JP3888728B2 - Method for producing high purity spherical silica - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
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]
[Prior art]
Ultra-high purity silica has strong development demands in the most advanced fields, for example, additives such as paints, pigments or resins, raw materials for optical components, catalyst carriers, column fillers, wafer polishing agents, semiconductor sealing materials, It has been regarded as promising as a raw material for producing polysilicon crucibles, semiconductor jigs, photomask glass substrates, and the like. In particular, spherical silica is excellent in filling property, dispersibility, etc., and can be used for various purposes, and its usefulness is high. 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, although there is a controllable method, since the relatively expensive raw material is used and a complicated process is required, the obtained spherical silica is extremely expensive and is not economical and not industrially suitable. . Therefore, the development of innovative and efficient new technology is desired.
[0003]
As a method for producing spherical silica fine particles having a uniform particle diameter, various methods have been proposed so far. 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 alcohol and hydrocarbon are mixed to obtain a uniform silica particle size. However, since a mixed solvent is used as described above, a complicated purification process is required to recover and reuse the solvent. Further, if it is discarded without being reused, not only will the manufacturing cost increase, but also the waste liquid processing will become complicated. In addition, this method uses an expensive raw material such as ethyl silicate or propyl silicate in order to facilitate control of the reaction. If this method is used, silica particles having an average particle size of about 0.3 to 1 μm can be produced. However, for the reasons described above, the price is extremely high and is not industrial.
[0004]
Japanese Examined Patent Publication No. 4-13293 discloses a process for producing silica in which aqueous ammonia is dissolved in an organic solvent having 3 or 4 carbon atoms capable of dissolving water, and then a solution of tetraalkoxysilane is added and hydrolyzed. ing. However, this method also uses expensive ethyl silicate in order to facilitate control of the reaction. In addition, since propanol, butanol, acetone or the like is 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 very expensive and not industrial.
[0005]
JP-A-62-52119 discloses a method for producing silica particles by hydrolyzing a hydrolyzable organosilicon compound without substantially changing the concentration of water and ammonia during the reaction. Yes. However, in this method, it is necessary to keep the concentration of water and ammonia constant during the reaction, and the reaction process becomes complicated. Therefore, the obtained silica is still expensive and not industrial. Also in the method of this publication, an expensive ethyl silicate whose reaction is easily controlled is used. If this method is used, silica particles having a particle size of about 0.05 to 50 μm can be produced. However, like the above, it is very expensive and not industrial and low in versatility.
[0006]
As another method for producing spherical silica fine particles having a uniform particle diameter, a method is known in which seed particles are formed in advance and then the silica particles are grown using the seed particles as nuclei to control the particle diameter. (Japanese Patent Publication No. 4-42324, Japanese Patent Publication No. 4-61810 and Japanese Patent 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.
[0007]
Also known are methods of producing spherical fused silica by injecting a silicon raw material into a furnace together with a gas soot (Japanese Patent Laid-Open Nos. 62-241541 and 58-145613). The spherical silica produced by the method has a relatively large particle size of about 20 to 70 μm.
[0008]
[Problems to be solved by the invention]
The present invention provides an industrially excellent method for producing ultra-high purity spherical silica particles having a particle size range that is currently low in versatility due to its high cost and is simple and inexpensive.
[0009]
[Means for Solving the Problems]
The present inventor has clarified how methyl silicate, which has not been used industrially in the past, is difficult to control the reaction and is not suitable for producing uniform and fine silica particles. For this reason, the inventors have tackled the problem of being able to easily and inexpensively produce uniform and fine spherical silica particles, and have made various studies. As a result, when the reaction is finally 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 size can be obtained. The present inventors have found that it can be produced easily and inexpensively and have completed the present invention.
[0010]
That is, the present invention
(1) In a method for producing spherical silica by hydrolyzing and condensing an alkyl silicate ester in a mixed medium of water and an organic solvent, methyl silicate is used as the alkyl silicate ester and only methanol is used as the organic solvent. , water, including methanol and acid or basic catalysts, however hydrolysis and condensation dropwise methyl silicate diluted with methanol under stirring Inakadachi, such include ammonium salt at a constant temperature between 0 ~ 20 ° C. By reacting ( here, the volume ratio of methanol to methyl silicate in the dropping liquid ( room temperature ) is 2 or more ) , it is characterized in that spherical silica having an average particle size after firing of 0.5 to 5 μm is produced. Is the way to do.
[0011]
The present invention uses methyl silicate. Therefore, it is not necessary to use expensive raw materials such as ethyl silicate and propyl silicate. Therefore, the spherical silica of the present invention can be produced at a low cost. Since methanol is used as the organic solvent, it is not necessary to separately separate methanol produced as a by-product in the hydrolysis reaction. Further, the methanol is easily separated from water as compared with other organic solvents. Therefore, the waste liquid treatment is easy, the cost can be further reduced, and the industrial value of silica can be remarkably increased. If ammonia is used as the catalyst, the above effects can be exhibited more effectively.
[0012]
Japanese Examined Patent Publication No. 1-59975 discloses a method for producing synthetic silica, characterized in that tetraalkoxysilane is hydrolyzed under basic conditions in the presence of an ammonium salt, and tetramethoxysilane as tetramethoxysilane is disclosed. It describes the production of spherical silica using silane and raising the reaction temperature in methanol (eg, changing from 20 ° C. to 55 ° C., or from 12 ° C. to 29 ° C.). Conventionally, it is known that when tetramethoxysilane is hydrolyzed in methanol, the reaction proceeds rapidly and it is difficult to control the particle size of silica. In this method, in order to prevent such a rapid reaction, an ammonium salt is used together with ammonia in hydrolysis. Thus, hydrolysis is performed at a pH lower than that of using ammonia alone to control the reaction. The reaction becomes mild and stable, but on the other hand, the produced silica particles agglomerate, and most of the produced silica has a large particle size of 20 μm or more. On the other hand, in the present invention, the reaction can be controlled without requiring an ammonium salt that causes such agglomeration of silica particles. That is, when methyl silicate is used, the reaction proceeds rapidly and it becomes difficult to control the particle size of silica. This was solved by controlling the particle size of the silicate droplets, and further preventing the aggregation of methyl silicate by stirring and producing silica particles by hydrolysis and condensation immediately after dropping under optimum reaction conditions. This succeeded in producing spherical silica having an average particle size of 0.5 to 5 μm and a relatively small particle size.
[0013]
As a preferred embodiment,
( 2 ) The method according to the above (1), wherein the volume ratio (room temperature) of methanol and methyl silicate in the dropping liquid is 2 to 5,
( 3 ) The method according to (1) or (2) above, wherein the volume ratio (room temperature) of methanol and water in the medium is 2 or more,
( 4 ) The method according to (1) or (2) above, wherein the volume ratio (room temperature) of methanol to water in the medium is 2 to 8,
( 5 ) 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) of 0.1 to 2 above (1) to ( 4 ) A method according to any one of the following:
( 6 ) 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 0.2 to 1 above (1) to ( 4 ) A method according to any one of the following:
( 7 ) The method according to any one of (1) to ( 6 ), wherein the catalyst used is ammonia.
( 8 ) The method as described in any one of (1) to ( 7 ) above, wherein the reaction temperature is 10 to 20 ° C.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, methyl silicate is used as the alkyl silicate ester. Conventionally, methyl silicate is less expensive than ethyl silicate, propyl silicate, etc., but it is difficult to control the reaction rate of hydrolysis, and it is difficult to produce fine silica particles having good monodispersibility. Therefore, 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 in the range of the present invention. The methyl silicate is, for example, a method in which methanol is allowed to act on silicon tetrachloride, a method in which methanol is allowed to act on silicon disulfide or magnesium silicide, metal silicon, iron silicide, silicon iron or a mixture thereof and methanol. Can be produced by a method of reacting in the presence of (No. 45-8217).
[0015]
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 (sodium, potassium, etc.), organic amines (triethylamine, etc.), 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 derivatives thereof (excluding ammonium salts) are preferable, and ammonia is particularly preferable among them in order to achieve ultra-high purity of silica and an average particle size within the range of the present invention. As the amount of the catalyst, the minimum amount that efficiently causes the reaction is preferably used.
[0016]
The organic solvent used in the present invention is methanol. Methanol can dissolve methyl silicate to be hydrolyzed and can be uniformly mixed with water at a certain ratio, and in the present invention, it is the same as methanol produced as a by-product in the hydrolysis reaction. Therefore, the waste liquid treatment after the reaction is remarkably facilitated. Therefore, it can greatly contribute to the reduction of the manufacturing cost of silica. Furthermore, since methanol can disperse | distribute methylsilicate appropriately, the particle size control of a silica can be performed appropriately.
[0017]
In the present invention, methyl silicate diluted with methanol is added dropwise to a medium at 0 to 20 ° C. containing water, methanol and an acid or basic catalyst, but not containing an ammonium salt, and subjected to hydrolysis and condensation reactions. .
[0018]
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 the dropping liquid is preferably 2.0, and the upper limit is preferably 5.0. If it is less than the said minimum, a hydrolysis reaction will advance comparatively rapidly and reaction control will not be easy but the particle diameter of the produced | generated silica will become large. If the upper limit is exceeded, the hydrolysis reaction is extremely slow, which is not economical.
[0019]
The lower limit of the volume ratio (room temperature) of methanol and water in the medium is preferably 2.0, and the upper limit is preferably 8.0. If it is less than the lower limit, the hydrolysis reaction proceeds relatively rapidly as described above, the reaction control is not easy, and not only the particle size of the generated silica is increased, but also the dispersed state of water becomes inappropriate and the generated silica Monodispersity also deteriorates. If the upper limit is exceeded, the hydrolysis reaction is extremely slow, which is not economical .
In a further, the present invention, the volume ratio of (dropping solution as methanol and the total amount of methyl silicate) and (total amount of methanol and water as a medium) (room temperature), the upper limit is preferably 2.0, particularly preferably 1.0, and the lower limit is preferably 0.1, and particularly preferably 0.2. If the upper limit is exceeded, the hydrolysis reaction is remarkably slow and not economical, and if it is less than the lower limit, the hydrolysis reaction proceeds relatively rapidly and the reaction control is not easy and the particle size of the produced silica becomes large.
[0020]
In the present invention, the temperature of the hydrolysis reaction is important for producing spherical silica particles having a predetermined average particle diameter. The upper limit of the temperature is 20 ° C, and the lower limit is 0 ° C, preferably 10 ° C. Beyond the above upper limit, the reaction proceeds too rapidly, and it is difficult to produce fine-particle silica having good monodispersibility and an average particle size in the range of the present invention. If it is less than the said minimum, since hydrolysis hardly advances, it is not preferable.
[0021]
The time for 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. Beyond the above upper limit, fine-particle silica having an average particle diameter in the range of the present invention has already been formed, and further reaction causes the aggregation of silica particles. If it is less than the said minimum, it cannot fully achieve a hydrolysis and is unpreferable.
[0022]
In the method of the present invention, the methyl silicate is preferably dropped and dispersed in a mixed medium of water, an organic solvent and a catalyst being stirred. Thereby, aggregation of methyl silicate can be prevented. The dropping speed and the stirring speed are not particularly limited as long as methyl silicate is not aggregated, and is determined depending on the scale and shape of the reaction apparatus.
[0023]
In the above hydrolysis reaction, a slurry of hard and spherical silica fine particles can be obtained. If necessary, separation and purification, and further drying and firing can produce a powder of spherical silica fine particles with ultra-high purity and high density. For example, the slurry is filtered, washed with pure water repeatedly, dried at 110-250 ° C, heated at 400-800 ° C for several hours, and further heated at 1000-2000 ° C for several hours. obtain. By heating in this way, generation of voids in the silica particles can be prevented, and the hardness of the silica particles can be improved.
[0024]
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 size outside the above range is not the object of the present invention because it can be produced at low cost by a currently widely used method. Here, the average particle diameter means a particle diameter (D ₅₀ ) corresponding to 50% by weight of the cumulative distribution, and the particle size of 1 μm or more is measured by laser diffraction, and the particle size of 1 μm or less is measured by laser scattering. It is a measured value. Further, the spherical silica of the present invention is excellent in monodispersity. Particles present in the range of particle diameter (1 ± 0.5) × D ₅₀ are preferably 70% or more, particularly preferably 85% or more.
[0025]
The spherical silica of the present invention is particularly suitable for optical component raw materials, catalyst carriers, for example, additives such as paints, pigments, resins, column fillers, abrasives, semiconductor sealing material raw materials, and the like.
[0026]
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.
[0027]
【Example】
Each characteristic value in the following examples and comparative examples was measured as follows.
<True specific gravity>
In accordance with JIS K 0061, measurement was performed using a Wardon specific gravity bottle.
<Average particle size>
About 1 micrometer or more particle | grains, it measured using the laser diffraction type particle size distribution measuring apparatus. The apparatus used is SALD-2000J (trademark) manufactured by Shimadzu Corporation.
Particles of 1 μm or less were measured using a laser scattering particle size distribution measurement method. The apparatus used is Coulter counter model N4 (trademark) manufactured by Coulter.
<Shape of silica particles>
100 silica particles were arbitrarily extracted and observed by an electron microscope for evaluation.
[0028]
[Example 1]
A 300 ml glass flask equipped with a stirrer, a dripping port, and a thermometer is charged with 120 ml of methanol and 40 ml of 25% ammonia water [volume ratio of methanol to water (room temperature): about 4.0], 250 rpm While stirring at 40 ° C., a mixed solution of 40 ml of tetramethyl silicate and 100 ml of methanol [volume ratio of methanol to tetramethyl silicate (room temperature): 2.5] was added at 15 ° C. from the dropping port of the flask. Was added dropwise over 60 minutes [volume ratio of dripping liquid and medium (room temperature): 0.93]. After completion of the addition, the reaction was completed by continuing stirring for another 30 minutes while maintaining the temperature of the flask at 15 ° C. Next, the produced solid matter was separated by filtration, washed with pure water several times, and then heated at 200 ° C., 400 ° C., 700 ° C., and 1000 ° C. for 1 hour in the air and calcined. Then, it stood to cool naturally and cooled to room temperature, and white powder (silica) was obtained with a yield of 98%.
[0029]
The obtained white powder was true spherical silica fine particles having a true specific gravity of 2.2, an average particle diameter (D ₅₀ ) of 1.1 μm, and 97% of particles present in the range of (1 ± 0.5) × D ₅₀ . . When 5 g of this product was extracted 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.). .1 ppm or less. Moreover, the electrical conductivity (electric conductivity meter AB-7 (trademark), manufactured by Organo Corporation) of the extract was 1 μS / cm or less, and it was confirmed that the silica was an ultra-high purity product.
[0030]
[Comparative Example 1]
The 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 a spherical silica particle having a true specific gravity of 2.1, an average particle diameter (D ₅₀ ) of 12 μm, and 48% of particles present in the range of (1 ± 0.5) × D ₅₀ .
[0031]
When tetraethyl silicate is used in this way, not only the yield is remarkably lowered, but also the particle size of the produced silica is larger than the range of the present invention, and the monodispersibility is remarkably deteriorated. Furthermore, tetraethyl silicate itself is relatively expensive, and the waste liquid is a mixture of methanol, ethanol, water and unreacted tetraethyl silicate, which is not industrial because separation and purification is expensive. Further, if the reaction temperature is raised in order to increase the yield, the particle size of the silica obtained will be further increased. Therefore, if spherical silica having an average particle diameter in the range of the present invention is to be produced from tetraethyl silicate, various complicated production methods as mentioned in the above description of the prior art must be employed, and the cost is reduced. Invite high.
[0032]
[Comparative Example 2]
The white powder (silica) was obtained in 89% yield in the same manner as in Example 1 except that the hydrolysis temperature was 40 ° C.
[0033]
The white powder obtained 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 present in the range of (1 ± 0.5) × D ₅₀ .
[0034]
When the reaction temperature exceeds the range of the present invention, the reaction proceeds rapidly and the particle size of the silica produced is significantly increased, and the yield and monodispersibility are lowered. In addition, since a rapid reaction occurs, it is difficult to control the reaction on an industrial scale, which is not practical.
[0035]
[Comparative Example 3]
The 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.
[0036]
The white powder obtained was true spherical silica particles 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 .
[0037]
When ethanol is used as the solvent, not only the yield is remarkably lowered, but also the particle size of the produced silica becomes larger than the range of the present invention. In addition, the monodispersibility 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 is expensive.
[0038]
[Comparative Example 4]
Example 2 described in Japanese Patent Publication No. 4-15169 was additionally tested. 10 grams of tetraethyl silicate was added to 80 grams (1: 1 by weight) of a mixed solvent of ethanol and n-hexane, and heated to 50 ° C. with stirring at 300 rpm. Next, 20 g of aqueous ammonia (ammonia concentration 25%) 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.
[0039]
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 72% of particles present in the range of (1 ± 0.5) × D ₅₀ .
[0040]
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 materials are expensive and a mixed solvent is used, the waste liquid becomes a mixture of ethanol, n-hexane and water, and the treatment becomes expensive. Thus, the silica particles obtained are very expensive and not industrial.
[0041]
[Comparative Example 5]
A white powder (silica) was obtained in the same manner as in Example 1 except that 1% by weight of ammonium carbonate with respect to 25% aqueous ammonia was added to the glass flask together with methanol and aqueous ammonia. Obtained at 83%.
[0042]
The obtained 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 present in the range of (1 ± 0.5) × D ₅₀ .
[0043]
When ammonium carbonate is used in this manner, the silica particles are agglomerated, and the particle size of the produced silica is remarkably increased, and the yield and monodispersibility are lowered.
[0044]
【The invention's effect】
The present invention provides an industrially superior method for producing ultra-high purity spherical silica particles having a particle size range that is currently low in versatility due to its high cost and is simple and inexpensive.

Claims (5)

In a method for producing spherical silica by hydrolyzing and condensing an alkyl silicate ester in a mixed medium of water and an organic solvent, methyl silicate is used as the alkyl silicate ester, methanol alone is used as the organic solvent, water, comprising methanol and an acid or basic catalysts, however be allowed to hydrolysis and condensation reaction by dropwise addition of methyl silicate was diluted with methanol under stirring Inakadachi, such include ammonium salt at a constant temperature between 0 ~ 20 ° C. ( Wherein the volume ratio of methanol to methyl silicate in the dropping liquid ( room temperature ) is 2 or more ) to produce spherical silica having an average particle size after firing of 0.5 to 5 μm. The volume ratio of methanol and water in the medium (room temperature) The method of claim 1 Symbol placement is 2 or more. The volume ratio of (dropping solution as methanol and methyl silicate of the total amount of) the (total amount of methanol and water as a medium) (room temperature) The method of claim 1 or 2, wherein from 0.1 to 2. The process according to any one of claims 1 to 3 , wherein the catalyst used is ammonia. The process according to any one of claims 1 to 4 , wherein the reaction temperature is 10 to 20 ° C.