Stabilized aqueous solution of activated silica, silica sol using it, and manufacturing method

Abstract

Provided is a stabilized aqueous solution of reactive silica obtained by stabilizing an unstable aqueous solution of reactive silica, and a silica sol containing silica particles with controlled particle size distribution or particle shape using the stabilized reactive silica, and a method for manufacturing the same. A stabilized aqueous solution of active silicic acid contains at least one stabilizer A selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases, wherein the amount of stabilizer A is relative to the amount of SiO₂ contained in the aqueous solution of active silicic acid. The mass fraction of 2 is 0.167~10 mass% / SiO 2. The acid can be inorganic or organic. 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 Oswald method is used to determine SiO₂. A silica sol comprising silica particles with an average primary particle size of 5-300 nm. The viscosity of the prepared active silica aqueous solution, with a concentration of 2.8-3.3% by mass, is 0.5-20 mPa·s after being stored at 23°C for 3 days. Furthermore, the viscosity of the prepared active silica aqueous solution after being stored at 23°C for 3 days is within 5.0 times that of the prepared solution.

Description

Technical Field

[0001] This invention relates to a stable, high-purity, active aqueous solution of silica, a silica sol using the same, and a method for manufacturing the same. Prior Technology

[0002] The method for manufacturing silica sol involves the following steps: 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 highly dispersing the silica particles in the aqueous medium to manufacture silica sol. For example, it is disclosed that: an aqueous solution of silicic acid is treated with a cation exchange resin to remove cations to obtain an aqueous solution of active silicic acid; a strong acid (e.g., nitric acid) is added to the aqueous solution of active silicic acid, and then it is contacted with a cation exchange resin and an anion exchange resin to obtain an aqueous solution of active silicic acid; then, an alkali metal hydroxide is added and the temperature is maintained at 60-150°C with stirring, thereby obtaining silica particles with an average particle size of 10-30 nm, which is a method for manufacturing dispersed silica sol (see Patent Documents 1 and 2). Furthermore, it reveals a method for manufacturing silica sol by treating an aqueous solution of silicic acid with a cation exchange resin to remove cations, obtaining an aqueous solution of active silicic acid, adding a strong acid (such as nitric acid or hydrochloric acid) to the aqueous solution of active silicic acid, contacting it with a cation exchange resin and an anion exchange resin to obtain an aqueous solution of active silicic acid, and then adding an aqueous solution of ammonia to the aqueous solution of active silicic acid and aging it (see Patent Document 3). [Previous Technical Documents] [Patent Literature]

[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

[0004] [The problem that the invention aims to solve]

[0005] However, aqueous solutions of reactive silicic acid are unstable because reactive silicic acid undergoes polymerization and condensation in aqueous solutions. Therefore, the methods described in Patent Documents 1 to 3 present the problem of difficulty in controlling the particle size distribution and particle shape of silica particles. Therefore, the development of silica sols containing silica particles with controlled particle size distribution and particle shape is desirable. The present invention provides a stabilized aqueous solution of active silica obtained by stabilizing an unstable aqueous solution of active silica, and a silica sol obtained by using the stabilized aqueous solution of active silica, which disperses silica particles with controlled particle size distribution or particle shape, and a method thereof. [Methods for solving problems]

[0006] The first aspect of this invention is a stabilized aqueous solution of active silicic acid, which is an aqueous solution of active silicic acid containing at least one stabilizer A selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases. The content of stabilizer A is 0.167~10% of the mass of SiO2 in the aqueous solution of active silicic acid. As a second viewpoint, as described in the first viewpoint, the stabilized active silicic acid aqueous solution, wherein the aforementioned acid is an inorganic acid or an organic acid. As a third viewpoint, as described in the second viewpoint, the stabilized active silicic acid aqueous solution, wherein the aforementioned inorganic acid is sulfuric acid or nitric acid. As a fourth viewpoint, as described in the second viewpoint, the stabilized active silicic acid aqueous solution contains citric acid as the aforementioned organic acid. As a fifth point of view, as described in the first point of view, the stabilized active silicic acid aqueous solution, wherein the aforementioned organic base is an amine or quaternary ammonium hydroxide. As a sixth point of view, the stabilized active silica aqueous solution described in any of the first to fifth points of view, wherein the viscosity of the aforementioned active silica aqueous solution with a SiO2 concentration of 2.8 to 3.3% by mass after manufacturing at 23°C for no more than 3 hours is 0.5 to 20 mPa·s, and the viscosity of the active silica aqueous solution after being stored at 23°C for 3 days is no more than 5.0 times that of the viscosity measured at 23°C for no more than 3 hours after manufacturing. The seventh point is a silica sol comprising silica particles as polycondensates of active silica in a stabilized aqueous solution of active silica as described in any of the first to sixth points, wherein the average primary particle size of the silica particles is 5 to 300 nm. As the eighth point of view, the silica sol described in the seventh point of view contains potassium ions and sodium ions. When the SiO2 concentration is 20% by mass, the potassium ion content in the silica sol is 1500~5000 ppm, and the ratio of potassium ion concentration to sodium ion concentration is 100~1000. The ninth viewpoint is a method for manufacturing silica sol as described in the seventh or eighth viewpoint, comprising the following steps (a) to (b). (a) Step: comprising the steps of obtaining a stabilized aqueous solution of active silica (a1) and obtaining a seed solution (a2). The stage of obtaining the stabilized active silica aqueous solution (a1) involves containing a stabilizer A selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases in the active silica aqueous solution (a0) at a concentration of 0.167~10% by mass / SiO2. The stage of obtaining the seed solution (a2) involves introducing potassium hydroxide into the stabilized aqueous solution of active silica (a1) or into a silica sol containing silica particles with an average primary particle size of 5-90 nm, with a SiO2 / K2O molar ratio of 1.5-20. (b) Step: Heating the seed solution (a2) obtained in step (a) at 90~150°C. As the tenth point of view, the method for manufacturing silica sol as described in the ninth point of view, wherein the active silica aqueous solution (a0) used in the aforementioned step (a) is obtained through the following steps (c1) to (c3): (c1) step: cation exchange of water glass to obtain an active silica aqueous solution; (c2) step: adding acid to the active silica aqueous solution and aging it at a temperature above 0°C and below 40°C for 1 to 30 hours; (c3) step: cation exchange and anion exchange of the aged active silica aqueous solution to obtain an active silica aqueous solution (a0). As the 11th point of view, in the method for manufacturing silica sol as described in the 9th point of view, in the aforementioned (c2) step, the pH after adding acid is 0.5 to 3.0, and the pH of the active silica aqueous solution (a0) obtained through the (c3) step is greater than 3.0 and less than 6.0. As the 12th viewpoint, in the method for manufacturing silica sol as described in the 10th or 11th viewpoints, the acid used in the aforementioned step (c2) is sulfuric acid. As the 13th viewpoint, the method for manufacturing silica sol as described in any of the 9th to 12th viewpoints includes, in the aforementioned step (b), a further step of adding a stabilized feed solution (b1) to the heated seed solution (a2). The stabilized feed solution (b1) is a stabilizer B selected from the group consisting of an acid, potassium hydroxide, ammonia, and an organic base added to an active silica aqueous solution (a0). The stabilizer B is in an amount of 0.167 to 10% by mass based on the mass of SiO2 in the active silica aqueous solution. As the 14th viewpoint, the manufacturing method described in the 13th viewpoint, wherein the aforementioned stabilizer A is sulfuric acid, the aforementioned SiO2 / K2O molar ratio adjuster is potassium hydroxide, and the aforementioned stabilizer B is sulfuric acid. As the 15th viewpoint, the manufacturing method described in the 13th viewpoint, wherein the aforementioned stabilizer A is potassium hydroxide, the aforementioned SiO2 / K2O molar ratio adjuster is potassium hydroxide, and the aforementioned stabilizer B is potassium hydroxide. [The effects of the invention]

[0007] Alkaline ions are removed from an aqueous silicate solution using a cation exchange resin or similar method, thereby obtaining an active silicate aqueous solution. The silicic acid contained in the aqueous solution of reactive silicic acid undergoes polymerization and condensation to grow into silica particles, and the dispersion of these silica particles becomes silica sol. However, because the aqueous solution of reactive silicic acid is a very unstable substance, the reactive silicic acid (such as orthosilicic acid monomers and pyrosilicic acid dimers) in the aqueous solution will continue to slowly and repeatedly polymerize and condense even at room temperature, transforming into high molecular weight silica particles. Due to the uneven molecular weight of the silicic acid components in the aqueous solution of reactive silicic acid, it is difficult to control the particle size distribution or particle shape of silica particles during growth, and it is difficult to obtain reproducibility. This invention discovers that stable active silicic acid can be obtained by adding a specified amount of a stabilizer (e.g., acid, potassium hydroxide, ammonia, and organic base) to an aqueous solution of active silicic acid. Then, by adding an alkaline component to the stabilized aqueous solution of active silicic acid and performing particle growth, the particle size distribution or particle shape of the obtained silica particles can be controlled.

[0008] Furthermore, the active silica aqueous solution obtained from the silica alkaline aqueous solution contains metallic impurities contained in the raw materials. To remove these impurities, a strong acid such as sulfuric acid is added to the obtained active silica aqueous solution. The acid dissolves the metallic impurities as impurity ions. Then, the dissolved impurity ions are removed by cation exchange and anion exchange of the active silica aqueous solution, resulting in a more pure active silica aqueous solution. This invention also includes a specific amount of stabilizer in these high-purity active silica aqueous solutions to obtain a stable active silica aqueous solution. Furthermore, this invention uses this stable, high-purity active silica aqueous solution to perform condensation and coalescence of silica components to grow silica particles, thereby obtaining a silica sol containing silica particles with a controlled particle size distribution or shape. Implementation

[0009] [Optimal Form of Invention Implementation]

[0010] This invention relates to a stabilized aqueous solution of active silicic acid, containing at least one stabilizer A selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases, at a concentration of 0.167 to 10% by mass of SiO2. The SiO2 mentioned above refers to the SiO2 in the stabilized aqueous solution of active silicic acid. Specifically, the active silicic acid aqueous solution of this invention contains stabilizer A at a ratio of 0.167 to 10% by mass relative to the mass of SiO2 in the stabilized aqueous solution of active silicic acid. Furthermore, the SiO2 concentration in the stabilized aqueous solution of active silicic acid is 1 to 10% by mass.

[0011] An active silicic acid aqueous solution, which is the raw material of this invention, is obtained by dealkalizing an aqueous silicic acid solution. Examples of silicic acid bases include sodium silicate and potassium silicate, with sodium silicate being a preferred example. For instance, an aqueous solution of sodium silicate is also called water glass and is not particularly limited, but an aqueous solution of sodium silicate with a SiO₂ / Na₂O molar ratio in the range of 0.5 to 4.0 can be used. By removing the alkali metal from an aqueous silicic acid solution diluted to a solids concentration of several percent, an active silicic acid aqueous solution with a SiO₂ concentration of approximately 1 to 10% by mass can be obtained. Furthermore, in this specification, the term "solids" refers to the total composition after removing the solvent (water) from the active silicic acid aqueous solution or silica sol; the term "solids concentration" refers to the concentration of the total composition after removing the solvent (water) from the active silicic acid aqueous solution or silica sol. Alkali metals are removed using ion exchange with cation exchange resins. The active silicone aqueous solution obtained from the alkali silicone aqueous solution through dealkali removal is an aqueous solution containing 1-10% by mass of orthosilicone monomers and pyrosilicone dimers dissolved in water. Because the active silicone aqueous solution is highly unstable, even at room temperature, the active silicone in the solution will polymerize and condense within several hours, thus polymerizing (particle growth) to form silica particles. Since typical active silicone aqueous solutions are unstable, the active silicone particles grow slowly, posing a challenge in producing silica particles with uniform particle shapes. Therefore, a long-term stable active silicone aqueous solution is required. In particular, in the manufacturing method of silicon dioxide particles that use seed particles as nuclei and feed liquid to grow the particles, the manufacturing process becomes difficult because the active silica aqueous solution used as the feed liquid thickens.

[0012] In this invention, by including 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% by mass / SiO2 in the active silicic acid aqueous solution, the active silicic acid aqueous solution can be stably stored for a long period of time. For example, using the Ostwald method, the viscosity of an active silicic acid aqueous solution with a SiO2 concentration of 2.8 to 3.3% by mass after manufacturing at 23°C for 3 hours is measured to be 0.5 to 20 mPa·s. The viscosity of the active silicic acid aqueous solution after being stored at 23°C for 3 days is within 5.0 times, preferably within 3.0 times, for example, 0.5 to 5.0 times or 0.5 to 3.0 times, compared to the viscosity measured at 23°C for 3 hours after manufacturing. Therefore, the active silicic acid aqueous solution of this invention can be stably stored. In this application, the SiO2 concentration of the active silicic acid aqueous solution is not limited to the range of 2.8 to 3.3% by mass. An active silicic acid aqueous solution with a SiO2 concentration of about 1 to 10% by mass can be used.

[0013] The determination method of the Oswald method is based on JIS 2283 and JIS Z8803. First, using a commercially available Oswald viscometer No.2, the flow time TW(s) of pure water at 25°C was measured, and the viscometer coefficient A was calculated using the following formula (1). A = TW × 0.9970 ÷ 0.8902 ···(1) In the above formula (1), 0.9970 is the density of water at 25℃ (g / cm 3); 0.8902 is the viscosity of water at 25℃ (mPa·s). Next, using the Oswald Viscometer No.2, which measures the flow time of pure water, the flow time TS(s) of each active silica aqueous solution at 25°C was measured, and the Oswald viscosity ηS of each active silica aqueous solution was calculated using the following formula (2). η S(mPa·s) = TS × specific gravity of each active silicic acid aqueous solution ÷ A···(2) The specific gravity of each active silicic acid aqueous solution was determined using a hydrometer method after the active aqueous solution was adjusted to 20°C.

[0014] The average primary particle size of this silica sol is typically determined using the nitrogen adsorption method. This method involves measuring the specific surface area using nitrogen adsorption and then converting that specific surface area into spherical particles. The average primary particle size (Dnm) is provided by the specific surface area Sm² / g and the true specific gravity dg / cm³, using the formula D=6000 / (S×d).

[0015] The stabilizer A mentioned above can be a compound selected from at least one of the groups consisting of acids, potassium hydroxide, ammonia and organic bases. Examples of acids include inorganic acids and organic acids. Examples of inorganic acids include sulfuric acid or nitric acid, and examples of organic acids include citric acid. Furthermore, examples of organic bases include amines or quaternary ammonium hydroxides. Examples of amines 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 quaternary ammonium hydroxides include tetramethylammonium hydroxide and tetraethylammonium hydroxide.

[0016] The method for manufacturing silica sol of the present invention includes the following steps (a) to (b). (a) Step: comprising the steps of obtaining a stabilized aqueous solution of active silica (a1) and obtaining a seed solution (a2). The stage of obtaining the stabilized active silica aqueous solution (a1) involves containing a stabilizer A selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases in the active silica aqueous solution (a0) at a concentration of 0.167~10% by mass / SiO2. The stage of obtaining the seed solution (a2) involves introducing potassium hydroxide into the stabilized aqueous solution of active silica (a1) or into a silica sol containing silica particles with an average primary particle size of 5-90 nm, with a SiO2 / K2O molar ratio of 1.5-20. (b) Step: Heating the seed solution (a2) obtained in step (a) at 90~150°C.

[0017] The active silica aqueous solution (a0) used in this invention, as described above, is obtained by removing alkali metals from an alkaline silica aqueous solution. The active silica aqueous solution contains a few percent or less of the impurities contained in the alkaline silica aqueous solution used as a raw material. These are metallic impurities other than alkali metals, and in this invention, an active silica aqueous solution (a0) with such metallic impurities reduced to below 100 ppm / SiO₂ or below 50 ppm / SiO₂ can also be used. Examples of such metallic impurities include iron, aluminum, calcium, magnesium, titanium, zirconium, copper, nickel, chromium, and zinc.

[0018] A method for obtaining an activated silica aqueous solution (a0) with reduced metallic impurities includes: a step (c1) of obtaining the activated silica aqueous solution (a0) by dealkalizing the silica base aqueous solution; a step (c2) of adding an acid (e.g., sulfuric acid) to the obtained activated silica aqueous solution (a0 stage) in order to leach the metallic impurities by acid; and a step (c3) of contacting the activated silica aqueous solution with added acid with, for example, a cation exchange resin and an anion exchange resin to perform cation exchange and anion exchange to obtain the activated silica aqueous solution (a0). Metallic impurities can be dissolved from an aqueous solution of active silica by means of acid, for example, by aging at a temperature above 0°C but below 40°C for 1 to 30 hours.

[0019] The addition of acid used in the above leaching process can be carried out as follows: the pH of the activated silicic acid aqueous solution (a0 stage) after the addition of acid in step (c2) is 0.5 to 3.0, and the pH of the activated silicic acid aqueous solution (a0 stage) after dissolving metal impurities in step (c3) and contacting the cation exchange resin and anion exchange resin is greater than 3.0 and less than 6.0. Sulfuric acid is preferably used as the acid in step (c2).

[0020] Step (a) above may include a stage of obtaining a stabilized aqueous solution of active silica (a1), wherein obtaining the stabilized aqueous solution of active silica (a1) involves ensuring that the aforementioned metal impurities are reduced in the stabilized aqueous solution of active silica (a0) and that at least one stabilizer selected from the group consisting of acids, potassium hydroxide, ammonia, and organic bases is present in an amount of 0.167 to 10% by mass / SiO2. This stabilized aqueous solution of active silica can be used to manufacture the silica sol of the present invention. At this point, the concentration of stabilizer A only needs to be 0.167 to 10% by mass / SiO2. Stabilizer A can be added at a concentration of 0.167 to 10% by mass / SiO2. Furthermore, if the same acid such as sulfuric acid is used as stabilizer A and the acid used in the leaching process in step (c2) above, the acid concentration can also be set as follows: the acid of stabilizer A and the acid (sulfuric acid) added before leaching are added together to obtain an acid concentration of 0.167 to 10% by mass / SiO2 after contact with the cation exchange resin and anion exchange resin in step (c3) above. In the state of removing acid by fully contacting the cation exchange resin and anion exchange resin in the above (c3) step, it is preferable to add acid (stabilizer A) until it reaches the range of 0.167~10 wt% / SiO2.

[0021] As the stabilizer A used in the stabilized active silica aqueous solution (a1) mentioned above, sulfuric acid or potassium hydroxide are preferred, with sulfuric acid being more preferred. If the content of stabilizer A is less than 0.167% by mass / SiO2, the stabilization effect on the active silica aqueous solution is insufficient. If sulfuric acid is used as stabilizer A, sulfuric acid exceeding 10% by mass / SiO2 will react with potassium hydroxide or potassium carbonate added as the seed solution (a2), generating a large amount of salt within the system, making the active silica aqueous solution unstable, and therefore is unsuitable. Furthermore, if potassium hydroxide is used as stabilizer A, potassium hydroxide exceeding 10% by mass / SiO2 may hinder the growth of silica particles when the stabilized active silica aqueous solution is applied to the feed solution.

[0022] Step (a) above includes the stage of obtaining a seed solution (a2), which is achieved by adding potassium hydroxide or potassium carbonate in an amount with a SiO2 / K2O molar ratio of 1.5 to 20 after obtaining a stabilized aqueous solution of active silicic acid (a1). The potassium source is alkaline potassium, such as potassium hydroxide or potassium carbonate, preferably potassium hydroxide. By setting the SiO2 / K2O molar ratio of the stabilized aqueous solution of active silicic acid to 1.5 to 20, silica sol can be produced in step (b) by heating at 90 to 150°C while generating silica particles and adjusting the particle size. The silica component from the active silicic acid present in the solution of step (a) becomes the nucleus, and the surface is coated with silica component dissolved by potassium hydroxide, thus allowing silica particles to grow slowly. The silica component that forms the nucleus from active silicic acid can be exemplified by silica particles as polycondensates of active silicic acid.

[0023] Furthermore, in this invention, as the seed solution (a2), potassium hydroxide or potassium carbonate can be added to a silica sol containing silica particles with an average primary particle size of 5 to 90 nm in an amount where the SiO2 / K2O molar ratio is 1.5 to 20. As a silica sol containing silica particles with an average primary particle size of 5-90 nm, a commercially available silica sol or one adjusted by known methods can be used. For example, a silica sol obtained by heating the above-mentioned stabilized aqueous solution of active silicic acid (a1) can be used. Furthermore, for example, potassium hydroxide or potassium carbonate can be added to the silica sol obtained by the present invention in an amount where the SiO2 / K2O molar ratio is 1.5-20 to create a seed solution (a2). In this way, a silica sol containing silica particles with a growing particle size can be obtained in multiple stages.

[0024] In the method for manufacturing silica sol of the present invention, silica sol can also be manufactured by heating the above-mentioned seed solution (a2), or by using the seed solution (a2) and the feed solution (b1). In step (b), if seed solution and feed solution are used to manufacture large-diameter silica particles in stages, the active silica aqueous solution obtained in step (a) above becomes the seed solution, and the feed solution can be added in stages during the heating operation in step (b).

[0025] In the method for manufacturing silica sol of the present invention, step (b) includes the step of further adding feed liquid (b1). The feed solution (b1) is a stabilized active silica aqueous solution (b1) obtained by adding at least one stabilizer B selected from the group consisting of acid, potassium hydroxide, ammonia and organic base to an active silica aqueous solution (a0) at an amount of 0.167~10% by mass / SiO2.

[0026] In the relationship between seed solution and feed solution, a combination of stabilizing agent A (used in stabilized active silicic acid aqueous solution (a1) and stabilizing agent B (used in stabilized active silicic acid aqueous solution (b1)) and sulfuric acid can be cited. In this case, the stabilizing agent A used in the stabilized active silica aqueous solution (a1) is sulfuric acid, the SiO2 / K2O molar ratio adjuster in the seed solution (a2) is potassium hydroxide, and the stabilizing agent B used in the stabilized active silica aqueous solution (b1) of the feed solution is sulfuric acid.

[0027] Furthermore, regarding the relationship between seed solution and feed solution, a combination of stabilizing agent A (used in stabilized active silicic acid aqueous solution (a1) and stabilizing agent B (used in stabilized active silicic acid aqueous solution (b1)) being potassium hydroxide can be cited. In this case, the stabilizer A used in the stabilized active silica aqueous solution (a1) is potassium hydroxide, the SiO2 / K2O molar ratio adjuster in the seed solution (a2) is potassium hydroxide, and the stabilizer B used in the stabilized active silica aqueous solution (b1) of the feed solution is potassium hydroxide.

[0028] To reduce impurities in the resulting silica sol, cation exchange, anion exchange, or a combination thereof can be performed. Then, in order to adjust the SiO2 concentration of the silica sol, the SiO2 concentration can also be modulated to, for example, 20% to 50% by mass by ultrafiltration or evaporator.

[0029] The silica sol of the present invention comprises silica particles as a polycondensate of active silica in the above-mentioned stabilized aqueous solution of active silica. It also comprises engineered silica particles with the silica particles as a core and the surface coated with silica components dissolved by potassium hydroxide. The silica particles contained in the silica sol of the present invention have an average primary particle size of 5~300 nm.

[0030] Furthermore, the silica sol of the present invention may also contain other components such as potassium ions and sodium ions. For example, the potassium ion content in the silica sol when the SiO2 concentration is 20% by mass is 1500~5000 ppm, and the ratio of (potassium ion concentration) / (Na ion concentration) expressed in ppm is 100~1000. [Example]

[0031] (Example 1) (a) Steps A water-soluble alkali metal silicate, conforming to JIS 3 standard, was prepared as the raw material. The main components of this silicate, excluding water, were 28.8% by mass of SiO₂ and 9.47% by mass of Na₂O. 478g of the silicate was dissolved in 2992g of pure water to prepare 3470g of a sodium silicate aqueous solution. Next, the sodium silicate aqueous solution was passed through a column filled with Amberlite IR-120B hydrogen-form strong acid cation exchange resin at a space velocity of 4.5 per hour. The resulting active silicate aqueous solution (a₀) of 3000g was then collected in a container. An 8% sulfuric acid aqueous solution was added to the above-mentioned active silicic acid aqueous solution (a0) with a sulfuric acid content of 0.313% by mass / SiO2 as the stabilizer, to obtain a stabilized active silicic acid aqueous solution (a1). The viscosity of the obtained active silicic acid aqueous solution was determined using the Oswald method. It was 1.0 mPa·s immediately after manufacturing and 2.2 mPa·s after being stored at 23°C for 3 days. A reaction apparatus equipped with a stirrer and heating device was constructed using a 3L SUS pressure vessel. A seed solution (a2) with a pH adjusted to 12.1 was prepared using a stabilized aqueous solution of active silicic acid (a1, with a SiO2 content of 3.2% by mass), a 10% by mass potassium hydroxide aqueous solution, and pure water. The SiO2 / K2O molar ratio of the adjusted seed solution (a2) was 2.2. (b) Steps The seed solution (a2) was placed in the reaction apparatus and heated while stirring to adjust the liquid temperature in the container to 110-130°C. After the temperature in the container reached 100-130°C, the liquid temperature in the container was maintained at 110-130°C. The stabilized active silicic acid aqueous solution (a1) obtained in step (a) was then continuously supplied as feed solution (b1) until the pH of the reaction solution reached 11.2. The resulting reaction solution was continuously heated and stirred at 110–130°C for 2 hours to obtain silica sol 1. Using a commercially available ultrafiltration apparatus equipped with a polyurethane tubular ultrafiltration membrane with a pore size of approximately 5 nm, the obtained silica sol 1 was concentrated at room temperature until the SiO2 concentration reached 40% by mass. During this concentration, silica sol 1 was stable, and the concentration proceeded very smoothly. The primary particle size of the silica particles in silica sol 1, calculated by nitrogen adsorption, was 44 nm.

[0032] (Example 2) In step (a), an 8% sulfuric acid aqueous solution is added to the active silica aqueous solution (a0) in such a way that the content of sulfuric acid as a stabilizer is 0.938% by mass / SiO2, thereby obtaining a stable active silica aqueous solution (a1). Otherwise, the process is carried out in the same manner as in Example 1 to obtain silica sol 2. The viscosity of the stabilized active silicic acid aqueous solution (a1) was determined using the Oswald method. Immediately after preparation, it was 1.0 mPa·s, and after being stored at 23°C for 3 days, it was 1.3 mPa·s. The pH of the seed solution (a2) was 12.1, and the pH after the feed solution in step (b) was 11.1. Then, the primary particle size of the silica particles in silica sol 2, calculated by nitrogen adsorption, was 43 nm.

[0033] (Example 3) In step (a), an 8% sulfuric acid aqueous solution was added to the active silica aqueous solution (a0) in such a way that the content of sulfuric acid as a stabilizer was 9.38% by mass / SiO2, to obtain an active silica aqueous solution (a1). Otherwise, the process was carried out in the same manner as in Example 1 to obtain silica sol 3. The viscosity of the stabilized active silicic acid aqueous solution (a1) was determined using the Oswald method. Immediately after preparation, it was 1.0 mPa·s, and after being stored at 23°C for 3 days, it was 1.1 mPa·s. The pH of the seed solution (a2) was 12.2, and the pH was 9.7 after the feed solution was supplied in step (b). Then, the primary particle size of the silica particles in silica sol 3 was calculated to be 50 nm using the nitrogen adsorption method.

[0034] (Example 4) In step (a), a 10% aqueous nitric acid solution was added to the active silica aqueous solution (a0) in such a way that the content of nitric acid as a stabilizer was 0.938% by mass / SiO2, to obtain a stabilized active silica aqueous solution (a1), otherwise the same as in Example 1. The viscosity of stabilized active silica aqueous solution (a1) was determined using the Oswald method. It was 1.0 mPa·s immediately after manufacturing and 1.2 mPa·s after being stored at 23°C for 3 days.

[0035] (Example 5) In step (a), citric acid monohydrate is added to the active silicic acid aqueous solution (a0) in such a way that the content of citric acid as a stabilizer is 9.38% by mass / SiO2, to obtain the stabilized active silicic acid aqueous solution (a1), otherwise the same as in Example 1. The viscosity of stabilized active silica aqueous solution (a1) was determined using the Oswald method. It was 1.2 mPa·s immediately after manufacturing and 2.0 mPa·s after being stored at 23°C for 3 days.

[0036] (Example 6) In step (a), a 28% ammonia aqueous solution is added to an active silica aqueous solution (a0) in such a way that the content of ammonia as a stabilizer is 0.938% by mass / SiO2, to obtain a stabilized active silica aqueous solution (a1), otherwise the same as in Example 1. The viscosity of stabilized active silica aqueous solution (a1) was determined using the Oswald method. It was 1.6 mPa·s immediately after manufacturing and 1.4 mPa·s after being stored at 23°C for 3 days.

[0037] (Example 7) In step (a), N,N-diethylmethylamine, as a stabilizer, is added to an active silicic acid aqueous solution (a0) in such a way that the content of N,N-diethylmethylamine is 9.38% by mass / SiO2, to obtain a stabilized active silicic acid aqueous solution (a1). Otherwise, the process is carried out in the same manner as in Example 1 to obtain silica sol 7. The viscosity of stabilized aqueous solution of active silica (a1) was determined using the Oswald method. It was 2.9 mPa·s immediately after manufacturing and 2.5 mPa·s after being stored at 23°C for 3 days.

[0038] (Example 8) In step (a), a 10% potassium hydroxide aqueous solution is added to the active silica aqueous solution (a0) in such a way that the content of potassium hydroxide as a stabilizer is converted to 0.938% by mass of potassium oxide / SiO2, to obtain a stabilized active silica aqueous solution (a1). Otherwise, the process is carried out in the same manner as in Example 1 to obtain silica sol 8. The viscosity of stabilized aqueous solution of active silica (a1) was determined using the Oswald method. It was 11.0 mPa·s immediately after manufacturing and 13.3 mPa·s after being stored at 23°C for 3 days.

[0039] (Comparative Example 1) An aqueous solution of reactive silica (a0) was synthesized in the same manner as in Example 1. The aqueous solution of reactive silica (a0) without the addition of a stabilizer gelled the following day.

[0040] (Comparative Example 2) In step (a), an 8% sulfuric acid aqueous solution is added to an active silica aqueous solution (a0) in such a way that the sulfuric acid used as a stabilizer is 0.156% by mass / SiO2, thereby obtaining an active silica aqueous solution with added sulfuric acid as a stabilizer. Otherwise, the process is the same as in Example 1. The viscosity of the reactive silicic acid aqueous solution, with sulfuric acid added as a stabilizer, immediately after manufacturing was determined using the Oswald method to be 1.0 mPa·s. However, the reactive silicic acid aqueous solution gelled after being stored at 23°C for 3 days.

[0041] (Comparative Example 3) In step (a), an 8% sulfuric acid aqueous solution is added to an active silica aqueous solution (a0) in such a way that the sulfuric acid used as a stabilizer is 18.8% by mass / SiO2, thereby obtaining an active silica aqueous solution with added sulfuric acid as a stabilizer. Otherwise, the process is the same as in Example 1. The viscosity of the active silicic acid aqueous solution with added sulfuric acid as a stabilizer was determined using the Oswald method. Immediately after manufacturing, it was 1.0 mPa·s, and it remained at 1.0 mPa·s after being stored at 23°C for 3 days. The pH of the seed solution (a2) was adjusted to 10.4, and the adjusted SiO2 / K2O molar ratio was 1.2. However, after the feed solution was supplied in step (b), a large amount of gel was generated, and silica sol could not be obtained.

[0042] (Comparative Example 4) In step (a), an 8% sulfuric acid aqueous solution is added to an active silica aqueous solution (a0) in such a way that the sulfuric acid used as a stabilizer is 31.3% by mass / SiO2, thereby obtaining an active silica aqueous solution with added sulfuric acid as a stabilizer. Otherwise, the process is the same as in Example 1. The viscosity of the active silicic acid aqueous solution with added sulfuric acid as a stabilizer was determined using the Oswald method. Immediately after manufacturing, it was 1.0 mPa·s, and it remained at 1.0 mPa·s after being stored at 23°C for 3 days. The pH of the seed solution was adjusted to 10.4, and the adjusted SiO₂ / K₂O molar ratio was 0.7. However, after the feed solution was supplied in step (b), a large amount of gel was generated, and silica sol could not be obtained. [Industrial applicability]

[0043] A stabilized aqueous solution of reactive silica is provided by stabilizing an unstable aqueous solution of reactive silica. Using this reactive silica, silica sol with controlled particle size distribution or particle shape is obtained.

Claims

1. A stabilized aqueous solution of active silicic acid, comprising an 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 stabilizer A is 0.167 to 10% by mass relative to the mass of SiO2 in the active silicic acid aqueous solution, and the viscosity of the aforementioned active silicic acid aqueous solution with a SiO2 concentration of 2.8 to 3.3% by mass after manufacturing at 23°C for no more than 3 hours is determined using the Oswald method to be 0.5 to 20 mPa·s, and the viscosity of the active silicic acid aqueous solution after being stored at 23°C for 3 days is no more than 5.0 times that of the viscosity measured after manufacturing at 23°C for no more than 3 hours.

2. As in claim 1, the stabilized aqueous solution of active silica, wherein, The aforementioned acids are inorganic acids or organic acids.

3. As in claim 2, the stabilized aqueous solution of active silica, wherein, The aforementioned inorganic acid is sulfuric acid or nitric acid.

4. As in claim 2, the stabilized aqueous solution of active silica, wherein, The aforementioned organic acid is citric acid.

5. The stabilized aqueous solution of reactive silica, as described in claim 1, wherein, The aforementioned organic base is an amine or a quaternary ammonium hydroxide.

6. A silica sol comprising silica particles as a polycondensate of active silica in a stabilized aqueous solution of active silica according to any one of claims 1 to 5, wherein the average primary particle size of the silica particles is 5 to 300 nm.

7. As in claim 6, the silica sol, wherein, The aforementioned silica sol contains potassium ions and sodium ions. When the SiO2 concentration is 20% by mass, the potassium ion content in the silica sol is 1500~5000 ppm, and the ratio of potassium ion concentration to sodium ion concentration (in ppm) is 100~1000.

8. A method for manufacturing a silica sol as claimed in claim 6 or claim 7, comprising the following steps (a) to (b): (a) Step: comprising the steps of obtaining a stabilized aqueous solution of active silica (a1) and obtaining a seed solution (a2), wherein the step of obtaining the stabilized aqueous solution of active silica (a1) is to contain a 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 / SiO2; wherein the step of obtaining the seed solution (a2) is to contain potassium hydroxide in the stabilized aqueous solution of active silica (a1) or in a silica sol containing silica particles with an average primary particle size of 5 to 90 nm in such a way that the SiO2 / K2O molar ratio is 1.5 to 20; (b) Step: Heating the seed solution (a2) obtained in step (a) at 90~150°C.

9. The method for manufacturing silica sol as described in claim 8, wherein, The active silica aqueous solution (a0) used in step (a) above is obtained through the following steps (c1) to (c3): (c1) Step: cation exchange of water glass to obtain the active silica aqueous solution; (c2) Step: adding acid to the obtained active silica aqueous solution and aging it at a temperature above 0°C and below 40°C for 1 to 30 hours; (c3) Step: cation exchange and anion exchange of the aged active silica aqueous solution to obtain the active silica aqueous solution (a0).

10. The method for manufacturing silica sol as described in claim 9, wherein, In step (c2) above, the pH after adding acid is 0.5 to 3.0, and the pH of the active silicic acid aqueous solution (a0) obtained by step (c3) is greater than 3.0 and less than 6.

0.

11. A method for manufacturing silica sol as described in claim 9 or claim 10, wherein, The acid used in step (c2) above is sulfuric acid.

12. A method for manufacturing silica sol as described in any one of claims 8 to 10, wherein, The aforementioned step (b) includes a further step of adding a stabilized feed solution (b1) to the heated seed solution (a2). The stabilized feed solution (b1) is a stabilizer B selected from the group consisting of acid, potassium hydroxide, ammonia and organic base added to an active silicic acid aqueous solution (a0). The stabilizer B is in an amount of 0.167 to 10% by mass based on the mass of SiO2 in the active silicic acid aqueous solution.

13. The manufacturing method as described in claim 12, wherein, The aforementioned stabilizer A is sulfuric acid, the aforementioned SiO2 / K2O molar ratio adjuster is potassium hydroxide, and the aforementioned stabilizer B is sulfuric acid.

14. The manufacturing method as described in claim 12, wherein, The aforementioned stabilizer A is potassium hydroxide, the aforementioned SiO2 / K2O molar ratio adjuster is potassium hydroxide, and the aforementioned stabilizer B is potassium hydroxide.