JPH08208213A - Production of aqueous dispersion of flocculated large-sized silica particle - Google Patents

Abstract

PURPOSE: To obtain flocculated large-sized silica particles by incorporating an aqueous dispersion composed of an aqueous medium and noncrystalline silica particles with hydrosilicofluoric acid or a slat thereof and an alkali enough to form silica to effect conducting a reaction. CONSTITUTION: First, an aqueous dispersion of silica particles is prepared by dispersing under agitation 0.5-30 pts.wt., in terms of SiO2 , of noncrystalline silica particles each 5-1000nm in average diameter in 100 pts.wt. of an aqueous medium such as water. Secondly, the aqueous dispersion is heated to about 40-100 deg.C and then incorporated, under agitation, with such an amount of hydrosilicofluoric acid or a salt thereof as to form 0.05-25wt.% of free fluorine ions based on the SiO2 content of the noncrystalline silica particles and such an amount of an aqueous alkali solution such as NH4 OH as to be enough to maintain 0.5-25 pts.wt. of the whole SiO2 based on 100 pts.wt. of the aqueous medium, to effect conducting a reaction to produce an aqueous dispersion of flocculated large-sized silica particles. Subsequently, the aqueous dispersion is filtered, and the flocculated large-sized silica particles are filtered off and washed with water and dried, thus obtaining the objective flocculated large-sized silica particles each having 0.1-10μm diameter determined by centrifugal sedimentation method.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing an aqueous dispersion of large agglomerated silica particles having a particle size of 0.1 to 10 microns as measured by the centrifugal sedimentation method. The powder particles obtained by drying the aqueous dispersion of the large particles of the aggregated silica have a porous property, and particularly, the ink absorbent,
It is useful as a catalyst carrier.

[0002]

2. Description of the Related Art US Pat. No. 2,680,721 discloses that a sol of amorphous silica having a dense structure and a spherical shape is bonded between these spherical silica particles when contaminated with a small amount of an electrolyte or a polyvalent metal salt. Occurs and aggregated silica particles are formed in the sol, and when the aggregated silica particle-containing sol contains ionic silica or fine silica, heating of the sol causes the formation of silica on the aggregated silica particles. Although it is explained that the growth of the aggregated silica particles occurs by deposition, it is explained that the non-aggregated spherical silica sol is more useful than the sol composed of such aggregated silica particles.

Japanese Unexamined Patent Publication (Kokai) No. 1-317115 discloses that 5 to 40 nm
An elongated shaped amorphous silica sol having a uniform thickness extension of and a particle size of 40-500 nm as measured by dynamic light scattering is shown. This publication discloses a method for producing such a sol in which a SiO ₂ concentration of 0.5 to 25% by weight and a 1
Silica aqueous sol having pH of -5 and silica particle size of 3-30 nm, water-soluble Ca salt, Mg salt, etc. against SiO ₂ of sol
After adding 0.15 to 1.00 wt% as CaO or MgO, alkali metal hydroxides, water-soluble organic bases, water-soluble silicates, etc. are added to the SiO ₂ / M when the alkali is represented by M ₂ O.
₂ O molar ratio of 20 to 300, and 60 to 30
Disclosed is a method comprising heating at 0 ° C. for 0.5-40 hours.

Japanese Unexamined Patent Publication (Kokai) No. 4-214022 discloses 7 to 100 nm.
Thickness and 10 to 150 times this thickness, but 100 to 1000 nm
Flat-shaped silica sols with planar particle sizes in the range of are shown. Further, this publication discloses a method for producing such a sol by adding a basic Al to an aqueous sol of negatively charged silica of 7 to 30 nm having a SiO ₂ concentration of 2 to 50% by weight and a pH of ₂ to 5.
Salt, basic Zr salt, etc. are added, and alkali is further added to convert it into an aqueous sol of positively charged silica, and then the aqueous sol of negatively charged silica is added to this aqueous sol of positively charged silica, and an alkali is further added to make it negative. Disclosed is a method for producing a charged silica by repeating the conversion into an aqueous sol of a charged silica while controlling the amounts of these basic Al salt and basic Zr salt and the amount of an aqueous sol of negatively charged silica added.

JP-A-3-215312 discloses that precipitated silica particles having a size of several μ to several tens of μ can be obtained by reacting hydrosilicofluoric acid or its salt with an alkali in an aqueous medium. As for the formation of these precipitated particles, initially colloidal silica (primary particles) having a size of several nm to several tens of nm is generated, and then the colloidal silica is bonded to form a size of about 150 to 600 nm. It explains the mechanism that aggregated silica particles (secondary particles) that it has are formed, and that the aggregated silica particles combine to form the ultimate precipitated particles having a size of several μ to several tens of μ. The publication further provides a colloidal silica sol having a size of 150 to 700 nm measured by a centrifugal sedimentation method by wet pulverizing the precipitated silica particles having a size of several μ to several tens of μ. Is disclosed.

Japanese Unexamined Patent Publication (Kokai) No. 5-301707 discloses that an amount of ore that gives a neutralization rate of 20 to 40% while adding salts such as Glauber's salt to an aqueous solution of alkali silicate having a SiO ₂ concentration of 7 to 10% by weight. Acid is added at 10-45 ° C, the resulting liquid is aged at its boiling point-95 ° C, and then mineral acid is added to this liquid to form a solution.
By adjusting the pH to 5 or less, 1 to 500 μ formed by aggregation of primary particles having a size of 8 to 50 nm
A method for producing hydrous silicic acid (SiO ₂ .nH ₂ O) having a size of 1 is disclosed. And this hydrous silicic acid is 100 ~ 30
Pore having a specific surface area of 0 m ² / g, pores having a pore radius of 50000 angstroms or less to an integrated volume of 1.9 to 4.0 ml / g, and 0.5 ml of pores having a pore radius of 3000 to 40 000 angstrom. / g or more, and 100 ~
0.6 m pores with a 1000 angstrom pore radius
It has been shown that it has a structure that it has a cumulative volume of l / g or more and that it is used as a filling amount for paper.

[0007]

Problems to be Solved by the Invention US Patent No. 268
No. 0721 teaches agglomeration of spherical colloidal silica particles by a sol-contaminating amount of electrolytes or polyvalent metal salts and growth of these agglomerated silica particles by ionic silica or fine silica in the sol. It does not disclose a preferred method for producing a sol or dispersion of agglomerated silica particles.

The sol of elongated silica particles described in Japanese Patent Laid-Open No. 1-317115 does not contain free Ca ions, Mg ions, etc. in the medium, and the elongated silica particles produced do not contain these impurities as impurities. Contained as. The above-mentioned JP
The silica particles having a flat shape described in JP-A-4-214022 are also particles containing Al and Zr as impurities.

The number μ described in the above-mentioned JP-A-3-215312
~ The ultimate precipitated silica particles with a size of several tens of μ, colloidal silica particles with a size of 150-700 nm obtained by wet pulverizing these have high purity, but the primary particles are densely aggregated. An aqueous slurry of these ultimate particles, a sol obtained by wet pulverization, or the like having the above structure does not give a powder exhibiting high ink absorbability when they are dried.

The silica particles described in JP-A-5-301707 are particles of hydrous silicic acid which are porous but are represented by SiO ₂ .nH ₂ O. The present invention provides an aqueous dispersion of stable, agglomerated silica large particles having high purity, a sparse agglomerated structure, and a particle size of 0.1-10 microns as measured by centrifugal sedimentation.
The present invention is intended to provide a method for manufacturing easily and efficiently.

[0011]

Means for Solving the Problems A method for producing an aqueous dispersion of large particles of agglomerated silica having a particle size of 0.1 to 10 microns measured by the centrifugal sedimentation method of the present invention comprises 100 parts by weight of an aqueous medium and SiO ₂ As an aqueous dispersion of the silica particles comprising 0.5 to 30 parts by weight of amorphous silica particles having an average particle diameter of 5 to 1000 nm, 0.05 to 25 parts by weight based on the SiO ₂ content of the amorphous silica particles. Forming an aqueous dispersion of agglomerated silica particles consisting of an interparticle bond of the amorphous silica particles by supplying a free amount of free fluorine ions, and an aqueous medium thereof in an aqueous dispersion of the agglomerated silica particles. 0.5 to 25 parts by weight per 100 parts by weight of the total SiO ₂ content is maintained, and an amount sufficient to generate silica from hydrofluoric acid or a salt thereof and the hydrofluoric acid or a salt thereof. The alkalinity of the produced water Comprising reacting in the body.

The particle size of the large particles of agglomerated silica can be easily measured by the centrifugal sedimentation method by using a commercially available measuring device such as a centrifugal sedimentation type particle size distribution measuring device manufactured by Shimadzu Corporation. . Amorphous silica particles having an average particle size of 5 to 1000 nm are particles formed by dense build-up of silica, and their shape and particle size can be easily observed by an electron micrograph. The amorphous silica particles can be easily produced as an alkaline or acidic silica aqueous sol by a known method, or can be obtained as a commercial product.

Spherical amorphous silica alkaline aqueous sols having an average particle size of 100 nm or less can be prepared, for example, by the method described in US Pat. No. 3,440,174, and have an average particle size of 100 nm or more. Spherical amorphous silica alkaline sol having a particle size is described in, for example, US Pat.
It can be produced by the method described in the specification of 3538015. An acidic aqueous sol can be produced by decationizing these alkaline aqueous sols with a cation exchange resin and, if desired, further performing deanionization with an anion exchange resin.

100 parts by weight of an aqueous medium and 0.5 as SiO _2.
As an aqueous dispersion of the silica particles consisting of ˜30 parts by weight of amorphous silica particles having an average particle size of 5 to 1000 nm, an aqueous sol of amorphous silica of the above size containing water in the above ratio. May be used as it is, or may be obtained by mixing water and an aqueous sol of the above amorphous silica so as to give the above ratio. Preferably,
An aqueous sol of the above amorphous silica having a ratio of 1 to 25 parts by weight as SiO ₂ to 100 parts by weight of the aqueous medium is used.

The free fluorine ion is a water-soluble fluoride, preferably ammonium fluoride, sodium fluoride, potassium fluoride, a water-soluble amine hydrofluoride, a water-soluble quaternary ammonium fluoride or the like. Can be supplied as a salt. The supply of free fluorine ions can be carried out, for example, by adding the water-soluble fluoride to the aqueous dispersion of the amorphous silica particles, or in the aqueous dispersion of the amorphous silica particles. It may be generated.

As a method for generating free fluorine ions in the aqueous dispersion of the above-mentioned amorphous silica particles, for example, water-soluble hydrofluoric acid or a salt thereof, a water-soluble base, and the above-mentioned amorphous material can be used. A method of causing a reaction to form silica and water-soluble fluoride in the aqueous dispersion of amorphous silica particles by mixing with the aqueous dispersion of silica particles can be mentioned.

The reaction of hydrosilicofluoric acid with ammonium hydroxide as a representative of the base is represented by the following formula (1) H ₂ SiF ₆ +6 NH ₄ OH → SiO ₂ +6 NH ₄ F +4 H ₂ O ... ... represented by (1), and the reaction of ammonium silicofluoride as a representative of hydrofluoric acid salt with ammonium hydroxide as a representative of base is represented by the following (2) formula (NH ₄ ) ₂ SiF ₆ +4 NH ₄ OH → SiO ₂ + 6 NH ₄ F + 2 H ₂ O ・ ・ ・ (2) In the above formula (1) and the above formula (2)
A chemical formula in which NH ₄ OH is replaced with another base described above can be easily described by a person skilled in the art.

Preferred water-soluble bases include water-soluble amines such as ammonium hydroxide, sodium hydroxide, potassium hydroxide, monoethanolamine and diethanolamine, and water-soluble amines such as dimethyldiethanolammonium hydroxide and diethyldiethanolammonium hydroxide. Quaternary ammonium hydroxide and the like. Preferred water-soluble hydrofluoric acid salts are salts of water-soluble bases and hydrosilicofluoric acid as described above, for example, ammonium silicofluoride, sodium silicofluoride, potassium silicofluoride, silicofluoride. Examples thereof include monoethanolamine and dimethyldiethanol ammonium silicofluoride, with ammonium silicofluoride being particularly preferred.

The hydrosilicofluoric acid or its salt added to the aqueous dispersion of the amorphous silica particles is preferably an aqueous solution of 0.5 to 30% by weight, and the water-soluble hydrofluoric acid added to this aqueous dispersion. The base is preferably an aqueous solution of 2 to 20% by weight. In the aqueous dispersion of the amorphous silica particles, an amount of 0.05 to 25% by weight with respect to the SiO ₂ content of the silica, preferably,
By supplying 0.1 to 20% by weight of the above free fluorine ion, agglomerated silica particles composed of an interparticle bond of the above amorphous silica particles are produced, and an aqueous dispersion of the agglomerated silica particles is formed. The pH and temperature of the liquid are not particularly limited, but the pH is 7.0 to 11.5 and the freezing point of the liquid is 100 ° C or less, particularly
Temperatures of 40-100 ° C are preferred.

Large aggregated silica particles are prepared by mixing an aqueous dispersion of the produced aggregated silica particles, a water-soluble hydrosilicofluoric acid or a salt thereof, and a water-soluble base, and mixing these water-soluble silica particles. An aqueous solution of agglomerated silica large particles produced by reacting hydrofluoric acid or its salt with a water-soluble base in this aqueous dispersion, which has a particle size of 0.1-10 microns as measured by centrifugal sedimentation. A dispersion is obtained. This reaction is also represented by the above formula (1) or (2), and is above the freezing point of the liquid mixture and below 100 ° C, especially at a temperature of 40 to 100 ° C, and after this reaction, the liquid mixture has a pH of 7.0 to 11.5. It is preferable to carry out as follows.

As the water-soluble hydrofluoric acid salt used for mixing the agglomerated silica particles with the aqueous dispersion, the hydrofluoric acid salts exemplified above are preferable, and the water-soluble hydrofluoric acid salt used for the mixing is used. The above-exemplified bases are also preferable as the base. The water-soluble hydrofluoric acid or salt thereof and the water-soluble base used for this mixing are 0.5 to 25 parts by weight, preferably 1 to 25 parts by weight, based on 100 parts by weight of the aqueous medium of the aqueous dispersion obtained by the above mixing. Used in an amount such that ˜20 parts by weight of total SiO ₂ content is maintained. As the total SiO ₂ content, the total amount of the SiO ₂ content derived from the amorphous silica particles having an average particle size of 5 to 1000 nm and the SiO ₂ content of silica produced by the above mixing is adopted. The amount of the water-soluble hydrofluoric acid or its salt and the water-soluble base to be used for this mixing is such that the SiO ₂ content of the amorphous silica particles having an average particle diameter of 5 to 1000 nm is ₂ As
The amount is preferably 0.03 to 5 times by weight, particularly 0.03 to 3 times by weight silica. The hydrofluoric acid or salt thereof to be subjected to this mixing is preferably used as an aqueous solution of 0.5 to 30% by weight, and the water-soluble base is preferably 2 to
Used as a 20% by weight aqueous solution.

The preparation of the aqueous dispersion of large aggregated silica particles according to the present invention can be carried out in various preferred embodiments.
For example, in the embodiment (1), 0.5 to 30% by weight of hydrosilicofluoric acid is added to an aqueous sol of amorphous silica having an average particle diameter of 5 to 1000 nm and having a SiO ₂ concentration of 0.5 to 23% by weight. Alternatively, a method of continuously supplying an aqueous solution of a salt thereof and an aqueous solution of 2 to 20% by weight, as an aspect (2), the above-mentioned 5 to 1000 n
Aqueous sol of amorphous silica having an average particle diameter of m is mixed with an aqueous solution of a base adjusted to the above concentration, and the aqueous sol of base-containing silica thus obtained is subjected to silicofluorination adjusted to the above concentration. As a method (3) of continuously supplying an aqueous solution of hydrous acid or a salt thereof, the above-mentioned concentration is adjusted to an aqueous sol of amorphous silica having an average particle diameter of 5 to 1000 nm. Examples include a method in which an aqueous solution of an acid or a salt thereof is mixed, and an aqueous solution of a base adjusted to the above concentration is continuously supplied to the silica aqueous sol containing hydrosilicofluoric acid or a salt obtained thereby. .

The production rate of this silica in an aqueous dispersion of agglomerated silica particles is about 0.5 to 5 g per hour per 1000 m ² of surface area of the above-mentioned amorphous silica particles having a particle diameter of 5 to 1000 nm used. The higher the temperature, the higher the rate of silica formation is allowed. The production rate of this silica can be controlled by adjusting the amount of hydrosilicofluoric acid or its salt which reacts every hour with a sufficient amount of base. For example, in the method of the above aspect (1), depending on the feed rate of the aqueous solution of hydrofluoric acid or its salt and the aqueous solution of the base,
In the method of the above aspect (2), the production rate of silica is controlled by the feed rate of the aqueous solution of hydrofluoric acid or a salt thereof, and in the method of the above aspect (3), by the feed rate of the aqueous solution of the base. It

When the particle size of the agglomerated silica large particles is about 0.1 to 0.4 micron, the aqueous dispersion has a form of silica aqueous sol, and when it is about 0.4 to 10 micron,
The aqueous dispersion has a mixed form of silica sol and slurry. The aqueous dispersion of the large particles of aggregated silica is purified by a conventional purification method, for example, an ultrafiltration method, an ion exchange method, etc. Etc. can be removed. Further, by filtering the aggregated silica large particles from the aqueous dispersion of the aggregated silica large particles, the wet cake of the obtained aggregated silica large particles is washed with water and then dispersed again in an aqueous medium to obtain a highly pure aggregated silica large particle. An aqueous dispersion of particles is obtained.

[0025]

[Operation] When an aqueous solution of ammonium silicofluoride and an aqueous solution of ammonium hydroxide are continuously supplied to a 2 wt% alkaline aqueous sol of colloidal silica having a particle diameter of about 20 nm, the aqueous solution is supplied from the middle of this supply. When the sol becomes cloudy, the cloudiness is further intensified when the supply is continued, and when the silica particles of the clouded sol are observed by an electron micrograph, colloidal silica particles having a particle size of about 20 nm are found. It was found to be large particles of agglomerated silica having a loosely agglomerated structure.
It was found to be different from the precipitated silica particles having a form in which fine silica particles described in Japanese Patent No. 312 have a dense aggregation. Further, the shape of the agglomerated silica large particles observed in this electron micrograph is different from the elongated shape described in JP-A-1-317115 or the flat shape described in JP-A-4-214022. ing. It was found that the large particles of agglomerated silica were composed of densely built-up amorphous silica particles having a particle diameter of 5 to 1000 nm.

Separately, in a 4% by weight aqueous sol of colloidal silica having a particle size of about 20 nm,
Even when 0.8% by weight of ammonium fluoride was added as its aqueous solution, cloudiness of the aqueous sol was observed, and if the ammonium silicofluoride aqueous solution and the ammonium hydroxide aqueous solution were continuously supplied to this cloudy aqueous sol as described above. In the same manner as above, large particles of agglomerated silica having a structure in which colloidal silica particles having a particle diameter of about 20 nm are sparsely agglomerated are generated,
It was also found that precipitated silica particles having a form in which fine silica particles described in JP-A No. 3-215312 are densely aggregated are not formed. However, the agglomerated silica particles formed by adding 0.8% by weight of ammonium fluoride to a 4% by weight aqueous sol of colloidal silica having a particle size of about 20 nm are unstable,
The particle shape is easily destroyed by strong stirring, strong alkali, etc.

Probably, the silica produced by the reaction of ammonium silicofluoride and ammonium hydroxide is silicic acid or its low degree of polymerization polymer immediately after its production, but this silicic acid or its low degree of polymerization polymer is uniquely polymerized. Then, without forming the nucleus particles of silica, the colloidal silica particles coexisting in the liquid are deposited to build up the colloidal silica particles, and the ammonium fluoride by-produced in the above reaction is accumulated in the liquid. Due to the aggregation of the colloidal silica particles and the further progress of the reaction between ammonium silicofluoride and ammonium hydroxide, the increased ammonium by-product further promotes the aggregation between the colloidal silica particles, between the aggregated silica particles or between these particles. And the resulting silicic acid or its low-polymerization degree polymer causes deposition on the aggregated silica particles. It is believed that agglomerated silica large particles which can maintain the shape stably generated. Then, based on further studies, a preferable method for producing large aggregated silica particles was completed.

An aqueous dispersion of amorphous silica particles having a particle size of 5 to 1000 nm used for producing aggregated silica particles by free fluoride ions is used in an amount of 30 parts by weight per 100 parts by weight of the aqueous medium. Aqueous dispersions of amorphous silica particles are prone to gelation when they have a high SiO ₂ concentration and, conversely, when they have a SiO ₂ concentration of less than 0.5 parts by weight, the aqueous dispersion of the large agglomerated silica particles obtained later. The silica concentration of the dispersion also becomes low, and the amount of water to be removed increases when the dispersion is dried for use or concentrated.

The amount of free fluorine ions supplied to an aqueous dispersion of amorphous silica particles having a SiO ₂ content of 0.5 to 30 parts by weight with respect to 100 parts by weight of an aqueous medium is the amount of the amorphous silica particles. A sufficient amount is required for agglomeration, and the larger the amount of this free fluorine ion, the easier the agglomeration of the above-mentioned amorphous silica particles, but the amount of 25% by weight or more relative to the SiO ₂ content of the amorphous silica particles. Then, the aqueous dispersion of amorphous silica particles is gelled and its viscosity is increased.

When the hydrosilicofluoric acid or its salt and the above base are reacted in the aqueous dispersion of aggregated silica particles, if the concentration of the total SiO ₂ content in the aqueous dispersion of aggregated silica particles is too high. The aqueous dispersion is prone to gelation during the reaction between the hydrofluoric acid or its salt and the above base. Based on 100 parts by weight of the aqueous medium in the aqueous dispersion of aggregated silica particles,
By maintaining the total SiO ₂ content in this aqueous dispersion at 25 parts by weight or less, such gelation can be avoided.
However, when the total SiO ₂ content is lower than 0.5 parts by weight with respect to 100 parts by weight of the aqueous medium in this aqueous dispersion, when the obtained aqueous dispersion of aggregated silica large particles is dried or concentrated as described above, The amount of water to be removed increases.

Amorphous silica particles having an SiO ₂ content of 5 to 1000 nm in the silica produced by the reaction of hydrosilicofluoric acid or a salt thereof with the above base in an aqueous dispersion of agglomerated silica particles. When the amount of SiO ₂ is more than 5 times by weight,
Other than when the rate of formation of this silica is low,
The silica particles in the form of densely agglomerated fine silica particles described in JP-A-3-215312 are easily generated. And to produce a large amount of silica at a low rate in this reaction,
The time required to complete the reaction is undesirably long. Rather, the amount of silica produced by this reaction is preferably as small as possible, as long as stable large aggregated silica particles are produced.

The reaction of hydrosilicofluoric acid or its salt with the above base is considered to proceed rapidly. When a large amount of hydrosilicofluoric acid or its salt and alkali are supplied in a short time to an aqueous dispersion of amorphous silica particles or agglomerated silica particles,
In this aqueous dispersion, a large amount of silicic acid or its low polymerization degree polymer is formed in a short time, and this large amount of silicic acid or its low polymerization degree polymer is not only deposited on these silica particles but also polymerized independently. To newly generate fine core particles of silica. The large amount of by-produced fluorine ions causes not only the agglomeration of the amorphous silica particles but also the agglomerates of the core particles of the produced silica, and thus the agglomerated silica large particles and the fine agglomerates of the silica particles are densely agglomerated silica. An aqueous dispersion is formed in which the particles are mixed. Since the silica particles in the form in which such fine core particles are densely aggregated are the same kind as the silica particles described in the above-mentioned JP-A-3-215312, such fine core particles are densely aggregated. In order to use in an application where the mixture of silica particles having a different shape is not preferable, an aqueous dispersion of large particles of agglomerated silica is produced by a method of suppressing the formation of silica particles having a shape in which such fine core particles are densely aggregated. It is desirable to do.
The method of the above aspect (1), the method of the aspect (2) and the method of the aspect (3) are all effective for avoiding the formation of silica particles in the form of dense aggregation of such fine core particles. is there. Furthermore, a method of carrying out the reaction of hydrosilicofluoric acid or a salt thereof with the above base at a temperature as high as possible so that the silicic acid or the low-polymerization degree polymer thereof is rapidly deposited on the amorphous silica particles or the agglomerated silica particles is It is effective in suppressing the formation of silica particles in a form in which such fine core particles are densely aggregated.

[0033]

EXAMPLES Aqueous hydrofluoric acid salt solutions (F ₁ ) for use in the examples and comparative examples, silica aqueous sol as an aqueous dispersion of amorphous silica particles having an average particle size of 5 to 1000 nm ( S
₁ ) to (S ₅ ) and aqueous alkaline solutions (A ₁ ) and (A ₂ ) were prepared as follows. (A) Hydrofluoric acid salt aqueous solution (F ₁ ): A 9.8% by weight aqueous hydrofluoric acid solution was prepared by diluting 40% by weight aqueous hydrofluoric acid solution with water. Separately, 28 wt% ammonia water was diluted with water to prepare 10 wt% ammonia water. This 9.8
A 10% by weight aqueous solution of ammonium silicofluoride was prepared by adding 114.8 parts by weight of this 10% by weight aqueous ammonia to 485.2 parts by weight of an aqueous solution of hydrofluoric acid by weight with stirring.

(B) Silica aqueous sol (S ₁ ): 40 wt% SiO ₂ concentration, 21 nm particle size and 2.5
A commercially available aqueous silica sol (trade name: Snowtex O-40, manufactured by Nissan Chemical Industries, Ltd.) having a pH of 3 was prepared. (S ₂ ): 40 wt% SiO ₂ concentration, 45 nm particle size and 9.6
A commercially available aqueous silica sol (trade name: Snowtex XL manufactured by Nissan Chemical Industries, Ltd.) having a pH of 3 was prepared.

(S ₃ ): A commercially available aqueous silica sol (trade name Snowtex YL manufactured by Nissan Chemical Industries, Ltd.) having a SiO ₂ concentration of 40% by weight, a particle size of 62 nm and a pH of 9.5 was prepared. (S ₄ ): SiO ₂ concentration of 40% by weight, particle size of 83 nm and 9.3
A commercially available aqueous silica sol (trade name: Snowtex ZL manufactured by Nissan Chemical Industries, Ltd.) having a pH of 3 was prepared.

(S ₅ ): An aqueous silica sol having a SiO ₂ concentration of 20% by weight, a particle size of 550 nm and a pH of 9.5 was prepared by the method described in US Pat. No. 3,538,015. (C) Alkaline aqueous solution (A ₁ ): 28% by weight of commercially available reagent, aqueous ammonia, was prepared. (A ₂ ): A 10% by weight aqueous sodium hydroxide solution was prepared by dissolving a commercially available reagent, sodium hydroxide, in water.

For the measurement of silica particles by the centrifugal sedimentation method,
Centrifugal sedimentation type particle size distribution analyzer SA- manufactured by Shimadzu Corporation
A CP3 model was used. Example 1 A polyethylene container having an internal volume of 5 liters was charged with 1842 g of pure water and 158 g of an alkaline aqueous solution (A ₁ ), and 200 g of silica was added to the container while stirring the liquid. Aqueous dispersion of amorphous silica particles containing 2.6 moles of NH ₄ OH by adding aqueous sol (S ₁ ) and containing 3.6 parts by weight of SiO ₂ for 100 parts by weight of water. Was prepared.

Next, while heating the aqueous dispersion of the amorphous silica particles to 65 ° C., the aqueous dispersion of the amorphous silica particles was stirred with stirring at 6 ° C.
00 g of ammonium silicofluoride aqueous solution (F ₁ ) is applied for 10 minutes per minute.
It was fed continuously at a rate of g. After starting this supply
At 20 minutes, the aqueous dispersion of the amorphous silica particles became cloudy. From the total amount of ammonium silicofluoride supplied up to this point, the amount of fluorine ions by-produced by the reaction of the above formula (2) was 16% by weight with respect to the amount of SiO _{2 of the} amorphous silica particles.
%, And 1.0% by weight for the aqueous medium in the aqueous dispersion.

After the completion of the supply of the total amount of the ammonium silicofluoride aqueous solution (F ₁ ) over 60 minutes, the stirring was continued for further 15 minutes. As a result, the pH was 8.91, the viscosity was 18 mPa · s at 20 ° C., and the viscosity was 3.6.
Aqueous slurry of crude silica with SiO ₂ concentration by weight.
2800 g were obtained. From the supplied amount of ammonium silicofluoride, the SiO ₂ amount of silica produced by the above formula (2) is calculated to be 0.25 times the SiO ₂ amount derived from the silica aqueous sol (S ₁ ).

The total amount of silica in the aqueous slurry of unpurified silica was filtered with Toyo Filter Paper No. 5C and washed with pure water to obtain 426 g of a wet cake of silica. To 426 g of this wet cake, 52 g of pure water was added and stirred.
SiO ₂ concentration of 0.5% by weight, viscosity of 20 mC at 15 mPa · s, and 9.
478 g of purified silica aqueous dispersion having a pH of 05 were obtained. The yield of silica is calculated to be 98% as SiO ₂ . The particle size of silica particles in this purified silica aqueous dispersion was measured by centrifugal sedimentation and found to be 4.09 microns.

The purified silica aqueous dispersion has a pH of 1
After adding an aqueous solution of sodium hydroxide so as to be 0.1 and stirring vigorously, the particle size of the silica particles was measured by the centrifugal sedimentation method to be 4.01 μm, and almost no change was observed. Example 2 A polyethylene container having an internal volume of 5 liters was charged with 780 g of pure water and 350 g of alkaline aqueous solution (A ₁ ), and 125 g of silica aqueous sol was added to the container while stirring the liquid. An aqueous dispersion of amorphous silica particles containing 5.8 mol of NH ₄ OH and 4.0 parts by weight of SiO ₂ for 100 parts by weight of water was prepared by adding (S ₁ ). did.

Then, while heating the aqueous dispersion of the amorphous silica particles to 65 ° C., the aqueous dispersion of the amorphous silica particles was stirred for 15 minutes.
00 g of ammonium silicofluoride aqueous solution (F ₁ ) is applied for 10 minutes per minute.
It was fed continuously at a rate of g. After 150 minutes was required to complete the supply of the total amount of the above ammonium silicofluoride aqueous solution (F ₁ ), stirring was continued for another 15 minutes. The pH was 8.23, 22 mPa
2755 g of an aqueous slurry of crude silica having a 20 ° C. viscosity of s ₂ and a SiO ₂ concentration of 3.6% by weight were obtained. From the amount of supplied ammonium silicofluoride, the amount of SiO _{2 of} silica produced by the above formula (2) is the amount of SiO ₂ derived from the silica aqueous sol (S ₁ ).
Calculated as 1.0 times.

513 g of a wet cake of silica was obtained by filtering off the total amount of silica in the aqueous slurry of unpurified silica with Toyo Filter Paper No. 5C and washing with pure water. When 43 g of pure water was added to the entire amount of the wet cake and stirred, a SiO ₂ concentration of 18.0 wt%, a viscosity of 20 mC at 18 mPa · s, and a p of 8.59 were obtained.
556 g of a purified silica aqueous dispersion with H were obtained. The particle size of silica particles in this purified silica aqueous dispersion was measured by centrifugal sedimentation and found to be 7.75 microns.

Example 3 In this example, an aqueous dispersion of amorphous silica particles was prepared.
2800 g of an aqueous slurry of unwashed silica was obtained in the same manner as in Example 1 except that the ammonium silicofluoride aqueous solution (F ₁ ) was supplied while the temperature was kept at ℃. This slurry has a pH of 8.99, 26 mPa
It had a 20 ° C. viscosity of s and a SiO ₂ concentration of 3.6% by weight.

Then, in the same manner as in Example 1, 476 g of a purified aqueous dispersion of silica was obtained. This purified silica aqueous dispersion had a SiO ₂ concentration of 20.0 wt%, a 20 ° C. viscosity of 20 mPa · s, a pH of 8.87, and a centrifugal precipitated silica particle size of 5.64 microns. Example 4 2403 g of pure water and 47 g of alkaline aqueous solution (A ₁ ) were put into a polyethylene container having an internal volume of 5 liters, and 150 g of silica aqueous sol was added to the container while stirring the liquid.
An aqueous dispersion of amorphous silica particles containing 0.8 mol of NH ₄ OH and 2.7 parts by weight of SiO ₂ for 100 parts by weight of water was prepared by adding (S ₁ ). did.

Then, while heating the aqueous dispersion of the amorphous silica particles at 65 ° C., the aqueous dispersion of
00 g of ammonium silicofluoride aqueous solution (F ₁ ) per minute 6.
It was fed continuously at a rate of 7 g. After the supply of the entire amount of the above ammonium silicofluoride aqueous solution (F ₁ ) was completed over 30 minutes,
When stirring was continued for another 15 minutes, the pH was 9.28, 9 mPa · s
2800 g of an aqueous slurry of unpurified silica having a viscosity of 20 ° C. and a SiO ₂ concentration of 1.8% by weight were obtained. From the amount of supplied ammonium silicofluoride, the SiO ₂ amount of silica produced by the above formula (2) is 0.11 of the SiO ₂ amount derived from the silica aqueous sol (S ₁ ).
Calculated as double.

Concentration and desalting were carried out using an ultrafiltration membrane while supplying pure water to this aqueous slurry of unpurified silica. As a result, the SiO ₂ concentration was 13.1% by weight and 8 mPa · s was 20 ° C. Purified silica aqueous dispersion having viscosity and pH of 8.91 503
g was obtained. The particle size of silica particles in this purified silica aqueous dispersion was measured by centrifugal sedimentation and found to be 0.62 micron.

Example 5 1127 g of pure water and 221 g of alkaline aqueous solution (A ₁ ) were put into a polyethylene container having an internal volume of 5 liters, and 624 g of silica was added to the container while stirring the liquid. Aqueous dispersion of amorphous silica particles containing 3.6 mol NH ₄ OH by adding aqueous sol (S ₂ ) and containing 12.7 parts by weight of SiO ₂ for 100 parts by weight of water. Was prepared.

Then, while heating the aqueous dispersion of the amorphous silica particles to 65 ° C., the aqueous dispersion of the amorphous silica particles is stirred under stirring.
8 g of ammonium silicofluoride solution (F ₁ ) 10.3 per minute
It was fed continuously at a rate of g. After the supply of the total amount of the above ammonium silicofluoride aqueous solution (F ₁ ) was completed over 80 minutes,
After stirring for another 15 minutes, the pH was 8.64, 28 mPas
2800 g of an aqueous slurry of unpurified silica having a viscosity of 20 ° C. and a SiO ₂ concentration of 10.0% by weight were obtained. From the amount of supplied ammonium silicofluoride, the SiO ₂ amount of silica produced by the above formula (2) is 0.11 of the SiO ₂ amount derived from the silica aqueous sol (S ₁ ).
Calculated as double.

The total amount of silica in this aqueous slurry of unpurified silica was filtered with Toyo Filter Paper No. 5C and washed with pure water to obtain 769 g of a wet cake of silica. To 769 g of this wet cake, 31 g of pure water was added and stirred.
SiO ₂ concentration by weight, 92 mPa · s 20 ° C. viscosity, and 8.62
800 g of purified silica aqueous dispersion having a pH of was obtained.
The particle diameter of the silica particles in this purified silica aqueous dispersion was measured by centrifugal sedimentation and found to be 4.11 microns.

Example 6 In this example, 2793 g of an aqueous slurry of unwashed silica was prepared in the same manner as in Example 1 except that silica aqueous sol (S ₄ ) was used as the aqueous dispersion of amorphous silica particles. Obtained. This slurry had a pH of 9.02, a viscosity of 6 mPas at 20 ° C, and 3.
It had a SiO ₂ concentration of 6% by weight.

Then, in the same manner as in Example 1, 333 g of a purified silica aqueous dispersion was obtained. The purified silica aqueous dispersion had a SiO ₂ concentration of 30.0 wt%, a 20 ° C. viscosity of 17 mPa · s, a pH of 8.24, and a centrifugal precipitated silica particle size of 0.32 micron. Example 7 To a polyethylene container having an internal volume of 5 liters, 790 g of pure water and 718 g of an alkaline aqueous solution (A ₁ ) were added, and 129 g of silica aqueous sol ( S by ₅₎ to introduce, contain 11.8 mol NH ₄ OH, and preparing an aqueous dispersion of amorphous silica particles containing SiO ₂ minutes 1.6 parts by weight per 100 parts by weight of water .

Then, while heating the aqueous dispersion of the amorphous silica particles to 65 ° C. with stirring, 1745 g of an ammonium fluoride aqueous solution (F ₁ ) was continuously added thereto at a rate of 1.2 g per minute. Supplied. After the completion of the supply of the entire amount of the above ammonium silicofluoride aqueous solution (F ₁ ) over 1440 minutes, stirring was continued for another 30 minutes. The pH was 7.59, the viscosity was 12 mPa · s at 20 ° C., and the concentration was 2.5% by weight. 3380 g of an aqueous slurry of crude silica with a SiO ₂ concentration of From the supplied amount of ammonium silicofluoride, the SiO ₂ amount of silica produced by the above formula (2) is calculated to be 2.28 times the SiO ₂ amount derived from the silica aqueous sol (S ₅ ). The total amount of silica in the aqueous slurry of unpurified silica was filtered with Toyo Filter Paper No. 5C and washed with pure water to obtain 168 g of a wet silica cake. 112 g of pure water was added to 168 g of this wet cake, and the mixture was stirred.
SiO ₂ concentration of wt.%, 20 ° C. viscosity of 13 mPa · s, and of 7.59
280 g of purified silica aqueous dispersion having a pH were obtained. The particle size of silica particles in this purified silica aqueous dispersion was measured by centrifugal sedimentation and found to be 7.68 microns.

Example 8 In a polyethylene container having an internal volume of 5 liters, 1591 g of pure water and 129 g of 40% by weight of hydrosilicofluoric acid aqueous solution were charged, and the liquid in the container was stirred. By adding 289 g of alkaline aqueous solution (A ₂ ) and 215 g of silica aqueous sol (S ₃ ) to this, 0.36 mol of sodium silicofluoride was contained, and 3.9 parts by weight to 100 parts by weight of water. An aqueous dispersion of amorphous silica particles containing SiO ₂ content of was prepared.

Next, while the aqueous dispersion of the amorphous silica particles was heated to 100 ° C. with stirring, an aqueous alkali solution (A ₂ ) was continuously supplied thereto at a rate of 4.1 g per minute.
It takes 140 minutes and the total amount of the above alkaline aqueous solution (A ₂ ) is 576 g.
Was continuously supplied for 30 minutes, 10.29
2800 g of an aqueous slurry of unrefined silica having a pH of, a 20 ° C. viscosity of 17 mPa · s and a SiO ₂ concentration of 3.9% by weight were obtained. From the amount of supplied sodium hydroxide, the SiO ₂ amount of silica produced by the above formula (2) is calculated to be 0.25 times the SiO ₂ amount derived from the silica aqueous sol (S ₃ ).

The total amount of silica in the aqueous slurry of unpurified silica was filtered with Toyo Filter Paper No. 5C and washed with pure water to obtain 454 g of a wet cake of silica. To 454 g of this wet cake, 86 g of pure water was added and stirred to obtain 540 g of a purified silica aqueous dispersion having a SiO ₂ concentration of 20% by weight, a viscosity of 20 mC at 8 mPa · s, and a pH of 8.87. The particle size of the silica particles in this purified silica aqueous dispersion was measured by the centrifugal sedimentation method and found to be 1.12 microns.

Example 9 In a polyethylene container having an internal volume of 5 liters, 1844 g of pure water and 83 g of 40% by weight aqueous hydrofluoric acid solution were charged,
While stirring the liquid in this container, by adding 187 g of an alkaline aqueous solution (A ₂ ) and 312 g of a silica aqueous sol (S ₃ ) to this, 0.23 mol of sodium silicofluoride was contained, and
An aqueous dispersion of amorphous silica particles was prepared containing 5.1 parts by weight of SiO ₂ content per 100 parts by weight of water.

Then, the aqueous dispersion of the amorphous silica particles was heated to 70 ° C. with stirring, and the aqueous alkali solution (A ₂ ) was continuously supplied thereto at a rate of 4.1 g per minute.
It takes 150 minutes and the total amount of the above alkaline aqueous solution (A ₂ ) is 373 g.
After continuing to stir for another 30 minutes,
2800 g of an aqueous slurry of unpurified silica having a pH of 20 ° C. of 12 mPa · s and a SiO ₂ concentration of 5.0% by weight were obtained.
From the amount of sodium hydroxide supplied, the SiO ₂ amount of silica produced by the above formula (2) is derived from the silica aqueous sol (S ₃ ).
It is calculated to be 0.11 times the amount of SiO ₂ .

The total amount of silica in the aqueous slurry of unpurified silica was filtered with Toyo Filter Paper No. 5C and washed with pure water to obtain 301 g of a wet silica cake. When 349 g of pure water was added to 301 g of the wet cake and stirred, a SiO ₂ concentration of 20 wt%, a viscosity of 20 mPa · s at 20 ° C., and a p of 9.24 were obtained.
650 g of purified silica aqueous dispersion with H were obtained. The particle size of silica particles in this purified silica aqueous dispersion was measured by a centrifugal sedimentation method and found to be 0.27 micron.

Example 10 2032 g of pure water and 42 g of 40% by weight aqueous solution of hydrosilicofluoric acid were placed in a polyethylene container having an internal volume of 5 liters,
While stirring the liquid in this container, by adding thereto 93 g of an alkaline aqueous solution (A ₂ ) and 230 g of silica aqueous sol (S ₃ ), 0.12 mol of sodium silicofluoride was contained, and
An aqueous dispersion of amorphous silica particles containing 3.8 parts by weight of SiO ₂ content per 100 parts by weight of water was prepared.

Then, the aqueous dispersion of the amorphous silica particles was heated to 70 ° C. with stirring, and the aqueous alkali solution (A ₂ ) was continuously supplied thereto at a rate of 4.4 g per minute.
It takes 100 minutes and the total amount of the above alkaline aqueous solution (A ₂ ) is 187 g.
After continuing to stir for an additional 30 minutes,
2584 g of an aqueous slurry of crude silica having a pH of 20 ° C. of 9 mPa · s and a SiO ₂ concentration of 3.87% by weight were obtained.
From the amount of sodium hydroxide supplied, the SiO ₂ amount of silica produced by the above formula (2) is derived from the silica aqueous sol (S ₃ ).
It is calculated to be 0.075 times the amount of SiO ₂ .

Deionization and concentration were carried out using an ultrafiltration membrane while supplying pure water to this aqueous slurry of unpurified silica. As a result, a SiO ₂ concentration of 10 wt% and a temperature of 20 ° C. of 5 mPa · s were obtained. Purified silica aqueous dispersion 1000 with viscosity and pH of 8.88
g was obtained. The particle size of the silica particles in this purified silica aqueous dispersion was measured by the centrifugal sedimentation method and found to be 0.17 micron.

Example 11 In a polyethylene container having an internal volume of 5 liters, 1716 g of pure water and 158 g of an alkaline aqueous solution (A ₁ ) were charged, and while stirring the liquid in the container, 200 g thereof was added. When the silica aqueous sol (S ₁ ) was charged, and then 126 g of a 10 wt% ammonium fluoride aqueous solution was charged, the liquid in the container became cloudy.

While heating this cloudy liquid to 65 ° C.,
600 g of ammonium silicofluoride aqueous solution (F ₁ ) was added to this solution under stirring.
Was continuously fed at a rate of 10 g per minute. After the completion of the supply of all the above ammonium silicofluoride aqueous solution (F ₁ ) over 60 minutes, stirring was continued for another 15 minutes.
2800 g of an aqueous slurry of unpurified silica having a pH of 20 ° C. of 23 mPa · s and a SiO ₂ concentration of 3.6% by weight were obtained. From the supplied amount of ammonium silicofluoride, the SiO ₂ amount of silica produced by the above formula (2) is calculated to be 0.25 times the SiO ₂ amount derived from the silica aqueous sol (S ₁ ).

A wet cake of silica was obtained in the same manner as in Example 1. 90 g of pure water was added to 399 g of this wet cake and stirred. As a result, 488 g of a purified silica aqueous dispersion having a SiO ₂ concentration of 20.0% by weight, a viscosity of 18 mPa · s at 20 ° C., and a pH of 9.02.
was gotten. The particle size of silica particles in this purified silica aqueous dispersion was measured by centrifugal sedimentation to be 5.23 microns.

Example 12 The purified silica aqueous dispersions obtained in Examples 1 to 6 were dried at 150 ° C. to obtain dried powder. Yuasa Ionics Co., Ltd. Porosimeter pore distribution measuring device Autoscan-60 model was used to measure the average pore diameter and pore volume by mercury porosimetry.
The results shown in Table 1 were obtained.

[0067] Comparative Example 1 A sol in which water was added to a silica aqueous sol (S ₁ ) to adjust the SiO ₂ concentration to 20% by weight was added to the aqueous medium under stirring as a fluorine ion in an amount of 1000 ppm by weight, 2500 ppm by weight, 5000 ppm by weight. pp
When an ammonium fluoride aqueous solution was added in an amount of m and 10000 ppm by weight, the silica aqueous sol did not become cloudy at 1000 ppm by weight.
When it was ppm, it became cloudy, when it was 5000 ppm by weight, it became more cloudy, and when it was 10000 ppm by weight, it thickened and gelled.

The silica particles of the liquid clouded with the above-mentioned 5000 ppm by weight of fluorine ion had a particle size of 2.8 microns by the centrifugal sedimentation method, but the liquid obtained by vigorously stirring this cloudy liquid The silica particles showed a particle size of 0.6 micron by the centrifugal sedimentation method, and it was confirmed that the agglomerated silica particles which were only agglomerated by fluoride ions were unstable.

Comparative Example 2 This example is an example in which a fluorine ion is produced by a reaction between a hydrosilicofluoride salt and a base in an amorphous silica aqueous dispersion having a high SiO ₂ concentration. In a polyethylene container with an internal volume of 5 liters, add 259 g of alkaline aqueous solution (A ₁ ),
While stirring the liquid in this container, 1631 g of silica aqueous sol (S ₁ ) was added to it to obtain 1.5 mol of NH ₄ OH.
And 34.5 parts by weight for 100 parts by weight of water.
An aqueous dispersion of amorphous silica particles containing SiO ₂ content was prepared.

Then, while heating the aqueous dispersion of the amorphous silica particles to 65 ° C., the aqueous dispersion is stirred with stirring.
51% by weight of 10% by weight ammonium silicofluoride aqueous solution per minute
It was fed continuously at a rate of g. At 9 minutes after starting the feeding, the aqueous dispersion of the amorphous silica particles gelled. The gel contains 28.4 parts by weight of SiO ₂ content per 100 parts by weight of water, and 1500 parts by weight of this SiO ₂ content.
Contains 0 ppm by weight of fluorine ion.

Comparative Example 3 This example is an example in which a hydrosilicofluoride salt and a base were reacted in an aggregated silica aqueous dispersion having a high SiO ₂ concentration.
To a polyethylene container having an internal volume of 5 liters, 600 g of an alkaline aqueous solution (A ₁ ) was charged, and while stirring the liquid in this container, 1631 g of a silica aqueous sol (S ₁ ) was charged to the container, whereby 3.5 An aqueous dispersion of amorphous silica particles was prepared containing moles of NH ₄ OH and containing 29.2 parts by weight of SiO ₂ content per 100 parts by weight of water.

Then, while heating the aqueous dispersion of the amorphous silica particles to 65 ° C., the aqueous dispersion is stirred while stirring,
20% of 30% by weight ammonium silicofluoride aqueous solution per minute
It was fed continuously at a rate of g. After starting this supply
Gelation occurred at 10 minutes. The gel contained 27.7 parts by weight of SiO ₂ content per 100 parts by weight of water, and the SiO ₂
It contains 9200 ppm by weight of fluoride ions per minute.

[0073]

According to the invention, the amorphous silica particles are converted into their agglomerate particles without gelling the aqueous sol or dispersion of 5-1000 nm amorphous silica particles, and By stabilizing these aggregate particles simply and efficiently, the value of 0.1 ~
Aqueous dispersions of large agglomerated silica particles having a particle size of 10 microns can be produced.

The large particles of agglomerated silica show the stability that the particle shape is not impaired by strong stirring, strong alkali, etc., and when the aqueous dispersion of the large particles of agglomerated silica is dried, it has a porous property. A powder having is obtained. An acidic aqueous dispersion of large aggregated silica particles free of cations and anions is obtained by treating the aqueous dispersion of large aggregated silica particles with a cation and anion exchange resin or by ultrafiltration treatment. Can be obtained. Then, an alkaline aqueous dispersion can be obtained by adding an alkali to this acidic aqueous dispersion.

By replacing the aqueous medium of the aqueous dispersion of large particles of aggregated silica with a hydrophilic organic solvent, a dispersion of hydrophilic organic solvents of large particles of aggregated silica can be obtained. As a method of this substitution, while adding a hydrophilic solvent to the aggregated silica large particle aqueous dispersion, a mixed solution of water and a hydrophilic solvent formed by this addition, a method of removing through an ultrafiltration membrane, Alternatively, an ordinary method such as a method of removing by distillation may be used. The hydrophilic organic solvent dispersion of large aggregated silica particles can be similarly replaced with a hydrophobic organic solvent.

The dry powder of the aqueous dispersion of the agglomerated silica large particles or the organic solvent dispersion has a large pore volume, for example, 0.2 to 1 g of the pores having a controlled diameter ranging from 8 to 300 nm. It has a volume of 3.0 ml, and is particularly useful as an ink absorbent, a catalyst carrier, etc., and can also be used as a filler for paper, a filler to be mixed with resin for use, and the like.

The aqueous dispersion of large particles of agglomerated silica, the organic solvent dispersion, and the like can be used as a composition with a resin emulsion having miscibility with them in coatings and other conventionally used applications. it can.

Claims (1)

[Claims] 1. 100 parts by weight of an aqueous medium and as SiO ₂
An aqueous dispersion of the silica particles comprising 0.5 to 30 parts by weight of amorphous silica particles having an average particle size of 5 to 1000 nm is used in an amount of 0.05 to 25% by weight based on the SiO ₂ content of the amorphous silica particles. Forming an aqueous dispersion of agglomerated silica particles consisting of interparticle bonds of the amorphous silica particles by supplying an amount of free fluorine ions, and the aqueous medium in the aqueous dispersion of the agglomerated silica particles. 0.5 to parts by weight
The amount of hydrosilicofluoric acid or a salt thereof and an amount of an alkali sufficient to produce silica from the hydrofluoric acid or a salt thereof are maintained in an amount such that 25 parts by weight of total SiO ₂ content is maintained. A process for producing an aqueous dispersion of large aggregated silica particles having a particle size of 0.1 to 10 microns as measured by centrifugal sedimentation, comprising reacting in an aqueous dispersion of aggregated silica particles.