Silicon nitride powder and resin composition using same

Abstract

The silicon nitride powder contains a plurality of silicon nitride particles and has an Rsp value with respect to ethanol of less than 105.6.

Description

Technical Field

[0001] This disclosure relates to silicon nitride powder and resin compositions using the same. Background Technology

[0002] Heat generated by energizing electronic components is dissipated via a heat sink. To improve heat dissipation efficiency, a technique is known to fill the space between the electronic components and the heat sink with a heat-dissipating material.

[0003] As a heat dissipation material, resin compositions containing resin and inorganic particles are known, and silicon nitride powder can be used as the inorganic particles (e.g., Patent Document 1).

[0004] Patent document 1 discloses low-aluminum spherical β-silicon nitride powder used as a filler in electronic packaging materials. 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 Document 2 discloses a method for manufacturing silicon nitride powder suitable for producing silicon nitride sintered bodies and the silicon nitride powder obtained by the method. The average particle size of the silicon nitride powder is 1 to 50 μm, the content of metal oxides is 0 to 10 wt%, and the content of impurities is less than 1 wt%. Preferably, the content of metal oxides in the silicon nitride powder is less than 1 wt%. The thermal conductivity of the sintered body is 90 W / mK or higher, and the flexural strength is 700 MPa or higher. The preferred sintering conditions for the sintered body are: mixing the silicon nitride powder with MgO and Y2O3, grinding, dry pressing the blank, and sintering the blank under gas pressure at 1900°C and 1 MPa for 8 hours.

[0006] Patent document 3 discloses silicon nitride powder suitable for manufacturing high thermal conductivity silicon nitride sintered bodies. The silicon nitride powder is characterized by containing columnar particles with a β fraction of 30-100%, an oxygen content of less than 0.5 wt%, an average particle size of 0.2-10 μm, an aspect ratio of less than 10, and grooves formed along the long axis of the particles.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Publication No. 2022-522814

[0010] Patent Document 2: Japanese Patent Publication No. 2022-541208

[0011] Patent Document 3: Japanese Patent Application Publication No. 2004-262756 Summary of the Invention

[0012] Semiconductor components in electronic parts are at risk of performance degradation due to moisture. If the resin composition used as a heat dissipation material contains a large amount of moisture, there is a risk that moisture will seep out of the resin composition and reach the electronic components. To minimize the moisture content of the resin composition, it is ideal to use silicon nitride powder with low moisture content as a filler.

[0013] Patent document 1 does not study the moisture content of silicon nitride particles used as fillers.

[0014] Patent documents 2 and 3 disclose silicon nitride powders for use in silicon nitride sintered bodies; therefore, they do not study silicon nitride powders that can be mixed with resin to form resin compositions, nor do they study silicon nitride powders suitable as fillers for resin compositions. Furthermore, patent documents 2 and 3 do not study the moisture content of silicon nitride particles.

[0015] In view of this situation, one embodiment of the present invention aims to provide a silicon nitride powder with low water content that can be used as a filler in a resin composition. Furthermore, another embodiment of the present invention aims to provide a resin composition using the silicon nitride powder of one embodiment.

[0016] Method 1 of the present invention is a silicon nitride powder containing a plurality of silicon nitride particles, having an Rsp value of less than 105.6 for ethanol.

[0017] The second embodiment of the present invention is the silicon nitride powder according to the first embodiment, wherein the surface roughness Ra is less than 0.97 nm.

[0018] The third embodiment of the present invention is silicon nitride powder according to embodiment 1 or 2, wherein the silicon nitride particles have a specific surface area equivalent diameter exceeding 0.71 μm.

[0019] Embodiment 4 of the present invention is silicon nitride powder according to any one of Embodiments 1 to 3, wherein the specific surface area is less than 2.66 m². 2 / g.

[0020] Embodiment 5 of the present invention is silicon nitride powder according to any one of embodiments 1 to 4, wherein the apparent density exceeds 3.17 g / cm³. 3 .

[0021] The sixth embodiment of the present invention is a silicon nitride powder according to any one of embodiments 1 to 5, wherein the maximum particle size of the silicon nitride particles having a ratio (L2 / L1) of less than 1% of the total length L2 of the inner boundary line is 6.8 μm or more.

[0022] Embodiment 7 of the present invention is a resin composition comprising a resin and silicon nitride powder as described in any one of embodiments 1 to 6.

[0023] By using silicon nitride powder according to one embodiment of the present invention as a filler, a resin composition with low water content can be obtained. Detailed Implementation

[0024] Silicon nitride powder

[0025] The moisture contained in the resin composition may have an adverse effect on electronic components. Therefore, the inventors have studied methods for reducing the moisture content of the resin composition and believe that it is important to control the moisture content of the silicon nitride powder used as a filler in the resin composition.

[0026] The inventors conducted in-depth research and discovered for the first time that the Rsp value, which can be obtained by pulse MNR measurement, especially the Rsp value for ethanol, is suitable as an indicator of the moisture content of silicon nitride powder, thus completing this invention.

[0027] It should be noted that the Rsp value relative to water is considered suitable as an indicator for controlling the moisture content of silicon nitride powder. However, determining the Rsp value relative to water presents challenges in sample preparation and may result in inaccurate values. Therefore, the inventors investigated the use of dispersion media other than water. Their findings revealed that using the Rsp value relative to ethanol makes sample preparation easier and yields more accurate values, making it suitable as an indicator for controlling the moisture content of silicon nitride powder.

[0028] (Rsp value for ethanol is less than 105.6)

[0029] The Rsp value for ethanol is an indicator related to the mobility of molecules (ethanol molecules) of the dispersion medium adsorbed on the surface of silicon nitride powder. Silicon nitride powder dispersed in silicon nitride slurry is dispersed in the silicon nitride slurry in a state in which molecules of the dispersion medium are constrained on its surface.

[0030] Here, if the number of dispersion medium molecules constrained on the surface of silicon nitride powder increases, the transverse relaxation time (T2) becomes shorter, and therefore the Rsp value increases. Furthermore, if the number of dispersion medium molecules constrained on the surface of silicon nitride powder increases, the state dispersed in the dispersion medium becomes more stable, thus improving the dispersibility of the silicon nitride powder.

[0031] Therefore, if the Rsp value increases, there is a tendency for the dispersibility of silicon nitride powder to improve. Thus, the Rsp value is sometimes used as an indicator of dispersibility.

[0032] In this embodiment, the Rsp value is used as an indicator of the amount of molecules (ethanol molecules) of the dispersion medium confined to the surface. Silicon nitride powder with a high Rsp value for ethanol has a high affinity for ethanol molecules and can be said to readily adsorb onto the surface. It is hypothesized that since ethanol molecules are hydrophilic polar molecules, silicon nitride powder with a high affinity for ethanol molecules also has a high affinity for water molecules, and the inventors conducted in-depth research on this. Their results confirmed a correlation between the Rsp value of silicon nitride powder for ethanol and the amount of water that the silicon nitride powder can adsorb, and that the amount of water that the silicon nitride powder can adsorb can be suppressed to a level suitable for use as a filler in resin compositions by keeping the Rsp value less than 105.6.

[0033] That is, by controlling the Rsp value of silicon nitride powder with ethanol to less than 105.6, silicon nitride powder with low water content can be obtained, and resin compositions with low water content can be made by using this silicon nitride powder.

[0034] The Rsp value of the silicon nitride powder for ethanol is less than 105.6, preferably 90.0 or less, more preferably 80.0 or less, even more preferably 70.0 or less, and particularly preferably 65.0 or less. The lower limit of this Rsp value is not particularly limited; for example, it can be 0.5 or more, or 1.0 or more.

[0035] To determine the Rsp value, pulsed NMR was first used to measure the Rsp values ​​of silicon nitride slurry in which silicon nitride powder was dispersed in a dispersion medium (ethanol) and in a blank solution only. 1 The restorative time of the H nucleus (the time it takes for the magnetized nucleus to return to its original thermal equilibrium after pulse excitation). Using the obtained measurement results, the Rsp value is calculated by the following formula (1).

[0036] Rsp value = (Rav - Rb) / Rb (1)

[0037] Here, Rav is the reciprocal of the transverse relaxation time when pulse NMR is performed on a silicon nitride slurry (e.g., volume X (ml)) in which silicon nitride powder is dispersed in a dispersion medium. Rb is the reciprocal of the transverse relaxation time when pulse NMR is performed on only the dispersion medium (e.g., volume X (ml)) of the silicon nitride slurry. It should be noted that the liquid consisting only of the dispersion medium (ethanol) is sometimes referred to as the "blank solution." Typically, the volume of the blank solution is the same as the volume of the silicon nitride slurry used in the pulse NMR measurement.

[0038] Pulse NMR measurements of silicon nitride slurry can be performed, for example, using a pulse NMR apparatus called "The Minispec MQ20" manufactured by Bruker. Measurement conditions, for example, are: measurement frequency: 20 MHz, measurement nucleus: 1HNMR, determination method: T2 (transverse relaxation time), sample volume: 0.3 ml, temperature: 25℃.

[0039] (Surface roughness Ra)

[0040] The surface roughness Ra (arithmetic mean roughness) of the silicon nitride powder is preferably less than 0.97 nm. If the surface roughness Ra is less than 0.97 nm, the surface area of ​​the silicon nitride particles can be reduced, thereby reducing the amount of water adsorbed on the surface of the silicon nitride particles.

[0041] The surface roughness Ra is preferably less than 0.97 nm, more preferably less than 0.95 nm, even more preferably less than 0.93 nm, even more preferably less than 0.90 nm, even more preferably less than 0.80 nm, and particularly preferably less than 0.70 nm.

[0042] In the determination of surface roughness Ra, a 100 nm × 100 nm measurement area is observed using a scanning probe microscope (SPM) on the surface of any silicon nitride particle. The surface roughness Ra is calculated based on the obtained shape image. The surface roughness Ra is measured using four silicon nitride particles, and their average value is taken as the surface roughness Ra of the silicon nitride powder.

[0043] (Equivalent diameter of silicon nitride particle with specific surface area)

[0044] The specific surface area equivalent diameter (DBET) of the silicon nitride particles is preferably greater than 0.71 μm. If the specific surface area equivalent diameter is greater than 0.71 μm, the number of silicon nitride particles contained in each unit mass of silicon nitride powder can be reduced, and thus the amount of water adsorbed in the silicon nitride powder can be reduced.

[0045] DBET is preferably greater than 0.71 μm, more preferably 1.10 μm or more, even more preferably 1.40 μm or more, even more preferably 3.00 μm or more, and particularly preferably 8.00 μm or more. The upper limit of DBET is not particularly limited; for example, it can be less than 50 μm, less than 40 μm, and even less than 30 μm.

[0046] The specific surface area diameter (DBET) of silicon nitride particles is calculated by the general formula (2) that represents the relationship between the particle size and specific surface area of ​​spherical particles.

[0047] DBET(μm)=6 / (S×ρ) (2)

[0048] in,

[0049] S: Specific surface area of ​​silicon nitride particles (m²) 2 / g),

[0050] ρ: Apparent density of silicon nitride particles (g / cm³) 3 ).

[0051] The values ​​of S and ρ used to calculate DBET are obtained as follows.

[0052] S (specific surface area of ​​silicon nitride particles) is essentially the same as the specific surface area of ​​silicon nitride powder, therefore the determination result of the specific surface area of ​​silicon nitride powder determined by the method described later is used.

[0053] ρ (apparent density of silicon nitride particles) is substantially the same as the apparent density of silicon nitride powder, therefore the result of the apparent density determination of silicon nitride powder determined by the method described later is used.

[0054] (Specific surface area)

[0055] The specific surface area of ​​the silicon nitride powder in this embodiment is based on the BET specific surface area determined by krypton adsorption method according to JIS Z 8830:2013. The specific surface area of ​​the silicon nitride powder is preferably less than 2.66 m². 2 / g can reduce the amount of water adsorbed on the surface.

[0056] The specific surface area of ​​silicon nitride powder is more preferably 2.00 m². 2 / g or less, more preferably 1.50m 2 Below / g, and even more preferably less than 1.36m 2 / g, further preferably 0.50m 2 / g or less, especially preferably 0.24m 2 Below / g. There is no particular limit to the lower limit of specific surface area; for example, it can be 0.01m². 2 / g or more, or 0.05m 2 / g or more.

[0057] (apparent density)

[0058] The apparent density of silicon nitride powder is preferably greater than 3.17 g / cm³. 3 More preferably, exceeding 3.18 g / cm³ 3 This yields silicon nitride powder containing a small amount of silicon nitride particles with numerous internal voids, resulting in silicon nitride powder with low internal moisture content. The upper limit of the apparent density is, for example, 3.44 g / cm³. 3 It should be noted that by ensuring the apparent density is not too high, it is expected to be less prone to sedimentation and easier to disperse when mixed with resin. To achieve this effect, the apparent density of the silicon nitride powder is preferably 3.30 g / cm³. 3 The preferred value is 3.25 g / cm³. 3 the following.

[0059] The apparent density of silicon nitride particles is determined by hydrometer method according to JIS R 1620:1995. The measurement should be performed at least five times, and the average value is taken as the apparent density of the silicon nitride powder. For example, an Accupyc 1330 (Micromeritics) can be used for measurement.

[0060] (Average aspect ratio of silicon nitride particles)

[0061] The average aspect ratio of the minor axis to the major axis of the silicon nitride particles contained in the silicon nitride powder is preferably greater than 0.50, more preferably greater than 0.60, even more preferably greater than 0.65, and even more preferably greater than 0.67. On the other hand, the average aspect ratio of the silicon nitride particles is preferably less than 0.87, more preferably less than 0.85.

[0062] The average length and width of the silicon nitride particles were measured as follows.

[0063] SEM images of silicon nitride particles contained in the silicon nitride powder were analyzed using image processing software (e.g., Image J, manufactured by the National Institute of Health). The maximum particle size of the silicon nitride was determined (designated as the "major axis"), and the particle size in the direction orthogonal to the major axis was designated as the "minor axis". The major and minor axes 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.

[0064] (β-conversion rate)

[0065] The β-saturation of the silicon nitride powder is preferably 65% ​​or more. More preferably, it is 70% or more, even more preferably 80% or more, and even more preferably 85% or more, and particularly preferably 90% or more.

[0066] In this specification, "β-type silicon nitride content" refers to the percentage (by volume) of β-type silicon nitride relative to the total silicon nitride contained in the silicon nitride powder.

[0067] In the calculation of β-concentration, silicon nitride powder was determined by powder X-ray diffraction, and the diffraction pattern was analyzed by Gazzara & Messier method (GP Gazzara and DPMessier, “Determination of Phase Content of Si3N4 by X-ray Diffraction Analysis”, Am. Ceram. Soc. Bull., 56[9]777-80(1977)) to calculate β-concentration.

[0068] (Silicon nitride particles with a total inner boundary length L2 to outer edge length L1 ratio (L2 / L1) of less than 1% have a maximum particle size of 6.8 μm or more.)

[0069] The fewer grain boundaries and voids within silicon nitride particles, the less water can be retained inside. Therefore, the ratio of the total length L2 of the boundary line to the length L1 of the outer edge (L2 / L1) is introduced as an indicator of the grain boundary content within silicon nitride particles. L1 and L2 are determined by cross-sectional observation of the silicon nitride particles. It should be noted that here, "grain boundary" and "boundary line" refer to boundaries where the crystal orientation difference (hinged angle) exceeds 15° as determined by EBSD analysis (also known as large-angle grain boundaries).

[0070] When the length of the outer edge of a silicon nitride particle is defined as L1 and the total length of the boundary lines of the silicon nitride particle is defined as L2, silicon nitride particles with a small L2 / L1 ratio can be considered as silicon nitride particles with a low boundary line content. In this embodiment, silicon nitride particles with an L2 / L1 ratio of less than 1% are considered as silicon nitride particles composed of single crystals (referred to as "single crystal particles").

[0071] In this embodiment, the maximum particle size of silicon nitride particles with an L2 / L1 ratio of 1% or less (i.e., single crystals) is preferably 6.8 μm or more, more preferably 10.0 μm or more, even more preferably 20.0 μm or more, even more preferably 40 μm or more, and particularly preferably 60 μm or more.

[0072] (The cumulative particle size distribution on a volumetric basis, representing the cumulative 50% of the particle size D50 from the microparticle side)

[0073] The cumulative particle size distribution of the silicon nitride powder, from the microparticle side, comprising 50% of the particle size D50 (hereinafter sometimes simply referred to as "D50"), preferably has a particle size of 1.5 μm or more, more preferably 2.0 μm or more, further preferably 5.0 μm or more, even more preferably 10.0 μm or more, and particularly preferably 30 μm or more. There is no particular upper limit, but for example, it is preferably 500.0 μm or less, more preferably 300.0 μm or less, and even more preferably 200.0 μm or less.

[0074] The D50 of silicon nitride powder is determined by laser diffraction. Specifically, the powder dispersed in water is irradiated with a laser beam, and the diffraction is measured to determine the particle size. The measuring apparatus can be a CILAS 1090L model, etc.

[0075] [Method for manufacturing silicon nitride powder]

[0076] The method for manufacturing silicon nitride powder according to embodiments of the present invention will be described.

[0077] Silicon nitride powder includes:

[0078] (1) A process of synthesizing silicon nitride composite crystals by combustion synthesis under a nitrogen atmosphere using raw materials containing Si;

[0079] (2) The process of crystallizing and crushing the silicon nitride composite to obtain coarse silicon nitride powder; and

[0080] (3) The process of micro-pulverizing coarse silicon nitride powder to obtain micro-pulverized silicon nitride powder.

[0081] Furthermore, it can arbitrarily include:

[0082] (4) The process of heat-treating the micronized silicon nitride powder.

[0083] • Process (1): The process of crystallizing the synthesized silicon nitride.

[0084] As a raw material containing Si, Si powder is used, for example.

[0085] The average particle size D50 of the raw material is, for example, in the range of 2–10 μm. This allows for the suppression of oxygen impurities and increases the combustion rate, thereby raising the synthesis temperature and resulting in good crystal growth. Although this is just one example, the average particle size D50 of Si is 5 μm.

[0086] A diluent is used to adjust the Si content in the raw material. A separately prepared silicon nitride powder is used as the diluent. This diluent can be either α-type silicon nitride powder or β-type silicon nitride powder, or they can be mixed. The average particle size D50 of the diluent is preferably in the range of 0.5 to 2.0 μm. Although this is an example, the average particle size D50 of the diluent is 1.0 μm. The amount of diluent added is less than 10% by mass relative to the total raw material (including the diluent). As an example, the diluent is added in the range of 5 to 8% by mass relative to the total raw material. By adding the diluent within the above range, a specified amount of silicon nitride particles with an Rsp value of less than 105.6 relative to ethanol can be generated.

[0087] In this embodiment, a diluent is mixed with the raw materials and filled into a heat-resistant and insulating container. The heat-resistant and insulating container has a thermal conductivity of less than 1 W / mK and can be made of alumina or zirconium oxide, but carbon is preferred to account for impurities. After filling, the container is covered with a lid made of the same material as the heat-resistant and insulating container. Furthermore, to increase the internal temperature of the synthesized body during combustion, the thickness of the mixed raw materials exceeds 100 mm, preferably exceeding 100 mm but less than 150 mm. Combustion synthesis is carried out under a nitrogen atmosphere in the range of 0.5 to 1 MPa (e.g., 0.9 MPa). By adjusting the pressure range to the above range, synthesis can be effectively carried out while suppressing the increase in equipment costs.

[0088] When filling the crucible with the mixed raw materials, a layer of powder (silicon nitride) with a thickness of 1 mm to 80 mm is laid on the bottom and sides of the crucible before filling with the mixed raw materials, and then the top is covered with another layer of powder with a thickness of 1 mm to 80 mm. By covering the entire surface with powder, the mixed raw materials can be kept at a constant temperature, and a specified amount of silicon nitride particles with an Rsp value of less than 105.6 relative to ethanol can be generated.

[0089] To more effectively promote crystal growth, catalysts can be used, such as adding approximately 0.01–0.1% by mass of Y₂O₃, Fe₂O₃, CaO, Ni, Co, C, etc. Additionally, external auxiliary heating in the range of 500°C–1700°C (e.g., 1500°C) can be applied, and the combustion temperature is also increased through a combustion synthesis method based on auto-ignition.

[0090] • Process (2): The process of obtaining coarsely ground silicon nitride powder

[0091] The silicon nitride composite crystal is a form formed by the aggregation of multiple silicon nitride particles. In step (2), coarse silicon nitride powder is obtained by crushing the silicon nitride composite crystal. For example, the composite is crushed using a general coarse crushing device such as a hammer mill or disc mill until it passes through a sieve with a specified mesh size (for example, a sieve with a mesh size in the range of 400 μm to 500 μm).

[0092] • Process (3): The process of obtaining silicon nitride micronized powder

[0093] Silicon nitride coarse powder is further finely pulverized to obtain finely pulverized silicon nitride powder. Fine pulverization can be carried out using equipment such as jet mills or ball mills. The obtained finely pulverized powder can be classified as needed. Classification can be performed by sieving, wet classification, etc.

[0094] The obtained micronized powder can be used directly as silicon nitride powder. Alternatively, the material after heat treatment of the micronized powder (step (4) described later) can also be used as silicon nitride powder.

[0095] • Process (4): The process of heat-treating the micronized silicon nitride powder.

[0096] Silicon nitride micronized powder can be heat-treated arbitrarily. Heat treatment forms an oxide film on the surface of the silicon nitride particles, thus chemically stabilizing them. Heat treatment can be performed, for example, at atmospheric temperature between 500°C and 1200°C. The heat treatment time can be adjusted appropriately according to the heat treatment temperature. For example, a heat treatment time of 5 hours.

[0097] In the method for manufacturing silicon nitride powder, silicon nitride composite crystals are synthesized by the heat of combustion synthesis, and then crushed, graded and micronized to produce the silicon nitride powder of this embodiment.

[0098] [Resin Composition]

[0099] The silicon nitride powder of embodiments of the present invention is suitable as a filler for resin compositions. The resin composition comprises a resin and the silicon nitride powder of embodiments of the present invention.

[0100] The mixing ratio of silicon nitride powder to resin in embodiments of the present invention can be appropriately determined according to the purpose and application. As an example, the ratio can be 5-75% by volume of resin and 95-25% by volume of silicon nitride powder relative to the resin composition (composite).

[0101] It should be noted that the filling rate of silicon nitride powder into the resin composition refers to the content (volume%) of silicon nitride powder when the volume of the resin composition (containing silicon nitride powder) is set to 100 vol%.

[0102] The method for manufacturing the resin composition is described.

[0103] A resin composition can be obtained by mixing silicon nitride powder and resin using generally known methods. For example, when the resin is liquid (e.g., liquid epoxy resin), the resin composition can be obtained by mixing the liquid resin, silicon nitride powder, and curing agent, and then curing it with heat or ultraviolet light. The curing agent, mixing method, and curing method can also use known substances and methods. On the other hand, when the resin is solid, the target resin composition can be obtained by mixing the silicon nitride powder and resin and then kneading it using known methods such as melt kneading.

[0104] The resin used in the resin composition can be a known resin such as epoxy resin. The type of resin can be selected from thermoplastic resins, thermoplastic elastomers, and thermosetting resins. It should be noted that one type of resin can be used alone, or two or more types can be used in combination.

[0105] Furthermore, in these resin compositions, one or more known additives such as plasticizers, curing accelerators, coupling agents, fillers, pigments, flame retardants, antioxidants, surfactants, compatibilizers, weathering agents, antiblocking agents, antistatic agents, leveling agents, and release agents may be appropriately added as needed, without impairing the effect of the invention.

[0106] Example

[0107] Hereinafter, embodiments implemented to clarify the effects of the embodiments of the present invention will be described in detail. It should be noted that the embodiments of the present invention are not limited in any way by the following embodiments.

[0108] <Preparation of Silicon Nitride Powder>

[0109] (Samples No. 1-3, 9)

[0110] Si powder (particle size = 5 μm) was mixed with separately prepared silicon nitride powder (particle size = 1 μm) as a diluent using a rotary ball mill. The amount of diluent added was 5-8% by mass relative to the total raw material (including diluent). The mixed powder was filled into a carbonaceous, heat-resistant, insulating container with a powder coating of 1 mm to 80 mm thickness on the bottom and sides, with the raw material layer being more than 100 mm but less than 150 mm thick. The raw material layer was then covered with a powder coating of 1 mm to 80 mm thickness. A lid made of carbonaceous heat-resistant insulating material was then placed on top, and synthesis was carried out under a nitrogen atmosphere of 0.9 MPa. After synthesis, the powder was coarsely pulverized (crushed) in a mortar until it passed through a sieve with a specified mesh size. The mesh size of the sieves for each sample is shown in Table 1.

[0111] The coarsely pulverized powder was further pulverized using a nano-jet burner (manufactured by Aishin Nanotech). The nano-jet burner model listed in Table 1 was used for pulverization. The resulting pulverized powder was classified according to the method described in Table 1. It should be noted that sample No. 2 was not classified.

[0112] Then, the obtained graded powder (samples No. 1, 3, 9) and micronized powder (sample No. 2) were placed in an alumina crucible and heat-treated in an atmospheric atmosphere using a small-scale electric furnace (AS ONE MMF series) under the conditions (heat treatment temperature and heat treatment time) recorded in Table 1 to obtain silicon nitride powder (samples No. 1 to 3, 9).

[0113] (Samples No. 5-7)

[0114] Prepare coarsely ground powder in the same manner as for "Samples No. 1-3, 9" above. It should be noted that the sieve used for coarse grinding (crushing) has a mesh size of 500 μm.

[0115] The coarsely ground powder was then finely ground using a ball mill. The finely ground powder was then sieved using a vibrating screen according to the following steps, followed by wet classification to obtain silicon nitride powder with the desired D50 (samples No. 5-7).

[0116] • Sample No. 5: Silicon nitride particles (D50 192.0 μm) remaining on the sieve after sieving using a 150 μm mesh sieve.

[0117] • Sample No. 6: Powder remaining under the sieve after sieving with a 106 μm sieve was further sieved with a 75 μm sieve, and the silicon nitride particles remaining on the sieve (D50 is 83.0 μm) were the following.

[0118] • Sample No. 7: Silicon nitride particles (D50 22.0 μm) remaining under the sieve after sieving using a 63 μm mesh sieve.

[0119] (Sample No. 8)

[0120] Using the aforementioned silicon nitride particles (sample No. 6), the particles were placed in an alumina crucible and heat-treated in an atmospheric atmosphere at a temperature of 900°C for 5 hours using a small programmable furnace (AS ONE MMF series) to obtain silicon nitride powder (sample No. 8).

[0121] [Table 1]

[0122]

[0123] Various measurements were performed on the obtained samples No.1 to 3 and 5 to 9 (examples) and on the 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 "sample No. 4") as a comparative example.

[0124] (1) Determination of β-saturation of silicon nitride powder

[0125] The diffraction pattern of the sample (silicon nitride powder) was obtained using a powder X-ray diffraction apparatus (Rigaku Electron apparatus). The measurement conditions are as follows.

[0126] X-ray source: CuKα rays

[0127] X-ray output: 45kV, 200mA

[0128] Graphite monochromator

[0129] • Diffraction angle (2θ): Step scans are performed in increments of 0.02° across a range of 2–90°.

[0130] • Scanning speed: 21.7 deg / minute

[0131] When the sample contains components other than silicon nitride, the proportions of these components are determined by comparing their peaks with the corresponding peaks of standard samples containing those components. In samples No. 1–9, the obtained powder X-ray diffraction patterns confirmed that the samples consisted only of α-type and β-type silicon nitride. Based on this, the proportion of β-type silicon nitride (β-ratio) in the samples was calculated using the Gazzara & Messier method.

[0132] (2) L2 / L1 is the maximum particle size of silicon nitride particles below 1% (maximum particle size of single crystal particles).

[0133] Cross-sectional observation specimens were prepared using silicon nitride particles. In the preparation of the cross-sectional observation specimens, silicon nitride particles were embedded in resin, and then the resin and silicon nitride particles were cut using a diamond tool. Then, Pt was deposited as a protective film on the cross-section, and the cross-section was prepared by Ar ion milling. It was then fixed to the SEM sample stage with Cu double-sided tape, and SEM-EBSD measurements were performed without evaporation. The observation position was determined by ensuring that two or more silicon nitride particles were completely within the observation area (i.e., two or more silicon nitride particles did not contact the edge of the observation area). Measurements were performed using β-type silicon nitride particles.

[0134] The following equipment is used for sample pretreatment and EBSD determination.

[0135] • Use of equipment

[0136] Ion milling equipment: E-3500 (manufactured by Hitachi High Technology Co., Ltd.)

[0137] Ion sputtering equipment: E-1030 (manufactured by Hitachi, Ltd.)

[0138] Schottky field emission scanning electron microscope: SU5000 (manufactured by Hitachi High Technology Co., Ltd.)

[0139] Backscattered electron diffraction apparatus: Velocity (manufactured by METEK Co., Ltd.)

[0140] The conditions for EBSD determination are as follows.

[0141] • Measurement area: 500.0 μm × 400.0 μm

[0142] Accelerating voltage: 15.0kV

[0143] ·Magnification:×500

[0144] Vacuum degree: 30Pa

[0145] In the obtained EBSD image, select two or more silicon nitride particles that do not contact the border of the observation area, and calculate the average value of the length L1 of the outer edge of each silicon nitride particle using image processing software Image J (made by the National Institute of Health). Additionally, calculate the total length L2 of the boundary lines. The "total length L2 of the boundary lines" is the sum of the boundary lines contained within the silicon nitride particle, excluding the outer edge of the silicon nitride particle. The total length L2 of the boundary lines is obtained by adding the total length of the grain boundaries within the silicon nitride particle to the total length of the inner walls of the voids (when there are voids within the silicon nitride particle).

[0146] This measurement is performed once using any 20 silicon nitride particles. Silicon nitride particles with an L2 / L1 ratio of less than 1% are considered as single-crystal particles, and their major axis length is measured as the "maximum particle size of a single crystal particle". In the case where the 20 measured silicon nitride particles include multiple single-crystal particles, the arithmetic mean of their maximum particle sizes is calculated.

[0147] (3) Specific surface area diameter (DBET) of silicon nitride particles

[0148] The specific surface area diameter of silicon nitride particles is calculated by the following formula (2).

[0149] DBET(μm)=6 / (S×ρ) (2)

[0150] Specific surface area of ​​silicon nitride particles (m²) 2 The specific surface area of ​​ / g) is substantially the same as that of silicon nitride powder, so the specific surface area measured in "(5) Specific Surface Area" described later is substituted into S in formula (2).

[0151] Apparent density of silicon nitride particles (g / cm³) 3 The apparent density is essentially the same as that of silicon nitride powder. Therefore, the apparent density measured in “(8) Apparent density of silicon nitride powder” is substituted into ρ in equation (2).

[0152] (4) Average aspect ratio of silicon nitride particles

[0153] Take SEM images of the sample (silicon nitride powder). Use the following equipment for taking the images.

[0154] • Use of equipment

[0155] Scanning electron microscope: JSM-IT200 (manufactured by Nippon Electron Ltd.)

[0156] The shooting conditions are as follows.

[0157] Accelerating voltage: 5.0kV

[0158] Signal: SED

[0159] Irradiation current: Std.-PC55

[0160] Shooting magnification: 1000x

[0161] For SEM images, the aspect ratio of any 20 silicon nitride particles in the image was determined using ImageJ (made by the National Institute of Health) image processing software. The maximum diameter of the silicon nitride particle was defined as the major axis, and the particle diameter in the direction orthogonal to the major axis was defined as the minor axis. The major and minor axes of any 20 silicon nitride particles were measured, 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 (referred to as "aspect ratio" in the table).

[0162] (5) Specific surface area

[0163] The specific surface area of ​​the sample (silicon nitride powder) was determined.

[0164] The method for determining the specific surface area of ​​powders (solids) using gas adsorption is based on JIS Z 8830:2013, using krypton as the adsorbed gas. During the measurement, 1g of silicon nitride powder is placed in a sample tube, and adsorption / desorption isotherms are obtained. The specific surface area (m²) is calculated using the multi-point curve method. 2 / g).

[0165] (6) Measurement of surface roughness Ra

[0166] For the determination of surface roughness Ra, a Seiko Instruments SPA300HV scanning probe microscope was used. The measurement conditions are as follows.

[0167] Probe station / unit SPI4000 / SPA300HV

[0168] Cantilever: SI-DF20

[0169] Scanner: 20μm

[0170] Data type: Shape image

[0171] Observation Mode: DFM (Dynamic Force Mode Microscpoe)

[0172] Scanning area: 100nm × 100nm

[0173] Scan frequency: 0.25Hz

[0174] Analysis software: (included with the measuring device)

[0175] Five arbitrary silicon nitride particles were selected from the image, and a 100 nm × 100 nm measurement area was observed on the surface of each particle using a scanning probe microscope (SPM). The surface roughness Ra of each particle was calculated from the obtained shape image, and the average value was taken as the surface roughness Ra of the silicon nitride powder.

[0176] (7) Determination of Rsp value of silicon nitride powder for ethanol

[0177] 0.2 g of the sample (silicon nitride powder) was mixed with 0.3 mL of dispersion medium (ethanol) to prepare the test solution. The transverse relaxation time (T2) of the test solution was determined using a pulsed NMR apparatus "the minispec mq20" manufactured by Bruker. The measurement conditions were: resonance frequency: 20 MHz, analyte: 1H NMR, measurement method: T2, sample volume: 0.3 mL, and temperature: 25 °C. In addition, the transverse relaxation time (T2) of the blank solution was determined using pure water under the same measurement conditions. The reciprocal of the transverse relaxation time (T2) of the silicon nitride slurry was set as Rav, and the reciprocal of the transverse relaxation time (T2) of the blank solution was set as Rb. Rsp was calculated by the following formula (1).

[0178] Rsp value = (Rav - Rb) / Rb (1)

[0179] (8) Apparent density of silicon nitride powder

[0180] The apparent density of the sample (silicon nitride powder) was determined according to JIS R1620:1995. The determination method and conditions are as follows.

[0181] • Measurement method: Gas displacement method

[0182] • Sample drying: 200℃ for more than 8 hours

[0183] • Device used: Accupyc 1330 (Micromeritics)

[0184] • Measurement conditions

[0185] 10 blows

[0186] Purge filling pressure: 15.0 psig

[0187] Number of measurements: 5

[0188] Filling pressure measured: 15.0 psig

[0189] Equilibrium pressure: 0.005 psig / min

[0190] Precision setting measurement: Yes

[0191] Tolerance for deviation: 0.05%

[0192] Sample well dimensions: 10cm 3

[0193] (9) Determination of D50 of silicon nitride powder

[0194] The particle size distribution of the sample (silicon nitride powder) was determined, and the cumulative 50% particle size D50 was calculated.

[0195] The particle size distribution of silicon nitride powder was determined by laser diffraction. A laser beam was irradiated onto the sample dispersed in water, and the diffraction was measured to determine the particle size. A CILAS 1090L model was used for the determination. The particle size was measured as the equivalent circular diameter. The equivalent circular diameter refers to the diameter of a true circle with the same area as the projected particle image. Furthermore, the particle size was based on volume.

[0196] (10) Determination of moisture content in silicon nitride powder

[0197] The moisture content of the sample (silicon nitride powder) was determined. The moisture content was determined according to JIS K0068:2001 "Method for determination of moisture content of chemical products" and based on the Karl Fischer method.

[0198] (11) Determination of moisture content in resin composition (complex)

[0199] Epoxy resin (main agent: room temperature curing embedding resin type 53 (manufactured by SANKEI CO.,LTD.) 010-8140, curing agent: room temperature curing embedding resin type 53 (manufactured by SANKEI CO.,LTD.) 010-8143) and the sample (silicon nitride powder) were mixed at a ratio of 50:50 (volume ratio) using an Awatori Rentaro (manufactured by Thinky Co., Ltd.) stirrer to obtain an epoxy resin-filler (silicon nitride powder) composite. The silicon nitride powder was added to the resin composition at a filling rate of 50% by volume.

[0200] As a mold, a 1cm × 10cm rectangular hole was made in an aluminum plate with a thickness of 1mm. A PET film coated with a release agent (back side film) was attached to the back side of the mold, with the release agent coating side facing the mold, covering the rectangular hole. The stirred composite was injected into the rectangular hole of the mold, and a PET film coated with a release agent (surface side film) was attached to it, with the release agent coating side facing the mold and resin composition. Then, pressure was gently applied from the surface side film using a metal roller to mix the composite into the rectangular hole of the mold. Another aluminum plate was placed on the surface side film, and the mixture was heated at 100°C for 1 hour to cure the composite. After curing, the mixture was cooled. When the temperature of the aluminum plate dropped to approximately room temperature, the aluminum plate was removed, and the surface side and back side PET films were further peeled off from both sides of the cured composite to obtain a sheet sample for moisture content determination.

[0201] The moisture content of the obtained sheet-like sample was determined.

[0202] The moisture content was determined according to JIS K0068:2001 "Method for determination of moisture content of chemical products" and based on the Karl Fischer method.

[0203] A water content of less than 380 ppm in the resin composition is evaluated as acceptable (〇), and a water content of more than 380 ppm is evaluated as unacceptable (×).

[0204] The measurement results are summarized in Tables 2 and 3.

[0205] [Table 2]

[0206]

[0207] [Table 3]

[0208]

[0209] The results of the measurement are discussed below.

[0210] The silicon nitride powders in samples No. 1 to 3 and 5 to 9 that meet the requirements of this embodiment have low moisture content. Therefore, the moisture content of resin compositions made using these silicon nitride powders can be reduced.

[0211] On the other hand, the silicon nitride powder in sample No. 4, which does not meet the requirements of this embodiment, has a high moisture content. Therefore, the resin composition made using this silicon nitride powder has a higher moisture content.

[0212] This application is accompanied by a priority claim based on Japanese Patent Application No. 2023-058739, filed on March 31, 2023. Japanese Patent Application No. 2023-058739 is incorporated herein by reference.

Claims

1. A silicon nitride powder comprising a plurality of silicon nitride particles, having an Rsp value of less than 105.6 for ethanol.

2. The silicon nitride powder according to claim 1 has a surface roughness Ra of less than 0.97 nm.

3. The silicon nitride powder according to claim 1, wherein, The silicon nitride particles have a specific surface area equivalent diameter exceeding 0.71 μm.

4. The silicon nitride powder according to claim 1, having a specific surface area of ​​less than 2.66 m². 2 / g.

5. The silicon nitride powder according to claim 1, with an apparent density exceeding 3.17 g / cm³. 3 .

6. The silicon nitride powder according to claim 1, wherein, The maximum particle size of silicon nitride particles with a ratio of less than 1% (L2 / L1) between the total length L2 of the inner boundary line and the length L1 of the outer edge is greater than 6.8 μm.

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

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