JP2000327320A - Production of fine granular silica gel and granular silica gel containing metal compound fine particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a silica gel having fine granular state in high productivity by reacting an alkali metal silicate with a mineral acid to obtain a silica hydrogel having a specific SiO2 to water ratio, forming a slurry having a specific SiO2 concentration, heat-treating under stirring to finely pulverize to a specific particle size, further finely pulverizing under hydrothermal condition and drying the product. SOLUTION: An aqueous solution of an alkali metal silicate (sodium silicate) is made to react with an aqueous solution of a mineral acid (sulfuric acid) to effect the hydrogelatinization to obtain a silica hydrogel having a weight ratio of water to SiO2 of 1.5-5.0. The obtained silica hydrogel is thoroughly washed with water, converted to a slurry having an SiO2 concentration of 5.0-15.0 wt.%, subjected to hydrothermal treatment under stirring to obtain a slurry of a finely pulverized silica hydrogel having an average particle diameter of <=100 μm and the slurry is dried e.g. by spray drying to obtain the objective finely pulverized silica gel.

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 microparticulate silica gel in which fine particles of silica, fine spherical silica gel, and fine particles of a metal compound such as a metal oxide are included.

[0002]

2. Description of the Related Art Microparticle silica gel such as microspheres is
Separating agents for liquid chromatography, fillers for cosmetics,
It is used for various applications such as resin fillers, catalyst carriers and spacers.

[0003] Further, particulate silica gel such as microspheres in which metal compound fine particles are included in particles is used as an ultraviolet ray shielding agent, a photo-oxidation catalyst, an antibacterial agent and the like.

[0004] Conventionally, various methods have been proposed as a method for producing microparticle silica gel such as microspheres.

For example, as described in JP-A-6-64915, an aqueous solution of an alkali metal silicate is emulsified and dispersed in a nonpolar organic halide solvent containing a surfactant, and then gelled with a gelling agent. A method for causing this is known. In this method, the individual droplets are made spherical by utilizing the interfacial tension at the liquid / liquid interface of the generated micro-dispersed droplets, and then reacted with a gelling agent such as carbon dioxide in that state to form a gel. It will solidify. The resulting gel is p
After an H adjusting step and an aging step, solid / liquid separation is performed to wash and remove by-product alkali metal salts with water, followed by drying to obtain fine spherical silica gel. In this method, it is easy to obtain spherical particles, but since an organic solvent is used, troublesome solvent separation,
A recovery step is required, and the number of steps is large, resulting in a complicated process.

Japanese Patent Application Laid-Open No. 3-183616 discloses that an aqueous solution of an alkali metal silicate is sprayed into an acidic gas to collect generated droplets and / or gelled products, and then treated with an acid-containing solution and then washed with water. Thus, a method for producing a spherical silica gel is described. However, the method of causing a contact reaction between a droplet and an acidic gas is inevitably an economically problematic one because the utilization rate of the acidic gas as a gelling agent in one pass must be low.

Further, as described in JP-A-62-128916 and JP-A-62-128917, fine spherical particles having a specific water content are obtained by spray drying an alkali metal silicate aqueous solution. Next, a method of producing spherical porous silica by subjecting the particles to an acid treatment under a specific temperature condition, washing with water, and drying is known. However, these methods have a disadvantage that it is difficult to obtain particles having a large pore volume even if the water content of the fine spherical particles and the temperature of the acid treatment are slightly changed.

Further, as described in JP-B-6-99135, a silica hydrogel obtained by reacting an alkali metal silicate with a mineral acid is mechanically wet-pulverized, and then the silica hydrogel is mixed with water. In the method of obtaining spherical silica gel by spray-drying the slurry with, the amount of water in the slurry at the time of spray-drying, from the point of securing the slurry state and particle strength to silica hydrogel, 0.2 to 0.2 1.5 weight times, preferably 0.3-1.
A production method of adjusting the weight to 4 times is known.

Here, the pulverization of the silica hydrogel is usually carried out by
Ball mill, vibration mill, stirring ball mill, rod mill,
Using a friction disk mill, a stone mill type colloid mill, or the like, the silica hydrogel in the slurry is subjected to mechanical wet pulverization until the particle diameter becomes 1 to 50 μm, preferably 10 to 30 μm. In addition, 100 to 100 mechanically using a mechanical pulverizer such as an impact pulverizer, a jet pulverizer, a ball mill,
It is stated that coarse pulverization may be performed to about 200 μm.

Before the wet pulverization, the silica hydrogel is suspended in demineralized water and the pH in the system is adjusted to 1 to 10 by adding aqueous ammonia or the like.
It is said that hydrothermal treatment at a temperature of 0 ° C. for 1 to 50 hours is preferable.

In this production method, the particle size after the hydrothermal treatment is larger than 100 to 200 μm.
It is intended to grind it down to 1 to 50 μm exclusively by mechanical grinding.

However, since the individual particles constituting the silica hydrogel are a kind of viscoelastic material, it is difficult to wet-pulverize the silica hydrogel into fine particles.
Technically very difficult. Regardless, in this production method, as a method of reducing the particle diameter, the particle diameter is being reduced to a predetermined 50 μm or less by a mechanical pulverization method, which is technically difficult. I have to say.

On the other hand, in order to solve such difficulties, Japanese Patent Application Laid-Open No. 7-196310 discloses a method in which an aqueous solution of an alkali metal silicic acid is reacted with an aqueous solution of an acid, and a temperature of 100 to 170 ° C.
In the silica hydrogel obtained by a heat treatment, in particular a slurry concentration SiO ₂ concentration is referred to as 15 to 25 wt%, and 5
A method has been proposed in which a wet milling under high-speed shearing at a specific temperature not exceeding 0 ° C. is carried out to obtain a slurry of silica hydrogel having a particle diameter of 4 μm or less, which is spray-dried to produce fine spherical silica granules. ing.

After the silica hydrogel after the heat treatment is washed with water,
First, the particle diameter is adjusted to 20 to 100 μm by mechanical coarse pulverization, and then 5 μm using a known high-speed shearing wet pulverizer such as a dyno mill manufactured by Shinmaru Enterprises.
Mechanically wet-pulverized at a temperature of 0 ° C or less, particle size of 4 μm
After finely pulverizing to the following, spray-drying is performed to obtain fine spherical silica gel.

This is because the viscosity of the slurry is reduced in the above specific SiO ₂ slurry concentration and temperature range, so that a large shear force can be applied.

However, according to the study of the present inventors, in this manufacturing method, even if the viscosity of the slurry is slightly reduced from a macroscopic view due to the adjustment of the slurry concentration, etc.
Microscopically, individual particles of the silica hydrogel are still viscoelastic, and such viscoelastic particles are wet-milled to finer particles only by a mechanical grinding mechanism. Attempting to do so is in principle a technically very difficult process. Of course, there is no technical idea to make the silica hydrogel into fine particles by hydrothermal treatment.

On the other hand, as a method for producing microparticulate silica gel in which metal compound fine particles are encapsulated in particles, for example, as described in JP-A-8-104515,
There is known a method of making particles spherical by using the interfacial tension of a liquid.

In this method, for example, zinc oxide fine particles are added to an aqueous solution of an alkali metal silicate and mixed, and a highly dispersed mixed slurry is emulsified and dispersed in an organic solvent containing a surfactant to form individual droplets into spheres. At the same time, it reacts with the gelling agent in that state to cause gelation and solidification. The resulting gel is subjected to a pH adjusting step and an aging step, and is then subjected to solid / liquid separation to remove by-product alkali metal salts with water and dried to obtain fine particulate silica gel containing zinc oxide fine particles and the like.

In this method, as described above, although spherical particles are easily obtained, since an organic solvent is used, troublesome solvent separation and recovery steps are required. There are difficulties.

[0020]

In a method for producing silica gel having a fine spherical shape or the like by a conventionally known method, a silica hydrogel obtained by reacting an alkali metal silicate with a mineral acid is used as a starting material. A method of obtaining a silica hydrogel slurry by refining the particle diameter and drying the silica hydrogel slurry by means such as spray drying is basically suitable for mass production and economical. Are better.

On the other hand, in the above-mentioned known production method, when a silica hydrogel obtained by reacting an alkali metal silicate with a mineral acid is used as a starting material, the alkali metal salt in the silica hydrogel formed by the reaction is usually used. Is performed by washing with water.

In the step of washing and removing the alkali metal salt from the silica hydrogel with water, the particle diameter of the silica hydrogel before washing with water is 0.1 mm or more, preferably 0.5 m
It is preferable to perform a packed fixed bed type washing operation in which a fixed particle layer of silica hydrogel is formed in a washing tank, and washing water is circulated through the filled layer to wash the particles. In such a packed bed type water washing method, when the average particle diameter of the silica hydrogel is sufficiently large, a stable packed bed can be formed, and a large amount of the silica hydrogel can be easily washed with water, and further, no filtration device is particularly required. Therefore, it is suitable for mass production and is economical.

However, when the silica hydrogel is reduced to a small particle size of, for example, less than 0.1 mm and then the salt formed by the reaction is washed with water, a stable packed layer is not formed. However, filtration of the silica hydrogel is eventually required, and a fairly large filtration device is required, which is problematic in terms of economy.

According to the study of the present inventors, it has been found that a method of obtaining a fine spherical silica gel by subjecting a sufficiently washed silica hydrogel containing almost no alkali metal to a fine silica hydrogel slurry and spray-drying the silica hydrogel is also considered. It is difficult to perform fine pulverization by mechanical wet pulverization.

For example, even if an attempt is made to finely fine particles by mechanical means from coarse particles having an average particle diameter of 0.5 mm or more to fine particles having an average particle diameter of several μm, as described above, silica hydrogel particles are a kind of particles. Since it is a viscoelastic body, it is not easy to apply mechanical shearing force to pulverize. In practice, it has been found that there is a great problem that the number of stages of the pulverization process must be increased to pulverize to a predetermined average particle size.

Thus, an object of the present invention is to provide a silica hydrogel obtained by reacting an alkali metal silicate with a mineral acid, preferably by sufficiently washing with water to obtain a silica hydrogel containing substantially no alkali metal salt formed by the reaction. And then
In a method of obtaining a silica hydrogel slurry in which the particle diameter of the silica hydrogel is refined and the slurry is subjected to spray drying or the like to obtain microspherical silica gel, the method of refining the silica hydrogel is not performed by mechanical wet pulverization. To provide a manufacturing method which can be performed with high productivity.

It is another object of the present invention to provide a novel method for producing microparticulate silica gel containing metal compound fine particles.

[0028]

Means for Solving the Problems As a result of intensive studies from the above viewpoint, the present inventors have found that a silica hydrogel obtained by reacting an alkali metal silicate with a mineral acid is preferably sufficiently washed with water and reacted. In the production method of obtaining a silica hydrogel containing almost no alkali metal salt formed in the above, and then forming a silica hydrogel slurry in which the particle size of the silica hydrogel is reduced, and drying the slurry to obtain microspherical silica gel, after washing with water At the stage of silica hydrogel, by selecting the numerical value of the weight ratio of water to the weight of SiO ₂ in the silica hydrogel in an appropriate range, even if the average particle diameter is a coarse silica hydrogel of several mm,
Average particle size of 100μ without mechanical wet grinding
m, preferably 50 μm or less, more preferably 2 μm or less.
It has been found that miniaturization can be easily performed down to 0 μm or less.

That is, a slurry obtained by adding water to a silica hydrogel in which the weight ratio of H ₂ O / SiO ₂ is adjusted to a specific range is appropriately stirred while being stirred, for example, in an autoclave provided with stirring blades for stirring ordinary liquids. By performing hydrothermal treatment under conditions such as silica concentration, temperature, and time, it is said that before hydrothermal treatment, the silica hydrogel particle diameter having an average particle diameter of several mm can be easily reduced to 20 μm or less in some cases. We have found a surprising phenomenon that can be referred to as "heat pulverization."

Further, the present inventors have found that fine silica gel particles can be obtained efficiently by drying the silica hydrogel slurry after the hydrothermal fine grinding treatment by means such as spray drying.

In addition, the above-mentioned hydrothermal pulverization treatment is performed,
For example, a silica hydrogel slurry that has been refined to an average particle size of 20 μm or less can be easily pulverized to an average particle size of 3.0 μm or less when wet-milling the slurry under high-speed shearing. It has also been found that by drying or the like, for example, fine particulate silica gel having an average particle size of 10 μm or less can be obtained.

Thus, by carrying out the method including the hydrothermal fine pulverizing treatment, the particle size is 1 to 100 μm, preferably 1 to 50 μm, without necessarily performing mechanical pulverization.
More preferably 1 to 30 μm, most preferably 1 to 1
It has been found that 0 μm microparticulate silica gel can be produced as the final dried silica gel product.

The present invention has been made based on such findings. In the present invention, the silica gel is a porous granular silica that is amorphous by X-ray diffraction analysis and has substantially no crystalline peak.

That is, according to the present invention, (1) in the method for producing microparticulate silica gel, an alkali metal silicate is reacted with a mineral acid, and the ratio of the weight of water to the weight of SiO ₂ is 1. A hydrogelation step of obtaining a silica hydrogel that is 5 to 5.0 times by weight,

The obtained silica hydrogel was treated with SiO ₂
Hydrothermal pulverization step of performing hydrothermal treatment with stirring in a slurry state having a concentration of 5.0 to 15.0% by weight to form a finely divided silica hydrogel slurry having an average particle diameter of 100 μm or less; and

There is provided a method for producing microparticulate silica gel, comprising a drying step of drying the micronized hydrogel slurry.

Further, according to the present invention, there is provided (2) a method for producing microparticulate silica gel in which fine metal compound fine particles are included in the particles,

The alkali metal silicate is reacted with a mineral acid, and the ratio of the weight of water to the weight of SiO ₂ is 1.5
A hydrogelation step of obtaining a silica hydrogel which is about 5.0 times by weight, and

The obtained silica hydrogel was treated with SiO ₂
A step of preparing a finely divided silica hydrogel slurry comprising a hydrothermal finely pulverizing step of performing hydrothermal treatment with stirring in a slurry state having a concentration of 5.0 to 15.0% by weight to obtain a finely divided silica hydrogel slurry having an average particle diameter of 100 μm or less. With

A mixing slurry step of introducing fine metal compound particles into the finely divided silica hydrogel slurry to obtain a mixed slurry of silica hydrogel fine particles and metal compound fine particles;

There is provided a method for producing microparticulate silica gel containing fine metal compound fine particles, characterized by performing a drying step of drying the mixed slurry.

[0042]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. First, a method for producing the microparticulate silica gel of the present invention will be described.

First, a hydrogelation step of reacting an alkali metal silicate with a mineral acid to obtain a silica hydrogel having a water to SiO ₂ ratio of 1.5 to 5.0 times by weight is performed. The conversion step is performed, for example, by the following method. That is,

The alkali aqueous solution and an aqueous mineral acid solution of a metal silicate, is introduced from a separate inlet into a container equipped with a discharge outlet and instantaneously uniformly mixed, 130 g in terms of SiO ₂ concentration /
In this method, a silica sol having a pH of at least 1 and a pH of 7 to 9 is generated, immediately released from the discharge port into a gaseous medium such as air, and gelled in the air while being drawn in a parabola. At the drop point, leave an aging tank filled with water,
Drop it here and let it ripen for several minutes to tens of minutes.

Here, examples of the alkali metal include Na, K and the like, and Na is most preferable in terms of economy. Examples of the mineral acid include H ₂ SO ₄ , HCl and the like.
₂ SO ₄ is most preferred.

An appropriate acid is added to the mixture to lower the pH and stop the ripening. The obtained silica hydrogel is spherical particles having an average particle diameter of several mm. Since this silica hydrogel contains an alkali metal salt such as Na ₂ SO ₄ formed by the reaction, the silica hydrogel is sufficiently removed by washing with water according to a conventional method, and a spherical particle having an average particle diameter of few mm containing almost no alkali metal salt. The silica hydrogel is preferably used.

At this time, as described above, in the step of washing and removing the alkali metal salt from the silica hydrogel, the silica hydrogel particles are filled in a washing tank to form a packed fixed layer. It is preferable to carry out a packed fixed bed type washing operation in which the washing is carried out by circulating washing water. In such a packed bed type water washing method, since the average particle diameter of the silica hydrogel is sufficiently large, a stable packed bed can be formed, and a large amount of the silica hydrogel can be easily washed with water, and further, no filtering device is particularly required. .

When this silica hydrogel is roughly pulverized by, for example, a roll crusher, the average particle diameter is 0.1 to 5 m.
m can easily be obtained. This particle size is a preferable range for effectively performing a stirring operation or the like in the next hydrothermal fine grinding step.

As another method for obtaining a silica hydrogel, an aqueous solution of an alkali metal silicate and an aqueous solution of a mineral acid are uniformly mixed in a reaction vessel in a short time to form a silica sol. A method of gelling on a plate may be used.

After this gel is crushed to a size of several cm to several mm in diameter, water adjusted for pH is added and aged.
The ripening is stopped by adding acid to lower the pH. Since the obtained amorphous silica hydrogel having an average particle diameter of several cm to several mm contains an alkali metal salt generated by the reaction, it is washed with water by the above-described method or the like to sufficiently remove the alkali metal, and Average particle size few cm to several mm containing almost no salt
To obtain an amorphous silica hydrogel.

When the silica hydrogel is roughly pulverized by a roll crusher or the like in the same manner as described above, a crushed silica hydrogel having an average particle size of 0.1 to 5 mm can be easily obtained.

In the present invention, the ratio of the weight of water to the weight of SiO ₂ in the silica hydrogel after washing with water is 1.
It is preferably 5 to 5.0 times by weight. This SiO ₂
The ratio of water to is measured by the following method. That is,

2 g of the washed silica hydrogel was weighed,
Using a drier to dry under drying conditions of 180 ° C. × 4 hr,
This is regarded as an absolutely dry state, the weight of SiO ₂ is determined, and the weight reduction is defined as the water content.

The ratio of the weight of water to the weight of SiO ₂ is
If it is less than 1.5 times by weight, the effect of reducing the average particle size of the silica hydrogel in the next hydrothermal treatment step under liquid stirring becomes small. Probably, if the weight ratio of water to SiO ₂ in the silica hydrogel is smaller than this, the bonds between the primary particles of the silica hydrogel become extremely strong, and even if a hydrothermal treatment is performed, this can be smoothly separated and crushed. It is presumed to be difficult.

On the other hand, when the ratio of the weight of water to the weight of SiO ₂ exceeds 5.0 times by weight, the mechanical strength of the silica hydrogel becomes extremely weak, which is not preferable because the subsequent handling is difficult.

The ratio of the weight of water to the weight of SiO ₂ in the silica hydrogel is controlled by the respective concentration conditions of the aqueous alkali metal silicate solution and the aqueous mineral acid solution to be mixed and the aging conditions (temperature and pH) of the formed gel. Can be. In addition, when it exceeds the above range, it is possible to adjust the water content by performing an appropriate drying operation.

Next, the silica hydrogel thus obtained was subjected to hydrothermal treatment with stirring in a slurry state having an SiO ₂ concentration of 5.0 to 15.0% by weight, and an average particle diameter of 100 μm.
A hydrothermal fine pulverization step is performed to make the silica hydrogel slurry finer than m.

As the hydrothermal treatment apparatus, an autoclave, which is a high-pressure apparatus with stirring blades, is usually used. As the stirring blade, a propeller type, a paddle type, an anchor type, a faudler type, a helical ribbon type, a bull margin type, a turbine type, a max blend type, etc. which are generally used for stirring a liquid can be used, but are not limited thereto. Not something.

As the heating method for the autoclave, an indirect heating method in which high-pressure steam or a heating medium is supplied to the jacket, an indirect heating method using an electric heater, and a direct heating method in which steam is directly blown into the liquid in the tank can be used.

The average particle size of the silica hydrogel charged into the autoclave is 0.1 to 5 mm, more preferably 0.5 to 5 mm. If the average particle diameter is too large and exceeds 5 mm, the particles are too large and even if the liquid is stirred in the autoclave, the particles do not float sufficiently, and a part of the particles tends to deposit on the bottom of the tank. May cause handling problems.

When the average particle size is 0.1 to 5 mm, the average particle size is 100 μm only by hydrothermal treatment with stirring.
m or less, 20 μm or less 1
Fine particles can be easily formed into a particle size of μm or more.

The autoclave is charged with the silica hydrogel particles after washing with water and water to prepare a silica hydrogel slurry. The SiO ₂ concentration in the silica hydrogel slurry is 5.0 to 15.0% by weight. preferable. If the SiO ₂ concentration exceeds 15.0% by weight, it becomes difficult to sufficiently stir the slurry in the autoclave tank. On the other hand, if the SiO ₂ concentration is less than 5.0% by weight, the amount of water in the obtained silica slurry is large, and the water evaporation load in the subsequent spray drying step is undesirably large.

It should be noted that, in the hydrothermal treatment under stirring of the liquid, the silica hydrogel is finely ground (hydrothermal fine pulverization), which is also referred to as chemical pulverization. So-called Os to adjust the structure
Aging like twald Ripening is also possible.

Depending on the target pore structure, a hydrothermal treatment using only the above-mentioned silica hydrogel-water slurry can sufficiently achieve the object. In this case, the pH of the slurry is 1
~ 7.

On the other hand, a method in which a small amount of an alkali such as an alkali metal hydroxide or ammonia is added to the above silica hydrogel-water-based slurry to adjust the pH of the slurry to about 7 to 11 and then subjected to hydrothermal treatment is also a target. Depending on the pore structure, it can be applied.

It should be noted that the autoclay in the hydrothermal fine grinding treatment
Of silica hydrogel slurry with stirring blades
As the stirring energy, ordinary viscosity is not particularly high
Standard stirring energy levels for liquids and slurries
5 to 2,000 W / m ^Three (Liquid or slurry)
Degree is enough. Liquid or slurry 1m^Three Stirring per hit
Energy is 5W / m^Three If less than
Some of the coarse silica hydrogel particles are sufficiently suspended in the tank
Without dissolving, it is easy to accumulate on the bottom of the tank,
Occurs.

On the other hand, when the stirring energy per 1 m ^{3 of} the liquid or slurry exceeds 2,000 W / m ³ ,
The hydrothermal treatment has little effect of further reducing the particle size of the silica hydrogel and only increases the stirring energy.

The temperature range of the hydrothermal treatment is from 130 to 230
° C, preferably 150 to 230 ° C, more preferably 1 to
80-230 degreeC is desirable. If the temperature is lower than 130 ° C., the effect of hydrothermal treatment on the reduction of the particle size of the silica hydrogel is poor, while if it exceeds 230 ° C., the particle size of the silica hydrogel by hydrothermal treatment is commensurate with the increase in the temperature level. The effect of promoting the miniaturization is small, and the heating energy simply increases, which is technically and economically meaningless.

The time of the hydrothermal pulverization treatment can vary depending on the temperature of the hydrothermal treatment, but is usually from 0.2 to 24 hours. If the hydrothermal treatment time is less than 0.2 hr, a sufficient effect of reducing the particle size of the silica hydrogel by the hydrothermal treatment cannot be obtained. When the hydrothermal treatment time exceeds 24 hours, a reagglomeration phenomenon of the particles occurs, and the hydrothermal treatment departs from the purpose of the hydrothermal fine pulverizing treatment of reducing the particle size of the silica hydrogel, which is not preferable. .

In the present invention, the particle size distribution of the silica hydrogel is a value measured by a Coulter counter (manufactured by Coulter Electronics Co., Ltd.) or the like.

The silica hydrogel slurry was dried to obtain an average particle size of 1 as measured by a Coulter counter.
In order to obtain a dried silica gel particle product having a particle size of 00 μm or less, the average particle diameter based on the particle volume of a silica hydrogel particle subjected to a drying step such as spray drying measured by a Coulter counter is set to 100 μm or less. The average particle diameter is preferably 1 to 50 μm, more preferably 1 to 2 μm.
0 μm, more preferably 1 to 10 μm, most preferably 1 to 5 μm.

In particular, when it is intended to obtain fine spherical particles having an average particle diameter of 100 μm or less (spherical particles), the average particle diameter of the silica hydrogel to be supplied to the drying step is 1 μm.
It is preferably from 10 to 10 μm, more preferably from 1 to 5 μm, most preferably from 1 to 3 μm. If the average particle size exceeds this value, the spherical shape of the resulting microspherical particles and the smoothness of the particle surface are relatively reduced.

On the other hand, if the average particle size is less than 1 μm, the sphericity of the dry particles and the smoothness of the particle surface are not remarkably improved in proportion to the reduction in the particle size, and the energy required for making the silica hydrogel particles fine is not increased. It is only excessive and is not preferred.

Further, depending on the target pore structure, a slight amount of alkali such as alkali metal hydroxide or ammonia is added to the silica hydrogel-water slurry to adjust the pH of the silica hydrogel slurry to about 8 to 11. From the hydrothermal fine pulverization process. In this case, before or after a drying step such as spray drying, the allowable content of alkali metal impurities in the microspherical silica gel obtained by drying the silica hydrogel slurry satisfies the allowable value determined by the use of the product. May be performed by washing the silica hydrogel with water.

Further, the target average particle diameter of the fine spherical silica gel obtained by drying the silica hydrogel slurry is 10%.
When it is desired to obtain smaller particles of 0 μm or less, preferably 10 μm or less, the silica hydrogel slurry finely divided to an average particle diameter of 20 μm or less by hydrothermal fine pulverization is mechanically wet-pulverized to obtain silica hydrogel. Is preferably further reduced to 1 to 3 μm. By such a pulverizing treatment, the micro-spherical silica gel obtained by spray drying or the like can be obtained which has a more nearly spherical shape and a smoother particle surface.

As the wet pulverizer used here, a bead mill which is a wet medium stirring mill using beads having a particle diameter of 1 mm or less, a wet medium stirring pulverizer using balls having a particle diameter of several mm, a wet ball mill, and the like are applied. However, the present invention is not limited to these crushers.

As described above, the silica hydrogel slurry was first hydrothermally pulverized to obtain an average particle diameter of 20 μm.
Even if the step of further pulverizing the finely divided silica hydrogel slurry of μm or less to be wet-pulverized and pulverizing to an average particle diameter of 1 to 3 μm is also used, the silica hydrogel having an average particle diameter of several mm is not hydrothermally pulverized. Compared with the case where the average particle diameter is reduced to 1 to 3 μm only by the mechanical wet pulverization, the load of the mechanical wet pulverization is much smaller, and thus can be implemented much more easily.

Next, a drying step of drying the hydrogel slurry finely divided as described above is performed. As a drying apparatus for drying the silica hydrogel slurry to obtain monodispersed fine silica gel particles, a type in which particles and droplets are dispersed in hot air without forming a fixed layer to prevent aggregation of the particles is preferable, for example, Spray dryers, fluidized bed media dryers, flash dryers and the like are suitable.

In particular, in the case of obtaining micro-spherical silica gel, a spray drier is suitable as a drying apparatus, and the method of atomizing the slurry liquid of the spray drier is not particularly limited. However, a high-speed rotating disk, a one-fluid pressure nozzle, a two-fluid nozzle, an ultrasonic nozzle, or the like is applied.

Hereinafter, a case where a spray dryer is used as a drying apparatus will be described as an example. However, other dryers can be applied as they are with appropriate modifications.

When the silica hydrogel slurry is supplied to the spray dryer, the silica hydrogel can be supplied at the same concentration as that of the silica hydrogel slurry after the hydrothermal pulverization treatment. Accordingly, the concentration may be adjusted by adding water.

The amount of silica hydrogel and water in the silica hydrogel slurry supplied to the spray dryer is measured by the following method.

That is, the silica hydrogel slurry 50
g of the resulting mixture was placed in a beaker, the whole amount was filtered using a millipore filter having a pore size of 0.45 μm under a reduced pressure of 5 mmHg, and dehydrated for 40 minutes. The weight of the filtrate is the amount of water, and the weight of the obtained wet cake is the weight of the silica hydrogel.

Incidentally, the weight of SiO ₂ in the wet cake was measured for 4 hours at a temperature of 180 ° C. with a dryer as described above.
r It is determined from the weight after drying.

The silica hydrogel slurry supplied to the spray dryer is not particularly limited, but the ratio of the weight of water to the weight of the silica hydrogel obtained by the above-described measurement method is 1.5 to 5.0 times by weight. Are preferred.

If the ratio of the weight of water to the weight of silica hydrogel is less than 1.5 times, the spherical shape and the smoothness of the particle surface of the spherical silica gel obtained by spray drying are reduced.

On the other hand, when the ratio of the weight of water to the weight of silica hydrogel exceeds 5.0 times, the load of water evaporation in spray drying is undesirably large.

As described above, the silica hydrogel slurry in which the ratio of the weight of water to the weight of silica hydrogel is 1.5 to 5.0 times by weight is supplied to the spray dryer, and the operating conditions of the spray dryer are selected. As a result, a fine spherical silica gel having excellent spherical shape and smooth particle surface can be obtained.

In the prior art such as Japanese Patent Publication No. 6-99135, which discloses that the silica hydrogel is refined only by mechanical wet pulverization, the silica hydrogel slurry to be spray-dried is used. From the viewpoint of securing and particle strength, the weight ratio of water to the weight of the silica hydrogel in the slurry is 0.2 to 1.5 times the weight as described above.

On the other hand, in the present invention, the silica hydrogel slurry supplied to the spray drier is hydrothermally pulverized to an average particle diameter of 100 μm or less, preferably 20 μm or less. The weight ratio of water to hydrogel weight is 1.5
It is preferable to carry out at about 5.0 weight times.

As described above, in the present invention, the silica hydrogel slurry having the above-mentioned weight ratio, which has been subjected to hydrothermal pulverization treatment in advance, is spray-dried, so that it has a particle shape much closer to a true sphere than the above-mentioned known examples. A fine spherical silica gel with a smooth surface can be obtained.

Next, another embodiment of the present invention, a method for producing microspherical silica gel containing metal compound fine particles in particles, will be described.

In this case, the above-mentioned (1) hydrogelation is performed by reacting an alkali metal silicate with a mineral acid to obtain a silica hydrogel having a water to SiO ₂ ratio of 1.5 to 5.0 times by weight. Process, and

(2) The obtained silica hydrogel was treated with Si
In a slurry state having an O ₂ concentration of 5 to 15% by weight, a hydrothermal treatment is carried out with stirring to obtain a finely divided silica hydrogel slurry having an average particle diameter of 100 μm or less, and a preparation step of a finely divided silica hydrogel slurry comprising a hydrothermal fine grinding step

(3) The method is characterized by having a mixed slurrying step of introducing metal compound fine particles into the finely divided silica hydrogel slurry to obtain a mixed slurry of silica hydrogel fine particles and metal compound fine particles.

The mode of introducing the metal compound fine particles into the silica hydrogel slurry is arbitrary. For example, the hydrothermal fine pulverizing step (2) can be performed in the coexistence of the metal compound fine particles, and when the wet pulverizing step is performed following the hydrothermal fine pulverizing step, the wet pulverizing is performed by the metal compound fine particles. It can be performed in coexistence.

[0097] As the metal compound fine particles, fine particles are preferable, and what is called ultra-fine particles are particularly preferable.

What can be used as the metal compound fine particles are, for example, metal oxide fine particles, such as titanium oxide, titanium peroxide, zinc oxide, cerium oxide, ferrous oxide, ferric oxide, zirconium oxide, and chromium oxide. , Aluminum oxide, magnesium oxide, silver oxide, cuprous oxide, cupric oxide, cobalt oxide, cobalt tetraoxide, cobalt oxide, nickel oxide, nickel oxide, thorium oxide, tungsten oxide , Molybdenum oxide, manganese dioxide, manganese trioxide, uranium oxide, thorium oxide, germanium oxide, stannous oxide, stannic oxide, lead monoxide, lead tetroxide, lead dioxide, antimony trioxide, antimony pentoxide, Bismuth trioxide is preferred. Among them, fine particles selected from the group consisting of titanium oxide, zinc oxide, cerium oxide, iron oxide and zirconium oxide are particularly preferred.

In addition to metal oxides, sulfide fine particles and sulfate fine particles such as cadmium sulfide, zinc sulfide, antimony sulfide, lead sulfide, nickel sulfide, strontium sulfate and barium sulfate; phosphates such as copper pyrophosphate; Carbide fine particles or halide fine particles such as tantalum, zirconium carbide, tungsten carbide, vanadium carbide, titanium carbide, silicon carbide, and calcium fluoride can also be used. Fine particles of a metal such as gold, silver, platinum, copper, and aluminum or an alloy thereof may also be used in some cases.

The fine particles of the metal compound in the present invention also include those referred to as so-called ultrafine particles as described above, wherein the primary particles have a size (particle size) of 0.002 to 0.5.
μm. And 0.01-0.5 micrometers is preferable, and what is 0.01-0.3 micrometers is more preferable. If it is less than 0.002 μm, the specific surface area is in an agglomerated state from the beginning and the fine particles cannot be sufficiently dispersed into the silica hydrogel slurry. On the other hand, if it exceeds 0.5 μm, the particle diameter is too large as compared with the particle diameter of the silica gel, and it becomes difficult to be encapsulated in a state of being well dispersed in the silica gel particles, which is not preferable.

The ratio of the introduced metal compound fine particles to SiO ₂ in the mixed slurry is preferably 5 to 80% by weight, more preferably 5 to 45% by weight.

As a specific embodiment, the silica hydrogel slurry finely divided by the above-mentioned hydrothermal fine grinding step or, if necessary, the silica hydrogel slurry further finely divided by wet grinding is used. For example, titanium dioxide having an average particle size of 0.002 to 0.5 μm,
Fine particles of a metal compound such as zinc oxide, cerium oxide, iron oxide, and zirconium oxide are added and introduced in an amount of 5 to 80% by weight based on the weight of SiO ₂ as described above, and sufficiently dispersed.
This is to obtain a mixed slurry of silica hydrogel fine particles and metal compound fine particles. In this case, the pH of the slurry may be adjusted in order to prevent aggregation and sufficiently disperse.
This dispersion is preferably performed in an autoclave or a wet pulverizer for performing the hydrothermal fine pulverization treatment as described above.

The mixed slurry thus obtained is
By performing spray drying or the like in the same manner as in the case of obtaining fine particulate silica gel, fine particulate silica gel containing fine metal compound fine particles can be obtained.

The metal compound fine particles encapsulated in the silica gel have a particle size much smaller than that of the silica gel particles, and one or more metal compound fine particles are contained in one silica gel.
Usually, several, preferably many, metal compound fine particles are included in a dispersed state. "Inclusion" in the present invention means that the metal compound fine particles are contained in the silica gel particles in such a state.

In the case of silica gel particles having a large number of pores, in the course of drying the silica gel particles, only the liquid phase of the slurry filling the pores is volatilized and dried, and the nonvolatile metal compound fine particles are dried. It is presumed that it remains in a state of being supported by the pores inside the silica gel. This is considered to be a mode in which the metal compound fine particles are included in the silica gel particles.

The particulate silica gel containing such metal compound fine particles is useful for various uses.
For example, it can be suitably used as an ultraviolet shielding agent. When the metal compound is anatase-type titanium oxide,
It can be suitably used for photooxidation catalyst applications.

[0107]

EXAMPLES The present invention will now be described specifically with reference to examples, but the technical scope of the present invention is not limited to these examples.

Example 1 (Hydrogelation Step) An aqueous solution of sodium silicate having an SiO ₂ / Na ₂ O = 3.0 (molar ratio) and an SiO ₂ concentration of 21.0% by weight was subjected to 2.0 l / min and sulfuric acid. Concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly. The flow rate ratio of the two liquids was adjusted so as to be 8.0, and the silica sol liquid uniformly mixed was continuously discharged into the air from the discharge port. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water was placed at the dropping point, and the ripening tank was dropped and ripened.

After aging, the pH was adjusted to 6, and the mixture was sufficiently washed with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 6 mm. SiO in the silica hydrogel particles
The weight ratio of water to ₂ weight is 4.5 times by weight,
The residual sodium in the silica hydrogel particles is 103p
pm.

(Hydrothermal fine pulverizing step) Next, the silica hydrogel was subjected to an average particle size of 1.
Coarsely pulverized to 0 mm. In a 50-liter autoclave equipped with an anchor-type stirring blade, 22,000 g of the above-ground silica hydrogel and 18,000 water were added.
g in a slurry state having a SiO ₂ concentration of 10.0% by weight, at a temperature of 200 ° C. for 3 hours and a stirring rotation speed of 90 rpm.
m, a hydrothermal fine grinding treatment was performed. The pH of the silica hydrogel slurry was 6.

The silica hydrogel particles in the slurry after the hydrothermal pulverization treatment are finely pulverized, and are used in a Coulter counter (MAII type, manufactured by Coulter Electronics Co., Ltd.).
The average particle diameter was 15 μm in the particle diameter measurement using an aperture tube diameter of 280 μm. The concentration of SiO _{2 in} the slurry after the hydrothermal treatment was 10.3% by weight.

(Wet crushing step) Next, the slurry was subjected to a wet crushing machine at the same concentration (Dyno-mill manufactured by Shinmaru Enterprises, using beads having a diameter of 0.5 mm).
And further pulverized. Coulter counter (MAII) for silica hydrogel particles in slurry after milling
The average particle diameter was 1.6 μm according to the mold and aperture tube diameter of 50 μm).

Further, the amounts of silica hydrogel and water in the silica hydrogel slurry after the above pulverization were measured by the following method.

50 g of the silica hydrogel slurry was placed in a beaker, and the whole amount was filtered under reduced pressure of 5 mmHg absolute pressure using a Millipore filter having a pore size of 0.45 μm.
Dehydrate for a minute. The weight of the obtained filtrate is the amount of water, and the weight of the obtained wet cake is the weight of the silica hydrogel. The weight of SiO ₂ in the obtained wet cake is obtained from the weight after drying at 180 ° C. for 4 hours using a dryer.

The ratio of the weight of water to the weight of silica hydrogel in the slurry determined by this measuring method was 4.4.
It was weight-fold.

(Drying Step) Next, the slurry was supplied to the slurry at a concentration of 13 ml / m using a small spray dryer (GA32 type manufactured by Yamato Scientific Co., Ltd.) at the same concentration.
in, spray pressure 1.2 kg / cm ² (G), hot air temperature 2
Spray drying was performed at 00 ° C. to obtain finely dried silica gel particles. Coal counter (MAII) of the obtained dried particles
The average particle size was 4.5 μm according to the mold and aperture tube diameter of 50 μm). The particle shape was almost spherical and the particle surface was smooth. FIG. 1 shows a scanning electron micrograph of the dried silica gel particles.

Example 2 (Hydrogelation step) An aqueous solution of sodium silicate having an SiO ₂ / Na ₂ O = 3.0 (molar ratio) and an SiO ₂ concentration of 21.0% by weight was subjected to 2.0 l / min and sulfuric acid. Concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly, so that the pH of the liquid discharged into the air from the discharge port is 7.5. The flow rate ratio of the two liquids was adjusted so as to be 8.0, and the silica sol liquid uniformly mixed was continuously discharged into the air from the discharge port. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water was placed at the dropping point, and the ripening tank was dropped and ripened.

After aging, the pH was adjusted to 6, and the mixture was sufficiently washed with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 5 mm. SiO in the silica hydrogel particles
The weight ratio of water to ₂ weight is 4.5 times by weight,
The residual sodium in the silica hydrogel particles is 100 p
pm.

(Hydrothermal Pulverization Step) Next, the silica hydrogel was treated with a roll crusher to obtain an average particle size of 1.
Coarsely pulverized to 0 mm. In a 50-liter autoclave equipped with an anchor-type stirring blade, 22,000 g of the above-ground silica hydrogel and 18,000 water were added.
g in a slurry state having a SiO ₂ concentration of 10.0% by weight, at a temperature of 200 ° C. for 20 hours and a stirring rotation speed of 50 r
A hydrothermal fine grinding treatment was performed at pm. The pH of the silica hydrogel slurry was 6.

The silica hydrogel particles in the slurry after the hydrothermal pulverization treatment are finely pulverized, and are subjected to a coulter counter (MAII type, manufactured by Coulter Electronics Co., Ltd.).
The average particle diameter was 13 μm in the particle diameter measurement using an aperture tube diameter of 280 μm. The SiO ₂ concentration in the slurry after the hydrothermal treatment was 10.3% by weight.
Met.

(Wet Pulverization Step) Next, the slurry was further finely pulverized using the same wet pulverizer as in Example 1 while keeping its concentration. The average particle size of the silica hydrogel particles in the finely pulverized slurry measured by a Coulter counter (MAII type, using an aperture tube of 50 μm) was 1.5 μm.

Further, in the same manner as in Example 1, the amounts of silica hydrogel and water in the finely ground silica hydrogel slurry were measured. The ratio of the weight of water to the weight of silica hydrogel was 4.4. It was weight-fold.

(Drying Step) Next, the slurry was supplied to the slurry at a concentration of 13 ml / m using a small spray drier (GA32 type manufactured by Yamato Scientific Co., Ltd.) at the same concentration.
in, spray pressure 1.2 kg / cm ² (G), hot air temperature 2
Spray drying was performed at 00 ° C. to obtain finely dried silica gel particles. Coal counter (MAII) of the obtained dried particles
The average particle size was 4.5 μm according to the mold and aperture tube diameter of 50 μm). The particle shape was almost spherical and the particle surface was smooth.

Example 3 (Hydrogelation step) An aqueous solution of sodium silicate having an SiO ₂ / Na ₂ O = 3.0 (molar ratio) and SiO ₂ concentration = 21.0% by weight was subjected to 2.0 l / min and sulfuric acid. Concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly. The flow rate ratio of the two liquids was adjusted so as to be 8.0, and the silica sol liquid uniformly mixed was continuously discharged into the air from the discharge port. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water was placed at the dropping point, and the ripening tank was dropped and ripened.

After aging, the pH was adjusted to 6, and the mixture was sufficiently washed with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 4 mm. SiO in the silica hydrogel particles
The weight ratio of water to ₂ weight is 4.5 times by weight,
The remaining sodium in the silica hydrogel particles is 95 pp
m.

(Hydrothermal pulverization treatment step) Next, the silica hydrogel was treated with a roll crusher to obtain an average particle diameter of 0.1%.
It was coarsely crushed to 8 mm. In a 50-liter autoclave equipped with an anchor-type stirring blade, 22,000 g of the above-ground silica hydrogel and 18,000 water were added.
g in a slurry having a SiO ₂ concentration of 10.0% by weight, at a temperature of 185 ° C. for 20 hours and a stirring rotation speed of 10%.
The hydrothermal fine grinding treatment was performed at 0 rpm. The pH of the silica hydrogel slurry was 6.

The silica hydrogel particles in the slurry after the hydrothermal pulverization treatment are finely pulverized, and are subjected to a Coulter counter (MAII type, manufactured by Coulter Electronics Co., Ltd.).
The average particle diameter was 17 μm in the particle diameter measurement using an aperture tube diameter of 280 μm. The SiO ₂ concentration in the slurry after the hydrothermal treatment was 10.3% by weight.
Met.

(Wet Pulverization Step) Next, the slurry was finely pulverized at the same concentration by using the same wet pulverizer as in Example 1. The average particle size of the silica hydrogel particles in the finely pulverized slurry measured with a Coulter counter (MAII type, using an aperture tube of 50 μm) is 1.7.
μm.

The amounts of silica hydrogel and water in the finely ground silica hydrogel slurry were measured in the same manner as in Example 1. The ratio of the weight of water to the weight of silica hydrogel was 4.4. It was weight-fold.

(Drying step) A small spray dryer (GA3 manufactured by Yamato Scientific Co., Ltd.)
2) using a slurry supply rate of 13 ml / min, a spray pressure of 1.2 kg / cm ² (G), and a hot air temperature of 200 ° C.
Then, spray drying was performed to obtain finely dried silica gel particles. The average particle diameter of the obtained dried particles measured by a Coulter counter (using an aperture tube diameter of 50 μm) is 4.5.
μm. The particle shape was almost spherical and the particle surface was smooth.

Example 4 (Hydrogelation Step) An aqueous solution of sodium silicate having an SiO ₂ / Na ₂ O = 3.0 (molar ratio) and an SiO ₂ concentration of 21.0% by weight was subjected to 2.0 l / min and sulfuric acid. Concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly, so that the pH of the liquid discharged into the air from the discharge port is 7.5. The flow rate ratio of the two liquids is adjusted so as to be 8.0, and the uniformly mixed silica sol liquid is continuously discharged from the discharge port into the air. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water is placed at the drop point, and the ripening tank is dropped here to ripen. After aging, the pH was adjusted to 6, and further washed sufficiently with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 5 mm. Si in the silica hydrogel particles
The weight ratio of water to O ₂ was 4.0 times by weight, and the residual sodium in the silica hydrogel particles was 98%.
ppm.

(Hydrothermal fine pulverization treatment step) Next, the silica hydrogel was subjected to an average particle size of 1.
It was coarsely pulverized to 5 mm. In a 50-liter autoclave equipped with an anchor-type stirring blade, 20,000 g of the above coarsely ground silica hydrogel and 20,000 water were added.
a slurry state was charged g, by addition of aqueous sodium hydroxide, SiO ₂ concentration of 10 was adjusted to pH 10.
0% by weight silica hydrogel slurry at a temperature of 200 ° C.
Then, hydrothermal fine pulverization treatment was performed at a stirring rotation speed of 90 rpm for 3 hours.

The silica hydrogel particles in the slurry after the hydrothermal pulverization treatment are finely pulverized, and are subjected to a coulter counter (MAII type, manufactured by Coulter Electronics Co., Ltd.).
The average particle diameter was 13 μm in the particle diameter measurement using an aperture tube diameter of 280 μm. The SiO ₂ concentration in the slurry after the hydrothermal treatment was 10.2% by weight.

(Wet Pulverization Step) Next, the slurry was wet pulverized at the same concentration by using the same wet pulverizer as in Example 1. The average particle diameter of the silica hydrogel particles in the slurry after the wet pulverization measured by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) is as follows:
It was 1.4 μm.

Further, the ratio of the weight of water to the weight of the silica hydrogel in the slurry after the fine pulverization obtained by the same measuring method as in Example 1 was 3.5 times by weight.

(Drying Step) A small spray dryer (GA3 manufactured by Yamato Scientific Co., Ltd.)
2) using a slurry supply rate of 13 ml / min, a spray pressure of 1.2 kg / cm ² (G), and a hot air temperature of 200 ° C.
Then, spray drying was performed to obtain finely dried silica gel particles. The obtained dried particles are coated with a Coulter counter (MAII type,
The average particle size was 5.2 μm, the particle shape was almost spherical, and the particle surface was smooth. FIG. 2 shows a scanning electron micrograph of the dried silica gel particles.

Example 5 (Hydrogelation step) 2.0 l / min of an aqueous solution of sodium silicate having SiO ₂ / Na ₂ O = 3.0 (molar ratio) and SiO ₂ concentration = 23.0% by weight and sulfuric acid Concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly, so that the pH of the liquid discharged into the air from the discharge port is 7.5. The flow rate ratio of the two liquids is adjusted so as to be 8.0, and the uniformly mixed silica sol liquid is continuously discharged into the air from the discharge port. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water is placed at the drop point, and the ripening tank is dropped here to ripen. After aging, the pH was adjusted to 6, and further washed sufficiently with water to obtain a silica hydrogel. The particle shape of the obtained silica hydrogel particles was spherical, and the average particle diameter was 3 mm. SiO _{2 in} silica hydrogel particles
The weight ratio of water to weight is 1.7 weight times, and the residual sodium in the silica hydrogel particles is 108 pp.
m.

(Hydrothermal fine pulverization step) Next, the silica hydrogel was treated with a roll crusher to obtain an average particle diameter of 0.1 μm.
It was coarsely pulverized to 2 mm. In a 50-liter autoclave equipped with an anchor-type stirring blade, 20,000 g of the above coarsely ground silica hydrogel and 30,000 water were added.
g in a slurry state having a SiO ₂ concentration of 14.8% by weight, at a temperature of 210 ° C., for 24 hours, at a stirring rotation speed of 12
The hydrothermal fine grinding treatment was performed at 0 rpm. The pH of the silica hydrogel slurry was 6.

[0139] The silica hydrogel particles in the slurry after the hydrothermal treatment were refined, and were coagulated with a Coulter counter (MAII).
The average particle diameter was 20 μm in the particle diameter measurement using a mold and an aperture tube diameter of 280 μm manufactured by Coulter Electronics Co., Ltd.). The SiO ₂ concentration in the slurry after the hydrothermal treatment was 14.5% by weight.

(Wet Pulverization Step) The slurry was wet pulverized using the same wet pulverizer as in Example 1 while keeping its concentration. The average particle diameter of the silica hydrogel particles in the slurry after the wet pulverization measured by a Coulter counter (MAII type, using an aperture tube having a diameter of 50 μm) was 2.0 μm.

Further, the ratio of the weight of water to the weight of the silica hydrogel in the finely pulverized slurry obtained by the same measuring method as in Example 1 was 1.7 times by weight.

(Drying Step) Next, the slurry was supplied to the slurry at a concentration of 13 ml / m using a small spray dryer (GA32 type, manufactured by Yamato Scientific Co., Ltd.) at the same concentration.
in, spray pressure 1.2 kg / cm ² (G), hot air temperature 2
Spray drying was performed at 00 ° C. to obtain finely dried silica gel particles. The average particle size of the obtained dried particles by a Coulter counter (using an aperture tube diameter of 50 μm) is
The particle size was 9.0 μm, and the particle shape was spherical.

Example 6 (Hydrogelation Step) An aqueous solution of sodium silicate having a SiO ₂ / Na ₂ O = 3.0 (molar ratio) and a SiO ₂ concentration of 21.0% by weight was subjected to 2.0 l / min and sulfuric acid. Concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly, so that the pH of the liquid discharged into the air from the discharge port is 7.5. The flow rate ratio of the two liquids is adjusted so as to be 8.0, and the uniformly mixed silica sol liquid is continuously discharged from the discharge port into the air. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water is placed at the drop point, and the ripening tank is dropped here to ripen. After aging, the pH was adjusted to 6, and further washed sufficiently with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 5 mm. Si in the silica hydrogel particles
The weight ratio of water to O ₂ weight was 4.2 times by weight, and the residual sodium in the silica hydrogel particles was 10%.
It was 0 ppm.

(Hydrothermal Pulverization Step) The silica hydrogel was crushed with a roll crusher to an average particle diameter of 2.0 m.
m. Contents 5 with anchor type stirring blade
Into a 0 liter autoclave were charged 22,000 g of the above coarsely crushed silica hydrogel and 18,000 g of water, and in a slurry state having a SiO ₂ concentration of 10.0% by weight, at a temperature of 200 ° C. for 3 hours and a stirring rotation speed of 100 r.
A hydrothermal fine grinding treatment was performed at pm. The pH of the silica hydrogel slurry was 6.

[0145] The silica hydrogel particles in the slurry after the hydrothermal treatment were refined, and were coagulated with a Coulter counter (MAII).
The average particle diameter was 18 μm in the particle diameter measurement using a mold and an aperture tube diameter of 280 μm manufactured by Coulter Electronics Co., Ltd.). The concentration of SiO _{2 in} the slurry after the hydrothermal treatment was 10.2% by weight.

In the same manner as in Example 1, the amounts of silica hydrogel and water in the silica hydrogel slurry after the hydrothermal treatment were measured. The ratio of the weight of water to the weight of silica hydrogel was 2.0 times by weight. Met.

(Drying Step) Next, the above slurry was used as it was in a medium fluidized bed drier (SFD manufactured by Okawara Seisakusho)
-Mini type), using 65ml / mi slurry supply rate
n, spray drying was performed at a hot air temperature of 255 ° C. to obtain finely dried silica gel particles. The average particle size of the obtained dried particles measured by a Coulter counter (MAII type, using an aperture tube of 50 μm) was 8.9 μm, and the particle shape was irregular. FIG. 3 shows a scanning electron micrograph of the dried silica gel particles.

Example 7 (Hydrogelation Step) An aqueous solution of sodium silicate having an SiO ₂ / Na ₂ O = 3.0 (molar ratio) and an SiO ₂ concentration of 21.0% by weight was subjected to 2.0 l / min and sulfuric acid. Concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly, so that the pH of the liquid discharged into the air from the discharge port is 7.5. The flow rate ratio of the two liquids is adjusted so as to be 8.0, and the uniformly mixed silica sol liquid is continuously discharged from the discharge port into the air. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water is placed at the drop point, and the ripening tank is dropped here to ripen. After aging, the pH was adjusted to 6, and further washed sufficiently with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 6 mm. Si in the silica hydrogel particles
The weight ratio of water to O ₂ weight was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 98%.
ppm.

(Hydrothermal fine pulverization treatment step) Next, the silica hydrogel was treated with a roll crusher to obtain an average particle diameter of 0.1 μm.
It was coarsely crushed to 7 mm. In a 50 liter autoclave equipped with anchor-type stirring blades, 20,000 g of the above coarsely ground silica hydrogel and 7,970 g of water were placed.
The resultant mixture was a slurry state, with the addition of aqueous sodium hydroxide, SiO ₂ concentration of 13 was adjusted to pH 10.
0% by weight silica hydrogel slurry at a temperature of 200 ° C.
The hydrothermal fine pulverization treatment was performed for 24 hours at a stirring rotation speed of 90 rpm.

[0150] The silica hydrogel particles in the slurry after the hydrothermal treatment were refined, and were coagulated with a Coulter counter (MAII).
The average particle diameter was 19 μm in the particle diameter measurement by using a mold, an aperture tube diameter of 280 μm manufactured by Coulter Electronics Co., Ltd.). The SiO ₂ concentration in the slurry after the hydrothermal treatment was 13.2% by weight.

(Wet Pulverization Step) The slurry was wet pulverized using the same wet pulverizer as in Example 1 at the same concentration. The average particle size of the silica hydrogel particles in the slurry after the wet pulverization measured with a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 1.7 μm.

The ratio of the weight of water to the weight of the silica hydrogel in the slurry after the fine pulverization obtained by the same measuring method as in Example 1 was 3.5 times by weight.

(Drying step) Next, the slurry was supplied at a slurry supply rate of 13 ml / m using a small spray dryer (GA32 type, manufactured by Yamato Scientific Co.) at the same concentration.
in, spray pressure 1.2 kg / cm ² (G), hot air temperature 2
Spray drying was performed at 00 ° C. to obtain finely dried silica gel particles. Coal counter (MAII) of the obtained dried particles
The average particle size was 9.8 μm, the particle shape was almost true sphere, and the particle surface was smooth.

Example 8 (Hydrogelation Step) An aqueous solution of sodium silicate having an SiO ₂ / Na ₂ O = 3.0 (molar ratio) and SiO ₂ concentration = 21.0% by weight was subjected to 2.0 l / min and sulfuric acid. Concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly, so that the pH of the liquid discharged into the air from the discharge port is 7.5. The flow rate ratio of the two liquids is adjusted so as to be 8.0, and the uniformly mixed silica sol liquid is continuously discharged from the discharge port into the air. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water is placed at the drop point, and the ripening tank is dropped here to ripen. After aging, the pH was adjusted to 6, and the mixture was sufficiently washed with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 5 mm. Si in the silica hydrogel particles
The weight ratio of water to O ₂ was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 10%.
It was 0 ppm.

(Hydrothermal pulverization treatment step) Next, the silica hydrogel was treated with a roll crusher to obtain an average particle diameter of 0.1 μm.
It was coarsely pulverized to 2 mm. In a 50 liter content autoclave equipped with an anchor type stirring blade, 22,000 g of the above coarsely ground silica hydrogel and 18,000 water were added.
g of a slurry, and an aqueous solution of sodium hydroxide was added to adjust the pH to 10 to obtain a SiO ₂ concentration of 1
0.0% by weight silica hydrogel slurry at a temperature of 210
C, a hydrothermal fine pulverization treatment was performed at a stirring rotation speed of 120 rpm for 24 hours. The pH of the silica hydrogel slurry was 10.

The silica hydrogel particles in the slurry after the hydrothermal fine pulverization treatment were refined, and the average particle diameter was 6 μm in the particle diameter measurement using a Coulter counter (MAII type, manufactured by Coulter Electronics Co., Ltd., using an aperture tube diameter of 280 μm). there were. The SiO ₂ concentration in the slurry after the hydrothermal treatment was 10.3% by weight.

The ratio of the weight of water to the weight of the silica hydrogel in the slurry after the hydrothermal milling determined by the same measuring method as in Example 1 was 1.6 times by weight.

(Drying Step) Next, the slurry was supplied at a concentration of 80 ml / ml using a spray dryer (1.5 m in diameter, the spraying section was a high-speed rotating disk system) while keeping the concentration.
The spray drying was performed at a hot air temperature of 200C for min.

The obtained dried particles had an average particle size of 52 μm as measured by a Coulter counter (MAII type, using an aperture tube diameter of 280 μm), and were spherical in shape.

Example 9 (Hydrogelation step) An aqueous solution of sodium silicate having an SiO ₂ / Na ₂ O = 3.0 (molar ratio) and an SiO ₂ concentration of 21.0% by weight was subjected to 2.0 l / min and sulfuric acid. Concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly, so that the pH of the liquid discharged into the air from the discharge port is 7.5. The flow rate ratio of the two liquids is adjusted so as to be 8.0, and the uniformly mixed silica sol liquid is continuously discharged from the discharge port into the air. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water is placed at the drop point, and the ripening tank is dropped here to ripen. After aging, the pH was adjusted to 6, and the mixture was sufficiently washed with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 4 mm. Si in the silica hydrogel particles
The weight ratio of water to O ₂ was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 10%.
It was 1 ppm.

(Hydrothermal Pulverization Treatment Step) Next, the silica hydrogel was subjected to an average particle size of 1.
Coarsely pulverized to 0 mm. In a 50 liter content autoclave equipped with anchor-type stirring blades, 22,000 g of the above coarsely ground silica hydrogel and 18,000 water were added.
g in a slurry having a SiO ₂ concentration of 10.0% by weight in a slurry state at a temperature of 200 ° C. for 3 hours and a stirring rotation speed of 90 r.
A hydrothermal fine grinding treatment was performed at pm. The pH of the silica hydrogel slurry was 6.

[0162] The silica hydrogel particles in the slurry after the hydrothermal treatment were refined, and were coagulated with a Coulter counter (MAII).
The average particle diameter was 17 μm in the particle diameter measurement using a mold and an aperture tube diameter of 280 μm manufactured by Coulter Electronics Co., Ltd.). The concentration of SiO _{2 in} the slurry after the hydrothermal treatment was 10.2% by weight.

(Wet milling step) The slurry was wet milled using the same wet mill as in Example 1 while maintaining its concentration. The average particle diameter of the silica hydrogel particles in the slurry after the fine pulverization measured by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 1.6 μm.

(Mixing Slurry Step) 200 g of titanium oxide (trade name: TTO-51A, average particle diameter 0.02 μm, rutile type) manufactured by Ishihara Sangyo Co., Ltd. was added to 17,000 g of the silica hydrogel slurry after the above wet pulverization, and Sumitomo. 600 g of zinc oxide (trade name: ZnO-310, average particle size 0.03 μm) manufactured by Osaka Cement Co., Ltd. was added, and the pH of the slurry was adjusted to 10. Then, using the same wet mill as described above, silica hydrogel, Titanium oxide and zinc oxide were mixed and dispersed.

(Drying Step) The slurry after dispersion was supplied to the slurry at a concentration of 13 ml / m using a small spray dryer (GA32 type, manufactured by Yamato Scientific Co., Ltd.) at the same concentration.
in, spray pressure 1.2 kg / cm ² (G), hot air temperature 2
Spray drying was performed at 00 ° C. to obtain fine spherical particles in which fine particles of titanium oxide and zinc oxide were dispersed and included in silica gel particles. The obtained particle shape was almost true sphere, and the particle surface was smooth.

The average particle diameter measured by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was as follows:
It was 5.6 μm.

The result of analyzing the chemical composition of the particles is as follows.
₂ 68.2 wt%, TiO ₂ 7.9 wt%, ZnO2
It was 3.9% by weight.

(Measurement of Spectral Transmittance) To 0.4 g of the above-mentioned fine spherical particles, 1.12 g of petrolatum and 0.1 g of liquid paraffin were added.
The paste obtained by adding 48 g and dispersing well using three rolls is sandwiched between two 2 mm-thick quartz plates, spread until the layer thickness becomes 25 μm, and is measured using a self-recording spectrophotometer. The spectral transmittance was measured.

The wavelength of 400 nm or more is in the visible light range,
80 nm is an ultraviolet light region. The smaller the transmittance in the ultraviolet light region, the better the ultraviolet shielding effect, and the higher the transmittance in the visible light region, the higher the transparency observed by the naked eye.

At 500 nm, the transmittance is 81.3%, 400
At 6 nm, the transmittance is 69.4%, and at 360 nm, the transmittance is 2
1.2%, transmittance of 18.0% at 320 nm, 290n
m, the transmittance was 17.6%.

FIG. 4 shows a scanning electron micrograph of the dried silica gel particles containing the metal oxide fine particles.

Example 10 (Hydrogelation step) An aqueous solution of sodium silicate having an SiO ₂ / Na ₂ O = 3.0 (molar ratio) and SiO ₂ concentration = 21.0% by weight was subjected to 2.0 l / min and sulfuric acid. Concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly, so that the pH of the liquid discharged into the air from the discharge port is 7.5. The flow rate ratio of the two liquids is adjusted so as to be 8.0, and the uniformly mixed silica sol liquid is continuously discharged from the discharge port into the air. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water is placed at the drop point, and the ripening tank is dropped here to ripen. After aging, the pH was adjusted to 6, and the mixture was sufficiently washed with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 6 mm. Si in the silica hydrogel particles
The weight ratio of water to O ₂ was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 97%.
ppm.

(Hydrothermal Pulverization Step) Next, the silica hydrogel was subjected to an average particle size of 1.
Coarsely pulverized to 0 mm. In a 50 liter content autoclave equipped with an anchor type stirring blade, 22,000 g of the above coarsely ground silica hydrogel and 18,000 water were added.
g in a slurry having a SiO ₂ concentration of 10.0% by weight in a slurry state at a temperature of 200 ° C. for 3 hours and a stirring rotation speed of 90 r.
A hydrothermal fine grinding treatment was performed at pm. The pH of the silica hydrogel slurry was 6.

[0174] The silica hydrogel particles in the slurry after the hydrothermal treatment are refined, and are subjected to a Coulter counter (MAII
The average particle diameter was 15 μm in the particle diameter measurement using a mold, Coulter Electronics Co., Ltd., using an aperture tube diameter of 280 μm. The concentration of SiO _{2 in} the slurry after the hydrothermal treatment was 10.3% by weight.

(Wet grinding step) The slurry was wet ground using the same wet grinding machine as in Example 1 while keeping its concentration. The average particle diameter of the silica hydrogel particles in the slurry after the fine pulverization was 1.4 μm measured by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm).
m.

(Mixed Slurry Step) To 17,000 g of the silica hydrogel slurry after the above-mentioned wet pulverization, 915 g of titanium oxide (product name: TTO-51A, average particle diameter 0.02 μm, rutile type) manufactured by Ishihara Sangyo Co., Ltd. was added. Then, using the same wet grinder as described above, two of silica hydrogel and titanium oxide were mixed and dispersed.

(Drying Step) The slurry after the dispersion was supplied to the slurry at a concentration of 13 ml / m using a small spray dryer (GA32 type, manufactured by Yamato Scientific Co., Ltd.) at the same concentration.
in, spray pressure 1.2 kg / cm ² (G), hot air temperature 2
Spray drying was performed at 00 ° C. to obtain fine spherical particles in which titanium oxide fine particles were dispersed and included in silica gel particles. The particle shape was almost true spherical, and the particle surface was smooth.

The average particle diameter measured by a Coulter counter (MAII type, using an aperture tube having a diameter of 50 μm) was as follows:
It was 5.2 μm. The result of analyzing the chemical composition of the particles was as follows: 64.8% by weight of SiO ₂ , 35.2% by weight of TiO ₂
Met.

(Measurement of Spectral Transmittance) To 0.4 g of the above-mentioned fine spherical particles, 1.12 g of petrolatum and 0.1 g of liquid paraffin were added.
The paste obtained by adding 48 g and dispersing well using three rolls is sandwiched between two 2 mm-thick quartz plates, spread until the layer thickness becomes 25 μm, and is measured using a self-recording spectrophotometer. The spectral transmittance was measured.

At 500 nm, the transmittance is 56.3% and 400.
At 4 nm, the transmittance is 11.9% at 360 nm, and 1 at 360 nm.
3.0%, transmittance is 7.5% at 320 nm, 290 nm
In this case, the transmittance was 7.8%. FIG. 5 shows a scanning electron micrograph of the dried silica gel particles containing the metal oxide fine particles.

[Example 11] (Hydrogelation step) An aqueous solution of sodium silicate having SiO ₂ / Na ₂ O = 3.0 (molar ratio) and SiO ₂ concentration = 21.0 wt% was added at 2.0 l / min. Sulfuric acid concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly, so that the pH of the liquid discharged into the air from the discharge port is 7.5. The flow rate ratio of the two liquids is adjusted so as to be 8.0, and the uniformly mixed silica sol liquid is continuously discharged from the discharge port into the air. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water is placed at the drop point, and the ripening tank is dropped here to ripen. After aging, the pH was adjusted to 6, and the mixture was sufficiently washed with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 4 mm. Si in the silica hydrogel particles
The weight ratio of water to O ₂ was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 10%.
It was 8 ppm.

(Hydrothermal fine pulverizing step) Next, the silica hydrogel was subjected to an average particle size of 1.
Coarsely pulverized to 0 mm. In a 50 liter content autoclave equipped with an anchor type stirring blade, 22,000 g of the above coarsely ground silica hydrogel and 18,000 water were added.
g in a slurry state having a SiO ₂ concentration of 10.0% by weight, at a temperature of 200 ° C. for 4 hours and a stirring rotation speed of 90 r.
A hydrothermal fine grinding treatment was performed at pm. The pH of the silica hydrogel slurry was 6.

The silica hydrogel particles in the slurry after the hydrothermal treatment were refined, and were subjected to a Coulter counter (MAII
The average particle diameter was 15 μm in the particle diameter measurement using a mold, Coulter Electronics Co., Ltd., using an aperture tube diameter of 280 μm. Further, the SiO ₂ concentration in the slurry after the hydrothermal fine grinding treatment was 10.3% by weight.

(Wet grinding step) The slurry was wet ground using the same wet grinding machine as in Example 1 while keeping its concentration. The average particle size of the silica hydrogel particles in the slurry after the fine pulverization measured with a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) is 1.6 μm.
Met.

(Mixed Slurry Step) 915 g of anatase type titanium oxide having an average particle diameter of 0.02 μm was added to 17,000 g of the silica hydrogel slurry after the above-mentioned wet pulverization, and the silica hydrogel was mixed with the same wet pulverizer as described above. And titanium oxide were mixed and dispersed.

(Drying Step) The slurry after dispersion was supplied to the slurry at a concentration of 13 ml / m using a small spray dryer (GA32 type manufactured by Yamato Scientific Co., Ltd.) at the same concentration.
in, spray pressure 1.2 kg / cm ² (G), hot air temperature 2
Spray drying was performed at 00 ° C. to obtain fine spherical particles in which titanium oxide fine particles were dispersed and included in silica gel particles. The particle shape was almost true spherical, and the particle surface was smooth.

The average particle size measured by a Coulter counter (using an aperture tube having a diameter of 50 μm) was 4.5 μm.
Met. The result of analyzing the chemical composition of the particles was SiO ₂
It was 65.1% by weight and 34.9% by weight of TiO ₂ .

[Reference Example 1] (Hydrogelation step) An aqueous solution of sodium silicate having a SiO ₂ / Na ₂ O content of 3.0 (molar ratio) and an SiO ₂ concentration of 21.0% by weight was added at 2.0 l / min. Sulfuric acid concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly, so that the pH of the liquid discharged into the air from the discharge port is 7.5. The flow rate ratio of the two liquids is adjusted so as to be 8.0, and the uniformly mixed silica sol liquid is continuously discharged from the discharge port into the air. The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water is placed at the drop point, and the ripening tank is dropped here to ripen. After aging, the pH was adjusted to 6, and further washed sufficiently with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 6 mm. Si in the silica hydrogel particles
The weight ratio of water to the weight of O ₂ was 4.0 times by weight, and the residual sodium in the silica hydrogel particles was 10%.
It was 0 ppm.

Next, the silica hydrogel particles were dried in a dryer at 50 ° C. to evaporate the water in the silica hydrogel particles, and the weight of SiO ₂ in the silica hydrogel particles was determined.
Silica hydrogel particles having a weight ratio of water of 1.3 times by weight were obtained. The shape of the obtained silica hydrogel particles was spherical.

(Hydrothermal fine pulverization step) Next, the above silica hydrogel was coarsely pulverized to an average particle diameter of 1.0 mm using a roll crusher. In a 50 liter autoclave equipped with anchor-type stirring blades, 12,000 g of the above coarsely ground silica hydrogel and 38.0 g of water were added.
Then, a hydrothermal treatment was performed at a temperature of 200 ° C. for 24 hours and a stirring rotation speed of 90 rpm in a slurry state having an SiO ₂ concentration of 10.4% by weight. The pH of the silica hydrogel slurry was 6.

The silica hydrogel particles in the slurry after the hydrothermal treatment were hardly refined because the weight ratio of water to SiO ₂ was too low.
When passed through a wire mesh of μm, most of the particles remained without passing through the wire mesh.

Reference Example 2 (Hydrogelation step) An aqueous solution of sodium silicate having a SiO ₂ / Na ₂ O = 3.0 (molar ratio) and a SiO ₂ concentration of 21.0% by weight was subjected to 2.0 l / min. Sulfuric acid concentration = 2
A 0.0% by weight aqueous sulfuric acid solution is introduced into a container provided with a discharge port from a separate inlet, and is mixed instantaneously and uniformly. By adjusting the flow ratio of the two liquids so as to be 8.0, the uniformly mixed silica sol liquid is continuously discharged into the air from the discharge port.
The released liquid forms spherical droplets in the air, and gels in the air while flying in a parabola for about 1 second. An aging tank filled with water is placed at the drop point, and the ripening tank is dropped here to ripen. After aging, the pH was adjusted to 6, and the mixture was sufficiently washed with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 6 mm. S in the silica hydrogel particles
The weight ratio of water to the weight of iO ₂ was 4.5 times, and the residual sodium in the silica hydrogel particles was 10%.
It was 5 ppm.

(Hydrothermal Pulverization Step) Next, the silica hydrogel was treated with a roll crusher to give an average particle size of 1.
Coarsely pulverized to 0 mm. To a 50-liter autoclave equipped with an anchor-type stirring blade, 22,000 g of the coarsely-crushed silica hydrogel and 18,000 g of water were added, and a slurry having a SiO ₂ concentration of 10.0% by weight was heated to a temperature of 120. 24 hours at 90 ° C., 90 rpm stirring speed
Hydrothermal treatment was performed at pm. The pH of the silica hydrogel slurry was 6.

The silica hydrogel particles in the slurry after the hydrothermal treatment were hardly finely divided, probably because the temperature of the hydrothermal treatment was not sufficiently high. When the slurry was passed through a 210-μm wire mesh, most of the particles passed through the wire mesh. I left without passing.

[0195]

According to the present invention, there is provided a production method capable of obtaining fine-particle silica gel with high productivity by hydrothermally pulverizing silica hydrogel and drying the hydrogel by means such as spray drying. Provided.

Further, according to the present invention, there is provided a novel method for producing microparticulate silica gel in which metal compound fine particles are encapsulated in particles without using a solvent.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph showing the surface structure of dried silica gel particles.

FIG. 2 is a scanning electron micrograph showing the surface structure of dried silica gel particles.

FIG. 3 is a scanning electron micrograph showing the surface structure of dried silica gel particles.

FIG. 4 is a scanning electron micrograph showing the surface structure of dried silica gel particles containing metal oxide fine particles.

FIG. 5 is a scanning electron micrograph showing the surface structure of dried silica gel particles containing metal oxide fine particles.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Eiichi Ono 13-1 Kitaminato-cho, Wakamatsu-ku, Kitakyushu-city, Fukuoka Prefecture F-term in Dokai Chemical Co., Ltd. 4G072 AA28 AA35 AA36 AA37 BB05 BB07 CC10 CC11 CC13 DD03 DD04 DD05 DD06 DD07 DD08 GG03 HH21 HH22 JJ13 JJ26 LL06 LL07 MM01 MM02 MM21 MM23 MM26 MM31 PP06 PP17 QQ01 RR06 RR12 RR19 TT01 UU09 UU15 UU17 UU30

Claims (12)

[Claims] 1. A method for producing microparticulate silica gel, comprising the steps of: (1) reacting an alkali metal silicate with a mineral acid so that the ratio of the weight of water to the weight of SiO ₂ is 1.5
A hydrogelation step of obtaining a silica hydrogel having a weight of up to 5.0 times, (2) converting the obtained silica hydrogel into SiO ₂
Hydrothermal pulverization step of performing hydrothermal treatment with stirring in a slurry state having a concentration of 5.0 to 15.0% by weight to form a finely divided silica hydrogel slurry having an average particle diameter of 100 μm or less; and
(3) A method for producing microparticulate silica gel, comprising a drying step of drying the micronized hydrogel slurry. 2. An average particle diameter of 0.1 m in the hydrogelation step.
2. The method according to claim 1, wherein a silica hydrogel having a particle size of at least m is obtained, and this is converted into a silica hydrogel slurry which has been refined to an average particle size of 20 μm or less in a hydrothermal fine grinding step. 3. An average particle diameter of 0.5 m in the hydrogelation step.
3. The production method according to claim 2, wherein the silica hydrogel is at least m. 4. The method according to claim 1, further comprising a step of washing the silica hydrogel obtained in the hydrogelation step with water before performing the hydrothermal pulverization step. 5. The production method according to claim 1, wherein the drying step is performed by a flash dryer, a spray dryer, or a fluidized-bed media dryer. 6. A method for producing microparticulate silica gel in which fine metal compound fine particles are encapsulated in particles, (1)
A hydrogelation step of reacting an alkali metal silicate with a mineral acid to obtain a silica hydrogel having a weight ratio of water to the weight of SiO ₂ of 1.5 to 5.0 times by weight, and
(2) Hydrothermal pulverization of the obtained silica hydrogel in a slurry state having an SiO ₂ concentration of 5.0 to 15.0% by weight with stirring under hydrothermal treatment to obtain a finely divided silica hydrogel slurry having an average particle diameter of 100 μm or less. (3) Along with the step of preparing a finely divided silica hydrogel slurry comprising
Having a mixed slurrying step of introducing metal compound fine particles into the finely divided silica hydrogel slurry to obtain a mixed slurry of silica hydrogel fine particles and metal compound fine particles,
Further, (4) a method for producing microparticulate silica gel containing fine metal compound fine particles, wherein a drying step of drying the mixed slurry is performed. 7. An average particle diameter of 0.1 m in the hydrogelation step.
7. The method according to claim 6, wherein a silica hydrogel having a particle size of at least m is obtained, and this is converted into a silica hydrogel slurry that has been refined to an average particle size of 20 μm or less in a hydrothermal fine grinding step. 8. An average particle size of 0.5 m in the hydrogelation step.
8. The method according to claim 7, wherein the silica hydrogel has a particle size of m or more. 9. The method according to claim 6, further comprising a step of washing the silica hydrogel obtained in the hydrogelation step with water before performing the hydrothermal pulverization step. 10. The production method according to claim 6, wherein the drying step is performed by a flash dryer, a spray dryer or a fluidized bed medium dryer. 11. The production method according to claim 6, wherein a ratio of the weight of the metal compound fine particles to the weight of SiO ₂ of the silica hydrogel in the mixed slurry is 5 to 80% by weight. 12. The method according to claim 6, wherein the metal compound fine particles are fine particles selected from the group consisting of titanium oxide, zinc oxide, cerium oxide, iron oxide and zirconium oxide.