Stabilized activated silicic acid aqueous solution, silica sol using the same, and manufacturing method

Abstract

[Problem] To provide: a stabilized aqueous active silica solution which is produced by stabilizing an unstable aqueous active silica solution; a silica sol which contains silica particles having a controlled particle diameter distribution and a controlled particle shape and is produced using the stabilized aqueous active silica solution; and a method for producing the stabilized aqueous active silica solution. [Solution] Provided is a stabilized aqueous active silica solution which contains at least one stabilizing agent A selected from the group consisting of an acid, potassium hydroxide, ammonia and an organic base, in which the content of the stabilizing agent A is 0.167 to 10% by mass / SiO2 relative to the mass of SiO2 contained in the aqueous active silica solution. The acid is an inorganic acid or an organic acid. The inorganic acid is sulfuric acid or nitric acid. The organic acid is citric acid. The organic base is an amine or quaternary ammonium hydroxide. The viscosity of the aqueous active silica solution that has a SiO2 concentration of 2.8 to 3.3% by mass, which is measured by the Ostwald method at 23°C within 3 hours after the production, is 0.5 to 20 mPa･s. The viscosity of the aqueous active silica solution which is measured after the storage at 23°C for 3 days is higher by 5.0 times or less than the viscosity of the aqueous active silica solution measured at 23°C within 3 hours after the production. Also provided is a silica sol which contains silica particles having an average primary particle diameter of 5 to 300 nm.

Description

[Technical Field]

[0001] The present invention relates to a stable, high-purity aqueous solution of activated silicic acid, a silica sol using the same, and methods for producing the same. [Background technology]

[0002] A method for producing silica sol involves removing cations from water glass to obtain an aqueous solution of active silicic acid, polymerizing the active silicic acid in the aqueous solution to form silica particles in an aqueous medium, and producing a silica sol in which the silica particles are highly dispersed in the aqueous medium. For example, a method for producing a silica sol in which silica particles having an average particle size of 10 to 30 nm are dispersed has been disclosed, in which an aqueous solution of alkali silicate is treated with a cation exchange resin to remove cations to obtain an aqueous solution of activated silicic acid, a strong acid (e.g., nitric acid) is added to the aqueous solution of activated silicic acid, and the aqueous solution is then brought into contact with a cation exchange resin and an anion exchange resin to obtain an aqueous solution of activated silicic acid, and an alkali metal hydroxide is then added and the mixture is kept at 60 to 150°C with stirring (see Patent Documents 1 and 2). Also disclosed is a method for producing a silica sol by treating an aqueous alkali silicate solution with a cation exchange resin to obtain an aqueous solution of activated silicic acid from which cations have been removed, adding a strong acid (such as nitric acid or hydrochloric acid) to the aqueous solution of activated silicic acid, and then contacting the aqueous solution with a cation exchange resin and an anion exchange resin to obtain an aqueous activated silicic acid solution, and then adding an aqueous ammonia solution to the aqueous activated silicic acid solution and aging the solution (see Patent Document 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 63-285112 [Patent Document 2] Japanese Patent Application Publication No. 5-097422 [Patent Document 3] Japanese Patent Application Publication No. 63-021212 Summary of the Invention [Problem to be solved by the invention]

[0004] However, an aqueous solution of active silicic acid is unstable and undergoes polycondensation in the aqueous solution, making it difficult to control the particle size distribution and particle shape of the silica particles using the methods described in Patent Documents 1 to 3. Therefore, there is a need for the development of a silica sol in which silica particles with a controlled particle size distribution and particle shape are dispersed. The present invention provides a stabilized active silicic acid aqueous solution by stabilizing an unstable active silicic acid aqueous solution, and also provides a silica sol obtained by using the stabilized active silicic acid aqueous solution and having dispersed silica particles with a controlled particle size distribution and particle shape, and a method for producing the same. [Means for solving the problem]

[0005] In a first aspect, the present invention provides a stabilized active silicic acid aqueous solution containing at least one stabilizer A selected from the group consisting of an acid, potassium hydroxide, ammonia, and an organic base, wherein the content of the stabilizer A is 0.167 to 10 mass% relative to the mass of SiO in the active silicic acid aqueous solution. As a second aspect, the stabilized active silicic acid aqueous solution according to the first aspect, wherein the acid is an inorganic acid or an organic acid. As a third aspect, the stabilized activated silicic acid aqueous solution according to the second aspect, wherein the inorganic acid is sulfuric acid or nitric acid. As a fourth aspect, the stabilized activated silicic acid aqueous solution according to the second aspect, wherein the organic acid is citric acid. As a fifth aspect, the stabilized active aqueous silicic acid solution according to the first aspect, wherein the organic base is an amine or a quaternary ammonium hydroxide. As a sixth aspect, the stabilized active silicic acid aqueous solution according to any one of the first to fifth aspects, wherein the viscosity of the active silicic acid aqueous solution having an SiO concentration of 2.8 to 3.3 mass % measured by the Ostwald method at 23°C within 3 hours after production is 0.5 to 20 mPa s, and the viscosity of the active silicic acid aqueous solution measured after storage at 23°C for 3 days is within 5.0 times the viscosity measured at 23°C within 3 hours after production. According to a seventh aspect, there is provided a silica sol comprising silica particles that are a polycondensate of active silicic acid in the stabilized aqueous solution of active silicic acid according to any one of the first to sixth aspects, wherein the silica particles have an average primary particle size of 5 to 300 nm. According to an eighth aspect, the silica sol is the silica sol according to the seventh aspect, which contains potassium ions and sodium ions, and when the SiO concentration is 20% by mass, the content of potassium ions contained in the silica sol is 1500 to 5000 ppm, and the ratio (potassium ion concentration) / (Na ion concentration) expressed in ppm is 100 to 1000. As a ninth aspect, the method comprises the following steps (a) to (b): Step (a): a step comprising: a step of adding at least one stabilizer A selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases to an active silicic acid aqueous solution (a0) in an amount of 0.167 to 10 mass% / SiO2 to obtain a stabilized active silicic acid aqueous solution (a1); and a step of adding potassium hydroxide to the stabilized active silicic acid aqueous solution (a1) or a silica sol containing silica particles having an average primary particle size of 5 to 90 nm so that the SiO2 / K2O molar ratio is 1.5 to 20 to obtain a seed liquid (a2); Step (b): heating the seed solution (a2) obtained in step (a) at 90 to 150°C; The method for producing a silica sol according to the seventh or eighth aspect, As a tenth aspect, the method for producing a silica sol according to the ninth aspect, wherein the activated silicic acid aqueous solution (a0) used in the step (a) is obtained by: step (c1): subjecting water glass to cation exchange to obtain an activated silicic acid aqueous solution; step (c2): adding an acid to the activated silicic acid aqueous solution and maturing at a temperature higher than 0°C and lower than 40°C for 1 to 30 hours; and step (c3): subjecting the aged activated silicic acid aqueous solution to cation exchange and anion exchange to obtain the activated silicic acid aqueous solution (a0). According to an eleventh aspect, there is provided the method for producing a silica sol according to the ninth aspect, in which, in the step (c2), the pH after the addition of the acid is 0.5 to 3.0, and the pH of the active silicic acid aqueous solution (a0) obtained in the step (c3) is greater than 3.0 and not greater than 6.0. As a twelfth aspect, the method for producing a silica sol according to the tenth aspect or the eleventh aspect, in which the acid used in the step (c2) is sulfuric acid; As a thirteenth aspect, the method for producing a silica sol according to any one of the ninth to twelfth aspects, comprising a step of adding, to the seed liquid (a2) being heated, in the step (b), a feed liquid (b1) stabilized by adding at least one stabilizer B selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases to the activated silicic acid aqueous solution (a0) in an amount of 0.167 to 10 mass % based on the mass of SiO in the activated silicic acid aqueous solution; As a fourteenth aspect, the method according to the thirteenth aspect, in which the stabilizer A is sulfuric acid, the SiO2 / K2O molar ratio adjuster is potassium hydroxide, and the stabilizer B is sulfuric acid; and As a fifteenth aspect, the present invention relates to the production method according to the thirteenth aspect, in which the stabilizer A is potassium hydroxide, the SiO2 / K2O molar ratio adjuster is potassium hydroxide, and the stabilizer B is potassium hydroxide. [Effects of the Invention]

[0006] An activated silicic acid aqueous solution can be obtained by removing alkali ions from an alkali silicate aqueous solution using a cation exchange resin or the like. The silicic acid contained in the aqueous solution of activated silicic acid undergoes polycondensation and grows into silica particles, and the dispersion of these silica particles becomes a silica sol. However, because the aqueous solution of activated silicic acid is a very unstable substance, the activated silicic acid (orthosilicate monomer, pyrosilicate dimer, etc.) in the aqueous solution of activated silicic acid undergoes gradual polycondensation even at room temperature, transforming into high molecular weight silica particles. Due to variations in the molecular weight of the silicic acid component in the aqueous solution of activated silicic acid, it is difficult to control the particle size distribution and particle shape of the silica particles when they grow into silica particles, making it difficult to achieve reproducibility. In the present invention, it has been discovered that stable activated silicic acid can be obtained by adding a predetermined amount of a stabilizer (e.g., acid, potassium hydroxide, ammonia, or an organic base) to an aqueous solution of activated silicic acid. Then, by adding an alkali component to the stable aqueous solution of activated silicic acid to grow particles, it becomes possible to control the particle size distribution and particle shape of the resulting silica particles.

[0007] Furthermore, the activated silicic acid aqueous solution obtained from the alkali silicate aqueous solution contains metal impurities contained in the raw materials. To remove these impurities, a strong acid such as sulfuric acid is added to the obtained activated silicic acid aqueous solution, and the metal impurities are leached (eluted) as impurity ions by the acid. The activated silicic acid aqueous solution is then subjected to cation and anion exchange to remove the eluted impurity ions, thereby obtaining a higher purity activated silicic acid aqueous solution. In the present invention, a stable activated silicic acid aqueous solution is obtained by adding a specific amount of stabilizer to this high-purity activated silicic acid aqueous solution. Furthermore, in the present invention, the stable high-purity activated silicic acid aqueous solution is used to polycondense the silicic acid component to grow silica particles, thereby obtaining a silica sol in which silica particles with controlled particle size distribution and particle shape are dispersed. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention provides a stabilized active silicic acid aqueous solution containing at least one stabilizer A selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases in an amount of 0.167 to 10 mass% / SiO2. The SiO2 is the SiO2 in the stabilized active silicic acid aqueous solution. That is, the active silicic acid aqueous solution of the present invention contains stabilizer A in a proportion of 0.167 to 10 mass% relative to the mass of SiO2 in the stabilized active silicic acid aqueous solution. The SiO2 concentration in the stabilized active silicic acid aqueous solution is 1 to 10 mass%.

[0009] The activated silicic acid aqueous solution, which is the raw material of the present invention, is obtained by dealkalization of an alkali silicate aqueous solution. Examples of alkali silicates include sodium silicate and potassium silicate, with sodium silicate being preferred. For example, sodium silicate aqueous solution, also known as water glass, is used, and although not particularly limited, an SiO2 / Na2O molar ratio in the range of 0.5 to 4.0 is used. By removing alkali metals from an alkali silicate aqueous solution diluted to a solids concentration of several percent, an activated silicic acid aqueous solution with an SiO2 concentration of approximately 1 to 10 mass% can be obtained. Note that, in this specification, the term "solids" refers to all components of the activated silicic acid aqueous solution or silica sol excluding the solvent (water), and the term "solids concentration" refers to the concentration of all components of the activated silicic acid aqueous solution or silica sol excluding the solvent (water). The alkali metals are removed by an ion exchange method using a cation exchange resin. The activated silicic acid aqueous solution obtained by dealkalization of the alkali silicate aqueous solution is an aqueous solution in which orthosilicate monomers and pyrosilicate dimers are dissolved in water at a total solids content of 1 to 10 mass%. Because activated silicic acid aqueous solutions are very unstable, the activated silicic acid in the solution polymerizes (particle growth) through polycondensation to form silica particles within a few hours, even at room temperature. Because ordinary activated silicic acid aqueous solutions are unstable, the activated silicic acid gradually grows into particles, making them difficult to handle when producing silica particles with uniform particle shapes. For this reason, there has been a demand for an activated silicic acid aqueous solution that is stable over long periods of time. In particular, in silica particle production methods in which seed particles are used as nuclei to grow particles in a feed liquid, the viscosity of the activated silicic acid aqueous solution, which is the feed liquid, can increase, making production difficult.

[0010] In the present invention, the active silicic acid aqueous solution can be stored stably for a long period of time by adding at least one stabilizer A selected from the group consisting of acid, potassium hydroxide, ammonia, and organic base in an amount of 0.167 to 10% by mass of SiO2 to the active silicic acid aqueous solution. For example, the viscosity of an active silicic acid aqueous solution with an SiO2 concentration of 2.8 to 3.3% by mass measured by the Ostwald method at 23°C within 3 hours after preparation is 0.5 to 20 mPa·s, and the viscosity measured after 3 days of storage at 23°C is within 5.0 times, preferably within 3.0 times, of the viscosity measured at 23°C within 3 hours after preparation, for example, 0.5 to 5.0 times or 0.5 to 3.0 times, thereby ensuring the stability of the active silicic acid aqueous solution of the present invention. However, the SiO2 concentration of the active silicic acid aqueous solution of the present invention is not limited to the range of 2.8 to 3.3% by mass. An active silicic acid aqueous solution with an SiO2 concentration of approximately 1 to 10% by mass can be used.

[0011] The measurement method by the Ostwald method conforms to JIS 2283 and JIS Z8803. First, using a commercially available Ostwald viscometer No. 2, the flow time T of pure water at 25°C was measured. W (s) is measured, and the viscometer coefficient A is calculated using the following formula (1). A=T W ×0.9970÷0.8902 (1) The 0.9970 in the above formula (1) is the density of water at 25°C (g / cm 3 ) and 0.8902 is the viscosity of water at 25°C (mPa·s). Next, using the Ostwald viscometer No. 2 that measured the flow time of pure water, the flow time T S (s) was measured, and the Ostwald viscosity η of each active silicic acid aqueous solution was calculated using the following formula (2) S Calculate. η S (mPa·s)=T S × specific gravity of each activated silicic acid solution ÷ A (2) The specific gravity of each activated silicic acid aqueous solution is measured by the hydrometer method using an activated aqueous solution adjusted to 20°C.

[0012] The average primary particle diameter of this silica sol is the nitrogen adsorption particle diameter obtained by converting the specific surface area measured by the nitrogen adsorption method into spherical particles. The average primary particle diameter (D nm) is calculated by the specific surface area S m 2 / g and true specific gravity dg / cm 3 Therefore, it is given by the formula D = 6000 / (S × d).

[0013] The stabilizer A may be at least one compound selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases. The acid includes inorganic acids and organic acids, inorganic acids include, for example, sulfuric acid or nitric acid, and organic acids include citric acid. The organic base may be an amine or a quaternary ammonium hydroxide. Examples of the amine include primary amines such as monomethylamine and monoethylamine, secondary amines such as dimethylamine and diethylamine, and tertiary amines such as trimethylamine and triethylamine. Examples of the quaternary ammonium hydroxide include tetramethylammonium hydroxide and tetraethylammonium hydroxide.

[0014] The method for producing a silica sol of the present invention includes the following steps (a) to (b): Step (a): a step comprising: a step of adding at least one stabilizer A selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases to an active silicic acid aqueous solution (a0) in an amount of 0.167 to 10 mass% / SiO2 to obtain a stabilized active silicic acid aqueous solution (a1); and a step of adding potassium hydroxide to the stabilized active silicic acid aqueous solution (a1) or a silica sol containing silica particles having an average primary particle size of 5 to 90 nm so that the SiO2 / K2O molar ratio is 1.5 to 20 to obtain a seed liquid (a2); Step (b): heating the seed solution (a2) obtained in step (a) at 90 to 150°C; Includes:

[0015] The activated silicic acid aqueous solution (a0) used in the present invention is obtained by removing alkali metals from an alkali silicate aqueous solution, as described above. The activated silicic acid aqueous solution contains impurities contained in the alkali silicate aqueous solution used as the raw material, at levels of up to a few percent. These are metal impurities other than alkali metals, and the present invention can also use an activated silicic acid aqueous solution (a0) in which the metal impurities have been reduced to 100 ppm / SiO2 or less, or 50 ppm / SiO2 or less. Examples of such metal impurities include iron, aluminum, calcium, magnesium, titanium, zirconium, copper, nickel, chromium, and zinc.

[0016] The method for obtaining an activated silicic acid aqueous solution (a0) with reduced metal impurities includes the steps of: obtaining an activated silicic acid aqueous solution (a0) by dealkalization of an alkali silicate aqueous solution (step c1); adding an acid (e.g., sulfuric acid) to the obtained activated silicic acid aqueous solution (a0 stage) to dissolve (leach) the metal impurities with the acid (step c2); and contacting the acid-added activated silicic acid aqueous solution with, for example, a cation exchange resin and an anion exchange resin to perform cation exchange and anion exchange, thereby obtaining an activated silicic acid aqueous solution (a0) to remove the dissolved metal impurities and the added acid from the activated silicic acid (step c3). The elution of metal impurities from the aqueous activated silicic acid solution with an acid can be carried out, for example, by aging the solution at a temperature above 0°C and below 40°C for 1 to 30 hours.

[0017] The acid used for the elution can be added so that the pH of the activated silicic acid aqueous solution (stage a0) after the addition of the acid in step (c2) is 0.5 to 3.0, and the pH of the activated silicic acid aqueous solution (stage a0) after the metal impurities are eluted in step (c3) and contacted with the cation exchange resin and the anion exchange resin is greater than 3.0 and not greater than 6.0. Sulfuric acid is preferably used as the acid used in step (c2).

[0018] The above step (a) can include a step of adding at least one stabilizer A selected from the group consisting of acid, potassium hydroxide, ammonia, and organic bases to the activated silicic acid aqueous solution (a0) in which metal impurities have been reduced, in an amount of 0.167 to 10 mass% / SiO2, to obtain a stabilized activated silicic acid aqueous solution (a1). The silica sol of the present invention can be produced using this stabilized activated silicic acid aqueous solution. The concentration of stabilizer A at this time needs only to be 0.167 to 10 mass% / SiO2, and stabilizer A can be added to give 0.167 to 10 mass% / SiO2. In addition, when the same acid, such as sulfuric acid, is used for stabilizer A and the acid used for leaching in the above step (c2), the acid of stabilizer A and the acid remaining after the acid (sulfuric acid) added during the previous leaching comes into contact with the cation exchange resin and anion exchange resin in the above step (c3) can be added together to give an acid concentration of 0.167 to 10 mass% / SiO2. In the above step (c3), when the acid is removed by sufficient contact with the cation exchange resin and the anion exchange resin, it is preferable to add an acid (stabilizer A) to the range of 0.167 to 10 mass % / SiO2.

[0019] The stabilizer A used in the stabilized activated silicic acid aqueous solution (a1) is preferably sulfuric acid or potassium hydroxide, with sulfuric acid being particularly preferred. If the content of stabilizer A is less than 0.167% by mass / SiO2, the effect of stabilizing the activated silicic acid aqueous solution is insufficient. When sulfuric acid is used as stabilizer A, an amount of sulfuric acid exceeding 10% by mass / SiO2 is undesirable because it reacts with potassium hydroxide or potassium carbonate added to form seed solution (a2), producing a large amount of salt in the system and destabilizing the activated silicic acid aqueous solution. Furthermore, when potassium hydroxide is used as stabilizer A, an amount of potassium hydroxide exceeding 10% by mass / SiO2 may inhibit silica particle growth when the stabilized activated silicic acid aqueous solution is applied to a feed solution.

[0020] The above-mentioned step (a) includes a step of obtaining a stabilized activated silicic acid aqueous solution (a1) and then adding potassium hydroxide or potassium carbonate in an amount such that the SiO2 / K2O molar ratio is 1.5 to 20 to obtain a seed solution (a2). The potassium source is alkaline potassium, such as potassium hydroxide or potassium carbonate, with potassium hydroxide being preferred. By adjusting the SiO2 / K2O molar ratio of the stabilized activated silicic acid aqueous solution to 1.5 to 20, silica particles can be generated by heating to 90 to 150°C in step (b), and silica sol can be produced while sizing the particles. The silica component derived from the activated silicic acid present in the solution in step (a) serves as a nucleus, and the surface of the nucleus is coated with the silica component dissolved by potassium hydroxide, thereby gradually growing the silica particles. The silica component derived from the activated silicic acid that serves as a nucleus can be silica particles that are a polycondensation product of activated silicic acid.

[0021] In the present invention, the seed liquid (a2) may be a silica sol containing silica particles having an average primary particle diameter of 5 to 90 nm to which potassium hydroxide or potassium carbonate has been added in an amount such that the SiO2 / K2O molar ratio is 1.5 to 20. As the silica sol containing silica particles with an average primary particle diameter of 5 to 90 nm, commercially available silica sols or silica sols prepared by known methods can be used. For example, a silica sol obtained by heating the above-mentioned stabilized activated silicic acid aqueous solution (a1) can be used. Alternatively, for example, potassium hydroxide or potassium carbonate can be added to the silica sol obtained by the present invention in an amount such that the SiO2 / K2O molar ratio is 1.5 to 20 to prepare a seed solution (a2). This allows for the production of a silica sol containing silica particles whose particle diameter has been grown in multiple stages.

[0022] In the method for producing a silica sol of the present invention, the silica sol can be produced by heating the seed liquid (a2) or by using the seed liquid (a2) and the feed liquid (b1). In the step (b), when silica particles with larger particle sizes are produced in stages using a seed liquid and a feed liquid, the activated silicic acid aqueous solution obtained in the step (a) serves as the seed liquid, and the feed liquid can be added in stages during the heating operation in the step (b).

[0023] In the method for producing a silica sol of the present invention, the step (b) further comprises a step of adding a feed liquid (b1). The feed liquid (b1) is a stabilized activated silicic acid aqueous solution (b1) obtained by adding at least one stabilizer B selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases to the activated silicic acid aqueous solution (a0) in an amount of 0.167 to 10 mass % / SiO2.

[0024] In relation to the seed liquid and the feed liquid, a combination in which the stabilizer A used in the stabilized activated silicic acid aqueous solution (a1) is sulfuric acid and the stabilizer B used in the stabilized activated silicic acid aqueous solution (b1) is sulfuric acid can be mentioned. In this case, the stabilizer A used in the stabilized activated silicic acid aqueous solution (a1) is sulfuric acid, the SiO2 / K2O molar ratio adjuster in the seed solution (a2) is potassium hydroxide, and the stabilizer B in the stabilized activated silicic acid aqueous solution (b1) used as the feed solution is sulfuric acid.

[0025] In addition, in relation to the seed liquid and the feed liquid, a combination can be mentioned in which the stabilizer A used in the stabilized activated silicic acid aqueous solution (a1) is potassium hydroxide, and the stabilizer B used in the stabilized activated silicic acid aqueous solution (b1) is potassium hydroxide. In this case, the stabilizer A used in the stabilized activated silicic acid aqueous solution (a1) is potassium hydroxide, the SiO2 / K2O molar ratio of the seed solution (a2) is adjusted with potassium hydroxide, and the stabilizer B used in the stabilized activated silicic acid aqueous solution (b1) of the feed solution is potassium hydroxide.

[0026] The resulting silica sol can be further subjected to cation exchange, anion exchange, or a combination thereof to reduce impurities. In order to adjust the SiO2 concentration of the silica sol, it is possible to adjust the SiO2 concentration to, for example, 20% by mass to 50% by mass using ultrafiltration or an evaporator.

[0027] The silica sol of the present invention contains silica particles that are a polycondensate of active silicic acid in the above-mentioned stabilized aqueous solution of active silicic acid, and also contains silica particles that have grown by coating the surfaces of the silica particles as nuclei with silica components dissolved by potassium hydroxide. The silica particles contained in the silica sol of the present invention have an average primary particle diameter of 5 to 300 nm.

[0028] The silica sol of the present invention may also contain other components such as potassium ions and sodium ions. For example, when the SiO2 concentration is 20 mass %, the content of potassium ions contained in the silica sol is 1500 to 5000 ppm, and (potassium ion concentration) / (Na ion concentration)=100 to 1000 expressed in ppm. [Example]

[0029] Example 1 (a) Process JIS No. 3 sodium water glass was prepared as the raw material water-soluble alkali metal silicate. The main components of this water glass, other than water, were 28.8% by mass as SiO2 and 9.47% by mass as Na2O. 478 g of the water glass was dissolved in 2992 g of pure water to prepare 3470 g of aqueous sodium silicate solution. The aqueous sodium silicate solution was then passed through a column packed with Amberlite IR-120B hydrogen-form strongly acidic cation exchange resin at a space velocity of 4.5 per hour, and 3000 g of the resulting activated aqueous silicic acid solution (a0) was collected in a container. An 8% aqueous solution of sulfuric acid was added to the above aqueous solution of activated silicic acid (a0) so that the content of the stabilizer, sulfuric acid, was 0.313 mass% / SiO2, to obtain a stabilized aqueous solution of activated silicic acid (a1). The viscosity of the obtained aqueous solution of activated silicic acid, measured by the Ostwald method, was 1.0 mPa·s immediately after production and 2.2 mPa·s after storage at 23°C for 3 days. A reactor was used, consisting of a 3 L stainless steel pressure vessel equipped with a stirrer, a heater, etc. A stabilized activated silicic acid aqueous solution (a1, 3.2 mass% as SiO2), a 10 mass% potassium hydroxide aqueous solution, and pure water was used to prepare a seed solution (a2) with a pH of 12.1. The SiO2 / KO molar ratio of the prepared seed solution (a2) was 2.2. (b) Process The seed solution (a2) was placed in a reactor and heated with stirring to adjust the liquid temperature in the vessel to 110 to 130° C. After the temperature in the vessel reached 100 to 130° C., the stabilized activated silicic acid aqueous solution (a1) obtained in step (a) was continuously fed as a feed liquid (b1) to the reactor while maintaining the liquid temperature in the vessel at 110 to 130° C. until the pH of the reaction liquid reached 11.2. The resulting reaction solution was then heated and stirred for 2 hours while maintaining the temperature at 110-130°C, yielding Silica Sol 1. The resulting Silica Sol 1 was concentrated at room temperature to an SiO2 concentration of 40% by mass using a commercially available ultrafiltration device equipped with a tubular ultrafiltration membrane made of polysulfone with a pore size of approximately 5 nm. Silica Sol 1 remained stable during this concentration, and the concentration process was extremely smooth. The primary particle diameter of the silica particles in Silica Sol 1, calculated by nitrogen adsorption, was 44 nm.

[0030] Example 2 Silica sol 2 was obtained in the same manner as in Example 1, except that in step (a), an 8% aqueous sulfuric acid solution was added to the active silicic acid aqueous solution (a0) so that the content of the stabilizer, sulfuric acid, was 0.938 mass% / SiO2, thereby obtaining a stable active silicic acid aqueous solution (a1). The viscosity of the stabilized activated silicic acid aqueous solution (a1), measured by the Ostwald method, was 1.0 mPa·s immediately after production and 1.3 mPa·s after storage at 23°C for 3 days. The pH of the seed solution (a2) was 12.1, and the pH after feeding the feed solution in step (b) was 11.1. The primary particle diameter of the silica particles in silica sol 2, calculated by the nitrogen adsorption method, was 43 nm.

[0031] Example 3 Silica sol 3 was obtained in the same manner as in Example 1, except that in step (a), an 8% aqueous sulfuric acid solution was added to the active silicic acid aqueous solution (a0) so that the content of sulfuric acid as a stabilizer was 9.38 mass% / SiO2, thereby obtaining an active silicic acid aqueous solution (a1). The viscosity of the stabilized activated silicic acid aqueous solution (a1), measured by the Ostwald method, was 1.0 mPa·s immediately after production and 1.1 mPa·s after storage at 23°C for 3 days. The pH of the seed solution (a2) was 12.2, and the pH after feeding the feed solution in step (b) was 9.7. The primary particle diameter of the silica particles in silica sol 3, calculated by the nitrogen adsorption method, was 50 nm.

[0032] Example 4 The procedure was the same as in Example 1, except that in step (a), a 10% aqueous nitric acid solution was added to the active silicic acid solution (a0) so that the content of the nitric acid as a stabilizer was 0.938 mass% / SiO2, thereby obtaining a stabilized active silicic acid solution (a1). The viscosity of the stabilized activated silicic acid aqueous solution (a1), measured by the Ostwald method, was 1.0 mPa·s immediately after preparation and 1.2 mPa·s after storage at 23°C for 3 days.

[0033] Example 5 The procedure was the same as in Example 1, except that in step (a), citric acid monohydrate was added to the active silicic acid aqueous solution (a0) so that the content of citric acid as a stabilizer was 9.38 mass% / SiO2, thereby obtaining a stabilized active silicic acid aqueous solution (a1). The viscosity of the stabilized activated silicic acid aqueous solution (a1), measured by the Ostwald method, was 1.2 mPa·s immediately after preparation and 2.0 mPa·s after storage at 23°C for 3 days.

[0034] Example 6 The procedure was the same as in Example 1, except that in step (a), a 28% aqueous ammonia solution was added to the aqueous activated silicic acid solution (a0) so that the content of ammonia as a stabilizer was 0.938 mass% / SiO2, thereby obtaining a stabilized aqueous activated silicic acid solution (a1). The viscosity of the stabilized activated silicic acid aqueous solution (a1), measured by the Ostwald method, was 1.6 mPa·s immediately after preparation and 1.4 mPa·s after storage at 23°C for 3 days.

[0035] Example 7 Silica sol 7 was obtained in the same manner as in Example 1, except that in step (a), N,N-diethylmethylamine as a stabilizer was added to the active silicic acid aqueous solution (a0) so that the content of N,N-diethylmethylamine was 9.38 mass% / SiO2, thereby obtaining a stabilized active silicic acid aqueous solution (a1). The viscosity of the stabilized activated silicic acid aqueous solution (a1), measured by the Ostwald method, was 2.9 mPa·s immediately after preparation and 2.5 mPa·s after storage at 23°C for 3 days.

[0036] Example 8 Silica sol 8 was obtained in the same manner as in Example 1, except that in step (a), a 10% aqueous solution of potassium hydroxide was added to the aqueous solution of activated silicic acid (a0) so that the content of potassium hydroxide as a stabilizer was 0.938 mass% / SiO2 in terms of potassium oxide, thereby obtaining a stabilized aqueous solution of activated silicic acid (a1). The viscosity of the stabilized activated silicic acid aqueous solution (a1), measured by the Ostwald method, was 11.0 mPa·s immediately after preparation and 13.3 mPa·s after storage at 23°C for 3 days.

[0037] (Comparative Example 1) An active silicic acid aqueous solution (a0) was synthesized in the same manner as in Example 1. The active silicic acid aqueous solution (a0) to which no stabilizer was added gelled the next day.

[0038] (Comparative Example 2) The same procedure as in Example 1 was carried out except that in step (a), an 8% aqueous sulfuric acid solution was added to the active silicic acid aqueous solution (a0) as a stabilizer so that the sulfuric acid / SiO2 concentration was 0.156 mass% to obtain an active silicic acid aqueous solution containing sulfuric acid as a stabilizer. The viscosity of the activated silicic acid aqueous solution containing sulfuric acid as a stabilizer immediately after production was 1.0 mPa·s, as measured by the Ostwald method. However, the activated silicic acid aqueous solution gelled after being stored at 23°C for 3 days.

[0039] (Comparative Example 3) The same procedure as in Example 1 was carried out except that in step (a), an 8% aqueous sulfuric acid solution was added to the active silicic acid aqueous solution (a0) as a stabilizer so that the sulfuric acid / SiO2 content was 18.8 mass % to obtain an active silicic acid aqueous solution containing sulfuric acid as a stabilizer. The viscosity of the activated silicic acid aqueous solution containing sulfuric acid as a stabilizer, measured by the Ostwald method, was 1.0 mPa·s immediately after production and 1.0 mPa·s after storage at 23°C for 3 days. The pH of the seed solution (a2) was adjusted to 10.4, and the SiO2 / K2O molar ratio after adjustment was 1.2. However, after supplying the feed solution in step (b), a large amount of gel was generated, and silica sol was not obtained.

[0040] Comparative Example 4 The same procedure as in Example 1 was carried out except that in step (a), an 8% aqueous sulfuric acid solution was added to the active silicic acid aqueous solution (a0) as a stabilizer so that the sulfuric acid / SiO2 content was 31.3 mass% to obtain an active silicic acid aqueous solution containing sulfuric acid as a stabilizer. The viscosity of the activated silicic acid aqueous solution containing sulfuric acid as a stabilizer, measured by the Ostwald method, was 1.0 mPa·s immediately after production and 1.0 mPa·s after storage at 23°C for 3 days. The pH of the seed solution was adjusted to 10.4, and the SiO2 / K2O molar ratio after adjustment was 0.7. However, a large amount of gel was generated after the feed solution was supplied in step (b), and a silica sol was not obtained. [Industrial Applicability]

[0041] By stabilizing an unstable aqueous solution of activated silicic acid, a stabilized aqueous solution of activated silicic acid is provided, and a silica sol having a controlled particle size distribution and particle shape can be obtained using the activated silicic acid.

Claims

1. An activated silicic acid aqueous solution containing at least one stabilizer A selected from the group consisting of an acid, potassium hydroxide, ammonia, and an organic base, The content of the stabilizer A is SiO in the aqueous solution of activated silicic acid. ２ 0.167 to 10% by mass relative to the mass of A stabilized aqueous solution of active silicic acid contains silica particles, which are polycondensates of active silicic acid, and the silica particles have an average primary particle size of 5 to 300 nm.

2. 2. The stabilized active silicic acid aqueous solution according to claim 1, wherein the acid is an inorganic acid or an organic acid.

3. 3. The stabilized active silicic acid aqueous solution according to claim 2, wherein the inorganic acid is sulfuric acid or nitric acid.

4. 3. The stabilized aqueous solution of activated silicic acid according to claim 2, wherein the organic acid is citric acid.

5. 2. The stabilized active silicic acid aqueous solution according to claim 1, wherein the organic base is an amine or a quaternary ammonium hydroxide.

6. SiO measured by the Ostwald method at 23°C within 3 hours after production ２ 6. The stabilized active silicic acid aqueous solution according to claim 1, wherein the viscosity of the active silicic acid aqueous solution having a concentration of 2.8 to 3.3 mass % is 0.5 to 20 mPa·s, and the viscosity of the active silicic acid aqueous solution measured after storage at 23°C for 3 days is within 5.0 times the viscosity measured at 23°C within 3 hours after production.

7. A silica sol comprising silica particles which are a polycondensate of active silicic acid in the stabilized aqueous solution of active silicic acid according to any one of claims 1 to 6, wherein the average primary particle diameter of the silica particles is 5 to 300 nm.

8. the silica sol contains potassium ions and sodium ions, and SiO ２ 8. The silica sol according to claim 7, wherein the content of potassium ions contained in the silica sol when the concentration is 20% by mass is 1500 to 5000 ppm, and the ratio (potassium ion concentration) / (Na ion concentration) expressed in ppm is 100 to 1000.

9. The following steps (a) and (b): Step (a): Adding at least one stabilizer A selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases to an activated silicic acid aqueous solution (a0) in an amount of 0.167 to 10% by mass / SiO ２ and a step of obtaining a stabilized active silicic acid aqueous solution (a1) containing the stabilized active silicic acid aqueous solution (a1) or a step of adding SiO to the stabilized active silicic acid aqueous solution (a1) or a silica sol containing silica particles having an average primary particle diameter of 5 to 90 nm. ２ / K ２ and obtaining a seed solution (a2) containing potassium hydroxide having an O molar ratio of 1.5 to 20; The method for producing a silica sol according to claim 7 or 8, comprising: (b) a step of heating the seed liquid (a2) obtained in the (a) step at 90 to 150°C.

10. The activated silicic acid aqueous solution (a0) used in the step (a) is Step (c1): A step of cation-exchanging water glass to obtain an active silicic acid aqueous solution; (c2) Step: Adding an acid to the obtained aqueous solution of activated silicic acid and aging the solution at a temperature higher than 0°C and lower than 40°C for 1 to 30 hours; Step (c3): A step of subjecting the aged activated silicic acid aqueous solution to cation exchange and anion exchange to obtain an activated silicic acid aqueous solution (a0); The method for producing a silica sol according to claim 9, wherein the silica sol is obtained by the following steps.

11. 11. The method for producing a silica sol according to claim 10, wherein in the step (c2), the pH after adding the acid is 0.5 to 3.0, and the pH of the active silicic acid aqueous solution (a0) obtained in the step (c3) is more than 3.0 and 6.0 or less.

12. The method for producing a silica sol according to claim 10 or 11, wherein the acid used in the step (c2) is sulfuric acid.

13. In the step (b), the seed solution (a2) is heated, and the activated silicic acid aqueous solution (a0) is further added with at least one stabilizer B selected from the group consisting of acid, potassium hydroxide, ammonia, and an organic base, to stabilize the SiO in the activated silicic acid aqueous solution. ２ 13. The method for producing a silica sol according to claim 9, further comprising adding a stabilized feed liquid (b1) in an amount of 0.167 to 10% by mass based on the mass of the silica sol.

14. The stabilizer A is sulfuric acid, and the SiO ２ / K ２ The method according to claim 13, wherein the molar ratio adjuster for O is potassium hydroxide and the stabilizer B is sulfuric acid.

15. The stabilizer A is potassium hydroxide, and the SiO ２ / K ２ 14. The method according to claim 13, wherein the molar ratio adjuster for O is potassium hydroxide, and the stabilizer B is potassium hydroxide.

16. An activated silicic acid aqueous solution containing at least one stabilizer A selected from the group consisting of an acid, potassium hydroxide, ammonia, and an organic base, The content of the stabilizer A is 0.167 to 10 mass % relative to the mass of SiO 2 in the active silicic acid aqueous solution, The viscosity of the activated silicic acid aqueous solution having an SiO 2 concentration of 2.8 to 3.3 mass % measured by the Ostwald method at 23°C within 3 hours after production is 0.5 to 20 mPa·s, and the viscosity of the activated silicic acid aqueous solution measured after storing at 23°C for 3 days is 0.5 to 20 mPa·s within 3 hours after production. A stabilized aqueous solution of activated silicic acid, the viscosity of which is within 5.0 times the viscosity of the aqueous solution.

17. The stabilized activated silicic acid aqueous solution according to claim 16, wherein the acid is an inorganic acid or an organic acid.

18. The stabilized activated silicic acid aqueous solution according to claim 17, wherein the inorganic acid is sulfuric acid or nitric acid.

19. The stabilized activated silicic acid aqueous solution according to claim 17, wherein the organic acid is citric acid.

20. The stabilized activated silicic acid aqueous solution according to claim 16, wherein the organic base is an amine or a quaternary ammonium hydroxide.