JP2512835B2 - Method for producing silica fine particles - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fine silica particles having a monodispersed particle size distribution, and more particularly to a method for producing fine silica particles suitable as a spacer for liquid crystal display devices and standard particles.

[0002]

2. Description of the Related Art A method for producing monodisperse silica fine particles is
(St.ober, J. Colloid and I.
interface Sci. , 26, 62-69 (19
68) or Kojiro Shimodaira et al., Powder and Powder Metallurgy 23, 4, 137 (1976)). In this method, a silicon polyalkoxide is subjected to a hydrolytic polycondensation reaction in the presence of a strong alkali to obtain monodispersed fine particles, and the concentration of silica in the liquid is about 0.1 mol / l (silica 6 g / l as a weight percentage). It is said that the monodisperse fine particles are not generated unless it is below.

In the method described in the above document, particles of up to 2 μm are synthesized using silicon pentoxide as a raw material, but the raw material is more expensive than general ethoxide and is not economical. Therefore, in order to synthesize micron-order particles, Japanese Patent Laid-Open No. 62-52119 has been proposed.
JP, two ways in JP-A-63 -94224 are proposed, these methods, both had technical problems described below.

[0004]

In the method disclosed above, seed particles are not used, but in the process of continuously adding alkoxide, particles formed in the initial stage of addition (initial stage of reaction) serve as seeds. The method is to continue the growth with the added alkoxide. This method is characterized in that it always adopts a method of keeping the concentrations of ammonia and water constant. Specifically, in a mixed solution of ammonia water and alcohol, a solution obtained by diluting ammonia with alcohol and a solution obtained by diluting silicon alkoxide with alcohol or a solution containing only alkoxide is mixed at a constant ratio so that the concentration of ammonia and water does not change. In this case, they are separately dropped and mixed.

However, the fluctuation rate ([σ _n-1 / X] × 100,
σ _n-1 : standard deviation, X: average particle size), 0.3 μm is 1
0%, 1.8 μm is 5%, 5.26 μm is 4%, 14.
3μm is 4%, and when used as a liquid crystal spacer, the particle size in the range (<10μm) seems to be about 4%. When the average particle size is 5.26μm, the standard deviation is 0.21μm. However, the standard deviation is 0.1 μm
The following is not sufficient for a liquid crystal spacer which is considered desirable.

On the other hand, in the above publication, seed particles are prepared from silicon alkoxide, ammonia, water and alcohol, and the raw material liquid is gradually added thereto to grow the particle size. Disclosed is a manufacturing method characterized in that, immediately after the addition of the raw material liquid, an aqueous solution of NaOH is added to form a heel sol in which the dispersion of generated particles is stabilized. When the silica fine particles produced by this method are used as a spacer for liquid crystal, Na is used inside the particles.
⁺ Ions may remain and elute, which may deteriorate liquid crystal molecules that are weak against alkali. Also, in the method of
The scent is added when adding the alkoxide.
Alkoxide that has already formed in the reaction system
Added and consumed only to grow the particle size
It is not always possible. That is, the added alkoxy
Silica seed particles are newly generated from a part of the
A portion of the coxides formed the size of the newly formed seed particles.
It is consumed as a lengthening factor. Therefore relatively large
Of small particles that are newly by-produced with silica particles of various sizes
Generation is inevitable.

Therefore, the inventors of the present invention completed the present invention by earnestly studying a method for producing monodisperse silica fine particles which can solve the above problems.

[0008]

In order to achieve the above object, the present invention is to produce seed particles having a monodisperse particle size by the hydrolysis and polycondensation reaction of silicon alkoxide, and then the dispersion liquid of the seed particles. In the presence of a catalyst, silicon alkoxide is added to the seed particles to grow the seed particles to increase the particle size. It is characterized by repeating the operation of repeating the operation of growing the classified monodisperse fine particles as seed particles after classifying the polydisperse fine particles into monodisperse particles after each growth process. .

In this manufacturing method, only the alkoxide is added to the solution containing seed particles, ammonia, water and alcohol.
Alternatively, a solution obtained by diluting an alkoxide with alcohol is added to cause hydrolysis, and the resulting hydrolysis product is superposed on seed particles to increase the particle size.

The silicon alkoxide is preferably particles having an alkoxyl group having 4 or less carbon atoms, but methoxide and ethoxide are preferably used because they are easily available and inexpensive. Further, as the solvent, any solvent may be used as long as it is a mixture with ammonia and an alkoxide, but an alkyl alcohol having 4 or less carbon atoms, that is,
It is desirable to use methanol, ethanol, propanol or butanol.

When synthesizing fine particles having a desired particle size from seed particles, it is necessary to generate only small particles having a distribution not overlapping with those having a desired particle size. In this case, it is necessary that at least the maximum diameter (S _max ) of the distribution of the particle groups on the small particle size mode side is smaller than 1/2 of the average diameter (X _L ) of the target particles to be obtained. .
At this time, the average particle size (X _s ) of the smaller distribution is X _s <
S _max , but the ratio of S _{max to} X _s is 2/3
Smaller makes classification easier. On the contrary, when the maximum diameter of the small particles is larger than 1/2 of the average diameter of the target particles, it is not only difficult to completely remove the particles even if the classification is repeated, but the classification operation takes a very long time. It is not economical. Also, if small particles are mixed in the seed particles before classification, they also grow at the same time as the seed particles, so that S _max / X _L exceeds 1/2 and classification becomes difficult.

The monodisperse fine particles having a desired diameter are obtained by wet or dry classification of a dispersion liquid of silica fine particles having a bimodal particle size distribution having the above two distributions to remove smaller particles. To be In the wet classification, the volatile components are removed from the liquid after synthesis and the dried powder is dispersed in an organic solvent or the like, and smaller particles may be removed by sedimentation by a sieve or centrifugal sedimentation type classifier or a centrifuge, natural sedimentation and the like. In addition, the liquid after synthesis may be directly removed by a sieve, a classifier, a centrifugal separator, a natural sedimenter, or the like, but in order to prevent ammonia from leaking out of the container, the device becomes complicated, so a rotary evaporator, It is more preferable to remove ammonia and alcohol having a low boiling point from the liquid after synthesis to obtain an aqueous dispersion using a fractionator or the like, and then perform wet classification to remove small particles.

When classifying through a porous membrane such as a sieve or membrane filter, particles having a large pore size and those between the average diameters of small particles are used, but when the particle size exceeds about 1 micron, Sedimentation becomes faster, and clogging due to accumulation of particles tends to occur during classification. Therefore, it is preferable to prevent the larger particles from settling on the sieve and the filter by irradiating ultrasonic waves or stirring the dispersion liquid on the filter.

[0014] When S _max / _X L <seed particles size Ru camphor in 0.5 conditions, the concentration of the silica fine particles in the synthesis solution can be increased than the conventional method. For example, it is possible to synthesize with a silica content of more than 10%.

[0015]

EXAMPLES Example 1 In a cylindrical reaction vessel having a capacity of 20 l, 14,800 ml of methanol and 4,090 ml of 25% ammonia water were added and mixed, and the mixture was set in a constant temperature bath at 30 ° C. To this solution, add 1,110 ml of tetraethoxysilane all at once with stirring.
m particles were produced. After aging for 6 hours or more, alcohol and ammonia were removed using a rotary evaporator to obtain a 13.0 wt% silica fine particle aqueous dispersion.

The resulting 0.3 μm aqueous dispersion 282.6
ml in a 20 l reaction vessel with 8,780 ml of methanol and 5,480 ml of 25% aqueous ammonia, then 3,500 ml of tetraethoxysilane under stirring at 5 g /
It was dripped at the speed of minute. After completion of dropping, the mixture was aged for 6 hours or more with stirring. In the liquid, 1.0 μm monodisperse fine particles were formed. Alcohol and ammonia were removed by a rotary evaporator to obtain a 12.0 wt% silica fine particle aqueous dispersion.

1450 ml of the obtained 1.0 μm aqueous dispersion
Was mixed with 11,600 ml of methanol and 5,000 ml of 25% aqueous ammonia in a 20-liter reaction vessel, and then 1,950 ml of tetraethoxysilane was added dropwise with stirring at a rate of 10.0 g / min. After completion of dropping, the mixture was aged for 6 hours or more with stirring. Do not overlap each other in the liquid 2
Spherical particles with a distribution of species were formed.

As a result of measurement with an electron microscope and a particle size distribution meter, the larger average particle size X _L was 1.90 μm, and the particles with a smaller distribution had a maximum size S _max of 0.73 μm and an average particle size R _{S of} 0. 73 μm and S _max / X _L = 0.38
Met. Alcohol and ammonia were removed by a rotary evaporator to obtain an aqueous dispersion, which was then wet-classified to remove particles having a smaller average particle size distribution. The average particle size of the obtained monodisperse 1.90 μm particles is the variation rate of the particle size (= standard deviation [μm] / average particle size [μm]).
Was 2.2%.

143 ml of an aqueous dispersion containing 13.4% by weight of the obtained 1.90 μm monodisperse silica fine particles, 429 ml of 25% aqueous ammonia and 1143 ml of methanol were added to 2000 parts.
The mixture was placed in a 30 ml container, set in a constant temperature bath at 30 ° C., and 286 ml of tetraethoxysilane was added dropwise at a rate of 1 g per minute while stirring. After the completion of dropping, the mixture was aged with stirring for 6 hours or more.

From measurement by an electron microscope and a particle size distribution meter, spherical particles having two kinds of distributions which do not overlap each other were obtained. As a result of measuring the particle size by an electron microscope,
The average particle size X _L of the larger distribution is 2.99 μm,
In the smaller distribution, the maximum diameter S _max was 1.16 μm, the average particle diameter was 0.82 μm, and S _max / X _L = 0.39. Ammonia and methanol were removed from the obtained dispersion liquid of the particles by an evaporator to obtain an aqueous dispersion liquid, which was then wet-classified to remove particles having a smaller particle size distribution. The average particle diameter of the finally obtained monodisperse silica fine particles is 2.99 μm, and the standard deviation of the particle diameter is 0.048 μm.
The variation rate was 1.61%.

Example 2 The monodisperse silica fine particles having a particle size of about 3.0 μm produced in Example 1 were used as seed particles.
196 an aqueous dispersion containing 16.6% by weight of the seed particles
Silica fine particles were prepared in accordance with Example 1 except that 25 ml of 25% aqueous ammonia, 500 ml of methanol, and 250 ml of tetraethoxysilane were used.
As a result of measuring the particle size by an electron microscope, the average particle size X _L of the larger distribution is 4.18 μm, and the maximum size S _max of the smaller distribution is 2.0 μm and the average particle size is 1.1.
4 μm, and S _max / X _L = 0.48. When the obtained fine particles were wet classified to remove the smaller particles, the average particle size was 4.18 μm, the standard deviation of the particle size was 0.056 μm, and the variation rate was 1.35%.

Example 3 The seed particles having a particle size of about 3.0 μm prepared in Example 1 were used as seed particles. 142 ml of an aqueous dispersion containing 16.6% by weight of the seed particles was prepared, and 25% ammonia water 63
Silica fine particles were produced according to Example 1 except that 6 ml, methanol 727 ml, and tetraethoxysilane were 455 ml. As a result of measuring the particle size by an electron microscope, the average particle size X _L of the larger distribution is 4.97 μ.
m, and the smaller diameter has a maximum diameter S _max of 2.2 μ.
m, the average particle size is 1.54 μm, and S _max / X _L =
It was 0.44 . When the smaller particles were removed by wet classification, the average particle diameter was 4.97 μm, the standard deviation of the particle diameter was 0.083 μm, and the variation rate was 1.68%.

[0023]

As described above in detail in the embodiments,
The production method according to the present invention is a method of increasing the particle size in several steps. For example, when synthesizing 1 μm to 2 μm particles, the same number of 1 μm particles produces 8 times the weight of 2 μm silica. In other words, when synthesizing with the same silica concentration, it is possible to synthesize silica fine particles of 2 μm about 8 times with one particle of 1 μm. Therefore, if particles of each particle size are stocked as seed particles, the desired particle size can be synthesized in a short time.

Further, according to the present invention, the monodisperse fine particles can be obtained even if the concentration of silica in the synthesis solution is increased up to about 10%, so that a large amount of the monodisperse fine particles can be synthesized with a small batch volume.

Claims (2)

(57) [Claims] 1. A seed particle having a monodisperse particle size is produced by hydrolysis and polycondensation reaction of a silicon alkoxide, and then a silicon alkoxide is added to a dispersion liquid of the seed particle in the presence of a catalyst to obtain the seed particle. In order to obtain the monodispersed silica fine particles through the growth process of growing the particle size and increasing the particle size, the growth process is performed a plurality of times with respect to the target particle size and is in a polydisperse state after the end of each growth process. A method for producing silica fine particles, which comprises repeating the operation of classifying the fine particles into a monodisperse state and then growing the classified monodisperse fine particles as seed particles. 2. The particle size distribution of the polydisperse fine particles after the completion of each growth process has two distributions, a distribution on the large particle size mode side and a distribution on the small particle size mode side. 2. The method for producing silica fine particles according to claim 1, wherein the average particle diameters on the large particle size mode side are at least twice the maximum particle diameter of the distribution on the small particle size mode side. .