydroxide at a temperature of 1400°C or higher, and is also called heavy-burned magnesium oxide or magnesia clinker. The dead-burned magnesium oxide sintered body has almost no activity and has high water resistance, high insulation, and high thermal conductivity. In the present invention, since the raw material particles are composed of a dead-burned magnesium oxide sintered body, the magnesium oxide particles of the present invention become useful as a thermal conductivity filler. In addition to dead-burned magnesium oxide, light-burned magnesium oxide is also known. Light-burned magnesium oxide is obtained by firing magnesium hydroxide at 450°C to 1300°C and is also called calcined magnesium oxide. Light-burned magnesium oxide is different from dead-burned magnesium oxide in that it has relatively high activity, low water resistance, and low thermal conductivity.

[0016] The raw material particles may be polycrystals or single crystals.

[0017] 2. Magnesium Oxide Particles Next, the magnesium oxide particles of the present invention, which are spherical bodies in which a plurality of the above-described raw material particles, i.e., dead-burned magnesium oxide particles, are partially fused, will be described. The magnesium oxide particles of the present invention have a large number of voids. By having voids, it becomes possible to lower the apparent density of the magnesium oxide particles of the present invention. In the magnesium oxide particles of the present invention, due to the fact that sintering between the raw material particles hardly proceeds in the manufacturing method described later, the voids of the granulated product are retained. These voids become open pores that connect to the particle surface.

[0018] When the degree of voids present in the magnesium oxide particles of the present invention is expressed as the porosity, the porosity is preferably 10% or more and 50% or less, more preferably 10% or more and 45% or less, and still more preferably 12% or more and 40% or less. When the magnesium oxide particles of the present invention have such a high porosity, when the magnesium oxide particles are blended with, for example, a resin to produce a resin composition, the resin composition is suppressed from an excessive increase in specific gravity and exhibits high thermal conductivity. The method for measuring the porosity is as follows. Mix silicone resin KE-106 manufactured by Shin-Etsu Chemical Co., Ltd. and magnesium oxide particles, and mold them into a sheet with a thickness of 1 mm. Polish this sheet with a cross-section polisher manufactured by JEOL Ltd. to produce a cross-section. Photograph the cross-section with a scanning electron microscope MT400II manufactured by Hitachi High-Tech, and perform image analysis on the cross-section observation image using image analysis software "A Image-kun" manufactured by Asahi Kasei Engineering Co., Ltd. to measure the area ratio of magnesium oxide inside the magnesium oxide particles and the void part other than magnesium oxide, and obtain the porosity. The porosity (%) is defined as the area of the void part other than magnesium oxide / (the area of magnesium oxide + the area of the void part other than magnesium oxide) × 100.

[0019] Due to the fact that the magnesium oxide particles of the present invention have voids composed of a large number of open pores, the oil absorption amount of the magnesium oxide particles of the present invention is large. The oil absorption amount is a measure of the apparent density of the particles, and the larger the oil absorption amount, the lower the apparent density of the magnesium oxide particles of the present invention. From this perspective, the oil absorption amount of the magnesium oxide particles of the present invention is preferably 30 ml / 100 g or more, more preferably 31 ml / 100 g or more, and still more preferably 32 ml / 100 g or more. There is no particular limitation on the upper limit value of the oil absorption amount, but for example, it can be 40 ml / 100 g or less. The oil absorption amount is measured in accordance with JIS K5101-13-1 using 5 g of magnesium oxide particles and boiled linseed oil.

[0020] The magnesium oxide particles of the present invention have a low BET specific surface area and low activity by using dead-burned magnesium oxide as raw material particles. Therefore, the reactivity with moisture is low and the water resistance is high. The BET specific surface area of the magnesium oxide particles of the present invention is preferably 0.05 m 2 / g or more and 2.0 m 2 / g or less, more preferably 0.05 m 2 / g or more and 1.0 m 2 / g or less, and still more preferably 0.10 m 2 / g or more and 0.5 m 2It is even more preferable that the value be less than or equal to / g. The BET specific surface area is measured using a monosorb manufactured by Yuasa Ionics Corporation, after degassing at 180°C for 10 minutes as a pretreatment, and then measured using the BET single-point method.

[0021] The magnesium oxide particles of the present invention consist of spherical bodies formed by the partial fusion of multiple calcined magnesium oxide particles. Partial fusion means that the primary particles of the calcined magnesium oxide particles are not completely fused together, but rather fused while leaving unfused portions, that is, they are fused in such a way that voids are created between the primary particles. The definition of "primary particle" is as described above.

[0022] The spherical shape of the magnesium oxide particles of the present invention allows for easy and high-density filling of resins. As a result, the thermal conductivity of the resin composition can be improved. From this viewpoint, the spherical magnesium oxide particles of the present invention preferably have a circularity of 0.7 or higher, more preferably 0.72 or higher, and even more preferably 0.75 or higher. The circularity is calculated based on the projection image of the spherical magnesium oxide particles of the present invention. Specifically, the particle shape evaluation device PITA-3 manufactured by Seishin Corporation is used to measure the circularity by dispersing 0.1 g of magnesium oxide particles in 20 mL of a 0.2 mass% sodium hexametaphosphate aqueous solution. To obtain sufficient measurement accuracy, more than 3000 particles are measured.

[0023] The magnesium oxide particles of the present invention, which consist of spherical bodies, have an average particle diameter D 50 It is preferable that the average particle size D is between 10 μm and 200 μm from the viewpoint of high dispersibility and packing when mixed with resin, and water resistance. From the viewpoint of making this advantage even more pronounced, 50 It is more preferably 20 μm to 150 μm, even more preferably 30 μm to 100 μm, and even more preferably 40 μm to 60 μm. Average particle diameter D 50This is the median diameter measured using the MT3300EX particle size distribution analyzer from Microtrac-Bell Corporation (hereinafter referred to as "D"). 50 When this phrase is used, it refers to the value measured using this method.

[0024] The magnesium oxide particles of the present invention have an average particle diameter D 50 When D2 is the particle diameter converted to BET specific surface area and D1 is the particle diameter, it is preferable that the ratio of D2 to D1, D2 / D1, is between 3 and 10, from the viewpoint of exhibiting high thermal conductivity and having high porosity and low apparent density. From the viewpoint of making this advantage even more pronounced, it is preferable that the value of D2 / D1 is between 3 and 9. While the value of D2 / D1 is preferably within the range described above, the value of D1, i.e., the particle diameter of the spherical body converted to BET specific surface area, is preferably 3.0 μm to 15 μm, provided that the value of D2 / D1 is within the range described above, from the viewpoint of obtaining magnesium oxide particles that exhibit high thermal conductivity and have a large degree of circularity. From the viewpoint of making this advantage even more pronounced, it is even more preferable that D1 be 3.5 μm to 15 μm, and even more preferable that it be 4.0 μm to 15 μm.

[0025] 3. Method for producing magnesium oxide particles Next, a preferred method for producing magnesium oxide particles of the present invention will be described. This production method is broadly divided into three steps: (1) preparation of raw material particles of calcined magnesium oxide, (2) granulation, and (3) calcination of the granules. Each of these steps will be described below.

[0026] (1) Preparation process for raw material particles of calcined magnesium oxide For calcined magnesium oxide, those commonly sold as electrofused magnesia or magnesia clinker can be used without any particular restrictions. Calcined magnesium oxide can be produced by methods such as calcining and thermally decomposing magnesium salts such as magnesium hydroxide, magnesium carbonate, magnesium chloride, magnesium nitrate, and magnesium sulfate. As magnesium hydroxide, you can use the precipitate formed by the reaction of magnesium salts in seawater with calcium hydroxide. Magnesite ore can be used as a source of magnesium carbonate.

[0027] There are no particular restrictions on the calcination method for magnesium hydroxide or magnesium carbonate; a general-purpose calcination furnace can be used. The firing temperature is preferably 1300°C or higher, more preferably in the range of 1300°C to 2800°C, and more preferably in the range of 1400°C to 2400°C. The firing time should be sufficient to generate dead-calcined magnesium oxide, and is generally within the range of 10 minutes to 10 hours.

[0028] The particles of the sintered magnesium oxide body obtained in this way are then processed into primary particles having a desirable average particle size through a sizing process that combines crushing and classification. <Crushing / classification process> The crushing process can be appropriately selected according to the properties of the calcined magnesium oxide particles to be crushed. For example, crushing devices such as roll crushers and jaw crushers, and crushing devices such as rolling ball mills, vibrating ball mills and air-flow mills can be used individually or in combination of two or more types. A classification process may be performed after the crushing process, or in combination with the crushing device. In the classification process, vibrating screens, wind classifiers and cyclone classifiers can be used individually or in combination of two or more types. Alternatively, a crushing device with a classification mechanism can be used. The average particle size D of the raw material particles of calcined magnesium oxide obtained in the crushing and classification process. 50 As mentioned above, the particle size is preferably 1.0 μm or more and 20 μm or less, more preferably 3.0 μm or more and 15.0 μm or less, and even more preferably 5.0 μm or more and 10.0 μm or less.

[0029] (2) Granulation process The raw material particles of calcined magnesium oxide obtained through the crushing and classification process described above are granulated into granules of a predetermined size by spray drying in the granulation process. Examples of spray drying methods include a spray drying method in which a raw material composition consisting of a suspension containing the raw material particles of calcined magnesium oxide obtained through the classification process and a flux component is used, and the raw material composition is sprayed into hot air.

[0030] The flux component is not particularly limited in type, as long as it promotes the grain growth of the raw magnesium oxide particles in the subsequent calcination process and fuses the raw material particles together at the calcination temperature in the calcination process. For example, lithium compounds, boron compounds, silicon compounds, and halogen compounds, which are flux components that can obtain a flux effect in a temperature range of 1100°C to 1700°C, are preferred from the viewpoint of balancing flux effect and economic efficiency.

[0031] Examples of lithium compounds used as flux components include lithium hydroxide, lithium acetate, lithium nitrate, lithium sulfate, lithium oxide, lithium peroxide, lithium nitride, lithium sulfide, lithium metasilicate, lithium titanium dioxide, lithium formate, lithium carbonate, lithium dodecyl sulfate, lithium oxalate, lithium citrate, lithium lactate, lithium salicylate, lithium stearate, lithium tartrate, lithium hydroxybutyrate, lithium 2-ethylhexanoate, lithium cyclohexanebutyrate, lithium amide, lithium benzoate, lithium pyruvate, lithium cyclopentadienide, and lithium acetylacetonate. Examples of boron compounds include boric acid, boron oxide, boron hydroxide, boron nitride, boron carbide, and ammonium borate. Examples of silicon compounds include sodium silicate, silicon dioxide, and polymethylsiloxane. Examples of halogen compounds include lithium fluoride and magnesium fluoride. These flux components can be used individually or in combination of two or more.

[0032] For the suspension containing the calcined magnesium oxide raw material particles and flux components, water or an organic solvent can be used as the medium. From the viewpoint of suitable granulation, the concentration of calcined magnesium oxide in the suspension is preferably 10% by mass or more and 40% by mass or less, and more preferably 15% by mass or more and 35% by mass or less. From the viewpoint of successfully fusing the calcined magnesium oxide, the concentration of the flux component in the suspension is preferably 0.1% by mass or more and 10% by mass or less per 100 units of magnesium oxide, and more preferably 1% by mass or more and 5% by mass or less.

[0033] The raw material composition consisting of a suspension may contain a binder in addition to the calcined magnesium oxide raw material particles and flux components. Examples of binders include polyacrylates such as ammonium polyacrylate. From the viewpoint of suitable granulation, the concentration of the binder in the suspension is preferably 0.1% to 10% by mass, and more preferably 1% to 5% by mass, per 100 units of magnesium oxide.

[0034] The granules produced in the granulation process have an average particle diameter of preferably 20 μm to 300 μm, more preferably 30 μm to 200 μm, and even more preferably 30 μm to 100 μm. The granules consist of spherical porous bodies having multiple open pores.

[0035] (3) Sintering process of granules The granules with multiple open pores obtained in the granulation process are calcined in the calcination process, causing the raw material particles of calcined magnesium oxide that constitute the granules to partially fuse together. As a result, single spherical magnesium oxide particles are obtained. Since the raw material particles consist of calcined magnesium oxide, the change in particle size due to calcination is small, and voids are created between the raw material particles due to partial fusion by the low-melting-point flux component.

[0036] To fuse the raw material particles while retaining open pores in the calcined magnesium oxide granules, the calcination process involves calcining the granules at a high temperature, preferably between 900°C and 1700°C, and more preferably between 1000°C and 1600°C. Various calcination devices can be used to achieve this high temperature. The heat source of the calcination device is not particularly limited as long as the required temperature can be obtained, and electric furnaces, gas furnaces, etc., can be selected according to the scale of production. The calcination temperature and calcination time can be appropriately selected depending on the type and amount of flux.

[0037] 4. Thermally conductive fillers The magnesium oxide particles produced by the above method are suitably used as a thermally conductive filler, taking advantage of the high thermal conductivity of calcined magnesium oxide. This thermally conductive filler can be mixed with various resins to form a resin composition. Since the thermally conductive filler is spherical, it can be densely packed into the resin. Furthermore, because the thermally conductive filler is spherical, it has the advantage of maintaining its shape more easily during mixing with the resin compared to, for example, needle-shaped fillers. The thermally conductive filler made of magnesium oxide particles according to the present invention exhibits a high thermal conductivity of 1.2 W / mK or higher when filled into a resin at a 40% volume rate.

[0038] The method for measuring the thermal conductivity of magnesium oxide particles is as follows: A mixture of magnesium oxide particles and KE-106 silicone resin manufactured by Shin-Etsu Chemical Co., Ltd. is molded into a 1 mm thick sheet. The thermal conductivity of this sheet is measured using a TPS2500S thermal conductivity measuring device manufactured by Kyoto Electronics Manufacturing Co., Ltd. The magnesium oxide particles are added to the silicone resin at a volume of 40% by volume, representing the occupancy volume of magnesium oxide without voids.

[0039] 5. Thermally conductive resin composition The thermally conductive filler of the present invention can enhance the thermal conductivity of a resin composition by filling it into the resin. Furthermore, the thermally conductive filler of the present invention can be used as a thermally conductive filler in combination with particles of other materials such as silicon oxide, aluminum oxide, magnesium oxide, silicon nitride, aluminum nitride, and boron nitride. The particles of the other materials may be spherical, similar to the thermally conductive filler of the present invention, or they may have other shapes.

[0040] The resin into which the thermally conductive filler of the present invention is incorporated can be appropriately set depending on the application. For example, it may be a silicone resin oil or grease, a thermosetting resin such as epoxy resin, a polyamide resin, a polyphenylene sulfide resin, or a thermoplastic resin such as a liquid crystalline polymer. In a resin composition, it is preferable that, when the total mass of the resin composition is 100%, the amount of each component is 1% to 90% by mass of the thermally conductive filler and 10% to 99% by mass of the resin. By including 1% or more of the thermally conductive filler, the thermal conductivity of the resulting resin composition can be made sufficiently high. Furthermore, by including 90% or less of the thermally conductive filler, it is possible to maintain the resin properties while providing sufficient thermal conductivity. In particular, the thermally conductive filler of the present invention can achieve equivalent thermal conductivity with a smaller amount of additive compared to conventional thermally conductive fillers made of magnesium oxide.

[0041] The resin composition containing the thermally conductive filler of the present invention can be manufactured by mixing a resin and the thermally conductive filler by a known method. The resulting thermally conductive resin composition can be molded by a known method such as extrusion molding and processed into a desired shape.

[0042] For the purpose of improving the dispersibility and mixability when mixing the resin and the thermally conductive filler, and for the purpose of improving the mechanical properties of the resulting resin composition, the thermally conductive filler may be surface-treated before use. Examples of compounds that can be used for surface treatment include silane coupling agents having vinyl groups, alkyl groups, phenyl groups, amino groups, phenylamino groups, etc., metal soaps such as magnesium stearate, and surfactants such as sodium stearate. These surface treatment agents may be mixed with the thermally conductive filler in a mixer before kneading with the resin, or they may be mixed in an integral blend during the kneading of the resin and the thermally conductive filler.

[0043] The resin composition containing the thermally conductive filler of the present invention can be applied to various articles, and is particularly suitable for articles requiring high thermal conductivity and moisture resistance. Examples of such articles include lamp sockets and various electrical components in the automotive field. In the electronic equipment field, examples include heat sinks, die pads, printed circuit boards, semiconductor package components, cooling fan components, pickup components, connectors, switches, bearings, and case housings.

[0044] Furthermore, since the thermally conductive filler of the present invention can impart high thermal conductivity to resins with a low amount of additive, it can be suitably used as a thermally conductive filler for components where weight reduction is required. [Examples]

[0045] The present invention will be described in detail below based on examples, but these examples are not intended to limit the object of the present invention, nor are the present invention limited to these examples. In the following examples, unless otherwise specified, "%" means "mass%".

[0046] [Example 1] A sintered magnesium oxide body (magnesia clinker UBE995S manufactured by Ube Materials Co., Ltd. (MgO purity 99.5%)) was crushed to a size of 1 mm or less using a Makino MRCA-0 roll crusher, and then pulverized using a Shizuoka Plant 250BMS cyclone mill to obtain sintered magnesium oxide particles. These burnt magnesium oxide particles were processed using an Ashizawa Finetech CFA100 wind classifier to remove particles larger than 20 μm, and fine powder with an average particle size of 6 μm was recovered to be used as raw material for burnt magnesium oxide.

[0047] 500 g of calcined magnesium oxide raw material particles were dispersed in 1417 g of ion-exchanged water along with 8.9 g of ammonium polyacrylate and 14.5 g of lithium hydroxide to form a suspension. Granulation was performed using this suspension by spray drying. An FL-11 spray dryer manufactured by Okawara Chemical Machinery was used for granulation. The granulation conditions were an atomizer disk rotation speed of 14000 rpm, an inlet temperature of 220°C, and an outlet temperature of 105°C. This resulted in spherical granules with an average particle diameter of 49 μm.

[0048] The obtained spherical granules were calcined in a Motoyama electric furnace KL-2030D at 1300°C for 2 hours under an atmospheric atmosphere to obtain calcined material. This calcined material was crushed in a mortar and pestle and sieved to 75 μm to obtain the desired spherical porous magnesium oxide particles.

[0049] [Example 2] In Example 1, spherical porous magnesium oxide particles were obtained in the same manner as in Example 1, except that a sintered magnesium oxide body (magnesia clinker UBE975 manufactured by Ube Materials Co., Ltd. (MgO purity 97.5%)) was used as the sintered magnesium oxide body.

[0050] [Comparative Example 1] In this comparative example, commercially available magnesium oxide RF-98 (manufactured by Ube Materials, average particle size 56.6 μm) was used as a thermally conductive filler.

[0051] [Comparative Example 2] 500 g of hexagonal plate-shaped magnesium hydroxide particles (MgO purity 98.2% after ignition, average particle size 2 μm) were dispersed in 1423 g of ion-exchanged water along with 8.9 g of ammonium polyacrylate and 10 g of lithium hydroxide to form a suspension. Granulation was carried out by spray drying using this suspension in the same manner as in Example 1. This yielded spherical granules with an average particle size of 5 μm. The obtained spherical granules were calcined in a Motoyama electric furnace KL-2030D at 1300°C for 2 hours under an atmospheric atmosphere to obtain a calcined product. This calcined product was crushed in a mortar and pestle and sieved to 75 μm to obtain magnesium oxide particles.

[0052] [Comparative Example 3] 500 g of hexagonal plate-shaped magnesium hydroxide particles (MgO purity 98.2% after ignition, average particle size 4.0 μm) were dispersed in 1423 g of ion-exchanged water together with 8.9 g of ammonium polyacrylate to form a suspension. Granulation was carried out using this suspension by spray drying in the same manner as in Example 1. This yielded spherical granules with an average particle size of 55 μm. The obtained spherical granules were calcined in a Motoyama electric furnace KL-2030D at 1300°C for 2 hours under an atmospheric atmosphere to obtain a calcined product. This calcined product was crushed in a mortar and pestle and sieved to 75 μm to obtain magnesium oxide particles.

[0053] 〔evaluation〕 For the magnesium oxide particles obtained in the examples and comparative examples, the BET specific surface area, BET specific surface area equivalent particle diameter D1, average particle diameter D2, oil absorption, thermal conductivity, circularity, and porosity were measured using the method described above. The results are shown in Table 1 below.

[0054] [Table 1] [Industrial applicability]

[0055] The present invention provides magnesium oxide particles that are easy to knead with resins, exhibit high thermal conductivity even without high filler content in the resin, and as a result, do not cause the specific gravity of the resin composition to become excessively high, as well as a method for producing the same.

Claims

1. It consists of spherical bodies with open pores formed by the partial fusion of multiple burnt magnesium oxide particles. Magnesium oxide particles having an average particle diameter (D2) of 10 μm or more and 200 μm or less, and a circularity of the projected image of 0.7 or more.

2. The magnesium oxide particles according to claim 1, wherein the BET specific surface area equivalent particle diameter (D1) of the spherical body is 3.0 μm or more and 15 μm or less.

3. Magnesium oxide particles according to claim 1 or 2, wherein the porosity within the spherical body, determined by image analysis, is 10% or more and 50% or less.

4. Magnesium oxide particles according to claim 1 or 2, wherein the ratio D2 / D1 of the average particle diameter D2 of the spherical body to the BET specific surface area-converted particle diameter D1 of the spherical body is 3 or more and 10 or less.

5. Magnesium oxide particles according to claim 1 or 2, wherein the oil absorption amount measured in accordance with JIS K5101-13-1 is 30 mL / 100 g or more.

6. A process for producing granules by granulating a raw material composition containing burnt magnesium oxide particles and flux components having an average particle diameter of 1.0 μm or more and 20.0 μm or less into spherical shapes, A method for producing magnesium oxide particles, comprising the step of calcining the granulated material at a temperature of 900°C or higher and 1700°C or lower.

7. The manufacturing method according to claim 6, wherein the flux component is a lithium compound, a boron compound, a silicon compound, or a halogen compound.

8. It contains a spherical body having open pores formed by the partial fusion of multiple calcined magnesium oxide particles, A thermally conductive filler having an average particle diameter (D2) of 10 μm or more and 200 μm or less, and a circularity of the projected image of 0.7 or more.

9. A resin composition comprising the thermally conductive filler and resin according to claim 8.

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