Alumina powder, uses of same, and method for producing same

Abstract

Provided is an alumina powder which has an α-phase content of 95% or more and has a 100% cumulative particle diameter (D100) of 1-20 µm in a volume-based particle size distribution, wherein: the carbon content of the alumina powder is 0.01-2 mass%; and the electrical conductivity of a dispersion that contains 10 parts by mass of the alumina powder, 20 parts by mass of ethanol, and 70 parts by mass of ion exchanged water is 20 µS / cm or less at 25°C. The alumina powder is produced by subjecting the surfaces of alumina particles to an acid treatment and subsequently coating the surfaces with a silane coupling agent. As a result, the present invention provides: a sealant which has excellent fluidity and excellent thermal conductivity; and an alumina powder which is used for the sealant.

Description

Alumina powder, its uses and manufacturing method

[0001] The present invention relates to an alumina powder and a method for producing the same, a resin composition containing the alumina powder, a sealant made of the resin composition, and a cured product obtained by curing the resin composition.

[0002] In recent years, with the miniaturization and high performance of electronic components, it has become important to dissipate the heat generated by these electronic components to the outside. Therefore, sealants used in electronic components that generate a lot of heat, such as semiconductors, are required to have thermal conductivity in addition to insulation properties. Resin compositions in which alumina (aluminum oxide) particles with good thermal conductivity are dispersed in a resin are widely used as such sealants.

[0003] Patent Document 1 describes a resin composition in which the surfaces of two types of alumina powder, which differ in particle size and roundness, are treated with a silane coupling agent, a titanate coupling agent, or an aluminate coupling agent, and then blended with a resin. The resin composition does not become highly viscous even with a high degree of alumina particle filling, has excellent heat dissipation properties, and is said to be suitable as an encapsulating material for semiconductors.

[0004] Patent Document 2 describes a method for producing a spherical particle material, which includes a first pickling step in which a raw raw particle material mainly composed of alumina is immersed in an acid solution to produce a raw particle material, a melt-spheroidizing step in which the raw particle material is melted and rapidly cooled to produce a coarse spherical particle material, and a second pickling step in which the coarse spherical particle material is immersed in an acid solution to produce a spherical particle material.The spherical particle material thus obtained is dispersed in a resin to produce a thermally conductive sealant, and the two pickling steps reduce the uranium and thorium content and reduce the alpha radiation dose.

[0005] JP 2003-137627 A JP 2021-172546 A

[0006] With the recent trend toward miniaturization in semiconductor packaging technology, it is necessary to use fine alumina particles when filling narrow gaps with sealants. However, as the particle size decreases, the number of interfaces between the particles and the resin increases, which inevitably leads to a decrease in thermal conductivity and fluidity. In the case of sealants made of resin compositions using alumina particles as described in Patent Document 1 and Patent Document 2, the fluidity and thermal conductivity were still insufficient.

[0007] An object of the present invention is to provide an alumina powder that solves the above-mentioned problems and a method for producing the same. Another object of the present invention is to provide a sealant with excellent fluidity, which is made of a resin composition containing the alumina powder and a resin. Another object of the present invention is to provide a cured product of the sealant that has high thermal conductivity.

[0008] The present invention, which has been made to solve the above-mentioned problems, is as follows: [1] An alumina powder having an α-phase content of 95% or more and a cumulative 100% particle size D100 in a volume-based particle size distribution of 1 to 20 μm, wherein the carbon content of the alumina powder is 0.01 to 2 mass%, and the electrical conductivity of a dispersion at 25°C containing 10 parts by mass of the alumina powder, 20 parts by mass of ethanol, and 70 parts by mass of ion-exchanged water is 20 μS / cm or less. [2] The alumina powder according to [1], wherein, when the surface of the alumina powder is analyzed by an X-ray photoelectron spectroscopy (XPS) using Mg-Kα radiation, the mass ratio of silicon, titanium, or zirconium to aluminum is 0.01 to 0.8. [3] The alumina powder according to [1] or [2], wherein the circularity coefficient of the alumina powder is 0.85 to 0.95. [4] The alumina powder according to any one of [1] to [3], wherein the alumina powder has a cumulative 10% particle size D10 of 1.2 μm or less in a volumetric particle size distribution. [5] The alumina powder according to any one of [1] to [4], wherein the alumina powder satisfies any one of the following conditions (1) to (3): (1) The cumulative 100% particle size D100 in a volumetric particle size distribution is 1 μm or more and less than 4 μm, and the tap density is 1.3 to 2.0 g / mL. (2) The cumulative 100% particle size D100 in a volumetric particle size distribution is 4 μm or more and less than 7 μm, and the tap density is 1.7 to 2.4 g / mL. (3) The cumulative 100% particle size D100 in a volumetric particle size distribution is 7 μm or more and less than 10 μm, and the tap density is 2.1 to 2.8 g / mL. [6] A mixture of 75 parts by mass of the alumina powder and 25 parts by mass of bisphenol F type epoxy resin having a viscosity of 3500 mPa s at 25 ° C. is subjected to a shear rate of 100 sec －１The alumina powder according to any one of [1] to [5], having a viscosity of 1000 mPa·s or less at 100°C. [7] The alumina powder according to any one of [1] to [6], wherein a mass of alumina agglomerates that do not pass through a sieve with a mesh size of 45 μm, contained in a mixture of 80 parts by mass of the alumina powder and 20 parts by mass of a bisphenol F epoxy resin having a viscosity of 3500 mPa·s at 25°C, is 0.5 mass% or less relative to the mass of the alumina powder in the mixture. [8] The alumina powder according to any one of [1] to [7], which is used as a filler for a sealant. [9] A resin composition comprising the alumina powder according to any one of [1] to [8] and a resin.

[10] The resin composition according to [9], comprising 50 to 96 mass% of the alumina powder and 4 to 50 mass% of a resin.

[11] A sealant comprising the resin composition according to [9] or

[10] .

[12] A cured product having a thermal conductivity of 1.8 W / m·K or more, obtained by curing the resin composition according to [9] or

[10] .

[13] A method for producing an alumina powder, comprising: an acid treatment step of acid-treating the surfaces of alumina particles; and a surface treatment step of coating the surfaces of the alumina particles after the acid treatment step with at least one coupling agent selected from a silane coupling agent, a titanate coupling agent, a zirconate coupling agent, and an aluminate coupling agent, wherein the obtained alumina powder has an α-phase content of 95% or more and a cumulative 100% particle size D100 in a volume-based particle size distribution of 1 to 20 μm.

[14] The method for producing an alumina powder according to

[13] , wherein, in the acid treatment step, the alumina particles are dispersed in an acidic aqueous solution with a pH of 2 or less.

[15] The method for producing an alumina powder according to

[13] or

[14] , wherein, in the surface treatment step, 0.1 to 2 parts by mass of the coupling agent is added to 100 parts by mass of the alumina particles after the acid treatment and mixed.

[16] A method for producing an alumina powder according to any one of [1] to [8], comprising: an acid treatment step of treating the surfaces of alumina particles with an acid; and a surface treatment step of coating the surfaces of the alumina particles after the acid treatment step with at least one coupling agent selected from a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, and a zirconate coupling agent.

[0009] The sealant of the present invention has excellent fluidity, allowing it to easily penetrate narrow gaps when sealing electronic components such as semiconductor chips, making it easy to handle. Furthermore, the cured product obtained by curing the sealant has excellent thermal conductivity, allowing it to effectively dissipate heat generated by electronic components to the outside. Such sealants and cured products can be obtained by using a resin composition containing the alumina powder of the present invention and a resin. Furthermore, such alumina powder can be produced by the manufacturing method of the present invention.

[0010] 1 is a chart obtained by XPS analysis of the surface of the alumina powder obtained in Example 1. An Al peak (near 77 eV) and a Si peak (near 105 eV) were observed. FIG. 2 is a chart obtained by XPS analysis of the surface of the alumina powder used in Comparative Example 3. An Al peak (near 77 eV) was observed, but no Si peak (near 105 eV) was observed.

[0011] The alumina powder of the present invention has an α-phase content of 95% or more and a cumulative 100% particle size D100 in a volume-based particle size distribution of 1 to 20 μm, and the carbon content of the alumina powder is 0.01 to 2 mass %, and a dispersion containing 10 parts by mass of the alumina powder, 20 parts by mass of ethanol, and 70 parts by mass of ion-exchanged water at 25°C has an electrical conductivity of 20 μS / cm or less. Because the alumina powder contains a predetermined amount of carbon and the dispersion containing the alumina powder has low electrical conductivity, a resin composition containing the alumina powder and a resin has excellent fluidity and a cured product obtained by curing the resin composition has high thermal conductivity. The present invention will be described in detail below.

[0012] The alumina powder of the present invention has an α-phase content of 95% or more. A high α-phase content improves thermal conductivity. The α-phase content is preferably 97% or more, more preferably 99% or more, and even more preferably 100%. The α-phase content can be measured using an X-ray diffraction device. The α-phase has a diffraction peak for the (1 1 3) plane at 2θ = 43.3°, the δ-phase has a diffraction peak for the (4 0 12) plane at 2θ = 66.9°, and the γ-phase has a diffraction peak for the (4 4 0) plane at 2θ = 67.3°, all of which are peaks with the maximum intensity for each phase. The α-phase peak intensity divided by the sum of the peak intensities for the α-phase, δ-phase, and γ-phase is calculated as [α / (α + δ + γ)] × 100, which is the α-phase content (%). In the measurement method described in the Examples, if the α-phase is observed but no diffraction peaks of δ- or γ-phase crystals are observed, the α-phase content is 100%. Here, "no diffraction peaks are observed" means that no diffraction peaks are observed when measured at a resolution equivalent to the measurement conditions described in the Examples. To obtain an alumina powder having such a crystal structure, α-alumina powder may be used as a raw material and subjected to the acid treatment step and surface treatment step of the present invention.

[0013] The alumina powder of the present invention preferably has a circularity coefficient of 0.85 or more. A circularity coefficient of 0.85 or more facilitates the filling of alumina particles into a resin composition, resulting in a resin composition with good thermal conductivity and improved fluidity. The circularity coefficient is more preferably 0.86 or more, and even more preferably 0.87 or more. On the other hand, the circularity coefficient of the alumina powder of the present invention may be preferably 0.95 or less. A circularity coefficient exceeding 0.95 may reduce the contact area between particles in the resin, resulting in reduced thermal conductivity. Furthermore, alumina particles produced by methods such as the flame fusion method, in which alumina droplets melted in a high-temperature gas are rapidly cooled, tend to be spherical with a circularity coefficient exceeding 0.95. However, rapid cooling can easily result in crystal forms with poor thermal conductivity, such as the δ phase or γ phase. The circularity coefficient is more preferably 0.94 or less, and even more preferably 0.93 or less. From the viewpoint of the balance between packing property, fluidity, and thermal conductivity, it is preferable that the circularity coefficient of the alumina powder of the present invention is 0.85 to 0.95. Here, the circularity coefficient is calculated by calculating the projected area (S) and projected perimeter (L) of a particle from an image of a powder sample, and then using the following formula: Circularity coefficient = 4πS / L ２

[0014] The alumina powder of the present invention has a cumulative 100% particle size D100 in the volume-based particle size distribution of 1 to 20 μm. With the recent trend toward miniaturization of electronic components, the inclusion of coarse particles in the sealant results in insufficient filling of narrow gaps with the sealant. Therefore, D100 is preferably 15 μm or less, more preferably 10 μm or less. When sealing electronic components with particularly narrow gaps, D100 may be 8 μm or less, or even 6 μm or less. On the other hand, if the coarse particles are reduced in size to a value less than 1 μm, the alumina particles will be too small, resulting in a decrease in interparticle heat transfer efficiency and a decrease in the thermal conductivity of the sealant. Furthermore, the viscosity of the sealant will be too high, making filling difficult. D100 may be 1.5 μm or more, or even 2 μm or more.

[0015] The alumina powder of the present invention preferably has a cumulative 50% particle size D50 in the volume-based particle size distribution of 0.2 to 10 μm. Having an average particle size in this range allows for a sealant with an excellent balance between thermal conductivity and fluidity. D50 is more preferably 8 μm or less. When sealing electronic components with particularly narrow gaps, D50 may be 5 μm or less, or even 3 μm or less. On the other hand, if the average particle size is reduced to less than 0.2 μm, the alumina particles will be too small, reducing the interparticle heat transfer efficiency and reducing the thermal conductivity of the sealant, while the viscosity of the sealant will be too high, making filling difficult. D50 may be 0.3 μm or more, 0.5 μm or more, or even 1 μm or more.

[0016] The alumina powder of the present invention preferably has a cumulative 10% particle size D10 of 1.2 μm or less in the volume-based particle size distribution. By including a certain amount of particles with such small particle sizes, it becomes easier to fill the resin composition with alumina particles, resulting in a resin composition with good thermal conductivity. The particle size D10 may be 1.0 μm or less. While the lower limit of the particle size D10 is not particularly limited, from the viewpoint of ensuring flowability and preventing aggregation, the particle size D10 is preferably 0.1 μm or more.

[0017] The cumulative 10% particle diameter D10, cumulative 50% particle diameter D50, cumulative 90% particle diameter D90, and cumulative 100% particle diameter D100 in the volume-based particle size distribution can be measured in the liquid phase using a laser diffraction particle size analyzer as described in the Examples. By adjusting the D10, D50, D90, and D100 values, the performance of the resulting resin composition can be adjusted. For example, even if powders have similar D50 values, if the difference between the D10 and D90 values ​​is large, i.e., if the particle size distribution is wide, the maximum loading amount of alumina particles in the resin composition may increase, resulting in improved thermal conductivity.

[0018] The specific surface area of ​​the alumina powder of the present invention is 10 m from the viewpoint of improving dispersibility in resin. ２ / g or less, and ２ / g or less is more preferable, and 5m ２ On the other hand, if the specific surface area is too small, the particle size of the alumina powder may become too large. ２ / g or more is preferred.

[0019] From the viewpoint of improving the fillability into resin, the tap density of the alumina powder of the present invention is preferably 1.0 g / mL or more, more preferably 1.3 g / mL or more, and even more preferably 1.5 g / mL or more. When it is particularly desired to increase the maximum fill amount into resin, the tap density may be 1.6 g / mL or more, 1.7 g / mL or more, or 1.8 g / mL or more. On the other hand, the tap density is usually 2.5 g / mL or less.

[0020] The alumina powder of the present invention preferably satisfies any one of the following conditions (1) to (3): (1) The particle diameter D100 of 100% cumulative volumetric particle size distribution is 1 μm or more and less than 4 μm, and the tap density is 1.3 to 2.0 g / mL. (2) The particle diameter D100 of 100% cumulative volumetric particle size distribution is 4 μm or more and less than 7 μm, and the tap density is 1.7 to 2.4 g / mL. (3) The particle diameter D100 of 100% cumulative volumetric particle size distribution is 7 μm or more and less than 10 μm, and the tap density is 2.1 to 2.8 g / mL. Generally, the smaller the particle diameter D100, the lower the tap density tends to be. Therefore, the above conditions (1) to (3) specify desirable tap density ranges for each particle diameter within a given range. In condition (1), the tap density is more preferably 1.5 to 1.9 g / mL. In condition (2), the tap density is more preferably 1.8 to 2.3 g / mL, and in condition (3), the tap density is more preferably 2.2 to 2.7 g / mL.

[0021] The carbon content of the alumina powder of the present invention is 0.01 to 2% by mass. The presence of organic groups on the surface of the alumina powder of the present invention improves its affinity with resins and improves the dispersibility of the alumina powder in resins. A carbon content of 0.01% by mass or more effectively improves dispersibility. The carbon content is preferably 0.02% by mass or more, and more preferably 0.05% by mass or more. On the other hand, if the carbon content is too high, a condensation reaction occurs between the surface treatment agents, increasing the viscosity of the resin composition containing the alumina powder. The carbon content is 2% by mass or less, preferably 1% by mass or less, and more preferably 0.5% by mass or less. The carbon content of the alumina powder can be measured using an organic elemental analyzer. The carbon content is calculated by completely combusting organic matter bonded to the surfaces of the alumina particles and quantifying the carbon dioxide generated using this device.

[0022] When the surface of the alumina powder of the present invention is analyzed using an X-ray photoelectron spectrometer (XPS) with Mg-Kα radiation, the mass ratio of silicon, titanium, or zirconium to aluminum is preferably 0.01 to 0.8. These elements can be bonded to the surface of the alumina particles as silane coupling agents, titanate coupling agents, or zirconate coupling agents to introduce organic groups. By maintaining this mass ratio at a certain value or higher, organic groups are effectively introduced, improving the dispersibility of the alumina powder in resins. Here, Mg-Kα radiation (1253.6 eV) is a relatively low-energy X-ray that penetrates only a few nanometers from the surface of a material, allowing the content of elements at the particle surface to be measured. The mass ratio is preferably 0.01 or greater, more preferably 0.02 or greater, and even more preferably 0.03 or greater. On the other hand, if the mass ratio is too large, condensation reactions occur between the coupling agents, increasing the viscosity of resin compositions containing the alumina powder. The mass ratio is preferably 0.8 or less, more preferably 0.4 or less, and even more preferably 0.2 or less. Among these elements, it is preferable to contain silicon derived from a silane coupling agent. That is, it is preferable that the mass ratio (Si / Al) obtained by the above analysis is a value within the above range.

[0023] From the viewpoint of preventing corrosion of electronic components when a resin composition containing the alumina powder of the present invention is used as a sealant, the sodium content of the alumina powder is preferably 10 ppm or less, more preferably 5 ppm or less, and even more preferably 2.5 ppm or less. The contents of potassium, magnesium, and calcium are also preferably 10 ppm or less, more preferably 5 ppm or less, respectively. These elements may also promote corrosion of electronic components. The contents of these cations can be measured by dispersing the alumina powder in an alcohol aqueous solution and heating it under high temperature and pressure to extract these cations, followed by ICP atomic emission spectroscopy.

[0024] Similarly, from the viewpoint of preventing corrosion of electronic components when a resin composition containing the alumina powder of the present invention is used as a sealant, the chlorine content of the alumina powder is preferably 10 ppm or less, more preferably 5 ppm or less, and even more preferably 2.5 ppm or less.

[0025] Examples of elements that may accelerate corrosion of electronic components include sodium and chlorine. Therefore, the sodium content of the alumina powder of the present invention is preferably 10 ppm or less and the chlorine content is preferably 10 ppm or less. In this case, the sodium content is more preferably 5 ppm or less, and even more preferably 2.5 ppm or less. Furthermore, the chlorine content is more preferably 5 ppm or less, and even more preferably 3 ppm or less.

[0026] If a sealant made of a resin composition containing alumina powder contains uranium, the uranium may become a source of alpha rays, potentially causing soft errors in the encapsulated semiconductor memory. Therefore, the uranium content of the alumina powder of the present invention is preferably 10 ppb or less, more preferably 8 ppb or less, even more preferably 5 ppb or less, and particularly preferably 3 ppb or less. Such trace amounts of uranium content can be measured using an inductively coupled plasma mass spectrometer (ICP-MS).

[0027] A dispersion at 25°C containing 10 parts by mass of the alumina powder of the present invention, 20 parts by mass of ethanol, and 70 parts by mass of ion-exchanged water has an electrical conductivity of 20 μS / cm or less. Alumina powder with low electrical conductivity in this dispersion has fewer ions eluted from the powder into an aqueous solvent. Therefore, when a resin composition containing the alumina powder of the present invention is used as a sealant, corrosion of electronic components can be suppressed. The electrical conductivity is preferably 15 μS / cm or less, more preferably 10 μS / cm or less, and even more preferably 5 μS / cm or less. Here, an aqueous solution containing ethanol is used as the dispersion medium rather than water because the alumina powder of the present invention, which has hydrophobic groups on its surface, does not disperse in water due to poor wetting. However, an aqueous ethanol solution allows the alumina powder to be uniformly dispersed in the dispersion.

[0028] The method for producing an alumina powder of the present invention will be described below. The method for producing an alumina powder of the present invention includes an acid treatment step of treating the surfaces of alumina particles with an acid, and a surface treatment step of coating the surfaces of the alumina particles after the acid treatment step with at least one coupling agent selected from a silane coupling agent, a titanate coupling agent, a zirconate coupling agent, and an aluminate coupling agent. The alumina powder obtained has an α-phase content of 95% or more and a cumulative 100% particle size D100 in the volume-based particle size distribution of 1 to 20 μm. That is, in this production method, the acid treatment step and the surface treatment step are carried out in this order on a raw material alumina powder.

[0029] The alumina powder used as the raw material is not particularly limited, and can be any alumina powder with an α-phase content of 95% or more and a cumulative 100% particle size D100 in the volumetric particle size distribution of 1 to 20 μm. Furthermore, the cumulative 50% particle size D50 in the volumetric particle size distribution is preferably 0.2 to 10 μm. The crystal morphology and particle size distribution of the alumina powder generally do not change significantly depending on the acid treatment process and surface treatment process. The method for producing the raw alumina powder is not particularly limited, and known methods can be used, such as heating aluminum hydroxide or aluminum alkoxide to obtain aluminum oxide particles. A particularly suitable method is, for example, the method described in JP-A-7-206432, which involves calcining transition alumina or an alumina compound in an atmosphere containing hydrogen halide gas or halogen gas to obtain α-alumina powder with controlled particle size and particle size distribution. In the examples described below, α-alumina powder produced according to the method described in JP-A-7-206432 was used.

[0030] In the manufacturing method of the present invention, the raw alumina powder is subjected to an acid treatment step. In this acid treatment step, the alumina particles are dispersed in an acidic aqueous solution with a pH of 2 or less. This allows the surface of the alumina particles, particularly the surface of α-alumina crystals, to be modified, allowing a coupling agent to be uniformly and sufficiently attached in the subsequent surface treatment step. Specifically, it is believed that the acid treatment increases the number of hydroxyl groups on the alumina particle surface. This also allows impurity elements, which are often contained as fine particles, to be removed.

[0031] Examples of acids contained in the acidic aqueous solution used in the acid treatment step include nitric acid, sulfuric acid, and hydrochloric acid. Among these, nitric acid is preferred. The pH of the acidic aqueous solution is 2 or less, preferably 1.5 or less, and more preferably 1 or less. The temperature of the acidic aqueous solution in the acid treatment step is not particularly limited, but is preferably 20°C or higher, more preferably 40°C or higher, and even more preferably 60°C or higher. By heating the acidic aqueous solution, the surface of the alumina particles can be efficiently modified. From a safety standpoint, the temperature of the acidic aqueous solution is usually 150°C or lower. The time period for the acid treatment step is not particularly limited, but is preferably 10 minutes or more and 1 day or less. In the acid treatment step, it is preferred to stir the acidic aqueous solution in which the alumina particles are dispersed.

[0032] The alumina particles treated with acid in the acid treatment step are then neutralized as necessary and washed. The alkali used for neutralization is not particularly limited, but volatile ammonia is preferably used. In the washing step, the particles are repeatedly washed with water to thoroughly remove ionic components. The solid matter obtained by filtration is then thoroughly dried to obtain acid-treated alumina powder. The drying temperature is not particularly limited, but is preferably 50°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher. Thorough drying can prevent the alkoxide coupling agent from being hydrolyzed and consumed by moisture. The drying temperature is usually 200°C or lower. If the drying temperature is too high, strong coagulation between the alumina particles due to hydrogen bonding may occur, preventing uniform surface treatment.

[0033] After the acid treatment step, the alumina particles are typically washed and dried before the surface treatment step. In the surface treatment step, the surfaces of the alumina particles are coated with at least one coupling agent selected from silane coupling agents, titanate coupling agents, zirconate coupling agents, and aluminate coupling agents. Among these coupling agents, silane coupling agents are preferred. The silane coupling agent is not particularly limited, as long as it has multiple alkoxy groups, such as methoxy or ethoxy groups, that can react with hydroxyl groups on the alumina surface, and an organic group containing a functional group capable of chemically bonding with a resin. Examples of such functional groups include amino groups, epoxy groups, vinyl groups, methacrylic groups, and mercapto groups, and are selected based on the resin to be mixed. For example, when mixing with an epoxy resin, it is preferable that an organic group containing an amino group that can react with an epoxy group be bonded to a silicon atom. The number of carbon atoms in the organic group is typically 2 to 15.

[0034] In the surface treatment step, it is preferable to add and mix 0.1 to 2 parts by mass of a coupling agent per 100 parts by mass of the acid-treated alumina particles. By blending 0.1 parts by mass or more of the coupling agent per 100 parts by mass of the alumina particles, the dispersibility of the alumina powder in the resin is improved. The amount of the coupling agent blended is more preferably 0.15 parts by mass or more, and even more preferably 0.2 parts by mass or more. On the other hand, if the amount of the coupling agent blended is too high, a condensation reaction occurs between the coupling agents, which increases the viscosity of the resin composition containing the alumina powder. The amount of the coupling agent blended is more preferably 1.5 parts by mass or less, and even more preferably 1 part by mass or less.

[0035] The treatment method in the surface treatment step is not particularly limited as long as it can coat the surfaces of the alumina particles with a coupling agent. When mixing the alumina particles with the coupling agent, the coupling agent can be diluted with an organic solvent such as alcohol before mixing with the alumina particles, or it can be mixed with the alumina particles without dilution. When using an organic solvent, the alumina particles, the coupling agent, and the organic solvent can be mixed to obtain a dispersion, and the organic solvent can then be removed to obtain alumina powder coated with the coupling agent. In this case, the coupling agent can be added to a dispersion in which the alumina particles are dispersed in an organic solvent and mixed, or the alumina particles can be dispersed in a mixture of an organic solvent and a silane coupling agent to obtain a dispersion. The device used to mix the alumina particles with the coupling agent is not particularly limited, and any mixing device capable of sufficiently stirring the powder and dispersion, such as a Henschel mixer, ball mill, tumbler mixer, tabletop blender, disperser mixer, or homogenizer, can be used. The dispersion in this case includes a slurry-like dispersion with a high powder content. The organic solvent to be used is not particularly limited, but is preferably a polar solvent such as alcohol or ketone in consideration of affinity with the coupling agent and alumina powder, and is preferably one having a boiling point of 120° C. or less under atmospheric pressure in consideration of volatility. Two or more types of organic solvents may be used.

[0036] The alumina powder of the present invention, which has been surface-treated as described above, has organic groups on the particle surface, improving its affinity for organic substances. Therefore, it has excellent dispersibility when mixed with various organic substances. In particular, it has excellent dispersibility when mixed with resins, so a preferred embodiment is a resin composition containing the alumina powder of the present invention and a resin.

[0037] The resin to be mixed with the alumina powder of the present invention is not particularly limited. Depending on the application, epoxy resin, silicone resin, phenol resin, melamine resin, urea resin, unsaturated polyester, fluororesin, polyamide, polyimide, polyamideimide, polyetherimide, polyester, polyphenylene ether, polyphenylene sulfide, wholly aromatic polyester, polysulfone, liquid crystal polymer, polyethersulfone, polycarbonate, maleimide-modified resin, ABS resin, AAS (acrylonitrile-acrylic rubber-styrene) resin, AES (acrylonitrile-ethylene-propylene-diene rubber-styrene) resin, etc. are used. Among these, when used as a sealant, thermosetting resins such as epoxy resin and phenol resin are preferred, and epoxy resin is particularly preferred.

[0038] While the ratio of alumina powder to resin in the resin composition of the present invention is not particularly limited, a resin composition containing 50 to 96% by mass of alumina powder and 4 to 50% by mass of resin is preferred. In resin compositions containing a large amount of alumina powder, the use of the highly dispersible alumina powder of the present invention is highly significant. It is particularly suitable for applications that utilize the high thermal conductivity of α-phase alumina powder. The content of alumina powder in the resin composition is preferably 50% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and particularly preferably 82% by mass or more. In this case, the content of resin is preferably 50% by mass or less, more preferably 25% by mass or less, even more preferably 20% by mass or less, and particularly preferably 18% by mass or less. On the other hand, in order to obtain a uniform mixture of alumina powder and resin and a cured product with a certain strength, the content of alumina powder in the resin composition is preferably 96% by mass or less, more preferably 95% by mass or less. In this case, the content of resin is preferably 4% by mass or more, more preferably 5% by mass or more. Here, the resin content is calculated based on the mass including all organic components that are incorporated into the cured resin, such as the curing agent, curing accelerator, and mold release agent.

[0039] A mixture of 75 parts by mass of the alumina powder of the present invention and 25 parts by mass of bisphenol F type epoxy resin having a viscosity of 3500 mPa·s at 25°C was subjected to a shear rate of 100 sec －１ Preferably, the viscosity at 100°C is 1000 mPa·s or less. The low viscosity at high shear rates allows the resin composition containing alumina powder and resin to quickly penetrate narrow gaps when used as a sealant. The viscosity is more preferably 750 mPa·s or less, and even more preferably 500 mPa·s or less. The viscosity is usually 100 mPa·s or more.

[0040] In a mixture of 80 parts by mass of the alumina powder of the present invention and 20 parts by mass of a bisphenol F epoxy resin having a viscosity of 3,500 mPa·s at 25°C, the mass of alumina agglomerates that do not pass through a 45 μm mesh sieve is preferably 0.5% by mass or less relative to the mass of the alumina powder in the mixture. Use of the alumina powder of the present invention suppresses the formation of alumina agglomerates in the resin, thereby improving the fluidity of the resin composition, preventing clogging, and suppressing poor appearance of the cured product. The proportion of alumina agglomerates may be 0.4% by mass or less, 0.3% by mass or less, or even 0.2% by mass or less. Since aggregation is particularly likely when a large amount of fine particles are included, it is particularly important to reduce the proportion of alumina agglomerates when the cumulative 10% particle diameter D10 in the volume-based particle size distribution of the alumina powder is 1.2 μm or less, or 1.0 μm or less. Specifically, the 45 μm sieve residue is calculated by using Epiclon 830 manufactured by DIC Corporation as a bisphenol F type epoxy resin, kneading the resin composition in a rotary mixer at 1600 rpm for 2 minutes, then degassing the resin composition at 200 rpm for 2 minutes and 1600 rpm for 4 minutes, pouring acetone onto the resin composition to remove the resin and alumina particles that pass through the sieve, measuring the mass of the particles remaining on the sieve, and using the following formula: 45 μm sieve residue (mass %) = [mass of particles remaining on the sieve / (mass of resin composition×0.8)]×100

[0041] A suitable application of the resin composition of the present invention is as a sealant. That is, a suitable application of the alumina powder of the present invention is as a filler for sealants. In such applications, it is important to efficiently dissipate heat generated from electronic components to the outside. In particular, the sealant of the present invention is suitable for sealing electronic components that dissipate large amounts of heat from a small area, such as semiconductors. In such applications, when high heat dissipation performance is required, the content of the alumina powder in the resin composition may be 85% by mass or more, 88% by mass or more, 90% by mass or more, or 92% by mass or more. In this case, the content of the resin may be 15% by mass or less, 12% by mass or less, 10% by mass or less, or 8% by mass or less.

[0042] A cured product can be obtained by curing the resin composition of the present invention. When a thermoplastic resin is used, a cured product can be obtained simply by cooling after melt molding. On the other hand, in the case of a thermosetting resin, a curing agent and other additives are added and then the resin is cured by heating. The heating temperature varies depending on the resin, and may be 50°C or higher, 100°C or higher, or 150°C or higher. The heating temperature is usually 300°C or lower. It is also preferable to apply pressure together with heating.

[0043] The thermal conductivity of the cured product thus obtained is preferably 1.8 W / m K or more, more preferably 2.4 W / m K or more, even more preferably 2.8 W / m K or more, and particularly preferably 3 W / m K or more. By sealing with a cured product having such high thermal conductivity, heat generated by the electronic component can be effectively released to the outside.

[0044] The sealant of the present invention is used to seal various electronic components. Because it has high fluidity and excellent heat dissipation, it is particularly suitable for sealing semiconductors. In recent semiconductor packages, chips are arranged in smaller spaces and lead wiring is arranged at finer pitches, increasing the need to fill narrow gaps with sealant. Therefore, there is a demand for sealants that use fine-particle alumina powder yet have excellent fluidity and heat dissipation properties, and the sealant of the present invention is ideal for such applications.

[0045] The present invention will be described in more detail below with reference to examples. The analytical and evaluation methods used in these examples are as follows.

[0046] (1) Particle size distribution Measurement of particle size distribution on a volume basis using a laser diffraction particle size distribution analyzer (Microtrac MT3000, manufactured by Nikkiso Co., Ltd.), the particle diameter at 10% cumulative was D10, the particle diameter at 50% cumulative was D50, the particle diameter at 90% cumulative was D90, and the particle diameter at 100% cumulative was D100. 0.08 parts by mass of the powder obtained in the examples and comparative examples was mixed with 10.3 parts by mass of a 30% by volume aqueous isopropyl alcohol solution and irradiated with ultrasound for 20 minutes to disperse alumina particles. The particle size distribution was measured in a 30% by volume aqueous isopropyl alcohol solution. At this time, the refractive index of the isopropyl alcohol solution was set to 1.358, the refractive index of the alumina particles was set to 1.77, and the particle shape was calculated as non-spherical.

[0047] (2) Electrical Conductivity 10 parts by mass of a powder sample and 20 parts by mass of ethanol were weighed and stirred in a resin container, and then 70 parts by mass of ion-exchanged water was added and stirred to prepare a suspension. The electrical conductivity of the resulting suspension was measured using an EC electrode (3551-10D) of a pH meter (LAQUA act, D-210C, manufactured by HORIBA, Ltd.).

[0048] (3) Carbon Content The carbon (C) content of the powder was measured using an organic elemental analyzer (Microcoder JM1000CN, manufactured by J Science Lab Co., Ltd.) using 5 mg, 10 mg, 15 mg, and 20 mg of hippuric acid, a standard sample with a known C content. A calibration curve of the detected C value and the C content was created from the measurement results, and the C content (% by mass) was calculated by applying the detected C value obtained when measuring the powder samples obtained in the Examples and Comparative Examples to the calibration curve. Each powder was weighed out to 1500 mg ± 500 mg so that it fell within the range of the calibration curve.

[0049] (4) Cation Content 5 g of the powder samples obtained in the Examples and Comparative Examples, 10 g of ethanol, and 35 g of ion-exchanged water were placed in a 100 mL sealed pressure-resistant container made of polytetrafluoroethylene, and heat-treated in a sealed state at 120°C for 20 hours. After cooling, the solution was filtered through a membrane filter with a pore size of 0.1 μm, and the Na content in the filtrate was measured. ＋ , Ca ２＋ , K. ＋ and Mg ２＋ was measured by ICP atomic emission spectroscopy using a plasma emission spectrometer "SPECTRO ARCOS" manufactured by Hitachi High-Tech Science Corporation. The same analysis was also carried out for the comparative example in which the surface was treated with a silane coupling agent. The comparative example in which the surface was not treated with a silane coupling agent was analyzed in the same manner, except that 5 g of the powder sample and 50 g of ion-exchanged water were mixed.

[0050] (5) Chlorine Content The powder samples obtained in the examples and comparative examples were subjected to a combustion decomposition process in a combustion decomposition apparatus AQF-2100H manufactured by Nitto Seiko Analytech Co., Ltd. under the conditions of an Ar gas flow rate of 200 mL / min and O ２The gas flow rate was set to 400 mL / min, the heater inlet temperature was set to 900°C, and the outlet temperature was set to 1000°C, allowing for complete combustion. The gas generated during powder combustion was absorbed with an absorbent, and 25 μL of the absorbent was introduced into an ion chromatograph (Thermo Fisher Scientific, Dionex Integrion HPIC) to obtain a chromatogram using an electrical conductivity detector. The Cl content was calculated from the obtained chromatogram using a calibration curve method. The measurement conditions were as follows: Separation column: Dionex IonPac AS18-Fast (4 × 150 mm); Guard column: Dionex IonPac AG18-Fast (4 × 30 mm); Absorbent: Ultrapure water; Eluent: KOH (60 mM); Flow rate: 1.0 mL / min; Detector and column temperature: 35°C; Suppressor: ADRS-600.

[0051] (6) Uranium Content The powder samples obtained in the Examples and Comparative Examples were dissolved using sulfuric acid, and the uranium content was measured using an inductively coupled plasma mass spectrometer (ICP-MS: Agilent 8900 manufactured by Agilent Technologies).

[0052] (7) Tap Density The powder samples obtained in the examples and comparative examples were filled into a 20 mL measuring cylinder and tapped 200 times using a powder density measuring device (TAPDENSER, KYT-4000, manufactured by Seishin Enterprise Co., Ltd.). The filled volume after tapping was read, and the tap density was calculated from this volume and the mass of the filled powder sample.

[0053] (8) XPS Surface Element Analysis Using an X-ray photoelectron spectroscopy analyzer (XPS: Shimadzu Corporation, ESCA-3400), the powder was filled into a cup-type sample holder, the surface element ratio was measured, and the mass ratio of silicon to aluminum (Si / Al) on the particle surface was calculated. The measurement conditions were as follows. Note that in all of the examples and comparative examples of the present invention, neither the titanium peak (near 458 to 466 eV) nor the zirconium peak (near 178 to 182 eV) was observed. (Measurement conditions) X-ray: Mg-Kα ray Filament voltage-current: 12 kV-15 mA Degree of vacuum: 1.0 x 10 －６Less than Pa Measurement range: 500 to 50 eV Number of times of accumulation: 3

[0054] (9) Specific Surface Area The specific surface areas of the powder samples obtained in the examples and comparative examples were measured by the BET single-point method using a fully automatic specific surface area measuring device (Macsorb HM, model-1208, manufactured by Mountec Co., Ltd.) The measurement was performed after degassing in a nitrogen gas atmosphere at 150°C for 20 minutes.

[0055] (10) Circularity Coefficient Images of the powder samples obtained in the Examples and Comparative Examples were taken using a scanning electron microscope (SEM: S-4800, manufactured by Hitachi High-Technologies Corporation), and the projected area (S) and projected perimeter (L) of the particles were calculated using an image analyzer (Mac-View Ver. 4, manufactured by Mountec Co., Ltd.), and the circularity coefficient was calculated using the following formula. The circularity coefficient was calculated for 200 particles to obtain an arithmetic average value. Circularity coefficient = 4πS / L ２

[0056] (11) α-phase content Using an X-ray diffractometer (EMPYREA, manufactured by PANalytical), powder samples of the examples and comparative examples were measured using Cu-Ka radiation at an X-ray output of 45 kV, 40 mA, a step interval of 0.01313 °, a measurement width of 5 to 110 °, and a scan speed of 0.164 ° / sec. Peak fitting was performed using analysis software (HighScore Plus, manufactured by PANalytical). From the obtained peaks, the α-phase was determined at 2θ = 43.3 °, the δ-phase was determined at 66.9 °, and the γ-phase was determined at 67.3 °. The peak intensity of the α-phase was calculated by dividing the peak intensity of the α-phase, δ-phase, and γ-phase by the sum of the peak intensities, and the resulting number was multiplied by 100 to determine the α-phase content (%).

[0057] (12) Viscosity of resin composition (100 ° C) 75 parts by mass of the powder obtained in the examples and comparative examples and 25 parts by mass of bisphenol F type epoxy resin (Epiclon 830, viscosity at 25 ° C. 3500 mPa s, manufactured by DIC Corporation) were mixed in advance in an ointment jar and kneaded for 2 minutes at 1600 rpm for rotation and revolution using a rotary mixer (Awatori Rentaro, ARE-400TWIN, manufactured by Thinky Corporation), and then degassed for 4 minutes at 200 rpm and 1600 rpm for revolution. The viscosity of the resin composition was measured using a viscoelasticity measuring device (HAAKE MARS60, manufactured by Thermo Fisher Scientific Co., Ltd.). The measurement conditions were as follows: a φ35 mm titanium metal parallel plate, a gap of 0.3 mm, and a shear rate of 100 / s. The viscosity of the resin composition was measured at 100 ° C.

[0058] (13) Maximum Filling Amount 66 parts by mass of biphenyl-type epoxy resin (YX4000H, manufactured by Mitsubishi Chemical Corporation), 33 parts by mass of phenol novolac curing agent (PSM-4261, manufactured by Gun-ei Chemical Industry Co., Ltd.), 0.5 parts by mass of curing accelerator (triphenylphosphine), and 0.5 parts by mass of release agent (carnauba wax) were added to the powders obtained in the Examples and Comparative Examples in amounts varying from 400 to 1900 parts by mass and premixed for 5 minutes using a mortar. The mixture obtained by premixing was kneaded in a two-roll mill (manufactured by Irie Iron Works) at a roll temperature of 100°C and through two rolls rotating at speeds of 16 rpm and 21 rpm (gap 0.3 mm) to disperse the alumina particles in the resin. After 3 minutes, the amount of alumina particles blended when the entire mixture was uniform and smoothly flowing and the highest filler addition amount was taken as the maximum filling amount (% by mass).

[0059] (14) Thermal Conductivity of Cured Product According to (13) above, the resin composition obtained by kneading with the maximum filling amount was pulverized in an agate mortar, filled into a φ10 mm mold, and then pressurized and heated at 20 kN-180°C for 3 minutes to cure the resin composition, which was then machined to obtain a disk-shaped measurement sample with a diameter of 10 mm and a thickness of 500±10 μm. The thermal diffusion coefficient, specific heat, and density of the sample were measured, and the thermal conductivity (W / m·K) was calculated using the following formula. Here, the thermal diffusion coefficient (m ２The specific heat (W s / kg K) was measured using a differential scanning calorimeter (DSC 7020, Hitachi High-Tech Science Corporation). ３ The thermal conductivity (W / m·K) was calculated by measuring the volume and mass of the resin composition.

[0060] (15) Viscosity of Resin Composition (25°C) 73 parts by mass of the powders obtained in the Examples and Comparative Examples, 19 parts by mass of bisphenol F epoxy resin (YDF-8170C, manufactured by Nippon Steel Chemical & Material Co., Ltd.), and 8 parts by mass of an amine-based curing agent (KAYAHARD A-A, manufactured by Nippon Kayaku Co., Ltd.) were premixed in an ointment jar and kneaded for 2 minutes at 1600 rpm rotation and revolution for each in a rotary mixer (Awatori Rentaro, ARE-400TWIN, manufactured by Thinky Corporation), followed by degassing and premixing for 4 minutes at 200 rpm rotation and 1600 rpm revolution. The resulting mixture was kneaded for 3 minutes in a three-roll mill (BR-100VIII, manufactured by AIMEX) at a finishing roll rotation speed of 160 rpm, a gap of 0.01 mm, and room temperature. The viscosity of the resulting resin composition was measured using a viscoelasticity measuring device (HAAKE MARS60, manufactured by Thermo Fisher Scientific Co., Ltd.) The measurement conditions were as follows: using titanium metal parallel plates having a diameter of 35 mm, the viscosity of the resin composition was measured at 25°C under a gap of 0.3 mm and a shear rate of 20 / sec.

[0061] (16) 45 μm sieve residue in liquid epoxy resin composition 80 parts by mass of the powder obtained in the Examples and Comparative Examples and 20 parts by mass of bisphenol F-type epoxy resin (Epiclon 830, manufactured by DIC Corporation) were pre-mixed in an ointment jar and kneaded for 2 minutes at 1600 rpm rotation and revolution using a rotary and revolving mixer (Awatori Rentaro, ARE-400TWIN, manufactured by Thinky Corporation), followed by degassing for 4 minutes at 200 rpm rotation and 1600 rpm revolution. 2.5 g of the resulting resin composition was placed on a 45 μm mesh sieve, and 300 mL of acetone was poured onto it to remove resin and alumina particles that passed through the sieve. The mass of the particles remaining on the sieve was measured, and the 45 μm sieve residue was calculated using the following formula: 45 μm sieve residue (mass %)=[mass of particles remaining on the sieve / (mass of resin composition×0.8)]×100

[0062] (17) 75 μm sieve residue in solid epoxy resin composition: 88 parts by mass of the powder obtained in the Examples and Comparative Examples, 7.92 parts by mass of biphenyl-type epoxy resin (YX4000H, manufactured by Mitsubishi Chemical Corporation), 3.96 parts by mass of phenol novolac curing agent (PSM-4261, manufactured by Gun-ei Chemical Industry Co., Ltd.), 0.06 parts by mass of curing accelerator (triphenylphosphine), and 0.06 parts by mass of release agent (carnauba wax) were premixed in a mortar for 5 minutes. The premixed mixture was kneaded for 3 minutes in a two-roll mill (manufactured by Irie Iron Works) at a roll temperature of 100°C by passing through two rolls (gap 0.3 mm) rotating at 16 rpm and 21 rpm, respectively, to disperse the alumina particles in the resin. The resulting resin composition was cooled and pulverized at room temperature. 150 g of the pulverized material and 500 mL of acetone were placed in a 1-L container and shaken for 10 minutes. The shaken liquid was passed through a sieve with 75 μm openings to remove resin and alumina particles that passed through the sieve. The mass of the particles remaining on the sieve was measured, and the 75 μm sieve residue was calculated using the following formula: 75 μm sieve residue (mass%) = [mass of particles remaining on the sieve / (mass of resin composition × 0.88)] × 100

[0063] Example 1: 2330 g of ion-exchanged water was added to 1000 g of α-alumina powder having a volumetric particle size distribution of D10 1.4 μm, D50 2.0 μm, D90 3.0 μm, and D100 5.5 μm to prepare an aqueous dispersion with an alumina concentration of 30% by mass. After adding 60% by mass of nitric acid to the aqueous dispersion so that the pH of the aqueous dispersion was 1 or less, the mixture was heated to 80°C and stirred for 3 hours while maintaining the temperature at 80°C to perform an acid treatment process, thereby modifying the alumina particle surface. The mixture was then neutralized to pH 7 using 28% aqueous ammonia, and decantation was repeated until the electrical conductivity of the aqueous dispersion reached 5 μS / cm or less to remove ionic components. The decanted aqueous dispersion was recovered by filtration and dried at 120°C for 12 hours to obtain an acid-treated alumina powder. To 1000 g of the acid-treated alumina powder in this manner, 2.5 g of N-phenyl-3-aminopropyltrimethoxysilane (KBM-573, manufactured by Shin-Etsu Chemical Co., Ltd.) was added, and a surface treatment step was carried out using a Henschel mixer to obtain alumina powder surface-treated with a silane coupling agent, which was then analyzed and evaluated according to the above-mentioned analytical and evaluation methods. The results are summarized in Tables 1 and 2. Furthermore, as shown in Figure 1, in the X-ray photoelectron spectroscopy analysis, Al peaks and Si peaks were observed, but neither Ti peaks nor Zr peaks were observed.

[0064] Comparative Example 1 An alumina powder, a resin composition, and a cured product were prepared, and analyzed and evaluated in the same manner as in Example 1, except that the acid treatment step in Example 1 was not performed and the raw material α-alumina powder was used and the surface treatment step was performed in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0065] Comparative Example 2 An alumina powder, a resin composition, and a cured product were prepared by subjecting the acid-treated alumina powder to the acid treatment step in the same manner as in Example 1 to no surface treatment step, and the results were analyzed and evaluated. The results are shown in Tables 1 and 2.

[0066] Comparative Example 3 In Example 1, neither the acid treatment step nor the surface treatment step was performed, and an alumina powder as a raw material, a resin composition using the alumina powder, and a cured product were prepared, and then analyzed and evaluated. The results are shown in Tables 1 and 2. Furthermore, as shown in Figure 2, in the X-ray photoelectron spectroscopy analysis, an Al peak was observed, but no Si peak, Ti peak, or Zr peak was observed.

[0067] [Example 2] An acid-treated and surface-treated alumina powder was obtained in the same manner as in Example 1, except that an α-alumina powder having a particle size distribution shown in Table 1 was used as a raw material instead of the α-alumina powder having a D50 of 2.0 μm in Example 1, and the amount of silane coupling agent added per 1000 g of alumina powder was changed to 9 g. The results of analysis and evaluation of the obtained alumina powder are summarized in Tables 1 and 2.

[0068] [Example 3] An acid-treated and surface-treated alumina powder was obtained in the same manner as in Example 1, except that an α-alumina powder having a particle size distribution shown in Table 1 was used as a raw material instead of the α-alumina powder having a D50 of 2.0 μm in Example 1, and the amount of silane coupling agent added per 1000 g of alumina powder was changed to 6 g. The results of analysis and evaluation of the obtained alumina powder are summarized in Tables 1 and 2.

[0069] Example 4 An acid-treated and surface-treated alumina powder was obtained in the same manner as in Example 1, except that an α-alumina powder having a particle size distribution shown in Table 1 was used as the raw material instead of the α-alumina powder having a D50 of 2.0 μm in Example 1, and the amount of silane coupling agent added per 1000 g of alumina powder was changed to 2.5 g. The analysis and evaluation results of the obtained alumina powder are summarized in Tables 1 and 2.

[0070] [Example 5] An acid-treated and surface-treated alumina powder was obtained in the same manner as in Example 1, except that an α-alumina powder having a particle size distribution shown in Table 1 was used as a raw material instead of the α-alumina powder having a D50 of 2.0 μm in Example 1, and the amount of silane coupling agent added per 1000 g of alumina powder was changed to 4.5 g. The results of analysis and evaluation of the obtained alumina powder are summarized in Tables 1 and 2.

[0071] [Example 6] An acid-treated and surface-treated alumina powder was obtained in the same manner as in Example 1, except that an α-alumina powder having a particle size distribution shown in Table 1 was used as a raw material instead of the α-alumina powder having a D50 of 2.0 μm in Example 1, and the amount of silane coupling agent added per 1000 g of alumina powder was changed to 4.5 g. The analysis and evaluation results of the obtained alumina powder are summarized in Tables 1 and 2.

[0072] Comparative Example 4 In Example 1, instead of the α-alumina powder with a D50 of 2.0 μm, 1000 g of alumina powder produced by a flame fusion method and having the particle size distribution shown in Table 1 was used. The alumina powder used contained no α-phase but contained γ-phase and δ-phase. This raw alumina powder was not subjected to the acid treatment step, but instead was subjected to the surface treatment step in the same manner as in Example 1. An alumina powder, a resin composition, and a cured product were produced, and analyzed and evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

[0073] Example 7 Using α-alumina powder having the particle size distribution shown in Table 1 as a raw material, an acid treatment step was carried out in the same manner as in Example 1 to obtain an acid-treated alumina powder. A solution was prepared by mixing 350 g of isopropyl alcohol and 0.9 g of N-phenyl-3-aminopropyltrimethoxysilane (KBM-573, manufactured by Shin-Etsu Chemical Co., Ltd.), and 150 g of the acid-treated alumina powder was added and mixed therein. The resulting mixture was subjected to a dispersion treatment using an ultrasonic homogenizer (US-1200T, manufactured by Nippon Seiki Seisakusho Co., Ltd.) to obtain a dispersion. The resulting alumina powder dispersion was heated and dried while shaking under reduced pressure to obtain an alumina powder surface-treated with a silane coupling agent. The analysis and evaluation results of the obtained alumina powder are summarized in Tables 1 and 2.

[0074]

[0075]

[0076] [Examples 8 to 12] Alumina powders surface-treated with a silane coupling agent were obtained in the same manner as in Example 7, except that α-alumina powders having particle size distributions shown in Table 3 were used instead of the α-alumina powder used in Example 7, and the amount of silane coupling agent was changed to the amount shown in Table 3. The results of analysis and evaluation of the obtained alumina powders are summarized in Tables 3 and 4.

[0077] Comparative Example 5 Alumina powder having the particle size distribution shown in Table 3 was used as is and analyzed and evaluated in the same manner as in Example 7. The results of the analysis and evaluation of the alumina powder are summarized in Tables 3 and 4.

[0078]

[0079]

Claims

1. An alumina powder having an α-phase content of 95% or more and a cumulative 100% particle size D100 in a volumetric particle size distribution of 1 to 20 μm, wherein the carbon content of the alumina powder is 0.01 to 2 mass%, and wherein a dispersion containing 10 parts by mass of the alumina powder, 20 parts by mass of ethanol, and 70 parts by mass of ion-exchanged water at 25°C has an electrical conductivity of 20 μS / cm or less.

2. The alumina powder according to claim 1, wherein the mass ratio of silicon, titanium, or zirconium to aluminum is 0.01 to 0.8 when the surface of the alumina powder is analyzed by an X-ray photoelectron spectrometer (XPS) using Mg-Kα radiation.

3. The alumina powder according to claim 1 or 2, wherein the alumina powder has a circularity coefficient of 0.85 to 0.

95.

4. The alumina powder according to claim 1 or 2, wherein the cumulative 10% particle size D10 in the volume-based particle size distribution of the alumina powder is 1.2 μm or less.

5. The alumina powder according to claim 1 or 2, wherein the alumina powder satisfies any one of the following conditions (1) to (3): (1) The particle diameter D100 of 100% of the cumulative total in the volumetric particle size distribution is 1 μm or more and less than 4 μm, and the tap density is 1.3 to 2.0 g / mL. (2) The particle diameter D100 of 100% of the cumulative total in the volumetric particle size distribution is 4 μm or more and less than 7 μm, and the tap density is 1.7 to 2.4 g / mL. (3) The particle diameter D100 of 100% of the cumulative total in the volumetric particle size distribution is 7 μm or more and less than 10 μm, and the tap density is 2.1 to 2.8 g / mL.

6. A mixture of 75 parts by mass of the alumina powder and 25 parts by mass of bisphenol F epoxy resin having a viscosity of 3500 mPa·s at 25°C was subjected to a shear rate of 100 sec －１ 3. The alumina powder according to claim 1, having a viscosity at 100°C of 1000 mPa·s or less.

7. The alumina powder according to claim 1 or 2, wherein the mass of alumina agglomerates that do not pass through a sieve with 45 μm openings contained in a mixture of 80 parts by mass of the alumina powder and 20 parts by mass of bisphenol F-type epoxy resin having a viscosity of 3,500 mPa·s at 25°C is 0.5 mass% or less relative to the mass of the alumina powder in the mixture.

8. The alumina powder according to claim 1 or 2, which is used as a filler for a sealant.

9. A resin composition comprising the alumina powder according to claim 1 or 2 and a resin.

10. The resin composition according to claim 9, comprising 50 to 96% by mass of the alumina powder and 4 to 50% by mass of the resin.

11. A sealant comprising the resin composition according to claim 9.

12. A cured product obtained by curing the resin composition according to claim 9, having a thermal conductivity of 1.8 W / m·K or more.

13. A method for producing an alumina powder, comprising: an acid treatment step of treating the surfaces of alumina particles with an acid; and a surface treatment step of coating the surfaces of the alumina particles after the acid treatment step with at least one coupling agent selected from a silane coupling agent, a titanate coupling agent, a zirconate coupling agent, and an aluminate coupling agent; wherein the resulting alumina powder has an α-phase content of 95% or more and a cumulative 100% particle size D100 in the volume-based particle size distribution of 1 to 20 μm.

14. The method for producing an alumina powder according to claim 13, wherein in the acid treatment step, the alumina particles are dispersed in an acidic aqueous solution having a pH of 2 or less.

15. A method for producing an alumina powder according to claim 13 or 14, wherein in the surface treatment step, 0.1 to 2 parts by mass of the coupling agent is added and mixed with 100 parts by mass of the alumina particles after the acid treatment.

16. A method for producing an alumina powder according to claim 1 or 2, comprising an acid treatment step of treating the surfaces of alumina particles with acid, and a surface treatment step of coating the surfaces of the alumina particles after the acid treatment step with at least one coupling agent selected from a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, and a zirconate coupling agent.

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