Method for producing alumina particles and method for producing resin composition

Abstract

This method for producing alumina particles comprises subjecting a liquid mixture that contains a dispersion medium and surface-treated alumina particles that are at least partially aggregated to a wet crushing treatment and subjecting the liquid mixture that has been subjected to the wet crushing treatment to a wet sorting treatment. This method for producing a resin composition comprises mixing a resin with alumina particles obtained through the aforementioned production method.

Description

Method for producing alumina particles and method for producing resin compositions

[0001] This disclosure relates to a method for producing alumina particles and a method for producing a resin composition.

[0002] In recent years, mobile devices such as smartphones, as well as electronic devices installed in vehicles, have become remarkably smaller, lighter, and thinner. As a result, the density of electronic components such as IC chips and memory mounted on printed circuit boards inside electronic devices is increasing, and the heat density inside electronic devices tends to increase even further. When the heat density inside electronic devices increases, the temperature rise due to the heat generated becomes significant, leading to a decrease in the operating performance and reliability of electronic components. Therefore, it is necessary to quickly transfer the heat generated by electronic components to the outside for heat dissipation.

[0003] As a means to solve the above problem, a method is being considered in which highly thermally conductive inorganic particles are packed into insulating resin materials that constitute the packaging and substrate materials of electronic devices at a high packing density. Known highly thermally conductive inorganic particles include alumina particles, magnesia particles, boron nitride particles, and aluminum nitride particles, but alumina particles are widely used from the viewpoint of chemical resistance and moisture absorption stability.

[0004] From the viewpoint of facilitating mixing with resin at a high packing density, the shape of the inorganic particles is preferably spherical. It is known that spherical alumina particles can be produced, for example, by spraying Bayer process alumina, which is used as a raw material, into a flame and rapidly cooling it while it melts to form spheroids (thermal spraying method) (see Patent Document 1).

[0005] Conventional thermal spraying methods yield spherical alumina particles with a high α-alumina content (hereinafter also referred to as the α-conversion rate) when the particle size is large, around 50 μm. However, as the particle size decreases, the content of low-temperature phases such as δ-alumina increases, leading to problems such as a decrease in the thermal conductivity of the alumina particles. Therefore, it has been investigated to increase the α-conversion rate by heat-treating the alumina particles (see Patent Document 2).

[0006] Japanese Patent Publication No. 11-147711 Japanese Patent Publication No. 2014-9140

[0007] However, when alumina particles are heat-treated, the spherical alumina particles can aggregate and become coarser, which can result in insufficient packing of the alumina particles into the resin.

[0008] Furthermore, while dry crushing and dry classification (collectively referred to as "dry processing") are widely known methods for reducing the aggregation of inorganic particles, applying these methods to alumina particles does not fundamentally solve the problem. Specifically, when relatively hard alumina particles are subjected to dry processing, the surface tends to chip due to collisions between the alumina particles, generating fine particles. Also, if the alumina particles have been surface-treated, foreign matter may be generated due to the peeling off of the surface treatment agent. Therefore, when alumina particles that have undergone dry processing are filled into resin, the fluidity of the resin decreases due to the fine particles and foreign matter, and the filling of the resin tends to be insufficient. In addition, if the resin is a curable resin, the smoothness of the resin surface after curing may be impaired.

[0009] Therefore, one aspect of this disclosure aims to provide a method for manufacturing alumina particles that can be filled into a resin with a high filling rate and, when filled into a curable resin, can suppress a decrease in the smoothness of the resin surface after curing. Another aspect of this disclosure aims to provide a method for manufacturing a resin composition containing alumina particles and a resin obtained by the said manufacturing method.

[0010] This disclosure includes, for example, the following aspects: [1] A method for producing alumina particles, comprising: wet crushing a mixed liquid containing surface-treated alumina particles, at least partially aggregated, and a dispersion medium; and wet classification of the mixed liquid after the wet crushing treatment. [2] The method according to [1], wherein the α-conjugation rate of the surface-treated alumina particles is 40% or more. [3] The method according to [1] or [2], wherein the surface-treated alumina particles are alumina particles surface-treated with a silane coupling agent. [4] The method according to any one of [1] to [3], wherein the mixed liquid subjected to the wet crushing treatment contains 10% by mass or more of the surface-treated alumina particles based on the total amount of the mixed liquid. [5] The method according to any one of [1] to [4], wherein the wet classification treatment is performed using a centrifugal separator. [6] The method according to any one of [1] to [5], wherein the wet classification treatment includes performing a top cut on the surface-treated alumina particles. [7] The manufacturing method according to any one of [1] to [6], wherein the wet classification treatment removes particles with a particle size of 5 μm or more from the surface-treated alumina particles having a D50 of 0.1 to 10 μm. [8] A method for producing a resin composition, comprising mixing alumina particles obtained by the manufacturing method according to any one of [1] to [7] with a resin. [9] The manufacturing method according to [8], wherein the resin is a curable resin and the thermal conductivity of the cured product of the resin composition is 0.5 W / (m·K) or more.

[0011] According to one aspect of this disclosure, it is possible to provide a method for manufacturing alumina particles that can be filled into a resin with a high filling rate and, when filled into a curable resin, can suppress a decrease in the smoothness of the resin surface after curing. According to another aspect of this disclosure, it is possible to provide a method for manufacturing a resin composition containing the alumina particles obtained by this manufacturing method and a resin.

[0012] Figure 1 is an SEM image of the alumina particles obtained in Example 1. Figure 2 is an SEM image of the alumina particles obtained in Comparative Example 1. Figure 3 is an SEM image of the surface of the test composite prepared using the alumina particles obtained in Example 1. Figure 4 is an SEM image of the surface of the test composite prepared using the alumina particles obtained in Comparative Example 1.

[0013] The embodiments of this disclosure will be described below, but this disclosure is not limited to these embodiments.

[0014] In this specification, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit of a numerical range in one step can be arbitrarily combined with the upper or lower limit of a numerical range in another step. In numerical ranges described in this specification, the upper or lower limit of that numerical range may be replaced with the values ​​shown in the examples. "A or B" means that either A or B is included, or both are included. Unless otherwise specified, the materials exemplified in this specification can be used individually or in combination of two or more. The content of each component in a composition means the total amount of multiple substances present in the composition if multiple substances corresponding to each component exist in the composition, unless otherwise specified.

[0015] The method for producing alumina particles according to this embodiment comprises subjecting a mixed liquid containing surface-treated alumina particles, in which at least a portion are aggregated, and a dispersion medium to a wet crushing treatment, and subjecting the mixed liquid after the wet crushing treatment to a wet classification treatment. That is, the method for producing alumina particles according to this embodiment involves subjecting a mixed liquid containing surface-treated alumina particles, in which at least a portion are aggregated, and a dispersion medium to a wet crushing treatment and a wet classification treatment in this order.

[0016] According to the inventors' research, it was found that the smoothness of the cured resin composition is easily impaired after filling alumina particles into a resin, partly because the fluidity of the resin composition containing alumina particles and resin is insufficient. One method to improve the fluidity of the resin composition is to surface treat the alumina particles, but even after surface treating the alumina particles, it was sometimes not possible to obtain a resin composition with sufficient fluidity. Further investigation by the inventors revealed that the fluidity of the resin composition is reduced by fine particles generated when alumina particles are chipped during dry treatment, and by foreign matter generated when the surface treatment agent is removed from the surface of the alumina particles. To address these problems, the inventors found that by subjecting surface-treated alumina particles to wet crushing and wet classification (collectively referred to as "wet treatment"), chipping of alumina particles and removal of the surface treatment agent from the surface of the alumina particles can be sufficiently suppressed. Furthermore, the fluidity of alumina particles treated with a wet process when filled into resin is improved compared to the fluidity of alumina particles treated with a dry process when filled into resin. By improving the fluidity of the resin composition, the surface smoothness of the cured resin composition can be improved.

[0017] The method for producing alumina particles may further comprise preparing surface-treated alumina particles that are at least partially aggregated prior to the wet crushing treatment.

[0018] [Preparation of Alumina Particles] Alumina particles can be produced by any of the following methods, for example: thermal spraying, Bayer process, ammonium alum pyrolysis, organoaluminum hydrolysis, aluminum water discharge method, freeze-drying. From the viewpoint of easily obtaining spherical alumina particles, thermal spraying may be used as the method for producing alumina particles.

[0019] Thermal spraying is a method of producing alumina particles by introducing raw material powders that can serve as an aluminum source into a high-temperature flame (for example, 2100°C or higher), melting the raw material powders, and forming them into spherical particles due to surface tension.

[0020] Examples of raw material powders include aluminum oxide powder, aluminum hydroxide powder, and metallic aluminum powder. It is preferable to use a raw material powder with a low sodium content. Examples of raw material powders with a low sodium content include low-soda alumina powder produced by the Bayer process.

[0021] The shape of the raw material powder is not limited, but it may be non-spherical from the viewpoint of easily obtaining spherical alumina particles. Non-spherical means that the circularity of the particles contained in the raw material powder is less than 0.90. In this specification, circularity means the average value of the value calculated by the following formula for 2000 or more particles, where S is the area of ​​the projection of the particle and L is the perimeter: (4 × π × S) / L ２

[0022] The area S and perimeter L are measured using a shape measuring device (for example, FPIA-3000 from Malvern Panalytical). As a pretreatment, approximately 10 g of particles are placed in a metal sieve with a diameter of 200 mm and a mesh size of 25 μm, and particles larger than 25 μm are removed with shower water. Next, the particles below the sieve are transferred to a plastic container to be used as the measurement sample. When using the FPIA-3000 as the shape measuring device, the measurement conditions are LPF / HPF standard (20x lens) and bright-field, and particle sheath (Malvern Panalytical) is used as the measurement solvent. 2 g of the measurement sample is weighed into a 50 mL beaker, 50 mL of pure water is added, and the sample is dispersed for 3 minutes using a 200 W ultrasonic disperser, so that the number of effective particles is 2000 or more and the ratio of effective particles to total particles is 55-70%, then the sample is placed in the device, and the area S and perimeter L of the particle projection are measured to calculate the circularity. As part of post-measurement data processing, any instances where multiple particles exist on a single screen are deleted.

[0023] The D50 of the raw material powder may be 0.1 to 40 μm, 0.5 to 10 μm, or 1 to 5 μm, from the viewpoint of easily obtaining alumina particles of a size suitable for heat dissipation fillers. In this specification, D50 means the 50% particle size in the volume-based cumulative particle size distribution measured using a laser diffraction / scattering particle size distribution analyzer. D50 can be measured using nanoSAQLA manufactured by Otsuka Electronics Co., Ltd. Specifically, a glass cell is prepared, and a slurry in which alumina particles are adjusted to 0.1% by mass with MIBK (methyl isobutyl ketone) is filled into the glass cell to measure D50.

[0024] The raw material powder is heated in a heating furnace, such as a vertical furnace or a horizontal furnace. The shape of the heating furnace is not limited, but examples include cylindrical shapes and polygonal prism shapes such as hexagonal prisms. The shape of the heating furnace may be cylindrical from the viewpoint of easily controlling the temperature inside the heating furnace uniformly. The discharge section of the heating furnace may be an inverted cone shape with the discharge hole side narrowing from the viewpoint of improving the collection efficiency of alumina particles.

[0025] The material of the inner wall of the heating furnace is not limited, but it may be made of stainless steel from the viewpoint of reducing contamination of alumina particles with impurities. A water-cooling jacket may be provided around the outer circumference of the heating furnace from the viewpoint of improving the cooling rate of the heating furnace.

[0026] The heating furnace is equipped with a burner for heating the raw material powder. The burner is a device that mixes a flammable gas and a combustion-supporting gas to form a flame inside the heating furnace. The burner is supplied with flammable gas from a flammable gas supply source and combustion-supporting gas from a combustion-supporting gas supply source. Examples of flammable gases include liquefied natural gas (LNG) and LPG. Examples of combustion-supporting gases include air, oxygen gas, and oxygen-enriched air.

[0027] The temperature at which the raw material powder is heated should be above the melting point of alumina (approximately 2070°C), and may be 2100°C or higher from the viewpoint of easily obtaining spherical alumina particles. The temperature may be 2500°C or lower, or 2300°C or lower, from the viewpoint of suppressing burner deterioration and from the viewpoint of cost advantage.

[0028] When introducing raw material powder into the heating furnace, a carrier gas may be used to introduce the raw material powder. Examples of carrier gases include air, nitrogen, oxygen, and carbon dioxide.

[0029] The alumina particles obtained by thermal spraying may be spherical. Spherical means that the circularity is 0.90 or greater. The circularity of the alumina particles may be 1.00 or less.

[0030] The specific gravity of alumina particles is 3.80 g / cm³, chosen because of its high α-alumina content and excellent thermal conductivity. ３ The above, or 3.85 g / cm³ ３ The above is sufficient, and from a similar viewpoint, 4.00 g / cm³ ３ The following, or 3.97 g / cm³ ３ The following may be the case. From these perspectives, the specific gravity of alumina particles is 3.80 to 4.00 g / cm³. ３ , or 3.85-3.97 g / cm³ ３ That's fine.

[0031] After generating alumina particles in the heating furnace, a pre-cooling treatment may be performed to cool the alumina particles to a temperature suitable for the cooling and washing treatment, prior to the cooling and washing treatment described later. This pre-cooling treatment allows the temperature of the alumina particles to be cooled to a temperature suitable for the cooling and washing treatment in a short time.

[0032] The pre-cooling treatment may be, for example, a treatment in which water is sprayed onto alumina particles. Examples of equipment for spraying water include showers. The equipment for performing the pre-cooling treatment (e.g., a shower) may be installed between the heating furnace (or the high-temperature region of the heating furnace) and the water tank used in the cooling and washing treatment.

[0033] After generating alumina particles in a heating furnace, or after pre-cooling the alumina particles, a cooling and washing process may be performed in which the alumina particles are placed in a cooling and washing water tank. The cooling and washing process is a process that cools and washes the alumina particles simultaneously. If the cooling and washing of the alumina particles are not performed simultaneously, the alumina particles generated in the heating furnace will be air-cooled while the alumina particles are collected using a collector such as a cyclone, and the collected alumina particles will be washed. However, by performing the cooling and washing process, the equipment for cooling and washing the alumina particles can be made smaller, and the overall process time can be shortened. In addition, by performing the cooling and washing process, variations in the degree of crystallinity of the alumina particles can be suppressed.

[0034] The cooling and washing tank contains cooling and washing water for cooling and washing alumina particles. To improve the washing efficiency of the alumina particles, the cooling and washing water may be agitated. The cooling and washing water is not limited to this type, but may be, for example, tap water (city water).

[0035] The temperature of the cooling and cleaning water may be 50°C or higher, 60°C or higher, or 70°C or higher from the viewpoint of efficiently removing impurities (e.g., ionic impurities) present on the surface of alumina particles, and may be 80°C or lower from the viewpoint of suppressing deterioration of the device due to thermal load. From these viewpoints, the temperature of the cooling and cleaning water may be 50-80°C, 60-80°C, or 70-80°C.

[0036] The cooling and washing process may be carried out by introducing the alumina particles into the cooling and washing water within 5 seconds of the alumina particles being discharged from the heating furnace, from the viewpoint of suppressing variations in the degree of crystallinity of the alumina particles.

[0037] In the cooling and cleaning process, the temperature of the alumina particles introduced into the cooling and cleaning water may be 200°C or lower, 150°C or lower, or 100°C or lower, from the viewpoint of suppressing evaporation of the cooling and cleaning water and enabling stable cooling and cleaning of the alumina particles. The temperature of the alumina particles can be calculated using simulation software (for example, Ansys Fluent from Ansys).

[0038] After subjecting the alumina particles to a cooling and washing treatment, the alumina particles are separated from the cooling and washing water, and the alumina particles are recovered. Examples of the method for recovering the alumina particles include a method in which the alumina particles dispersed in the cooling and washing water are allowed to settle, the supernatant liquid is removed with a pump or the like, and the settled alumina particles are recovered. According to this method, the washing and removal of ionic impurities such as Na ＋ and Ca ２＋ adhering to the surface of the alumina can be efficiently performed.

[0039] After recovering the alumina particles from the cooling and washing water, the alumina particles may be dried. By drying the alumina particles, the moisture adhering to the alumina particles is removed. The drying method is not limited and may be natural drying or heat drying.

[0040] After drying the alumina particles, from the viewpoint of increasing the α-phase conversion rate of the alumina particles, the alumina particles may be heat-treated at 1100 °C or higher. By heat-treating the alumina particles at 1100 °C or higher, the transition from a phase other than the α-crystalline phase with low thermal conductivity of the alumina particles (for example, an amorphous phase, a γ-crystalline phase, a δ-crystalline phase, a θ-crystalline phase) to the α-crystalline phase with high thermal conductivity can be promoted. The heat treatment of the alumina particles may be performed at 1300 °C or lower from the viewpoints of suppressing roughening of the surface of the alumina particles and suppressing aggregation of the alumina particles. From these viewpoints, the heat treatment of the alumina particles may be performed at 1100 to 1300 °C.

[0041] The time for heat-treating the alumina particles may be 1 hour or longer from the viewpoint that the transition time of the alumina particles to the α-crystalline phase is sufficient and it is easy to sufficiently increase the α-phase conversion rate of the alumina particles, and may be 4 hours or shorter from the viewpoint of suppressing aggregation of the alumina particles and easily obtaining alumina particles having a target particle diameter. From these viewpoints, the time for heat-treating the alumina particles may be 1 to 4 hours.

[0042] The heat treatment of the alumina particles may be performed, for example, in a trolley furnace, a tunnel furnace, or a rotary kiln furnace. The atmosphere for the heat treatment may be, for example, an air atmosphere.

[0043] From the viewpoint of easily obtaining high thermal conductivity, the alpha-gelatinization rate of alumina particles may be 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more. The alpha-gelatinization rate of alumina particles may be 100% or less, 99% or less, or 98% or less. Since the alpha-gelatinization rate of alumina particles does not change before and after surface treatment, wet crushing treatment, and wet classification treatment, the alpha-gelatinization rate of alumina particles after surface treatment, wet crushing treatment, and wet classification treatment can be considered to be the same as the alpha-gelatinization rate of alumina particles before surface treatment, wet crushing treatment, and wet classification treatment. From these viewpoints, the alpha-gelatinization rate of alumina particles may be 40-100%, 50-100%, 60-100%, 70-100%, 80-100%, 90-100%, 90-99%, or 90-98%.

[0044] The alpha-adsorption rate of alumina particles is calculated using the following formula, where X is the maximum peak intensity at a diffraction angle 2θ = 35.2° ± 0.2° for the alpha-alumina crystal phase, and Y is the maximum peak intensity at a diffraction angle 2θ = 67.3° ± 0.2° for the crystal phase other than alpha-alumina. The alpha-adsorption rate of alumina particles can be measured by the method described in the examples below. Alpha-adsorption rate = (X / (X + Y)) × 100 (%)

[0045] From the viewpoint of easily obtaining high thermal conductivity, the D50 of the heat-treated alumina particles may be 0.1 μm or more, 0.5 μm or more, or 1 μm or more. From the viewpoint of improving the ability to fill the resin, the D50 of the heat-treated alumina particles may be 40 μm or less, 30 μm or less, 20 μm or less, 10 μm or less, or 5 μm or less. From these viewpoints, the D50 of the heat-treated alumina particles may be 0.1 to 40 μm, 0.5 to 10 μm, or 1 to 5 μm.

[0046] After preparing the alumina particles, the alumina particles are subjected to surface treatment. This surface treatment may be performed, for example, using a separable flask equipped with a stirring blade.

[0047] Examples of surface treatment agents include silane compounds (e.g., silane coupling agents), titanium compounds (e.g., titanium coupling agents), and aluminate compounds (e.g., aluminate coupling agents). The surface treatment agent may have alkoxy groups, alkoxysilyl groups, phenyl groups, vinyl groups, epoxy groups, acryloyl groups, methacryloyl groups, amino groups, ureido groups, mercapto groups, isocyanate groups, etc. From the viewpoint of easily obtaining excellent fluidity when alumina particles are filled into the resin, the surface treatment agent may contain silane compounds, and may contain silane compounds having alkoxysilyl groups.

[0048] From the viewpoint of easily obtaining excellent fluidity when alumina particles are filled into a resin, the silane compound may include a silane compound having an alkoxysilyl group, specifically a silane compound having an alkoxy group bonded to a silicon atom. In the silane compound, the number of alkoxy groups bonded to the silicon atom may be 1 to 4, 1 to 3, 2 to 3, or 3 to 4, from the viewpoint of easily obtaining excellent fluidity when alumina particles are filled into a resin.

[0049] The silane compound may include a nitrogen-containing organic group, from the viewpoint of easily obtaining excellent fluidity when alumina particles are filled into the resin. Examples of nitrogen-containing organic groups include alkylamino groups, alkylaminoalkyl groups, arylamino groups, arylaminoalkyl groups, heteroarylamino groups, and heteroarylaminoalkyl groups. The nitrogen-containing organic group may include arylaminoalkyl groups, phenylaminoalkyl groups, and phenylaminopropyl groups, from the viewpoint of easily obtaining excellent fluidity when alumina particles are filled into the resin.

[0050] Examples of silane compounds include N-phenyl-3-aminopropyltrimethoxysilane, phenyltrimethoxysilane, vinyltrimethoxysilane, epoxytrimethoxysilane, methacrylictrimethoxysilane, aminotrimethoxysilane, ureidotrimethoxysilane, mercaptopropyltrimethoxysilane, isocyanatetopropyltrimethoxysilane, phenylaminotrimethoxysilane, acrylictrimethoxysilane, p-styryltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-isocyanatetopropyltrimethoxysilane, and 3-aminopropyltrimethoxysilane. From the viewpoint of easily obtaining excellent fluidity when alumina particles are filled into the resin, the silane compound may include N-phenyl-3-aminopropyltrimethoxysilane.

[0051] From the viewpoint of easily obtaining excellent fluidity when alumina particles are filled into the resin, the amount of surface treatment agent added may be 0.01 parts by mass or more, 0.05 parts by mass or more, 0.1 parts by mass or more, 0.3 parts by mass or more, or 0.5 parts by mass or more per 100 parts by mass of alumina particles (excluding the content of the surface treatment agent), and from the same viewpoint, it may be 10 parts by mass or less, 8 parts by mass or less, 5 parts by mass or less, 3 parts by mass or less, 2 parts by mass or less, 1 part by mass or less, 0.8 parts by mass or less, or 0.5 parts by mass or less. From these viewpoints, the amount of surface treatment agent added may be 0.01 to 10 parts by mass, 0.05 to 5 parts by mass, or 0.1 to 2 parts by mass.

[0052] The reaction temperature between the alumina particles and the surface treatment agent may be determined according to the type and amount of surface treatment agent added. From the viewpoint of allowing sufficient reaction between the alumina particles and the surface treatment agent, the reaction temperature may be 40°C or higher, 50°C or higher, or 60°C or higher, and 80°C or lower, or 70°C or lower. From these viewpoints, it may be 40-80°C, 50-80°C, or 60-70°C.

[0053] The reaction time between the alumina particles and the surface treatment agent may be determined according to the type and amount of surface treatment agent added. From the viewpoint of allowing sufficient reaction between the alumina particles and the surface treatment agent, the reaction time may be 0.5 hours or more, or 1 hour or more, and may be 2 hours or less, or 1.5 hours or less. From these viewpoints, it may be 0.5 to 2 hours, or 1 to 1.5 hours.

[0054] The surface treatment of alumina particles may be carried out in a mixed solution containing alumina particles, a surface treatment agent, and a liquid medium such as water or an organic solvent, from the viewpoint of suppressing the generation of fine particles due to chipping of the surface of the alumina particles and easily obtaining excellent fluidity when the alumina particles are filled into resin. In other words, the surface treatment of alumina particles may be a wet surface treatment. In this specification, a liquid medium means a compound that is liquid at 1 atmosphere and 25°C.

[0055] Organic solvents include ketone compounds such as methyl isobutyl ketone (MIBK), methyl ethyl ketone (MEK), diisobutyl ketone, acetone, cyclohexanone, acetophenone, and benzophenone (excluding compounds that fall under the category of alcohol); aromatic hydrocarbon compounds such as benzene, toluene, xylene, styrene, and dielbenzene; aliphatic hydrocarbon compounds such as pentane, hexane, heptane, octane, nonane, and decane; alicyclic hydrocarbon compounds such as cyclohexane, methylcyclohexane, and decahydronaphthalene; chlorinated hydrocarbon compounds such as chlorobenzene, dichlorobenzene, trichlorobenzene, methylene chloride, chloroform, carbon tetrachloride, and tetrachloroethylene; methanol, ethanol, 1-propanol (n-propyl alcohol), 2-propanol (isopropyl alcohol), propylene glycol 1-monomethyl ether, 1-butanol, 2-butanol, t-butanol, 1-pentanol, 2-pentanol, 3-pentanol, and diamine. Examples include alcohols such as cetone alcohol, 1-hexanol, 2-ethyl-1-hexanol, cyclohexanol, and benzyl alcohol; phenolic compounds such as cresol; ether compounds such as dibenzyl ether, ethyl ether, ethylene glycol monomethyl ether, diethylene glycol monobutyl ether, anisole, phenyl ether, dioxane, and tetrahydrofuran (excluding compounds that fall under the category of alcohol); ester compounds such as ethyl acetate, butyl acetate, benzyl acetate, ethyl benzoate, benzyl benzoate, and γ-butyrolactone; nitrile compounds such as acetonitrile; sulfoxide compounds such as dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, and diphenyl sulfoxide; amide compounds such as formamide, N,N-dimethylacetamide, 1-methyl-2-pyrrolidone, and N-methyl-2-pyrrolidone; carbonate compounds such as ethylene carbonate and propylene carbonate; and acid anhydrides such as acetic anhydride. The liquid medium may contain an organic solvent and may also contain methyl isobutyl ketone, from the viewpoint of easily reducing the viscosity ratio and easily obtaining excellent dispersibility of alumina particles.

[0056] After surface treatment of the alumina particles, the surface-treated alumina particles may be recovered from the solution containing the treated particles. Recovery of the surface-treated alumina particles may be performed, for example, by centrifugation. After recovering the surface-treated alumina particles, the particles may be washed with an organic solvent (e.g., ethanol) to remove any unreacted surface treatment agents. After washing the alumina particles with an organic solvent, the particles may be dried to remove any organic solvent adhering to them.

[0057] [Wet crushing treatment of alumina particles] After obtaining surface-treated alumina particles (hereinafter, surface-treated alumina particles will also be simply referred to as "alumina particles"), a mixed liquid containing the alumina particles and a dispersion medium is prepared, and a wet crushing treatment is performed. At this time, at least a portion of the alumina particles aggregates and forms aggregates. That is, the mixed liquid contains aggregates of alumina particles and a dispersion medium.

[0058] Through wet crushing treatment, at least a portion of the aggregated alumina particles are crushed and dispersed in the mixed liquid as alumina particles. In other words, at least a portion of the alumina particle aggregates in the mixed liquid are crushed, and the alumina particles that constituted the alumina particle aggregates are dispersed in the mixed liquid. Wet crushing treatment can also be described as a process in which a wet crushing treatment is applied to a mixed liquid containing alumina particles (alumina particle aggregates) and a dispersion medium, thereby obtaining a mixed liquid containing alumina particles (alumina particle aggregates) produced by the crushing of aggregated alumina particles (alumina particle aggregates) and a dispersion medium. The fact that at least a portion of the aggregated alumina particles (alumina particle aggregates) have been crushed by wet crushing treatment can be confirmed by performing particle size distribution measurements, sedimentation tests, etc., before and after wet crushing treatment, and observing the change in the average particle size of the alumina particles before and after wet crushing treatment.

[0059] The dispersion medium may be a liquid medium such as water or an organic solvent. The organic solvent used can be the same type used when surface-treating alumina particles.

[0060] The mixed liquid subjected to the wet crushing treatment may contain, for example, 10% or more by mass, 20% or more by mass, 30% or more by mass, 40% or more by mass, or 45% or more by mass of surface-treated alumina particles (alumina particles constituting aggregates and alumina particles not constituting aggregates), based on the total volume of the mixed liquid, and may contain 80% or less by mass, 70% or less by mass, or 65% or less by mass of surface-treated alumina particles (alumina particles constituting aggregates and alumina particles not constituting aggregates). In other words, the content of surface-treated alumina particles in the mixed liquid subjected to the wet crushing treatment may be within the above range based on the total volume of the mixed liquid. From these viewpoints, it may also be 10 to 80% by mass, 30 to 70% by mass, or 45 to 65% by mass.

[0061] Wet crushing can be carried out using equipment such as nanomizers, homogenizers, mixers, ball mills, bead mills, pot mills, media stirring mills, automatic mixing bowls, and ultrasonic processing devices. Wet crushing may also be performed using a nanomizer, as this makes it easier to obtain excellent fluidity when alumina particles are packed into resin.

[0062] When the wet crushing process is performed using a nanomizer, the conditions for the crushing process may be set, for example, to a pressure of 50-250 MPa, 50-200 MPa, 100-250 MPa, 100-200 MPa, or 200-250 MPa, and the number of passes through the nanomizer may be one or more, from the viewpoint of easily obtaining excellent fluidity when the alumina particles are filled into the resin.

[0063] The processing time for the wet crushing treatment may be adjusted according to the content of alumina particles in the mixed liquid. From the viewpoint of obtaining good fluidity when the alumina particles are filled into the resin, the processing time may be, for example, 10 to 180 seconds, 10 to 120 seconds, 10 to 60 seconds, 30 to 180 seconds, 30 to 60 seconds, 60 to 180 seconds, or 60 to 120 seconds.

[0064] The D50 of the alumina particles after wet crushing treatment may be 0.01 to 50 μm, 0.01 to 10 μm, 0.1 to 50 μm, or 0.1 to 10 μm from the viewpoint of improving the ability to fill the resin, and may be 1 to 50 μm or 1 to 10 μm from the viewpoint of easily obtaining high thermal conductivity.

[0065] [Wet Classification of Alumina Particles] A mixed liquid containing alumina particles is subjected to a wet crushing treatment, and then the mixed liquid after the wet crushing treatment is subjected to a wet classification treatment. The wet crushing treatment removes at least a portion of the alumina particles in the mixed liquid (especially alumina particles with a relatively large particle size, such as aggregated alumina particles that were not crushed by the wet crushing treatment). The particle size of the alumina particles removed by the wet classification treatment may be determined according to the target particle size of the alumina particles.

[0066] Wet classification can be carried out using equipment such as a centrifuge, gravity sedimentation tank, or flotation device. Wet classification may also be performed using a centrifuge, as this facilitates obtaining excellent fluidity when alumina particles are packed into the resin.

[0067] When the wet classification process is performed using a centrifugal separator, the conditions for the classification process may be, from the viewpoint of easily obtaining excellent fluidity when the alumina particles are filled into the resin, for example, a flow rate of 1 to 50 L / h, 1 to 10 L / h, 1 to 5 L / h, or 10 to 50 L / h, a pressure of 0.05 to 0.5 MPa, 0.05 to 0.2 MPa, 0.05 to 0.1 MPa, 0.1 to 0.5 MPa, or 0.1 to 0.2 MPa, and a rotational speed of 2000 to 10000 rpm, 2000 to 8000 rpm, 2000 to 5000 rpm, 5000 to 10000 rpm, 5000 to 8000 rpm, or 8000 to 10000 rpm.

[0068] The processing time for the wet classification treatment may be adjusted according to the alumina particle content in the mixed liquid. From the viewpoint of obtaining good fluidity when the alumina particles are filled into the resin, the processing time may be, for example, 0.5 to 2 hours, 0.1 to 1 hour, or 1 to 2 hours per liter of mixed liquid.

[0069] The wet classification process may include top-cutting of alumina particles, from the viewpoint of easily obtaining excellent fluidity when the alumina particles are packed into the resin. Top-cutting refers to the process of removing alumina particles larger than a predetermined particle size.

[0070] The wet classification process may include removing alumina particles with a predetermined particle size or larger from alumina particles whose D50 is within a predetermined range. The D50 of the alumina particles before the wet classification process may be within the range of the D50 of the alumina particles after the wet crushing process described above. The wet classification process may include, for example, removing alumina particles with a particle size of 1 μm or larger, 3 μm or larger, or 5 μm or larger from alumina particles whose D50 is 0.01 to 50 μm, 0.01 to 10 μm, 0.1 to 50 μm, or 0.1 to 10 μm. If the wet classification process includes top cutting, the top cutting may include removing alumina particles with a predetermined particle size or larger from alumina particles whose D50 is within a predetermined range. By performing top cutting, when forming a thin film from a resin material containing alumina particles, impurities and protrusions in the film are less likely to occur, resulting in fewer product defects. Furthermore, when the resin material passes through the narrow spaces of the electronic material like a capillary, the absence of coarse alumina particles in the resin material allows the resin material to flow more smoothly, improving work efficiency.

[0071] The D50 of the alumina particles after wet classification may be 0.01 to 50 μm, 0.01 to 10 μm, 0.1 to 50 μm, or 0.1 to 10 μm from the viewpoint of improving the packing ability into the resin, and may be 1 to 50 μm or 1 to 10 μm from the viewpoint of easily obtaining high thermal conductivity.

[0072] The alumina particles may be recovered from the mixture after wet classification. The alumina particles may be recovered, for example, by centrifugation.

[0073] [Method for Manufacturing Resin Composition] The alumina particles obtained by the method described above can be suitably used in applications requiring high thermal conductivity, such as heat dissipation materials and semiconductor encapsulants. The alumina particles obtained by the method described above are mixed with a resin and used in the manufacture of a resin composition containing alumina particles and resin. That is, another embodiment of the present disclosure is a method for manufacturing a resin composition, comprising mixing alumina particles obtained by the method for manufacturing alumina particles described above with a resin.

[0074] Examples of resins include thermosetting resins and thermoplastic resins. Examples of thermosetting resins include epoxy resins, phenolic resins, unsaturated imide resins, amino resins such as melamine resins, unsaturated polyester resins, allyl resins, dicyclopentadiene resins, silicone resins, and triazine resins. From the viewpoint of excellent moldability and electrical insulation properties, the thermosetting resin may be an epoxy resin. Resins may be used individually or in combination of two or more types.

[0075] Examples of epoxy resins include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, biphenyl type epoxy resin, alicyclic epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, bisphenol A novolac type epoxy resin, bisphenol F novolac type epoxy resin, dicyclopentadiene type epoxy resin, naphthalene type epoxy resin, and anthracene type epoxy resin.

[0076] Examples of thermoplastic resins include polyethylene, polypropylene, polystyrene, polyphenylene ether resin, phenoxy resin, polycarbonate resin, polyester resin, polyamide resin, polyamide-imide resin, polyimide resin, xylene resin, polyphenylene sulfide resin, polyetherimide resin, polyetheretherketone resin, and polyetherimide resin.

[0077] The resin composition may further contain inorganic fillers other than alumina particles. Examples of inorganic fillers other than alumina particles include aluminum hydroxide, zinc oxide, magnesium oxide, magnesium carbonate, magnesium hydroxide, titanium oxide, silicon oxide, and boron nitride. From the viewpoint of easily obtaining high thermal conductivity, the inorganic filler other than alumina particles may be at least one selected from the group consisting of aluminum hydroxide, zinc oxide, magnesium oxide, and boron nitride.

[0078] The resin composition may contain any components other than those listed above. Examples of optional components include curing agents, curing accelerators, flame retardants, ultraviolet absorbers, antioxidants, organic solvents, and surface treatment agents.

[0079] Examples of curing agents include polyfunctional phenol compounds such as phenol novolac and cresol novolac; amine compounds such as dicyandiamide, diaminodiphenylmethane, and diaminodiphenylsulfone; and acid anhydrides such as phthalic anhydride, pyromellitic anhydride, maleic anhydride, and maleic anhydride copolymers. The curing agents may be used alone or in combination of two or more.

[0080] Examples of curing accelerators include imidazole compounds and their derivatives; organophosphorus compounds; secondary amines; tertiary amines; and quaternary ammonium salts. The curing accelerators may be used alone or in combination of two or more.

[0081] Examples of imidazole compounds and their derivatives include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 1-benzyl-2-methylimidazole, 2-heptadecylimidazole, 4,5-diphenylimidazole, 2-methylimidazole, 2-phenylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-isopropylimidazole, 2,4-dimethylimidazole, 2-phenyl-4-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2,4-dimethylimidazole, and 2-phenyl-4-methylimidazole. Imidazole compounds and their derivatives may be masked with a masking agent. Examples of masking agents include acrylonitrile, phenylenediisocyanate, toluidine isocyaninate, naphthalene diisocyanate, methylene bisphenyl isocyanate, and melamine acrylate.

[0082] Examples of organophosphorus compounds include ethylenephosphine, propylphosphine, butylphosphine, phenylphosphine, trimethylphosphine, triethylphosphine, tributylphosphine, trioctylphosphine, triphenylphosphine, tricyclohexylphosphine, triphenylphosphine / triphenylborane complexes, and tetraphenylphosphonium tetraphenylborate.

[0083] Examples of secondary amines include morpholine, piperidine, pyrrolidine, dimethylamine, diethylamine, dicyclohexylamine, N-alkylarylamine, piperazine, diallylamine, thiazoline, and thiomorpholine.

[0084] Examples of tertiary amines include benzyldimethylamine, 2-(dimethylaminomethyl)phenol, and 2,4,6-tris(dimethylaminomethyl)phenol.

[0085] Examples of quaternary ammonium salts include tetrabutylammonium iodide, tetrabutylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium fluoride, benzalkonium chloride, benzyl di(2-hydroxyethyl)ethylammonium chloride, and decyl di(2-hydroxyethyl)methylammonium bromide.

[0086] The resin composition may further contain organic solvents for the purpose of adjusting viscosity. The organic solvents may be removed after the impregnation or coating treatment of the resin composition.

[0087] Examples of organic solvents include alcohols such as methanol, ethanol, propanol, and butanol; glycol ethers such as methyl cellosolve, butyl cellosolve, and propylene glycol monomethyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as butyl acetate and propylene glycol monomethyl ether acetate; ethers such as tetrahydrofuran; aromatic hydrocarbons such as toluene and xylene; nitrogen atom-containing solvents such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone; and sulfur atom-containing solvents such as dimethyl sulfoxide. Organic solvents may be used individually or in combination of two or more.

[0088] The organic solvent may be at least one selected from the group consisting of methyl isobutyl ketone, methyl ethyl ketone, propylene glycol monomethyl ether, and methyl cellosolve, from the viewpoint of resin solubility, and at least one selected from the group consisting of methyl isobutyl ketone and propylene glycol monomethyl ether, from the viewpoint of low toxicity.

[0089] In the method for producing a resin composition, the mixing of alumina particles, resin, and optional components may be carried out by known methods. The resin composition may also be produced by mixing alumina particles, resin, and optional components in a mixer, kneading the mixture with a mixing roll, extruder, etc., and then cooling it. More specifically, the resin composition may be produced by mixing alumina particles, resin, and optional components, kneading the mixture in a kneader, roll, extruder, etc., preheated to 70 to 140°C, and then cooling the kneaded mixture.

[0090] From the viewpoint of easily obtaining high thermal conductivity, the alumina particle content may be 50% or more by volume, or 60% or more by volume, based on the total amount of the resin composition. From the viewpoint of excellent moldability of the resin composition, the alumina particle content may be 90% or less by volume, or 85% or less by volume, based on the total amount of the resin composition. From these viewpoints, it may be 50 to 90% by volume, or 60 to 85% by volume.

[0091] The resin composition can be used as a heat dissipation material, insulating material, encapsulating material, etc. For example, it can be used as an encapsulating material for electronic components. The resin composition can be suitably used in semiconductor packages and printed circuit boards where high thermal conductivity is required.

[0092] When the resin in the resin composition is a curable resin, the thermal conductivity of the cured product of the resin composition may be 0.5 W / (m·K) or higher, 1.0 W / (m·K) or higher, 1.5 W / (m·K) or higher, 1.7 W / (m·K) or higher, 1.8 W / (m·K) or higher, 1.9 W / (m·K) or higher, or 2.0 W / (m·K) or higher, from the viewpoint of suitably using the resin composition as a heat dissipation material. The thermal conductivity is calculated by the product of the thermal diffusivity, the low-pressure specific heat capacity, and the density, and can be measured specifically by the method described in the examples below.

[0093] The resin composition may be impregnated into a substrate to form a prepreg. The prepreg can be suitably used in semiconductor packages and printed circuit boards where high thermal conductivity is required.

[0094] Examples of substrate materials include inorganic fibers such as E-glass, D-glass, S-glass, and Q-glass. Examples of substrate forms include woven fabrics, non-woven fabrics, rawhide, chopped strand mats, and surfacing mats. The substrate material and form can be determined according to the application and performance of the prepreg, and may be used individually or in combination of two or more materials and forms as needed.

[0095] The base material may be surface-treated from the viewpoint of heat resistance, moisture resistance, and processability. Examples of surface treatments include surface treatment with a silane coupling agent and mechanical fiber opening treatment. The thickness of the base material may be, for example, 0.01 to 0.2 mm.

[0096] A prepreg can be manufactured, for example, by impregnating a substrate with a resin composition whose viscosity has been adjusted with an organic solvent, and then removing the organic solvent. When manufacturing a prepreg, the solid content in the resin composition may be 40 to 90% by mass, or 50 to 85% by mass, relative to the total resin composition. After impregnating the substrate with the resin composition, the resin composition may be partially cured by heating.

[0097] A cured prepreg can be produced by heating and pressurizing the prepreg. A laminate of multiple prepregs may also be produced, and a laminate of prepregs can be produced by heating and pressurizing multiple layers of prepregs. The number of layers of prepregs may be, for example, 2 to 20. Examples of equipment for heating and pressurizing the prepreg or the laminate of prepregs include multi-stage presses, multi-stage vacuum presses, continuous molding machines, and autoclave molding machines. The heating and pressurizing conditions can be selected according to the thermosetting resin, curing agent, etc. contained in the resin composition. For example, the heating and pressurizing conditions are a temperature of 100 to 250°C, a pressure of 0.2 to 10 MPa, and a time of 0.1 to 5 hours.

[0098] The cured prepreg, or the cured prepreg laminate, may be a metal-clad laminate by arranging a metal foil on at least one main surface of the cured material. The metal foil may be one used for electronic component applications. Examples of metal foil include copper foil and aluminum foil.

[0099] Metal-clad laminates can be manufactured, for example, by heating and pressurizing a prepreg, or a stack of prepregs with metal foil placed on one or both sides. The heating and pressurizing apparatus and conditions may be the same as those used to manufacture cured prepregs and cured prepreg laminates.

[0100] When a resin composition is used as a encapsulant for an electronic component device, the electronic component device comprises an element and a cured resin composition that encapsulates the element. Examples of encapsulation methods using a resin composition include low-pressure transfer molding, injection molding, and compression molding. Examples of elements include active elements such as semiconductor chips, transistors, diodes, and thyristors, and passive elements such as capacitors, resistors, and coils.

[0101] Examples of electronic component devices include those in which elements are mounted on support members such as lead frames, pre-wired tape carriers, wiring boards, glass, silicon wafers, and organic substrates, and the resulting element portion is sealed with a resin composition. More specifically, DIP (Dual Inline Package), PLCC (Plastic Leaded Chip Carrier), QFP (Quad Flat Package), SOP (Small Outline Package), SOJ (Small Outline J-lead package), TSOP (Thin Small Outline Package), TQFP (Thin Quad Flat) have a structure in which elements are fixed on a lead frame, the terminal parts of the elements such as bonding pads and the lead parts are connected by wire bonding, bumps, etc., and then sealed by transfer molding using a resin composition. Examples include general resin-encapsulated ICs such as Packages; TCPs (Tape Carrier Packages) having a structure in which elements connected to a tape carrier with bumps are encapsulated in a resin composition; COB (Chip On Board) modules, hybrid ICs, multi-chip modules, etc., having a structure in which elements connected to wiring formed on a support member by wire bonding, flip-chip bonding, solder, etc., are encapsulated in a resin composition; and BGAs (Ball Grid Arrays), CSPs (Chip Size Packages), MCPs (Multi Chip Packages), etc., having a structure in which elements are mounted on the surface of a support member having terminals for wiring board connection formed on the back side, and the elements are connected to the wiring formed on the support member by bumps or wire bonding, and then the elements are encapsulated in a resin composition.

[0102] The present disclosure will be described in more detail below with reference to examples. However, the present disclosure is not limited to these examples.

[0103] <Preparation of Alumina Particles> Spherical alumina particles A were obtained by melting raw alumina powder (D50: 1.8 μm) in a high-temperature region of 2200°C formed in a heating furnace by a flame formed by LPG and oxygen. The obtained alumina particles A were added to 80°C cooling wash water within 5 seconds of being discharged from the heating furnace to obtain a slurry containing alumina particles A. A high-concentration alumina particle A slurry was recovered by removing the supernatant liquid from the slurry containing alumina particles A. The high-concentration alumina particle A slurry was dried in a dryer in an atmospheric atmosphere at an ambient temperature of 180°C to recover alumina particles B. The recovered alumina particles B were heated in a muffle furnace in an atmospheric atmosphere at a temperature of 1250°C for 4 hours to improve the α-gelatinization rate of alumina particles B and obtain alumina particles C. The α-gelatinization rate of alumina particles C was 95.5%. The alpha-conversion rate was calculated using the relationship (%) = (X / (X + Y)) × 100, where X is the maximum peak intensity of the α-alumina crystal phase at a diffraction angle 2θ = 35.2° ± 0.2° in X-ray diffraction measurements, and Y is the maximum peak intensity of the crystal phase other than α-alumina at a diffraction angle 2θ = 67.3° ± 0.2°. X-ray diffraction measurements of alumina particles C were performed using an X-ray diffractometer PW3040 / 60X'Pert-MRD (Malvern Panalogical), with a copper X-ray tube, under conditions of tube voltage 45kV and tube current 40mA.

[0104] (Example 1) 100 parts by mass of alumina particles C, 0.5 parts by mass of silane coupling agent (N-phenyl-3-aminopropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KBM-573"), 3.5 × 10 －２ A mixture was obtained by mixing parts by mass of pure water and 42.8 parts by mass of methyl isobutyl ketone in a beaker. Next, the beaker containing the mixture was placed in a 60°C water bath, and then stirred at a rotation speed of 150 min using a three-one motor with two stirring blades (made of Teflon®). －１By performing a wet treatment for one hour, the surface of alumina particles C was treated, and a slurry containing alumina particles D (including aggregated surface-treated alumina particles C) was obtained. The obtained slurry contained 50% by mass of alumina particles D based on the total amount of the slurry.

[0105] A slurry containing alumina particles D was subjected to wet disintegration by cavitation using a nanomizer (manufactured by Yoshida Machinery Industry Co., Ltd., product name "NM2-2000AR") and a film mixer (manufactured by Primix Corporation, product name "FM40-40L") (nanomizer treatment conditions: passed through the nozzle three times; film mix treatment conditions: 40 m / s, 1 minute).

[0106] Subsequently, alumina particles with a particle size of 5 μm or larger were subjected to top-cutting and wet classification using a centrifuge (manufactured by Satake Multimix Co., Ltd., product name "i-Classifier") to obtain a particle dispersion containing alumina particles E. The particle dispersion contained 50% by mass of alumina particles E based on the total volume of the particle dispersion. The alumina particle E content was pre-selected as the alumina particle E for a particle dispersion in which the boundary state between non-Bingham fluid and dilatant fluid was achieved by checking the viscosity behavior with respect to rotation speed using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., product names "TV-22" and "TV-33") while changing the alumina particle E in the particle dispersion by 5% by mass increments. Figure 1 shows the SEM image obtained when observing the obtained alumina particles E using a scanning electron microscope (SEM; manufactured by Hitachi High-Tech Corporation, product name "SU5000").

[0107] (Comparative Example 1) In the same manner as in Example 1, alumina particles C were roughly crushed using a roll crusher as a preliminary crushing. Next, dry crushing was performed using a swirling flow jet mill. Then, dry classification was performed using an elbow jet to obtain alumina particles G. Figure 2 shows an SEM image of the obtained alumina particles G when observed using an SEM.

[0108] <Preparation of Resin Composite> Using the alumina particles E obtained in Example 1 and the alumina particles G obtained in Comparative Example 1, 39 g of alumina particles E or G were mixed with an epoxy mold compound resin containing 4.58 g of epoxy resin, 3.34 g of a polyfunctional phenol compound as a curing agent, and 0.10 g of a phosphorus-based accelerator as a curing accelerator, so that the packing rate was 60 vol%. The mixture was then diluted with 39 g of methyl ethyl ketone and stirred using a mix rotor to produce a varnish with a solid content of 75% by mass. The alumina particles G were wet surface treated with a silane coupling agent before mixing with the resin, then wet crushed, and mixed with pure water and methyl isobutyl ketone to form a slurry. The viscosity of the alumina particle dispersion dispersed in MIBK was measured using a TV-100E viscometer manufactured by Toki Sangyo Co., Ltd., and the slurry of Example 1 had a viscosity of 120 to 150 mPA·s at a rotation speed of 2.5 rpm.

[0109] The obtained varnish was coated onto a release PET film to a thickness of 200 μm and dried at a temperature of 110°C for 10 minutes. The dried resin composition was then pulverized. To form a test composite using the pulverized resin composition, the press pressure was increased to 10 kN while holding the heating temperature at 80°C for 3 minutes in a heated vacuum press. Once 10 kN was reached, the temperature was increased to 160°C at a rate of 20°C / 3 minutes, and when the heating temperature reached 100°C, the press pressure was increased from 10 kN to 40 kN. The heating temperature reached 160°C and was held for 16 minutes to produce a resin composite with a thickness of 1 mm. The resin composite was cured at 175°C for 6 hours to obtain a test composite. The surfaces of test composites prepared using alumina particles E obtained in Example 1 and alumina particles G obtained in Comparative Example 1 were observed using a scanning electron microscope (SEM; Hitachi High-Tech Corporation, product name "SU5000"). When the surface of the test composite prepared using alumina particles E obtained in Example 1 was observed with an SEM, as shown in Figure 3, there was no uneven distribution of resin or voids, and the surface was smooth. On the other hand, when the surface of the test composite prepared using alumina particles G obtained in Comparative Example 1 was observed with an SEM, as shown in Figure 4, uneven distribution of resin and voids were observed.

[0110] <Measurement of Thermal Conductivity> The thermal conductivity was measured using test composites. Thermal conductivity was calculated by the product of thermal diffusivity, low-pressure specific heat capacity, and density. Thermal diffusivity was measured using a xenon flash analyzer (NETZSCH JAPAN Co., Ltd., product name "LFA647 HyperFlash"). Constant-pressure specific heat capacity was calculated from the specific heat capacity of each material and its mixing ratio. Density was measured using an electronic hydrometer (Alpha Mirage Co., Ltd., product name "MDS-3000"). Thermal diffusivity and density were measured at 23°C, and the specific heat capacity at 25°C was used for the constant-pressure specific heat capacity. The thermal conductivity of the test composite made using alumina particles E obtained in Example 1 was 2.1 W / (m·K), and the thermal conductivity of the test composite made using alumina particles G obtained in Comparative Example 1 was 1.6 W / (m·K).

Claims

1. A method for producing alumina particles, comprising: subjecting a mixed liquid containing surface-treated alumina particles, at least partially of which are aggregated, and a dispersion medium to a wet crushing treatment; and subjecting the mixed liquid after the wet crushing treatment to a wet classification treatment.

2. The manufacturing method according to claim 1, wherein the gelatinization rate of the surface-treated alumina particles is 40% or more.

3. The manufacturing method according to claim 1, wherein the surface-treated alumina particles are alumina particles surface-treated with a silane coupling agent.

4. The manufacturing method according to claim 1, wherein the mixed liquid subjected to the wet crushing treatment contains 10% by mass or more of the surface-treated alumina particles based on the total amount of the mixed liquid.

5. The manufacturing method according to claim 1, wherein the wet classification process is a process using a centrifugal separator.

6. The manufacturing method according to claim 1, wherein the wet classification process includes performing a top cut on the surface-treated alumina particles.

7. The manufacturing method according to claim 1, wherein the wet classification process includes removing particles with a particle size of 5 μm or more from the surface-treated alumina particles having a D50 of 0.1 to 10 μm.

8. A method for producing a resin composition, comprising mixing alumina particles obtained by the manufacturing method described in any one of claims 1 to 7 with a resin.

9. The manufacturing method according to claim 8, wherein the resin is a curable resin and the thermal conductivity of the cured product of the resin composition is 0.5 W / (m·K) or more.

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