TW201540669A - Low-soda [alpha]-alumina powder having excellent viscosity characteristics, and production method therefor - Google Patents

Abstract

Provided is a highly fillable low-soda [alpha]-alumina powder, which has a low soda fraction, an average particle diameter of 2 to 5 [mu]m, a sharp particle size distribution, and a low viscosity during resin filling. Also provided is a production method therefor. The low-soda [alpha]-alumina powder, which is an [alpha]-alumina powder prepared from aluminum hydroxide obtained by the Bayer method, has excellent viscosity characteristics, a soda (Na2O) fraction of 0.1% by mass or less, an average particle diameter (Dp50) of 2 to 5 [mu]m, a particle size distribution with an amount above 45 [mu]m sieve (+45 [mu]m) of 100 ppm or lower, and a span value [(Dp90 - Dp10)/Dp50] of 1.1 or lower. The [alpha]-alumina powder is prepared as follows: aluminum hydroxide having a soda (Na2O) fraction of 0.3% by mass or less is added with a halogen-type mineralization agent, fired so as to yield a formed density (forming pressure: 98.07 MPa) of 2.05 g/cm3 or greater and a BET specific surface area of 0.9 m2/g or less, and ground so that the particle size ratio (Dav/DBET), of the average particle diameter (Dav) after grinding over the BET-corresponding diameter (DBET) prior to grinding, is in the range of 1.10 to 1.45.

Description

Low soda alpha alumina powder with excellent viscosity characteristics and manufacturing method thereof

The present invention relates to an alpha alumina powder produced by the aluminum hydroxide obtained by the Bayer process, in particular to a low soda alpha alumina powder having a low viscosity of soda and highly filled in a resin or rubber. And its manufacturing method.

Alumina has been widely used as a filler filled in various resins in the past, and one of its main uses is as a heat-dissipating filler having both electrical insulating properties and chemical stability, such as a heat-dissipating sheet, an optical pickup member, a heat-dissipating grease, A bonding agent for a circuit board, a tape or an adhesive for imparting heat dissipation, various injection molded articles, a packaging material for a motor or IC, a copper-clad layer substrate, and the like are used in various fields and used in various applications.

When alumina is used as a heat-dissipating filler for resin filling, in order to fully achieve this purpose, in addition to a low soda (Na ₂ O) component, it is required to fill alumina with resin or rubber at an achievable ratio of as high as possible. In order to achieve high thermal conductivity. However, when the filling rate of the resin or the rubber is increased, the viscosity of the obtained alumina-filled resin composition (viscosity at the time of resin filling) is increased, the fluidity is deteriorated, and the moldability is lowered. In the case of use such as a heat dissipating sheet, in addition to the increase in hardness, the flexibility is insufficient to follow the unevenness of the object to be coated, and it is more difficult to degas and generate voids. Further, the amount of alumina to be filled cannot be increased, and thus there is a problem that the intended thermal conductivity cannot be obtained.

Therefore, several methods for solving the problems of thermal conductivity and moldability have been proposed in the past.

For example, in Patent Document 1, it is proposed that substantially no trimming (cutting surface) is provided, and three kinds of α-aluminas A, B, and C having different particle sizes are prepared, and the three kinds of α-alumina A are blended at a predetermined ratio. A method of forming a mixed powder by B and C, and adding the mixed powder to a resin or a rubber to form a molding resin or a rubber composition. However, in the method described in Patent Document 1, it is necessary to prepare three kinds of α-aluminas A, B, and C having different particle sizes, and to prepare the mixed powder at a predetermined ratio, and to separately prepare the three kinds of particle diameters. Different aluminas are used to eliminate the trimming process, increase the number of manufacturing steps, and the manufacturing equipment, quality management, and the like become complicated, and there is a problem that the manufacturing cost rises. In addition, the method of increasing the particle size distribution to achieve high filling has been carried out in the past, but the method has deteriorated the dispersibility due to the presence of fine particles, and is compared with the case where the same amount of filler having a sharp particle size is filled. The thermal conductivity of the composition is lowered, and further high filling is required in order to exhibit performance, so that the quality of the composition is also increased.

Further, Patent Document 2 proposes an alpha alumina which is composed of an aluminum salt obtained by a method other than the Bayer process, an alkane alumina, aluminum hydroxide, and transition alumina, and which is derived from alumina by firing. Precursor, with a particle size of 40 nm or less and a particle size super A mixture of crystal grains having a ratio of particles of 100 nm or more of 1% or less is fired in an atmosphere having a hydrogen chloride content of 1 to 20% by volume to produce a useful polyhedron and fineness as a filler to be added to the resin. A method of alpha alumina particles. However, in the method described in Patent Document 2, the α-alumina precursor obtained by a method other than the Bayer method must be fired together with a specific seed crystal in a hydrogen chloride-containing atmosphere, so that minute seed crystals must be prepared in advance. Particles, in addition, this treatment will take a lot of effort, not only industrially, costly and realistic, and the resulting alumina particles are nanometer size, which is not suitable for use in heat-dissipating fillers.

Further, in Patent Document 3, a fluorine compound-based mineralizer containing 0.02 to 0.3% by weight, and 0.5 to 10% by weight, based on fluorine, is added to an alumina raw material such as aluminum hydroxide or transition alumina. The α-alumina powder having an average particle diameter of 1 μm or less is filled in a sintered powder container, and calcined at a temperature of 1,500 ° C or lower, followed by pulverization to produce a low-soda alpha alumina. However, in the method described in Patent Document 3, low-soda alumina for ceramic use can be obtained, but the use of a filler such as a heat-dissipating filler which is most suitable for use as a filler material having the most importance of viscosity characteristics can not be obtained. performance.

Further, in Patent Document 4, a method is proposed in which a halide-depleted halide is added to aluminum hydroxide, and the resulting mixture is fired in a closed container composed of an alumina tight-fitting casing or a cordierite-tight casing. Then, a method of pulverizing to produce alumina having an α-direction as a main phase is carried out. However, in the method described in Patent Document 4, aluminum hydroxide having fine particles having a BET specific surface area of 3 to 20 m ² /g as a raw material for firing is not limited by the firing method and the like, and the casing cannot be improved. The amount of filling is markedly deteriorated, and the handling property after firing is also lowered.

Further, in Patent Document 5, it is proposed to heat-treat a composition containing a halide other than alumina, alumina hydrate, ammonium chloride, and ammonium chloride in a baking container, and also containing a boron compound. Next, a method of pulverizing by a jet mill to produce alumina composed of particles having a circular shape is produced. However, in the method described in Patent Document 5, since the mixed raw material of alumina and alumina hydrate is fired, a mixing step of alumina and alumina hydrate is required, and the production steps are complicated. Since the pulverized alumina is re-fired, additional cost is incurred, which is not suitable for mass production. Further, when the filling amount is equal, the particles having a circular shape have a problem that the contact point between the particles is lowered and the thermal conductivity of the composition is lowered as compared with the particles having an unformed shape.

Further, in Patent Document 6, it is proposed to add a fluorine compound or a fluorine compound and a boron compound to an alumina raw material composed of pseudo soft boehmite and/or transition alumina at a predetermined ratio, and to obtain The mixture is filled in a mullite-containing container, fired at a temperature of 1100 ° C or higher, and then pulverized to produce a method having a polyhedral shape and a narrow particle size distribution of α-alumina. However, in the method described in Patent Document 6, since pseudo-boehmite or transition alumina having a high specific surface area is used as the alumina raw material, the production of the alumina raw material requires a lot of cost, and when the filling amount is equal, In comparison, as the sphericity increases, the thermal conductivity of the composition decreases. Therefore, further high filling is required.

Therefore, it is required to develop a soda with a soda (Na ₂ O) content of 0.1% by mass or less and an average particle diameter of 2 to 5 μm, and the particle size distribution is sharp, and even if it is filled in a resin or a rubber at a high filling rate, it is obtained. The viscosity of the alumina-filled resin composition (viscosity at the time of resin filling) is also low, and the dispersibility is good, and an alumina powder of an alumina-filled resin composition having excellent moldability can be prepared, and it is required to use Bayer method. The obtained inexpensive aluminum hydroxide is used as a raw material to produce a method which is inexpensive.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 3,937,494

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2007-186,379

[Patent Document 3] Japanese Patent No. 3,389,642

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2003-201,116

[Patent Document 5] Japanese Patent Laid-Open Publication No. 2005-022963

[Patent Document 6] Japanese Patent Laid-Open Publication No. 2008-127,257

Therefore, the present inventors have developed an alumina alumina powder having a low soda, an average particle diameter of 2 to 5 μm, a sharp particle size distribution, and a low viscosity when the resin is filled, using the inexpensive aluminum hydroxide obtained by the Bayer process. The method was carefully investigated, and it was unexpectedly found that a specific firing container was used and sintered at a molding density (forming pressure: 98.07 MPa) of 2.05 g/cm ³ or more and a BET specific surface area of 0.9 m ² /g or less. The particle size ratio (D _av /D _BET ) of the average particle diameter (D _av ) after pulverization and the BET equivalent diameter (D _BET ) before pulverization is pulverized so as to be in a range of a predetermined value, thereby achieving the purpose of production. The alpha alumina is thus completed in the present invention.

Accordingly, an object of the present invention is to provide a low soda alpha alumina powder which has a low soda and an average particle diameter of 2 to 5 μm, a sharp particle size distribution, and good dispersibility during resin filling and low viscosity.

Further, another object of the present invention is to provide an inexpensive aluminum hydroxide obtained by the Bayer process as a raw material, which can produce the above-mentioned low soda and has an average particle diameter of 2 to 5 μm, a sharp particle size distribution, and good dispersibility when filled with a resin. The method for producing low-soda soda alpha alumina powder with low viscosity.

That is, the present invention is a low-soda alpha alumina powder having excellent viscosity characteristics, which is obtained by firing and pulverizing aluminum hydroxide obtained by a Bayer process, which is an alpha alumina powder. It is characterized in that the content of soda (Na ₂ O) is 0.1% by mass or less and the average particle diameter (Dp50) is 2 to 5 μm, and the particle size distribution is 45 μm on the sieve (+45 μm) and 100 ppm or less and the span value [(Dp90-Dp10) /Dp50]1.1 or less.

Further, the present invention is a method for producing a low soda alpha alumina powder having excellent viscosity characteristics, characterized in that a halogen-based mineralizer is added and mixed in a soda (Na ₂ O) fraction obtained by the Bayer process to be 0.3. 5% by mass or less of the aluminum hydroxide, and the obtained mixture is filled in a firing container made of alumina ceramic containing cerium oxide, and has a molding density (molding pressure: 98.07 MPa) of 2.05 g/cm ³ or more and a BET specific surface area. 0.9 m ² /g or less is fired in the range of 1100 to 1600 ° C, and the obtained fired product is obtained so that the average particle diameter (D _av ) after pulverization and the BET equivalent diameter before pulverization (D _BET ) The particle size ratio (D _av /D _BET ) is pulverized so as to be in the range of 1.10 to 1.45.

The low soda alpha alumina powder of the present invention has a soda (Na ₂ O) component of 0.1% by mass or less, and has an electrical insulating property, preferably 0.08% by mass or less, and an average particle diameter (Dp50) of 2 μm or more. 5 μm or less, the raw material is aluminum hydroxide derived from the Bayer process, and the dispersibility or thermal conductivity is considered, preferably 2.5 μm or more and 4.0 μm or less. Further, for the particle size distribution, the 45 μm sieve amount (+45 μm) is 100 ppm. Hereinafter, it is preferably 50 ppm or less, and the span value [(Dp90-Dp10)/Dp50] is 1.1 or less, preferably 1.0 or less.

Here, the amount of soda (Na ₂ O) is different depending on the use of the α-alumina powder. For example, in the use of electronic components, it is necessary to be 0.1% by mass or less, and when it exceeds 0.1% by mass, electricity cannot be obtained. Insulation problem. Further, when the average particle diameter is increased, the thermal conductivity of the molded product is increased for the average particle diameter (Dp50), and when the aluminum hydroxide obtained by the Bayer process is used as a raw material, it is difficult to form the α alumina powder. The primary particle diameter is formed to be 5 μm or more.

In addition, for the particle size distribution, the 45 μm sieve amount (+45 μm) must be 100 ppm or less, when the 45 μm sieve amount (+45 μm) is exceeded. When the α-alumina powder is filled in a resin composition as a filler, the coarse alumina is protruded from the surface of the resin composition, and the resin molded article having a small thickness cannot be used. In addition, the adhesion to the heat source may be impaired, and the desired heat dissipation effect may not be obtained. In addition, when the span value [(Dp90-Dp10)/Dp50] becomes wider than 1.1, it is equivalent to the filling. The thermal conductivity is lower than that of the filler having a sharper particle size distribution, and the agglomerated particles increase with the increase of the particulate fraction, and there is a problem that the alumina is difficult to uniformly disperse, and the preparation has a desired particle size, for example. It is difficult to design the particle size distribution when the α-alumina powder for use in the distribution of the heat-dissipating sheet, the sheet, and the heat-dissipating grease.

For the determination of the particle size distribution, the value of the 45 μm sieve amount (+45 μm) is the value measured using the test sieve of JIS Z8801-1 (mesh opening 45 μm), and in addition, the span value [(Dp90-Dp10)/ Dp50], using a laser scattering particle size analyzer [Microtrac 9320HRA (×100) manufactured by Nikkiso Co., Ltd.], and measuring the particle diameter (Dp90) corresponding to the cumulative particle size distribution rate of 90% by weight, respectively, corresponding to the integrated particle size distribution The particle diameter (Dp50) of 50% by weight, and the value (Dp10) corresponding to the particle size distribution ratio of 10% by weight, and the particle diameter ratio [(Dp90-Dp10)/Dp50] (span value) The system shows the sharpness of the particle size distribution, the smaller the span value, the sharper the particle size distribution.

Further, the low soda alpha alumina powder having excellent viscosity characteristics of the present invention is added to the unsaturated polyester resin in an amount of 200 parts by weight of the α alumina powder (acid value: 10.0 mgKOH/g or less at 25 ° C) Viscosity: 3.7 ± 0.7 poise, and density: 1.08 ± 0.02 g / cm ³ ) 100 parts by weight, using an impeller mill (Impeller Mill) and stirring at a peripheral speed of 2.6 m / sec and 10 minutes to modulate oxidation When the aluminum resin is filled with the resin composition, the viscosity of the obtained alumina-filled resin composition is measured using a Brookfield Viscometer at a rotor rotation speed of 12 rpm and a measurement temperature of 25 ° C (viscosity at the time of resin filling). It is 60 Poise or less, preferably less than 55 Poise, and particularly preferably 50 Poise or less. When the viscosity at the time of filling the resin exceeds 60 Poise, it is difficult to perform kneading with the resin, and the fluidity is also deteriorated during molding, so that the filling property in the resin or the rubber is lowered, and it is difficult to obtain the desired. In addition to the high thermal conductivity, the molding processability is lowered to cause voids in the resin molded article.

Next, a method for producing the low soda alpha alumina powder having excellent viscosity characteristics of the present invention will be described in detail.

In the present invention, a halogen-based mineralizer is added and mixed to the above-described aluminum hydroxide, and the resulting mixture is fired under predetermined conditions, and then the obtained fired product is pulverized under predetermined conditions.

In the production of the low soda alpha alumina powder having excellent viscosity characteristics of the present invention, the alumina raw material is aluminum hydroxide having a soda (Na ₂ O) fraction obtained by the Bayer process of 0.3% by mass or less, preferably used. The average secondary particle diameter measured by a laser scattering particle size analyzer [Microtrac 9320HRA (×100) manufactured by Nikkiso Co., Ltd.) is 10 μm or more and 200 μm or less, and more preferably 30 μm or more and 150 μm or less of aluminum hydroxide. When the average secondary particle diameter of the aluminum hydroxide used as the alumina raw material is less than 10 μm, it is difficult to obtain α-alumina having a desired particle diameter, and the handleability is deteriorated, and there is a concern that the production efficiency is lowered. On the contrary, it is more than 200 μm. In the case where sintering unevenness occurs in the particles, the particle size distribution is made flat, and the time required for the pulverization is increased, and there is a fear that the unpulverized particles remain. The alumina raw material obtained by a method other than the Bayer method, for example, the neutralization method, has a high specific surface area, and thus is difficult to use in the present invention.

Here, examples of the halogen-based mineralizer added to aluminum hydroxide include fluoride-based mineralizers such as aluminum fluoride, sodium fluoride, cryolite, magnesium fluoride, and calcium fluoride, or It is a chloride-based mineralizer such as hydrogen chloride, ammonium chloride or aluminum chloride, or an iodide-based mineralizer such as ammonium iodide, and a halogen-based mineralizer added to aluminum hydroxide. Depending on the type of the mineralizer to be used, for example, in the case of a fluoride-based mineralizer, the fluorine-converted blending ratio in the mixture is 0.05% by mass or more and 1.0% by mass or less, preferably 0.1% by mass or more. A ratio of 0.5% by mass or less. When the amount of the halogen-based mineralizer added is less than 0.05% by mass, the particle growth effect of alumina is insufficient, and alumina particles having a sufficient particle diameter may not be obtained. Conversely, when it is more than 1.0% by mass, the alumina particles are obtained. In the form of a plate, there is a problem that the viscosity is deteriorated or the particles are easily broken.

Next, the mixture obtained by adding and mixing a halogen-based mineralizer to aluminum hydroxide is fired, and in the firing of the mixture, the mixture must be filled in a firing container made of alumina ceramic containing cerium oxide. The molded density (molding pressure: 98.07 MPa) of the obtained fired product is 2.05 g/cm ³ or more, preferably 2.1 g/cm ³ or more and 2.5 g/cm ³ or less, and the BET specific surface area is 0.9 m ² /g or less. It is preferably calcined in a manner of 0.4 m ² /g or more and 0.8 m ² /g or less. The specific baking temperature and firing time are due to the particle size of aluminum hydroxide used as an alumina raw material, or The type and amount of the halogen-based mineralizer to be added are different, and usually the firing temperature is in the range of 1100 ° C to 1600 ° C, preferably in the range of 1400 ° C to 1550 ° C, and the firing time is usually several minutes or more. It is 24 hours or less, preferably several hours or more and 20 hours or less. When the molding density (molding pressure: 98.07 MPa) of the obtained fired product is less than 2.05 g/cm ³ , the particle shape of the alumina tends to be plate-like, or the viscosity is deteriorated, and the average particle diameter when pulverized to the destination is obtained. When (Dp50) is 2 to 5 μm, there is a concern that the viscosity at the time of resin filling exceeds 60 Poise, and when the BET specific surface area exceeds 0.9 m ² /g, the particles formed by firing become grown. Insufficient, even if the particle size ratio (D _av /D _BET ) of the average particle diameter (D _av ) after pulverization to the BET equivalent diameter (D _BET ) before pulverization is 1.10 or more and 1.45 or less, there is also an objective average particle. The diameter (Dp50) is less than 2~5μm, or the span value exceeds 1.1. In addition, when the baking temperature is lower than 1,100 ° C, the primary particles cannot grow to the intended particle diameter, and conversely, when the temperature exceeds 1600 ° C, the aluminum oxide is melted or the like, and the handleability is deteriorated.

Here, the above-mentioned molding density (molding pressure: 98.07 MPa) was measured by using a hydraulic pressure type 20 ton compression tester (manufactured by Maeda Test Machine Co., Ltd.), and measuring the mass and volume of a block molded into 40 mm × 20 mm × 10 mm. In addition, the BET specific surface area is a value measured by an N ₂ gas adsorption method using a specific surface area automatic measuring device (Flow Sorb II 2300 manufactured by Micromeritics Co., Ltd.).

Then, the ratio of the particle diameter (D _av /D _BET ) of the average particle diameter (D _av ) after pulverization to the BET equivalent diameter (D _BET ) before pulverization is 1.10 or more and 1.45 or less, in the calcined product obtained above. The pulverization is preferably carried out so as to be in the range of 1.15 or more and 1.40 or less. In the pulverization of the fired product, when the particle diameter ratio (D _av / D _BET ) is less than 1.45, the pulverization is insufficient, and the viscosity at the time of resin filling is increased by more than 60 poise, and conversely, less than 1.10. In the case of excessive pulverization, a large amount of cracked particles (fine particles) are generated, and not only the particle size distribution is flattened, but also the cracked particles are aggregated to generate coarse particles, which makes it difficult to uniformly disperse the alumina.

In the pulverization of the fired product, the particle diameter ratio (D _av /D _BET ) of the average particle diameter (D _av ) after pulverization and the BET equivalent diameter (D _BET ) before pulverization is managed to be 1.10 or more and 1.45 or less. Specifically, the BET specific surface area S (m ² /g) of the fired product is measured before the start of the pulverization of the fired product, and the measured value of the BET specific surface area S (m ² /g) and α are used. The density of alumina (true specific gravity ρ: 3.98 g/cm ³ ), from the following BET specific surface area S (m ² /g) and density (true specific gravity ρ (g/cm ³ ), that is, BET equivalent In the diameter (D _BET )=6/Sρ (but S is the BET specific surface area, and ρ is the true specific gravity of the α alumina of 3.98), the BET equivalent diameter (D _BET ) is calculated, and the BET equivalent diameter (D) is calculated. _BET ) is an index so that the particle diameter ratio (D _av /D _BET ) of the average particle diameter (D _av ) after pulverization is in the range of 1.10 or more and 1.45 or less.

The means for pulverizing the above-mentioned fired product is not particularly limited as long as the target particle diameter ratio (D _av /D _BET ) of 1.10 or more and 1.45 or less can be achieved, and for example, a vibrating mill or a vibrating ball mill can be used. A container-driven media mill such as a rotary ball mill or a planetary mill, or a medium agitating mill, a jet mill, a reverse jet mill, a jet mill or the like, or the like.

In the α-alumina powder produced by the method of the present invention, even if the aluminum hydroxide obtained by the Bayer process is used as an alumina raw material, the soda (Na ₂ O) fraction is 0.1% by mass or less, and the average particle diameter is 0.1% by mass or less. (Dp50) is 2~5μm, and the particle size distribution is 45μm sieve amount (+45μm) 100ppm or less, and the distribution width [(Dp90-Dp10)/Dp50]: 1.1 or less is sharp, and the viscosity is low when the resin is filled. Highly filled low soda alpha alumina powder.

The low soda alpha alumina powder having excellent viscosity characteristics of the invention is low soda and has an average particle diameter of 2 to 5 μm, has a sharp particle size distribution, and has good dispersibility during resin filling and low viscosity, and is not only used as a resin. The aluminum oxide for filling is easy to carry out the particle size distribution design when preparing the alumina powder having a specific particle size distribution.

Further, according to the method for producing an α-alumina powder of the present invention, the aluminum hydroxide obtained by the Bayer process can be used to inexpensively produce the above-mentioned low soda alpha alumina powder having excellent viscosity characteristics, and can be easily and surely Perform step management of the manufacturing steps.

Hereinafter, embodiments of the present invention will be specifically described based on examples and comparative examples.

[Example 1]

The aluminum fluoride which is a halogen-based mineralizer is added and mixed in a ratio of 0.4% by mass in terms of alumina to the aluminum hydroxide obtained by the Bayer process (average secondary particle diameter: 55 μm and soda (Na ₂ O) (Part: 0.2% by mass), the obtained mixture was filled in a firing vessel made of alumina ceramic containing cerium oxide, and fired at 1500 ± 10 ° C for about 15 hours using a tunnel kiln. .

The soda (Na ₂ O) part, the molding density, and the BET specific surface area of the obtained fired product were measured. The results are shown in Table 1.

Then use the 6 liter (L) tank to contain 15mm A 7.6 kg vibration ball mill (manufactured by Chuo Seiki Co., Ltd.) for alumina ball so that the average particle diameter (D _av : Dp50) after pulverization becomes 3.0 μm, and the average particle diameter (D _av ) after pulverization and before pulverization The particle diameter ratio (D _av / D _BET ) of the BET equivalent diameter (D _BET ) was 1.23, and 1.5 kg of the fired product obtained by the above baking was pulverized to obtain α-alumina.

For the obtained α-alumina, a 45 μm sieve amount (+45 μm) as a particle size distribution was measured, and a particle diameter (Dp90) corresponding to an integrated particle size distribution ratio of 90% by weight and a particle size corresponding to a cumulative particle size distribution ratio of 50% by weight were measured. The diameter (Dp50) and the particle diameter (Dp10) corresponding to a cumulative particle size distribution ratio of 10% by weight were calculated for the span value [(Dp90-Dp10)/Dp50], and the viscosity at the time of resin filling was measured. The results are shown in Table 1.

[Embodiment 2]

Grinding machine for 300 liters (L) contains 20mm A 255 kg rotating ball mill (manufactured by Chuo Seiki Co., Ltd.) was used to make the average particle diameter (D _av : Dp50) after the pulverization to 3.1 μm, and the average particle diameter (D _av ) after pulverization and before pulverization The particle diameter ratio (D _av / D _BET ) of the BET equivalent diameter (D _BET ) was 1.27, and 50 kg of the fired product obtained in Example 1 was pulverized to obtain α-alumina.

With respect to the obtained α-alumina, the 45 μm sieve amount (+45 μm) and the span value as the particle size distribution were determined in the same manner as in Example 1, and the viscosity at the time of resin filling was measured. The results are shown in Table 1.

[Example 3]

The same rotating ball mill (manufactured by Central Chemicals Co., Ltd.) as in Example 2 was used so that the average particle diameter (D _av : Dp50) after the pulverization was 2.9 μm, and the average particle diameter (D _av ) after the pulverization and before the pulverization. The particle diameter ratio (D _av / D _BET ) of the BET equivalent diameter (D _BET ) was 1.19, and 50 kg of the fired product obtained in Example 1 was pulverized to obtain α-alumina.

With respect to the obtained α-alumina, the 45 μm sieve amount (+45 μm) and the span value as the particle size distribution were determined in the same manner as in Example 1, and the viscosity at the time of resin filling was measured. The results are shown in Table 1.

[Example 4]

The grinding machine used in the 300 liter (L) contains 15mm A 255 kg rotating ball mill (manufactured by Chuo Seiki Co., Ltd.) was used to make the average particle diameter (D _av : Dp50) after the pulverization to 3.1 μm, and the average particle diameter (D _av ) after pulverization and before pulverization The particle diameter ratio (D _av / D _BET ) of the BET equivalent diameter (D _BET ) was 1.27, and 50 kg of the fired product obtained in Example 1 was pulverized to obtain α-alumina.

With respect to the obtained α-alumina, the 45 μm sieve amount (+45 μm) and the span value as the particle size distribution were determined in the same manner as in Example 1, and the viscosity at the time of resin filling was measured. The results are shown in Table 1.

[Example 5]

The fired product prepared in the same manner as in Example 1 and having the soda (Na ₂ O) portion, the molding density, and the BET specific surface area shown in the first table was pulverized in the same manner as in Example 1 to obtain α. Alumina.

With respect to the obtained α-alumina, the 45 μm sieve amount (+45 μm) and the span value as the particle size distribution were determined in the same manner as in Example 1, and the viscosity at the time of resin filling was measured. The results are shown in Table 1.

[Comparative Example 1]

The fired product prepared in the same manner as in Example 1 and having the soda (Na ₂ O) portion, the molding density, and the BET specific surface area shown in the first table so as to have an average particle diameter after the pulverization (D _av : Dp 50 ) 3.7 μm, and the particle diameter ratio (D _av /D _BET ) of the average particle diameter (D _av ) after the pulverization and the BET equivalent diameter (D _BET ) before the pulverization was 1.48, and the α oxidation was obtained. aluminum.

With respect to the obtained α-alumina, the 45 μm sieve amount (+45 μm) and the span value as the particle size distribution were determined in the same manner as in Example 1, and the viscosity at the time of resin filling was measured. The results are shown in Table 1.

[Comparative Example 2]

Alumina (3 μm alumina) having an average particle diameter (Dp50) of 3 μm after mixing and pulverization at a mass ratio (3 μm alumina/5 μm alumina) of 8:2, and an average particle diameter (Dp50) after pulverization of 5 μm. Alumina (5 μm alumina) was prepared, and α-alumina having a soda (Na ₂ O) fraction of 0.07% by mass and having an average particle diameter (Dp50) after mixing of 2.8 μm was prepared.

With respect to the obtained α-alumina, the 45 μm sieve amount (+45 μm) and the span value as the particle size distribution were determined in the same manner as in Example 1, and the viscosity at the time of resin filling was measured. The results are shown in Table 1.

[Comparative Example 3]

The fired product prepared in the same manner as in Example 1 and having the soda (Na ₂ O) portion, the molding density, and the BET specific surface area shown in the first table so as to have an average particle diameter after the pulverization (D _av : Dp 50 ) 2.7 μm, and the particle diameter ratio (D _av /D _BET ) of the average particle diameter (D _av ) after the pulverization and the BET equivalent diameter (D _BET ) before the pulverization was 1.93, and the α oxidation was obtained. aluminum.

With respect to the obtained α-alumina, the 45 μm sieve amount (+45 μm) and the span value as the particle size distribution were determined in the same manner as in Example 1, and the viscosity at the time of resin filling was measured. The results are shown in Table 1.

[Comparative Example 4]

The fired product prepared in the same manner as in Example 1 and having the soda (Na ₂ O) portion, the molding density, and the BET specific surface area shown in the first table so as to have an average particle diameter after the pulverization (D _av : Dp 50 ) 3.8 μm, and the particle diameter ratio (D _av /D _BET ) of the average particle diameter (D _av ) after the pulverization and the BET equivalent diameter (D _BET ) before the pulverization was 1.57, and the α oxidation was obtained. aluminum.

With respect to the obtained α-alumina, the 45 μm sieve amount (+45 μm) and the span value as the particle size distribution were determined in the same manner as in Example 1, and the viscosity at the time of resin filling was measured. The results are shown in Table 1.

From the first table, it is understood that the α-alumina powders of Examples 1 to 5 are not only 0.1% by mass or less of soda (Na ₂ O) parts but also have an average particle diameter (Dp50) of 2 to 5 μm and 45 μm. The amount of sieve (+45 μm) is low, the span value is 1.1 or less, and the particle size distribution is sharp. Further, the viscosity at the time of resin filling is 60 poise or less, and the resin is excellent in resin filling property.

On the other hand, in the α-alumina powder of Comparative Example 1, the span value showed a lower value, but the 45 μm sieve amount (+45 μm) and the resin-filled viscosity showed a higher value, and the α oxidation of Comparative Example 2 The aluminum powder, the 45 μm sieve amount (+45 μm) and the viscosity at the time of resin filling showed a lower value, but the span value was higher, and in addition, the α alumina powder of Comparative Example 3 showed a lower span value. Value, but the viscosity at the time of resin filling showed an extremely high value. Further, the alpha alumina powder of Comparative Example 4 showed a lower value of the span value, but the amount of 45 μm sieve (+45 μm) and the resin filling Viscosity shows a higher value.

Claims (3)

A low-soda alpha alumina powder having excellent viscosity characteristics, which is obtained by firing and pulverizing aluminum hydroxide obtained by a Bayer process, and is characterized by: soda (Na) ₂ O) is 0.1% by mass or less and the average particle diameter (Dp50) is 2 to 5 μm, and the particle size distribution is 45 μm on the sieve (+45 μm) and 100 ppm or less and the span value [(Dp90-Dp10)/Dp50] 1.1 or less. a low soda alpha alumina powder having the excellent viscosity characteristic of claim 1, wherein the α alumina powder is added to 100 parts by weight of the unsaturated polyester resin in 200 parts by weight of the α alumina powder, and When the alumina filling resin composition was prepared by stirring at a peripheral speed of 2.6 m/sec and 10 minutes, the obtained alumina-filled resin composition was measured using a Brookfield Viscometer at a rotor rotation speed of 12 rpm. The viscosity of the alumina-filled resin composition (viscosity at the time of resin filling) measured at a temperature of 25 ° C was 60 poise or less. A method for producing a low soda alpha alumina powder having excellent viscosity characteristics, characterized in that a halogen-based mineralizer is added and mixed with hydrogen having a soda (Na ₂ O) fraction obtained by a Bayer process of 0.3% by mass or less Alumina, the obtained mixture is filled in a firing vessel made of alumina ceramic containing cerium oxide, and has a molding density (molding pressure: 98.07 MPa) of 2.05 g/cm ³ or more and a BET specific surface area of 0.9 m ² /g. The following method is fired in the range of 1100 to 1600 ° C, and the obtained fired product is then subjected to a particle diameter ratio of the average particle diameter (D _av ) after the pulverization to the BET equivalent diameter (D _BET ) before the pulverization ( D _av /D _BET ) is pulverized in such a manner as to be in the range of 1.10 to 1.45.