Inorganic powder and resin composition using same

Abstract

This inorganic powder includes amorphous particles with an aspect ratio of less than 0.90, and spherical particles with an aspect ratio of 0.90 or more, and has an angle of repose of between 33° and 56° (non-inclusive).

Description

Inorganic powder and resin composition using the same

[0001] The present disclosure relates to an inorganic powder and a resin composition using the same.

[0002] Heat generated by passing current through an electronic component is dissipated via a heat sink. A known technique involves filling the space between the electronic component and the heat sink with a heat dissipation material in order to improve heat dissipation efficiency. One example of the heat dissipation material is a resin composition containing a resin and an inorganic powder. Examples of the inorganic powder include silicon nitride particles (see, for example, Patent Document 1), alumina particles (see, for example, Patent Document 2), or both (see, for example, Patent Document 3).

[0003] Patent Document 1 discloses a liquid encapsulating resin composition before curing, which contains as essential components (A) an epoxy resin, (B) an epoxy resin curing agent, and (C) silicon nitride powder.

[0004] Patent Document 2 discloses a liquid encapsulating resin composition before curing, which contains a resin material and a filler made of an inorganic material, and preferably uses alumina particles as the filler. It also discloses that the generation of voids can be suppressed by improving the flowability of the resin composition before curing, for example by reducing the filler content.

[0005] Patent Document 3 discloses a resin composition containing silicon nitride, spherical thermally conductive particles (alumina particles), and a resin. The 50% particle size of the silicon nitride is 0.1 to 15 μm, and the 50% particle size of the alumina particles is 10 to 100 μm. The resin composition contains 2 to 30% by volume of silicon nitride, 30 to 80% by volume of alumina particles, and 55 to 85% by volume of silicon nitride and alumina particles combined.

[0006] JP 2000-109651 A JP 2013-134983 A Japanese Patent No. 6508508 A

[0007] In recent years, the increase in heat generation in electronic components has become a problem due to the increase in heat generation in ICs caused by the high integration of ICs in electronic devices and the use of high-current-driven electronic components due to the electrification of electric vehicles, aircraft, etc. In order to achieve more effective heat dissipation, it is important to form a resin composition with high thermal conductivity.

[0008] In order to improve the thermal conductivity of a resin composition, the inventors considered using an inorganic powder containing two types of inorganic particles with different aspect ratios as a filler for the resin composition, and discovered that the resin composition tends to have more voids than when a single inorganic particle is used as a filler.Since voids in a resin composition cause a decrease in the thermal conductivity of the resin composition, it is important to reduce the voids in the resin composition in order to improve the heat dissipation properties of the resin composition.

[0009] None of Patent Documents 1 to 3 discusses the increase in voids in a resin composition when an inorganic powder containing such two types of inorganic particles is used as a filler, and therefore it has not been known what kind of inorganic powder can suppress the formation of voids in a resin composition. Therefore, one embodiment of the present invention aims to provide an inorganic powder containing two types of particles with different aspect ratios, which, when used as a filler for a resin composition, can produce a resin composition with few voids. Furthermore, another embodiment of the present invention aims to provide a resin composition using the inorganic powder.

[0010] A first aspect of the present invention is an inorganic powder comprising irregular particles having an aspect ratio of less than 0.90 and spherical particles having an aspect ratio of 0.90 or more, and having an angle of repose of more than 33° and less than 56°.

[0011] A second aspect of the present invention is the inorganic powder according to the first aspect, wherein the irregular particles are silicon nitride particles, and the spherical particles are alumina particles.

[0012] A third aspect of the present invention is the inorganic powder according to the second aspect, which satisfies the following formula (1): 0.1<[SiN] / [Al ２O ３ ] < 15.0 (1) where [SiN] and [Al ２ O ３ ] are the contents (vol %) of the silicon nitride particles and the alumina particles, respectively, when the total content of the alumina particles and the silicon nitride particles is taken as 100 vol %.

[0013] A fourth aspect of the present invention is the inorganic powder according to the second or third aspect, wherein the silicon nitride particles have a β-phase ratio of 65% or more.

[0014] A fifth aspect of the present invention is the inorganic powder according to any one of the second to fourth aspects, wherein the alumina particles have a particle diameter D50 of 10 μm or less at 50% cumulative particle size from the fine particle side in a cumulative particle size distribution based on volume.

[0015] A sixth aspect of the present invention is a resin composition comprising the inorganic powder according to any one of the first to fifth aspects and a resin.

[0016] By using the inorganic powder according to one embodiment of the present invention as a filler, a resin composition with few voids can be produced.

[0017] 1 is a part of a cross-sectional SEM image of a resin composition according to an embodiment.

[0018] The present inventors have conducted extensive research to find a way to suppress the formation of voids in resin compositions that use inorganic powders containing particles of different shapes (irregular particles and spherical particles) as fillers, and have found for the first time that the formation of voids in resin compositions can be reduced by controlling the angle of repose of the inorganic powder, thereby completing the present invention. Hereinafter, an inorganic powder 15 according to this embodiment and a resin composition 10 using the same (see FIG. 1 ) will be described in detail.

[0019] [Inorganic Powder] The inorganic powder 15 contains particles with an aspect ratio of less than 0.90 (these are referred to as "irregular shaped particles 20") and particles with an aspect ratio of 0.90 or more (these are referred to as "spherical particles 30").

[0020] In this specification, "irregular particles 20" refers to all particles having an aspect ratio of less than 0.90. However, particles generally used in resin compositions for heat dissipation materials rarely contain particles having an aspect ratio of less than 0.10. Therefore, the "irregular particles 20" according to one embodiment may be limited to particles having an aspect ratio of 0.10 or more and less than 0.90. Even in this case, the resin composition according to this embodiment may contain a small amount of particles having an aspect ratio of less than 0.10 (for example, 10% by mass or less when all particles are taken as 100% by mass).

[0021] In this specification, the term "spherical particles 30" refers to all particles having an aspect ratio of 0.90 or more. Since the maximum aspect ratio is 1.00, the aspect ratio of the "spherical particles 30" may be expressed as 0.90 or more and 1.00 or less.

[0022] The angle of repose of the inorganic powder is greater than 33° and less than 56°. It has been revealed that when such an inorganic powder is used to prepare a resin composition, it is possible to reduce voids in the resin composition 10. The reason for this is not clear, but it is presumed to be due to the following mechanism.

[0023] The angle of repose is an indicator of the fluidity of the powder itself; the smaller the angle of repose, the higher the fluidity of the powder. In the inorganic powder of the present invention, the angle of repose is less than 56°, which improves the fluidity of the inorganic powder 15 and makes it easier to disperse uniformly when mixed with a resin. Furthermore, the angle of repose is greater than 33°, which prevents the inorganic powder from flowing too easily in the resin and settling, making it easier for the inorganic powder to remain in its position after being dispersed in the resin. In other words, the resin can be cured with a sufficient amount of resin present between adjacent particles. This reduces the likelihood of internal cavities (caused by a lack of resin between the inorganic powder 15) forming, resulting in a resin composition with fewer cavities.

[0024] The angle of repose is preferably 34° or more and 50° or less, more preferably 35° or more and 45° or less, even more preferably 36° or more and 44° or less, and particularly preferably 37° or more and 43° or less, and from the viewpoint of further reducing voids in the resin composition, it may be 39° or more and 43° or less, or 40° or more and 43° or less.

[0025] (Measurement of Angle of Repose) The angle of repose of an inorganic powder is measured in accordance with the description of JIS R 9301-2-2:1999. The ambient atmosphere during angle of repose measurement is a temperature of 23°C, a humidity of 40%, and a mass of the powder to be measured of 5 g. If the inorganic powder is not yet mixed with the resin, the inorganic powder can be used as is for measuring the angle of repose. On the other hand, in order to measure the angle of repose of an inorganic powder contained within a resin composition, it is necessary to separate the inorganic powder from the resin composition. Specifically, the resin contained in the resin composition is removed by, for example, dissolving it in an organic solvent or heating it to a temperature of 500°C or higher to pyrolyze the resin, and then the inorganic powder alone can be separated and used to measure the angle of repose.

[0026] (Measuring the amount of voids in a resin composition) Methods for determining the amount of voids in a resin composition include a method using specific gravity and a method analyzing a cross-sectional SEM image. In the method using specific gravity, the measured value of the specific gravity of the resin composition is compared with the theoretical value of the specific gravity calculated from the composition of the resin composition. Since a resin composition containing voids has a low specific gravity, it can be said that a resin composition whose measured specific gravity value is significantly lower than the theoretical value contains many voids, and a resin composition whose measured specific gravity value is closer to the theoretical value contains few voids. In the method using specific gravity, the average void ratio of the resin composition can be calculated by targeting the voids contained in the entire resin composition. Therefore, the amount of voids in a resin composition is basically measured using the method using specific gravity.

[0027] In a method using a cross-sectional SEM image of a resin composition, the cross-sectional SEM image is subjected to image processing to determine the area ratio of voids in the observation region. By regarding this area ratio as the volume ratio of voids in the resin composition, the content of voids in the resin composition can be determined. Although the method using a cross-sectional SEM image allows direct observation of voids, it is practically difficult to observe the entire resin composition. In the case of a very small resin composition, where it is difficult to measure voids using the method using specific gravity, the method using a cross-sectional SEM image can be used instead.

[0028] As described above, the angle of repose is an indicator of the fluidity of the powder itself. Therefore, by controlling the shape and physical properties of the irregular particles and spherical particles that make up the inorganic powder, as well as the content ratio (compounding ratio) of the irregular particles to the spherical particles, an inorganic powder with an angle of repose of more than 33° and less than 56° can be obtained. For example, with regard to the compounding ratio of irregular particles to spherical particles, as the compounding ratio of irregular particles increases, the angle of repose of the inorganic powder tends to decrease. When measuring the angle of repose of an inorganic powder consisting only of spherical particles, it is thought that they tend to pile up into a relatively tall cone (i.e., a high angle of repose). It is presumed that adding irregular particles to spherical particles prevents the inorganic powder from piling up high, resulting in a relatively low cone (a cone that spreads horizontally), resulting in a low angle of repose.

[0029] A method for distinguishing irregular particles from spherical particles contained in inorganic powders and an index relating to the shape of irregular particles will be described below.

[0030] (Method for distinguishing irregular particles from spherical particles) First, an SEM image of the inorganic powder is obtained. The conditions for taking a cross-sectional SEM image are a magnification of 100 to 100,000 times, and the observation area is, for example, 1,000 μm × 2,000 μm at a magnification of 250 times, and 4 μm × 3 μm at a magnification of 100,000 times.

[0031] The SEM image of the inorganic powder is analyzed to determine the aspect ratio of the particles shown in the SEM image. This makes it possible to distinguish between irregular particles 20 and spherical particles 30. Each particle shown in the SEM image is analyzed using image processing software (e.g., Image J (manufactured by the National Institute of Health)). The maximum particle size (referred to as the "major axis") of the particle is identified, and the particle size in the direction perpendicular to the major axis is referred to as the "minor axis." For each particle, the ratio of the minor axis to the major axis (minor axis / major axis) is taken as the aspect ratio of that particle.

[0032] Based on this result, particles with an aspect ratio of less than 0.90 can be classified as "irregular particles" and particles with an aspect ratio of 0.90 or more can be classified as "spherical particles."

[0033] The ratio (compounding ratio) of the content (volume %) of the irregular particles to the spherical particles is preferably 93:7 to 10:90, more preferably 90:10 to 40:60, and particularly preferably 85:15 to 55:45.

[0034] In the inorganic powder of this embodiment, it is preferable that the irregular particles are silicon nitride particles and the spherical particles are alumina particles. Since both silicon nitride particles and alumina particles are inorganic materials with high thermal conductivity, the use of particles made of these as fillers can further improve the thermal conductivity of the resin composition. It can be determined, for example, by SEM-EDX analysis of the inorganic powder that the irregular particles are silicon nitride particles and the spherical particles are alumina particles. In an SEM image, the irregular particles and spherical particles are each identified, and the elements detected by EDX measurement (e.g., Si element and Al element) are confirmed. This allows for confirmation that the irregular particles are silicon nitride particles and the spherical particles are alumina particles.

[0035] Furthermore, after the inorganic powder is filled into the resin (i.e., in the state of resin composition 10), it can be identified by SEM-EDX analysis of a cross section of resin composition 10. The irregular particles 20 and spherical particles 30 contained in resin composition 10 are each identified from a cross-sectional SEM image (see, for example, FIG. 1), and the element mapping (e.g., element mapping of Si element and Al element) obtained by EDX measurement is confirmed. This makes it possible to confirm that the irregular particles are silicon nitride particles and the spherical particles are alumina particles.

[0036] It may also contain a small amount of amorphous alumina particles (e.g., 10.0% by volume or less of the total alumina particles) and a small amount of spherical silicon nitride particles (e.g., 10.0% by volume or less of the total silicon nitride particles), neither of which will interfere with the objectives of the present embodiment.

[0037] Next, silicon nitride particles and alumina particles suitable for the inorganic powder of this embodiment will be described in detail. The content and physical properties of the silicon nitride particles and alumina particles may be measured after isolating the silicon nitride particles and alumina particles from the inorganic powder. The inorganic powder is separated into silicon nitride particles and alumina particles based on differences in specific gravity, particle size, etc. Separation methods based on differences in specific gravity include sedimentation or centrifugation in liquid, or methods using a dry sieve or a specific gravity separator.

[0038] (Silicon nitride particle / alumina particle ratio) The ratio of the content (volume %) of silicon nitride particles 20 to the content (volume %) of alumina particles 30 (referred to as the "silicon nitride particle / alumina particle ratio") is preferably greater than 0.1 and less than 15.0. In other words, it is preferable to satisfy the following formula (1). This makes it possible to control the mobility and arrangement of each particle when the inorganic powder is deposited, and to control the angle of repose of the inorganic powder within a predetermined range. This allows the inorganic powder to exhibit appropriate fluidity, and a resin composition can be formed that is less likely to have internal cavities. The silicon nitride particle / alumina particle ratio is more preferably 0.2 or more and 12.0 or less, even more preferably 0.5 or more and 10.0 or less, and particularly preferably 1.1 or more and 9.0 or less. 0.1<[SiN] / [Al ２ O３ ] < 15.0 (1) where [SiN] and [Al ２ O ３ ] are the contents (vol %) of silicon nitride particles and alumina particles, respectively, when the total content of alumina particles and silicon nitride particles is taken as 100 vol %.

[0039] (β-phase ratio of silicon nitride particles) The β-phase ratio of the silicon nitride particles 20 is preferably 65% ​​or more, which improves the thermal conductivity of the silicon nitride particles 20 and further improves the thermal conductivity of the resin composition 10 containing the silicon nitride particles 20. The β-phase ratio is more preferably 70% or more, even more preferably 80% or more, still more preferably 85% or more, and particularly preferably 90% or more. The β-phase ratio of the silicon nitride particles may be 100% or less.

[0040] In this specification, the "β-phase ratio" refers to the content (vol %) of β-type silicon nitride relative to all silicon nitride contained in the silicon nitride particles.

[0041] In calculating the β-phase ratio, silicon nitride particles are measured by powder X-ray diffraction, and the diffraction pattern is analyzed by the Gazzara & Messier method (G. P. Gazzara and D. P. Messier, "Determination of Phase Content of Si ３ N ４ The specimen is analyzed by "X-ray Diffraction Analysis", Am. Ceram. Soc. Bull., 56[9]777-80 (1977)).

[0042] (D50 of Alumina Particles) The alumina particles 30 preferably have a particle diameter D50 (hereinafter simply referred to as "D50") of less than 10 μm at the cumulative 50% from the fine particle side of the volume-based cumulative particle size distribution. By making the alumina particles relatively small in diameter, the tendency for the alumina particles, which have a high specific gravity, to separate to the bottom and the silicon nitride particles, which have a low specific gravity, to separate to the top when the inorganic powder is deposited can be alleviated, making it easier for the alumina particles and silicon nitride particles to be deposited in a well-mixed state. Even when the inorganic powder is added and dispersed in a resin, making the alumina particles small in diameter can alleviate the tendency for the alumina particles to separate to the bottom and the silicon nitride particles to separate to the top due to their specific gravity, and is expected to suppress the aggregation of the respective particles within the resin and the generation of voids.

[0043] If the alumina particles and silicon nitride particles separate during deposition, the angle of repose of the inorganic powder will vary depending on the degree of separation (it is believed that the angle of repose of the inorganic powder will decrease as separation progresses). By making the D50 of the alumina particles relatively small, it is possible to prevent the angle of repose of the inorganic powder from becoming excessively low.

[0044] The D50 of the alumina particles is more preferably 8 μm or less, further preferably 7 μm or less, and particularly preferably 6 μm or less. From the viewpoint of dispersibility of the alumina particles in resin, the D50 of the alumina particles is preferably 0.1 μm or more.

[0045] The alumina particles may be of one type only, or may be of a mixed alumina particle comprising a mixture of two types of alumina particles having different D50s. In this specification, when a mixed alumina particle comprising two types of alumina particles having different D50s is used, the alumina particles having the larger D50 may be referred to as "first alumina particles," and the alumina particles having the smaller D50 may be referred to as "second alumina particles."

[0046] The D50 of the first alumina particles is preferably 3 μm or more and 10 μm or less, and the D50 of the second alumina particles is preferably 0.01 μm or more and 2 μm or less. The second alumina particles, which have a small particle size, easily enter the gaps that occur between other particles (first alumina particles and silicon nitride particles) with a large particle size. Since the gaps between particles tend to become cavities in the resin composition, filling the gaps between particles with the second alumina particles can suppress the formation of cavities in the resin composition. The ratio (compounding ratio) of the content (volume %) of the first alumina particles to the second alumina particles is preferably 90:10 to 10:90, more preferably 20:80 to 80:20, even more preferably 30:70 to 80:20, and particularly preferably 40:60 to 80:20.

[0047] (D50 of Silicon Nitride Particles) It is preferable that the particle diameter D50 of the cumulative 50% from the fine particle side of the volume-based cumulative particle size distribution of the silicon nitride particles 20 is greater than 1 μm. This prevents aggregation of particles in the inorganic powder, allows the particles to be uniformly dispersed in a resin composition containing the inorganic powder, and allows a resin composition with few voids to be obtained.

[0048] The D50 of the silicon nitride particles is more preferably 2 μm or more, and even more preferably 3 μm or more. From the viewpoint of easily obtaining a resin composition with few voids, the D50 of the silicon nitride particles may be 300 μm or less, 200 μm or less, or 150 μm or less. From the viewpoint of easily obtaining a resin composition with few voids while increasing the filling rate in the resin composition, the D50 of the silicon nitride particles may be 50 μm or less, or 20 μm or less.

[0049] The D50 of silicon nitride particles and the D50 of alumina particles are measured by laser diffraction. Specifically, powder dispersed in water is irradiated with a laser beam, and the diffraction is measured to determine the particle size. A measuring device such as the 1090L manufactured by CILAS can be used.

[0050] [Resin Composition 10] Resin composition 10 contains the inorganic powder according to this embodiment (including a plurality of irregular particles 20 and a plurality of spherical particles 30) and a resin 40. In the cross-sectional SEM image of FIG. 1, the resin 40 is the dark gray portion, and the irregular particles 20 and spherical particles 30 are the light gray portions. In this example, spherical particles 30 with small particle diameters are dispersed among irregular particles 20 with large particle diameters. Resin 40 fills the gaps between the plurality of irregular particles 20 and the plurality of spherical particles 30. By using the inorganic powder according to this embodiment, a dense resin composition with few voids can be molded.

[0051] The preferred contents (filling rates) of the irregular particles 20 and spherical particles 30 contained in the resin composition 10 are as follows. The "content (filling rate)" refers to the content (volume %) of the target particles when the total of the irregular particles 20, spherical particles 30, and resin 40 is taken as 100% by volume. The content (filling rate) of the irregular particles 20 is preferably 10 to 90% by volume, more preferably 20 to 85% by volume, even more preferably 30 to 80% by volume, and particularly preferably 45 to 75% by volume. The content (filling rate) of the spherical particles 30 is preferably 3 to 80% by volume, more preferably 4 to 70% by volume, even more preferably 5 to 50% by volume, and particularly preferably 6 to 35% by volume.

[0052] The total content (total filling rate) of the irregular particles 20 and the spherical particles 30 is preferably 20 to 98% by volume, more preferably 30 to 95% by volume, and particularly preferably 40 to 93% by volume.

[0053] When measuring the physical properties of the inorganic powder contained in the resin composition 10, the resin 40 contained in the resin composition 10 is first removed, for example, by dissolving it in an organic solvent or by heating it to a temperature of 500°C or higher to thermally decompose the resin.

[0054] [Resin 40] Suitable resins 40 for the resin composition 10 according to the embodiment include known resins such as silicone resins, epoxy resins, and acrylic resins. The type of resin can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins. One type of resin may be used alone, or two or more types may be used in combination. From the viewpoints of moldability and thermal conductivity, it is preferable to use a silicone resin.

[0055] [Other Additives] Furthermore, these resin compositions may contain, as needed, known additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weather resistance agents, antiblocking agents, antistatic agents, leveling agents, and release agents, either singly or in combination, within the scope of the invention.

[0056] [Method for producing inorganic powder] The inorganic powder can be produced by mixing irregular particles 20 and spherical particles 30 in a predetermined ratio. Irregular particles 20 (e.g., silicon nitride particles) suitable for the inorganic powder can be produced, for example, by the method described below. Spherical particles 30 (e.g., alumina particles) suitable for the inorganic powder may be, for example, commercially available spherical alumina particles, or may be spherical alumina particles produced by a known method (e.g., flame fusion method).

[0057] [Method for Producing Irregular Particles 20] A method for producing silicon nitride particles will be described as an example of a method for producing the irregular particles 20 used in producing the resin composition 10. The silicon nitride particles include the following steps: (1) synthesizing silicon nitride synthetic crystals by combustion synthesis under a nitrogen atmosphere using raw materials containing Si, (2) crushing the silicon nitride synthetic crystals to obtain coarsely pulverized silicon nitride powder, (3) finely pulverizing the coarsely pulverized silicon nitride powder to obtain finely pulverized silicon nitride powder, and (4) heat-treating the finely pulverized silicon nitride powder to obtain silicon nitride particles.

[0058] Step (1): Synthesizing silicon nitride composite crystals. The Si-containing raw material is, for example, Si powder. The D50 of the raw material Si is, for example, in the range of 1 to 10 μm. This suppresses the amount of oxygen impurities and increases the combustion rate, allowing for a higher synthesis temperature and achieving good crystal growth.

[0059] The diluent is used to adjust the amount of Si in the mixed raw material. Separately prepared silicon nitride particles are used as the diluent. The diluent may be either α-type silicon nitride particles or β-type silicon nitride particles, or a mixture of these. The D50 of the diluent is preferably in the range of 0.5 to 10.0 μm.

[0060] In this embodiment, raw material Si and a diluent are mixed and filled into a heat-resistant container. The heat-resistant container is preferably made of ceramic or carbon. After filling the raw materials, the container is covered with a lid made of the same material as the heat-resistant container, and combustion synthesis is carried out in a nitrogen atmosphere at a pressure of 0.1 to 1 MPa.

[0061] To promote crystal growth more effectively, a catalyst may be used, for example, Y ２ O ３ , Fe ２ O ３ , CaO, Ni, Co, C, etc. are added in an amount of about 0.01 to 0.1 mass %. In addition, external auxiliary heating is performed in the range of 500°C to 1700°C (for example, 1500°C), and the combustion temperature is also increased in the combustion synthesis method by self-ignition.

[0062] Step (2): Obtaining a coarsely pulverized silicon nitride powder. The silicon nitride synthetic crystal is in the form of an aggregate of multiple silicon nitride particles. In step (2), the silicon nitride synthetic crystal is crushed to obtain a coarsely pulverized silicon nitride powder. For example, the synthetic crystal is crushed using a general crushing device such as a hammer mill or a disk mill until it passes through a sieve with a specified mesh size (for example, a sieve with mesh sizes in the range of 400 μm to 500 μm).

[0063] Step (3): Obtaining a finely pulverized silicon nitride powder The coarsely pulverized silicon nitride powder is further pulverized to obtain a finely pulverized silicon nitride powder. The pulverization is carried out using a pulverizing device such as a ball mill. If necessary, the obtained finely pulverized powder may be classified. Classification can be carried out by sieving, wet classification, or the like.

[0064] Step (4): Step of Obtaining Silicon Nitride Particles The finely pulverized silicon nitride powder is heat-treated to obtain silicon nitride particles. The heat treatment forms an oxide film on the surface of the silicon nitride particles, chemically stabilizing the silicon nitride particles. The heat treatment is carried out in the atmosphere at a temperature of 500°C or higher and 1200°C or lower. The heat treatment time can be adjusted appropriately according to the heat treatment temperature. The heat treatment time is, for example, 5 hours.

[0065] In the method for producing silicon nitride particles, silicon nitride synthetic crystals are synthesized using the heat generated by the combustion synthesis method, and then the silicon nitride particles according to this embodiment can be produced by crushing, classifying, and pulverizing the synthesized crystals.

[0066] [Method of Manufacturing Resin Composition 10] A method of manufacturing the resin composition 10 will be described. The resin composition 10 can be obtained by using an inorganic powder with a controlled angle of repose and applying a known method to the inorganic powder. For example, when the resin is liquid (e.g., liquid silicone resin), the resin composition 10 can be obtained by mixing the liquid resin, inorganic powder containing amorphous particles 20 and spherical particles 30, and a curing agent, and then curing the mixture with heat or ultraviolet light. Known curing agents, mixing methods, and curing methods can be used. On the other hand, when the resin is solid, the desired resin composition 10 can be obtained by mixing the inorganic powder and resin and then kneading them using a known method such as melt kneading.

[0067] The present invention will be described in detail below with reference to examples carried out to clarify the effects of the present invention, but the present invention is not limited to the following examples.

[0068] <Preparation of Silicon Nitride Particles> Silicon nitride particles a were prepared having the physical properties shown in Tables 2 and 3. Silicon nitride particles a were then immersed in an aqueous solution of pH 14 and heated at 900°C for 5 hours in a nitrogen atmosphere. The resulting aggregated powder was pulverized in a mortar and sieved through a sieve with 80 µm openings to obtain silicon nitride particles b, which remained on the sieve.

[0069] <Preparation of Alumina Particles> Three types of alumina particles were prepared. As the first alumina particles, DAW-05 manufactured by Denka (Sample Nos. 1 to 7) or DAW-45 manufactured by Denka (Sample No. 8) was used, and as the second alumina particles, AA-04 manufactured by Sumitomo Chemical Co., Ltd. was used. Mixed alumina particles obtained by mixing the first alumina particles and the second alumina particles at a predetermined ratio were used as "alumina particles."

[0070] Various measurements were carried out on the silicon nitride particles a to b, the first alumina particles, and the second alumina particles.

[0071] <Measurement of D50 of each particle> The particle size distribution of silicon nitride particles and alumina particles was measured to determine the D50 of each particle. The particle size distribution of each particle was measured by laser diffraction. A sample dispersed in water was irradiated with a laser beam, and the diffraction was measured to determine the particle size. The measuring device used was a CILAS 1090L model. The particle diameter was taken as the circle-equivalent particle diameter. The circle-equivalent particle diameter is the particle diameter of a perfect circle that has the same area as a projected particle image. The particle diameter D50 was measured based on volume.

[0072] The measurement results of D50 for each particle are shown in Table 2. The D50 of the mixed alumina particles (a mixture of first alumina particles and second alumina particles) was not measured. However, based on the D50 (5 μm) of the first alumina particles before mixing and the D50 (0.5 μm) of the second alumina particles, it can be said that the D50 of the mixed alumina particles was 5 μm or less. In other words, the D50 of the alumina particles (mixed alumina particles) used in the examples was less than 10 μm.

[0073] <Measurement of aspect ratio of each particle> SEM images were taken for each of the silicon nitride particles, the first alumina particles, and the second alumina particles. The following equipment was used for the images. Equipment used: Scanning electron microscope: Helios G4 UX (manufactured by FEI Japan Co., Ltd.) The imaging conditions were as follows: Acceleration voltage: 5.0 kV Signal: BSE Probe current: 0.1 nA Magnification: 250x (particles with D50 of more than 20 μm), 1000x (particles with D50 of 20 μm or less), 100,000x (particles with D50 of 1 μm or less)

[0074] The aspect ratios of all particles in the SEM images were determined using image processing software Image J (manufactured by the National Institute of Health). First, the longest particle diameter of each particle was defined as the longest diameter, and the particle diameter in the direction perpendicular to the longest diameter was defined as the shortest diameter. The longest and shortest diameters of each particle were then measured, and the ratio of the shortest diameter to the longest diameter (shortest diameter / longest diameter) was then determined. As a result, it was confirmed that the silicon nitride particles were amorphous particles 20 (aspect ratio less than 0.90), and that the first alumina particles and the second alumina particles were both spherical particles 30 (aspect ratios of 0.90 or more).

[0075] The average aspect ratio of each particle was determined as a reference for understanding the aspect ratio of each particle. The average aspect ratio of each particle was determined by randomly selecting 20 particles from the SEM image of each particle and calculating the arithmetic mean of the aspect ratios of those particles. Note that this average aspect ratio does not indicate the aspect ratio of each particle. Therefore, it should be noted that the average aspect ratio cannot be used to determine whether each particle is an irregular particle or a spherical particle. The measurement results of the average aspect ratio of the silicon nitride particles are shown in Table 3. The average aspect ratio of the first alumina particles (Denka DAW-05 and Denka DAW-45) was 0.97, and the average aspect ratio of the second alumina particles was 0.91.

[0076] The average aspect ratio of the silicon nitride particles is preferably 0.50 or more and less than 0.90, more preferably 0.55 or more and 0.86 or less, and particularly preferably 0.60 or more and 0.85 or less. The average aspect ratio of the alumina particles is preferably 0.90 or more and 1.00 or less, and more preferably 0.91 or more and 1.00 or less. By setting the average aspect ratios of the silicon nitride particles and the alumina particles within appropriate ranges, the mobility and arrangement of each particle when the inorganic powder is deposited can be appropriately controlled, making it easy to control the angle of repose of the inorganic powder within a predetermined range.

[0077] <Measurement of the β-phase ratio of silicon nitride particles> The diffraction pattern of the silicon nitride particles was obtained using a powder X-ray diffractometer (manufactured by Rigaku Denki). The measurement conditions were as follows: X-ray source: CuKα radiation; X-ray output: 45 kV, 200 mA; graphite monochromator; diffraction angle (2θ): step scan in 0.02° increments over the range of 2 to 90°; scanning speed: 21.7 deg / min.

[0078] When the silicon nitride particles contained components other than silicon nitride, the peaks of those components were compared with the corresponding peaks of standard samples of those components to determine the proportions of those components. The obtained powder X-ray diffraction patterns confirmed that all silicon nitride particles were composed exclusively of α-type silicon nitride and β-type silicon nitride. The proportion of β-type silicon nitride in the sample (β-conversion ratio) was then calculated using the Gazzara & Messier method. The calculation results are shown in Table 3.

[0079] <Silicon nitride particle / alumina particle ratio in inorganic powder> From the compounding ratio of each particle (silicon nitride particles, first alumina particles, second alumina particles) shown in Table 2, the ratio of the content (volume %) of silicon nitride particles to the total content (volume %) of the first alumina particles and the second alumina particles (silicon nitride particle / alumina particle ratio) was calculated and shown in Table 2.

[0080] <Measurement of Angle of Repose of Inorganic Powder> The particles (silicon nitride particles, first alumina particles, second alumina particles) were blended in the blending ratios shown in Table 2, and stirred and mixed using a Foam Blender (manufactured by Thinky Corporation) to prepare an inorganic powder. The angle of repose of the inorganic powder was measured in accordance with the description of JIS R 9301-2-2:1999. The ambient atmosphere during measurement was a temperature of 23°C, a humidity of 40%, and the mass of the inorganic powder used for measurement was 5 g. The measurement results are shown in Table 3.

[0081] <Preparation of Resin Composition> Each particle (silicon nitride particles, first alumina particles, second alumina particles) was blended with a silicone resin (base: DOWSIL (trademark) CY 52-276 A manufactured by Dow Chemical; curing agent: DOWSIL (trademark) CY 52-276 B manufactured by Dow Chemical). The blending ratio of each particle and the silicon nitride particle / alumina particle ratio are shown in Table 2. Note that in Sample No. 6, only silicon nitride particles were used, and no alumina particles (first alumina particles and second alumina particles) were blended. In Sample No. 8, no second alumina particles were blended. The silicone resin and each particle, blended in a blending ratio of 30% by volume of silicone resin and 70% by volume of total particles, were stirred and mixed using a WAWATORI MIXER (manufactured by THINKY CORPORATION), to obtain a liquid resin composition.

[0082] A 1 mm thick aluminum plate with a 1 cm x 10 cm rectangular hole was prepared as a mold frame. A transparent PET film (backside film) coated with a release agent was attached to the back side of the mold frame so as to cover the rectangular hole, with the release agent-coated surface facing the mold frame. 3 g of liquid resin composition (gray) was poured into the rectangular hole in the mold frame, and then a transparent PET film (frontside film) coated with a release agent was attached on top of it, with the release agent-coated surface facing the mold frame and resin composition. Furthermore, light pressure was applied from above the frontside film with a metal roller to fit the resin composition into the rectangular hole in the mold frame and form it into a 1 cm x 10 cm strip. Another aluminum plate was then placed on top of it, heated at 120 °C for 8 hours, and allowed to stand to harden the resin. After curing was complete, the aluminum plate was allowed to cool, and when the temperature had dropped to about room temperature, the two PET films were peeled off from both sides of the cured resin composition to obtain a sheet-shaped resin composition for measurement.

[0083] <Measurement of specific gravity difference rate of resin composition> To determine the actual measured value of specific gravity, the specific gravity of the sheet-shaped resin composition prepared by the above procedure was measured. The density was measured using an electronic hydrometer MDS-300 (Alpha Mirage Co., Ltd.). The density was determined by the Archimedes method (solid density measurement) based on the following formula. The actual measured value of specific gravity was also determined from the density: ρ = A ÷ (A - B) × (ρ ０ -ρ Ｌ ) + ρ Ｌ where, ρ: density of the sheet-shaped resin composition, A: weight of the sheet-shaped resin composition measured in the air, and B: weight of the sheet-shaped resin composition measured in the displacement liquid (water). ０ : Density of the replacement liquid (water) (1.0000 g / cm ３ ) ρ Ｌ : air density (0.0012 g / cm ３ The measurement was carried out by cutting two 1 cm square test pieces from the sheet-shaped resin composition, and the arithmetic mean value of these was taken as the average measured value of specific gravity SG １ It was decided.

[0084] Calculated specific gravity SG ２ was calculated according to formula (2). In formula (2), SG ２ is the theoretical specific gravity when voids in the resin composition are ignored, and ρa ｎ is the specific gravity of the nth type of irregular particles among the x types of irregular particles, and Va ｎ is the ratio of the volume of the nth type of irregular particles to the total volume of the irregular particles, spherical particles, and resin, and ρb ｍ is the specific gravity of the mth spherical particle among the y types of spherical particles, and Vb ｍ is the ratio of the volume of the mth spherical particle to the total volume of the irregular particles, spherical particles, and resin, and ρc ｌ is the specific gravity of the lth resin among the z types of resin, and Vc ｌ is the ratio of the volume of the lth resin to the total volume of the irregular particles, spherical particles, and resin, and n, m, l, x, y, and z are positive integers. Note that x = 1, y = 2, z = 1, and ρa １ is the specific gravity of silicon nitride, and ρb １(specific gravity of the first alumina particles), and ρb ２ (specific gravity of second alumina particles) is the specific gravity of alumina, and ρc １ The specific gravity of the silicone resin was determined using the values ​​shown in Table 1. For reference, the specific gravities of materials that can be used as amorphous particles (aluminum nitride, boron nitride) are also listed.

[0085]

[0086] The specific gravity of the resin composition obtained by the above procedure (the average measured value SG of the specific gravity of the resin composition) １ and the theoretical specific gravity SG when voids in the resin composition are ignored. ２ ) was used to calculate the specific gravity difference rate of the resin composition using the following formula (3). The calculated specific gravity difference rate is shown in Table 3. １ / SG ２ ) x 100 (3)

[0087]

[0088]

[0089] The results in Table 3 will be discussed below. The resin compositions using inorganic powders of Samples 1 to 6, which satisfied the requirements of this embodiment, had small specific gravity difference rates. This confirmed that resin compositions with few voids could be produced. On the other hand, the resin compositions using inorganic powders of Samples 7 and 8, which did not satisfy the requirements of this embodiment, had large specific gravity difference rates. In other words, it was confirmed that these resin compositions had many voids.

[0090] This application claims priority from Japanese Patent Application No. 2024-024851, filed February 21, 2024. Japanese Patent Application No. 2024-024851 is incorporated herein by reference.

[0091] 10 Resin composition 15 Inorganic powder 20 Amorphous particles 30 Spherical particles 40 Resin

Claims

1. An inorganic powder containing irregular particles with an aspect ratio of less than 0.90 and spherical particles with an aspect ratio of 0.90 or more, and having an angle of repose of more than 33° and less than 56°.

2. The inorganic powder according to claim 1, wherein the irregular particles are silicon nitride particles and the spherical particles are alumina particles.

3. The inorganic powder according to claim 2, which satisfies the following formula (1): 0.1<[SiN] / [Al ２ O ３ ] < 15.0 (1) where [SiN] and [Al ２ O ３ ] are the contents (vol %) of the silicon nitride particles and the alumina particles, respectively, when the total content of the alumina particles and the silicon nitride particles is taken as 100 vol %.

4. The inorganic powder according to claim 2, wherein the silicon nitride particles have a beta-phase ratio of 65% or more.

5. The inorganic powder according to claim 2, wherein the particle diameter D50 of the cumulative 50% from the fine particle side of the cumulative particle size distribution on a volume basis of the alumina particles is 10 μm or less.

6. A resin composition comprising the inorganic powder according to any one of claims 1 to 5 and a resin.

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