High-purity alumina particles and method for producing same, and resin composition for electronic devices and method for producing same

Abstract

Provided are: high-purity alumina particles which have improved purity by reducing the amount of impurities remaining in alumina particles derived from metallic aluminum and also by reducing the amount of metallic aluminum; and a method for producing the high-purity alumina particles. The aluminum oxide particles derived from metallic aluminum have a uranium element content of not more than 5 ppb, a thorium element content of not more than 5 ppb, a metallic aluminum content of not more than 5 ppm, a sodium content of not more than 10 ppm, and an iron content of not more than 10 ppm, and a metallic aluminum powder is introduced into a flame to be gasified and oxidized, and is spheroidized by surface tension during cooling to form spherical aluminum oxide particles. Spherical alumina particles are introduced into an alkaline solution to dissolve metallic aluminum remaining in the particles, and the spherical alumina particles are dried.

Description

Technical Field

[0001] This invention relates to high-purity alumina particles and their manufacturing method, as well as resin compositions for electronic devices containing high-purity alumina particles and their manufacturing method. Background Technology

[0002] For sealing materials used in precision electronic components such as semiconductors, inorganic fillers are added to the resin composition. These fillers require insulating properties and a low coefficient of thermal expansion. Alumina is commonly used.

[0003] Alumina is produced by crushing high-purity natural ore to a specified particle size. Even with high purity, the presence of impurities other than alumina is unavoidable due to its natural ore origin. In particular, in the case of alumina derived from natural sources, elements such as uranium and thorium are present. To improve semiconductor processing speed, processing precision and integration have been further promoted. Therefore, the impact of external electromagnetic noise on semiconductors is considered a problem more than ever before. In the case of alumina derived from natural sources, alpha rays generated by the radioactive decay of uranium and thorium are known to be a cause of malfunctions.

[0004] Therefore, in order to reduce impurities contained in the resulting fillers, a manufacturing method combining pulverization and exposure to flame was proposed (see Patent Document 1). Furthermore, in order to improve the manufacturing method of Patent Document 1, a manufacturing method was proposed in which raw materials in a metallic state, such as aluminum, are processed into oxides and then impurity aluminum is dissolved in an alkaline solution (see Patent Document 2).

[0005] Previous manufacturing methods have significantly improved the reduction of impurities. However, amphoteric metals such as aluminum are not easily dissolved in alkaline solutions. In the case of aluminum, depending on the purity of the metal, an oxide film can form on the metal surface, inhibiting its dissolution in alkaline solutions.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2012-206870

[0009] Patent Document 2: Japanese Patent Application Publication No. 2014-101239 Summary of the Invention

[0010] Then, the inventors conducted repeated and in-depth research on the dissolution of metallic aluminum in alkaline solutions. As a result, the inventors discovered that by appropriately controlling the dissolution of the raw material's metal in alkaline solutions, the dissolution efficiency of metallic aluminum in alkaline solutions can be improved, thus opening a pathway to reduce impurities originating from the metallic raw material.

[0011] The present invention is made in view of the above aspects, and provides high-purity alumina particles that reduce the amount of residual impurities in alumina particles derived from metallic aluminum used as fillers in sealing materials, and also reduce the amount of aluminum in the metallic state itself to improve purity, as well as a method for manufacturing the same, and a resin composition for electronic devices using the high-purity alumina particles and a method for manufacturing the same.

[0012] That is, the high-purity alumina particles of the embodiment are characterized in that they are alumina particles derived from metallic aluminum, the uranium content in the alumina particles is 5 ppb or less, the thorium content in the alumina particles is 5 ppb or less, the metallic aluminum content in the alumina particles is 5 ppm or less, the sodium content in the alumina particles is 10 ppm or less, and the iron content in the alumina particles is 10 ppm or less.

[0013] Furthermore, in high-purity alumina particles, the residual amount of aluminum particles with a particle size of 20 μm or larger from the raw material metallic aluminum can be less than 10 per 50g of alumina particles.

[0014] Furthermore, the resin composition for electronic devices is characterized by having high-purity alumina particles and a resin composition.

[0015] The method for manufacturing high-purity alumina particles according to the embodiments is characterized by comprising: a particle formation step in which aluminum powder is fed into a flame to vaporize and oxidize it, and spherical alumina particles are obtained by spheroidization based on surface tension during cooling; a dissolution step in which the spherical alumina particles are fed into an alkaline solution to dissolve the aluminum in a metallic state remaining in the spherical alumina particles; and a drying step in which the spherical alumina particles are dried.

[0016] Furthermore, in the method for manufacturing high-purity alumina particles, the alkaline solution can be an aqueous solution of an amine compound.

[0017] Furthermore, in the dissolution process of the method for manufacturing high-purity alumina particles, spherical alumina particles can be dissolved in an alkaline solution with a pH of 9 or higher and a liquid temperature of 20 to 60°C to dissolve the metallic aluminum remaining in the spherical alumina particles.

[0018] Furthermore, the aforementioned spherical alumina particles can be screened during the dissolution process in the method for manufacturing high-purity alumina particles.

[0019] Furthermore, a cleaning step for cleaning the aforementioned spherical alumina particles can be added to the method for manufacturing high-purity alumina particles.

[0020] Furthermore, the method for manufacturing a resin composition for electronic devices is characterized by comprising: a particle formation step in which aluminum powder is fed into a flame to vaporize and oxidize it, thereby obtaining spherical alumina particles by spheroidization based on surface tension during cooling; a dissolution step in which the spherical alumina particles are fed into an alkaline solution with a pH of 9 or higher and a liquid temperature of 20 to 60°C to dissolve the metallic aluminum remaining in the spherical alumina particles; a drying step in which the spherical alumina particles are dried; and a resin dispersion step in which the spherical alumina particles obtained in the drying step are dispersed in a resin composition to obtain a resin dispersion.

[0021] According to the present invention, high-purity alumina particles and a method for manufacturing high-purity alumina particles can be obtained, and the purity of high-purity alumina particles can be improved by reducing the amount of aluminum in the metallic state remaining in the alumina particles derived from metallic aluminum, while the manufacturing method can be established.

[0022] Furthermore, according to the resin composition for electronic devices and its manufacturing method, it is possible to reduce the dose of particle rays and electromagnetic waves emitted from the spherical particles contained in the resin composition, suppress external interference factors such as noise, and reduce adverse conditions such as equipment malfunctions. Detailed Implementation

[0023] In preparing the high-purity alumina particles of the embodiment, a manufacturing method is implemented by processing aluminum powder as a raw material according to the following steps. Furthermore, the resin composition for electronic devices is a resin composition containing high-purity alumina particles, and its manufacturing method includes a step of dispersing the particles in the resin composition in the final stage. The high-purity alumina particles are alumina particles whose total weight is 99.8% or more aluminum oxide.

[0024] First, aluminum powder is prepared as a raw material and then placed in a flame. In the flame, the aluminum powder is vaporized and oxidized. The resulting alumina cools from the gas to a liquid state. Due to surface tension, the alumina spheroidizes. This produces microparticle-like spherical alumina particles ("particle formation process"). This process is a type of deflagration reaction and is known as the VMC (Vaporized Metal Combustion Method), etc.

[0025] The flame in the particle formation process is formed by the combustion of a combustible gas mixed with an oxygen-containing combustion-supporting gas. The temperature of the furnace's refractory structure, which serves as an indicator of the furnace temperature, ranges from 900°C to 1500°C at its highest point (furnace body temperature). The furnace body temperature is preferably between 900°C and 1100°C as the lower limit, and more preferably between 1300°C and 1500°C as the upper limit. The combustion-supporting gas can be air or oxygen. The combustible gas and the combustion-supporting gas can be supplied to the furnace separately or in a pre-mixed state.

[0026] The flow rate of the combustible gas is preferably 0.1 m / s or more, more preferably 0.5 m / s or more, and even more preferably 1 m / s or more. The flow rate of the combustion-supporting gas is preferably 5 m / s or more, more preferably 7 m / s or more, and even more preferably 9 m / s or more. The combustible gas / combustion-supporting gas ratio is preferably 0.5 or less, more preferably 0.3 or less, and even more preferably 0.1 or less. The supply amounts of the combustible gas and the combustion-supporting gas are determined by the amount of combustible gas that can form a flame large enough to fully heat the supplied raw material particles and the amount of combustion-supporting gas that can fully combust the combustible gas. For example, the combustible gas is 0.5 Nm³ relative to the unit weight of the pulverized material being processed. 3 / h to 5Nm 3 / h, the oxygen content as a combustion-supporting gas is 50 Nm³. 3 / h~500Nm 3 / h or so.

[0027] There are no particular limitations on the method of supplying aluminum powder into the flame; it can be supplied to the flame while dispersed in a carrier gas. Examples of carrier gases include air, oxygen, and nitrogen.

[0028] In the spherical alumina particles produced by the particle formation process, not all metallic aluminum is oxidized to alumina; a small amount of metallic aluminum may remain. Therefore, in order to remove the metallic aluminum, the spherical alumina particles are placed in an alkaline solution to dissolve the metallic aluminum remaining in the spherical alumina particles ("dissolution process").

[0029] When dissolving amphoteric aluminum in an alkaline solution, the alkaline solution used must be free of alkali metals. Generally, aqueous solutions of alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide are strongly alkaline. However, if the alkali metals from the alkaline solution remain in the spherical alumina particles, it will reduce the purity of the final spherical alumina particles, and is therefore not preferred.

[0030] Therefore, aqueous solutions of amine compounds are used as alkaline solutions that do not contain alkali metals. Ammonia, primary amines, secondary amines, tertiary amines, quaternary ammonium hydroxides (ammonium salts), aromatic amines, silazanes, hydrazine, etc., are suitable amine compounds.

[0031] More specifically, the amine compound is one or more compounds selected from ammonia, methylamine, ethylamine, propylamine, dimethylamine, diethylamine, pyrrolidine, trimethylamine, triethylamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, benzyltrimethylammonium hydroxide, methyltripentylammonium hydroxide, methyltripentylammonium hydroxide, methyltributylammonium hydroxide, pyrrolidine, piperidine, pyridine, quinoline, imidazole, indole, pyrimidine, hexamethyldisilazane, hydrazine, diazabicycloundecene, diazabicyclononene, etc. In preparing aqueous solutions, the amine compound can be a single type or a mixture of two or more.

[0032] When using amine compounds as organic compounds, the compound molecules volatilize and decompose with subsequent processing steps. Therefore, the amine compounds are almost entirely absent from the final formed spherical alumina particles, which is preferable. Regarding the concentration of the amine compounds in the aqueous solution, when dissolving the metallic aluminum remaining in the spherical alumina particles, the pH of the alkaline solution is 9 or higher, more preferably 10 or higher, and the metallic aluminum remaining in the spherical alumina particles is heated using this alkaline solution at a liquid temperature of 20 to 60°C, more preferably about 40 to 60°C. At temperatures below 40°C, the time until precipitation becomes longer. Furthermore, at temperatures above 60°C, precipitation is less likely to occur due to the influence of the liquid temperature. According to the examples described later, the control of pH and temperature conditions is primarily based on insights that are effective in reducing the dissolved residue of metallic aluminum.

[0033] Here, regarding the relationship between the amount of alkali and the aluminum metal to be dissolved, the amount of alkali (wt%) relative to the amount of aluminum (Al) (g) is preferably in the range of 0.04 to 2 wt%. The amount of alkali is easy to weigh by converting molar amount to wt% (weight percentage).

[0034] It is known that metallic aluminum remaining within spherical alumina particles forms an oxide film (such as aluminate) on the metal surface when reacting with acids or bases. By forming this oxide film, the hydration reaction ends when the alkali or similar substance does not come into contact with the metallic aluminum further in than the oxide film. That is, undissolved aluminum (dissolved residue) is inevitably produced. Therefore, hydration needs to be advanced by reacting metallic aluminum with an alkaline solution (an aqueous solution of an amine compound) as vigorously as possible. It is speculated that the oxide film formed on the surface of high-purity aluminum—i.e., high-purity alumina—is so pure that even ammonia-based alkalis cannot completely dissolve the oxide film, thus preventing the dissolution of the internal aluminum.

[0035] The above conditions are for a slow reaction at a mild temperature based on room temperature, while ensuring the pH required for the formation of aluminum hydroxide. Of course, these conditions can be adjusted depending on the type and concentration of the amine compound used.

[0036] Furthermore, spherical alumina particles can be screened as needed during the dissolution process. Although spheroidization can be achieved in the particle size reduction process, it is not possible to homogenize the particle size of the spherical alumina particles. Additionally, the spherical alumina particles may sometimes disintegrate due to the strong alkali present during dissolution. Therefore, spherical alumina particles with uneven particle size are removed by screening before the next process. During screening, known sieves are used to separate the spherical alumina particles according to the specified particle size.

[0037] Following the dissolution process, the spherical alumina particles are dried (“drying process”). It should be noted that prior to the drying process, the spherical alumina particles are washed to remove the alkaline solution (“washing process”). First, in the washing process, the spherical alumina particles are washed with water. The washing apparatus and number of washes are appropriate, and the washing process ends when the pH of the wastewater after washing reaches approximately 7. In the drying process, natural drying, exposure to warm or hot air from a dryer, etc., are appropriate methods.

[0038] For spherical alumina particles formed after the drying process, the particles tend to become larger and less uniform due to agglomeration during intermediate processes. Therefore, crushing is applied to adjust to a homogeneous final product. Either wet crushing or dry crushing can be used during crushing. Furthermore, known equipment for crushing solids, such as ball mills, vibratory mills, chopping and stirring crushers, jet mills, and atomizers, can be used as the crushing device. In this embodiment, solids and alumina balls are added to a crushing pan, the pan is rotated, and wet crushing is performed. It should be noted that the pan rotation time (crushing time) is adjusted according to the target particle size. After wet crushing, the crushed material recovered from the pan is dried by spray drying or the like.

[0039] Here, the average particle size of the spherical alumina particles in each process refers to the median particle size (D) measured by known particle size determination methods such as laser diffraction scattering and dynamic scattering. 50 Therefore, the average particle size (D) of spherical alumina particles 50 The size is 30 μm or less, and more preferably 20 μm or less.

[0040] As illustrated in the series of descriptions, the spherical alumina particles (i.e., high-purity alumina particles) produced from aluminum raw materials through particle formation, dissolution, drying, and cleaning as needed, significantly reduce the total amount of uranium, thorium, and impurities such as sodium and iron compared to the original aluminum raw material stage. As will be clear from the examples described later, the amount of aluminum (the unoxidized portion that transforms into alumina) contained in the spherical particles is further reduced to less than 1 / 10 of the amount contained in the original aluminum raw material, and further reduced to less than 6 / 100. Therefore, the dose of electromagnetic waves such as alpha rays, beta rays, and gamma rays emitted from the spherical particles can be further reduced, thus minimizing the impact on electronic components and the like.

[0041] By dissolving spherical aluminum particles, formed from the oxidation of aluminum powder, in an alkaline solution, the aluminum remaining in the spherical particles changes from a metallic state to aluminum hydroxide. It is assumed that at this point, the amount of impurities in the aluminum raw material is less than the amount that dissolves in the alkaline solution. Since heavy elements such as U (uranium) and Th (thorium) are not amphoteric, they are difficult to dissolve in alkaline solutions and remain as insoluble components. This ease of dissolution in alkaline solutions allows for the separation of uranium, thorium, and other impurities. Therefore, compared to the preparation of oxides used as fillers in the past, the amount of impurities can be further reduced.

[0042] Furthermore, based on the dissolution conditions in alkaline solutions, the oxide film formed on the surface of metallic aluminum is also dissolved when in contact with alkaline solutions, thus suppressing the amount of metallic aluminum remaining as undissolved components in high-purity alumina particles.

[0043] The high-purity alumina particles are characterized by being prepared from alumina particles derived from metallic aluminum. Furthermore, the uranium content in the alumina particles is 5 ppb or less, preferably 1 ppb or less, and the thorium content in the alumina particles is 5 ppb or less, preferably 1 ppb or less. This significantly reduces the amounts of uranium and thorium, which are desired to be minimized.

[0044] Furthermore, the sodium content in the alumina particles is 10 ppm or less, preferably 5 ppb or less, and more preferably 1 ppb or less; the iron content in the alumina particles is 10 ppm or less, preferably 5 ppb or less, and more preferably 1 ppm or less. This reduces impurities other than aluminum, thus enabling the production of very pure, high-purity alumina particles.

[0045] Furthermore, the content of metallic aluminum in the high-purity alumina particles (alumina particles) is 5 ppm or less, preferably 3 ppb or less, and more preferably 1 ppm or less. That is, the residual metallic aluminum in the final form of high-purity alumina particles (spherical alumina particles) is suppressed as much as possible. If metallic aluminum remains in the high-purity alumina particles, as mentioned above, the effects of residual uranium and thorium elements cannot be eliminated. Furthermore, since metallic aluminum is a conductor, there is a risk of conductivity when using high-purity alumina particles as a filler for electronic materials. Therefore, in order to promote the dissolution of metallic aluminum in alkaline solutions as much as possible, the amount of metallic aluminum remaining in the final high-purity alumina particles (spherical alumina particles) is specified.

[0046] Furthermore, the residual amount of aluminum particles with a particle size of 20 μm or larger from the raw material aluminum is 10 or less, preferably 5 or less, and more preferably 0 (not detected) in 50 g of high-purity alumina particles (spherical alumina particles). If aluminum particles with a size of 20 μm or larger remain in the final high-purity alumina particles (spherical alumina particles), the electrical insulation of the high-purity alumina particles decreases. That is, since aluminum is conductive, its insulating properties as a filler decrease. This poses a risk of short circuits and other electrical defects occurring at the sites coated with resin compositions containing high-purity alumina particles as fillers. Therefore, the quality of high-purity alumina particles can be managed by suppressing the presence of aluminum particles in the high-purity alumina particles.

[0047] The high-purity alumina particles prepared by the manufacturing method of the embodiments described above are mainly used as fillers for electronic materials. A resin composition for electronic devices (a resin composition containing fillers for electronic materials) is prepared by adding high-purity alumina particles to a resin ("resin dispersion step" in the manufacturing method of the resin composition for electronic devices).

[0048] Examples of resins that can be added include polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene, other olefin resins, polyimide resins, thermoplastic resins such as liquid crystal polymers, fluoropolymers, urea resins, phenolic resins, and thermosetting resins such as polyphenylene ether and bismaleimide. Furthermore, it can also be added to elastic resins such as styrene-butadiene rubber and isoprene rubber, and silicone resins. For example, epoxy resin is used as the resin in the manufacture of resin substrates for packaging electronic components, interlayer insulating films, etc.

[0049] Examples of epoxy resins used in resin compositions include bisphenol A type epoxy resin, bisphenol F type epoxy resin, biphenyl type epoxy resin, phenolic varnish type epoxy resin, naphthalene type epoxy resin, and phenoxy type epoxy resin. From the viewpoint of heat resistance and coefficient of thermal expansion, a higher weight percentage of high-purity alumina particles in the resin composition is preferred. It is desirable to add at least 80% by weight of high-purity alumina particles (filler for electronic materials) relative to the overall mass of the resin composition.

[0050] Furthermore, for the high-purity alumina particles (filler for electronic materials) of the embodiments, the electronic material filler can be dispersed to prepare an electronic material slurry having a substantially water-free liquid dispersion medium. As this dispersion medium, solvents such as methanol, ethanol, isopropanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, toluene, N-methylpyrrolidone, γ-butyrolactone, propylene glycol monomethyl ether, and propylene glycol monomethyl ether acetate can be used. Multiple dispersion media can be used alone or in combination. Additionally, suitable dispersants can also be used.

[0051] As described in the description of high-purity alumina particles, the properties characteristic of resin compositions for electronic devices (resin compositions containing fillers for electronic materials) can reduce the dose of particle rays and electromagnetic waves emitted from the spherical particles contained in the resin composition. Therefore, the impact of particle rays and electromagnetic waves from the processing areas of the resin composition on electronic components can be reduced. As a result, external interference factors such as noise are suppressed, potentially reducing malfunctions such as equipment failure.

[0052] Example

[0053] To verify the method for manufacturing high-purity alumina particles, test examples 1 to 29 were prepared, and the physical properties of each test example were evaluated. The following descriptions follow the order of raw materials used, manufacturing method, and measurement and evaluation methods. Details of each test example are provided in Tables 1 to 6, which are described later.

[0054] [Raw Materials Used]

[0055] The aluminum used in Examples 1 to 6 was general-purpose aluminum powder with an average particle size of 20 μm.

[0056] The aluminum used in Examples 7 to 22 was high-purity aluminum powder with an average particle size of 20 μm.

[0057] The alumina particles used in Test Examples 23, 25, and 27 were of high purity and had an average particle size of 0.2 μm.

[0058] The alumina particles used in Test Examples 24, 26, 28, and 29 were of high purity and had an average particle size of 10 μm.

[0059] The following amine compounds are used when preparing alkaline solutions.

[0060] Ammonia: Manufactured by Fujifilm and Wako Pure Chemical Industries, Ltd.

[0061] Dimethylamine: Manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd.

[0062] Tetramethylammonium hydroxide (hereinafter referred to as TMAH): Manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd.

[0063] DAZA-Bicycloundecene (hereinafter referred to as DBU): Manufactured by Fujifilm and Kojun Pharmaceutical Co., Ltd.

[0064] [Confirmation of the solubility of metallic aluminum]

[0065] • Test Examples 1 to 22

[0066] Mix 0.2g of metallic aluminum particles, 100g of ion-exchanged water, and aqueous solutions of the alkalis listed in the table for each test example. Heat the mixture to 40°C while stirring for the specified time. Test examples 1 to 12 are 28% ammonia solutions, test examples 13 to 20 are 50% dimethylamine solutions, test example 21 is 25% TMAH, and test example 22 is a DBU solution.

[0067] [Verification of the Production of High-Purity Alumina Particles]

[0068] • Test cases 23 to 29

[0069] Experiments 23 to 29 used alumina particles as the starting material. They attempted to verify the removal of metallic aluminum remaining in alumina particles prepared by the VMC (Vaporized Metal Combustion Method), a type of deflagration reaction.

[0070] For each test example, 100g of alumina particles were used, along with 100g of deionized water. An amine compound was added as a base and dissolved in the water. The amount of base corresponds to the amount in the test examples listed in the table. The solutions for each test example were then stirred at 25°C for 5 hours. After stirring, the solutions were dried at 160°C to recover the spherical alumina particles.

[0071] • Component analysis

[0072] When analyzing the atomic composition of oxide powder, ICP (inductively coupled plasma optical emission spectrometry) devices manufactured by Shimadzu Corporation were used, including ICP-MS (determination of U and Th) and ICP-AES (determination of alumina and other impurities).

[0073] During the determination, the alumina powder of each test example was completely dissolved and soluble using sulfuric acid and then supplied to the apparatus.

[0074] • Determination of residual metallic aluminum

[0075] When determining the amount of residual metallic aluminum, 50 g of alumina powder from each test example (both before and after immersion in alkaline solution) was weighed and placed into a 500 mL Erlenmeyer flask. 220 mL of 2M sodium hydroxide solution was added to the flask, and after rapid sealing, the mixture was stirred at 1000–1200 rpm using a magnetic stirrer. The air temperature at the start of stirring was measured: T1.

[0076] Stirring was continued under sealed conditions for approximately 15 minutes until the reaction between metallic aluminum and sodium hydroxide was complete, and the generated hydrogen was collected in the conical flask. Immediately after stirring stopped, a hydrogen detection tube (manufactured by Komei Rikan Chemical Co., Ltd., Kitagawa type hydrogen detection tube 137U) was inserted through a sealing plug, and a gas collector (manufactured by Komei Rikan Chemical Co., Ltd., Kitagawa type gas collector AP-20) was installed. 50 mL of gas was drawn from the sealed conical flask, and the hydrogen concentration was measured.

[0077] Remove the detection tube and gas collector, and measure the temperature inside the conical flask using the sealing plug: T3. Then, pour water into the conical flask and measure the volume of the space inside the conical flask using the volume of water: V.

[0078] Based on the above measurements, the concentration of residual metallic aluminum was determined using the following formula, which follows the ideal gas law and Boyle-Charles law.

[0079] (Residual aluminum concentration: ppm) = Hydrogen concentration (%) × (273(K) + T1(℃)) × (V(mL) + Gas extraction volume (mL)) / {V(mL) × (273(K) + T3(℃))} × 10000 × V(mL) / 1000 × 1 / {22.4(L) × (273(K) + T1(℃)) / 273(K)} × (Molar ratio of residual metal material to hydrogen) × Atomic weight of unburned metal × 1 / Sample amount used (g)

[0080] Here, (the molar ratio of residual aluminum to hydrogen) represents how many moles of hydrogen are generated for every 1 mole of residual aluminum, which is 1.5 in the case of aluminum.

[0081] • Determination of residual metallic aluminum particles

[0082] Along with the residual metallic aluminum concentration, the amount of residual granular metallic aluminum was determined as the amount of conductive aluminum particles larger than 20 μm. 300 g of alumina powder (both before and after immersion in alkaline solution) was weighed, 0.1 g of sodium hexametaphosphate was added, and the sample was sieved using a 20 μm sieve. The alumina powder was cleaned by continuously spraying isopropanol onto the sieve for approximately 8 hours, and then allowed to stand for 24 hours to dry.

[0083] After drying, the number of objects considered to be foreign matter in the alumina powder was counted visually using an optical microscope, and then separated from the alumina powder. For the separated foreign matter, electrical conductivity was confirmed using a tungsten needle. Foreign matter that could be confirmed to be conductive was qualitatively analyzed using a dispersion X-ray diffraction (SEM-EDX) system to confirm it as aluminum.

[0084] [result]

[0085] Experimental Examples 1 to 22 are the results shown in Tables 1 to 4. In each table, starting from the top, the following information is provided: weight of metallic aluminum (g), amount of water in the alkaline solution (g), type of alkali, amount of alkali relative to the amount of metallic aluminum (Al) (mol%) (mol%), pH, temperature (°C), time (h), amount of uranium and thorium in the final state (ppb), amount of sodium and iron in the final state (ppm), and solubility evaluation (A, B, C, and D).

[0086] Solubility is evaluated in four stages: A is the best, B is good, C is average, and D is poor.

[0087] Evaluation A indicates whitening, where all metal particles are transformed into aluminum hydroxide.

[0088] Evaluation B indicates that although a certain degree of whitening has been applied, the aluminum is still visibly metallic.

[0089] Evaluation C indicates that the amount of aluminum in the metallic state is greater than that in evaluation B above.

[0090] A rating of D indicates that it is almost impossible to confirm that the change is aluminum hydroxide.

[0091] Examples 23 to 29 are equivalent to adding a dissolution method in an alkaline solution to the conventional method of producing alumina powder from metal powder using the VMC method. Here, the VMC method utilizes the deflagration phenomenon of metal powder to produce true spherical oxide particles.

[0092] [Table 1]

[0093]

[0094] [Table 2]

[0095]

[0096] [Table 3]

[0097]

[0098] [Table 4]

[0099]

[0100] [Investigation of the dissolution of metallic aluminum powder]

[0101] Examples 1 to 6 use general-purpose aluminum powder, which generally contains more impurities compared to the high-purity aluminum powder used in Examples 7 to 22. Due to the low purity of the aluminum, even adjusting the pH of the alkaline solution has little effect on the solubility evaluation (see Examples 4, 5, and 6). In contrast, in Examples 10, 11, and 12 using high-purity aluminum powder, the solubility evaluation deteriorated even under the same conditions. Therefore, it is difficult to directly apply the conditions for dissolving general-purpose aluminum powder in alkaline solution to the conditions for dissolving high-purity aluminum powder in alkaline solution.

[0102] Therefore, as shown in Experimental Examples 13 to 22, by using the type of amine compound in the alkaline solution and its alkalinity, pH, and dissolution time, high-purity metallic aluminum powder can also be well dissolved in alkaline solutions.

[0103] Experimental Examples 23 to 29 are the results shown in Tables 5 and 6. In each table, starting from the top, the following values ​​are represented: weight of alumina powder (g), amount of water in alkaline solution (g), type of alkali, alkali content relative to the amount of metallic aluminum (Al) (mol%), pH, temperature (°C), time (h), amount of metallic aluminum in alumina powder (both before and after immersion in alkaline solution) (ppm), amount of conductive aluminum particles larger than 20 μm (both before and after immersion in alkaline solution) (particles / 50 g), amount of uranium and thorium in the final state (ppb), and amount of sodium and iron in the final state (ppm).

[0104] [Table 5]

[0105]

[0106] [Table 6]

[0107]

[0108] [Investigation of the solubility of alumina powder]

[0109] Even though the amount and number of metallic aluminum particles were high before immersion in the alkaline solution in Examples 23 to 29, a reduction in the amount and number of metallic aluminum particles was confirmed after immersion in the alkaline solution, regardless of the initial amount. Specifically, the reduction was below 1 ppm and the number of particles was zero. Therefore, the effectiveness of subsequent immersion in alkaline solution was clearly demonstrated for alumina particles (powder). It should be noted that the amount of alkali in Example 27 was considered too low.

[0110] Based on a series of results, it is possible to reduce impurities in the preparation of alumina powder starting from metallic aluminum, and subsequently reduce poorly dissolved metallic aluminum from the alumina powder, thereby significantly improving the filler properties of the alumina powder. Therefore, a contribution to the improvement of resin compositions for electronic devices is expected.

Claims

1. A high-purity alumina particle, characterized in that, It consists of alumina particles derived from metallic aluminum. The uranium content in the alumina particles is below 5 ppb. The thorium content in the alumina particles is less than 5 ppb. The aluminum content in the alumina particles is less than 5 ppm. The sodium content in the alumina particles is less than 10 ppm. The iron content in the alumina particles is less than 10 ppm.

2. The high-purity alumina particles according to claim 1, wherein, The residual amount of aluminum particles with a particle size of 20 μm or larger from the aluminum metal used as raw material is less than 10 per 50 g of alumina particles.

3. A resin composition for electronic devices, characterized in that, It comprises the high-purity alumina particles as described in claim 1, and a resin composition.

4. A method for manufacturing high-purity alumina particles, characterized in that, The method for manufacturing high-purity alumina particles according to claim 1 comprises: The particle formation process involves feeding aluminum powder into a flame to vaporize and oxidize it, and then spherical alumina particles are obtained through spheroidization based on surface tension during cooling. The dissolution process involves immersing the spherical alumina particles in an alkaline solution to dissolve the metallic aluminum remaining within the spherical alumina particles. The drying process involves drying the spherical alumina particles.

5. The method for manufacturing high-purity alumina particles according to claim 4, wherein, The alkaline solution is an aqueous solution of an amine compound.

6. The method for manufacturing high-purity alumina particles according to claim 4, wherein, In the dissolution process, the spherical alumina particles are dissolved in an alkaline solution with a pH of 9 or higher and a liquid temperature of 20 to 60°C, thereby dissolving the metallic aluminum remaining in the spherical alumina particles.

7. The method for manufacturing high-purity alumina particles according to claim 4, wherein, The spherical alumina particles are screened during the dissolution process.

8. The method for manufacturing high-purity alumina particles according to claim 4, wherein, A cleaning process for cleaning the spherical alumina particles is added before the drying process.

9. A method for manufacturing a resin composition for electronic devices, characterized in that, The method for manufacturing the resin composition for electronic devices according to claim 3 comprises: The particle formation process involves feeding aluminum powder into a flame to vaporize and oxidize it, and then spherical alumina particles are obtained through spheroidization based on surface tension during cooling. In the dissolution process, the spherical alumina particles are placed in an alkaline solution with a pH of 9 or higher and a temperature of 20 to 60°C to dissolve the metallic aluminum remaining within the spherical alumina particles. The drying process involves drying the spherical alumina particles, and The resin dispersion process involves dispersing the spherical alumina particles obtained from the drying process into a resin composition to obtain a resin dispersion.

Images