Magnesium oxide powder and resin composition using the same

Abstract

Provided are a magnesium oxide powder that has excellent moisture resistance and can achieve such a low dielectric loss tangent as to be applicable to devices for high frequency band, and a resin composition using the same.　A magnesium oxide powder (I) comprising coated particles (X) in which the surface of a core particle (A) containing magnesium oxide is coated with a coating layer (B) containing MgAl2O4, wherein: the ratio of MgAl2O4 to the total mass of the magnesium oxide powder (I) is more than 1 mass% but less than 38 mass%; and the median diameter (Di50) of the magnesium oxide powder (I) is 25-180 μm inclusive.

Description

[Technical Field]

[0001] The present invention relates to a magnesium oxide powder and a resin composition using the same. [Background technology]

[0002] In fields such as semiconductor encapsulation, inorganic metal oxide powders such as silica and alumina are used as fillers to improve the coefficient of thermal expansion, thermal conductivity, flame retardancy, etc. However, silica has a relatively low thermal conductivity, and alumina has a higher thermal conductivity than silica, but is also hard, which causes a problem of wear on the equipment used. Therefore, magnesium oxide powder, which has a higher thermal conductivity than silica and alumina but is also less hard than alumina, is being investigated as a filler applicable to the above fields.

[0003] It is known that magnesium oxide powder has low moisture resistance and reacts with moisture in the air to form magnesium hydroxide. Since the thermal conductivity tends to decrease when magnesium hydroxide is formed, the surface of the magnesium oxide powder is coated to improve its moisture resistance. For example, Patent Documents 1 and 2 describe coating the surface of magnesium oxide powder with alumina or a double oxide containing aluminum to improve the moisture resistance of the magnesium oxide powder.

[0004] In recent years, with the increase in the amount of information communication in the field of communications, the use of high-frequency band signals has become widespread in electronic devices, communication devices, and the like. However, the application of high-frequency band signals to such devices has also caused a problem of increased transmission loss of circuit signals. Therefore, for fillers used in high-frequency band devices, materials with low dielectric loss tangents are required.

[0005] [Patent Document 1] Japanese Patent Application Publication No. 63-248716 [Patent Document 2] Patent No. 4302690 Summary of the Invention

[0006] Therefore, an object of the present invention is to provide a magnesium oxide powder (I) that has excellent moisture resistance and can achieve a low dielectric loss tangent that is applicable to high-frequency band devices, and a resin composition using the same.

[0007] As a result of extensive research, the present inventors have discovered that a magnesium oxide powder that can solve all of the above-mentioned problems can be obtained by providing a magnesium oxide powder containing coated particles in which the surface of a core particle containing magnesium oxide is coated with a layer containing a certain amount of MgAl2O4, and by adjusting the median diameter (D50) of the magnesium oxide powder to 25 μm or more and 180 μm or less, and have thus completed the present invention. That is, the present invention has the following aspects. [1] A magnesium oxide powder (I) comprising coated particles (X) in which the surface of a core particle (A) containing magnesium oxide is coated with a coating layer (B) containing MgAl2O4, The proportion of MgAl2O4 is more than 1 mass% and less than 38 mass% with respect to the total mass of the magnesium oxide powder (I), Magnesium oxide powder (I), wherein the median diameter (Di50) of the magnesium oxide powder (I) is 25 μm or more and 180 μm or less. [2] The magnesium oxide powder (I) according to [1], wherein the proportion of periclase relative to the total mass of the magnesium oxide powder (I) is 80 mass % or more. [3] The magnesium oxide powder (I) according to [1] or [2], wherein the average circularity (ARi) of the magnesium oxide powder (I) is 0.75 or more. [4] The magnesium oxide powder (I) according to any one of [1] to [3], wherein the magnesium hydroxide content after testing measured under the following conditions is less than 50 mass%. <Measurement conditions> 10 g (M1) of magnesium oxide powder (I) is left standing in a test device at a temperature of 135°C and a humidity of 85%RH for 168 hours. After standing, the mass (M2) of the magnesium oxide powder (I) is measured, and the change in mass before and after standing is substituted into the following formula (1) to calculate the magnesium hydroxide content. {(M2-M1) / 18.0}×(40.3 / M1)×100 ···(1) (In formula (1), M1 is the mass (g) of the magnesium oxide powder (I) before standing, M2 is the mass (g) of the magnesium oxide powder (I) after standing, and 18.0 and 40.3 are the molecular weights of HO and MgO, respectively.) [5] The magnesium oxide powder (I) according to any one of [1] to [4], which has a viscosity of 2,000 Pa·s / 25°C or less as measured under the following conditions: <Measurement conditions> The viscosity of a resin composition consisting of 60% by volume of bisphenol A liquid epoxy resin (epoxy equivalent: 184 to 194) and 40% by volume of magnesium oxide powder (I) is measured using a rotational rheometer at a shear rate of 1.0 / s, plate shape: circular flat plate (10 mmφ), sample thickness: 1 mm, and temperature: 25±1°C. [6] The magnesium oxide powder (I) according to any one of [1] to [5], which is for use in resin filling. [7] A resin composition comprising the magnesium oxide powder (I) according to any one of [1] to [6] and at least one resin selected from thermoplastic resins and thermosetting resins. [8] The resin composition according to [7], which is for use as an encapsulant, a TIM material, or a substrate for a high-frequency band device.

[0008] According to the present invention, it is possible to provide a magnesium oxide powder (I) that has excellent moisture resistance and can achieve a low dielectric loss tangent that is applicable to high-frequency band devices, and a resin composition containing the same. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an example of an image in which the aluminum component is mapped on a cross-sectional image of the magnesium oxide powder (I) of the present invention using a field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will be described in detail below. The present invention is not limited to the following embodiment, and can be carried out by making appropriate modifications within the scope that does not impair the effects of the present invention. When a specific explanation given for one embodiment also applies to other embodiments, that explanation may be omitted in other embodiments. In this specification, the expression "α to β" indicating a numerical range means "above α and below β." Furthermore, in this specification, "powder" means "an aggregate of multiple particles."

[0011] [Magnesium oxide powder (I)] The magnesium oxide powder according to this embodiment is a magnesium oxide powder (I) comprising coated particles (X) in which the surface of a core particle (A) containing magnesium oxide is coated with a coating layer (B) containing MgAl2O4. The magnesium oxide powder (I) is characterized in that the proportion of MgAl2O4 relative to the total mass of the magnesium oxide powder (I) is greater than 1% by mass and less than 38% by mass, and the median diameter (Di50) of the magnesium oxide powder (I) is 25 μm or more and 180 μm or less. The magnesium oxide powder (I) according to this embodiment (hereinafter sometimes simply referred to as "powder (I)") has excellent moisture resistance and can achieve a low dielectric loss tangent suitable for use in high-frequency devices. Furthermore, the magnesium oxide powder (I) according to this embodiment also has good thermal conductivity. The magnesium oxide powder (I) according to this embodiment is described in detail below.

[0012] <Coated particles (X)> The powder (I) according to this embodiment contains coated particles (X) in which the surface of a core particle (A) containing magnesium oxide is coated with a coating layer (B) containing MgAlO. By containing such coated particles (X), the moisture resistance of the powder (I) is improved.

[0013] (Core particle (A)) The core particles (A) are particles containing magnesium oxide as a main component. "Containing magnesium oxide as a main component" means that the core particles contain more than 50% by mass of magnesium oxide relative to all components (100% by mass) that constitute the core particles. The core particles (A) may contain components other than magnesium oxide. Examples of components other than magnesium oxide include alkali components, boron, iron, and the like that are added during the production of magnesium oxide particles. When the powder (I) according to this embodiment is used, for example, as a filler for semiconductor encapsulation, the proportion of magnesium oxide in the core particles (A) is preferably 90% by mass or more, and more preferably 95% by mass or more, based on the total components (100% by mass) that constitute the core particles. Particles containing magnesium oxide in such a proportion can be obtained, for example, by an electric melting method, a firing method, or the like.

[0014] (Coating layer (B)) The coated particles (X) contained in the magnesium oxide powder (I) according to this embodiment have a coating layer (B) containing MgAl2O4. MgAl2O4 (hereinafter sometimes referred to as "spinel") is a double oxide of magnesium and aluminum. By including coated particles (X) in which the surface of a core particle (A) is coated with a coating layer (B) containing spinel, the moisture resistance of the powder (I) is improved.

[0015] The amount of spinel contained in powder (I) according to this embodiment is more than 1% by mass and less than 38% by mass, relative to the total mass of powder (I). In one embodiment, the amount of spinel may be 1.5 to 37% by mass, 1.5 to 35% by mass, 1.5 to 30% by mass, 2.0 to 30% by mass, or 2.0 to 29% by mass, relative to the total mass of powder (I). From the viewpoint of easily obtaining a resin composition with a lower viscosity when blended with a resin, the amount of spinel relative to the total mass of powder (I) may be more than 1% by mass and less than 29% by mass, or more than 1.0% by mass and 20% by mass or less. It has been conventionally practiced to improve the moisture resistance of magnesium oxide powder by coating the surfaces of magnesium oxide particles with inorganic metal oxide powder containing spinel (for example, Patent Documents 1 and 2 mentioned above). The present inventors have discovered that by controlling the amount of spinel contained in the coating layer of powder (I) containing coated particles (X) within a certain range and also adjusting the median diameter (Di50) of powder (I) within a certain range, it is possible to obtain magnesium oxide powder that not only has excellent moisture resistance but also achieves a lower dielectric tangent.

[0016] Whether the powder (I) according to this embodiment contains the coated particles (X) can be confirmed by observing the powder (I) with a scanning electron microscope, etc. The amount of spinel in the powder (I) can be confirmed by measuring the X-ray diffraction pattern of the powder (I) using an X-ray diffractometer, etc. For example, it can be measured by the following method. <Method for measuring spinel content> As a measuring device, a horizontal sample multipurpose X-ray diffractometer (for example, manufactured by Rigaku Corporation, product name "RINT-UltimaIV") is used, and the X-ray diffraction pattern of the powder (I) is measured under the following measuring conditions. X-ray source:CuKα Tube voltage: 40kV Tube current: 40mA Scan speed: 10.0° / min 2θ scan range: 10°~80° Furthermore, quantitative analysis of the crystalline phase is performed by Rietveld analysis of the obtained X-ray diffraction pattern. Specifically, Rietveld method software (for example, MDI, product name "Integrated Powder X-ray Software Jade+9.6") is used. The proportion (mass%) of the spinel crystalline phase can be calculated using the ICDD card (number: 01-075-1796).

[0017] In one embodiment, the coating layer (B) may contain a component other than spinel. Examples of the component other than spinel include inorganic metal oxides or inorganic metal double oxides (excluding spinel) containing at least one element selected from titanium, aluminum, magnesium, silicon, and calcium. Specific examples include forsterite (MgSiO), magnesium ferrite (FeMgO), magnesium titanate (MgTiO), alumina (AlO), MgO-AlO double oxide, SiO, and MgO-SiO double oxide. The coating layer (B) may contain one or more of these inorganic metal oxides or inorganic metal double oxides. To obtain a powder (I) with better moisture resistance, the coating layer (B) may be composed solely of spinel. The proportion of components other than spinel in the powder (I) can be calculated using the same method as used to measure the amount of spinel.

[0018] The coated particles (X) are particles in which a portion of the surface of the core particle (A) is coated with a coating layer (B). From the viewpoint of easily achieving high moisture resistance and a low dielectric tangent, the coated particles (X) are preferably core-shell particles in which the entire surface of the core particle (A) is coated with a coating layer (B). Note that the term "core-shell particle" refers to a coated particle in which most of the surface of the core particle (A) is coated. Whether the coated particle (X) is a core-shell particle can be determined, for example, by observing a cross-sectional image of the coated particle (X) obtained by a field emission scanning electron microscope (e.g., Carl Zeiss, product name "MERLIN, FE-SEM") and an energy dispersive X-ray spectroscopy (e.g., Bruker, product name "QUANTAX System XFlash6 / 60SDD, EDS"), that the ratio (rc / ra) of the cross-sectional perimeter ra of the core particle (A) to the perimeter rc of the portion of the cross-section of the core particle (A) that is coated with the coating layer (B) is 0.6 or more, indicating that the core particle (A) is mostly coated with the coating layer (B) (i.e., it is a core-shell particle).

[0019] In one embodiment, the proportion of coated particles (X) in powder (I) is preferably 80% or more, more preferably 90% or more. Powder (I) according to this embodiment may contain particles other than coated particles (X) (other particles) within a range that allows the powder (I) to maintain its physical properties, such as the amount of spinel and the median diameter (Di50). Examples of other particles include uncoated core particles (A) and particles of inorganic metal oxides or inorganic metal double oxides (e.g., alumina particles, silica particles, spinel particles). These may be contained alone or in combination of two or more. The inorganic metal oxide or inorganic metal double oxide particles may be particles added during production as a coating component for core particles (A).

[0020] In one embodiment, the powder (I) may contain only coated particles (X), or may contain only core-shell particles as the coated particles (X). The proportion of coated particles (X) in the powder (I) may be calculated by, for example, observing the powder (I) using the aforementioned field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectroscopy (EDS) and determining the proportion of coated particles (X) among 50 particles measured. For example, if 50 random particles within the area are observed and all 50 particles are coated particles (X), the proportion of coated particles (X) in the powder (I) can be considered to be 100%.

[0021] In one embodiment, the thickness of the coating layer (B) of the coated particle (X) may be 40 μm or less, or may be 35 μm or less, from the viewpoint of easily maintaining high thermal conductivity. From the viewpoint of easily obtaining a resin composition with a lower viscosity and good flowability when filled into a resin, the thickness may be 30 μm or less, or may be 26 μm or less. The thickness of the coating layer (B) may be a value calculated from the difference between the median diameter (Da50) of the raw material powder constituting the core particle (A) and the median diameter (Di50) of the final powder (I) during the production of the powder (I) according to this embodiment, or may be a value measured with a scanning electron microscope.

[0022] FIG. 1 shows an example of a photograph of the powder (I) according to this embodiment, taken using a field-emission scanning electron microscope (FE-SEM) and energy-dispersive X-ray spectroscopy (EDS). From FIG. 1, it can be seen that the powder (I) contains coated particles (X). The powder (I) according to this embodiment, which contains such coated particles (X), has better moisture resistance and is more likely to achieve a low dielectric tangent.

[0023] <Median diameter (Di50) of magnesium oxide powder (I)> The median diameter (Di50) of the powder (I) according to this embodiment is 25 μm or more and 180 μm or less. The powder (I) according to this embodiment can achieve both high moisture resistance and low dielectric loss tangent because the ratio of spinel to the total mass of the powder (I) is within the aforementioned range and the median diameter (Di50) is 25 to 180 μm. In one embodiment, the median diameter (Di50) of the powder (I) may be 25 to 170 μm, 30 to 170 μm, or 30 to 150 μm. In this specification, the term "median diameter (D50)" refers to the average particle diameter (D50) at which the cumulative value is 50% in the volume-based particle size distribution measured by the laser diffraction light scattering method. The cumulative particle size distribution is represented by a distribution curve with the particle diameter (μm) on the horizontal axis and the cumulative value (%) on the vertical axis. Specifically, the measurement can be performed under the following conditions. (Method for measuring median diameter (Di50)) The median diameter (Di50) of the powder (I) is determined by measuring the volumetric particle size distribution using a laser diffraction particle size distribution analyzer (for example, Beckman Coulter, Inc., product name "LS 13 320" or Microtrackbell, Inc., product name "MT3300EXII"). Specifically, a 50 cm diameter glass beaker is filled with a 50 cm diameter powder. 3100g of pure water and 0.1g of powder (I) are added and dispersed for 60 seconds using an ultrasonic homogenizer (e.g., Microtec Nichion Co., Ltd., product name "Smurt NR-50M (titanium alloy tip φ3 (NS-50M-MT3))"). The dispersed dispersion of powder (I) is added drop by drop using a dropper to the laser diffraction particle size analyzer, and measurement is performed 30 seconds after the specified amount is added. The refractive index of water is 1.33, and the refractive index of powder (I) is 1.74.

[0024] In one embodiment, from the viewpoint of easily achieving high moisture resistance and low dielectric tangent, the BET specific surface area (Si) of the powder (I) is 2.7 m 2 / g, and may be less than 2.1m 2 / g or less, and 2 From the viewpoint of improving the flowability when filled into the resin, the amount of the hydroxyl group may be 0.01 to 2.1 m / g or less. 2 / g, and 0.05 to 1.9m 2 The BET specific surface area can be measured by the following method. (Method for measuring BET specific surface area (Si)) 5 g of powder (I) is filled into the measurement cell of a fully automatic specific surface area measuring device (for example, Mountech, product name "Macsorb HM model-1201", BET one-point method), and the specific surface area is measured. Degassing conditions before measurement can be 200°C for 10 minutes. Helium can be used as the carrier gas, and nitrogen (mixed concentration: 30.5%) can be used as the adsorption gas.

[0025] In one embodiment, the average circularity (ARi) of the powder (I) may be 0.75 or more, 0.80 or more, 0.85 or more, or 0.90 or more. If the average circularity (ARi) of the powder (I) is 0.75 or more, the magnesium oxide powder tends to have a lower dielectric tangent. The average circularity (ARi) of the powder (I) can be measured by the following method. (Method for measuring average circularity (ARi)) The powder (I) is fixed with carbon tape and then coated with osmium. Then, using a scanning electron microscope (e.g., manufactured by JEOL Ltd., product name "JSM-7001F SHL"), the particles constituting the powder (I) are photographed at a magnification of 500 to 50,000 times, and the projected area (A) of the particles is calculated using an image analyzer (e.g., manufactured by Nippon Roper Co., Ltd., product name "Image-Pro Premier Ver. 9.3"). p After calculating the diameter (mm) and projected perimeter (L), the circularity is calculated using the following formula (2). The circularity of 200 randomly selected particles is calculated, and the average value is taken as the average circularity (ARi). Circularity = 4πA p / L 2 ···(2)

[0026] In one embodiment, the proportion of periclase (magnesium oxide crystals) relative to the total mass of powder (I) is preferably 80 mass% or more, more preferably 85 mass% or more, and even more preferably 87 mass% or more. In one embodiment, the total amount of periclase and spinel in powder (I) may be 100 mass%. If the proportion of periclase in powder (I) is 80 mass% or more, the proportion of components other than periclase and spinel in powder (I) decreases, making powder (I) more likely to have excellent moisture resistance and a low dielectric tangent.

[0027] In one embodiment, the periclase crystallite size of the powder (I) is 50×10 -9 The crystallite diameter is preferably 50×10 -9 Powders (I) with a diameter of m or more tend to have good thermal conductivity. The "crystallite size" refers to the value calculated using the Scherrer formula using X-ray diffraction. If the particles in the powder are polycrystalline, the crystallite size indicates the average size of the single crystals in the polycrystalline body.

[0028] In one embodiment, the average particle density of the powder (I) is 0.1 to 7.0 g / cm 3 is preferred, and 0.5 to 5.5 g / cm 3 More preferably, the average particle density is 0.1 to 7.0 g / cm3 If the powder (I) is used, it can be easily dispersed uniformly in the resin, and the thermal conductivity and dielectric properties are likely to be good. The average particle density of the powder (I) can be measured by the following method. (Method for measuring average particle density) 2.0 g of powder (I) is placed in a measurement sample cell, and the average particle density is measured by the gas (helium) substitution method using a dry density meter (for example, Shimadzu Corporation, product name "Accupyk II 1340").

[0029] Powder (I) according to this embodiment has excellent moisture resistance. In one embodiment, the magnesium hydroxide content measured under the following conditions is preferably less than 50% by mass, more preferably 30% by mass or less, and even more preferably 10% by mass or less. Because powder (I) according to this embodiment has excellent moisture resistance, magnesium hydroxide is less likely to be produced. (Conditions for measuring magnesium hydroxide content after test) 10 g (M1) of magnesium oxide powder (I) is left standing for 168 hours in a test device (for example, Espec Corp., product name: Highly Accelerated Life Test Device EHS-212M, condition: unsaturated mode) at a temperature of 135°C and a humidity of 85%RH. After leaving it standing, the mass (M2) of the magnesium oxide powder (I) is measured, and the change in mass before and after leaving it is substituted into the following formula (1) to calculate the magnesium hydroxide content. {(M2-M1) / 18.0}×(40.3 / M1)×100 ···(1) (In formula (1), M1 is the mass (g) of the magnesium oxide powder (I) before standing, M2 is the mass (g) of the magnesium oxide powder (I) after standing, and 18.0 and 40.3 are the molecular weights of HO and MgO, respectively.)

[0030] In one embodiment, the viscosity of powder (I) measured under the following conditions is preferably 2,000 Pa·s / 25°C or less, more preferably 1,000 Pa·s / 25°C or less, and even more preferably 500 Pa·s / 25°C or less. Powder (I) according to this embodiment is a powder containing particles with relatively good surface smoothness, and therefore tends to have good flowability when filled into a resin. (Viscosity measurement conditions) A resin composition consisting of 60% by volume of bisphenol A liquid epoxy resin (epoxy equivalent: 184 to 194, for example, Mitsubishi Chemical Corporation, product name "JER828") and 40% by volume of powder (I) is measured for viscosity using a rotational rheometer at a shear rate of 1.0 / s, plate shape: circular flat plate (10 mmφ), sample thickness: 1 mm, and temperature: 25±1°C.

[0031] In one embodiment, the powder (I) may be surface-treated with a surface treatment agent to improve fillability and flowability in resin. This also facilitates the reduction of polar functional groups on the particle surfaces constituting the powder, making it easier to achieve a lower dielectric tangent. Examples of surface treatment agents include silane coupling agents and aluminate coupling agents. These may be used alone or in combination of two or more. Among these, treatment with a silane coupling agent is preferred to facilitate the reduction of polar functional groups on the particle surfaces, and silazanes such as hexamethyldisilazane (HMDS) and silane coupling agents having a vinyl group such as vinyltrimethoxysilane are more preferred. The presence or absence of surface treatment of the powder (I) can be confirmed by analyzing the powder using, for example, IR, TG-DTA, mass spectrometry, or the like.

[0032] In one embodiment, the thermal conductivity of powder (I) measured under the following conditions may be 4.0 to 8.0 W / mK, or 5.0 to 7.0 W / mK. Powder (I) according to this embodiment has excellent moisture resistance and can achieve a low dielectric tangent, while also easily maintaining high thermal conductivity. (Thermal conductivity measurement conditions) Powder (I) and spherical alumina powder (e.g., manufactured by Denka Co., Ltd., product names "DAW-07" or "ASFP-40") are mixed in a volume ratio of 51:49 to prepare a mixed powder. The mixed powder is filled into a silicone resin (e.g., manufactured by Shin-Etsu Chemical Co., Ltd., product names "SE1885:A" or "SE1885:B") so that the mixed powder ratio is 77.5 volume % to prepare an evaluation sheet. The evaluation sheet is measured using a thermal resistance measuring device (e.g., manufactured by Hitachi Technology & Services, Ltd., product name "TRM-046RHHT") to determine the thermal conductivity.

[0033] In one embodiment, the dielectric loss tangent at 36 GHz of a resin sheet containing powder (I) (a sheet made of polyethylene resin and powder (I). The proportion of powder (I) in the resin sheet is 20% by volume), measured under the conditions described below, is 4.0 × 10 -4 Less than 3.5 x 10 is preferable. -4 Less than 3.0 x 10 is preferable. -4 The following is more preferable. The "dielectric loss tangent" is a filler-equivalent dielectric loss tangent (tanδ) calculated from the following formula (3): f ) refers to

[0034] tanδ c =V f tanδ f +(1-V f )·tanδ r ···(3) In formula (3), V f represents the filler content (mass%), and tanδ c represents the dielectric tangent of the resin sheet, and tanδ r represents the dielectric loss tangent of polyethylene resin (PE).

[0035] As described above, the powder (I) according to this embodiment has excellent moisture resistance and can achieve a low dielectric loss tangent suitable for use in high-frequency band devices. The reason why the powder (I) according to this embodiment can achieve a low dielectric loss tangent is thought to be that the total amount of polar functional groups can be reduced by reducing the particle surface area, and that the introduction of a spinel layer can reduce the surface OH groups and surface adsorbed water.

[0036] [Method for producing magnesium oxide powder (I)] The magnesium oxide powder (I) according to this embodiment can be produced, for example, by a method including coating a raw material powder containing magnesium oxide with a coating component containing aluminum, followed by firing (step (1)). Hereinafter, one embodiment of the method for producing the powder (I) including step (1) will be described.

[0037] <Process (1)> In the manufacturing method according to the present embodiment, step (1) involves coating a raw material powder containing magnesium oxide with a coating component containing aluminum, followed by firing. Here, the "raw material powder" refers to the core particles (A) containing magnesium oxide as a main component.

[0038] (Raw material powder) In one embodiment, the median diameter (Da50) of the raw material powder is preferably 10 to 150 μm, from the viewpoint of easily controlling the median diameter (Di50) of the resulting powder (I) to a range of 25 to 180 μm. The median diameter (Da50) may be 15 to 150 μm, 20 to 140 μm, or 40 to 130 μm. When the median diameter (Da50) of the raw material powder is within the above range, it becomes easier to obtain a magnesium oxide powder (I) having a low dielectric tangent.

[0039] In one embodiment, the average circularity (ARa) of the raw material powder may be 0.70 or more, 0.80 or more, or 0.90 or more, from the viewpoint of easily improving fillability into resin. The average circularity (ARa) of the raw material powder can be measured in the same manner as the average circularity (ARi) of powder (I) described above. In one embodiment, the ratio of the average circularity (ARi) of powder (I) to the average circularity (ARa) of the raw material powder ((ARi) / (ARa)) may be 1.0 or more, or 1.05 or more. When (ARi) / (ARa) is 1.0 or more, the coating layer is more likely to be formed uniformly, and the surface irregularities of the particles constituting powder (I) are more likely to be reduced.

[0040] In one embodiment, the BET specific surface area (Sa) of the raw material powder is 0.01 to 20 m 2 / g, and may be 0.01 to 10m 2 / g, and may be 0.01 to 1m 2 / g. The BET specific surface area (Sa) of the raw material powder can be measured by the same method as for powder (I). In one embodiment, the ratio of the BET specific surface area (Si) of powder (I) to the BET specific surface area (Sa) of the raw material powder ((Si) / (Sa)) may be 5.0 or less. If (Si) / (Sa) is 5.0 or less, the resulting powder (I) is likely to have better fluidity and fillability when filled into a resin.

[0041] The method for preparing the raw material powder is not particularly limited, and may be, for example, prepared by calcining magnesium hydroxide powder.

[0042] The raw material powder contains impurities such as alkali metal elements such as Li, Na, and K, and metal elements such as Fe, as well as Cl, from the viewpoint of reducing the dielectric loss tangent and ensuring the reliability of electronic materials. - , Br - It is preferable that the content of anions such as these is low. Specifically, it is preferable that the total amount of these impurities and anions in the raw material powder is 0.01 mass % or less.

[0043] (Coating method) In the production method according to this embodiment, the method for coating the raw material powder is not particularly limited, and examples that can be used include a shaking mixer, a flame fusion method, tumbling fluidized bed coating, etc. Among these, it is preferable to coat the raw material powder by tumbling fluidized bed coating, from the viewpoints that it is easy to control the amount of spinel in the obtained powder (I) and it is easier to control the BET specific surface area (Si) and the average circularity (ARi).

[0044] (Tumbling Fluidized Bed Coating) In one embodiment, step (1) can include spraying a slurry containing an aluminum-containing coating component onto the raw material powder to perform tumbling fluidized bed coating. Tumbling fluidized bed coating, also known as tumbling fluidized bed coating or tumbling fluidized granulation coating, is a coating technique using a coating device equipped with a blade rotor at the bottom of a general fluidized bed device. The aluminum-containing coating component preferably contains an inorganic metal oxide powder (B1) containing alumina powder. The inorganic metal oxide powder (B1) may contain other powders besides alumina powder, such as silica powder. In a preferred embodiment, the ratio of the median diameter (Db150) of the inorganic metal oxide powder (B1) to the median diameter (Da50) of the raw material powder ((Db150) / (Da50)) is 8.0×10 -6 ~1.0×10 -1 may be 5.0 x 10 -5 ~5.0×10 -2 If (Db150) / (Da50) is within the above range, the surface of the raw material powder can be more efficiently coated.

[0045] In one embodiment, the proportion of the coating component containing aluminum in the slurry may be 0.1 to 80 mass% or 1 to 50 mass% relative to the total mass of the slurry, from the viewpoint of easily adjusting the amount of spinel contained in the obtained powder (I) to more than 1 mass% and less than 38 mass%.

[0046] In one embodiment, the dispersion medium contained in the slurry preferably contains water or ethanol, and more preferably contains water. The slurry may also contain components other than the coating component and the dispersion medium. Examples of other components include dispersants and binders. These other components may be contained alone or in combination of two or more.

[0047] In one embodiment, the amount of the aluminum-containing coating component sprayed onto the raw material powder is preferably 1 to 25 mass% relative to the total amount (100 mass%) of the raw material powder and the aluminum-containing coating component, from the viewpoint of easily adjusting the amount of spinel contained in the resulting powder (I) to more than 1 mass% and less than 38 mass%. That is, when the raw material powder is coated by tumbling fluidized bed coating, the slurry may be sprayed onto the raw material powder so that the proportion of the aluminum-containing coating component relative to the total amount (100 mass%) of the raw material powder and the aluminum-containing coating component is 1 to 25 mass%. In other embodiments, the amount of the coating component sprayed may be 1 mass% or more and less than 25 mass%, 1 to 20 mass%, 1 mass% or more and less than 20 mass%, or 1 to 18 mass% relative to the total amount.

[0048] In one embodiment, the tumbling fluidized bed coating may be carried out under conditions of 20 to 150°C, 30 to 100°C, or 50 to 90°C. The coating time is not particularly limited as long as it is a time that allows the surface of the raw material powder to be sufficiently coated. From the viewpoint of easily forming a uniform coating layer (B), the coating time may be 0.01 to 24 hours, 0.05 to 24 hours, or 0.1 to 12 hours.

[0049] The tumbling fluidized bed coating can be carried out using a conventionally known tumbling fluidized bed apparatus, such as the "Tumbling Fluidized Granulation Coating Apparatus MP (Multiplex)" manufactured by Powrex Corporation.

[0050] <Firing> In the production method according to this embodiment, step (1) involves firing the raw material powder after coating it. From the viewpoint of easily forming a uniform coating layer (B), the firing temperature is preferably 500 to 1600°C, more preferably 700 to 1600°C, even more preferably 1000 to 1600°C, and particularly preferably 1000 to 1400°C. In one embodiment, the firing temperature may be higher than 1000°C and equal to or lower than 1600°C. Furthermore, from the viewpoint of easily forming a uniform coating layer (B), the firing time is preferably 0.5 to 10 hours, more preferably 1 to 8 hours.

[0051] <Other processes> After step (1), the powder (I) obtained may be in the form of aggregates. Therefore, a crushing treatment may be carried out as necessary. The crushing method is preferably carried out under conditions that make it difficult for the BET specific surface area (Si) of the powder (I) to change, and for example, a mortar, a bead mill, a ball mill, or the like can be used.

[0052] The method may also include a step of surface-treating the obtained powder (I) with a surface treatment agent, a washing step for reducing impurities (such as the above-mentioned anions) in the powder (I), and the like.

[0053] In one embodiment, after firing the raw material powder, the obtained powder (I) may be classified by sieving, air classification, etc. By classifying the powder (I), it becomes easier to control the median diameter (Di50), BET specific surface area (Si), etc. of the powder (I) within a suitable range.

[0054] [Application] The powder (I) according to this embodiment has excellent moisture resistance, and when filled into a resin, it can achieve a low dielectric loss tangent suitable for use in high-frequency band devices. Therefore, the powder (I) according to this embodiment can be suitably used as a filler for resins, particularly as a filler for resin compositions used in sealing materials for high-frequency band devices. Another embodiment of the powder (I) is its use as an inorganic filler for sealing materials for high-frequency band devices, or a method for using the same. Here, the "high-frequency band device" may be a mobile phone or an automobile load member that uses high-frequency radio waves.

[0055] [Resin composition] The resin composition according to this embodiment contains the magnesium oxide powder (I) and at least one resin selected from thermoplastic resins and thermosetting resins. The content of powder (I) in the resin composition is not particularly limited and can be adjusted appropriately depending on the purpose. Since the powder (I) according to this embodiment has good fluidity when filled into a resin, the amount of powder blended in the resin composition can be adjusted as desired to obtain desired dielectric properties. For example, when used as a substrate material for high frequency bands or an insulating material, the powder may be blended in an amount ranging from 1 to 99% by mass, more preferably from 10 to 90% by mass, based on the total mass of the resin composition.

[0056] <Resin> The resin composition according to the present embodiment includes at least one resin selected from thermoplastic resins and thermosetting resins. More specifically, examples of the resin include polyethylene resins, polypropylene resins, epoxy resins, silicone resins, phenolic resins, melamine resins, urea resins, unsaturated polyester resins, fluororesins, polyamide-based resins such as polyimide resins, polyamide-imide resins, and polyetherimide resins, polyester-based resins such as polybutylene terephthalate resins and polyethylene terephthalate resins, polyphenylene sulfide resins, wholly aromatic polyester resins, polysulfone resins, liquid crystal polymer resins, polyethersulfone resins, polycarbonate resins, maleimide-modified resins, ABS resins, AAS (acrylonitrile-acrylic rubber-styrene) resins, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resins, hydrocarbon-based elastomer resins, polyphenylene ether resins, and aromatic polyene-based resins. These may be used alone or in combination of two or more.

[0057] The resin composition according to this embodiment may contain a curing agent, a curing accelerator, a release agent, a coupling agent, a colorant, a flame retardant, an ion scavenger, etc., within the range that does not impair the effects of the present invention.

[0058] <Method of manufacturing resin composition> The method for producing the resin composition is not particularly limited, and the resin composition can be produced by stirring, dissolving, mixing, and dispersing predetermined amounts of each material. The apparatus for mixing, stirring, dispersing, etc., of these mixtures is not particularly limited, and examples that can be used include a mortar and pestle machine equipped with a stirring and heating device, a three-roll mill, a ball mill, and a planetary mixer. These apparatuses may also be used in appropriate combination.

[0059] As described above, the resin composition containing the magnesium oxide powder according to this embodiment has excellent moisture resistance and can achieve a low dielectric loss tangent. Furthermore, the resin composition containing the magnesium oxide powder according to this embodiment has low viscosity, and therefore is also excellent in processability and workability. [Example]

[0060] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following description.

[0061] [Example 1] As the raw material powder, magnesium oxide powder (manufactured by Denka Co., Ltd., product name "DMG-50", median diameter (Da50): 50 μm, BET specific surface area (Sa): 0.2 m) was used. 2 / g, average circularity (ARa): 0.93) was used as the coating component, and alumina powder (manufactured by Cabot Specialty Chemicals, Inc., product name "CAB-O-SPERSE PG008"), median diameter (Db iA slurry containing 50:100 nm of magnesium oxide powder was sprayed onto the raw material powder to perform tumbling fluidized bed coating. The slurry was sprayed onto the magnesium oxide powder in an amount such that the ratio of the coating component to the total amount (100 mass%) of the magnesium oxide powder and the coating component was 5 mass% (magnesium oxide powder 95 mass%, coating component 5 mass% (equivalent to alumina powder)). The magnesium oxide powder was then fired at 1,000°C for 1 hour to obtain magnesium oxide powder (I). The spinel content, periclase content, BET specific surface area (Si), presence or absence of coated particles (X), median diameter (Di50), and average circularity (ARi) of the obtained magnesium oxide powder (I) were measured under the following conditions. The physical property values ​​of the raw material powder and alumina powder were also measured under the following conditions. The results are shown in Table 1.

[0062] <Method for measuring the amount of spinel in powder (I)> The X-ray diffraction pattern of powder (I) was measured using a horizontal sample multipurpose X-ray diffractometer (Rigaku Corporation, product name "RINT-UltimaIV") under the following measurement conditions. X-ray source:CuKα Tube voltage: 40kV Tube current: 40mA Scan speed: 10.0° / min 2θ scan range: 10°~80° Furthermore, quantitative analysis of the crystalline phase was performed by Rietveld analysis of the obtained X-ray diffraction pattern. Specifically, Rietveld analysis software (MDI, product name "Integrated Powder X-ray Software Jade+9.6") was used for the analysis. The proportion (mass%) of the spinel crystalline phase was calculated using an ICDD card (number: 01-075-1796).

[0063] <Method for measuring the amount of periclase in powder (I)> The X-ray diffraction pattern of powder (I) was measured using a horizontal sample multipurpose X-ray diffractometer (Rigaku Corporation, product name "RINT-UltimaIV") under the following measurement conditions. X-ray source:CuKα Tube voltage: 40kV Tube current: 40mA Scan speed: 10.0° / min 2θ scan range: 10°~80° The crystalline phase was quantitatively analyzed by Rietveld analysis of the obtained X-ray diffraction pattern. Specifically, the analysis was performed using Rietveld method software (MDI, product name "Integrated Powder X-ray Software Jade+9.6"). The proportion (mass%) of the periclase crystalline phase was calculated using an ICDD card (number: 00-045-0946).

[0064] <Measuring method for median diameter (Di50) of powder (I)> The median diameter (D50) of each material was determined by measuring the volumetric particle size distribution using a laser diffraction particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name "LS 13 320"). Specifically, a 50 cm 3 100g of pure water and 0.1g of raw powder (or powder (I)) were placed in a container, and dispersion was performed for 60 seconds at 25W output using an ultrasonic homogenizer (Microtec Nichion Co., Ltd., product name "Smurt NR-50M (titanium alloy tip φ3 (NS-50M-MT3))"). The dispersion of the raw powder (or powder (I)) that had been dispersed was added dropwise to the laser diffraction particle size analyzer using a dropper, and measurements were performed 30 seconds after the specified amount was added. The refractive index of water was 1.33, and the refractive index of powder (I) was 1.74. The median diameter (D50) was calculated from the particle diameter corresponding to the 50% cumulative value in the volume-based cumulative particle size distribution of the particle diameters to be measured.

[0065] <Method for measuring the BET specific surface area (Si) of powder (I)> 5 g of powder (I) was filled into the measurement cell of a fully automatic specific surface area analyzer (BET single-point method) (Mountech Macsorb HM model-1201 fully automatic specific surface area analyzer), and the specific surface area was measured. The degassing conditions before the measurement were 200°C and 10 minutes. Helium was used as the carrier gas, and nitrogen (mixed concentration: 30.5%) was used as the adsorption gas.

[0066] <Presence or absence of coated particles (X) and core-shell particles> The powder (I) was observed with a scanning electron microscope (JEOL Ltd., product name "JSM-7001F") to confirm the presence or absence of coated particles (X). Furthermore, cross-sectional images of the powder (I) were obtained using a field-emission scanning electron microscope (Carl Zeiss, product name "MERLIN, FE-SEM") and energy-dispersive X-ray spectroscopy (Bruker, product name "QUANTAX System XFlash6 / 60SDD, EDS") to calculate the ratio (rc / ra) of the cross-sectional perimeter of the coated particle to the perimeter of the portion of the coated particle covered with the coating layer (B) in the cross section. The presence or absence of core-shell particles was confirmed. The measurements were performed at an image acquisition magnification of 1000x, a voltage of 10 kV, a current of 500 nA, and a measurement time of 30 seconds. Elemental mapping of aluminum and magnesium was performed. Image analysis was performed using ImageJ, and for each particle image, ra was the perimeter of the magnesium component mapping area, which forms the core, and rc was the perimeter of the area surrounding the magnesium component that is in contact with the aluminum component, which forms the shell (it was determined to be "in contact" if the area one pixel outside the magnesium component was the mapping area of ​​the aluminum component), and rc / ra was calculated; particles with rc / ra of 0.6 or greater were determined to be core-shell particles. The results are shown in Table 1.

[0067] <Method for measuring average circularity (ARi)> The magnesium oxide powder (I) was fixed with carbon tape and then coated with osmium. Then, using a scanning electron microscope (manufactured by JEOL Ltd., product name "JSM-7001F SHL"), the particles constituting the powder (I) were photographed at a magnification of 500 to 50,000 times, and the projected area (A) of the particles was calculated using an image analyzer (manufactured by Nippon Roper Co., Ltd., product name "Image-Pro Premier Ver. 9.3"). p After calculating the diameter (mm) and projected perimeter (L), the circularity was calculated using the following formula (2): The circularity was calculated for 200 randomly selected particles, and the average value was taken as the average circularity (ARi). Circularity = 4πA p / L 2 ···(2)

[0068] Next, the moisture resistance and dielectric loss tangent of the obtained powder (I) were evaluated under the following conditions. The thermal conductivity and fluidity were also evaluated. The results are shown in Table 1.

[0069] <Moisture resistance evaluation> The powder (I) was subjected to a moisture resistance test under the following conditions, and the magnesium hydroxide content after the test was measured and evaluated according to the following evaluation criteria. 10 g (M1) of magnesium oxide powder (I) was left to stand for 168 hours in a test device (manufactured by Espec Corporation, product name "Highly Accelerated Life Test Device EHS-212M" under unsaturated mode) at a temperature of 135°C and a humidity of 85%RH. The mass (M2) of the magnesium oxide powder (I) after standing was measured, and the change in mass before and after standing was substituted into the following formula (1) to calculate the magnesium hydroxide content. {(M2-M1) / 18.0}×(40.3 / M1)×100 ···(1) (In formula (1), M1 is the mass (g) of the magnesium oxide powder (I) before standing, M2 is the mass (g) of the magnesium oxide powder (I) after standing, and 18.0 and 40.3 are the molecular weights of HO and MgO, respectively.) (Evaluation criteria) Excellent: Conversion rate to magnesium hydroxide is less than 10% by mass. Good: The rate of conversion to magnesium hydroxide is 10% by mass or more and less than 30% by mass. Acceptable: Conversion rate to magnesium hydroxide is 30% by mass or more but less than 50% by mass. Unacceptable: Conversion rate to magnesium hydroxide is 50% or more by mass.

[0070] <Evaluation of dielectric loss tangent> Powder (I) and polyethylene resin powder (manufactured by Sumitomo Seika Chemicals Co., Ltd., trade name "Flothane (registered trademark) UF-20S") were weighed so that the loading of powder (I) was 20% by volume, and mixed using a vibration mixer (manufactured by Resodyn) at an acceleration of 60 G for a processing time of 2 minutes to obtain a resin composition. The obtained resin composition was placed in a metal frame with a diameter of 3 cm in an amount to give a thickness of approximately 0.3 mm, and sheeted using a nanoimprinting device (manufactured by SCIVAX, trade name "X-300") under conditions of 140°C, 5 minutes, and 30,000 N. The obtained sheet was cut into a size of 1.5 cm x 1.5 cm to obtain an evaluation sample. Next, a 36 GHz cavity resonator (manufactured by Samtec Co., Ltd.) was connected to a vector network analyzer (manufactured by Keysight Technologies, product name "85107"), and the evaluation sample was placed so as to cover a 10 mm diameter hole in the cavity resonator, and the resonance frequency (f0) and unloaded Q value (Qu) were measured. The evaluation sample was rotated 60 degrees for each measurement, and similar measurements were repeated five times. The average values ​​of the obtained f0 and Qu were used as the measured values, and the dielectric loss tangent (tanδ) was calculated using the following equation (3) using analysis software (manufactured by Samtec Co., Ltd.): f The measurement was carried out at a temperature of 20°C and a humidity of 60% RH. The obtained dielectric loss tangent values ​​were evaluated according to the following evaluation criteria. tanδ c =V f tanδ f +(1-V f )·tanδ r ···(3) (In formula (3), V f represents the filler content (mass%), and tanδ c represents the dielectric tangent of the resin sheet, and tanδ r represents the dielectric tangent of polyethylene resin (PE). (Evaluation criteria) Excellent: Dielectric tangent is 3.0 x 10 -4 below. Good: Dielectric tangent is 3.0 x 10 -4 Super 3.5×10 -4 below. Acceptable: Dielectric tangent is 3.5 x 10 -4 Super 4.0×10 -4below. Unacceptable: Dielectric tangent is 4.0 x 10 -4 Super.

[0071] <Thermal conductivity evaluation> A mixed powder was prepared by mixing magnesium oxide powder and spherical alumina powder (a mixture of DAW-07 and ASFP-40 powders manufactured by Denka Co., Ltd., with a volume ratio of (DAW-07) / (ASFP-40) = 70 / 30). The mixed powder was then filled into a silicone resin (a mixture of SE1885:A and SE1885:B manufactured by Shin-Etsu Chemical Co., Ltd., with a volume ratio of (SE1885:A) / (SE1885:B) = 50 / 50). The mixed powder was mixed to a ratio of 77.5% by volume and mixed using a mixer equipped with a stirring blade to obtain a resin composition. The resin composition was then molded using a sheet coater to obtain a 3-mm-thick evaluation sheet. The evaluation sheet was measured using a thermal resistance measuring device (manufactured by Hitachi Technology and Services, Ltd., product name "TRM-046RHHT") to determine the thermal conductivity. The measurement was performed in a constant load mode with a set load of 2N. Evaluation was also performed according to the following evaluation criteria, with a rating of B or higher being considered a pass. (Evaluation criteria) Excellent: Thermal conductivity exceeds 6.0 W / mK. Good: Thermal conductivity is greater than 4.0 W / mK and less than 6.0 W / mK. Not acceptable: Thermal conductivity is 4.0W / mK or less.

[0072] <Liquidity evaluation> A resin composition was prepared by mixing 60% by volume of a bisphenol A liquid epoxy resin (epoxy equivalent: 184-194, manufactured by Mitsubishi Chemical Corporation, product name "JER828") and 40% by volume of powder (I) and kneading the mixture with a planetary mixer (manufactured by Thinky Corporation, product name "Awatori Rentaro (registered trademark) AR-250", rotation speed 2000 rpm). Next, the shear viscosity of the resulting resin composition at 25°C was measured using a rotational rheometer (manufactured by Anton Paar, product name "MCR-302") under the following conditions. Plate shape: circular flat plate 10mmφ Sample thickness: 1 mm Temperature: 25±1℃ Speed: 1.0 / s The viscosity thus obtained was evaluated according to the following evaluation criteria, and a rating of C or higher was deemed to be acceptable. Excellent: Viscosity of resin composition is 500 Pa·s / 25°C or less. Good: Viscosity of the resin composition is more than 500 Pa·s / 25°C and 1,000 Pa·s / 25°C or less. Acceptable: Viscosity of resin composition is over 1,000 Pa·s / 25°C and up to 2,000 Pa·s / 25°C. Not permitted: Viscosity of resin composition exceeds 2,000 Pa·s / 25°C.

[0073] [Examples 2 to 8 and Comparative Examples 1 to 6] Powder (I) was prepared in the same manner as in Example 1, except that the raw material powders and production conditions were as shown in Table 1. For each powder (I), the spinel content, periclase content, BET specific surface area, presence or absence of coated particles (X), median diameter (Di50), and average circularity (ARi) were measured under the same conditions as in Example 1. In addition, the moisture resistance, dielectric loss tangent, fluidity, and thermal conductivity were evaluated under the same conditions as in Example 1. The results are shown in Table 1.

[0074] The raw materials used in each example are as follows: <Raw material powder (core particle (A))> DMG50: Magnesium oxide powder (manufactured by Denka Co., Ltd., median diameter (Da50): 50 μm, BET specific surface area (Sa): 0.2 m 2 / g, average circularity (ARa): 0.93). DMG120: Magnesium oxide powder (manufactured by Denka Co., Ltd., median diameter (Da50): 120 μm, BET specific surface area (Sa): 0.1 m 2 / g, average circularity (ARa): 0.94). COOLMAG: Magnesium oxide powder (manufactured by Tateho Chemical Co., Ltd., median diameter (Da50): 10.4 μm, BET specific surface area (Sa): 0.3 m 2 / g, average circularity (ARa): 0.84). <Coating component> Al2O3 powder: Cabot Specialty Chemicals, Inc., product name "PG008", median diameter (Dbi 50):100nm.

[0075] [Table 1]

[0076] As shown in Table 1, the powders (I) of Examples 1 to 8, which satisfy the constitution of the present invention, were excellent in moisture resistance and achieved a low dielectric loss tangent. Furthermore, the flowability and thermal conductivity were also good. On the other hand, Comparative Example 1, in which the median diameter (Di50) of the powder (I) was less than 25 μm, Comparative Example 2, in which the ratio of spinel in the powder (I) was 0 mass%, Comparative Examples 4 and 5, in which the ratio of spinel in the powder (I) was 1 mass%, and Comparative Example 6, in which the median diameter (Di50) exceeded 180 μm, exhibited poor moisture resistance and high dielectric loss tangent values. Comparative Example 3, in which the ratio of spinel in the powder (I) was 38 mass%, exhibited good moisture resistance but a high dielectric loss tangent. The dielectric loss tangent value of uncoated magnesium oxide powder not containing coated particles (X), measured by the above method, was 6.7 × 10 -4 The powders (I) of Examples 1 to 8 achieved a lower dielectric loss tangent than the uncoated magnesium oxide powder. From the above results, it was confirmed that the powder (I) according to this embodiment has excellent moisture resistance and can achieve a low dielectric loss tangent. The dielectric loss tangent of the powder (I) according to this embodiment was a value that was sufficient for application as a filler for high-frequency band devices. [Industrial Applicability]

[0077] The powder (I) according to this embodiment has excellent moisture resistance and can achieve a low dielectric loss tangent when filled in a resin. Therefore, the powder (I) according to this embodiment and a resin composition using the powder (I) can be used as a ceramic filler for high-frequency devices.

Claims

1. The surface of the core particle (A) containing magnesium oxide is ２ O ４ A magnesium oxide powder (I) comprising coated particles (X) coated with a coating layer (B) comprising: MgAl contained in magnesium oxide powder (I) ２ O ４ The total amount of is more than 1% by mass and less than 38% by mass relative to the total mass of the magnesium oxide powder (I), The magnesium oxide powder (I) has a median diameter (Di50) of 25 μm or more and 180 μm or less.

2. 2. The magnesium oxide powder (I) according to claim 1, wherein the proportion of periclase relative to the total mass of the magnesium oxide powder (I) is 80 mass% or more.

3. The magnesium oxide powder (I) according to claim 1 or 2, wherein the magnesium oxide powder (I) has an average circularity (ARi) of 0.75 or more.

4. 3. The magnesium oxide powder (I) according to claim 1 or 2, wherein the magnesium hydroxide content after testing measured under the following conditions is less than 50 mass%. <Measurement conditions> 10 g (M1) of magnesium oxide powder (I) was left standing for 168 hours in a test device at a temperature of 135°C and a humidity of 85% RH. The mass (M2) of the magnesium oxide powder (I) after standing was measured, and the change in mass before and after standing was substituted into the following formula (1) to calculate the magnesium hydroxide content. {(M2-M1) / 18.0}×(40.3 / M1)×100...(1) (In formula (1), M1 is the mass (g) of the magnesium oxide powder (I) before standing, M2 is the mass (g) of the magnesium oxide powder (I) after standing, 18.0 and 40.3 are respectively H ２ are the molecular weights of MgO and MgO.

5. 3. The magnesium oxide powder (I) according to claim 1 or 2, having a viscosity measured under the following conditions of 2,000 Pa·s / 25°C or less. <Measurement conditions> The viscosity of a resin composition consisting of 60% by volume of a bisphenol A type liquid epoxy resin (epoxy equivalent: 184 to 194) and 40% by volume of magnesium oxide powder (I) is measured using a rotational rheometer at a shear rate of 1.0 / s, a plate shape of a circular flat plate (10 mmφ), a sample thickness of 1 mm, and a temperature of 25±1°C.

6. The magnesium oxide powder (I) according to claim 1 or 2, which is for use in filling resins.

7. A resin composition comprising the magnesium oxide powder (I) according to claim 1 or 2 and at least one resin selected from thermoplastic resins and thermosetting resins.

8. The resin composition according to claim 7, which is used as an encapsulant, a TIM material, or a substrate for a high-frequency band device.

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