Resin composition

Abstract

A resin composition containing inorganic particles and a resin, wherein the ratio of the viscosity at a shear rate of 1 / s with respect to the viscosity at a shear rate of 17.8 / s at a temperature of 25°C is greater than 1.3.

Description

resin composition

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

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

[0003] Patent Document 1 discloses a liquid encapsulating resin composition before curing, which contains (A) an epoxy resin, (B) an epoxy resin curing agent, and (C) silicon nitride powder as essential components. Patent Document 2 discloses a liquid encapsulating resin composition before curing, which contains a resin material and a filler made of an inorganic material, and which preferably uses alumina particles as the filler.

[0004] Patent Document 3 discloses a resin composition containing silicon nitride, spherical thermally conductive particles (alumina particles), and a resin. The 50% particle size of the silicon nitride is 0.1 to 15 μm, and the 50% particle size of the alumina particles is 10 to 100 μm. The resin composition contains 2 to 30% by volume of silicon nitride, 30 to 80% by volume of alumina particles, and 55 to 85% by volume of silicon nitride and alumina particles combined.

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

[0006] In recent years, the increase in heat generation in electronic components has become a problem due to the increased integration of ICs in electronic devices and the use of high-current-driven electronic components due to the electrification of electric vehicles, aircraft, 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 without trapping air bubbles. 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 be sufficiently filled. Therefore, a resin composition that can be easily removed and refilled (sometimes referred to as a "resin composition with excellent reworkability") is desired.

[0007] Patent Documents 1 to 3 do not discuss the reworkability of the resin composition. Therefore, an object of an embodiment of the present invention is to provide a resin composition having excellent reworkability.

[0008] A first aspect of the present invention is a resin composition comprising inorganic particles and a resin, wherein the ratio of the viscosity at a shear rate of 1 / s to the viscosity at a shear rate of 17.8 / s at a temperature of 25°C is greater than 1.3.

[0009] A second aspect of the present invention is the resin composition according to the first aspect, wherein the viscosity at a shear rate of 1 / s exceeds 1 Pa·s.

[0010] A third aspect of the present invention is the resin composition according to the first or second aspect, wherein the inorganic particles contain silicon nitride particles in an amount of 40% by volume or more.

[0011] A fourth aspect of the present invention is the resin composition according to the third aspect, wherein the silicon nitride particles have a β-phase ratio of 65% or more.

[0012] A fifth aspect of the present invention is the resin composition according to any one of the first to fourth aspects, which has a modulus of rigidity of more than 3 Pa.

[0013] According to an embodiment of the present invention, a resin composition having excellent reworkability can be provided.

[0014] The present inventors conducted extensive research to provide a resin composition with excellent reworkability. As a result, they discovered that a resin composition with excellent reworkability can be realized by adjusting the ratio of the viscosity at a shear rate of 1 / s to the viscosity at a shear rate of 17.8 / s at a temperature of 25°C in a resin composition (a mixture of resin and inorganic particles) before curing so that it exceeds a predetermined value. This is thought to be because the viscosity at a shear rate of 17.8 / s is relatively low and the viscosity at a shear rate of 1 / s is relatively high, allowing the inorganic particles to be uniformly dispersed in the resin and maintaining this uniform state as curing proceeds, resulting in low adhesion to surrounding components and, as a result, achieving excellent reworkability. The requirements of this embodiment are described in detail below. The resin composition according to this embodiment may be liquid at a temperature of 25°C.

[0015] [Resin Composition] The resin composition according to this embodiment contains inorganic particles and a resin, and has a viscosity ratio (hereinafter simply referred to as "viscosity ratio") of the viscosity at a shear rate of 1 / s to the viscosity at a shear rate of 17.8 / s at a temperature of 25°C greater than 1.3. This results in excellent reworkability of the resin composition. Here, the value of "17.8 / s" may correspond to the shear rate used when the resin composition is actually filled between an electronic component and a heat sink. Therefore, the viscosity ratio, which is the ratio of the shear rate to a shear rate of 1 / s assuming a state in which almost no shear force is applied, is considered to be suitable as an evaluation standard assuming actual use of the resin composition. The viscosity ratio is preferably 1.5 or greater, more preferably 2.0 or greater, even more preferably 3.0 or greater, and particularly preferably 4.0 or greater. From the viewpoint of improving the reworkability of the resin composition, the viscosity ratio is preferably 400 or less, more preferably 300 or less, even more preferably 250 or less, even more preferably 200 or less, and particularly preferably 100 or less. The viscosity ratio can be measured by the method described in the Examples below.

[0016] The resin composition according to this embodiment preferably has a viscosity of more than 1 Pa·s at a shear rate of 1 / s at a temperature of 25°C. This makes it easier to maintain the inorganic particles in a uniformly dispersed state, facilitates curing while maintaining this state, and improves the reworkability of the resin composition. The viscosity is more preferably 10 Pa·s or more, even more preferably 50 Pa·s or more, and even more preferably 100 Pa·s or more, and may be 150 Pa·s or more, 200 Pa·s or more, or 270 Pa·s or more. On the other hand, the viscosity is preferably 2000 Pa·s or less, more preferably 1500 Pa·s or less. This allows the inorganic particles to be uniformly dispersed in the resin, and makes it easier to fill narrow gaps with the resin composition.

[0017] The resin composition according to this embodiment preferably has a viscosity of 500 Pa·s or less, more preferably 200 Pa·s or less, even more preferably 150 Pa·s or less, and particularly preferably 115 Pa·s at a temperature of 25°C and a shear rate of 17.8 / s. This facilitates uniform dispersion of the inorganic particles in the resin and improves reworkability. Meanwhile, the viscosity is preferably 0.1 Pa·s or more, more preferably 0.5 Pa·s or more, and even more preferably 1.0 Pa·s or more. This facilitates maintaining uniform dispersion of the inorganic particles in the resin and improves reworkability.

[0018] The resin composition according to this embodiment preferably has a modulus of rigidity exceeding 3 Pa. This can further improve the reworkability of the resin composition. The modulus of rigidity is more preferably 4 Pa ​​or more, and even more preferably 10 Pa or more. This allows the resin composition to be removed without adhering to surrounding members, making re-coating easy. There is no particular upper limit to the modulus of rigidity, but it may be, for example, 100 Pa or less, or 60 Pa or less. The modulus of rigidity is the slope of a shear strain-shear stress graph, and can be measured by the method in the Examples described below.

[0019] Preferred inorganic particles are ceramics such as silica, alumina, aluminum nitride, boron nitride, silicon nitride, and silicon carbide. Particles made of inorganic materials with high thermal conductivity are particularly preferred, for example, particles made of inorganic materials with a thermal conductivity of 15 W / mK or more. Suitable inorganic materials include ceramics such as alumina, aluminum nitride, boron nitride, silicon nitride, and silicon carbide. The inorganic particles are preferably ceramic particles. Because ceramics have high thermal conductivity, the use of ceramic particles can improve the heat dissipation performance of the resin composition. Furthermore, when insulating ceramics are used as inorganic particles, short circuits in semiconductor devices can be suppressed. Therefore, insulating ceramic particles are more preferred, and specifically, alumina, aluminum nitride, boron nitride, and silicon nitride are more preferred. It is even more preferred that the inorganic particles be at least one inorganic material with higher thermal conductivity selected from the group consisting of alumina and silicon nitride.

[0020] When the total of the inorganic particles and the resin is taken as 100% by volume, the content of the inorganic particles is preferably 20 to 98% by volume, more preferably 30 to 95% by volume, particularly preferably 40 to 93% by volume, and may be 50 to 93% by volume or 65 to 93% by volume.

[0021] The inorganic particles preferably include irregular particles having an aspect ratio of less than 0.90. This makes it easier to achieve the desired viscosity ratio. In this specification, "irregular particles" refers to all particles having an aspect ratio of less than 0.90. However, particles commonly used in resin compositions for heat dissipation materials rarely contain particles having an aspect ratio of less than 0.10. Therefore, the "irregular particles" according to one embodiment may be limited to particles having an aspect ratio of 0.10 or more but 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).

[0022] It is more preferable that the inorganic particles include, in addition to the amorphous particles, spherical particles having an aspect ratio of 0.90 or more. This makes it easier to adjust the viscosity ratio to a desired range. In this specification, "spherical particles" refers to all particles having an aspect ratio of 0.90 or more. Since the maximum aspect ratio is 1.00, the aspect ratio of "spherical particles" may be expressed as 0.90 or more and 1.00 or less.

[0023] Irregular particles and spherical particles can be distinguished by taking an SEM image, which is taken at a magnification of 100 to 100,000 times and an observation area of, for example, 1,000 μm×2,000 μm.

[0024] The SEM image is analyzed to determine the aspect ratio of the inorganic particles shown in the SEM image. This makes it possible to distinguish between irregular particles, which are particles with an aspect ratio of less than 0.90, and spherical particles, which are particles with an aspect ratio of 0.90 or more. Each inorganic 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 of the inorganic particle 20 (referred to as the "major axis") is identified, and the particle size in the direction perpendicular to the major axis is referred to as the "minor axis." For each inorganic particle, the ratio of the minor axis to the major axis (minor axis / major axis) is taken as the aspect ratio of that inorganic particle.

[0025] The average aspect ratio of the amorphous 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 spherical particles is preferably 0.90 or more and 1.00 or less, more preferably 0.91 or more and 1.00 or less. This controls the dispersion state of the particles in the resin composition, making it easier to obtain the desired viscosity ratio in the resin composition. The average aspect ratio of each particle is determined by arbitrarily selecting 20 particles from the SEM image of each particle and calculating the arithmetic average of the aspect ratios of those particles.

[0026] The amorphous particles are preferably silicon nitride particles, and the spherical particles are preferably alumina particles. Since both silicon nitride particles and alumina particles are inorganic materials with high thermal conductivity, the thermal conductivity of the resin composition can be further improved by using particles made of these as a filler.

[0027] The fact that the irregular particles are silicon nitride particles and the spherical particles are alumina particles can be identified, for example, by SEM-EDX analysis. The irregular particles and spherical particles are each identified from an SEM image, and elemental mapping (e.g., elemental mapping of Si and Al elements) obtained by EDX measurement is confirmed. This makes it possible to confirm that the irregular particles are silicon nitride particles and the spherical particles are alumina particles.

[0028] It may contain a small amount of amorphous alumina particles (e.g., 10.0% by volume or less of the total alumina particles) and / or a small amount of spherical silicon nitride particles (e.g., 10.0% by volume or less of the total silicon nitride particles), neither of which will interfere with the objectives of this embodiment.

[0029] In one embodiment of the present invention, the inorganic particles preferably contain silicon nitride particles, from the viewpoint of obtaining a desired viscosity ratio and high thermal conductivity of the resin composition. The silicon nitride particles are considered to have an appropriate shape, specific gravity, surface properties, etc., for obtaining the desired viscosity ratio.

[0030] In one embodiment of the present invention, the inorganic particles preferably contain 40% by volume or more of silicon nitride particles. This makes it easier to obtain a desired viscosity ratio in the resin composition, and curing proceeds while maintaining the particles in a uniformly dispersed state, thereby improving the thermal conductivity of the cured resin composition. More preferably, the inorganic particles contain 45% by volume or more of silicon nitride particles. The upper limit of the content of silicon nitride particles relative to the inorganic particles is preferably 99% by volume or less, more preferably 95% by volume or less. This improves the dispersibility of the particles in the resin composition, making it easier to obtain a desired viscosity ratio.

[0031] The particle diameter D50 (hereinafter also referred to simply as "D50") of the silicon nitride particles at the cumulative 50% from the fine side of the volume-based cumulative particle size distribution is preferably greater than 15 μm, more preferably 30 μm or more, and even more preferably 40 μm or more. This makes it easier to obtain the desired viscosity ratio in the resin composition, and curing proceeds while maintaining the particles in a uniformly dispersed state, thereby improving the thermal conductivity of the cured resin composition. The D50 of the silicon nitride particles is preferably 250 μm or less. This makes it easier to uniformly disperse the particles in the resin composition and obtain the desired viscosity ratio.

[0032] In this embodiment, the D50 of the silicon nitride particles can be measured by laser diffraction. Specifically, particles dispersed in water are irradiated with a laser beam, and the diffraction is measured to determine each particle size. A measuring device such as the CILAS 1090L can be used. The D50 of the silicon nitride particles contained in the resin composition can be measured by appropriately removing the resin contained in the resin composition, separating the silicon nitride particles, and using the separated particles.

[0033] The average aspect ratio of the silicon nitride particles is preferably 0.50 or more and less than 0.90, more preferably 0.55 or more and 0.86 or less, and particularly preferably 0.60 or more and 0.85 or less. This controls the dispersion state of the particles in the resin composition, making it easier to obtain a desired viscosity ratio in the resin composition. The average aspect ratio of the silicon nitride particles can be determined by selecting any 20 silicon nitride particles from the SEM image and calculating the arithmetic average of the aspect ratios of those particles.

[0034] The β-phase ratio of the silicon nitride particles is preferably 65% ​​or more, which improves the thermal conductivity of the silicon nitride particles and can further improve the thermal conductivity of a resin composition containing the silicon nitride particles. Furthermore, it becomes easier to obtain a desired viscosity ratio in the resin composition. The β-phase ratio is more preferably 70% or more, even more preferably 80% or more, even more preferably 85% or more, and particularly preferably 90% or more. The β-phase ratio of the silicon nitride particles may be 100% or less.

[0035] 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.

[0036] 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)).

[0037] In one embodiment of the present invention, the inorganic particles preferably further contain alumina particles in addition to silicon nitride particles, from the viewpoint of obtaining a desired viscosity ratio. By further containing alumina particles having a specific gravity different from that of the silicon nitride particles, an appropriate interaction occurs between the particles and the resin, making it easier to adjust the viscosity ratio of the resin composition to a desired value.

[0038] The volume ratio of silicon nitride particles to alumina particles is preferably 0.6 to 19, more preferably 0.7 to 9, even more preferably 0.8 to 6, and particularly preferably 0.9 to 4. This allows for appropriate interaction between the particles and the resin, making it easier to adjust the viscosity ratio to the desired value.

[0039] The D50 of the alumina particles is preferably 0.1 μm or more and less than 20 μm, more preferably 0.2 μm or more and less than 10 μm. This improves the dispersibility of the particles in the resin composition, making it easier to adjust the viscosity ratio of the resin composition to a desired value. The D50 of the alumina particles can be measured in the same manner as the D50 of the silicon nitride particles.

[0040] The D50 of the alumina particles is preferably 0.001% or more and 70% or less, more preferably 0.1% or more and 60% or less, of the D50 of the silicon nitride particles. This improves the dispersibility of the particles in the resin composition and makes it easier to adjust the viscosity ratio of the resin composition to a desired value. When the resin composition contains multiple types of alumina particles, it is preferable that the D50 of all types of alumina particles and the D50 of the silicon nitride particles satisfy the above relationship.

[0041] 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."

[0042] The D50 of the first alumina particles is preferably 3 μm or more and 10 μm or less, and the D50 of the second alumina particles is preferably 0.01 μm or more and 2 μm or less. This improves the dispersibility of the particles and makes it easier to adjust the viscosity ratio of the resin composition to a desired value. 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.

[0043] 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. This improves the dispersibility of the particles in the resin composition, making it easier to obtain a desired viscosity ratio in the resin composition. The average aspect ratio of the alumina particles can be determined by arbitrarily selecting 20 alumina particles from the SEM image and calculating the arithmetic mean of the aspect ratios of those particles.

[0044] In this embodiment, for example, alumina particles which are irregular particles (e.g., 10.0% by volume or less of the total alumina particles) and / or silicon nitride particles which are spherical particles (e.g., 10.0% by volume or less of the total silicon nitride particles) may be contained, neither of which will interfere with the object of this embodiment.

[0045] The resin contained in the resin composition according to this embodiment may be a known liquid resin such as a thermosetting resin, for example, a silicone resin, an epoxy resin, or an acrylic resin. The resin may be used alone or in combination of two or more. From the viewpoints of moldability and thermal conductivity, it is preferable to use a silicone resin.

[0046] 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.

[0047] [Method of manufacturing resin composition] A method of manufacturing a resin composition according to this embodiment will be described. A resin composition can be obtained by mixing inorganic particles and a resin by a known method. For example, a liquid resin, inorganic particles, and a curing agent can be mixed, and then cured by heat, ultraviolet light, or the like to obtain a resin composition. Known curing agents, mixing methods, and curing methods can be used.

[0048] The inorganic particles (e.g., silicon nitride particles) used in the method for producing the resin composition may be produced by the method described below, or, in the case of alumina particles, for example, they may be commercially available alumina particles or alumina particles produced by a known method (e.g., a flame fusion method).

[0049] As an example of a method for producing inorganic particles used in the production of a resin composition, a method for producing silicon nitride particles will be described. The silicon nitride particles are produced by the following steps: (1) synthesizing silicon nitride synthetic crystals using a raw material containing Si by combustion synthesis under a nitrogen atmosphere; (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.

[0050] Step (1): Synthesizing silicon nitride composite crystals. For example, Si powder is used as the Si-containing raw material. The D50 of the raw Si material is, for example, in the range of 2 to 10 μm. This allows the amount of oxygen impurities to be suppressed, and the combustion rate to be increased, allowing for a higher synthesis temperature, resulting in good crystal growth. As an example, the D50 of Si is 5 μm.

[0051] The diluent is used to adjust the amount of Si in the mixed raw materials. Separately prepared silicon nitride particles are used as the diluent. The diluent may be either α-type silicon nitride particles or β-type silicon nitride particles, or a mixture of these. The D50 of the diluent is preferably in the range of 0.5 to 2.0 μm. As an example, the D50 of the diluent is 1.0 μm. The amount of diluent added is less than 10% by mass of the total raw materials (including the diluent). As an example, the diluent is added in an amount of 5 to 8% by mass of the total raw materials. By adding the amount of diluent within the above range, a predetermined amount of the desired silicon nitride particles used in the resin composition according to this embodiment can be produced.

[0052] In this embodiment, raw material Si and a diluent are mixed and filled into an insulated heat-resistant container. This insulated heat-resistant container has a thermal conductivity of 1 W / mK or less, and although alumina or zirconia can be used as the material, carbon is preferred to prevent impurities from being mixed in. After the raw materials are filled, the container is covered with a lid made of the same material as the insulated heat-resistant container. Furthermore, to increase the temperature inside the composite during combustion, the thickness of the mixed raw materials is set to more than 100 mm, preferably more than 100 mm and not more than 150 mm. Combustion synthesis is performed in a nitrogen atmosphere in the range of 0.5 to 1 MPa (e.g., 0.9 MPa). Adjusting the pressure range within this range enables efficient synthesis while suppressing increases in equipment costs.

[0053] When the mixed raw material is filled into the crucible, a layer of powder (silicon nitride) having a thickness of 1 mm to 80 mm is spread on the bottom and sides of the crucible, the mixed raw material is then filled, and the top surface is further covered with a layer of powder having a thickness of 1 mm to 80 mm. By covering the entire surface with powder, the mixed raw material can be kept warm, and a predetermined amount of the desired silicon nitride particles used in the resin composition according to this embodiment can be produced.

[0054] 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.

[0055] 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).

[0056] 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.

[0057] 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.

[0058] 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.

[0059] The present embodiment will be described in detail below with reference to examples carried out to clarify the effects of the present embodiment, but the present embodiment is not limited to the following examples.

[0060] <Preparation of Silicon Nitride Particles> Si powder (D50 = 5 μm) and silicon nitride powder (D50 = 1 μm) prepared separately as a diluent were mixed in a tumbling ball mill. The amount of diluent added was 5 to 8 mass% of the total raw material (including diluent). The mixed powder was filled into a carbonaceous, heat-resistant container with a layer of powder 1 mm to 80 mm thick on the bottom and sides, so that the raw material layer was thicker than 100 mm and not more than 150 mm, and the raw material layer was further covered with a layer of powder 1 mm to 80 mm thick. A lid made of a carbonaceous, heat-resistant material was then placed in the container, and synthesis was carried out under a nitrogen atmosphere at 0.9 MPa. After synthesis, the mixture was coarsely pulverized (crushed) in a mortar until it passed through a sieve with the specified openings.

[0061] The obtained coarsely pulverized powder was finely pulverized in a ball mill. The obtained finely pulverized powder was sieved using a vibrating sieve and then wet classified to obtain the following silicon nitride particles a to d. - When sieving using a 106 μm sieve, the powder remaining below the sieve was further sieved using a 75 μm sieve, and silicon nitride particles a (D50 is 83.0 μm) remained on the sieve. - When sieving using a 75 μm sieve, the powder remaining below the sieve was further sieved using a 63 μm sieve, and silicon nitride particles b (D50 is 58.0 μm) remained on the sieve. - When sieving using a 75 μm sieve, the powder remaining below the sieve was further sieved using a 63 μm sieve, and silicon nitride particles c (D50 is 22.0 μm) remained on the sieve. - Silicon nitride particles d (D50 is 56.0 μm) obtained by mixing silicon nitride particles a, b, and c.

[0062] For comparison, silicon nitride particles e (D50: 3.6 μm) having the physical properties shown in Table 1 were also prepared.

[0063] <Preparation of Alumina Particles> Three types of alumina particles were prepared. The first alumina particles were DAW-05 manufactured by Denka Co., Ltd., the second alumina particles were AA-04 manufactured by Sumitomo Chemical Co., Ltd., and the third alumina particles were DAW-45 manufactured by Denka Co., Ltd. Mixed alumina particles obtained by mixing the first alumina particles and the second alumina particles at a predetermined ratio were used as "alumina particles."

[0064] Various measurements were carried out on the silicon nitride particles a to e, the first alumina particles, and the second alumina particles.

[0065] <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.

[0066] The measurement results of D50 of each particle are shown in Table 1. The D50 of the mixed alumina particles (a mixture of the first alumina particles and the second alumina particles) was not measured. However, from the D50 (6.0 μm) of the first alumina particles and the D50 (0.5 μm) of the second alumina particles before mixing, it can be said that the D50 of the mixed alumina particles was 6.0 μm or less.

[0067] <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)

[0068] 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 of the above measurements, all silicon nitride particles were particles with an aspect ratio of less than 0.90 (i.e., irregular particles), and all alumina particles were particles with an aspect ratio of 0.90 or more (i.e., spherical particles). The average aspect ratio of each particle was determined as a reference for understanding the aspect ratio of each particle. The average aspect ratio of each particle was determined by arbitrarily selecting 20 particles from the SEM image of each particle and calculating the arithmetic mean of the aspect ratios of those particles. The measurement results of the average aspect ratios of the silicon nitride particles are shown in Table 1. The first alumina particles had an average aspect ratio of 0.97, and the second alumina particles had an average aspect ratio of 0.91.

[0069] <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.

[0070] When the silicon nitride particles contained components other than silicon nitride, the peaks of those components were compared with the corresponding peaks of standard samples of those components to determine the proportions of those components. The obtained powder X-ray diffraction patterns confirmed that all silicon nitride particles were composed exclusively of α-type silicon nitride and β-type silicon nitride. The proportion of β-type silicon nitride in the sample (β-conversion ratio) was then calculated using the Gazzara & Messier method. The calculation results are shown in Table 1.

[0071] <Preparation of Resin Composition> Each particle (silicon nitride particles, first alumina particles, second alumina particles) was blended into a silicone resin (main component: DOWSIL (trademark) CY 52-276 A manufactured by The Dow Chemical Company). The silicone resin and inorganic particles were blended in the blending ratios shown in Table 1, and the mixture was stirred and mixed using a Awatori Rentaro (manufactured by Thinky Corporation) to obtain a liquid resin composition.

[0072] <Shear rate-viscosity and rigidity modulus measurement> The shear rate-viscosity of the liquid resin composition was measured using a Modular Compact Rheometer (MCR302e manufactured by Anton Paar). The measurement conditions were as follows: Geometry: Φ20 mm parallel plates Gap: 0.5 mm Shear rate: 0.1 s-1 to 1000 s-1 Measurement temperature: 25°C Measurement time: 20 minutes The sample was set on a plate stabilized at the measurement temperature within 5 minutes, and the measurement was started.

[0073] The viscosity was measured at shear rates of 1.0 / s and 17.8 / s, and the ratio of the viscosity at a shear rate of 1.0 / s to the viscosity at a shear rate of 17.8 / s was calculated. Furthermore, the shear stress versus shear strain was plotted at five points from 0.1 / s to 1.0 / s, and the modulus of rigidity was calculated by the least squares method from the slope of the plot.

[0074] <Measurement of Adhesion Amount> A mold was prepared by drilling a rectangular hole measuring 1 cm x 10 cm in a 1 mm thick aluminum plate. A transparent PET film coated with a release agent (rear side film) was attached to the back side of the mold so as to cover the rectangular hole, with the release agent-coated surface facing the mold. 3 g of the liquid resin composition (gray) was poured into the rectangular hole in the mold, and then a transparent PET film coated with a release agent (front side film) was attached on top of it, with the release agent-coated surface facing the mold and resin composition. Furthermore, light pressure was applied from above with a metal roller to the front side film, forcing the resin composition into the rectangular hole in the mold and forming it into a 1 cm x 10 cm strip. Another aluminum plate was then placed on top of it, heated at 120°C for 8 hours, and left to stand to cure the resin. The mass of the front side film was measured before attachment. After curing was complete, the aluminum plate was allowed to cool, and when the temperature had dropped to about room temperature, the surface-side film of the cured resin composition was peeled off. The mass of the peeled surface-side film was measured, and the adhesion amount was determined from the mass difference with the film before attachment. In addition, for samples with an adhesion amount of 0.04 g or less, the state of the film after peeling (appearance and presence or absence of resistance when rubbed with a fingertip) was confirmed as follows. A: No unevenness in appearance, and no resistance felt when rubbed. B: No unevenness in appearance, but slight resistance felt when rubbed. C: Unevenness seen in appearance, and resistance felt when rubbed.

[0075]

[0076] The results in Table 1 are discussed below. The resin compositions of Samples 1 to 6, which satisfied the requirements of this embodiment, had a small amount of composite attached to the film and exhibited excellent reworkability. Furthermore, the resin compositions of Samples 1 to 5 satisfied the preferred requirement of a viscosity ratio of 2.0 or more and 200 or less, and the film state after peeling was A to B, demonstrating even better reworkability. Furthermore, the resin compositions of Samples 1 to 3 and 5 satisfied the even more preferred requirement of a viscosity ratio of 3.0 or more and 200 or less, and the film state after peeling was A, demonstrating particularly excellent reworkability. On the other hand, the resin composition of Sample 7, which did not satisfy the requirements of this embodiment, had a large amount of composite attached to the film and exhibited poor reworkability.

[0077] This application claims priority from Japanese Patent Application No. 2024-024841, filed February 21, 2024. Japanese Patent Application No. 2024-024841 is incorporated herein by reference.

Claims

1. A resin composition comprising inorganic particles and a resin, wherein the ratio of the viscosity at a shear rate of 1 / s to the viscosity at a shear rate of 17.8 / s at a temperature of 25°C is greater than 1.

3.

2. The resin composition according to claim 1, wherein the viscosity at a shear rate of 1 / s exceeds 1 Pa·s.

3. The resin composition according to claim 1, wherein the inorganic particles contain silicon nitride particles in an amount of 40% by volume or more.

4. The resin composition according to claim 1, having a modulus of rigidity of more than 3 Pa.

5. The resin composition according to claim 3, wherein the silicon nitride particles have a beta-phase ratio of 65% or more.

Images