Method for producing silica sol

Abstract

A method for producing a silica sol, comprising: a first step of adding an organic acid to at least one of a liquid (A) and a liquid (C), wherein the liquid (A) comprises an alkali catalyst, water and a first organic solvent, and the liquid (C) comprises water; and a second step of mixing a liquid (B) and the liquid (C) in the liquid (A) after the first step to prepare a reaction liquid, wherein the liquid (B) comprises an alkoxysilane or a condensate thereof, and a second organic solvent.

Description

Technical Field

[0001] The present invention relates to a method for producing silica sol. Background Art

[0002] Conventionally, chemical mechanical polishing (CMP) using a polishing composition has been performed on the surfaces of materials such as metals, semi-metals, non-metals, and their oxides. It is known that the polishing composition is generally composed of a mixture / dispersion of an aqueous solution having a chemical polishing effect and particles (abrasives) having a mechanical polishing effect, and silica sol is used as the abrasive.

[0003] It is known that the performance of silica sol during grinding varies depending on the particle size and shape of the silica particles. For example, it is known that the grinding speed of the grinding object is higher for irregular silica particles that are associated with two or more silica particles than for spherical silica particles that are not associated with other silica particles (see the 2007 Precision Engineering Society Spring Conference Academic Lecture Papers Collection, pp. 1147-1148).

[0004] On the other hand, International Publication No. 2017 / 022552 (equivalent to U.S. Patent Application Publication No. 2019 / 010059, Chinese Patent Application Publication No. 107848811, and Taiwan Patent Application Publication No. 201716328) discloses a method for producing a silica sol, the method comprising: mixing a liquid (A) containing an alkali catalyst, a liquid (B) containing an alkoxysilane or a condensate thereof, and a liquid (C) containing water to prepare a reaction liquid. By this method, a silica sol having a uniform particle size of silica particles can be stably produced regardless of the particle size of the silica particles. Summary of the invention

[0005] Problem that the invention aims to solve

[0006] However, the silica sol obtained by the method of International Publication No. 2017 / 022552 (equivalent to the specification of U.S. Patent Application Publication No. 2019 / 010059, the specification of Chinese Patent Application Publication No. 107848811, and the specification of Taiwan Patent Application Publication No. 201716328) has a large roundness of the silica particles contained in it. From the perspective of obtaining irregular-shaped silica particles with a small roundness that can improve the grinding performance, there is still room for improvement.

[0007] Solutions for solving problems

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a silica sol, which can stably produce a silica sol having a smaller average circularity of silica particles.

[0009] In order to solve the above problems, the inventors of the present invention have repeatedly conducted in-depth research. As a result, it was found that the above problems can be solved by the following method for producing silica sol, thereby completing the present invention; the production method includes the following steps: a first step, adding an organic acid to at least one of liquid (A) and liquid (C), wherein the liquid (A) contains an alkali catalyst, water and a first organic solvent, and the liquid (C) contains water; and a second step, after the first step, mixing liquid (B) and the liquid (C) in the liquid (A) to prepare a reaction liquid, wherein the liquid (B) contains an alkoxysilane or a condensate thereof, and a second organic solvent.

[0010] Effects of the Invention

[0011] According to the present invention, there is provided a method for producing a silica sol, which can stably produce a silica sol having a smaller average circularity of silica particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a diagram showing irregularly shaped silica particles.

[0013] Figure 2 This is a photograph of the silica sol produced in the example observed with a scanning electron microscope. DETAILED DESCRIPTION

[0014] Hereinafter, the implementation of the present invention will be described, but the present invention is not limited to the following implementation. It should be noted that, unless otherwise specified, the operation and physical properties are measured under the conditions of room temperature (20-25°C) / relative humidity 40-50%RH. In addition, in this specification, "X-Y" indicating a range means "above X and below Y".

[0015] The method for producing silica sol according to one embodiment of the present invention comprises: a first step of adding an organic acid to at least one of a liquid (A) containing an alkali catalyst, water and a first organic solvent (also referred to as "liquid (A)" in this specification) and a liquid (C) containing water (also referred to as "liquid (C)" in this specification); and a second step of mixing a liquid (B) containing an alkoxysilane or a condensate thereof and a second organic solvent (also referred to as "liquid (B)" in this specification) and the liquid (C) in the liquid (A) after the first step to prepare a reaction liquid. In the first step, the organic acid is added to at least one of the liquid (A) and the liquid (C). Thus, in the second step, in the presence of the organic acid, the alkoxysilane or the condensate thereof is hydrolyzed and polycondensed in the reaction liquid to produce silica sol. According to the above configuration, in the method for producing silica sol of the present invention, silica sol having a smaller average circularity of silica particles can be stably produced.

[0016] The reason for exerting the above-mentioned effect by the manufacturing method of the present invention is not yet clear, but it can be considered as follows. By adding an organic acid to at least one of liquid (A) and liquid (C) in the first step, liquid (B) is mixed with liquid (A) and liquid (C) in the presence of an organic acid in the second step. That is, it is believed that it may be: when alkoxysilane or its condensate contacts the base catalyst of liquid (A), there is an organic acid, thereby, the phenomenon that alkoxysilane or its condensate is locally contacted with a large amount of base catalyst is alleviated, thereby suppressing rapid particle growth, thereby forming silica particles with a smaller average circularity (preferably less than 0.60). However, the mechanism is only a guess, and of course does not limit the scope of the technology of the present invention.

[0017] In a preferred embodiment of the present invention, liquid (C) is a liquid (C1) containing water and having a pH of 5.0 or more and less than 8.0; or liquid (C) is a liquid (C2) containing water and not containing an alkali catalyst. That is, it is preferred that the silica sol is produced using a liquid (C1) containing the largest amount of "water for hydrolysis" measured in a molar ratio in such a manner that the concentration of the alkali catalyst among the three components controlling the reaction rate does not become concentrated locally. Or it is preferred that the silica sol is produced using a liquid (C2) containing water and not containing an alkali catalyst on the addition side in such a manner that the concentration of the alkali catalyst does not become concentrated locally. Thus, in a multi-component reaction of more than three components, silica particles with a smaller roundness can be formed, and a silica sol with a uniform particle size of silica particles can be stably produced.

[0018] In the present invention, from the viewpoint of the purity (high purification) of the obtained silica sol, it is particularly preferred to produce the silica sol by a sol-gel method. The sol-gel method refers to a method in which a metal organic compound solution is used as a starting material, the solution is made into a sol in which metal oxide or hydroxide particles are dissolved by hydrolysis and polycondensation of the compound in the solution, and the reaction is further carried out to obtain a gelled amorphous gel; in the present invention, the silica sol can be obtained by hydrolyzing alkoxysilane or its condensate in an organic solvent containing water.

[0019] However, the production method of the present invention is not limited to silica sol, and can also be applied to the synthesis of metal oxides other than silica sol using a sol-gel method.

[0020] 《Method for producing silica sol》

[0021] The method for producing silica sol of the present invention comprises: a first step of adding an organic acid to at least one of liquid (A) and liquid (C), wherein the liquid (A) contains an alkali catalyst, water and a first organic solvent, and the liquid (C) contains water; and a second step of mixing liquid (B) and liquid (C) in liquid (A) after the first step to prepare a reaction liquid, wherein the liquid (B) contains an alkoxysilane or a condensate thereof, and a second organic solvent. In the prepared reaction liquid, the alkoxysilane or the condensate thereof generates silica sol by hydrolysis and polycondensation. The structural features of the method for producing silica sol of the present invention are described below.

[0022] In the present invention, the liquid (C) is preferably a liquid (C1) containing water and having a pH of 5.0 or more and less than 8.0, or a liquid (C2) containing water and not containing an alkali catalyst. Hereinafter, the method of using the liquid (C) containing water is referred to as the first embodiment, the method of using the liquid (C1) containing water and having a pH of 5.0 or more and less than 8.0 as the liquid (C) is referred to as the second embodiment, and the method of using the liquid (C2) containing water and not containing an alkali catalyst as the liquid (C) is referred to as the third embodiment.

[0023] [Liquid (A) containing a base catalyst, water and a first organic solvent]

[0024] The liquid (A) in the first to third embodiments of the present invention is common, and the following description is also common.

[0025] The liquid (A) comprising an alkali catalyst, water and a first organic solvent of the present invention can be prepared by mixing an alkali catalyst, water and a first organic solvent. In addition to the alkali catalyst, water, an organic solvent and an organic acid added as required, the liquid (A) may also contain other components within the range that does not impair the effects of the present invention.

[0026] As the base catalyst contained in the liquid (A), those known in the past can be used. From the viewpoint of being able to minimize the mixing of metal impurities, etc., the base catalyst is preferably at least one of ammonia, tetramethylammonium hydroxide, other ammonium salts, etc. From the viewpoint of excellent catalytic effect, ammonia is more preferred among these. Ammonia has high volatility and can therefore be easily removed from the silica sol. It should be noted that the base catalyst can be used alone or in combination of two or more.

[0027] From the viewpoint of minimizing the mixing of metal impurities and the like, the water contained in the liquid (A) is preferably pure water or ultrapure water.

[0028] As the first organic solvent contained in the liquid (A), a hydrophilic organic solvent is preferably used, and specific examples thereof include alcohols such as methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, and 1,4-butanediol; and ketones such as acetone and methyl ethyl ketone.

[0029] In particular, in the present invention, alcohols are preferred as the first organic solvent. When the silica sol is subjected to water replacement as described later, the use of alcohols can easily replace alcohols and water by heating and distillation. In addition, from the viewpoint of recovery and reuse of the organic solvent, it is preferred to use an alcohol of the same type as the alcohol generated by the hydrolysis of the alkoxysilane.

[0030] Among alcohols, at least one of methanol, ethanol, and isopropanol is particularly preferred. However, when tetramethoxysilane is used as the alkoxysilane, methanol is preferably used as the first organic solvent.

[0031] The first organic solvent may be used alone or in combination of two or more.

[0032] The contents of the alkali catalyst, water and the first organic solvent in the liquid (A) are not particularly limited. The alkali catalyst, water and the first organic solvent used can be changed according to the desired particle size, and the respective contents can also be appropriately adjusted according to the substances used. In the production method of the present invention, the particle size of the silica particles can be controlled by controlling the content of the alkali catalyst in the liquid (A).

[0033] For example, when ammonia is used as the base catalyst, the lower limit of the ammonia content is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, relative to the total amount (100% by mass) of the liquid (A), from the viewpoint of its effect as a hydrolysis catalyst or the growth of silica particles. In addition, the upper limit of the ammonia content is not particularly limited, but is preferably 50% by mass or less, more preferably 40% by mass or less, and further preferably 20% by mass or less, from the viewpoint of productivity and cost.

[0034] The lower limit of the content of water can be adjusted according to the amount of alkoxysilane or its condensate used in the reaction, and from the viewpoint of the hydrolysis of alkoxysilane, it is preferably 5% by mass or more relative to the total amount (100% by mass) of liquid (A), and more preferably 10% by mass or more. In addition, from the viewpoint of compatibility with liquid (B), the upper limit of the content of water is preferably 50% by mass or less relative to the total amount (100% by mass) of liquid (A), and more preferably 40% by mass or less. From the viewpoint of compatibility with liquid (B), the lower limit of the content of the first organic solvent is preferably 10% by mass or more relative to the total amount (100% by mass) of liquid (A), and more preferably 20% by mass or more. In addition, from the viewpoint of dispersibility, the upper limit of the content of the first organic solvent is preferably 94% by mass or less relative to the total amount (100% by mass) of liquid (A), and more preferably 90% by mass or less.

[0035] When methanol is used as the first organic solvent, the lower limit of the content of methanol is preferably 10% by mass or more, and more preferably 20% by mass or more, relative to the total amount (100% by mass) of the liquid (A), from the viewpoint of compatibility with the liquid (B). In addition, from the viewpoint of dispersibility, the upper limit of the content of the first organic solvent is preferably 94% by mass or less, and more preferably 90% by mass or less, relative to the total amount (100% by mass) of the liquid (A).

[0036] [Liquid (B) containing alkoxysilane or its condensate and second organic solvent]

[0037] The liquid (B) in the first to third embodiments of the present invention is common, and the following description is also common.

[0038] The liquid (B) comprising an alkoxysilane or a condensate thereof and a second organic solvent of the present invention can be prepared by mixing an alkoxysilane or a condensate thereof with a second organic solvent. Since the concentration of the alkoxysilane or a condensate thereof is too high and the reaction is violent, a gel-like substance is easily generated, and from the viewpoint of miscibility, it is preferred to prepare the liquid by dissolving the alkoxysilane or a condensate thereof in an organic solvent.

[0039] The liquid (B) may contain other components in addition to the alkoxysilane or its condensate and the second organic solvent, within a range not impairing the effects of the present invention.

[0040] As the alkoxysilane or its condensate contained in liquid (B), tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, or their condensates can be cited. These can be used alone or in combination of two or more. Among them, tetramethoxysilane is preferred from the viewpoint of having appropriate hydrolysis reactivity.

[0041] As the second organic solvent contained in the liquid (B), a hydrophilic organic solvent is preferably used, and specific examples thereof include alcohols such as methanol, ethanol, n-propanol, isopropanol, ethylene glycol, propylene glycol, and 1,4-butanediol; and ketones such as acetone and methyl ethyl ketone.

[0042] In particular, in the present invention, alcohols are preferred as the second organic solvent. By using alcohols, when the silica sol is subjected to the water replacement described later, alcohols and water can be easily replaced by heating distillation. In addition, from the viewpoint of recovery and reuse of the organic solvent, it is preferred to use an alcohol of the same type as the alcohol generated by the hydrolysis of the alkoxysilane. Among the alcohols, methanol, ethanol and isopropanol are particularly preferred. For example, when tetramethoxysilane is used as the alkoxysilane, methanol is preferably the second organic solvent. The second organic solvent can be used alone or in combination of two or more. In addition, from the viewpoint of recovery and reuse of the organic solvent, the second organic solvent contained in the liquid (B) is preferably the same as the first organic solvent contained in the liquid (A). Therefore, as a more preferred embodiment, the first organic solvent and the second organic solvent are methanol.

[0043] The content of the alkoxysilane or its condensate and the second organic solvent in the liquid (B) is not particularly limited and can be appropriately adjusted according to the desired shape, particle size, etc. The upper limit of the content of the alkoxysilane or its condensate can be adjusted according to the amount of the alkoxysilane or its condensate used in the reaction. From the viewpoint of the hydrolysis of the alkoxysilane, it is preferably 98% by mass or less relative to the total amount (100% by mass) of the liquid (B), and more preferably 95% by mass or less. In addition, the lower limit of the content of the alkoxysilane or its condensate is preferably 50% by mass or more relative to the total amount (100% by mass) of the liquid (B), and more preferably 60% by mass or more. The lower limit of the content of the second organic solvent is preferably 2% by mass or more relative to the total amount (100% by mass) of the liquid (B), and more preferably 5% by mass or more. In addition, the upper limit of the content of the second organic solvent is preferably 50% by mass or less relative to the total amount (100% by mass) of the liquid (B), and more preferably 40% by mass or less.

[0044] For example, when tetramethoxysilane is used as alkoxysilane and methanol is used as the second organic solvent, the upper limit of the content of tetramethoxysilane is preferably 98% by mass or less relative to the total amount (100% by mass) of liquid (B), and more preferably 95% by mass or less. In addition, the lower limit of the content of tetramethoxysilane is preferably 50% by mass or more relative to the total amount (100% by mass) of liquid (B), and more preferably 60% by mass or more. If the content of alkoxysilane is 50% by mass or more and 98% by mass or less, the miscibility when mixed with liquid (A) is improved, it is difficult to generate a gel-like substance, and a high-concentration silica sol can be prepared. When methanol is used as the second organic solvent, the lower limit of the content of methanol is preferably 2% by mass or more relative to the total amount (100% by mass) of liquid (B), and more preferably 5% by mass or more. In addition, from the viewpoint of dispersibility, the upper limit of the content of methanol as the second organic solvent is preferably 50% by mass or less relative to the total amount (100% by mass) of liquid (B), and more preferably 40% by mass or less.

[0045] [Liquid containing water (C)]

[0046] The liquid (C) containing water in the first embodiment of the present invention contains water. The liquid (C) may contain other components in addition to water and an organic acid added as needed, within a range that does not impair the effects of the present invention.

[0047] [Liquid (C1) containing water and having a pH of 5.0 or more and less than 8.0]

[0048] The liquid (C1) containing water and having a pH of 5.0 or more and less than 8.0 in the second embodiment of the present invention contains water. The liquid (C1) may contain other components in addition to water and an organic acid added as needed, within a range that does not impair the effects of the present invention and within a range of pH 5.0 or more and less than 8.0.

[0049] The pH of the liquid (C1) is 5.0 or more and less than 8.0. When the pH of the liquid (C1) is less than 8.0, the local increase in the concentration of the hydroxide ions in the reaction solution can be suppressed, so the reaction can be stably carried out. In addition, when the pH is 5.0 or more, the gelation of the reaction solution can be suppressed. From the viewpoint of further suppressing the gelation of the reaction solution, the pH of the liquid (C1) is preferably 5.5 or more, more preferably 6.0 or more. The determination of the pH of the liquid (C1) is based on the value obtained by the method measured in accordance with the embodiment.

[0050] From the viewpoint of minimizing the inclusion of metal impurities and the like, the water contained in the liquid (C1) is preferably pure water or ultrapure water.

[0051] In the second embodiment of the present invention, the liquid (C1) may or may not contain an alkali catalyst. However, it is preferred that the liquid (C1) contain no alkali catalyst from the viewpoints of obtaining uniform silica particles and increasing the concentration of silica particles.

[0052] [Liquid (C2) containing water and not containing an alkali catalyst]

[0053] The liquid (C2) in the third embodiment of the present invention contains water and does not contain an alkali catalyst. Since the liquid (C2) does not contain an alkali catalyst, a local increase in the concentration of the alkali catalyst in the reaction liquid can be suppressed, and thus silica particles having a uniform particle size can be obtained.

[0054] From the viewpoint of minimizing the inclusion of metal impurities and the like, the water contained in the liquid (C2) is preferably pure water or ultrapure water.

[0055] [First step of adding organic acid]

[0056] The production method of the present invention includes a first step of adding an organic acid to at least one of a liquid (A) and a liquid (C), wherein the liquid (A) contains an alkali catalyst, water, and a first organic solvent, and the liquid (C) contains water. In the first step, the organic acid is preferably added to the liquid (A) containing an alkali catalyst, water, and a first organic solvent. The liquid (C) in the first step is preferably liquid (C1) or liquid (C2).

[0057] Specific examples of the organic acid added in the first step include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, 2-methylbutyric acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric acid, 4-methylvaleric acid, n-heptanoic acid, 2-methylhexanoic acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic acid, salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, tartaric acid, citric acid, lactic acid, diglycolic acid, 2-furancarboxylic acid, 2,5-furandicarboxylic acid, 3-furancarboxylic acid, 2-tetrahydrofurancarboxylic acid, methoxyacetic acid, methoxyphenylacetic acid, and phenoxyacetic acid. Organic sulfuric acids such as methanesulfonic acid, ethanesulfonic acid, and 2-hydroxyethanesulfonic acid can also be used. Among these, dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid, malic acid, and tartaric acid, tricarboxylic acids such as citric acid, and methanesulfonic acid are preferred from the viewpoint of high versatility. More preferred is at least one selected from the group consisting of maleic acid and methanesulfonic acid.

[0058] The amount of the organic acid added is preferably 0.003% by mass or more, more preferably 0.006% by mass or more, relative to the total amount of liquid (100% by mass) after mixing all the components of liquid (A), liquid (B) and liquid (C), from the viewpoint that it does not affect the particle shape even when added to any one of the liquids (A) and (C). In addition, from the viewpoint of generating aggregates during synthesis, the upper limit of the amount of the organic acid added is preferably 0.600% by mass or less, more preferably 0.300% by mass or less, and further preferably 0.150% by mass or less, relative to the total amount of liquid (100% by mass) after mixing all the components of liquid (A), liquid (B) and liquid (C).

[0059] [Second step of preparing a reaction solution]

[0060] The production method of the present invention includes a second step of preparing a reaction liquid by mixing liquid (B) and liquid (Cx) in liquid (A) (in this specification, liquid (Cx) refers to a general concept including at least one selected from the group consisting of liquid (C), liquid (C1) and liquid (C2)). Alkoxysilane or its condensate is hydrolyzed and polycondensed in the prepared reaction liquid to generate silica sol. Therefore, the silica sol can be used in its own state according to the purpose, or in the form of a liquid obtained after the water replacement step and the concentration step described later, or in the form of an organic sol dispersed in an organic solvent.

[0061] According to the method for producing a silica sol of the present invention, a silica sol having silica particles of uniform particle diameter can be stably obtained.

[0062] When liquid (B) and liquid (Cx) are mixed in liquid (A), the method for adding liquid (B) and liquid (Cx) is not particularly limited. Approximately a certain amount of liquid (B) and liquid (Cx) can be added to liquid (A) simultaneously, or liquid (B) and liquid (Cx) can be added to liquid (A) alternately. Or liquid (B) and liquid (Cx) can also be added randomly. Among these, from the viewpoint of the change of the amount of water used for the synthetic reaction in the suppression reaction solution, it is preferred to use a method for adding liquid (B) and liquid (Cx) simultaneously, and it is more preferred to use a method for adding liquid (B) and liquid (Cx) simultaneously with a certain amount of liquid (B) and liquid (Cx).

[0063] Furthermore, from the viewpoint of suppressing a local increase in the concentration of the base catalyst in the reaction liquid, the method of adding liquid (B) and liquid (Cx) to liquid (A) is preferably a method of adding liquid (B) and liquid (Cx) to liquid (A) in batches or continuously.

[0064] Batch addition means that when adding liquid (B) and liquid (Cx) to liquid (A), the entire amount of liquid (B) and liquid (Cx) is not added at once, but added discontinuously or continuously in two or more batches. Specific examples of batch addition include dropwise addition.

[0065] Continuous addition means that when adding liquid (B) and liquid (Cx) to liquid (A), the entire amount of liquid (B) and liquid (Cx) is not added at once, but the addition is performed continuously without interruption.

[0066] The time required when the total amount of liquid (B) and liquid (Cx) is added to liquid (A) is different according to the liquid amount of liquid (B) and liquid (Cx), for example, it can be more than 10 minutes, and it can be appropriately adjusted according to the desired particle size. From the viewpoint of suppressing the concentration of the alkali catalyst in the reaction solution to rise locally, the time required when adding the total amount of liquid (B) and liquid (Cx) in liquid (A) is preferably more than 15 minutes, more preferably more than 20 minutes. When adding liquid (B) and liquid (Cx) in liquid (A), from the viewpoint that the concentration of each component in the reaction solution does not deviate, it is not preferred to put in the total amount in a short time rather than spend a certain time or put the total amount of liquid (B) and liquid (Cx) into liquid (A) at one go. In addition, the upper limit of the time required when adding the total amount of liquid (B) and liquid (Cx) in liquid (A) is not particularly limited, and productivity can be considered and appropriately adjusted according to the desired particle size.

[0067] When liquid (B) and liquid (Cx) are mixed in liquid (A), from the viewpoint of making the particle size of the silica particles uniform, a preferred method for adding liquid (B) and liquid (Cx) is a method in which liquid (B) and liquid (Cx) are added simultaneously in substantially constant amounts, respectively, and the addition is completed over a certain period of time.

[0068] The temperatures of liquid (A), liquid (B) and liquid (Cx) when preparing the reaction liquid are not particularly limited. Here, the temperatures of liquid (A), liquid (B) and liquid (Cx) when preparing the reaction liquid refer to the temperatures of the liquids when liquid (B) and liquid (Cx) are added to liquid (A). By controlling the temperature of the reaction liquid (each liquid), the particle size of the silica particles can be controlled.

[0069] The lower limit of the temperature of each liquid is preferably 0°C or more, more preferably 10°C or more. In addition, the upper limits of the temperatures of the aforementioned liquids may be the same or different, and are preferably 70°C or less, more preferably 60°C or less, and further preferably 50°C or less. That is, the temperatures of liquid (A), liquid (B) and liquid (Cx) are each independently preferably 0 to 70°C. When the temperature is 0°C or more, freezing of alkoxysilane can be prevented. On the other hand, when the temperature is 70°C or less, volatilization of the organic solvent can be prevented.

[0070] As described above, the temperatures of liquid (A), liquid (B) and liquid (Cx) may be the same or different, and from the viewpoint of making the particle size of the silica particles uniform, the temperature difference of liquid (A), liquid (B) and liquid (Cx) is preferably within 20° C. Here, the temperature difference refers to the difference between the highest temperature and the lowest temperature among the three liquids.

[0071] In the method for producing silica sol according to the embodiment of the present invention, the hydrolysis and polycondensation reactions can be performed under reduced pressure, normal pressure, or increased pressure, but are preferably performed under normal pressure from the viewpoint of production cost.

[0072] The molar ratio of the alkoxysilane or its condensate, water, the base catalyst, and the first organic solvent and the second organic solvent in the reaction liquid is not particularly limited and can be appropriately adjusted according to the content of the base catalyst contained in the liquid (A) and the alkoxysilane or its condensate contained in the liquid (B).

[0073] In this specification, "reaction liquid" refers to a liquid obtained by mixing liquid (B) and liquid (Cx) in liquid (A), and refers to a liquid in a state where hydrolysis and polycondensation of alkoxysilane or its condensate are progressing (before progressing). On the other hand, "silica sol" refers to a liquid after completion of hydrolysis and polycondensation.

[0074] That is, the molar ratio is the molar ratio of the alkoxysilane or its condensate, water, the base catalyst and the organic solvent (the total amount of the first organic solvent and the second organic solvent) contained in the total amount of the liquid (A), liquid (B) and liquid (Cx) used in the reaction, that is, the total amount of the reaction liquid when the total amount of the liquid (A), liquid (B) and liquid (Cx) is mixed. In short, it refers to the molar ratio in the total amount of the reaction liquid (liquid (A) + liquid (B) + liquid (Cx)) after adding the liquid (B) and the liquid (Cx) to the liquid (A).

[0075] When the number of moles of alkoxysilane is set to 1.0, the molar ratio of water contained in the reaction solution is preferably 2.0 to 12.0 moles, and more preferably 3.0 to 6.0 moles. When the molar ratio of water is 2.0 moles or more, the amount of unreacted products can be reduced. When the molar ratio of water is 12.0 moles or less, the concentration of silica particles in the obtained silica sol can be increased. It should be noted that when a condensate of an N-mer (N represents an integer greater than 2) of alkoxysilane is used, the molar ratio of water in the reaction solution is N times that when an alkoxysilane is used. That is, when a condensate of a dimer of alkoxysilane is used, the molar ratio of water in the reaction solution becomes twice that when an alkoxysilane is used.

[0076] When the molar number of the alkoxysilane or its condensate is set to 1.0, the molar ratio of the base catalyst contained in the reaction solution is preferably 0.1 to 1.0 mole. When the molar ratio of the base catalyst is 0.1 or more, the amount of unreacted products can be reduced. When the molar ratio of the base catalyst is 1.0 or less, the reaction stability can be improved.

[0077] When the number of moles of the alkoxysilane or its condensate is 1.0, the molar ratio of the total amount of the first organic solvent and the second organic solvent contained in the reaction solution is preferably 2.0 to 20.0 mol, and more preferably 4.0 to 17.0 mol. When the molar ratio of the organic solvent is 2.0 mol or more, the amount of unreacted products can be reduced, and when it is 20.0 mol or less, the concentration of silica particles in the obtained silica sol can be increased.

[0078] That is, the molar ratio of the alkoxysilane, water, alkaline catalyst, and the first organic solvent and the second organic solvent in the reaction liquid is preferably (alkoxysilane): (water): (alkaline catalyst): (organic solvent) = (1.0): (2.0 to 12.0): (0.1 to 1.0): (2.0 to 20.0). In addition, when the condensate of alkoxysilane is made into an N-mer (N represents an integer greater than 2), the molar ratio of the condensate of alkoxysilane, water, alkaline catalyst, and the first organic solvent and the second organic solvent in the reaction liquid is preferably (condensate of alkoxysilane): (water): (alkaline catalyst): (organic solvent) = (1.0): (2.0×N to 12.0×N): (0.1 to 1.0): (2.0 to 20.0).

[0079] The shape of the silica particles in the silica sol is preferably non-spherical. Specifically, the average circularity of the silica particles in the silica sol is preferably 0.60 or less. In this specification, the average circularity refers to the value calculated by the average value of the circularity of the silica particles contained in the silica sol. In this specification, the average circularity refers to the value calculated by the method described in the embodiments described later. The closer the circularity is to 1, the more spherical it is, and therefore, the closer the average circularity is to 1, the more the proportion of approximately spherical particles contained in the silica sol is. By the production method of the present invention, a silica sol having an average circularity of less than 0.60 based on the image observed by a scanning electron microscope can be stably obtained. That is, the present invention can produce a large amount of silica sol containing non-spherical silica particles with smaller circularity. Therefore, by using the silica sol obtained by the production method of the present invention as an abrasive for a polishing composition, a polishing composition with better polishing performance such as suppression of dishing and improvement of polishing speed can be made.

[0080] The average aspect ratio of the silica particles in the silica sol is preferably 1.00 or more, more preferably 1.05 or more, further preferably 1.1 or more, and most preferably 1.2 or more. In this specification, the average aspect ratio refers to the value calculated by the average value of the aspect ratios of the silica particles contained in the silica sol. In this specification, the average aspect ratio refers to the value calculated by the method described in the examples described later. The closer the aspect ratio is to 1, the closer it is to a non-flat shape. Therefore, the closer the average aspect ratio is to 1, the greater the proportion of particles that are approximately non-flat contained in the silica sol.

[0081] The silica sol obtained by the production method of the present invention has a small average circularity even when the average aspect ratio of the silica particles is 1 or close to 1, so that high polishing performance can be exhibited. Figure 1 The reason is explained. Figure 1 (a) shows triangular irregular-shaped silica particles in which three particles are bonded (hereinafter referred to as "triangular irregular-shaped silica particles"). Figure 1 (b) shows an elliptical irregular silica particle (hereinafter referred to as "elliptical irregular silica particle") in which two particles are bonded. The particle size of the triangular irregular silica particles and the elliptical irregular silica particles is about 78 nm, but the aspect ratio of the triangular irregular silica particles is 1.00, and the aspect ratio of the elliptical irregular silica particles is 1.54. However, the triangular irregular silica particles, which have a higher degree of association than the elliptical irregular silica particles, have a shape that improves grinding performance such as suppression of dishing and high grinding speed. Therefore, it is believed that the shape of the silica particles that improves the grinding performance cannot be determined by the aspect ratio alone. In the present invention, focusing on the circularity of the silica particles, by repeatedly studying the timing of adding the organic acid, it was found that a silica sol containing silica particles with a small circularity that can improve the grinding performance can be obtained, thereby completing a new method for producing a silica sol.

[0082] The size of the silica particles in the silica sol is not particularly limited, and the lower limit of the average primary particle size of the silica particles is preferably more than 5nm, more preferably more than 7nm, and more preferably more than 10nm. In addition, in the grinding composition of the present invention, the upper limit of the average primary particle size of the silica particles is preferably less than 120nm, more preferably less than 80nm, and more preferably less than 50nm. If it is such a range, it is possible to suppress the defects such as scratches that may occur on the surface of the grinding object after grinding using the grinding composition. It should be noted that the average primary particle size of abrasive particles is calculated, for example, based on the specific surface area of ​​abrasive particles measured by the BET method.

[0083] The average secondary particle size of the silica particles in the silica sol obtained by the manufacturing method of the present invention can select the desired particle size, preferably 5.0 to 1000.0 nm. The lower limit of the average secondary particle size of the silica particles is preferably 10 nm or more, more preferably 15 nm or more, further preferably 20 nm or more, particularly preferably 50 nm or more, and most preferably 55 nm or more. In addition, in the polishing composition of the present invention, the upper limit of the average secondary particle size of the silica particles is preferably 350 nm or less, more preferably 250 nm or less, further preferably 200 nm or less, particularly preferably 150 nm or less, and most preferably 100 nm or less. If it is such a range, it is possible to suppress defects such as scratches on the surface of the polishing object after polishing with the polishing composition. It should be noted that the value of the average secondary particle size of the silica particles can be measured, for example, in the form of a volume average particle size using a dynamic light scattering method. Specifically, based on the dynamic light scattering method, the particle size of the silica particles is measured, and the particles having particle sizes of d1, d2, ..., di, ..., dk are set to n1, n2, ..., ni, ..., nk, respectively. In addition, the volume of each particle is set to vi. At this time, the volume average particle size is calculated by Σ(vidi) / Σ(vi), which is the volume-weighted average particle size.

[0084] The concentration of silica particles in the silica sol produced by the production method of the present invention varies depending on the particle size of the obtained silica particles, but is preferably 5 mass % to 30 mass % and more preferably 7 mass % to 25 mass % when the average secondary particle size is 50 to 350 nm.

[0085] The pH of the silica sol produced by the production method of the present invention is preferably 7.0 to 13.0, more preferably 8.0 to 12.0.

[0086] Through the production method of the present invention, the total content of metal impurities contained in the silica sol, such as Al, Ca, B, Ba, Co, Cr, Cu, Fe, Mg, Mn, Na, Ni, Pb, Sr, Ti, Zn, Zr, U, Th, etc., can be reduced to less than 1 ppm.

[0087] <Post-process>

[0088] In the method for producing the silica sol of the present invention, in addition to the step of preparing the reaction solution, the following post-step may be performed.

[0089] Specifically, at least one of a water replacement step of replacing the organic solvent present in the silica sol with water and a concentration step of concentrating the silica sol may be performed. More specifically, only a concentration step of concentrating the silica sol may be performed, or only a water replacement step of replacing the organic solvent in the silica sol with water may be performed, or a water replacement step of replacing the organic solvent in the concentrated liquid with water may be performed after the concentration step, or a concentration step of concentrating the liquid replaced with water may be performed after the water replacement step. In addition, multiple concentration steps may be performed, and in this case, a water replacement step may be performed between the concentration steps. For example, a water replacement step of replacing the organic solvent in the concentrated liquid with water may be performed after the concentration step, and then a concentration step of concentrating the liquid replaced with water may be performed.

[0090] [Water replacement process]

[0091] The method for producing the silica sol of the present invention may include, as one embodiment of the present invention, a step of replacing the organic solvent contained in the silica sol with water (hereinafter referred to as "water replacement step"). The silica sol of this embodiment also includes a silica sol that has been subjected to a concentration step (concentrated silica sol).

[0092] By replacing the organic solvent in the silica sol with water, when ammonia is selected as the base catalyst, the pH of the silica sol can be adjusted to a neutral range, and unreacted substances contained in the silica sol can be removed, thereby obtaining a water-substituted silica sol that is stable for a long time.

[0093] The method of replacing the organic solvent in the silica sol with water can be a conventionally known method, for example, a method of replacing the organic solvent by heating and distilling while keeping the liquid volume of the silica sol at a certain amount or more. In this case, the replacement operation is preferably performed until the liquid temperature and the tower top temperature reach the boiling point of the replaced water.

[0094] From the viewpoint of minimizing the mixing of metal impurities and the like, the water used in this step is preferably pure water or ultrapure water.

[0095] Another method of replacing the organic solvent in the silica sol with water is to centrifuge the silica sol to separate the silica particles, and then disperse the particles again in water.

[0096] [Concentration process]

[0097] The method for producing silica sol of the present invention may include, as one embodiment of the present invention, a step of further concentrating the silica sol (also referred to as "concentration step" in this specification). It should be noted that the silica sol of this embodiment also includes a silica sol that has undergone a water replacement step (water-replaced silica sol).

[0098] The method for concentrating the silica sol is not particularly limited, and a conventionally known method can be used, and examples thereof include a heating concentration method and a membrane concentration method.

[0099] In the heating concentration method, concentrated silica sol can be obtained by heating and concentrating the silica sol under normal pressure or reduced pressure.

[0100] In the membrane concentration method, for example, silica sol can be concentrated by membrane separation based on ultrafiltration that can filter silica particles. The molecular weight cutoff of the ultrafiltration membrane is not particularly limited, and the molecular weight cutoff can be screened according to the particle size generated. The material constituting the ultrafiltration membrane is not particularly limited, and examples thereof include polysulfone, polyacrylonitrile, sintered metal, ceramic, carbon, etc. The form of the ultrafiltration membrane is not particularly limited, and spiral type, tubular type, hollow fiber type, etc. can be cited. In the ultrafiltration method, the operating pressure is not particularly limited, and can be set to be below the operating pressure of the ultrafiltration membrane used.

[0101] The embodiments of the present invention have been described in detail, but these are merely for illustration and example only and are not limiting. The scope of protection of the present invention should obviously be interpreted by the appended claims.

[0102] The present invention includes the following aspects and modes.

[0103] 1. A method for producing a silica sol, comprising:

[0104] A first step of adding an organic acid to at least one of a liquid (A) and a liquid (C), wherein the liquid (A) comprises an alkali catalyst, water, and a first organic solvent, and the liquid (C) comprises water; and

[0105] In the second step, after the first step, a reaction liquid is prepared by mixing a liquid (B) and a liquid (C) with the liquid (A), wherein the liquid (B) contains an alkoxysilane or a condensate thereof and a second organic solvent.

[0106] 2. The method for producing a silica sol according to 1. above, wherein the liquid (C) is a liquid (C1) containing water and having a pH of 5.0 or more and less than 8.0.

[0107] 3. The method for producing a silica sol according to 2. above, wherein the liquid (C1) does not contain an alkali catalyst.

[0108] 4. The method for producing a silica sol according to 1. above, wherein the liquid (C) is a liquid (C2) containing water and not containing an alkali catalyst.

[0109] 5. The method for producing a silica sol according to any one of 1. to 3. above, wherein in the second step, the temperatures of the liquid (A), the liquid (B), and the liquid (C) or the liquid (C1) are each independently 0 to 70°C.

[0110] 6. The method for producing a silica sol according to 1. or 4. above, wherein in the second step, the temperatures of the liquid (A), the liquid (B), and the liquid (C) or the liquid (C2) are independently 0 to 70°C.

[0111] 7. The method for producing a silica sol according to any one of 1. to 6. above, wherein the alkoxysilane is tetramethoxysilane.

[0112] 8. The method for producing a silica sol according to any one of 1. to 7. above, wherein the base catalyst contained in the liquid (A) is at least one of ammonia and an ammonium salt.

[0113] 9. The method for producing a silica sol according to 8. above, wherein the alkaline catalyst contained in the liquid (A) is ammonia.

[0114] 10. The method for producing a silica sol according to any one of 1. to 9. above, wherein the first organic solvent and the second organic solvent are methanol.

[0115] 11. The method for producing a silica sol according to any one of 1. to 10. above, wherein the organic acid is at least one selected from the group consisting of maleic acid and methanesulfonic acid.

[0116] 12. The method for producing a silica sol according to any one of 1. to 11. above, wherein an average circularity of the silica particles calculated based on an image observed with a scanning electron microscope is 0.60 or less.

[0117] Example

[0118] The present invention is described in detail using the following examples and comparative examples. However, the technical scope of the present invention is not limited to the following examples. It should be noted that, unless otherwise specified, "%" and "part" mean "mass %" and "mass part" respectively. In addition, in the following examples, unless otherwise specified, the operation is carried out under the conditions of room temperature (20-25°C) / relative humidity 40-50%RH.

[0119] <Example 1>

[0120] (Silica Sol Preparation Process; First Process and Second Process)

[0121] 0.28 g of maleic acid was mixed with a solution (A) obtained by mixing 121 g of pure water and 73 g of a 29 wt% aqueous ammonia solution in 1222 g of methanol. Then, a solution (B) obtained by dissolving 507 g of tetramethoxysilane (TMOS) in 190 g of methanol and a solution (C) obtained by dissolving 120 g of pure water were added dropwise to the solution (A) over 60 minutes while maintaining the temperature of each solution at 35°C, thereby preparing a reaction solution to obtain a silica sol.

[0122] The molar ratio of TMOS, pure water, ammonia and methanol in the reaction solution is TMOS:pure water:ammonia:methanol=1.0:4.0:0.37:13 (when water derived from the ammonia solution is included, TMOS:water:ammonia:methanol=1.0:4.9:0.37:13).

[0123] (Silica Sol Concentration Process)

[0124] 2233 g of the silica sol obtained in the silica sol preparation step was added to a heating container, and the heating container was heated at normal pressure by a jacketed heating stirrer model: MS-ES10 to concentrate the container, thereby obtaining concentrated silica sol.

[0125] (Silica sol water replacement process)

[0126] The silica sol water replacement step was performed by heating and distilling the silica sol obtained in the silica sol concentration step. During the heating and distillation of the silica sol, water was added to keep the liquid volume of the silica sol at a certain level or more, and methanol in the silica sol was replaced with water, thereby obtaining the silica sol of Example 1.

[0127] <Example 2>

[0128] The same operation as in Example 1 was performed except that 0.28 g of maleic acid added to the solution (A) was changed to 0.28 g of methanesulfonic acid to prepare a reaction solution and obtain a silica sol. Thereafter, the silica sol concentration step and the silica sol water replacement step were also performed in the same manner as in Example 1 to obtain the silica sol of Example 2.

[0129] <Comparative Example 1>

[0130] A reaction solution was prepared to obtain silica sol in the same manner as in Example 1 except that 0.28 g of maleic acid was not added to solution (A). Thereafter, the silica sol concentration step and the silica sol water replacement step were performed in the same manner as in Example 1 to obtain silica sol of Comparative Example 1.

[0131] <Comparative Example 2>

[0132] A reaction liquid was prepared in the same manner as in Example 1 except that 0.28 g of maleic acid was not added to the liquid (A) and the liquid (B) and the liquid (C) were added dropwise for 15 minutes to obtain a silica sol of Comparative Example 2. In Comparative Example 2, the silica sol concentration step and the silica sol water replacement step were not performed.

[0133] <Comparative Example 3>

[0134] A reaction solution was prepared in the same manner as in Example 1 except that 0.28 g of maleic acid was not added to the solution (A) and the temperature of each solution was changed to 25° C. when preparing the reaction solution, thereby obtaining a silica sol of Comparative Example 3. In Comparative Example 3, the silica sol concentration step and the silica sol water replacement step were not performed.

[0135] <Comparative Example 4>

[0136] After preparing the reaction solution, 0.28 g of maleic acid was added to the obtained silica sol in the same manner as in Example 1 except that 0.28 g of maleic acid was not added to the solution (A). Thereafter, the silica sol concentration step and the silica sol water replacement step were carried out in the same manner as in Example 1 to obtain the silica sol of Comparative Example 4.

[0137] The raw materials and reaction conditions of Examples 1, 2 and Comparative Examples 1 to 4 are shown in Table 1. It should be noted that in Table 1, the reaction temperature is a value obtained by using a Lacom tester pH & conductivity meter PCWP300 (manufactured by Universal Technics Co., Ltd.), immersing the electrode of the device in the reaction solution, and measuring the temperature of the reaction solution from the start of addition (start of synthesis). The reaction temperature represents the temperature of liquid (A). It should be noted that liquid (B) and liquid (C) are added to liquid (A) at room temperature (20 to 25°C), so that the temperature of each liquid of liquid (B) and liquid (C) is room temperature (20 to 25°C).

[0138] [Determination of physical property values]

[0139] The following physical property values ​​were measured for the silica particles in the silica sols of Examples and Comparative Examples prepared above.

[0140] (Average secondary particle size)

[0141] The average secondary particle size was measured as a volume average particle size by a dynamic light scattering method using a particle size distribution analyzer (UPA-UT151, manufactured by Nikkiso Co., Ltd.).

[0142] (Image observation)

[0143] Using a scanning electron microscope SU8000 (manufactured by Hitachi High-Technologies Corporation), an image of the silica sol was observed in the following procedure.

[0144] The silica sol obtained above was dispersed in alcohol and then dried, and placed in a scanning electron microscope, irradiated with a 5.0 kV electron beam, and photographed at several points in the observation field at a magnification of 50,000 times.

[0145] (Circularity and aspect ratio)

[0146] The circularity (average circularity) and aspect ratio (average aspect ratio) of the captured SEM image were calculated by the following formula using image analysis type particle size distribution measurement software Mac-View Ver.4 (manufactured by Mountech Co., Ltd.).

[0147] It should be noted that circularity and aspect ratio are values ​​obtained by taking SEM images of more than 150 and less than 200 silica particles by SEM, and analyzing the image. Therefore, the average circularity is to obtain the area (S) of each particle and the perimeter (L) of each silica particle, and the circularity of each particle is calculated by the following formula (each) circularity, and the value obtained by averaging the circularity of each particle. In addition, the average aspect ratio is to obtain the minor diameter and major diameter of the circumscribed quadrilateral with the smallest area for each particle, and the aspect ratio (each) is calculated by the following formula, and the aspect ratio of each particle is averaged. It should be noted that the silica particles used for the calculation of average circularity and average aspect ratio are based on all particles of the SEM image taken. That is, the SEM image is adjusted in a manner that the number of particles becomes more than 150 and less than 200, and all particles in the SEM image of the field of view are subjected to image analysis, and the average circularity and average aspect ratio are calculated.

[0148] Circularity = 4πS / L 2 (S = area of ​​the circle, L = circumference)

[0149] Aspect ratio = (minor diameter of the circumscribed quadrilateral with the smallest area) / (major diameter of the circumscribed quadrilateral with the smallest area)

[0150] (Silicon dioxide concentration)

[0151] Specifically, the silica concentration is a value calculated from the residual amount of silica sol after evaporation, drying and hardening.

[0152] Regarding the silica concentration when the concentration step and the water replacement step were not performed, the concentration of silica particles in the silica sol was measured using a silica sol prepared by mixing the liquid (B) and the liquid (C) with the liquid (A) to prepare a reaction liquid.

[0153] In addition, regarding the silica concentration after concentration and water replacement, liquid (B) and liquid (C) are mixed in liquid (A) to prepare a reaction solution, and the obtained silica sol is subjected to a concentration step and a water replacement step. After these steps, the obtained silica sol is used to measure the concentration of silica particles in the silica sol.

[0154] (Viscosity)

[0155] The viscosity of the silica sol was measured by the following method. Viscometers of Cannon-Fenske type No. 100 (viscometer constant 0.015), No. 200 (viscometer constant 0.1), and No. 300 (viscometer constant 0.25) manufactured by Shibata Scientific Co., Ltd. were fully dried in an air bath at 100°C and then returned to room temperature. It should be noted that the silica sols of No. 75 were used in Examples 1, 2, and Comparative Example 4, and the silica sol of No. 300 was used in Comparative Example 1.

[0156] Invert the Cannon-Finsk viscometer that has returned to room temperature and fill the device with silica sol. After preparing a water bath at 25°C, fully immerse it in the water bath so that the liquid temperature becomes the same temperature. After that, in order to measure the outflow time, restore the top and bottom of the Cannon-Finsk type, and use a stopwatch to measure the movement time between the time measurement lines recorded in the device. In addition, use a portable density / specific gravity / concentration meter made by Anton Paar to measure the density of the silica sol. Calculate the viscosity based on the following formula based on the obtained value.

[0157] Kinematic viscosity (mm 2 / s) = viscometer constant × outflow time (seconds)

[0158] Viscosity (mPa·s) = kinematic viscosity (mm 2 / s)×density(g / cm 3 ).

[0159] The results of the above-mentioned physical property values ​​are shown in Table 2. In Table 2, “-” indicates that the value was not calculated. Figure 2 An image (magnification 100,000 times) of the silica sol of Example 1 observed by a scanning electron microscope is shown.

[0160] [Table 1]

[0161]

[0162] [Table 2]

[0163]

[0164] As shown in Table 2, the average aspect ratio of the silica particles in Comparative Examples 1 to 3 was 1.2 or more, but the average circularity was not less than 0.60. In Comparative Example 4, in which an organic acid was added after the reaction solution was prepared, the average circularity of the silica particles exceeded 0.60. This shows that in order to obtain silica particles with low circularity, an organic acid must be present during the preparation of the reaction solution.

[0165] The average aspect ratio of the silica particles obtained in Examples 1 and 2 was 1.2 or more, and the average circularity was 0.60 or less. Figure 2 It is found that most of the silica particles contained in the silica sol of Example 1 are non-spherical.

[0166] In Examples 1 and 2, even if an organic acid is present in the reaction system during the preparation of the silica sol, the reaction time and reaction temperature are not affected, and the silica sol can be suitably prepared. In addition, the silica sol obtained in Examples 1 and 2 does not aggregate, and it can be confirmed that the organic acid does not affect the stability of the silica sol.

[0167] This application is based on Japanese Patent Application No. 2019-171827 filed on September 20, 2019, the disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A method for producing a silica sol, comprising: Step 1: adding an organic acid to at least one of liquid A and liquid C, wherein the liquid A comprises an alkali catalyst, water, and a first organic solvent, and the liquid C comprises water; and Step 2: After the step 1, a reaction solution is prepared by mixing the solution B and the solution C with the solution A, wherein the solution B contains an alkoxysilane or a condensate thereof, and a second organic solvent. The organic acid is at least one selected from the group consisting of maleic acid and methanesulfonic acid, The average circularity of the silica particles calculated based on an image observed with a scanning electron microscope was 0.60 or less.

2. The method for producing silica sol according to claim 1, wherein: The liquid C is a liquid C1 containing water and having a pH of 5.0 or more and less than 8.

0.

3. The method for producing a silica sol according to claim 2, wherein: The liquid C1 does not contain an alkaline catalyst.

4. The method for producing a silica sol according to claim 1, wherein: The liquid C is a liquid C2 containing water and not containing an alkali catalyst.

5. The method for producing silica sol according to claim 1, wherein: In the second step, the temperatures of the liquid A, the liquid B, and the liquid C are independently 0 to 70°C.

6. The method for producing a silica sol according to claim 2, wherein: In the second step, the temperature of the liquid C1 is 0 to 70°C.

7. The method for producing silica sol according to claim 3, wherein: In the second step, the temperature of the liquid C1 is 0 to 70°C.

8. The method for producing silica sol according to claim 1, wherein: In the second step, the temperatures of the liquid A, the liquid B, and the liquid C are independently 0 to 70°C.

9. The method for producing a silica sol according to claim 4, wherein: In the second step, the temperature of the liquid C2 is 0 to 70°C.

10. The method for producing silica sol according to claim 1, wherein: The alkoxysilane is tetramethoxysilane.

11. The method for producing a silica sol according to claim 1, wherein: The base catalyst contained in the liquid A is at least one of ammonia and an ammonium salt.

12. The method for producing a silica sol according to claim 11, wherein: The base catalyst contained in the liquid A is ammonia.

13. The method for producing silica sol according to claim 1, wherein: The first organic solvent and the second organic solvent are methanol.

14. The method for producing a silica sol according to claim 1, wherein: The average aspect ratio of the silica particles is 1.00 or more.

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