Resin composition

Abstract

This resin composition contains inorganic particles and one or more kinds of resins. The inorganic particles include: one or more kinds of amorphous particles which have an aspect ratio of less than 0.90; and one or more kinds of spherical particles which have an aspect ratio of 0.90 or more. The resin composition has a specific gravity difference ratio calculated from formulas (1) and (2) of 2.5% or more and less than 19.7%.　Specific gravity difference ratio (%) = (1-SG1 / SG2) × 100 (1) [Formula 1]

Description

resin composition

[0001] The present disclosure relates to a resin composition containing 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, resin compositions used in various electronic components have been required to have not only sufficient thermal conductivity but also good appearance with little light scattering. The resin compositions disclosed in Patent Documents 1 to 3 have not been examined for improving appearance. Therefore, an object of an embodiment of the present invention is to provide a resin composition that has good appearance and sufficient thermal conductivity.

[0007] Aspect 1 of the present invention is a resin composition containing inorganic particles and one or more types of resins, wherein the inorganic particles include one or more types of irregular particles having an aspect ratio of less than 0.90 and one or more types of spherical particles having an aspect ratio of 0.90 or more, and the resin composition has a specific gravity difference rate calculated from equations (1) and (2) of 2.5% or more and less than 19.7%. Specific Gravity Difference Rate (%) = (1 - SG １ / SG ２ ) x 100 (1) In formula (1), SG １ is the specific gravity of the resin composition, and in formula (2), 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, the spherical particles, and the 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, the spherical particles, and the 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 first type resin to the total volume of the irregular particles, the spherical particles, and the resin, and n, m, l, x, y, and z are positive integers.

[0008] A second aspect of the present invention is the resin composition according to the first aspect, 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.

[0009] A third aspect of the present invention is the resin composition according to the first or second aspect, wherein the irregular particles are silicon nitride particles, and the inorganic particles contain the silicon nitride particles in an amount of 45% by volume or more and 75% by volume or less.

[0010] A fourth aspect of the present invention is the resin composition according to any one of the first to third aspects, wherein the amorphous particles are silicon nitride particles, the spherical particles are alumina particles, and the volume ratio of the silicon nitride particles to the alumina particles is 0.9 or more and 3.9 or less.

[0011] Aspect 5 of the present invention is the resin composition according to any one of Aspects 1 to 4, wherein the irregular particles are silicon nitride particles, and the silicon nitride particles have a particle diameter D50 of 1 μm or more and 250 μm or less at a cumulative 50% point from the fine particle side in a volume-based cumulative particle size distribution.

[0012] A sixth aspect of the present invention is the resin composition according to any one of the third 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, it is possible to provide a resin composition that has a good appearance and sufficient thermal conductivity.

[0014] The present inventors have conducted extensive research to provide a resin composition having a good appearance and sufficient thermal conductivity. In order to achieve a good appearance with little light scattering, the present inventors have found that increasing the voids, specifically the actual specific gravity (SG) of the resin composition (which may include the voids), １ and the specific gravity SG calculated from the solid content contained in the resin composition, assuming that the resin composition does not contain voids. ２ The ratio of the difference between the １ / SG ２" × 100 (%), hereinafter simply referred to as "specific gravity difference ratio"). However, it was found that simply increasing the specific gravity difference ratio would result in a decrease in thermal conductivity due to the large number of voids. Therefore, the present inventors have discovered for the first time that by mixing particles of different shapes (irregular particles with an aspect ratio of less than 0.90 (hereinafter simply referred to as "irregular particles") and spherical particles with an aspect ratio of 0.90 or more (hereinafter simply referred to as "spherical particles")) as filler particles, it is possible to realize a resin composition with a relatively large specific gravity difference ratio, a good appearance, and sufficient thermal conductivity. This is thought to be because, although a relatively large specific gravity difference ratio would normally result in a decrease in thermal conductivity, the mixture of irregular and spherical particles allows the irregular particles to form a skeleton, and the spherical particles are interposed between the irregular particles, forming sufficient heat conduction paths. The requirements of this embodiment will be described in detail below.

[0015] [Resin composition] The resin composition according to this embodiment contains inorganic particles and one or more types of resins, and the inorganic particles include one or more types of irregular particles having an aspect ratio of less than 0.90 and one or more types of spherical particles having an aspect ratio of 0.90 or more, and the specific gravity difference rate calculated from the formulas (1) and (2) is 2.5% or more and less than 19.7%. Specific gravity difference rate (%) = (1 - SG １ / SG ２ ) x 100 (1) In formula (1), SG １ is the specific gravity of the resin composition, and in formula (2), SG ２ is the theoretical specific gravity of the resin composition 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, the spherical particles, and the resin, and ρb ｍ is the specific gravity of the mth spherical particle among the y types of spherical particles, and Vb ｍis the ratio of the volume of the mth spherical particle to the total volume of the irregular particles, the spherical particles, and the 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 first type resin to the total volume of the irregular particles, the spherical particles, and the resin, and n, m, l, x, y, and z are positive integers. The resin composition has a good appearance and sufficient thermal conductivity.

[0016] Preferred inorganic particles are ceramics such as silica, alumina, aluminum nitride, boron nitride, silicon nitride, and silicon carbide. Particles made of inorganic materials with high thermal conductivity are particularly preferred, for example, particles made of inorganic materials with a thermal conductivity of 15 W / mK or more. Suitable inorganic materials include ceramics such as alumina, aluminum nitride, boron nitride, silicon nitride, and silicon carbide. The inorganic particles 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. Furthermore, when insulating ceramics are used as inorganic particles, short circuits in semiconductor devices can be suppressed. Therefore, insulating ceramic particles are more preferred, and specifically, alumina, aluminum nitride, boron nitride, and silicon nitride are more preferred. As inorganic particles, one or more inorganic materials with higher thermal conductivity selected from the group consisting of alumina and silicon nitride are even more preferred.

[0017] As the resin, known resins such as silicone resin, epoxy resin, and acrylic resin can be used. The type of resin can be selected from thermoplastic resin, thermoplastic elastomer, and thermosetting resin. The resin may be used alone or in combination of two or more. From the viewpoints of moldability and thermal conductivity, it is preferable to use a silicone resin.

[0018] The inorganic particles include irregular particles with an aspect ratio of less than 0.90 and spherical particles with an aspect ratio of 0.90 or more. By including both irregular and spherical particles, the specific gravity difference ratio can be adjusted to the desired range, resulting in a resin composition with good appearance and sufficient thermal conductivity. Even if the specific gravity difference ratio can be adjusted to the desired range by adjusting the manufacturing method, etc., using only either irregular or spherical particles would not result in a resin composition with good appearance and sufficient thermal conductivity. In this specification, "irregular particles" refers to all particles with an aspect ratio of less than 0.90. However, particles commonly used in resin compositions for thermally conductive materials rarely contain particles with an aspect ratio of less than 0.10. Therefore, the "irregular particles" according to one embodiment may be limited to particles with an aspect ratio of 0.10 or more but less than 0.90. Even in this case, the resin composition according to the present 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" 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" may be expressed as 0.90 or more and 1.00 or less.

[0019] Irregular particles and spherical particles in a resin composition can be distinguished by obtaining a cross-sectional SEM image of the resin composition. The cross-section to be observed by SEM is not particularly limited, but in the case of a sheet-shaped resin composition, a cross-section in the thickness direction is preferable. In the case of a resin composition of any shape, if the heat conduction direction can be identified, a cross-section in the heat conduction direction is preferable. The conditions for taking a 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.

[0020] A cross-sectional SEM image of the resin composition is subjected to image analysis to determine the aspect ratio of the inorganic particles shown in the cross-sectional SEM image. This makes it possible to distinguish between amorphous 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. Each inorganic particle 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 particle 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, the ratio of the minor axis to the major axis (minor axis / major axis) is taken as the aspect ratio of that inorganic particle.

[0021] The resin composition according to this embodiment has a specific gravity difference rate calculated from the following formulas (1) and (2) of 2.5% or more and less than 19.7%. １ / SG ２ ) x 100 (1) In formula (1), SG １ is the specific gravity of the resin composition, and in formula (2), SG ２ is the theoretical specific gravity of the resin composition 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, the spherical particles, and the 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, the spherical particles, and the resin, and ρc ｌ is the specific gravity of the lth resin among the z types of resin, and Vc ｌis the ratio of the volume of the first type of resin to the total volume of the irregular particles, the spherical particles, and the resin, and n, m, l, x, y, and z are positive integers. Regarding the "type" of irregular particles (or spherical particles, or resin), when the compositions are different, such as alumina, aluminum nitride, boron nitride, or silicon nitride, different specific gravities are used for the different types. For example, the specific gravity of alumina is 3.90 g / cm. ３ The specific gravity of aluminum nitride is 3.30 g / cm ３ The specific gravity of boron nitride is 2.25 g / cm ３ The specific gravity of silicon nitride is 3.19 g / cm ３ can be used.

[0022] When the specific gravity difference rate is 2.5% or more, the amount of voids in the resin composition is less likely to decrease, and the appearance is more likely to be good. The specific gravity difference rate is preferably 3.0% or more, more preferably 4.5% or more. On the other hand, when the specific gravity difference rate is less than 19.7%, the amount of voids in the resin composition is not excessive, and the thermal conductivity is more likely to be increased. The specific gravity difference rate is preferably 15.0% or less, more preferably 12.0% or less, and even more preferably 10.0% or less. SG １ and S.G. ２ can be measured by the method described in the Examples below.

[0023] When the total of the inorganic particles and the resin is taken as 100% by volume, the content of the inorganic particles is preferably 55% by volume or more, more preferably 65% ​​by volume or more, and particularly preferably 75% by volume or more. This makes it easier to ensure a heat conduction path within the resin composition. When the total of the inorganic particles and the resin is taken as 100% by volume, the content of the inorganic particles 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 resin as a binder, making it easier to suppress detachment of inorganic particles from the resin composition. Therefore, it is easier to obtain a resin composition with a desired specific gravity difference rate.

[0024] The inorganic particles preferably contain 45% by volume or more, more preferably 50% by volume or more, of irregular particles. This facilitates the formation of a skeleton of irregular particles within the resin composition. On the other hand, the inorganic particles preferably contain 75% by volume or less of irregular particles. This allows an appropriate amount of spherical particles to be contained, making it easier for the spherical particles to be interposed between the irregular particles, forming a resin composition containing an appropriate amount of voids, and making it easier to obtain a resin composition with a desired specific gravity difference ratio.

[0025] The volume ratio of irregular particles to spherical particles is preferably 0.9 or more, more preferably 1.0 or more. This makes it easier for the irregular particles to form a skeleton within the resin composition. On the other hand, this volume ratio is preferably 3.9 or less, more preferably 2.5 or less, and even more preferably 2.2 or less. This makes it easier for the spherical particles to be interposed between the irregular particles, allowing the formation of a resin composition containing an appropriate amount of voids, making it easier to obtain a resin composition with a desired specific gravity difference ratio.

[0026] The particle diameter D50 (hereinafter sometimes simply referred to as "D50") of the irregular particles at 50% cumulative from the fine particle side of the volume-based cumulative particle size distribution is preferably 1 μm or more, more preferably 20 μm or more, even more preferably 40 μm or more, and particularly preferably 50 μm or more. This facilitates the formation of a skeleton of irregular particles within the resin composition. The D50 of the irregular particles is preferably 250 μm or less, more preferably 200 μm or less. This allows an appropriate amount of spherical particles to be contained, making it easier for the spherical particles to be interposed between the irregular particles, forming a resin composition containing an appropriate amount of voids, and making it easier to obtain a resin composition with the desired specific gravity difference ratio.

[0027] The D50 of the spherical particles 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 to fill the spaces between the irregular particles, resulting in a resin composition containing an appropriate amount of voids. On the other hand, the D50 of the spherical particles 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.

[0028] The D50 of the spherical particles is preferably 70% or less of the D50 of the irregular particles. This allows the relatively large irregular particles to form a skeleton, making it easier for the relatively small spherical particles to disperse into the gaps. As a result, the irregular particles form the main heat conduction paths within the resin composition, and the spherical particles filling the spaces between the irregular particles form auxiliary heat conduction paths, thereby further improving the thermal conductivity of the resin composition. The D50 of the spherical particles is more preferably 60% or less of the D50 of the irregular particles, even more preferably 50% or less, and particularly preferably 40% or less. On the other hand, the D50 of the spherical particles is preferably 0.001% or more of the D50 of the irregular particles, and more preferably 0.1% or more of the D50 of the irregular particles. This makes it easier for the spherical particles to form auxiliary heat conduction paths. Furthermore, when the D50 of the spherical particles is within the above range, a resin composition containing an appropriate amount of voids can be formed, and a resin composition having a good appearance can be obtained. When the resin composition contains multiple types of spherical particles, it is preferable that the D50 of all types of spherical particles and the D50 of the irregular particles satisfy the above relationship.

[0029] In this embodiment, the D50 of the irregular particles and spherical particles can be measured by laser diffraction. Specifically, particles dispersed in water are irradiated with a laser beam, and the diffraction is measured to determine each particle size. A CILAS 1090L or similar measuring device can be used. The D50 of the irregular particles and spherical particles contained in the resin composition can be measured by removing the resin contained in the resin composition, 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 and spherical particles, and using these particles.

[0030] Another method for determining the D50 of irregular particles and spherical particles is to use image analysis. The resin composition may be subjected to cross-sectional observation using an SEM, and all irregular particles and spherical particles 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).

[0031] 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 by the 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 mean of the aspect ratios of those particles.

[0032] The amorphous particles are preferably silicon nitride particles, and the spherical particles are preferably alumina particles. Since both silicon nitride particles and alumina particles are inorganic materials with high thermal conductivity, the thermal conductivity of the resin composition can be further improved by using particles made of these as a filler.

[0033] The fact that the irregular particles are silicon nitride particles and the spherical particles are alumina particles can be identified, for example, by SEM-EDX analysis of a cross section of the resin composition. The irregular particles and spherical particles contained in the resin composition are each identified from a cross-sectional SEM image, and elemental mapping (e.g., elemental mapping of Si and Al elements) 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.

[0034] 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.

[0035] 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, allowing the formation of a resin composition containing an appropriate amount of voids. 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.

[0036] 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."

[0037] 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, making it easier to form a resin composition containing an appropriate amount of voids. 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 70:30, and particularly preferably 40:60 to 60:40.

[0038] The β-phase ratio of the silicon nitride particles 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.

[0039] 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.

[0040] 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)).

[0041] The physical properties of silicon nitride particles and alumina particles may be measured in the form of a resin composition containing these particles. However, if measurement is difficult in the form of a resin composition, the silicon nitride particles and alumina particles may be isolated from the resin composition and then measured. To isolate the silicon nitride particles and alumina particles from the resin composition, 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 pyrolyze 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.

[0042] Furthermore, these resin compositions may contain, as needed, one or more of 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, as long as the effects of the present embodiment are not impaired.

[0043] In one embodiment of the present invention, the thermal conductivity of the resin composition is preferably 5.0 W / (m K) or more, more preferably 5.8 W / (m K) or more, and even more preferably 6.5 W / (m K) or more. When the thermal conductivity of the resin composition is above the lower limit, it can have sufficient heat dissipation properties when used in electronic components. The thermal conductivity of the resin composition can be determined, for example, by the method described in the examples below.

[0044] [Method of Manufacturing Resin Composition] A method of manufacturing the resin composition according to this embodiment will be described. The resin composition according to this embodiment can be obtained by using irregular particles and spherical particles as inorganic particles and applying a known method to these. For example, when the resin is liquid (e.g., liquid silicone resin), the resin composition can be obtained by mixing the liquid resin, irregular particles 1, spherical particles, and a curing agent and then curing with heat or ultraviolet light. Known curing agents, mixing methods, and curing methods can be used. When the resin is solid, the desired resin composition can be obtained by mixing the irregular particles, spherical particles, and resin and then kneading them using a known method such as melt kneading.

[0045] The amorphous particles (e.g., silicon nitride particles) used in the method for producing a resin composition can be produced, for example, by the method described below. The spherical particles (e.g., alumina particles) used in the method for producing a resin composition may be, for example, commercially available spherical alumina particles or spherical alumina particles produced by a known method (e.g., flame fusion method).

[0046] As an example of a method for producing amorphous particles for use in the production of a resin composition, a method for producing silicon nitride particles will be described. The silicon nitride particles are produced by the following steps: (1) synthesizing silicon nitride composite crystals using a raw material containing Si by combustion synthesis under a nitrogen atmosphere; (2) crushing the silicon nitride composite 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.

[0047] 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.

[0048] 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 adding the amount of diluent 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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).

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] <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.

[0058] 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.

[0059] <Preparation of Alumina Particles> Three types of alumina particles were prepared. The first alumina particles were DAW-05 manufactured by Denka Co., Ltd., the second alumina particles were AA-04 manufactured by Sumitomo Chemical Co., Ltd., and the third alumina particles were DAW-120 manufactured by Denka Co., Ltd. Mixed alumina particles obtained by mixing the first to third alumina particles at a predetermined ratio were used as "alumina particles."

[0060] Various measurements were carried out on the silicon nitride particles A to F and the first to third alumina particles.

[0061] <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.

[0062] 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, second alumina particles, and / or third alumina particles) was not measured. However, in the mixture of the first alumina particles and the second alumina particles, it can be said that the D50 of the mixed alumina particles was 6.0 μm or less, based on the D50 (6.0 μm) of the first alumina particles and the D50 (0.5 μm) of the second alumina particles before mixing.

[0063] <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)

[0064] 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 2. The average aspect ratios of the first and third alumina particles were 0.97, and the average aspect ratio of the second alumina particles was 0.91.

[0065] <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.

[0066] 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 2.

[0067] <Preparation of Resin Composition> Each particle (silicon nitride particles, first alumina particles, second alumina particles, third 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 no third alumina particles were blended in Samples No. 1 to 6 and 8, and no silicon nitride particles were blended in Sample No. 7. The silicone resin and each particle, blended in a blending ratio of 20% by volume of silicone resin and 80% by volume of total particles, were stirred and mixed using a WAWATORI MIXER (manufactured by THINKY CORPORATION), to obtain a liquid resin composition.

[0068] 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.

[0069] <Measurement of specific gravity difference rate of resin composition> Actual measured value of specific gravity SG １ In order to calculate the specific gravity of the sheet-shaped resin composition prepared by the above procedure, the specific gravity was measured. The density was measured using an electronic hydrometer MDS-300 (Alpha Mirage Co., Ltd.). The density was calculated by the Archimedes method (solid density measurement) based on the following formula. The specific gravity SG １ 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 )

[0070] Calculated specific gravity SG ２ was calculated according to the above formula (2). Note that x = 1, y = 3, z = 1, and ρa １ is the specific gravity of silicon nitride, and ρb １ (specific gravity of the first alumina particles), ρb ２ (specific gravity of the second alumina particles) and ρb ３ (specific gravity of the third 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 shown in Table 1.

[0071]

[0072] The specific gravity difference rate of the resin composition was calculated using the above formula (1) and is shown in Table 2.

[0073] <Measurement of thermal conductivity of resin composition> The thermal diffusivity and specific heat 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 0.5 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 measurement device. The thermal diffusivity was measured at three arbitrary points on one measurement sample piece, and the average value was calculated from the measurement results of the three points.

[0074] 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 silicon nitride particles was 0.67 (kJ / (kg K)), and the specific heat of the alumina particles was 0.75 (kJ / (kg K)).

[0075] The measured thermal diffusivity and specific heat, as well as the density measured in the above <Measurement of specific gravity difference rate of resin composition>, were substituted into the following formula to calculate the thermal conductivity, which is shown in Table 2. Thermal conductivity = thermal diffusivity × specific heat × density

[0076] <Appearance Evaluation of Resin Composition> The appearance of the sheet-shaped resin composition was confirmed under an illuminance of 1000 lx and evaluated as follows, with A being acceptable. A: Light scattering on the surface was weak and the appearance was good. B: Light scattering on the surface was strong. C: Light scattering on the surface was even stronger.

[0077]

[0078] The results in Table 2 will be discussed below. The resin compositions of Samples 1 to 6, which satisfied the requirements of this embodiment, had good appearance and sufficient thermal conductivity. On the other hand, the resin compositions of Samples 7 and 8, which did not satisfy the requirements of this embodiment, were poor in appearance and thermal conductivity.

[0079] This application claims priority from Japanese Patent Application No. 2024-024843, filed February 21, 2024. Japanese Patent Application No. 2024-024843 is incorporated herein by reference.

Claims

1. A resin composition containing inorganic particles and one or more types of resins, wherein the inorganic particles include one or more types of irregular particles with an aspect ratio of less than 0.90 and one or more types of spherical particles with an aspect ratio of 0.90 or more, and wherein the specific gravity difference rate calculated from formulas (1) and (2) is 2.5% or more and less than 19.7%. Specific gravity difference rate (%) = (1 - SG １ / SG ２ ) x 100 (1) In formula (1), SG １ is the specific gravity of the resin composition, and in formula (2), 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, the spherical particles, and the 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, the spherical particles, and the 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 first type resin to the total volume of the irregular particles, the spherical particles, and the resin, and n, m, l, x, y, and z are positive integers.

2. The resin composition according to claim 1, wherein the content of said inorganic particles is 55% by volume or more when the total of said inorganic particles and said resin is 100% by volume.

3. The resin composition according to claim 1, wherein the amorphous particles are silicon nitride particles, and the inorganic particles contain 45% by volume or more and 75% by volume or less of the silicon nitride particles.

4. The resin composition according to claim 1, wherein the amorphous particles are silicon nitride particles, the spherical particles are alumina particles, and the volume ratio of the silicon nitride particles to the alumina particles is 0.9 or more and 3.9 or less.

5. The resin composition according to claim 1, wherein the amorphous particles are silicon nitride particles, and the particle diameter D50 of the silicon nitride particles at 50% cumulative from the fine particle side of the volume-based cumulative particle size distribution is 1 μm or more and 250 μm or less.

6. The resin composition according to any one of claims 3 to 5, wherein the silicon nitride particles have a beta conversion rate of 65% or more.

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