Resin composition

Abstract

This resin composition comprises inorganic particles and a resin, wherein the content of the inorganic particles is 55% by volume or more, with the total content of the inorganic particles and the resin taken as 100% by volume; the inorganic particles include amorphous particles, which are particles having an aspect ratio of less than 0.90, and spherical particles, which are particles having an aspect ratio of 0.90 or more; and the cumulative 50% particle diameter D50 from the fine particle side in the volume-based cumulative particle size distribution of the amorphous particles is more than 15 μm.

Description

resin composition

[0001] The present disclosure relates to a resin composition containing inorganic particles and a resin, and particularly to a resin composition for use as a heat dissipating material.

[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 inorganic particles. Examples of inorganic particles 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 (A) an epoxy resin, (B) an epoxy resin curing agent, and (C) silicon nitride powder as essential components. 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 which preferably uses alumina particles as the filler.

[0004] 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.

[0005] JP 2000-109651 A JP 2013-134983 A Japanese Patent No. 6508508 A

[0006] In recent years, the increase in heat generation in electronic components has become a problem due to the increased 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 improve the thermal conductivity of resin compositions. Although the resin compositions disclosed in Patent Documents 1 to 3 use inorganic particles with high thermal conductivity, such as silicon nitride particles and alumina particles, as fillers to increase the thermal conductivity of the resin compositions, further improvements in thermal conductivity are desired. Therefore, an embodiment of the present invention aims to provide a resin composition having better thermal conductivity than conventional resin compositions.

[0007] Aspect 1 of the present invention is a resin composition containing inorganic particles and a resin, wherein the content of the inorganic particles is 55% by volume or more when the total of the inorganic particles and the resin is 100% by volume, the inorganic particles include irregular particles which are particles with an aspect ratio of less than 0.90 and spherical particles which are particles with an aspect ratio of 0.90 or more, and the particle diameter D50 of the irregular particles at 50% cumulative from the fine particle side of the volume-based cumulative particle size distribution is greater than 15 μm.

[0008] A second aspect of the present invention is the resin composition according to the first aspect, wherein the irregular particles are silicon nitride particles, and the spherical particles are alumina particles.

[0009] A third aspect of the present invention is the resin composition according to the second aspect, wherein the inorganic particles contain 15% by volume or more and 85% by volume or less of the silicon nitride particles.

[0010] A fourth aspect of the present invention is the resin composition according to the second or third aspect, wherein the volume ratio of the silicon nitride particles to the alumina particles is 0.2 or more and less than 9.0.

[0011] A fifth aspect of the present invention is the resin composition according to any one of the second to fourth aspects, wherein the alumina particles have a particle diameter D50 of 50% cumulative from the fine particle side in a volume-based cumulative particle size distribution of less than 20 μm.

[0012] A sixth aspect of the present invention is the resin composition according to any one of the second to fifth aspects, wherein the silicon nitride particles have a β-phase ratio of 65% or more.

[0013] According to an embodiment of the present invention, a resin composition having a thermal conductivity superior to that of conventional resin compositions can be provided.

[0014] 1 is a part of a cross-sectional SEM image of a resin composition according to Sample No. 3 of an example.

[0015] [Resin Composition] The resin composition according to this embodiment is a resin composition containing inorganic particles and a resin, wherein the content of the inorganic particles is 55% by volume or more when the total of the inorganic particles and the resin is 100% by volume, the inorganic particles include irregular particles having an aspect ratio of less than 0.90 and spherical particles having an aspect ratio of 0.90 or more, and the particle diameter D50 of the irregular particles at the cumulative 50% from the fine particle side of the volume-based cumulative particle size distribution is greater than 15 μm. This resin composition has superior thermal conductivity compared to conventional resin compositions.

[0016] As an example of a resin composition according to this embodiment (hereinafter also referred to as "resin composition 10"), FIG. 1 shows a portion of a cross-sectional SEM image of a resin composition prepared in an example. Resin composition 10 contains inorganic particles 20, including particles with an aspect ratio of less than 0.90 (referred to as "irregular particles 21") and particles with an aspect ratio of 0.90 or more (referred to as "spherical particles 22"). Resin composition 10 also contains resin 30. In the cross-sectional SEM image of FIG. 1, resin 30 is the dark gray portion, and inorganic particles 20 (irregular particles 21 and spherical particles 22) are the light gray portion. Note that, in this specification, "irregular particles 21" refers to all particles with an aspect ratio of less than 0.90. However, particles commonly used in resin compositions for heat dissipation materials rarely contain particles with an aspect ratio of less than 0.10. Therefore, the "irregular particles 21" 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). Furthermore, in this specification, "spherical particles 22" 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 "spherical particles 22" may be expressed as 0.90 or more and 1.00 or less.

[0017] When the total of the inorganic particles 20 and the resin 30 is taken as 100% by volume, the content of the inorganic particles 20 is 55% by volume or more to ensure a heat conduction path within the resin composition 10. Furthermore, the inorganic particles 20 include irregular particles 21 and spherical particles 22, and the particle diameter D50 (hereinafter also simply referred to as "D50") of the irregular particles 21 at 50% cumulative from the fine particle side of the volume-based cumulative particle size distribution is greater than 15 μm. By satisfying these requirements, the resin composition 10 has excellent thermal conductivity. This is thought to be because, within the resin composition 10, the skeleton is formed by the relatively large irregular particles 21, and the spherical particles 22 are interposed between the irregular particles 21, thereby forming a sufficient heat conduction path.

[0018] The irregular particles 21 and spherical particles 22 in the resin composition 10 can be distinguished by obtaining a cross-sectional SEM image of the resin composition 10 as shown in FIG. 1. The cross-section to be observed by SEM is not particularly limited, but in the case of a sheet-shaped resin composition 10, it is preferable to observe a cross-section in the thickness direction (T direction in FIG. 1). In the case of a resin composition 10 of any shape, if the heat conduction direction can be identified, it is preferable to observe a cross-section in the heat conduction direction. The conditions for photographing the cross-sectional SEM image are a magnification of 100 to 100,000 times, and an observation area of, for example, 1,000 μm × 2,000 μm.

[0019] A cross-sectional SEM image of the resin composition 10 is subjected to image analysis to determine the aspect ratio of the inorganic particles 20 shown in the cross-sectional SEM image. This makes it possible to distinguish between amorphous particles 21, which are particles with an aspect ratio of less than 0.90, and spherical particles 22, which are particles with an aspect ratio of 0.90 or more. Each inorganic particle 20 shown in the cross-sectional SEM image is analyzed using image processing software (e.g., Image J (manufactured by the National Institute of Health)). The maximum particle size of the inorganic particles 20 (referred to as the "major axis") is identified, and the particle size in the direction perpendicular to the major axis is referred to as the "minor axis." For each inorganic particle 20, the ratio of the minor axis to the major axis (minor axis / major axis) is taken as the aspect ratio of that inorganic particle 20.

[0020] When the total of the inorganic particles 20 and the resin 30 is taken as 100% by volume, the content of the inorganic particles 20 is preferably 60% by volume or more, more preferably 70% by volume or more, and even more preferably 75% by volume or more. This makes it easier to ensure a heat conduction path in the resin composition. It is preferably 98% by volume or less, more preferably 95% by volume or less, and even more preferably 93% by volume or less. This makes it possible to contain an appropriate amount of the resin 30 as a binder, making it easier to suppress detachment of the inorganic particles 20 from the resin composition 10.

[0021] When the total amount of inorganic particles 20 contained in the resin composition is taken as 100% by volume, the inorganic particles 20 preferably contain 15% by volume or more of the irregular particles 21. This makes it easier for the irregular particles 21 to form a skeleton within the resin composition 10. The inorganic particles 20 more preferably contain 30% by volume or more of the irregular particles 21, and even more preferably contain 45% by volume or more. On the other hand, the inorganic particles 20 preferably contain 85% by volume or less of the irregular particles 21. This allows an appropriate amount of spherical particles 22 to be contained, making it easier for the spherical particles 22 to be interposed between the irregular particles 21. The inorganic particles 20 more preferably contain 80% by volume or less of the irregular particles 21, and even more preferably contain 75% by volume or less of the irregular particles 21.

[0022] The volume ratio of the irregular particles 21 to the spherical particles 22 is preferably 0.2 or more, and more preferably 0.5 or more. This makes it easier for the irregular particles 21 to form a skeleton within the resin composition 10. On the other hand, this volume ratio is preferably less than 9.0. This makes it easier for the spherical particles 22 to be interposed between the irregular particles 21. This volume ratio is more preferably 6.0 or less, and even more preferably 3.9 or less.

[0023] The D50 of the irregular particles 21 is preferably 20 μm or more, more preferably 35 μm or more, and even more preferably 50 μm or more. This makes it easier for the irregular particles 21 to form a skeleton within the resin composition 10. The D50 of the irregular particles 21 is preferably 250 μm or less, and more preferably 200 μm or less. This makes it easier for the spherical particles 22 to be interposed between the irregular particles 21.

[0024] The D50 of the spherical particles 22 is preferably less than 20 μm, more preferably less than 10 μm, even more preferably 8 μm or less, even more preferably 7 μm or less, and particularly preferably 6 μm or less. This makes it easier for the spherical particles 22 to fill in the spaces between the irregular particles 21. On the other hand, the D50 of the spherical particles 22 is preferably 0.1 μm or more, and more preferably 0.5 μm or more. This makes it easier to form heat conduction paths within the resin composition 10.

[0025] The D50 of the spherical particles 22 is preferably 70% or less of the D50 of the irregular particles 21. This allows the relatively large irregular particles 21 to form a skeleton, making it easier for the relatively small spherical particles 22 to disperse into the gaps. As a result, the irregular particles 21 form the main heat conduction paths within the resin composition 10, and the spherical particles 22 filling the spaces between the irregular particles 21 form auxiliary heat conduction paths, thereby further improving the heat conduction efficiency of the resin composition 10. The D50 of the spherical particles 22 is more preferably 60% or less, even more preferably 50% or less, and particularly preferably 40% or less of the D50 of the irregular particles 21. On the other hand, the D50 of the spherical particles 22 is preferably 0.001% or more of the D50 of the irregular particles 21, and more preferably 0.1% or more of the D50 of the irregular particles 21. This allows the spherical particles 22 to more easily form auxiliary heat conduction paths. When the resin composition 10 contains a plurality of types of spherical particles 22, it is preferable that the D50 of all types of spherical particles 22 and the D50 of the irregular-shaped particles 21 satisfy the above relationship.

[0026] In this embodiment, the D50 of the irregular particles 21 and the spherical particles 22 can be measured by laser diffraction. Specifically, particles dispersed in water are irradiated with a laser beam, and the diffraction is measured to determine the particle size. A CILAS 1090L or similar measuring device can be used. The D50 of the irregular particles 21 and the spherical particles 22 contained in the resin composition 10 can be measured by removing the resin contained in the resin composition 10, 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, separating the irregular particles 21 and the spherical particles 22, and using these particles.

[0027] Another method for determining D50 of the irregular particles 21 and the spherical particles 22 is to use image analysis. The resin composition 10 may be subjected to cross-sectional observation using an SEM, and all of the irregular particles 21 and spherical particles 22 contained in a predetermined observation area (e.g., 1000 μm × 2000 μm) may be subjected to image analysis, and the particle diameters equivalent to D50 may be calculated based on the measurement results of their particle diameters (equivalent circle diameters).

[0028] The average aspect ratio of the irregular 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. This facilitates the formation of a skeleton of irregular particles. The average aspect ratio of the spherical particles is preferably 0.90 or more and 1.00 or less, more preferably 0.91 or more and 1.00 or less. This facilitates the interposition of the spherical particles between the irregular particles. The average aspect ratio of each particle is determined by arbitrarily selecting 20 particles from the SEM image of each particle and calculating the arithmetic average of the aspect ratios of those particles.

[0029] The inorganic particles 20 (and the amorphous particles 21 and spherical particles 22 contained therein) are preferably ceramics such as silica, alumina, aluminum nitride, boron nitride, silicon nitride, and silicon carbide. In particular, particles made of an inorganic material with high thermal conductivity are preferred, for example, particles made of an inorganic material with a thermal conductivity of 15 W / mK or more are preferred. Suitable inorganic materials include ceramics such as alumina, aluminum nitride, boron nitride, silicon nitride, and silicon carbide. The inorganic particles 20 are preferably ceramic particles. Because ceramics have high thermal conductivity, the use of ceramic particles can improve the heat dissipation performance of the resin composition 10. Furthermore, when insulating ceramics are used as the inorganic particles 20, short circuits in the semiconductor device can be suppressed. Therefore, the inorganic particles 20 are more preferably insulating ceramic particles, and more preferably alumina, aluminum nitride, boron nitride, and silicon nitride. It is even more preferred that the inorganic particles 20 be one or more inorganic materials with higher thermal conductivity selected from the group consisting of alumina and silicon nitride.

[0030] Preferably, the amorphous particles 21 are silicon nitride particles, and the spherical particles 22 are alumina particles. Since both silicon nitride particles and alumina particles are inorganic materials with high thermal conductivity, the thermal conductivity of the resin composition 10 can be further improved by using particles made of these as a filler.

[0031] The fact that the irregular particles 21 are silicon nitride particles and the spherical particles 22 are alumina particles can be identified, for example, by SEM-EDX analysis of a cross section of the resin composition 10. The irregular particles 21 and spherical particles 22 contained in the resin composition 10 are each identified from the cross-sectional SEM image, 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 21 are silicon nitride particles and the spherical particles 22 are alumina particles.

[0032] It may contain a small amount of amorphous alumina particles (e.g., 10.0% by volume or less of the total alumina particles) and / or 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 this embodiment.

[0033] 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. This facilitates the formation of a skeleton by the silicon nitride particles. The average aspect ratio of the alumina particles is preferably 0.90 or more and 1.00 or less, more preferably 0.91 or more and 1.00 or less. This facilitates the interposition of the alumina particles between the silicon nitride particles. The average aspect ratio of each particle is determined by arbitrarily selecting 20 particles from the SEM image of each particle and calculating the arithmetic mean of the aspect ratios of those particles.

[0034] 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."

[0035] 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. This makes it easier for the alumina particles to be interposed between the silicon nitride particles. The ratio (compounding ratio) of the contents (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 70:30, and particularly preferably 40:60 to 60:40.

[0036] The β-phase ratio of the silicon nitride particles is preferably 65% ​​or more, which improves the thermal conductivity of the silicon nitride particles and further improves the thermal conductivity of the resin composition 10 containing the silicon nitride particles. The β-phase ratio is more preferably 70% or more, even more preferably 80% or more, even 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.

[0037] 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.

[0038] 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 SiN by X-ray Diffraction Analysis”, Am. Ceram. Soc. Bull., 56[9]777-80(1977)).

[0039] Measurement of the physical properties of the silicon nitride particles and alumina particles may be performed in the state of the resin composition 10 containing these particles. However, if measurement is difficult in the state of the resin composition 10, the silicon nitride particles and alumina particles may be isolated from the resin composition 10 and then measured. To isolate the silicon nitride particles and alumina particles from the resin composition 10, the resin contained in the resin composition 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. The resulting mixture of silicon nitride particles and alumina particles is separated 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.

[0040] As the resin 30, known resins such as silicone resin, epoxy resin, and acrylic resin can be used. The type of resin 30 can be selected from thermoplastic resin, thermoplastic elastomer, and thermosetting resin. The resin 30 may be used alone or in combination of two or more types. From the viewpoints of moldability and thermal conductivity, it is preferable to use a silicone resin.

[0041] Furthermore, these resin compositions 10 may contain, as needed, known additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weather resistance agents, anti-blocking agents, antistatic agents, leveling agents, and release agents, either singly or in combination, within the scope of not impairing the effects of this embodiment.

[0042] [Method of Manufacturing Resin Composition] A method of manufacturing the resin composition 10 will be described. The inorganic particles 20 are amorphous particles 21 with controlled particle size and spherical particles 22, and the resin composition 10 can be obtained by applying a known method to these. For example, when the resin 30 is liquid (e.g., liquid silicone resin), the liquid resin, amorphous particles 21, spherical particles 22, and a curing agent are mixed together, and then cured with heat or ultraviolet light to obtain the resin composition 10. Known curing agents, mixing methods, and curing methods can be used. When the resin 30 is solid, the amorphous particles 21, spherical particles 22, and resin 30 are mixed together, and then kneaded using a known method such as melt kneading to obtain the desired resin composition 10.

[0043] The amorphous particles 21 (e.g., silicon nitride particles) used in the method for producing the resin composition 10 can be produced, for example, by the method described below. The spherical particles 22 (e.g., alumina particles) used in the method for producing the resin composition 10 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).

[0044] A method for producing silicon nitride particles will be described as an example of a method for producing amorphous particles 21 used in the method for producing resin composition 10. The method for producing silicon nitride particles includes the steps of: (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.

[0045] Step (1): Synthesizing silicon nitride composite crystals. For example, Si powder is used as the Si-containing raw material. The D50 of the raw Si material is, for example, in the range of 2 to 10 μm. This allows the amount of oxygen impurities to be suppressed, and the combustion rate to be increased, allowing for a higher synthesis temperature, resulting in good crystal growth. As an example, the D50 of Si is 5 μm.

[0046] The diluent is used to adjust the amount of Si in the mixed raw materials. 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 2.0 μm. As an example, the D50 of the diluent is 1.0 μm. The amount of diluent added is less than 10% by mass of the total raw materials (including the diluent). As an example, the diluent is added in an amount of 5 to 8% by mass of the total raw materials. By keeping the amount of diluent added within the above range, a predetermined amount of the desired silicon nitride particles used in the resin composition according to this embodiment can be produced.

[0047] In this embodiment, raw material Si and a diluent are mixed and filled into an insulated heat-resistant container. This insulated heat-resistant container has a thermal conductivity of 1 W / mK or less, and although alumina or zirconia can be used as the material, carbon is preferred to prevent impurities from being mixed in. After the raw materials are filled, the container is covered with a lid made of the same material as the insulated heat-resistant container. Furthermore, to increase the temperature inside the composite during combustion, the thickness of the mixed raw materials is set to more than 100 mm, preferably more than 100 mm and not more than 150 mm. Combustion synthesis is performed in a nitrogen atmosphere in the range of 0.5 to 1 MPa (e.g., 0.9 MPa). Adjusting the pressure range within this range enables efficient synthesis while suppressing increases in equipment costs.

[0048] When the mixed raw material is filled into the crucible, a layer of powder (silicon nitride) having a thickness of 1 mm to 80 mm is spread on the bottom and sides of the crucible, the mixed raw material is then filled, and the top surface is further covered with a layer of powder having a thickness of 1 mm to 80 mm. By covering the entire surface with powder, the mixed raw material can be kept warm, and a predetermined amount of the desired silicon nitride particles used in the resin composition according to this embodiment can be produced.

[0049] 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.

[0050] 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).

[0051] 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.

[0052] 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.

[0053] 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.

[0054] The present embodiment will be described in detail below with reference to examples carried out to clarify the effects of the present embodiment, but the present embodiment is not limited to the following examples.

[0055] <Preparation of Silicon Nitride Particles> Si powder (D50 = 5 μm) and silicon nitride powder (D50 = 1 μm) prepared separately as a diluent were mixed in a tumbling ball mill. The amount of diluent added was 5 to 8 mass% of the total raw material (including diluent). The mixed powder was filled into a carbonaceous, heat-resistant container with a layer of powder 1 mm to 80 mm thick on the bottom and sides, so that the raw material layer was thicker than 100 mm and not more than 150 mm, and the raw material layer was further covered with a layer of powder 1 mm to 80 mm thick. A lid made of a carbonaceous, heat-resistant material was then placed in the container, and synthesis was carried out under a nitrogen atmosphere at 0.9 MPa. After synthesis, the mixture was coarsely pulverized (crushed) in a mortar until it passed through a sieve with the specified openings.

[0056] The obtained coarsely pulverized powder was finely pulverized in a ball mill. The obtained finely pulverized powder was sieved using a vibrating sieve and then wet-classified to obtain the following silicon nitride particles A to F. When sieved using a 150 μm sieve, silicon nitride particles A remained on the sieve (D50 is 192.0 μm). When sieved using a 150 μm sieve, the powder remaining below the sieve was further sieved using a 106 μm sieve, and silicon nitride particles B remained on the sieve (D50 is 118.0 μm). When sieved using a 106 μm sieve, the powder remaining below the sieve was further sieved using a 75 μm sieve, and silicon nitride particles C remained on the sieve (D50 is 83.0 μm). When sieving using a sieve with a 75 μm opening, the powder remaining below the sieve was further sieved using a 63 μm sieve to obtain silicon nitride particles D (D50 is 58.0 μm) remaining on the sieve; when sieving using a sieve with a 75 μm opening, silicon nitride particles E (D50 is 22.0 μm) remaining below the sieve; and silicon nitride particles F (D50 is 56.0 μm) obtained by mixing silicon nitride particles C, D, and E.

[0057] Furthermore, as a comparative example, silicon nitride particles G (D50: 3.6 μm) having the physical properties shown in Table 1 were prepared.

[0058] <Preparation of Alumina Particles> Two types of alumina particles were prepared. The first alumina particles were DAW-05 manufactured by Denka, and the second alumina particles were AA-04 manufactured by Sumitomo Chemical Co., Ltd. Mixed alumina particles obtained by mixing the first alumina particles and the second alumina particles at a predetermined ratio were used as "alumina particles."

[0059] Various measurements were carried out on the silicon nitride particles A to G, the first alumina particles, and the second alumina particles.

[0060] <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.

[0061] The measurement results of D50 of each particle are shown in Table 1. The D50 of the mixed alumina particles (a mixture of the first alumina particles and the second alumina particles) was not measured. However, from the D50 (6.0 μm) of the first alumina particles and the D50 (0.5 μm) of the second alumina particles before mixing, it can be said that the D50 of the mixed alumina particles was 6.0 μm or less.

[0062] <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)

[0063] The aspect ratios of all particles in the SEM image were determined using image processing software Image J (manufactured by the National Institute of Health). First, the maximum particle diameter of the particle was defined as the major axis, and the particle diameter in the direction perpendicular to the major axis was defined as the minor axis. The major axis and minor axis of each particle were measured, and then the ratio of the minor axis to the major axis (minor axis / major axis) was determined. As a result of the above measurement, all silicon nitride particles were particles with an aspect ratio of less than 0.90 (i.e., irregular particles), and all first alumina particles and all second alumina particles were particles with an aspect ratio of 0.90 or more (i.e., spherical particles). The average aspect ratio of each particle was determined as a reference for understanding the overview of the aspect ratio of each particle. The average aspect ratio of each particle was determined by arbitrarily selecting 20 particles from the SEM image of each particle and calculating the arithmetic mean of the aspect ratios of those particles. The measurement results of the average aspect ratios of the silicon nitride particles are shown in Table 1. The average aspect ratio of the first alumina particles was 0.97, and the average aspect ratio of the second alumina particles was 0.91.

[0064] <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.

[0065] 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 1.

[0066] <Measurement of Thermal Conductivity of Resin Composition> The particles (silicon nitride particles, first alumina particles, second alumina particles) were blended together. The blending ratio of each particle is shown in Table 1.

[0067] A glass cloth tape was attached to a PET film to create a mold for determining the outer shape of the film, and this was placed on top of an aluminum plate. The stirred and mixed liquid resin composition was poured into the mold, and a PET film was placed on top of it so as not to trap air. Another aluminum plate was then placed on top of this, heated to 50 to 70°C, and left to harden the resin. After hardening was complete, the aluminum plate was allowed to cool, and when the temperature of the aluminum plate had dropped to about room temperature, the two PET films were peeled off from both sides of the hardened resin composition to obtain a sheet-like resin composition for measurement.

[0068] The thermal diffusivity, specific heat, and density of the obtained sheet-shaped resin composition were measured to determine the thermal conductivity. A measurement sample piece measuring 10 mm long x 10 mm wide x 0.1 mm thick was prepared from the above-mentioned sheet-shaped resin composition, and the thermal diffusivity was measured at room temperature using temperature wave thermal analysis (TWA). An iPhase Mobile manufactured by iPhase Corporation was used as the measuring device. The thermal diffusivity was measured at three arbitrary points on one measurement sample piece, and the average value of the three measurement points was calculated as the measured value.

[0069] The specific heat of the resin composition was calculated from the blending ratio of the resin and each particle. The specific heat of the silicone resin was 0.98 (kJ / (kg K)), the specific heat of the acrylic resin was 0.98 (kJ / (kg K)), the specific heat of the silicon nitride particles was 0.67 (kJ / (kg K)), and the specific heat of the alumina particles was 0.75 (kJ / (kg K)).

[0070] The density was measured using an electronic hydrometer MDS-300 (Alpha Mirage Co., Ltd.). The density was calculated using the Archimedes method (solid density measurement) based on the following formula. The specific gravity was also calculated 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 / cm３ )

[0071] The measured results of thermal diffusivity, specific heat, and density were substituted into the following formula to calculate the thermal conductivity, which is shown in Table 1. Thermal conductivity = thermal diffusivity × specific heat × density

[0072]

[0073] The results in Table 1 will be discussed below. The resin compositions of Samples 1 to 14, which satisfied the requirements of this embodiment, exhibited excellent thermal conductivity. On the other hand, the resin composition of Sample 15, which did not satisfy the requirements of this embodiment, exhibited poor thermal conductivity.

[0074] This application claims priority from Japanese Patent Application No. 2024-024846, filed February 21, 2024. Japanese Patent Application No. 2024-024846 is incorporated herein by reference.

[0075] 10 Resin composition 20 Inorganic particles 21 Amorphous particles 22 Spherical particles 30 Resin

Claims

1. A resin composition containing inorganic particles and a resin, wherein the content of the inorganic particles is 55% by volume or more when the total of the inorganic particles and the resin is 100% by volume, the inorganic particles include irregular particles having an aspect ratio of less than 0.90 and spherical particles having an aspect ratio of 0.90 or more, and the particle diameter D50 of the irregular particles at the cumulative 50% from the fine particle side of the volume-based cumulative particle size distribution is greater than 15 μm.

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

3. The resin composition according to claim 2, wherein the inorganic particles contain 15% by volume or more and 85% by volume or less of silicon nitride particles.

4. The resin composition according to claim 2, wherein the volume ratio of said silicon nitride particles to said alumina particles is 0.2 or more and less than 9.

0.

5. The resin composition 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 less than 20 μm.

6. The resin composition according to claim 2, wherein the silicon nitride particles have a beta-phase ratio of 65% or more.

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