Silicon nitride powder and resin composition using same

Abstract

A silicon nitride powder includes a plurality of silicon nitride particles having an angle of repose greater than 40 DEG.

Description

TECHNICAL FIELD

[0001] The present application relates to a silicon nitride powder and a resin composition using the same. BACKGROUND

[0002] Heat generated by energization of an electronic component is dissipated via a heat sink. In order to improve the heat dissipation efficiency, a technique of filling a heat dissipation material between the electronic component and the heat sink is known.

[0003] As a heat dissipation material, a resin composition containing a resin and inorganic particles is known, and as the inorganic particles, a silicon nitride powder can be used (for example, Patent Literature 1).

[0004] Patent Literature 1 discloses a low-aluminum type spherical β-silicon nitride powder used as a filler for an electronic packaging material. The silicon nitride powder is characterized by a sphericity of 0.5 to 0.99, an Al impurity content of less than 500 ppm, and a particle size range of 0.5 μm to 50 μm.

[0005] Patent Literature 2 discloses a method for producing a silicon nitride powder suitable for producing a silicon nitride sintered body and a silicon nitride powder obtained by the method. The silicon nitride powder has an average particle size of 1 to 50 μm, a content of metal oxides of 0 to 10 wt%, and a content of impurities of less than 1 wt%. Preferably, the content of metal oxides in the above silicon nitride powder is less than 1 wt%, the sintered body after sintering has a thermal conductivity of 90 W / mK or more and a bending strength of 700 MPa or more, and the sintering conditions of the above sintered body are preferably such that the above silicon nitride powder is mixed with MgO and Y2O3 and is ground, a green body is dry-press formed, and the above green body is subjected to pressure sintering under a nitrogen pressure of 1 MPa at 1900°C for 8 h.

[0006] Patent Literature 3 discloses a silicon nitride powder suitable for producing a high-thermal-conductivity silicon nitride sintered body. The silicon nitride powder is characterized by including columnar particles having a β fraction of 30 to 100%, an oxygen content of less than 0.5 wt%, an average particle diameter of 0.2 to 10 μm, an aspect ratio of 10 or less, and a groove portion formed in the long axis direction of the particles.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] PATENT LITERATURE : Japanese Patent Application Laid-Open No. 2022-522814

[0010] PATENT LITERATURE : Japanese Patent Application Laid-Open No. 2022-541208

[0011] PATENT LITERATURE Japanese Patent Application Laid-Open Publication No. 2004-262756 SUMMARY

[0012] It is known that in the process of gradually using silicon nitride powder as described above, when the productivity is further improved, there are problems that silicon nitride powder easily adheres to other components and the like.

[0013] In view of such circumstances, an object of one embodiment of the present application is to provide a silicon nitride powder used as a filler for a resin composition, and which can inhibit adhesion to other components. Further, an object of another embodiment of the present application is to provide a resin composition using a silicon nitride powder.

[0014] One embodiment of the present application is a silicon nitride powder including a plurality of silicon nitride particles, and a rest angle is greater than 40°.

[0015] Another embodiment of the present application is the silicon nitride powder according to one embodiment of the present application, in which a compression degree is less than 34.4 %.

[0016] A further embodiment of the present application is the silicon nitride powder according to one embodiment or another embodiment of the present application, in which a difference between a particle diameter D90 at which 90 % of the cumulative volume-based particle size distribution is accumulated from the fine particle side and a particle diameter D10 at which 10 % of the cumulative volume-based particle size distribution is accumulated from the fine particle side is less than or equal to 150.0 μm.

[0017] A still further embodiment of the present application is the silicon nitride powder according to one embodiment to another embodiment of the present application, in which an average aspect ratio of a short diameter to a long diameter of the silicon nitride particles is greater than 0.50.

[0018] A still further embodiment of the present application is the silicon nitride powder according to one embodiment to another embodiment of the present application, in which a ratio (L2 / L1) of a total length L2 of boundary lines in the interior to a length L1 of the outer edge is less than or equal to 1 %, and a maximum particle diameter of the silicon nitride particles is greater than or equal to 6.8 μm.

[0019] One embodiment of the present application is a resin composition including a resin and the silicon nitride powder according to one embodiment to another embodiment of the present application.

[0020] According to one embodiment of the present application, a silicon nitride powder which can inhibit adhesion to other components can be provided. DETAILED DESCRIPTION

[0021] [Silicon Nitride Powder]

[0022] The present inventors and others have conducted research from various viewpoints in order to achieve a silicon nitride powder that inhibits adhesion to other components, focusing on the angle of repose. As a countermeasure to inhibit adhesion to other components, generally, reducing the angle of repose to increase fluidity is considered. In contrast, the present inventors and others have found that, instead, by increasing the angle of repose to a prescribed value or more, the silicon nitride powder is easily concentrated and the like, and as a result, is less likely to adhere to other components (for example, polystyrene components and the like). Hereinafter, the detailed contents of each element prescribed by the embodiments of the present invention are shown.

[0023] (Angle of repose)

[0024] The silicon nitride powder according to the embodiments of the present invention includes a plurality of silicon nitride particles, and the angle of repose is greater than 40°. Thereby, the silicon nitride powder is less likely to adhere to other components (for example, polystyrene components and the like). In addition, by having the angle of repose in the above range, in a resin composition including the silicon nitride powder, the silicon nitride powder is somewhat concentrated and easily forms a heat diffusion path and the like, and thus the heat diffusion rate of the resin composition can be increased. The angle of repose is preferably 41° or more. On the other hand, the angle of repose is preferably 60° or less. Thereby, the fluidity of the silicon nitride powder can be somewhat ensured, the silicon nitride powder is easily dispersed in the resin composition, and the heat diffusion rate of the resin composition can be increased. The angle of repose is more preferably 58° or less, further preferably less than 56°, even further preferably 50° or less, still further preferably 47° or less, and particularly preferably 45° or less.

[0025] The angle of repose of the silicon nitride powder is measured in accordance with the description of JIS R 9301-2-2:1999. As the surrounding environment at the time of angle of repose measurement, a temperature of 23°C and a humidity of 40% are set.

[0026] (Compression degree)

[0027] The compression degree of the silicon nitride powder according to the embodiments of the present invention is preferably less than 34.4%. Thereby, the fluidity of the silicon nitride powder is increased, the silicon nitride powder is further dispersed in the resin composition, and the heat diffusion rate of the resin composition can be further increased. The compression degree is more preferably 34.0% or less, further preferably less than 33.6%, even further preferably less than 24.1%, and particularly preferably 17.0% or less. On the other hand, the compression degree is preferably 3.0% or more, whereby the silicon nitride powder is less likely to scatter. The compression degree is more preferably 5.0% or more, further preferably 7.0% or more, and even further preferably 8.0% or more.

[0028] The compression degree of the silicon nitride powder is measured in accordance with the description of JIS Z 2512:2012 "Metallic powders - Determination of tapped density" to measure the tapped density, and the bulk density before tapping is set as D0 (g / cm 3), the tap density (i.e., the bulk density after tapping) is set to Dl (g / cm 3 ) and is calculated by (Dl - D0) / Dl.

[0029] The tap density (i.e., the bulk density after tapping) Dl (g / cm 3 ) of the above is high, meaning that the silicon nitride powder can be densely packed. In addition, if a resin composition is formed using a silicon nitride powder having a high tap density, more silicon nitride powder can be kneaded, and it can be expected that the thermal diffusivity of the resin composition can be increased. Therefore, Dl is preferably greater than 0.54 g / cm 3 , more preferably 1.00 g / cm 3 , and even more preferably 1.17 g / cm 3 or more. On the other hand, by lowering the tap density to some extent, the particles are difficult to be compacted with each other, and the dispersibility can be increased. Therefore, Dl is preferably 2.00 g / cm 3 or less, more preferably 1.90 g / cm 3 or less, and even more preferably less than 1.80 g / cm 3 .

[0030] The bulk density D0 (g / cm 3 ) before tapping is not particularly limited and can be, for example, 0.35 to 1.60 g / cm 3 .

[0031] (the difference between the particle size D90 at which 90% of the particles are accumulated from the fine particle side of the cumulative particle size distribution on a volume basis and the particle size DlO at which 10% of the particles are accumulated from the fine particle side of the cumulative particle size distribution on a volume basis)

[0032] The silicon nitride powder having a sharp particle size distribution is preferable because it is easily used as a filler for a resin composition, and the selectivity and degree of freedom when mixed with other powders (particles) are increased. For example, the difference between the particle size D90 at which 90% of the particles are accumulated from the fine particle side of the cumulative particle size distribution on a volume basis (hereinafter, sometimes abbreviated as "D90") and the particle size DlO at which 10% of the particles are accumulated from the fine particle side of the cumulative particle size distribution on a volume basis (hereinafter, sometimes abbreviated as "DlO") is preferably 150.0 μm or less. More preferably, it is 130.0 μm or less.

[0033] As described above, the difference between D90 and the particle size D50 at which 50% of the particles are accumulated from the fine particle side of the cumulative particle size distribution on a volume basis (hereinafter, sometimes abbreviated as "D50") is preferably 100.0 μm or less, and more preferably 80.0 μm or less.

[0034] On the other hand, in the case where the particle size distribution of the silicon nitride powder is somewhat wide, the filling property is improved due to the entry of small particles into the gaps between large particles and the like, and the silicon nitride powder can be mixed more into the resin, which can contribute to an increase in the thermal diffusivity of the resin composition. Therefore, the difference between D90 and D10 is preferably 3.0 μm or more, more preferably greater than 3.3 μm, further preferably greater than 6.6 μm, more further preferably 20.0 μm or more, and particularly preferably 40.0 μm or more.

[0035] As described above, the difference between D90 and D50 is preferably 1.5 μm or more, more preferably greater than 2.0 μm, further preferably 5.0 μm or more, more further preferably greater than 5.5 μm, still further preferably 20.0 μm or more, and particularly preferably 25.0 μm or more.

[0036] The D90, D50, and D10 of the silicon nitride powder are measured by a laser diffraction method. Specifically, laser light is irradiated to a powder dispersed in water, and the diffraction thereof is measured to find the respective particle sizes. As the measuring device, a CILAS Model 1090L or the like can be used.

[0037] (Average aspect ratio of silicon nitride particles)

[0038] The average aspect ratio of the silicon nitride particles contained in the silicon nitride powder is preferably greater than 0.50, more preferably greater than 0.60, and further preferably 0.65 or more. On the other hand, the average aspect ratio of the silicon nitride particles is preferably less than 0.87, more preferably 0.86 or less, and further preferably 0.85 or less.

[0039] If the average aspect ratio of the silicon nitride particles is within an appropriate range, the filling rate in the resin composition can be further increased, and a resin composition having a higher thermal diffusivity can be obtained.

[0040] The average aspect ratio of the silicon nitride particles is measured as follows.

[0041] The SEM image of the silicon nitride particles contained in the silicon nitride powder is analyzed by an image processing software (for example, Image J (manufactured by National Institute of Health)). The maximum particle size of the silicon nitride particles is determined (which is taken as the "long diameter"), and the particle size in the direction orthogonal to the long diameter is taken as the "short diameter". The long diameter and the short diameter are measured for any 20 silicon nitride particles, and the ratio of the short diameter to the long diameter (short diameter / long diameter) is found for each particle. The arithmetic mean of these ratios is taken as the average aspect ratio of the silicon nitride particles.

[0042] (The maximum particle size of the silicon nitride particles having a ratio (L2 / L1) of the total length L2 of the boundary lines in the interior to the length L1 of the outer edge of 1% or less is 6.8 μm or more)

[0043] The fewer the grain boundaries and voids inside the silicon nitride particles, the more the thermal diffusivity of the silicon nitride particles is improved. Therefore, as an index of the content of the grain boundaries inside the silicon nitride particles, the ratio (L2 / L1) of the total length L2 of the boundary lines to the length L1 of the outer edge is introduced. L1 and L2 are found from the cross-sectional observation of the silicon nitride particles. Note that "grain boundaries" and "boundary lines" herein refer to boundaries (also referred to as high-angle grain boundaries) in which the crystal orientation difference (misorientation) exceeds 15° in the EBSD analysis results.

[0044] When the length of the outer edge of one silicon nitride particle is set to L1 and the total length of the boundary lines possessed by the silicon nitride particle is set to L2, a silicon nitride particle in which the value of L2 / L1 is small can be said to be a silicon nitride particle in which the content of the boundary lines is small. In the present embodiment, a silicon nitride particle in which L2 / L1 is 1% or less is regarded as a silicon nitride particle composed of a single crystal (referred to as a "single-crystal particle"). The thermal diffusivity of a single-crystal particle is high, and thus the thermal diffusivity is easily improved when used as a filler for a resin composition.

[0045] In the present embodiment, the maximum particle diameter of the silicon nitride particle (i.e., a single-crystal particle) in which L2 / L1 is 1% or less is preferably 6.8 μm or more, more preferably 10.0 μm or more, further preferably 15.0 μm or more, more further preferably 30.0 μm or more, still further preferably 45.0 μm or more, and particularly preferably 55.0 μm or more. Such a silicon nitride particle forms a long thermal conduction path when filled into a resin, and thus the thermal diffusivity of the resin composition can be improved.

[0046] (β Conversion Rate)

[0047] The β conversion rate of the silicon nitride powder is preferably 65% or more. By making the β conversion rate 65% or more, the thermal diffusivity of the silicon nitride powder and the resin composition can be improved.

[0048] The β conversion rate is more preferably 70% or more, further preferably 80% or more, more further preferably 85% or more, and particularly preferably 90% or more.

[0049] In the present specification, the "β conversion rate" refers to the content ratio (vol%) of the β-type silicon nitride contained in the silicon nitride powder with respect to the entire silicon nitride.

[0050] In the calculation of the β conversion rate, a diffraction pattern of the silicon nitride powder is obtained by powder X-ray diffraction method (X-ray source: Cu Kα ray), the diffraction pattern is analyzed by Gazzara & Messier method (G.P. Gazzara and D.P. Messier, "Determination of Phase Content of Si3N4 by X-ray Diffraction Analysis", Am. Ceram. Soc. Bull., 56 [9] 777-80 (1977)), and the β conversion rate is calculated.

[0051] [Method for manufacturing silicon nitride powder]

[0052] The silicon nitride powder according to the embodiment of the present application can be manufactured by a manufacturing method including:

[0053] (1) a step of synthesizing a silicon nitride bulk crystal by combustion synthesis method using a raw material containing Si under a nitrogen atmosphere,

[0054] (2) a step of crushing the silicon nitride bulk crystal to obtain a coarse crushed powder of silicon nitride, and

[0055] (3) a step of performing microcrushing on the coarse crushed powder of silicon nitride to obtain a microcrushed powder of silicon nitride.

[0056] Further, it can arbitrarily include

[0057] (4) a step of performing heat treatment on the microcrushed powder of silicon nitride.

[0058] Each step is described in detail below.

[0059] • Step (1): Step of synthesizing silicon nitride bulk crystal

[0060] As the raw material containing Si, for example, Si powder is used.

[0061] The average particle diameter D50 of the raw material is, for example, in the range of 2 to 10 μm. Thereby, the combustion speed can be increased while suppressing the oxygen impurity, the synthesis temperature can be increased, and good crystal growth can be obtained. As an example, the average particle diameter D50 of Si is 5 μm.

[0062] The diluent is used to adjust the amount of Si contained in the raw material. As the diluent, a separately prepared silicon nitride powder is used. The diluent can be either of an α-type silicon nitride powder, a β-type silicon nitride powder, or a mixture thereof. The average particle diameter D50 of the diluent is preferably in the range of 0.5 to 2.0 μm. As an example, the average particle diameter D50 of the diluent is 1.0 μm. The amount of the diluent added is set to be less than 10 mass% with respect to the entire raw material including the diluent. As an example, the diluent is added in an amount of 5 to 8 mass% with respect to the entire raw material. By setting the amount of the diluent added in the above range, it is easy to obtain a silicon nitride powder having a prescribed angle of repose and a prescribed compressibility, and the like.

[0063] In the present embodiment, the diluent is mixed in the raw material and filled into the heat-insulating heat-resistant container. The thermal conductivity of the heat-insulating heat-resistant container is 1 W / mK or less, and the material can be alumina or zirconia, and in view of the incorporation of impurities, carbon is preferable. In addition, after the raw material is filled, the top is capped with a substance of the same material as the heat-insulating heat-resistant container. Furthermore, in order to increase the temperature inside the synthetic body at the time of combustion, the thickness of the mixed raw material is greater than 100 mm, and preferably greater than 100 mm and 150 mm or less. The combustion synthesis is performed under a nitrogen atmosphere in the range of 0.5 to 1 MPa (for example, 0.9 MPa). By setting the pressure range in the above range, it is possible to synthesize efficiently while suppressing an increase in equipment cost.

[0064] When the mixed raw material is filled into the crucible, a powder layer (silicon nitride) having a layer thickness of 1 mm to 80 mm is laid on the bottom surface and the side surface of the crucible, and then the mixed raw material is filled, and furthermore, the top surface is covered with a powder layer having a layer thickness of 1 mm to 80 mm. The thickness of the powder layer is 100 mm or less, and preferably 1 mm to 80 mm. By covering with the powder layer, it is possible to keep the mixed raw material warm, and it is easy to obtain a silicon nitride powder having a prescribed angle of repose, compressibility, and the like.

[0065] In order to more effectively promote crystal growth, a catalyst can be used, for example, Y2O3, Fe2O3, CaO, Ni, Co, C, or the like is added in an amount of about 0.01 to 0.1 mass%. In addition, external auxiliary heating in the range of 500°C to 1700°C (for example, 1500°C) is performed, and even with a combustion synthesis method by self-ignition, the combustion temperature is increased.

[0066] • Step (2): a step of obtaining a coarsely pulverized powder of silicon nitride

[0067] The silicon nitride synthetic body crystal is a form in which a plurality of silicon nitride particles are agglomerated. In Step (2), by crushing the silicon nitride synthetic body crystal, a coarsely pulverized powder of silicon nitride can be obtained. For example, using a general coarsely pulverizing device such as a hammer mill or a disk mill, the synthetic body is crushed to pass through a sieve having a prescribed mesh size (for example, a sieve having a mesh size in the range of 400 μm to 500 μm).

[0068] • Step (3): a step of obtaining a finely pulverized powder of silicon nitride

[0069] The coarsely pulverized powder of silicon nitride is further finely pulverized to obtain a finely pulverized powder of silicon nitride. The fine pulverization is performed by, for example, a jet mill, a ball mill, or the like. If necessary, the obtained finely pulverized powder can be classified. The classification can be performed by sieving, wet classification, or the like.

[0070] • Step (4): a step of heat-treating the finely pulverized powder of silicon nitride

[0071] The finely pulverized powder of silicon nitride can be heat-treated as appropriate. By the heat treatment, an oxide film is formed on the surface of the silicon nitride particles, and thus the silicon nitride particles are chemically stabilized. The heat treatment is performed at, for example, 500°C or higher and 1200°C or lower in the air. The heat treatment time can be appropriately adjusted depending on the heat treatment temperature. The heat treatment time is, for example, 5 hours.

[0072] In the method for producing the silicon nitride powder, a silicon nitride synthetic crystal is synthesized by using the heat of combustion synthesis, and is subjected to crushing, classification, and fine pulverization, whereby the silicon nitride powder according to the present embodiment can be produced.

[0073] [Resin composition]

[0074] The resin composition according to the present embodiment contains a resin and the silicon nitride powder according to the present embodiment. The blending ratio of the resin / silicon nitride powder of the resin composition according to the present embodiment can be appropriately determined depending on the purpose and / or use. As one example, the ratio of the resin to the silicon nitride powder can be 5 to 75% by volume of the resin and 95 to 25% by volume of the silicon nitride powder, with respect to the resin composition (composite).

[0075] Note that the filling rate of the silicon nitride powder in the resin composition means the content (volume %) of the silicon nitride powder when the volume of the resin composition (including the silicon nitride powder) is assumed to be 100% by volume.

[0076] A method for producing the resin composition will be described.

[0077] The resin composition can be obtained by mixing the silicon nitride powder with a resin using a generally used known method. For example, in the case where the resin is in a liquid state (e.g., a liquid epoxy resin or the like), the resin composition can be obtained by mixing a liquid resin, the silicon nitride powder, and a curing agent, and then curing the mixture using heat or ultraviolet rays or the like. The curing agent, the mixing method, and the curing method can use known curing agents and methods. On the other hand, in the case where the resin is in a solid state, the resin composition can be obtained by mixing the silicon nitride powder with the resin and then kneading the mixture by a known method such as melt kneading.

[0078] As the resin used in the resin composition, a known resin such as an epoxy resin can be used. As the type of the resin, a thermoplastic resin, a thermoplastic elastomer, or a thermosetting resin can be selected. Note that the resin can be used alone or in combination with two or more kinds.

[0079] Further, if necessary, a known additive such as a plasticizer, a curing accelerator, a coupling agent, a filler, a pigment, a flame retardant, an antioxidant, a surfactant, a compatibilizer, a weathering agent, an antiblocking agent, an antistatic agent, a leveling agent, a release agent, or the like can be added alone or appropriately mixed and added in the resin composition without impairing the effects of the present application.

[0080] The silicon nitride powder and the resin composition containing the same according to the embodiments are particularly suitable for heat dissipation material applications. Thus, in one embodiment of the present disclosure, a heat dissipation silicon nitride powder and a heat dissipation resin composition can be provided.

[0081] Examples

[0082] Hereinafter, the embodiments of the present application will be described in detail based on examples that were implemented in order to clarify the effects of the embodiments of the present application. Note that the embodiments of the present application are not limited by the following examples in any way.

[0083] Preparation of Silicon Nitride Powder

[0084] The Si powder (particle diameter = 5 μm) and another prepared silicon nitride powder (particle diameter = 1 μm) as a diluent were mixed by a rotary ball mill. The diluent was added in an amount of 5 to 8 mass% relative to the entire raw material (including the diluent). The mixed powder was filled in a carbonaceous heat-insulating refractory container in which a powder layer having a thickness of 1 to 80 mm was laid on the bottom surface and the side surface, in such a manner that the raw material layer had a thickness of more than 100 mm and 150 mm or less, and further, the raw material layer was covered with a powder layer having a thickness of 1 to 80 mm. Then, a lid made of a carbonaceous heat-insulating refractory material was put on, and synthesis was performed under a nitrogen atmosphere at 0.9 MPa. After the synthesis, coarse crushing (pulverization) was performed in a mortar until the powder passed through a sieve having a predetermined mesh size. The mesh size of the sieve for each sample is shown in Table 1.

[0085] (Coarse pulverized powder)

[0086] The obtained coarse pulverized powder was further micro-pulverized by a nano jet mill (manufactured by Aishin nanotechnologies Co., Ltd.). The micro-pulverization was performed using a nano jet mill of the type described in Table 1. The obtained micro-pulverized powder was classified according to the method described in Table 1. Note that a part of the micro-pulverized powder (Sample No. 2) was not classified.

[0087] Then, the obtained classified powder (Sample No. 1, No. 3), micro-pulverized powder (Sample No. 2) was put into an alumina crucible, and heat treatment was performed under the conditions (heat treatment temperature, heat treatment time) described in Table 1 in an atmosphere using a powder small program electric furnace (MMF series, manufactured by AsOne) to obtain silicon nitride powder (Sample No. 1 to 3).

[0088] (Coarse pulverized powder)

[0089] The coarse pulverized powder was prepared in the same manner as in the above "Sample No. 1 to 3". Note that the mesh of the sieve used at the time of coarse pulverization (crushing) was set to 500 μm.

[0090] The obtained coarse pulverized powder was micro-pulverized using a ball mill. The obtained micro-pulverized powder was classified by sieving using a vibrating sieve according to the following procedure, and then further classified by wet classification to obtain silicon nitride powder having a desired D50 (Sample No. 5 to 10).

[0091] • The powder remaining on the sieve at the time of sieving using a sieve having a mesh of 150 μm (Sample No. 5, D50: 192.0 μm)

[0092] • The powder remaining on the sieve at the time of sieving using a sieve having a mesh of 150 μm was further sieved using a sieve having a mesh of 106 μm, and the powder remaining on the sieve (Sample No. 6, D50: 118.0 μm)

[0093] • The powder remaining on the sieve at the time of sieving using a sieve having a mesh of 106 μm was further sieved using a sieve having a mesh of 75 μm, and the powder remaining on the sieve (Sample No. 7, D50: 83.0 μm)

[0094] • The powder remaining on the sieve at the time of sieving using a sieve having a mesh of 75 μm was further sieved using a sieve having a mesh of 63 μm, and the powder remaining on the sieve (Sample No. 8, D50: 58.0 μm)

[0095] The powder remaining on the sieve at the time of sieving using a sieve having a mesh of 63 μm (Sample No. 9, D50: 22.0 μm)

[0096] When the powder of Test No. 9 was further sieved using a sieve having a mesh size of 10 μm, the powder remaining on the sieve (Test No. 10, D50: 3.5 μm)

[0097] [Table 1]

[0098]

[0099] Various measurements were performed on the obtained Test Nos. 1 to 3 and 5 to 10 (Examples) and a commercially available silicon nitride powder (Aldrich Corporation, silicon nitride (predominantly β-phase, ≤10 micron primary particle size, product number 248622): hereinafter referred to as "Test No. 4") as a comparative example.

[0100] (1) Angle of repose

[0101] The angle of repose of the test sample (silicon nitride powder) was measured in accordance with the description of JIS R 9301-2-2: 1999. The amount of the test sample at the time of the angle of repose measurement was 20 ml, and the surrounding environment was set to a temperature of 23°C and a humidity of 40%.

[0102] (2) Compression degree

[0103] The compression degree of the test sample (silicon nitride powder) was measured in accordance with the description of JIS Z 2512: 2012 "Metallic powder - Determination of tapped density" for the measurement of the tapped density, the bulk density before tapping was set to D0, and the bulk density after tapping (i.e., the tapped density) was set to D1, and (D1-D0) / D1 was calculated.

[0104] (3) (D90-D10) and (D90-D50)

[0105] The particle size distribution of the test sample (silicon nitride powder) was measured, D90, D50, and D10 were calculated, and (D90-D10) and (D90-D50) were calculated using them.

[0106] The particle size distribution of the silicon nitride powder was measured by a laser diffraction method. Laser light was irradiated to the test sample dispersed in water, and the diffraction thereof was measured to calculate the particle size. The measuring device used was a CILAS 1090L. The particle size was set to the equivalent circle particle size. The equivalent circle particle size refers to the particle size of a right circle having the same area as the projected particle image. In addition, the basis of the particle size was set to the volume.

[0107] (4) Average aspect ratio of silicon nitride particles

[0108] SEM images of the test sample (silicon nitride powder) were taken. The taking used the following device.

[0109] • Use equipment

[0110] Scanning electron microscope: JSM-IT200 (manufactured by JEOL Ltd.)

[0111] The photographing conditions were set as follows.

[0112] Accelerating voltage: 5.0 kV

[0113] Signal: SED

[0114] Irradiation current: Std.-PC55

[0115] Photographing magnification: 1000 times

[0116] For the SEM images, the aspect ratio was calculated by an image processing software Image J (manufactured by National Institute of Health) using any 20 silicon nitride particles in the SEM images as the evaluation objects. The maximum diameter of the silicon nitride particle was taken as the major axis, and the particle diameter in the direction orthogonal to the major axis was taken as the minor axis. The major axis and the minor axis were measured for any 20 silicon nitride particles, and the ratio of the minor axis to the major axis (minor axis / major axis) was calculated for each particle. The arithmetic mean of these ratios was taken as the average aspect ratio of the silicon nitride particles (denoted as "aspect ratio" in Table 2).

[0117] (5) Maximum particle diameter of the silicon nitride particles (maximum particle diameter of the single crystal particles) having an L2 / L1 of 1% or less

[0118] A cross-section observation sample was prepared using the sample (silicon nitride particles). In the preparation of the cross-section observation sample, after the silicon nitride particles were resin-embedded, the resin and the silicon nitride particles were cut using a diamond cutter. Then, Pt was vapor-deposited on the cross-section as a protective film, cross-section preparation was performed by Ar ion milling, and the sample was fixed on a SEM sample stage using Cu double-sided tape, and SEM-EBSD measurement was performed without vapor deposition. The observation position was determined in such a manner that two or more silicon nitride particles completely entered the observation area (i.e., two or more silicon nitride particles did not contact the frame of the observation area). The measurement was performed using β-type silicon nitride particles.

[0119] The sample pretreatment and the EBSD measurement used the following equipment.

[0120] • Equipment used

[0121] Ion milling device: E-3500 (manufactured by Hitachi High-Tech Corporation)

[0122] Ion sputtering device: E-1030 (manufactured by Hitachi, Ltd.)

[0123] Schottky scanning electron microscope: SU5000 (manufactured by Hitachi High-Tech Corporation)

[0124] Back scattering electron diffraction apparatus: Velocity (manufactured by METEK Corporation)

[0125] The conditions for EBSD measurement were set as follows.

[0126] • Measurement area: 500.0 μm x 400.0 μm

[0127] • Acceleration voltage: 15.0 kV

[0128] • Magnification: x 500

[0129] • Vacuum degree: 30 Pa

[0130] In the obtained EBSD image, two or more silicon nitride particles not in contact with the frame of the observation area were selected, and the average value of the length L1 of the outer edge of each silicon nitride particle was calculated by the image processing software Image J (manufactured by National Institute of Health). In addition, the total length L2 of the boundary line was calculated. The "total length L2 of the boundary line" is the sum of the boundary lines contained in the interior of the silicon nitride particle, and does not include the outer edge of the silicon nitride particle. The total length L2 of the boundary line is obtained by adding the total length of the grain boundaries in the interior of the silicon nitride particle and (in the case where there is a void in the interior of the silicon nitride particle) the total length of the inner wall of the void. Note that, here, the "grain boundary" and the "boundary line" refer to boundaries (also referred to as high-angle grain boundaries) in which the crystal orientation difference (misorientation) exceeds 15° in the EBSD analysis results.

[0131] This measurement was performed once for each of any 20 silicon nitride particles, and the silicon nitride particles for which L2 / L1 was 1% or less were regarded as single crystal particles, and the length of the major axis was measured as the "maximum particle diameter of the single crystal particles". In the case where the 20 silicon nitride particles measured contained a plurality of single crystal particles, the arithmetic average of the maximum particle diameters thereof was calculated.

[0132] (6) β Conversion Rate

[0133] The diffraction pattern of the sample (silicon nitride powder) was obtained by a powder X-ray diffraction apparatus (Rigaku Corporation). The measurement conditions were set as follows.

[0134] • X-ray source: Cu Kα ray

[0135] • X-ray output: 45 kV, 200 mA

[0136] • Graphite monochromator

[0137] • Diffraction angle (2θ): stepwise scanning was performed in the range of 2 to 90° at a scale of 0.02°

[0138] • Scanning speed: 21.7 deg / min

[0139] In the case where the test sample contains components other than silicon nitride, the proportions of these components are calculated by comparing the peaks of these components with the peaks of standard samples of these components. In Test Samples No. 1 to 4, it was confirmed from the obtained powder X-ray diffraction patterns that the test samples were composed of only α-type silicon nitride and β-type silicon nitride. On this basis, the proportion of β-type silicon nitride in the test sample (β conversion rate) was calculated by the Gazzara & Messier method.

[0140] (7) Adhesion to other members

[0141] A polystyrene medicine spoon (area of medicine spoon surface: 236 mm 2 ) was used to scoop up 1 cup (1 g) of the test sample (silicon nitride powder), and the adhesion of the powder to the medicine spoon surface was evaluated as follows after the powder was divided into another container.

[0142] O: Adhesion area of powder was less than 5 mm 2

[0143] X: Adhesion area of powder was 5 mm 2 or more

[0144] (8) Thermal diffusivity of resin composition (composite)

[0145] An epoxy resin (main agent: normal-temperature curing type embedding resin 53 type (manufactured by San-Aid Co., Ltd.) 010-8140, curing agent: normal-temperature curing type embedding resin 53 type (manufactured by San-Aid Co., Ltd.) 010-8143), and a test sample (silicon nitride powder) were mixed at a mixing ratio (volume ratio) of 50:50, and stirring and mixing were performed using a stirring defoaming machine (Tori-Kasei Rikurito) (manufactured by Thinky Co., Ltd.) to obtain a composite of an epoxy resin-filler (silicon nitride powder). The filling rate of the resin composition was 50 vol%.

[0146] As a mold frame, a mold frame in which a rectangular hole of 1 cm x 10 cm was formed in an aluminum plate having a thickness of 1 mm was prepared. A PET film (back surface side film) to which a release agent was applied was attached to the back surface of the mold frame in such a manner that the application surface of the release agent faced the mold frame, in a manner so as to cover the rectangular hole of the mold frame. After the compounded material was injected into the rectangular hole of the mold frame, a PET film (surface side film) to which a release agent was applied was attached from above the same in such a manner that the application surface of the release agent faced the mold frame and the resin composition. Further, the compounded material was filled in the rectangular hole of the mold frame by slightly pressing it with a metal roller from above the surface side film. Another aluminum plate was placed above the surface side film, and the compounded material was cured by heating at 100°C for 1 hour. After the curing was completed, the aluminum plate was removed after the temperature of the aluminum plate dropped to around room temperature, and the surface side and back surface side PET films were further peeled off from both surfaces of the cured compounded material, to obtain a sheet-shaped sample for thermal diffusivity measurement.

[0147] The thermal diffusivity of the obtained sheet-shaped sample was measured.

[0148] The thermal diffusivity was measured at room temperature by a temperature wave analysis method (TWA method) from a sheet-shaped sample for the resin composition described above, in which a measurement sample piece having a length of 10 mm, a width of 10 mm, and a thickness of 1 mm was prepared. As a measurement device, an ai-Phase Mobile manufactured by ai-Phase Co., Ltd. was used.

[0149] As for the thermal diffusivity, one measurement sample piece was measured at three arbitrary points, and the average value was calculated from the measurement results of the three points.

[0150] The measurement results are summarized in Tables 2 and 3.

[0151] [Table 2]

[0152]

[0153] [Table 3]

[0154]

[0155] Hereinafter, the measurement results will be discussed.

[0156] The adhesion of the silicon nitride powder to other components was suppressed for the samples No. 1 to 3 and 5 to 10 that satisfied the requirements of the present embodiment. On the other hand, the amount of adhesion of the silicon nitride powder to other components was large for the sample No. 4 that did not satisfy the requirements of the present embodiment.

[0157] In addition, the resin composition containing the samples No. 1 to 3 and 5 to 10 was superior in thermal diffusivity to the resin composition containing the sample No. 4.

[0158] This application claims priority to Japanese Patent Application, No. 2023-058723, filed March 31, 2023, the priority date of which is March 31, 2023. Japanese Patent Application No. 2023-058723 is hereby incorporated by reference into the present specification.

Claims

1. A silicon nitride powder comprising a plurality of silicon nitride particles, the angle of repose being greater than 40°.

2. The silicon nitride powder according to claim 1, wherein The compressibility is less than 34.4%.

3. The silicon nitride powder according to claim 1, wherein, The difference between the particle diameter D90, which is 90% of the cumulative particle size distribution on a volume basis from the fine particle side, and the particle diameter DlO, which is 10% of the cumulative particle size distribution on a volume basis from the fine particle side, is 150.0 μm or less.

4. The silicon nitride powder of claim 1, wherein, The average aspect ratio of the short diameter to the long diameter of the silicon nitride particles is greater than 0.

50.

5. The silicon nitride powder of claim 1, wherein, The ratio L2 / L1 of the total length L2 of the boundary lines in the interior to the length LI of the outer edge is 1% or less.

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

Images