JPH0687608A - Production of monodispersive spherical silica - Google Patents

Abstract

PURPOSE:To provide a method where monodispersive spherical silica particles of 0.1-10mum average particle diameter and <=15% fluctuation factor are easily and effectively obtained. CONSTITUTION:The method consists of a pretreatment process where an alkoxysilane, alkali adjusted water and organic solvent are continuously injected into a prereaction tank and mixed to form a silicic acid-contg. liquid which is hydrolysate of the alkoxysilane and a main reaction process where liquid contg. the hydrolysate is continuously fed into a main reaction tank holding reaction liquid which the seeds of spherical silica are dispersed in an alkaline organic dispersion medium and the fine silica formed by dehydration condensation of the hydrolysate is stuck to the surface of the seeds, causing the particles to grow, allowing them to have large diameter.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Silica powder consisting of spherical particles with a particle size of submicron to micron and extremely narrow particle size distribution is used for spacers of liquid crystal display devices, various packing materials, packing materials for chromatography, and precision packing materials. It has attracted attention as a material suitable for use as an abrasive. In order to obtain such silica powder particles, the present invention is a method of growing a spherical silica seed to increase the particle size, particularly by hydrolyzing and dehydrating polycondensation of alkoxysilane to give an average particle size of 0.1 to 10 μm.
The present invention relates to a novel method for obtaining monodisperse spherical silica. In the present specification, monodisperse means that the coefficient of variation of particle size distribution (percentage value of standard deviation of particle size based on average particle size) is 15%.
It means the following.

[0002]

2. Description of the Related Art A method for obtaining monodisperse spherical silica of about 0.05 to 2 .mu.m by hydrolyzing and dehydrating polycondensed alkoxysilane is known (W. Stober, Journal).
ofColloid & Interface Sc
i. , 26, 62-69, 1968). This reaction will be described below using tetraethoxysilane as an example. First, in a raw material liquid prepared by diluting tetraethoxysilane with ethyl alcohol, adjust the pH of necessary amount of water and ammonia water.
When a regulator is added and stirred to form a mixed liquid, ethoxysilane in the raw material liquid is hydrolyzed by water in the added liquid to form silicic acid and ethyl alcohol, as shown in the following chemical formula 1. Then, when the concentration of silicic acid in the liquid reaches the supersaturation point, extremely fine silica is produced by dehydration polycondensation, as shown in Chemical formula 2, and these are gradually aggregated to increase the size of the reaction conditions. The spherical silica has a relatively uniform particle size.

[0003]

Embedded image Si (OC ₂ H ₅ ) ₄ + 4H ₂ O → Si (OH) ₄ + 4C ₂ H ₅ OH

[0004]

Embedded image Si (OH) ₄ + → SiO ₂ + 2H ₂ O

In the meantime, the mixed solution changes from a transparent state to a semitransparent state, the transparency is reduced and the degree of white turbidity is increased. Very fine silica has already been formed in a state where it is visibly transparent to slightly translucent, and becomes opaque or cloudy as it aggregates and becomes larger in diameter. A large number of large-diameter silica and a small amount of silica or fine silica are mixed therein, and it is difficult to directly obtain a monodisperse spherical silica having a large diameter of 10 μm from this mixed solution.

Therefore, a liquid containing the spherical silica is used as a reaction liquid, or a liquid obtained by dispersing spherical silica obtained by fractionating the liquid in a separately prepared dispersion medium is used as a reaction liquid, and alkoxysilane is added to the liquid. The raw material liquid dissolved in the organic solvent is continuously added dropwise, and addition liquids such as water and pH adjusting liquid necessary for the reaction are continuously added dropwise, and the reaction liquid shown in the above chemical formula 1 and chemical formula 2 is used. The fine silica particles produced in step (3) are aggregated with seeds to further increase the diameter. This is also known (Japanese Patent Laid-Open No. 62-62-62).
275005, JP-A-63-21016, etc.).

In this seed growth method, in general, the above-mentioned alkoxysilane raw material liquid is successively and dropwise added to the reaction liquid in one tank in which the seed is dispersed, and water for adjusting the pH and pH necessary for the reaction are adjusted. The additive liquid is dropped and supplied from different supply sources, and the hydrolysis reaction of the raw material alkoxysilane and the subsequent production of silica by the dehydration polycondensation reaction are allowed to proceed in parallel in one tank containing the reaction liquid. . According to this method, the diameter of the seed can be certainly increased, but at the same time, it is easy to newly generate fine silica and spherical silica having a small diameter which do not contribute to the growth of the seed in the reaction solution, and the seed growth is also unsuccessful. In reality, it is difficult to stably produce spherical silica having a desired particle size and a uniform particle size distribution.

[0008]

The object of the present invention is to solve the above-mentioned drawbacks found in the conventional manufacturing techniques, to have an average particle size in the range of 0.1 to 10 μm, and a coefficient of variation of 15% or less. It is an object of the present invention to provide a novel production method capable of easily and stably obtaining spherical silica.

[0009]

The inventors of the present invention have conducted extensive research to achieve the above-mentioned object, and as a result, the above-mentioned drawbacks of the conventional seed growth method have been found to result in the presence of a small amount of alkoxysilane in the reaction solution. Since the raw material liquid containing water and the additive liquid for water and pH adjustment are successively added dropwise and the alkoxysilane is hydrolyzed in the reaction liquid, the reaction liquid is stirred by a normal stirring operation. It was presumed that it was difficult to mix the liquid and each additive liquid uniformly in the whole reaction liquid of large volume.
Then, according to the experiment, when the conventional seed growth method was used, the state of the new silica formation due to the hydrolysis reaction in the reaction solution in the above tank and the subsequent condensation polymerization became locally inhomogeneous. It was confirmed that the particle growth by aggregates on the seeds of finely divided silica was locally heterogeneous.

The inventors of the present invention have studied the means for solving the above problems, and have found that the following method is effective, and have reached the present invention. That is, the solution principle of the present invention avoids, as much as possible, the hydrolysis reaction of the added alkoxysilane and the growth of the seed in the reaction solution in one tank at the same time.
There is a way to do both in separate places.
We succeeded in easily and stably obtaining the desired monodisperse spherical silica by performing these two processes separately in one tank without coexisting them in one tank.

The features of the present invention based on this solution principle are:
As described in the claims, alkoxysilane,
Alkali-adjusted water and an organic solvent are continuously poured into a preliminary reaction tank and mixed to prepare a liquid containing silicic acid which is a hydrolyzate of alkoxysilane, and a liquid containing the hydrolyzate. Is continuously supplied to the main reaction tank in which the reaction liquid in which the spherical silica seed is dispersed in the alkaline organic dispersion medium is stored, and the fine silica produced by the dehydration condensation reaction of the hydrolyzate is used as the seed. And a main reaction step of adhering to the surface of the particles to grow the particles to increase the diameter thereof.

(General Description of the Invention) The features of the constitution of the method of the present invention will be described below in order. Pretreatment step: In the pretreatment step, the alkoxysilane in the organic solvent is hydrolyzed with water and alkali adjusted water to prepare a liquid containing silicic acid. The alkoxysilane, alkali-adjusted water and organic solvent may be those conventionally used in the production of silica particles utilizing the hydrolysis / condensation reaction of alkoxysilane. As the alkoxysilane, tetraethoxysilane (ethyl silicate) or tetramethoxysilane (methyl silicate) is suitable and easily available. As the organic solvent, ethanol, methanol, propanol and the like are suitable. Ammonia or caustic soda is preferably used as the alkali source.

The alkoxysilane is preferably dissolved in an organic solvent in advance. The concentration of alkoxysilane in the liquid charged into the preliminary reaction tank is 0.1 mol / l to 2 m.
It is better to adjust to the range of ol / l. (In this case, the concentration in the solvent is preferably in the range of 15 vol.% To 40 vol.%. If the concentration of the alkoxysilane in the solvent is out of this range, disadvantage occurs.) Alkali pretreatment step Acts as a reaction catalyst in the polycondensation for the hydrolysis of the alkoxysilane in and the formation of silica in the main reaction step. Add water to adjust the reaction rate and prevent dissolution of silica particles.
Used as alkali adjusted water of 11-14. Water in alkali-adjusted water has a water concentration of 1 to 50 in the reaction solution of the pretreatment.
Adjust so that it becomes mol / l.

It is preferable that alkaline adjusted water is also dissolved in an organic solvent in advance, but the concentration in the solvent is 12.5 vo.
l. % To 50 vol. % Is preferable. If the concentration of the alkali-adjusted water in the solvent is too high, the hydrolysis will be too large, and if it is too low, the hydrolysis rate will be small and unreacted alkoxysilane will remain, both of which are particles of silica particles in the main reaction step. It becomes difficult to control the diameter.

In the pretreatment, alkali adjusted water adjusted to a predetermined pH value is dissolved in an organic solvent, the temperature of this solution is adjusted to the set temperature of the pretreatment tank, and the alkoxysilane is also adjusted to a predetermined concentration. After dissolving in, the temperature of this solution is adjusted in the same manner. Then, these solutions are continuously added to the pretreatment tank, and mixed by stirring. Although the hydrolysis reaction of the chemical formula 1 mainly occurs in the tank to generate heat, the temperature of the mixed reaction liquid can be easily adjusted because the amount of heat is small. The reaction temperature is appropriately determined in consideration of the boiling point and freezing point of the alkoxysilane, the organic solvent, and the alkali-adjusted water. Temperature is usually 0
The range of ˜70 ° C. is preferred. The temperature of the preliminary reaction does not have to be the same as the temperature of the main reaction, and can be different temperatures in order to improve the particle size distribution of the final product and the production efficiency.

The supply rate of the liquid after the pretreatment process into the main reaction tank varies depending on the concentration and the amount of the silica seed particles in the main reaction tank. If the speed is too high, self-nucleation is likely to occur. However, if the speed is too low, particle growth will be delayed, so 3 x 1 of hydrolyzate per silica seed is generally used.
It is preferably 0 ^{-11 to} 3 × 10 ^-14 mol / hour or less.

Main reaction step: The silica seed to be stored in the main reaction tank in advance has a particle size of 0.5 μm or less and a particle size variation coefficient of 15% or less. It is necessary to disperse the seed particles in an alkaline organic solution, and if the number concentration is low, the fine silica particles generated in the reaction tank will not form aggregates in the seeds and will form independent self-nuclei, resulting in a particle size distribution. When the number density is high, the grown spherical silica particles are aggregated with each other and become coarse. Therefore, 1 × 10 ¹⁰ pieces / l to 1 × 10 ¹⁵
Ke / l, preferably 1 × 10 ¹³ ke / l to 1 × 10 ¹⁴
It should be in the range of 1 / l. As the organic dispersion medium for dispersing the seed particles, the same solvent as that used in the pretreatment step can be used. P of this liquid
In order to stabilize the condensation reaction and obtain spherical silica particles having a uniform particle size, H is a pH value of the silicic acid solution that is supplied through a pretreatment step after adjusting the pH value by using the appropriate alkali source. It is preferable to match with.

[0018]

EXAMPLES Next, preferred examples of the present invention will be described together with comparative examples. (Example 1) A microtube from the upper part of a preliminary reaction tank (capacity: 10 ml) having a vertically long cylindrical shape and having a stirring rod in which a plurality of horizontal blades are attached to a vertical axis in order to have a function of preventing the advance of liquid. With an ethanol solution containing 1.6 mol / l of ethoxysilane by a pump, pH 12.5
Ammonia water of 25 vol. % Ethanol solution was added at a rate of 0.25 ml / min, and the mixture was stirred and mixed. The pH of this mixed liquid is 11.9 and the liquid temperature is 20 ° C. The average residence time of the pouring liquid in the tank is 1 minute, during which the ethoxysilane in the liquid finishes the required reaction and becomes a uniform hydrolysis solution, that is, a silicic acid solution, and reaches the lower part of the preliminary reaction layer. On the other hand, in the main reaction layer (capacity 1 liter), silica monodisperse particles having an average particle diameter of 0.343 μm and a coefficient of variation of 9%, which were previously obtained by hydrolysis / polycondensation of alkoxysilane, of 6 × 10 ¹³ pieces / l were used. Alkaline ethanol solvent containing ammonia so that the number concentration becomes 1
It is stored after being diluted and dispersed in 00 ml.

Then, a solution containing silicic acid obtained by the above hydrolysis is continuously added dropwise to the main reaction tank through the lower outlet of the preliminary reaction tank, and an alkaline organic material in which silica seeds are dispersed in the main reaction tank. Particle growth from seed particles was performed by stirring and mixing with a solvent (temperature; 10 ° C.). After 23 hours, the supply of the silicic acid solution was stopped, the obtained slurry was subjected to solid-liquid separation, and the particle size was evaluated by SEM photograph observation. The average particle size was 1.60 μm, and the variation coefficient was 4%. Silica particles could be obtained. In addition, photograph observation by SEM is JXA manufactured by JEOL Ltd.
-840A type was used.

Example 2 Using the preliminary reaction vessel used in Example 1 (with a capacity of 20 ml), propoxysilane was added to 1.6 m from the top by a microtube pump.
ol / l of an ethanol solution and ammonia water having a pH of 12.5 at 25 vol. % Ethanol solution was added at a rate of 0.25 ml / min, and the mixture was stirred and mixed.
The pH of this mixed solution is 11.9 and the solution temperature is 10 ° C. The average residence time of the pouring liquid in the tank is 2 minutes, during which the propoxysilane in the liquid completes the required reaction and becomes a uniform hydrolyzed solution, that is, silicic acid solution, reaching the lower part of the preliminary reaction tank. On the other hand, in the same manner as in Example 1, 6 × of silica monodisperse particles having an average particle diameter of 0.343 μm and a coefficient of variation of 9%, which were previously obtained by hydrolysis / condensation of alkoxysilane, were placed in the main reaction tank (volume: 1 l). It is stored by being diluted and dispersed in 100 ml of an alkaline ethanol solvent containing ammonia so that the number concentration thereof is 10 ¹³ pieces / l.

Then, a solution containing silicic acid obtained by the above hydrolysis is continuously added dropwise to the main reaction tank through the lower outlet of the preliminary reaction tank, and an alkaline organic material in which silica seeds are dispersed in the main reaction tank is supplied. Particle growth from seed particles was performed by stirring and mixing with a solvent (temperature; 8 ° C.). After 25 hours, the supply of the silicic acid solution was stopped, the obtained slurry was subjected to solid-liquid separation, and the particle size was evaluated by SEM photograph observation. The average particle size was 2.53 μm, and the variation coefficient was 3%. Silica particles could be obtained.

Comparative Example An ethanol solution of ethoxysilane and an ethanol solution of alkali adjusted water having the same composition as that used in Example 1 and an ethanol dispersion of the same silica seed particles as used in the same example were used. Each of them was directly dropped into the main reaction vessel and charged to grow seed particles under the same conditions as in the example. The particle size of the obtained slurry product was evaluated in the same manner as above. The average particle size was 0.95 μm, and the shape of the particle size distribution chart was such that the particle size was smaller than the peak centered on the average particle size. It had a long trailing edge and showed a polydisperse particle distribution with a coefficient of variation of 23.3%. Therefore, it is possible to control the growth of particles by preliminarily hydrolyzing the alkoxysilane in the pretreatment step and then adding a liquid containing this hydrolyzate to the main reaction liquid in which the silica seed particles are dispersed to control the particle growth. It has been proved necessary and beneficial for stable and efficient growth.

Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-mentioned embodiments. That is, the average particle size obtained by the method of Example 1 was 1.6 μm.
It is also easy to separate silica particles of about m from the main reaction solution, use this as a seed and disperse the solution as the main reaction solution, and further drop a preliminary reaction solution similar to the previous one to grow the particles. Thus, it is possible to easily obtain powder particles of monodispersed spherical silica having an arbitrary particle diameter and suitable for various uses.

[0024]

As described above, the method of growing monodisperse spherical silica particles from the silica seed particles of the present invention is carried out by preliminarily treating the alkoxysilane with a hydrolyzate obtained in this step in a solvent. By subjecting the dispersed silica seed particles to polycondensation on the surface and performing the main reaction step of growing the particles separately, it is possible to obtain monodisperse spherical silica having an average particle diameter of 0.1 to 10 μm and a coefficient of variation of 15% or less. Since the particles can be easily and efficiently obtained as compared with the conventional method, they are industrially useful.

Claims (1)

[Claims] 1. A pretreatment step of continuously adding and mixing an alkoxysilane, alkali-adjusted water and an organic solvent into a preliminary reaction tank to obtain a liquid containing silicic acid which is a hydrolyzate of alkoxysilane. , A liquid containing the hydrolyzate is continuously supplied into a main reaction tank containing a reaction liquid in which spherical silica seeds are dispersed in an alkaline organic dispersion medium, and a dehydration condensation reaction of the hydrolyzate is performed. A method for producing monodisperse spherical silica, which comprises a main reaction step of adhering the generated fine silica to the surface of the seed to grow particles to increase the diameter.