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

Abstract

Provided are: high-purity alumina particles with increased purity achieved by reducing the amount of impurities that remain in the alumina particles and that originate from metallic aluminum and by reducing the amount of metal state aluminum itself; and a method for producing the high-purity alumina particles. In alumina particles of the present invention, the contained amounts of uranium elements, thorium elements, metallic aluminum, sodium, and iron originating from metallic aluminum are 5 ppb or less, 5 ppb or less, 5 ppm or less, 10 ppm or less, and 10 ppm or less, respectively. The present invention involves obtaining spherical alumina particles through inputting of a powder of metallic aluminum in a flame to vaporize and oxidize the same, and through spheroidization of the same caused by surface tension when being cooled. The spherical alumina particles are inputted to a basic solution to dissolve metal state aluminum remaining in the particles. Then, the spherical alumina particles are dried.

Description

High-purity alumina particles and their manufacturing method, and resin composition for electronic devices and their manufacturing method

[0001] The present invention relates to high-purity alumina particles and a method for producing the same, as well as a resin composition for electronic devices containing high-purity alumina particles and a method for producing the same.

[0002] Insulators used to seal precision electronic components such as semiconductors contain inorganic fillers added to resin compositions. Fillers are required to have insulating properties and a low coefficient of thermal expansion. Alumina (aluminum oxide) is commonly used.

[0003] Alumina is made into fillers by crushing natural, high-purity ores to a specified particle size. In other words, even if it is highly pure, because it is derived from natural ores, the presence of impurities other than aluminum oxide is inevitable. In particular, in the case of naturally derived alumina, uranium and thorium elements are present. Aiming to improve semiconductor processing speeds, processing precision and integration are further promoted. Therefore, the impact of external electromagnetic noise on semiconductors is becoming a greater concern than ever. In the case of naturally derived alumina, it is known that alpha rays and other radiation are generated by the radioactive decay of uranium and thorium, which are thought to be the cause of malfunctions.

[0004] Therefore, a manufacturing method that combines pulverization and exposure to flame has been proposed for the purpose of reducing impurities contained in the finished filler, etc. (see Patent Document 1). Furthermore, in order to improve the manufacturing method of Patent Document 1, etc., a manufacturing method has been proposed in which a raw material in a metallic state such as aluminum is processed into an oxide, and then the impurity aluminum is dissolved in a basic solution (see Patent Document 2).

[0005] Previous manufacturing methods have made great progress in reducing impurities. However, dissolving amphoteric metal elements such as aluminum in a basic solution has not been easy. In particular, in the case of aluminum, depending on the purity of the metal, an oxide film can form on the metal surface, inhibiting dissolution in a basic solution.

[0006] JP 2012-206870 A JP 2014-101239 A

[0007] The inventor then conducted extensive research into the dissolution of metallic aluminum in a basic solution, and as a result, by appropriately controlling the dissolution of the raw material metal in a basic solution, the inventor was able to increase the efficiency of dissolving metallic aluminum in a basic solution and thereby pave the way for reducing impurities resulting from the metallic raw material.

[0008] The present invention has been made in view of the above points, and provides high-purity alumina particles for use as a filler to be added to a sealing material, which have an increased purity by reducing the amount of impurities derived from metallic aluminum remaining in the alumina particles and also reducing the amount of aluminum in a metallic state itself, a method for producing the same, and a resin composition for electronic devices that uses the high-purity alumina particles and a method for producing the same.

[0009] That is, the high-purity alumina particles of the embodiment are alumina particles derived from metallic aluminum, characterized in that 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.

[0010] Furthermore, in the high-purity alumina particles, the amount of residual aluminum particles having a particle size of 20 μm or more derived from the raw material aluminum metal may be 10 or less per 50 g of alumina particles.

[0011] Furthermore, the resin composition for electronic devices is characterized by having high-purity alumina particles and a resin composition.

[0012] The method for producing high-purity alumina particles according to the embodiment is characterized by comprising a granulation step in which metallic aluminum powder is introduced into a flame to vaporize and oxidize it, and then spherical alumina particles are obtained through spheroidization due to surface tension upon cooling; a dissolution step in which the spherical alumina particles are introduced into a basic solution to dissolve the metallic aluminum remaining in the spherical alumina particles; and a drying step in which the spherical alumina particles are dried.

[0013] Furthermore, in the method for producing high-purity alumina particles, the basic solution may be an aqueous solution of an amine compound.

[0014] Furthermore, in the dissolution step of the method for producing high-purity alumina particles, the spherical alumina particles may be dissolved in a basic solution having 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.

[0015] Furthermore, in the melting step of the method for producing high-purity alumina particles, the spherical alumina particles may be sieved.

[0016] Furthermore, the method for producing high-purity alumina particles may include a washing step of washing the spherical alumina particles.

[0017] In addition, a method for producing a resin composition for electronic devices is characterized by comprising a granulation step in which metallic aluminum powder is introduced into a flame to vaporize and oxidize it, and then spherical alumina particles are obtained through spheroidization due to surface tension upon cooling; a dissolution step in which the spherical alumina particles are introduced into a basic solution having 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 that have been dried are dispersed in a resin composition to obtain a resin dispersion.

[0018] According to the high-purity alumina particles and the method for producing high-purity alumina particles of the present invention, it is possible to obtain high-purity alumina particles for use as a filler to be added to a sealing material, the purity of which is increased by reducing the amount of metallic aluminum remaining in the alumina particles derived from metallic aluminum, and it is also possible to establish a method for producing the high-purity alumina particles.

[0019] Furthermore, the resin composition for electronic devices and its manufacturing method make it possible to reduce the dose of particle rays and electromagnetic waves emitted from the spherical particles contained in the resin composition, which is expected to suppress external disturbance factors such as noise and reduce malfunctions and other problems with the devices.

[0020] In preparing the high-purity alumina particles of the embodiment, a manufacturing method is carried out in which a raw material, metallic aluminum powder, is subjected to the following steps in order. The resin composition for electronic devices is a resin composition containing high-purity alumina particles, and the manufacturing method includes a final step of dispersing the high-purity alumina particles in the resin composition. The high-purity alumina particles are alumina particles whose total weight is 99.8% or more of which is aluminum oxide.

[0021] First, metallic aluminum powder is prepared as a raw material and is introduced into a flame. In the flame, the metallic aluminum powder is vaporized and oxidized. The aluminum oxide (alumina) produced by oxidation cools from a gas to a liquid. At this time, the aluminum oxide (alumina) becomes spherical due to surface tension. As a result, fine spherical alumina particles are produced (the "particulation process"). This process is a type of deflagration reaction and is also known as the VMC (Vaporized Metal Combustion) Method.

[0022] The flame in the granulation process is formed by mixing a combustible gas with a combustion supporting gas containing oxygen and burning it. As an indicator of the furnace temperature, the temperature of the refractory structure of the furnace is in the range of 900°C to 1500°C at the highest point (furnace body temperature). The furnace body temperature preferably has a lower limit of 900°C to 1100°C and an upper limit of 1300°C to 1500°C. Air or oxygen is used as the combustion supporting gas. When the combustible gas and the combustion supporting gas are supplied to the furnace, they may be supplied separately or in a pre-mixed state.

[0023] The flow velocity 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 velocity 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 flow velocity ratio of combustible gas / combustion supporting gas is preferably 0.5 or less, more preferably 0.3 or less, and even more preferably 0.1 or less. The supply amounts of combustible gas and combustion supporting gas are determined by the amount of combustible gas that can form a flame large enough to sufficiently heat the raw material particles being supplied, and the amount of combustion supporting gas that can sufficiently combust the combustible gas. For example, the amount of combustible gas per unit weight of the pulverized material to be processed is 0.5 Nm ３ / h to 5Nm ３ / h, oxygen as a combustion supporting gas is 50 Nm ３ / h to 500 Nm ３ / h.

[0024] The method for supplying the aluminum powder into the flame is not particularly limited, but it can be supplied to the flame in a state dispersed in a carrier gas, such as air, oxygen, or nitrogen.

[0025] In the spherical alumina particles produced by the granulation process, not all of the metallic aluminum is necessarily oxidized to aluminum oxide, and a small amount of metallic aluminum may remain. Therefore, in order to remove the metallic aluminum, the spherical alumina particles are put into a basic solution, and the metallic aluminum remaining in the spherical alumina particles is dissolved ("dissolution process").

[0026] The basic solution used when dissolving metallic aluminum, which is an amphoteric element, in a basic solution is a solution that does not contain alkali metals. Generally, aqueous solutions of alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide are strongly basic. However, if the alkali metals in the basic solution remain in the spherical alumina particles, this undesirably reduces the purity of the final spherical alumina particles.

[0027] Therefore, an aqueous solution of an amine compound is used as a basic solution that does not contain an alkali metal, such as ammonia, primary amine, secondary amine, tertiary amine, quaternary ammonium hydroxide (ammonium salt), arylamine, silazane, or hydrazine.

[0028] 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, methyltriamylammonium hydroxide, methyltributylammonium hydroxide, pyrrolidine, piperidine, pyridine, quinoline, imidazole, indole, pyrimidine, hexamethyldisilazane, hydrazine, diazabicycloundecene, diazabicyclononene, etc. When preparing the aqueous solution, the amine compound may be a single type or a mixture of two or more types.

[0029] When an organic amine compound is used, the compound molecules volatilize and decompose during subsequent processing steps. Therefore, it is desirable that the amine compound hardly remains in the final spherical alumina particles. Of course, with regard to the concentration of the amine compound in the aqueous solution, when dissolving the metallic aluminum remaining in the spherical alumina particles, the pH of the basic solution is 9 or higher, more preferably 10 or higher, and the metallic aluminum remaining in the spherical alumina particles is heated in the basic solution at a liquid temperature of 20 to 60°C, more preferably approximately 40 to 60°C. If the temperature is lower than 40°C, the time until precipitation increases. Furthermore, if the temperature exceeds 60°C, precipitation becomes less likely due to the influence of the liquid temperature. The examples described below demonstrate that controlling the pH and temperature conditions is primarily effective in reducing the amount of undissolved metallic aluminum.

[0030] Regarding the relationship between the amount of base and the amount of metallic aluminum to be dissolved, the amount of base (wt%) relative to the amount of metallic aluminum (Al) (g) is preferably in the range of 0.04 to 2 wt%. The amount of base is converted from a molar amount to wt% (weight percent) for ease of measurement.

[0031] It is known that residual aluminum metal within spherical alumina particles forms an oxide coating of alumina (such as anodized aluminum) on the metal surface when reacting with an acid or base. The formation of this oxide coating on the surface prevents the base from coming into contact with the internal aluminum metal beyond the oxide coating, resulting in the hydroxide reaction being completed. In other words, undissolved aluminum metal (residuals) is inevitably produced. Therefore, it is necessary to promote hydroxide formation by reacting aluminum metal with a basic solution (an aqueous solution of an amine compound) as vigorously as possible. It is believed that the oxide coating formed on the surface of high-purity aluminum, i.e., high-purity alumina, is so pure that a base such as ammonia cannot completely dissolve the oxide coating, resulting in the internal aluminum not dissolving.

[0032] The above conditions are those for gradually progressing the reaction at a mild temperature equivalent to room temperature while maintaining the pH required for forming aluminum hydroxide, although adjustments may be made depending on the type and concentration of the amine compound used.

[0033] Furthermore, in the dissolution process, the spherical alumina particles are sieved as necessary. Although spheroidization is possible in the granulation process, the particle size of the spherical alumina particles cannot be made uniform. Furthermore, in the dissolution process, the spherical alumina particles may be disintegrated due to the influence of the strong base during dissolution. Therefore, prior to the next process, spherical alumina particles with non-uniform particle sizes are removed by sieving. During sieving, known sieves are used to separate the spherical alumina particles according to the desired particle size.

[0034] After the dissolving step, the spherical alumina particles are dried ("drying step"). Before the drying step, the spherical alumina particles are washed to remove the basic solution ("washing step"). First, in the washing step, the spherical alumina particles are washed with water. The washing device and number of times are appropriate, and the washing is completed when the pH of the wastewater after washing reaches approximately 7. In the drying step, natural drying, drying by exposure to warm or hot air using a dryer, etc. are appropriate.

[0035] The spherical alumina particles produced through the drying process tend to become large and uneven due to agglomeration during the process. Therefore, crushing is performed to obtain a homogeneous final product. Either wet crushing or dry crushing may be used for crushing. Furthermore, known devices for crushing solids, such as ball mills, vibration mills, chopper-agitation crushers, jet mills, and atomizers, are used as crushing devices. In this embodiment, the solidified material and alumina balls are placed in a crushing pod, and the pod is rotated to perform wet crushing. The rotation time of the pod (crushing time) is adjusted depending on the target particle size. After wet crushing, the crushed material recovered from the pod is dried by spray drying or the like.

[0036] Here, the average particle size of the spherical alumina particles in each step is the median diameter (D ５０ ) and the average particle diameter (D ５０ ) is preferably 30 μm or less, more preferably 20 μm or less.

[0037] As explained above, spherical alumina particles (i.e., high-purity alumina particles) produced from metallic aluminum through a granulation process, a dissolution process, a drying process, and optionally washing have significantly reduced amounts of impurities such as uranium and thorium, as well as sodium and iron, compared to the metallic aluminum raw material stage. As will be apparent from the examples described below, the metallic aluminum contained in the spherical particles (components that were not oxidized to alumina) is reduced to 1 / 10 or less, or even 6 / 100 or less, of the amount contained in the original metallic aluminum raw material. This makes it possible to further reduce the dose of particle rays such as alpha rays and beta rays, and electromagnetic waves such as gamma rays, emitted from the spherical particles, thereby reducing the impact on electronic components, etc.

[0038] When spherical aluminum particles produced by oxidation of metallic aluminum powder are dissolved in a basic solution, the metallic aluminum remaining in the spherical aluminum particles changes from a metallic state to aluminum hydroxide, which is a hydroxide. At this point, the amount of impurities contained in the metallic aluminum raw material is thought to be less than the amount that dissolves in the basic solution. Heavy elements such as U (uranium) and Th (thorium) are not amphoteric elements, so they are difficult to dissolve in the basic solution and remain as insoluble components. This ease of dissolution in the basic solution makes it possible to separate the uranium element, thorium element, and other impurity components. Therefore, it is possible to further reduce impurities compared to conventional methods for preparing oxides for fillers.

[0039] Furthermore, depending on the dissolution conditions in the basic solution, the oxide coating formed on the surface of metallic aluminum upon contact with the basic solution is also dissolved, and therefore the amount of metallic aluminum remaining on the high-purity alumina particles as undissolved matter can be reduced.

[0040] The high-purity alumina particles are characterized by being prepared from alumina particles derived from metallic aluminum. 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. The amounts of uranium and thorium, which are particularly desired to be reduced, can be significantly reduced.

[0041] The sodium content in the alumina particles is 10 ppm or less, preferably 5 ppb or less, and more preferably 1 ppb or less, and the iron content in the alumina particles is 10 ppm or less, preferably 5 ppb or less, and more preferably 1 ppm or less. In this way, impurity components other than aluminum are reduced, and therefore, very high-purity alumina particles can be obtained.

[0042] In addition, 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. In other words, the amount of metallic aluminum remaining in the final high-purity alumina particles (spherical alumina particles) is minimized. If metallic aluminum remains in the high-purity alumina particles, as described above, the effects of the uranium and thorium elements remaining in the metallic aluminum cannot be eliminated. Furthermore, because metallic aluminum is a conductor, there is a risk of electrical conduction when the high-purity alumina particles are used as a filler for electronic materials. Therefore, the amount of metallic aluminum remaining in the final high-purity alumina particles (spherical alumina particles) is specified to promote the dissolution of metallic aluminum in a basic solution as much as possible.

[0043] Furthermore, the residual amount of aluminum particles with a particle size of 20 μm or more derived from the raw material metallic aluminum is 10 or less, preferably 5 or less, and more preferably 0 (undetectable) per 50 g of high-purity alumina particles (spherical alumina particles). If metallic aluminum particles with a size of 20 μm or more remain in the final high-purity alumina particles (spherical alumina particles), the electrical insulation properties of the high-purity alumina particles are reduced. In other words, because metallic aluminum is conductive, its insulating performance as a filler is reduced. This may cause electrical defects such as short circuits in areas where a resin composition containing high-purity alumina particles as a filler is applied. Therefore, the metallic aluminum particles present in the high-purity alumina particles can be suppressed to control the quality of the high-purity alumina particles.

[0044] The high-purity alumina particles prepared by the method for producing high-purity alumina particles according to the embodiment described above are mainly used as a filler for electronic materials. The high-purity alumina particles are added to a resin to prepare a resin composition for electronic devices (a filler-containing resin composition for electronic materials) (the "resin dispersion step" in the method for producing a resin composition for electronic devices).

[0045] Resins to which the epoxy resin can be added include thermoplastic resins such as polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, polystyrene, other olefin resins, polyimide resins, and liquid crystal polymers, as well as thermosetting resins such as fluororesins, urea resins, and phenolic resins, polyphenylene ether, and bismaleimide. It can also be added to elastic resins such as styrene-butadiene rubber and isoprene rubber, and silicone resins. For example, epoxy resins are used as resins when producing resin substrates such as package substrates for electronic components and interlayer insulating films.

[0046] Examples of epoxy resins used in the resin composition include bisphenol A epoxy resins, bisphenol F epoxy resins, biphenyl epoxy resins, phenol novolac epoxy resins, naphthalene epoxy resins, and phenoxy epoxy resins. The weight of the high-purity alumina particles blended into the resin composition is preferably large from the viewpoints of heat resistance and thermal expansion coefficient. It is desirable to add 80% by mass or more of the high-purity alumina particles (filler for electronic materials) to the total mass of the resin composition.

[0047] Furthermore, the high-purity alumina particles (filler for electronic materials) of the embodiment can be dispersed in a liquid dispersion medium substantially free of water to prepare a slurry for electronic materials. Examples of the dispersion medium include methyl alcohol, ethyl alcohol, isopropyl alcohol, 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. The dispersion medium can be used alone or in combination. An appropriate dispersant can also be used.

[0048] As explained above regarding high-purity alumina particles, a characteristic property of resin compositions for electronic devices (resin compositions containing fillers for electronic materials) is that they can reduce the dose of particle radiation and electromagnetic waves emitted from the spherical particles contained in the resin composition. This reduces the effects of particle radiation and electromagnetic waves on electronic components and the like from the processed portion of the resin composition. As a result, disturbance factors such as noise can be suppressed, and malfunctions and other problems with the equipment can be reduced.

[0049] To demonstrate the method for producing high-purity alumina particles, Test Examples 1 to 29 were prepared and the physical properties of each Test Example were evaluated. Hereinafter, the raw materials used, the production method, and the measurement and evaluation methods will be described in that order. For details of each test example, see Tables 1 to 6 below.

[0050] [Raw Materials Used] General-purpose aluminum powder with an average particle size of 20 μm was used as the metallic aluminum in Test Examples 1 to 6. High-purity aluminum powder with an average particle size of 20 μm was used as the metallic aluminum in Test Examples 7 to 22. High-purity alumina particles with an average particle size of 0.2 μm were used as the metallic aluminum in Test Examples 23, 25, and 27. High-purity alumina particles with an average particle size of 10 μm were used as the metallic aluminum in Test Examples 24, 26, 28, and 29.

[0051] The following amine compounds were used in preparing the basic solution: Ammonia: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Dimethylamine: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Tetramethylammonium hydroxide (hereinafter referred to as TMAH): manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Diazabicycloundecene (hereinafter referred to as DBU): manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0052] [Confirmation of Solubility of Metallic Aluminum] Test Examples 1 to 22 0.2 g of metallic aluminum particles of each Test Example, 100 g of ion-exchanged water, and an aqueous solution of the base species shown in the table were mixed and stirred for the time indicated for each Test Example while heating to 40° C. Test Examples 1 to 12 used a 28% aqueous ammonia solution, Test Examples 13 to 20 used a 50% aqueous dimethylamine solution, Test Example 21 used 25% TMAH, and Test Example 22 used an aqueous DBU solution.

[0053] [Verification of Production of High-Purity Alumina Particles] Test Examples 23 to 29 Test Examples 23 to 29 use alumina particles as the starting material. These are verifications aimed at removing metallic aluminum remaining within alumina particles prepared by the VMC (Vaporized Metal Combustion) method, which is a type of deflagration reaction.

[0054] For each test example, 100 g of alumina particles were mixed with 100 g of ion-exchanged water, to which an amine compound serving as a base species was added and dissolved. The amount of the base species was determined according to the test example in the table. The solution for each test example was then stirred at 25°C for 5 hours. After stirring, the solution was dried at 160°C, and the spherical alumina particles were collected.

[0055] Component Analysis The atomic composition of the oxide powder was analyzed using an ICP (inductively coupled plasma atomic emission spectroscopy) analyzer ICP-MS (measurement of U and Th) and ICP-AES (measurement of alumina and other impurities) manufactured by Shimadzu Corporation. For the measurement, the alumina powder of each test example was completely dissolved in sulfuric acid to form a solution, which was then fed to the analyzer.

[0056] Measurement of the amount of residual metallic aluminum When measuring the amount of residual metallic aluminum, 50 g of alumina powder sample from each test example (both before and after immersion in the basic solution) was weighed and placed in a 500 mL Erlenmeyer flask. 220 mL of 2 M sodium hydroxide solution was added to the flask, which was quickly sealed and then stirred at 1000 to 1200 rpm using a magnetic stirrer. The temperature at the start of stirring, T1, was then measured.

[0057] Stirring was continued in a sealed state for approximately 15 minutes until the reaction between metallic aluminum and sodium hydroxide was thought to be complete, and the generated hydrogen was collected in an Erlenmeyer flask. Immediately after stirring was stopped, a hydrogen detector tube (Kitagawa-type gas detector tube Hydrogen 137U, manufactured by Komyo Rikagaku Kogyo Co., Ltd.) was inserted through the seal and a detector tube gas sampler (Kitagawa-type gas sampler AP-20, manufactured by Komyo Rikagaku Kogyo Co., Ltd.) was attached, and 50 mL of gas was sucked from the sealed Erlenmeyer flask to measure the hydrogen concentration.

[0058] The detector tube and gas sampler were removed, and the temperature in the Erlenmeyer flask (T3) was measured through the airtight stopper. Water was then poured into the Erlenmeyer flask, and the volume of the water was used to measure the volume of the space in the Erlenmeyer flask (V).

[0059] From the above-mentioned measured values, the residual metallic aluminum concentration was measured using the following equation, which follows the equation of state for an ideal gas and Boyle's law: (residual metallic aluminum concentration: ppm) = hydrogen concentration (%) x (273 (K) + T1 (°C)) x (V (mL) + gas intake volume (mL)) / {V (mL) x (273 (K) + T3 (°C))} x 10,000 x V (mL) / 1,000 x 1 / {22.4 (L) x (273 (K) + T1 (°C)) / 273 (K)} x (reaction molar ratio of remaining metal material to hydrogen) x atomic weight of unburned metal x 1 / amount of sample used (g), where (reaction molar ratio of remaining metallic aluminum to hydrogen) is a value indicating how many moles of hydrogen are produced per mole of remaining metallic aluminum, and in the case of metallic aluminum, it is 1.5.

[0060] Measurement of residual metallic aluminum particles: The residual metallic aluminum concentration was measured, along with the amount of conductive aluminum particles of 20 μm or larger. A 300 g sample of alumina powder (both before and after immersion in the basic solution) was weighed, 0.1 g of sodium hexametaphosphate was added, and the sample was sieved through a 20 μm sieve. Isopropanol was sprayed continuously from above the sieve for about 8 hours to wash the alumina powder, and then the sample was left to dry for 24 hours.

[0061] After drying, the alumina powder was visually inspected using an optical microscope to count the number of objects that appeared to be foreign matter, and these were then separated from the alumina powder. Electrical continuity of the separated foreign matter was confirmed using a tungsten needle. Qualitative analysis of the foreign matter that was confirmed to be conductive was performed using an energy dispersive X-ray analyzer (SEM-EDX), and it was confirmed that it was aluminum.

[0062] [Results] The results of Test Examples 1 to 22 are shown in Tables 1 to 4. In each table, from the top to bottom, the weight (g) of metallic aluminum, the amount of water (g) of the basic solution, the type of base, the amount of base (mol %) relative to the amount (mol) of metallic aluminum (Al), pH, temperature (°C), time (h), the amounts of uranium and thorium in the final state (ppb), the amounts of sodium and iron in the final state (ppm), and the solubility evaluation (A, B, C, and D).

[0063] The solubility was evaluated on the following four-level scale, with A being the best, B being good, C being average, and D being poor. Grade A indicates that the metal particles have turned white and all have been converted to aluminum hydroxide. Grade B indicates that the metal particles have turned white to some extent, but that the aluminum in a metallic state can still be seen with the naked eye. Grade C indicates that the amount of aluminum in a metallic state is greater than that of the aforementioned grade B. Grade D indicates that the conversion to aluminum hydroxide is barely noticeable.

[0064] Test Examples 23 to 29 correspond to a method in which dissolution in a basic solution is added to the conventional method of producing alumina powder by the VMC method starting from a metal powder. Here, the VMC method is a method for producing spherical oxide fine particles by utilizing the deflagration phenomenon of metal powder.

[0065]

[0066]

[0067]

[0068]

[0069] [Considerations on dissolution of metal aluminum powder] Test Examples 1 to 6 are general-purpose metal aluminum powders, and the impurity amounts are generally higher than those of the high-purity metal aluminum powders of Test Examples 7 to 22. Because the purity of aluminum is not high, adjusting the pH of the dissolution conditions in the basic solution has little effect on the solubility evaluation (see Test Examples 4, 5, and 6). In contrast, the solubility evaluation of Test Examples 10, 11, and 12, which are high-purity metal aluminum powders, deteriorated despite being under similar conditions. Therefore, it is difficult to use the conditions for dissolving a general-purpose metal aluminum powder in a basic solution as the conditions for dissolving a high-purity metal aluminum powder in a basic solution.

[0070] Therefore, as shown in Test Examples 13 to 22, by controlling the type of amine compound in the basic solution, the amount of base, pH, and dissolution time, it was possible to achieve good dissolution of high-purity metallic aluminum powder in the basic solution.

[0071] The results of Test Examples 23 to 29 are shown in Tables 5 and 6. In each table, from the top to bottom, the weight (g) of the alumina powder, the amount of water (g) of the basic solution, the type of base, the amount of base (mol %) relative to the amount of metallic aluminum (Al) (mol), pH, temperature (°C), time (h), the amount of metallic aluminum in the alumina powder (both before and after immersion in the basic solution) (ppm), the amount of conductive aluminum particles of 20 μm or more (both before and after immersion in the basic solution) (pieces / 50 g), the amount of uranium and thorium in the final state (ppb), and the amount of sodium and iron in the final state (ppm).

[0072]

[0073]

[0074] [Considerations on dissolution of alumina powder] In Test Examples 23 to 29, even though the amount and number of metallic aluminum particles were large before immersion in the basic solution, it was confirmed that the amount and number of metallic aluminum particles decreased after immersion in the basic solution, regardless of the initial amount. Specifically, the amount was 1 ppm or less, and the number was 0. Therefore, the effectiveness of immersing alumina particles (powder) in a basic solution afterward was clear. Note that the amount of base in Test Example 27 is considered to be too small.

[0075] These results suggest that the reduction of impurities in the preparation of alumina powder from metallic aluminum and subsequent reduction of poorly soluble metallic aluminum from the alumina powder can be achieved, dramatically improving the filler properties of the alumina powder. This is expected to contribute to the improvement of resin compositions for electronic devices.

Claims

1. High-purity alumina particles derived from metallic aluminum, characterized in that 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.

2. High purity alumina particles as described in claim 1, in which the amount of residual aluminum particles having a particle size of 20 μm or more derived from the raw material aluminum metal is 10 or less per 50 g of the alumina particles.

3. A resin composition for electronic devices, comprising the high purity alumina particles according to claim 1 and a resin composition.

4. A method for producing high-purity alumina particles as described in claim 1, comprising: a granulation step of introducing metallic aluminum powder into a flame to vaporize and oxidize it, and obtaining spherical alumina particles through spheroidization due to surface tension upon cooling; a dissolution step of introducing the spherical alumina particles into a basic solution to dissolve the metallic aluminum remaining within the spherical alumina particles; and a drying step of drying the spherical alumina particles.

5. The method for producing high purity alumina particles according to claim 4, wherein the basic solution is an aqueous solution of an amine compound.

6. A method for producing high purity alumina particles as described in claim 4, wherein in the dissolving step, the spherical alumina particles are dissolved in the basic solution having a pH of 9 or higher and a liquid temperature of 20 to 60°C to dissolve the metallic aluminum remaining within the spherical alumina particles.

7. A method for producing high purity alumina particles according to claim 4, wherein the spherical alumina particles are sieved in the dissolving step.

8. The method for producing high purity alumina particles according to claim 4, further comprising the step of washing the spherical alumina particles prior to the drying step.

9. A method for producing a resin composition for electronic devices as described in claim 3, comprising: a granulation step of introducing metallic aluminum powder into a flame to vaporize and oxidize it, and obtaining spherical alumina particles through spheroidization due to surface tension upon cooling; a dissolution step of introducing the spherical alumina particles into a basic solution having a pH of 9 or higher and a liquid temperature of 20 to 60°C to dissolve the aluminum in a metallic state remaining in the spherical alumina particles; a drying step of drying the spherical alumina particles; and a resin dispersion step of dispersing the spherical alumina particles that have undergone the drying step into a resin composition to obtain a resin dispersion.

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