JP5417248B2 - Method for producing spherical alumina powder - Google Patents

Description

  The present invention relates to a method for producing spherical alumina powder, in which spheroidization is performed by supplying aluminum hydroxide powder having specific physical properties into a flame.

  Aluminum hydroxide powder, alumina powder, and aluminum powder supplied into a flame and sprayed into spheroidized alumina powder are excellent in thermal conductivity, filling properties, and insulation properties when blended with resin. Therefore, it is used as a filler for a resin for an insulating material such as a substrate. Particularly in recent years, spherical alumina is often blended into a resin for the purpose of heat dissipation, and it is necessary to increase the filling amount in order to impart high thermal conductivity. However, the spherical alumina powder produced by flame melting has a problem that it is inferior in filling property due to its narrow particle size distribution. Furthermore, since alumina has a higher α dose than silica, it is necessary to extremely reduce the uranium content in order to eliminate operation errors due to α rays when used for semiconductor applications.

  In order to solve this problem, for example, in Japanese Patent Application Laid-Open No. 2001-226117, spherical alumina powder having excellent filling properties is prepared by mixing spherical alumina having different average particle diameters produced by flame melting at a specific ratio. Have gained. However, this method has a drawback in that the number of steps increases because it undergoes a process of mixing after spheronization. Moreover, when the raw material powders having different average particle sizes are mixed in the stage before flame melting and then flame-melted to produce alumina powder, there is a problem that the particles are coalesced.

  Further, Japanese Patent Laid-Open No. 11-92136 discloses a method for producing a spherical alumina powder having a low α dose suitable for use in a semiconductor sealing material, after high-purity aluminum is melted in a high-purity graphite crucible, and then atomized. Thus, a method is disclosed in which an aluminum powder having an amount of uranium and thorium adjusted to less than 1 ppb is produced, and this is supplied into an air stream containing oxygen and burned. By this method, a low α-dose alumina powder having a uranium content of 10 ppb or less can be produced. However, this method is not preferable from the viewpoint of productivity because it comprises a two-step process in which high-purity aluminum is once melted and then flame-melted. Further, as is clear from the use of a high-purity graphite crucible, a measure for preventing contamination from an apparatus for melting aluminum is required.

JP 2001-226117 A JP-A-11-92136

  The object of the present invention is not only to produce spherical alumina with high thermal conductivity at low cost and high productivity, but also to resin compositions such as semiconductor encapsulants, which have excellent filling properties and low uranium content. It is providing the manufacturing method for obtaining spherical alumina powder which can provide high thermal conductivity.

  As a result of investigations to solve the above-mentioned problems, the present inventors, as a result, sprayed and supplied aluminum hydroxide powder having specific physical properties into a flame, so that spherical alumina has excellent filling properties and low uranium content. The inventors have found that powder can be produced efficiently and have arrived at the present invention.

That is, the present invention provides the following [1] to [6].
[1] In the particle size distribution measured by the laser diffraction scattering method, the average particle diameter D50 that is 50% by weight from the fine particle side is 2 μm or more and 100 μm or less, and the particle diameter that is 10% by weight from the fine particle side. A method for producing a spherical alumina powder, characterized by spraying aluminum hydroxide powder having a particle size distribution index D90 / D10 of 13 or more according to D10 and a particle diameter D90 of 90% by weight into a flame.
[2] D50 / (2 × R50) when the average pore radius of the aluminum hydroxide powder measured by the mercury intrusion method is R50 is 5 or more, according to the above [1] Production method.
[3] The production method according to [1] or [2], wherein the aluminum hydroxide powder has a uranium content of 10 ppb or less.
[4] In the particle size distribution measured by the laser diffraction scattering method, the average particle diameter D50 that is 50% by weight accumulated from the fine particle side is 2 μm or more and 100 μm or less, and the particle diameter that is 10% by weight accumulated from the fine particle side. D10 and a particle size distribution index D90 / D10 of 90% by weight particle size D90 is 4 or more and 12 or less, a specific surface area measured by a nitrogen adsorption method is 1 m ² / g or more and 4 m ² / g or less, and contains uranium A spherical alumina powder for resin filling, characterized in that the amount is 10 ppb or less.
[5] In the particle size distribution measured by the laser diffraction scattering method, the average particle diameter D50 that is 50% by weight accumulated from the fine particle side is 2 μm or more and 100 μm or less, and the particle diameter that is 10% by weight accumulated from the fine particle side D10 and the particle size distribution index D90 / D10 with a particle size D90 of 90% by weight is 13 or more, and D50 / (2 × R50) is 5 or more when the average pore radius measured by the mercury intrusion method is R50. An aluminum hydroxide powder for producing spherical alumina, characterized in that
[6] The aluminum hydroxide powder for producing spherical alumina as described in [5] above, wherein the uranium content is 10 ppb or less.

  According to the production method of the present invention, it is possible to obtain a low-a dose spherical alumina powder having excellent filling properties and low uranium content.

FIG. 1 is a diagram illustrating an apparatus for producing spherical alumina powder in the present invention.

  Hereinafter, the present invention will be described in detail.

  The average particle diameter D50 of the raw aluminum hydroxide powder (hereinafter sometimes referred to as “raw aluminum hydroxide powder”) used in the production method of the present invention is 2 μm or more and 100 μm or less, preferably 3 μm or more and 70 μm or less, More preferably, it is 3 μm or more and 50 μm or less. Here, in the present invention, the average particle diameter D50 (hereinafter sometimes simply referred to as “D50”) is an average particle that is 50% by weight cumulative from the fine particle side in the particle size distribution measured by the laser diffraction scattering method. The diameter. When the average particle diameter D50 of the raw aluminum hydroxide powder is smaller than 2 μm, the collection efficiency is lowered, and when it is larger than 100 μm, the surface may be roughened during spheroidization.

  The particle size distribution index D90 / D10 of the raw aluminum hydroxide powder used in the production method of the present invention is 13 or more, preferably 15 or more. Here, in the present invention, D10 and D90 refer to particle diameters that are 10% by weight and 90% by weight, respectively, accumulated from the fine particle side in the particle size distribution measured by the laser diffraction scattering method. This value is an index indicating the width of the particle size distribution, and the larger the value, the wider the particle size distribution. When the value of D90 / D10 of the raw aluminum hydroxide powder is 13 or more, the particle size distribution of the obtained spherical alumina powder becomes wide, the resin viscosity when blending the spherical alumina powder into the resin is lowered, and the filling amount is reduced. Since it can increase, it is preferable. The upper limit value of D90 / D10 is not particularly limited, but is preferably 30 or less. When the value of D90 / D10 is too large, the difference in particle size between the fine particles and the coarse particles tends to be large, and the fine particles tend to adhere to the surface of the coarse particles, and there is a possibility that they may be fused during flame melting.

  The particle size distribution index D80 / D20 of the raw aluminum hydroxide powder used in the production method of the present invention is preferably 5 or more and 15 or less, more preferably 5 or more and 10 or less. In the present invention, D20 and D80 refer to particle sizes that are 20% by weight and 80% by weight, respectively, accumulated from the fine particle side in the particle size distribution measured by the laser diffraction scattering method. When this value is in the above range, the resin filling property tends to be further improved, which is preferable.

The raw aluminum hydroxide powder used in the production method of the present invention preferably has a D50 / (2 × R50) of 5 or more, more preferably 5 or more, where the average pore radius measured by the mercury intrusion method is R50. Is 10 or more. Further, D50 / (2 × R50) is preferably 50 or less. Here, in the present invention, the average pore radius (μm) is measured from the range of 0.0010 μm to 100 μm as the pore radius by mercury porosimetry, and the total pore volume V (ml / g) The pore area A (m ² / g) is calculated, and the pore radius (μm) calculated from the formula (2 × V) / A. If this value is too small, the viscosity when the obtained spherical alumina powder is blended with the resin is increased, and the filling amount cannot be increased. On the other hand, if the size is too large, the gap between the particles is extremely small, so that adjacent particles are fused in the process of spheronization, and there is a possibility that a spherical alumina powder having a desired particle size distribution cannot be obtained. Furthermore, as a result, the viscosity may increase when blended in the resin, which is not preferable.

In the production method of the present invention, the lower limit of the specific surface area measured by the nitrogen adsorption method of the aluminum hydroxide powder used as a raw material is preferably 0.5 m ² / g or more, more preferably 1 m ² / g or more. It is. When the specific surface area of the raw aluminum hydroxide powder is too small, the particle size distribution of the resulting spherical alumina powder becomes sharp, which tends to deteriorate the resin filling property of the spherical alumina powder, which is not preferable. Moreover, it is preferable that the upper limit of a specific surface area is 10 m < ² > / g or less, More preferably, it is 8 m < ² > / g or less. When the specific surface area is too large, the amount of fine particles increases, and there is a possibility that a spherical alumina powder having a desired average particle size and particle size distribution may not be obtained, which is not preferable. In addition, the particle surface may be roughened or pores may be formed. In this case, the resin filling property tends to deteriorate.

  Examples of the crystal form of the starting aluminum hydroxide powder used in the production method of the present invention include trihydrates such as gibbsite and bayerite, and monohydrates such as boehmite and diaspore. Among these, gibbsite is preferable because it is relatively low in hardness and can easily obtain aluminum hydroxide having an average particle diameter of 2 μm or more, which can avoid wear of manufacturing equipment. When the raw aluminum hydroxide powder contains crystalline aluminum hydroxide other than gibbsite, the content is preferably 5% by weight or less. The content of aluminum hydroxide having other crystal types can be calculated from the intensity ratio of the main peak by X-ray diffraction measurement.

When the spherical alumina powder is used for a semiconductor element sealing material, it is necessary to have a low α dose, that is, a low uranium content in the spherical alumina powder. Specifically, it is desirable to suppress the uranium content in the spherical alumina powder to 10 ppb or less. Here, since the uranium content in the spherical alumina powder depends on the uranium content contained in the raw aluminum hydroxide powder, in order to produce a spherical alumina powder with a low uranium content, aluminum hydroxide as a raw material is used. It is important to keep the content of uranium as small as possible.
Therefore, the uranium content of the starting aluminum hydroxide powder used in the production method of the present invention is preferably 10 ppb or less, and more preferably 8 ppb or less. It is preferable to use a raw aluminum hydroxide powder having a uranium content of 10 ppb or less because a low α-dose spherical alumina powder having a uranium content of 10 ppb or less can be obtained. The lower limit of the uranium content in the raw aluminum hydroxide powder is not particularly limited and is preferably as low as possible, but is usually about 3 ppb.

As described in JP-A-60-246220, the uranium content in aluminum hydroxide as a raw material is several hundreds of uranium in aluminum hydroxide obtained by the buyer method using bauxite as a raw material. It is known that there are many ppb. This is because the organic matter extracted from bauxite is gradually accumulated in the liquid by circulating the sodium aluminate aqueous solution in the Bayer method.
Therefore, for example, the raw material for obtaining the sodium aluminate aqueous solution is changed from bauxite to aluminum hydroxide having an organic content of less than 0.1% by weight, thereby reducing the organic content in the aqueous sodium aluminate solution. be able to. Specifically, it can be 10 mg / L or more and 1000 mg / L or less, preferably 10 mg / L or more and 500 mg / L or less. Further, by adding an adsorbent to the aqueous solution to remove organic matter having high adsorptive property or decomposing the organic matter using an oxidizing agent, an aqueous sodium aluminate solution having a lower organic matter content can be obtained. . By precipitating aluminum hydroxide using the sodium aluminate aqueous solution thus obtained, the uranium content in the obtained aluminum hydroxide can be reduced to 10 ppb or less.

Even when the spherical alumina powder is used for electronic parts such as a semiconductor encapsulant, it is important to reduce the amount of soluble Na from the viewpoint of moisture resistance reliability. This amount of soluble Na depends on the amount of Na contained in aluminum hydroxide as a raw material. For this reason, the smaller the amount of non-soluble and soluble Na contained in the raw aluminum hydroxide powder, the less the gasified Na produced during spheronization, and the soluble Na amount of the resulting spherical alumina powder. Can be reduced. Therefore, the amount of Na contained in the raw material aluminum hydroxide powder used in the production method of the present invention is 0 in terms of the total amount of non-soluble and soluble Na and converted to oxide (Na ₂ O). It is preferably 20% by weight or less, and more preferably 0.15% by weight or less.

  The manufacturing method of the raw material aluminum hydroxide powder used in the manufacturing method of the present invention is not particularly limited, and can be manufactured by a method generally used in this field, but manufactured by the buyer method. Is preferred. Specifically, for example, aluminum hydroxide as a seed is added to a sodium aluminate aqueous solution manufactured by the Bayer method, and the liquid temperature is maintained at 30 to 90 ° C. It can be produced by decomposing and precipitating the aluminum content. The crystal form of aluminum hydroxide produced by this method is usually a gibbsite type.

Furthermore, the raw material aluminum hydroxide powder may be surface-treated. As the surface treatment agent used for the surface treatment, a surface treatment agent generally used in this field can be used, and examples thereof include silane coupling agents, titanate coupling agents, and fatty acids such as stearic acid. In particular, by using aluminum hydroxide coated with a silane coupling agent or titanate coupling agent, the surface treatment agent is thermally decomposed during thermal spraying even if the content of Na ₂ O in the aluminum hydroxide powder as a raw material is high. As a result, an inorganic oxide layer is formed on the surface of the spherical alumina powder, and the effect of reducing the amount of soluble Na can be expected.

  The surface treatment method is not particularly limited and may be either a wet method or a dry method. From the viewpoint of productivity, the dry method is preferable. Specifically, it can be carried out by flowing aluminum hydroxide powder in a super mixer or a V-type mixer, and adding and mixing a surface treatment agent there. In addition, for example, a method of adding a surface treatment agent in the step of pulverizing with a vibration mill or a ball mill can be mentioned.

In the case of a coupling agent, the amount of the surface treatment agent is preferably 0.5% by weight or less in terms of SiO ₂ and TiO ₂ . When the amount of the surface treatment agent exceeds 0.5% by weight, the surface coating amount increases, so that the surface area decreases, but the particles may coalesce to produce coarse particles.
Moreover, it is preferable that the compounding quantity of a surface treating agent is 0.01 weight part or more and 1 weight part or less with respect to 100 weight part of aluminum hydroxide powder.

  The raw material aluminum hydroxide powder having the physical properties described above is not limited to the production method of the present invention, but can be used as a raw material for producing spherical alumina by a general method in this field. In particular, it is possible to produce a spherical alumina powder that is particularly efficient and has excellent filling properties and a low uranium content.

  The production method of the present invention can be carried out, for example, using an apparatus as shown in FIG. The spherical alumina powder production apparatus shown in FIG. 1 passes through a thermal spraying furnace 1 and a thermal spraying furnace in which a burner 2 connected to a combustible gas supply pipe 3, a combustion-supporting gas supply pipe 4, and a raw material supply pipe 5 is set on the top. It consists of a cyclone 6, a bag filter 7 and a blower 8 for collecting the powder.

  Specifically, by supplying the raw aluminum hydroxide powder into the flame from the raw material supply pipe in a state of being dispersed in the carrier gas, the aluminum hydroxide can be spheroidized to produce a spherical alumina powder.

The raw aluminum hydroxide can be supplied, for example, by dispersing the raw aluminum hydroxide powder in water and supplying it in a slurry state. However, in the production method of the present invention, from the viewpoint of productivity, it depends on the latent heat of evaporation of water during spraying. Since there is no loss of heat, the raw material aluminum hydroxide is sprayed in powder form.
The amount of water contained in the raw aluminum hydroxide powder is preferably 0.5% by weight or less. When the water content is within the above range, the adhesion between the particles is weak, and when the powder is supplied into the flame, it is possible to suppress the formation of coarse particles due to the coalescence of the particles, which is preferable.

  The raw aluminum hydroxide powder is sprayed and supplied into the flame by the carrier gas. Examples of the carrier gas include oxygen, air, nitrogen, etc., but oxygen is preferably used. The concentration (aluminum hydroxide powder supply amount (g) / carrier gas supply amount (NL)) when supplying aluminum hydroxide powder dispersed in the carrier gas is preferably 1.0 or more and 10.0 or less. . If the concentration is too high, the concentration of the aluminum hydroxide powder in the carrier gas is increased, the dispersibility of the powder is reduced when supplied into the flame, and the powders are fused in the process of spheroidization. This is not preferable because the particle diameter of the resulting spherical alumina powder tends to increase.

  The supply amount of the raw aluminum hydroxide powder into the flame is 0.01 to 2.0 in terms of the concentration in the flame (aluminum hydroxide powder supply amount (g) / gas supply amount (NL)). preferable. Here, the gas supply amount refers to the total amount of the combustible gas supply amount, the combustion support gas supply amount, and the carrier gas supply amount. When the concentration is too low, the supply amount of the aluminum hydroxide powder is reduced, so that the productivity is lowered. On the other hand, when the amount is too high, the amount of the aluminum hydroxide powder that contacts the flame at a time increases, so that fusion between the particles occurs and the particle diameter of the resulting spherical alumina powder tends to increase, which is not preferable.

  Further, the supply amount of the raw aluminum hydroxide powder into the flame is preferably 10.0 or less in terms of the combustible gas ratio (aluminum hydroxide powder supply amount (g) / combustible gas supply amount (NL)). More preferably, it is 6.0 or less. If the combustible gas ratio is too high, the amount of aluminum hydroxide powder supplied to the flame at a time increases, making it difficult to spheroidize the entire amount, so that the desired spherical alumina powder of the present invention can be obtained. It is not preferable. The lower limit of the combustible gas ratio is usually 0.1 or more from the viewpoint of productivity.

  In the production method of the present invention, examples of the flammable gas include propane, butane, propylene, acetylene, hydrogen, and the like. Among them, propane [for example, liquefied propane gas (LPG)] is preferable. Examples of the combustion-supporting gas include air and oxygen. Among these, oxygen is preferable. The supply conditions of the combustible gas and the combustion-supporting gas can be appropriately set depending on, for example, the production amount, but are usually adjusted according to the supply amount of the raw material powder.

  The raw aluminum hydroxide powder sprayed in the flame is converted into alumina by a high-temperature flame and is spheroidized into a spherical alumina powder. The spherical alumina powder thus obtained is collected by a cyclone by being sucked by a blower. The powder not collected by the cyclone is collected by a bag filter, and then the exhaust gas is released to the atmosphere.

  The average particle diameter D50 of the spherical alumina powder of the present invention is 2 μm or more and 100 μm or less, preferably 3 μm or more and 70 μm or less, and more preferably 3 μm or more and 50 μm or less. Here, the average particle diameter D50 refers to an average particle diameter of 50% by weight accumulated from the fine particle side in the particle size distribution measured by the laser diffraction scattering method. When the average particle diameter D50 of the spherical alumina powder is smaller than 2 μm, the surface area becomes large, and there is a possibility that the mechanical properties are deteriorated when blended with the resin material. Sexuality gets worse.

  Furthermore, the particle size distribution index D90 / D10 of the spherical alumina powder of the present invention is preferably 4 or more and 12 or less, more preferably 4 or more and 10 or less. Here, D10 and D90 refer to particle sizes of 10% by weight and 90% by weight, respectively, accumulated from the fine particle side in the particle size distribution measured by the laser diffraction scattering method. When the particle size distribution index is too small, the filling property to the resin tends to be poor. When the particle size distribution index is too large, the coarse particles increase, so that the appearance tends to be deteriorated when the resin is filled.

The specific surface area measured by the nitrogen adsorption method of the spherical alumina powder of the present invention is 1 m ² / g or more and 4 m ² / g or less, preferably 1 m ² / g or more and 3 m ² / g or less. When the specific surface area is too small, the amount of fine particles is relatively reduced, and the filling property into the resin is deteriorated. On the other hand, when the specific surface area is too large, the surface of the particles becomes rough and the amount of fine particles increases, which may cause a significant increase in viscosity when mixed with the resin, which is not preferable.

  The uranium content of the spherical alumina powder of the present invention is 10 ppb or less, preferably 8 ppb or less. If the uranium content is 10 ppb or less, malfunction of the semiconductor element can be prevented, which is suitable for use as a semiconductor sealing material. The amount of uranium in the spherical alumina powder can be quantified by a known method such as glow discharge mass spectrometry, inductively coupled plasma mass spectrometry, or fluorescence spectrophotometry, but since the lower limit of quantification is small, Inductively coupled plasma mass spectrometry is preferred.

  In the spherical alumina powder of the present invention, the sphericity in the particle diameter range of 3 μm to 20 μm is preferably 0.90 or more. When the sphericity is 0.90 or more, the filling property to the resin is preferably improved.

  The amount of soluble Na in the spherical alumina powder of the present invention is preferably 1000 ppm or less in terms of Na, more preferably 500 ppm or less, and particularly preferably 300 ppm or less. When the amount of soluble Na contained in the spherical alumina powder is in the above range, the insulating property can be maintained and it can be suitably used as a filler for heat dissipation. The lower limit of the amount of soluble Na in the spherical alumina powder is not particularly limited, but it is preferably reduced as much as possible, and is usually about 1 ppm. In addition, when the moisture resistance reliability of the obtained spherical alumina powder is not sufficient, soluble Na adhering to the surface can be removed by a known method such as washing with water.

  The dioctyl phthalate oil absorption (ml / 100 g) (hereinafter sometimes referred to as “DOP oil absorption”) of the spherical alumina powder of the present invention is preferably 20 (ml / 100 g) or less, and 18 (ml / 100 g). 100g) or less is more preferable. The DOP oil absorption is an index indicating the filling property to the resin. The smaller the DOP oil absorption amount, the better the filling property to the resin, and it is possible to fill more spherical alumina powder per unit volume of resin. means. When the DOP oil absorption is in the above range, the spherical alumina powder can be filled into the resin well, and by adding the spherical alumina powder to the resin, high conductivity can be imparted to the resulting resin composition. This is preferable because it is possible. The lower limit value of the DOP oil absorption amount is not particularly limited and is preferably as small as possible, but is usually about 10 (ml / 100 g).

  In particular, the spherical alumina powder of the present invention can be efficiently produced by the production method of the present invention.

  The spherical alumina powder of the present invention is suitable for resin filler applications, and a wide range of resins can be applied. Specific examples include polyolefin resins typified by polyethylene and polypropylene, thermoplastic resins such as acrylic resins, thermosetting resins such as epoxy resins and phenol resins, and silicone resins composed of organosilicon compounds. . By blending the spherical alumina powder of the present invention with these resins, high thermal conductivity and insulation can be imparted, and therefore, it is particularly suitable for a heat radiating member of an electronic component.

  A resin composition can be obtained by mixing the spherical alumina powder of the present invention and a resin using a commonly used known method. For example, when the resin is in a liquid state (for example, a liquid epoxy resin), the resin composition can be obtained by mixing the liquid resin, the spherical alumina powder, and the curing agent and then curing the mixture with heat, ultraviolet light, or the like. A well-known thing and method can be used for a hardening | curing agent, a mixing method, and the hardening method. On the other hand, when the resin is in a solid state (for example, a polyolefin resin or an acrylic resin), after mixing the spherical alumina powder and the resin, the resin composition is obtained by kneading by a known method such as melt-kneading. Can do.

  The blending ratio of the spherical alumina powder of the present invention to the resin is preferably 90 to 20% by volume of the spherical alumina powder with respect to 10 to 80% by volume of the resin. When the blending ratio of the spherical alumina powder exceeds 90% by volume, the adhesiveness with the resin is lowered, so that the powder is liable to be detached, and the suppleness peculiar to the resin is impaired due to the hardened composition. Problems are likely to occur. On the other hand, when the blending ratio of the spherical alumina is less than 20% by volume, there is a possibility that sufficient improvement in thermal conductivity cannot be obtained.

  Hereinafter, the present invention will be described in more detail with reference to examples.

(1) Average particle size (D50), 10 wt% particle size (D10), 20 wt% particle size (D20), 80 wt% particle size (D80), 90 wt% particle size (D90)
The particle size was measured using a laser scattering type particle size distribution measuring device [“MICROTRACK HRA X-100” manufactured by Nikkiso Co., Ltd.]. The powder to be measured was added to a 0.2 wt% sodium hexametaphosphate aqueous solution, adjusted to a measurable concentration, then irradiated with ultrasonic waves with an output of 40 W for 5 minutes, and then measured (n = 2). The particle size was determined. The refractive index was 1.57 when measuring the raw aluminum hydroxide powder and 1.76 when measuring the spherical alumina powder.
D50 was determined from the particle size distribution obtained from a particle size of 50% by weight from the fine particle side, and D10, D20, D80, and D90 were determined from a particle size distribution obtained with a step size of 0.038 of [log (particle size)].

(2) Average pore radius (R50)
The average pore radius was calculated based on the measurement by mercury porosimetry. Using an Autopore III9420 manufactured by Micromeritics, the measurement was performed in the range from 0.0010 μm to 100 μm, and the total pore volume V (ml / g) and the total pore area A (m ² / g) were calculated. 2 * V) / A.

(3) Specific surface area According to the method prescribed | regulated to JIS-Z-8830, the specific surface area was calculated | required by the nitrogen adsorption method.

(4) Dioctyl phthalate oil absorption (ml / 100g)
The DOP oil absorption was measured according to the method specified in JIS-K-6221.

(5) Uranium content By heating aluminum hydroxide powder and spherical alumina powder in a mixed aqueous solution of sulfuric acid and phosphoric acid, the powder was dissolved to prepare an aqueous solution. Thereafter, uranium contained in the aqueous solution was extracted by contacting with a cyclohexane solution of tributyl phosphate, which is widely used as a uranium extractant. Thereafter, uranium transferred to the aqueous phase by back extraction brought into contact with pure water again was measured by the intensity of U238amu using ICP-MS. A standard solution manufactured by SPEX was used for preparing the calibration curve.

[Example 1]
As a raw material aluminum hydroxide, specific surface area: 3.5 m ^{2 /} g, D10: 1.6 μm, D20: 2.8 μm, D50: 7.8 μm, D80: 19.2 μm, D90: 26.8 μm, D90 / D10: 17, Gibbsite type aluminum hydroxide powder having physical properties of D80 / D20: 6.8, R50: 0.19 μm, D50 / (2 × R50): 21 was used. Conditions under which aluminum hydroxide powder was supplied and spheroidized in a high-temperature flame of 1500 ° C. or higher formed from combustible gas and combustion-supporting gas are as follows.
(1) Concentration in carrier gas (aluminum hydroxide powder supply amount (g) / carrier gas supply amount (NL)): 4.0
(2) Concentration in flame (aluminum hydroxide powder supply amount (g) / gas supply amount (NL)): 0.4
(3) Combustible gas ratio (aluminum hydroxide powder supply amount (g) / combustible gas supply amount (NL)): 2.4
(4) Combustible gas / flammable gas ratio: 0.23
Note that LPG was used as the combustible gas, and oxygen was used as the combustion-supporting gas and the carrier gas. Then, spherical alumina powder was obtained by collecting powder with a cyclone.

The obtained spherical alumina powder had physical properties of a specific surface area: 1.4 m ² / g, D50: 9.6 μm, D90 / D10: 4.3, DOP oil absorption: 16 ml / 100 g.

[Example 2]
A spherical alumina powder was obtained in the same manner as in Example 1 except that a gibbsite type aluminum hydroxide powder having the physical properties shown in Table 1 was used as the raw material aluminum hydroxide powder. Table 2 shows the physical properties of the obtained spherical alumina powder.

[Comparative Example 1]
A spherical alumina powder was obtained in the same manner as in Example 1 except that a gibbsite type aluminum hydroxide powder having the physical properties shown in Table 1 was used as the raw material aluminum hydroxide powder. Table 2 shows the physical properties of the obtained spherical alumina powder.

  From the results shown in Table 2, it was confirmed that according to the production method of the present invention, it is possible to obtain a spherical alumina powder having a low DOP oil absorption and excellent filling properties and a low uranium content.

  According to the production method of the present invention, it is possible to provide a low α-dose spherical alumina powder having excellent filling properties and low uranium content.

DESCRIPTION OF SYMBOLS 1 Thermal spray furnace 2 Burner 3 Flammable gas supply pipe 4 Supporting gas supply pipe 5 Raw material supply pipe 6 Cyclone 7 Bag filter 8 Blower

Claims (6)

  In the particle size distribution measured by the laser diffraction scattering method, the average particle diameter D50 that is 50% by weight accumulated from the fine particle side is 2 μm or more and 100 μm or less, and the particle diameter D10 that is 10% by weight accumulated from the fine particle side; A method for producing a spherical alumina powder, characterized in that an aluminum hydroxide powder having a particle size distribution index D90 / D10 of 13 or more with a particle diameter D90 of 90% by weight is sprayed into a flame.   2. The production method according to claim 1, wherein D50 / (2 × R50) of the aluminum hydroxide powder is 5 or more when an average pore radius measured by a mercury intrusion method is R50.   The method according to claim 1 or 2, wherein the aluminum hydroxide powder has a uranium content of 10 ppb or less. In the particle size distribution measured by the laser diffraction scattering method, the average particle diameter D50 that is 50% by weight accumulated from the fine particle side is 2 μm or more and 100 μm or less, and the particle diameter D10 that is 10% by weight accumulated from the fine particle side; The particle size distribution index D90 / D10 with a particle diameter D90 of 90% by weight is 4 or more and 12 or less, the specific surface area measured by the nitrogen adsorption method is 1 m ² / g or more and 4 m ² / g or less, and the uranium content is 10 ppb. A spherical alumina powder for resin filling, characterized by:   In the particle size distribution measured by the laser diffraction scattering method, the average particle diameter D50 that is 50% by weight accumulated from the fine particle side is 2 μm or more and 100 μm or less, and the particle diameter D10 that is 10% by weight accumulated from the fine particle side; The particle size distribution index D90 / D10 with a particle diameter D90 of 90% by weight is 13 or more, and D50 / (2 × R50) is 5 or more when the average pore radius measured by the mercury intrusion method is R50. An aluminum hydroxide powder for producing spherical alumina.   6. The aluminum hydroxide powder for producing spherical alumina according to claim 5, wherein the uranium content is 10 ppb or less.

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