Large particle silica sol dispersed in alcohol and method of producing the same

Abstract

To provide large-particle silica sol dispersed in an alcohol solvent, having low settleability, and high re-dispersibility even when settled, and to provide a method of producing the same.SOLUTION: A silica sol formed of silica particles of a mean particle diameter measured by a dynamic light scattering method of 300 to 600nm dispersed in a 1-5C alcohol, has the following settleability which is measured by carrying out a storage stability test comprising steps of storing the silica sol in a round-bottomed cylindrical transparent container, sealing and shaking the container 1000 times in five minutes, and allowing the sealed container to stand still for 30 days at a temperature of 20°C, in which the boundary between a light-transmittable segment and a light un-transmittable segment observed on the opposite surface of the container is present at a height a from the bottom of the container, and the liquid surface of the silica sol is present at a height b from the boundary, showing the settleability by the ratio of a:b=10:0 to 8.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a large-particle silica sol dispersed in alcohol and a method for producing the same.

Background Art

[0002] Large-particle silica sols are used in various applications by utilizing the characteristics of large-particle silica particles. For example, by incorporating a large-particle silica sol into a coating agent and applying it to the film surface, it is possible to prevent film damage by utilizing the unevenness of the film surface, use it as an anti-blocking agent for the purpose of suppressing adhesion, or use it as a strength improver as a filler contained in a coating agent or an adhesive.

[0003] As a method for using large-particle silica sols, a method of wet-grinding silica powder into a sol has been conventionally known. For example, Patent Document 1 describes a method of obtaining a wet silica dispersion by dispersing wet silica obtained by a precipitation method, and Patent Document 2 describes a silica slurry composition containing 50 to 85% by mass of spherical silica powder having a volume average particle diameter of 0.46 to 1.3 μm, a standard deviation value with respect to the volume average particle diameter of 45 to 110%, and a reactive silanol group amount of 1.5 to 3.0 per nm 2 is described.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present invention aims to provide a silica sol in which large-particle silica is dispersed in an alcohol solvent, the silica sol having low sedimentation properties and high redispersibility even after sedimentation, and a method for producing the same.

Means for Solving the Problems

[0006] In a first aspect, the present invention is a silica sol in which silica particles having an average particle diameter measured by dynamic light scattering method of 300 to 600 nm are dispersed in an alcohol having 1 to 5 carbon atoms, the silica sol having the following sedimentation properties: Sedimentation properties: When a storage test is performed in which the silica sol is placed in a transparent container having a cylindrical shape and a round bottom, sealed, shaken 1000 times in 5 minutes, and then the sealed container is left standing at 20°C for 30 days, the boundary between the light-transmissible part and the light-non-transmissible part observed on the opposite side of the container is at a height of a from the bottom of the container, and the liquid level of the silica sol is at a height of b from the boundary, and a:b = 10:0 to 8, sedimentation properties. In a second aspect, the silica sol according to the first aspect, further having the following redispersibility: Redispersibility: When the silica sol is placed in a transparent container having a cylindrical shape and a round bottom, sealed, shaken 1000 times in 5 minutes, left standing at 20°C for 30 days for storage, and then the container is shaken 100 times in 30 seconds, the solid content (c: mass%) of the silica sol is 60 to 100% with respect to the solid content (d: mass%) of the silica sol immediately before the storage test, redispersibility. In a third aspect, the silica sol according to the first or second aspect, in which the particle size range of D20 to D80 by laser diffraction method is present in the range of 250 nm to 550 nm. In a fourth aspect, the silica sol according to any one of the first to third aspects, wherein the alcohol is methanol, ethanol, propanol, isopropanol, butanol, isobutanol, propylene glycol monomethyl ether, or propylene glycol monoethyl ether. In a fifth aspect, the silica sol according to any one of the first to fourth aspects, in which the decrease in pH after storage at 50°C for 28 days is within 2.0. As a sixth aspect, the silica sol according to any one of the first to fifth aspects, wherein the viscosity is 2 to 10 mPa·s when the SiO2 concentration is 20% by mass, As a seventh aspect, the silica sol according to any one of the first to sixth aspects, wherein the absorbance at a wavelength of 350 nm of the silica sol having a SiO2 concentration of 0.05% by mass is 1.5 or less, As an eighth aspect, the silica sol according to any one of the first to seventh aspects, containing 0.1 to 5.0% by mass of water, As a ninth aspect, the following steps (A) to (B): (A) step: a step of producing an aqueous silica sol having an average particle diameter by dynamic light scattering method of 300 to 600 nm, (B) step: a step of solvent substitution of the aqueous medium of the aqueous silica sol obtained in the step (A) with an alcohol having 1 to 5 carbon atoms using an ultrafiltration device, a method for producing the silica sol according to any one of the first to eighth aspects, As a tenth aspect, the method for producing a silica sol according to claim 9, wherein the aqueous silica sol used in the step (A) is a silica sol obtained by adding an alkali component and an acidic aqueous silica solution to silica particles generated from an aqueous solution of silicic acid obtained by cation-exchanging an aqueous solution of alkali silicate to grow the particles, and As an eleventh aspect, the method for producing a silica sol according to the ninth or tenth aspect, wherein an acid is added to the aqueous sol in the step (B) in a range of 50 to 5000 μS / cm as electric conductivity, and the solvent is substituted with an alcohol having 1 to 5 carbon atoms using an ultrafiltration device until the electric conductivity becomes less than 5 to 50 μS / cm.

Advantages of the Invention

[0007] The production of large-particle silica sol has been carried out by a method of dispersing or wet-milling silica powder in an aqueous medium or an organic solvent. The silica powder has a particle diameter of several μm, but particle subdivision occurs during the dispersion or wet-milling stage. At that time, the particle size distribution becomes wide, and a silica sol having a wide particle size distribution from fine silica particles to coarse silica particles is formed. These silica sols tend to have coarse silica particles settle, which can be an obstacle to obtaining a highly dispersible sol. In addition, since it is mechanical pulverization, the particle shape may become non-uniform or the particle size distribution may spread during the process of crushing the particles, which may be unsuitable depending on the application.

[0008] The present invention uses a technique for increasing the particle size of silica particles in an aqueous medium, and by solvent-exchanging sufficiently increased silica particles into an organic solvent (for example, an alcohol having 1 to 5 carbon atoms), an organic solvent-dispersed silica sol having dispersion stability can be obtained. Further, since there is no process such as pulverization, an organic solvent-dispersed silica sol with a regular particle shape can be obtained without the particle shape becoming non-uniform.

[0009] In the present invention, by solvent-exchanging the aqueous medium of a large-particle aqueous silica sol into an organic solvent, a large-particle silica sol dispersed in the organic solvent can be obtained. The solvent exchange can be carried out using an ultrafiltration device (UF device). When the solvent exchange is carried out by an evaporation method, the solvent to be replaced with the solvent removed to the outside by evaporation is not supplied so that the SiO2 solid content becomes constant, but is carried out under conditions where the SiO2 solid content fluctuates, which tends to cause precipitation of SiO2.

[0010] On the other hand, in the present invention, in order to solvent-exchange the aqueous medium of an aqueous silica sol using an ultrafiltration device (UF device) into an organic solvent, there is almost no change in the SiO2 solid content during the solvent exchange process, and therefore no precipitation of SiO2 occurs.

[0011] In the present invention, by solvent-exchanging the aqueous medium of a large-particle aqueous silica sol obtained by making large-particle silica particles have a uniform large particle size in an aqueous medium into an alcohol having 1 to 5 carbon atoms using an ultrafiltration device (UF device), a silica sol dispersed in a stable organic solvent with low sedimentation property can be obtained even for large-particle silica particles.

Brief Description of the Drawings

[0012]

Figure 1

Embodiments for Carrying Out the Invention

[0013] Hereinafter, preferred embodiments of the present invention will be described. However, the following embodiments are examples for explaining the present invention, and the present invention is not limited to the following embodiments at all. In one embodiment of the present invention, a silica sol in which silica particles having an average particle diameter by the dynamic light scattering method of 300 to 600 nm are dispersed in an alcohol having 1 to 5 carbon atoms is a silica sol having specific sedimentation properties.

[0014] This sedimentation property is evaluated as follows: When a silica sol is placed in a transparent container having a cylindrical shape and a round bottom, sealed, shaken 1000 times in 5 minutes, and then the sealed container is left standing at 20 ° C for 30 days, the boundary between the light-transmissible part and the light-non-transmissible part observed on the opposite side of the container is at a height of a from the bottom of the container, and the liquid level of the silica sol is at a height of b from the boundary, and the ratio of a:b = 10:0 to 8. Since the silica sol of the present invention has an average particle diameter by the dynamic light scattering method of 300 to 600 nm, a sufficiently dispersed silica sol is in the form of a white colloid and is not light-transmissive, but changes to a light-transmissible liquid as the particles settle. A boundary between a light-non-transmissible region and a light-transmissible region is formed, and the heights of the boundary from the bottom of the container and the boundary from the liquid level can be measured.

[0015] In one embodiment of the present invention, the silica sol can further have specific redispersibility. This redispersibility is evaluated as follows: When a silica sol is placed in a transparent container having a cylindrical shape and a round bottom, sealed, shaken 1000 times in 5 minutes, left standing at 20 ° C for 30 days for storage, and then the container is shaken 100 times in 30 seconds, the solid content (c: mass%) of the silica sol is 60 to 100% with respect to the solid content (d: mass%) of the silica sol immediately before the storage test, as the redispersibility.

[0016] The transparent container used in the above storage test is preferably a cylindrical container in which sedimentation can be confirmed in the vertical direction. A shape with a length in the height direction of 10 times or more, for example, 10 to 20 times the diameter of the cylinder is preferred. For example, a transparent test tube can be used. As the material, a glass or plastic material can be selected. Since the silica sol of the present invention has an average particle diameter of 300 to 600 nm by the dynamic light scattering method, a silica sol with a solid content of 10 to 50% by mass, or 20 to 40% by mass is white in appearance. When the silica particles in this silica sol settle to the bottom, it separates into a sediment part with a high SiO2 solid content concentration and a supernatant part with a dilute SiO2 solid content. In the present invention, a storage test is performed by allowing a silica sol in a sufficiently dispersed state to stand still in a sealed container at 20°C for 30 days. After the storage test is completed, the container is shaken 100 times in 30 seconds. This shaking can be carried out by bringing the storage test container into contact with a shaker and transmitting the vibration of the shaker to the storage container. Immediately after the above shaking, the solid content of the silica sol is measured, and it is 60 to 100%, or 70 to 100%, or 80 to 100%, or 90 to 100%, or 95 to 100% of the solid content immediately before the storage test.

[0017] In one embodiment of the present invention, the solid content measurement can be performed from the ratio of the mass of the residue before firing of the liquid extracted from the liquid part of the storage test container and fired at 1000°C.

[0018] Even when the above shaking is performed, if a solid adheres to the bottom, the solid content of the liquid present above the adherent is measured, and if the result is within the above solid content range, it can be used as the silica sol of the present invention. A value within the above solid content range is a silica sol with high redispersibility. The condition of the shaking time of 30 seconds used for evaluation is a sufficiently dispersed state, but by further extending it, a silica sol with a high degree of dispersibility can be obtained, which is shaking for 60 seconds or more, and further 60 to 600 seconds. For example, shaking for 300 seconds can be performed to obtain a highly dispersed silica sol.

[0019] The shaker used in the present invention has, for example, a power unit built into the pedestal at the lower part of the shaking table. The power unit uses a mechanism in which the rotation of the motor is converted into the reciprocating motion of the shaking table by transmitting power from the motor to the pulley via a belt.

[0020] In the present invention, the particle size range of D20 to D80 by the laser diffraction method can be in the range of 250 nm to 550 nm.

[0021] In this specification, the above X% cumulative diameter (D X ) refers to the particle diameter corresponding to the cumulative X volume% from the small particle side of the cumulative particle size distribution (the cumulative value in the volume frequency particle size distribution is X%).

[0022] The above cumulative diameter is determined as follows. First, for a dispersion of particles or the like to be targeted, the particle size distribution is measured using a laser diffraction scattering particle size distribution measuring device to obtain a cumulative particle size distribution curve based on volume. Then, in the obtained cumulative particle size distribution, the volume particle size at the time of X% cumulative is defined as the X% cumulative diameter (D X ) of the particles or the like.

[0023] In the present invention, examples of the alcohol having 1 to 5 carbon atoms include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, propylene glycol monomethyl ether, or propylene glycol monoethyl ether. In particular, silica particles with a large particle size can prevent sedimentation by a branched alcohol, and isopropyl alcohol can be preferably used.

[0024] In one embodiment of the present invention, the decrease in pH after storage at 50°C for 28 days can be adjusted within 2.0, for example, within 1.0. It is considered that silica particles with a large particle size have a low amount of silanol groups per unit volume and a small amount of adsorption and desorption of alkali ions, so the rate of change of pH is low.

[0025] In addition, silica particles with a large particle size have a low specific surface area, and the interaction between silica particles is also relaxed, so the viscosity can exist in the range of 2 to 10 mPa·s. When it is an alcohol solvent containing 0.1 to 5.0% by mass of water, a range of 2 to 10 mPa·s is preferable.

[0026] When the high refractive index particles and the silica particles of the present invention are used in combination, for example, when the high refractive index particles are titanium oxide, the silica of the present invention is permeable, and the absorbance at a wavelength of 350 nm of a silica sol with a SiO2 concentration of 0.05% by mass can be set to 1.5 or less.

[0027] In one embodiment of the present invention, the following steps (A) to (B): (A) step: A step of producing an aqueous silica sol having an average particle size by the dynamic light scattering method of 300 to 600 nm, (B) step: A step of replacing the aqueous medium with an alcohol having 1 to 5 carbon atoms using an ultrafiltration device for the aqueous silica sol obtained in the step (A). It can be produced including this step.

[0028] In one embodiment of the present invention, in the step (A), it can be produced by building up an aqueous silica sol.

[0029] (A) step is a silica aqueous sol obtained through the following steps (I) and (II) from a silica particle dispersion obtained by heating a silicic acid solution obtained by cation exchange of an alkaline aqueous solution of silicate, or a silica particle dispersion obtained by hydrolysis of tetraalkoxysilane, (I) step is a step (I-i) of adding an alkaline component to the silica particle dispersion and adding a silicic acid solution, a step (I-ii) of heating at 50 to 200 °C, or a combined step (I-iii) thereof. (II) step can be produced by performing cation exchange and anion exchange on the silica particle dispersion obtained in the step (I).

[0030] As the silicic acid solution used in the above step (I), an acidic silicic acid solution obtained by cation-exchanging an aqueous alkali metal hydroxide solution or a silicic acid solution obtained by hydrolyzing tetraalkoxysilane can be used. As the tetraalkoxysilane, tetraethoxysilane or tetramethoxysilane can be used.

[0031] In the above step (I), in order to prevent aggregation, it is desirable to perform particle growth in a state where silica is at a low concentration. For example, it can be carried out in the range of 0.1 to 20% by mass of silica concentration. An operation of concentrating the silica concentration to 20 to 60% by mass can be added during the process as the silica particle size increases. In addition, in order to simultaneously increase the silica particle size and concentrate the silica concentration, the addition of the silicic acid solution can be carried out in an open system.

[0032] In the above step (II), ions are reduced by ion exchange. At this time, cations and anions can be removed. In the present invention, since the silica particle size is in the range of 300 to 600 nm and has a large particle shape, the cohesive force between silica particles is lower than that of silica sol having a relatively small particle size, so it can exist stably even at a pH near neutrality.

[0033] (Step (B) is a step of replacing the aqueous medium of the aqueous silica sol obtained in step (A) with an alcohol having 1 to 5 carbon atoms. Examples of the above alcohol include methanol, ethanol, propanol, isopropanol, butanol, isobutanol, propylene glycol monomethyl ether, or propylene glycol monoethyl ether. Among them, isopropanol (that is, 2-propanol) can be preferably used.

[0034] In step (B), an acid can be added to the aqueous sol in the range of 50 to 5000 μS / cm or 50 to 500 μS / cm in terms of electrical conductivity, and solvent replacement with an alcohol having 1 to 5 carbon atoms can be carried out using an ultrafiltration device until the electrical conductivity becomes less than 5 to 50 μS / cm.

[0035] Examples of the acid include aqueous solutions of mineral acids such as sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid. Among them, sulfuric acid can be preferably used. These acids can be used, for example, at a concentration of 1 to 15% by mass or 5 to 10% by mass.

[0036] According to the above solvent substitution, it is possible to substitute from an aqueous medium to an alcohol solvent and remove the ions present in the medium. As the ions to be removed, both anions and cations can be reduced. In the present invention, as the reduction of anions, sulfate ions can be reduced until the electric conductivity becomes in the range of about 5 to 20 μS / cm or 10 to 20 μS / cm, and then solvent substitution can be performed.

[0037] As the remaining moisture in the process of substituting from an aqueous medium to an alcohol solvent, it can contain 0.1 to 5.0% by mass of moisture.

Examples

[0038] <Physical properties of the dispersion> · Specific gravity: Determined by the floating scale method. · pH: Determined by a pH meter (manufactured by Toa TDK Corporation). (20 °C) The aqueous dispersion silica sol was measured as it was, and the organic solvent dispersion silica sol was measured after being diluted with water at a mass ratio of 1:1. · Electric conductivity: Determined by an electric conductivity meter (manufactured by Toa TDK Corporation). (20 °C) The aqueous dispersion silica sol was measured as it was, and the organic solvent dispersion silica sol was measured after being diluted with water at a mass ratio of 1:1. · Viscosity: Measured at 25 °C using a B-II type viscometer (manufactured by Toki Sangyo Co., Ltd.).

[0039] · SiO2 concentration: Determined from the residual solid when fired at 1000 °C. · Moisture: Determined by the Karl Fischer titration method. · Average particle diameter by dynamic light scattering method (DLS): Diluted with a dispersion solvent and measured using a dynamic light scattering measurement device: Zetasizer manufactured by Malvern Instruments Ltd. · Volume-based D20, D50, D80 by laser diffraction method: Measured with a nanoparticle size distribution measuring device, SALD-7500nano, manufactured by Shimadzu Corporation. · Absorbance: Diluted to 0.05 mass% with the dispersion solvent, and the absorbance at a wavelength of 350 nm was measured using an ultraviolet-visible-near-infrared spectrophotometer, UV-3600Plus, manufactured by Shimadzu Corporation.

[0040] <Sedimentation property> The silica sol was placed in a transparent container having a cylindrical shape and a round bottom (manufactured by Tokyo Glass Kikai Co., Ltd., Fine common stopper test tube, capacity 20 mL, outer diameter 18 mm, inner diameter 14 mm, height 180 mm), sealed, and shaken 1000 times in 5 minutes. After that, a storage test was carried out by allowing the sealed container to stand at 20 °C for 30 days. Under visible light (wavelength 380 - 780 nm) irradiation by LED illumination (about 3500 lumens), the boundary between the transmissible part and the non-transmissible part observed on the opposite side of the container was visually determined. The height a of the boundary from the bottom of the container and the height b from the boundary to the liquid surface of the silica sol were determined, and their ratio (a:b) was obtained.

[0041] <Redispersibility> The silica sol was placed in a transparent container having a cylindrical shape and a round bottom, sealed, and shaken 1000 times in 5 minutes. After standing and storing at 20 °C for 30 days, when shaken 100 times in 30 seconds, the SiO2 concentration was c mass%, and the SiO2 concentration before standing was d mass%. It was calculated from the value of c / d (%).

[0042] (Example 1) An 8.0 mass% sulfuric acid aqueous solution was added to an aqueous silica sol (1) (manufactured by Nissan Chemical Industries, Ltd., trade name MP-4540M, containing 40.3 mass% as the mass of SiO2, average particle diameter 418 nm by dynamic light scattering method) to obtain an aqueous silica sol (2) (pH 3.1, containing 40.4 mass% as the mass of SiO2, average particle diameter 440 nm by dynamic light scattering method). Then, it was replaced with 2-propanol using an ultrafiltration device to obtain a 2-propanol dispersed silica sol (1). The obtained 2-propanol dispersed silica sol (1) contained 40.8 mass% as the mass of SiO2.

[0043] (Example 2) Similar to Example 1, the aqueous dispersion acidic silica sol (2) was replaced with 2-propanol using an ultrafiltration device to obtain a 2-propanol dispersion silica sol (2). The obtained 2-propanol dispersion silica sol (2) contained 19.0% by mass of SiO₂ as the mass of SiO₂.

[0044] (Comparative Example 1) Silica powder (manufactured by Admatechs Co., Ltd., SO-C2, particle size 0.4 - 0.6 μm, particle size measured by a laser analytical particle size distribution analyzer) was stirred with a dispersing stirring blade and dispersed in 2-propanol to obtain a 2-propanol dispersion silica sol (3). The obtained 2-propanol dispersion silica sol (3) contained 17.3% by mass of SiO₂ as the mass of SiO₂.

[0045] (Comparative Example 2) In a 500 mL plastic container, 35 g of silica powder (manufactured by Admatechs Co., Ltd., SO-C2, particle size 0.4 - 0.6 μm, particle size measured by a laser analytical particle size distribution analyzer), 333 g of zirconia balls (diameter 1 mm), and 375 g of water were put in, and treated at a rotation speed of 220 rpm for 72 hours to obtain an aqueous dispersion silica sol (3) (pH 6.5, containing 8.2% by mass of SiO₂ as the mass of SiO₂, average particle size 260 nm by dynamic light scattering method). The obtained aqueous dispersion silica sol (3) was used with an evaporator to distill off water while adding 2-propanol at 170 Torr to replace water with 2-propanol to obtain a 2-propanol dispersion silica sol (4). The obtained 2-propanol dispersion silica sol (4) contained 20.3% by mass of SiO₂ as the mass of SiO₂.

[0046] [Table 1]

[0047] The 2-propanol-dispersed silica sols obtained in Example 1 and Example 2 had suppressed sedimentation properties when allowed to stand at 20°C and good redispersibility compared to those obtained in Comparative Example 1 and Comparative Example 2. Furthermore, it was suggested that the aggregation of silica in the silica sol was suppressed in the 2-propanol-dispersed silica sols obtained in Example 1 and Example 2, as judged from the average particle size and the particle size distribution obtained by measurement using the laser diffraction method.

Industrial Applicability

[0048] The present invention provides a large-particle silica sol dispersed in an alcohol solvent, which has low sedimentation properties and high redispersibility even after sedimentation.

Claims

1. A silica sol in which silica particles having an average particle size of 300 to 600 nm as determined by a dynamic light scattering method are dispersed in an alcohol having 1 to 5 carbon atoms, the silica sol having the following sedimentation properties: Sedimentation property: When silica sol is placed in a cylindrical transparent container having a round bottom, sealed, and shaken 1000 times for 5 minutes, and then a storage test is performed in which the sealed container is left to stand at 20°C for 30 days, the boundary between the light-transmitting part and the light-opaque part observed on opposite sides of the container is at a height a from the bottom of the container, and the liquid surface of the silica sol is at a height b from the boundary, with the ratio of a:b=10:0-8.

2. The silica sol according to claim 1, further having the following redispersibility: Redispersibility: when the silica sol is placed in a cylindrical transparent container having a round bottom, sealed, and shaken 1,000 times for 5 minutes, and then allowed to stand and store at 20°C for 30 days, the container is shaken 100 times for 30 seconds. The redispersibility is such that the solid content (c: mass %) of the silica sol is 60 to 100% of the solid content (d: mass %) of the silica sol immediately before the storage test.

3. 3. The silica sol according to claim 1, wherein the particle size range of D20 to D80 by laser diffraction method is 250 nm to 550 nm.

4. 3. The silica sol according to claim 1 or 2, wherein the alcohol is methanol, ethanol, propanol, isopropanol, butanol, isobutanol, propylene glycol monomethyl ether, or propylene glycol monoethyl ether.

5. 3. The silica sol according to claim 1, which exhibits a decrease in pH of 2.0 or less after storage at 50°C for 28 days.

6. SiO ２ The silica sol according to claim 1 or 2, having a viscosity of 2 to 10 mPa·s when the concentration is 20% by mass.

7. SiO ２ 3. The silica sol according to claim 1 or 2, wherein the silica sol has an absorbance of 1.5 or less at a wavelength of 350 nm when the silica sol has a concentration of 0.05% by mass.

8. The silica sol according to claim 1 or 2, containing 0.1 to 5.0 mass % of water.

9. The following steps (A) and (B): Step (A): producing an aqueous silica sol having an average particle size of 300 to 600 nm as determined by a dynamic light scattering method; 3. The method for producing a silica sol according to claim 1 or 2, further comprising: (B) a step of subjecting the aqueous medium of the aqueous silica sol obtained in (A) to solvent replacement with an alcohol having 1 to 5 carbon atoms using an ultrafiltration apparatus.

10. The method for producing a silica sol according to claim 9, wherein the aqueous silica sol used in step (A) is a silica sol obtained by adding an alkali component and an acidic silicic acid aqueous solution to silica particles generated from a silicic acid aqueous solution obtained by cation exchange of an alkaline silicic acid aqueous solution to grow particles.

11. The method for producing a silica sol according to claim 10, wherein in the step (B), an acid is added to the aqueous sol in an amount equivalent to an electric conductivity of 50 to 5000 μS / cm, and the solvent is replaced with an alcohol having 1 to 5 carbon atoms using an ultrafiltration device until the electric conductivity becomes less than 5 to 50 μS / cm.

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