JPH0696445B2 - Fine fused spherical silica and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to fine fused spherical silica and a method for producing the same. More specifically, the present invention relates to a fused spherical silica having a narrow average particle size and a fine and specific surface area and an industrially advantageous production method thereof, and particularly useful when setting the particle size constitution of a semiconductor encapsulating material filler. And fused spherical silica.

[Conventional technology]

Conventionally, a crushed product of fused spherical silica has been used as a filler for a resin encapsulating material for semiconductors, but recently, as the degree of integration of semiconductors has increased, highly filled resin encapsulation is required,
In order to improve the fluidity of resin, fused spherical silica has become indispensable as a filler in place of conventional pulverized products.

The inventions described in Japanese Examined Patent Publication No. 54-43021 and Japanese Examined Patent Publication No. 61-57347 are directed to resin compositions of this type, and include fine spherical particles and fused spherical particles having an average particle size of 1 to 60 μm. It has been shown to use silica.

Bulletin Chemical Society of Japan vol.53, N
o.1, pp. 26-29, a manufacturing method based on the flame melting method of fused spherical silica of about 10 μm is reported.

[Problems to be Solved by the Invention]

However, the fine spherical particles used in the invention of Japanese Examined Patent Publication No. 54-43021 are extremely fine silica powder of 1 to 800 μm, but this is not fused silica. In addition, Japanese Examined Sho 61-5
The fused spherical silica of the invention 7347 has a very wide particle size distribution, and in many cases has an average diameter of more than 10 μm.
The method for producing the fine fused spherical particles is not disclosed.

The fused spherical silica listed in Bueletin Chemical Society of Japan uses fine silica based on a dry method as a raw material, but this method is industrially costly and impractical, and what kind of particle size distribution There is almost no study on the means for controlling the particle size of the product.

By the way, fused spherical silica has hitherto been exclusively used for semiconductor encapsulating materials, but the average particle size used for this purpose is in the range of 10 μm to 40 μm. The production method of such silica is carried out by pulverizing natural silica stone or synthetic silica to an average particle size of 5 to 50 μm by a ball mill or the like, dispersing them in an oxygen-combustible gas flame (hydrogen or propane gas), and melting and sphering. ing. Average particle size is 40 μm
The above-mentioned silica is difficult to manufacture due to the melting ability because the melting and spheroidizing of the powder is governed by the flame temperature and the residence time. On the other hand,
In order to make fine fused spherical silica having an average particle size of 10 μm or less, the particle size of the raw silica must be 10 μm or less, but in a commonly used pulverization method such as a ball mill, the pulverization equilibrium is 6 to 8 μm. However, it is not possible to obtain a product having an average particle diameter of fused spherical silica of 8 μm or less. Even if the crushed particle size is 10 μm or less, fine fused particles are usually fused and grown in the flame in the melting process, and the particle size increases. Therefore, fine fused spherical silica with an average particle size of 2 to 8 μm is used. It's hard to get. Although it is possible to obtain finer particles of fused spherical silica by a method such as induction plasma having a temperature higher than the flame temperature, this method has a problem in that it cannot be mass-produced and its energy efficiency is low, which is economical.

In this way, it is possible to industrially produce fine fused spherical silica having an average particle size of 10 μm or less by the flame melting method.
It's very difficult and has never been known to be a reality.

In view of the above problems, the inventors of the present invention have conducted extensive research and many experiments based on this in order to produce fine fused spherical silica, and as a result of strictly setting special pulverization and melting conditions, The inventors have completed the present invention by finding that fused spherical silica can be produced with a sharp distribution.

[Means for Solving the Problems]

That is, the present invention relates to fine fused spherical silica having an average particle diameter of 2 to 8 μm and a specific surface area of 0.5 to 7 m ² / g.

Still another invention relates to a method for producing such silica, which is characterized in that a high-purity silica raw material is finely pulverized by a jet mill to have an average particle diameter of 2 to 5 μm. Is dispersed in an oxygen-combustible gas flame and melt spheroidized.

The present invention will be described in detail below.

The fused spherical silica according to the present invention is characterized in that it is fine particles having the above-mentioned specific surface area and average particle diameter.

The particle size distribution of such silica is very sharp, as can be seen from the narrow range of the average particle size, and in many cases, it is 8% or less for 1 μm or less and 42% for 12 μm or more.
It is in the following range. In addition, the particle diameter in the present invention is defined as that obtained by the particle size distribution measuring method based on the laser light scattering method.

In addition, although such silica particles are fine, BE particles
T specific surface area is in the range of 0.5 to 7 m ² / g, preferably 1 to 5 m ² / g
It can be understood that it is substantially in a molten glass state from the range of.

Further, the fused spherical silica according to the present invention is of high purity, and particularly conductive impurities such as Na and Cl are 5 ppm or less, and α-radioactive impurities such as U and Th are 1 ppb or less, respectively. Suitable as a filler.

Whether the fused silica particles are spherical or not can be easily confirmed by an electron microscope, and the fine silica particles according to the present invention are all spherical or substantially spherical particle state. Is recognized.

Next, a method for producing fine fused spherical silica according to the present invention will be described, which comprises two steps as described above.

First, the first step is a powder step of raw material silica, but the present invention is characterized in that the pulverization is carried out based on the jet mill method, not the usual pulverizing means.

The type of pulverization based on the jet mill may be any mode such as a microanalyzer type, jetmizer type, Macjack mill type, etc., but in order to suppress contamination of impurities as much as possible, classification is performed in a fluidized bed type. Majack mill with function is effective. When using a micronizer or jet mizer, it is necessary to selectively use a device in which the liner portion is made of a wear resistant material. With these jet mills, the raw material silica can be obtained by adjusting the average particle diameter to an arbitrary particle diameter in the range of 2 μm to 5 μm.

At this time, if the silica is pulverized by a ball mill, a vibration mill or the like which is generally adopted as described above, the pulverization equilibrium of these pulverizers becomes 6 to 8 μm, and even until this particle size is reached. Not only does it take a long time to
Impurities are significantly mixed due to abrasion of the grinding medium, and the purity of the crushed silica is extremely poor. However, if the crushing method of the present invention is adopted, the average particle size becomes 8 μm or less in a short time, and mass production is possible. It is possible to pulverize economically with less contamination of.

The silica raw material that can be used in this step is not particularly limited, but it is desirable to use natural or synthetic silica having the highest possible purity.

Examples of natural silica include refined silica stone, silica sand, and quartz. Synthetic silica is based on hydrolysis of silicon halide, hydrolyzate of organosilicate such as ethyl silicate, or neutralization of alkaline silicate aqueous solution. Examples thereof include silica.

In particular, the present applicant has already succeeded in developing a method for producing high-purity silica obtained by neutralizing an alkaline silicate aqueous solution with a mineral acid, and it can be used as an industrially advantageous silica raw material. However, the details thereof are described in, for example, JP-A-61-48421, JP-A-61-48422, and JP-A-61-1.
It is described in JP-A-78414, JP-A-62-12608 and the like.

Next, the second step is an important step in which the finely pulverized particles of the raw material silica obtained in the previous step are supplied to a flame melting furnace to melt and spheroidize.

In particular, in the present invention, since it is necessary to melt the fine silica raw material and not fuse the raw material particles to each other to form the independent spherical particles as they are, it is necessary to perform sufficiently controlled flame melting. .

That is, the melt spheroidization is performed by a flame by combustion of oxygen-combustible gas, in most cases, an oxygen-propane flame, but the raw material silica powder is in a steady state in the center of the flame at a temperature equal to or higher than the melting point of silica. In a distributed manner. In this case, whether the fine silica particles of the raw material are fused and become coarse spherical particles or become independent fine spherical particles as it is mainly depends on the control of the heat load in the furnace, but this condition is The heat load of the melting burner and the heat load in the furnace are two, and in particular, the former condition control is unique and important.

Therefore, based on many experiments, the heat load of the melting burner should be less than 200,000 kcal / H, especially
The range of 100 to 200,000 kcal / H is suitable.

These melting conditions inevitably change depending on the feed rate of the raw material silica to the burner, the state of the flame due to the shape of the burner, etc., but at least the setting of the heat load is an important setting for fine melting spheroidization. It is a matter.

That is, when the heat load exceeds 200,000 kcal / H, the mutual fusion phenomenon between particles becomes remarkable, resulting in fused spherical particles exceeding 8 μm. Conversely, if it is too low, the particles become independent. Although the properties are maintained, fused spherical particles having a large specific surface area or unmelted particles are mixed to cause deterioration of quality.

Further, the melting of silica affects the melting phenomenon of silica depending on the heat load per unit volume in the heating furnace,
This is the second one.

Therefore, a preferable condition in the present invention is that the heat load in the furnace does not exceed 2 million kcal / m ³ H.

In an operation that exceeds this value, even if the heat load of the burner is within the predetermined setting conditions, the phenomenon of fusion between silica particles occurs, leading to the tendency that fine fused spheres cannot be obtained and the furnace wall Undesired phenomena such as vigorous adhesion of silica occur, and on the other hand, it is disadvantageous in terms of energy cost, and it is necessary to perform heat management so as not to apply a heat load above the predetermined level as much as possible.

Thus, according to the present invention, fine fused spherical silica can be selectively produced.

The collection of fused silica can be easily recovered by a conventional collection method such as a cyclone or a bag filter.

[Action]

According to the present invention, the average particle size is 2 to 8 μm and the specific surface area is 0.5.
There is provided fused spherical silica having a fine and substantially molten glass state having a particle characteristic of ˜7 m ² / g, and having a high purity of radioactive element impurities such as uranium and thorium of 1 ppm or less.

The high-performance fused spherical silica can be stably obtained by the synergistic action of the first step using the pulverization method by the jet mill and the second step of performing the melting treatment under the controlled heat load condition.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Example 1 Granular silica gel (U: 0.04 ppb, Th: 0.20) obtained by adding JIS No. 3 sodium silicate to 35 wt% hydrochloric acid and conducting a neutralization reaction
ppb, Na: 0.38 ppm, Fe: 0.38 ppm, water content 7 wt%) were pulverized by a Macjack type jet mill having a classification function to prepare a raw material silica having an average particle diameter of 3.2 μm.

Next, the raw material silica was fed into a melting furnace having a powder discharge hole at the center and a gas burner having a gas flame hole on the central axis, and the raw material silica was supplied and operated under the following conditions.

That is, a gas flame consisting of propane 100 l / M and oxygen 440 l / M was formed, and the heat load of the burner was set to 135,000 kcal / H.
0.0 kg / hr was dispersed and supplied together with oxygen (60 l / M) as a carrier gas to melt silica. The heat load of the melting furnace at this time was 1.07 million kcal / m ³ · hr. The spherical silica thus fused was cooled with air and then collected by a cyclone and a bag filter. After the continuous operation for 24 hours, the inside of the furnace was inspected, but almost no adhesion of silica to the furnace wall was observed.

When the obtained cyclone recovered product was evaluated, it was confirmed to be fine fused spherical silica as shown in Table 1.

Examples 2 to 4 and Comparative Examples 1 to 3 Using the same ground silica particles as Example 1 as a raw material, Example 1
In the melting furnace provided with the same melting burner as above, the heat load was changed to perform flame melting to obtain fused silica.

The respective execution conditions and the obtained results are shown in Table 2.

[Effects of the Invention] The fine fused spherical silica according to the present invention has an average particle size of 2 to
High-purity fused silica particles in the range of 8 μm and having a specific surface area of 0.5 to 7 m ² / g, which are spherical or substantially spherical high-purity fused silica particles, and are used for adjusting the particle size of a resin-like filler for semiconductors. It is effective as a part.

Such silica particles can be produced industrially advantageously in stable operation by adopting the two controlled steps of the present invention.

Claims (5)

[Claims] 1. A fine fused spherical silica having an average particle size of 2 to 8 μm and a specific surface area of 0.5 to 7 m ² / g. 2. The fine fused spherical silica according to claim 1, wherein the contents of uranium and thorium are 1 ppb or less. 3. A first step in which a high-purity silica raw material is finely pulverized by a jet mill so that the average particle diameter is in the range of 2 to 5 μm, and the obtained powder silica is dispersed in an oxygen-combustible gas flame to be melt-spheroidized. A method for producing fine fused spherical silica, comprising a second step. 4. A method for producing fine fused spherical silica according to claim 3, comprising a second step of flame melting using a flame burner with an oxygen-propane gas flame at a heat load of 200,000 kcal / H or less. 5. The method for producing fine fused spherical silica according to claim 3, comprising a second step of flame melting using an oxygen-propane gas flame at a furnace heat load of 2 million kcal / m ³ H or less.