JPH10287415A - Production of highly pure spherical silica - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an industrially excellent method for readily and cheaply producing highly pure spherical silica particles within a particle diameter range which makes the silica particles have little generality because of a high price. SOLUTION: This method for producing spherical silica by hydrolyzing an alkyl silicate in a mixed solvent of water with an organic solvent comprises using methyl silicate as the alkyl silicate, using methanol alone as the organic solvent, and adding dropwise the methyl silicate diluted by the methanol to a medium comprising the water, the methanol and an acidic or basic catalyst without containing an ammonium salt at 0-20 deg.C while stirring to carry out a hydrolysis and condensation reaction thereof to provide the objective spherical silica having 0.5-5 μm. The volume ratio (at a room temperature) of the methanol to methyl silicate in the dropping liquid is preferably >=2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing spherical silica, and more particularly to a method for producing ultra-high-purity spherical silica fine particles by a sol-gel method.

[0002]

2. Description of the Related Art Ultra-high-purity silica is strongly required to be developed in the most advanced fields. For example, additives such as paints, pigments or resins, raw materials for optical components, catalyst carriers, column fillers, abrasives for wafers, and semiconductors It is promising as a raw material for producing sealing materials for use, crucibles for pulling up polysilicon, jigs for semiconductors, glass substrates for photomasks, and the like. In particular, spherical silica has excellent filling properties and dispersibility, can be used for various applications, and has high utility. However, in particular, in the production of spherical silica having an average particle size of 0.5 to 5 μm, it is not easy to control the particle size and particle size distribution of the generated silica particles with the current technology. On the other hand, there is a controllable method, but using relatively expensive raw materials and requiring complicated steps, the resulting spherical silica is extremely expensive and economically unsuitable, and is not industrially suitable. . Therefore, the development of a revolutionary and efficient new technology is desired.

Various methods have been proposed to produce spherical silica fine particles having a uniform particle size.
For example, Japanese Patent Publication No. 4-15169 discloses a method in which an alkyl silicate, ammonia and water are mixed and contacted in a solvent containing an alcohol and a hydrocarbon.
In this method, the reaction is controlled by using a solvent in which an alcohol and a hydrocarbon are mixed to obtain a uniform silica particle diameter. However, since a mixed solvent is used as described above, a complicated purification step is required to recover and reuse the solvent. Further, discarding as it is without reuse not only increases the manufacturing cost but also complicates waste liquid treatment. Further, this method uses an expensive raw material such as ethyl silicate or propyl silicate in order to easily control the reaction. If this method is used, silica particles having an average particle size of about 0.3 to 1 μm can be produced, but for the above reasons, the price becomes extremely high and it is not industrial.

In Japanese Patent Publication No. 4-13293, after dissolving aqueous ammonia in an organic solvent having 3 or 4 carbon atoms capable of dissolving water, a solution of tetraalkoxysilane is added.
A process for producing hydrolyzable silica is disclosed. But,
The method also uses expensive ethyl silicate to help control the reaction. In addition, since propanol, butanol, acetone, and the like are used as the organic solvent, there is a disadvantage that the treatment of the waste liquid after the reaction becomes complicated as described above. If this method is used, silica particles having a particle size of about 0.5 μm can be produced. However, as described above, it is extremely expensive and is not industrial.

JP-A-62-52119 discloses a method for producing silica particles by hydrolyzing a hydrolyzable organosilicon compound without substantially changing the concentrations of water and ammonia during the reaction. It has been disclosed. However, in this method, it is necessary to keep the concentrations of water and ammonia constant during the reaction, which complicates the reaction process. Therefore, the obtained silica is still expensive and not industrial. Further, also in the method of this publication, expensive ethyl silicate which is easy to control the reaction is used. If the method is used, it is about 0.05 to 50 μm
Can be produced, but as in the above case, it is extremely expensive, not industrial, and has low versatility.

As another method for producing spherical silica fine particles having a uniform particle size, there is known a method in which seed particles are formed in advance, and then the silica particles are grown with the seed particles as nuclei to control the particle size. (4-4)
No. 2324, Japanese Patent Publication No. 4-61810 and Japanese Patent Application Laid-Open No. 3-218915). However, these methods employ a two-step reaction of generating seed particles and growing silica particles, which complicates the manufacturing process and inevitably increases costs.

Also, a method of producing spherical fused silica by injecting a silicon-containing raw material into a furnace together with a gas flame (Japanese Patent Laid-Open No. Sho 62
Japanese Patent Application Laid-Open Nos. 241541 and 58-145613) are also known, but the spherical silica produced by this method has a relatively large particle size of about 20 to 70 μm.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides an industrially superior method for producing ultra-high-purity spherical silica particles having a particle size range which is low in versatility at present due to high cost, easily and inexpensively. It is.

[0009]

SUMMARY OF THE INVENTION The present inventor has argued that it has been difficult to control the reaction and is not suitable for producing uniform and fine silica particles. The inventors addressed the problem of how to use methyl silicate, which had not been used, to produce uniform and fine spherical silica particles easily and inexpensively, and made various studies. As a result, finally, when the reaction is performed under the following predetermined conditions, surprisingly, the hydrolysis and condensation reaction of methyl silicate can be appropriately controlled, and high-purity spherical silica having a predetermined fine particle diameter can be obtained. They have found that they can be manufactured easily and inexpensively, and have completed the present invention.

That is, the present invention provides (1) a method for producing spherical silica by hydrolyzing and condensing an alkyl silicate in a mixed medium of water and an organic solvent, wherein methyl silicate is used as the alkyl silicate. Hydrolysis of methanol-diluted methyl silicate with stirring in a 0-20 ° C medium containing water, methanol and an acid or basic catalyst, but containing no ammonium salt, using only methanol as an organic solvent. And a condensation reaction to produce spherical silica having an average particle size of 0.5 to 5 μm.

The present invention uses methyl silicate. Therefore, there is no need to use expensive raw materials such as ethyl silicate and propyl silicate. Therefore, the spherical silica of the present invention can be produced at low cost. Since methanol is used as the organic solvent, there is no need to separately separate methanol by-produced in the hydrolysis reaction. Further, the methanol is easier to separate from water than other organic solvents. Therefore,
Waste liquid treatment is easy, cost can be further reduced, and the industrial value of silica can be significantly increased. If ammonia is used as a catalyst, the above effects can be more effectively exerted.

Japanese Patent Publication No. 59975/1992 discloses a method for producing synthetic silica, characterized in that tetraalkoxysilane is hydrolyzed under basic conditions in the presence of an ammonium salt. To produce spherical silica by using tetramethoxysilane as a catalyst and increasing the reaction temperature in methanol (for example, changing from 20 ° C. to 55 ° C. or from 12 ° C. to 29 ° C.). . Conventionally, it has been known that when tetramethoxysilane is hydrolyzed in methanol, the reaction proceeds rapidly and it becomes difficult to control the particle size of silica. In this method, in order to prevent such a sudden reaction, an ammonium salt is used together with ammonia in the hydrolysis. This allows hydrolysis to occur at a lower pH compared to using ammonia alone,
To control the reaction. The reaction becomes mild and stable, but on the other hand, agglomeration of the produced silica particles occurs, and most of the produced silica has a large particle diameter of 20 μm or more. On the other hand, in the present invention, it is possible to control the reaction without requiring an ammonium salt which causes such agglomeration of silica particles. That is, the conventional drawback that the use of methyl silicate causes a rapid progress of the reaction and makes it difficult to control the particle size of silica is reduced by appropriately diluting methyl silicate in advance with methanol and dropping it. The problem was solved by controlling the particle size of the silicate droplets and, furthermore, hydrolyzing and condensing immediately after the dropwise addition under the optimum reaction conditions while preventing the aggregation of methyl silicate by stirring to produce silica particles. This allows
It has succeeded in producing spherical silica having a relatively small average particle diameter of 0.5 to 5 μm.

As a preferred embodiment, (2) the method according to the above (1), wherein the volume ratio of methanol to methyl silicate (room temperature) in the dripping liquid is 2 or more, and (3) the methanol / methyl silicate in the dripping liquid. Volume ratio (room temperature) is 2-5
(4) The method according to (1), wherein the volume ratio (room temperature) of methanol and water in the medium is 2 or more.
(5) The method according to any one of (1) to (3), wherein (5) the volume ratio of methanol to water in the medium (room temperature) is 2 to 8. Method (6)
Any one of the above (1) to (5), wherein a volume ratio (room temperature) of (total amount of methanol and methyl silicate as a dropping liquid) to (total amount of methanol and water as a medium) is 0.1 to 2. (7) The volume ratio (room temperature) of (total amount of methanol and methyl silicate as a dropping solution) to (total amount of methanol and water as a medium) is 0.
(1) The method according to any one of (1) to (5), wherein the catalyst is ammonia. And (9) the method according to any one of (1) to (8) above, wherein the reaction temperature is from 10 to 20 ° C.

[0014]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, methyl silicate is used as an alkyl silicate ester. Conventionally,
Methyl silicate is inexpensive compared to ethyl silicate, propyl silicate, etc., but it is difficult to control the reaction rate of hydrolysis, it has good monodispersibility, and it is difficult to produce fine silica particles. It has not been used industrially in the production of relatively fine silica. In particular, it was not suitable for producing spherical silica having an average particle size within the range of the present invention. The methyl silicate is, for example, a method of reacting methanol on silicon tetrachloride, a method of reacting methanol on silicon disulphide or magnesium silicide, metal silicon, iron silicide, iron silicon silicide or a mixture thereof with methanol and metal methylate (Japanese Patent Publication No. 45-8217) and the like.

In the present invention, an acid or basic catalyst is used to promote hydrolysis. Here, examples of the basic catalyst include hydroxides of alkali metals (such as sodium and potassium), organic amines (such as triethylamine), ammonia, and derivatives thereof. Examples of the acid include mineral acids (such as hydrochloric acid and sulfuric acid) and organic acids (such as formic acid, acetic acid, and oxalic acid). For example, formic acid, acetic acid, ammonia or a derivative thereof (excluding an ammonium salt) is preferable in order to achieve ultra-high purification of silica and an average particle diameter in the range of the present invention, and among them, ammonia is particularly preferable. As the amount of the catalyst, preferably, the minimum amount that efficiently causes the reaction is used.

The organic solvent used in the present invention is methanol. Methanol is capable of dissolving the methyl silicate to be hydrolyzed, and not only can be uniformly mixed with water at a fixed ratio, but also in the present invention, it must be the same as methanol by-produced in the hydrolysis reaction. Therefore, waste liquid treatment after the reaction is remarkably facilitated.
Therefore, it can greatly contribute to the reduction in the production cost of silica. Further, since methanol can disperse methyl silicate appropriately, the particle size of silica can be appropriately controlled.

In the present invention, methyl silicate diluted with methanol is added dropwise to a medium containing water, methanol and an acid or basic catalyst at 0 to 20 ° C., which does not contain an ammonium salt, with stirring to effect hydrolysis and condensation. Perform the reaction.

In the present invention, the lower limit of the volume ratio (room temperature) of methanol to methyl silicate in methyl silicate diluted with methanol as a dropping liquid is preferably 2.0 or less.
And the upper limit is preferably 5.0. Below the lower limit, the hydrolysis reaction proceeds relatively rapidly, and the control of the reaction is not easy, and the particle size of the generated silica increases. If it exceeds the above upper limit, the hydrolysis reaction is remarkably slowed down, which is not economical.

Volume ratio of methanol to water in the medium (room temperature)
Has a lower limit of preferably 2.0 and an upper limit of preferably 8.0. Below the lower limit, not only is the hydrolysis reaction relatively rapid progressing as described above, the reaction control is not easy, and not only the particle size of the generated silica becomes large, but also the dispersion state of water becomes inappropriate and the generated silica Monodispersity also worsens. If it exceeds the above upper limit, the hydrolysis reaction is remarkably slowed down, which is not economical. Here, the lower limit of the amount of water used for the hydrolysis reaction is preferably 4.0 mol, particularly preferably 6.0 mol, from the viewpoint of performing a better hydrolysis reaction. On the other hand, if the amount of water is too large, the treatment of the waste liquid after the reaction becomes inefficient, so the upper limit is preferably 20.0 mol, particularly preferably 10.0 mol. Furthermore, in the present invention, the upper limit of the volume ratio (room temperature) of (total amount of methanol and methyl silicate as a dropping solution) and (total amount of methanol and water as a medium) is preferably 2.0, particularly preferably 1%. .0,
The lower limit is preferably 0.1, particularly preferably 0.2. If it exceeds the above upper limit, the hydrolysis reaction is remarkably slowed down, and it is not economical. If it is less than the above lower limit, the hydrolysis reaction proceeds relatively rapidly, the reaction control is not easy, and the particle size of the generated silica increases.

In the present invention, in order to produce spherical silica particles having a predetermined average particle size, the temperature of the hydrolysis reaction is important. The temperature has an upper limit of 20 ° C and a lower limit of 0 ° C, preferably 10 ° C. If the upper limit is exceeded, the reaction proceeds too rapidly, and it is difficult to produce finely divided silica having good monodispersibility and an average particle diameter within the range of the present invention. If it is less than the above lower limit, the hydrolysis hardly proceeds, which is not preferable.

The time of the hydrolysis reaction varies depending on the reaction temperature, the type of the catalyst, etc., but the upper limit is preferably 3 hours, particularly preferably 2 hours, and the lower limit is preferably 15 minutes, particularly preferably 30 minutes. is there. Above the upper limit, silica in the form of fine particles having an average particle size within the range of the present invention has already been formed, and any further reaction causes aggregation of the silica particles. Below the lower limit, hydrolysis cannot be sufficiently achieved, which is not preferable.

In the method of the present invention, it is preferable that the methyl silicate is dropped and dispersed in a mixed medium of stirring water, an organic solvent and a catalyst. Thereby, aggregation of methyl silicate can be prevented. The dropping speed and the stirring speed are not particularly limited as long as aggregation of methyl silicate does not occur, and is determined depending on the scale and shape of the reactor.

In the above-mentioned hydrolysis reaction, a slurry of hard and spherical silica fine particles can be obtained. However, if necessary, separation and purification, and further drying and firing can be performed to produce a powder of ultra-high-purity and high-density spherical silica fine particles. it can. For example, after filtering the slurry, washing with pure water is repeated,
After drying at 0 to 250 ° C, it can be manufactured by heating at 400 to 800 ° C for several hours, and further heating at 1000 to 2000 ° C for several hours. By heating in this manner, the generation of cavities in the silica particles can be prevented, and the hardness of the silica particles can be improved.

The upper limit of the average particle diameter of the spherical silica obtained by the method of the present invention is 5 μm, preferably 3 μm, and the lower limit is 0.5 μm, preferably 1.0 μm. Spherical silica having an average particle diameter outside the above range is not the object of the present invention since it can be produced at low cost by a method widely used at present. Here, the average particle diameter indicates a particle diameter (D ₅₀ ) corresponding to 50% by weight of the cumulative distribution, and particles of 1 μm or more are measured by laser diffraction, and particles of 1 μm or less are measured by laser scattering. It is a measured value. Further, the spherical silica of the present invention is excellent in monodispersibility. Particle size (1 ± 0.5) × D
_The particles present in the range of ₅₀ are preferably at least 70%, particularly preferably at least 85%.

The spherical silica of the present invention is particularly suitable as a raw material for optical parts, a catalyst carrier, for example, an additive such as a paint, a pigment, a resin, a column filler, an abrasive, and a raw material for a semiconductor sealing material.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0027]

EXAMPLES Each characteristic value in the following examples and comparative examples was measured as follows. <True specific gravity> The true specific gravity was measured using a Wordon specific gravity bottle according to JIS K0061. <Average particle size> Particles having a particle size of 1 μm or more were measured using a laser diffraction particle size distribution analyzer. The used apparatus is SALD-2000J (trademark) manufactured by Shimadzu Corporation. The particle size of 1 μm or less was measured using a laser scattering particle size distribution measuring method. The equipment used was Co
Ulter Coulter Counter Model N4 (trademark). <Shape of Silica Particles> 100 silica particles were arbitrarily extracted and observed and evaluated with an electron microscope.

[0028]

Example 1 A 300 ml glass flask equipped with a stirrer, a dropping port, and a thermometer was charged with 120 ml of methanol and 40% aqueous 25% ammonia.
Add milliliters (volume ratio of methanol and water (room temperature): about 4.0), and stir at 250 rpm with 40 ml of tetramethyl silicate and 100 ml of methanol.
A mixed solution (volume ratio of methanol and tetramethyl silicate (room temperature): 2.5) with milliliter was added dropwise from the dropping port of the flask over 60 minutes while maintaining both the medium and the dropping solution at 15 ° C. [ Volume ratio of dropping liquid to medium (room temperature): 0.93]. After the addition was completed, stirring was continued for 30 minutes while maintaining the temperature of the flask at 15 ° C. to complete the reaction. Next, the produced solid matter was separated by filtration, washed several times with pure water, and then fired in air at 200 ° C., 400 ° C., 700 ° C., and 1000 ° C. for 1 hour in order. Thereafter, the mixture was allowed to cool to room temperature, and white powder (silica) was obtained at a yield of 98%.

The white powder thus obtained is a true spherical silica fine particle having a true specific gravity of 2.2, an average particle diameter (D ₅₀ ) of 1.1 μm, and 97% of particles existing in the range of (1 ± 0.5) × D _50. Met.
After extracting 5 g of this product with 45 g of pure water at 121 ° C. for 2 hours, the amount of ionic impurities in the extract was measured (ion chromatograph, DX-AQ2211 (trademark), manufactured by Nippon Dionex Co., Ltd.). 0.1 ppm or less. In addition, the electric conductivity of the extract (electrical conductivity meter AB-7)
(Trademark, manufactured by Organo Corporation) was 1 μS / cm or less, and it was confirmed that the silica was an ultra-high purity product.

[0030]

Comparative Example 1 A white powder (silica) was obtained in a yield of 74% in the same manner as in Example 1, except that tetraethyl silicate was used instead of tetramethyl silicate. The obtained white powder was spherical silica particles having a true specific gravity of 2.1, an average particle size (D ₅₀ ) of 12 μm, and 48% of particles existing in the range of (1 ± 0.5) × D ₅₀ .

When tetraethyl silicate is used as described above, not only the yield is remarkably lowered, but also the particle size of the formed silica is larger than the range of the present invention, and the monodispersity is significantly deteriorated. Furthermore, tetraethyl silicate itself is relatively expensive, and the waste liquid is methanol,
It is a mixture of ethanol, water and unreacted tetraethyl silicate, and is not industrial because separation and purification are costly. Further, if the reaction temperature is increased in order to increase the yield, the particle size of the obtained silica is further increased.
Therefore, if spherical silica having an average particle diameter in the range of the present invention is to be produced from tetraethylsilicate, various complicated production methods such as those described in the above-mentioned prior art must be employed, and cost is reduced. Invite high.

[0032]

Comparative Example 2 A white powder (silica) was obtained in a yield of 89% in the same manner as in Example 1 except that the hydrolysis temperature was changed to 40 ° C.

The resulting white powder was spherical silica particles having a true specific gravity of 2.2, an average particle diameter (D ₅₀ ) of 27 μm, and 63% of particles existing in the range of (1 ± 0.5) × D ₅₀ .

When the reaction temperature exceeds the range of the present invention, the particle diameter of silica produced by the rapid progress of the reaction is remarkably increased, and the yield and the monodispersity are lowered. Also,
Since a sudden reaction occurs, it is difficult to control the reaction on an industrial scale, which is not practical.

[0035]

Comparative Example 3 A white powder (silica) was obtained in a yield of 68% in the same manner as in Example 1 except that ethanol was used instead of methanol as a solvent.

The obtained white powder was a true spherical silica particle having a true specific gravity of 2.1, an average particle diameter (D ₅₀ ) of 16 μm, and 38% of particles present in the range of (1 ± 0.5) × D _50. Was.

When ethanol is used as a solvent, not only the yield is remarkably reduced, but also the particle size of the produced silica becomes larger than the scope of the present invention. In addition, the monodispersity is significantly reduced. Furthermore, the waste liquid after the production is a mixture of methanol, ethanol and water, which is not industrial because separation and purification are costly.

[0038]

Comparative Example 4 Example 2 described in JP-B-4-15169 was additionally tested. 10 g of tetraethyl silicate was added to 80 g of a mixed solvent of ethanol and n-hexane (1: 1 by weight), and 50 g of the mixture was stirred at 300 rpm.
Heated to ° C. Next, 20 g of aqueous ammonia (25% ammonia concentration) was added, and the mixture was further stirred for 20 minutes to prepare silica fine particles. Here, the molar ratio of ammonia / tetraethyl silicate was 6, and the molar ratio of water / tetraethyl silicate was 17.

The obtained white powder was spherical silica fine particles having a true specific gravity of 2.2, an average particle diameter (D ₅₀ ) of 0.6 μm, and particles having a particle size of (1 ± 0.5) × D ₅₀ of 72%. Was.

According to this method, spherical silica particles having an average particle size comparable to that of the present invention can be produced. However, since the raw material is expensive and a mixed solvent is used, the waste liquid becomes a mixture of ethanol, n-hexane and water, and the treatment becomes expensive. Therefore, the obtained silica particles are very expensive and not industrial.

[0041]

Comparative Example 5 The same procedure as in Example 1 was repeated except that 1% by weight of ammonium carbonate based on 25% aqueous ammonia was added to a glass flask together with methanol and aqueous ammonia. Silica) was obtained with a yield of 83%.

The resulting white powder was spherical silica particles having a true specific gravity of 2.1, an average particle diameter (D ₅₀ ) of 32 μm, and 76% of particles existing in the range of (1 ± 0.5) × D ₅₀ .

The use of ammonium carbonate in this way causes aggregation of silica particles, resulting in a remarkable increase in the particle size of the produced silica and a decrease in yield and monodispersity.

[0044]

According to the present invention, there is provided an industrially superior method for producing ultra-high-purity spherical silica particles having a particle size range which is currently expensive and thus not widely used, simply and inexpensively.

Claims (6)

[Claims] 1. A method for producing spherical silica by hydrolyzing and condensing an alkyl silicate in a mixed medium of water and an organic solvent, wherein methyl silicate is used as the alkyl silicate and methanol alone is used as the organic solvent. By using water, methanol and an acid or basic catalyst, but containing 0 to 20 ° C. containing no ammonium salt, a methyl silicate diluted with methanol is added dropwise under stirring to a hydrolysis and condensation reaction. A method comprising producing spherical silica having an average particle size of 0.5 to 5 µm. 2. The method according to claim 1, wherein the volume ratio (room temperature) of methanol to methyl silicate in the dropping solution is 2 or more. 3. The method according to claim 1, wherein the volume ratio (room temperature) of methanol and water in the medium is 2 or more. 4. The volume ratio (room temperature) of (total amount of methanol and methyl silicate as a dropping liquid) to (total amount of methanol and water as a medium) is 0.1 to 2. The method according to any one of the above. 5. The process according to claim 1, wherein the catalyst used is ammonia. 6. The method according to claim 1, wherein the reaction temperature is 10 to 20 ° C.
The method according to any one of claims 1 to 5.