JPH0764548B2 - Method for producing monodispersed silica particles - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing monodispersed silica particles having a sharp particle size distribution.

TECHNICAL BACKGROUND OF THE INVENTION Silica particles having a sharp particle size distribution are ceramic raw materials,
It is expected to be used as a filler for resins and a spacer for liquid crystal cells. In particular, the particle size is as large as 0.1 μm or more,
Moreover, silica particles having a sharp particle size distribution are expected to be used as spacers for liquid crystal cells.

In order to produce the above silica particles, conventionally known is a method of hydrolyzing an alkoxysilane in a water-alcohol solvent in the presence of an alkali catalyst.

As such a method, for example, the inventors of the present invention have
In JP-A-62-275005, in a water-alcohol-based solvent in which a seed that is a nucleus of particle growth is dispersed, a metal alkoxide such as alkoxysilane is hydrolyzed, and a hydrolyzate is attached onto the seed to form particles. Disclosed is a method for obtaining monodispersed particles having a large particle size by growing the particles.

According to this method, the particle size is as large as 0.1 to 10 μm,
In addition, monodispersed silica particles having a sharp particle size distribution can be obtained.

By the way, in the method as described above, a part of the particles may aggregate when the particles grow or when the generated particles settle. If such agglomerated particles are generated, redispersion becomes difficult even when subjected to dispersion treatment with ultrasonic waves, etc., and the resulting particles are likely to have a nonuniform particle size. Therefore, it is desired to develop a method for producing monodispersed particles that are more uniform and stable without particles agglomerating during the particle growth process or when the produced particles settle.

The present invention has been made in view of the above-mentioned conventional techniques, and provides a method for producing silica particles having a sharp particle size distribution and capable of producing monodispersed silica particles. Is intended.

SUMMARY OF THE INVENTION The method for producing monodispersed silica particles according to the present invention comprises a tetraalkoxysilane in a water-alcohol-based dispersion in which a metal oxide or a metal hydroxide is dispersed as a seed, while keeping the dispersion alkaline. And a silicic acid solution are added to cause the tetraalkoxysilane hydrolysis product and the silicic acid polymer to adhere to the seeds for grain growth.

According to the present invention, it is possible to efficiently obtain monodispersed silica particles having a large particle size and a sharp particle size distribution. Furthermore, since the concentration of oxide-equivalent particles in the reaction system can be increased, there is an effect that the production cost of particles can be reduced.

DETAILED DESCRIPTION OF THE INVENTION The method for producing monodispersed silica particles according to the present invention will be specifically described below.

In the present invention, first, a water-alcohol dispersion liquid (hereinafter sometimes referred to as heel sol) in which a metal oxide or a metal hydroxide is dispersed as a seed is prepared.

In the present invention, metal oxide particles or metal hydroxide particles are used as seeds. As such seeds, particles of SiO ₂ , Al ₂ O ₃ , TiO ₂ , ZrO ₂ or the like having a uniform particle diameter slightly smaller than the intended silica particle diameter can be used. In some cases, metal oxide particles,
Particles having a uniform particle size other than the metal hydroxide particles can also be used.

Such a water-alcohol-based dispersion liquid (heel sol) in which seeds are dispersed may be prepared by adding seeds to a water-alcohol-based mixed solution, or particles that become seeds in the water-alcohol-based mixed solution. May be produced and prepared.
Of these, the latter heel sol is preferably used. For example, metal oxide particles such as silica particles obtained by hydrolyzing a metal alkoxide such as alkoxysilane according to a conventional method in a water-alcohol mixture are dispersed as seeds. The water-alcohol-based dispersion thus prepared is preferably used. The seed generation method is described, for example, in “Powder and powder metallurgy” 23 , (4), 19-24 (1976).

The heel sol thus obtained preferably has an alkaline pH so as to prevent the seeds from aggregating.

The alcohol concentration in the heel sol is preferably 35 to 97% by weight. Examples of the alcohol used here include lower alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol and isobutanol. These can be used alone or as a mixed solvent thereof.

In addition to water and alcohol, other organic solvent can be used as the water-alcohol dispersion liquid. As such an organic solvent, one having a good compatibility with water and alcohol and a good compatibility with a tetraalkoxysilane and a silicic acid solution is used.

The seed concentration in heel sol is 0 in terms of oxide equivalent.
It is preferably from 05 to 20% by weight. If the oxide conversion concentration of the seed is less than 0.05% by weight, new seeds may be generated in the process of growing the particles described later, and the particle diameter of the obtained silica particles tends to be non-uniform. On the other hand, when the equivalent oxide concentration of the seed exceeds 20% by weight, the particles tend to aggregate during the particle growth process, which affects the uniformity of the particle size.

Next, tetraalkoxysilane and silicic acid solution are added while keeping the heel sol obtained as described above alkaline.

The tetraalkoxysilane used in the present invention has the general formula
It can be represented by Si (OR) ₄ .

In the formula, R is an alkyl group having 1 to 7 carbon atoms, and preferably an alkyl group having 1 to 4 carbon atoms. Specific examples of such a tetraalkoxysilane include tetramethoxysilane (methyl silicate), tetraethoxysilane (ethyl silicate), tetraisopropoxysilane,
Tetrabutoxysilane etc. are mentioned.

The tetraalkoxysilane may be used as it is, or may be diluted with alcohol or the like and used.

The silicic acid solution used in the present invention is an aqueous solution of a low-polymerized silicic acid, and specifically, it is obtained by dealkalizing an aqueous solution of an alkali silicate such as sodium silicate with a cation exchange resin or the like. To be

A silicic acid solution having a SiO ₂ concentration of about 0.1 to 10% by weight is preferably used.

In the present invention, when the tetraalkoxysilane and the silicic acid solution as described above are added to the heel sol, a method of simultaneously adding both, a method of alternately adding both over several times, and initially only tetraalkoxysilane is used. Any method such as a method of adding the particles to cause grain growth and finally adding the silicic acid solution can be adopted.

Of these, the method of adding both separately is preferred,
According to the method of alternately adding, the dispersion and the produced particles can be obtained with good stability.

When the above method is used, the amount of each addition is not particularly limited, and any amount can be added alternately.

In the present invention, the outermost layer of the finally obtained silica particles is preferably formed of a silicic acid polymer, and it is preferable to use a silicic acid solution at the time of addition.

When tetraalkoxysilane and silicic acid solution are added to heel sol by the above method, hydrolysis reaction of tetraalkoxysilane and polymerization reaction of silicic acid occur, these reactants are deposited on the seeds, and particle growth occurs. Is done. Further, at this time, when the pH of the reaction system decreases and approaches neutrality, not only the particles tend to agglomerate but also new seeds are easily generated, so the particles finally obtained have a non-uniform particle size. It is easy to become. Therefore, when the tetraalkoxysilane and the silicic acid solution are added, it is preferable to maintain the pH value of the dispersion liquid at 9 to 14, preferably 10 to 13. It is preferable that the pH value of the dispersion liquid does not fluctuate within the above range as much as possible.

To keep the dispersion alkaline, an alkali may be added to the reaction system. Specifically, ammonia gas, ammonia water, amines, alkali metal hydroxides, quaternary ammonium salts, etc. may be used alone or in combination. Used.

Moreover, the reaction system temperature in the particle growth process is not particularly limited, but when the temperature is higher than the boiling point of water or alcohol, it is preferable to pressurize so that the solution can maintain the liquid phase.

In the present invention, the alcohol concentration in the reaction system is 35 to
It is preferably 97% by weight. If the alcohol concentration is less than 35% by weight, the compatibility with the tetraalkoxysilane is lowered, the heel sol is easily emulsified, and the seeds are likely to be aggregated or non-spherical amorphous components are easily generated. On the other hand, when the alcohol solution exceeds 97% by weight, the rate of hydrolysis of tetraalkoxysilane becomes slow.

The alcohol concentration in the reaction system is adjusted by adding water and alcohol to the reaction system, and the addition amount of each is tetraalkoxysilane (SiO ₂ conversion).
2.0 to 24.0 mol of water and 0.4 to 1.1 of alcohol for 1 mol
It is preferably added in molar amounts.

The silica particles dispersed in the water-alcohol-based dispersion medium thus obtained consist of a hydrolyzed condensate of tetraalkoxysilane having a metal oxide or metal hydroxide as a nucleus and a silicic acid polymer, both of which are It may have a mixed structure, a structure in which both layers are alternately laminated, or a structure in which the outermost layer of particles of an alkoxysilane hydrolysis-condensation product is covered with a silicic acid polymer layer. In the present invention, in any of the above structures, the outermost layer is preferably a layer made of silicic acid polymer.

The silica particles as described above are spherical, have a sharp particle size distribution, and are monodispersed in the dispersion medium without agglomeration. Further, it is possible to obtain particles having an arbitrary particle diameter ranging from a small particle diameter of about 0.01 μm to a large particle diameter of 10 μm or more. The concentration of particles in the dispersion medium can be as high as about 20.0% by weight in terms of SiO ₂ , and can be significantly increased as compared with the conventional manufacturing method. Therefore, the production efficiency of silica particles can be increased, and the production cost can be reduced.

The concentration of the particles can be increased up to about 60.0% by weight by further concentrating the dispersion liquid in which the silica particles obtained by the present invention are monodispersed.

In order to further enhance the stability of the silica particles monodispersed in the dispersion obtained according to the present invention, a stabilizer such as an alkali can be added to the obtained dispersion, and the aging treatment can be performed in this manner. By applying it, particles in the dispersion do not aggregate for a long period of time. Further, the alcohol in the dispersion can be replaced with another organic solvent.

Effects of the Invention The silica particles obtained in the present invention have a structure in which a hydrolyzed condensate of tetraalkoxysilane and a silicic acid polymer are mixed or alternately laminated, and particularly the outermost layer is composed of a silicic acid polymer layer. It is preferable.

Therefore, compared to silica particles obtained by conventional methods,
It is possible to obtain silica particles with less aggregation of particles and further improved monodispersity.

Furthermore, the monodispersed silica particles of the present invention have a weak cohesive force between the dry particles even when used after drying, are less likely to be charged with static electricity, and have excellent fluidity as a powder. Therefore, for example, powder suitable for dry spraying can be obtained.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 487 g of ethyl alcohol, 256 g of 28% ammonia water and water
The 205 g mixed solution was stirred while maintaining it at 35 ° C., and 17.5 g of ethyl silicate (28 wt% as SiO ₂ ) was added to it.
Was added. Then, stirring is continued for 2 hours to obtain SiO ₂ of 0.5.
A heel sol in which silica particles corresponding to wt% were dispersed was obtained.

While stirring 974 g of this heel sol at 35 ° C., first add 2 g of silicic acid solution (concentration as SiO ₂ is 5.0% by weight) gradually, and then add ethyl alcohol / water mixed solution (weight ratio 1.0 / 0.8). 47 g and ethyl silicate (as SiO ₂
28 wt%) 10.5 g were added slowly at the same time. At this time, the pH of the reaction solution was maintained at 11.5 with ammonia gas.

The above-mentioned addition operation was repeated, and the predetermined amount was added over 19 hours so that the outermost layer of the obtained silica particles became a layer of the polymer of the silicic acid solution. The total amount added of each was 117 g of silicic acid solution, 2698.5 g of ethyl alcohol / water mixed solution and 606 g of ethyl silicate.

After the completion of addition of the whole amount, 204 g of a 1 wt% NaOH aqueous solution was added to the reaction solution, and the mixture was kept at 70 ° C. for 2 hours to obtain a dispersion liquid in which silica particles were monodispersed.

Note silicic acid solution used herein is a water glass (SiO ₂ 24
It was prepared by diluting 3% by weight of SiO ₂ / Na ₂ O in a molar ratio with water so that the SiO ₂ concentration was 5% by weight and then dealkalizing with a cation exchange resin.

Example 2 While stirring 974 g of the heel sol of Example 1 at 35 ° C.,
First, 2 g of the same silicic acid solution as in Example 1 was gradually added. Next, 82 g of ethyl alcohol / water / ammonia mixed solution (weight ratio 1.0 / 1.4 / 0.7) and ethyl silicate (as SiO ₂
28% by weight) and 10.5 g were added at the same time. This operation was repeated, and the predetermined amount was added over 10 minutes so that the outermost layer became a layer of the polymer of the silicic acid solution. The total amount added of each was 117 g of silicic acid solution, 4679.5 g of ethyl alcohol / water / ammonia mixed solution and 606 g of ethyl silicate.

After adding the whole amount, the same treatment as in Example 1 was carried out to obtain a dispersion liquid in which silica particles were monodispersed.

Example 3 An ethyl alcohol / water mixed solution (weight ratio 1.0 / 0.8) was added with S
The average particle size is 8 μm so that the iO ₂ concentration is 0.5% by weight.
The spherical silica particles of 1 were added to prepare a heel sol in which the spherical silica particles were dispersed.

1910 g of this heel sol was stirred while maintaining the temperature at 35 ° C., 3 g of the same silicic acid solution as in Example 1 was added, and then 8.5 g of an ethyl alcohol / water mixed solution (weight ratio 1.0 / 1.1) and ethyl silicate (SiO ₂ As 28 wt%) 1 g. This operation was repeated while maintaining the pH at 11, so that the outermost layer of the obtained silica particles became a layer of a polymer of a silicic acid solution, and a predetermined amount was added.

The total addition amount of each was 60 g of silicic acid solution, 149 g of ethyl alcohol / water mixed solution, and 22 g of ethyl silicate, and the addition time was 3 hours. Then, in the same manner as in Example 1, a dispersion liquid in which silica particles were monodispersed was obtained.

Example 4 Silica sol having an average particle size of 0.08 μm and a SiO ₂ concentration of 40% by weight (SI
-80P, manufactured by Catalysts & Chemicals Industry Co., Ltd.) (2.5 g), about 0.1 wt% NaOH aqueous solution (81.5 g) and ethyl alcohol (100.5 g) were mixed to prepare a heel sol.

First, 24.5 g of an ethyl alcohol / water mixed solution (weight ratio 1.0 / 0.9) and 7 g of ethyl silicate (28% by weight of SiO ₂ ) were simultaneously added to this dispersion under the same conditions as in Example 1, and then the same as in Example 1. 1.5 g of silicic acid solution was added. This operation is pH
While maintaining at 11.5, the outermost layer of the silica particles obtained was repeatedly formed so as to be a layer of a polymer of a silicic acid solution, and a predetermined amount was added in 19 hours. The total addition amount of each is 1401 g of ethyl alcohol / water mixture, 393 g of ethyl silicate,
The silicic acid solution was 76 g. After adding the whole amount, 1% by weight NaOH aqueous solution 3
7 g was added and treated at 70 ° C. for 2 hours to obtain a dispersion liquid in which silica particles were monodispersed.

Example 5 486.5 g of isopropanol, 214 g of water and 28% ammonia
A mixed solution of 256 g was kept at 35 ° C., and 17.5 g of titanium tetrapropoxide was added thereto over 2 hours while maintaining the pH at 11 or more with ammonia gas.

A part of the obtained TiO ₂ particle dispersion liquid was taken and diluted with isopropanol to prepare 184 g of a seed dispersion liquid having a TiO ₂ concentration of 0.5% by weight.

The dispersion was stirred while maintaining the pH at 11.5 at 35 ° C., 3 g of the same silicic acid solution as in Example 1 was added, and then 47 g of an isopropanol / water mixed solution (weight ratio 1.0 / 0.8) and ethyl silicate (SiO ₂ 28 wt%) as 16.5 g were added simultaneously. This operation was repeated so that the outermost layer was a layer of a polymer of silicic acid solution, and 76 g of silicic acid solution, 1129.5 g of isopropanol / water mixed solution and 393 g of ethyl silicate were added over 4 hours. Then, the temperature was maintained at 70 ° C. for 2 hours to obtain a silica dispersion liquid.

Example 6 249 g of spherical silica having an average particle size of 5.0 μm was dispersed in a mixed solution of 3685.5 g of ethyl alcohol, 1365 g of water and 921.5 g of 28% ammonia water, and then a 1% by weight NaOH aqueous solution 16
1 g was added and ultrasonic treatment was performed to prepare a heel sol.

This heel sol was placed in an autoclave and heated to 120 ° C. While maintaining this temperature, Example 1 and 4 g of silicic acid solution
Then, 131.5 g of a mixed solution of ethyl alcohol / water / ammonia (weight ratio 1.0 / 0.3 / 0.1) and 21 g of ethyl silicate were simultaneously added. This operation was repeated so that the outermost layer of the silica particles became a layer of a polymer by the silicic acid solution, and 50.5 hours later, 120.5 g of the silicic acid solution, 3937.5 g of ethyl alcohol / water / ammonia mixed solution and 625 g of ethyl silicate were added. Was added. After adding the whole amount, 1% by weight of Na
After adding 117g of OH aqueous solution, hold at 150 ℃ for 1 hour,
A dispersion liquid in which silica particles were monodispersed was obtained.

Example 7 974 g of heel sol obtained in Example 1 was kept at 65 ° C., and an ethyl alcohol / water / ammonia mixed solution (weight ratio 1.0 / 2.
5 / 0.2) 1103 g and ethyl silicate (28% by weight as SiO ₂ ) 627 g were added simultaneously over 19 hours. Then 70
Maintained at 0 ° C for 2 hours. Then, 1263 g of the silicic acid solution of Example 1 was added to this dispersion at 70 ° C. over 6 hours to obtain a monodisperse silica particle dispersion.

Table 1 shows the properties of the monodisperse silica particles obtained in Examples 1 to 7.
Shown in 1. Each measuring method is as follows.

(1) Average particle size Electron micrographs were measured with an image analyzer.

(2) Uniformity coefficient It was calculated by the following formula from the average particle diameter and standard deviation obtained in (1).

(3) Aggregation state The ratio (n / N) between the number n of aggregated particles and the total number N of particles in a certain field of an electron micrograph was calculated.

(4) Angle of repose The angle of repose was measured using a cylindrical rotary type tip angle measuring device (manufactured by Tsutsui Rikagiki Kiki).

Claims (2)

[Claims] 1. A tetraalkoxysilane is prepared by adding a tetraalkoxysilane and a silicic acid solution to a water-alcohol dispersion liquid in which a metal oxide or a metal hydroxide is dispersed as a seed, while keeping the dispersion liquid alkaline. A method for producing monodispersed silica particles, which comprises depositing a hydrolysis product and a silicic acid polymer on the seed to perform particle growth. 2. The method for producing monodispersed silica particles according to claim 1, wherein the outermost layer of the silica particles is formed of the silicic acid polymer.