JP2006199579A - Spherical alumina powder and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide low-soda spherical alumina powder having excellent moisture resistance reliability, thermal conductivity, packing properties and wear resistance, and suitable as a filler, and to provide its production method. <P>SOLUTION: In the spherical alumina powder obtained by thermal-spraying alumina raw material powder into flame, so as to be spherical, the surface of the spherical alumina powder is provided with a silica coating layer using silica fine powder with the average particle diameter of <2 μm, and the content of soda in an extract extracted from the surface of the spherical alumina powder at ordinary temperature is ≤40 ppm. The production method uses the same. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a spherical alumina powder obtained by spraying an alumina raw material powder into a flame to form a spheroid, and a method for producing the same.
Specifically, the present invention relates to a low-soda spherical alumina powder that is excellent in moisture resistance reliability, thermal conductivity, filling property, and abrasion resistance, and suitable as a filler, and a method for producing the same.

Spherical alumina powder obtained by spraying alumina raw material powder into a flame to form spheroids is excellent in thermal conductivity and filling properties, so it is used for fillers and substrates for semiconductor encapsulants, and aluminum hydroxide. In general, a method of spheroidizing a raw material powder such as alumina in a high-temperature flame and spraying is known.
According to this method, a spherical alumina powder having excellent fluidity can be obtained, but since the alumina raw material powder used is an aluminum hydroxide powder produced by the Bayer method, it contains at least several hundred ppm of soda components. There is a problem that it remains in a product made of spherical alumina powder and impairs moisture resistance reliability.

In order to solve this problem, for example, in Japanese Patent Application Laid-Open No. 2001-199719, an alumina raw material powder is sprayed into a high-temperature flame to produce spherical alumina. A production method is described in which a soda component is 20 ppm or less by adding 1 to 50% of siliceous powder of 2.0 mm in terms of SiO2.
However, in the method described in Japanese Patent Application Laid-Open No. 2001-199719, since the silica particle size is too large and cannot be separated with a cyclone, the particle size contained in the powder recovered with a cyclone or the like is 0.1 to 2.0 mm. The silica powder had to be separated and removed using a sieve / classifier.

Further, the reduction of soda components has a problem that the production efficiency is low because the soda component volatilized from the alumina raw material powder has been achieved by reaction or adsorption with fumed silica.
Regarding spherical alumina whose surface is coated with silica, JP-A-61-266456 discloses a high thermal conductive epoxy resin molding material using alumina whose surface is coated with silica as part or all of the filler. Are listed.
However, the alumina coated with silica described in JP-A-61-266456 improves the thermal conductivity, and in order to greatly improve the moisture resistance reliability which is the subject of the present invention, The conditions were not fully elucidated.

Regarding a method for modifying the surface of the powder A by spraying an inorganic oxide powder (powder A) and a fine inorganic oxide powder (powder B) having a smaller particle diameter in a flame. JP-A-2004-262673.
However, in the method described in Japanese Patent Application Laid-Open No. 2004-262673, viscosity improvement when the produced particles are blended with the resin is described. However, the moisture resistance reliability of the produced particles, which is an object of the present invention, is described. The conditions for improvement were not clarified and were insufficient.
JP 2001-199719 A JP-A 61-266456 JP 2004-262673 A

  The present invention solves the problems of the prior art as described above, and provides a low-soda spherical alumina powder that is excellent in moisture resistance reliability, thermal conductivity, filling property, wear resistance, and suitable as a filler, and a method for producing the same. The task is to do.

As a result of intensive studies to solve the above-mentioned problems, the present invention forms a silica coating layer on the surface of the spherical alumina powder and seals the soda component in the alumina powder, thereby providing moisture resistance reliability and thermal conductivity. The present invention provides a low-soda spherical alumina powder excellent in fillability and wear resistance and suitable as a filler, and a method for producing the same, the gist of which is as described in the claims below. .
(1) A spherical alumina powder obtained by spraying an alumina raw material powder into a flame to form a spheroid, the surface of the spherical alumina powder having a silica coating layer using a silica fine powder having an average particle size of less than 2 μm, A spherical alumina powder characterized in that the soda content in an extract extracted from the surface of the spherical alumina powder at room temperature is 40 ppm or less.
(2) The spherical alumina powder according to claim 1, wherein a surface coverage ratio in the spherical alumina powder of the silica coating layer is 0.7 or more.

(3) A method for producing a spherical alumina powder in which an alumina raw material powder is sprayed into a flame to form a spheroid, and 0.5 to 20% by weight of silica fine powder having an average particle size of less than 2 μm is present in the alumina raw material powder. Then, a silica coating layer is formed on the surface of the spherical alumina particles by thermal spraying in a flame.
(4) The method for producing spherical alumina powder according to claim 2, wherein the silica fine powder present in the alumina raw material powder is 2.0 to 20% by weight.
(5) The method for producing a spherical alumina powder according to (3) or (4), wherein the silica fine powder has a specific surface area of 10 to 400 m2 / g.
(6) The method for producing a spherical alumina powder according to (3) or (4), wherein the silica fine powder has a specific surface area of 10 to 25 m 2 / g.
(7) Any of (3) to (6), characterized in that a mixer having a shear energy of 100 kcal / mol or more that crushes agglomeration of fine powder is used as a method of premixing alumina raw material powder and silica fine powder 2. A method for producing a spherical alumina powder according to item 1.

According to the present invention, the silica coating layer is formed on the surface of the spherical alumina powder, and the soda component in the alumina powder is hermetically sealed, so that the moisture resistance reliability, thermal conductivity, filling property, and wear resistance are excellent. A low-soda spherical alumina powder suitable as a material and a method for producing the same can be provided.
Specifically, by forming a silica coating layer on the surface of the alumina spherical particles and sealing the soda component in the alumina particles, a low soda spherical alumina powder excellent in moisture resistance reliability can be produced.
In addition, the addition of silica fine powder provides a significant industrially useful effect, such as the need to sieve and separate the powder recovered by the cyclone.

The best mode for carrying out the invention will be described in detail with reference to FIG.
FIG. 1 is a diagram illustrating an apparatus for producing spherical alumina powder in the present invention.
In FIG. 1, 1 is a thermal spray furnace, 2 is a burner, 3 is a combustible gas supply pipe, 4 is a combustion gas supply pipe, 5 is a raw material supply pipe, 6 is a cyclone, 7 is a bag filter, and 8 is a blower.

As shown in FIG. 1, the apparatus for producing spherical alumina powder according to the present invention has a burner 2 set at the top of a thermal spraying furnace 1, which includes a combustible gas supply pipe 3, a combustion support gas supply pipe 4, and a raw material supply pipe 5 Are connected, and by spraying alumina raw material powder such as aluminum hydroxide from the raw material supply pipe 5 and spraying it into the flame, angular alumina is spheroidized to produce spherical alumina having an average particle size of 1 to 80 μm can do.
The powder that has passed through the thermal spraying furnace is sucked by the blower 8 and collected by the cyclone 6 and the bag filter 7.
The powder recovered by the cyclone 6 is a silica-coated spherical alumina powder.

In the present invention, 0.5 g to 20 wt%, preferably 2 to 20 wt% of silica fine powder having an average particle diameter of less than 2 μm is present in the alumina raw material powder and sprayed in a flame to thereby form the spherical alumina. A silica coating layer is formed on the surface of the particles.
Alumina raw material powder is mixed with silica fine powder in advance and discharged into the flame from the raw material supply pipe, so that the melted spheroidized alumina powder and an amorphous silica coating layer with a film thickness of about 100 to 400 nm on its surface Can be formed.

A spherical alumina powder obtained by spraying an alumina raw material powder into a flame by this method, and having a silica coating layer using silica fine powder having an average particle size of less than 2 μm on the surface of the spherical alumina powder, A spherical alumina powder having a soda content of 40 ppm or less in an extract extracted at room temperature from the surface of the spherical alumina powder can be produced.
Moreover, it is preferable that the surface cover ratio in the spherical alumina powder of the silica coating layer is 0.7 or more.
By covering 70% or more of the entire surface of the spherical alumina powder with a silica coating layer, the soda component in the alumina powder can be sealed to further improve the moisture resistance reliability.
In the present invention, the surface cover ratio means that the spherical alumina powder is crushed, the crushed pieces are observed with a microscope, 100 pieces of crushed pieces recognized as the sphere surface are selected as detailed observation samples, and these are observed in detail. Is the ratio of the number of samples found on the sphere surface.

  As a method for mixing silica fine powder with alumina raw material powder, a method using a V-type mixer is generally known, but it has a high shear energy of 100 kcal / mol or more to break up agglomeration of fine powder. A mixer having a high impact force that adheres to the substrate, such as a Henschel type mixer, is more effective for uniform formation of a coating film. When such a mixer is used, the silica fine powder is hardly segregated with respect to the alumina raw material powder, and the silica fine powder is mixed around the alumina particles. This is because, when such a mixture is sprayed into a flame, a coating layer in which silica is uniformly melted and adhered to the surface of the alumina particles is generated, so that the effect of confining the soda content is increased.

In many cases, the soda component in the alumina particles during the thermal spraying deposits on the surface layer and becomes a higher level than before the thermal spraying. The soda content in the extract extracted from the surface of the powder at room temperature can be reduced to 40 ppm or less, and as a result, the moisture resistance reliability of the spherical alumina particles can be improved.
The average particle diameter of the silica fine powder is less than 2 μm because the silica powder with a small particle diameter can be easily melted in a high-temperature flame and can easily form a silica coating on the surface of the alumina spherical particles. This is because the bonding force at the interface between the alumina spherical particles and the silica coating layer can be strengthened by thermal spraying.

Further, the silica fine powder is present in an amount of 0.5 to 20% by weight because if less than 0.5% by weight, the soda component cannot be sealed as a result of not forming a sufficient silica coating layer on the surface of the alumina powder. In addition, the reason why the silica fine powder is 20% by weight or less is that the sealing effect of the soda component by the coating layer is saturated even if the silica addition amount is further increased.
Moreover, the preferable range of the silica fine powder which exists in an alumina raw material powder shall be 2.0-20 weight% because the sealing effect of a soda component improves further by containing 2.0% or more of silica fine powder. It is.
The specific surface area of the silica fine powder is preferably 10 to 400 m2 / g.

If the particle size of the silica fine powder is in the extremely fine powder region, sufficient accuracy cannot be obtained by the laser diffraction scattering particle size analysis method. Therefore, when expressing the degree of silica powder to be added, the specific surface area is mainly used.
By making the specific surface area of the silica fine powder 10 m2 / g or more and increasing the difference from the specific surface area of the alumina powder, it can be separated and removed by the cyclone 6, and the powder collected by the cyclone etc. is sieved as before. There is no need to separate and remove with a classifier.

Moreover, by making the specific surface area of silica fine powder 400 m <2> / g or less, almost all silica fine powder that can be usually obtained can be used.
The specific surface area of the silica fine powder is more preferably 10 to 25 m2 / g.
This is because if the specific surface area of the silica fine powder exceeds 25 m2 / g, the particles become extremely fine, and the amount of evaporated particles increases, making it difficult to contribute to the coating on the alumina particle surface.
Although it is also possible to use titanium oxide instead of the silica fine powder of the present invention, titanium oxide is subject to deterioration of organic material due to oxidation when exposed to sunlight (basically ultraviolet rays) for a long time. There are restrictions on places of use. On the other hand, since silica does not have such a problem, it is not limited.

An experiment for producing spherical alumina powder was conducted using the apparatus shown in FIG.
A V-type mixer was used for premixing the alumina raw material powder and the silica powder.
In the experiment, a high-temperature flame of 1500 ° C. or higher was formed under the conditions of LPG33Nm3 / Hr as the combustible gas and 110Nm3 / Hr as the support gas.
As a carrier gas for the raw material powder, oxygen was 55 Nm3 / Hr, and the raw material powder was discharged into the flame at a rate of 80 kg / Hr.
The gas (including combustion gas) flowing into the cyclone is 1000 Nm3 / Hr.
With the above, the cyclone inflow gas velocity was secured at 10 m / sec or more. As a result, fine powder of 10 m 2 / g or more is not collected by the cyclone but collected by the bag filter.

The alumina raw material powder having an average particle diameter of 21.6 μm and a soda component of 14 ppm is used. The average particle diameter of the silica fine powder to be added is 0.5 μm and blended under the conditions shown in Table 1, and the powder mixed beforehand is used. And subjected to thermal spraying. The specific surface area of the silica fine powder to be added was 200 m2 / g.
Table 1 shows the results of measuring the soda component content, the average particle diameter, and the specific surface area of the powder recovered by the cyclone.

For the soda component measurement, 4 g of sample was put into a container at 40 ° C. in pure water at room temperature, manually stirred for 10 seconds, and then quickly applied to a centrifuge for 10 minutes, and Na ⁺ in the extract after solid-liquid separation was changed to Toa. It was measured with a medical electronic ion chromatograph.
The average particle size was measured by CILAS particle size distribution measurement, which is a laser diffraction / scattering particle size analysis method.
The surface cover ratio is measured by putting about 1 g of the sample into a smoked mortar, pulverizing it with a strong impact using the same pestle, sampling the broken sample, and observing and measuring the fractured surface with a JEOL JEM-4000EX microscope. did.
The coating condition was observed with JEOL JEM-4000EX.
FIG. 2 is a diagram showing a limited-field electron diffraction image showing a silica coating layer formed on the surface of the spherical alumina powder of the present invention.
As shown in FIG. 2, an amorphous silica coating layer is formed on the surface of a spherical alumina powder made of a crystalline layer.

As shown in Table 1, it was confirmed that the content of soda component was reduced with the increase in the amount of silica fine powder added, and the effect of the present invention was confirmed.
That is, Experiment No. 3-No. As shown in FIG. 10, by adding 0.5% by weight or more of silica fine powder, which is within the scope of the present invention, the soda component content can be made 40 ppm or less, and by adding 2% by weight or more, the soda component content is 10 ppm. The effects can be noticeable.
Moreover, since the specific surface area value of alumina powder does not become large after silica fine powder addition, it turns out that the added silica is efficiently coated on the surface of alumina particles.
It has also been found that the soda component content can be reduced to 40 ppm or less by setting the surface cover ratio in the spherical alumina powder of the silica coating layer to 0.7 or more.
<Comparative example>

The experiment was performed using the same apparatus as in the above-described embodiment under the same gas and powder supply conditions.
The same alumina raw material powder is used.
Using 0.0% of particles having a size of μm and 32 μm or less, blended under the conditions shown in Table 2, and pre-mixed powder was subjected to thermal spraying. The specific surface area of this silica coarse powder was 0.2 m2 / g.
Table 2 shows the results obtained by sieving the powder collected by the cyclone at 32 μm and measuring the soda component, average particle diameter, and specific surface area of the powder under the sieve.

As shown in Table 2, it can be seen that as the amount of silica coarse powder increases, soda component content decreases, but it is necessary to separate coarse silica by sieving in advance at 32 μm. There wasn't.
In addition, the content of soda component is not less than 10 ppm unless 30.0% or more of silica coarse powder is added.

The raw material premixing method and the experimental apparatus are the same as in Example 1. The silica fine powder to be mixed was prepared by adjusting the fine powder in several levels in advance.
Tables 3 to 5 show the results of examining how much the soda component content is affected by the value of the specific surface area of the silica fine powder together with the comparative example.
Table 3 shows the case where the silica powder addition rate is 0.5%. Experiment NO18 is a comparative example to which silica coarse powder is added, and experiment NO3 and experiments NO14 to 17 are invention examples to which silica fine powder is added.
Table 4 shows the case where the silica powder addition rate is 2.0%. Experiment NO23 is a comparative example to which silica coarse powder is added, and Experiment NO5 and Experiment NO19 to 22 are invention examples to which silica fine powder is added.
Table 5 shows the case where the silica powder addition rate is 5.0%. Experiment NO28 is a comparative example to which silica coarse powder is added, and experiment NO7 and experiments NO24 to 27 are invention examples to which silica fine powder is added.

In the said Table 3-Table 5, all the soda component content rates of the invention example which added the silica fine powder are less than the soda component content rate of the comparative example which added the silica coarse powder.
Moreover, when the silica fine powder specific surface area is 30 m2 / g or more, the soda component content is higher than the range of 10 to 25 m2 / g. As a cause of this, it is considered that it is difficult to contribute to the coating on the alumina surface because the specific surface area of the silica fine powder is too large.

The experimental apparatus is the same as that of Example 1 except that a Henschel type mixer was used for the raw material premixing method. The results of these experiments are shown in Experiments NO29-31 in Table 6 and Experiments NO32-34 in Table 7.
Table 6 shows the result of adding silica fine powder having a specific surface area of 200 m 2 / g compared with the case of mixing with a V-type mixer, but the soda component content is lower when a Henschel mixer is used.
Table 7 compares the results when the silica fine powder addition rate is 5.0% with the case of mixing with the V-type mixer, but in this case as well, the soda component content is lower when the Henschel mixer is used. The result is obtained.

It is a figure which illustrates the manufacturing apparatus of the spherical alumina powder in this invention. It is a figure which shows the restricted visual field electron diffraction image which shows the silica coating layer formed in the surface of the spherical alumina powder of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Thermal spray furnace 2 Burner 3 Combustible gas supply pipe 4 Combustion gas supply pipe 5 Raw material supply pipe 6 Cyclone 7 Bag filter

Claims (7)

A spherical alumina powder obtained by spraying alumina raw material powder into a flame and spheroidizing,
On the surface of the spherical alumina powder, there is a silica coating layer using silica fine powder having an average particle size of less than 2 μm,
A spherical alumina powder characterized in that a soda content in an extract extracted at room temperature from the surface of the spherical alumina powder is 40 ppm or less.   2. The spherical alumina powder according to claim 1, wherein a surface cover ratio of the spherical alumina powder of the silica coating layer is 0.7 or more. A method for producing a spherical alumina powder in which an alumina raw material powder is sprayed into a flame and spheroidized,
A silica coating layer is formed on the surface of the spherical alumina particles by spraying 0.5 to 20% by weight of silica fine powder having an average particle size of less than 2 μm in the alumina raw material powder and spraying in a flame. A method for producing a spherical alumina powder. 3. The method for producing a spherical alumina powder according to claim 2, wherein the silica fine powder present in the alumina raw material powder is 2.0 to 20% by weight.   The method for producing spherical alumina powder according to claim 3 or 4, wherein the silica fine powder has a specific surface area of 10 to 400 m2 / g.   The method for producing a spherical alumina powder according to claim 3 or 4, wherein the silica fine powder has a specific surface area of 10 to 25 m2 / g. The method according to any one of claims 3 to 6, wherein a mixer having a shear energy of 100 kcal / mol or more for crushing agglomeration of the fine powder is used as a method of premixing the alumina raw material powder and the silica fine powder. The manufacturing method of spherical alumina powder of description.

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