JP2019210166A - LOW-SODA α-ALUMINA POWDER AND PRODUCTION METHOD THEREOF - Google Patents

Abstract

To provide a low-soda α-alumina powder that is low-soda, is highly fillable into resins and rubbers and is excellent in viscosity properties as well; and also provide a production method thereof.SOLUTION: There is provided a low-soda α-alumina powder that has an average particle diameter (Dp50) of 2 μm to 5 μm, a total soda (T-NaO) content of 0.1 mass% or less, a free soda (f-NaO) of 0.001 mass% or more and 0.015 mass% or less, with the free soda having adhered to particle surfaces removable by washing, and a BET specific surface area of 1.0 m/g or more and less than 2.0 m/g. A production method thereof is also provided.SELECTED DRAWING: None

Description

  The present invention is an α-alumina powder produced from aluminum hydroxide obtained by the Bayer method, and particularly low soda and low soda α-alumina excellent in viscosity characteristics that can be filled in a resin or rubber. The present invention relates to a powder and a manufacturing method thereof.

  Alumina has been widely used as a filler for filling various resins, and one of its main uses is as a heat dissipating filler that combines electrical insulation and chemical stability. Sheets, optical pickup parts, heat release grease, circuit board potting agents, heat-dissipating tapes and adhesives, various injection molded products, motor and IC sealing materials, copper-clad laminates, and various other types Used in a wide range of applications in the field.

  As such industrially used alumina, calcined alumina obtained by calcining aluminum hydroxide obtained by the Bayer method is produced in large quantities. However, the soda component is unavoidably included in the aluminum hydroxide derived from the Bayer method, and if this is brought into the alumina as it is, the soda component will interfere with the electrical insulation, so the soda component is removed as much as possible. There is a need to.

  In addition, when alumina is used as a heat-dissipating filler for resin filling, in order to sufficiently fulfill its purpose, in addition to low soda content, alumina is filled in resin or rubber at the highest possible mixing ratio. To achieve high thermal conductivity. However, usually, when the filling rate into the resin or 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 molding processability is decreased. When used in applications such as heat-dissipating sheets, its hardness increases, flexibility is insufficient, and it may become impossible to follow the unevenness of the object to be coated, and it becomes difficult to deaerate and voids are generated. To do. Furthermore, there is a problem that the amount of alumina filling does not increase and the desired thermal conductivity cannot be obtained.

Therefore, in Patent Document 1, a soda content obtained by the Bayer method is added as Na ₂ O to 0.3% by mass or less of aluminum hydroxide and mixed with a halogen-based mineralizer, and a specific baking container is used. And then calcined so that the molding density (molding pressure: 98.07 MPa) is 2.05 g / cm ³ or more and the BET specific surface area is 0.9 m ² / g or less, and then the average particle diameter (D _av ) after pulverization and before pulverization by particle size ratio of the BET equivalent diameter _{(D BET) (D av /} D BET) is crushed so as to fall within a predetermined value range, the average particle size with a low soda is 2 to 5 [mu] m, Moreover, α-alumina powder having a sharp particle size distribution is obtained.

  The α-alumina powder in Patent Document 1 has good dispersibility at the time of resin filling and has a low viscosity at the time of resin filling, and is useful as an alumina for resin filling. However, there is a demand for further reducing the amount of soda when used as a heat dissipating filler such as an insulating material or an electronic component material, or as a ceramic application.

  Therefore, for example, as described in Patent Document 2, a method is known in which α-alumina powder is washed with repulp and further washed with flowing pure water to reduce the soda content. However, when such a cleaning treatment is applied to the α-alumina powder described in Patent Document 1, although the effect of reducing the soda content is confirmed, the filling property to the resin and the viscosity at the time of resin filling deteriorate. It has been found that this may cause a new problem.

  For example, as in Patent Document 3 and Patent Document 4, the surface of alumina is coated with a silane coupling agent to improve the compatibility with a matrix resin or rubber, or an alumina-filled resin composition Although it is known that the mechanical strength of a cured product obtained by curing is increased, the coating treatment with these silane coupling agents is different from that for removing the soda content of alumina.

Japanese Patent Laying-Open No. 2015-166294 JP 2008-150238 A Japanese Patent Laid-Open No. 11-209618 JP-A-3-237151

  When the α-alumina powder described in Patent Document 1 described above is washed with water, the problem of filling into the resin and the deterioration of the viscosity at the time of resin filling have been studied to investigate the cause. It was confirmed that the BET specific surface area of the washed α-alumina powder was increased. The reason for this is not completely clarified at this time, but it is considered that the surface of the alumina particles is hydrated. That is, it is considered that the surface of the alumina particles is roughened due to hydration, the BET specific surface area is increased, and the filling property and viscosity of the resin are deteriorated. Further, when the BET specific surface area is increased, the alumina particles are likely to aggregate, resulting in an undesirable quality for filler use, and further, heat resistance may be reduced by hydration. Moreover, there exists a possibility of causing the hardening inhibition of a silicone resin.

  Therefore, the present inventors have made extensive studies to obtain a low soda α-alumina powder that can be highly filled into a resin or rubber while further reducing soda content, and has excellent viscosity characteristics. The α-alumina powder is placed in a treatment aqueous solution in which an organic silane compound having a decomposable group is added to water, and the mixture is stirred to remove soda and to hydrate the surface of the alumina particles. It was found that the increase in the BET specific surface area can be prevented by being suppressed. The low-soda α-alumina powder obtained in this way can be filled in a resin or rubber with high viscosity and has excellent viscosity characteristics, thus completing the present invention.

  Accordingly, an object of the present invention is to provide a low soda α-alumina powder that is low soda, can be filled in a resin or rubber, and has excellent viscosity characteristics.

  Another object of the present invention is to use low-grade soda α-, which is low in soda and can be filled in a resin or rubber, and has excellent viscosity characteristics. An object of the present invention is to provide a method for producing a low soda α-alumina powder capable of obtaining an alumina powder.

That is, according to the present invention, the average particle size (Dp50) is 2 μm or more and 5 μm or less, the total soda (T-Na ₂ O) content is 0.1% by mass or less, and it adheres to the particle surface and is washed. Removable free soda (f-Na ₂ O) content is 0.001% or more and 0.015% or less and BET specific surface area is 1.0m ² / g or more and less than 2.0m ² / g This is a low soda α-alumina powder.

The present invention also provides a raw material alumina comprising an α-alumina powder having an average particle size (Dp50) of 2 μm or more and 5 μm or less and a total soda (T-Na ₂ O) content of 0.1% by mass or less. The ratio of the organic silane compound in the treatment aqueous solution to the raw material alumina powder is 0.010 mol / kg-Al ₂ O with respect to the treatment aqueous solution in which the organic silane compound having a hydrolyzable group is added to water. ₃ was charged so that the above is performed silanized to stirred, and solid-liquid separation, after drying the solid component, by crushing, of the free washable remove adhering to the particle surfaces soda ( Low soda α-alumina powder having a f-Na ₂ O) content of 0.001% by mass or more and 0.015% by mass or less and a BET specific surface area of 1.0 m ² / g or more and less than 2.0 m ² / g. A method for producing a low-soda α-alumina powder characterized in that a body is obtained.

The low soda α-alumina powder having excellent viscosity characteristics according to the present invention has an average particle diameter (Dp50) of 2 μm or more and 5 μm or less, and the raw material is aluminum hydroxide derived from the Bayer method, considering dispersibility and thermal conductivity. Preferably, it is 2.5 μm or more and 4.0 μm or less, and the total content of soda (T-Na ₂ O) is 0.1% by mass or less, preferably 0.08% by mass or less considering electric insulation. In addition, the content of free soda (f-Na ₂ O) that can be adhered to the particle surface and removed by washing is 0.001% by mass to 0.015% by mass, preferably 0.001% by mass to 0%. The BET specific surface area is 1.0 m ² / g or more and less than 2.0 m ² / g, preferably 1.2 m ² / g or more and 1.8 m ² / g or less.

Of these, the average particle size (Dp50) can be obtained by the Bayer method, although the larger the average particle size, the higher the thermal conductivity of the molded product made of a composition filled with resin or rubber as a filler. When aluminum hydroxide is used as a raw material, it is difficult to make the primary particle diameter of α-alumina 5 μm or more.
Further, the total content of soda (T-Na ₂ O) varies depending on the use of the α-alumina powder, but for example, in electronic parts use, it is essential that the content is 0.1% by mass or less. When it exceeds 0.1% by mass, there is a problem that electrical insulation cannot be obtained. Here, the raw material alumina powder before the silane treatment in the present invention contains about 0.02 to 0.03% by mass of free soda (f-Na ₂ O). Since the soda (f-Na ₂ O) content is reduced, the total soda (T-Na ₂ O) content of the low soda α-alumina powder according to the present invention is preferably as described above (0.08 mass). % Or less). In addition, it is needless to say that the total content of soda (T-Na ₂ O) should be reduced, but considering that the aluminum hydroxide derived from the Bayer method is used as a raw material, the low content according to the present invention. It is considered that the total soda content in the soda α-alumina powder and the raw material alumina powder described later is difficult to be less than 0.001% by mass with the current technology.
Regarding the BET specific surface area, when aluminum hydroxide obtained by the Bayer method is used as a raw material and the alumina obtained by firing it is pulverized, the BET specific surface area is less than 1.0 m ² / g. On the other hand, if it exceeds 2.0 m ² / g, as a result, the filling property into the resin or rubber is deteriorated, and in the case of the heat radiating sheet, the thermal conductivity is inferior.

Here, regarding the particle diameter of the alumina powder in the present invention, both are measured using a laser scattering particle size measuring instrument [Microtrac 9320HRA (× 100) manufactured by Nikkiso Co., Ltd.], and the average particle diameter (Dp50) is The particle size (Dp50) corresponds to an integrated particle size distribution rate of 50% by volume. The particle size (Dp90) described later is a particle size (Dp90) corresponding to an integrated particle size distribution rate of 90% by volume, and the particle size (Dp10) is a particle size (Dp10) corresponding to an integrated particle size distribution rate of 10% by volume. is there. The BET specific surface area is a value measured by an N ₂ gas adsorption method using a specific surface area automatic measuring device (Microsorbex Flowsorb II2300 type).

In addition, the total soda (T-Na ₂ O) content is determined by measuring the fluorescent X-ray intensity using a fluorescent X-ray analyzer (manufactured by Rigaku, ZSX100e), and calculating the content (mass by mass). %) Is quantified. On the other hand, the content of free soda (f-Na ₂ O) is such that water is added to the alumina powder (alumina powder: water = 1: 60 by mass ratio), and Na is eluted for 30 minutes in a boiling water bath. It was measured using an atomic absorption spectrophotometer (manufactured by Hitachi High-Technologies Corporation, Z-2000, measurement mode; atomic absorption, measurement wavelength range; 589.0 nm), and calculated by Na ₂ O conversion.

The low soda α-alumina powder in the present invention preferably has a silicon dioxide (SiO ₂ ) content of 0.040 mass% or more and 0.500 mass% or less. In general, the α-alumina powder contains SiO ₂ as an impurity, which is derived from a raw material or mixed in the course of firing, and the content thereof is about 0.01 to 0.03% by mass. On the other hand, in the present invention, Si derived from an organosilane compound is further included in the silane treatment, and therefore the surface of the alumina particles is roughened by hydration by using the SiO ₂ content as an index. It can be said that an increase in the BET specific surface area is suppressed. The silicon dioxide (SiO ₂ ) content is obtained by quantitatively converting Si into SiO ₂ by molybdenum blue absorptiometry using a double beam spectrophotometer (U-3010, manufactured by Hitachi, Ltd.).

  The low soda α-alumina powder in the present invention preferably has a DOP oil absorption of 15 ml / 100 g or more and 25 ml / 100 g or less, more preferably 15 ml / 100 g or more and 20 ml / 100 g or less. Good. If the DOP oil absorption is within this range, in addition to kneadability with resin and rubber, fluidity during molding and the like will be good, viscosity characteristics and filling properties will be excellent, and for example, voids will occur during molding. Not even that. Here, the DOP oil absorption is measured according to JIS K5101-1991. Specifically, the DOP oil is dropped on 5.0 g of alumina particles, and the amount of oil until it is combined into one dumpling is measured. The amount converted to 100 g of alumina particles is shown.

Such low soda α-alumina powders can be obtained by the following production method.
That is, the low soda α-alumina powder of the present invention has an average particle diameter (Dp50) of 2 μm or more and 5 μm or less, and a total soda (T-Na ₂ O) content of 0.1% by mass or less. -Alumina powder is used as raw material alumina powder, and this is put into a treatment aqueous solution in which an organic silane compound having a hydrolyzable group is added to water, followed by stirring silane treatment, solid-liquid separation, solid component Is dried and then crushed to produce.

First, with respect to the treatment aqueous solution used for the silane treatment, an organic silane compound having a hydrolyzable group is added to water, and at least a part of this hydrolyzable group is hydrolyzed and silanolated. An aqueous solution (that is, a treated aqueous solution containing an organic silanol). By treating the raw material alumina powder with such a treatment aqueous solution, it is possible to clean the free soda (f-Na ₂ O) content adhering to the surface of the alumina particles, and organic silanol is formed on the surface of the alumina particles. Since it adheres, the hydration of alumina particles can be suppressed, and an increase in the BET specific surface area can be suppressed.

Here, the organosilane compound is preferably an organic functional group (R ³ and R ⁵ ) and a hydrolyzable group (R ³ ) in one molecule as represented by the following general formulas (1) and (2). OR ¹ and OR ⁴ ), for example, by adding one or more of such organosilane compounds to water and stirring, a treatment aqueous solution as described above can be obtained. .
(R ¹ O) _3-m R ² _m Si-R ³ (1)
(In the formula, R ¹ independently represents an alkyl group having 1 to 2 carbon atoms which may have a substituent, and R ² represents an alkyl group having 1 carbon atom which may have a substituent. R ³ has at least one functional group selected from the group consisting of an epoxy group, a styryl group, a methacryl group, an acrylic group, an amino group, a ureido group, a mercapto group, and an isocyanate group in the chain and / or at the terminal. Represents an alkyl group, and m represents an integer of 0 to 1.)
(R ⁴ O) _4-n Si—R ⁵ _n (2)
[Wherein, R ⁴ independently represents an alkyl group having 1 to 2 carbon atoms which may have a substituent. R ⁵ independently represents an organic group having 1 to 10 carbon atoms (an alkyl group, an alkenyl group or an aryl group), and specifically includes a methyl group, a propyl group, a hexyl group, an octyl group, a decyl group, a vinyl group, a phenyl group. Groups and the like. N represents an integer of 1 to 2]

When the raw material alumina powder is treated with the treatment aqueous solution, the ratio of the organic silane compound in the treatment aqueous solution to the raw material alumina powder can be determined by the number of moles of the organosilane compound per 1 kg of the raw material alumina powder. moles (mol) / alumina raw material powder (kg-Al ₂ O _3)] is 0.010mol / kg-Al ₂ O ₃ or more, so preferably a 0.011mol / kg-Al ₂ O ₃ or more, The raw material alumina powder is put into the treatment aqueous solution and stirred. If this ratio is less than 0.010 mol / kg-Al ₂ O ₃ , the hydration of the alumina particles is not sufficiently suppressed, and the BET specific surface area increases. From the viewpoint of surely suppressing the hydration of alumina particles, there is no problem with the increase of this ratio, but the effect is saturated if it becomes too high, and it is derived from an organosilane compound during solid-liquid separation. Since the excess of organic silanol is removed, the cost effectiveness is reduced, and the processing amount of the raw material alumina powder is relatively reduced, and the processing efficiency (yield) is reduced. Therefore, if the upper limit is specified, about 0.20 mol / kg-Al ₂ O ₃ is sufficient.

  Further, the amount of the organosilane compound added in the treatment aqueous solution is preferably 0.1% by mass or more and 5.0% by mass or less, more preferably 0.1% by mass or more and 2.0% by mass or less. There should be. If this addition amount is 0.1% by mass or more, hydration of the alumina particles can be reliably suppressed, and an increase in the BET specific surface area can be suppressed. On the other hand, if the amount of the organic silane compound added to the treatment aqueous solution becomes too large, the removal effect of soda may be reduced, or excessive silane may adhere to the device, and it may take a lot of time to clean the equipment used. Therefore, the content is preferably 5.0% by mass or less.

  When the raw material alumina powder is treated with the treatment aqueous solution, the treatment aqueous solution charged with the raw material alumina powder is preferably stirred for about 1 to 24 hours, and preferably 12 hours to ensure the removal of the soda. It is good to stir above. On the other hand, since the effect is saturated even when the stirring time exceeds 24 hours, it can be said that the upper limit of the stirring time is about 24 hours in consideration of economy and the like.

Preferably, the raw material alumina powder is treated with the treatment aqueous solution so that the increase in the silicon dioxide (SiO ₂ ) content after the silane treatment is 0.02% by mass or more. That is, the content C1 of silicon dioxide (SiO ₂ ) in the raw material alumina powder is compared with the content C2 of silicon dioxide (SiO ₂ ) in the low soda α-alumina powder after silane treatment, and the difference C2 -C1 should be 0.02% by mass or more. Further, the upper limit of the difference C2−C1 is not particularly limited, but it can be said that 0.10% by mass is sufficient.

  After the silane treatment, the treated aqueous solution containing the raw material alumina powder is separated into solid and liquid using a vacuum filter, centrifuge, pressure filter, etc., and the solid components are recovered and dried. After that, crush. This solid component drying process may be performed by heating to about 100 to 110 ° C. In addition, since the solid components after drying are in a state of being partially agglomerated, for example, a mortar, a ball mill, or other general powder crushers and grinders are used for the crushing treatment. A material having an average particle diameter (Dp50) derived from the raw material alumina powder can be obtained.

In addition, α-alumina having an average particle diameter (Dp50) of 2 μm or more and 5 μm or less and a total content of soda (T-Na ₂ O) of 0.1% by mass or less is used as the raw material alumina powder in the present invention. About powder, it can obtain suitably by the method described in Unexamined-Japanese-Patent No. 2015-166294 (patent document 1). That is, a halogen mineralizer is added to and mixed with aluminum hydroxide having a total soda (T-Na ₂ O) content of 0.3% by mass or less obtained by the Bayer method, and the resulting mixture is subjected to predetermined conditions. Then, the fired product obtained is pulverized under predetermined conditions.

  Here, the aluminum hydroxide used as the alumina raw material in order to obtain the raw material alumina powder in the present invention is preferably an average of two measured by a laser scattering particle size measuring instrument (Microtrac 9320HRA (× 100) manufactured by Nikkiso Co., Ltd.). The secondary particle size may be 10 μm or more and 200 μm or less, more preferably 30 μm or more and 150 μm or less. If the average secondary particle diameter of the aluminum hydroxide is smaller than 10 μm, it is difficult to obtain a raw material alumina powder having a desired particle diameter, and handling properties may be deteriorated, resulting in a decrease in production efficiency. On the other hand, if it exceeds 200 μm, uneven firing occurs in the particles, the particle size distribution becomes broad, the time required for pulverization may increase, and unmilled particles may remain. In addition, since the alumina raw material obtained by methods other than the Bayer method, for example, the neutralization method, has a generally high specific surface area, its use is difficult in the present invention.

  Examples of halogen mineralizers added to aluminum hydroxide include fluoride mineralizers such as aluminum fluoride, sodium fluoride, cryolite, magnesium fluoride, calcium fluoride, hydrogen chloride, Examples thereof include chloride mineralizers such as ammonium chloride and aluminum chloride, and iodide mineralizers such as ammonium iodide. The amount of halogen-based mineralizer added to aluminum hydroxide varies depending on the type of mineralizer used. For example, in the case of a fluoride-based curing agent, the blending ratio in terms of fluorine in the mixture is 0.05% by mass. The ratio is 1.0% by mass or less, preferably 0.1% by mass or more and 0.5% by mass or less. If the addition amount of the halogen-based mineralizer is lower than 0.05% by mass, the alumina particle growth effect may be insufficient, and alumina particles having a sufficient particle size may not be obtained. If it is higher than%, the alumina particles become plate-like, resulting in problems that the viscosity is deteriorated and the particles are easily broken.

Next, a mixture obtained by adding and mixing a halogen-based mineralizer to aluminum hydroxide is fired. In firing the mixture, the mixture is filled in a firing container made of silica-containing alumina ceramic. green density (molding pressure: 98.07MPa) the baked product 2.05 g / cm ³ or more, preferably 2.1 g / cm ³ or more 2.5 g / cm ³ or less, and a BET specific surface area 0.9m ² / g or less, preferably calcined to be equal to or less than 0.4 m ² / g or more 0.8 m ² / g.

Here, the specific firing temperature and firing time vary depending on the particle size of aluminum hydroxide used as the alumina raw material, the type and amount of the halogen-based mineralizer to be added, and the firing temperature is usually 1100 ° C. The temperature is 1600 ° C. or lower, preferably 1400 ° C. or higher and 1550 ° C. or lower, and the firing time is usually several minutes or longer and 24 hours or shorter, preferably several hours or longer and 20 hours or shorter. Further, when the molding density (molding pressure: 98.07 MPa) of the obtained fired product is lower than 2.05 g / cm ³ , the alumina particle shape tends to be plate-like, the viscosity is deteriorated, and the target average particle diameter ( Dp50) When pulverized to 2 to 5 μm, there is a possibility that the viscosity of the low soda α-alumina powder according to the present invention, which is finally obtained, is deteriorated during resin filling. Furthermore, if the BET specific surface area exceeds 0.9 m ² / g, particle growth due to firing is insufficient, and even if pulverized, the target average particle diameter (Dp50) may be reduced. When the firing temperature is lower than 1100 ° C., primary particles can no longer grow to the target particle diameter. On the other hand, when the temperature exceeds 1600 ° C., welding of the low-soda α-alumina powder as the final target occurs. Handling may be deteriorated.

The molding density (molding pressure: 98.07 MPa) was measured by measuring the mass and volume of a piece molded into 40 mm × 20 mm × 10 mm using a hydraulic 20-ton compression tester (manufactured by Maekawa Tester). This is the calculated value. Further, BET specific surface area described above, using a specific surface area automatic measuring apparatus (Micromeritics Tex manufactured by Flow Sorb II2300 form), is a value measured by N ₂ gas adsorption method.

The fired product obtained as described above, then, the average particle size after pulverization (D _av) and the particle diameter ratio (D _av / D _BET) of the BET equivalent diameter before pulverization (D _BET) is It grind | pulverizes so that it may become 1.10 or more and 1.45 or less, Preferably it is 1.15 or more and 1.40 or less. In the pulverization of the fired product, if the above particle size ratio (D _av / D _BET ) is higher than 1.45, the pulverization is insufficient, and the resin filling of the low soda α-alumina powder of the present invention finally obtained is required. There is a risk that the viscosity at the time increases and the viscosity deteriorates. On the other hand, if it is lower than 1.10, pulverization is excessive and the generation of chipping particles (fine particles) increases, the particle size distribution becomes broad, and coarse particles in which the chipping particles are aggregated are generated, which is the final target product. There is a possibility that uniform dispersion of the low soda α-alumina powder may be difficult.

In the pulverization of the fired product, the particle size ratio (D _av / D _BET ) between the average particle diameter after pulverization (D _av ) and the BET equivalent diameter before pulverization (D _BET ) is 1.10 or more and 1.45 or less. to manage the range of, specifically, a BET specific surface area S of the calcined product before beginning the grinding of the fired product (m ² / g) was measured and the BET specific surface area S (m ² / g) The BET specific surface area S (m ² / g) and density (true specific gravity) below using the measured value of α and the density of the α-alumina powder as the raw material alumina powder (true specific gravity ρ: 3.98 g / cm ³ ) Relational expression with ρ (g / cm ³ ), that is, BET equivalent diameter (D _BET ) = 6 / Sρ (where S is the BET specific surface area, and ρ is the true specific gravity of α-alumina powder 3.98. ) To calculate the BET equivalent diameter (D _BET ), and using this BET equivalent diameter (D _BET ) as an index, the particle size ratio (D _av / D _BET ) to the average particle diameter (D _av ) after pulverization is 1. 10 or more .45 perform grinding so that within the following ranges.

The means for pulverizing the fired product is not particularly limited as long as the target particle size ratio (D _av / D _BET ) of 1.10 or more and 1.45 or less can be achieved. In addition, a container driving medium mill such as a vibration ball mill, a rotating ball mill, and a planetary mill, a medium agitation mill, an air flow type pulverizer such as a jet mill, a counter jet mill, and a jet mizer can be used.

The α-alumina powder produced by the above-described method has a total soda (T-Na ₂ O) content of 0.1% by mass or less despite the fact that aluminum hydroxide obtained by the Bayer method is used as the alumina raw material. The average particle size (Dp50) is 2 μm or more and 5 μm or less, and it is suitable as a raw material alumina powder for producing the low soda α-alumina powder according to the present invention. In addition, the α-alumina powder thus obtained preferably has a particle size distribution with a 45 μm sieve top amount (+45 μm) of 100 ppm or less, and a span value [(Dp90−Dp10 ) / Dp50] is 1.1 or less, more preferably 1.0 or less. Therefore, the low-soda α-alumina powder of the present invention produced using this α-alumina powder as a raw material alumina powder exhibits a similar particle size distribution, so that it has a low filling viscosity in resin and rubber. It becomes one of the factors that make a low-soda α-alumina powder.

  The low soda α-alumina powder of the present invention is further useful as alumina for resin filling because the soda content is further reduced, and it can be filled into a resin or rubber at a high level and has excellent viscosity characteristics. It is. In addition, the low soda α-alumina powder production method of the present invention uses calcined alumina obtained by calcining aluminum hydroxide derived from the Bayer method, and has low viscosity soda properties as described above. The powder can be produced inexpensively and industrially advantageously.

FIG. 1 is obtained by a preliminary test for examining the influence of α-alumina powder on water treatment, and is a graph showing the BET specific surface area of α-alumina powder before and after water treatment. . FIG. 2 is a graph showing the relationship between the ratio of the organic silane compound in the treatment aqueous solution to the raw material alumina powder (number of moles of the organic silane compound per 1 kg of the raw material alumina powder) and the BET specific surface area. Fig. 3 is a graph showing the relationship between the ratio of organosilane compound in the treated aqueous solution to the raw alumina powder (number of moles of organosilane compound per kg of raw alumina powder) and free soda (f-Na ₂ O) content. It is a thing. FIG. 4 shows the raw material alumina powder A after water treatment in which the raw material alumina powder A was treated in the same manner as in Comparative Example 2, and the α-alumina powder of Example 1 using the raw material alumina powder A as a raw material. This is a result of differential thermal analysis.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, this invention is not restrict | limited to these content. In addition, unless otherwise indicated, evaluation of the following physical property etc. was performed with the measuring instrument mentioned above and the measuring method.

[Preliminary experiment: Effect of water treatment on α-alumina powder]
First, in order to investigate the influence of α-alumina powder due to water treatment, the following preliminary experiment was conducted.
Aluminum fluoride obtained by the Bayer method (average secondary particle size: 55 μm and total soda (T-Na ₂ O) content: 0.2% by mass) was converted to 0.4 in terms of alumina as an aluminum fluoride as a halogen-based mineralizer. The mixture is added and mixed at a rate of mass%, and the obtained mixture is filled in a firing container made of alumina ceramic containing silica, and fired in a tunnel kiln furnace at 1500 ° C. ± 10 ° C. for about 15 hours. did. The molding density (molding pressure: 98.07 MPa) at that time and the BET specific surface area of the obtained fired product are as shown in Table 1.

Next, using a vibrating ball mill (manufactured by Chuo Kakoki Co., Ltd.) in which 7.6 kg of 15 mmφ alumina balls are contained in a 6 liter (L) pot, 1.5 kg of the fired product obtained by the above firing is pulverized. An α-alumina sample was obtained. At that time, the grinding time was changed so that the grinding time was 0 hours (Experiment No. 1), the grinding time was 2 hours (Experiment No. 2), the grinding time was 5 hours (Experiment No. 3), and the grinding time was Five α-alumina samples having 10 hours (Experiment No. 4) and a grinding time of 15 hours (Experiment No. 5) were prepared. Table 1 shows the pulverization conditions (pulverization time, particle size ratio (D _av / D _BET )) for obtaining these α-alumina samples, the physical properties of each α-alumina sample, etc. (α-alumina sample before water treatment) ).

Here, for the measurement of loss on ignition (LOI) of the α-alumina sample, the sample alumina powder was weighed W (g), ignited in the atmosphere at 1100 ° C. for 1 hour, and cooled alumina powder. The body weight loss W ′ (g) was obtained, and the alumina powder was separately weighed w (g), heated in the atmosphere at 300 ° C. for 3 hours, and the alumina powder weight loss w ′ (g) after cooling. Was calculated from the following formula (3). Of these, the weight loss w ′ by heating at 300 ° C. for 3 hours corresponds to the moisture adhering to the alumina particles, and by removing this weight loss (%), the alumina hydrate on the surface of the alumina particles ( The weight loss (%) corresponding to (crystal water) can be evaluated.
Loss on ignition (%) = [(W ′ / W) × 100] − [(w ′ / w) × 100] (3)

  Next, with respect to the five α-alumina samples prepared above, the experiment No. Each 100 g of α-alumina sample was placed in a polypropylene container containing 200 milliliters (mL) of pure water and treated with a three-one motor for 1 hour. After the treatment, solid-liquid separation was performed using a Buchner funnel, and the recovered α-alumina sample was dried at 110 ° C. for 24 hours, and then crushed in the mortar until no coarse aggregated particles were obtained, An α-alumina sample after water (pure water) treatment was obtained. The α-alumina sample thus obtained is shown in Table 1 together with physical properties and the like (α-alumina sample after water treatment). FIG. 1 is a graph showing the BET specific surface area of these α-alumina samples before and after water treatment.

As is clear from FIG. 1, the BET specific surface area before and after the water treatment is as follows: when the calcination time of the fired product is 0 hour (Experiment No. 1) and when the pulverization time is 2 hours (Experiment No. 2). Almost unchanged. On the other hand, when the grinding time is longer than these, it can be seen that the BET specific surface area of the α-alumina sample after water treatment is increased. Such a difference is considered to be due to the degree of pulverization in obtaining the α-alumina sample before water treatment. That is, Experiment No. 1 and Experiment No. The α-alumina sample of No. 2 had a particle size ratio (D _av / D _BET ) of 1.10 to an average particle diameter (D _av ) after pulverizing the fired product and a BET equivalent diameter (D _BET ) before pulverization. When the degree of pulverization is outside the upper limit of 1.45 and the degree of pulverization is weak (remaining pulverization), the BET specific surface area is not affected by water treatment, but the degree of pulverization is strong (in a state close to primary particles) ), The BET specific surface area is increased by water treatment.

  Regarding this point, it is clear from the loss on ignition (LOI) of the α-alumina sample shown in Table 1. 1 and no. In 2, the change in value before and after the water treatment was not so great. In 3-5, the value after a water treatment is large. That is, Experiment No. The 3-5 alpha-alumina samples are presumed that the surface of the alumina particles was hydrated by the water treatment.

[Adjustment of raw alumina powder]
(Raw material alumina powder A)
Aluminum fluoride obtained by the Bayer method (average secondary particle diameter: 55 μm and total soda (T-Na ₂ O) content: 0.2% by mass) as a halogen-based mineralizer is converted to 0.4 in terms of alumina. The mixture is added and mixed at a rate of mass%, and the obtained mixture is filled in a firing container made of alumina ceramic containing silica, and fired in a tunnel kiln furnace at 1500 ° C. ± 10 ° C. for about 15 hours. did. The molding density at that time (molding pressure: 98.07 MPa) and the BET specific surface area of the obtained fired product are as shown in Table 2.

Next, by using a rotating ball mill (manufactured by Chuko Seiki Co., Ltd.) filled with 20 mmφ alumina balls in an amount corresponding to 44 vol% with respect to the internal volume of the ball mill, the fired product obtained by the above-mentioned firing is used as the internal volume of the ball mill. The average particle diameter after grinding (D _av ) is 3.1 μm in an amount of 0.18 kg per liter, and the average particle diameter after grinding (D _av ) and the BET equivalent diameter before grinding (D _BET ) To a particle size ratio (D _av / D _BET ) of 1.27, raw material alumina powder A was obtained. Table 2 summarizes the pulverization conditions (pulverization time, particle size ratio (D _av / D _BET )) for obtaining the raw material alumina powder A, the physical properties of the raw material alumina powder A, and the like. Further, the amount of the raw alumina powder A on the 45 μm sieve (+45 μm) was 18 ppm, and the span value was 1.1. The amount on the 45 μm sieve (+45 μm) was measured using a JIS Z8801-1 test sieve (aperture 45 μm). In addition, the span value was adjusted to a particle size (Dp90) corresponding to an integrated particle size distribution rate of 90% by volume using a laser scattering particle size measuring instrument (Microtrac 9320HRA (X100) manufactured by Nikkiso Co., Ltd.) The corresponding particle size (Dp50) and the particle size (Dp10) corresponding to an integrated particle size distribution rate of 10% by volume were measured and obtained from [(Dp90-Dp10) / Dp50].

(Raw material alumina powder B)
A fired product was obtained in the same manner as the raw material alumina powder A using the aluminum hydroxide obtained by the Bayer method used in the raw material alumina powder A. Table 2 shows the molding density (molding pressure: 98.07 MPa) and the BET specific surface area of the obtained fired product. Next, the obtained fired product was pulverized so that the average particle size (D _av ) after pulverization was 3.0 μm and the particle size ratio (D _av / D _BET ) was 1.18. The raw material alumina powder B was obtained by pulverizing in the same manner as the raw material alumina powder A. Table 2 summarizes the pulverization conditions (pulverization time, particle size ratio (D _av / D _BET )) for obtaining the raw material alumina powder B, the physical properties of the raw material alumina powder B, and the like.

(Raw material alumina powder C)
A fired product was obtained in the same manner as the raw material alumina powder A using the aluminum hydroxide obtained by the Bayer method used in the raw material alumina powder A. Table 2 shows the molding density (molding pressure: 98.07 MPa) and the BET specific surface area of the obtained fired product. Next, the obtained fired product was pulverized so that the average particle size (D _av ) after pulverization was 2.9 μm and the particle size ratio (D _av / D _BET ) was 1.14. The raw material alumina powder C was obtained by pulverization in the same manner as the raw material alumina powder A. Table 2 summarizes the pulverization conditions (pulverization time, particle size ratio (D _av / D _BET )) for obtaining the raw material alumina powder C, the physical properties of the raw material alumina powder C, and the like.

(Raw material alumina powder D)
A fired product was obtained in the same manner as the raw material alumina powder A using the aluminum hydroxide obtained by the Bayer method used in the raw material alumina powder A. Table 2 shows the molding density (molding pressure: 98.07 MPa) and the BET specific surface area of the obtained fired product. Next, using a vibrating ball mill (manufactured by Chuo Kako Co., Ltd.) in which 7.6 kg of 15 mmφ alumina balls are housed in a 6 liter (L) pot, 1.5 kg of the fired product obtained by the above firing is pulverized. The raw material alumina powder D was obtained by pulverizing so that the later average particle size (D _av ) was 2.6 μm and the particle size ratio (D _av / D _BET ) was 1.25. Table 2 summarizes the pulverization conditions (pulverization time, particle size ratio (D _av / D _BET )) for obtaining the raw material alumina powder D, the physical properties of the raw material alumina powder D, and the like.

(Example 1)
0.4 g of vinyltrimethoxysilane (trade name: KBM-1003, molecular weight: 148.2, manufactured by Shin-Etsu Chemical Co., Ltd.) is placed in a polypropylene container containing 400 ml (mL) of pure water and made of Teflon (registered trademark). The mixture was stirred with a stirring blade for 1 hour to obtain a treated aqueous solution. 400 g of the raw material alumina powder A was added to this treated aqueous solution and stirred at room temperature for 24 hours for silane treatment. At this time, the number of moles of vinylmethoxysilane per 1 kg of the raw material alumina powder (hereinafter referred to as silane ratio) is 0.017 mol / kg-Al ₂ O ₃ . Subsequently, solid-liquid separation was performed using a Buchner funnel, and the solid component was dried at 110 ° C. all day and night, and then crushed in a mortar to obtain a low soda α-alumina powder.

Total soda (T-Na ₂ O) content of the obtained low soda α-alumina powder, free soda (f-Na ₂ O) content, silicon dioxide (SiO ₂ ) content, after silane treatment The increase in the silicon dioxide (SiO ₂ ) content, the average particle diameter (Dp50), the BET specific surface area, and the DOP oil absorption were measured. The results are shown in Table 3. The amount of the low soda α-alumina powder on the 45 μm sieve (+45 μm) was 0 ppm, and the span value was 1.1.

(Examples 2 to 6)
As shown in Table 3, except that the type of raw material alumina powder, the type of organic silane compound used in the silane treatment, the amount of silane added (the amount of organic silane compound added in the treatment aqueous solution), and the ratio of silane were changed. In the same manner as in Example 1, a low soda α-alumina powder was obtained.
Total soda (T-Na ₂ O) content of the obtained low soda α-alumina powder, free soda (f-Na ₂ O) content, silicon dioxide (SiO ₂ ) content, after silane treatment The increase in the silicon dioxide (SiO ₂ ) content, the average particle diameter (Dp50), the BET specific surface area, and the DOP oil absorption were measured. The results are shown in Table 3. In Table 3, vinylsilane represents vinyltrimethoxysilane (same as above), epoxysilane represents 3-glycidoxypropyltrimethoxysilane (trade name: KBM-403, molecular weight 236.3, manufactured by Shin-Etsu Chemical Co., Ltd.), methylsilane Represents methyltrimethoxysilane (trade name: KBM-13, molecular weight 136.2, manufactured by Shin-Etsu Chemical Co., Ltd.).

(Comparative Example 1)
The raw material alumina powder D obtained above was used as Comparative Example 1 without any silane treatment or water washing treatment, and the total soda (T-Na ₂ O) content of the obtained α-alumina powder. free soda (f-Na ₂ O) content content, silicon (SiO ₂₎ content dioxide, silicon dioxide after silane treatment (SiO ₂₎ content increase, the average particle diameter (Dp50), BET specific surface area And DOP oil absorption was measured. The results are shown in Table 4.

(Comparative Example 2)
Water and raw material alumina powder D were mixed at a mass ratio of water: raw material alumina powder D = 1: 2 and stirred for 1 hour. This aqueous solution was subjected to solid-liquid separation using a Buchner funnel, water passing through alumina: pure water = 1: 1 was performed once, the solid components were dried at 110 ° C. all day and night, and then crushed in a mortar to obtain α-alumina powder. Got.
The obtained α-alumina powder was measured in the same manner as described above. The results are shown in Table 4.

(Comparative Examples 3 and 4)
Feed the raw material alumina powder A and the organosilane compound (liquid) shown in Table 4 to the Henschel mixer so that the number of moles of the organosilane compound in the treatment aqueous solution per kg of the raw material alumina powder becomes the value shown in Table 4. The mixture was stirred for 20 minutes, and the raw material alumina powder A was dry-treated with an organosilane compound.
The obtained α-alumina powder was measured in the same manner as described above. The results are shown in Table 4.

(Comparative Example 5)
Using the raw material alumina powder B and vinyltrimethoxysilane (vinylsilane), the silane addition amount (addition amount of the organic silane compound in the treatment aqueous solution) and the ratio of silane (treatment per 1 kg of the raw alumina powder) shown in Table 4 Α-alumina powder was obtained in the same manner as in Example 1 except that the number of moles of the organic silane compound in the aqueous solution was changed.
The obtained α-alumina powder was measured in the same manner as described above. The results are shown in Table 4.

(Comparative Examples 6 and 7)
1.0 kg of alumina powder B was added to a polypropylene container containing 2.0 liters (L) of pure water and stirred with a three-one motor for 1 hour to obtain an alumina slurry. In addition, 5.0 g of the organosilane compound shown in Table 4 was put in a high-density polyethylene container containing 2.0 liters (L) of pure water, and the mixture was 1 using a Teflon (registered trademark) stirring blade. Stirring for hours gave a treated aqueous solution. This treated aqueous solution was added to the resulting alumina slurry, stirred at room temperature for 24 hours, solid-liquid separated using a Buchner funnel, and the solid component was dried at 110 ° C. overnight, and then crushed with a ball mill to obtain α -Alumina powder was obtained.
The obtained α-alumina powder was measured in the same manner as described above. The results are shown in Table 4.

As shown in Tables 3 and 4, in the low soda α-alumina powders of Examples 1 to 6, the free soda (f-Na ₂ O) content was reduced (0.001 mass% or more and 0.015 mass% or less). However, the increase in the BET specific surface area was suppressed (1.0 m ² / g or more and less than 2.0 m ² / g), and the DOP oil absorption was low.
In contrast, in Comparative Examples 1-7, the free soda (f-Na ₂ O) content of the reduction and to satisfy the increased inhibition of BET specific surface area at the same time was obtained. That is, the α-alumina powder obtained by the water treatment of Comparative Example 2 shows a low value for free soda (f-Na ₂ O) compared to Comparative Example 1 when no treatment was performed. However, the BET specific surface area showed a high value. The α-alumina powder obtained by dry-treating the organosilane compounds of Comparative Examples 3 and 4 showed a low BET specific surface area, but a high free soda (f-Na ₂ O) content. The α-alumina powder with a small amount of silane added in Comparative Example 5 showed a low value for free soda (f-Na ₂ O), but a high BET specific surface area. The α-alumina powders of Comparative Examples 6 and 7 obtained by slurrying alumina with water and adding the treatment aqueous solution showed a low value for free soda (f-Na ₂ O). The BET specific surface area showed a high value.

Here, in order to confirm the influence of the number of moles of the organosilane compound (ratio of silane) in the treatment aqueous solution per 1 kg of the raw alumina powder on the BET specific surface area of the treated α-alumina, the ratio of silane and BET The relationship between the specific surface areas is shown graphically in FIG. Similarly, in order to confirm the effect of this silane ratio on the free soda (f-Na ₂ O) content of α-alumina after treatment, the silane ratio and the free soda (f-Na ₂ O) content The relationship is shown as a graph in FIG. In each case, a circle (●) represents an example and a rhombus (は) represents a comparative example, and numerals attached to the respective numbers indicate the numbers of the example and the comparative example.

  Further, in order to confirm the cause of the increase in the BET specific surface area, the raw material alumina powder A obtained by subjecting the raw material alumina powder A to water treatment in the same manner as in Comparative Example 2 and the raw material alumina powder A were used as raw materials. The α-alumina powder of Example 1 was subjected to differential thermal analysis using a thermal analyzer (manufactured by Rigaku, TG8120). The results are as shown in FIG. When measured at normal pressure and a heating rate of 10 ° C./min, the raw material alumina powder A after water treatment has a specific endothermic peak not found in the α-alumina powder of Example 1 at 250 ° C. Observed nearby. Such a peak was not observed in the α-alumina powder of Example 1 in which the increase in the BET specific surface area was suppressed, and this endothermic peak is presumed to be due to desorption of hydrated water.

As described above, according to the present invention, it is possible to obtain a low soda α-alumina powder in which the soda content is further reduced while suppressing an increase in the BET specific surface area. It is extremely useful as an alumina for filling. In particular, in the present invention, since calcined alumina obtained by calcining aluminum hydroxide derived from the Bayer method is used, such a low soda α-alumina powder can be produced inexpensively and industrially advantageously. .

Claims (7)

Free soda that has an average particle size (Dp50) of 2 μm or more and 5 μm or less, a total soda (T-Na ₂ O) content of 0.1% by mass or less, and can be attached to the particle surface and removed by washing. The content of (f-Na ₂ O) is 0.001% by mass or more and 0.015% by mass or less, and the BET specific surface area is 1.0 m ² / g or more and less than 2.0 m ² / g, Low soda α-alumina powder. The low soda α-alumina powder according to claim 1, wherein the content of silicon dioxide (SiO ₂ ) is 0.040 mass% or more and 0.500 mass% or less.   The low-soda α-alumina powder according to claim 1 or 2, wherein the low-soda α-alumina powder is calcined alumina obtained by calcining aluminum hydroxide obtained by the Bayer method. A raw material alumina powder comprising α-alumina powder having an average particle diameter (Dp50) of 2 μm or more and 5 μm or less and a total soda (T-Na ₂ O) content of 0.1% by mass or less is hydrolyzed. The ratio of the organosilane compound in the treatment aqueous solution to the raw material alumina powder is 0.010 mol / kg-Al ₂ O ₃ or more with respect to the treatment aqueous solution in which the organosilane compound having a functional group is added to water. Free soda (f-Na ₂ O) that can be washed and removed by adhering to the particle surface by performing solid-liquid separation, drying the solid components, and then crushing. min content is not more than 0.015 mass% to 0.001 mass%, characterized in that the BET specific surface area to obtain a low soda α- alumina powder of less than 1.0 m ² / g or more 2.0 m ² / g A method for producing low-soda α-alumina powder.   The method for producing a low-soda α-alumina powder according to claim 4, wherein the addition amount of the organosilane compound in the treatment aqueous solution is 0.1 mass% or more and 5.0 mass% or less. The raw material alumina powder is a mixture obtained by adding a halogen-based mineralizer to aluminum hydroxide having a total soda (T-Na ₂ O) content of 0.3% by mass or less obtained by the Bayer method and mixing them. Is filled in a firing container made of silica-containing alumina ceramics and the molding density (molding pressure: 98.07 MPa) is 2.05 g / cm ³ or more and the BET specific surface area is 0.9 m ² / g or less at 1100 to 1600 ° C. Then, the obtained fired product has a particle size ratio (D _av / D _BET ) of the average particle size (D _av ) after pulverization to the BET equivalent diameter (D _BET ) before pulverization. The method for producing a low soda α-alumina powder according to claim 4 or 5, wherein the low soda α-alumina powder is obtained by pulverization to a range of 10 to 1.45. The method for producing low-soda α-alumina powder according to any one of claims 4 to 6, wherein an increase in the content of silicon dioxide (SiO ₂ ) after the silane treatment is 0.02% by mass or more.

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