JP4059365B2 - Method for producing fine-particle silica gel and metal compound-encapsulated particulate silica gel - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a microparticulate silica gel in which metal compound fine particles such as microparticulate silica gel, microspherical silica gel and metal oxide are encapsulated in the particles.
[0002]
[Prior art]
Microparticulate silica gels such as microspheres are used in various applications such as liquid chromatography separation agents, cosmetic fillers, resin fillers, catalyst carriers and spacers.
[0003]
In addition, particulate silica gel such as microspheres in which metal compound fine particles are encapsulated in particles is used for ultraviolet shielding agents, photooxidation catalysts, antibacterial agents, and the like.
[0004]
Conventionally, various methods have been proposed as a method for producing a microparticulate silica gel such as a microsphere.
[0005]
For example, as described in JP-A-6-64915, there is a method in which an alkali metal silicate aqueous solution is emulsified and dispersed in a nonpolar organic halide solvent containing a surfactant and then gelled with a gelling agent. It is known. This uses the interfacial tension at the liquid / liquid interface of the generated finely dispersed droplets to spheroidize individual droplets, and then react with a gelling agent such as carbon dioxide gas in that state to form a gel. It will solidify. The produced gel is subjected to a pH adjustment step and an aging step, and then solid / liquid separation is performed to wash away and remove the by-product alkali metal salt, followed by drying to obtain a fine spherical silica gel. In this method, although spherical particles can be easily obtained, since an organic solvent is used, a troublesome solvent separation / recovery step is required, resulting in a complicated process with many steps.
[0006]
Japanese Patent Laid-Open No. 3-183616 discloses that an alkali metal silicate aqueous solution is sprayed into an acidic gas to collect the generated droplets and / or gelled product, and after being treated with an acid-containing solution, washed with water. A method for producing spherical silica gel is described. However, the method in which the liquid droplets and the acid gas are brought into contact with each other inevitably has a low utilization rate of the acid gas as a gelling agent in one pass and is an economically problematic method.
[0007]
Further, as described in JP-A-62-128916 and JP-A-62-129717, fine spherical particles having a specific water content are obtained by spray drying an alkali metal silicate aqueous solution, and then the particles There is known a method of producing spherical porous silica after acid treatment under specific temperature conditions, followed by washing with water and drying. However, these methods have a drawback 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.
[0008]
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 a slurry of the silica hydrogel and water is obtained. In the method of obtaining spherical silica gel by spray drying, the amount of water in the slurry at the time of spray drying is 0.2 to 1.5 from the viewpoint of securing the slurry state and particle strength with respect to the silica hydrogel. A production method for adjusting the weight by weight, preferably 0.3 to 1.4 times by weight, is known.
[0009]
Here, the silica hydrogel is usually pulverized using a ball mill, vibration mill, stirring ball mill, rod mill, friction disk mill, stone mill colloid mill, etc., and the silica hydrogel in the slurry has a particle size of 1 to 50 μm, preferably 10 to 30 μm. Until it becomes a mechanical wet grinding. In addition, it is said that preliminary pulverization may be performed to about 100 to 200 μm with a mechanical pulverizer such as an impact pulverizer, a jet pulverizer, a ball mill, or a stone mill.
[0010]
Before 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 and then at a temperature of 50 to 200 ° C. for 1 to 50 hours. Hydrothermal treatment is preferred.
[0011]
In this production method, the particle diameter after hydrothermal treatment is larger than 100 to 200 μm, and it is intended to pulverize it to 1 to 50 μm exclusively by mechanical pulverization.
[0012]
However, since the silica hydrogel is composed of a kind of viscoelastic body, the silica hydrogel is technically very difficult to wet pulverize the silica hydrogel into fine particles. Regardless of this, in this production method, as a method for reducing the particle size, the particle size is to be refined to a predetermined 50 μm or less by a mechanical pulverization method, and this is a method with technical difficulties. I must say.
[0013]
On the other hand, in order to solve such difficulties, in JP-A-7-196310, a silica hydrogel obtained by reacting an alkali metal silicic acid aqueous solution with an acid aqueous solution and heat-treating at a temperature of 100 to 170 ° C. ₂ At a specific slurry concentration of 15 to 25% by weight and at a specific temperature not exceeding 50 ° C., wet grinding is performed under high-speed shear to obtain a silica hydrogel slurry having a particle size of 4 μm or less. A method of producing fine spherical silica particles by spray drying has been proposed.
[0014]
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, using a known high-speed shearing wet pulverizer such as Dynomill manufactured by Shinmaru Enterprises, 50 ° C. or less The mixture is mechanically wet pulverized at a temperature of 5 μm, pulverized to a particle size of 4 μm or less, and then spray-dried to obtain microspherical silica gel.
[0015]
This is the specific SiO ₂ This is because, in the slurry concentration and temperature range, the viscosity of the slurry decreases, so that a large shear force can be applied.
[0016]
However, according to the study of the present inventors, in this production method, even if the viscosity of the slurry is slightly reduced by adjusting the slurry concentration or the like when viewed macroscopically, the individual particles of the silica hydrogel are microscopically microscopic. However, it is technically very difficult to wet crush particles of such viscoelastic bodies into fine particles only by a mechanical crushing mechanism. It must be said that this is a difficult method. Of course, there is no technical idea that silica hydrogel is made into fine particles by hydrothermal treatment.
[0017]
On the other hand, as a method for producing a microparticulate silica gel in which metal compound fine particles are encapsulated, for example, as described in JP-A-8-104515, particles are formed into a spherical shape by utilizing the liquid / liquid interfacial tension. There is a known method to make it.
[0018]
This is because, for example, zinc oxide fine particles are added and mixed in an alkali metal silicate aqueous solution, and the highly dispersed mixed slurry is emulsified and dispersed in an organic solvent containing a surfactant to make individual droplets spherical. It is made to react with a gelling agent in a state to be gelled and solidified. The produced gel is subjected to a pH adjustment step and an aging step, followed by solid / liquid separation to wash away and remove the by-product alkali metal salt, and then dried to obtain fine particulate silica gel containing zinc oxide fine particles and the like.
[0019]
As described above, in this method, it is easy to obtain spherical particles, but since an organic solvent is used, troublesome solvent separation and recovery steps are required, and it is difficult to have a complicated process with many steps. There is.
[0020]
[Problems to be solved by the invention]
Among the conventionally known methods for producing silica gel such as microspheres, silica hydrogel obtained by reacting alkali metal silicate and mineral acid is used as a starting material, and then the particle diameter is refined to obtain silica hydrogel. A method of obtaining a fine spherical silica gel by making a slurry and drying the silica hydrogel slurry by means such as spray drying is basically suitable for mass production and is also economical.
[0021]
On the other hand, in the known production method described above, 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 produced by the reaction is usually washed with water. The water washing process to remove is implemented.
[0022]
In the step of washing and removing the alkali metal salt from the silica hydrogel, the particle size of the silica hydrogel before washing is 0.1 mm or more, preferably 0.5 mm or more, and the silica hydrogel is contained in the washing tank. It is preferable to perform a packed fixed bed type washing operation in which a packed fixed layer is formed, and the packed bed is washed by circulating washing water. 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, a large amount of silica hydrogel can be easily washed with water, and no filtration device is required. Therefore, it is suitable for mass production and is economical.
[0023]
However, when the silica hydrogel is washed with the salt produced by the reaction after making the particle size smaller than, for example, less than 0.1 mm, a stable packed bed is not formed. In the end, it is necessary to filter silica hydrogel, and a considerably large filter is essential, which is problematic in terms of economy.
[0024]
According to the study by the present inventors, the silica hydrogel containing almost no alkali metal and finely pulverized into the silica hydrogel slurry by pulverizing the silica hydrogel into a silica hydrogel slurry by spray drying etc. Is difficult to perform by mechanical wet grinding.
[0025]
For example, as described above, silica hydrogel particles are a kind of viscoelastic material, even when trying to finely pulverize from coarse particles having an average particle size of 0.5 mm or more to fine particles having an average particle size of several μm. Therefore, it is not easy to pulverize by applying a mechanical shearing force. In reality, it has been found that there is a big problem that the pulverization process must be multistaged and pulverized to a predetermined average particle size.
[0026]
Thus, an object of the present invention is to obtain a silica hydrogel containing almost no alkali metal salt produced by the reaction, preferably by sufficiently washing the silica hydrogel obtained by reacting an alkali metal silicate with a mineral acid, In the production method of obtaining a fine spherical silica gel by making the silica hydrogel into a silica hydrogel slurry having a fine particle diameter of the silica hydrogel and spray drying, the method for refining the silica hydrogel is not based on mechanical wet grinding. Therefore, it is to provide a manufacturing method with high productivity.
[0027]
It is another object of the present invention to provide a novel method for producing fine particulate silica gel in which metal compound fine particles are encapsulated.
[0028]
[Means for Solving the Problems]
As a result of intensive studies from such a viewpoint, the present inventors have found that silica hydrogel obtained by reacting an alkali metal silicate with a mineral acid is preferably washed thoroughly with water and contains almost no alkali metal salt produced by the reaction. In the production method of obtaining a silica hydrogel slurry in which the silica hydrogel has a finer particle size and then drying the slurry to obtain a microspherical silica gel, in the silica hydrogel stage after washing, SiO ₂ By selecting the numerical value of the weight ratio of water to the weight within an appropriate range, even if the silica hydrogel is a coarse silica hydrogel having an average particle diameter of several mm, the average particle diameter is 100 μm without using mechanical wet grinding. In the following, it was found that it can be easily miniaturized to preferably 50 μm or less, more preferably 20 μm or less.
[0029]
That is, H ₂ O / SiO ₂ A slurry obtained by adding water to a silica hydrogel having a weight ratio adjusted to a specific range, for example, in an autoclave equipped with a stirring blade for stirring a normal liquid, under conditions such as suitable silica concentration, temperature, and time while stirring. As a result of the hydrothermal treatment, a surprising phenomenon that can be referred to as “hydrothermal pulverization” is that the hydrogel particle diameter can be easily refined to 20 μm or less in some cases before the hydrothermal treatment. I found it.
[0030]
Furthermore, the present inventors have found that finely particulate silica gel can be obtained efficiently by drying the silica hydrogel slurry after the hydrothermal pulverization treatment by means such as spray drying.
[0031]
In addition, the silica hydrogel slurry that has been hydrothermally pulverized as described above and refined to an average particle diameter of 20 μm or less, for example, when further wet-pulverized under high-speed shearing, has an average particle diameter of 3.0 μm or less. It was also found that finely pulverized silica gel having an average particle diameter of 10 μm or less can be obtained by spray-drying the slurry.
[0032]
Thus, by carrying out the method including the hydrothermal pulverization treatment, the particle size is 1 to 100 μm, preferably 1 to 50 μm, more preferably 1 to 30 μm, and most preferably 1 to 1 μm without necessarily performing mechanical pulverization. It has been found that 10 μm microparticulate silica gel can be produced as the final dry silica gel product.
[0033]
The present invention has been made based on such knowledge.
In the present invention, silica gel is porous granular silica that is amorphous by X-ray diffraction analysis and has substantially no crystalline peak.
[0034]
That is, according to the present invention,
(1) In a method for producing fine particulate silica gel,
(1) Reaction of alkali metal silicate with mineral acid to produce SiO ₂ Hydrogelation step of obtaining a silica hydrogel having a ratio of water weight to weight of 1.5 to 5.0 times by weight;
[0035]
(2) The resulting silica hydrogel is converted into SiO ₂ A hydrothermal pulverization step in which the slurry is hydrothermally treated with stirring in a slurry state having a concentration of 5.0 to 15.0% by weight to obtain a refined silica hydrogel slurry having an average particle size of 100 μm or less, and
[0036]
(3) There is provided a method for producing a microparticulate silica gel comprising a drying step of drying the refined hydrogel slurry.
[0037]
Also, according to the present invention,
(2) In a method for producing a fine particulate silica gel containing fine metal compound fine particles in a particle,
[0038]
(1) Reaction of alkali metal silicate with mineral acid to produce SiO ₂ A hydrogelation step to obtain a silica hydrogel having a ratio of the weight of water to the weight of 1.5 to 5.0 times by weight; and
[0039]
(2) The resulting silica hydrogel is converted into SiO ₂ A process for preparing a refined silica hydrogel slurry comprising a hydrothermal pulverization process in which a hydrothermal heat treatment is performed under stirring in a slurry state having a concentration of 5.0 to 15.0% by weight to obtain a refined silica hydrogel slurry having an average particle size of 100 μm or less. With
[0040]
(3) A mixed slurrying step for obtaining a mixed slurry of silica hydrogel fine particles and metal compound fine particles by introducing metal compound fine particles into the fine silica hydrogel slurry,
[0041]
(4) A method for producing a fine particulate silica gel containing fine metal compound fine particles, characterized by carrying out a drying step of drying the mixed slurry.
[0042]
DETAILED DESCRIPTION OF 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.
[0043]
First, an alkali metal silicate and a mineral acid are reacted to form SiO ₂ The hydrogelation step is carried out to obtain a silica hydrogel having a ratio of water to water of 1.5 to 5.0 times by weight. This hydrogelation step is performed, for example, by the following method. That is,
[0044]
An aqueous solution of an alkali metal silicate and an aqueous mineral acid solution are introduced into a container equipped with a discharge port through a separate inlet and instantaneously and uniformly mixed. ₂ This is a method in which a silica sol having a concentration of 130 g / l or more and a pH of 7 to 9 is generated and immediately discharged into a gaseous medium such as air from the above-mentioned outlet and gelled in the air while drawing a parabola and making it stay in the air. . An aged tank filled with water is placed at the dropping point, and it is dropped here and aged for several minutes to several tens of minutes.
[0045]
Here, examples of the alkali metal include Na and K, and Na is most preferable in terms of economy. As mineral acids, H ₂ SO _Four , HCl, etc., and economically H ₂ SO _Four Is most preferred.
[0046]
Appropriate acid is added to this to lower the pH and to stop ripening. The obtained silica hydrogel is spherical particles having an average particle diameter of several mm. This silica hydrogel is formed by reaction with Na. ₂ SO _Four Since it contains an alkali metal salt such as, it is preferable to remove it sufficiently by washing with water according to a conventional method to obtain a spherical silica hydrogel having an average particle diameter of several millimeters and containing almost no alkali metal salt.
[0047]
At this time, as already described, in the step of washing and removing the alkali metal salt from the silica hydrogel, the silica hydrogel particles are filled in the washing tank to form a filling fixed layer, and the filling layer is washed with water. It is preferable to carry out a packed fixed bed type washing operation in which the washing is carried out by circulating. In such a packed bed type water washing method, since the average particle size of the silica hydrogel is sufficiently large, a stable packed bed can be formed, a large amount of silica hydrogel can be easily washed with water, and no filtration device is required. .
[0048]
If this silica hydrogel is roughly pulverized with, for example, a roll crusher, a crushed product silica hydrogel having an average particle size of 0.1 to 5 mm can be easily obtained. This particle size is a preferable range in order to effectively perform the stirring operation and the like in the subsequent hydrothermal pulverization step.
[0049]
As another method for obtaining silica hydrogel, an alkali metal silicate aqueous solution and a mineral acid aqueous solution are uniformly mixed in a reaction vessel in a short time to form a silica sol, and then the solution is placed on another saucer plate. A gelling method may be used.
[0050]
After this gel is crushed to a size of several centimeters to several millimeters in diameter, water adjusted for pH is added and ripened, and acid is added to lower pH to stop ripening. Since the obtained amorphous silica hydrogel having an average particle diameter of several centimeters to several millimeters contains an alkali metal salt produced by the reaction, it is washed with water by the above-described method or the like to sufficiently remove the alkali metal salt. An amorphous silica hydrogel having an average particle diameter of several centimeters to several millimeters containing almost no salt is obtained.
[0051]
If the silica hydrogel is roughly pulverized with, for example, a roll crusher 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.
[0052]
In the present invention, SiO in the silica hydrogel after washing with water. ₂ The ratio of the weight of water to the weight is preferably 1.5 to 5.0 times by weight. This SiO ₂ The ratio of water to water is measured by the following method. That is,
[0053]
2 g of silica hydrogel after washing with water is weighed and dried using a dryer under the drying conditions of 180 ° C. × 4 hr. ₂ The weight is the water content.
[0054]
SiO ₂ When the ratio of the weight of water to the weight is less than 1.5 times, the effect of refining the average particle size of the silica hydrogel is reduced in the subsequent hydrothermal treatment step with liquid stirring. Probably SiO in silica hydrogel ₂ If the weight ratio of water to water is smaller than this, the primary particles of silica hydrogel are strongly bonded, and it is assumed that even if hydrothermal treatment is performed, it is difficult to separate and disintegrate them smoothly. .
[0055]
On the other hand, SiO ₂ When the ratio of the weight of water to the weight exceeds 5.0 times by weight, the mechanical strength of the silica hydrogel becomes extremely weak, which is not preferable because it causes difficulty in subsequent handling.
[0056]
SiO in silica hydrogel ₂ The ratio of the weight of water to the weight can be controlled by the concentration conditions of the alkali metal silicate aqueous solution and mineral acid aqueous solution to be mixed and the aging conditions (temperature and pH) of the resulting gel. Moreover, when it exceeds the said range, it is also possible to perform a suitable drying operation and to adjust a moisture content.
[0057]
Next, the silica hydrogel thus obtained is converted into SiO 2. ₂ In a slurry state having a concentration of 5.0 to 15.0% by weight, a hydrothermal pulverization step is performed by hydrothermal treatment with stirring to obtain a refined silica hydrogel slurry having an average particle size of 100 μm or less.
[0058]
As the hydrothermal treatment apparatus, an autoclave that 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 fiddler type, a helical ribbon type, a bull margin type, a turbine type, a max blend type, etc. that are generally used for stirring liquids can be used, but are not limited thereto. It is not a thing.
[0059]
In addition, as an autoclave heating method, an indirect heating method in which high-pressure steam or a heat medium is supplied to the jacket, an indirect heating method using an electric heater, or a direct heating method in which steam is directly blown into the liquid in the tank can be used as appropriate.
[0060]
The average particle size of the silica hydrogel charged in the autoclave is 0.1 to 5 mm, more preferably 0.5 to 5 mm. If the average particle size is too large and exceeds 5 mm, the particle size is too large, and even if the liquid is stirred in the autoclave, the particles will not float sufficiently and some of them will easily accumulate on the bottom of the tank. May cause handling problems.
[0061]
If the average particle size is 0.1 to 5 mm, the particles can be easily made into fine particles only by hydrothermal treatment under liquid agitation to an average particle size of 100 μm or less, and by selection of the conditions described above, 20 μm or less and 1 μm or more.
[0062]
In the autoclave, silica hydrogel particles after washing with water and water are charged to form a silica hydrogel slurry. ₂ The concentration is preferably 5.0 to 15.0% by weight. SiO ₂ When the concentration exceeds 15.0% by weight, it becomes difficult to sufficiently stir the slurry in the autoclave tank. On the other hand, SiO ₂ If the concentration is less than 5.0% by weight, the amount of water in the resulting silica slurry is large, and the moisture evaporation load in the subsequent spray drying step is increased, which is not desirable.
[0063]
What should be noted in the present invention is that in this hydrothermal treatment under liquid agitation, refinement (hydrothermal pulverization), which is also referred to as chemical pulverization of silica hydrogel, is performed, and at the same time, the pore structure of silica hydrogel is adjusted. It is possible to perform aging such as so-called Ostwald Ripening.
[0064]
Depending on the target pore structure, the objective can be sufficiently achieved by hydrothermal treatment only with the silica hydrogel-water-based slurry. The pH of the slurry in this case is 1-7.
[0065]
On the other hand, a method of adding a trace amount of alkali metal hydroxide or ammonia or the like to the silica hydrogel-water slurry and adjusting the slurry pH to about 7 to 11 and then hydrothermally treating the silica pores is also a target pore structure. Some may apply.
[0066]
The stirring energy of the silica hydrogel slurry by the stirring blades in the autoclave tank during the hydrothermal pulverization treatment is a standard stirring energy level for normal liquids and slurries that are not particularly high in viscosity. 2,000W / m ^Three (Liquid or slurry) is sufficient. Liquid or slurry 1m ^Three The stirring energy per hit is 5 W / m ^Three If it is less than this, some of the coarse silica hydrogel particles will not float sufficiently in the tank during the hydrothermal treatment, and will be easily deposited on the bottom of the tank, resulting in handling problems.
[0067]
On the other hand, liquid or slurry 1m ^Three The stirring energy per hit is 2,000 W / m ^Three In the case of exceeding 1, the effect of further promoting the refinement of the particle size of silica hydrogel by hydrothermal treatment is small, and only the stirring energy is increased.
[0068]
The temperature range of the hydrothermal treatment is desirably 130 to 230 ° C, preferably 150 to 230 ° C, and more preferably 180 to 230 ° C. When the temperature is lower than 130 ° C., the effect of reducing the particle size of silica hydrogel by hydrothermal treatment is poor, whereas when it exceeds 230 ° C., the particle size of silica hydrogel by hydrothermal treatment commensurate with the increase in temperature level. There is little promotion effect of miniaturization, and it is meaningless technically and economically only by increasing heating energy.
[0069]
The hydrothermal pulverization time may vary depending on the hydrothermal treatment temperature, but is usually 0.2 to 24 hours. When the hydrothermal treatment time is less than 0.2 hr, a sufficient effect of reducing the particle diameter of silica hydrogel by hydrothermal treatment cannot be obtained. Further, when the hydrothermal treatment time exceeds 24 hours, the reaggregation phenomenon of the particles occurs, which is not preferable because it deviates from the purpose of the hydrothermal pulverization treatment of refining the particle size of the silica hydrogel by the hydrothermal treatment. .
[0070]
In the present invention, the particle size distribution of the silica hydrogel is a value measured by a Coulter counter (manufactured by Coulter Electronics) or the like.
[0071]
By drying the silica hydrogel slurry, in order to obtain a fine dry silica gel particle product having an average particle diameter of 100 μm or less by Coulter counter measurement, by Coulter counter measurement of silica hydrogel particles subjected to a drying process such as spray drying. The average particle diameter based on the particle volume is set to 100 μm or less. The average particle diameter is preferably 1 to 50 μm, more preferably 1 to 20 μm, still more preferably 1 to 10 μm, and most preferably 1 to 5 μm.
[0072]
In particular, when obtaining fine spherical particles (true spherical particles) having an average particle size of 100 μm or less, the silica hydrogel supplied to the drying step preferably has an average particle size of 1 to 10 μm. More preferably, it is -5 micrometers, and it is most preferable that it is 1-3 micrometers. When the average particle diameter exceeds this value, the sphericity of the shape of the obtained microspherical particles and the smoothness of the particle surface are relatively lowered.
[0073]
On the other hand, if the average particle size is less than 1 μm, no significant improvement in the sphericity of the dry particles and the smoothness of the particle surface commensurate with the refinement of the particle size is observed, and the energy required for refinement of the silica hydrogel particles becomes excessive. It is only unfavorable.
[0074]
Depending on the target pore structure, a small amount of alkali metal hydroxide or ammonia such as ammonia is added to the silica hydrogel-water slurry, and the pH of the silica hydrogel slurry is adjusted to about 8 to 11 before hydrothermal heat. There may be a case where fine grinding is performed. In that case, before or after the drying step such as spray drying so that the allowable content of alkali metal impurities in the fine spherical silica gel obtained by drying the silica hydrogel slurry satisfies the allowable value determined by the use of the product. The silica hydrogel may be washed with water.
[0075]
Further, when the target average particle size of the microspherical silica gel obtained by drying the silica hydrogel slurry is to be smaller than 100 μm, preferably 10 μm or less, the average particle size is 20 μm by hydrothermal pulverization. It is preferable that the silica hydrogel slurry refined below is mechanically wet pulverized to further refine the average particle size of the silica hydrogel to 1 to 3 μm. By such pulverization treatment, a fine 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.
[0076]
As the wet pulverizer used here, a bead mill which is a wet medium agitation mill using beads having a particle diameter of 1 mm or less, a wet medium agitation pulverizer using a ball having a particle diameter of several mm, a wet ball mill, etc. are applied. It is not limited to the pulverizer.
[0077]
As described above, the silica hydrogel slurry is first hydrothermally pulverized to obtain a refined silica hydrogel slurry having an average particle size of 20 μm or less, which is further wet pulverized to refine the average particle size to 1 to 3 μm. Even in the case where the steps are used in combination, compared with a case where a silica hydrogel having an average particle diameter of several mm is refined to an average particle diameter of 1 to 3 μm only by mechanical wet pulverization without hydrothermal pulverization, it is mechanically wet. The grinding load is much smaller and can be implemented much more easily.
[0078]
Next, the drying process which dries the hydrogel slurry refined | miniaturized as mentioned above is performed.
As a drying apparatus for drying a silica hydrogel slurry to obtain monodispersed fine silica gel particles, a form in which particles and droplets are dispersed in hot air without forming a fixed layer in order to prevent aggregation of the particles is preferable. Spray dryers, medium fluidized bed dryers, air dryers, and the like are suitable.
[0079]
In particular, when trying to obtain microspherical silica gel, a spray dryer is suitable as the drying device, and the method of spray atomization of the slurry liquid of the spray dryer is not particularly limited. High-speed rotating disk, one-fluid pressure nozzle, two-fluid nozzle, ultrasonic nozzle, etc. are applied.
[0080]
Hereinafter, although the case where a spray dryer is used as a drying device will be described as an example, other dryers can be applied as they are with appropriate modifications.
[0081]
When the silica hydrogel slurry is supplied to the spray dryer, the silica hydrogel concentration can be supplied as the concentration of the silica hydrogel slurry after the hydrothermal pulverization treatment, and if necessary, The concentration may be adjusted by adding water.
[0082]
The amount of silica hydrogel and water in the silica hydrogel slurry supplied to the spray dryer is measured by the following method.
[0083]
That is, 50 g of silica hydrogel slurry is taken in a beaker, and the whole amount is filtered using a Millipore filter having a pore diameter 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.
[0084]
In addition, SiO in the wet cake ₂ The weight is obtained from the weight after drying for 4 hours at a temperature of 180 ° C. with a dryer as described above.
[0085]
The silica hydrogel slurry to be supplied to the spray dryer is not particularly limited, but a silica water gel ratio of 1.5 to 5.0 times the weight of the silica hydrogel weight determined by the above measurement method is used. preferable.
[0086]
When the ratio of the weight of water to the weight of silica hydrogel is less than 1.5 times, the sphericity and particle surface smoothness in the particle shape of the spherical silica gel obtained by spray drying are lowered.
[0087]
On the other hand, if the ratio of the weight of water to the weight of silica hydrogel exceeds 5.0 times, the water evaporation load in spray drying becomes large, which is not desirable.
[0088]
As described above, the silica hydrogel slurry having a ratio of water weight to silica hydrogel weight of 1.5 to 5.0 times by weight is supplied to the spray dryer, and the operating conditions of the spray dryer are selected. A fine spherical silica gel having excellent shape sphericity and a smooth particle surface can be obtained.
[0089]
In known techniques such as Japanese Examined Patent Publication No. 6-99135, in which the refinement of silica hydrogel is conventionally performed only by mechanical wet pulverization, the slurry state is ensured and the particles are related to the silica hydrogel slurry to be spray-dried. From the viewpoint of strength, the weight ratio of water to the weight of silica hydrogel in the slurry is 0.2 to 1.5 times by weight as described above.
[0090]
In contrast, in the present invention, a slurry hydrothermally pulverized to an average particle size of 100 μm or less, preferably 20 μm or less is used as the silica hydrogel slurry supplied to the spray dryer. The weight ratio of water is preferably about 1.5 to 5.0 times by weight.
[0091]
As described above, in the present invention, the silica hydrogel slurry having the above-mentioned weight ratio that has been hydrothermally pulverized in advance is spray-dried, so that it is much closer to a sphere and has a smooth particle surface compared to the above-mentioned known examples. Microspherical silica gel is obtained.
[0092]
Next, a method for producing a microspherical silica gel in which metal compound fine particles are encapsulated in another particle according to another embodiment of the present invention will be described.
[0093]
In this case, the above-mentioned (1) alkali metal silicate and mineral acid are reacted to form SiO. ₂ Hydrogelation step to obtain a silica hydrogel having a ratio of water to water of 1.5 to 5.0 times by weight; and
[0094]
(2) The obtained silica hydrogel was converted into SiO ₂ In a slurry state with a concentration of 5 to 15% by weight, hydrothermal treatment with stirring, together with a preparation process of a refined silica hydrogel slurry comprising a hydrothermal pulverization process to make a refined silica hydrogel slurry having an average particle size of 100 μm or less,
[0095]
(3) It is characterized by having a mixed slurrying step of introducing metal compound fine particles into the fine silica hydrogel slurry to obtain a mixed slurry of silica hydrogel fine particles and metal compound fine particles.
[0096]
The mode of introducing the metal compound fine particles into the silica hydrogel slurry is arbitrary. For example, the hydrothermal pulverization step (2) can be performed in the presence of metal compound fine particles, and when the wet pulverization step is performed subsequent to the hydrothermal pulverization step, the wet pulverization is performed on the metal compound fine particles. It can also be performed in the coexistence.
[0097]
As the metal compound fine particles, fine particles are preferable, and so-called ultrafine particles are particularly preferable.
[0098]
Examples of usable metal compound fine particles include metal oxide fine particles, such as titanium oxide, titanium peroxide, zinc oxide, cerium oxide, ferrous oxide, ferric oxide, zirconium oxide, chromium oxide, and aluminum oxide. , Magnesium oxide, silver oxide, cuprous oxide, cupric oxide, cuprous oxide, cobalt trioxide, cupric oxide, cuprous oxide, cuprous nickel oxide, cupric oxide, thorium oxide, tungsten oxide, molybdenum oxide , Manganese dioxide, manganese trioxide, uranium oxide, thorium oxide, germanium oxide, stannous oxide, stannic oxide, lead monoxide, lead trioxide, lead dioxide, antimony trioxide, antimony pentoxide, bismuth trioxide And the like are preferable. Among these, fine particles selected from the group consisting of titanium oxide, zinc oxide, cerium oxide, iron oxide, and zirconium oxide are particularly preferable.
[0099]
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; tantalum carbide, carbonized Carbide fine particles and halide fine particles such as zirconium, tungsten carbide, vanadium carbide, titanium carbide, silicon carbide, and calcium fluoride can also be used. In addition, fine particles of a metal such as gold, silver, platinum, copper, and aluminum or an alloy thereof can be used depending on circumstances.
[0100]
The metal compound fine particles in the present invention include those referred to as so-called ultrafine particles as described above, and the primary particle size (particle size) is 0.002 to 0.5 μm. And 0.01-0.5 micrometer is preferable and what is 0.01-0.3 micrometer is more preferable. If it is less than 0.002 μm, it is in an agglomerated state from the beginning when the specific surface area is increased, and cannot be introduced into the silica hydrogel slurry in a sufficiently dispersed state. On the other hand, if it exceeds 0.5 μm, it is relatively unfavorable compared to the particle size of silica gel, and it becomes difficult to encapsulate the silica gel particles in a well dispersed state.
[0101]
In addition, SiO in the mixed slurry of the introduced metal compound fine particles ₂ The ratio to is 5 to 80% by weight, preferably 5 to 45% by weight.
[0102]
Specific embodiments include, for example, average particles in the silica hydrogel slurry refined by the hydrothermal pulverization step, or in the silica hydrogel slurry further refined by wet pulverization as necessary. Metal compound fine particles such as titanium dioxide, zinc oxide, cerium oxide, iron oxide and zirconium oxide having a diameter of 0.002 to 0.5 μm are made of SiO. ₂ As described above, 5 to 80% by weight is added and dispersed sufficiently with respect to the weight 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 wet pulverizer that performs hydrothermal pulverization as described above.
[0103]
The mixed slurry thus obtained is spray-dried in the same manner as in the case of obtaining fine particulate silica gel, thereby obtaining fine particulate silica gel containing fine metal compound fine particles.
[0104]
The metal compound fine particles encapsulated in the silica gel have a particle size far smaller than that of the silica gel particles, and one or more, usually several, preferably many metal compound fine particles are contained in one silica gel. It is included in a distributed state. The “encapsulation” in the present invention means that the metal compound fine particles are contained in the silica gel particles in such a state.
[0105]
Probably, in silica gel particles having a large number of pores, in the process of drying the silica gel particles, only the liquid phase of the slurry filling the pores is volatilized and dried. It is presumed that it remains in the state of being supported on the pores. This is considered to be an embodiment in which fine metal compound particles are encapsulated in silica gel particles.
[0106]
The particulate silica gel in which such metal compound fine particles are encapsulated is useful for various applications, and can be suitably used, for example, as an ultraviolet shielding agent. Moreover, when a metal compound is an anatase type titanium oxide, it can use suitably for a photo-oxidation catalyst use.
[0107]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples, but the technical scope of the present invention is not limited thereto.
[0108]
[Example 1]
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a sulfuric acid concentration = 20.0% by weight are introduced into a container equipped with a discharge port through a separate inlet, and instantaneously The flow rate of the two liquids is adjusted so that the pH of the liquid discharged from the discharge port into the air becomes 7.5 to 8.0, and the uniformly mixed silica sol solution is continuously discharged from the discharge port. Were released into the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. A ripening tank filled with water was placed at the dropping point, and it was dropped and aged here.
[0109]
After aging, the pH was adjusted to 6 and washed thoroughly 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 ₂ The weight ratio of water to weight was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 103 ppm.
[0110]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle size of 1.0 mm using a roll crusher. An autoclave having an internal volume of 50 liters equipped with an anchor type stirring blade is charged with 22,000 g of the above coarsely pulverized silica hydrogel and 18,000 g of water, and SiO 2 ₂ In a slurry state with a concentration of 10.0% by weight, hydrothermal pulverization was performed at a temperature of 200 ° C. for 3 hours at a stirring rotation speed of 90 rpm. The pH of the silica hydrogel slurry was 6.
[0111]
The silica hydrogel particles in the slurry after the hydrothermal pulverization treatment are finely pulverized. In the particle size measurement using a Coulter counter (MAII type, manufactured by Coulter Electronics, 280 μm aperture tube diameter), the average particle size is 15 μm. there were. In addition, SiO in the slurry after hydrothermal treatment ₂ The concentration was 10.3% by weight.
[0112]
(Wet grinding process)
Subsequently, the slurry was further finely pulverized using the wet pulverizer (Dyno-Mill manufactured by Shinmaru Enterprises Co., Ltd., using beads having a diameter of 0.5 mm) while maintaining the concentration. The average particle size of the silica hydrogel particles in the slurry after pulverization was 1.6 μm using a Coulter counter (MAII type, aperture tube diameter of 50 μm used).
[0113]
Moreover, the measurement of the quantity of the silica hydrogel and water in the silica hydrogel slurry after the said fine grinding | pulverization was performed with the following method.
[0114]
50 g of silica hydrogel slurry is taken in a beaker, and the whole amount is filtered using a Millipore filter having a pore diameter of 0.45 μm under a reduced pressure of 5 mmHg and dehydrated for 40 minutes. 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. In addition, SiO in the obtained wet cake ₂ The weight is obtained from the weight after drying for 4 hours at a temperature of 180 C with a dryer.
[0115]
The ratio of the weight of water to the weight of silica hydrogel in the slurry determined by this measurement method was 4.4 times by weight.
[0116]
(Drying process)
Next, the slurry was supplied at a slurry supply rate of 13 ml / min and a spraying pressure of 1.2 kg / cm using a small-sized spray dryer (GA32 type manufactured by Yamato Kagaku Co., Ltd.) while maintaining its concentration. ² (G) Spray drying was performed at a hot air temperature of 200 ° C. to obtain fine dry silica gel particles. The average particle diameter of the obtained dried particles by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 4.5 μm. The particle shape was almost spherical, and the particle surface was smooth.
A scanning electron micrograph of the dried silica gel particles is shown in FIG.
[0117]
[Example 2]
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a sulfuric acid concentration = 20.0% by weight are introduced into a container equipped with a discharge port through a separate inlet, and instantaneously The flow rate of the two liquids is adjusted so that the pH of the liquid discharged from the discharge port into the air becomes 7.5 to 8.0, and the uniformly mixed silica sol solution is continuously discharged from the discharge port. Were released into the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. A ripening tank filled with water was placed at the dropping point, and it was dropped and aged here.
[0118]
After aging, the pH was adjusted to 6 and washed thoroughly 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 ₂ The weight ratio of water to weight was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 100 ppm.
[0119]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle size of 1.0 mm using a roll crusher. An autoclave having an internal volume of 50 liters equipped with an anchor type stirring blade is charged with 22,000 g of the above coarsely pulverized silica hydrogel and 18,000 g of water, and SiO 2 ₂ Hydrothermal pulverization was performed in a slurry state having a concentration of 10.0% by weight at a temperature of 200 ° C. for 20 hours at a stirring rotation speed of 50 rpm. The pH of the silica hydrogel slurry was 6.
[0120]
The silica hydrogel particles in the slurry after the hydrothermal pulverization treatment are pulverized, and the average particle size is 13 μm in the particle size measurement with a Coulter counter (MAII type, manufactured by Coulter Electronics, using an aperture tube diameter of 280 μm). there were. In addition, SiO in the slurry after hydrothermal treatment ₂ The concentration was 10.3% by weight.
[0121]
(Wet grinding process)
Next, the slurry was further finely pulverized using the same wet pulverizer as in Example 1 while maintaining the concentration. The average particle size of the silica hydrogel particles in the finely pulverized slurry by a Coulter counter (MAII type, using an aperture tube size of 50 μm) was 1.5 μm.
[0122]
Further, the amount of silica hydrogel and water in the finely pulverized silica hydrogel slurry was measured in the same manner as in Example 1, but the ratio of the weight of water to the weight of silica hydrogel was 4.4 times by weight. there were.
[0123]
(Drying process)
Next, the slurry was supplied at a slurry supply rate of 13 ml / min and a spraying pressure of 1.2 kg / cm using a small-sized spray dryer (GA32 type manufactured by Yamato Kagaku Co., Ltd.) while maintaining its concentration. ² (G) Spray drying was performed at a hot air temperature of 200 ° C. to obtain fine dry silica gel particles. The average particle diameter of the obtained dried particles by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 4.5 μm. The particle shape was almost spherical, and the particle surface was smooth.
[0124]
Example 3
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a sulfuric acid concentration = 20.0% by weight are introduced into a container equipped with a discharge port through a separate inlet, and instantaneously The flow rate of the two liquids is adjusted so that the pH of the liquid discharged from the discharge port into the air becomes 7.5 to 8.0, and the uniformly mixed silica sol solution is continuously discharged from the discharge port. Were released into the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. A ripening tank filled with water was placed at the dropping point, and it was dropped and aged here.
[0125]
After aging, the pH was adjusted to 6 and washed thoroughly 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 ₂ The weight ratio of water to the weight was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 95 ppm.
[0126]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle size of 0.8 mm using a roll crusher. An autoclave having an internal volume of 50 liters equipped with an anchor type stirring blade is charged with 22,000 g of the above coarsely pulverized silica hydrogel and 18,000 g of water, and SiO 2 ₂ In a slurry state having a concentration of 10.0% by weight, hydrothermal pulverization was performed at a temperature of 185 ° C. for 20 hours at a stirring rotation speed of 100 rpm. The pH of the silica hydrogel slurry was 6.
[0127]
The silica hydrogel particles in the slurry after the hydrothermal pulverization treatment are finely pulverized, and the average particle size is 17 μm in the particle size measurement with a Coulter counter (MAII type, manufactured by Coulter Electronics, using an aperture tube diameter of 280 μm). there were. In addition, SiO in the slurry after hydrothermal treatment ₂ The concentration was 10.3% by weight.
[0128]
(Wet grinding process)
Next, the slurry was finely pulverized using the same wet pulverizer as in Example 1 while maintaining the concentration. The average particle diameter of the silica hydrogel particles in the finely pulverized slurry by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 1.7 μm.
[0129]
Further, the amount of silica hydrogel and water in the finely pulverized silica hydrogel slurry was measured in the same manner as in Example 1, but the ratio of the weight of water to the weight of silica hydrogel was 4.4 times by weight. there were.
[0130]
(Drying process)
The slurry is supplied at a concentration of 13 ml / min and a spray pressure of 1.2 kg / cm using a small spray dryer (GA32 type manufactured by Yamato Kagaku Co., Ltd.) with its concentration. ² (G) Spray drying was performed at a hot air temperature of 200 ° C. to obtain fine dry silica gel particles. The average particle diameter of the obtained dried particles by a Coulter counter (using an aperture tube diameter of 50 μm) was 4.5 μm. The particle shape was almost spherical, and the particle surface was smooth.
[0131]
Example 4
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a sulfuric acid concentration = 20.0% by weight are introduced into a container equipped with a discharge port through a separate inlet, and instantaneously The flow rate of the two liquids is adjusted so that the pH of the liquid discharged from the discharge port into the air becomes 7.5 to 8.0, and the uniformly mixed silica sol solution is continuously discharged from the discharge port. To the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. Place a ripening tank filled with water at the dropping point, drop it here and let it mature. After aging, the pH was adjusted to 6 and washed thoroughly 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 ₂ The weight ratio of water to weight was 4.0 times by weight, and the residual sodium in the silica hydrogel particles was 98 ppm.
[0132]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle size of 1.5 mm using a roll crusher. 20,000 g of the above coarsely pulverized silica hydrogel and 20,000 g of water are charged into an autoclave having an internal volume of 50 liters equipped with an anchor-type stirring blade to prepare a slurry, and an aqueous sodium hydroxide solution is added to adjust the pH to 10. SiO ₂ A hydrothermal pulverization treatment was performed on a silica hydrogel slurry having a concentration of 10.0% by weight at a temperature of 200 ° C. for 3 hours at a stirring rotation speed of 90 rpm.
[0133]
The silica hydrogel particles in the slurry after the hydrothermal pulverization treatment are finely pulverized. In the particle size measurement using a Coulter counter (MAII type, manufactured by Coulter Electronics, 280 μm aperture tube diameter), the average particle size is 13 μm. there were. SiO in the slurry after hydrothermal treatment ₂ The concentration was 10.2% by weight.
[0134]
(Wet grinding process)
Next, the slurry was wet pulverized using the same wet pulverizer as in Example 1 while maintaining the concentration. The average particle diameter of the silica hydrogel particles in the slurry after the wet pulverization by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 1.4 μm.
[0135]
The ratio of the weight of water to the weight of silica hydrogel in the finely pulverized slurry obtained by the same measurement method as in Example 1 was 3.5 times the weight.
[0136]
(Drying process)
The slurry is supplied at a concentration of 13 ml / min and a spray pressure of 1.2 kg / cm using a small spray dryer (GA32 type manufactured by Yamato Kagaku Co., Ltd.) with its concentration. ² (G) Spray drying was performed at a hot air temperature of 200 ° C. to obtain fine dry silica gel particles. The obtained dried particles had an average particle size of 5.2 μm by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm), the particle shape was almost spherical, and the particle surface was smooth.
A scanning electron micrograph of the dried silica gel particles is shown in FIG.
[0137]
Example 5
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration of 23.0% by weight and an aqueous solution of sulfuric acid having a sulfuric acid concentration of 20.0% by weight are introduced into a container equipped with a discharge port through a separate inlet, and instantaneously The flow rate of the two liquids is adjusted so that the pH of the liquid discharged from the discharge port into the air becomes 7.5 to 8.0, and the uniformly mixed silica sol solution is continuously discharged from the discharge port. To the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. Place a ripening tank filled with water at the dropping point, drop it here and let it mature. After aging, the pH was adjusted to 6 and washed thoroughly with water to obtain a silica hydrogel. The obtained silica hydrogel particles had a spherical particle shape and an average particle diameter of 3 mm. SiO in silica hydrogel particles ₂ The weight ratio of water to weight was 1.7 times by weight, and the residual sodium in the silica hydrogel particles was 108 ppm.
[0138]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle size of 0.2 mm using a roll crusher. In a 50 liter autoclave equipped with an anchor type stirring blade, 20,000 g of the above coarsely pulverized silica hydrogel and 30,000 g of water were charged, and SiO 2 ₂ Hydrothermal pulverization treatment was performed in a slurry state with a concentration of 14.8% by weight at a temperature of 210 ° C. for 24 hours with a stirring rotation speed of 120 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 the average particle size was 20 μm in the particle size measurement using a Coulter counter (MAII type, manufactured by Coulter Electronics Co., Ltd., aperture tube diameter 280 μm). In addition, SiO in the slurry after hydrothermal treatment ₂ The concentration was 14.5% by weight.
[0140]
(Wet grinding process)
The slurry was wet crushed using the same wet pulverizer as in Example 1 while maintaining the concentration. The average particle diameter of the silica hydrogel particles in the slurry after the wet pulverization by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 2.0 μm.
[0141]
Further, the ratio of the weight of water to the weight of silica hydrogel in the finely pulverized slurry obtained by the same measurement method as in Example 1 was 1.7 times by weight.
[0142]
(Drying process)
Next, the slurry was supplied at a slurry supply rate of 13 ml / min and a spraying pressure of 1.2 kg / cm using a small-sized spray dryer (GA32 type manufactured by Yamato Kagaku Co., Ltd.) while maintaining its concentration. ² (G) Spray drying was performed at a hot air temperature of 200 ° C. to obtain fine dry silica gel particles. The average particle diameter of the obtained dried particles by a Coulter counter (using an aperture tube diameter of 50 μm) was 9.0 μm, and the particle shape was spherical.
[0143]
Example 6
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a concentration of sulfuric acid = 20.0% by weight are introduced into a container equipped with a discharge port through a separate inlet, and instantaneously The flow rate of the two liquids is adjusted so that the pH of the liquid discharged into the air from the discharge port is 7.5 to 8.0, and the uniformly mixed silica sol solution is continuously discharged from the discharge port. To the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. Place a ripening tank filled with water at the dropping point, drop it here and let it mature. After aging, the pH was adjusted to 6 and washed thoroughly 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 ₂ The weight ratio of water to weight was 4.2 times by weight, and the residual sodium in the silica hydrogel particles was 100 ppm.
[0144]
(Hydrothermal pulverization process)
The silica hydrogel was coarsely pulverized to a mean particle size of 2.0 mm using a roll crusher. An autoclave with an internal volume of 50 liters equipped with an anchor type stirring blade is charged with 22,000 g of the above-ground silica hydrogel and 18,000 g of water, and SiO 2 ₂ Hydrothermal pulverization was performed in a slurry state having a concentration of 10.0% by weight at a temperature of 200 ° C. for 3 hours at a stirring rotation speed of 100 rpm. The pH of the silica hydrogel slurry was 6.
[0145]
The silica hydrogel particles in the slurry after the hydrothermal treatment were refined and measured with a Coulter counter (MAII type, manufactured by Coulter Electronics, using an aperture tube diameter of 280 μm), and the average particle diameter was 18 μm. In addition, SiO in the slurry after hydrothermal treatment ₂ The concentration was 10.2% by weight.
[0146]
In the same manner as in Example 1, the amount of silica hydrogel and water in the silica hydrogel slurry after the hydrothermal treatment was measured, but the ratio of the weight of water to the weight of silica hydrogel was 2.0 times by weight. .
[0147]
(Drying process)
Next, the slurry is spray-dried at a slurry supply rate of 65 ml / min and a hot air temperature of 255 ° C. using a fluidized bed dryer (SFD-mini type manufactured by Okawara Seisakusho) at the same concentration to obtain fine dry silica gel particles. It was. The average particle diameter of the obtained dried particles by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 8.9 μm, and the particle shape was indefinite.
A scanning electron micrograph of the dried silica gel particles is shown in FIG.
[0148]
Example 7
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a concentration of sulfuric acid = 20.0% by weight are introduced into a container equipped with a discharge port through a separate inlet, and instantaneously The flow rate of the two liquids is adjusted so that the pH of the liquid discharged into the air from the discharge port is 7.5 to 8.0, and the uniformly mixed silica sol solution is continuously discharged from the discharge port. To the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. Place a ripening tank filled with water at the dropping point, drop it here and let it mature. After aging, the pH was adjusted to 6 and washed thoroughly 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 ₂ The weight ratio of water to weight was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 98 ppm.
[0149]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle diameter of 0.7 mm using a roll crusher. In a 50 liter autoclave equipped with an anchor-type stirring blade, 20,000 g of the above coarsely pulverized silica hydrogel and 7,970 g of water are charged to form a slurry, and an aqueous sodium hydroxide solution is added to adjust the pH to 10. Adjusted SiO ₂ A hydrothermal pulverization treatment was performed on a silica hydrogel slurry having a concentration of 13.0% by weight at a temperature of 200 ° C. for 24 hours with a stirring rotation speed of 90 rpm.
[0150]
The silica hydrogel particles in the slurry after the hydrothermal treatment were refined, and the average particle size was 19 μm as measured by a Coulter counter (MAII type, manufactured by Coulter Electronics, using an aperture tube diameter of 280 μm). In addition, SiO in the slurry after hydrothermal treatment ₂ The concentration was 13.2% by weight.
[0151]
(Wet grinding process)
The slurry was wet crushed using the same wet pulverizer as in Example 1 while maintaining the concentration. The average particle diameter of the silica hydrogel particles in the slurry after the wet pulverization by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 1.7 μm.
[0152]
Further, the ratio of the weight of water to the weight of silica hydrogel in the finely pulverized slurry obtained by the same measurement method as in Example 1 was 3.5 times the weight.
[0153]
(Drying process)
Next, the slurry was supplied at a slurry supply rate of 13 ml / min and a spraying pressure of 1.2 kg / cm using a small-sized spray dryer (GA32 type manufactured by Yamato Kagaku Co., Ltd.) while maintaining its concentration. ² (G) Spray drying was performed at a hot air temperature of 200 ° C. to obtain fine dry silica gel particles. The average particle size of the obtained dried particles by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 9.8 μm, the particle shape was almost spherical, and the particle surface was smooth.
[0154]
Example 8
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a sulfuric acid concentration = 20.0% by weight are introduced into a container equipped with a discharge port through a separate inlet, and instantaneously The flow rate of the two liquids is adjusted so that the pH of the liquid discharged from the discharge port into the air becomes 7.5 to 8.0, and the uniformly mixed silica sol solution is continuously supplied from the discharge port. To the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. Place a ripening tank filled with water at the dropping point, drop it here and let it mature. After aging, the pH was adjusted to 6 and further 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 ₂ The weight ratio of water to weight was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 100 ppm.
[0155]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle size of 0.2 mm using a roll crusher. Into a 50 liter autoclave equipped with an anchor type stirring blade, 22,000 g of the above coarsely pulverized silica hydrogel and 18,000 g of water were charged to form a slurry, and an aqueous sodium hydroxide solution was added to adjust the pH to 10. Adjusted SiO ₂ A hydrothermal pulverization treatment was performed on a silica hydrogel slurry having a concentration of 10.0% by weight at a temperature of 210C for 24 hours at a stirring rotation speed of 120 rpm. The pH of the silica hydrogel slurry was 10.
[0156]
The silica hydrogel particles in the slurry after the hydrothermal pulverization treatment were refined, and the average particle size was 6 μm in the particle size measurement with a Coulter counter (MAII type, manufactured by Coulter Electronics, using an aperture tube diameter of 280 μm). SiO in the slurry after hydrothermal treatment ₂ The concentration was 10.3% by weight.
[0157]
The ratio of the weight of water to the weight of silica hydrogel in the slurry after hydrothermal pulverization obtained by the same measurement method as in Example 1 was 1.6 times the weight.
[0158]
(Drying process)
Next, the slurry was spray-dried at a slurry supply rate of 80 ml / min and a hot air temperature of 200 C using a spray dryer (diameter: 1.5 m, spraying part is a high-speed rotating disk system) with the concentration being kept.
[0159]
The obtained dried particles had an average particle size of 52 μm and a spherical shape by a Coulter counter (MAII type, aperture tube diameter 280 μm used).
[0160]
Example 9
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a sulfuric acid concentration = 20.0% by weight are introduced into a container equipped with a discharge port through a separate inlet, and instantaneously The flow rate of the two liquids is adjusted so that the pH of the liquid discharged from the discharge port into the air becomes 7.5 to 8.0, and the uniformly mixed silica sol solution is continuously supplied from the discharge port. To the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. Place a ripening tank filled with water at the dropping point, drop it here and let it mature. After aging, the pH was adjusted to 6 and further 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 ₂ The weight ratio of water to weight was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 101 ppm.
[0161]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle size of 1.0 mm using a roll crusher. An autoclave with an internal volume of 50 liters equipped with an anchor type stirring blade is charged with 22,000 g of the above-ground silica hydrogel and 18,000 g of water, and SiO 2 ₂ Hydrothermal pulverization was performed in a slurry state having a concentration of 10.0% by weight at a temperature of 200 ° C. for 3 hours at a stirring rotation speed of 90 rpm. The pH of the silica hydrogel slurry was 6.
[0162]
The silica hydrogel particles in the slurry after the hydrothermal treatment were refined, and the average particle size was 17 μm as measured by a Coulter Counter (MAII type, manufactured by Coulter Electronics, using an aperture tube diameter of 280 μm). In addition, SiO in the slurry after hydrothermal treatment ₂ The concentration was 10.2% by weight.
[0163]
(Wet grinding process)
The slurry was wet crushed using the same wet pulverizer as in Example 1 while maintaining the concentration. The average particle size of the silica hydrogel particles in the slurry after pulverization was 1.6 μm using a Coulter counter (MAII type, aperture tube diameter of 50 μm used).
[0164]
(Mixed slurry process)
To 17,000 g of the silica hydrogel slurry after wet pulverization, 200 g of titanium oxide (product name: TTO-51A, average particle size: 0.02 μm, rutile type) manufactured by Ishihara Sangyo Co., Ltd., zinc oxide manufactured by Sumitomo Osaka Cement Co., Ltd. (Product name: ZnO-310, average particle size: 0.03 μm) After adding 600 g and adjusting the pH of the slurry to 10, using the same wet pulverizer as above, silica hydrogel, titanium oxide, and zinc oxide were added. , Mixed and dispersed.
[0165]
(Drying process)
Using a small spray dryer (GA32 type manufactured by Yamato Kagaku Co., Ltd.) with the concentration of the dispersed slurry, the slurry supply rate is 13 ml / min, and the spray pressure is 1.2 kg / cm ² (G) Spray drying was performed at a hot air temperature of 200 ° 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 spherical and the particle surface was smooth.
[0166]
The average particle size by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 5.6 μm.
[0167]
The result of analyzing the chemical composition of the particles is SiO 2 ₂ 68.2% by weight, TiO ₂ They were 7.9 wt% and ZnO 23.9 wt%.
[0168]
(Measurement of spectral transmittance)
A paste obtained by adding 1.12 g of petroleum jelly and 0.48 g of liquid paraffin to 0.4 g of the fine spherical particles and dispersing well using three rolls is sandwiched between two 2 mm thick quartz plates, The film was spread until the thickness reached 25 μm, and the spectral transmittance was measured using a self-recording spectrophotometer.
[0169]
400 nm or more is a visible light region, and 400 to 280 nm is an ultraviolet light region. The smaller the transmittance in the ultraviolet light region, the better the ultraviolet shielding effect, and the larger the transmittance in the visible light region, the higher the transparency observed with the naked eye.
[0170]
The transmittance was 81.3% at 500 nm, 69.4% at 400 nm, 21.2% at 360 nm, 18.0% at 320 nm, and 17.6% at 290 nm.
[0171]
A scanning electron micrograph of the dried silica gel particles enclosing the metal oxide fine particles is shown in FIG.
[0172]
Example 10
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a sulfuric acid concentration = 20.0% by weight are introduced into a container equipped with a discharge port through a separate inlet, and instantaneously The flow rate of the two liquids is adjusted so that the pH of the liquid discharged from the discharge port into the air becomes 7.5 to 8.0, and the uniformly mixed silica sol solution is continuously supplied from the discharge port. To the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. Place a ripening tank filled with water at the dropping point, drop it here and let it mature. After aging, the pH was adjusted to 6 and further 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 ₂ The weight ratio of water to weight was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 97 ppm.
[0173]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle size of 1.0 mm using a roll crusher. An autoclave with an internal volume of 50 liters equipped with an anchor type stirring blade is charged with 22,000 g of the above-ground silica hydrogel and 18,000 g of water, and SiO 2 ₂ Hydrothermal pulverization was performed in a slurry state having a concentration of 10.0% by weight at a temperature of 200 ° C. for 3 hours at a stirring rotation speed of 90 rpm. The pH of the silica hydrogel slurry was 6.
[0174]
The silica hydrogel particles in the slurry after the hydrothermal treatment were refined and measured with a Coulter counter (MAII type, manufactured by Coulter Electronics, using an aperture tube diameter of 280 μm), and the average particle diameter was 15 μm. In addition, SiO in the slurry after hydrothermal treatment ₂ The concentration was 10.3% by weight.
[0175]
(Wet grinding process)
The slurry was wet crushed using the same wet pulverizer as in Example 1 while maintaining the concentration. The silica hydrogel particles in the finely pulverized slurry had an average particle size of 1.4 μm using a Coulter counter (MAII type, aperture tube diameter of 50 μm used).
[0176]
(Mixed slurry process)
915 g of titanium oxide (product name: TTO-51A, average particle size: 0.02 μm, rutile type) manufactured by Ishihara Sangyo Co., Ltd. was added to 17,000 g of the silica hydrogel slurry after the wet pulverization, and the same wet pulverizer as above was used. Two silica hydrogels and titanium oxide were mixed and dispersed.
[0177]
(Drying process)
Using a small spray dryer (GA32 type manufactured by Yamato Kagaku Co., Ltd.) with the concentration of the dispersed slurry, the slurry supply amount is 13 ml / min, and the spraying pressure is 1.2 kg / cm. ² (G) Spray drying was performed at a hot air temperature of 200 ° 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 spherical and the particle surface was smooth.
[0178]
The average particle size by a Coulter counter (MAII type, using an aperture tube diameter of 50 μm) was 5.2 μm.
The analysis result of the chemical composition of the particles is SiO 2 ₂ 64.8% by weight, TiO ₂ It was 35.2% by weight.
[0179]
(Measurement of spectral transmittance)
A paste obtained by adding 1.12 g of petroleum jelly and 0.48 g of liquid paraffin to 0.4 g of the fine spherical particles and dispersing well using three rolls is sandwiched between two 2 mm thick quartz plates, The film was spread until the thickness reached 25 μm, and the spectral transmittance was measured using a self-recording spectrophotometer.
[0180]
The transmittance was 56.3% at 500 nm, the transmittance was 41.9% at 400 nm, the transmittance was 13.0% at 360 nm, the transmittance was 7.5% at 320 nm, and the transmittance was 7.8% at 290 nm.
A scanning electron micrograph of the dried silica gel particles enclosing the metal oxide fine particles is shown in FIG.
[0181]
Example 11
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a sulfuric acid concentration = 20.0% by weight were introduced into a container equipped with a discharge port through a separate inlet, and instantly The flow rate of the two liquids is adjusted so that the pH of the liquid discharged from the discharge port into the air is 7.5 to 8.0, and the uniformly mixed silica sol solution is discharged from the discharge port. Discharge continuously into the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. Place a ripening tank filled with water at the dropping point, drop it here and let it mature. After aging, the pH was adjusted to 6 and further 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 ₂ The weight ratio of water to weight was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 108 ppm.
[0182]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle size of 1.0 mm using a roll crusher. An autoclave with an internal volume of 50 liters equipped with an anchor type stirring blade is charged with 22,000 g of the above-ground silica hydrogel and 18,000 g of water, and SiO 2 ₂ Hydrothermal pulverization was performed in a slurry state having a concentration of 10.0% by weight at a temperature of 200 ° C. for 4 hours at a stirring rotation speed of 90 rpm. The pH of the silica hydrogel slurry was 6.
[0183]
The silica hydrogel particles in the slurry after the hydrothermal treatment were refined and measured with a Coulter counter (MAII type, manufactured by Coulter Electronics, using an aperture tube diameter of 280 μm), and the average particle diameter was 15 μm. In addition, SiO in the slurry after the hydrothermal pulverization treatment ₂ The concentration was 10.3% by weight.
[0184]
(Wet grinding process)
The slurry was wet crushed using the same wet pulverizer as in Example 1 while maintaining the concentration. The average particle size of the silica hydrogel particles in the slurry after pulverization was 1.6 μm using a Coulter counter (MAII type, aperture tube diameter of 50 μm used).
[0185]
(Mixed slurry process)
915 g of anatase-type titanium oxide having an average particle size of 0.02 μm is added to 17,000 g of the silica hydrogel slurry after the wet pulverization, and the silica hydrogel and titanium oxide are mixed using the same wet pulverizer as described above.・ Dispersed.
[0186]
(Drying process)
Using a small spray dryer (GA32 type manufactured by Yamato Kagaku Co., Ltd.) with the concentration of the dispersed slurry, the slurry supply amount is 13 ml / min, and the spraying pressure is 1.2 kg / cm. ² (G) Spray drying was performed at a hot air temperature of 200 ° 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 spherical and the particle surface was smooth.
[0187]
The average particle diameter by a Coulter counter (using an aperture tube diameter of 50 μm) was 4.5 μm.
The result of analyzing the chemical composition of the particles is SiO 2 ₂ 65.1% by weight, TiO ₂ It was 34.9% by weight.
[0188]
[Reference Example 1]
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a sulfuric acid concentration = 20.0% by weight were introduced into a container equipped with a discharge port through a separate inlet, and instantly The flow rate ratio of the two liquids is adjusted so that the pH of the liquid discharged from the discharge port into the air is 7.5 to 8.0, and the uniformly mixed silica sol solution is discharged from the discharge port. Discharge continuously into the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. Place a ripening tank filled with water at the dropping point, drop it here and let it mature. After aging, the pH was adjusted to 6 and washed thoroughly 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 ₂ The weight ratio of water to the weight was 4.0 times by weight, and the residual sodium in the silica hydrogel particles was 100 ppm.
[0189]
Next, the silica hydrogel particles are evaporated in a dryer at 50 ° C. to evaporate the water in the silica hydrogel particles, and the SiO2 in the silica hydrogel particles is evaporated. ₂ Silica hydrogel particles having a weight ratio of water to weight of 1.3 times by weight were obtained. The shape of the obtained silica hydrogel particles was spherical.
[0190]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle size of 1.0 mm using a roll crusher. To the autoclave having an internal volume of 50 liters equipped with an anchor type stirring blade, 12,000 g of the above coarsely pulverized silica hydrogel and 38,000 g of water were added, and SiO 2 ₂ Hydrothermal treatment was performed in a slurry state having a concentration of 10.4% by weight at a temperature of 200 ° C. for 24 hours and at a stirring rotation speed of 90 rpm. The pH of the silica hydrogel slurry was 6.
[0191]
Silica hydrogel particles in the slurry after hydrothermal treatment are SiO ₂ Since the weight ratio of water to weight was too low, it was hardly refined, and when the slurry was passed through a 210 μm wire mesh, most of the particles remained without passing through the wire mesh.
[0192]
[Reference Example 2]
(Hydrogelation process)
SiO ₂ / Na ₂ O = 3.0 (molar ratio), SiO ₂ An aqueous solution of sodium silicate having a concentration = 21.0% by weight of 2.0 l / min and an aqueous solution of sulfuric acid having a sulfuric acid concentration = 20.0% by weight were introduced into a container equipped with a discharge port through a separate inlet, and instantly The two liquids are adjusted so that the pH of the liquid discharged from the discharge port into the air is 7.5 to 8.0, and the uniformly mixed silica sol solution is discharged from the discharge port. Continuously released into the air. The discharged liquid becomes spherical droplets in the air and gels in the air while staying in a parabola for about 1 second. Place a ripening tank filled with water at the dropping point, drop it here and let it mature. After aging, the pH was adjusted to 6 and further 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 ₂ The weight ratio of water to the weight was 4.5 times by weight, and the residual sodium in the silica hydrogel particles was 105 ppm.
[0193]
(Hydrothermal pulverization process)
Next, the silica hydrogel was coarsely pulverized to a mean particle size of 1.0 mm using a roll crusher. To the autoclave having an internal volume of 50 liters equipped with an anchor type stirring blade, 22,000 g of the above coarsely pulverized silica hydrogel and 18,000 g of water were added, and SiO 2 ₂ Hydrothermal treatment was performed in a slurry state having a concentration of 10.0% by weight at a temperature of 120 ° C. for 24 hours at a stirring rotation speed of 90 rpm. The pH of the silica hydrogel slurry was 6.
[0194]
The silica hydrogel particles in the slurry after the hydrothermal treatment are hardly refined because the temperature of the hydrothermal treatment is not sufficiently high. When the slurry is passed through a 210 μm wire mesh, most of the particles do not pass through the wire mesh. It has remained.
[0195]
【The invention's effect】
According to the present invention, there is provided a production method in which fine particles of silica gel can be obtained with high productivity by hydrothermally pulverizing silica hydrogel and drying it by means such as spray drying.
[0196]
Moreover, according to this invention, the novel manufacturing method of the microparticulate silica gel which encloses the metal compound fine particle which does not use a solvent in a particle | grain is provided.
[Brief description of the drawings]
FIG. 1 is a scanning electron micrograph showing the surface structure of dry silica gel particles.
FIG. 2 is a scanning electron micrograph showing the surface structure of dry silica gel particles.
FIG. 3 is a scanning electron micrograph showing the surface structure of dry silica gel particles.
FIG. 4 is a scanning electron micrograph showing the surface structure of dry silica gel particles enclosing metal oxide fine particles.
FIG. 5 is a scanning electron micrograph showing the surface structure of dry silica gel particles enclosing metal oxide fine particles.

Claims (12)

In the method for producing a microparticulate silica gel, (1) a silica hydrogel in which 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 1.5 to 5.0 times by weight. (2) The obtained silica hydrogel is hydrothermally treated with stirring in a slurry state having a SiO ₂ concentration of 5.0 to 15.0% by weight to obtain a refined silica hydrogel slurry having an average particle size of 100 μm or less. And a hydrothermal pulverization step, and (3) a drying step of drying the refined hydrogel slurry.  The process according to claim 1, wherein a silica hydrogel having an average particle size of 0.1 mm or more is obtained in the hydrogelation step, and this is made into a silica hydrogel slurry refined to an average particle size of 20 µm or less in the hydrothermal pulverization step.  The production method according to claim 2, wherein a silica hydrogel having an average particle diameter of 0.5 mm or more is formed in the hydrogelation step.  The production method according to any one of claims 1 to 3, comprising a step of washing the silica hydrogel obtained in the hydrogelation step with water before performing the hydrothermal pulverization step.  The manufacturing method in any one of Claims 1-4 which performs a drying process with an airflow dryer, a spray dryer, or a medium fluidized bed dryer. In the particles, titanium oxide, titanium peroxide, zinc oxide, cerium oxide, ferrous oxide, ferric oxide, zirconium oxide, chromium oxide, aluminum oxide, magnesium oxide, silver oxide, cuprous oxide, second oxide Copper, Cobalt oxide, Cobalt tetroxide, Cobalt oxide, Nickel oxide, Nickel oxide, Thorium oxide, Tungsten oxide, Molybdenum oxide, Manganese dioxide, Manganese trioxide, Uranium oxide, Thorium oxide, Oxidation Microscopically encapsulating fine metal compound fine particles selected from the group consisting of germanium, stannous oxide, stannic oxide, lead monoxide, lead trioxide, lead dioxide, antimony trioxide, antimony pentoxide and bismuth trioxide. a method for producing a particulate silica, (1) reacting an alkali metal silicate and a mineral acid, relative to the weight of SiO ₂ The ratio of the weight, hydrogel step of obtaining the silica hydrogel is from 1.5 to 5.0 times by weight, and (2) obtained silica hydrogel, SiO ₂ concentration of 5.0 to 15.0 wt% Along with the preparation process of a refined silica hydrogel slurry consisting of a hydrothermal pulverization process that is hydrothermally treated with stirring in a slurry state to obtain a refined silica hydrogel slurry having an average particle size of 100 μm or less, (3) In the refined silica hydrogel slurry It has a mixed slurry to obtain a mixed slurry of silica hydrogel particles and metal compound particles by introducing the metal compound fine particles, further, above which comprises carrying out the drying step of drying (4) the mixed slurry A method for producing a fine particulate silica gel containing fine metal compound fine particles.  The process according to claim 6, wherein a silica hydrogel having an average particle size of 0.1 mm or more is obtained in the hydrogelation step, and this is made into a silica hydrogel slurry refined to an average particle size of 20 µm or less in the hydrothermal pulverization step.  The production method according to claim 7, wherein the hydrogelation step is carried out to obtain a silica hydrogel having an average particle size of 0.5 mm or more.  The production method according to any one of claims 6 to 8, comprising a step of washing the silica hydrogel obtained in the hydrogelation step with water before performing the hydrothermal pulverization step.  The manufacturing method in any one of Claims 6-9 which performs a drying process with an airflow dryer, a spray dryer, or a medium fluidized bed dryer. In the mixed slurry, the production method according to any one of claims 6-10 ratio SiO ₂ by weight of the weight of the silica hydrogel of the metal compound fine particles is 5 to 80 wt%.  The method according to any one of claims 6 to 11, 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.

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