Inorganic powder and resin composition using same

Abstract

Provided is an inorganic powder that contains amorphous particles having an aspect ratio of less than 0.90 and spherical particles having an aspect ratio of 0.90 or more, and that has a compressibility of more than 15.1% and no more than 60.0%.

Description

Inorganic powder and resin composition using the same

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

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

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

[0004] Patent Document 2 discloses a liquid encapsulating resin composition before curing, which contains a resin material and a filler made of an inorganic material, and it is preferable to use alumina particles as the filler.

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

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

[0007] In recent years, the increase in heat generation in electronic components has become a problem due to the increased integration of ICs in electronic devices and the use of high-current-driven electronic components due to the electrification of electric vehicles, aircraft, and other devices. Therefore, efficient heat dissipation has been achieved by inserting a thermal interface material (TIM) between a heat-generating element, such as an IC, and a heat-dissipating element, such as a heat sink. To improve heat dissipation, it is desirable to fill the gap between the heat-generating element and the heat-dissipating element with a resin composition for TIM use so as to prevent voids from forming. However, the gap between the heat-generating element and the heat-dissipating element is very narrow, and the resin composition may not be able to fill it sufficiently, resulting in voids. If there are many voids in the gap between the heat-generating element and the heat-dissipating element, the resin composition must be removed and refilled. Therefore, a resin composition that allows for easy removal and refilling (sometimes referred to as a "resin composition with excellent reworkability") is desired.

[0008] Although it is easy to imagine that the tackiness of the resin used has a large effect on the reworkability of the resin composition, the effect of the physical properties of the filler used has not been considered. Patent Documents 1 to 3 do not consider at all the reworkability of the resin composition or the relationship between the reworkability and the physical properties of the filler.

[0009] Therefore, an object of one embodiment of the present invention is to provide an inorganic powder used as a filler for a resin composition, which can be used to produce a resin composition having excellent reworkability. Furthermore, an object of another embodiment of the present invention is to provide a resin composition using the inorganic powder.

[0010] A first aspect of the present invention is an inorganic powder comprising irregular particles having an aspect ratio of less than 0.90 and spherical particles having an aspect ratio of 0.90 or more, and having a compressibility of more than 15.1% and not more than 60.0%.

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

[0012] A third aspect of the present invention is the inorganic powder according to the second aspect, which satisfies the following formula (1): 0.1<[SiN] / [Al ２ O ３ ] < 9.9 ... (1) where [SiN] and [Al ２ O ３ ] are the contents (vol %) of the silicon nitride particles and the alumina particles, respectively, when the total content of the alumina particles and the silicon nitride particles is taken as 100 vol %.

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

[0014] A fifth aspect of the present invention is a resin composition comprising the inorganic powder according to any one of the first to fourth aspects and a resin.

[0015] A sixth aspect of the present invention is the resin composition according to the fifth aspect, wherein the resin composition has a loss modulus of more than 639 Pa.

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

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

[0018] The present inventors have conducted extensive research into fillers that can improve the reworkability of resin compositions, and as a result have discovered that the reworkability of inorganic powders containing a mixture of particles of different shapes (irregular particles and spherical particles) can be improved by controlling the degree of compression, thereby completing the present invention. Hereinafter, an inorganic powder 15 according to this embodiment and a resin composition 10 using the same (see FIG. 1) will be described in detail.

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

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

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

[0022] The compressibility of the inorganic powder is more than 15.1% and not more than 60.0%. It has been found that when a resin composition is prepared using such inorganic powder 15, the resin composition is less likely to adhere to surrounding components during molding. The reason for this is unclear, but the following mechanism is presumed to be involved.

[0023] The degree of compression is an index indicating the fluidity of the powder itself; the smaller the degree of compression, the higher the fluidity of the powder. In the inorganic powder of the present embodiment, the degree of compression is 60.0% or less, thereby improving the fluidity of the inorganic powder and facilitating uniform dispersion when mixed with a resin. Furthermore, the degree of compression is greater than 15.1%, preventing the inorganic powder from flowing too easily in the resin and settling, thereby making it easier for the inorganic powder to be retained in its position after dispersion in the resin. In other words, by controlling the degree of compression to greater than 15.1% and less than 60.0%, aggregation of the inorganic powder within the resin can be reduced. Since aggregation of the inorganic powder within the resin causes the resin composition to easily adhere to surrounding components, using an inorganic powder that can suppress aggregation can reduce the adhesiveness of the resin composition. This allows the resin composition to be cleanly removed from the gap between the heating element and the heat dissipation component, even if the resin composition is not properly injected into the gap. In other words, according to this embodiment, a resin composition that is easy to remove and refill (i.e., a resin composition with excellent reworkability) can be obtained.

[0024] In addition, in resin compositions using inorganic powders with a high degree of compressibility, it is believed that when stress is applied, the resin composition is compressed and its volume decreases, and when the stress is removed, the resin composition expands and its volume increases. Therefore, when a resin composition is used as a TIM and injected into the gap between a heat generating element and a heat dissipation member, the resin composition is injected into the gap in a compressed state (small volume) due to the stress at the time of injection. Then, when the stress is removed after injection is completed, the resin composition expands and spreads throughout the gap between the heat generating element and the heat dissipation member, making it less likely that voids will remain in the gap between the heat generating element and the heat dissipation member. Therefore, it is expected that resin compositions using inorganic powders with a high degree of compressibility can further improve thermal conduction between the heat generating element and the heat dissipation member.

[0025] The degree of compression is preferably more than 15.1% and not more than 55.0%, which improves the flowability of the inorganic powder and makes it easier to disperse uniformly when mixed with a resin. The degree of compression is more preferably 20.0% or more and 50.0% or less, even more preferably 25.0% or more and 48.0% or less, and particularly preferably 36.0% or more and 46.0% or less.

[0026] (Measurement of Compressibility) The compressibility of the inorganic powder was measured by measuring the tap density in accordance with the description of JIS Z2512:2012 "Metal Powder - Tap Density Measurement Method", and the bulk density before tapping was defined as D ０ (g / cm ３ ) and the bulk density after tapping (i.e., tap density) is D １ (g / cm ３ ) and then (D １ -D ０ ) / D １ The compressibility is calculated by the following formula. If the inorganic powder has not yet been mixed with the resin, the inorganic powder can be used as is to measure the compressibility. On the other hand, in order to measure the compressibility of the inorganic powder contained inside the resin composition, it is necessary to separate the inorganic powder from the resin composition. Specifically, the resin contained in the resin composition can be removed by, for example, dissolving it in an organic solvent or by heating it to a temperature of 500°C or higher to thermally decompose the resin, and then the inorganic powder alone can be separated, and the compressibility can be measured using the inorganic powder.

[0027] As described above, the degree of compression is an indicator of the fluidity of the powder itself. Therefore, by controlling the shape and physical properties of the irregular particles and spherical particles that make up the inorganic powder, as well as the content ratio of the irregular particles to the spherical particles, it is possible to obtain an inorganic powder with a degree of compression of more than 15.1% and not more than 60.0%.

[0028] A method for distinguishing irregular particles from spherical particles contained in inorganic powders and an index relating to the shape of irregular particles will be described below.

[0029] (Method for distinguishing irregular particles from spherical particles) First, an SEM image of the inorganic powder is obtained. The conditions for taking a cross-sectional SEM image are a magnification of 100 to 100,000 times, and the observation area is, for example, 1,000 μm × 2,000 μm at a magnification of 250 times, and 4 μm × 3 μm at a magnification of 100,000 times.

[0030] The SEM image of the inorganic powder is analyzed to determine the aspect ratio of the particles shown in the SEM image. This makes it possible to distinguish between irregular particles 20 and spherical particles 30. Each particle shown in the SEM image is analyzed using image processing software (e.g., Image J (manufactured by the National Institute of Health)). The maximum particle size (referred to as the "major axis") of the particle is identified, and the particle size in the direction perpendicular to the major axis is referred to as the "minor axis." For each particle, the ratio of the minor axis to the major axis (minor axis / major axis) is taken as the aspect ratio of that particle.

[0031] Based on this result, particles with an aspect ratio of less than 0.90 can be classified as "irregular particles" and particles with an aspect ratio of 0.90 or more can be classified as "spherical particles."

[0032] The ratio (compounding ratio) of the content (volume %) of the irregular particles to the spherical particles is preferably 90:10 to 20:80, more preferably 85:15 to 30:70, and particularly preferably 80:20 to 40:60.

[0033] In the inorganic powder of this embodiment, it is preferable that the irregular particles are silicon nitride particles and the spherical particles are alumina particles. Since both silicon nitride particles and alumina particles are inorganic materials with high thermal conductivity, the use of particles made of these as fillers can further improve the thermal conductivity of the resin composition. It can be determined, for example, by SEM-EDX analysis of the inorganic powder that the irregular particles are silicon nitride particles and the spherical particles are alumina particles. In an SEM image, the irregular particles and spherical particles are each identified, and the elements detected by EDX measurement (e.g., Si element and Al element) are confirmed. This allows for confirmation that the irregular particles are silicon nitride particles and the spherical particles are alumina particles.

[0034] Furthermore, after the inorganic powder is filled into the resin (i.e., in the state of resin composition 10), it can be identified by SEM-EDX analysis of a cross section of resin composition 10. The irregular particles 20 and spherical particles 30 contained in resin composition 10 are each identified from a cross-sectional SEM image (see, for example, FIG. 1), and the element mapping (e.g., element mapping of Si element and Al element) obtained by EDX measurement is confirmed. This makes it possible to confirm that the irregular particles are silicon nitride particles and the spherical particles are alumina particles.

[0035] It may also contain a small amount of amorphous alumina particles (e.g., 10.0% by volume or less of the total alumina particles) and a small amount of spherical silicon nitride particles (e.g., 10.0% by volume or less of the total silicon nitride particles), neither of which will interfere with the objectives of the present embodiment.

[0036] The 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 even more preferably 0.60 or more and 0.85 or less. 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. When the aspect ratios of the irregular particles and the spherical particles are within the above ranges, it is easy to adjust the compressibility of the inorganic powder within a predetermined range, and it is easy to improve the reworkability of the resin composition containing these particles.

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

[0038] (Silicon nitride particle / alumina particle ratio) The ratio of the content (volume %) of silicon nitride particles 20 to the content (volume %) of alumina particles 30 (referred to as "silicon nitride particle / alumina particle ratio") is preferably greater than 0.1 and less than 9.9. In other words, it is preferable to satisfy the following formula (1): 0.1<[SiN] / [Al ２ O ３ ] < 9.9 ... (1) where [SiN] and [Al ２ O ３ ] are the contents (vol %) of silicon nitride particles and alumina particles, respectively, when the total content of alumina particles and silicon nitride particles is taken as 100 vol %.

[0039] Because the crystalline structure of β-silicon nitride is hexagonal, it tends to have a columnar structure, and many silicon nitride particles have small flat surfaces. When silicon nitride particles come into contact with each other, they tend to align along their respective flat surfaces, resulting in a powder with fewer gaps between particles (low bulk powder). Therefore, as the content of silicon nitride particles in the inorganic powder increases, the compressibility of the inorganic powder tends to decrease. By lowering the content of silicon nitride particles in the inorganic powder to a certain extent, that is, by lowering the silicon nitride particle / alumina particle ratio to a certain extent, it is thought that the probability of silicon nitride particles coming into contact with each other can be reduced, thereby increasing the compressibility of the inorganic powder. The silicon nitride particle / alumina particle ratio is preferably less than 9.9, for example.

[0040] The silicon nitride particle / alumina particle ratio is preferably greater than 0.1. This promotes contact between the silicon nitride particles, reduces the gaps between the particles in the powder, and reduces the degree of compression, making it easier to maintain the degree of compression of the inorganic powder within a predetermined range. The silicon nitride particle / alumina particle ratio is more preferably 0.2 to 8.9, even more preferably 0.5 to 8.5, and particularly preferably 1.0 to 5.0.

[0041] (β-phase ratio of silicon nitride particles) The β-phase ratio of the silicon nitride particles 20 is preferably 65% ​​or more, which improves the thermal conductivity of the silicon nitride particles 20 and further improves the thermal conductivity of the resin composition 10 containing the silicon nitride particles 20. The β-phase ratio is more preferably 70% or more, even more preferably 80% or more, even more preferably 85% or more, and particularly preferably 90% or more. This increases the number of silicon nitride particles with a columnar structure, making it easier to maintain the degree of compression within a predetermined range. The β-phase ratio of the silicon nitride particles may be 100% or less.

[0042] 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.

[0043] 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)).

[0044] (D50 of Alumina Particles) The particle diameter D50 (hereinafter simply referred to as "D50") of the cumulative 50% from the fine particle side of the volume-based cumulative particle size distribution of the alumina particles 30 is preferably less than 10 μm. By making the alumina particles relatively small in particle size, the tendency for the alumina particles, which have a high specific gravity, to separate to the bottom and the silicon nitride particles, which have a low specific gravity, to separate to the top when the inorganic powder is filled is alleviated, making it easier to fill the alumina particles and silicon nitride particles in a well-mixed state. By suppressing excessive settling or aggregation of the alumina particles in the inorganic powder, it is possible to control the particle filling state in the inorganic powder before and after tapping, and to easily control the degree of compression within a predetermined range. Furthermore, when the inorganic powder is added and dispersed in a resin, by making the alumina particles small in particle size, the tendency for the alumina particles to separate to the bottom and the silicon nitride particles to separate to the top due to specific gravity can be alleviated, and aggregation of the respective particles within the resin is suppressed, resulting in low adhesion of the resin composition and a resin composition with excellent reworkability.

[0045] The D50 of the alumina particles is more preferably 8 μm or less, further preferably 7 μm or less, and particularly preferably 6 μm or less. From the viewpoint of dispersibility of the alumina particles in resin, the D50 of the alumina particles is preferably 0.1 μm or more.

[0046] 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."

[0047] The D50 of the first alumina particles is preferably 3 μm or more and 10 μm or less, and the D50 of the second alumina particles is preferably 0.01 μm or more and 2 μm or less. The second alumina particles, which have a small particle size, easily enter the gaps that occur between other particles (first alumina particles and silicon nitride particles) with a large particle size. Since the gaps between particles tend to become cavities in the resin composition, filling the gaps between particles with the second alumina particles suppresses the formation of cavities in the resin composition, resulting in a resin composition with excellent reworkability. 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.

[0048] (D50 of Silicon Nitride Particles) It is preferable that the particle diameter D50 of the cumulative 50% from the fine particle side of the volume-based cumulative particle size distribution of the silicon nitride particles 20 is greater than 1 μm. This improves the dispersibility of the silicon nitride particles in resin, and allows for the production of a resin composition with low adhesion and excellent reworkability.

[0049] The D50 of the silicon nitride particles is more preferably 2 μm or more, and even more preferably 3 μm or more. The D50 of the silicon nitride particles may be 300 μm or less, 200 μm or less, or 150 μm or less. From the viewpoint of increasing the filling rate in the resin composition and easily obtaining a resin composition with excellent reworkability, the D50 of the silicon nitride particles may be 50 μm or less, or 20 μm or less.

[0050] The D50 of silicon nitride particles and the D50 of alumina particles are measured by laser diffraction. Specifically, powder dispersed in water is irradiated with a laser beam, and the diffraction is measured to determine the particle size. A measuring device such as the 1090L manufactured by CILAS can be used.

[0051] [Resin Composition 10] Resin composition 10 contains the inorganic powder according to this embodiment (including a plurality of irregular particles 20 and a plurality of spherical particles 30) and a resin 40. In the cross-sectional SEM image of FIG. 1, the resin 40 is the dark gray portion, and the irregular particles 20 and spherical particles 30 are the light gray portions. In this example, spherical particles 30 with small particle diameters are dispersed among the irregular particles 20 with large particle diameters. The resin 40 fills the gaps between the plurality of irregular particles 20 and the plurality of spherical particles 30. By using the inorganic powder according to this embodiment, a resin composition with low adhesion to surrounding components and excellent reworkability can be molded.

[0052] (Loss modulus) The loss modulus of the resin composition is an index showing the viscoelasticity of the resin composition after curing, and is preferably greater than 639 Pa. This suppresses deformation when contacting surrounding members, resulting in low adhesion. The loss modulus is more preferably 1000 Pa or more, even more preferably 5000 Pa or more, and particularly preferably 12000 Pa or more. The loss modulus may be 40000 Pa or less, or may be 30000 Pa or less. The loss modulus can be measured using a rheometer.

[0053] The preferred contents (filling rates) of the irregular particles 20 and spherical particles 30 contained in the resin composition 10 are as follows. The "content (filling rate)" refers to the content (volume %) of the target particles when the total of the irregular particles 20, spherical particles 30, and resin 40 is taken as 100% by volume. The content (filling rate) of the irregular particles 20 is preferably 10 to 90% by volume, more preferably 20 to 80% by volume, even more preferably 30 to 70% by volume, and particularly preferably 31 to 65% by volume. The content (filling rate) of the spherical particles 30 is preferably 5 to 80% by volume, more preferably 10 to 70% by volume, even more preferably 15 to 60% by volume, and particularly preferably 20 to 50% by volume.

[0054] The total content (total filling rate) of the irregular particles 20 and the spherical particles 30 is preferably 20 to 98% by volume, more preferably 30 to 95% by volume, and particularly preferably 40 to 93% by volume.

[0055] When measuring the inorganic powder contained in the resin composition 10, first, the resin 40 contained in the resin composition 10 is 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.

[0056] [Resin 40] Suitable resins 40 for the resin composition 10 according to the embodiment include known resins such as silicone resins, epoxy resins, and acrylic resins. The type of resin can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins. One type of resin may be used alone, or two or more types may be used in combination. From the viewpoints of moldability and thermal conductivity, it is preferable to use a silicone resin.

[0057] [Other Additives] Furthermore, these resin compositions may contain, as needed, known additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weather resistance agents, antiblocking agents, antistatic agents, leveling agents, and release agents, either singly or in combination, within the scope of the invention.

[0058] [Method for producing inorganic powder] The inorganic powder can be produced by mixing irregular particles 20 and spherical particles 30 in a predetermined ratio. Irregular particles 20 (e.g., silicon nitride particles) suitable for the inorganic powder can be produced, for example, by the method described below. Spherical particles 30 (e.g., alumina particles) suitable for the inorganic powder may be, for example, commercially available spherical alumina particles, or may be spherical alumina particles produced by a known method (e.g., flame fusion method).

[0059] [Method for Producing Irregular Particles 20] A method for producing silicon nitride particles will be described as an example of a method for producing the irregular particles 20 used in producing the resin composition 10. The silicon nitride particles include the following steps: (1) synthesizing silicon nitride synthetic crystals by combustion synthesis under a nitrogen atmosphere using raw materials containing Si, (2) crushing the silicon nitride synthetic crystals to obtain coarsely pulverized silicon nitride powder, (3) finely pulverizing the coarsely pulverized silicon nitride powder to obtain finely pulverized silicon nitride powder, and (4) heat-treating the finely pulverized silicon nitride powder to obtain silicon nitride particles.

[0060] Step (1): Synthesizing silicon nitride composite crystals. The Si-containing raw material is, for example, Si powder. The D50 of the raw material Si is, for example, in the range of 1 to 10 μm. This suppresses the amount of oxygen impurities and increases the combustion rate, allowing for a higher synthesis temperature and achieving good crystal growth.

[0061] The diluent is used to adjust the amount of Si in the mixed raw material. Separately prepared silicon nitride particles are used as the diluent. The diluent may be either α-type silicon nitride particles or β-type silicon nitride particles, or a mixture of these. The D50 of the diluent is preferably in the range of 0.5 to 10.0 μm.

[0062] In this embodiment, raw material Si and a diluent are mixed and filled into a heat-resistant container. The heat-resistant container is preferably made of ceramic or carbon. After filling the raw materials, the container is covered with a lid made of the same material as the heat-resistant container, and combustion synthesis is carried out in a nitrogen atmosphere at a pressure of 0.1 to 1 MPa.

[0063] 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.

[0064] 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).

[0065] 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.

[0066] 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.

[0067] 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.

[0068] [Method of Manufacturing Resin Composition 10] A method of manufacturing the resin composition 10 will be described. The resin composition 10 can be obtained by using an inorganic powder with a controlled angle of repose and applying a known method to the inorganic powder. For example, when the resin is liquid (e.g., liquid silicone resin), the resin composition 10 can be obtained by mixing the liquid resin, inorganic powder containing amorphous particles 20 and spherical particles 30, and a curing agent, and then curing the mixture with heat or ultraviolet light. Known curing agents, mixing methods, and curing methods can be used. On the other hand, when the resin is solid, the desired resin composition 10 can be obtained by mixing the inorganic powder and resin and then kneading them using a known method such as melt kneading.

[0069] The present invention will be described in detail below with reference to examples carried out to clarify the effects of the present invention, but the present invention is not limited to the following examples.

[0070] <Preparation of Silicon Nitride Particles> Silicon nitride particles a having the physical properties shown in Tables 1 and 2 were prepared. Furthermore, silicon nitride particles a were immersed in an aqueous solution of pH 14 and then heated at 900°C for 5 hours in a nitrogen atmosphere. The resulting agglomerated powder was pulverized in a mortar and mortar, and then sieved through a sieve with 80 μm openings to obtain silicon nitride particles b, which remained on the sieve. For the comparative example, commercially available silicon nitride powder (manufactured by Aldrich, silicon nitride (predominantly β-phase, ≦10 micron primary particle size, product code 248622); hereinafter referred to as "silicon nitride particles c") was used.

[0071] <Preparation of Alumina Particles> Three types of alumina particles were prepared. As the first alumina particles, DAW-05 manufactured by Denka (Sample Nos. 1 to 7) or DAW-45 manufactured by Denka (Sample No. 8) was used, and as the second alumina particles, AA-04 manufactured by Sumitomo Chemical Co., Ltd. was used. Mixed alumina particles obtained by mixing the first alumina particles and the second alumina particles at a predetermined ratio were used as "alumina particles."

[0072] Various measurements were carried out on the silicon nitride particles a to c, the first alumina particles, and the second alumina particles.

[0073] <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.

[0074] The measurement results of D50 for each particle are shown in Table 1. The D50 of the mixed alumina particles (a mixture of first alumina particles and second alumina particles) was not measured. However, from the D50 (6.0 μm) of the first alumina particles before mixing and the D50 (0.5 μm) of the second alumina particles, it can be said that the D50 of the mixed alumina particles was 6.0 μm or less. In other words, the D50 of the alumina particles (mixed alumina particles) used in the examples was less than 10 μm.

[0075] <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)

[0076] The aspect ratios of all particles in the SEM images were determined using image processing software Image J (manufactured by the National Institute of Health). First, the longest particle diameter of each particle was defined as the longest diameter, and the particle diameter in the direction perpendicular to the longest diameter was defined as the shortest diameter. The longest and shortest diameters of each particle were then measured, and the ratio of the shortest diameter to the longest diameter (shortest diameter / longest diameter) was then determined. As a result, it was confirmed that the silicon nitride particles were amorphous particles 20 (aspect ratio less than 0.90), and that the first alumina particles and the second alumina particles were both spherical particles 30 (aspect ratios of 0.90 or more).

[0077] The average aspect ratio of each particle was determined as a reference for understanding the aspect ratio of each particle. The average aspect ratio of each particle was determined by randomly selecting 20 particles from the SEM image of each particle and calculating the arithmetic mean of the aspect ratios of those particles. Note that this average aspect ratio does not indicate the aspect ratio of each particle. Therefore, it should be noted that the average aspect ratio cannot be used to determine whether each particle is an irregular particle or a spherical particle. The measurement results of the average aspect ratio of the silicon nitride particles (referred to as "aspect ratio" in Table 2) are shown in Table 2. The average aspect ratio of the first alumina particles (Denka DAW-05 and Denka DAW-45) was 0.97, and the average aspect ratio of the second alumina particles was 0.91.

[0078] The average aspect ratio of the silicon nitride particles is preferably 0.50 or more and less than 0.90, more preferably 0.55 or more and 0.86 or less, and particularly preferably 0.60 or more and 0.85 or less. The average aspect ratio of the alumina particles is preferably 0.90 or more and 1.00 or less, and more preferably 0.91 or more and 1.00 or less. By setting the average aspect ratios of the silicon nitride particles and the alumina particles within appropriate ranges, the alumina particles become interposed between other particles, and when the inorganic powder is tapped, the volume of the gaps between the particles is adjusted to an appropriate range, making it easy to control the compressibility of the inorganic powder within a predetermined range.

[0079] <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.

[0080] 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.

[0081] <Silicon nitride particle / alumina particle ratio in inorganic powder> From the compounding ratio of each particle (silicon nitride particles, first alumina particles, second alumina particles) shown in Table 1, the ratio of the content (volume %) of silicon nitride particles to the total content (volume %) of the first alumina particles and the second alumina particles (silicon nitride particle / alumina particle ratio) was calculated and shown in Table 1.

[0082] <Measurement of Compressibility of Inorganic Powder> The particles (silicon nitride particles, first alumina particles, second alumina particles) were blended in the blending ratios shown in Table 1, and stirred and mixed using a WAWATORI MIXER (manufactured by THINKY CORPORATION) to prepare an inorganic powder. The bulk density (tap density) after tapping was measured in accordance with the description in JIS Z2512:2012 "Metal Powders - Method for Measuring Tap Density." Specifically, 20 mL of the inorganic powder was measured into a 100 mL resin graduated cylinder, and tapping was performed once per second for 3 minutes. After confirming that the volume of the inorganic powder had not further decreased, the mass and volume of the inorganic powder were measured.

[0083] The bulk densities before and after tapping were calculated using the following formula. Note that the mass of the inorganic powder does not change before and after tapping, but the volume of the inorganic powder after tapping becomes smaller than that before tapping (20 mL). Bulk density (g / cm３ ) = mass of inorganic powder (g) / volume of inorganic powder (cm ３ )

[0084] Using the bulk density values ​​before and after tapping, the compressibility was calculated using the following formula: Compressibility (%) = (D １ -D ０ ) / D １ × 100 where D ０ is the bulk density before tapping (g / cm ３ ), D １ is the bulk density after tapping (g / cm ３ The bulk density and compression ratio before and after tapping are shown in Table 3.

[0085] <Preparation of Resin Composition> Each particle (silicon nitride particles, first alumina particles, second alumina particles) was blended with a silicone resin (base: DOWSIL (trademark) CY 52-276 A manufactured by Dow Chemical; curing agent: DOWSIL (trademark) CY 52-276 B manufactured by Dow Chemical). The blending ratio of each particle and the silicon nitride particle / alumina particle ratio are shown in Table 1. Note that in Sample No. 6, only silicon nitride particles were used, and no alumina particles (first alumina particles and second alumina particles) were blended. In Sample No. 7, no second alumina particles were blended. The silicone resin and each particle, blended in a blending ratio of 30% by volume of silicone resin and 70% by volume of total particles, were stirred and mixed using a WAWATORI MIXER (manufactured by THINKY CORPORATION), to obtain a liquid resin composition.

[0086] 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 12 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.

[0087] <Measurement of adhesion amount> When preparing the resin composition, the adhesion amount of the resin composition adhered to the PET film was measured. The mass of the surface side film used to prepare the resin composition was measured in advance. The resin composition was prepared according to the preparation method described above, and after curing, the surface side film was peeled off from the resin composition, and the mass of the surface side film was measured again. The difference between the mass of the surface side film measured in advance and the mass of the surface side film after peeling was taken as the adhesion amount of the resin composition. The adhesion amount results are shown in Table 3.

[0088] <Measurement of Loss Modulus> The loss modulus of the sheet-shaped resin composition was measured. Using a Modular Compact Rheometer (MCR302e manufactured by Anton Paar), the shear rate-viscosity measurement of the sheet-shaped resin composition was carried out at a constant strain. The measurement conditions were as follows: Geometry: Φ20 mm parallel plates Gap: 0.5 mm Shear strain: 4% Frequencies: 1 to 100 rad / s Measurement temperature: 25°C Measurement time: 5 minutes The sample was set on a plate stabilized at the measurement temperature within 5 minutes, and the measurement was started. The loss modulus was calculated from the results of the shear rate-viscosity measurement and is shown in Table 3.

[0089]

[0090]

[0091]

[0092] The results in Table 3 will be discussed below. The resin compositions of Samples 1 to 7, which satisfied the requirements of this embodiment, exhibited low adhesion amounts and excellent reworkability. On the other hand, the resin composition of Sample 8, which did not satisfy the requirements of this embodiment, exhibited high adhesion amounts and poor reworkability. Furthermore, it is believed that the resin compositions of Samples 1 to 7, which satisfied the requirements of this embodiment, had loss moduli of more than 639 Pa, which suppressed deformation when they came into contact with surrounding components and reduced adhesion amounts.

[0093] This application claims priority from Japanese Patent Application No. 2024-024853, filed February 21, 2024. Japanese Patent Application No. 2024-024853 is incorporated herein by reference.

[0094] 10 Resin composition 15 Inorganic powder 20 Amorphous particles 30 Spherical particles 40 Resin

Claims

1. An inorganic powder containing irregular particles with an aspect ratio of less than 0.90 and spherical particles with an aspect ratio of 0.90 or more, and having a degree of compression of more than 15.1% and not more than 60.0%.

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

3. The inorganic powder according to claim 2, which satisfies the following formula (1): 0.1<[SiN] / [Al ２ O ３ ] < 9.9 ... (1) where [SiN] and [Al ２ O ３ ] are the contents (vol %) of the silicon nitride particles and the alumina particles, respectively, when the total content of the alumina particles and the silicon nitride particles is taken as 100 vol %.

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

5. A resin composition comprising the inorganic powder according to any one of claims 1 to 4 and a resin.

6. The resin composition according to claim 5, having a loss modulus of greater than 639 Pa.

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