JPH0696446B2 - Method for producing ultrafine silica - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing ultrafine particle silica used for a resin modifier or the like.

More specifically, the present invention relates to a simple and low-cost method for producing ultrafine particle silica having a narrow particle size distribution and a small average particle size.

[Conventional technology]

The ultrafine particle silica to which the present invention is applied is an ultrafine particle having an average particle size of 50Å to 1 µm and having crystalline or amorphous SiO ₂ as a main component, and is generally called fumed silica.

Conventionally such fumed silica is silicon tetrachloride (SiCl ₄ ).
Was produced by a gas phase method, for example, an oxygen oxidation method or a flame hydrolysis method, using a silicon compound mainly containing

However, the conventional manufacturing techniques have the following serious drawbacks. That is, the smaller the average particle size of fumed silica, the more difficult it is to produce, the broader particle size distribution of the obtained fumed silica, and the slower reaction rate for producing fumed silica from the raw silicon compound. Is.

As a result, in order to obtain the desired average particle size of fumed silica,
In addition to the reason that it requires an expensive and complicated classifying device and operation, the manufacturing cost of the fumed silica is greatly increased, which is a great disadvantage.

Fumed silica is used in various fields as a scrip agent added to a resin or mixed with a paint to give a thixotropic effect.

In such a field, fumed silica having a small average particle size and a narrow particle size distribution is desired. It has been extremely difficult to easily deal with such a situation with conventional manufacturing techniques.

[Object of the Invention]

An object of the present invention is to provide a method for producing fumed silica having a small average particle diameter and a narrow particle diameter distribution, that is, ultrafine particle silica at a high speed and with high productivity.

[Basic idea]

The present inventors, as a result of diligent studies in consideration of such points,
The present invention has been completed by finding that all of these objects can be achieved only by using a specific perchloropolysilane instead of silicon tetrachloride as a raw material and performing gas phase opposites.

[Disclosure of Invention]

That is, according to the present invention, in the method for producing ultrafine particle silica using a silicon compound as a raw material by a vapor phase method, the raw material is Si _n Cl _{2n + 2} (n
Is an integer of 2 or more), and a method for producing ultrafine particle silica is provided.

The perchloropolysilane used as the starting material silicon compound (silicon compound) in the present invention is represented by the general formula Si _n Cl _{2n + 2} (n is an integer of 2 or more).

Examples of such perchloropolysilane include hexachlorodisilane (Si ₂ Cl ₆ ), octachlorotrisilane (Si ₃ Cl ₈ ), decachlorotetrasilane (Si ₄ Cl ₁₀ ), dodecachloropentasilane (Si ₅ Cl _12). ), Tetradecachlorohexasilane (Si ₆ Cl ₁₄ ), and the like. Among them, hexachlorodisilane and octachlorotrisilane are preferable because they are easily available and easy to handle. These may be used alone or as a mixture.

The perchloropolysilane used in the present invention preferably has high purity, and it is preferable to remove specific impurities depending on the purpose. For example, when fumed silica is used as a semiconductor-related material, it is preferable to remove radioisotopes such as uranium and thorium in perchloropolysilane.

Perchloropolysilane that is generally available is often mixed with silicon tetrachloride, which is a raw material used in the prior art. When such a mixture is used for the reaction, first, perchloropolysilane is decomposed to accelerate the reaction, and silicon tetrachloride is mixed in as the case may be in order to generate uniform growth nuclei in the system. However, the characteristics of the present invention are not damaged.

That is, generally, 90%, preferably 50%, and more preferably about 20% is allowed to be mixed.

As these perchloropolysilanes, those produced by a known method can be used. Usually calcium silicon,
It is obtained by chlorinating particles of an alloy of metal and silicon such as magnesium silicon or ferrosilicon at high temperature or chlorinating silicon particles themselves at high temperature. (For example, U.S. Pat. Nos. 2,602,728 and 2,621,111) Suitable for perchloropolysilane in order to adjust the physical properties of the fumed silica produced by the method of the present invention, such as acidity, electrostatic value, surface hydroxyl group and the like. Amounts of titanium tetrachloride, aluminum trichloride and the like may be used in combination.

Although there are various gas phase reactions for producing fumed silica in the present invention, typical methods include (i) a direct oxidation method of oxidizing a silicon compound with oxygen at a high temperature of 1000 to 1500 ° C., and (ii) ) In an oxyhydrogen flame of a silicon compound, there is a high temperature hydrolysis reaction in which a high temperature is hydrolyzed at 700 to 1300 ° C. In carrying out these reactions, nitrogen, argon, helium or the like may be used as a diluent gas to control the reaction rate or reaction temperature, or hydrogen chloride may be mixed as a reaction regulator.

The fumed silica produced by the reaction. It can be collected with a filter, a cyclone, an electrostatic collector, or the like.

〔The invention's effect〕

Now, the method of the present invention, that is, the method of manufacturing using perchloropolysilane as a silicon raw material, has the following great effects (merits) compared with the method of manufacturing using the silicon raw material of the prior art. .

The resulting fumed silica has a smaller average particle size.

The resulting fumed silica has a narrower particle size distribution.

The production rate of fumed silica is high.

Moreover, the fumed silica obtained by the method of the present invention has exactly the same crystal structure and chemical composition as those of the conventional ones. Therefore, the fumed silica obtained by the method of the present invention can be used as it is in various applications in which the fumed silica produced by the prior art is used, while maintaining its superior morphology.

As described above, the feature of the method of the present invention is that, in view of the physical properties of the fumed silica produced, it is easy to prepare fumed silica having a small average particle diameter and fumed silica having a narrow particle diameter distribution, which were difficult by the conventional method. Is that you can get
Also, from the viewpoint of manufacturing cost, the classification device that was required in the conventional method is no longer required, product loss is reduced, and the productivity is dramatically improved in combination with the significant improvement in reaction speed.
It is possible to greatly reduce costs.

[Preferred modes for carrying out the invention]

The present invention will be described in more detail below with reference to Examples, but these are merely examples, and the technical scope of the present invention (Patent Law No. 70
Article) is not bound by them.

Example 1 1. Experimental method A central part of a quartz tube having an outer diameter of 10 mm and a length of 1 m is arranged so that it can be heated by an electric furnace. Then, a pipe for supplying air, nitrogen or oxygen and a pipe for supplying nitrogen are connected to one end of the quartz pipe. A bubbler for saturating the silicon compound is connected in the middle of the nitrogen pipe.

The silicon compound causes an oxidation reaction in the quartz reaction tube to generate fumed silica (SiO ₂ ) and chlorine. While measuring the weight (A) of the produced fumed silica, the weight (B) of the fumed silica (SiO ₂ ) stoichiometrically produced from the silicon compound used in the reaction is estimated. (A)
Let / (B) be the decomposition rate and use it as a guide for comparison of reaction rates.

The average particle size and particle size distribution of the generated fumed silica are
Observe with a surface scanning electron microscope.

The average particle diameter is displayed as a number average particle diameter and a weight average particle diameter.

The crystal structure was determined by X-ray spectrum analysis.

2. Experimental conditions The electric furnace is heated to 1400 ° C to heat the quartz tube.

The bubbler is charged with hexachlorodisilane, kept at 75 ° C, and nitrogen is passed through at a feed rate of 250 ml / min. This evaporated 2.3 g of hexachlorodisilane in 20 minutes. Oxygen 100 ml / min and nitrogen 150 ml / min were supplied through separate pipes. The gases in both pipes were mixed just before the quartz pipe. Supply gas amount of oxygen 100 ml / min, nitrogen 400 ml / min, total 500 ml / min
It is min.

Hexachlorodisilane is oxidized by oxygen in the reaction section to generate ultrafine particle silica, and chlorine is by-produced.

3. Results The decomposition rate was 80%. The average particle size of the generated fumed silica is 95 Å for number average particle size and 18 for weight average particle size.
It was 0Å.

The particle size distribution was from 50Å to 300Å. The crystal structure of fumed silica was amorphous SiO ₂ .

Comparative Example 1 The experiment method was the same as in Example 1 except that silicon tetrachloride was used as the silicon compound raw material.

The experimental conditions were as follows.

The electric furnace was heated to 1400 ° C. as in Example 1. Charge the bubbler with silicon tetrachloride, keep it at 25 ℃, and add nitrogen at 50 ml / min.
Was passed through. This evaporated 2.4 g of silicon tetrachloride in 20 minutes. Oxygen (100 ml / min) and nitrogen (350 ml / min) were supplied through separate pipes. The gases in both pipes were mixed just before the quartz pipe. As in Example 1, 100 ml / min of oxygen, 400 ml / min of nitrogen, and a total of 500 ml were passed through the heating section. The decomposition rate of silicon tetrachloride was 40%.

The decomposition rate of hexachlorodisilane of Example 1 was 2% of that of this example.
It can be seen that the reaction rate is extremely fast.

The generated fumed silica had an average particle size of 170Å and an average particle size of 650Å.

The particle size distribution was from 60Å to 1000Å.

It can be seen that the fumed silica produced from hexachlorodisilane by the method of the present invention clearly has a narrow molecular size distribution.

The crystal structure of fumed silica was amorphous SiO ₂ as in Example 1.

Comparative Example 2 Under the same experimental method and experimental conditions as in Comparative Example 1, the oxygen supply rate was reduced to 50 ml / sec and nitrogen was increased to 450 ml / sec instead.

That is, the nitrogen flown into the bubbler is 50 ml / sec, which is the same as in Comparative Example 1, but with separate piping, oxygen 50 ml / sec and nitrogen 400 ml / sec.
supplied sec.

The decomposition rate of silicon tetrachloride was 38%.

Average particle size is number average particle size 165Å, weight average particle size 600
It was Å.

The particle size distribution was 60Å to 1000Å. When silicon tetrachloride is used as the silicon compound raw material, Comparative Example 1
Even if the amount of oxygen blown in was reduced and the O ₂ / Si ratio was reduced, the decomposition rate was still low, the average particle size was large, and the particle size distribution was wide.

Comparative Example 3 Under the same experimental method and experimental conditions as in Comparative Example 1, the supply amount of silicon tetrachloride was reduced to 1.2 g.

That is, the nitrogen flown through the bubbler was changed to 25 ml / sec, and oxygen was supplied at 10 ml / sec and nitrogen was supplied at 375 ml / sec through separate pipes.

The decomposition rate of silicon tetrachloride was 41%.

The number average particle diameter was 170Å and the weight average particle diameter was 650Å.

The particle size distribution was 50 to 1000Å.

When silicon tetrachloride was used, the decomposition rate was still low, the average particle size was large, and the particle size distribution was wide, even when the amount of silicon tetrachloride supplied was reduced compared to Comparative Example 1.

Example 2 The same experimental method as in Example 1 was used, except that a mixture of hexachlorodisilane and octachlorotrisilane was used as the silicon compound raw material.

The experimental conditions were as follows.

The electric furnace was heated to 1400 ° C. to heat the quartz tube. The bubbler was charged with a mixture of 60 mol% hexachlorodisilane and 40 mol% octachlorotrisilane, and the mixture was kept at 100 ° C and nitrogen
A flow rate of 0 ml / min was passed.

This caused 0.92 g of the above mixture to be evaporated in 20 minutes. Oxygen 80 ml / min and nitrogen 270 ml / min were supplied through separate pipes.

The amount of supply gas is 400 ml in total for oxygen 80 ml / min and nitrogen 320 ml / min
ml / min.

The amounts of hexachlorodisilane and octachlorotrisilane in the gas at the inlet and outlet of the quartz tube were converted to Si atoms, and the ratio was taken as the decomposition rate. The result was 88%.

The number average particle size is 90Å and the weight average molecular weight is 17
It was 0Å.

The particle size distribution was 50-300Å.

The crystal structure was Lamorphus SiO ₂ .

[Operation of the invention]

A feature of the present invention is the use of perchloropolysilane as a raw material for the production of fumed silica, in place of the silicon compounds shown in the prior art, in particular silicon tetrachloride.

The reason why the average particle size of fumed silica becomes smaller and the particle size distribution becomes narrower when perchloroposyrilan is used,
And the detailed reason or mechanism of the great effect that the formation rate is dramatically increased is not clear at present, but probably the Si-Si bond existing in the molecular structure of perchloropolysilane is more likely to react. Rich in properties, as a result, the entire reaction system reacts homogeneously, so the particle size is smaller than when using silicon tetrachloride,
It is estimated that the particle size distribution is narrow and the reaction rate is fast.

[Industrial availability]

According to the method of the present invention, since ultrafine silica particles having a small average particle size and a narrow particle size distribution can be obtained, they were applied to a resin modifier (slip agent) or a paint modifier (thixotropic agent). Further effects can be expected.

Further, according to the method of the present invention, the productivity is remarkably improved, and a simple and extremely economical manufacturing method is provided.

Therefore, it must be said that the industrial applicability of the present invention is extremely high.

Claims (1)

[Claims] 1. A method for producing ultrafine particle silica using a vapor phase method using a silicon compound as a raw material, wherein Si is used as the raw material.
_A method for producing ultrafine particle silica, which comprises using perchloropolysilane represented by _n Cl _{2n + 2} (n is an integer of 2 or more).